abrasion hazard: A surface that presents an unreasonable risk of irritation to the skin upon contact.

AC: See Alternating Current.

accessible: 1. Easily and readily exposed for inspection and the replacement of materials and/or parts with the use of tools. 2. Methods providing access to physically challenged users.

acid: A liquid or dry chemical used to lower the pH and/or alkalinity of water.

acid demand: The amount of acid needed to lower the pH and total alkalinity of water to a desired level.

acid demand test: Acid of known strength is added in increments to a measured water sample to determine the amount of acid needed to achieve a desired pH in a pool, spa, or hot tub.

acidic: Having a pH below 7.0. Opposite of Basic.

acid wash: Procedure that uses an acid solution to clean an interior surface of a pool or spa, with subsequent neutralization of the acid.

acrylic: A thermoplastic material that can be extruded, injection molded, or vacuum formed into usable shapes and surfaces.

action pool: A wave pool in which standing waves are generated in an assortment of patterns.

activated carbon: A charcoal-like material used to remove colors, odors, and/or excess oxidizer from water.

activity pool: A pool designed primarily for play activity that uses constructed features and devices such as lily pad walks, flota­tion devices, slide features, and similar attractions.

admixture: A material (other than aggregate, cement, or water) added in small quantities to concrete to produce a desired change in properties.

adult supervision: A situation whereby a child at rest or play is within the constant sight and hearing of an adult charged with safeguarding the child. Adult supervision must be of a nature that is uninterrupted-without absences, voids, or distractions that separate adult from child by distance, obstacles, or any hindrance to sight and sound communication.

AF: See Alkalinity Factor.

aggregate: Marble dust, sand, rocks, pebbles, colored quartz, dolomite, and other similar materials used as components of concrete or plaster.

aggressive water: Water that is corrosive because it is low in pH, and/or calcium hardness, and/or alkalinity.

air blower: A mechanical device that forces air through the floor, seat, jets, or bubbler ring of a pool, spa, or hot tub, to increase water turbulence and hydrotherapy action.

air button: A plunger or diaphragm connected to a button for pushing air through tubing. Used to activate an air switch on the opposite end of the tubing.

air channel: A perforated, hollow duct in the pool, spa, or hot tub wall, floor or bench through which air is pumped by an air blower.

air control: A valve used to regulate air flow in the air induction system.

air entrained concrete: A type of concrete mixture that is more resistant to freezing when exposed to water and deicing chemicals.

air entrainment: Process in which minute air bubbles 0.01-0.001 inches (0.25-0.03 mm) in size are mixed in a concrete mortar mix. Improves workability and frost resistance of the concrete. air induction system: System where a volume of air is introduced into a pool, spa, or hot tub floor, bench, or hydrotherapy jets.

air lock: A condition where air is trapped in the plumbing so that the pump cannot prime, the heater cannot fire, or the water cannot flow while the motor is running.

air switch: A pneumatically activated switching device. The switch changes state via a puff of air pushing against a diaphragm that, in turn, makes or breaks the contacts. Activation may be latching, momentary or sequencing, depending on the applica­tion.

algae: Microscopic plant life containing chlorophyll that can grow in untreated or undertreated recreational water and on surfaces.

algicide: Any chemical or material that kills algae. Also spelled ALGAECIDE.

algistatic: Able to inhibit the growth of algae.

alkali: A term applied to bases-usually carbonates, bicarbonates, and hydroxides-that raise pH and alkalinity when added to water.

alkali demand, base demand: The amount of alkaline chemical needed to raise the pH of pool, spa, or hot tub water to a desired level.

alkaline: Having a pH above 7.0.

alkalinity: See Total Alkalinity.

alkalinity factor (AF): A number used to calculate the Saturation Index of water.

alternating current (AC): Household electrical current and voltage; commonly used to power pool and spa load devices (pump, blowers, heaters, etc.). Developed by mechanical means from a spinning (alternating) device, AC voltage has no positive or negative post. The current alternates from negative to positive in cycles (hertz), at 60 times per second in North America, 50 in Europe, ASia, and Australia.

alum, aluminum sulfate, (AI2S04)3: A compound used to cause suspended solids in the water to form filterable masses (flocculate).

ammeter: A device that measures the flow of electric current in amperes (amps). Also AMP METER. See Multimeter.

ammonia (NH3): A chemical compound of hydrogen and nitrogen. In pool, spa, and hot tub water, it reacts with chlorine to form chloramines, or with bromine to form bromamines.

amp clamp: An ammeter which measures electric current (in amperes) when the jaws of the meter encircle one conductor of the circuit.

amperage: The flow of a current of electricity expressed in amperes.

ampere (amp): The unit of measure for current in a complete circuit; shows the amount of flow of electrons in the circuit. 1 ampere = the steady current produced by 1 volt applied across a resistance of 1 ohm.

analog meter: A testing device in which a needle is used to indicate readings on the dial face.

ancillary facility: Area used in conjunction with, or in the operation of, a pool, such as public dressing, locker, shower, or bathroom area, equipment room, pool deck area or building space intended to be used by pool users.

ANSI, American National Standards Institute: An organization that promotes and facilitates voluntary U.S. consensus standards and ensures their integrity (see www.ansi.org).

antivortex drain cover (antivortex plate or cover): A plate or cover affixed to the main outlets of a pool, spa, or hot tub, that prevents a vortex from forming as water passes through to the main outlet.

aquatic recreation facility: A facility designed for free-form aquatic play and recreation. Facilities may include, but are not limited to, wave or surf action pools, leisure rivers, sand bottom pools, vortex pools, activity pools, inner-tube rides and body slides, and interactive play attractions.

APSP (The Association of Pool & Spa Professionals): Formerly NSPI; the world's largest international trade association representing the swimming pool, spa, hot tub and recreational water industries (www.APSP.org).

ASME (The American Society of Mechanical Engineers): A profes­sional organization focused on technical, educational and research issues of the engineering and technology community. Develops internationally recognized industrial and manufactur­ing codes and standards that enhance public safety.

available chlorine: A rating of a chemical's total chlorine content based on a comparison to elemental (gaseous) chlorine having 100% available chlorine.


backboard: Device for immobilizing a person with a suspected injury to the spinal column.

back pressure: Resistance to flow, normally expressed in pounds per square inch/kilograms per square centimeter.

backwash: The process of cleansing the filter medium and/or elements by the reverse flow of water through the filter.

backwash cycle: The time required to backwash the filter medium and/or elements and to remove debris in the filter vessel.

backwash rate: The rate of water flow through the filter medium per unit of area during backwash. One U.S. gallon per minute per square foot (1 gprn/ft') = 40.75 liters per minute per square meter (40.75 Lprn/rn").

bacteria: Single-celled microorganisms of various forms, some of which cause infection or disease. See Recreational Water Illness.

bactericide, biocide, germicide: A chemical or material that kills bacteria.

balance, balanced water: A condition of water that is neither scale-forming nor corrosive. See Saturation Index.

ball valve: A device that can partially or totally obstruct the flow of water using a ball-shaped diverter.

barrier: A means to limit, delay, or restrict access to a pool, spa, or hot tub. (Refer to ANS/jAPSP-8, Model Barrier Code for Residential Swimming Pools, Spas, and Hot Tubs, 2005 or latest revision.)

base: A chemical used to raise the pH and/or total alkalinity of water.

base demand, alkali demand: A measure of the amount of alka­line material required to raise pH to a predetermined level. This can be accomplished by use of a base demand test, whereby a standard base is added by drop to the pH test solution until the desired pH is reached.

basic: Having a pH above 7.0. Opposite of Acidic.

bather: Any person using a pool, spa, hot tub or water feature and adjoining deck area for the purpose of water sports, recreation, therapy or related activities. Also USER.

bather load: The number of persons in a pool, spa, or hot tub at any given moment or during a stated period of time. Also SWIMMER LOAD.

BCDMH (bromo chloro-dimethyl hydantoin): Sanitizer products used to generate available bromine. They contain available bromine and available chlorine.

beach entry: Sloping entry starting above the waterline at deck level and ending below the waterline. (Does not refer to sand only). Also ZERO ENTRY.

beginner's area: Those areas in pools that are three feet (3 ft./ .91 rn) or less in water depth.

bench (underwater): See Seat.

blguanlde: See Polyhexamethylene Biguanide.

biofilm: 1. A community of microorganisms such as bacteria, algae, or fungi, encased in a protective matrix, usually attached to surfaces. 2. A deposit containing bacteria, polymers, and mineral salts that lines plumbing pipes, filter vessels, and other surfaces. A community of microorganisms such as bacteria, algae, or fungi, encased within a protective matrix, usually attached to wet surfaces. One example is slime in or around pool/spa surfaces, pipes, and/or filters.

bleach (NaOCI): Sodium hypochlorite. A chlorine source that typically has between 5% and 16% available chlorine. Also LIQUID CHLORINE.

bleeder valve: A device that allows air to be vented from a system.

blister: An area of raised surface detached from the structural matrix of a material.

Bluestone: A type of flagstone commonly used for decking in the eastern United States.

bluestone (CUS04): A blue inorganic salt, sometimes used as an algicide. Also COPPER SULFATE.

body coat: A layer of diatomaceous earth (DE) or similar materi­als on a filter element that acts as the filtering media.

body feed: A controlled amount of diatomaceous earth or similar materials continuously added to the filter element during the course of a filter run to help maintain filter porosity.

bond beam: Typical extra-structural strength or rigidity provided along the top edge of a pool wall.

bond failure: Failure of plaster or other surfaces to adhere to the underlying subsurface; delamination.

bonding, electrical: The joining of all metallic parts by means of a single #8 or larger solid copper wire to form an electrically conductive path to ground, so that all metal components have equal electrical potential at all times.

bonding lug: An electrical connector used for bond wire connec­tion.

booster pump: A pump that is completely independent of the filtration and heating system. Used to provide support for hydrotherapy jets, cleaning systems, gas chlorinators, or special water features. See also Jet Pump.

bottom rail: The lower portion of an aboveground pool frame used as a structural retainer for aboveground pool wall.

break in grade, break point: Point where the slope of a pool floor changes. See also Transition.

breakpoint chlorination, BPC: The process of adding free chlorine to oxidize or remove combined chlorine (CC), using the following formula:

breakpoint chlorination = [combined chlorine (CC) x 10] - free available chlorine (FAC)

bridge rectifier: A semiconductor device used to convert AC voltage to DC. See Alternating Current, Direct Current.

bridging: Build-up of a body coat on diatomaceous earth (DE) filter elements to the point where the body coats of two adjacent elements touch.

broadcast: To apply chemicals spreading them uniformly over the water surface.

bromamines: Bromine-ammonia compounds exhibiting sanitizing properties similar to hypobromous acid.

bromide: A salt that contains a bromide (Br") ion. Bromide becomes hypobromous acid when it reacts with oxidizers such as chlorine, ozone, or persulfates.

brominator: A device to add or deliver bromine disinfectant at a controlled rate.

bromine (Br2): The element in several chemicals that yields hypobromous acid when added to water. A member of the halogen family.

bromine feeder: A device to add or deliver bromine sanitizer at a controlled rate.

bromine generator: See Electrolytic Chlorine/Bromine Generator. BTU (British thermal unit): A unit of measurement used to define the capabilities of heaters. 1 BTU is capable of raising the temperature of 1 pound of water by 1°F, or 1 kg of water by 1.22 °C. See also Therm.

buffer: Chemical that when dissolved in water will resist pH change. Also a chemical solution used to calibrate a pH instrument.

burner: The component of a heater where the combustion of fossil fuel takes place.

bypass valve: A valve used to limit or adjust the amount of water flowing through a device in a bypass loop to divert flow to an alternate plumbing path.


calcification: Formation of calcium carbonate deposits on pool, spa, or hot tub walls, pipes, filters, or equipment, due to the low solubility of calcium salts.

calcium carbonate (CaC03): An insoluble calcium compound that is the major component of scale. CaC03 occurs normally in limestone, marble, various eggshells, seashells, etc. Also SCALE.

calcium chloride (CaCI2): A soluble white salt used to raise the calcium hardness of water.

calcium hardness: A measure of the amount of calcium dissolved in water and expressed as calcium carbonate in parts per million (ppm) or milligrams per liter (mgjL).

calcium hardness factor, CF, F(CH): A number based on the calcium hardness, which is used to calculate the Saturation Index of water.

calcium hypochlorite, Ca(OCI)2: A solid white form of chlorine found in both granular and tablet forms (65%-75% available chlorine). Also CAL HYPO.

cantilever: A projecting beam supported only at one end. capacitor: A device used to store a charge or delay the phase of an applied voltage to produce torque.

1. In pump motors, a capacitor delays the timing of the AC sine wave due to the time it takes to charge and discharge.

2. In PCB controls, a filter capacitor stores a charge to its rated maximum with each peak. As voltage drops off, the capacitor discharges to effectively remove any ripple in the voltage output.

capacity: The maximum amount of fluid that can be contained in a pool, spa, hot tub or other container, expressed as gallons or liters. 1 U.S. gallon = 3.79 liters. See also Gallonage.

carbon dioxide (C02): Common gas found in air. Can be used to lower pH in water.

carbonate, bicarbonate: A salt of carbonic acid.

carbonic acid: A weak acid formed by carbon dioxide in water. carcinogen: A cancer-causing agent.

cardiopulmonary resuscitation (CPR): A lifesaving technique involving both chest compressions and mouth-to-mouth breath­ing, to circulate oxygen and blood to vital organs.

cartridge: A replaceable porous filter element designed to retain suspended particles from water.

cartridge filter: A filtering system that uses a replaceable porous element. .

catch pool: A pool or designated section of a pool used as a terminus for waterslide flumes. See Splash Pool.

caustic: Very alkaline; having a high pH.

caustic soda (NaOH), caustic: Sodium hydroxide or lye; a chemical used in pools, spas, and hot tubs; an extremely high pH alkalizer.
Caution: See Signal Word.

cavitation: Formation of partial vacuums when pump capacity exceeds water replacement supply.

CC, combined chlorine: See Chloramines.


cellulose fiber: An organic dry powder filter aid that can be used to enhance filtration in cartridge and sand filters.

Celsius: International temperature scale based on the freezing and boiling points of water (0°-100°C). Also CENTIGRADE.

cement: A powdered substance of lime and clay generally mixed with water and aggregate to make concrete.

centrifugal force: The outward force exhibited by a circular motion.

centrifugal pump: A pump that circulates water using a shaft­mounted impeller powered by an electric motor or gasoline engine. The centrifugal force of the spinning impeller creates flow through the pump.

CF: See Calcium Hardness Factor.

CFM, cubic feet per minute (of air): One cubic foot per minute = 0.028 cubic meters per minute.

channeling: An undesirable process where filter sand is perme­ated by tubes or channels of calcified or oily material, allowing water to pass freely, without being filtered.

check valve: A device used to insure that air or water flows in only one direction in a plumbing circuit, or to force the flow to travel a selected path at a given speed.

chelating agent, sequestering agent: A chemical that combines with metals, keeping them in solution and preventing them from depositing on and staining pool, spa, and hot tub surfaces.

chemical feeder: A device for adding a chemical to pool, spa, or hot tub water.

chemical feeder output rate: Amount of chemical or active ingredient delivered by a feeder in a given amount of time (for example, pounds of chlorine per hour). One pound per hour = 0.45 kilograms per hour.

children's pool/ride: Pool, ride, flume ride, or other slide attrac­tion at a water theme park, designed primarily for the use of small children.

chiara mines: Chemical compounds formed when free chlorine combines with ammoniated, nitrogen-containing compounds (for example: perspiration, ammonia). Chloramines can cause eye and skin irritation, and have strong objectionable odors and low sanitizing capability. Also COMBINED CHLORINE.

chlorinated Isocyanurates (ISOs): Sanitizer products that self­stabilize by releasing free available chlorine and cyanuric acid as they dissolve.

chlorinator: A device to add or deliver a chlorine sanitizer at a controllable rate.

chlorine (CI2): A member of the Halogen family. See Calcium Hypochlorite, Sodium Dichlor, Isocyanurates, Sodium Hypoch/cr rite, and Trichloro-/socyanurate.

chlorine demand: The amount of chlorine that will be consumed by readily oxidizable impurities in pool, spa, or hot tub water.

chlorine gas (CI2): A gaseous form of chlorine used to sanitize pools and spas. Contains 100% available chlorine.

chlorine generator: See Electrolytic Chlorine/Bromine Generator.

chlorine neutralizer: A chemical used to reduce chlorine residuals, e.g., sodium thiosulfate.

chlorine residual: See Residual.

circuit: The complete path of an electric current.

circuit board, printed circuit board, PCB: A platform for mounting components used for making, breaking or redirecting current or tage.

circuit breaker: A safety device for protecting users and equipment from excess current draw within a circuit. A latching differential metal switch, which breaks connection when the friction of cur­rent flowing in the circuit causes the temperature to rise above a set
point. Must be manually reset.

Circuit protection device: A device used to protect people, circuits and devices, from overloading or current leakage to ground. Some examples are: circuit breakers, fuses, and GFCls (ground-­fault circuit interrupters).

circulation equipment: The components of a circulation system. circulation pump: A small fractional horsepower, low wattage pump that typically runs all day, every day, to perform the maintenance tasks of filtration and heating. Also CIRC PUMP.

circulation system: A coordinated system for maintaining pool, spa, or hot tub water temperature, clarity, and chemical balance. Circulation equipment includes, but is not limited to, pumps, hair and lint strainers, filters, valves, gauges, meters, heaters, surface skimmers, inlet/outlet fittings, and chemical feeding devices.

clarifier: A chemical that causes fine suspended solids in water to combine into filterable clusters. See Flocculant.

clarity: The degree of transparency of water. Characterized by the ease with which an object can be seen through a given depth of water.

closed circuit: An electrical circuit where all switches are closed or connected, so that current can flow from, and return to, the source. Also CONTINUOUS CIRCUIT.

coil voltage: The voltage required to initiate the activation method of a relay, contactor or solenoid. Depending on the device, this voltage may be AC or DC.

coliform bacteria: Bacteria found in the intestines and fecal matter of warm-blooded animals. The detection of coliform is used to indicate the possibility of disease-causing bacteria.

collector, solar: An assembly of components used to collect solar energy for heating, i.e., rooftop structure, floating device, etc.

color comparator: A transparent block used to determine the pH and sanitizer residual in recreational water.

combination circuit: An electrical circuit with components connected in both series and parallel. The series section has all the current flowing through it. The parallel section has branch circuits through which the current divides and flows.

combination switching device: A device activated by a small load device (magnetic coil or motor).

commercial/public pool: Any pool, other than a residential pool, that is intended to be used for swimming or bathing and is operated by an owner, lessee, operator, licensee, or conces­sionaire, regardless of whether a fee is charged for use. (Refer to ANSf/APSP-l, Standard for Public Swimming Pools.)
Commercial/public pools shall be further classified and defined as follows:

Class A, competition pool:Any pool intended for use for accredited competitive aquatic events such as those held by the Federation Internationale De Natation Amateur (FINA), U.S. Swimming, U.S. Diving, National Collegiate Athletic Association (NCAA), National Federation of State High School Associations (NFSHSA), etc. The use of the pool is not limited to competitive events.

Class B, public pool:Any pool intended for public recreational use.

Class C, semi-public pool: Any pool operated solely for and in conjunction with lodgings such as hotels, motels, apartments, condominiums, etc.

Class D, other pools: Any pools operated for medical treatment, therapy, exercise, lap swimming, recreational play, and other special purposes, including, but not limited to, wave or surf action pools, activity pools, splasher pools, kiddie pools, and play areas.

Class D-1, wave action pool: Pool designed to simulate breaking or cyclic waves for purposes of general play or surfing.

Class D-2, activity pool: Pool designed for casual water play ranging from simple splashing activity to the use of attractions placed in the pool for recreation.

Class D-3, catch pool: Body of water located at the termina­tion of a manufactured waterslide attraction, provided for the purpose of terminating the slide action and providing a means for exit to a deck or walkway area.

Class D-4, leisure river: Manufactured stream of near-constant depth in which the water is moved by pumps or other means of propulsion to provide a riverlike flow that transports bathers over a defined path that may include water features and play devices.

Class D-5, vortex pool: Circular pool equipped with a method of transporting water in the pool for the purpose of propelling riders at speeds dictated by the velocity of the moving stream.

Class D-6, sand bottom pool: Pool that uses sand as an interior floor finish over an impervious surface and is equipped to treat and filter the water in the sand areas to maintain a healthful sand condition

Class 0-7, interactive play attractions: Manufactured devices that use sprayed, jetted, or other water sources contacting the bathers, and do not incorporate standing or captured water as part of the bather activity area.

Class D-8, amusement park attractions: Manufactured features designed for bather interaction or incidental contact with static, splashing, or flowing water.

Class D-9, natural bodies of water: Natural or man-made aquatic play areas normally regarded as oceans, lakes, ponds, streams, quarries, or bodies of water that the local jurisdiction has designated as "natural bodies of water." (The design or construc­tion of these facilities is not included in the scope of ANSI! APSP standards.)

Class E: Pools used for instruction, play or therapy and with temperatures above 86°F/30°C.

Public pools may be diving or non-diving. If diving, they shall be further classified into types as an indication of the suitability of a pool for use with diving equipment.

Types VI-IX:Public pools suitable for the installation of diving equipment by type.

Type N:A non-diving public pool (no diving allowed). competitive diving equipment: Equipment that includes diving boards and adjustable fulcrum-setting diving stands intended for competitive diving.

conditioner, stabilizer: A chemical used to help prevent chlorine from dissipating in the ultraviolet rays of sunlight. See Cyanuric Acid.

conductor: A material with low resistance, which readily allows electrons to flow through it. Examples of conductors: copper, aluminum, brass, gold, water containing ions.

conductive pathway: A complete electrical circuit from the source to a load and back to the source.

conduit: Channel or pipe for protecting electric cables or conduc­tors.

contact rating: The amount of current and/or voltage a switch device can safely make or break during normal operation (Example: 30 amps at 277 VAC).

contactor: A magnetically activated switching device used to open and close a circuit frequently.

continuity: The unbroken- path of a circuit, allowing current to pass through.

continuity test: Test to determine whether a circuit is open or closed.

control: The assembly responsible for sequence of operation, timing, and monitoring required to operate pool, spa, or hot tub equipment. Turns equipment on or off at the appropriate time.

coping: The cap on the wall that provides a finishing edge around a pool or spa. Can be formed, cast in place, precast, brick, stone, or prefabricated from metal or plastic materials. May be used as part of the system that secures a vinyl liner to the top of the pool wall.

copper sulfate (CUS04), bluestone: A blue inorganic salt, sometimes used as an algicide.

corona discharge: A method of producing ozone using high voltage electrical current.

corrosive: Wearing away gradually, usually by chemical action.

cove: The radius that joins the floor and wall of a pool or spa.

cover: Something that covers, protects, or shelters a pool, spa, or hot tub. Types of covers are:
safety cover: As defined by ASTM in F1346-91 (2003), Standard performance specification for safety covers and labeling requirements for all covers for swimming pools, spas and hot tubs, latest edition, a barrier (intended to be completely removed before entry of users) for swimming pools, spas, hot ­tubs or wading pools, attendant appurtenances and/or anchor­ing mechanisms that will, when properly labeled, installed, used, and maintained in accordance with the manufacturer’s published instructions, reduce the risk of drowning of children ­under five years of age by inhibiting their access to the contained body of water and by providing for the removal ofany substantially hazardous level of collected surface water.

(These covers may be power or manual)
solar cover: A cover that when placed on a pool, spa, or surface increases the water temperature by solar activity a reduces evaporation and heat loss.
thermal cover: An insulating cover used to prevent evaporation ­and heat loss from pools or spas.
winter cover: A cover that is secured around the perimeter pool or spa that provides a barrier to debris when the pool r spa is closed for the season.

craze: See Surface Checks.

cross connection: An unprotected connection between domestic water supply and pool water or other non-potable water, contamination of the domestic system could occur. cross-over deterrent: A feature to deter a person from crossing over a barrier wall or fence to the opposite side (e.g., a pointed picket fence).

CSA: The Canadian Standards Association, a not-for-profit member association serving business, industry, government a consumers. Works in Canada and around the world to develop standards that enhance public safety and health, advance the quality of life, help to preserve the environment, and facilitate ­trade. See www.csa.ca.

cuddle cove: See Swimout

current The flow of electrons in an electric circuit

cut-off head: See Shut-off Head.

cyanuric acid (CYA): A chemical used to help prevent chlorine from dissipating in the ultraviolet rays of sunlight. Also CONDI­TIONER, ISOCYANURIC ACID, STABILIZER, TRIAZINETRIONE. cycle (electrical): A single complete flow of AC electric current, from source to load and back, measured in hertz (Hz). cycle (timer): A time period set on a pool, spa, or hot tub control 'or filtration, heating, ozonation or purge cleaning sequence modes


Danger: See Signal Word.

DC: See Direct Current.

dead load: The weight of all permanent structural and nonstructural components of a building, such as walls, floors, roofs, ceilings, stairways, and fixed service equipment.

deck: Area immediately adjacent to or attached to a pool or spa that is specifically constructed or installed for sitting, standing, or walking. Generally made of concrete, wood, or masonry.

deck dive: A dive performed from the deck area of a pool into 5 feetj1.52 meters or more of water depth.

dedicated circuit: An AC power circuit wired directly to the electri­cal service, to which no other appliance is connected. The NEC (National Electrical Code) states that the total circuit current draw may never exceed 80% of the rated current; therefore, a pool, spa, or hot tub should not share service with another appliance.

deep area: Area where water depth exceeds 5 feetj1.52 meters.

defoamer: A substance, usually containing silicone emulsions, that breaks up and dissipates foam from the water's surface.

degreaser: A chemical designed to remove grease, oil, and organic substances from filter vessels and filter media.

design rate of flow: The rate of flow, specified by the engineer, of a circulation system or a piece of equipment in the circulation system.

diaphragm pump: A type of positive displacement pump.

diatomaceous earth (DE): A white powder used as a filtering medium; composed of the microscopic fossil skeletons of diatoms.

diatornaceous earth filter: A filter that uses a coating of diatoma­ceous earth (DE) or other filter media over a porous fabric as its
filter medium.

diatomite filter element: Device used in a filter tank; a filter grid or element coated with a fabric that traps diatomite on its surface.

dichlor: See Sodium Dichlor.

diethylphenylene diamine (DPD): A chemical testing reagent that measures total bromine or free available and total chlorine; produces a series of colors from pale pink to dark red.

diffuser: A component of a pump that functions to reduce velocity and increase static pressure of a fluid passing through a system.

digital display: A means of displaying information representing the condition of a pool, spa, or hot tub, or a control operation. Usually includes LED (light emitting diode) arrays or LCD (liquid crystal diode) panels. Most often used in conjunction with a topside control for user interface. See LCD, LED.

digital multimeter: An electrical test meter with an LED or LCD display. See LCD, LED.

diode: A semiconductor device which allows current to flow in one direction for all voltage above a certain level, and the opposite direction for voltage below a certain level.

direct current (DC): DC voltage has distinct positive and negative poles; electrons flow in one direction only, from the negative to the positive pole.

discharge head: Resistance, caused by friction and/or changes in elevation, to the water flow, encountered on the discharge side of the pump back to the swimming pool, spa, or hot tub.

disinfectant: A chemical agent capable of reducing the level of pathogenic bacteria by 99.999% in 5-10 seconds. Not capable of killing all viruses and spores. Disinfectants are rated as compared to the effectiveness of phenol against a standard microbe. A disinfectant has a higher ability to kill pathogenic bacteria than a sanitizer.

dive: A free-fall entry into water from a planned acrobatic maneuver into a designated diving area of a pool.

diverter valve: Valve used to redirect water or air to different inlet openings in a pool, spa. or hot tub. See Valve.

diving area: Area of a swimming pool that is designed for diving. diving board: A flexible board secured at one end that is used for diving.

diving platform: A stationary platform designed for diving. diving stand: Any supporting device for a springboard or diving board.

door interlock: A magnetic interlock used by some pools or spas that prevents power from reaching the system if the access door to the equipment bay is opened. Controlled by a magnetic reed switch or a spring-loaded microswitch.

double pole: A device with two inputs; a type of switch. See Switch.

double throw: A device with two possible outputs for each input; a type of switch. See Switch.

draft hood: Part of a heater venting system.

drain, outlet: A means to remove water from a pool, spa, or hot tub.

dry acid (NaHS04): See Sodium Bisulfate.

dry chemical feeder: Timer-controlled device that meters and moves a dry chemical product into a tank of water connected to the pool, spa or hot tub circulation system.
dry niche light: See Underwater Light.

dual voltage: Describes a component or mechanical device that can operate on either of two different source voltages, such as 120 V/240 V, when properly wired or connected.

dynamic head, total dynamic head, TDH: The sum of the total resistance, caused by friction and/or changes in elevation, of the water flow through the entire circulation system, that the pump must overcome to achieve the necessary flow rate.


edge guard: Shield designed to cover sharp edges in above­ground pools.

effective filter area: Total surface area through which designed flow rate will be maintained during filtration.

cartridge type: The total effective filter area is the cartridge fabric area that is exposed to the direct flow of water, expressed in square feet. This excludes cartridge ends, seals, supports, and other areas where flow is impaired.

diatomaCeous earth (DE) type: The effective area of the element is the actual area of the porous fabric septum, less any area of
a septum support member greater than one-fourth inch
(% in./6.35 mm) wide contacting the septum during filtration.

permanent medium type: The effective filter area is the filter surface that is perpendicular to the flow direction.

sand filtration type: The top surface area of the filter medium within the filter, expressed in square inches/square feet, or square meters.

effluent: The outflow of water from a filter, pump, or pool. egress: Means of exit.

electric immersion heater: A type of heater directly immersed in the water stream, which heats water flowing over it. Powered by conducting an electric current through a resistive element.

electrical induction: The process by which an object having electrical or magnetic properties produces similar properties in a nearby object, usually without direct contact.

electrolysis: Flow of electric current through a material that causes a chemical change, such as corrosion of metal.

electrolytic chlorlnator/bromlnator, electrolytic chlorine/bromine generator: An device that uses electrolysis to generate a chlorine or bromine residual from either chloride or bromide salts.

electromagnetism: The interactions of electrical charges and currents associated with electrical magnetic fields.

electromechanical (EM) control: Control that performs the switch functions required for pool, spa, or hot tub operation via a separately wired switching device manually or pneumatically controlled by the user.

electromotive force (EMF): The force that causes electrons to move in an electrical circuit. Also called VOLTAGE.

electron: A minute, negatively charged particle in an atom. electronic (EE) control: Control that performs the functions of a pool, spa, or hot tub via switching devices located on a printed circuit board (PCB). User input is accomplished with a topside or remote control.

entry pool: Pool at a water theme park that is provided at the entrance to a water slide or inner-tube ride.

enzyme: An organic protein that is nontoxic and biodegradable. Enzymes help reduce filter cartridge maintenance, the amount of sanitizer required, and the "scum line" which forms on the waterline, by digesting body oils and organics and off-gassing carbon dioxide and hydrogen.

EPA (U.S. Environmental Protection Agency): A federal regulatory agency that protects human health and the natural environment.

EPA-registered product: A product bearing the EPA stamp, indicating that it meets EPA standards for efficacy, human health and safety, environmental impact, use instructions, and product labeling. All products that claim to kill or control bacteria, algae, insects, rodents, etc., are required to be EPA-registered.

equalizer line: 1. A line below the pool surface to the body of a skimmer that prevents air from being drawn into the pump. 2. A pipe between two pools or spas to equalize water levels.

equipment area: Area used to house recirculation and disinfecting equipment and related appurtenances.

equivalent pipe length: Friction loss created by pipe fittings and valves is expressed as feet of equivalent pipe length; the fitting causes the same friction loss as that length of pipe.

erosion: 1. The act of destroying or dissolving by slow disintegration or wearing away. 2. In an erosion feeder, the way water dissolves the chemical being fed.

erosion feeder: A device that dispenses a sanitizer by directing a flow of water past tablets, briquettes, or pellets. See also Floating Dispenser.

error codes: Digital displays on electronic control systems that indicate a failure and its likely source, using a sequence of lights, icons or alphanumeric characters. Codes are usually specific to a given manufacturer.

etching: Corrosion of a surface; the pitting or eating away of a material such as the surface of plaster.

ETL (Intertech ETL Semko): A company that tests, inspects, and certifies products for manufacturers and retailers.

evaporation: Conversion of liquid molecules into vapor.

exercise bar: A rail attached to the wall of a pool, spa or swim spa to use as a handhold while exercising.

external bond: A wiring system that connects all pool, spa, or hot tub equipment to a common electrical point connected to a common ground.


FAC, free available chlorine: That portion of the total chlorine that is available as a sanitizer. Also FREE CHLORINE, FC.

faceplate: The front end section of a pump's wet end.

fault current: Current flow to ground, or a short circuit. May be a large flow and therefore hazardous.

fecal streptococci: A group of microorganisms including but not limited to, the bacteria S. faecalis, and S. faecium, which inhabit the gastrointestinal tract of warm-blooded animals. These organisms indicate contamination in water. Ingestion of fecal streptococci can cause illness.

feet of head: A measure of the resistance in a hydraulic system, based on the height of a column of water that would cause the same resistance.
100 feet of head = 43 psi = 3.02 kgjcm2 = 296.47 kPa 1 psi = 70.2 gjc2 = 6.89 kPa = 2.33 feet of head. See also Head, Pressure, Total Dynamic Head.

ferric iron (Fe+3 or Iron III): A mineral that is generally insoluble in water, commonly precipitating as rust.

ferrous iron (Fe+2 or Iron II): A mineral found in groundwater. It is soluble in water and will generally impart a green color. In the presence of oxidizers, it will convert to Iron III.

fiberglass: Fine-spun filaments of glass in a rope or mat form. Used in combination with polyester resins and hardeners to form pools, spas, hot tubs, and related equipment.

fiber-optic: Thin transparent glass or plastic fibers that are enclosed by material of a lower index of refraction, and that transmit light throughout their length by internal reflections.

FIFRA: Federal Insecticide, Fungicide and Rodenticide Act

filter: A vessel that removes undissolved particles from water by circulating the water through a porous substance (a filter medium or element). Can be either a suction type (i.e., a skim filter), or a pressure type, with a removable lid or body secured by a locking ring. Three basic mediums are used; cartridge, diatomaceous earth (DE), and sand.

Some filters use a combination of mediums.

cartridge filter: A filter that uses a pleated porous paper or fabric element as its medium.

diatomaceous earth filter: A filter that uses a thin coating of Diatomaceous Earth (DE) or another filter aid over a porous fabric as its medium.
permanent medium filter, sand filter: A filter that uses filter sand as its medium.

filter agitation: Mechanical or manual movement to dislodge the filter aid and dirt from the filter element.

filter aid: 1. A usually powder-like substance, such as diatoma­ceous earth (DE) or volcanic ash, used to coat a septum-type or sand filter. 2. Finely divided medium (diatomaceous earth, processed perlite, etc.) used to coat the septum of a diatomite filter.

filter cartridge: A filtering element, usually of fibrous material. filter cycle: 1. A programmed filtration period.
2. The operating time between cleaning or backwash cycles.

filter element: Device within a filter designed to entrap solids and conduct water to a manifold, collection header, pipe, or similar conduit and return it to a pool, spa, or hot tub. Usually consists of a septum and septum support, or a cartridge.

filter medium: A finely graded material (such as sand, diatoma­ceous earth, polyester fabric, anthracite, etc.) that removes solid particles from the water.

filter sand: Quartz silica of a specific size and shape, used as the medium in sand filters.

filtration: The process of removing undissolved particles from water by recirculating the water through a porous substance (a filter medium or elements).

filtration flow: The design rate of flow, in volume per time (gprn, gph, Lpm, Lph) through the filter system installed per manufacturer's instructions with a new, clean filter medium or element. 1 U.S. gallon per minute = 3.79 liters per minute 1 U.S. gallon per hour = 3.79 liters per hour

filtration rate: The rate of water flowing through a given area of filter medium or element during a given period of time. Expressed as gallons per minute per square foot, or liters per minute per square meter, of effective filter area.
1 gpm/ft' = 40.75 tpm/rn", Also FILTRATION FLOW RATE.

firebox: Chamber in a pool or spa heater where combustion takes place.

fireman's switch: A mechanism adapted to the time clock that will turn the heater off long enough for it to cool down before the time clock turns off the pump.

float valve: A valve controlled by the level of a fluid.

floater, floating dispenser: A non-mechanized, free-floating plastic device used to sanitize pools or spas through the controlled release of compressed chlorine or bromine, as the chemical dissolves. FLOATER. See Erosion Feeder.

flocculant (floc): A chemical that causes fine suspended solids in water to combine into large clusters that settle out.

floor: The interior bottom surface of a pool, spa, or hot tub.

flow, water flow: The rate of the movement of water, in gallons or liters per minute.
1 U.S. gallon per minute = 3.79 liters per minute.

flow balance valve: Device that regulates the flow from skimmers, drains, or other outlets.

flow meter: A device that measures the rate of flow of water or other liquid through piping.

flow rate: The volume of liquid flowing past a given point in a specified time period. Expressed in gallons per minute (gprn) or per hour (gph), or liters per minute (Lpm) or per hour (Lph).
1 U.S. gpm = 3.79 liters per minute (Lpm)
1 U.S. gph = 3.79 liters per hour (Lph)

flow rider: Pool at a waterpark that uses wave sheet technology for body boarding or body surfing activity.

flow switch: A safety device that prevents the heater or other equipment from operating unless there is adequate water flow through the system.

flume: A trough-like or tubular structure, generally recognized as a water slide, that directs the path of travel and the rate of descent by the rider.

flume slide: Slides of various configurations characterized by deep riding channels, vertical and lateral curves, and high water flows, which accommodate riders using or not using mats, tubes, rafts, and other transport vehicles. Includes but is not limited to family raft rides, inner-tube rides, body slides, and speed slides.

frame: The structure that defines and/or supports the outline or shape of an aboveground pool wall.

free available chlorine (FAC): That portion of the total chlorine that is available as a sanitizer. Also FREE CHLORINE, FC.

freeboard: The clear vertical distance between the top of the filter medium and the lowest outlet of the upper distribution system in a permanent medium filter.

freeze sensor: A protective control device that can detect ambient air or water temperature, and will operate specified equipment until the threat of freezing is over.

freeze-thaw cycle: Seasonal weather and temperature changes that can cause stress to a surface.

friction head, friction loss: Resistance to flow specifically caused by friction or drag. Every portion of the circulation system (filter, heater, chemical feeders, valves and the pipe and fittings) creates a given friction head.

fuse: A device used to protect electrical circuits from overloading. See also Circuit Protection Device.

fusible link (gas heater): A thermal safety cut-off device in the control circuitry that melts if temperature parameters are exceeded.


gallonage: The maximum amount of fluid that can be contained in a pool, spa, hot tub or other container, expressed in gallons. 10,000 U.S. gallons = 37.85 kL. See also Capacity.

gallons per minute (gprn): Flow rate. 1 U.S. gallon per minute = 3.79 liters per minute.

galvanic action: The creation of electrical current by the process of electro-chemical action of dissimilar metals in a liquid.

galvanic corrosion: The deterioration of metal caused when two dissimilar metals are exposed to the electrical current produced by electrochemical action.

gas chlorinator: A device used to sanitize pools by drawing chlorine gas into the circulation system.

gate valve: A device in a pipe that partially or totally obstructs the flow of water with an internal "gate" that moves in and out as the valve is operated.

gelcoat: A colored polyester-resin material applied in liquid form that hardens to a smooth, durable form when applied over a mold.

GFCI, ground-fault circuit interrupter: A safety device that monitors electric current entering and leaving a circuit and will instantly de-energize the circuit if the current to ground exceeds 5/1000 (0.005) of an ampere. Also RESIDUAL CURRENT DEVICE (RCD).

gpd: Gallons per day. 1 U.S. gallon per day = 3.79 liters per day. gph: Gallons per hour. 1 gallon per hour = 3.79 liters per hour. gpm: Gallons per minute. 1 U.S. gallon per minute = 3.79 liters
per minute.

grab bar/rail: Rail used to enter or leave a pool, spa, or hot tub. ground: Connection representing a volts, and the lowest point to which all electricity wants to reach. It represents earth potential and is a safety connection for current/voltage to travel should any electricity escape the circuit. It is not meant to be a current­carrying connection.

ground clearance: Distance between the surface of the ground and the bottom of a fence. This distance should be small enough to prevent entrapment or entry.

ground wire (equipment grounding conductor): A safety device to prevent injury from live current leaking to ground. Attached to the equipment frame rather than the electric circuit; generally identified by green or predominantly green insulator coating.

grounded circuit: Occurs when an energized wire from the electric circuit of a piece of equipment touches the grounded metal structure of the equipment. Also IMPROPER GROUND CONDITION.

grounding: Connecting to or providing a conducting path to earth or ground.

grounding lug: An electrical connector used for grounding and bonding wire.

gunite, dry shotcrete: A pneumatically applied (sprayed) concrete that is a dry mixture of cement, aggregate, and/or sand. Water is applied to the mix at the hose nozzle. See also Shotcrete.

gutter: Overflow trough in the perimeter wall of a pool that is a component of the circulation system or flows to waste.


hair and lint strainer: A device attached on or in front of a pump to which the influent line (suction line) is connected for the purpose of trapping lint, hair, or other debris that could damage the pump.

hair/lint pot: A strainer body, containing a basket, through which the water passes in a circulation system. See Strainer Basket.

halogen: Any of the family of chemical elements including fluorine, chlorine, bromine, and iodine. Chlorine and bromine are commonly used as sanitizers and oxidizers of recreational water.

handhold/handrail: A support device intended to be gripped by a user for the purpose of resting or steadying.

hardness: The amount of calcium and magnesium dissolved in water; measured by a test kit and expressed as parts per million (ppm) of equivalent calcium carbonate.

Hartford loop: A plumbing configuration that helps to prevent water from siphoning toward electrical equipment, air blowers, or ozonators.

hazard: A condition or set of circumstances that has the potential of causing or contributing to injury or death.

head, feet of head: A measure of the amount of pressure or resistance in a hydraulic system. 100 feet of head = 43 psi = 3.02 kgj ern? = 296.47 kPa 1 psi = 70.2 gjc2 = 6.89 kPa = 2.33 feet of head. See also Feet of Head, Total Dynamic Head.

head loss (resistance head): 1. The total loss of pressure from every part of a circulation system (filter, heater, chemical feeders, valves, pipes, and fittings) as resistance increases.

header: A manifold in a gas or oil-fired heater that directs the flow of water into and out of the heat exchanger.

heater: Fossil-fueled, electric or passive device to heat the water of a pool, spa, or hot tub.

direct electric: Uses resistive heating element placed in line with the circulation system.

fossil-fueled: Burns natural gas, propane gas, or fuel oil to transfer heat to water flowing through a heat exchanger,

heat pump: Device that uses a compressor with a closed freon loop to exchange heat between either the ambient air, or an external water source, and pool, spa, or hot tub water.

radiant in-floor: Circulates warmed refrigerant through flexible tubing installed below the pool or spa floor.

solar: Uses energy from the sun to heat the collector or, through the blanket, to heat the water. Other ways to categorize heaters include: direct heaters: Heat the tubes in which water circulates. indirect heaters: Circulate steam or hot water inside a heat exchanger through which water flows.

heat exchanger: A device with coils, tubes, and plates that takes heat from a liquid or air and transfers that heat to another fluid without intermixing the fluids.

heat loss: The natural drop in water temperature as heat is transferred to the surrounding air.

heat pump: A refrigeration compressor operated in reverse. To obtain heat, the evaporator side (cooling coil) is exposed to water, air, or ground. The coil transfers heat from this source to a condenser COil, which transfers it to the pool, spa, or hot tub water.

heat recovery system: A heating system that transfers energy produced by the pump's motor to the water. It can be used as a primary or supplemental heating source.

heat sink: A type of device capable of absorbing and dissipating heat.

hertz (Hz): A measure of the frequency of alternating current. A frequency of 60 cycles per second is described as 60 Hz.

High Limit sensor: A device found in an electronic control system, that senses water or heater high-temperature events, triggering error-message displays and possible equipment shutdown.

High Limit switch: A temperature control switch used in an elec­tromechanical system to shut off a pool, spa, or hot tub heater when the temperature of the water or supporting equipment exceeds a preset limit. Some can be manually reset.

high permeability element: Mechanically interlocked, non-woven filter material designed to remove suspended solids.

hoop: A device used to secure sections of a filter together. horsepower (hp): The performance rating of an electric motor based on the voltage supplied and the current developed. 1 hp = 33,000 foot-pounds per minute = 42.41 BTU per minute = 745.7 watts.

hose bibb, hose bib: A valve with a threaded connection, specifi­cally used as a hose connection.

hot: A term indicating the supply side of voltage applied to a load. Also known as Ll, L2 or line.

hot side (load side): The output side of an electric circuit, where the power is used to perform work.

hot tub: A manufactured or prefabricated vessel with self-con­tained equipment that circulates, filters and heats chemically treated water.

self-contained hot tub:A hot tub that has a cabinet that houses the controls, the pump, heater, and filter. Most are made of an acrylic thermoplastic shell and are surrounded by a cabinet made of wood, alternative wood, or thermoplastic. A "self-contained hot tub" can be moved to another location and reinstalled. A "self-contained hot tub" has all control, water heating and water circulating equipment as an integral part of the product. A "self-contained hot tub" may be permanently wired or cord connected. Also known as a "portable hot tub."

hydraulics: The science of water in motion. Deals with the physical movement of water through the circulation system and is concerned with such matters as friction and turbulence generated in the pipes and other components of the system by the moving water.

hydrochloric acid (HCI): A by-product of the addition of chlorine to water. A very strong acid used for pH control and certain specific cleaning needs. Extreme caution is required in handling. Also called Muriatic Acid when diluted.

hydrogen peroxide (H202): Compound consisting of hydrogen and oxygen supplied in an aqueous solution. Used as an oxidizer. Will neutralize halogen sanitizer in water.

hydrojet: A fitting that blends air and water to create a high-velocity turbulent stream of air-enriched water. Also HYDROTHERAPY JET, JET.

hydrostatic pressure: The pressure created by a depth of water, such as the upward pressure exerted by high ground water on the structure of a pool or spa.

hydrostatic relief valve: A fitting installed in the bottom of a pool or spa that is designed to open automatically or manually. Relieves upward ground water pressure by allowing water to flow into the pool or spa.

hypobromous acid (HOBr): A chemical compound that acts as a sanitizer and algicide in water.

hypochlorinator: A chemical feeder through which liquid solu­tions of chlorine-bearing chemicals are fed into pool, spa, or hot tub water at a controlled rate. See Chlorinator.
hypochlorite: A family of chemical compounds including calcium hypochlorite, lithium hypochlorite, sodium hypochlorite, etc., found in various forms: Used as a chlorine carrier in pool, spa, or hot tub water.

hypochlorite ion (OCI-): The anion from ionization of hypochlo­rous acid.

hypochlorous acid (HOCI): The most powerful chlorine-based sanitizer of water; also acts as an algicide. Formed when a chlorine product is dissolved in water.


IC: See Integrated Circuit.

impeller: The rotating part of a centrifugal pump, which creates the flow of water.

1. A quantitative relationship between a changing magnetic field and the electric field created by the change.
2. In electromagnetism, the production of voltage across a conductor situated in a changing magnetic field.

induction motor: An alternating-current (AC) motor in which torque (rotating force) is produced by the reaction between a varying magnetic field generated in the stator (containing primary and secondary windings) and the current induced i the coils of the rotor.

inductive load: A load whose performance is based on rnagn fields produced by electron flow through internal coils or viin ings, rather than on current pushing past resistance. Magne . fields produce a counter voltage, which will oppose curren flow based on field strength and/or revolutions per minute. Electric motors and transformers are considered inductive loads.

inertia: The tendency of all matter to persist in its state of rest - uniform motion until acted upon by some external force.

influent: Water entering a filter or other device.

ingress: Means of entry.

inlet fitting: A pipe that allows water to enter a pool, spa, or 0: tub.

insulator: A material with high electrical resistance, that does not readily allow electrons to flow through it; a non-conducto . Examples of insulators: rubber, plastic, wood, glass, etc.

integrated circuit, IC, chip: A system combining the functions of several discrete devices or components in one package arranged on a single semiconductor.

interlock system: See Door Interlock,

intermediate pool: Any section of a quiescent water flow between the entry and landing pools in attractions at a waterpark that utilize a series of pools.

intermittent ignition device: An electrical device used to igni "E gas heater.

1. A process whereby a compound in solution separates in positive ions (cations) and negative ions (anions).
2. A chemical process which uses copper and silver ions inhibit the growth of bacteria and algae.

ionizer: A device that electrochemically generates metal ions such as silver, copper and zinc ions, from anodes of these metals.

iron: See Ferric Iron or Ferrous Iron.

isocyanurates (ISOs): Sanitizer products that self-stabilize by releasing free available chlorine and cyanuric acid as they dissolve. See Chlorinated Isocyanurates.
jet: See Hydrojet.


jet flow: The flow of water through hydrotherapy jets; measured in gallons per minute (gpm) or liters per minute (Lpm).

jet pump: A pump used to support hydrotherapy jets or special water features.

jump board: A manufactured diving board that has a coil spring, leaf spring, or comparable device located beneath the board that is activated by the force exerted by jumping on the board's end.

jumping jet: A hydraulic device used in fountains to fluctuate the stream of water by blowing through it with another stream of water or air to deflect its flow.


kilohm (kG): Equal to 1000 ohms. See Ohm. kilovolt (kV): Equal to 1000 volts. See Volt.

kilowatt: A unit of power equal to 1000 watts. Equivalent to 56.89 BTU per minute/1.341 horsepower. See Watt.

kilowatt hour: A unit of work or energy equal to that expended by one kilowatt in an hour. 1 kilowatt hour = 3413 BTU = 3.6 million joules


ladder: A structure for ingress/egress that usually consists of two long parallel side pieces joined at intervals by crosspieces (treads). Ladders for aboveground/onground pools consist of the following (also see ANSI! APSP-4 Standard for Aboveg­round/Onground Residential Swimming Pools, 2007 or latest edition):

"A-Frame" ladder: An entry ladder that straddles an aboveg­round/onground pool wall and is either removable or has a built-in entry limiting feature.
double access ladder (Type A): An "A-Frame" ladder that straddles the pool wall of an aboveground pool and provides ingress and egress and is intended to be removed when not in use.

limited access ladder (Type B): An "A-Frame" ladder that staddles the pool wall of an aboveground/onground pool. Type B ladders are removable and have built-in features that prevent entry to the pool when the pool is not in use.

staircase ladder (Type C): A "ground to deck" staircase ladder that allows access to an aboveground pool deck and has a built-in entry-limiting feature.

"in-pool" staircase ladder (Type E): Located in the pool to provide a means of ingress and egress from the pool to the deck.

landing pool: Pool at a waterpark that is located at the end of a flume; designed to safely receive the rider of an attraction.

Langelier Saturation Index: A numerical calculation based on the Langelier water balance equation, that indicates whether water may be corrosive or scale forming.
SI = pH + F(T) + F(TA) + F(CH) - 12.1. See also Saturation Index.

latching switch: A type of on/off switch where, once acted on, the contacts move and remain in position until acted on again. Manually or electronically activated. See Switch.

LeD (liquid crystal display): A flat panel display using a liquid crystal located between glass or plastic polarizing layers. When electric current is applied, the liquid crystal becomes opaque and causes a contrast which appears as characters.

LED (light emitting diode): A low-voltage semiconductor device that emits visible light when electric current passes through it. Commonly used for indicator lights, mood lighting, and control panel displays.

leaching: The extracting of a soluble substance from some material, such as calcium from plaster.

lifeguard: A qualified person who is responsible for supervision and lifesaving at a pool.

lifeline: An anchored line thrown to aid in rescue.

line voltage: Electrical power delivered to homes and businesses through aboveground or underground powerlines.

liner: See Vinyl Liner.

liquid acid (Hel): Chemical used to lower pH and total alkalinity, most commonly muriatic acid.

liquid chlorine: See Sodium Hypochlorite. liquid chlorinator: See Solution Feeder.

liquid propane gas: The liquid form of propane gas, a heavy hydrocarbon occurring naturally in petroleum.

lithium hypochlorite (UOel): A white, solid chemical compound used as a water sanitizer and oxidizer. Has a pH of approxi­mately 9 and typically contains 35% available chlorine.

load: 1. An electrical term for equipment that does work. Loads drop voltage and produce current while doing work (Le., produc­ing heat, light, motion, etc.).
2. user load: The number of people in a pool, spa, or hot tub at anyone time.

load side: The output side of a switching device.

local disconnect: A readily accessible electrical device used, in addition to the main circuit panel breaker, to shut off power to an electrical system. Also QUICK DISCONNECT.

logic: The timing of events used to properly operate the devices of a pool, spa, or hot tub. See Sequencing Logic, Switch Logic.

logic voltage, control Voltage: The voltage used by a control or circuit board to activate and deactivate the switching functions of a system. Usually isolated from the voltage used to activate relays or to power load devices.

lower distribution system: A device used in the bottom of a permanent medium filter to collect water during filtering and distribute it during backwashing. Also UNDERDRAIN.


magnesium hardness: A measure of the amount of magnesium dissolved in water and expressed in parts per million (ppm) or milligrams per liter (mgjL) as calcium carbonate.

main drains: Outlets located at the bottom of a pool, spa, or hot tub to conduct water to the recirculating pump. Also SUCTION OUTLETS.

make-up water: Water used to fill or refill a pool, spa, hot tub, or water feature. Also SOURCE WATER.

manifold (heater): A means of mounting a heater element so that it is fully immersed in the flow of water. Heater manifolds may also provide mounting for safety devices and locations for sensors to take samples.

manifold (plumbing): A fitting with several openings for making multiple connections.

manometer: An instrument that measures vacuum or pressure differential.

manufactured diving equipment: Includes diving boards, jump boards, springboards, and starting platforms. Architectural features such as decorative rocks and elevated bond beams are not considered to be manufactured diving equipment.

maximum user load: The maximum number of people allowed in a pool, spa, or hot tub at anyone time.

mechanical seal: A device to prevent the passage of water into or out of a centrifugal pump at the motor shaft.

medical facility pool: Special purpose pool used by a medical institution.

meniscus: CUNe in the level of water caused by the surface of a container and the surface tension of the water. For accurate measurement, the lower part of the CUNe is read.

mesh restraining barrier/fence: A combination of materials, including fabric, posts, and other hardware to form a barrier around a swimming pool or other areas.

methyl ethyl ketone (MEK): A solvent used to repair surface scratches in pools, spas or hot tubs manufactured from certain plastics. Also used to clean PVC pipe and fittings prior to gluing.

micron: One millionth of a meter. Used to describe the size of particles that filters are capable of trapping.

microorganism: A unit of microscopic plant or animal life, such as bacteria, protozoa, and algae.

microprocessor: An integrated circuit, mounted on a PCB, that monitors and controls the operations of a pool, spa, or hot tub. Also MICROCONTROLLER.

millivolt (mV): A measure of electrical potential equal to one­thousandth (0.001) of a volt.

millivolt ignition (flame): A type of gas heater ignition system where electricity is generated by the pilot flame.

mineral purifier, mineral system: A device that supplies a stream of copper, silver, and/or zinc ions to pool, spa

or hot tub water as a supplemental water treatment. Copper ions provide an algicide, while silver or zinc ions work as a bactericide.
moment: Rotation force.

momentary switch: A switching device where the contacts do not latch.

mother board: See Circuit Board.

mottling: 1. A different coloration of plaster, similar to the shad­ing difference of cumulus clouds with no apparent pattern.
2. A blotch, spot, or streak of different shades of color, usually in a variegated pattern.

motor: A machine for converting electrical energy into mechani­cal energy. When electrical current is supplied to a series of wires (windings), a magnetic field is created that spins the rotor and shaft to drive a pump impeller.

MSDS, Material Safety Data Sheet: Information provided by the manufacturer about a hazardous material or chemical.

multimeter: An electrical testing device that combines the functions of voltmeter (for measuring voltage), ohmmeter (for measuring resistance) and ammeter (for measuring current) in one package.

multiport valve: A device that allows for the multidirectional control of the passage or flow of water through a system.
muriatic acid (HCI): A commercial name for hydrochloric acid. HydrochloriC acid when diluted to 31.45% acid to water.


NEC (National Electrical Code): The generally recognized author­ity on safe and proper electrical installation; used in the United States, Mexico and Puerto Rico. NEC is a registered trademark of the National Fire Protection Association (NFPA).

NEMA (National Electrical Manufacturers Association): A U.S. trade association representing manufacturers of products used in the generation, transmission and distribution, control, and end-use of electricity.

natural gas: A mixture of gaseous hydrocarbons, chiefly methane, naturally occurring underground, often in association with petroleum products.

negative edge: See Vanishing Edge.

neutral side: The side of an electric circuit where the current returns from the load to the source.

nitrogen (N2): An element present in ammonia, sweat, urine, fertilizers, some personal care products, and environmental sources. In pool, spa, and hot tub water, it reacts with chlorine to form chloramines, or with bromine to form bromamines.

non-swimming area: Any portion of a pool where water depth, offset ledges, or other irregularities prevent normal swimming activities.

nontoxic: Generally having no adverse physiological effect on human beings or other living organisms.

normally closed (N.C.): Terminal where a switch connection is made to the common terminal before activation.

normally open (N.O.): Terminal where the switch connection is made with the common terminal after activation.

NSF International (National Sanitation Foundation): An independent, nonprofit organization of scientists, engineers, educators, and others engaged in research and testing and in the development of standards in selected public health and environmental areas. See www.nsf.org.

NSPF (National Swimming Pool Foundation): A nonprofit organization dedicated to research and education in aquatic safety. See www.nspf.org.

NSPI (National Spa & Pool Institute): See APSP.


OEM: Original equipment manufacturer, or brand name.

ohm (Q): The unit of measure of the resistance to electron flow in a circuit.

Ohm's law: An equation showing the relationship between voltage, current, and resistance, expressed as:
current = voltage+ resistance, or I = E.;. R. Also:
volts = amps x ohms
amps = volts » ohms
ohms = volts .;. amps

ohmmeter: A device that measures resistance to the flow of an electric current. See Multimeter.

open circuit: Circuit where an electrical switch or other device (load) is open (off or disconnected), or where the electrical pathway is broken, and therefore, current cannot flow.

open impeller: An impeller with vanes covered on the back but exposed on the front, allowing for adjustment. See Impeller.

organic matter: Carbon-based substances, generally originating from living organisms, often introduced into pools or spas by bathers and the environment. For example: perspiration, urine, saliva, suntan oil, cosmetics, lotions, dead skin.

organisms: Plant or animal life, usually algae or bacteria-like growth in water.

orifice: An opening in a device, usually calibrated in size, through which water, air, or gas flows.

orifice plate: A disk, placed in a water flow line, with a concentric, sharp-edged circular opening in the center that creates a differential pressure to measure flow and to operate feeders, instruments, or other hydraulic equipment.

ORP: See Oxidation·reduction Potential.

Orthotolidine (OTO): A colorless reagent that reacts with chlorine or bromine to produce yellow-to-orange colors that indicate the amount of total chlorine or bromine in water. A suspected carcinogen.

OSHA, Occupational Safety and Health Administration: A part of the U.S. Department of Labor with the task of addressing and preventing workplace hazards and injuries. Defines and enforces safe working environments.

outdoor stack: A type of equipment used with outdoor heaters in windy areas.

outlet: An aperture or fitting through which water flows from a pool, spa, or hot tub.

outlet, suction: See Suction Outlet.

overflow gutter: The gutter around the top perimeter of a pool or spa, which is used to skim the surface of the water and carry off the waste or collect it for return to the filters.

overflow system: The removal of pool or spa surface water through the use of overflows and surface water collection systems.

overloading: A condition that occurs when too much current is forced through a conductor unable to carry it.

oxidation: A chemical process where a material or chemical is combined with oxygen. Used to destroy contaminants.

oxidation-reduction potential (ORP): A measure of the effective­ness of oxidizing chemicals in water. It is generally measured by an electronic millivolt meter and depends upon the types and concentrations of oxidizing (sanitizing) and reducing (contami­nating) chemicals in the water.

oxidizer: A product used to destroy organic and inorganic contaminants in water.

ozonator, ozone generator: A device that produces ozone, generally by exposing oxygen or air to corona discharge or ultraviolet light.

ozone (03): A gaseous molecule composed of three (3) ionized atoms of oxygen. Used for oxidation of water contaminants.
It can also be used to regenerate bromine from bromide ions and as a supplemental contact sanitizer in conjunction with an EPA-registered sanitizer that provides a constant residual.

ozone contact concentration: The amount of ozone dissolved in pool, spa, or hot tub water.


panel (panelboard): 1. Part of the general household electrical service, of which the pool, spa, or hot tub electrical system is often a branch circuit. 2. A part or parts of a pool, spa, or hot tub control system

parallel circuit: A circuit that allows current to flow along more than one conductor at the same time.

parts per million (ppm): The unit of measurement used in chemical testing that indicates the parts by weight in relation to one million parts by weight of water. Essentially identical to the term milligrams per liter (mgjL).

pathogen: Disease-causing microorganism. See Recreational Water Illness.

pathological agents: Toxins, microbes, etc., capable of causing diseases.

PCB, printed circuit board: See Circuit Board.

perimeter overflow system, rimflow overflow system: Pool or spa in which the overflow rim is at the same elevation as the deck.

peristaltic pump: A type of positive displacement pump. permanently installed swimming pool: A pool constructed in the ground or in a building in such a manner that it cannot be readily disassembled for storage.

pH: A value used to express the acidity of a substance. Expressed as a number on a logarithmic scale of 0-14, with 7.0 being neutral. Values less than 7.0 are acidic and values greater than 7.0 are basic. The letters stand for potential Hydrogen.

pH meter: An electronic device that measures pH by means of a pH electrode immersed in the water to be tested.

phase: A type of electric current. In single-phase, there is only one alternating current or voltage in a circuit. In North America, three-phase has three alternating currents delivered on three separate wires, each 1200 out of phase with the others, to enable smoother, more efficient operation of equipment.

Phenol Red: A test kit reagent used to measure pH in the range between 6.8 and 8.4 The color changes from yellow to red to purple as pH increases.

PHMB: See Polyhexamethylene Biguanide.

phosphate: An inorganic chemical containing phosphorus. Sometimes used to control pH fluctuation.

pilot duty: A switch that indirectly controls power to a device, usually by controlling the coil on a relay or contactor.

pilot generator: The component in a millivolt ignition system that transforms heat from the pilot flame into electrical energy. Also THERMAL COUPLING, THERMOCOUPLE.

pilot light: A small flame used to ignite gas at the burner. pinching hazard: Any configuration or component that may pinch the user.

piston pump: A type of positive displacement pump.

pitting: A form of etching or the deterioration of the integrity of a surface.

plaster: Mixture of Portland cement, water and sand; used as a interior and exterior wall finish material. A variety of finishes a~~ ornamental designs may be formed with plaster. Also MARCrTE QUAR1Z PLASTER, TOPCOAT, WHITE COAT.

plaster dust: Fine particles of calcium carbonate formed when e carbonates in water react with the calcium hydroxide (Ca(OH): in new plaster.

polarity: The charge (positive or negative) of a voltage or materia. poles: The number of circuits being switched in a switch package.

polyhexamethylene biguanide (PHMB): A manufactured organic polymer that is EPA-registered for sanitization of bacteria in recreational water.

polymeric biguanide: See PolyhexamethyJene Biguanide.

polyvinyl chloride (PVC): Thermoplastic resin commonly used for pool, spa, and hot tub piping, plumbing components, and for pool liners.

pool: A body of water contained in a reservoir used for recreation­al purposes. See Residential Pool, Commercial/Public Pool.

pool slide: An attraction having a configuration as defined in The Code of Federal Regulations (CFR) Ch. II, Part 1207, or is similar in construction to a playground slide used to allow users to slide from an elevated height to a pool.

pool user: Any person using a pool and adjoining deck area for the purpose of water activities or other related activities. BATHER, SWIMMER. positive displacement pump, solution feeder: A small pump used to automatically dispense sanitizer or other chemical solutions.

potable water: Water that is safe and satisfactory for drinking. potential: The difference of voltage between two points. See Voltage.

potentiometer (pot): 1. A device for measuring electromotive force or potential difference by comparison with a known voltage. 2. A variable resistor for controlling voltage.

potassium monopersulfate (KHS05): A solid oxidizer used to prevent the buildup of organic contaminants in pool, spa, or hot tub water. Also POTASSIUM PEROXYMONOSULFATE.

pounds per square inch (psi): A unit of pressure. 1 psi = 70.3 grams/em? = 6.89 KiloPascal (kPa)

power: The time rate of doing work as measured in watts.

Power Equation, Watt's Law: Equation that shows the relationship between power in watts, current in amps, and voltage in volts.
P (watts) = I (amps) x E (volts)
I (amps) = P (watts)+ E (volts)
E (volts) = P (watts)+ I (amps)

power supply: 1. A group of components in a PCB control, combining a transformer, a bridge rectifier, and a filter capacitor. 2. The incoming service on an electromechanical control.

ppm: See Parts Per Million.

precipitate: 1. A substance that separates from a liquid in the form of solid particles, or remains as a haze in suspension (turbidity). 2. To cause a substance to separate from a liquid and settle out as particles, or remain as a haze in suspension.

pre-coat: The coating of filter aid on the septum of a diatoma­ceous earth filter at the beginning of each filter cycle.

pre-coat feeder: A chemical feeder designed to inject filter agents such as diatomaceous earth into a filter in sufficient quantity to coat the filter septum at the start of a filter run.

pressure: A type of force that is exerted uniformly in all directions. Expressed in pounds per square inch (psi), grams or kilograms per square centimeter, kiloPascal, feet of head, and inches of mercury (Hg), 1 psi = 70.2 g/crn" = 6.89 kPa = 2.33 feet of head 1 in. Hg = .49 psi = 3.386 kPa = 1.145 feet of head

pressure differential: The difference in pressure between two parts of a hydraulic system, such as the inlet and outlet of a filter.

pressure gauge: A gauge that measures the amount of pressure within a closed system.

pressure switch (heater): A device that will not allow the heater to operate unless there is adequate water pressure in the system. Also WATER PRESSURE SWITCH.

pressure test: A test for leaks in a closed system.

priming: A term used to define the establishment of water flow through the pump(s) and the removal of air from the plumbing
psi: See Pounds per Square Inch.

public pool: See Commercial/Public Pool.

pump: A mechanical device, usually powered by an electric motor, that creates hydraulic pressure to drive a liquid. Typically, a centrifugal pump drives water for the circulation, filtration, and heating of a pool, spa, or hot tub. Booster pumps are used to supplement the main pump, inject ions or chemicals into
the water, or power jets and water features. See Booster Pump, Centrifugal Pump, Circulation Pump, Jet Pump.

pump capacity: The volume of liquid a pump is capable of moving during a specified period of time against a given total head.

pump curve: A graph showing the performance characteristics of a given pump under varying horsepower, flow, and resistance factors. Used in checking and sizing a pump.

pump strainer: A device, placed on the suction side of a pump, that contains a removable strainer basket designed to trap debris in the water flow with a minimum of flow restriction. Also HAIR/LINT POT, TRAP.

puncture hazard: Any protrusion that is capable of causing injury to skin.

push-pull valve: A device that allows for the dual directional control of water flow through a system. See Valve.


quaternary ammonium (quat): Organic compound of ammonia used as an algistat or algicide to assist in recreational water sanitation. A low-level disinfectant effective against bacteria, but not against spores or viruses.

quick disconnect: See Local Disconnect. radius corner: A rounded corner.


radius of curvature: The curved surface from the springline (vertical sidewall) to the pool bottom. Also WALL COVE,

rated pressure: The pressure rating specified for a piece of equipment.

rate of flow: The quantity of water flowing past a point within a given time, such as the number of gallons flowing in one minute (gprn). 1 gallon per minute = 3.79 liters per minute.

RCD: Residual current device. See GFCI. RC network: See Snubber.

reagent: A chemical used to test various aspects of water quality. recessed treads: A series of vertically spaced cavities in a pool or
spa wall creating tread areas for step holes,

recirculation system: See Circulation System. recreational water illness (RWI): An infectious disease spread rectify voltage: To convert alternating current into direct current. See Bridge Rectifier.

regulated voltage: A specific voltage level which is held to a stated tolerance.

relay: A device that responds to a current or voltage change by activating switches in an electric circuit.

relay voltage: Voltage produced by the power supply that is used to select or deselect relay coils and lighting circuits on a PCB,

remodel: To install cosmetic changes, accessory add-ons, or modernizations to a residential or commercial installation.

remote switch: A device used to activate or deactivate an apparatus from a distance.

removable: Capable of being easily disassembled or removed. renovate: Material alteration. To restore all or part of a pool or spa structure and its component parts including the rebuilding and/or replacing of worn and broken components. See also Remodel.

residential pool: Any pool intended for non-commercial use as a swimming pool by three (3) families or less and their guests and that is over twenty-four inches (24 in.j60.96 cm) in water depth and has a volume greater than 3250 gallons/12.3 kL. (Refer to ANSf/APSP-5, Standard for Residentiallnground Swimming Pools.)

residential aboveground swimming pool- Type 0: A pool of any shape that has a minimum water depth of thirty-six inches (36 in.j 0.91m) and a maximum water depth of forty-eight inches (48 in./1.22 m) at the wall. The wall is located on the surrounding ground and is capable of being disassembled or stored and reassembled to its original integrity. Diving and the use of a water slide are prohibited (Refer to ANSI! APSP-4, Standard for Aboveground/Onground Residential Swimming Pools). See Residential Onground Swimming Pool.

residential onground swimming pool- Type 0: A pool package whose walls rest fully on the surrounding ground and has an excavated area below the ground level where diving and the use of a water slide are prohibited. (Refer to ANSI/APSP-4, Standard for Aboveground/Onground Residential Swimming Pools). The slope adjacent to the shallow area shall have a maximum slope of 3:1, and the slope adjacent to the sidewalls shall have a maximum slope of 1: 1. See Residential Aboveground Swimming Pool.

Type I-V: Residential pool suitable for the installation of diving equipment by type.

Type 0: Residential pool where the installation of diving equip­ment is prohibited.

residual: The measurable sanitizer present in water.

resistance (electrical): Opposition to the flow of electric current, measured in ohms. See Ohm.

resistance head, head loss: Opposition to flow, which increases as water flows through the turns and bends in a circulation system.

resistor capacitor: A device used to smooth spikes and sharp edges from an electrical signal.

resistance test: A test to measure the resistance in an electrical circuit or component.

resistive load: An electrical load in which voltage and current are converted to energy in the form of heat (i.e., an electric heater).

response time: The time between recognition of pool user distress and rescue by a lifeguard.

return inlet: The aperture or fitting through which water under positive pressure returns into a pool, spa, or hot tub.

return piping: The piping that returns water to the pool, spa, 0 hot tub.

reverse circulation: A water circulation system in which water is taken from the surface and returned through inlets at e bottom of a pool, spa, or hot tub.

ring buoy: A ring-shaped floating buoy capable of supporting a user. Usually attached to a throwing line.

riser: The vertical part of a stair.

rocker switch: A manually operated on/off or mode selection switch whose actuator has a rocking motion. When one side d the switch is raised, the other is depressed. See Switch.

rotor: The rotating winding of an electric motor, which turns the drive shaft.

rope and float line: A continuous line not less than one-fourth inch (% in.j6.35 mm) in diameter that is supported by buoys and attached to opposite sides of a pool to separate the deep and shallow ends.

runout: That part of a waterslide where riders are intended to decelerate and/or come to a stop. The runout is a continua­tion of the waterslide flume surface.


safety switching device: A switching device whose activation method monitors the performance of a circuit and will deactivate it if the system goes out of tolerance.

safety vacuum release system (SVRS): A device designed to shut off a pump that loses water flow due to a suction blockage.

salinity: The salt content of water.

sand filter: A filter using sand or sand and gravel as a filter medium.

sanitizer: An agent which can reduce 99.999% of a specific bacterial population within 30 seconds. Its main function is to reduce the number of microorganisms to a safe level. although it may not destroy all pathogenic bacteria. Increasing the concentration of a sanitizer may make it a disinfectant, which has a higher ability to destroy pathogenic bacteria than ­a sanitizer.

SARA, Superfund Amendment Reauthorization Act, Title "I, "Community Right-to-Know Act": A U.S. federal law mandating that companies that handle hazardous substances must info their communities. Saturation Index: A number that indicates whether water will  have a tendency to deposit calcium carbonate from a solution or whether it will be potentially corrosive. Five factors are used in the computation: pH (acidity), total alkalinity, calcium hardness, temperature, and total dissolved solids (TDS). When correctly balanced, the water will be neither scale-forming corrosive. See also Langelier Saturation Index.

scale: The precipitate that forms on surfaces in contact with water when the calcium hardness, pH, alkalinity level, or Satura­tion Index is too high.

sealant: A substance applied on a surface or between surfaces to prevent the entry of moisture.

seal plate: The motor-side section of a centrifugal pump's wet end, which holds the shaft seal.

seat (underwater): An underwater ledge that is placed completely inside the perimeter shape of the pool; generally located in the shallow end of the pool. Also BENCH (UNDERWATER).

sediment trap: A device used on gas piping and other systems to collect sediment and moisture.

self priming: Description of a centrifugal pump, indicating that it is capable of operating above the water level, after being initially filled with water.

semiconductor: A material (silicon, germanium, etc.) of medium electrical conductivity at room temperature-less than a conduc­tor, but more than an insulator.

sensor: A device which measures a specific parameter, such as water temperature, and transmits a signal to a control device or system.

septum: Part of a diatomaceous earth (DE) filter element consist­ing of cloth, wire screen, or other porous material on which the filter medium is deposited.

sequencing logic: A control system using one or two user-input devices to control multiple device functions in a pool, spa, or hot tub.

sequencing switch: A mechanical switching device that uses a cam to activate and deactivate switch contacts in a sequence, controlling two or more pool, spa, or hot tub functions. Also FOUR-FUNCTION SWITCH, SEQUENCER, STEPPER SWITCH.

sequestering agent: See Chelating Agent.

series circuit: A circuit with a single conductive pathway for current to use. If a break or open occurs, current stops.

service factor: The degree to which an electric motor can be operated above its rated horsepower without danger of overload failure.

shaft seal assembly: See Mechanical Seal.

shallow area: Portion of a pool or spa with water depth less than five feet (5 ft.f/1.52 m).

sheath: The portion of an electric heater element that is immersed in water, usually made of a metal that resists dam­age from water, heat, and chemicals (stainless steel, Incoloy, titanium)

shocking, shock treatment: The practice of adding significant oxidizing chemical to water to destroy contamination. Also OXIDATION.

short circuit, shorted circuit, short: A circuit where the electrons take a shortcut to the source, avoiding the load. If a circuit has zero resistance from any load wired into it, it has a short or is a short circuit.

shotcrete: Concrete or mortar sprayed in either a dry- or wet-mix process. Both methods are used to build the concrete floors and walls of swimming pools, spas, and water features.

1. Dry shotcrete is a mixture of sand and cement, blown through a nozzle where water is added. See also Gunite.

2. Wet shotcrete is a pneumatically applied (sprayed) mixture of sand, cement, aggregate and water and pumped wet through a nozzle where air is added.

shut-off head: The amount of resistance (head) against which a pump can no longer circulate water.

sight barrier: A fence system that prevents entry but allows visual observation. See Barrier.

signal word: A visual alerting device in the form of a decal or label placard or other marking such as an embossing, stamping, etching, or other process that advises the observer of the nature and degree of the potential hazard(s) that can cause property damage, injury, or death. It can also provide safety precau­tions or evasive actions to take, or provide other directions to eliminate or reduce the hazard. Aquatic safety sign age shall conform to specifications as described in the ANSI Z-535 series of standards on product safety signs and labels.

signal word: A word that conveys the gravity of the risk. consequences: What will likely happen if the warning is not heeded.

instructions: Appropriate behavior to reduce or eliminate the hazard.

CAUTION: Indicates a potentially hazardous situation that, if not avoided, could result in minor or moderate injury. It may also be used to alert against unsafe practices.

DANGER: Indicates an imminently hazardous situation that, if not avoided, will result in death or serious injury. This signal word is to be limited to the most extreme situations.

WARNING: Indicates a potentially hazardous situation that, if not avoided, could result in death or serious injury.

single-phase current: Electrical alternating current flow that reaches one peak in each direction per cycle.

single pole: A switch with one input (switching device). See Switch.

single throw: A switch with one output per single switching device. See Switch.

skim filter: A waterline suction outlet, including a filter cartridge.

skimmer: A device installed in a pool or spa that permits the removal of floating debris and surface water to the filter.

skimmer lid: A removable lid to close deck opening to the skim­mer housing.

skimmer equalizer pipe: Connection from skimmer housing to a pool or spa below the weir, sized to satisfy pump demand and prevent air lock or pump loss of prime.

skimmer equalizer valve: A device on the equalizer line that oper­ates to draw water from the equalizer line when the water level inside the skimmer body drops below operating level.

skimmer housing: Structure that attaches to or contains the skimmer weir, strainer basket, float valve, and other devices used in the skimming operation.

skimmer weir: Part of a skimmer that adjusts automatically to small changes in water level to ensure a continuous flow of water to the skimmer.

slip resisting: Describes a surface that has been treated or con­structed to significantly reduce the chance of a user slipping: the surface is not an abrasion hazard.

slow-blow fuse: A safety device that protects equipment from over current by breaking the connection if the friction of the electron flow causes the temperature to rise above a preset limit. There is a delay before the fuse opens the circuit. Most useful with inductive devices such as pump and blower motors, which can cause current spikes as they start up.

slurry: A free-flowing, pumpable suspension of fine, solid material in liquid (usually DE).

snubber: A device used to smooth spikes and sharp edges from an electrical signal (to filter electrical noise). Also RC NETWORK.

soda ash: See Sodium Carbonate.

sodium bicarbonate (NaHC03): A white powder (pH = 8.3) used to raise total alkalinity in water. Also BAKING SODA, SODIUM HYDROGEN CARBONATE.

sodium bisulfate (NaHS04): A granule used to lower pH and/or total alkalinity in water. Also DRY ACID.

sodium carbonate (Na2C03): A white powder used to raise the pH of water. Also SODA ASH.

sodium dichlor (sodium dichloro-isocyanurate) (C3N303CbNa): Sanitizer product that is self-stabilizing due to the release of free available chlorine and cyanuric acid when it dissolves. Contains between 56% and 64% available chlorine. Also SODIUM DICHLORO-S-TRIAZINETRIONE.

sodium hydroxide (NaOH): A highly alkaline substance.

sodium hypochlorite (NaOCI): A clear liquid form of an inorganic chlorine compound obtainable in concentrations of 5% to 16% available chlorine. Also LIQUID CHLORINE, BLEACH.

sodium sesquicarbonate: A chemical containing soda ash and sodium bicarbonate. Used to raise both TA and pH.

sodium thiosulfate (Na2S203): A chemical used to reduce or neutralize the chlorine or bromine level in water.

soft water: Water that has a low calcium and magnesium content.

solar panel: An assembly of components used to collect solar energy for heating, i.e., rooftop structure, floating devices, etc. Also COLLECTOR.

solid chemical feeder: A device that dispenses a dry chemical product into water; may be mechanized or work by erosion.

solution feeder, positive displacement pump: A small pump that automatically dispenses sanitizers or other chemicals into recreational water.

solvent welding: Method of joining plastic pipe and fittings which "glues" joints by melting the plastic together with a solvent.

soot: A black, powdery, carbonaceous substance created by improper air-fuel mixture in combustion of fossil fuels; a byproduct of incomplete combustion.

source VOltage: Voltage from the device which produces electro­motive force between poles.

spa: A permanently installed warm water reservoir with hydromas­sage jets, that is constructed out of concrete (gunite, shotcrete, etc.). Mayor may not be attached to a pool.

permanent residential spa: A spa in which the water heating and water circulating equipment is not an integral part of the product. The spa shall be intended as a permanent plumb­ing fixture and shall not be intended to be moved. (Refer to ANSI/APSP-3, Standard for Permanently Installed Residential Spas.)

public spa:Any spa other than a permanent residential spa or pool or spa that is intended to be used for bathing and is operated by an owner, licensee, concessionaire, regardless of whether a fee is charged for use. (Refer to ANSI/APSP-2, Standard for Public Spas.)

hydrotherapy spa: A unit having a therapeutic use, but that is not drained, cleaned, or refilled for each individual. It includes. but is not limited to hydrotherapy jet circulation, hot water, cold water mineral baths, air induction bubbles, or any combination thereof. Industry terminology for a spa includes, but is not limited to
(1) a therapeutic pool, (2) a hydrotherapy pool, (3) a whirlpool, (4) a hot tub, etc. ANSI pool and spa standards exclude facilities used by, or under direct supervision and control of, licensed medical personnel.

swim spa: Variant of a factory built residential portable spa which consists of a large unobstructed volume of water that allows the 99% male/female to swim utilizing swim jets for a treadmill-like workout, primarily designed for, and constructed with specific equipment required to produce a water flow intended to allow recreational physical activity including, but not limited to, swimming in place. Swim spas may include peripheral jetted seats intended for water therapy, heater, circulation and filtration system, or may be a separate distinct portion of a combination spa/swim spa with separate controls.

spa-side control: See Topside Control.

spa user: Any person using a spa and adjoining deck area for the purpose of water activity or other related activity.

special purpose pool: A pool intended to be used exclusively for a specific activity, such as instruction diving, competition, or medical treatment.

splash pool: A pool having a water depth not exceeding 18 inches (18 in.j0.46m) that has as its intended primary use random play by small children. The pool could include constructed play devices including small flume type water slides and other play devices. See also Children's Activity Pool, Catch Pool.

splasher (wader) pools: A splasher pool shall have a maximum water depth of thirty-six inches (36 in.jO.9m). These pools are not intended to be covered within the scope of current ANSI/ APSP standards.

spray pool: A pool or basin occupied by constructed features that spray water in various arrays for the purpose of wetting the persons playing in the spray streams. Maximum depth of accumulated water in the pool or basin area is six inches (6 in.j lS.24cm).

springline: A line at which the pool wall breaks from vertical and begins its radius arc of the curvature.

stabilizer: Cyanuric acid (CYA), which is used to help prevent chlorine from breaking down in the presence of strong ultravio­let rays from sunlight.

static head: Head resistance caused by the weight of a standing water column to be moved. It is encountered on both the suction and discharge side of the circulation system.

static suction head: The vertical distance in feet between the pump centerline and the level of the liquid being pumped when the liquid is below the impeller centerline, expressed in feet of head.

static suction lift: Vertical distance from the center line of the pump impeller to the pool, spa, or hot tub water level.

stator: The stationary winding of an electric motor.

steps: See Stairs.

step-down transformer: A device for reducing the AC voltage level of a circuit.

step-down voltage: To reduce the AC voltage level to a circuit.

strainer basket: Readily removable, perforated or otherwise porous container used in the strainer pot or hair/lint pot of a pump to catch large debris before it enters the pump.

structural crack: A break or split that weakens the structural integrity of a pool, spa, or hot tub.

suction head: The head that a pump must provide on the inlet side to raise the liquid from the pool, spa, or hot tub supply. well to the level of the pump. See Head.

suction outlet: A wall aperture or fitting, other than a skimmer, through which water under negative pressure (vacuum) is drawn from the pool, spa, or hot tub to the pump or circulation system.

suction piping (influent): Piping that is connected to the suction side of the pump.

sump pump: A portable pump used to remove water from a pit or a reservoir, such as a pool, spa, or hot tub. May be partially or totally immersed in water during use. Also SUBMERSIBLE PUMP.

superchlorinate: To add a sufficient amount of a chlorinating compound to raise the free available chlorine level to 10 times (or more) the combined chlorine level. Done to reduce cloudy water, slime formation, musty odors, or algae and bacteria counts, and/or to improve the ability to maintain sanitizer residuals.

surface checks: A surface crack pattern resembling spider­webbing. Not all the way through; not an open crack. Also CRAZE.

surface crack: A repairable break in a plaster surface that is not major and not self-curing.

surface skimming system: A device or system installed in a pool, spa, or hot tub that permits the removal of floating debris and surface water to the filter.

surge: Displacement of water in a pool-static and dynamic. Also WAVE ACTION.

surge capacity: The storage volume in a surge chamber, gutter, and plumbing lines. See also System Surge Capacity.

surge chamber: A storage vessel within the pool recirculating system used to absorb the water displaced by bathers. Also SURGE PIT.

surge suppressor: A device that protects electrical and electronic equipment from sudden spikes of electricity, such as those caused by pump motors turning on and off. Works by collecting and diffusing excess power through a grounding wire. Cannot protect against lightning strikes. Also SURGE PROTECTOR.

swimmer load: See Bather Load.

swimming area: Area of pool in excess of three feet (3 ft./O.91m) in depth that is devoted to swimming.

swimout: An underwater seat area that is placed completely outside of the perimeter shape of the pool. When located at the deep end, swimouts are permitted to be used as the deep-end means of entry/exit of the pool. Also CUDDLE COVE, LOVE SEAT.

switch, switching device: A device which opens or closes an electric circuit, or redirects the flow of current. Made up of two parts; the contacts, which move to make, break or redirect current, and the activation, or work that is performed to move the contacts (manual, pneumatic, hydraulic, etc.). Switch types include Double Pole, Double Throw, Latching, Momentary, Rocker, Single Pole, Single Throw, and Toggle.

switch logic: A control system using a single switch for a single function, so that each device is controlled by its own switch. Commonly used for pool, spa, and hot tub controls.

system resistance: The calculated circulation resistance of the plumbing system.

system surge capacity: The total storage, including surge tank, gutter system and piping, within the pool circulation system used to absorb the water displaced by bathers.


TAC, total available chlorine: The sum, in parts per million, of free available chlorine (FAC) and combined chlorines (CC).

tailpiece: A plumbing fitting used to attach PVC or ABS piping to a metal manifold.

tamperproof: Requiring tools to alter or remove portions of the equipment. Also VANDAL-PROOF.

target pressure: The pressure required to deliver a required flow rate. Determined by calculating the quantity and type of jets and their recommended flow rates, and the pressure (psi) required to deliver the combined flow rate.

temperature factor, TF, F(T): A number used in determining the Saturation Index.

temperature rise: The difference between the desired and actual water temperature.

temperature sensor: A discrete device, used on most electronic controls, to determine the need for heat.

terminal strip: Device to make a secure electrical connection between wires and components. Also TERMINAL BLOCK.

test kit: Equipment used to determine specific chemical residuals and the physical properties of water.

test strip: A paper strip printed with dry reagents. Used to test specific chemical residuals and the physical properties of water.

therm: A unit of heat measurement equal to 100,000 BTUs. See BTU.

thermal disc: A type of High Limit switch.

thermal overload protector: A safety device designed to keep a pump motor from overheating.

thermostat: A temperature-controlling device that cycles the heater on and off to maintain the desired temperature.

thermostat bulb: The sensing element of most non-solid state thermostats. The bulb contains an alcohol solution that expands when heated, creating pressure on the activator of a micro­switch.

thermowell: A receptacle used to isolate a sensor probe (e.g., thermostat, High Limit) from the surrounding water or other media, but transfers heat from the media to the sensor probe. The thermowell allows removal and replacement of the probe without disturbing the surrounding water, and protects it from corrosion and excessive pressure.

three-phase current: Electric current in North America in which there are 3 alternating currents in a circuit, each 1200 out of phase with the others, enabling smoother, more efficient operation of equipment.

3-wire service, 4-wire service: In 1969, the National Electrical Code (NEC) was changed to require all electrical outlets in homes to include a ground wire as well as hot and neutral wires. All 120 VAC pools, spas, and hot tubs require 3-wire electrical service (hot, neutral and ground). 240 VAC pools, spas, and
hot tubs require either a 3-wire (hot L1, hot L2 and a ground) or 4-wire service (hot L1, hot L2, neutral and ground).

throws: The number of possible outputs for each switch inside a device package.

time clock: A device that automatically controls the periods that a pump, filter, heater, blower, and other electrical devices are' operation.

timer: A mechanical or electronic switching device that controls the amount of time a pool, spa, or hot tub will run on low sp to filter the water, when not in use.

titration: A method of measuring water alkalinity, hardness, available chlorine and other chemical parameters by adding measured amounts of reagents to cause a predictable color change.

toggle switch: A manually operated on/off, or variable function switch whose actuator snaps into 2 or more distinct positions. See Switch.

top coat: See Plaster.

top rail: The part of the frame located on top of or adjacent outer edges of an aboveground/onground pool wall.

topside control: An electromechanical or electronic switching control device, located at or near the top perimeter of a spa or hot tub. May regulate water temperature, system diagnostics, sanitation, jet operation, etc. Also REMOTE CONTROL, SPA SIDE CONTROL, TOUCHPAD.

total alkalinity (TA): A measure of the pH buffering capacity of water. Total alkalinity is generally expressed in parts per million ­(ppm) or milligrams per liter (mgjL) as calcium carbonate.

total alkalinity factor, F(TA): A number based on the total alkalinity ­which is used in determining the Saturation Index.

total chlorine (TC): The sum, in parts per million, of free available chlorine (FAC) and combined chlorines (CC).

total dissolved solids (TOS): A measure of all the dissolved and suspended organic and inorganic material in water (such as minerals). Usually expressed in parts per million, or ppm. Typically measured by an electrical conductivity meter.

total dynamic head (TOH): 1. The sum of all resistances in a complete circulation system at a given flow rate. Expressed in Feet of Head.
2. The pressure at which a pump can produce a given flow rate.

toxic: A substance having an adverse physiological effect on human beings or other living organisms.

transfer system: A device or combination of devices to facilitate user access to a pool. May include a platform, steps, and other stru ctu res.

transformer: A device used in AC circuits to increase, decrease, or isolate the primary source voltage to the other circuits downstream.

transformer primary: The input side of a transformer.

transformer secondary: The output side of a transformer.

transistor: Semiconductor switching device that uses polarity differences to induce electron flow through the device.

transition: Any point(s) on the floor of a pool where the angle/ slope changes. See also Break Point.

tread: The horizontal part of a stair; the part stepped on.

tread contact surface: Foot contact surfaces of a ladder, step, stair, or ramp.

triac: An AC electronic switch used to provide variable voltage for multi-speed blowers and dimmable lights.

Trichlor: See Trichloro-isocyanurate.

trichloro-isocyanurate (C3N303Ch): Sanitizer product that self-stabilizes by releasing free available chlorine and cyanuric acid as it dissolves. A form of organic chlorine that reacts with water to form 90% available chlorine and cyanuric acid. Also TRICHLORO-S-TRIAZINETRIONE. See Isocyanurates.

tsunami pool: A wave pool designed to generate a single transitional wave in each cycle. These pools are character­ized by strong cross-currents and counter currents after the passage of each wave. The operating pattern for the tsunami pool produces a single wave form at frequencies ranging from several seconds to several minutes.

tube ride: A gravity flow attraction found at a waterpark, designed to convey riders on an inner-tube-like device through a series of chutes, channels, flumes, or pools.

turbidity: Cloudy condition of water due to the presence of extremely fine particulate materials in suspension that interfere with the passage of light.

turnover rate: The period of time required to circulate a volume of water equal to the pool, spa, or hot tub capacity.

two-speed pump: A centrifugal pump that has a motor that operates at two different speeds.


UL (Underwriters Laboratories): A testing facility that writes standards and tests products to ensure compliance with minimum safe operating standards. Assemblies can be listed or approved depending on the depth of the testing performed.

ultraviolet light (UV): A specific bandwidth of light; a component of sunlight, which can also be generated artificially. Some­times characterized as UV-A, UV-B, and UV-C, for wavelengths of 315-400, 290-315, and 220-290 nanometers, respec­tively.

underwater ledge: A narrow shelf projecting from the side of a vertical structure whose dimensions are defined in the appropriate standard.

underwater light: A fixture designed to illuminate from beneath the water surface.

wet niche light: A watertight and water-cooled light unit placed in a submerged niche in a pool, spa, or hot tub wall and accessible only from the interior.

dry niche light: A light unit placed behind a watertight window in a pool, spa, or hot tub wall.

union: A plumbing fitting providing a removable joint in a run of PVC or ABS pipe.

upper distribution system: Those devices designed to distribute the water entering a permanent medium filter in a manner to prevent movement or migration of the filter medium. Also collects water during filter backwashing unless other means are provided.

upright support: That portion of the frame that is adjacent to the aboveground/onground wall in a vertical position that supports the top rail and braces the wall.

user: Any person engaging in water activities or related activities at a pool, spa, hot tub, or waterpark, including the adjoining deck. Also BATHER.

usable perimeter: The perimeter of a pool that is available for ingress and egress. Perimeter areas available only to staff or for emergency situations are not included.
user load: The total number of persons permitted in a pool/spa complex at any given time. Also BATHER LOAD


vacuum: The reduction of atmospheric pressure within a pipe, tank, pump, or other vessel. Vacuum is measured in inches of mercury. One inch of mercury = 1.13 feet of head = 345.3 kg per square meter.

vacuum filter: A filter through which water is pulled by the pump. The filter is mounted on the suction side of the pump.

vacuum switch: A switch which opens or closes when a specified negative pressure (vacuum) is sensed.

valve: A device in a pipe that will partially or totally obstruct the flow of water (such as a ball, gate, globe, or butterfly valve) or permit flow in one direction only (check or foot valve).

vanishing edge, negative edge: Water-feature detail in which water flows over the edge of at least one of the pool walls and is collected in a catch basin.

velocity: The speed at which a liquid flows between two given points, expressed in feet or meters per second. 1 foot per second (fps) = 0.30 meters per second (mps).

velocity head: In a hydraulic system, a measure of pressure or resistance equal to the height of a column of water that would cause the same pressure or resistance. Velocity head = v2/(2g). The principal factors of "head" are vertical distances and resistance due to friction of the flow of water against the walls of a pipe or vessel.

venting (heaters): The system responsible for the introduction of air for combustion and for dispersal of the flue products.

venturi: A device used to create a venturi effect.

venturi effect: The intake of a substance by water in a closed­pipe system, as the water passes through a constricted pipe.

venturi jet: See Hydrojet.

venturi tube: A tube with a constriction mounted in a circulation line. The constriction causes a pressure differential that can be used to measure the flow rate or to inject chemicals.

vertical wall: A wall that may slope outward up to 11 ° (eleven degrees) from plumb.

vinyl liner: A material constructed of vinyl or vinyl compounds that acts as a container for water when used in conjunction with a structural support system.

volt (V): The unit of measurement of a difference in potential, or electromotive force.

voltage: The measure of electrical potential or electromotive force in units called volts.

voltage drop: The reduction of electromotive force as work is performed in a circuit.

voltage potential: See Electromotive Force.

voltmeter: A device that measures the voltage of an electric circuit. See Multimeter.

volume: The amount of space contained by a specified con­tainer, such as a pool, spa, or hot tub, expressed in cubic feet or cubic meters. 1 cubic foot = 0.03 cubic meters.

volute: The housing section of a pump, which includes the impeller and diffuser.


wading pool: A pool that has a shallow depth used for wading.

wall closure: A fastening device that connects aboveground pool wall ends together.

Warning: See Signal Word.

waste water disposal system: A water disposal system approved by the authority having jurisdiction, such as a storm sewer, sanitary sewer, open pit, leach field, or irrigation system.

waterline: The level of the surface of the water. Positioned according to one of the following: 1. skimmer system: The waterline shall be at the midpoint of the operating range of the skimmers when there are no users in a pool or spa. 2. overflow system: The waterline shall be at the top of the overflow rim.

water pressure switch: See Pressure Switch.

water replacement interval (WRI): A formula used to determine when recreational water should be drained and replaced, based on bather load and volume of water.

watt: A unit of measure of electrical power converted to work. Calculated by multiplying voltage times current (volts x amperes). 1 watt = 1/746 horsepower unit.

watt density: The amount of watts generated in a heating element per square inch. The lower the amount of watts per square inch, the lower the density. 1 square inch = 6.45 cm2,

wattmeter: A device used to measure the wattage of an electri­cal circuit.

wave pool caisson: A large chamber used in wave generation. This chamber houses pulsing water and air surges in the wave generation process and is not meant for human occupancy.

weir: A shaped spillway for conducting water into a catchpool or other reservoir.
See also Skimmer Weir.

wet end: The part of a centrifugal pump which comes in contact with water; generally everything except the motor.

wet niche light: See Underwater Light.

white coat: See Plaster.

winterized liner: A vinyl liner that is manufactured with sufficient plasticizers to withstand exposure to a rated lowest tem­perature of -20 of/-29°C per ASTM standard D-1790-99, Standard Test Method for Brittleness Temperature of Plastic Sheeting by Impact, latest edition.

winterizing: Preparation of pools, spas, or hot tubs for cold or freezing weather.

wrinkle: An unintentional ridge or crease in a vinyl liner.






zero entry: See Beach Entry.