A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

ACID - a chemical used to lower pH and or alkalinity of the pool water. Most commonly used acids are liquid (Hydrochloric Acid) or dry (Sodium Bisulphate).

ACID DEMAND - the amount of acid required to bring high pH and total alkalinity down to their proper levels. Determined by the Acid Demand Test.

ACID WASH - a procedure using an acid solution to clean the interior surface of a plaster, gunite, or shotcrete pool with subsequent neutralization of the acid.

AGGREGATE - the major component of plaster, composed of sand, marble dust, pebbles and other solid material.

AIR SWITCH - a pneumatic control device used to operate pool and spa equipment safely. A button located near the water and convenient for use is pushed which sends air pressure through a small flexible tube or hose to a switch.

ALGAE - plant organisms, which grow at a rapid rate to discolour the pool water and interior finish.

ALGACIDES - products/chemicals used to prevent or control algae growth, available in many forms and types. These products are a supplement to your sanitiser and are specifically intended to kill all forms of algae. Warning- check with your local pool shop / maintenance person prior to purchase for compatibility with your pool maintenance systems.

ALKALI - a chemical with a pH above 7.

AIR BLOWER - a mechanical device that forces air through holes in the floor, bubbler ring or hydrotherapy jets in a spa.

AMPERAGE - (amps) the term used to describe the strength of an electrical current. It represents the volume of current passing through a conductor in a given amount of time. Amps=watts/volts.

ANODE - the electrode (positive) that attracts negatively charged anions. The positive pole of an electrodialysis system.

ANTI-VORTEX DRAIN COVER - a cover or grate attached to the main drain that prevents a vortex (whirlpool) from forming as the water passes through it.

AUTOMATIC CONTROLLER - a device that automatically executes the decision making necessary to determine the proper adjust of a chemical parameter. Controllers are currently capable of automatically adjusting pH and sanitiser levels in water.

AUTOMATIC POOL CLEANER - pool maintenance system that will agitate or vacuum debris from the pool interior.

AVAILABLE CHLORINE - the amount of chlorine, both free and combined in the pool water that is available to sanitize or disinfect the water. Sometimes called residual chlorine.

BACKFLOW - the backing up of water through a pipe in the direction opposite to normal flow.

BACK PRESSURE - resistance to flow, normally expressed in pounds per square inch (psi).

BACWASH - the process of thoroughly cleaning the filter by reversing the flow of water through it with the dirt and rinse water going to waste.

BALL VALVE - simple non-return valve consisting of a ball resting on a cylindrical seat within a liquid passageway.

BLOWER - an electrical device that produces a continuous rush of air to create the optimal bubbling effect in a spa, hot-tub or whir-pool. It is usually plumbed in with the hydrotherapy jets or to a separate bubbler ring.

BOND BEAM - the top of a wall or spa that is built stronger than the wall so it will support the coping and surrounding deck.

BOOSTER PUMP - a water pump added to a spa circulation system to add pressure to the jets. Also used for some automatic pool cleaners.

BROMINE - a common name for a chemical compound containing bromine that is used as a Disinfectant to destroy bacteria and algae in swimming pools and spas. Available as a tablet or as sodium bromide, a granular salt. Most commonly used in spas because of its tolerance to hot water.

BROMINATOR - a mechanical or electrical device for dispensing bromine at a controlled rate. Most often a canister or floater filled with tablets of bromine.

BUFFER - a substance or compound that stabilises the pH value of a solution. Its also the waters resistance to change in pH. An alternative name for sodium bicarbonate which is used to raise pH and total alkalinity.

BYPASS - an arrangement of pipes, gates and valves by which the flow of water may be passed around a piece of equipment or diverted to another piece of equipment; a controlled diversion.

CALCIFICATION - the formation of calcium carbonate on the walls or pipes, or in a heater due to the precipitation of calcium carbonate.

CALCIUM HARDNESS - the calcium content of the water. Calcium hardness is sometimes confused with the terms water hardness and total hardness. Too little calcium hardness and the water is corrosive. Too much calcium hardness and the water is scale forming. One of the basic water tests necessary to determine water balance. Minimum level 150ppm. Ideal range is 200-400ppm.

CARTRIDGE FILTER - a pool or spa water filter that uses a replaceable porous element made of paper or polyester.

CATHODE - the negative electrode that attracts positively cations. The negative pole of an electrolytic system.

CAULKING MATERIAL - (usually silicone) used to fill a gap in a joint and provide a waterproof seal.

CAVITATION - the formation of partial vacuum when pump capacity exceeds water replacement supply. The formation and sudden collapse of vapour bubbles in a liquid, usually resulting from low local pressures, as on the trailing edge of a propeller.

CHECK VALVE - a mechanical device in a pipe the permits the flow of water or air in one direction only.

CHEMICAL BALANCES - a composite term covering those aspects of water which should be adjusted to achieve water suitable for swimmers, sanitisers and the pool surface and equipment. Pool water is chemically balanced when the pH, Total Alkalinity and Calcium Hardness levels are within certain parameters.

CHEMICAL FEEDER - any of several types of devices that dispense chemicals into the pool or spa water at a predetermined rate. Some dispense chlorine or bromine while others dispense pH adjusting chemicals.

CHLORINATION - the adding of chlorine to the pool water.

CHLORINATOR - a mechanical or electrical device for dispensing chlorine at a controlled rate. Normally of three forms:

SALT WATER CHLORINATOR- a unit which manufactures chlorine through the electrolytic conversation of salt. Chlorine levels will depend on several variables including running time of the unit.

CHLORINE CONTROLLER- a machine which feeds liquid chlorine into the pool water. Normally integrated with the filtration cycle, these units have electronic control on chlorine.

EROSION FEEDER- a canister or floater containing solid tri-chlor tablets which dissolve in the water, these units control the rate of chlorine addition through a manual valve which varies the water flow over the tablets.

CHLORINE - a term used to describe any type of chlorine compound used as a disinfectant in swimming pool and spa water to kill, destroy or control bacteria and algae. In addition, chlorine oxidisers ammonia and nitrogen compounds (swimmer and bather waste). It is pH dependent. There are many different types available. Check with your pool shop and or maintenance person for the most suitable for your pool.

CHLORINE GENERATOR - an electrical device that generates chlorine from a salt solution in a tank or from salt added to the pool water.

CHLORINE DEMAND - amount of chlorine required to kill all the pollutants in the swimming pool water.

CLOUDY WATER - the visible effect in water created by material in suspension. A condition of the water due to the pressure of extremely fine particles in suspension that can not be trapped by the filter because they are too small. Adding a clarifier such as an organic polymer or alum will coagulate the particles and make the filter more efficient.

CLARITY - how clear the swimming pool water is- degree of transparency of the water.

COMBINED CHLORINE - chlorine which has combined with nitrogen based compounds to form chloramines. Associated with very strong chlorine like smell, this compound is a pool sanitiser and indicates the need for more chlorine.

CONTROLLER - a device that automatically executes the decision making necessary to determine the proper adjust of a chemical parameter. Controllers are currently capable of automatically adjusting pH and sanitizer levels in water.

COPING - the walkway immediately surrounding the swimming pool or spa, cap or top lip that provides a finished edge.

COUPLING - a plumbing fitting that is used to connect two pieces of pipe.

CYANURIC ACID - (also known as conditioner and stabilizer) chemically, conditioner is cyanuric acid, chemical formula. It protects chlorine in the water from being destroyed by sunlight.

DIAMETER - the length of a straight line measured through the centre of a circle from one side to the other.

DISSOLVE - the separation into component parts creating a process of solid particles mixing with a liquid and then taking on the appearance of the liquid. Like mixing sugar into water.

DIVERTER / THREE WAY VALVE - a plumbing fitting used to change the direction or re-direct the flow of water. Some diverter valves are used on pool/spa combination to allow the use of the spa and then switch the flow back to the pool.

DRAIN - this term usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs. Sometimes called the main-drain, it is located at the deepest part of the pool, spa or hot-tub. It is not a drain, such as a drain on a kitchen sink. Main drains can allow the pool to drain to waste, but usually connect to the pump for circulation and filtration.

FILTRATION - the process of passing the pool water through the filter medium to remove dirt and debris particles.

FILTER - a device that removes undisclosed or suspended particles from water by recirculation the water through a porous substance (a filter medium or element). The three types of filters used in swimming pools and spas are sand, cartridge and D.E. (diatomaceous earth).

FILTER CYCLE - the operating time between cleaning or backwashing cycles of a filter. Also the amount of time the filter has water flowing through it each day expressed in hours.

FILTER SAND - a type of filter media composed of hard, sharp silica, quartz or similar particles with proper grading for size and uniformity. The most common grade used is No. 20 in sand filters.

FLOW RATE - the quantity of water flowing past a designated point within a specified time, such as the number of litres flowing past a point in one minute- abbreviated as lpm.

FREE AVAILABLE CHLORINE - that portion of chlorine in the pool water available to oxidise contaminants as opposed to ‘Combined Chlorine’ or ‘Total Chlorine’.

GUTTER - an overflow trough at the edge of the pool through which floating debris, oil and other‘lighter-than-waste’ things flow. Pools with gutters usually do not have skimmers.

HAIR AND LINT POT - used to trap finer particles that manage to pass through the skimmer box basket. This section of the circulating pump contains the secondary strainer basket for the filtration system. It requires regular cleaning.

HAND RAIL - a tubular steel or plastic device that can be gripped by swimmers or bathers for the purpose of steadying themselves. Usually located near the steps in the pool.

HARDNESS INCREASER - a chemical used to increase calcium or water hardness. It is usually calcium chloride.

HEAD - a measure of pressure at a given point in a water system, expressed as pounds per square inch (psi), or the height of a column of water that would produce the pressure.

HEADER - a manifold in the heater that directs flow of water into and out of the heat exchanger.

HEAT EXCHANGER - a device located inside the heater providing for the transfer of heat from the heat source of the water. This is usually a series of metallic tubes with fins located just above the flames.

HEAT PUMP - a refrigeration compressor, usually electrically driven, that is operated in reverse. To obtain heat, the evaporator side (cooling coil) is exposed to water, air or ground. The coil transfers the heat from this source to the condenser coil, where it discharges the heat to the water in the pool or spa.

HEATER - a fossil-fuelled, electric or solar devise used to heat the water of a pool, spa or hot-tub.

HIGH RATE SAND FILTER - a filter using sand for the filtration media designed for flows in excess of 5GPM but less than 20GPM per square foot.

HORSEPOWER - work done per unit of time. One horsepower equals 33,000 foot pounds of work per minute or approximately 746 watts. Motors for pumps are rated in horsepower.

HYDROJET - a fitting in the pool or spa on the water return line from the equipment that blends or mixes air and water, creating a high velocity, turbulent stream or air-enriched water.

HYDROCHLORIC ACID - a very strong acid used for various cleaning needs. Used in ‘acid washing’ a pool. Use extreme care in handling.

HYDROSTATIC PRESSURE - the force created by the water that tends to push pools up out of the ground.

HYDROSTATIC VALVE - spring loaded plug situated in the main-drain bowl. Designed to open if the water pressure under the pool is greater than the water pressure within the pool. Reduces the possibility of an empty pool lifting out of the ground.

IMPELLOR - an open or closed disc attached to the motor shaft which forces water through the filtration system.

INFLOOR CLEANING & CIRCULATION SYSTEM – the bottom of the pool is fitted with a series of jets. These jets push the dirt from the shallow end to the deep end, each jet sweeping the dirt toward the deepest part of the pool where the main drain would suck it into the filter system. The jets are connected to a diverter (water valve) at or near the pool / filtration equipment. As the water leaves the heater destined for the pool, it passes through the diverter which sends it to the floor jets on the shallow end first, then the deeper jets, and so on. In this type of system it is presumed that the dirt will come loose from the floor by these jets and not stick to the floor, and also the dirt will be only of the finer type that will not clog the main-drain. Last, it assumed that these jets, would equally cover all areas of the bottom.

INLET - a fitting in the pool or spa on the water return line from the equipment that water returns to the pool. Usually the last thing on the return line.

LEAF BASKET - a strainer basket situated in the skimmer box to trap large leaves and debris before they enter the lint pot.

LEAF RAKE - contains a net and are used to remove the leaf and other debris from the pool. The leaf rake shank fits into the telepole and clips in place.

LIGHT NICHE - the area in the pool or spa that houses the underwater light.

LIQUID CHLORINE - a sodium hypochlorite solution. Usually provides 10 to 12% available chlorine; has a pH of 13 and requires that small amounts of acid be added to the pool to neutralize the high pH. Good fro regular chlorination and super chlorination.

LPM - litres per minute (lpm).

MAIN DRAIN - this term usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs, and is located at the deepest part of the pool-can be used to drain the swimming pool.

MANIFOLD - the branch pipe arrangement that connects several input pipes into one chamber or the chamber into several output pipes. A filter manifold connects several input pipes from the filter septa back into one common pipe.

MECHANICAL SEAL - a mechanical device or assembly that forms a seal between a pump Casing and a rotating shaft to prevent leakage along the shaft.

MEDIA - a selected group of materials used in filters and filter devices to form barriers to the passage of certain solids or molecules that are suspended or dissolved in water. Media is the plural form of medium and refers to more than one type of barrier material. In the pool and spa industry, filters use either sand, polyester or diatomaceous earth (D.E) as the media.

MICRON - a unit of length equal to one millionth of a meter- it is .0000394 inch. Microns are used to describe the pore size of filter media. Sand filters have openings of 25-30 microns; cartridge filters have openings of 8-10 microns; and D.E (diatomaceous earth) filters have openings of 1-3 microns. Humans, without magnification, can see objects 35 microns or larger. A granule of table salt is between 90 and 110 microns. Abbreviated as m m.

MULTIPORT VALVE - also called a rotary-type backwash valve. This valve replaces as many as six regular gate valves. Water from the pump can be diverted for various functions by merely turning the valve handle. The water may be sent to waste, used for backwashing, bypassing the filter for maximum circulation, for normal filtration, filtering to waste (rinse), or the valve may be closed to not pass water. The pump must be off before changing a valve setting.

NICHE - the housing built into the wall of a pool or spa to accommodate a light fixture.

ORGANIC WASTE - also called swimmer or bather waste- all of soap, deodorant, suntan lotion, lipstick, makeup, cologne, body oils, sweat, spit, urine etc. brought into the water. They also form chloramines, which are foul-smelling and body irritants. Require large amounts of chlorine or non-chlorine shock to destroy.

O-RING - a round, circular rubber-material gasket shaped like the letter O that is used to seal around round objects, such as the ends of two pipes.

OVERFLOW SYSTEM - a system for the removal of pool surface water through the use of Overflows, surface skimmers, and surface water collection systems.

OXIDATION - to rid the water of ammonia, nitrogen compounds and swimmer waste (organic Compounds). These organic compounds disable chlorine, are body irritants and have a foul smell. Removal is accomplished by superchlorination or by shock treating with a non-chlorine oxidizer.

OZONATOR - electrical devices which produce ozone from air oxygen used for oxidation of water contaminants. Corona Discharge or CD ozone is produced by a discharge of electricity at ranges from 1 to 7 percent ozone in air. Ultraviolet or UV ozone is produced by a UV light or lamp at ranges from .001 to .01

OZONE - a gaseous molecule comprised of three atoms of oxygen. It is generated on site From air oxygen and used for oxidation of water contaminants.

PART PER MILLION - abbreviated as ppm. It is a “weight-to-weight” expression. It means one Part in one million parts, such as 1 pound of chlorine in one million pounds of water or 119,904 gallons. Many of the common pool water tests as well as acceptable ranges are stated as ppm. For instance, Free Available Chlorine should be kept between 1.0 and 3.0 ppm; Total Alkalinity should be between 80 and 120 ppm; and Water Hardness should be between 200 and 400 ppm. A ppm and a milligram per litre (mg/L) are considered equal.

PERIMETER - the distance around the outer edge of a shape. pH- a measure of the alkalinity (above 7.0) or acidity (below 7.0) of pool water. The slightly alkali range of 7.2 to 7.8 is recommended. The only acids which should be used to lower pH are Hydrochloric Acid or Sodium Bisulphate.

pH DECREASER - a chemical that decreases or lowers the pH of the water. Muriatic acid, dry acid and sodium bisulfate are examples.

pH INCREASER - a chemical that increases the pH of the water. Soda ash, sodium sesquicarbonate and sodium bicarbonate are examples of pH increasers.

PHENOL RED - a chemical reagent dye used to test for pH. It can measure pH from 6.8 to 8.4

PLASTER / RENDER - a mixture of white cement and sands used as an interior finish which can be tinted, coloured or left white, applied to gunite or shotcrete of a pool or spa.

POOL BRUSH - wall and floor brush is used to remove the dirt, stains and other material sticking on the interior surface. Made of either nylon bristle or wire with a shank that fits the telepole.

PPM - abbreviation for parts per million (ppm).

PRE-DILUTE - to dilute a chemical before adding it to the pool or spa water.

PRESSURE - the force pushing on a unit area. Water pressure is normally measured in pounds Per square inch (psi) or feet of head.

PRESSURE GAUGE - a gage with an analog dial indicating the pounds per square inch (psi) of pressure that has built up within a closed container, such as a filter.

PRIME - to fill a pump casing or siphon with water to remove air. Most pumps must be primed before start-up or they will not pump water.

PSI - an abbreviation for pounds per square inch.

PUMP – a mechanical device, usually powered by an electrical motor, which circulates water from the pool where water is drawn into the filtration system. Typically, a centrifugal pump is used for pools, spas and hot-tubs. An important part of this fixture is the floating weir flap which serves two functions; the first is it draws the top layer of water flow into the skimmer, removing debris floating on the water surface; secondly, the flap closes when the pump is not running, preventing the debris from floating back into the pool. Cleaning the skimmer basket is an important part of pool maintenance.

PUMP CAPACITY - the volume of liquid a pump is capable of moving during a specified period of time. This is usually litres per minute (lpm).

PUMP CURVE - (also called a pump performance curve). A graph that represents a pump’s water flow capacity at any given resistance.

PUMP LINT POT - or Pump Strainer Basket- a device placed on the suction side of the pump, which contains a removable strainer basket designed to trap debris in the water flow without causing much flow restriction. Sometimes called a ‘hair-and-lint trap’.

PVC - abbreviation for Poly Vinyl Chloride. An artificial polymer made from vinyl chloride monomer used in pipes for swimming pools and spas.

PVC PIPE - a type of pressure pipe for water distribution manufactured from poly vinyl chloride compound used to plumb swimming pools and spas.

RADIUS - the distance from the centre of a circle to its edge; one half of the diameter.

RATE OF FLOW - the quantity of water flowing past a designated point within a specified time; such as the number of litres flowing past a point in one minute- abbreviated as lpm.

RATE OF FLOW - the quantity of water flowing past a designated point within a specified time, such as the number of litres flowing past a point in one minute- abbreviated as lpm.

SALT WATER - water containing relatively high concentration of salt, usually over 1,000 ppm but less than the sea. The ocean has about 35,000 ppm.

SAND - usually refers to the filter medium used by a sand filter.

SAND FILTER - a filter using sand or sand and gravel as the filter medium.

SANITISE - to render sanitary: to kill all living things, including bacteria and algae.

SEAL - packing gland material or a mechanical device that fits around a pump shaft and prevents either air intake to the pump or water leakage.

SELF-PRIMING - a classification given to centifrugal pumps that indicates the pump is capable of operating above the pool water level after initially filling with water. Most self-priming pumps have a hair and lint strainer basket/pot attached to the front of the pump.

SENSOR - an electrical or electronic device that measures water quality. Examples are pH electrodes, pH meters, ORP (Oxidation Reduction Potential) probes and meters, TDS meters and probes.

SHOCK TREATMENT - the practice of adding significant amounts of chlorine or similar product- an oxidising chemical, to the water to destroy ammonia and nitrogen compounds or swimmer waste. This would be at least five times the normal dose.

SHOTCRETE - mixture of sand and cement sprayed onto contoured and supported surfaces to build a swimming pool or spa. Plaster is applied over the shotcrete. Shotcrete is premixed and pumped wet to the construction site.

SKIMMER - a device installed through the wall of the pool or spa that is connected to the suction line of the pump that draws water and floating debris in the water flow from the surface without causing much flow restriction, attached to one side/end of the pool used as the main suction point for vacuuming and or skimming of leaves.

SKIMMER BASKET - a removable, slotted basket or strainer placed in the skimmer on the suction side of the pump, which is designed to trap floating debris in the water flow from the surface without causing much flow restriction.

SKIMMER WEIR - part of the skimmer that adjusts automatically to small changes in water level to assure a continuous flow of water to the skimmer. The small floating ‘door’ on the side of the skimmer that faces the water over which water flows on its way to the skimmer. The weir also prevents debris from floating back into the pool when the pump shuts off.

SODIUM HYPOCHLORITE - liquid chlorine, hypochlorite solution, chemical formula NaOCI; usually Provides 10-12% available chlorine; has a pH of 13 and requires that small amounts of acid be Added to the pool to neutralize the high pH.

SOLAR COVER - a cover that, when placed on the water’s surface of a pool, spa or hot-tub, increases the water temperature by absorption and transmission of solar radiation, reduces evaporation and prevents wind-borne debris from entering the water.

SOLAR HEATING SYSTEM - it is usually panels or coils of plastic or metal through which water passes to increase the temperature from the sun’s radiant heat.

SOLENOID VALVE - an electrical device operated by a magnetic coil to make the valve either Open for flow or closed to shut off water flow.

SOURCE WATER - (also called ‘tap’ water). It is the water used to fill the swimming pool or spa.

STABILISER - Cyanuric Acid is used to screen the pool water from the sun’s UV radiation which attacks the chlorine. The use of this product is recommended for all chlorinated outdoor pools. Regular checking and maintenance during the swimming season is recommended. Stabiliser should not be used in indoor pools.

SUPER CHLORINATION - the practice of adding an extra large dose (5 to 10ppm) of chlorine to the water to destroy ammonia, nitrogen and swimmer waste, which can build up in the water. This level of chlorine is required to destroy all of the combined chlorine in the water, which is called breakpoint chlorination.

1) The destruction of compounds such as chloramines
2) Super sanitising to ensure the destruction of most harmful bacteria;
3) A super algaecidal effect to destroy algae spores resistant to normal chlorine levels

SURFACE AREA - the two-dimensional area of an object. The surface area of a swimming pool Is just the length times the width- no depth.

SWIMOUT - a recessed area outside the general perimeter of a swimming pool. Swimouts are Designed to allow entry and exit from the pool.

TELESCOPIC HANDLE - extension pole made of aluminium used to attach pool accessories.

TEST KIT - an apparatus or device used to monitor specific chemical residuals, levels, constituents or demands in the pool or spa water. The kit normally supplied with the pool to enable home testing of the water. Normal levels tested are pH, acid demand, total alkalinity and free available chlorine. Other functions, such as salt and stabiliser levels, calcium hardness, total dissolved solids and metals in solution can be tested at your Accredited Pool Shop or service person.

TEST STRIPS - small plastic strips with pads attached that have been impregnated with reagents that can be used to test pool water for residuals, levels, constituents or demands. The strips are usually dipped in the water and the resulting colours of the pads compared to a standard set of colours to determine concentration.

THERMOSTAT - a temperature control device that cycles a heater on and off to maintain a desired temperature.

TIME CLOCK - a mechanical or electrical device that automatically controls the periods that a pump, filter, heater, blower, automatic pool cleaner or other electrical devices are on or off.

TOTAL ALKALINITY - is the measure of bicarbonates, carbonates and hydroxide in the pool water. It is raised through adding sodium bicarbonate, also called “buffer”. As the chemicals used to adjust pH may also affect Total Alkalinity it is recommended that the two be measured together. The chemical reaction between pH and Total Alkalinity may require that they also be adjusted together. Both pH and Total Alkalinity levels should be tested frequently.

TOTAL DISSOLVED SOLIDS - the total amount of dissolved salts, calcium, chlorides and other material in the pool water. This cannot be measured correctly if salt or liquid chlorine is used in the pool.

TOTAL CHLORINE - the combination of free available chlorine and combined chlorine in the pool water.

TURNOVER - also called turnover rate. The period of time (usually in hours) required to circulate a volume of water equal to the volume of water contained in the swimming pool or spa. Pool capacity in litres, divided by pump flow rate in litres per minute (lpm), divided by 60 minutes in 1 hour, will give hours for 1 turnover.

UNDERWATER LIGHT - a fixture designed to illuminate a pool or spa from beneath the water’s surface.

VACUUM - this term can be used to define any number of devices that use suction to collect dirt from the bottom and sides of a pool or spa. Most common is a vacuum head with wheels that attaches to a tele-pole and is connected to the suction line usually via the opening in the skimmer. It must be moved about by a person, and debris is collected in the skimmer basket and filter.

VACUUM HEAD - attached to the hose and telescopic pole, and used to vacuum dirt from the floor of the pool.

VACUUM PLATE - designed to sit in the skimmer box above the leaf basket, has a hole in the centre to allow vacuum hose to fit in. Also used for circulating water from the bottom of the pool, in which case a screw-threaded cap is used to block the hole.

VALVE - a mechanical device installed in a water line to close off or regulate the flow of water.

VELOCITY - the speed at which a liquid flows between two points. Usually measured in feet per second.

VENTURI - a fitting or device that consists of a tube constricted in the middle and flared on both ends. A fluid’s velocity will increase and a fluid’s pressure will decrease while passing through the constriction. Placing a tube or pipe at the constriction point creates a vacuum. Fluid or air can be drawn in through the tube. A hydro-therapy jet draws air and mixes it with the water using this principal.

VOLUME - the amount of water a vessel will hold. It is a three-dimensional space occupied by an object. Formula for volume is” Length x Width x Average Depth = cubic metres x 1000 = the volume of the pool in litres.

VORTEX - a revolving mass of water that forms a whirlpool. A funnel-shaped opening is created downward from the water surface.

WATER BALANCE- water that has a pH of 7.4 to 7.6, a total alkalinity of 80 to 140ppm, calcium hardness of 200 to 400ppm, and a TDS of less than 2500ppm. The water is said to be “in balance” when the water is within these parameters.

WATER CLARIFIER - also called coagulant or flocculent. A chemical compound used to gather (coagulate or agglomerate) or to precipitate suspended particles so they may be removed by vacuuming or filtration. There are two types; in-organic salts of aluminium and other metals of water- soluble organic polyelectrolyte.

WATER HAMMER - the shock wave or series of waves produced by the abrupt acceleration or deceleration of water flow through a pipe, caused by inertia.

WATERLINE - the height to which the water is filled in the swimming pool and or spa. This is usually in the middle of the skimmer openings, the centre of the tile pattern or to the overflow if so constructed.