A-Z Glossary of plumbing terms
Plumber Radcliffe

Air admittance valve – A valve that vents a stack pipe within a building by drawing air into the pipework when an appliance is discharged. The valve reseals the pipework when the air pressure equalises so that foul air is contained within the pipework. 

Airlock – Blockage in the flow of water in the heating or hot water system, especially on the suction side of a pump caused by an air bubble in the line.

Automatic air vent – A mechanical device which automatically releases air trapped within a water system – normally fitted to the highest point of a plumbing system. 

Back siphonage – The reverse flow of liquid from a cistern or appliance into the pipe feeding it, this can lead to a contamination of the water supply. 

Back-to-wall cistern – A cistern that is separate from the WC pan, generally concealed behind a wall or within fitted furniture. 

Ball cock – A valve that is controlled by a float on the water surface to controls the flow of water into a tank or cistern. 

Bar – The unit of measurement of water pressure – one bar is approximately equivalent to a column of water 10m high or 14.5 lbf/in² or 100 kPa (kilopascal). 

Bleed To drain a pipe, tube, or hose of excess air by opening a valve at the end or systematically removing the air by force or suction.

Bleed valve – An air release valve that is used to release air from a central heating system. They are found on all water radiators and sometimes at high points in the pipework. 

Bottle trap – A trap found underneath basins or sinks. They are typically cylindrical and the bottom can be unscrewed for cleaning

Capillary connector – A pipe coupling that uses solder to give a watertight seal. The joints are not reusable.

Ceramic taps – Taps which use a rotating ceramic disc to control the flow of water – requiring only a quarter handle rotation to turn the flow on or off. 

Check valve – A plumbing fitting that allows water to flow in one direction only. 

Cistern – A container for storing water that is then usually used to flush a WC. They usually a float device to control that flow of water.

Close coupled WC – A pan and cistern syetm where the cistern sits on directly on the pan.

Cold water storage tank – A water storage that is usually used to provide a feed to domestic cold water and/or to a vented domestic hotwater system. 

Combination boiler – (combi) – a boiler that combines both a central heating water heat exchanger and a domestic water heater in one unit. A combi does not store hot water – water is heated when required either directly from the cold mains (for the domestic hot water) or within a pressurised ‘sealed’ central heating loop. 

Compression connector – A pipe coupling that uses threaded nuts to compress an ‘olive’ on the pipe to provide a watertight seal.

Dual flush cistern – A WC cistern that has the option of a water saving or full volume flush, normally determined by how the push button is operated. 

Earth bonding – A legal safety requirement to have all metal parts within a plumbing system connect to earth to prevent them becoming electrically dangerous. 

Earth bonding strap – A metal strap that joins metal pipes and fittings together to provide an electrical earth path. 

Expansion tank – A tank which will accommodate the expansion of water within a system as it heats up or to absorb pressure shock waves to reduce water hammer. May be open or sealed depending on whether the system is vented or sealed. 

Gate valve – A hand operated on/off valve permitting water flow in either direction. 

Grey water – Waste water from baths, basins, sinks, washing machines or dish-washers that has been used and is considered only mildly dirty. 

Heat exchange – The unit which transfers the heat from the burner to the water. In Combi boilers and Multipoint heaters these generally have a low water volume. 

High level cistern – A cistern mounted high on the wall and connected to the WC pan by a long flush-pipe, the flush is powerful and operated by a pull-chain and handle. 

Hot water cylinder – A closed vessel to store heated water under pressure. Generally come insulated to reduce heat and energy loss.

Immersion heater – An electrical water heater inserted into a hot water cylinder – it incorporates both the heating element and the thermostat). Two may be used with a single cylinder – one on ‘off peak’ electricity, the other switchable for use at other times if necessary. 

Indirect hot water cylinder – A hot water cylinder where the water heated by the boiler is fed through a coil of piping inside the cylinder to heat the domestic water. The tank often incorporates an electric immersion heater so that the tank can be heated when the boiler is switched off for the Summer. 

Lockshield valve – Fitted to the return side of a radiator and used to balance the system when it is first installed.

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Mixer shower – A simple shower using a valve to combine the domestic hot and cold water supplies to provide the required temperature and flow.

Mixer taps – A tap with separate hot and cold inputs and having a single output. The inputs can be adjusted to give the required temperature and flow.

Monobloc taps – A mixer tap for a single mounting hole. O-ring – A circular rubber sealing ring – often found in mixer taps and in waste pipe fittings.

Olive – A brass or copper compression ring used in compression couplings.

Overflow pipe – A pipe connected from a tank or cistern to discharge any surplus water into an area without causing damage, normally only coming into use when there is a fault such as a leaking valve.

P-bend – A form of trap used under basins, baths etc.

Plunger – An instrument usually with a rubber head, used to create suction in a drain line or a toilet to push a clog through the line.

Power shower – A shower using a pump to boost the flow of water to give a powerful shower spray.

Pressure relief valve – A safety device fitted to relieve excessive pressure within a heating boiler or system. Resets itself once the excess pressure has been relieved.

Pushfit connectors – Plumbing connectors which just push onto the pipework rather than compression or capillary connectors – maybe plastic but suitable for both hot and cold water.

PTFE tape – Polytetrafluorethylene tape used to seal threaded plumbing joints. Also known as ‘Plumber’s Tape For Everything’.

Rising main – The water pipe that supplies pressurised mains water to taps, tanks, appliances etc. Normally there is a single stop cock which controls the rising main within a property.

S-bend – A form of trap used under basins, baths etc.

Single lever mixer tap – Atap with a single lever that controls the water flow of both the hot and cold water supplies.

Stop cock – A hand operated on/off valve permitting water flow in one direction.

Surrey flange – A fitting inserted into the top of hot water cylinders that purges hot water of air before it is drawn off into the outlet. Normally used in the feed for shower pumps.

Thermostatic mixing valve – A hot and cold water mixing device that maintains a selected temperature at the outlet by automatically adjusting for variations in the temperature and/or pressure of the incoming supplies.

Thermostatic radiator valve (TRV) – A Radiator control valves which automatically opens and closes as necessary to achieve the pre-set room air temperature.

Trap – Curved section of drain line that prevents sewer odours from escaping into the atmosphere. All fixtures that have drains must have a “P” trap installed. A toilet is the only plumbing fixture with an “S” trap.

Two hole mixer tap – A mixer tap requiring two separate holes for the water feeds in the sink etc.

Vent pipe – An uninterrupted safety pipe which allows air or the expansion of water within a hot water system to escape – often positioned over a tank or cistern so that any water can be discharged into it.

Warning vent – An overflow pipe that is in a position that allows a simple, visual inspection.

York flange – A fitting inserted into the top of hot water cylinders which purges the hot water of air before it is drawn off into the outlet. Normally used in the feed for shower pumps.

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