Glossary of Plumbing terms.

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

Airlock - Trapped air in pipework where, due to its layout, the air cannot escape naturally resulting in no or very little flow of liquid along the pipe.

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

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

Back-to-wall cistern - A cistern separate from the WC pan which may be concealed behind a wall or within fitted furniture.

Ball cock - A valve used to control the flow of water into a tank or cistern, the valve being controlled by a float on the surface of the water in the tank/cistern. AKA Float Operated Valve.

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 valve - An air release valve used to release air from a central heating system - found on all water radiators and sometimes at high points in the pipework.

Bottle trap - A form of trap for basins and sinks etc - usually in a cylindrical form where the bottom can be unscrewed from the body for cleaning etc.

Capillary connector - A pipe coupling with a tight fit on the pipe, the gap being filled with solder once heated to provide a watertight seal. Some couplings incorporate a solder ring (AKA a Yorkshire fitting) while others need solder applied once the joint has been heated. The joints are not reusable. Available as straight, 'T', elbow and other configurations.

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

Check valve - A plumbing fitting designed to allow water flow in one direction only.

Cistern - A fixed container for holding water at atmospheric pressure, normally applied to the local water storage to flush a WC. It is normally fitted with a float operated valve and overflow pipe.

Close coupled WC - A pan/cistern combination where the underside of the cistern rests directly on the back of the WC pan creating a compact unit with low overall height. Generally the cistern is operated by a lever mounted on the front of the cistern or (more modern) a push button on the cistern top cover.

Cold water storage tank - A fixed container for holding water at atmospheric pressure usually used for providing a feed to domestic cold water and/or to a vented domestic hotwater system.

Combination boiler - AKA "combi" - a unit which combines both a central heating water heat exchanger and a domestic water heater in one compact, self-contained unit. Unlike an vented heating and hot water system, a combi does not store hot water, rather it heats water as and when required either directly from the cold mains (for the domestic hot water) or within a pressurised 'sealed' central heating loop. To see more details go to our combi boiler article.

Compression connector - A pipe coupling using threaded nuts to compress an 'olive' on the pipe to provide a watertight seal. More expensive than capillary joints but are easy to fit and generally reusable. Available as straight, 'T', elbow and other configurations.

Deck mounted taps - Taps designed to mount on the edge of the basin or bath (rather than being wall mounted).

Dual flush cistern - A WC cistern offering the option of a water saving or full volume flush, normally determined by how the handle 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 used to achieve 'earth bonding' by joining the metal pipes and fittings together to provide an electrical earth path.

Electrical heating element - A component used in an instantaneous electric shower to heat the water as it flows through.

Essex flange - A fitting inserted into the side of hot water cylinders, just below the top seam, which purges the hot water of air before it is drawn off into the outlet. Normally used in the feed for shower pumps. Alternatives York and Surrey flanges are fitted into the top outlet of hot water cylinders.

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.

Float operated valve - see Ball cock.

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

Grey water - The waste water from baths, basins, sinks, washing machines, dish-washers etc., which has been used to clean things and which is considered to be only mildly dirty.

Header tank - See Cold water storage tank.

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 (normally cylindrical) used to store heated water under pressure greater than atmospheric.

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.

Instantaneous electric shower - A shower that electrically heats the water as the water flows through it.

Instantaneous gas water heater - An appliance which heats water on demand as the the water flows through it.

Lockshield valve - Fitted at the return side of each radiator and used to balance the system when it is first installed. Generally there is no need to adjust them once set (they are normally covered with a cap), if they are closed to allow for the removal of a radiator, count the turns to the off position so that they can be reset when required.

Low level cistern - A cistern mounted on the wall just above the WC pan with a short flush pipe. Generally the cistern is operated by a lever mounted on the front of the cistern or (more modern) a push button on the cistern top cover.

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. The input pipes are smaller than 'normal' taps.

Multi Point water heater - An instantaneous water heater which will supply water to more than one outlet.

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 it will only come into use when there is a fault (i.e. a leaking valve etc). See also Warning vent.

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

Power shower - A shower using a pump to boost the flow of water to give a powerful shower spray. Generally used where there is insufficient water pressure on gravity fed water supplies.

Pressure relief device - A safety device fitted to relieve excessive pressure within an electric shower heater - generally a 'use once' device which requires replacement after the problem has been rectified.

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

Pushfit connectors - Plumbing connector which just push onto the pipework rather than compression or capillary connectors - maybe plastic but suitable for both hot and cold water - sometimes referred to as 'Speedfit connectors' (one of the early brands). Available as straight, 'T', elbow and other configurations.

PTFE tape - Polytetrafluorethylene tape used to seal threaded plumbing joints.

Rising main (AKA a riser) - 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.

Servicing Valve - A valve for shutting off the flow of water in a pipe connected to a water fitting to facilitate the maintenance or servicing of that fitting.

Single lever mixer tap - A mixer tap with a single lever handle to controls the water flow of both the hot and cold water supplies.

Solder connector - see capillary connector.

Stack pipe - High level vent pipe for the main soil pipe.

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 which purges the hot water of air before it is drawn off into the outlet. Normally used in the feed for shower pumps.

A Surrey Flange will suit female cylinder outlets - for male cylinder outlets, the equivalent is a York flange.

Tail (on a tap) - The threaded section (or copper pipes on a Monobloc tap) that are connected to the water supply pipe.

Tap seat - The supply orifice within a tap body (except ceramic taps) on to which the washer is compressed to seal off the water.

Thermostatic mixing valve - A hot and cold water mixing device which automatically adjusts for variations in the temperature and/or pressure of the incoming supplies, to maintain a selected temperature at the outlet.

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

Trap - A water filled seal in the waste run from a bath, basic, or sink, etc which prevents fumes coming back from the drains.

Two hole mixer tap - A mixer tap requiring two separate holes for the water feeds in the sink etc. - as opposed to a Monobloc tap.

U-bend - A form of trap - often used to refer to a WC trap.

Vent pipe - An uninterrupted safety pipe which allows air or the expansion of water within a hot water system to escape - normally positioned over a tank/cistern so that any water is discharged into it.

Wall hung toilet - A WC where the pan is suspended or hung from a wall rather than being fitted to the floor.

Warning vent - An overflow pipe positioned so that its outlet is in a conspicuous position where any discharge can be readily seen.

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.

A York Flange will suit male cylinder outlets - for female cylinder outlets, the equivalent is a Surrey flange.

Yorkshire fitting - A capillary connector incorporating a solder ring - an original brand name.