Thomas Dudley TD Rubber Diaphragm for HydroFlo Ballvalve, replacement seal, valve membrane, cistern float valve diaphragm

Valves start, stop, regulate or direct the flow of water, heating water, gas or air through pipework. This category covers isolating, servicing, ball, gate, check, pressure reducing, float and butterfly valves, from small domestic sizes up to large flanged valves for commercial and utility work.

Main types

• Isolating and servicing valves: shut off one tap, appliance or cistern for maintenance without draining the whole system.
• Ball valves: lever valves that open or close with a 90 degree turn and seal tightly.
• Gate valves: multi-turn valves with a clear bore when fully open, suited to isolation that is used occasionally.
• Check valves: also called non-return valves, they let water flow one way only and help protect the supply against backflow.
• Pressure reducing valves: lower and steady the incoming mains pressure.
• Butterfly valves: compact valves for large-bore pipework.

Key choices

Match the ends to the pipework: compression or push-fit for copper and plastic pipe, parallel or tapered BSP threads, or flanges on larger sizes. Check the pressure rating: a PN figure is the pressure in bar the valve is designed for at 20°C, and the safe working pressure falls as temperature rises. Bodies are made in brass, DZR brass, bronze, cast iron and plastics such as PVC-U and ABS; choose one suited to the fluid and temperature. Valves on drinking water must be suitable for that use.

How to choose

Start with what the valve has to do, then pick the size, end connection, pressure rating and material. For radiators, see thermostatic radiator valves; for joining pipe, see fittings.

Valves on gas pipework and gas appliances must only be fitted by a Gas Safe registered engineer.