# Water pressure reducing valve: why you need one and how to fit it

> Why fit a pressure reducing valve at the inlet, piston or diaphragm type, where to install it, how to set it with a gauge and how to tell when it is faulty.

Web page: https://watertrade.com.ua/en/articles/article/reduktor-davleniya-vody · Other languages: [UA](https://watertrade.com.ua/articles/article/reduktor-davleniya-vody.md), [RU](https://watertrade.com.ua/ru/articles/article/reduktor-davleniya-vody.md)

*November 10, 2026*

![Diagram: water inlet with a valve, a filter, a pressure reducing valve with its adjusting screw and two gauges before and after it](https://watertrade.com.ua/uploads/articles/pressure-reducer.jpg)

Mains pressure varies: 2 bar during the day, 6 at night, and sometimes more after repair work on the network. Mixers, flexible hoses, the water heater and the washing machine wear out faster, and a flexible hose under the sink can burst at night when nobody is home. A pressure reducing valve keeps the outlet pressure the same, whatever the inlet pressure is.

## What the diagram shows

1 — the reducing valve with its adjusting screw, 2 — a gauge before the valve, 3 — a gauge after it, 4 — a coarse filter that protects the valve from sand.

## When you need one

- The inlet pressure sometimes exceeds 4–5 bar — you can see it on a gauge or in how hard water spurts from a tap.
- You have a water heater: its safety valve releases water at high pressure, and with a reducer it drips far less often.
- The pipes hum and bang — excess pressure is often the reason.

## Which one to choose

- **Piston type** — compact and inexpensive, good for a flat. It is more sensitive to dirt, so a filter in front of it is a must.
- **Diaphragm type** — holds the pressure more precisely and tolerates sand better, but is larger and dearer. A good choice for a house.
- Size it to the inlet pipe: 1/2" for a flat, 3/4"–1" for a house. A port for a gauge is a useful extra.

## Where to fit it

After the main valve and the coarse filter, before the pipes branch off around the home. With a manifold system, the reducer goes before the manifold. The arrow on the body points with the flow, and the adjusting screw must stay accessible.

## Fitting and setting

1. Shut off the water, release the pressure and fit the valve with the arrow in the flow direction. Seal the threads with hemp and paste or tape.
2. Slowly open the main valve and check the joints.
3. Close every tap and read the gauge after the reducer. Turn the screw to set the pressure you need — 3 bar is usually enough for any household appliance.
4. Open a tap: the pressure drops a little and should come straight back once the tap closes.

> If the pressure after the reducer slowly creeps up with all taps closed, the valve is not holding: dirt has got inside or a seal is worn. Rinsing the filter in front of it and cleaning the valve seat usually helps.

How pressure relates to banging pipes is explained in [“Humming, whistling and banging pipes”](https://watertrade.com.ua/en/articles/article/shum-i-stuk-v-trubah). Reducing valves, ball valves and filters are in [valves and fittings](https://watertrade.com.ua/en/catalogue/zapornaa-armatura) and [filters](https://watertrade.com.ua/en/catalogue/filtry-dla-vody/setcatye-filtry).

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