# Check valve: why you need one and where to fit it

> How a check valve works, where it is essential in a system with a pump, a borehole and a water heater, and how to tell that it lets water flow back.

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*June 24, 2026*

![Diagram: cutaway check valve — disc, spring and seat, direction of flow and blocked back-flow](https://watertrade.com.ua/uploads/articles/check-valve.jpg)

A check valve lets water through in one direction only. When the flow goes the right way, the water pushes the disc open and passes. When the flow stops or tries to reverse, the spring presses the disc onto the seat and closes the passage.

## What the diagram shows

1 — the disc (closing element), 2 — the spring, 3 — the seat. The arrow on the valve body always shows the direction of flow.

## Where a check valve is essential

- **At the end of a booster set’s suction pipe.** Without it the water in the pipe drains back into the well and the pump has to be primed every time. A foot valve with a strainer is used here.
- **Right after a borehole pump.** Many pumps have one built in, but it is often duplicated at the outlet. In deep boreholes add another one every 20–30 m of pipe.
- **On the water heater inlet** — as part of the safety valve, so hot water does not flow into the cold pipe.
- **Before a meter and at mixing points** — where hot and cold water meet and could flow into each other.

## Which one to choose

1. A brass body for water supply and heating.
2. A brass disc outlasts a plastic one, especially when there is sand in the water.
3. A size no smaller than the pipe: the valve adds resistance by itself.

## Signs of a faulty valve

- The booster set cannot draw water in the morning — the water in the suction pipe has run back.
- The pump starts by itself at night although there are no leaks in the house.
- The gauge slowly drops with all taps closed.

> A valve with sand or rust under the disc stops sealing. Fit a strainer in front of it, and clean or replace the removed valve.

Everything for pump connections is in the [pump controls](https://watertrade.com.ua/en/catalogue/avtomatika-dla-nasosov) and [accessories](https://watertrade.com.ua/en/catalogue/komplektuusie-dla-gidroakkumulatorov) sections.

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