A check valve — also called a non-return valve (Dutch: keerklep) — is a valve that lets a liquid or gas pass in one direction only and automatically prevents backflow. The valve opens under pressure in the flow direction and closes (or springs shut) as soon as the flow stops or tries to reverse.
How it works
A check valve operates without any control: the flow itself opens and closes it.
- Passing — the pressure of the medium pushes the valve open.
- Blocking — on pressure loss or backflow the valve closes by gravity, a spring or the counter-pressure.
- Automatic — no manual or electrical operation is needed.
Common types are the swing check valve, the ball check valve and the spring-loaded check valve.
Application
- Drainage and sewerage — a check valve in the sewer connection stops sewage flowing back into the house during heavy rain or a blockage (important for a cellar or semi-basement below street level).
- Pump lines — prevents pumped water from running back when the pump stops.
- Heating and tap-water systems — keeps the flow direction in the system.
Points to watch
- Install the check valve in the correct flow direction; an arrow is marked on the valve or body.
- Inspect sewage check valves regularly: dirt or scale can stop them sealing.
- For dirty water, choose a design that flows freely and does not clog quickly.
Related terms
- Building services
- Rainwater drainage
- Pressure pipe
- Wastewater
- Semi-basement
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