Non-Return Valves

The most common sign is air leaking from the pressure switch unloader valve when the compressor is off. This means the non-return valve is letting air from the tank flow back towards the pump, which then escapes through the unloader.

Sizing is based on your motor power (kW). For example, our 1/2″ BSP valve is rated for compressors up to 2.2kW, while the 1″ BSP valve handles up to 7.5kW. Undersizing the valve will restrict airflow and cause the pump to overheat.

Most non-return valves rely on gravity or a spring to close. While spring-loaded valves (which ours are) can technically work horizontally or vertically, it is best practice to install them so the flow direction assists the seal. Always check the arrow on the valve body.

This is often caused by a stuck non-return valve. If the valve doesn’t seal, “back pressure” remains on the piston head. The motor then tries to start against high pressure, fails, and just hums. Replacing the non-return valve usually fixes this.

Yes, specific models in our range, such as the 1″ BSP valve, are rated for vacuum pumps up to 4kW and can handle vacuum pressure down to -1 bar. Always confirm the application before purchasing.