Check Valves Explained: Types, Applications, and How to Choose the Right One

Check valves are one of the simplest yet most essential components in any piping system. Their sole purpose is to allow flow in one direction and prevent it in the reverse direction — protecting pumps, compressors, and other equipment from damage caused by backflow. Despite their simplicity, choosing the wrong type of check valve can lead to water hammer, excessive pressure drop, or failure to prevent backflow in critical situations.

At Valves UK, we supply check valves across a range of types and materials for industrial, commercial, and utility applications. In this guide, we'll explain how check valves work, the different types available, and how to select the right one for your system.

How Does a Check Valve Work?

A check valve is an automatic valve that opens to allow forward flow and closes to prevent reverse flow. Unlike other valves, it requires no external actuation — it responds entirely to the pressure differential across it. When the upstream pressure exceeds the downstream pressure (plus the cracking pressure — the minimum pressure required to open the valve), the valve opens. When the flow stops or reverses, the valve closes under spring force or gravity, or by the reversing pressure itself.

Types of Check Valves

Swing Check Valves: A disc swings on a hinge pin to open and close. When flow is forward, the disc swings open. When flow stops or reverses, the disc swings shut under gravity or backpressure. These have very low pressure drop when open but can slam shut suddenly, causing water hammer. They are best suited to horizontal pipelines with relatively steady flow.

Lift Check Valves: A disc or piston lifts vertically off its seat to allow flow. The disc re-seats when flow stops or reverses. These offer tighter shut-off than swing check valves and are more resistant to water hammer, but have higher pressure drop. They can be installed in horizontal or vertical (upward flow) pipelines.

Dual Plate (Wafer) Check Valves: Two spring-loaded semicircular plates are mounted on a central hinge pin. They open to allow forward flow and snap shut quickly due to spring assistance, minimising water hammer. These are compact, lightweight, and suitable for high-flow applications. They are ideal for water treatment, HVAC, and general industrial service.

Ball Check Valves: A ball sits in a conical seat. Forward flow lifts the ball off the seat; reverse flow pushes the ball back onto the seat, sealing it. These are particularly suited to viscous fluids, slurries, and applications where clogging might be a concern, as the ball is self-cleaning. They are also common in pump discharge applications.

Non-Return Valves (Spring-Loaded): A spring-loaded poppet or disc closes against a seat. The spring provides consistent closing force, making these valves suitable for vertical installations with downward flow where gravity-assisted closure is not available. They provide quick, positive closure and are widely used in instrumentation, gas, and small-bore applications.

Water Hammer and How to Avoid It

Water hammer is the shockwave created when a column of flowing liquid is suddenly stopped or reversed. A slow-closing check valve (like a swing check) can allow significant backflow before closure, and the sudden slam of the disc creates a pressure spike that can damage pipework, joints, and equipment. Spring-loaded dual plate and lift check valves close much more quickly, minimising backflow and significantly reducing water hammer risk.

Installation Considerations

Check valves must be installed in the correct orientation — most types are directional and have a flow arrow marked on the body. Swing check valves generally require horizontal installation. Lift check valves can be installed horizontally or in vertical upward-flow applications. Dual plate check valves are typically suitable for horizontal, vertical upward, and vertical downward installation. Always consult the manufacturer's installation instructions. The valve should be installed downstream of sources of turbulence (pumps, elbows) to ensure stable flow past the valve disc or ball.

Materials of Construction

Check valve materials should be selected based on the media, pressure, and temperature requirements. Cast iron is used for water and general service at lower pressures. Stainless steel (316) is suitable for corrosive media, steam, and hygienic applications. Bronze or brass is used for potable water and low-pressure gas applications. PVC or CPVC is used in chemical handling and water treatment systems with aggressive media.

Conclusion

Check valves are critical protective devices in any piping system. Selecting the right type — considering flow conditions, orientation, water hammer risk, media compatibility, and pressure rating — is essential for reliable long-term performance. At Valves UK, our technical team can help you identify the best check valve solution for your application. Browse our range online or contact us today for expert guidance.