How Does A Non Return Valve Work

Release time:

2024-01-04

A non-return valve, also known as a check valve, is a mechanical device that allows fluid or gas to flow in one direction only. The valve works by using a disc or ball that opens and closes with the flow of fluid or gas. When the fluid or gas flows in the correct direction, the valve opens, allowing it to pass through. However, when the flow reverses, the disc or ball is pushed back against the valve seat, sealing the valve and preventing the fluid or gas from flowing back.

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There are different types of non-return valves, including swing check valves, lift check valves, and ball check valves. Each type operates in a slightly different way, but they all work on the same principle of allowing flow in one direction only. Non-return valves are commonly used in plumbing systems, pumps, and compressors to prevent backflow and protect equipment from damage.

Cracking pressure

A check valve requires a minimum upstream pressure (pressure differential between inlet and outlet) to open the valve and pass the media through it. This minimum upstream pressure at which the valve opens is called the check valve's ”cracking pressure.” The specific cracking pressure changes based on the valve design and size, so ensure that the system’s pressure can generate the cracking pressure of the chosen check valve(s).

Closing

If the upstream pressure falls below the cracking pressure or there is back pressure (flow attempting to move from the outlet to the inlet), the check valve will close. Typically, check valves have a gate, ball, diaphragm, or disc that is pressed against a seal to close the check valve. Gravity or spring can assist the closing process. As the inlet pressure decreases below the cracking pressure or there is backpressure, the valve closes by gravity, spring, and/or by using the backpressure.

Installation orientation

As a one-way valve only allows flow in one direction, it is crucial to know the correct installation orientation. Typically, an arrow on the valve’s housing indicates the flow direction. If there isn’t an arrow, examine the valve to ensure it is installed in the intended flow direction. If the valve is installed backward, media will not be able to move through the system, and the resulting pressure build-up can cause damage.

Normally open and normally closed check valves

A normally open check valve allows the medium to flow freely but shuts off the flow in case of backflow. A normally closed check valve prevents the flow of media through it until the cracking pressure builds up, at which point the valve opens.

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