What Is a Check Valve?

Check valves are usually installed in the pipeline to prevent backflow. A check valve is basically a one-way valve in which the flow can flow freely in one direction, but if the flow turns, the valve will be closed to protect the piping, other valves, pumps, etc. If the flow is diverted without a check valve installed, a water hammer may occur. Water hammer often occurs with extreme force and can easily damage pipes or components.

What is a water hammer?

In a pumping system, water is forced from a lower water level to a higher water level by the pump. Only when the pump is running, the fluid will flow in one direction. When the pump stops, the flow of fluid will decrease until the pump also stops. Because the entire pipeline will rise, when the fluid stops, it will return to the pipe. To prevent the fluid reversal from entering into the pump, well, or water inlet, a check valve is installed.

In many cases, the fluid reversal rate is not a concern, and the performance of standard check valves is also very good. However, in a pumping system, rapid backflow may occur, and it is critical to choose the correct check valve.

If the pump stops before the check valve is completely closed, and the forward fluid flows back into the pipeline to the pump, the fluid will force the valve door to hit its valve seat. In this case, the backflow can be stopped almost instantaneously, and it is this instantaneous stop that causes the water to hammer in the pipeline. This may produce a huge hammering noise. This is not the noise when the valve enters the seat position, but the stretching of the pipe under these conditions.

Check Valve

The ensuing pressure wave (surge) can cause considerable damage to the system, including pipe cracks, bursts, cavitation, and implosion due to the formation of vacuum pressure. It should also be noted that these failures may not be caused by a single, large impact pressure, but by repeated impacts that ultimately lead to system fatigue failure.

It is worth noting that in order to ensure that the system is safe and trouble-free, other factors need to be considered. The correct number, type, and size of air valves, closing and opening times of isolation valves, flow control valves, etc. all need to be considered to protect the system from pressure surges.

In order to prevent the occurrence of a check valve slam, the valve should be closed very quickly to prevent the onset of reverse flow or very slowly when reverse flow occurs. In order to close the check valve slowly, additional auxiliary equipment, such as a hydraulic damper, is needed to cushion the valve when it enters the seated position. However, this slower closure does allow fluid to pass through the check valve until the check valve closes, and the upstream pump must be considered to ensure that it is suitable for reverse spin and flow.

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