Check valve position
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May I ask whether the check valve on the PID should be installed upstream or downstream of the shut-off valve? What is the reason?
It is usually before the first shut-off valve. If, due to installation reasons such as the pump outlet being oriented upward, the pipe diameter being large, or the first shut-off valve being located at a high position, it can also be placed after the first shut-off valve; in this case, there should be a drain line between the two valves. A check valve is used to protect the pump, and in principle, it should be placed as close as possible to the equipment that needs protection.
For compression units, the check valve is of course placed in front of the shut-off valve. Under normal circumstances, the leakage level of the shut-off valve is higher than that of the check valve; if the check valve is located behind the shut-off valve, it is not possible to ensure that the unit is disconnected from the entire system once it is shut down!