Check valve behind the nitrogen-sealed self-regulating valve
Thread Content
In a constant-pressure tank, a nitrogen seal self-regulating valve is installed as required by the process; a check valve is also placed on the pipeline connected to the tank behind the valve. Is this necessary?
Since a nitrogen seal is in place, the medium inside the tank should not come into contact with air. Installing a check valve prevents the medium in the tank from leaking into the nitrogen seal pipeline in the event that the self-acting valve fails.
Will the resistance of the check valve affect the operation of the self-regulating valve? Does it cause instability in the pressure inside the tank?
HG/T20559.7-1993: Basic unit patterns for piping and instrumentation diagrams. On the pressure-recovery pipes of atmospheric-pressure, low-temperature liquefied gas tanks, nitrogen, a self-acting control valve assembly, and a check valve are required; however, the check valve is located before the self-acting control valve assembly. However, check valves are not required on the nitrogen sealing pipelines of liquid storage tanks, nor is their use specified in HG20570.16-95 for gas sealing.
It’s not necessary; the nitrogen pressure must be higher than that of the storage tank, and the tank is equipped with a vent valve.
I’m a newcomer, and I also think it’s not necessary
What was said upstairs is completely correct – the nitrogen pressure is higher than that in the storage tank, and the tank is equipped with a vent valve. The purpose of designing a check valve is merely as a safety measure; it is actually not used in normal circumstances.
Setting check valves in accordance with specifications is merely one of several protective measures to prevent contamination of the nitrogen pipeline network
It’s not clear whether this type of check valve is a good choice; generally, the nitrogen seal pressure is at a slight positive level, and the check valve introduces a certain pressure drop, which may make it difficult to open and close. Please pay attention to the selection of check valves by the poster; if there are any check valve models that are suitable for nitrogen sealing, please let me know. Thank you!
I’m also worried about the issue of backflow valve resistance, which can cause a system deviation between the pressure inside the tank and the signal from the self-acting control valve.