A check valve should preserve receiver vacuum and prevent reverse flow when the pump or forming circuit changes state. Leakage causes the receiver pressure to drift toward atmosphere during idle time or after the pump stops. The next cycle then begins from a different condition.
The receiver should be isolated and its pressure decay recorded with all intended valves closed. Each branch can then be isolated to distinguish check-valve leakage from receiver fittings, instruments, and downstream valves. Contamination on the seat may produce intermittent behavior that changes after several cycles.
The valve should be cleaned or replaced with a design suitable for the pressure range, flow direction, contamination level, and required response. Installing a larger pump will not correct stored-vacuum loss. After repair, both pressure retention and pump-down time should be verified.