Regarding the issue of starting the pump by closing the inlet valve
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Pump A replaced Pump B; since there was no check valve at the outlet, pump B was operated at reduced frequency while pump A was started at a lower frequency. It was observed that an abnormally loud noise was produced when the electric valve at the inlet of pump A was opened, and the current during startup reached 440 A for more than 5 seconds, after which the pump stopped (the rated current is 355 A). In this situation, can the pump be started first and then the inlet valve opened, given that the outlet valve is difficult to operate due to design issues?
Why isn’t the inlet valve fully opened before starting pump A? During the startup of the pump, no flow can be drawn at the inlet; as a result, the control valve will open further, which will affect the operating conditions of the pump!
Before starting the pump, open the inlet valve fully; after starting the pneumatic pump, gradually open the outlet valve
Not opening the inlet valve means idling, and this operation will damage the pump.
Due to design flaws, pumps that are operated in parallel with one in use and one as a backup should be equipped with outlet check valves; otherwise, backflow can occur when the backup pump starts and the outlet valve is opened, leading to the pump running in reverse. Furthermore, for pumps used to transport liquids, the inlet valve must be fully opened before starting the pump, in order to prevent cavitation that could damage the impeller
Why go through such a process? It’s not difficult to make modifications at the pump outlet to add a check valve. Doing this will cause significant damage to the pump.
Reduce the flow rate by closing the outlet valve of pump B, which in turn lowers the inlet flow; after that, start pump A, open the inlet valve and then the outlet valve