I’m seeking advice from fellow sailors,,,,,
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Why are the inlet and outlet valves closed when stopping a diaphragm pump? Why do some variable-frequency centrifugal pumps have a return line while others don’t?
Can’t the inlet and outlet valves be closed before shutting down the diaphragm pump? Positive displacement pumps are very sensitive to pressure, and doing this will cause pressure buildup. Centrifugal pumps now all come with variable frequency drives, allowing the speed to be controlled manually; if the flow rate is insufficient, the speed can be reduced, which prevents cavitation. Therefore, there is no need to install a return line.
It must be stopped before the outlet valve can be closed. If stopping requires shutting down the pump, of course the inlet and outlet valves must be closed. Generally, variable-frequency pump sets rarely have return lines; such features are usually found in high-speed pumps to meet the requirement for minimal flow rates
Both metering pumps and diaphragm pumps operate under back pressure; when this pressure is reduced, the medium at the inlet can flow directly to the outlet (the check valves at the inlet and outlet are in the same direction), so it is best to close the inlet and outlet valves； It depends on the magnitude of the frequency conversion adjustment; if the adjustment is significant enough to cause the minimum flow rate to fall below the pump’s minimum requirement, then a return line must be installed, otherwise it is not necessary.
1. It’s related to the working medium; it’s the issue of the check valve not being reliable. 2. It’s related to the pump’s performance curve – some pumps have a minimum flow rate of 0, so there’s definitely no need for such a setting
Everything analyzed upstairs makes sense; I’ve learned something! ! ! ! ! ! !
How can the pressure in the inlet line of a metering pump be higher than the pressure in the outlet line?
This situation does exist and has occurred before; we have experienced it. Furthermore, if the check valve at the inlet and outlet leaks internally, the medium at the outlet will flow back to the inlet.
So these are also the valves that close the inlet and outlet after the pump is stopped. I think turning it off before stopping the pump can cause the pump to become vacuumed and experience pressure buildup.