Outlet valve when the self-priming pump starts
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When a self-priming pump starts, the outlet valve is open – why is this different from ordinary centrifugal pumps? Is it prohibited to fully close the outlet valve when using a self-priming pump?
At the outlet of the centrifugal pump, it should be closed first and then opened to prevent excessive starting current. I wonder if this is really necessary; the starting current required to get the motor running is several times higher than that during normal operation, and since it’s also used for transporting liquid, this current doesn’t increase much anyway. In reality, under normal operation of our small pump, it only requires pressing the on/off button; once the valve is set properly, it remains unchanged. For large pumps, those with large outlet diameters, large valves, and high pressure, it is necessary to keep the outlet valve slightly open to prevent excessive outlet pressure from pushing the valve element and making it difficult to open the valve
Why is it prohibited to close the outlet valve of a self-priming pump completely?
Thank you. Why is it prohibited to close the outlet valve of a self-priming pump completely? A self-priming pump is also a centrifugal pump; I can’t understand this. If the outlet valve cannot be fully closed, no water can be pumped out because a vacuum cannot be created at the inlet. Can’t the liquid that enters the inlet displace the air inside the inlet chamber?