When does the minimum return flow of the pump start (before or after the pump starts)
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Dear heroes: I would like to ask whether the minimum return flow of the pump should be turned on before the pump is started, or after it is started. What a difference. Thank you!
Generally speaking, the minimum flow line of a high-pressure pump should be opened before starting to prevent pressure from being held up after starting.
The valve should be opened first. Only the return flow determines the initial valve opening.
It should be opened before starting, but the opening should not be fully opened. If the motor is fully opened, there will be no overcurrent (motor protection action). It should be slightly opened before starting, and immediately fully opened after stabilization.
For multi-stage centrifugal pumps used in high-pressure applications, open the return valve of the pump during switching (generally a throttle orifice plate is installed on the return line to limit the flow). This can not only prevent damage to the thrust bearing due to excessive axial force caused by the inlet and outlet differential pressure, but also avoid excessive starting current.
It should be turned on before starting, which is called the continuous minimum return flow of the pump. For non-displacement pumps, it ensures that the heat converted from the work done by the impeller is taken away.
The minimum flow line of the pressure pump should be opened before starting to prevent pressure from being held after starting.
If it is a high-speed and high-pressure pump, the return valve must be opened before starting the pump.； If it is a multi-stage centrifugal pump, you can open the return valve after starting the pump.
Usually it is opened before starting the pump. There will be a throttling orifice plate, so the opening is not a big problem.
It should be opened slightly before starting and fully opened immediately after stabilization.