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If it is necessary to control the backflow rate while maintaining system pressure, it is best to open it fully first, and then adjust by closing this reverse tank valve gradually, based on the fixed opening degree of the pump outlet valve (the opening degree at maximum rated current). The key question is what the function of this valve is.

When the centrifugal pump starts, the outlet valve is closed, and the return valve must also be closed; after it is started, regulation is carried out through the outlet valve and the return valve

Before starting the centrifugal pump, the outlet valve is closed; if it is to be opened, it should be opened to a small degree, otherwise the pump will start under load. The return line is the reflux pipeline; it is generally not turned on when the pump is started, and is activated only as needed after it comes into use.

For our multi-stage pumps and high-pressure pumps, the return line needs to be opened before starting the pump; for ordinary pumps, the return line is opened after the pump has started running

The minimum flow line, which is what you refer to as the return line, is usually installed at the outlet of multi-stage pumps. The pump is set to have a minimum flow rate; in simple terms, this is done to prevent the pump from being overloaded. The installation of a low-flow return pipeline for the pump serves to protect the pump itself; generally, this flow rate should not exceed 30% of the pump’s capacity. A flow control valve assembly is placed at the pump outlet, and when the flow rate at the outlet falls below 30%, these valves activate, allowing the fluid to flow back into the circulation pipeline or another pipeline that can directly lead to the tank. Taking centrifugal pumps as an example, once such a pump is started, there is a minimum flow rate required at the corresponding pressure. If this value cannot be maintained, air entrainment in the pump occurs, which prevents it from pumping fluid. Moreover, when the pump starts, it has its own fixed minimum flow rate, usually 20% of the rated flow rate. If the outlet is not opened and there is no minimum flow valve, the pump will still not be able to pump fluid after starting. The typical design for the minimum flow line is such that the minimum return line is connected back to the suction tank at the pump inlet, with the aim of preventing the medium from being pressurized and heated by the pump, which could cause some of the medium to heat up and vaporize. After entering the suction tank, the gas is separated in a timely manner to ensure the safe operation of the pump.

Is this valve opened after the pump is operating normally?