How is the minimum return flow rate of a centrifugal pump to the tank calculated? The normal flow rate is 10 m3/h; when selecting a pump, the flow rate to the return tank also needs to be taken into account...

Personal understanding: When selecting a pump, there is no need to consider the minimum return flow rate.

If the pump’s flow rate is sufficient, there is no need to consider a minimum backflow at this time. If 10 cubic meters represents a significant deviation from the pump’s optimal operating range, then it is necessary to consider this factor

It depends on the pump model chosen. If it is a magnetic drive pump, then the minimum continuous flow rate must be taken into consideration to prevent the outlet from closing, which could lead to an increase in the temperature of the material inside the pump and thus cavitation. The backflow rate should be provided by the manufacturer; in design, it is generally calculated at 30%； In the case of mechanical seal pumps, it is generally not necessary to consider a minimum return flow rate; this depends on the properties of the material, as well as factors such as temperature and boiling point

All centrifugal pumps must be equipped with a minimum return flow line, typically at a rate of not less than 30%. This line also needs to have an orifice that reduces pressure; as for the size of this orifice, a global valve is used

Typically, the flow rate for the minimum flow protection setting of a centrifugal pump is set at 30% of the rated flow rate; the final value shall be as recommended by the manufacturer； When selecting a pump, there is no need to consider the minimum flow backflow. The main functions of the minimum flow line are as follows: 1) When a centrifugal pump operates at low flow rates, fluid separation can occur inside the pump, which can lead to vibration and noise. The minimum flow protection ensures that a certain amount of fluid continuously flows through the pump after it starts up, thereby preventing cavitation ； 2) When pumps with high power are operated with the outlet valve closed, the fluid inside the pump becomes increasingly hot; in severe cases this can damage the bearings. The minimum flow rate protection ensures that fluid continues to flow through the pump at all times during operation, thereby preventing overheating ； 3) At low flow rates, the pump is subjected to additional radial forces; the minimum flow protection mechanism prevents the pump from experiencing excessive radial forces. Not all centrifugal pumps require a flow protection line; generally, minimum flow protection is necessary in the following situations: 1) High-pressure pumps (multi-stage pumps), that is, those with an inlet-to-outlet pressure difference of over 3.5 MPa ； 2) Motors with an installed power of ≥160kW. 3) Pumps and similar devices for which process requirements dictate a reduction in flow rate.

The return line is installed to maintain stable pressure in the feed pipeline; may I ask how to calculate the flow rate of this return flow?

The minimum return flow rate is provided by the pump manufacturer; in the absence of such data, an empirical value of 30% can be used. For pumps with a low flow rate, the return flow rate can be increased appropriately. Whether a minimum return flow is required for the rated flow depends on the design of the return pipeline; it is necessary if a orifice plate is used, but not necessary if a flow control valve is used.