Methods for switching between high and low pressure in vertical centrifugal pumps and selection of pipe diameter

Is it feasible to use a DN40 bypass with a stop valve for regulation?

According to the characteristics of centrifugal pumps, pressure regulation can be achieved by using the outlet valve; as long as there is sufficient flow to carry away the heat generated by the pump itself, preventing its temperature from rising, the smaller the opening of the outlet valve, the lower the current consumption, which is beneficial for energy savings. Therefore, it is sufficient to install an automatic valve for regulation in front of the outlet valve (pneumatic or electric); there is no need to use a variable-frequency device. If pressure is to be maintained in a closed system, a return line must be installed, with a valve on this return line for regulation. If money is not a concern, install an electric or pneumatic self-regulating valve, or a manual one. It would be best to include a simple process view for discussion and reference

The maximum head is 220 M; it’s a bit unreasonable to require a pressure of 0.1 MPA for such a high head. Centrifugal pumps can achieve a maximum pressure of 2.2 MPa, while the design pressure for pipelines should be at least 2.5 MPa; even with the outlet closed, this should not cause any damage to the pipeline. By setting the pump to operate at 25 Hz and adding a control valve at the pump outlet to regulate the pressure, this requirement can likely be met.

A DN20 bypass pipe and a stop valve have been installed, but this only allows the pressure to be reduced to 0.5 MPa. Now I want to increase the size of the bypass pipe; I’m not sure by how much it should be increased

Please refer to the flowchart that has been uploaded. Currently, it is not planned to install a pressure regulating valve at the outlet; instead, the pressure of 0.1 MPa is to be achieved by adjusting the bypass valve. The issue is that it is not clear what diameter the main pipeline should have – DN40 – so it is uncertain what size would be appropriate for the bypass pipeline

The main piping has been installed. The bypass pipe was previously DN20, and the centrifugal pump always operated at a low frequency; this seemed to affect its lifespan. Therefore, I want to increase the diameter of the bypass pipe so that the frequency can be kept above 25 Hz

At low pressure, the amount used at the rear determines the bypass flow. In the case of a centrifugal pump, the simplest way is to use an outlet valve to control the desired pressure, provided that there is a certain flow rate; this flow rate is determined by the heat generated by the centrifugal pump. There’s no need to set anything like frequency conversion. If bypass regulation must be installed, just use any DN25~20 size or similar. Because it is mainly controlled by valves. For reference.

If a centrifugal pump is equipped with an inverter-driven motor, the impact is minimal; however, if it isn’t an inverter-driven motor, there will be issues with heat dissipation at low frequencies. If a bypass is to be used for adjustment, it must at least have the same diameter as the main pipe; moreover, based on the pressure distribution, it seems that the pressure measured at the location of the remote pressure gauge will not reach 0.1 Mpa. Install a pressure gauge behind the outlet butterfly valve to regulate the pressure after the control valve using the outlet butterfly valve

This method is feasible; the DN20 pipes currently in use are too small, resulting in insufficient pressure reduction. I’m wondering if anyone has experience in this area – to what extent can pressure be reduced by using bypass pipes? If we use DN40 pipes, they will be as thick as the main pipes. I’m considering using two DN20 pipes or one DN25 pipe; I’m not sure if that will work