Pump load issue

Surely, the maximum load is achieved with the outlet fully open; if it is reduced, pressure will build up to a certain point after which further flow is not possible.

The characteristics of centrifugal pumps should be classified according to the properties of the medium. For centrifugal pumps operating in liquid media, closing the outlet valve and opening the inlet valve results in the lowest current (and thus the lowest power consumption). For centrifugal pumps (centrifugal compressors, fans) operating in a gaseous medium, the current is lowest (and power consumption is minimal) when the outlet valve is fully open (to allow discharge to the atmosphere) and the inlet valve is slightly open (otherwise vacuum surge will occur). Therefore, as a requirement for the preparatory work before starting the liquid pump, the inlet valve must be fully opened and the outlet valve must be fully closed. Only in this way are the starting conditions met, that is, the starting load is at its minimum. Otherwise, it will trip due to excessive starting load. After startup, use the opening degree of the outlet valve to control the rated current as specified. For centrifugal pumps (compressors, fans) operating in gas media, prior to startup the outlet valve must be fully opened to allow flow into the atmosphere, while the inlet valve should be slightly open. Only in this way can the starting load be minimized. For reference.

Actually, this is how we proceed in practice. But if the outlet is closed, won’t pressure build up in the pipeline? Will the pipe burst? It is very difficult to open the outlet valve after pressure buildup

In other words, when the pump outlet is closed, will the pressure at the pump outlet reach the maximum head?

High load when opened, pump stalls when closed

High load when opened; the pump will get stuck when closed

The current is at its highest moment when the centrifugal pump starts; closing the outlet valve prevents the excessive starting current from causing the motor to overload and shut down. The head when the outlet valve is closed should be the shut-off head; this is taken into account during the design of the pump. However, closing the outlet valve of the pump causes heating, leading to an increase in the temperature of the fluid.

Closing the outlet valve reduces the starting current of the pump, preventing the motor from being overloaded due to excessive starting current. If the outlet valve is closed, the pump will do work on the fluid, causing its temperature to rise and leading to cavitation