Does the pump’s net positive suction head change?
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Although the net positive suction head is determined once the pump is designed, can it change during operation due to wear or other factors?
NPSH is divided into required NPSH and available NPSH of the device. The net positive suction head of the device is related to the installation method, while the required net positive suction head must be determined by the pump itself.
The required net positive suction head is determined during the pump’s design; wear or other external changes can affect the pump’s operational efficiency, but they do not affect the pump’s inherent net positive suction head.
Yes, for example, the friction in the pump flow channel increases
The greater the flow rate of a centrifugal pump, the greater the net positive suction head required
This post was last edited by 156026692 on 2018-8-19 at 15:58. Indeed, when the flow rate remains constant, NPSHr does not change due to changes in the medium
1. The pump’s flow rate and speed affect NPSHr; therefore, methods such as variable frequency speed control or changes in flow rate while the pump is in operation can influence NPSHr. Similarly, any other factor related to flow rate (velocity) is also associated with it. 2. Installing an impeller at the pump inlet can reduce the required net positive suction head value for the pump. When the impeller becomes corroded or damaged, it affects the pump’s capacity to maintain a sufficient net positive suction head
If it is not an induction motor, the net positive suction head must remain constant; the pressure drop that occurs as the fluid enters the low-pressure area of the pump depends only on the pump itself. The effective net positive suction head is influenced by the local air pressure, the temperature and saturated vapor pressure of the fluid, as well as the installation height. Generally speaking, these factors remain fixed.