Selecting a pump, calculating pump inlet pressure
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This post was last edited by Qicai de Yangguang on 2018-7-19 09:49. When selecting a centrifugal pump for use in design, the formula for calculating the inlet pressure of the pump is as follows: P = P1 + 9.81*ρ*h*10^-3 – ΔP – ΔPe – u^2/2/g. Here, P represents the inlet pressure of the pump, in kPa; P1 is the pressure in the container at the inlet side, also in kPa; ρ is the density of the fluid, in kg/m3; h is the height difference between the liquid level in the container at the inlet side and the base of the pump, in meters; ΔP represents the pressure loss in the inlet pipe, in kPa; ΔPe represents the pressure loss due to the equipment at the inlet, also in kPa; u is the flow velocity at the inlet. Please share your opinions
Seeing your formula fills me with admiration, but I simply can’t understand it at all! I have a gentle question: should the inlet pressure of the pump be negative?
Why is the inlet pressure negative? There are usually two situations: backflow and suction
Do you mean gauge pressure? If the liquid level on the inlet side is slightly higher than the pump inlet level (with the excess amount exactly compensating for the pipeline losses), then the gauge pressure at the inlet is 0. If it is lower than this level, the gauge pressure is negative (i.e., a vacuum). If it is higher than this level, the gauge pressure is positive.
I’d like to ask everyone: what exactly are inlet pipe losses and inlet device losses? Isn’t the energy consumption associated with the inlet itself? Pardon my ignorance