The relationship between a pump’s head and pressure difference
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The head of a pump is roughly the difference between the inlet and outlet pressures. For example, if a pump previously had an inlet pressure of 1 bar and an outlet pressure of 9 bar, resulting in a head of 80 m, then if this same pump is connected to a high-pressure fluid stream, would the inlet pressure now be 2 bar and the outlet pressure 10 bar? Or does the head change? Ignoring pipeline resistance issues, another question is: why do high-head pumps burn out their motors when used for low-head applications? It is said online that the flow rate increases, which leads to an increase in current, but isn’t the head also lower? According to the performance curve, as the flow rate increases, the head decreases. Axial power equals head multiplied by flow rate; since one value increases while the other decreases, how can the motor burn out? The voltage remains constant, so why does the axial power not decrease and yet the current increase?
The head of a pump remains constant when its speed and impeller diameter stay unchanged. If the medium density is changed, the corresponding pressure will change, but the head remains constant.
Does a change in the inlet pressure of the pump lead to a change in its head? It seems similar to multi-stage centrifugal pumps, where multiple stages of compression result in an increased head; will an increase in inlet pressure also cause a change in the head?
Excuse me, I’m wondering how the relationship between head and flow rate is determined on the performance curve of a pump at a certain speed. When the flow rate is high, the head is low. If the pump’s speed and impellers remain unchanged, how can the head change with the flow rate? I’m a beginner, so my question might not be very well phrased. I hope for an answer
For a single pump, the specific relationship between flow rate and head is quite complex; as the flow rate of a centrifugal pump increases, its head decreases. The inlet pressure has no effect on the pump’s head
When the flow rate of a centrifugal pump is increased, the shaft power rises; the ratio of increase in flow rate to increase in head is not the same. It’s not that if the head and flow rate increase by 20%, the head will decrease by 20%
I see. Thank you for your reply; it’s been very helpful to me
1. The head of a pump is an inherent capability that it possesses from the time it is designed and manufactured; it does not change depending on the properties of the material being transported. It only varies depending on the installation location, as well as the distance and height over which the material is transported. The pump pressure at the outlet is related to the specific gravity of the material; the pressure = density * g * h + pressure in the target unit – pressure in the inlet unit. 2. When a high-head pump operates under low-head conditions, the absolute increase in flow rate is much greater than the decrease in head; as a result, the flow rate exceeds the limit, the motor power also exceeds the limit, which can lead to motor damage