What causes the pump outlet pressure to be greater than the pump’s maximum head plus the inlet pressure?
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As stated in the title, the centrifugal pump has a flow rate of 25 m3/h and a head of 40 meters. During factory testing, with the valve completely closed, the maximum pressure reached was 0.5 MPa; the medium used is water. Based on the actual operating conditions, the specific gravity of the medium is 1.37, the inlet pressure is 0.12 MPa, the outlet pressure is 0.69 MPa, and the flow rate is 26 m3/h. Logically, when the outlet flow rate is 26 m3/h, the pump’s head should be less than 40 meters; so why is the outlet pressure much higher than the inlet pressure plus the pump’s head?
The density of the medium is 1.37 times that of water, and the difference between 25 and 26 is only 1 cubic unit; therefore it is believed that a pressure of 40 meters can also be achieved. Using the formula, the pressure difference is 0.538. Adding the inlet pressure of 0.12 gives 0.658. Taking into account tolerances and errors in motor speed, it is also possible to reach this outlet pressure