What factors can cause a decrease in the head of the sewage pump

Yibocommunal
2 min readJul 11, 2023

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(1) Motor reversal
Due to wiring reasons, the direction of rotation of the motor may be opposite to the actual requirement of the sewage pump. Therefore, when starting, it is generally necessary to observe the direction of rotation of the sewage pump. If the direction of rotation is reversed, any two wires on the motor terminal should be exchanged.
(2) Impeller channel blockage
If the flow channel of the impeller is partially blocked, it will affect the work of the impeller and cause a decrease in outlet pressure. Therefore, it is necessary to disassemble the pump for inspection and removal of foreign objects. To prevent the problem from recurring, a filtering device can be installed before the inlet of the sewage pump if necessary.
(3) Internal leakage occurs
When the gap between the rotating and stationary parts of the sewage pump exceeds the design range, it will cause internal leakage, which is reflected in a decrease in the discharge pressure of the pump, such as the clearance between the impeller mouth ring and the interstage gap of the multi-stage pump. At this point, corresponding disassembly and inspection should be carried out to repair or replace the components that cause excessive clearance.
(4) Cavitation occurs at the inlet
If the suction pressure of the sewage pump is too low, lower than the saturated vapor pressure of the pumped medium, cavitation will form. At this time, check whether the inlet Plumbing is blocked or whether the opening of the inlet valve is too small, or increase the liquid level of the suction pool.
(5) Speed decrease
The important factors affecting the head of sewage pump are the outer diameter of the impeller and the speed of the pump. When Ceteris paribus, the head of the pump is in direct proportion to the second power of the speed. It can be seen that the speed has a great impact on the head. Sometimes the speed of the pump decreases for some external reason, which will reduce the head of the pump accordingly. At this point, the pump speed should be checked. If the speed is indeed insufficient, the cause should be checked and a reasonable solution should be found.
(6) The operating point shifts towards high flow and low head
In general, centrifugal pumps have a continuous downward performance curve, and the flow rate gradually increases with the decrease of head. During the operation process, due to some reason, the back pressure of the pump decreases, and the working point of the pump passively shifts towards the low head and high flow point with the device curve, which will cause the head to decrease. In fact, this is caused by external factors such as changes in the device, and has no special relationship with the pump itself. At this point, simply increasing the pump back pressure, such as closing the outlet valve a little, can solve the problem.

FJ-300 Molecular Pump Unit

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