How to Determine Whether the Cavitation Allowance of the Slurry Pump Meets the Requirements?

The slurry pump manufacturer will indicate the necessary cavitation allowance of the pump on the product manual or nameplate. This is an important basis for judging whether the cavitation margin meets the requirements. For example, the nameplate of a slurry pump is marked with NPSHr = 3.5m, indicating that when the pump is working normally, an effective cavitation allowance of at least 3.5m is required at the suction inlet to avoid cavitation.

Determine the effective cavitation allowance (NPSHa) under operating conditions: determined by calculation. The calculation formula is NPSHa = (liquid level pressure in the suction container - liquid vaporization pressure)/ (liquid density gravity acceleration)-suction pipe resistance loss - suction velocity head. Among them, the liquid level pressure of the suction container is usually atmospheric pressure (if it is an open container) or other given pressure (if it is a closed container); the liquid vaporization pressure is related to the liquid temperature, and the liquid vaporization pressure is different at different temperatures; the resistance loss of the suction pipeline can be calculated by hydraulic power, which is related to factors such as the length of the pipe, the diameter of the pipe, the roughness, the elbow and the number of valves; the suction speed head is related to the flow rate of the liquid at the suction port.

If NPSHaNPSHr, then the cavitation margin of the slurry pump meets the requirements, and it is unlikely that cavitation will occur in the pump under normal working conditions; if NPSHa < NPSHr, the slurry pump may cause cavitation, and measures need to be taken to increase the effective cavitation margin or replace the pump with a lower cavitation margin requirement.

When cavitation occurs, the flow and head of the slurry pump fluctuates. If the pump flow and head are found to drop suddenly, accompanied by unstable changes, it may be caused by cavitation. This is because the bubbles produced by cavitation break in the high-pressure zone, which will impact components such as the impeller, affecting the normal operation of the slurry pump, and thus causing the flow and head to drop.

Cavitation can cause abnormal noise and vibration in the slurry pump. When you hear a crackling sound in the pump, similar to the sound of a small stone hitting the metal, and the vibration of the pump body intensifies, it is likely caused by the bursting of bubbles caused by cavitation. In this case, it may be that the cavitation margin is insufficient, which leads to the occurrence of cavitation.