Is there a uniform requirement for the margin against cavitation with regard to the safety margin? How can the safety margin be determined accurately?
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Is there a uniform requirement for the margin against cavitation with regard to the safety margin? How can the safety margin be determined accurately?
npsha: NPSH of the pipeline, calculated by the design agency. It is related to the pipeline conditions and the specific gravity of the medium. npshr: Required net positive suction head, a parameter specific to the pump. Ensuring that npsha is greater than 1.3npshr prevents cavitation from occurring during pump operation. Under normal circumstances, an npsha-npshr value greater than 1 is also sufficient to meet the operational requirements. Example: If the net positive suction head available for the pipeline is 5 meters, a pump with a net positive suction head of 4 meters or less will suffice to meet the operating requirements
The calculation of installation allowance involves many parameters, which are generally provided by the design institute. If technical modifications are involved, it is generally advisable to choose pumps with higher specifications, trying to avoid altering the existing piping systems, as such modifications also require consideration of issues such as vibration and erosion at elbows and tees
The safety margin refers to Npsha-Npshr; generally, a value of not less than 0.6m is sufficient. If the safety margin lies between 0.6m and 1.0m, it is necessary to conduct tests on the required net positive suction head of the pump to ensure that there is no positive deviation in cavitation for the centrifugal pump