Required NPSH and plant NPSH

One is to consider the buyer’s perspective: I have this much headroom for cavitation available for you. One is from the seller’s perspective: if you want to use my pump, you must ensure a minimum net positive suction head

The basic condition for cavitation to occur is that the minimum liquid flow pressure pk at the blade inlet ≤ the vaporization pressure pv of the liquid at that temperature. To prevent cavitation, it is necessary to ensure that pk > pv; in other words, the energy head of the liquid at the pump inlet must be not only higher than the vaporization pressure pv of the liquid but also include a certain amount of excess energy head. This excess energy head is referred to as the net positive suction head, denoted by the symbol △h. Abroad, it is commonly called Net Positive Suction Head, abbreviated as NPSH. NPSH is further divided into effective NPSH △ha and the required NPSH for the pump △hr. (1) The effective net positive suction head is the effective pressure or head energy that the liquid flow possesses, after reaching the pump’s inlet through the suction pipeline, to push and accelerate the liquid into the impeller chambers above the vaporization pressure. The greater this excess amount, the less likely the pump is to experience cavitation. (2) The required net positive suction head of the pump, which reflects the total head loss of the fluid flow from the pump inlet to the lowest pressure point inside the impeller. The lower this value, the less likely the pump is to experience cavitation. △When ha > △hr, the pump does not experience cavitation; when △ha = △hr, cavitation begins to occur; △ha