Due to the complexity of fluid motion in the impeller machine, it is difficult to calculate where qi erosion may occur in theoretically, plus the phenomenon of air erosion depends not only on the fluidity characteristics of the fluid, but also the thermodynamic nature of the fluid itself itself. Therefore, it is more difficult to propose the judgment of qi erosion in theory. Therefore, in practice, it is often used to use experience and experiments to propose air erosion judgments. The concept of air erosion waste in the pump is one of the important judgments. It has certain theoretical significance and is one of the standards for product acceptance.

There are two concepts of water pump gas erosion waste: one is related to the installation method. It is called an effective air erosion balance NPSHA. That part of the energy is available available air erosion balance, which is a "user parameter"; the second is related to the pump knot itself, called the necessary air erosion waste NPSHR, which is the pressure of the fluid from the pump from the pump inlet to the lowest pressure. Reducing the value is a critical air erosion balance and belongs to the "factory parameters". To ensure that the water pump is not eroded during operation, it is necessary to ensure that the NPSHA ≥ K × NPSHR must be guaranteed in the installation, and the latter is guaranteed by the manufacturer. In this sense, the significance of reducing the amount of gas erosion in the pump is to ensure the absolute water lifting height of the pump and meet the requirements of the use.