If there is air leakage at the inlet, will the cavitation margin test results be higher or lower?

I checked the definition of net positive suction head; if there is air leakage at the inlet, the value should be on the higher side. Definition: NPSH refers to the excess energy per unit weight of liquid at the pump inlet, above its vaporization pressure. Therefore, I believe that the net positive suction head can be regarded as a margin that must be taken into account to overcome the vacuum that arises during operation inside the pump chamber. Thus, when there is a certain amount of air leakage in the inlet pipeline, the net positive suction head required to compensate for the effect of this leakage should be higher. This is just my personal opinion for reference only.

This post was last edited by 3983596_FPPZ on 2018-10-31 at 13:05. The answer is as follows: The first view holds that leakage at the inlet will increase the inlet pressure, leading to higher test results; it is argued that such leakage must be completely eliminated, and that cavitation tests should be conducted in a closed system whenever possible, rather than in an open system. The second view holds that air leakage into the inlet is equivalent to adding air to the inlet, which alleviates cavitation; therefore, at the same 3% critical NPSH value, the NPSH measured when there is leakage is lower, meaning that leakage improves the cavitation resistance. My opinion: I believe that air leakage during importation causes more bubbles to reach the inlet of the impeller ahead of time, leading to premature cavitation in the impeller; as a result, the cavitation margin value increases. Air leakage is equivalent to prolonging the cavitation process, causing the cavitation test curve to become flatter. Furthermore, the cavitation test values obtained on open-type test benches are higher than those on closed-type test benches; for pumps that require a strict, lower net positive suction head, it is recommended to conduct tests on closed-type benches in order to obtain more accurate values for the net positive suction head. Furthermore, theoretically, it is believed that when the impeller inlet reaches the critical cavitation point, the head will drop sharply. In reality, however, the rate of head decline is often much slower than predicted theoretically, and it is not as sharp; moreover, this effect is not as pronounced in practice.

Have studied it, and gained a deeper understanding of the concept of net positive suction head