Why does the NPSHr of chemical pumps being lower than that of pipeline pumps?

First, let me explain to you the concept of net positive suction head. NPSH refers to the difference between the total head of the liquid at the pump inlet and the pressure head required for the liquid to vaporize. It is expressed in meters (of water column) and denoted as (NPSH). It can be categorized as follows: NPSHa – this is known as the available NPSH or effective NPSH; the higher this value, the less likely cavitation will occur ； NPSHr —— pump net positive suction head, also known as the required net positive suction head or the dynamic pressure drop at the pump inlet; the lower this value, the better the pump’s resistance to cavitation ； NPSHc —— Critical net positive suction head, refers to the net positive suction head at which the pump’s performance declines by a certain amount ； ——The allowable NPSH is the NPSH used to determine the operating conditions of a pump, and it is usually taken as = (1.1～1.5) NPSHc. I believe everyone will understand better after seeing this explanation. Let me briefly explain it to the original poster: due to the nature of the fluids that chemical pumps transport – which are chemical liquids – factors such as their specific gravity, corrosiveness, and temperature result in higher requirements for NPSHr compared to pipeline pumps used for transporting water. As can be seen from this, the lower the value, the better the performance; this is the simple reason why chemical pumps have a lower NPSHr than pipeline pumps.

There is no comparability; it is mainly related to the hydraulic design of the impeller