Pump net positive suction head and head lift

There’s no direct relationship, I guess. High flow rates can easily lead to cavitation, due to the high pressure drop in the pump inlet pipeline.

Is there any relationship between the net positive suction head of a centrifugal pump and its head? How should we understand this? There is no direct relationship. If we have to draw a connection, then when the flow rate is high, the head decreases, the pressure loss at the pump inlet increases, NPSHr rises, and cavitation is more likely to occur. Can the outlet pressure of a pump be understood as the pump’s head? The head is measured in meters, while the outlet pressure is in Pascals; it’s important to distinguish between these two concepts. Head is the inlet and outlet pressure difference divided by the material density; it is a characteristic of centrifugal pumps, as for a given centrifugal pump, the head does not change with variations in density ； The outlet pressure is a pressure point that usually needs to be considered in conjunction with the inlet pressure. What is the relationship between the efficiency of a centrifugal pump, the net positive suction head, and head? Actually, there’s no direct connection either. The parameters related to the net positive suction head mainly include: inlet pressure, saturated vapor pressure at the operating temperature, inlet pressure loss, and material density. Study carefully the performance curves of typical centrifugal pumps, such as those shown in the figure below

Is the outlet pressure proportional to the head?

In casual speech, it might be expressed that way, but upon closer examination, if the inlet pressure is not constantly at 0 MPaG and the density does not remain constant, then this statement is incorrect. Strictly speaking, at a constant density, the pressure difference between the inlet and outlet is proportional to the head.

The net positive suction head and head loss are specified during the design and manufacture of pumps. Whether cavitation occurs in a pump is related to the pressure at the pump inlet, which in turn depends on the resistance and temperature in the inlet pipeline. The greater the resistance in the inlet pipeline and the higher the temperature, the more likely cavitation will occur. In chemical production, pumps are generally located at the bottom of towers and tanks; therefore, their performance is mainly influenced by the resistance in the inlet pipeline and the temperature of the fluid. Yang Cheng is also one of the design parameters for pumps; in actual production, the greater the flow rate, the lower the outlet pressure of the pump

Cavitation in centrifugal pumps usually occurs at the inlet blades of the pump impeller, mainly due to the low pressure at the inlet; when this pressure falls below the saturated vapor pressure of the medium at that temperature, cavitation occurs. Just like when water boils, the bubbles generated strike the blades, causing them to wear out quickly; this has little to do with the lift efficiency. NPSH is divided into available NPSH (or effective NPSH) and required NPSH. The available NPSH is determined by the conditions under which the pump is installed; in other words, it is determined by the system and the piping, such as the suction head and piping losses. The required net positive suction head is related to the pump’s design, such as the type of impellers and speed. To prevent cavitation in the pump, it is necessary that the available net positive suction head be greater than the required net positive suction head plus a safety margin; in other words, the higher the available net positive suction head, the less likely the pump is to experience cavitation

This post was last edited by 15195773025 on 2018-5-31 20:07. What is the relationship between the installation height of a pump and the required NPSH for it? I saw that the NPSH for pumps installed on the ground is 6 meters; how should this be understood?