Net Positive Suction Head

Operating Characteristics of a Centrifugal Pump

Thermodynamics Heat Transfer and Fluid Flow Volume 3 of 3
Page Navigation
52

Fluid Flow CENTRIFUGAL PUMPS Cavitation can be a very serious problem for centrifugal pumps. Some pumps can be designed to operate with limited amounts of cavitation. Most centrifugal pumps cannot withstand cavitation for significant periods of time; they are damaged by erosion of the impeller, vibration, or some other cavitation-induced problem. Net Positive Suction Head It is possible to ensure that cavitation is avoided during pump operation by monitoring the net positive suction head of the pump. Net positive suction head (NPSH) for a pump is the difference between the suction pressure and the saturation pressure of the fluid being pumped. NPSH is used to measure how close a fluid is to saturated conditions. Equation 3-19 can be used to calculate the net positive suction head available for a pump. The units of NPSH are feet of water. NPSH = P_suction - P_saturation (3-19) where: P_suction = suction pressure of the pump P_saturation = saturation pressure for the fluid By maintaining the available NPSH at a level greater than the NPSH required by the pump manufacturer, cavitation can be avoided. Pump Laws Centrifugal pumps generally obey what are known as the pump laws. These laws state that the flow rate or capacity is directly proportional to the pump speed; the discharge head is directly proportional to the square of the pump speed; and the power required by the pump motor is directly proportional to the cube of the pump speed. These laws are summarized in the following equations. (3-20) V n (3-21) H_p n² (3-22) p n³ Rev. 0 Page 49 HT-03

Privacy Statement
Press Release
Contact