The Net Positive Suction Head (NPSH) and Pump Operating Regions (POR) are two of the most commonly used technical terms in the pumping industry. As the leading industrial water pump suppliers in Mumbai, we can help you gain a deeper understanding of these technicalities, this article is for you.
Pressure and NPSH Terminology:
As the industrial water pump suppliers in Mumbai and beyond will explain to you, energy is described as the total head in meters or feet added. Head and pressure have a direct relationship. The pressure units used are PSIG (pound-force per square inch gauge). A pressure of 10 PSIG indicates that the units are “gauge pressure” that is, in addition to the pressure exerted by the atmosphere around us.
The NPSH available (NPSHA) stands for the total head at a particular point in the system, in feet or meters, greater than the vapor pressure of a liquid at operating temperature. It essentially indicates the relative closeness of a liquid to vaporizing.
Why it is important to operate a pump within its POR and with an adequate NPSH margin?
NPSHA must be evaluated at the pump suction. As soon as the liquid enters the impeller, the impeller eye has a point of the reduced head before the energy imparted by the impeller boosts the head. Due to the reduction in heat in the impeller eye, the fluid may fall below the vapor pressure, causing its vaporization and then suddenly condensing back to liquid form in a higher-pressure region of the impeller. The pump performance can get reduced due to the formation of vapor bubbles in the impeller. But the repeated collapse of the bubbles also causes erosion of the impeller, called “cavitation”. To prevent this and make your centrifugal pump as reliable as possible, it is necessary that a proper margin for NPSH exists.
Pump impellers operate at a particular flow rate where there are zero angles of incidence between the inlet impeller vane and the approaching liquid. This is known as shock less entry flow. The flow of shock less entry is usually near the Best Efficiency Point (BEP) of the pump. When the flow rate is higher or lower relative to the BEP, there could be a mismatch between the approaching liquid and the impeller vane inlet. A greater angle of incidence can increase cavitation. The pump must therefore operate as close to the BEP as possible.
Thus there are two important regions of pump operations –– Preferred Operating Region (POR) and Allowable Operating Region (AOR). POR is the range of flow on either side of the BEP within which the hydraulic efficiency and reliability of the pump are not significantly affected. The AOR is a larger range of flow beyond the POR within which the service life of the pump is acceptable.
When pumps are operated outside the POR, the flow is no longer uniform causing localized cavitation. The AOR of the pump is affected by hydraulic loads, vibration, temperature rise, power limits, liquid velocity, NPSH margin, pump size, the potential for clogging, etc. Your pump manufacturer or dealer can help determine this region.
For any further information on centrifugal pumps, and technicalities like NPSH, POR, and AOR, feel free to get in touch with VEMC by calling us at 022 43436655 or mailing us at email@example.com. VEMC is an authorized channel partner of KBL since the 1950s. We are the top industrial water pump suppliers in Mumbai.