There is a relationship between the net positive suction head and the liquid density; when using a pump to transport liquids with a density lower than that of water, the net positive suction head needs to be adjusted
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The net positive suction head of a pump is generally measured using water at 20 degrees Celsius; therefore, should the net positive suction head be adjusted when transporting liquids with a density lower than that of water? NPSHr (actual) = NPSHr (at 20°C with clean water) / specific gravity
There is no such relationship; it is related to relative density and saturated vapor pressure. There is a table in HG20570-5 that can be referenced.
The NPSH values listed in the pump performance table are also determined based on the transportation of clean water at 20°C; when transporting other liquids, a correction factor must be applied for adjustment. However, since the general correction factor is less than 1, it is used as an additional safety factor and no further correction is applied.
I know this statement is in the textbooks on chemical engineering principles, but is no correction needed even when transporting water at a 90-degree angle? Is no correction needed either when transporting liquids with a specific gravity of only 0.5?
NPSH is intended to ensure that the pressure at the pump inlet is higher than the saturated vapor pressure under operating conditions by a certain amount; NPSH is usually expressed in mH2O. Therefore, if the density of the liquid is significantly lower than that of water, a correction should be made
The net positive suction head on a pump’s performance curve is calculated based on water, but petrochemical pumps are generally used to pump oils. Especially when pumping light oils such as gasoline or liquefied gas, the net positive suction head is too low compared to the saturated vapor pressure of the medium at the operating temperature. How should this be adjusted?
The net positive suction head should have little relation to density; changes in density affect the pump’s power and head. What the original poster is likely asking about is the effect of temperature changes on the cavitation margin, right? Temperature changes affect the saturated vapor pressure of the medium; in such cases, the net positive suction head should be adjusted by modifying the pump’s installation height or the suction pressure at the pump inlet, based on the difference between the saturated vapor pressure under the designed conditions and that under the actual conditions, in order to prevent the liquid from vaporizing during suction.