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In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: The Available NPSH (NPSH A): a measure of how close the fluid at a given point is to flashing, and so to cavitation. Technically it is the absolute pressure head minus the vapour pressure of the liquid.
Suction cavitation is often identified by a sound like gravel or marbles in the pump casing. Common causes of suction cavitation can include clogged filters, pipe blockage on the suction side, poor piping design, pump running too far right on the pump curve, or conditions not meeting NPSH (net positive suction head) requirements. [46]
The fluid will cavitate in the suction of the pump if the Thoma number is smaller than the critical cavitation parameter or the critical Thoma number defined as = Where is the net positive suction head required to prevent cavitation. It is a parameter found experimentally for each pump model.
Cavitation—the net positive suction head of the system is too low for the selected pump; Wear of the impeller—can be worsened by suspended solids or cavitation; Corrosion inside the pump caused by the fluid properties; Overheating due to low flow; Leakage along rotating shaft.
Discharge Head, is the net head obtained at the outlet of a pump. For a centrifugal pump, the discharge pressure depends on the suction or inlet pressure as well, along with the fluid’s density. Thus, for the same flow rate of the fluid, we may have different values of discharge pressure depending on the inlet pressure.
Specific speed N s, is used to characterize turbomachinery speed. [1] Common commercial and industrial practices use dimensioned versions which are of equal utility. Specific speed is most commonly used in pump applications to define the suction specific speed —a quasi non-dimensional number that categorizes pump impellers as to their type and proportions.
During the pump operation, there is a drop of the liquid flow in the center of the rotor, causing the inflow of the liquid through the suction port. In the event of an excessive pressure decrease, in some parts of the rotor, the pressure can be lower than the saturation pressure corresponding to the temperature of the pumped liquid, causing the ...
NPSH represents the head (pressure and gravity head) of liquid in the suction line of the pump that will overcome the friction along the suction line. NPSHR is the amount of liquid pressure required at the intake port of a pre-designed and manufactured pump. This is known as NPSHR (Net Positive Suction Head Required).