# Net Positive Suction Head Vapor Pressure

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Net positive suction head vapor pressure, abbreviated as $$NPSH_v$$, is used in fluid mechanics, particularly in the design and operation of pumps.  It is related to the pressure conditions at the suction side of a pump and helps ensure that the pump doesn't experience cavitation.  Cavitation is a phenomenon where the local pressure in a liquid drops below its vapor pressure, causing the formation of vapor bubbles. When these bubbles collapse or implode, it can lead to damage to the pump components and a reduction in pump efficiency.

This equation essentially compares the pressure available at the suction side of the pump with the vapor pressure of the liquid.  If the NPSH_v is too low, there's a risk of cavitation.  Pump manufacturers often provide NPSH_v requirements for their pumps, and it's crucial for engineers to ensure that the system meets these requirements to prevent cavitation issues.

### Net Positive Suction Head Vapor Pressure formula

$$NPSH_v = - \gamma \; [\; NPSH - ( v^2 \;/\; 2 \; g ) - ( p \;/\; \gamma) \; ]$$     (Net Positive Suction Head Vapor Pressure)

$$NPSH = - ( p \; v \;/\; \gamma ) + ( v^2 \;/\; 2 \; g ) + ( p \;/\; \gamma^2 )$$

$$g = [\; 2 \; ( \gamma \; NPSH - p ) \;/\; v^2 \;] - ( p \;/\; v^2 )$$

$$p = ( 2 \; g \; \gamma \; NPSH \;/\; v ) - ( \gamma \; v \;/\; 2 )$$

Symbol English Metric
$$NPSH_v$$ = vapor pressure $$lbf \;/\; in^2$$ $$Pa$$
$$\gamma$$  (Greek symbol gamma) = specific weight $$lbf \;/\; in^3$$ $$N \;/\; m^3$$
$$NPSH$$ = net positive suction head $$lbf \;/\; in^2$$ $$Pa$$
$$v$$ = velocity $$ft \;/\; sec$$ $$m \;/\; s$$
$$g$$ = gravitational acceleration $$ft \;/\; sec^2$$ $$m \;/\; s^2$$
$$p$$ = pressure $$lbf \;/\; in^2$$ $$Pa$$