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 |
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\( NPSH_v \;=\; - \gamma \cdot \left( NPSH - \dfrac{ v^2 }{ 2 \cdot g } - \dfrac{ p }{ \gamma } \right) \) (Net Positive Suction Head Vapor Pressure) \( NPSH \;=\; - \dfrac{ p \cdot v }{ \gamma } + \dfrac{ v^2 }{ 2 \cdot g } + \dfrac{ p }{ \gamma^2 } \) \( g \;=\; \dfrac{ 2 \cdot ( \gamma \cdot NPSH - p ) }{ v^2 } - \dfrac{ p }{ v^2 } \) \( p \;=\; \dfrac{ 2 \cdot g \cdot \gamma \cdot NPSH }{ v } - \dfrac{ \gamma \cdot v }{ 2 } \) |
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| 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 | \(lbf \;/\; in^2\) | \(Pa\) |
