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Netto positiv sughöjd
Den absoluta höjd som krävs vid pumpens inlopp för att förhindra kavitation, betecknad med suffixet ”A” för tillgänglig i systemet eller ”R” för den som krävs av pumpen. Motsvarar NPIP.
What is net positive suction head (NPSH)?
Net positive suction head is the absolute head required at the inlet of the pump to prevent cavitation. Similar to net positive inlet pressure (NPIP).
Net positive suction head can be noted with the suffix “A” (NPSHA) for available NPSH from the system or "R" (NPSHR) for NPSH required by the pump. Similar to Net Positive inlet pressure (NPIP).
Understanding net positive suction head (NPSH)
NPSHA is a function of your system and must be calculated, whereas NPSHR is a function of the pump and must be provided by the pump manufacturer. NPSHA MUST be greater than NPSHR for the pump system to operate without cavitating. You must have more suction side pressure available than the pump requires or cavitation will occur.
What is cavitation?
Pump cavitation occurs when the pressure at the pump inlet drops below the vapor pressure of the liquid. Vapor bubbles form at the inlet of the pump and are moved to the outlet where they collapse, often taking small pieces of the pump with them.
Cavitation is often characterized by:
- Loud noise often described as a grinding or “marbles” in the pump
- Loss of capacity (bubbles are now taking up space where liquid should be)
- Pitting damage to parts as material is removed by the collapsing bubbles
To learn more, watch this video about cavitation.