NPSHr or NPSH3
net positive suction head required: NPSH that results in a 3 % loss of head (first-stage head in a multistage pump) determined by the vendor by testing with water.
- The NPSH available shall exceed NPSH required by a margin of at least 1 meter throughout the allowable operating region of flow.
- NPSH test shall be conducted under vacuum on a closed loop. {Phase 13 spec.}
- It will be considered that a 3% loss of first impeller head is a sign of cavitation. {Phase 13 spec.}
- NPSHR test shall be performed when the difference between NPSHR & NPSHA is <1 m or when requested by the purchaser.
- When required in the data sheet, NPSH3 test shall be performed. NPSH3 shall be determined at each test point except shutoff.
- The difference between the NPSHA and NPSHR shall not be less than 0.5 m throughout the allowable operating region of flow. {Total}
- Datum line is the shaft centerline for horizontal pumps, the suction nozzle centerline fir vertical in-line pumps and the top of foundation for vertically suspended pumps. {API 610}
Comments:
- The Vendor shall specify on the data sheets the NPSH3 based on water (at a temperature of less than 55°C (130 °F)) at the rated flow and rated speed. A reduction of correction factor for liquids other than water (such as hydrocarbons) shall not be applied. {API 610}
- The NPSHR specified on the data sheets and the performance curve shall correspond to the rated impeller diameter. {Total}
- If the difference between the NPSHA and NPSHR is less than 1 meter at the rated point, or if an inducer is proposed, the Vendor shall provide in the proposal the test NPSH curve. {Total}
- The NPSH requirements for variable speed pumps shall apply for all speeds required to meet the specified operating conditions. {Total}
- NPSH3 test procedure shall be submitted for Company approval before contract award. {Total}
- The NPSH available shall exceed NPSH required by a margin of at least 1 meter throughout the allowable operating region of flow.
- NPSHR test shall be performed when the difference between NPSHR & NPSHA is <1 m or when requested by the purchaser.
- When required in the data sheet, NPSH3 test shall be performed. NPSH3 shall be determined at each test point except shutoff.
- If the difference between the NPSHA and NPSHR is less than 1 meter at the rated point, or if an inducer is proposed, the Vendor shall provide in the proposal the test NPSH curve. {Total}
- NPSH3 test procedure shall be submitted for Company approval before contract award. {Total}
- NPSH tests shall be witnessed. {Total}
- If the contract covers several identical pumps, NPSH3 test shall be done on one pump only. {Total}