NPSH MARGIN AT RATED FLOW

NPSH margin@ rated flow = NPSHa – NPSHr @ rated flow ≥ 1

• The NPSH available shall exceed NPSH required by a margin of at least 1 meter throughout the allowable operating region of flow.
• Suppliers’ pump selections shall ensure there is an NPSH margin of at least 1 meter or 30% of NPSHA whichever is the greater, of NPSHA over NPSHR. The guaranteed NPSHR shall equal the maximum NPSH required between the minimum continuous flow and the maximum expected operating flow. For pumps operating singly, the maximum operating flow shall be taken as the API limit of 120% of the flow at BEP. For pumps operating in parallel, the maximum expected operating flow is defined as the flow at the point of intersection between the pump H-Q characteristic and the system head curve(s), on the loss of one or more of the operating pumps. Reference for the NPSH shall be pump shaft centerline for horizontal pumps and horizontal centerline of the suction nozzle for vertical pumps. {Kermanshah}

Recommended centrifugal pump NPSH margins (J.T. McGuire [2])

Comments:

• 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 less than 1 m or when requested by the purchaser.