Suction Specific Speed (Nss)
Suction Specific Speed as defined by API 610 is based on flow and NPSHr at Best Efficiency Point and Maximum Diameter impeller (see Annex A of API 610)
Nss (As defined by API 610): 10503
Suction Specific Speed calculations can be very useful in the pump selection process. It can be used as a"rough cut" in determining which speed and/or pump impeller may be required. Ie - single suction, double suction, 900, 1200, 1800, or 3600 rpm.
|Suction Specific Speed Evaluator||SS - 3600||DS-3600||SS-1800||DS-1800||SS-1200||DS-1200||SS-900||DS-900|
|BEP Flow (gpm) @ Maximum Diameter Impeller||278||139||278||139||278||139||278||139|
|Rotational Speed (rpm)||3600||3600||1800||1800||1200||1200||900||900|
|NPSH required at BEP flow (assume 3ft less than available)||5||5||5||5||5||5||5||5|
|Nss (As defined by API 610)||17944||12688||8972||6344||5981||4229||4486||3172|
- Flow as listed above refers to capacity per impeller eye. This is total flow rate for single suction impellers, or one half of total flow for double suction impellers.
- Suction Specific Speed as defined by API 610 is based on flow and NPSHr at Best Efficiency Point or Maximum Diameter impeller
- For evaluation purposes, we assume NPSHr at BEP = 3' less than NPSHa at rated flow.
- For evaluation purposes, we assume selection at 90% of BEP
- Typically, Nss less than 12,000 is acceptable/ over 12,000 in unacceptable.
- SS refers to Single Suction Impeller type.
- DS refers to Double Suction Impeller type.