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)

BEP Flow (gpm) @ Maximum Diameter Impeller:

Rotational Speed (rpm):

NPSH required at BEP flow:

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.

Enter Pump Rated Flow:  gpm

Enter NPSH Available:  ft

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

Notes:

1. 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.
2. Suction Specific Speed as defined by API 610 is based on flow and NPSHr at Best Efficiency Point or Maximum Diameter impeller
3. For evaluation purposes, we assume NPSHr at BEP = 3' less than NPSHa at rated flow.
4. For evaluation purposes, we assume selection at 90% of BEP
5. Typically, Nss less than 12,000 is acceptable/ over 12,000 in unacceptable.
6. SS refers to Single Suction Impeller type.
7. DS refers to Double Suction Impeller type.