Page 131 - Centrifugal Pumps Design and Application

NPSH 109

Notation

KI Friction and acceleration loss coefficient
Ka Blade entry loss coefficient
NPSHR Net positive suction head required (based on test or by calcula-
tion)
NPSHA Net positive suction head available on site
CMI Average meridional velocity at blade inlet (ft/sec) =
.321 Q/Ae
w Relative velocity of flow (ft/sec)
U t Peripheral velocity of impeller blade (ft/sec) = D tN/229
2
g Gravitational acceleration (ft/sec )
0 Angle of flow approaching blade
a Angle of incidence
„ Sigma = M|H

H Head generated per impeller (ft)
B 1 Blade angle at outer radius of impeller eye
C b Gas-to-liquid ratio factor
Q Pump capacity (GPM)
Q L Recirculated leakage entering impeller (GPM)
R t Factor in determining BI
D t Diameter at blade tip (in.)
N Speed (RPM)
N CO^°- 5
vv/
N ss Suction specific speed = —
5
(for double suction impellers, use (Q/2)° )
BEP Best efficiency point on performance curve
N s Specific speed = N ffi°' 5
Ae Impeller eye area at blade entry (sq in.)
U h Peripheral velocity of impeller blade at hub (ft/sec)
Ci Absolute velocity of flow (ft/sec)

References

Hydraulic Institute Standards Of Centrifugal Rotary And Reciprocating
Pumps, 14th edition.
Lobanoff, V., "What Is This NPSH, Oil &as Journal, February 24,
1958.
Ross, R. R., "Theoretical Prediction of Net Positive Suction Head Re-
quired (NPSHR) for Cavitation Free Operation of Centrifugal Pumps,"
United Centrifugal Pumps,