Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

44 Centrifugal Pumps: Design and Application
» To predict efficiency on both sides of BEP, use Figure 3-17.
• When designing a new pump, always have a performance curve and
general sectional drawing.
• Keep neat and accurate design records.
« Try to use a symmetrical impeller to avoid excessive axial thrust.
• Consider mechanical requirements applicable to the new design.
Notation
K u Speed constant = U 2 /(2gH) 5
LJ 2 Impeller peripheral velocity (ft/sec)
= D 2 X RPM/229
g Gravitational constant (32.2 ft/sec 2 )
H Impeller head (ft)
D 2 Impeller outside diameter (in.) - 1840K U H 5 /RPM
D t Impeller eye diameter (in.)
K m2 Capacity constant = C m2 /(2gH) 5
C m2 Radial velocity at impeller discharge (ft/sec) = Q .321/A 2
D 3 Volute cutwater diameter (in.)
Impeller discharge area (sq in.)
A 2
= (D 2 7T ~ ZS U )D 2
Z Number of impeller vanes
S u Vane thickness at D 2 (in.)
b 2 Inside impeller width at D 2 (in.) = Q .321/C m2 (D 2 7r - Z S u )
Q GPM at BEP
K 3 Volute velocity constant = C 3 /(2gH) 5
C 3 Volute velocity (ft/sec.)
A 8 Volute throat area (sq. in.)
= 0.04 Q/K 3 (H) 5
C m i Average meridianal velocity at blade inlet (ft/sec) = .321 Q/Ae
Ae Impeller eye area at blade entry sq in.
Wj Relative velocity of flow (ft/sec)
6 Angle of flow approaching vane
Cj Absolute velocity of flow (ft/sec)
Psi
C m |/Ri
RI Factor in determining BI
B] Blade angle at outer radius of impeller eye
U, Peripheral velocity of impeller blade (ft/sec)
= D, X RPM/229
Av Area between vanes at inlet sq in.