Page 61 - Centrifugal Pumps Design and Application

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

5
K u Speed constant = U 2/(2gH)
LJ 2 Impeller peripheral velocity (ft/sec)
= D 2 X RPM/229
2
g Gravitational constant (32.2 ft/sec )
H Impeller head (ft)
5
D 2 Impeller outside diameter (in.) - 1840K UH /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.)
A 2 Impeller discharge area (sq in.)
= (D 27T ~ 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 27r - 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 mi 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.