Page 103 - Centrifugal Pumps Design and Application

84 Centrifugal Pumps: Design and Application

11. Repeat Step 10 for Sections C-D or any other sections deemed
necessary.
12. Close sections with appropriate radii. These should be liberal for
castability and should follow a smooth transition in the end view.
13. Check areas and if necessary adjust end view and/or profile view
to satisfy area progression (Figure 7-4).

Example

Double Suction Pump:

• Eye diameter D| = 5.5 in.
» Shaft diameter = 3 in.
2
• Total eye area = 32 in.
• Area at A-B = 39 in. 2
• Suction nozzle = 8 in. Area = 50 in. 2
• Area section #6 = 19.5 in. 2
• Area section #5 = 14.6 in. 2
• Area section #4 = 9.75 in. 2
• Area section #3 = 4.9 in. 2
The double-suction casing in combination with a double-suction im-
peller has an inherent NPSH advantage over a single-suction combina-
tion. Reduction of the required NPSH is normally 40% to 50%. This
NPSH advantage of the double suction model makes it possible to be
adopted (in addition to the standard horizontally split, single-stage
pump) to many different types of centrifugal pumps such as:

« Double-suction single-stage vertically split casing pumps, suitable
for high temperatures and medium pressures.
» As a first stage in a horizontally split multi-stage double-volute-type
pump.
• As a first stage in the barrel-type multi-stage units, suitable for very
high pressures and temperatures up to 800 °F.
• To the overhung API process single-stage pumps.
• In vertical pumps (can type) as a single-stage or as a first-stage ar-
rangement, to reduce "can" length.
• Vertical in-line booster pumps.