1.0 PUMP TYPE SELECTION

The table below can be used as a guide for selecting the applicable pump standards.

1.1 Main design standards for centrifugal pumps are:

Standard Industrial Application
1 API 610 (American Petroleum Institute)/ISO 13709 Petroleum Industry Heavy Duty Utilities (Boiler Feed) Europe & USA
2 ISO 2858/5199 (International Organization for Standardization) Chemical (Mainly Europe)
3 ANSI (American National Standards Institute) General Industrial Service (Mainly USA)
4 ANSI B 73.1 Chemical (Mainly USA)
5 ASME Section VIII Div 1 (American Society Mechanical Engineers) American code for pressure vessels. generally applied in the USA for pump case wall thickness calculations.
6 NFPA 20 & 25 (National Fire Protection Association) Fire Water System (World wide application, originally USA)
7 DIN (Deutsches Institut Fϋr Normung) 24255 General purpose (water) application (Mainly Europe)

1.2 Operating and service criteria.

Operating conditions should address the following items as a minimum:

  • Flow/liquid medium; Density; Specific gravity
  • Viscosity
  • Vapor pressure
  • Capacity, minimum, maximum and normal flow
  • Operating temperature; minimum, maximum and normal
  • Ambient temperature
  • Inlet/Suction pressure
  • Discharge pressure
  • Differential head
  • Maximum operating pressure
  • NPSHA (Available)
  • Continuous or intermittent
  • Critical operating conditions

2.0 MAIN DESIGN CONFIGURATIONS

Applications and operating conditions will determine the pump design configuration. Three main categories of centrifugal pumps can be distinguished as:

  1. Radial flow
  2. Mixed flow
  3. Axial flow

Typical impeller lay out are show above in figure 1

Pump configuration:

Within the radial and mixed flow categories there two main configuration with regard to the hydraulic design

  1. Volute type pump configuration – Fig. 2 (showing clockwise rotation)
  2. Diffuser type pump configuration – Fig. 3 (showing counter clockwise rotation)

US manufacturers traditionally favor a volute design; while European manufactures traditionally provide centrifugal pumps with diffusers. A volute design configuration imposes radial loads on the pump shaft, whereas in a diffuser design the radial loads are neutralized as they balance each other out. However in double volute designs, the radial loads are also hydraulically balanced and thus neutralized.

3.0 SPECIFIC SPEED

The specific speed is dimensionless, and is universally used as indicator to show the relationship between speed (rpm\N), flow capacity (Q) and differential head (H) (wc = water column). Ns = (N x √Q) / H 3/4

General European practice
Q = Capacity in mᶾ/.sec.
H = Differential head in m (wc)

N = Pump rotating speed in rpm

General US practice
Q = Capacity in gpm
H = Differential head in feet (wc)

N = Pump rotating speed in rpm

Typical Ns Values are

European US
Radial flow 9.7 to 500 500 to 4000
Mixed flow 38,7 to 155 2000 to 8000
Axial flow 139,7 to 387,3 7000 to 20000
Most generally used Ns range for industrial applications is: European 15 to 40; US 775 to 2065