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:

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

Typical Ns Values are