Understanding Pump Selection

Design Factors

Pump selection is as much an art as it is science due to the many design factors that must be considered! You typically find that many pumps can meet flow rate and discharge pressure operating conditions. However, selecting the correct Model (e.g., D, P, AWF, U, H) and particular Type (e.g., 116-D, 114-P, or 316 AWF, etc.) depends on:

  • Available NPSH vs. Required NPSH of Pump
  • Size of Foot Print
  • Height of Tank Stand
  • Motor Horsepower
  • RPM
  • Cost
  • Vertical or Horizontal Orientation
  • Threaded or Flanged Suction
  • Floor-mounted or Elevated Receiver
  • Type of Motor Enclosure (ODP, TEFC, etc.)
  • Special Motor (e.g., explosion proof, wash down duty, etc.)

For steam applications that require pumping hot condensate, NPSH is a critical factor in steam applications.

Retrofitting Pumps

When retrofitting pumps, several additional design factors must be considered to avoid pump problems (such as cavitations) including:

  • Diameter of suction piping
  • Presence of suction strainers
  • Orientation of pump discharge flange
  • Type of application (e.g., underground or in-line recirculation)

Rules-of-Thumb (Water Pump)

Figure 1

The Pump & Motor Selector provides a guide to help users identify possible pump/motors based on pump flow rate and discharge pressure of an application (for water pumps). Figure 1 provides a "rule-of-thumb" for when a user should consider single-stage or multi-stage pumps. However, the user needs to consider all of the above factors before making a final selection. As part of the selection, the user should examine the pump performance curve of their pump selection.

  • If discharge pressure is in the range of 50 PSIG or less, typically single-stage pumps are used.
  • If the discharge pressure is 170 PSIG or greater, typically multi-stage pumps are used.
  • If discharge pressure is in the range of 60-170 PSIG, the user should examine BOTH single-stage and multi-stage pump options.
  • For high-flow, low-pressure applications a single-stage, 1750 RPM pump is typically used.
  • For low-flow, high-pressure applications turbine pumps are typically used.