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Pumps

Purchasing Tips

1. Examine pump and motor efficiency

Energy costs over the life of a pumping unit always exceed its purchase price, even though purchasers tend to emphasize initial cost when buying. Because energy costs are the single largest cost over the life of a pump, energy-efficient equipment may yield a fast payback, with energy savings continuing long after the pump has paid for itself, over the remaining 20-year life expectancy of the unit.

2. Examine the pumping system

You may find ways of reducing the flow and head required for your system that allow for a smaller pumping unit. For example:

  • model your entire system using a software program
  • reduce the flow rate through heat exchangers
  • close bypass valves
  • eliminate bottlenecks and drastic diameter changes in piping systems
  • install low-loss pipe fittings
  • eliminate throttle valves
  • make piping runs straight before they connect to the pumps to avoid disruptive flow
  • ensure that the pump and piping are properly aligned

3. Avoid oversizing

There is a tendency to oversize pumping units to meet anticipated future requirements. This can result in the need to throttle or operate the equipment at a higher capacity than necessary. Aim to operate the pump near the best efficiency point (BEP) at all times. Select a pump with room for a larger impeller to handle possible future increases in capacity. Consider trimming the impeller (reducing its diameter) in a pump that is too large for the current application.

4. Consider a variable speed drive

A variable speed drive can lower losses caused by throttle valves and bypass lines and is cost-effective in systems that have variable flow requirements. Most manufacturers offer compatible variable speed drives.

5. Two pumps may be better than one

Use two smaller pumps instead of one large pump so that excess capacity can be turned off. Two pumps can operate in parallel during peak demand, with only one pump operating during low demand. An alternative strategy is to combine a variable speed pump with one that runs at constant speed.

6. Use pump selection software

Internet research is an excellent way of finding the right pump for your application. In addition to providing a wealth of information on pumps, many pump selection software programs are available for download. At a cost from nil to several hundred dollars, they offer different levels of functionality, but most tend to follow a similar four-step approach:

Step 1. Application selection

The user selects the application for the pump, and the software will provide a broad selection of pumps that are suitable for that application.

Step 2. Performance selection

After the user enters operation characteristics, such as desired flow rate, head and net positive suction head (NPSH) margin, the software provides a short list of pumps suited to the task, with performance details.

Step 3. Efficiency selection

More sophisticated software provides access to performance curves for various pump speeds. The software displays a plot of the energy efficiencies of the pump, at and near the operating point, and provides ways to optimize efficiency.

Step 4. Final selection

Final pump selection should be based on life-cycle costs, including:

  • purchase price
  • cost of energy over the life of the unit
  • cost of repair and maintenance over the life of the unit
  • disposal cost

See our pump selection software links for examples of typical pump selection software.

Next: Operation and Maintenance Tips