In these applications, a vortex pump can be far more reliable, and the maintenance cost savings is much greater than the additional energy costs due to lower efficiency. One of the seminars I present to specifying engineers is titled “How Lower Pump Efficiency Can Reduce Costs.” It usually gets their attention.
If a pump is run by a gasoline engine, the case could be made that the pump’s efficiency is not too important. Although an 80 percent efficient pump should save quite a bit of energy over one that is 65 percent efficient, the gas engine (approximately 20 percent) brings their totals down to 16 percent and 13 percent respectively.
It may be hard to justify a higher initial pump cost for such a small energy savings, unless the pump is used frequently and for long periods of time.
Finally, some application design points exist for which reasonable efficiency cannot be attained, but a pump is still required. Suppose some million-dollar process line cannot use a positive displacement pump but, instead, requires a centrifugal pump that can deliver 20 gallons per minute at 3,000 feet of head.
Would it really matter if a single-stage pump had to be driven at 23,000 rpm and that its efficiency was less than 25 percent? Probably not, and there are far more of these types of applications than you might suspect.
There is definitely more than one side when it comes to pump efficiency. Efficiency is a good thing, and we should always consider a higher efficiency pump if the return on investment pencils out.
Often, a peak efficiency that adds one or two percentage points is not that important since few pumps operate at their best efficiency points (BEPs). The breadth of high efficiency, on either side of BEP, can be far more beneficial.