Does reduced speed testing have an effect?
Does reduced speed testing have an effect?
(OP)
Recently a vertical pump was tested on water at 53% speed and everything was calculated up to full speed with a S.G of 0.440. The efficiency was ridiculously high. My question is does reduced speed testing have an effect, e.g. how do you know that when the units at full speed, theres no power losses on seals, bearings, recirculation, or losses between bowls?





RE: Does reduced speed testing have an effect?
RE: Does reduced speed testing have an effect?
RE: Does reduced speed testing have an effect?
Depending on the pump design you could have some re-circulation that affects the test at low speeds. The pump affinity laws offer guidance, but are not absolute. Without knowing any of the specifics I would guess the affinity laws could be anywhere from 3 to 15 percent off at 50% speed.
I assume the test was performed at low speed due to the pump load and available power in the test facility. This would indicate you have a high flow pump, possibly high head too. Reducing flow by 50% could allow reverse flow inside the vanes. That depends on the impeller design.
Several years ago I saw a paper posted on this forum named “Stop Falling Off The Curve.” It detailed test that were performed at several speeds to confirm the accuracy of the affinity laws. I have not been able to find that paper, but it did prove affinity laws were not 100% accurate.
D23
RE: Does reduced speed testing have an effect?
RE: Does reduced speed testing have an effect?
I would take the indication of an absurd efficiency at rated speed by the scale-up calculations to be a sufficient indication that the scale-up is not sufficiently valid.
RE: Does reduced speed testing have an effect?
RE: Does reduced speed testing have an effect?
RE: Does reduced speed testing have an effect?