Minimum recommended motor power rating
Minimum recommended motor power rating
(OP)
When sizing an appropriate motor, although API-610 10Ed 6.1.3 using table 11 indicates that motor power rating as a percentage of the rated pump power, looks like the vendors don't follow API instead of using the pump max power at max impeller diameter as the number to determine minimum motor power rating. I think this selection is conservative and is for some future considerations such as capacity upgrade by replacing with a larger impeller.
Any insight on this? Thanks.
Any insight on this? Thanks.





RE: Minimum recommended motor power rating
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"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Minimum recommended motor power rating
Having a motor which is suitable for end of curve and or with maximum impeller duty only, is good for site to be able to change duties in a later life, however, motors are probably running nowhere near their best efficiency and so actually energy costs far outweigh costs for later modification IF increase is required.
I hope that makes sense, its late and my head knows what i want to say but not so sure my fat fingers are writing it in a 'make sense' manner ?????
Ash Fenn
www.cdrpumps.co.uk
RE: Minimum recommended motor power rating
For instance if the end of curve power is 10Kw then the next available motor is from memory,11Kw giving no margin for any error let alone any future upgrade whereas the next is 15Kw so this is what you will probably fit.
However, in some cases it becomes an engineering decision as the next availabe motor size may be marginal in terms of the codes requirement whereas the next motor size is way over-the-top.
RE: Minimum recommended motor power rating
Also, BigInch, I see that the requirement is for an increase of 5% head at rated flow by changing the impeller, not 10%.
RE: Minimum recommended motor power rating
Thanks for the correction.
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"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Minimum recommended motor power rating
you can find some good information in the bellow mentioned link:
http://www.p2pays.org/ref/40/39569.pdf
Reza
RE: Minimum recommended motor power rating
While that might be OK for small motors, I think that would be far too conservative for the very large, higher cost, motors, especially given such flat curves in the higher range. I wouldn't feel right recommending a motor that might cost 25% more than the one I really needed. Normally 10-15% is well more than enough. Besides, if you had to move lower flows where power consumption is 50-60% of pump rated power and selected your motor at 1.33 instead of 1.10, that would put your lowest efficient motor operating range at 67% of pump power, instead of 55%
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"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Minimum recommended motor power rating
One example: no difference in efficiency between 75% and 100% power:
http
Actually it wasn't my intent to create any new generalizations but to warn against generalizations. The curve for the motor you buy is the most relevant.
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Minimum recommended motor power rating
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Minimum recommended motor power rating
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Minimum recommended motor power rating
electricpete, thanks for the good info.
Reza