Pump is operating at normal flow or rated?
Pump is operating at normal flow or rated?
(OP)
I have a pump with rated flow is 338m3/hr, normal flow is 270m3/hr, BEP is 342m3/hr. Normal flow is 80% of BEP flow, which is clos to the manufacture recommended operating region lower limit but with a lower efficiency than BEP. Rated flow is 98.7% of BEP.
I am wondering in the field at most times pump is operating at normal flow or rated flow. Pump is designed by manufacture at rated flow which is very close to BEP. If in the practical field pump is always running at normal flow condition, why don't design the pump at normal flow?
Thanks.
I am wondering in the field at most times pump is operating at normal flow or rated flow. Pump is designed by manufacture at rated flow which is very close to BEP. If in the practical field pump is always running at normal flow condition, why don't design the pump at normal flow?
Thanks.





RE: Pump is operating at normal flow or rated?
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"The problem isn't finding the solution, its trying to get to the real question." BigInch
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RE: Pump is operating at normal flow or rated?
It is common practice to have more than one operating point specified for a pump duty. A "Normal" condition and a "Design" point. The "Normal" operating point is just that - the conditions under which the pump is expected to operate at most of the time, but with the capability to move to the "Design" point at a later time when process conditions require, without doing anything more than maybe changing impeller size. "Design" is synonymous with "Rated".
I know I am generalising here, but without knowing the details of your particular application, that's about all I can offer.
Cheers,
John
RE: Pump is operating at normal flow or rated?
roteng,
"I am wondering in the field at most times pump is operating at normal flow or rated flow."
The pump will usually be running at normal flow
"Pump is designed by manufacture at rated flow which is very close to BEP. If in the practical field pump is always running at normal flow condition, why don't design the pump at normal flow?"
Its common to select a pump with the nearest BEP to the normal flowrate to avoid special designs and high costs associated with custom designs for an exact BEP to normal flowrate match.
**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Pump is operating at normal flow or rated?
RE: Pump is operating at normal flow or rated?
RE: Pump is operating at normal flow or rated?
you are correct. The normal/rated flow is from the process engineer during the design stage for size the pump and other purpose only. Pump in the field is actually running within a range. This range shall be in the preferred operating region that pump manufacture recommended on the data sheet.
RE: Pump is operating at normal flow or rated?
Mainly due to the fact that the normal flow is not known until such times as the system comes online.
That is why you have design or rated flow as a staring point for all the friction loss calculations etc to be based on as well as the initial pump selection.
The problem of normal flow being a lot less than the rated or design flow usually comes from all the fudge factors built in by the various people involved, ie the process guy wants "x" flow plus a little just in case, the boss adds a bit just in case, the pipeline guys adds a factor just in case, the pump guy selects the pump output a little higher just in case. This results in the pump being oversized for the true requirement.
RE: Pump is operating at normal flow or rated?
RE: Pump is operating at normal flow or rated?
RE: Pump is operating at normal flow or rated?
Rated flow always exceeds Normal flow, and both should always be to the left of BEP flow for a good pump selection. As wear clearances open in the pump, BEP will shift to the left and drop slightly. Net efficiency will remain the same if you're to the left of BEP.
There's a distinction in API-610 as to the definition of Rated and Normal operating points (Sec 3.31). Normal operating point is the condition the pump is expected to operate under normal process conditions. Rated (3.45) is the point at which the pump vendor certifies that pump performance is going to be within the tolerances specified.
Did you know that 76.4% of all statistics are made up...
RE: Pump is operating at normal flow or rated?
RE: Pump is operating at normal flow or rated?
**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Pump is operating at normal flow or rated?
Dabluffrat, you mentioned that "Rated flow always exceeds Normal flow, and both should always be to the left of BEP flow for a good pump selection". But API-610 5.1.15 says BEP point should be preferably between the rated point and normal point. Can you explain why you think both rated and normal point should always be the left of BEP?
Thanks.
RE: Pump is operating at normal flow or rated?
Rated flow is the actual capacity realized by the actual, supplied centrifugal pump when running at the design speed and TDH.
Manufacturers will sell you an existing design of a pump. No manufacturer is going to initiate a special design and fabrication for your specific pump specifications.
The manufactuer selects the closest model pump that fits the conditions.
"We don't believe things because they are true, things are true because we believe them."
RE: Pump is operating at normal flow or rated?