Determining the lowest speed you can operate a pump without cavitation
Determining the lowest speed you can operate a pump without cavitation
(OP)
From looking at a pump curve, how do you know if what is the minimum speed you can operate the pump without cavitation? Will the pump curve be useful?





RE: Determining the lowest speed you can operate a pump without cavitation
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(2B)+(2B)' ?
RE: Determining the lowest speed you can operate a pump without cavitation
RE: Determining the lowest speed you can operate a pump without cavitation
RE: Determining the lowest speed you can operate a pump without cavitation
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(2B)+(2B)' ?
RE: Determining the lowest speed you can operate a pump without cavitation
RE: Determining the lowest speed you can operate a pump without cavitation
As already asked- send curve -- and some application data for a useful answer.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Determining the lowest speed you can operate a pump without cavitation
Running below MCSF does promote a form of cavitation called recirculation. This sounds like and can be just as destructive as vapour pressure cavitation. Often curves have MCSF actually displayed, it should at least be in the manual. Sometimes the curve is dashed below MCSF
RE: Determining the lowest speed you can operate a pump without cavitation
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Determining the lowest speed you can operate a pump without cavitation
RE: Determining the lowest speed you can operate a pump without cavitation
As another user stated, you only need to be concerned with the NPSH at your worst case scenario (high speed) and ensure that there is sufficient margin/ratio. Speeding down should not matter.
Typically the lowest speed I've seen in operation is 300 RPM for VFD applications - specifically for your pump size and configuration. I would contact Aurora and verify as their min. speed is probably higher compared to the upper tier Pump OEM's.
RE: Determining the lowest speed you can operate a pump without cavitation
rmw
RE: Determining the lowest speed you can operate a pump without cavitation
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Determining the lowest speed you can operate a pump without cavitation
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Determining the lowest speed you can operate a pump without cavitation
RE: Determining the lowest speed you can operate a pump without cavitation
Plus you should ask the supplier for a variable speed curve for this pump - then there is no guess work.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Determining the lowest speed you can operate a pump without cavitation
The lower speed limit might not have diddly to do with the pump. The VFD may be limited (by its design) in the lowest speed it can drive, or the pump motor may reach limits in which it can no longer be properly cooled at lower speeds. Have you talked to the Honeywell guys, or reviewed the VFD and motor manuals? The latter limit can be overcome with an auxilliary cooling fan if necessary.
RE: Determining the lowest speed you can operate a pump without cavitation
I second the notion that an impeller trim is in order.
RE: Determining the lowest speed you can operate a pump without cavitation
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Determining the lowest speed you can operate a pump without cavitation
RE: Determining the lowest speed you can operate a pump without cavitation
Ill remind you the point of this post was to determine the minimum speed. based on your description above, after numerous posts and discussions, it is clear that the minimum RPM is not the question, it is the minimum flow of the pump. This entirely has to do with flow and NOT cavitation.
in essence, aside from the info. recommending to contact the pump vendor and reducing the impeller diameter, all posts are off topic because of a poor initial description.
The min. flow is based on the pump design (recircluation of fluid, bearing vibration, etc.) from the OEM. Youll also notice the the min. flow isnt listed on the curve you provided us - these are the pitfalls of going with tier II/III pump companies.
Best advice - contact the OEM - first tell them the pump size, speed, and current impeller trim, the head and flow currently and the head and flow desired - ask them "what is the min. flow for this pump operating at a reduced speed to achieve the requested head?"
RE: Determining the lowest speed you can operate a pump without cavitation
Flow scales 1:1 with speed, so 1/2 original speed also means 1/2 original min flow for the pump. At some point, the pump will be making insufficient head to even move water through the system, that is the constraint.
RE: Determining the lowest speed you can operate a pump without cavitation
you are speaking from a process perspective - i am talking from a pump perspective.
Determine and min flow of the system ----> see if that is feasible with the current pump ------> if not, buy new pump.
RE: Determining the lowest speed you can operate a pump without cavitation
Since cavitation is not relevant, the question is effectively "what is the minimum speed you can operate the pump." The answer is: the lowest speed that the pump will still move fluid through the system. If it doesn't move the fluid, it will just spin and heat up. A pump spinning but not producing flow, is not actually "operating" in the literal sense.
op·er·ate
[op-uh-reyt] Show IPA verb, op·er·at·ed, op·er·at·ing.
verb (used without object)
1.
to work, perform, or function, as a machine does
RE: Determining the lowest speed you can operate a pump without cavitation
not to get into a battle - you sound knowledgeable. I am sure you can agree that there are instances where the min. flow of the system can be lower than the min. flow of the pump. I can name a number of them if you want to dispute it.
hence the process vs. pump perspectives.
regards.
RE: Determining the lowest speed you can operate a pump without cavitation
I think you may have mispoken: "there are instances where the min flow of the system can be lower than min flow of the pump" would mean limitation is with the pump. While I don't doubt the existence, but my only dispute to scenarios where min flow of the system is higher than the min flow of the pump, would be relevance to the original question.
In any event, I think we've covered all bases and then some. Always a good intellectual exercise to put such a general question under the magnifying glass, right?
RE: Determining the lowest speed you can operate a pump without cavitation
Temperature rise in centrifugal at reduced flow:
T = H/778 * (1/e - 1)
T = Temperature rise in Deg.F
H = total head in feet
e = pump efficiency at capacity corresponding to H
MCSF = (6 X BHP@Shutoff Head) / (permissible temperature rise, DegF)
Permissible T rise of course must come from the manufacturer or empirical data.