MCSF 0 ?
MCSF 0 ?
(OP)
Is there any problem if minimum continuous stable flow is zero for ANSI Centrifugal pumps? If so please explain if there should be some flow or not?
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RE: MCSF 0 ?
If pump is running it should not be cavitated on the suction or dead headed on the discharge. Look at the pump curve this will tell you what the minimum flow should be.
RE: MCSF 0 ?
You will not be able to have a reliable pump if you run below the MCSF for extended periods of time.
RE: MCSF 0 ?
Vendor quotes Allowable operating region: from 0 to end of the curve......is it true or is there a catch?
RE: MCSF 0 ?
RE: MCSF 0 ?
David
RE: MCSF 0 ?
It's a highly controversial topic (between myself and my operators) that is scattered with junk science and hearsay.
To my operators, MCSF is whatever you need it to be!
RE: MCSF 0 ?
RE: MCSF 0 ?
RE: MCSF 0 ?
Remember all the inefficiency of the pump will go straight into heat, vibration, and noise.
If it's under warranty, simplifies your control system, and you don't mind constant repair/replacement, then sure run it at shutoff constantly.
RE: MCSF 0 ?
I realize this may be an entirely different situation, as you're probably not in nuclear. But for pumps that are required to operate to provide nuclear core cooling following an accident, the US NRC has recommended, via a couple of information notices and bulletins, minimum flows of between 10 and 25 percent.
Could some pumps operate with a lower minimum continuous flow? Possibly. What it comes down to is how critical your system is if the pump stops working? If you don't mind the down time and have spare pumps sitting around, take a chance on that "0" flow. If it's going to cost you significant money and time, ignore what the vendor said and design your system with a minimum recirculation line.
Patricia Lougheed
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RE: MCSF 0 ?
There are two main effects to running at low flow: the energy input goes to heat generation, which I have seen happen and cause the pump to catastrophically fail (luckily not fatal to the worker who had just left the pump to get some tools), and also that the shaft bending increases, which will usually cause either a bearing or shaft failure.
RE: MCSF 0 ?
With split case, submersible, and turbine pumps there are bushings on both sides of the impeller(s) that can generate friction heat. It still takes very little flow of cool water to keep this heat from becoming a problem. The warmer the water and the greater number of impellers or bushings the more flow is required to keep the pump cool. However, the bushings on both sides of the impeller(s) limit problems from radial deflection.
RE: MCSF 0 ?
I suggest you to read the following thread.
http://www.eng-tips.com/viewthread.cfm?qid=104691
Take also a glance at the attached paper (Minimum flow)
RE: MCSF 0 ?
For a more serious answer, see other postings dealing with this general topic.
In short, operating a pump at zero flow more than momentarily is never a good idea, and it is likely to be very expensive.
Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.
RE: MCSF 0 ?
However, having seen many installations in which this does happen my observations are: pumps running at maximum design ie, at maximum design speed and full impeller diameter are a disaster waiting to happen, whereas pumps at reduced speed are more tolerant and less likely to destruct although they are subject to many problems as already detailed by others.
Consider any centrifugal pump designed for 2pole 60hz, running at 4 pole 60 hz, the max. power is 1/8 and the maximum disharge pressure is 1/4 - even less at 50hz and less again if operating at 6 pole - so damage/disaster/ recirc. cavitation /shaft deflection/bearing loads etc comes down to a function of speed.
But to write a spec accepting or requiring operation at zero flow is ridicules or it has been writen by someone who doesn't know their rear-end from their elbow.