Multistage pump failures 1

[LK365]

Hi guys,

Would greatly appreciate if I can get a feedback regarding a query on pumps which comes out of failure recurring failures of multistage pumps

This is a situation from a wet crushing plant. There is a raw water process that supplies water to a raw manifold ( a massive pipe manifold). This manifold supplies water to 13 other pumps, all of which might not run together always at the same time. So there is varying number of pumps running. All pumps are different and have different operating points (flowrate and TDH).

Among these 13 pumps getting supplied by the manifold, there are two multistage vertical axial pumps which are parallel and are supplied by a common line coming from this manifold. My query is - if say the pressure in the manifold is 50kPa, then does the flowrate through any pump, say these multistage pump, depend on the number of pumps (connected to the manifold) operating. That is, if there are 5 pumps operating along with this multistage pump then will the flowrate be different if compared to the case when all 13 pumps were running?

Thanks

 

[Artisi]

Are asking is the flowrate through the individual pumps different?

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.)

 

[georgeverghese]

Assuming this main suction manifold is sized to handle max flow, then the suction pressure to these vertical axial ( presume these are otherwise called vertical turbine pumps also ) would be the same as that for all other online pumps, even when all 13pumps are running flat out.

Flow through these 2 pumps will then be dependant on what the built up discharge pressure is at the exit nozzle, and that will depend on the no of pumps running, what flows they produce, the pressure at the terminus of this discharge line, the Q-h profile for these 2 pumps etc.

If you arent getting enough flow out these 2 pumps when all 13pumps are running (ie. they are running at less than min permissible continous flow), possible causes could be (a) design case pump head for these pumps was not selected for all 13pumps running (b)some mechanical or controls flaws.

In any case, there should be a min flow recycle facility dedicated (to each or both) to these 2 pumps if their Q-h curves are not the same as that for the other pumps - that would have avoided any pump failures due to to operation at less than min permissible continous flow. Presume there are no NPSH issues, given the description, even if these 2 pumps were to run out to end or curve for some operating cases?

 

[LittleInch]

It will depend on how the manifold reacts to increased flow. If you have inlet pressure of only 0.5barg when running with only 5 pumps then the minimum pressure with all 13 running would not be less than about 0.4bara. Hence a maximum of 1bar in the incoming pressure and 1bar in the discharge pressure.

You provide no information on pumps, flows, pressures, pipe sizes, what the failures is, how the piping is orientated, so I'm not sure how you expect anyone to give you any feedback.

It may be the issue is more to do with the joint inlet pipe than the main manifold.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[someguy79]

The trivial answer is yes, but depending on a bunch of things, the difference in flow rates between single pump operation and multiple pump operation might be small or very large.

If:
- we can assume that the suction head losses due to friction are small, and
- the system configuration doesn't vary except for pumps being on or off;

Then the primary influence on pump flow will be discharge head. This situation is fairly common, but not ubiquitous.

If we have affirmation of all the conditions above, ask yourself if the discharge pressure at one pump is linked to the discharge pressure at another pump. A common way that happens is if the pumps are operating in parallel.

The system description shows different operating points and pump types, so my guess is that you have a bunch of different services using the same source. Further, I'm guessing that these do not have any direct influence on each other, excepting suction conditions.

So, it doesn't sound like you will have big differences in any pump dependent on number of pumps operating. However, there isn't enough info to know for sure here.

I hope that helps.

 

[DubMac]

Totally depends upon the source feeding the manifold. Might not be able to feed 13 pumps the same as it does 2.

Get off your *ss and tell us more about your system. Laziness will get you nowhere around here.

 

[Artisi]

DubMac: Correct about getting nowhere.

Plus the original question was 'Multistage pump failures" and as of now we have no idea of the failure mode let alone any worthwhile operating conditions - crystal ball or meditative navel gazing might assist.

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.)