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positive displacement pump versus centrifugal pump 3

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Yobbo

Mechanical
Apr 22, 2003
85
Hi,

I would like to start a discussion about the differences and the working range of centrifugal pumps and positive displacement pumps in combination with low viscosity medium like water. The reason for this is that I wonder whether the considerations to choose one or the other might partly still be based on aged arguments. I am afraid I cannot speak out of long term experience about the positive displacement pumps. But I do know that there has been a time, where there was a transitional phase where the centrifugal pump got more and more application as a replacement for the positive displacement pump.
Just to give a first description of obvious differences I learned I would like to name the following ones:

PDP : positive displacement pump
CP : centrifugal pump

disadvantages PDP versus CP
- principally a source of pressure fluctuations, although
there are some that produce far less fluctuations than
others.
cure: pressurized vessels for damping fluctuations
- in general more gland problems
- dynamic problems with check valves when applicable
- in general higher maintenance costs
- need for safety relieve valve to protect the piping
against exceeding the design pressure of the system
- construction is in general more complex

advantages PDP versus CP
- higher efficiency with lower flows
- higher head achievable with relatively simple construction
- controllability of flow is better

Reviewing my list of (dis)advantages I am inclined to conclude, that applying a PDP is less favourable. But maybe I forgot some aspects that are important too. Also I wonder whether the weighing of these factors is still correct. They were made at a time, where the required power was still cheap and therefore the efficiency were less important. Qualitively spoken the difference in maintenance costs may still be in favour of the centrifugal pump, but hasn't the development of PDP's (especially the rotary ones) made this difference less? My drive to get the differences in application area more clear is the fact that the PDP's have the potential of saving power. All of course just in situations where both types of pump may be applied.
For example the rotary displacement pump to me looks a candidate with the least disadvantages of a PDP, that could operate advantageously compared to a CP. Especially in the area of low flow condensate recovery to a high pressure condensate system.
I wonder if anyone has ever performed a study on this subject. I am looking forward to your reactions.

With best regards,





Karel Postulart, The Netherlands
Nuon Power Generation
 
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