Multistage centrifugal boosted with piston pump 1

[Unotec]

We have this discussion going around regarding the booster pump for a multistage centrifugal.

We need to boost into the multistage due to filters between the pumps.

Typically, I use a centrifugal pump as a booster. Some people here are proposing using a piston pump for boosting.

This doesn't sit well with me but cannot articulate the reason.

Has anybody used a piston pump as a booster for a multistage centrifugal?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ö Damn that was fun!ö - Unknown>>

 

[TugboatEng]

Why even use the centrifugal pump, then? A piston pump should be able to easily exceed the head produced by the centrifugal pump.

 

[Artisi]

I would be concerned with likely pulsating flow from the piston pump into the inlet side of the centrifugal pump.
More tech data on the application might be you some meaningful feed-back.

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.)

 

[LittleInch]

A simple diagram would help here as I don't understand the "We need to boost into the multistage due to filters between the pumps"

Which pumps?

But either way, the design characteristics of the two pumps are different.

In essence a Centrifugal pump is a constant pressure device (~20% range) over a wide range of flow rates.

A PD pump (e.g. piston) is a constant flow device (~10%) over a wide range of differential pressures.

So unless your centrifugal pump only works within a narrow range of flows, the two devices are essentially incompatible and you start needing pressure reliefs, flow back loops, recirculation devices etc etc which is avoided if you just install a centrifugal booster pump.

The PD pump will always need a full flow pressure relief / recirculation device for the occasion when the outlet valve is closed otherwise the pressures can get very high until the pump motor stalls.

If the flow from the C/F pump exceeds the flow of the PD pump ( e.g. start up or change in outlet pressure, you can starve the C/F pump of liquid and either get cavitation or tripping on low inlet pressure.

PD pumps are often either limited in capacity or get very big for high flowrates, not to mention pulsation effects as noted by Artisi.

Overall a Bad idea IMHO

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

 

[Unotec]

Thanks,

I have attached the scheme.

Basically would mean replacing P-Q201 (a centrifugal) with a piston pump.

I understand the inconsistency of the flow from a piston pump and that the multistage would be jumping all over the curves in a very narrow band.

Pressure reliefs and other safeties are not what concerns me, it is more on the operation of the pumps.



<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ö Damn that was fun!ö - Unknown>>

 

[LittleInch]

Well it just reinforces what I posted earlier.

To install a PD pump in place of the current C/F P-Q201, would need re-circulation pipework added.

The risk to the pump is primarily low inlet pressure if the flow from Q301 exceeded the flow of the PD pump. The other risk is the pulsation issue.


The flow from the PD pump would be really quite consistent if the motor if a fixed speed.

The flow from the centrifugal is the thing that changes.

It can be done, but the advantages are few and disadvantages / extra pipe and equipment many.

Not sure what more you want?


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

 

[Unotec]

I am good, thanks

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ö Damn that was fun!ö - Unknown>>

 

[quark]

The only reason I can think of is to maintain constant flow from filter clean condition to near clogging condition (before they are replaced or cleaned). I agree with the previous posts about compatibility. I used many systems with centrifugal booster pumps and multistage centrifugals with filters in between. Very common in water treatment systems with discharge pressure of multistage up to 30 bar.