high pressure pump and booster pump (drop in pressure)

[momo2004]

Hi
I am new , We are running an R.O plant in an isolated island where it is very difficult to inspect during the summer because of severe weather conditions. The only connection between our office and the island is through phone.

The problem is as follow:-

· The high pressure(multi stage) pump is not delivering the desired head, instead of 54 bar it delivers only 47 bar. This shortage in pressure is effecting the result of water from the R.O plant which is the only water resource in the island.

The team there opened the multi stage H.P. pump and they found minor damage in some of the seals, they replaced them, but the problem continued with the same pressure drop.

Before the high pressure pump there is a booster pump with a pressure of 2.5 bar. But during this month the discharge pressure gage of the booster pump is not working though it appears that the booster pump is delivering the desired pressure.

My question :-

Can a small drop in the booster pump pressure effect the discharge pressure of the multi-stage high pressure pump (for example:- from 2.5 bar to 2 bar) .

Thanking you all

 

[TD2K]

If your HP pump is a centrifugal (since you said it's a multistage), a 0.5 bar drop in suction pressure shouldn't result in the drop in discharge pressure unless the HP pump has high NPSHA requirements and you are cavitating.

Get that pressure gauge replaced. Do a single gauge pressure survey through the system and compare them to what the pumps should be doing at design and the pressures the pumps need at design (eg suction pressure).

 

[Artisi]

TD2K- I think you need to add "of 7 bar" between drop ..... in discharge pressure etc,.
This will clarify your comment.

International College
Naresuan University
Phitsanulok
Thailand

 

[quadtracker]

1. Is there any strainers or filters ahead of the booster pump that could be cleaned or changed? Is the flush water rate (accross the R.O. membranes) to waste too high? What is the condition of the R.O. membranes,do they need cleaning? Does the HP pump have a relief valve to protect overpressure of the R.O. system, maybe the relief valve is leaking slightly, dropping your pressure. what is the purity of the water like from the R.O., some R.O. units have multiple membrane canisters, maybe you have a perforated membrane and your getting some water being bypassed which might indicate a pressure drop. There could be multiple reasons combined to effect the performance, sometimes its a matter of a bit more regular maintenace that can be overlooked.

 

[momo2004]

TD2K (Chemical)
Artisi (Mechanical)
quadtracker (Petroleum)


thank u all for ur kinde advice and time.

 

[MortenA]

Momo: You state that the desired head is 54 bar but delivered is 47 - now i have one question: Is the pump running at design flow rate or is the flow rate higher?

BTW: For you question: Head is summed for pumps in series. So a drop in discharge from your booster would result in a 0.5 drop in total - unless as TD2K says you get cavitation.

High speed (multi stage pumps) may have very high NPSHr. I resently oversaw deliverence of a water injection pump (for an oil filed). This pump has a NPSH of 8 bar (80 meter or approx 250 ft of head). So the initial "booster" pump had a discharge head of 16 barg!