what could be the possible reasons for high suction flow in boiler feed pump

[rananjai]

we have two BFPs with 100% capacity.one bfp is taking 20 to 30 amp more current as compare to other one and also it has higher suction flow. what could be the possible reasons. please help...thanks.

 

[HPost]

What should the current be?

If the 2 pumps are identical, then it is more likely that the pump with low current is restricted in some way, or there is a mechanical failure. It also assumed that the pumps are operating at the same speed.

All things being equal, a pump will under flow rather than over flow. The problem would appear to be in the pump that has the lowest flow.

Each pump could be operating at a different point on the performance curve. What could cause that?

HPost CEng MIMechE

 

[Artisi]

First up you need to establish which of the 2 pumps is running at least somewhere near to design. Once you have this info' you at least stand a chance of sorting out your problem. At the moment it's just crystal ball gazing.

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]

Possible reasons?

Blocked flow in one of the pumps,
Different piping configuration for one pump rather than the other so more piping losses
Normal variation between two "identical" pumps. 10% is not unknown

How are you measuring flow?

Do you mean higher inlet pressure or higher flow?

A layout and some more data required.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[JJPellin]

If you can measure flow, pressure and motor amps for each pump running individually, it is a simple exercise to evaluate the performance of each pump relative to the predicted curve. It could well be that the pump running higher amps is actually the healthy pump. Running on the curve at a higher flow should require more power. If the performance matches the curve and the power matches the curve at that flow, then the pump is just fine. At this point, it could be that the controls on the system are allowing the pump to run at too high a flow rate which is the cause of the high amps. Pinch back on the flow and the problem is solved.

When you complete the same evaluation of the pump that is not drawing higher amps, you may find that it is degraded and running below the predicted curve for flow and head. At the lower flow rate, you could expect it to draw lower power.

If the pump with high amps is drawing more power than predicted by the curve, then it could have another deficiency. If the pump had worn internal clearances, it could be experience high internal recirculation that can result in higher amp draw. But, in this condition, the pump head pressure should plot below the predicted curve. And with a given system resistance, the total flow should be lower than expected, not higher.

You have not provided enough data for us to know one way or the other. Are the pumps running in parallel or one at a time? How is the flow controlled? Is this a new problem on old pumps or a problem that has existed since the pumps were first installed? If it has changed over time, did it change slowly or suddenly? What style of pump is it? A diagram of the system would help. A cross-section of the pump would help.


Johnny Pellin