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Low Flow Discharge

Low Flow Discharge

Low Flow Discharge

(OP)
We have 2 Pumps runs parallel.  Pump Discharge before Turaround 70-72#. Pump Discharge right after Turnaround 65# of last year. We have about 7# differences ever since.  First we thought that might be we changed out the impeller, with new metal, it might slow down the flow. But now, we don't know what happened, no change in cooling water process, no one did anything to the valves neither the line services. We are looking at some causes such as: Check Valve Stuck, Impeller Wear/Erosion, Obstruction in Suction Line, Lower Turbine Speed.  
Does anyone ever encounter similar type of problem?

RE: Low Flow Discharge

Do you have total flow indication? If so an increase in total flow (in conjunction with decrease in pressure) indicates system change, decrease in total flow indicates pump change.

Do you have before/after vibration spectra which might indicate whether speed has changed?  Supply voltage decreased? Fluid temperature increase or other density decrease?  If only one pump runs, leaking check valve? Pump lift adjusted? Possible wearing problem?

There are certainly a lot of possibilities. What work was done during the outage?  others may be interested to know what type of pump?

RE: Low Flow Discharge

(OP)
Dear sir,

2 Pumps discharging the water from the Cooling Tower.  2 of the running Pumps are Steam Driven (Centrifugal). The 3rd one for back up is the Electrical Driven which is not used.  So the source of Voltage supplied, fluid temperature decrease/increase, pump lift are not the case.  We are ordering a new Impeller because of its delivery time for our January Shutdown.  
My question is what other possibilities you would think that might happened here.  We are thinking:
Check Valve Stuck, Impeller Wear/Erosion, Obstruction in Suction Line, Lower Turbine Speed.
We will have Dead Head measurements for each of the Pump. Does anyone else has any input for this problem.  Thank you ya so much in advance.

RE: Low Flow Discharge

If turbine powered, I'd take a close look at the governer setting and what the actual RPM is that you are running.

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