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Increase in GT hydralic oil filter DP
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We have GE-BHEL supplied Frame-VI Gas turbines. Frequently, we are facing problem with increase in hydraulic oil filter DP and consequent drop in hydraulic oil pressure. Hydraulic oil pressure dropped from 85 Kg/Cm2 to 76 Kg/Cm2 for the filter DP of 3.6 Kg/Cm2. Oil quality is analysed and filter dust is found at 1.15 mg/100ml. Can somebody explain what are the probable reasons for increase in hydraulic oil filters DP and what are the limits for filter dust in lube oil?
| Posted by CSA  on 16 October, 2012 - 11:21 am |
Ummmm,....
Errrr,....
Ehhhh,....
When the differential pressure across a pleated paper filter gets high enough the usual result is that the paper ruptures (tears) and a great deal of the contaminants which were contained in the pleats make their way en masse in to the hydraulic supply system with drastic results.
I just looked at two Device Summaries for GE-design heavy duty gas turbines, and both of them list the setpoint for the hydraulic filter differential pressure as approximately 4.0 bar. A third Device Summary listed the setpoint for the same switch at 1.02 bar.
When I have seen high hydraulic filter differential pressure I have never seen the hydraulic system pressure drop by a similar amount; the supply system pressure usually only drops by about 0.5-1.0 bar even with a 2- or 3 bar differential.
I believe the Service Manuals provided with the unit should have a specification for filtration and contaminants. I have seen detailed oil analysis reports with recommendations for correcting problems identified in the analysis; these companies are usually very tightly tied to oil refiners/suppliers and work hard to sell services and/or oil. What does your oil supplier/analyst recommend?
What does GE-BHEL recommend?
Are you using filters recommended by the packager?
Based on the information provided I would recommend you change those filters at the soonest possible time. Usually, there are duplex filters which can be transferred while the turbine is running (be sure to vent the filter canister being transferred to, using the transfer fill valve, and to close the transfer fill valve before opening the filter being transferred from to replace the filter element(s).
You REALLY don't want the filter to rupture and send a flood of dirt and contaminants downstream.
Errrr,....
Ehhhh,....
When the differential pressure across a pleated paper filter gets high enough the usual result is that the paper ruptures (tears) and a great deal of the contaminants which were contained in the pleats make their way en masse in to the hydraulic supply system with drastic results.
I just looked at two Device Summaries for GE-design heavy duty gas turbines, and both of them list the setpoint for the hydraulic filter differential pressure as approximately 4.0 bar. A third Device Summary listed the setpoint for the same switch at 1.02 bar.
When I have seen high hydraulic filter differential pressure I have never seen the hydraulic system pressure drop by a similar amount; the supply system pressure usually only drops by about 0.5-1.0 bar even with a 2- or 3 bar differential.
I believe the Service Manuals provided with the unit should have a specification for filtration and contaminants. I have seen detailed oil analysis reports with recommendations for correcting problems identified in the analysis; these companies are usually very tightly tied to oil refiners/suppliers and work hard to sell services and/or oil. What does your oil supplier/analyst recommend?
What does GE-BHEL recommend?
Are you using filters recommended by the packager?
Based on the information provided I would recommend you change those filters at the soonest possible time. Usually, there are duplex filters which can be transferred while the turbine is running (be sure to vent the filter canister being transferred to, using the transfer fill valve, and to close the transfer fill valve before opening the filter being transferred from to replace the filter element(s).
You REALLY don't want the filter to rupture and send a flood of dirt and contaminants downstream.
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