Hello team,
Onsite we have GE LM6000 Gas Turbine Generators and the Generator (Brush) & Gearbox Lube Oil System uses a mist oil extraction system to vent the GLO tank / system.
This mist oil extraction uses a single fan arrangement that also has a cooler and hepa filtration system.
We can adjust the fan air flow which in turn raises or lowers the tank vent pressure.
The system has a GLO tank pressure alarm set at -25mm/water.
With new filters installed and the air flow flap at 100% open, we can achieve a max pressure of approx -120mm/water.

My question is, does anyone know of the desired GLO tank system pressure?

Our GE manuals only reference the alarm value.
The risk is with the air flap set wide open, we have increased air flow, dragging excess oil mist, blocking the filters quickly, with a rapid decline in GLO tank pressure.
With the air flap closed, we run the risk of system oil leaks around shaft seals etc and hitting the alarm set point.

 

John, I maintain a couple of GE Frame units that use a mist eliminator to keep a negative pressure on the bearing cavities. In our units the flapper valve used to be manually controlled. The lube oil tank negative pressure would vary based on unit load. GE recommended setting the flapper to achieve -3 inH2O when the unit was at full load. At lower loads the pressure would be even lower. Several years ago we put a positioner on the flapper valve, and added a transmitter to monitor tank vacuum. We then inserted a PID in logic to control the valve and maintain -3 inH20 of H2O. The thought like you have I think is to maintain enough negative pressure to keep the oil where it belongs, but not draw in extra air that ends up plugging filters quicker. Sorry I can't give you a number, -3" H2O is what is defined for our system. Hope this helps.

 

Have you tried adjusting the flap to get just below the alarm level, say -30 mm and see how it goes

 

Have you tried adjusting the flap to get just below the alarm level, say -30 mm and see how it goes

No we haven't as we were concerned with creating an oil leak that might go unnoticed for sometime due to our run philosophy. If my question goes unanswered, I suppose we could schedule short run inspections and trial a low value....

 

John, I maintain a couple of GE Frame units that use a mist eliminator to keep a negative pressure on the bearing cavities. In our units the flapper valve used to be manually controlled. The lube oil tank negative pressure would vary based on unit load. GE recommended setting the flapper to achieve -3 inH2O when the unit was at full load. At lower loads the pressure would be even lower. Several years ago we put a positioner on the flapper valve, and added a transmitter to monitor tank vacuum. We then inserted a PID in logic to control the valve and maintain -3 inH20 of H2O. The thought like you have I think is to maintain enough negative pressure to keep the oil where it belongs, but not draw in extra air that ends up plugging filters quicker. Sorry I can't give you a number, -3" H2O is what is defined for our system. Hope this helps.

Thanks MikeVI, good info, we were considering a value around this mark. I suspect the frame and aero GLO systems have similarities. So failing a definite answer we will trial -75mm/H2O. I like your idea of a driver & positioner on the air flap to maintain constant pressure.

 

the main places it will leak oil is at the Auxiliarly G/Box no. 1 shaft forward seal and at the generator aft bearing. Keep a close watch there as you adjust but I reckon that if you stay below -30mm you should be ok but go a bit lower if you want to be safe