High lube oil tank Pressure in a frame 5D gas turbine


Thread Starter


Good Day,

Help needed to understand high lube oil tank pressure.
We use the frame 5D gas turbines that comes equip with a mist eliminator operated by a vacuum assisted blower. On some of our units we are experiencing high lube oil tank pressure.

During the last plan downtime, we took the opportunity to change out all the filters in the mist eliminators, replace all the butterfly valves, replace the motors, inspect the blowers, and clean the dead leg piping's that goes back to the lube oil tank. In addition, all gauges were calibrated.

However upon start up the the oil tank pressure for three (3) of the units didn't change. Below list the before and after readings.<pre>
+12mmH20 +17mmH2O
+12mmH20 +15mmH20
+15mmH20 +20mmH20</pre>
All the other units have the oil tank pressure between -51mmH20 and -10mmH20.


Bob Peterson

Does the gauge reading match the transmitter reading?

I ran into a case once where someone decided it would be a good idea to buy xmtrs that were 20-4 mA instead of 4-20 mA. A whole bunch of them. :)


The likely cause of higher than normal pressure (above atmospheric) L.O. tank pressure is either (1) excessive Cooling & Sealing Air pressure in one or more of the bearings, and/or (2) problems with the L.O. Mist Eliminator(s).

I have seen at least two L.O. Mist Eliminators that were "serviced" and when they were put back in service they didn't work as they had before. Management and workers were ADAMANT that the elements and baffles had been replaced correctly and that the tank top gasket had been installed correctly. However, after a LONG delay the vessels were opened to find the elements and baffles were NOT properly aligned or placed and the tank top gaskets were also pinched/cut and laying in the tank. One of the fan motor couplings had not been properly installed (the set screws had come loose) and though the fan motor was turning it was only drawing about 30-35% of rated current because the fan rotor was not turning.

It's also common for the "orifices" used in some of the Cooling and Sealing Air lines to be lost or for some people to think they are not necessary. Unfortunately, GE and packagers of GE turbines don't usually publish the maximum or minimum expected pressures and don't put gauges on the piping to check or confirm pressures.

I would suggest there is something mechanically wrong with the Cooling and Sealing Air Piping, and/or the L.O. Mist Eliminator re-assembly.

Please write back to let us know what you find.

Thanks for the information.

So far I've ruled out everything on the L.O Mist Eliminator except the check valve on the bypass line and the fan.

1. I'm currently looking to jstify whether the fans are working effectively for the rated current. Trying to get an ultra sonic flow meter to measure the volumetric flow rate.

2. Getting a replacement check valve.

Also, We had some issues with the sealing gas to the #2 Bearing in the past on one of the unit with high L.O tank pressure.Several steps were taking to rectify the problem. However, the L.O pressure only reduce a little but still has a high positive value.

Furthermore, the recent issues are occurring on units that didn't have the issue before the planned outage (both high L.O tank pressure). Making me question the re- assembly now.

As we all know, troubleshooting can be--and often is--a logical process of elimination.

What happens if you turn off the Mist Eliminator ven fan motor with the turbine running? Does the L.O. Tank pressure increase or decrease?

Is the turbine L.O. used for seal oil on the compressors?

There is usually a vent on the Accessory Gear Box that can become plugged; it's usually a small piece of SS tubing.

If the unit can burn liquid fuel and is equipped with an Access. Gear-driven atomizing air compressor could the compressor be leaking into the oil drain (bad seals)?
Greetings CSA,

Thank you for your suggestion. I would keep you update on whether we resolved the caption issue.