Hi there,

Our plant is using GE Frame MS 9001 GT. Right now, GT1 compressor bleed valve #4 (VA2-4) is always giving us problem. Due to the nature of the plant which is baseload, occasionally at night especially when demand is low, we will shut down 1 GT. VA2-4 getting stucked close always happen. We have checked the solenoid valve. The last time when it happened, we were wondering if the spring tension wasn't great enough to get the spring to push the valve into open position which is the venting position.

A modification proposal is done to install a permanent compressed air line so that the operators can do stroking. Right now, the immediate solution when the compressor bleed valve is stucked close, it is stroked a few times and it will work. Any1 has any ideas on how to deal with the problem?

 

Has anyone checked to see if the valve is actually moving or is this simply a limit switch issue? We have had similar occurrences, but generally the issue is with the limit switch either missing the drive arm from the actuator or the limit sticks. On a few occasions we have had issues with the seals in the actuators themselves but this is fairly infrequent.

 

This topic has been covered numerous times on control.com. Use the 'Search' feature in the far right corner of the menu bar at the top of every control.com page. Use the search term:

'+compressor +bleed +valve' (without the quotes).

For my part though, I don't understand how stroking the valve when the unit is shut down and on cooldown is going to prevent it from sticking when the unit has been running and the valve is hot.

The most common causes of sticking valves are dirty, moist air being supplied to the actuator (read the other threads about how this can happen) leading to scored actuator cylinder walls and/or failed seals/o-rings; misalignment between the actuator and the valve; improperly torqued mounting bolts; improperly aligned valve (between the flanges in the piping).

Clean, dry, plant instrument air is always better than filtered, wet axial compressor discharge extraction. Most sites do an extremely poor job of maintenance on the Poro-stone filter upstream of the compressor bleed valve solenoid, and of keeping the low-point orifices in the piping clean and flowing (yes, flowing). And, in some case, there are insufficient low-point drains to begin with, and in some cases they are removed for the wrong reason(s).

A switch to clean, dry, plant instrument air should be coupled with an analysis of the piping/tubing to the compressor bleed valve solenoid and from the solenoid to the bleed valve actuators.

 

We have had this issue a couple of times. Our sites valves are piped into plant instrument air, which does make it easy to test valves when offline. We have found on one occasion the gears in the actuator were getting bound up and on the second occasion the disk was getting stuck in it's seat. We were told by GE that the valves do fail so it likely needs to be replaced and the old one can be send out for repair. There are left and right valves with different parts numbers, so make sure you get the right one. You will need to put air one the actuator to close the old valve to get it out.

 

Hi there,

We have recently taken out the the bleed valve to overhaul and we tested it using instrument air at 8bars. The piston was able to move without obstruction or resistance. There is no problem with the bleed valve. As for the actuator drive arm, there seems to be a problem getting it back in place after energizing the bleed valve to close. A slight modification needed to be done to get it to work again. There is already plan to replace the compressor bleed valve and i believe this will solve the problem.

As for the permanent fixture of the instrument air to the body, is that a recommended suggestion? has any1 ever done that? The poro-stone filter should be in good condition. Therefore, i don't think the air is too moist since the bleed valve is working fine. the actuator is the one which is faulty.

 

Roger,

Glad to hear that you have a way forward. As for the modification to using instrument air. Our site performed this and has been operating this way for a number years.