Hello all,

7500 series combined SRV/GCV assembled together vertically.

We faced frequent failure on this type of valve specially after overhauling the GCV stem totally stuck to the bushing. What could be the reason? What are consequences if the gap between the GCV stem and the actuator bar is greater than 0.050"?

I'm looking for special manual instruction for this type explaining the procedures of overhauling plus adjusting the stem inside the field with doing the calibration for LVDT.

Thanks

 

Hello,

Is it the assembly used by Frame 5 and manufactured by Young and Franklin?

We recently contacted them to provide any information, but they replied that valve overhaul is 'risky' to be performed on-site and they can share any information regarding the process (clearances, tools, ...)

What have you done so far to overcome this issue?
Did you manage to get it working?
Did you manage to perform the recommended tests after overhauling (Quasi-static friction test, Hysteresis Cycle Test, ...)?

We are trying to gain a better understanding of maintenance scope of this valve.

 

hello again,

used by frame 7 ....manufactured by Young & Franklin.

I don't think so is a complicated valve. we found it normal valve. however, still we are looking for specific information from the manual. the valve was overhauled in our shop without manual instruction and was tested by nitrogen around 370 psi on close position. then reinstalled to the site and is working good.

 

dkra,

If I recall correctly, the GCV valve stem on the vertical combined SRV/GCV valve assembly is coupled to the GCV actuator rod and is not free to travel up and down when the valve is closed as is the SRV valve stem when the valve is closed.

If the GCV was tested and did not leak down, then it's likely okay. If the turbine control system has the gas valve leak check sequencing (where the P2 (intervalve) cavity is pressurized for a brief period during starting to check the integrity of both the SRV and the GCV) and the logic doesn't detect any leak, then it's likely okay.

The main thing about the two valves is that the SRV (Stop/Ratio Valve) is the one that must not leak when it is closed--hence the "Stop" part of the valve's name/function. And, LVDT calibration is NOT critical for the SRV LVDTs because the SRV is primarily a pressure loop (controlling P2 pressure as a function of shaft speed).

LVDT calibration is more critical for the GCV--especially at lower strokes when the valve is being positioned for firing and warm-up. Most newer Mark* turbine control systems (Mark V and later) use acceleration control to position the GCV after warm-up and during acceleration, and then speed control, and then temperature control.

The same vertical combined SRV/GCV was also used in many GE-design Frame 9E heavy duty gas turbines (with conventional, non-DLN combustors), and I believe the GCV valve stem was also coupled to the GCV actuator rod--so no free-moving GCV valve stem to worry about for those valves which have the coupling between the GCV valve stem and actuator rod.

The couplings I recall seeing were rectangular blocks, held together with one or two bolts to form a "square". If I recall correctly, some of the valve stems and actuator rods had threaded ends so the coupling could be used like a turnbuckle; others just had a groove in the ends of the valve stem and actuator rod, and there was a shoulder inside each end of the coupling which fit into the grooves.

Hope this helps!

By the way, I don't believe Y&F ever produced a manual that detailed how to calibrate LVDTs. They left that to GE, and we all know how that turned out....

 

CSA.

First, thank you for your reply.

Second, the GCV stem and its actuator are not coupled together. There is gap between them clearances. if my memory okay, i think that gap is between 0.030" - 0.050".

if that gap exceeds 0.050" I think the GCV will not travel fully open.

During the overhauling of this valve we found a lot of hydrocarbons attacking the internal parts causing scratch on the stem then valve stuck.

I think if you keep the gas process dry and clean this valve will not malfunctioning.

again this valve as dismantling and reassembling is not complicated, and I don't know why GE is not sharing the valve document through the internet.

thanks again CSA.......