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How to Repair the 6FA GT Speed Ratio Valve Oil Leakage
Leaking valve on GE make Mark V control system. Looking for advice on how to arrest the leakage. And for advice on proper procedure for dismantling and assembling the SRV.

Dear sir,

GE make Mark V control system control and protect the 6FA Gas Turbine. Moog make servo valve used in our plant. Gas Speed ratio valve control the P2 pressure. Combustion inspection work carried out on 12.08.16 after CI works, offline water wash work carried out and GT put back into service on 17.08.17. Physically inspection work carried out there was no problem at field, but oil leakage found in Gas Speed ratio valve.

Temporarily remedial arrangement of leakage hydraulic oil filtering and oil recirculate from SRV to Lube oil tank. After five days the oil leakage gradually corrected automatically and then oil leakage stopped. It is came to know that air lock may be in the SRV. The machine continuous running more than 275 days and regard created. On 18.05.17 the Gas Turbine got tripped on unit blackout and the unit synchronized. Now, again the oil leakage found in the SRV. 4 days continuously running, but leakage problem persist in THE SRV. How to attend the leakage arresting? The SRV dismantling and assembling work procedure and suggestion may be given please.


Is this a combination SRV & GCV or is it a stand alone SRV. If stand alone, can you give me a manufacturer and part number?

Where is the leakage? From fittings on the hydraulic manifold? From around the Moog sero-valve? From the hydraulic actuator?

I suspect this is one of the independent rotary Fisher Cam-Vee Ball valves. But without knowing where the leakage is originating from it's extremely difficult to offer any advice--except to ask if all of the hydraulic fittings have been properly installed and tightened.

It's also difficult to understand how continuous filtering of only the oil between the SRV and the L.O. tank could affect the leakage. It would seem that dirty oil would cause problems with the servo-valve and/or the actuator piston/ring but wouldn't have any effect on leakage. It could be that if the leakage is coming from the sealing ring around the shaft of the actuator that dirt could cause that, but, still, filtering the oil supplied to the valve wouldn't seem likely to stop the leakage. If this were the case, then it would be prudent to perform a high-flow flush of the hydraulic system, concentrating on the SRV.

Typically, the fluid used in the hydraulic systems of GE-design heavy duty gas turbines is Lube Oil, and it wouldn't seem logical that filtering a small portion of the hydraulic oil flow (because it also supplies the other gas control valve(s) and the IGVs at a minimum) would resolve a leak of some sort associated with the SRV. I suppose it's possible that this particular turbine has a separate hydraulic system, but the original post says the filtered oil was recirculated to the L.O. Tank, so that's not likely.

Further, it's difficult to understand how air in the SRV (actuator?) could cause hydraulic oil leakage. It would be helpful to know how it came to be known that air is present in the SRV--and where it's though to be. The typical GE-design heavy duty gas turbine hydraulic system has air-bleed check-valves in the hydraulic system to remove entrained air from the pump discharge(s). This is upstream of the hydraulic filters so if there was air in the filter canisters it could travel downstream.

We need to know exactly where the leak is coming from on the SRV. It would be great if the original poster could post photographs of the leakage and the valve on a web-sharing site (such as and then post a link to the location in this thread.

But, I agree with glenmorangie--we need more information--LOTS more information.