Is it possible for the Hydraulically-operated Liquid fuel stop valve to pass some liquid fuel to the Lube oil reservoir thought its drain when it fails to operate properly.

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ibrahimdowa,

What does the Liquid Fuel P&ID show?

I don't recall if there's a packing leak-off drain line from the liquid fuel stop valve, but even if there is--it should NOT be routed to the L.O. Tank. And, the Liquid Fuel Stop Valve (on most "newer" GE-design Frame 5 heavy duty gas turbines--since the mid-1980s, anyway) are located on the top of the L.O. tank, and the hydraulic actuator is below the valve, in the top of the L.O. Tank. So, by design, there's very little chance for any liquid fuel to mix with the hydraulic oil.

If the turbine was not packaged by GE, then it's possible the liquid fuel stop valve will be slightly different, but most of the licensed packagers followed GE's design philosophy for these kinds of valves/applications--to try to prevent possible contamination of the L.O. by liquid fuel.

But in any case, the P&ID should clearly show any valve leak-off/drain and where they are directed to. Also, the Low Pressure Liquid Fuel Piping Arrangement and Hydraulic System Piping Arrangement drawings in the Service Manual should show the exact locations of all piping associated with the liquid fuel stop valve (liquid fuel and hydraulic).

It should be possible to follow any packing leak-off or "drain" line from the liquid fuel stop valve to see where it drains to by visually following the pipe/tube to it's end. And, I would be very surprised to find any liquid fuel pipe/tube draining to the L.O. reservoir.

Even if it was possible for liquid fuel to get into the hydraulic actuator of the liquid fuel stop valve (remember--L.O. is used for the hydraulic fluid medium in GE-design heavy duty gas turbines) the liquid fuel flowing through the liquid fuel stop valve should be at approximately 4.1 barg, and the hydraulic pressure used in the actuator should be at approximately 100+ barg. This means that any leak between the actuator and the valve would result in hydraulic fluid (L.O.) leaking from the actuator into the liquid fuel stop valve.

I have seen a P&ID for an older GE-design Frame 5 heavy duty gas turbine that used low-pressure "control oil" (which is still L.O. at a slightly higher pressure than bearing header pressure, usually about 4-5 barg) to actuate the liquid fuel stop valve. We don't know how old the unit is at your site, and we don't know what is the pressure of the oil that is used in the actuator to open the valve.

There were some GE-design Frame 5 and 6 heavy duty gas turbine with diesel engine starting means that had a diesel fuel tank located just above the L.O. reservoir/below the diesel engine.... It was a small reservoir (about 12-15 cm tall and about the same footprint as the diesel engine as the diesel engine was essentially bolted to the top of the reservoir). I've often thought that if the fill line for the diesel engine reservoir wasn't properly identified (signage; unique paint color) that someone might accidentally put diesel fuel in the L.O. tank, or vice versa, when topping off one fluid or the other. What kind of starting means does the turbine at your site have?

Hope this helps!