Open/Close Test of Liquid Fuel Bypass Valve without LVDTs

W

Thread Starter

Wajid29

Hello,

I want to perform open/close test liquid fuel bypass valve servo valve 65FP on GE frame 9E machine. Mark-VI is used to control the turbine.

Can anyone please share the proper procedure to check liquid fuel bypass valve stroke. Servo valve (Moog) is installed to control the hydraulic oil and no LVDT's are installed for feedback. I read from some article that flow divider magnetic pickups are feedback reference to this valve? Further Details are given below:

GE Frame 9E Turbine
Mark-VI controller
 
Wajid29,

There are at least two possible options. One, change the regulator type to a position loop, download the configuration change, and then use the Manual positioning feature of AutoCalibrate. Using this method without actual LVDTs, when you input any position the valve will travel full stroke--in other words, it will not be possible to stop at any intermediate position because there is no feedback. But if all you're trying to do is see if the valve moves stop-to-stop, this will do just that. You need to remember to restore the regulator type and re-download when finished.

The second method--which I'm LOATHE to mention--involves forcing the output, which will have the same results because without any feedback from the liquid fuel flow divider the same thing is going to happen: the valve will go to the stop. Which, again, if all you're trying to do is stroke the valve stop-to-stop, will work just fine.

If you really want to see if you can control the valve to some intermediate position, you'd need to disconnect the liquid fuel flow divider speed inputs from the Mark VI, jumper the Mark VI input terminals together and connect a frequency generator (with zero D.C. Offset, or, a zero-based sine- or square- or sawtooth wave generator), and then you'll have to try to adjust the frequency to stop the valve at some intermediate position. It won't be easy or precise, but it will allow some (minimal) control of valve position. And, it will take some time to get the feel for the "balance " between reference and frequency to stop the valve at intermediate positions.

This is NOT calibrating the valve or the servo--ONLY LVDT feedback can be, and is ever, calibrated. But if you're just wanting to see the valve move under Mark VI control these are about the only options available.

The real way to test positioning/control is to perform a false fire. Select Liquid Fuel, disable the ignitors, select FIRE mode, initiate START, and record the FSR and liquid fuel flow divider feedback during FIRING. Liquid fuel will flow into the machine, so a good, long CRANK after the Failure to Ignite will be prudent and absolutely necessary, but this is the best way to make sure the Mark VI will control actual liquid fuel flow. (You DO NOT want to do this on a hot turbine and exhaust stack/HRSG!!!)

Hope this helps!
 
Dear CSA
I just learned about GE 6FA, I have the problem of not being able to stroke test Liquid Fuel Bypass Valve.
Could you please share the stroke test process on toolboxST for me?
Thank you very much for your help
 
AndyLe,

There isn't that much difference between (Legacy) Toolbox and ToolboxST.

The basic procedure would be the same as above.

I LOATHE telling people to force a servo-valve output--because then they think it's acceptable to force it when the turbine is running. AND IT'S NEVER ACCEPTABLE TO FORCE A SERVO-VALVE OUTPUT WHEN THE UNIT IS RUNNING!!!! NEVER!!! Full stop. Period. Under ANY conditions--it's NEVER ACCEPTABLE to force a servo-valve output when the unit is running.

Having said the above, with the liquid fuel isolation valve to the Liquid Fuel skid CLOSED, one can force the servo-valve output of the Liquid Fuel Bypass Valve when the unit is at rest, and the high-pressure liquid fuel pump IS NOT RUNNING and the Aux. L.O. and Aux. Hyd. Pumps are running and high-pressure hydraulic fluid is available to the LFBV servo/actuator mechanism and the valve will move. Because the regulator type for the LFBV is looking for flow divider feedback (and there won't be any under these circumstances) the LFBV will move from the full open condition (full bypass--NO FLOW to the fuel nozzles) to the full closed position (full flow to the fuel nozzles). If you can visually see the LFBV valve stem/actuator mechanism you will be able to detect LFBV movement.

By forcing the output I mean find the liquid fuel flow-rate reference output signal from the application code to the LFBV regulator (possibly something like FQROUT or something similar). With the appropriate ToolboxST privilege enabled, double-click on the green value of the signal in ToolboxST and then force the output in the pop-up window. AGAIN, NEVER do this when the unit is running--not with ANY fuel control valve or the IGVs. JUST DON'T DO IT. The consequences could be catastrophic, even mortally fatal. (GE should never have made forcing servo-valve outputs possible except with a very high privilege level known only to factory or trained field service personnel....) For testing purposes, this is satisfactory.

This is also a satisfactory method for testing servo-valve output polarity under the control of individual processors when replacing servo-valves (something which should be done EVERY TIME a servo-valve is replaced).

If you're looking for a step-by-step procedure with pictures and circles and arrows and numbered steps, I ain't got one. And, it will be slightly different for just about every GE-design heavy duty gas turbine out there so unless the procedure was written specifically for your unit it would probably not work without some modification (and patience and a lot of study and understanding of the Liquid Fuel P&ID and the application code).

Hope this helps!

Lastly, if you can describe why you think this is necessary, we might be able to help with some kind of test or suggestions for troubleshooting/verification.
 
Hi Gents

Allow me to contribute to these fruitful thread.
Personally when I try to tune or check the regulator during normal PM checks when the unit is in shutdown condition I do the following :
- Mainly I force the regulator setpoint fqrout (flow ref) to 0.5% or 1% a value slightly above 0% (remember the feedback of the regulator is the flow recorded at the flow divider by the flow pickups) and as the unit is in shutdown condition the flow feedback fql is 0%. with this slight positive error in the regulator I confirm the smoothness closure of the bypass valve (should neither be fast nor stable)
- In the mid stroke I usually put back the regulator setpoint to 0% to equalize the SP and FDBK. I confirm if the valve is stable or not (electrical null bias is well adjusted to be equal to the mechanical null bias). In other words if the bypass valve is opening > We need to increase the electrical bias and vice versa. (It can also corrected by adjusting the mechanical null bias on the servo but I DO NOT RECOMMEND THAT).

I hope this helps.
 
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