Open/Close Test of Liquid Fuel Bypass Valve without LVDTs


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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

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 <b>NOT</b> want to do this on a hot turbine and exhaust stack/HRSG!!!)

Hope this helps!