We have machine GE Frame9FA this unit we need to make calibration for Liquid Fuel Bypass valve (LFBV). Can any one tell me How to make calibration for LFBV and which the signals to be forced during calibration?

 

The only person who can answer your question about what needs to be forced is you, because only you have access to the P&IDs for the Liquid Fuel System at your site. You need to review the P&IDs to determine if there are any signals which need to be forced in order to energize solenoids to allow high-pressure hydraulic oil to pass through the LFBV servo in order to be able to stroke the LFBV for the purpose of calibrating the LVDT feedback (presuming LVDTs are present on the LFBV; not every LFBV has LVDTs).

And, we don't know how you will establish high-pressure hydraulic oil, either by forcing logic to run pump motors, or by using the manual feature of the MCC starters. So, we can't give you a step-by-step procedure for every logic signal which must be forced.

But now I have a comment and a question.

First, the comment. One does not calibrate a valve (or the IGVs). One calibrates the LVDT feedback from a valve (or the IGVs). So, if the device does not have LVDTs, then there is no "calilbration" necessary. (Again, some LFBVs do not have LVDTs, even on F-class machines. And on some F-class machines, the LVDTs only provide position indication; they are not used for LFBV operation.)

Now the question. Why is felt it is necessary to "calibrate the LFBV"? If the LFBV has LVDTS, then why is it felt it is necessary to calibrate the LVDT position feedback? Presuming the LFBV has LVDTs, has anyone checked the feedback to determine if it needs calibration? In other words, is the LFBV LVDT position feedback inaccurate? Has one or both of the LVDTs been replaced? Has the valve been disassembled and reassembled requiring a re-calibration of the LVDTs?

[NOTE: Replacing a servo does <b>NOT</b> require LVDTs to be re-calibrated, as replacing a servo does NOTHING to change the physical stroke of a device.]

LVDT feedback is secondary to LFBV operation. First and foremost, the regulator for the LFBV is a flow-rate control regulator, moving the LFBV to whatever position is required to make the scaled Liquid Fuel Flow Divider Feedback equal to the Liquid Fuel Flow-rate Reference. If the LFBV LVDT position feedback is even grossly inaccurate, the Speedtronic will still move the valve to whatever position is required to make the actual fuel flow-rate feedback equal to the fuel flow-rate reference.

LVDT position feedback is not critical to the operation of the LFBV. Even if the position feedback is out of calibration by 15 mm or more, the LFBV will still operate correctly because the Speedtronic will move the LFBV to whatever position is necessary to make the actual liq fuel flow-rate equal to the liq fuel flow-rate reference.

So, what is it that makes someone believe the LFBV needs to be "calibrated"? I ask because I hear all the time that someone thinks this problem or that problem can be solved by calibrating the valve or the IGVs, and then, hours and hours and hours are wasted trying to calibrate something that has no effect on the problem trying to be solved. And after the "calibration" the problem still exists, or in some cases, is even worse.

So, I'm trying to help people understand when it's necessary to calibrate LVDT feedback, and when it's not. To save time and trouble and lost generation and to avoid unnecessarily performing a procedure few people really know how to do and losing time and generation (and availability) in the process (not to mention in some cases credibility, too).

NOTE: The Gas Fuel Control valves are different; the Speedtronic does not have a gas fuel flow-rate reference that it compares to gas fuel flow-rate feedback. (Only the liquid fuel system converts liquid fuel FSR to a flow-rate reference; the gas fuel system does not.) For the gas fuel system it is assumed there will be a certain flow-rate through a valve when it is at a certain position, therefore the LVDT position feedback is more critical for Gas Fuel Control valves. And gas fuel FSR is calculated to provide a certain flow-rate for a certain position.

The Gas Fuel SRV is a pressure control loop, and so the LVDT calibration for the SRV is also not critical to the proper operation of the SRV.

 

Thanks for your reply sir

I need to inform u some times we need to Check the behaivior of the valve to confirm that it is working properly so we force the following signals:

L4_XTP=0 (Allows the trip card to pick up trip solenoid)

L3ADJ1,2,3,4= 1(calibration permissive for selected regulator)

L20TV1X=1 (if tripped you will not get fuel, gas only)

L20FG1X = 1 (needed to port hydraulic oil to the valve ,gas only)

L20FL1X= 1 (Dist - liquid fuel)

this signal need to force it during start to open and close the LFBV but it is not to accept to open by select regulator and right click and chose the calibration mode and select on mode and chose minimum value and maximum value to check the opening and closing.

pls can u inform me any signal need to forced more to accept to check the opening and closing

 

Mohamed,

You mentioned that unit at your site is 9FA one, so most probably LFBP VV Does not have LVDTs associated with. So calibration of this valve is different than other gas valves as SRV or GCVs.

If this assumption is true then the following statement is as well. First you have to make sure hydraulic pressure is established (start one aux LO PP & one Hyd oil PP) then to establish trip oil Pressure, the signals you mentioned should be forced.

Now, to proceed with calibration you should understand how LFBP VV control loop is actually works. Mainly it is a flow control loop, as flow feedback is from flow divider magnetic pickups (fql_pr1,2,3) and resulting feedback signal is FQL1 reference set point is directly proportional to FSR value represented in signal FQROUT (during shutdown this signal value is -25% or what is called saturated value).

If required to verify polarity check, FQL1 is normally 0 during SD so by forcing FQROUT in both positive and negative directions (let's say +1 & -1) the valve should be moved in close and open positions. And as per GE Calibration procedure, you have to repeat this check three times with one coil is connected in each time.

You can revert back to "control spec" diagram for your unit and it should have a general calibration guide for this valve and all gas related valves.

Hoping this would help you in any means.

Best regards,,,

 

Thank you for ur reply sir i tried to open and check the valve as u mention. it was moved by forcing FQROUT in both direction positive and negative

 

Congratulations!

You mentioned you need to check "...the behaivior of the valve to confirm that it is working properly..."

Will this procedure give you the information you seek?

Were you able to control the valve position? Could you stop the valve at any position?

The LFBV is a valve that closes to increase fuel flow. Negative servo current increases the fuel flow (closes the valve).

Can you tell us if the valve opened or closed when the current being applied was positive?

Because I submit that simply being able to move the LFBV without being able to control it and without being able to measure actual position versus reference, or to measure slew rate or observe stability doesn't tell a person much, if anything.

And without even seeing the P&IDs I will argue that it's not necessary to force any logic to stroke the LFBV.

But, please tell us how you can say the LFBV is behaving properly from what you just accomplished?

 

Dear sir

Thank u for your reply but the problem which we are faced is that when start the unit on liquid fuel the shut of valve for liquid fuel system is delayed for open, and also LFBV also delayed for open, and unit tripled with alarm "Fail to ignite"

after that we put the unit on "OFF COOLDOWEN", and the hydraulic filters for the shut off valve and for LFBV was cleaned. after that the unit start on liquid and synchronized. we identify that filter need to clean by open shutoff valve manually. and check the response and check also the local indication for filter "this for shut off valve and LFBV" but for LFBV in this time after force the previous signals and force the signal FQROUT (minus and positive direction). we check the moving and hearing the sound of moving the LFBV Without any feedback because magnetic pickup reading Zero value. we need only to know any chock in the filter or not instead of put the unit on "OFF COOLDOWEN"

regards
Mohamed Salem

 

As suspected. A review of this poster's other questions shows he provides virtually no feedback.

 

Mohamed Salem,

The thinking for this "problem" is all over the map. You opened this thread asking for a procedure to calibrate the LFBV, and you were told the LFBV doesn't require calibration if it doesn't have LVDTs. Then you said you needed to verify the behaviour of the LFBV but you needed to know which logic signals to force. Now you are saying the unit fails to fire when being started on liquid fuel and that the shut-off (stop) valve is slow to open on the first firing attempt and the LFBV is also slow to open on the first firing attempt.

So, for some reason you need to take the unit off cooldown in order to be able to change hydraulic filters. I've never seen a hydraulic filter on the Liq. Fuel Stop Valve actuator, but stranger things have happened and I haven't seen every configuration made. There are "last-chance" filters on the LFBV actuator, but they usually have visual, pop-up indicators to show when they are dirty and need to be changed.

Then you successfully stroked the LFBV by forcing FQROUT, which is the only method which would work if the LFBV didn't have LVDTs (since AutoCalibrate couldn't be used to stroke the LFBV if it doesn't have LVDTs) and you didn't tell us which logics, if any, you forced or needed to force to be able to move the LFBV. You seemed to indicate the LFBV does not have LVDTs, but you didn't state clearly if it does or not.

Then you say on the next start attempt on liquid fuel the unit fires successfully after all of this activity.

But you haven't told us how long it was since the last time the unit was started/fired on liquid fuel. Or, if the liq fuel start attempts or being performed shortly after a combustion inspection or other maintenance outage. When the liquid fuel lines and combustors are disassembled they are drained of liquid fuel and take some time to refill during the next start attempt; it's pretty common, especially on units with DLN combustors, to have some difficulty on liquid fuel firing attempts immediately after a maintenance outage or if there have been several weeks since the last liquid fuel operation. It is a well-known fact that air gets into the liquid fuel piping both before the liquid fuel stop valve and after the liquid fuel stop valve during long periods of non-liquid fuel operation.

So, there could be many reasons for the inability to fire on liquid fuel--most all of them <b>NOT</b> related to the "calibration" or "behavior" of the LFBV. Certainly, if the hydraulic filters were dirty, that would also cause problems with the liquid fuel system, but that would also indicate it's been some time since the last liquid fuel operation (since that's when the filters seem to get dirty on F-class units, during periods of low flow and low temperature when L.O. particulates collect in small passages).

One would think you are composing a procedure for future use based on your experience and the assistance provided, and that same procedure would be helpful for others reading this post in the future.

As for having to take the unit off cooldown to change the filters, I'm presuming that's required possibly because the hydraulic system is being used for jacking oil pressure to the bearings, but that's a guess since I can't see the P&IDs for your site.

We are trying to help you understand your system by asking these questions, and in the process help others to understand their systems. So, we are looking for answers when we ask questions.

Finally, you state, "we need only to know any chock in the filter or not instead of put the unit on "OFF COOLDOWEN"". I don't know how stroking the LFBV will tell you that. Again, the last-chance filters at the LFBV actuator typically have visual, pop-up indicators to tell the operator if the filter is dirty and needs to be replaced.

You might need to take the unit off cooldown to stop the hydraulic pump to change the last-chance filter. But you can leave the unit on cooldown to stroke the LFBV.

Again, the thought process for this problem is just all over the map. I suggest, as was suggested before, you take some time to study and learn the P&IDs for the unit, read the System Descriptions in the Service Manuals, and possibly get some training to help reinforce your studies.

And, if you've developed a procedure for stroking the LFBV at your site, it would be helpful to others if you post that procedure here.

 

Dear CSA

After greeting i need to inform u When i asked about the LFBV calibration. i need to stroke it manually from calibration face plate (By chose calibration on and chose manual and put the value and set manualy). in this time i don't know this valve not accept calibration because it does not have LVDT. and for the STOP valve and LFBV there is a small filter on the supply line for hydraulic valves (STOP and LFBV), we needed to stroke the valve (LFVB)to confirm there is no chock on the filter because sometimes this local gauge for dp pressure for filters not working properly. after study the P&ID and specification control we decide we should be force the flowing signals:-

L4_XTP=0 (Allows the trip card to pick up trip solenoid)

L3ADJ1,2,3,4= 1(calibration permissive for selected regulator)

L20TV1X=1 (Trip solenoid for IGV)
L20FG1X = 1 (Trip solenoid for valve ,gas only)

L20FL1X= 1 (Trip solenoid for liquid fuel)

this signal was forced to build up the hydraulic pressure. and after force this signal we start to change the value which is going to the servo valve RQROUT in both direction (-ve and +ve). and locally we heard the moving of bypass but u cant identify the direction of moving. we but the unit oFF COOLDOWEN because we don't have any isolation valves on the supply line for valves.

for the firing in liquid it is before minor inspection it is not accept to fire by (fail to ignite)

thanks
Mohamed salem