After replacing the srv servo valve, we checked the LVDT voltages and found as 0.74 V at 0%. Actual valve position is also -0.1 % in HMI.
In machine operation, srv passes even when it is in negative position (-2.1%) shown by the HMI value.

I tried to put -10% value and got LVDT voltage as 0.70 V. Then this value is put in IO configurator as 0%. On operation valve position is 0.1% and valves passes also.

How can I close the valve fully?

Should I reduce the LVDT position and voltage according to valve position?

Is the actual valve seat passing?

Can anyone give me a proper procedure of calibration in this case?

Thanks and Regards

 

iqbal,

Stop the auxiliary hydraulic oil pump and adjust the SRV LVDTs so that you read 0.7 volts for each LVDT at Mark V card.

Check the ACALIB.DAT file for max stroke and min stroke values of SRV.

Regards..
V.Venkatachallam

 

Please tell us what type of GE-design heavy duty gas turbine you are working on, and whether or not the SRV and GCV are combined into one assembly.

However, from the sounds of things, the SRV is passing. There is a pretty quick test for this: With no hydraulic pressure (i.e., the unit is shut down and the aux hydraulic pump is not running and has not been running for several minutes), and with gas fuel supply pressure upstream of the SRV, force 20VG-1 closed, and monitor P2 pressure (usually signal FPG2). If FPG2 increases then the SRV is passing.

Replacing the servo isn't going to stop the SRV from passing.

It's also not necessary to recalibrate LVDT feedback if the only thing that was done was to replace the servo-valve.

BUT, we need to know more about the unit and the configuration of the gas valves.

 

CSA,

You are right. The SRV must be passing. SRV and GCV are integrated one assembly. Ours is Hitachi H25 machine with MarkV TMR controls.

I didn't change the values or adjusted lvdt. when srv is shut and gas valve open, P2 pressure rises. I had to reduce the purge timer, K2VG2Z from 3min to 1 min to prevent intervalve pressure high trip. We will check the valve assembly during next maintenance.
Thanks