Isolation Valve for Hydraulic Tube Inlet to GCV, SRV, LCV


Thread Starter



When the gas control valve and speed ratio valve and the liquid fuel control valve need to maintenance during the on cool down, I suggest to install a isolation valve at the inlet tube of hydraulic oil.

Please help me to know there is not a problem for install this valve?

Thank you for reply

The reason the OEM doesn't provide such valves is that it's entirely too easy for them to be left in the wrong position, or to be moved to the wrong position during turbine operation. There would have to be limit switches to check the valves were in the proper position prior to a start, but that still wouldn't prevent someone from unknowingly or accidentally moving them to the wrong position during turbine operation.

Adding start check permissives reduces reliability (in the eyes of most plant managers), and not making things idiot-proof also reduces reliability.

You are free to make changes as you see fit, as long as you are willing to live with the consequences of your changes--which means you have sufficient knowledge and understanding and have reasoned through the changes and have anticipated most, and hopefully all, of the knock-on effects.

It's as simple as that. It really, really is. The change you are proposing may help reduce outage time, but have you considered the possibility of what would happen if the valve(s) weren't properly positioned prior to a START, or how to prevent someone from closing them while the unit was running?

Will you remove the valve handle(s) except when the valves are being worked on during cool-down.

Will you only use the valve handle to close the valve during a maintenance procedure, and to open the valve afterward, leaving the valve open and without a handle at all other times?

What happens if the valve moves when the handle is off--not that it would under most conditions, but how do accidents happen?

How will you ensure the valve(s) are in the proper position prior to a START? And remain in the proper position during turbine operation? Will you have some kind of limit switch for each condition? Will you alarm or trip on out-of-condition detection?

Will you have redundant switches with error-checking and alarms?

What if someone is working on the hydraulic servo-valve or the hydraulic actuator and the single isolation valve opens? Could someone be seriously hurt or worse? Will you have a double block and bleed set-up for each control valve? Will that increase system complexity?

Will you mark-up the P&IDs to reflect the addition of the valve(s)?

Will you modify the SOPs (Standard Operating Procedures) to reflect the addition of the valve(s)?

Will you modify the LOTO (Lock Out-Tag Out) procedures to reflect the addition of the valve(s)?

Will you train the operators and technicians in the newly configured systems?

Will you modify the System Descriptions in the Operations and Service Manuals to reflect the addition of the valve(s)?

It seems like a simple modification, but is it really? Remember: Reliability is king. Or it should be, because that's what the OEM is always being told. ALWAYS. And ANYTHING that adversely affects reliability is not a good thing. That's one big reason why control systems are becoming more and more complex--in an effort to improve reliability and reduce human error caused by inexperience and lack of training.

There really is a reason for lots of seemingly simple things like this--which seem so obvious at first glance.

Hope this helps!
We did this modification on our Frame 9E machines using lockable valves. They are locked in the permanent open position and only released to be closed under permit for repairs. This has saved us from full cooldown delays a few times.

As said above full documentation mods and strict procedures and training should be applied for their use.

Despite this we have had Overhaul contractors complaining that a permit had not been released properly because they could still see locks on valves that they were not used to.