Steam Turbine Throttle Valve

F

Thread Starter

Favy

We just caught up with an issue like the main steam inlet control Valve was not opening above 20% when the command to increase the Load was given. The unit was taken out and exercised to confirm any sort of issue with the servo valve, however it was opening wide 100% without any issues. Taking back into service, the issue remains the same.

Am just expecting like would there be something mechanically wrong? Just thinking can Steam Pressure, when getting in, make some kind of displacement in the Flange Disc that in turn stops it moving above certain area colliding with Valve cover? and when steam pressure not available, it moves as if nothing has happened.

Can someone share their view/experience on the same.

Thanks
 
> control Valve was not opening above 20%...
> unit was taken out and...it was opening wide 100% without any (steam pressure)...
> can Steam Pressure,....stops it moving above certain...?

YES.
the hydraulic force of the actuator must overcome the steam forces that would be across the CV disk. Most CV designs use a "balancing" arrangement to reduce this steam force. the design of balancing varies and a drawing would be needed to explain. the common design is a small diameter pilot valve disk inside the main disk which opens first. this could be where the pilot is opening 20%, but the actuator doesnot have the force to open the main disk.

HOWEVER, before you disassemble the valve (and you would need to have someone that knows how to evaluate the internal components) You need to VERIFY that the servo current goes to the GO OPEN value when at the stalling lift and not just at a normal servo current. It could be that during operation there is a limiter circuit that is over riding the expected CV opening demand and just positioning the CV at 20%

Good Luck and have a Great New Year

Ps...sorry for the delay in replying. Thanks Peg/Ken for assisting
 
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