suction pressure control valve

[reda08]

Please advice regarding the behaviour of a suction pressure control valve (during turbo compressor start up)which is located upstream the suction scrubber for a centrifugal gas compressor the valve is designed on upstream pressure 60 bar with pressure drop of 14.5 bar,but now the condition of the plant pressure is 48 bar and pressure drop varing between 8 to 12 barg (set point between 40 and 36 barg), in that case the valve is not stable (playing in 2-3 barg) around the set point.Please advisce is this due to varing between the design conditions and the site conditions or may be there is a problem in the valve itself

 

[TD2K]

How has the flow rate to the turbocompressor changed as a result of the lower supply pressure? Has there been any compositional changes?

You have a lower inlet pressure to the valve and a reduced dP, the valve should be operating more open which I wouldn't think should introduce an instability (I usually see instability when the valve is nearly closed and small movements can create large changes in Cv).

How is the valve responding in the field relative to the output signal? Is it moving in step or making sudden movements which could indicate binding or some problem.

 

[reda08]

The valve move in sudden movements open and close,and its moving (+ or - ) 4 bar around the setting point either when its on manual or automatic mode.

 

[TD2K]

If the valve isn't responding smoothing to manual movements made from the control system as you open and close the valve, you'll need to start troubleshooting the valve/actuator and start eliminating possible causes and narrowing down the source of the problem to the valve, the actuator and/or positioner if you have one, etc.

 

[reda08]

Thank You

 

[dcasto]

you might want to look at a valve possioner too.

 

[TD2K]

If the OP is still around, I'd be interested if they figured out what the problem was.