PSV Masoneilan 21700 LO DB (I/P 3 - 15 psi)

The valve when isolated work well. but after open, the upstream valve it can't close to 0%. we can see the plug stem lift up even with the valve in manual and command it's 0% (passing more than 10% for DCS command ="0 %") and DCS operators experienced troubles in controlling the pressure.

We check the loop and all it's ok.

Can be because there is a reduction pipe size from 4" (pipe) to 1" (body valve)?

Thank you for any help!

 

that is a common actator problem for high pressure drop services, thats whay it works when isolated that is 0 pressure drop

usual causes:

inadequate pressure available for the actuator
improperly sized control valve (actuator sizing)
damaged valve internals

 

Agree with d.

Most likely cause is the undersizing of the actuator. Try using a booster in between to increase the pneumatic signal from 3-15 to 9 to 21 psi.