I am looking for some technical information regarding fitting a mechanical stop to a control valve.
I am a process engineer and need to inhibit a valve from moving past around 80% of it s trave due to the limit of the downstream PSVs.  Replacing the valve is not an option.

The question is, how does one work, where is it fitted etc?  I am interested, and this will help me spec one when talking to the vendor.

You need to familiarize the method that the limit stop works.  For a rising stem control valve these may be described as an up-stop or a down-stop.  The control valve actuators are normally pneumatically actuated with one design for valves that are normally open or fail open on loss of the air supply; a different style for valves that are normally closed or fail closed on loss of air supply.

Often the valve trim can be replaced with lower capacity trim.  This could be selected from standard trim or custom trim if needed.  My preference would be to select a different trim instead of using a mechanical limit stop.  The limit stop is easily changed.  Changing the trim is less easy.

Also, you might consider a downstream flow restriction orifice plate to take pressure drop with high velocity.

Then there is the option of using two or three techniques.  It is usually just an issue of time and money.

The valve I have is a globe valve (Masoneilan), so I guess for this type then a mechanical screw stop of some kind would be fitted to prevent it being screwed out past a certain point?

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