4 replies to this topic

[EngLearning]

Hello,

 

I am a new member here and this is my first post. Thank you for taking my question. On P&IDs I have seen some valves that are actuated by solenoid and some other valves are pneumatically actuated (instrument air only). Can you please tell me when are solenoid used vs pneumatic actuation only?

 

Thanks again.

[thorium90]

Solenoid valves are not very powerful and are only used for small sizes. Typically 2in and below. Pneumatic valves can be used for larger sizes and can also be equipped with limit switches for feedback to a remote monitoring station.

[Art Montemayor]

EngLearning:

 

What P&IDs are you referring to?  It is important to know what process, pressures, flowrates, fluids, and actuation functions you are referring to.  For example, is it a ¼” instrument air line?  Or is it a 3” process gas shutdown valve?  What are the specific basic data?

What valves, specifically, have you seen?  What is their size, function, and fluids handled?

 

There are common sense reasons to not even think of using a solenoid valve on a process line.  The list is a long one.  I personally would never accept a solenoid on a process line.  If you furnish the specific information I request above, you may answer your own question.

[PhilippM]

I'm betting that the solenoid valve is not actually used on a process line, but on the pneumatic supply of the valve positioner of the actual process line valve. I've often seen P&IDs where some of these solenoid valves were shown, in order to clarify that an interlock switched off the electrical supply of the solenoid in order to make the main valve move to its fail-safe position

 

But without seeing the actual P&IDs (or at least the relevant parts of them) this of course is just speculation.

 

EDIT: Have you checked the valves and their actuators on-site? Maybe the P&IDs are just wrong.

Edited by PhilippM, 29 July 2019 - 05:17 PM.

[EngLearning]

Thank you all for your responses. I will have to look for a specific example from a P&ID. I will get back to you but it might take a few days. Thanks again.