Is pressure control valve good enough than solenoid

[delf]

Dear Sir

Sorry to bother you this simple solenoid question.
There are two case of pressure control valve.
I wonder why we always pick pressure control valve (case 1) instead of
pressure control valve with solenoid (case 2).
In my poor undestanding about control, flow and pressure singal is faster than
temperature control. But, why do we always only use
control valve instead of control valve with solenoid (except there is interlock singal required in this case)
in pressure control situation.



Any comment or suggestion will be appreciate
Thank you for your kindly help

 

[controlnovice]

With Case 1, the PV will be better controlled to a single setpoint. With Case 2, assuming deadband controller, the PV will rise and fall between a setpoint range.

The method in which Case 2 is shown would indicate that the control valve is being used as an On/Off valve, where PIC is a deadband controller.

More than likely, Case 2 should have the PIC wired straight to the control valve. The solenoid valve would be controlled by High or HighHigh Pressure (de-energize the solenoid on High/HighHigh pressure to fail close the control valve) or possibly some other interlock (high temperature, Emergency Shutdown, etc).



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This is normally the space where people post something insightful.

 

[glowing]

radar, ensure it is low frequency, not high, when dealing with froth / foam. Guided would be much better.

Don't rule out contacting systems. There are many great vendors, one of which is

http://www.ktekcorp.com.

Their Megnoresistive are pretty reliable. A capacitive probe would work well to, as it sounds like it will be a steady level. I have never used theirs, but Milltronics are great.

 

[glowing]

Think of it like your furnace. You may set a stat at 22C, but it is going to stray up and down a couple degrees (say 19-25C). Not a big deal in the house. If you use a VFD on the furnace you will maintain that 22C. View the VFD as said control valve.

 

[glowing]

sorry...last post was wrong thread