Precise PLC control of a ball valve?

[mnevans93]

You can always open your flow control valve to a preset position (for example, leave it in the last operating position or move it to 45 degrees) and use a separate solenoid valve in series with the control valve to control off/on operation of the air.

Edit: What I said here was exactly what you said in your post, Tom, but I guess I didn't read it properly. I feel silly. It's been one of those mornings, I guess.

I personally wish that the valve could be left as manually operated and upgraded to a needle valve, in which case we could just write down the operating positions for each unit, but my company wants full automation.

 

[reinhart]

how do i post a question on the forumn

 

[osmanmom]

others item also need to consider,

air accumulator tank,air flowsensor

 

[widelto]

Reinhart:
You did it, Please open a new thread

 

[mnevans93]

how do i post a question on the forumn

You have to create a new thread, reinhart. If you go to the LIVE PLC Questions and Answers area, the button for Start a New Thread should be on the top and bottom left of the thread list.

 

[BakedFresh]

Rotary actuators with precise positioning are common in the chemical process industry. The terminology is "modulating control" vs. "on/off control". For example, see Automax APEX pneumatic positioners, or Automax Centura electric actuators.

 

[kamenges]

If you use the Festo valve the change will be on the order of tens of milliseconds. From the literature I have the -3dB frequency for the largest flow valve is 65 Hz.

Keith

 

[Doug-P]

Does the PLC already exist or is it to be added to control the valve? Just asking because there are dedicated controllers for this purpose.

http://www.redlion.net/Products/ProcessControl.html

 

[mnevans93]

Does the PLC already exist or is it to be added to control the valve? Just asking because there are dedicated controllers for this purpose.

http://www.redlion.net/Products/ProcessControl.html

We have not selected a PLC yet, no. We're looking to keep the cost down as much as possible, so I've been considering a Plast-O-Matic full port ball valve with a 4-20 mA control electric actuator. I'm thinking that it has enough positions where it can perform what I need it to and open quickly enough where the temperature won't go outside the acceptable range. I just need some more specifics from the company on it, whom I'll be contacting today.

That being said, the PLC doesn't have to be incredibly complicated. I was looking at Click PLCs from Automation Direct. I just need to be able to have the PLC change the position of the ball valve according to the temperature fluctuation. If one of the valve positions doesn't allow for maintaining the proper temperature, the PLC will flip between the two closest to keep it floating around the right temperature. That's really all I need it to be able to do.

 

[BakedFresh]

mnevans : just a note. Electric actuators can be slow. It's fairly common to specify the required opening and/or closing time when specifying an actuator.

 

[Tom Jenkins]

A couple of items:
1) Check with the manufacturer to make sure the valve's pressure rating is right for your application with air service. Plast-O-Matic has some that may be OK, but not all plastic valves are recommended for air service because of the "explosion" hazard with a compressible fluid.
2) It looks like you can get the ball port customized for better throttling characteristics. That is also something to run by your supplier.

 

[TConnolly]

Ball valves are inherently non-linear in their flow response. Combine that with a compressible medium like air and chances are you are going to have a PID loop that is extremely difficult to tune. A fast actuator is just going to make things even worse.

If you want fast response and somewhat linear behavior then a valve like the Festo valve that was suggested is a better bet.

But I'm going to suggest something else, that though more physically complex will be easier to control: A bank of multiple small on/off solenoid type valves feeding a single nozzle. How many valves are on is determined by dividing the PID output range into zones. Three full flow valves plus a half flow valve with an orfice can give you control of the process in 16% increments. That is likely to already be better than you have with a manually opened ball valve, however by time proportioning the half flow valve you can get even finer control. A box of solenoid valves will cost quite a bit less than just a single ball valve actuator.

 

[kamenges]

I think TConnolly has a pretty good idea there. It will be reasonably fast and uses standard digital outputs.

Here is another valve option that is a better design match to what you are trying to do:
http://www.ascovalve.com/Common/PDFFiles/Product/PosiflowR3.pdf

I have no idea on cost on this thing but would guess in the $500-$1000 area.

Keith

 

[TConnolly]

Here is another valve option that is a better design match to what you are trying to do:
http://www.ascovalve.com/Common/PDFFiles/Product/PosiflowR3.pdf

:nodi: Beats the hell out of a ball valve for this kind of an application. You need to make sure the air source is clean.

 

[Luke_Mages]

I think TConnolly has a pretty good idea there. It will be reasonably fast and uses standard digital outputs.

Here is another valve option that is a better design match to what you are trying to do:
http://www.ascovalve.com/Common/PDFFiles/Product/PosiflowR3.pdf

I have no idea on cost on this thing but would guess in the $500-$1000 area.

Keith

great find.