I/P Location

Good evening everyone! I'd like to share a debate/discussion we have once in a while at work.

What is everyone's opinion on the location of the controls for an analog or a discrete valve?

If all things are equal, I prefer putting the I/P (analog valve) or solenoid (discrete valve) as an integral part of the positioner or valve. Some of my collegues prefer control panel mounting all components (I/P or solenoid). Their argument is that it eliminates some field wiring. Obviously instrument air will have to be run to the valve (for analog), but they claim having less field wiring is better.

In my opinion, (if all things are equal concerning location conditions), I would rather have the I/P integral to the positioner. I like the PMV positioners, the I/P is build into them. (for example, not trying to advertise here Phil) Just run your 4-20mA signal wire to them, and a supply air line and you're done. I prefer this because it makes valve tuning easier. Your I/P is right at the valve, makes troubleshooting easier also.

Of course there are advantages to panel mounting the I/P too.

I'd like to hear everyone's opinion as to what they prefer, if all things are equal. Obviously there are some "it depends" situations, where it is clearly advantageous one way or another. I just want to know if there's something I'm missing by prefering to mount the components in the field.

TIA,

Greg

It depends entirely on the situation.

In some cases, usually where there is heavy guaging, or lots of special control (volumetric valves) and such, we make a seperate enclosure for the pneumatic assemblies.

In most cases however, we just mount them somewhere on a machine; with or without manifolds depending on the number of valves.

If they are so concerned with saving wiring, go for a Fieldbus controllable valve stack, they are really nice to work with

We try to mount valves near the object being controlled for response time. Electricity is a lot faster than air or oil. Also with long lines, especially air, the compressibility can play a role.

Generally speaking we always run wiring to the field. We like the newer "smart" valve packages, with the I/P built into the positioner.

The only exception, Class I, Div 1 & 2 areas. Here we mount the I/P in a safe area and run air out to the hazardous area. The reason being cost explosion proof I/P's can be quite expensive.

Ken

Rick, Ken, good points and I agree.

I like to put the I/P on the valve because I HATE air lines. Air leaks are a pain in the #^#$%$ to find sometimes. I work in a mill that has miles of tubing running top to bottom of five boilers. At every opportunity I try to remove some tubing.

I place the valves on a manifold inside an enclosure near where the cylinders are located. We started putting them in enclosures because a lot of our applications are in washdown environments. I then run the wires from the remote control to the valve. I also have to worry about air compliance so I like to keep the air lines as short as possible.


Bob

Most of the time we put the valves directly or very close to the equipment.

But we are reconsidering this because of the extremely dirty and abrasive environment that we have. In the future we will probably put all pneumatic components in a box with the electrical connections as well. This box can then be located reasonably close to the equipment.

Close to the equipment, not the electrical box. For all the same reasons you guys mentioned above.

Im glad to see some of you have had success with the fieldbus valve packages. I was just checking some out for my next job.

Ken,

I have recently run accross a relativly cost effective intrinsically safe I/P from ABB (used to be Taylor Controls, I think). It is a DIN rail panel mount I/P unit for around $250 U.S.

Darren

It depends on distance, the enviroment, and serviceability.

For the most part, for reasons already stated, the valve should go were it will operate most efficently. Also its usually easer and cheaper to run long runs of wire then long runs of air line or piping.

My thought is that on large machines I would think the valves would be remote from the controller. On small or portable machines it might be best to place all the valves togeather. But it's really up to the customer...

I haven't worked enough pneumatic systems to have a strong opinion. But, I do know that instrument air can be dirty and wet. That's not something you really want in your control cabinet.

I agree that placing valves closer to the equipment (but at a safe location) makes sense. Especially, if servicing the machine could involve manually operating those valves. On the other hand, if operating the valves manually is dangerous, you could padlock them inside the control cabinet... It's an exercise in analyzing pros-and-cons, I guess.

AK

One thing that hasn't been mentioned here, and should be.

99.97225% of the time, this is not an issue, but that last 0.02775% of the time can lead to much swearing, hair-pulling, beating things with sticks, and walking off a job site, hitching a ride down to Key West, and opening a bar.

With Pneumatics, especially E/P's, I/P's and other regulators, READ THE MANUFACTURER INSTALLATION NOTES. Many have a minimum required post-valve air volume for proper operation. As I said, USUALLY not a problem, until someone gets the bright idea to port a valve directly into a small cylinder for example. (/sigh 2 days, 3 valve swaps, two swaps of the analog driver card in the PLC, finally trying with a potentiometer and a battery to figure that one out).