Vacuum Solenoid Valve Control

[SteveD123]

STOP right now!

Do you see the words "Pilot operated" in the valve spec? That means that pressure is used to enhance the operation of the valve.  I do not think this will operate as you want when you get close to your final vacuum levels. The spec also says "For use with: air, inert gas, water". The word Vacuum is missing. Unless you have it in writing that it is suitable for your exact application, I would be VERY cautious. Even if you are going to use this for re-admitting air to your chamber, I'd be careful, because the valve will be prone to freezing up, because of the cooling effect as air expands into a vacuum.

Many people have suggested an intermediate relay. There are 4 very good reasons to drive your vale through an isolating relay:

1. Complete electrical isolation will protect your expensive instrumentation hardware from external nastiness.  In your case, this could be the static charge that can be associated with free flowing gasses.
2. Grunt: You can size your relay and plant-side PSU to be whatever you need.
3. The relay provides you with a means of implementing whatever emergency-stop, safety interlock (only allow the vacuum valve to open when all chamber doors are shut for example) & sequencing functions you need without going through your PC & LabView code. This means that you stay well away from whatever regulations & laws you have in your state concerning safety-related programmable systems. It also means that it is much easier to convince a safety inspector/auditor that you have a safe system if no part of your safety case is dependent upon your PC & software working correctly.
4. The relay allows you to exercise your hardware and software separately, especially if it is the type with a built-in "Test" button.

However, a quick google for "variable vacuum exhaust valve 3/4 inch" brings up these people. I suggest you contact them: http://www.high-light.com.tw/en-global

[LabUseful]

I agree 100%, the valve needs to clearly be a ‘vacuum’ valve.

Also, if this is part of a safety system, or has some collateral safety concerns, you normally stay away from a PC controlled solution. In that case, a hybrid control solution is appropriate, a PC and a PLC; where the PLC controls the safety interlock logic directly.

[rlinklater]

I definitely messed up with the "pilot operated" part. I can't believe I missed that.

Our mechanical engineer has okay-ed the use of a gas solenoid for this application since the pressure we are dealing with is still well within the limits of the valve. We are doing assent testing using a small vacuum chamber, so I don't think safety is too much of a problem there. We have two people there with it at all times and they are able to turn off the pump or the valve at a moments notice. We are doing this automated because there is far too much human error in following the proper curve for the assent testing.