Vacuum controller

Hi all!

I have a problem and I wish to draw upon the collective genius of Arduino Forums…

I want to make a vacuum regulating device. Basically, I would program in some cycles (what vacuum, how long, repeat how many times) etc into an arduino that would then control a solenoid valve located in-line with the vacuum line. When I’m drawing a vacuum in the chamber, I’d apple a current to the normally-closed solenoid and allow the vacuum pump to suck the air out of the chamber. When I need to hold the vacuum, I’d simply stop applying current and let the solenoid valve close. When I need to release vacuum, I’d just use a vent valve on the chamber. Seems straight-forward enough… I realize that they need a lot of current, so I’d be using an external power source (most likely wall).

Right now, I’m thinking of using a MAP (manifold air pressure) sensor from an old vehicle for the vacuum sensor (so that I can detect when to switch the solenoid on or off). I need recommendations for vacuum solenoid valves that can take up to -28 inch of Hg. Also, are there any differences between solenoid valves and vacuum solenoid valves? Just because a solenoid is rated for 0~+X pressure shouldn’t mean that it can’t handle negative pressure…?

Cost is an issue and I’m hoping to keep the solenoid in the early~mid double digits if possible.

Thanks in advance!

The control logic sounds pretty straight-forward. I'd say the most complicated part is the user interface.

Do you have any idea what sort of signal you get out of the MAP sensor?

Also, are there any differences between solenoid valves and vacuum solenoid valves? Just because a solenoid is rated for 0~+X pressure shouldn't mean that it can't handle negative pressure...?

I don't know, but I'd assume you can install it backwards (I don't know if there's even a "direction") on an air/gas solenoid. And I would expect just about any air solenoid would work, since one atmosphere is low compared to most compressed-air systems.

I realize that they need a lot of current, so I'd be using an external power source (most likely wall).

If you use a 120V or 240V solenoid, you need to isolate the arduino from the high voltage. That means a relay, or an opto-isolator with a TRIAC. The simplest solution would be a solid-state relay, but that's usually not the cheapest way. If you can find a 12V or 24V solenoid, you'll need something to boost the voltage & current (a MOSFET or relay, etc.) but you don't need the isolation.

You'll also need to program-in some [u]Hysteresis[/b][/color][/url] to prevent "chatter". For example, when you program your heater/furnace to 70 degrees F, you want it to switch-on at around 69, and stay-on 'till the temperature hits about 71 degrees. Then, you don't want it to come on again 'till the temperature drops to 69. [/u]

I just found this on ebay: It sounds like a good, cheap solenoid valve. http://www.ebay.com/itm/NEW-MAC-PNEUMATIC-AIR-VACUUM-2-3-4-WAY-EXHAUST-BRAKE-VALVE-12V-SOLENOID-DIESEL-/130777153619?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item1e72ed0053

The MAP sensor outputs a voltage that I'll probably have to map/linearize around the pressure region of interest. I'm hoping it will be straightforward.

I've never heard of/used an opto-isolator or a TRIAC (been googling them over lunch). Do you have any good reference material/examples of these? I'm more familiar with diodes/relays. It'd be nice to experiment around and learn more during this project.

Thanks a lot for the input!

DVDdoug: The control logic sounds pretty straight-forward. I'd say the most complicated part is the user interface.

Do you have any idea what sort of signal you get out of the MAP sensor?

Also, are there any differences between solenoid valves and vacuum solenoid valves? Just because a solenoid is rated for 0~+X pressure shouldn't mean that it can't handle negative pressure...?

I don't know, but I'd assume you can install it backwards (I don't know if there's even a "direction") on an air/gas solenoid. And I would expect just about any air solenoid would work, since one atmosphere is low compared to most compressed-air systems.

I realize that they need a lot of current, so I'd be using an external power source (most likely wall).

If you use a 120V or 240V solenoid, you need to isolate the arduino from the high voltage. That means a relay, or an opto-isolator with a TRIAC. The simplest solution would be a solid-state relay, but that's usually not the cheapest way. If you can find a 12V or 24V solenoid, you'll need something to boost the voltage & current (a MOSFET or relay, etc.) but you don't need the isolation.

You'll also need to program-in some [u]Hysteresis[/b][/color][/url] to prevent "chatter". For example, when you program your heater/furnace to 70 degrees F, you want it to switch-on at around 69, and stay-on 'till the temperature hits about 71 degrees. Then, you don't want it to come on again 'till the temperature drops to 69. [/u] [u][/quote][/u]

Also, are there any differences between solenoid valves and vacuum solenoid valves? Just because a solenoid is rated for 0~+X pressure shouldn't mean that it can't handle negative pressure...?

Having worked in a oil refinery before retirement, I bought and installed lots of solenoid valves for lots of different applications and learned early on that you should never assume anything about the proper application of a specific solenoid valve in a specific service. If it's not stated explicitly in it's datasheet, then call a manufactures rep (beware sales vendors, they want to sell and don't always grok the tek) and ask, I always found them helpful if I couldn't find the information I needed in a datasheet.

Lefty