...the maximum draw allowed is 18A at 12V, so the pumps would have to fall withi n that spec (since both pumps will never be running at the same time, they can both draw up to 18A).
Which means I will need a valve that can act quickly enough to bring within range (hopefully within 1-2in Hg).
I will also need a pressure/vacuum sensor, and a solenoid valve to regulate pressure, something of which I have been looking into, but am hoping for someone with experience to chime in here as well.
Your container is going to be transparent, isn't it?(The pressure cookers I've seen have all been metal.)To be sciencey, are you going to provide some method of measuring the volume or size of the balloon?
Well a single 'absolute pressure' sensor will read from absolute zero pressure ( a perfect vacuum) to some maximum pressure value, depending on the measurement range of the sensor you select, so no need for separate sensors unless you want them for other reasons.A solenoid valve can only be controlled to be fully on or fully off, so not capable of regulating a pressure or vacuum stream, you need to either have variable speed control on the pumps or variable 'control values', where you can control the position of the valve from anywhere from fully closed to fully opened.Lefty
If the pumps require that much power, I'd suggest using 120V pumps (or 220V if you live in Europe). I don't have a lot of experience with vacuum pumps, but I suspect you'll need a separate pressure pump. I don't know if either one will work "backwards"... I kind of think the vacuum pump could be used backwards, but I wouldn't push it much above 1 atmosphere.If you use a very-small aperture, the vacuum/pressure will change slowly, and your valve won't have to be super-fast. Most solenoid valves should operate in a matter of milliseconds.
I was thinking that if the data from the sensor was used, that the arduino would energize the solenoid to open the valve when pressure/vacuum was too high and close it when pressure was optimal or too low. You don't think that will be accurate enough (honest question)?
What range of pressures do you intend to use? Vacuum is less dangerous than pressure and in any case you're limited to 1 bar differential but a couple of cubic feet of air under pressure could be very dangerous indeed. It would be much safer if your working fluid was water, and this would also be easier to pump.
Hard to say, you can only try and see. Also be sure any solenoid values you obtain will work in vacuum service, many won't so check their datasheets carefully or contact a manufacture rep and ask.Lefty