Pressurized Container Automation
There are potential safety concerns using a pressurized vessel for use outside of its design parameters. An air pig can easily be purchased with known ratings and pressure relief built in. Couple an air Pig with a pressure regulator and you'll have yourself a portable pressurized vessel that is safe and dialable. This is an example of an air pigwww.homedepot.com 

A regulator
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You won't get much use out of it in between charges due to the volume of the pressure vessel. To get a usable amount of air in the tank you may need to recharge frequently in order to do that you may want to get a portable air pump. 

Battery operated air pumphttps://www.googleadservices.com/pagead/aclk?sa=L&amp;ai=DChcSEwi7mov9_IHhAhWXtcAKHd3XCHkYABATGgJpbQ&amp;ohost=www.google.com&amp;cid=CAESEeD2amOzOw3QuE2L556cw1ed&amp;sig=AOD64_2n1jgSPZIA_daVlU_5O156gmhCYA&amp;ctype=46&amp;q=&amp;ved=2ahUKEwjp-IP9_IHhAhWO_YMKHVMCBokQzzl6BAgLEAc&amp;adurl=

Milwaukee also makes an digitally set battery operated air pump but I don't know the range. My friend has it. But I don't know if it goes down to 12psi. 

Edit

It does, here's a link. It's available in m12 or m18

milwaukee m12 pumphttps://toolguyd.com/milwaukee-m12-cordless-inflator-review