3d printed parts are most likely going to leak.. and pla would certainly not be the right choice for a part that could burst. Nylon/EPA, Taulman Alloy 910, maybe PETG, but no way would I attempt using PLA. 3mm may be think enough to hold air printed 100% depending on the surface are that is 3mm think but you would need to test at low pressure to see if it will leak. I have no experience with what you are trying to do, but I was an auto tech for 10 year and have and still use compressed air on a regular basis. Prototype with PLA and test it where no one but you can get hurt if it cuts loss.. good luck