"pneumatic pressure booster"
I need an electric device that can increase pressure in a sealed case. I assume it would have a piston and when electricity was applied, it would move forward and increase the air pressure in the box. Does such an off the shelf device exist?
You cannot increase the pressure inside a sealed box without some kind of gas input, unless of course you cause a chemical reaction inside the box that creates gas, or create a vacuum in an enclosed portion of the box. How much pressure are you after? A simple air pump that can achieve your pressure should do the job. For low pressures, something like an aquarium pump or higher pressures, a portable tire pump, electric or hand.
Pneumatic pressure booster
I'd go with Timelord: air pump or tire pump for higher pressure and simple hand tire pump for low pressure
Just as a ********** to the use of the above devices, if you require isolation of the gas inside the box then one possibility is to use an elastomeric bladder in the box (expanding this with air/gas pumped in with either of the above devices will then increase the pressure of the contained gas in the box). A simple pressure switch on the pressure supply connection to the box bladder will control the maximum box gas pressure.