The picture to the left shows the "boiler" connected to a wobbler engine I built. Fully charged, it can run the engine for about two minutes - not very long, but long enough for a quick demo, and much more convenient than using the compressor in my garage, or a large portable air tank.
This was a fun cheap project, but it was cheap only because I picked up the "boiler" for next to nothing (a new one would have cost around $60 - $70).
The heart of the system is a "Sure Shot" sprayer I picked up at a garage sale. A quick web search shows that the Sure Shot is still manufactured and sold by Milwaukee Sprayer. As you can see from the photo below left, the unit came with a brass spay nozzle, a pressure gauge (probably a later add-on replacement for a relief valve), handle with thumb trigger, and a bicycle type valve for pressurizing (the valve assembly also unscrews so you can fill the container). I had no idea if the unit still worked, or would hold pressure, so I was pleasantly surprised when I got home to find that it was in perfect working order, although a bit scratched up and dirty.
The "Sure Shot" sprayer as purchased.
Close-up of label.
Close-up of label on reverse side.
I removed the labels with some solvent, cleaned the outside thoroughly with some "soft-scrub" kitchen cleaner, and gave it a nice polish. The plastic cover on the pressure gauge was a bit yellowed, so I removed and cleaned it also. I unscrewed the spray nozzle and replaced it with a pressure regulator, using a custom machined adapter (and another adapter on the exit side to fit plastic tubing).
A hardwood stand was constructed to hold the unit (red oak coated with clear wipe-on polyurethane). The stand includes a levered cam to activate the thumb trigger and quickly turn the air supply on or off.
A pressure regulator (top) replaces the spray nozzle.
A levered wooden cam acts as an on-off switch.
Using my small pancake compressor, I am able to pressurize the unit to about 100 psi; this is sufficient to run a small wobbler engine for about two minutes. Here is a short video of the unit in action (click photo to see video):