Servo - December 2015

56 SERVO 12.2015

valve actuation and not really increasing the maximum possible flow through the diaphragm. This often involves doing something like replacing the solenoid with a blowgun valve, so the diaphragm can be actuated by a very rapid pressure change. We could understand how increasing the valve actuation speed could be the chief concern with smaller pneumatic devices like your classic spud gun. The chamber and barrel diameters in a spud gun are usually much smaller than our behemoth of a punkin chunker (soon to be a Christmas cannon).

In our Mark I, however, the speed of the valve actuation didn’t seem to be the main limiting factor. The problem was the limited flow through the diaphragm which was aggravated by the fact that our chamber and barrel diameters were so much bigger than the valve. All we wanted for our Christmas cannon was a new valve.

Jingle Ball Valves

Our initial instinct was to look for a larger electric valve. Ideally, we wanted a valve with input and output pipes that were as close as possible to the chamber and barrel diameters because this would minimize that pressure drop. We also wanted to find a valve with a lot more airflow than the small diaphragm in a sprinkler valve.

Finding an affordably priced, pressure-rated, large diameter electric valve was a little like scrambling to find a coveted Turbo Man doll on

Christmas Eve, however. Large electric valves like what we were looking for do indeed exist, but when you’re talking about such large pipe diameters that usually means you’re getting into industrial applications with very expensive valves. There had to be a way to get at what we wanted without breaking the bank. As we were perusing valves, we found that there were plenty of manually actuated valves in the sizes we were looking for that were also affordably priced. We figured a manual ball valve would be the way to go because we could add our own actuation to it later. It could be tricky, but no trickier than when the Teenage Mutant Ninja Turtles had to find Splinter a last minute gift on Christmas Eve. We returned to the specialty pipe store we discovered last time, and they had a smorgasbord of ball valves that had us feeling like kids in a toy store. They even had four inch valves. We wanted to get a sense of how tough they would be to actuate, so we tried opening and closing them, but to no avail. The four inch ball valves were as stubborn as the Burgermeister Meisterburger’s aversion to toys. We found that the three inch valves were much easier to actuate, which we thought would help us tremendously for initial manual testing. As it turns out, the slightly smaller three inch valve was probably the best choice. The pressure drop was definitely much less than the throttling that happened between the one inch valve tube and the four inch barrel, and the slightly smaller diameter actually created a useful backstop for projectiles that kept them from falling back through the valve when it was open. Unfortunately, creating the Mark II wouldn’t be as simple as swapping out the valves. The chamber and barrel LIKE THREE FESTIVUS POLES.