My Piston Valves
Table of Contents
- First Piston Valve and Earlier Derivatives
- Controlled Equalization
- Compacting Valves and DFTV Setups
Over the years I have built various piston valves in different materials (plastic, steel, copper... etc.).
The following page is a chronology of the valves I have built (for the most part). They are all plastic since that's the material I started off working with.
Back when I first started this hobby, piston valves weren't as well documented as they are now. the Pneumatic King clide started off earlier than I did, and had an admittedly much rougher time hacking things out, and was an early inspiration. I mainly learned how to build these valves hanging on the coat tails of an earlier Spudtech.com forum member Rmich732 who built similar valves that I subsequently used as templates.
So, here's a step back in spudding history.
First Piston Valve and Earlier Derivatives
I built my first piston valve in 2006. It had a 1-1/2" SCH-40 port (1.6" diameter outlet), and a 2" piston. For sealing and equalization, I merely wrapped the piston (a piece of 1-7/8" type II PVC round stock) in duct tape and coated it with petroleum jelly. To make up for the lack of controlled equalization, I used a 1/4" quick-exhaust valve for piloting.
The original cannon used a 2" chamber and 1-1/2" SDR-26 barrel for golfballs. I eventually hacked the valve portion off of this cannon and replaced the chamber with a 3" one, and the barrel with a 2" SCH-40 one for shooting tightly rolled T-shirts (among many other things).
After building this valve, I was talking at somebody at school the next day, mentioning piston valves, and stated that I could build a small one in one evening with no problems at all.
So, I built a smaller marble gun using a 1" piston and 1/2" SCH-40 outlet, utilizing a 1/4" ball valve pilot.
It was at this point I realized piston valves weren't complicated at all, and one could be made practically out of trash if one desired.
The attitude of the community at large changed to reflect my own throughout 2007 and 2008, and many more people started building them for even their first cannons.
Of course, wrapping a piston in tape and smearing it with lube wasn't the best way to go about controlling equalization around the piston.
I built a standard barrel sealer out of PVC pipe and fittings in 2009, utilizing a method that had been floating around for a while of using 1-1/4" pipe and fittings to make o-ring grooves for the piston. 1-1/4" socket fittings will fit in 2" pipe (with a little play), and the 1-1/4" pipe itself (or spigot fittings) can be used as the "bottom" of the o-ring groove. By hacking apart fittings and then gluing them together with spaces for o-rings, simple grooves can be created, and tightened up slightly by wrapping the bottoms with teflon tape.
I built a valve identical to the schematics on my piston valve page (indeed that's when I drew them up), and mounted it to a length of 2" pipe for testing.
To control equalization, I sealed the piston off completely using o-rings (as you can see), and drilled a very small equalization hole for air to flow through.
I had a video of testing this valve, but due to stupidity it is gone (I deleted my Google account before I could download all of my YouTube videos).
It actuated with a crisp "pop" though, and the bumper was more than adequate. If I ever built another simple outlet-sealing piston valve, this would be the template.
Compacting Valves and DFTV Setups
I had earlier attempted to make a more compact valve (with all components contained within a 2" tee), but it fell apart due to shoddy construction methods.
In 2011, I attempted again to make a valve completely contained within a 2" tee, and also with a DFTV operation.
Due to constraints on building at the time, though, and the fact I was nervous about the build and its reduced surface area for PVC glue to work on, I wound up not finishing the valve... which would have merely required a piston to be built and installed in the "shell".
I still have this lying around, and after some hydraulic testing, may incorporate it into a launcher, although PVC is not my material of choice these days...
I have built more valves than these... the one on Thorondor is probably the best performing one. These are merely some of the first few I've made, and a couple to illustrate the progress I (think I) made.