For this ible I will be making a small scale model. There is a 3in by roughly 18in air reservoir which transitions down to a 1in by roughly 24in barrel. * I apologize for the gee by guesses, I actually made this PoC a few months ago and put it into storage when I moved. I am actually looking at pictures that I took while making it to write this. *
By reading this ible, you the reader, assume any and all responsibility in your attempts to recreate or modify this design.
Step 1: Parts Needed
18in x 3in PVC Pipe
3in PVC Cap
3in PVC Coupler
3in to 2in PVC Reducer
2in PVC Coupler
2in to in PVC Reducer
1in PVC Coupler (Despite the picture showing two)
1in PVC Cap (Despite the picture showing none)
24in x 1in PVC Pipe
Grease of any kind
Considering the price of a butterfly valve this is a relatively cost effective way to create a pneumatic device.
Step 2: Preparing the Parts
You'll notice in the first picture the inside lip is already missing. The second picture actually shows how I ended up removing the lip. Originally I started with a file but that made the inside too jagged. I ended up slowly rotating a scour pad by hand but figured I needed a faster way. You'll know you're ready to continue when the 1in PVC pipe slides through both couplers with little effort. You don't want it to just drop right through, make sure there is a little give yet but not much.
Step 3: Air Intake
WARNING MAKE SURE ALL YOU PRESSURE TEST ALL PARTS AT LOW PSI BEFORE PUSHING IT TO THE MAX. IF THERE IS A LEAK YOU ENDANGER YOURSELF AND MORE IMPORTANTLY YOUR HEARING. WHEN PRESSURE TESTING LISTEN FOR A SMALL LEAK SOUND. IF YOU HEAR IT PUT THE PNEUMATIC DEVICE DOWN AND GET A DECENT WAYS AWAY FROM IT. WAIT TILL THE AIR HAS FULLY LEAKED. THEN PUT VERY LITTLE PRESSURE IN IT AND LOOK FOR THE LEAK. IF IT CAN BE PATCHED WITH A LITTLE EXTRA GLUE DO SO. OTHERWISE START OVER. I WAS HOSPITALIZE WITH EAR DAMAGE WHEN I HAD AN PNEUMATIC DEVICE EXPLODE IN MY HANDS!
The first picture shows the valve stem in place. The second show the thread compound I used.
Step 4: Priming and Glueing and Assemblyy
Prime and glue the 3in coupler to the 3in pipe then prime and glue the 3in reducer as shown in picture 1.
Custom PVC Fitting
Take the 1in coupler prime and glue the bottom of it to the top of the 2in to 1in reducer. Take the 2in coupler prime and glue the bottom as well as the inside and force it over the 1in coupler you glued to the 2in to 1in reducer. Push it all the way down. Pictures 2,3,4, and 5 show you what the final product looks like.
The 2in coupler over the 1in coupler is just for extra strength. While it isn't necessary, I highly suggest it. All in all this custom PVC piece is roughly 3 inches in length.
Now prime and glue the 1in cap to the 1in pipe. Measure 1.5in from the cap and drill a hole straight through the 1in pipe. Take your o-ring and slide it down the 1in pipe till it meets the 1in cap.
"Assembly Part 1"
Slide the 1in pipe through the custom PVC fitting. See Picture 6 and 7. I put a little grease around the o-rings to help air from leaking out.
"Assembly Part 2"
Prime and glue the custom PVC fitting and attach it to the 3in to 2in reducer. Finally Prime and glue the 3in cap the the opposite side of the 3in pipe. Allow several hours to fully cure. See picture 8 for fully assembled PoC.
Step 5: How to Use
Now I promised to tell you the downside to this PoC. Once there is pressure in the reservoir it tends to get pretty difficult to pull the barrel back to release the pressure. Although if cost is an issue this is a definite win.
Possibilities for this PoC would be to shot projectiles into the air a quick release drop valve. Let your mind go wild. ENJOY!