I've built several of these over the years. This one is the is one of the better designs I've come up with. This should be thought of as a launch system, and not just a launcher. If you you experiment with pipe sizes both in the launcher and the barrel, you can change the load out for all sorts of projectiles. I built this one to shoot paper rockets.
Use this with caution! Filling the tube too quickly may cause the glue joints to rupture! (I've never seen it but if you're not cautious it could...)
I'm sorry if my directions are hard to follow... Please refer to the pictures often! I will try to ensure they match the steps.
Step 1: Pieces and Parts...
These sizes and lengths are based on what I used, you can change these as you see fit. You should read my thoughts on varying pipe sizes on the last step!
All PVC should be Sched 40!
What you will need:
30" section of 3" PVC
5' section of 3/4" PVC
1 - 3" Cap
1 - 3" to 1.25" Reducer
1 - 1.25" to 3/4" Reducer
1 - 3/4" T
1 - 3/4" Check Valve (Can be replaced by a gate valve - RECOMMENDED)
1 - 3/4" Slip to 1/2" Female Threaded Reducer
2 - 3/4" Slip to 3/4" Male Threaded Adapters
1 - 3/4" Ball Valve (Don't be cheap, go with the brass! The handles turn easier and faster and last longer!
1 - 1/2' to 1/4" (Brass) Threaded Reducer
1 - 1.25" to 3/4" Reducer
1 - 1/4" Male Threaded Air Chuck (Male)
1 - Roll Teflon Thread Tape
Channel Lock Pliers
PVC Pipe Glue and Cleaner
Step 2: Just a Little Twisted!
Now that you have all the parts and tools, start the assembly with the threaded parts.
Wrap 2 to 3 rounds of thread tape on the air chuck and thread it into the 3/4 to 1/2 Brass reducer.
Thread tape and attach the 3/4" to 1/2" brass adapter into the 3/4 slip to 1/2" threaded reducer.
Thread tape the 3/4" slip to male threaded adapters and screw one into each end of the ball valve.
Putting all the threaded bits on the Slip parts before gluing will help ensure you get a good hold when gluing.
Step 3: Stick to It!
Glue the 3" cap to one end of the 3" pipe.
Now glue the 3" to 1.25" reducer to the other end.
Finally glue the 1.25" to 3/4" reducer into the reducer on the 3" pipe, place this assembly to the side.
Glue a 3" section of 3/4" PVC to each end of the T. Glue the ball valve assembly to one of the stems, then glue the check valve to one of the other ports.
NOTICE! Before attaching the Check Valve ensure air can flow towards the T, not way. The valve should be marked for flow direction.
Glue the Air Chuck assembly toe the inlet side of the check valve.
Finally take the new fill / valve assembly (Just created) and glue the remaining stem to the 3" tube created earlier.
Allow the glue to dry for at least 30 minutes before pressurizing! 30 minutes may be longer than needed to better safe than injured!
Step 4: Enjoy!
This launcher can be used to lots of projectiles!
If you wanted to use a 1 inch barrel you should use 1" through out the assembly. (Replacing the 3/4")
You can use 2" or larger for the pressure chamber but I wouldn't go smaller than 2". I've used everything up to 6" and can't tell much difference in 3" and 6".
The pipe in your valve assembly should never be smaller than your barrel, and you pressure tube should generally be 3x the size of your largest barrel. this will provide enough air for expansion.
BE VERY CAREFUL THIS IS NOT A TOY. I have used one of these at very high pressure and it will set a 12p nail at 25ft. You can kill someone if not used with care.
My rocket wasn't set up for 110psi. LOL No harm no foul!