The __jrP4__ - Junior Portable Pnuematic Projectile Propogator





Introduction: The __jrP4__ - Junior Portable Pnuematic Projectile Propogator

About: Just making things.

I have wanted to make something like this for a long time, but couldn't quite figure it out. Thank you to Scott Scriven - - for the idea.

Here was my goal:
1) Handheld
2) Air powered (relatively safe)


Step 1: Plan and Gather Parts

Parts list:

A. ~ 2' of 1/2" pvc (schd 40 or 80).
B. ~ 1' of 1 1/2" pvc (schd 40 or 80).
C. Some combination of fittings to go from 1/2" FS (female slip) to 1 1/2" FS. I picked up a few different combination of fittings, each of them producing a little different look. For this gun used a 1/2"FS x 1 1/2"MS and a 1 1/2" FSxFS.
D. 1 1/2" FS x 1 1/2" FT (female threaded).
E. Some combo of pieces to go 1 1/2" MT x 3/4" FT. I found a single fitting for this, but you may have to use multiple.
F. 3/4" MT x 3/4" FT elbow.
G. 3/4" MT end cap.
H. Two tank valves.
I. What they call a "Valve extender". This fits onto the tank valves and has a plunger to release the air. I have some other ideas on what else could replace this, but this is the most straight forward method.
J. Some semi-flexible rubber (or maybe plastic) material for the diaphram. I used some sheet gasket material.
K. Teflon pipe tape (not shown).
L. PVC cement (clear is best, to keep it looking clean).

You will need a drill and a tap set also. To thread for the tank valve, you need a 21/64 drill bit and 1/8-27 NPT tap head.

Step 2: Build Firing Chamber

This was the eastiest part of the assembly:

1) Cut (B) to the desired length. I went for about 8".
2) Cement (C) to (B). Cement (D) to the other end of the (B-C) assembly.

Step 3: Build Barrel and Diaphram

1) Whatever you chose for your parts for (C), you need to remove the stop ring on the inside of the 1/2" FS, so the 1/2" pipe will slide through it instead of just fitting on the end. I used a sanding drum on the end of a dremel.

2) Cut the diaphram to just barely fit into the inside of (D) (1 1/2" FT). It should fit freely, but not have a lot of room to slide side-to-side.

3) This is the most critical step in the process. Take the time to understand how the gun works. The inside end of the barrel must be flush with where the diaphram sits on the 1 1/2" FT end of (E). To do this, set the diaphram on the end of (E), holding it upright, and screw it into the chamber until it is snug, then back it off a little. Still holding it upright, slide the barrel in until it sits on top of the diaphram. This is where you want it cemented. Mark the location where barrel enters (E). Remove (E) and the diaphram and then cement the barrel in, making sure to keep the end centered in the chambe where it will meet the diaphram.

Step 4: Build Inlet and Trigger Valves

1) Drill and tap the trigger elbow (F) and the inlet valve end cap (G). You will need a 21/64 drill bit and a 1/8-27 NPT tap.

2) Wrap the threads on both of the tank valves and screw them in.

3) Wrap the 3/4 MT on (F) and (G).

4) I ground off the end rim on the valve extender so that the plunger could be pushed down flush. Then, attach it to the valve on (F).

Step 5: Final Assembly

Almost there.

1) First screw (F) and (G) together.

2) Screw the (F-G) combo into (E) very tightly (so you don't have any slip left when you seat the diaphram).

3) Wrap the 1 1/2 MT of (E). Lay the diaphram in place and screw the (E-F-G) assembly on until it just sits with the diaphram.

4) Before you attach the pump, test it out. I put about 20 lbs into it, shoved some tissue in the barrel and pushed the trigger.

5) Attach the pump and secure it to the chamber. I cut a small length of PVC, indented the ends to match the chamber and the pump, held it in place with a couple of zip ties and wrapped it all with electrical tape to keep it in place.

Step 6: Next Steps

So, what is next?

1) Install a new diaphram. The one shown here seemed to wear out after about 50 firings. Maybe too flexible?

2) Get a new pump, like this:,MW-INTTOPP.html

To make it a cock action gun.

3) Make one out of clear PVC, if I can justify the $$$$.

4) Make on out of brass.

5) Try out some different triggers. I have about 6-7 ideas floating right now.



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    I used galvanized

    It is rubber a little less than 1/8 in thick. I think you can get it in the plumbing supplies, but I just had it sitting around in the garage.

    yes, yes there are. But there are also funner ways which are incredibly dangerous and reletively idiotic. Either way, cheese wins Except it must first betray wisconsin to stupid cheese heads

    I Got the same computer ITS SO GREAT!!! also good instructable

    i have seen it many times, and still dont get it. what is the PVC ring with the blue ring? what is the blue ring?

    4 replies

    Do you mean the roll of teflon (R) tape - used to seal the pvc thread fittings?

    well is that the blue thing? what is teflon tape for? and why is it in that peice of PVC?

    Yes, that is a spool of teflon tape. The white piece around it is the cover for the tape spool (plastic but not PVC). Anytime you put a PVC threaded joint together, you should use teflon tape. The tape should be wrapped in a clockwise direction on the male fitting - to match how the threads will grab tape. They make special tape (yellow?) if you are using PVC for gas (natural or propane), but for normal water or electrical PVC the white tape is the thing to use.

    oh, okay. thank you. so you can just get it like at a hardware store? thanks for your help. lol.

    I made something like this but way bigger, took 10 min. to pump up, and could blow babies apart at 20 feet.

    1 reply

    I made several potato cannons... after reading about them online several years ago we decided that the sprinkler valve model would suit us best. If i can find pictures i'll upload them the thing looked harsh, it was 6 feet of tubing with a U shape, so only three foot total length. the chamber to hold the air was 2.5" by three foot, with the stuff to bring it down to the 1" tubing used by the valve. the valve had a 24 volt solinoid, i think it was supposed to be AC 24V, but we used 4 9V batteries hooked up to be 18V X2 in parallel. the switch was just a dinky pushbutton. the batteries and the pushbutton were mounted inside of a 2" PVC section that was then taped and later glued to the barrel. the barrel was either a 3/4" or 1" 2' long pvc pipe. i can't recall anymore. anyhow the chamber had a threaded bicylce tire nipple on it, and you'd charge it to 120PSI. load your ammunition into the barrel and push it down. SLing it over your shoulder, aim down the chamber and press the button, and FFFFFFFFFFFFWOOOMP, out came your projectile. the only method i've seen that's better for the pneumatic ones is using a diaphragm, but i could never figure out the instructions for those types. My favorite potato gun ever was one we made out of a 2 liter fire extinguiser and a length of exhaust pipe (from a car). We epoxied the two together, them wrapped heavy duty duct tape around the entire thing. drill a hole at the bottom of the fire extinguisher, and pour in your naptha (lighter fluid). spin the thing in the air horizontally to allow the mixture to get more oxygen, load it with an orange or whatever you want, set it on the ground and light it with a BBQ lighter. man that thing is loud, and it sent oranges sailing 2-3 blocks away if you aimed it right. :-D

    1 reply

    The best and easiest potato cannon I ever put together was just a straight cylinder with about a foot and a half of 6 inch diameter PVC joined to 2 feet of 3 inch. I capped the big end with a screw cap so that it can be removed and inserted a pezioelectric grill ignitor. Sealed all of the joints, wrapped the combustion chamber in duct tape to control shrapnel as these will occassionally explode as you up the anti, and it was done. Jam a potato (an apple is a softer projectile, and a balled sock will just knock the wind out of someone at close range) on the end, use a pole to force it to the beginning of the barrel (at the end of the combustion chamber), and you're almost done. The most important part is the fuel. Anything combustible works. Hairspray, starter fluid, paint, whatever. Airisol is easiest. However, for the potentially dangerously powerful result, you need to generate dry-particle spontanious combustion. Degree brand airasol deoderant works the best for me. Unscrew the end, spray for just a second, definately not as long as two or the fuel mix ratio starts to go, quickly recap, and press the button. I've put a potato through a quarter-inch piece of plywood with this design.

    again see how stupid i am! haha i accidently put "right" instead of "write" lol just gotta take that english class one more time...

    srry guys im new to this! first awsome instructions although why do you need the 2 inch 1/2 foot piece of pipe and sec. how do you load the ammo, third where can i find these valves ive asked evryone!! i even went to lowes & home depot but no one knows what im talking about! i feel so stupid :/ lollololo. ok enough drama but anyways can someone right back explaining atleast one of these ques.?

    I made a bigger diaphram valve type model a few years back, this is much more portable and compare faveribly to the biggergun.

    Lol! loving the sound it makes

    cool project. I made something similar to this a few years back. It wasn't quite as portable as I used a tire valve and a automotive air pump. I put a potatoe halfway through a wheelburrow at about 175 psi..... if anyone tries this modification, make sure to check the pressure ratings on your pvc (i think mine was rated for 250). too much pressure and you could end up with plastic shrapnel in your head. pneumatic guns can be quite powerful at higher pressures.... use caution.

    Great project! I tried to do something like this last year using an old pop gun design but modified to fire wine corks. Living in the wine country we got lots of those! Could be fun. I like your design. how's the valve work?