(Somehow this took longer to write than it did to make. This may have something to do with the fact that I have to share this computer, but I don't have to share my tools.)
It all started innocently enough. I was in a production of a Midsummer Night's Dream, and it was decided that for this production the cast party would be a water fight. Mind you, the only other thing I had that counted as a water gun was a small spray bottle that leaked a lot and had a range of about 7'. So my words on the occasion were, "If I bring a water gun, I will build if myself."
And wouldn't you know it, I did.
This is a powerful water gun, make that cannon, capable of delivering over a quart of water 25' or more, and due to its dangling hose design your reservoir can be as large as you want (I use a 5-gallon bucket). However, that same feature makes it cumbersome to carry around while in use; I just intended it for it to be stationary. All the parts are available for about $60 from Home Depot, and probably from Lowe's, although some parts were only available through the Home Depot website.
Step 1: Acquire Parts
The parts list is as follows:
2' of 2" PVC pipe
I believe this size is available precut in 2' lengths. But get 10' , this is mighty handy stuff.
2" of 1-1/4" PVC pipe
This is the first time I've ever had to use this size, so I got 2'.
2' of 3/4" PVC pipe
Alright, get the 2' lengths if you have to. But get 2 of them, as you'll need more for the connector tubes.
~1-1/2" of 3/4" PVC pipe (4)
For use as connector tubes. Length isn't critical.
3/4" PVC slip tee fitting
3/4" to 1-1/4" PVC reducing bushing
1-1/4" PVC coupler
1-1/4" PVC end cap
FRONT END PARTS:
2" PVC slip tee fitting
2" to 3/4" reducing bushings (2)
This part does not actually exist, so use whatever combination of fittings you have handy. I was going to use 2" to 1" and 1" to 3/4", but I ended up using 2" to 1-1/2", 1-1/2" to 1", and 1" to 3/4".
3/4" PVC end cap
3/4" PVC threaded adapter
A small (1" wide) hoseclamp
REAR END PARTS:
2" PVC threaded adapter
2" PVC cleanout plug
3/4" PVC in-line check valves (2)
More about O-ring sizing later.
5/8" to 3/4" FPThose barb fitting
5/8" ID tubing
I used 5/8" ID by 7/8" OD clear vinyl tubing. It comes in 10' lengths; I used the whole thing.
(Note: never fear, these parts will be shown later on.)
TOOLS AND SUCH:
Extra coarse, medium, and fine
Coarse round file
Or rotary tool
Drill, bits, and Unibit
Vise (or clamps)
PVC primer and cement
If you don't already have these, get the clear kind of both if available.
Thread sealing tape (Teflon Tape)
Electrical tape (if necessary)
Grease (Vaseline works)
Spray paint (or acetone)
Step 2: Dry Fit
Make sure all the PVC parts fit properly. Bushings especially tend to flare out slightly near the end and often do not fit, but a light sanding with extra coarse, medium, and then fine sandpaper soon fixes this. Note that the fittings and pipes don't have to fit all the way as shown in the picture, just about 2/3 of the way, as the PVC cement dissolves the outer layer slightly.
Step 3: Modify the Cleanout Plug
The cleanout plug is where the piston rod exits the cylinder, so it needs modification. Cut about 1/8" off the square end, then deburr it and widen the inside with a file or rotary tool until the piston rod fits through with a small gap as shown.
Step 4: Modify the End Cap
The end cap now becomes the nozzle. To mark the center of the cap: place some sandpaper at the bottom of a door frame, then hold the cap and the sandpaper against the door frame as shown and rotate it slightly to mark a spot on it, then use an awl to mark the center of that. Now you want a clean-edged 5/16" hole through it. A Unibit is best for this. You can use a drill press, or my bodged together drill press substitute design that use a V-Drill Guide (http://tapguide.com). Oh, and if you use a regular twist drill bit, start with a small size, as they're less likely to catch.
Step 5: Start Solvent Welding Stuff
I'm assuming you already know how to solvent weld. If not, it's simple process: follow the directions on the can(s).
Cement the 2" tee onto one end of the cylinder and the 2" threaded adapter onto the other, then the 2" to 3/4" bushings in the tee, then a 3/4" connector tube in the bushings. Now cement the check valves in place, and no, I will not forgive you if you cement them in backwards. There's an arrow on each valve to make it easier. Next is another connector tube in each check valve, followed by the end cap/nozzle on one and the 3/4" threaded adapter on the other.
Now onto the piston: cement the 3/4" tee onto the piston rod, then (and this is the important part) slide the modified 2" cleanout plug over the piston rod before cementing anything else on the end. Now cement the 3/4" to 1-1/4" bushing onto the piston rod, then the coupler, then the 2" of 1-1/4" pipe, and then the end cap, leaving a 3/16" gap between the coupler and end cap. A 3/16" metal rod can help with this. Set everything to cure overnight.
Step 6: Finishing
At this point some of the parts were still in the mail, so I decided to finish it while it was still unfinished. If you use clear primer and cement and make neat joints you can just remove the factory markings with acetone. Since I use purple primer, I decided to spray paint it. Krylon Fusion paint bonds well to PVC without primer, just a quick sanding with 320 grit sandpaper. In the photo you can see how I hung the body with twine, then masked off the ends of the connector tubes. Several coats of paint should cover both purple primer and factory markings.
Step 7: O-Ring Installation
The instructions for the PopSci design I was basing this on were a little sketchy, so I ended up getting a 1-/14" by 3/16" O-ring, which has too small an ID. As a result the piston was really leaky, so I shimmed the gap with electrical tape until it fit. When I get the proper O-ring size I promise I'll post it.
Step 8: Tubing Installation
Now comes the tubing. Wrap the threads of the hose barb fitting with Teflon tape in the direction oppositeof the way it's screwed in (to ensure a good seal), then screw the fitting in with a wrench. A slight gap is okay. Now jam the tubing onto the the end and hoseclamp it.
Step 9: Add a Filter
This is to prevent all sorts of nasty junk from getting sucked up the tubing and into the gun. Just cut a circle with tabs out of a window screen patch, fold the tabs back, and electrical tape it to the end of the tubing as shown. At this point, you're done.
Step 10: Use It
Like you need me to tell you to.
Usage is quite simple: pull to load, push to fire. Remember, kids, safety first: don't shoot people who don't want to be shot, and don't shoot people at close range. Other than that, have fun!
P.S. It turns out everyone else at the cast party had squirt bottles similar to mine. Go figure.