Time for a redesign... :(

[Specter]

Ok so I was at a "end of the year/good job for the season" picnic for my robotics team today. I decided to bring my water balloon launcher, and both barrels (4 foot 2"diam, and #long 1"diam). Well there were about 10-15 people there at that point. One of the other kids saw my launcher and was like "I shoulda brought my spud cannon". Ok so I had the 2"diam barrel on and filled it with about 1.5 liters of water or however much 1 and 1/2 bottles of Lipton Green Tea (big bottle) is. Now I hadn't used my cannon since last summer, it was stored indoors in a climate controlled area. I didnt think anything could go wrong because i had shot water out of it before. (yes about the same amount) It was only charged to about 40psi.

Well I opened the valve and everything that could go wrong did. There was so much recoil(which i had braced for because i knew what it was like when i had shot it last summer) that the barrel literally shot off the rest of the gun. Now it was at an OK spot because it had just dropped to the ground and since of the difference in weight at such a quick time i also dropped the PC.(it was about an 18"drop for both because I was holding it low) Now i had looked to the left real quick because of the reaction from the recoil (seeing the cannon falling in my periferal vision) and when i finally look to the ground in front of me the only words that came out about 5 or more times were "AH CRAP!" (yes those specific words because there were other kid's younger siblings around)
The rest can be self explained. Here are pictures of the "damage" after I just got home around 9:00 pm.

Well I guess its time for a redesign. Gotta go to Home depot for about 3-5 dollars worth of PVC parts. What I plan on doing is cutting the reducer section off and put either another reducer & bushing > 1" male adapter. Or put a 2" coupling and use a 2" > 1" reducer bushing to the male adapter.
Or I can buy a couple elbows and do the over-under design like originally planned. Hopefully this will work better with a shorter barrel as well now that it will be shortened by 3 inches or so.
I'm guessing I will have to sand the paint off before I rebuild(re-glue/cement) the barrel?

I still had some fun with the 1"diam barrel.
Moral of the day to me is that I won't be shooting water out of the large barrel anymore. Only the small one.

Pictures coming soon. i had to restart my computer
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[Ben]

I'll wait for the pictures before making a more detailed response.

Shooting water out of water balloon launcher or spud gun barrels is problematic from what I've been read. The pressure must spike when the air hits the water. The result is massive recoil and sometimes explosions.

[Specter]

If you need better images I can try to take better ones.

[Ben]

I think you have the right idea if you don't have the PVC repair drill bit we discussed in this thread. Aside from that I can't make any suggestions other than to be sure to get all the paint off, which you already knew, but you can't sand too closely because it will affect the fit of the fitting. I've read that sanding the pipe before cementing isn't recommended by the manufacturers because it'll affect the fit, so if you don't use the repair bit be careful.

The repair drill bit might be best. You'd probably save money not having to buy pressure rated fittings again with it.

[Specter]

I told my dad about that drill bit thing (i already knew about that thread, thanks) and since it costs sround $22 I think it would be easier and cheaper to just cut the old fittings off, scrape off the paint and rebuild the section of the launcher.
As I said, I might buy a couple 90* elbows and rebuild it as an over-under design.

I have a couple more photos. I took them with all manual settings so they wouldn't be so bright.

[Specter]

Originally Posted by Attachments

The scratches on the male adapter were from trying to get it out of the ball valve.

[aEx155]

That must've taken quite a lot of force to do damage like that, but luckily you don't seem to have to do a lot.

Like Ben said, drilling out the pipe is probably the best way to go, but it you're not able to get one, you could always try removing the paint using something other than sanding...that, though, might affect how the PVC reacts to the cement/how good the bond is.

[Specter]

Drilling the pipe out may be easier, IF i had the tool(s). The problem is, I don't and it would cost at least $25 to get it when i can spend about $3-5 and get new PVC fittings. It's a much simpler solution. Home Depot is less than 1 mile away from me. I would ride my bike there to get the fittings for my now decommissioned cannon. (except when i bought the 10 foot length of 2" and1" pvc)

[Silence]

Wow, DX has warned us about not shooting water like this, due to the pressure spike and impulse force, as Ben said. But his barrel apparently wasn't even glued to the ball valve when it shot off. I think there was a later incident though.

Well, fortunately you're not hurt and this is a fairly cheap repair.

How far is the ball valve from the water? I'm guessing the farther it is, the worse the effects could be, because the air rushes faster and in more volume before being trapped by the water. At any rate, it's safer to just build a water cannon, which is the same thing but with the valve after the water, not before.

Would you mind if we used your detailed pictures in a warning about this? Pneumatic launchers can be dangerous and a warning is necessary if you ask me, now that we know.

[Specter]

Would you mind if we used your detailed pictures in a warning about this? Pneumatic launchers can be dangerous and a warning is necessary if you ask me, now that we know.

Not at all.
I was just surprised because I had shot water out of it last summer and there were no problems.
Since this summer is almost over, I will probably wait till the fall/winter to get some extra money to buy the fittings to fix the cannon.(by then I should also have my bank card to load all my money on to so I'll find a place online for cheap PVC parts)(I would use www.usplastic.com but their shipping is a bajillion dollars)
I don't know what I'll do about repainting the new fittings because I used all of the can of orange paint that I had (it was a leftover can with some paint in it that my dad said I could use).
I'm wondering if i should redesign it with an over-under design or keep the inline design.

[DX]

Shooting water out of a barrel of a launcher is one of the only things in water warfare that is genuinely dangerous. You can get away with it at low pressure, but a barrel full of water at high pressure is going to fly. The incident in Chatham was with rocks at 120, but the one with water was in my old backyard at only 80. In the former, the barrel wasn't glued, but in the latter, it was the pc that shot off and that was definitely glued. The thing rocketed off and missed my friend's head by a foot or two [hence why you should never stand directly behind a launcher].

Make a launcher/water cannon hybrid if you want it to shoot water. That's where the air pressure side of water cannons came from, just a WBL adapted for water. A simple curved cannon will deliver 100x+ at long range as well as normal balloons in a launcher barrel.

The choice of inline or over-under really lies in what you use the launcher for. Think field mortar vs support artillery. Inline is meant for action and ambushing, the pc is smaller, range toned down, reloading faster. Over-under is meant for show or supporting fire. More range, more impressive power, can have larger pcs and support more features as you don't have to worry about sprinting with it. On the field of battle, you might fire an inline launcher from 200 from literally in a bush vs firing an over-under from 600 in plain sight with protection. Now people do use inline launchers for show, but they perform better in combat.

[Specter]

Well, I'm at step 1 of rebuilding my cannon. I was with my dad when he had to go to Lowes to look for something. I went and looked at the PVC section. They have a much broader selection than the Home Depot which is closer to me.
I found 2 fittings which should help me fix the cannon. One is a 1" x 2" SCH 80 pipe nipple. and a 2" x 1" - slip x threaded bushing. Little did I know I would need a 2" pipe coupling. I didn't find out until I got home to see how the bushing would fit in the pipe and its the same OD as the 2" pipe. I thought that I wouldn't have to sand the paint off, but I guess I still have to.
Anyways I'm a little bit closer to fixing it. The 2 fittings cost only $2.60 including tax. (my dad paid for them, i didn't have my wallet)

[Ben]

Nice dog.

Using threaded fittings would be a good idea if you anticipate anything like that happening again, or if you just want the option of repairing or replacing parts in the future. I try to put either threaded fittings or extra space where I think they are appropriate and it's work well so far, though often after building I think "Why didn't I put one there?"

There are fittings that fit inside pipe too, but you have to order them off the internet from what I know. I've never used them but I remember running across them.

[Specter]

oh haha, i didn't even notice I put a picture of my dog.

and thanks for the advice. Yeah i've seen "inside-of-the-pipe" fittings too, but didn't think the thing i got would still need an extra piece.