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Saftey question

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Saftey question

Unread postAuthor: Zagi » Fri Jul 03, 2009 2:57 am

Hey guys,

I just finished building my second spud gun today (has not been fired), but am having some doubts how safe it actually is. After some prodding from the guy at Lowes, I wound up buying non-pressure rated 4" cellcore for the chamber.

Lowes guy was convinced the gun wouldn't develop enough pressure to explode the chamber, but I have my doubts.

Heres some specs for ya'll to decide.

Fuel is metered propane.
Cellular Core PVC-DWV Schedule 40
Chamber is 20" overall length with cleanout plug at the end.
Barrel diameter is 2"

So, is it safe? Or should I rebuild?

Thanks guys
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Last edited by Zagi on Fri Jul 03, 2009 3:00 am, edited 1 time in total.
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Unread postAuthor: inonickname » Fri Jul 03, 2009 3:00 am

Is it PVC or ABS? Cellular core abs is much more common.

If it's cellular core PVC then it is most certainly not safe.

ABS is much safer because if it fails, it fails in a way that wouldn't result in you being schrapnelled.
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Unread postAuthor: Zagi » Fri Jul 03, 2009 3:01 am

Says PVC-DWV on the side of the pipe... So I assume its PVC?
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Unread postAuthor: Moonbogg » Fri Jul 03, 2009 5:16 am

If its PVC cellcore i'm afraid you'll have to return it and trade for ABS cellcore. Hopefully you can trade still. PVC cellcore is too weak and brittle and it will fragment. ABS is much tougher and has been used countless times for combustions for many years.
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Unread postAuthor: inonickname » Fri Jul 03, 2009 6:10 am

Yep. ABS cellcore was even used in Tech's pneumatic. It's annually tested to 100 psi without fail. I'm sure he'll chime in with a pic soon.
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Unread postAuthor: Zagi » Fri Jul 03, 2009 4:52 pm

Tried every building supplies store in town (small town) and no one carries pressure rated pipe larger than 3". Unless sewer pipe is pressure rated. The guy who worked there couldn't give me an answer. And no one carries ANY abs pipe, period. Looks like I'm out of luck until I can drive up to Tulsa...
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Unread postAuthor: Technician1002 » Fri Jul 03, 2009 4:59 pm

For a small town, try the farm supply for irrigation pipe. May have to hit a neighboring town. Many irrigation sprinkler systems use 3-6 inch pressure pipe.

You hit the right place if they have galvanized livestock water tanks out front.

Here is an example line of pumps with 6, 8, 10, and larger inch outlets.
http://www.wolfpumps.com/vertpump.html
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Unread postAuthor: Zagi » Fri Jul 03, 2009 5:01 pm

Have a farm supply just 2 miles from me. We'll see what they've got. Thanks :thumbup:
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Unread postAuthor: Zagi » Fri Jul 03, 2009 5:11 pm

Got smart and called rather than burn my gas... Strikes on both. And I live in the largest town in the county. Heh
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Unread postAuthor: Zagi » Fri Jul 03, 2009 5:59 pm

I apologize for the triple post, but would this strengthen the chamber enough to withstand temporary use (Just for the fourth)?

4" to 4" fittings end to end. Would the double layer give the chamber enough guts to withstand 20-30 shots? Until I can get to a large store on Monday.

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Bad picture, but hope it gets the point across better than my words.
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Unread postAuthor: Technician1002 » Fri Jul 03, 2009 8:32 pm

Zagi wrote:I apologize for the triple post, but would this strengthen the chamber enough to withstand temporary use (Just for the fourth)?

4" to 4" fittings end to end. Would the double layer give the chamber enough guts to withstand 20-30 shots? Until I can get to a large store on Monday.

Bad picture, but hope it gets the point across better than my words.


It is only as strong as the weakest part. A failure between couplings, or in the couplings between the pipe segments is your weak parts. Generally the joints are weaker than a pipe. The pipe with joints in a row is not recommended. Sorry.

inonickname wrote:Yep. ABS cellcore was even used in Tech's pneumatic. It's annually tested to 100 psi without fail. I'm sure he'll chime in with a pic soon.


That cannon is only tested to 85 PSI every year and operated from 35-65 PSI. The thought of a failure at 100 PSI scares me. Someday I may fill it with water and hydrostatic test it to 100. In the past I had it to 100 once.

Oh the pictures.. the link instead with pictures..
http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html
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Unread postAuthor: Zagi » Fri Jul 03, 2009 10:06 pm

Well, as it turns out, I managed to get all the parts I needed before the end of the day. Called my friend (who happens to be the retired city engineer) and he hooked me up with some scrap pipe and fittings. I forget the type of tubing (huge alpha numeric name), but he said it would take 200psi no problem.

My July 4th plans are saved. lol
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Unread postAuthor: jimmy101 » Sat Jul 04, 2009 10:59 am

In my experience cell core 4" PVC is OK for any propane combustion gun at 1X.

Peak pressure, even with a heavy tight fitting ammo, is only in the vicinity of 60-70 PSIG, which the pipe can handle. If your operating pressure is higher than that then the cleanout plug will probably be the first thing to fail. Cleanouts are always DWV parts since cleanouts aren't used in PWS systems.

But, pressure rated pipe is always better. Thought you still have a DWV only piece (the cleanout plug).
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Unread postAuthor: Technician1002 » Sat Jul 04, 2009 11:24 am

jimmy101 wrote:In my experience cell core 4" PVC is OK for any propane combustion gun at 1X.

Peak pressure, even with a heavy tight fitting ammo, is only in the vicinity of 60-70 PSIG, which the pipe can handle. If your operating pressure is higher than that then the cleanout plug will probably be the first thing to fail. Cleanouts are always DWV parts since cleanouts aren't used in PWS systems.

But, pressure rated pipe is always better. Thought you still have a DWV only piece (the cleanout plug).


In the Cellular test cannon, for strength, it originally had a 2 inch schedule 40 female fitting and schedule 40 plug for strength. (they exist) It was brittle and the female fitting shattered on a shot. Good thing I was wearing good leather shoes. Bad bruise, but no cuts or broken toes.

In my experience cell core 4" PVC is OK for any propane combustion gun at 1X.


ABS doesn't have the tendency to shatter like PVC.

Went to a better bumper and an ABS clean out to fix it. It has not failed.

4 inch cleanouts do tend to blow off combustion cannons.
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Schedule 40 pipe plug
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Unread postAuthor: jimmy101 » Sat Jul 04, 2009 12:18 pm

Technician1002 wrote:In the Cellular test cannon, for strength, it originally had a 2 inch schedule 40 female fitting and schedule 40 plug for strength. (they exist) It was brittle and the female fitting shattered on a shot. Good thing I was wearing good leather shoes. Bad bruise, but no cuts or broken toes.

You mean of course that;
1) SCH 40 cleanouts exist, they are DWV only parts. The lower photo is a SCH 40 DWV cleanout.
2) In addition, there are SCH 40 pressure rated threaded components (the upper photo) that include threaded plugs.

I believe a "cleanout" is, by definition, a DWV only part since "cleanouts" aren't needed/used in PWS systems.

In other words, both of your photos are of SCH 40 parts. The lower one is a DWV cleanout and is not pressure rated. The upper one is a threaded fitting with plug that is pressure rated. Technically, the upper one isn't a "cleanout", though it could be used as one.

EDIT: Tagged the photos backwards.
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