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Propane Cannon Building 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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Propane Cannon Building Question

Unread postAuthor: BFC » Sun Aug 01, 2010 2:09 pm

So Im looking to build a Adv. Propane cannon

Thing is finding all pressure rated piping is hard, Ive looked at all the local hardware stores, and getting anything 4" in pressure rated is like trying to find the pot of gold at the end of the rainbow.

So my question is, and this is probably stupid to ask but is it a bad idea to solvent weld abs to PVC to try and put together the cannon.

I have 4 in. pressure rated PVC pipe for the chamber, so Im looking at putting, 4 to 2 Abs reducer on both sides of the chamber, one leading to a ball valve for venting and the other leading to 2 abs 90 degree elbows then cam-lock to barrel.

I bought abs to PVC cement but where Im concerned is that PVC uses primer and cleaner and abs doesnt, and this glue is supposed to seal them both, but will it be fit for a propane cannon?

Thanks in advance,
BFC
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Unread postAuthor: SpudFarm » Sun Aug 01, 2010 2:16 pm

I would say go for it. And if you are in doubt you could just use screws to secure it additionaly.
Four bolts through the fittings and the pipe on each connection should ensure a secure joint.

Good luck on your cannon!
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Unread postAuthor: Lockednloaded » Sun Aug 01, 2010 2:22 pm

If you are going to do this, DO NOT use Pvc glue to glue ABS parts to PVC. Use some sort of epoxy reinforced with screws; PVC glue will not bond to ABS
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Unread postAuthor: BFC » Sun Aug 01, 2010 2:22 pm

I have special ABS to PVC cement i bought

yea, I think im going to do a few tests before I make my big one.


I have a big thick blanket Im going to throw over it while I test and Ive got a blast shield I have from long time ago. Im going to use both while I test. I really dont want to be having to pick pvc or abs out of a$$ if it goes south.

I just figured id ask before I went and did something stupid, you guys seem to be the #1 resource on these topics so I thought id stop in.

If it works ill put some pics and info up on it.

thanks,
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Unread postAuthor: SpudBlaster15 » Sun Aug 01, 2010 3:07 pm

In my experience, those transition cements don't work well for pressurized joints. The solubility values of PVC and ABS in ketone solvents are not similar enough for an effective bond to occur. ABS is very soluble in MEK/Acetone, and is typically joined using a single application of cement to each component. However, PVC is much more difficult to dissolve, and requires a multiple step solvent cementing process to be joined effectively.

Why can't you simply use 4" DWV ABS pipe for the chamber? It's safer than any type of PVC, especially if using PVC involves attempting to solvent weld two vastly different materials together.
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Unread postAuthor: BFC » Sun Aug 01, 2010 4:16 pm

I wanted to use 4" PVC for the chamber because of the fact that the PVC is pressure rated and then I wanted to use the ABS parts funnel the blast out of the chamber and into the barrel.

Maybe my idea was way off, but I had read on here on some different threads that ABS in Propane cannons can fail, although it supposedly is better if it fails because it is cellular core and it has a style of rip rather than a burst. But I had read that PVC adv. Combustions, if pressure rated, do not tend to fail.

So my plan was to use the pressure rated PVC everywhere possible to contain the ignition and use the ABS where I couldn't get the Pressure rated PVC.

But your point SpudBlaster, I wanted to check on here to find out if I would be able to reliably solvent weld these to types together, because I really wanted to stay away from ABS as the main chamber. But if I cant safely weld these two types together I will go with all ABS or try and get all pressure rated parts.

thanks,
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Unread postAuthor: Biopyro » Sun Aug 01, 2010 4:46 pm

My original combustion was ABS to PVC using sticks like sh*t glue. It has been fired hundreds of times, and I trust it enough to be upgrading it to metered mapp this summer.

If in doubt, you can just secure it with bolts, as bonding them together will only make the joint fail, the pipe itself is unlikely to explode.
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Unread postAuthor: BFC » Sun Aug 01, 2010 5:02 pm

Would putting bolts to hold the joints together weaken the fittings and the pipe?
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Unread postAuthor: Biopyro » Sun Aug 01, 2010 5:05 pm

Yes, but it won't be an amount that will be significant, bear in mind that nearly everyone has at least on hole in their chamber for ignition, some have fans, switching systems and a variety of other bits bolted in, I doubt it's anything to worry about.
At the end of the day if you want 100% peace of mind you are going to have to shell out, but for a normal air/propane mapp cannon, I don't think the risk of 4-8 bolts in a 110mm chamber is significant.
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Unread postAuthor: BFC » Sun Aug 01, 2010 7:21 pm

alright, that sounds like the bolts idea should work,

*EDIT*
@BioPyro
Hey,

You wrote about a glue that you used on your PVC/ABS cannon. I was wondering what exactly it was.

thanks for the info,
BFC
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Unread postAuthor: Biopyro » Mon Aug 02, 2010 12:07 pm

I am from the UK, so this may not be available where you are, and may well be called something else. It has apparently been renamed "sticks like" since I used it, and is a very strong "grab adhesive". It was very sticky, and I used it on all the joints in the gun, as the supplier I bought from didn't have any solvent glue and I was pretty impatient.
I don't think I would trust it for the sustained force of a pneumatic, but I am more than happy with it in my combustion.
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Unread postAuthor: SpudBlaster15 » Mon Aug 02, 2010 12:24 pm

Biopyro wrote:My original combustion was ABS to PVC using sticks like sh*t glue. It has been fired hundreds of times, and I trust it enough to be upgrading it to metered mapp this summer.


You're going to use metered MAPP in a PVC/ABS chamber that was assembled using an adhesive not designed to bond either material?

That's a VERY bad idea.
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