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Large Cannon Valve Ideas

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Large Cannon Valve Ideas

Unread postAuthor: Zippster » Wed Dec 19, 2007 7:21 pm

I was theorizing on making a really big WWII-esque spud-relocating artillery piece with HUGE, probably dual, chambers. The only valves I've used thus far are lubed-up ball-valves (yes I'm a noob, but I'm still surprised with the results) and I don't really trust myself with the pistons, and haven't yet got around to testing those out. If I were to make such a beast, what valves would you suggest (it will be at the MOST 125PSI - my dads a big stickler about high pressures)? Would modded sprinklers or QEV's have enough flow to be practical? And would a butterfly valve still suck? All the previous similar guns I've seen don't delve too much into the valve details, but if the solution is a piston, some pointers for a big one or duals would be much appreciated.
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Unread postAuthor: ShowNoMercy » Wed Dec 19, 2007 7:23 pm

You can buy dual 3/2 inch QEVs for 28 shipped.
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Unread postAuthor: elitesniper » Wed Dec 19, 2007 7:27 pm

what size chambers?
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Unread postAuthor: mopherman » Wed Dec 19, 2007 8:13 pm

why not a giant sprinkler valve? Great flow and easily moddable through the frow control stem. Consult pvc arsenal for tips on the mod.
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Unread postAuthor: DYI » Wed Dec 19, 2007 8:14 pm

If you want something on an artillery scale, you probably want 4" porting at the least. The cost of the sprinkler valves necessary to achieve that sort of porting would be prohibitively high, and QEVs would be even worse. Dual 3" porting would be slightly larger than 4" porting. Please also note that a 3" sprinkler doesn't have anywhere near 3" porting.

Due to the very low pressure you intend on using, a piston valve could be built out of socket weld PVC fittings with only basic tools. It could be housed in a 6" PVC tee, with the piston housed in the 6" part. A bushing with a bored out centre stop could be inserted into the tee, and the barrel pipe inserted through that. A piston could be built from epoxy (bulk quantities of liquid epoxy are available from McMaster-Carr), with a bolted on butyl rubber (innertube rubber) sealing face, and a thick rubber bumper.

If you want more than 4" porting, any way you do it will likely be horribly expensive.

EDIT: For a "large cannon" that 2" sprinkler is tiny. Dual 3" sprinklers might be an option, but the porting still wouldn't be anywhere near as good as a 4" porting barrel sealer.
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Unread postAuthor: mopherman » Wed Dec 19, 2007 9:22 pm

DYI wrote:If you want something on an artillery scale, you probably want 4" porting at the least. The cost of the sprinkler valves necessary to achieve that sort of porting would be prohibitively high, and QEVs would be even worse. Dual 3" porting would be slightly larger than 4" porting. Please also note that a 3" sprinkler doesn't have anywhere near 3" porting.

Due to the very low pressure you intend on using, a piston valve could be built out of socket weld PVC fittings with only basic tools. It could be housed in a 6" PVC tee, with the piston housed in the 6" part. A bushing with a bored out centre stop could be inserted into the tee, and the barrel pipe inserted through that. A piston could be built from epoxy (bulk quantities of liquid epoxy are available from McMaster-Carr), with a bolted on butyl rubber (innertube rubber) sealing face, and a thick rubber bumper.

If you want more than 4" porting, any way you do it will likely be horribly expensive.

EDIT: For a "large cannon" that 2" sprinkler is tiny. Dual 3" sprinklers might be an option, but the porting still wouldn't be anywhere near as good as a 4" porting barrel sealer.

he mentioned a "spud relocator" I assumed that he ment a spud barrel, for witch a 2' sprinkler valve would be exelent. i Thing duel 2' sprinklers would be more than enough fro even a 4' barrel
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Unread postAuthor: MaxuS » Thu Dec 20, 2007 4:37 am

mopherman wrote:i Thing duel 2' sprinklers would be more than enough fro even a 4' barrel


I don't think that they make 2ft sprinkler valves.
I think two 2" sprinkler valves will do it, I've got one and the power is incredible, you could pilot them both with a 1inch version.
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 20, 2007 6:05 am

have you considered a triggered burst disk?
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Unread postAuthor: BigGrib » Thu Dec 20, 2007 6:32 am

MaxuS wrote:
mopherman wrote:i Thing duel 2' sprinklers would be more than enough fro even a 4' barrel


I don't think that they make 2ft sprinkler valves.
I think two 2" sprinkler valves will do it, I've got one and the power is incredible, you could pilot them both with a 1inch version.


are you saying duel 2" sprinkler valves triggered by a 1" sprinkler valve triggered by a qev or a blowgun??
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Unread postAuthor: Hubb » Thu Dec 20, 2007 6:36 am

I would consider some type of burst disc as well. It will provide the highest flow and probably be exactly what you would want in an artillery piece. JSR mentioned a triggered burst disc but that may be a little much if you're not comfortable with it. Try a normal burst disc and, when you feel you are comfortable (which won't take long), try and go with a triggered version. Just make sure to keep your barrel removable.

@ DYI: For some reason, your avatar just freaks me out
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 20, 2007 6:46 am

hubb017 wrote:@ DYI: For some reason, your avatar just freaks me out


sorry :oops:
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Unread postAuthor: mark.f » Thu Dec 20, 2007 9:09 am

I would suggest either a triggered burst disk or a piston valve. Don't be too afraid to try out building a piston valve. Many people have built them successfully on their first try. For a 2" barrel, you could either build a 2" porting valve in a 2-1/2" or 3" tee, or a 1-1/2" porting valve in a 2" tee. The latter is a far more popular size of valve, and is cheaper to make. If it's still cheaper, (I don't know material prices where you live), you could build two 1-1/2" porting valves to get flow around the same as [3(√2)/2] diameter, (~2.12"), porting valve.

If you REALLY want a WWII-ish cannon, I suggest it be made of steel and be steam powered. You could go "MythBuster" on us and use a small water heater as your steam source, and a triggered burst disk would make the perfect valve.
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Unread postAuthor: DYI » Thu Dec 20, 2007 4:51 pm

A steam powered triggered burst disk cannon on the scale of the SCTBDC would be very impressive. If I could modify it to use steam, the performance would almost double from what it is now. In the SCTBDC, for a given pressure, it would provide performance almost 1.5x higher than hydrogen :shock:

This, combined with my new wide bore, wood/paraffin powered torch as a heating system would be an interesting combination (although using the wood torch would carry the risk of causing a catastrophic failure in the chamber pipe, as it can melt copper tubing in <30 seconds, as well as steel if given time)

On the other hand, steam powered cannons are horribly inconvenient, and have a slow ROF without a separate boiler (which is generally expensive and complicated to construct, as well as rather dangerous to operate).

The other advantage of steam is that you can obtain any pressure you care to, within reason, as you are unlimited by regulators or tank pressure.
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Unread postAuthor: Zippster » Thu Dec 20, 2007 10:14 pm

Thanks for the feedback! It was a lot more help than I usually get with my posts. Me and my friends, who are more than a little jealous of my pneumatic destruction, were thinking of pooling our money for a larger piece with some more power (which in reality means they'd help pay if they get to play with it too :D ), and hell, the school is in range so why not! What I meant by the piston comment was more of my dad's skepticism about anything that doesnt explicity state its capability to hold pressure and his continual reminders about how much power these guns really have ("I was 14 once too...") than my own incompetence, and seeing as I've already built 8 pieces and a couple trebuchets to boot, I guess I can try it. I dont exactly have much of what you'd call 'discretionary income', so metal, steam, and anything else thusly cost-prohibitive are out of the picture. One question though: by 'porting' do you mean piston valves? Again, thanks for all your input, it really helps to have more than 2 people reply.

PS: Yes I am 14 - I've just learned to impress english teachers, which helps a lot in highschool.
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Unread postAuthor: DYI » Fri Dec 21, 2007 10:06 am

By porting, we usually mean the size of the outlet on a valve, or the size of the worst flow restriction in a valve. Since the chamber port on a piston valve is usually the largest, the "porting" refers to the diameter of the barrel port.

Here's a design that would be relatively powerful, and built for a fairly low cost. The chamber size could be increased as cash flow allowed.
Chamber: 96" of 4" PVC
Barrel: 144" of 4" PVC (or 240" if you can find a piece that long)
Valve: 4" porting barrel sealing piston valve (made in a 6" tee)
Pilot valve: 2" spring loaded ball valve

It would be slightly more powerful than the current incarnation of the SCTBDC (it could fire a 1kg projectile @485fps at 120 psi)
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