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a couple questions

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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a couple questions

Unread postAuthor: Rogue » Sun Nov 04, 2007 6:14 pm

ok i have been on the cpu researching for 6 hourss. eahh. my questions are:

are burst disk valves reusable? (i think they are just wanted to make sure)
^what price will a 2" valve run for price wise in u.s.?

in a hybrid for oxygen injection is it compressed air? or where would i obtain an oxygen bottle?

and how much more powerful is a hybrid than a combustion or a pneumatic?
for example how far could a propane hybrid that was fairly well built throw a spud(2" barrel)?


and..ughhh 1 more lol..:how dangerous is a hybrid cannon if i made it with ALL sch. 80 pressure rated pvc(or what other pipe is the strongest)
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Unread postAuthor: Hubb » Sun Nov 04, 2007 6:21 pm

1) Burst disc valves are not reusable.

2) Usually. I've seen them at drug stores.

3) A hybrid is a lot more powerful than a pneumatic or combustion.

4) Sch80 generally holds up in a hybrid, but to be on the safe side, I would not put more than 3 or 4X in it. A more acceptable pipe would be steel.
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Unread postAuthor: hi » Sun Nov 04, 2007 6:35 pm

burst disks are just a peice of aluminum foil or a peice of rubber or plasic that hold back the pressure until it ignites and the pressure breaks the burst disk, then you have to put a new one in.

i would not build a hybrid out of pvc, period. i think pretty much every pvc hybrid has had some sort of failure. pvc is fine for combustions or pneumatics, but in my opinion, not hybrids. some people think it is safe to use SCH80 pvc, but i think it is a bad idea. use metal pipe.

hybrids usually double or even triple the power of a normal cannon, they are nothing to mess around with.

ps- burst disks are free, the "valve" is just a union, which range from $3-15, depending of material and size.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: Rogue » Sun Nov 04, 2007 7:05 pm

@hi

so i would NOT have to replace it everytime?

can you link me or give me a name to the "union"
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Unread postAuthor: hi » Sun Nov 04, 2007 7:09 pm

go to google and type in union. if you go to the hardware store and look at a union it will make a lot more sence. a union connects two pieces of pipe, the burst disk goes between the two.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

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Unread postAuthor: DYI » Sun Nov 04, 2007 7:11 pm

Burst disks themselves are replaceable, not reusable.

A 2" steel union shouldn't cost any more than $15.

Hybrids can use any means you wish to increase the amount of oxygen in the chamber. You can get an oxygen cylinder at a local compressed gas supply depot, along with the regulator, gauges, hoses, and quick connects that you'll need to do something useful with it.

Due to certain limits (think heat loss combined with slower combustion at extreme mixes and the increased risk of DDT), pneumatics can be made, per size, more powerful than any hybrid. Combined with gases like helium and hydrogen instead of air, which can equal or exceed the SOS in a hybrid chamber post-ignition, pneumatics are superior in terms of raw power.

The main reason that I can see for the use of hybrids is the performance that can be achieved for a relatively low cost at the lower to middle levels of their power range- a hybrid capable of achieving 500 psi will usually be cheaper than a helium setup capable of the same pressure. Where pneumatics start to come up on top is the 1000+ psi range, where hybrids start to meet a point of diminishing returns and compressed gas cylinders can be used unregulated for very low prices. Unfortunately, material costs are still high, and we rarely see anything running at those kinds of pressures here.

Nobody really knows how far it is possible to throw a spud. The theoretical velocity limit would be the point where the air resistance upon leaving the barrel is enough to heat the spud to the point that it either ignites or disentegrates. That point is probably far beyond anything that you will ever achieve, so, with a gradual acceleration, you could probably get ranges in excess of 1 mile with a large hybrid. Killjoy's FEAR has supposedly chronoed a spud leaving the barrel at 2700 feet per second, although that is disputed. Muzzle velocities in excess of Mach 1 have been confirmed for potatos before.

Finally, a hybrid cannon running at any mix high enough to be worth using is absolutely not safe to build out of any schedule of PVC. PVC does not have the impact resistance necessary to make it a suitable hybrid material, although it certainly has been done. A suitable building material for a hybrid could be aluminum, brass, steel, possibly copper, or ABS (as long as it's either pressure rated, or custom machined with relatively thick walls).
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Unread postAuthor: Rogue » Sun Nov 04, 2007 8:05 pm

okay thanks i get the whole union thing now. so you just slide the burst disk in?

i just remembered i have acess to a HUGE helicopter part supplier/builder/repairer. free metal pipe and i can get a custom bored piece of steel. yay :D :D :D



one more question...what can i use spud bucks for???
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Unread postAuthor: Hubb » Sun Nov 04, 2007 8:09 pm

Then you should be able to build a super launcher, but get your feet wet with other type first before you attempt a hybrid (if you haven't already).

As far as spudbux, check here and here.
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Unread postAuthor: hi » Sun Nov 04, 2007 11:04 pm

Nobody really knows how far it is possible to throw a spud



i know that this ahs nothing to do with this disscussion, but i have recently discovered that if you throw a potato the same way you throw a football then it spirles and accually goes pretty far. i can get it about 150 feet if i really arch it...

just thought you guys would want to try it next time your out shooting.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

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