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hybrid theorie (90% sure that is spelled wrong)

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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hybrid theorie (90% sure that is spelled wrong)

Unread postAuthor: SpudFarm » Thu May 08, 2008 9:06 am

after i look at the "DDT has it ever happened in a hybrid" thread and saw the gun from the archive i started to think of this:

people is using PVC for their chambers and PVC is really threatened by shock loads (cause tiny cracks) so i started to think that when a hybrid of plastic is mounted on the chamber and have no recoil absorber the recoil gets right into the pipe (chamber) and it may be like dropping it.

i got up with something against this but i will not write it until i am sure i am not a complete idiot
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Re: hybrid theorie (90% sure that is spelled wrong)

Unread postAuthor: Ragnarok » Thu May 08, 2008 9:26 am

Actually, that's a bloody damn good theory...
The light weight of PVC (and thus high recoil velocities), and lack of recoil absorption would probably explain away why PVC hybrids are rather prone to failure.

spudfarm wrote:... I am not a complete idiot

I know I'm a complete idiot. A pretty smart idiot, but a nitwit nonetheless.

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Unread postAuthor: paaiyan » Thu May 08, 2008 9:28 am

You know, for a while it was pretty much accepted as fact that using PVC for a hybrid was just plain stupid.
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Unread postAuthor: CpTn_lAw » Thu May 08, 2008 9:35 am

I don't trust plastic for anything. Use metal. Plastic fails, and when it does, it sends little shrapnels everywhere (aka in your face) and once you're all messed up, you realize "plastic wasn't a good option".
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Unread postAuthor: bigbob12345 » Thu May 08, 2008 9:36 am

paaiyan wrote:You know, for a while it was pretty much accepted as fact that using PVC for a hybrid was just plain stupid.


And it still should be
Dont make a hybrid out of pvc
Its not that they develop micro fractures because of the recoil, it is because the pressure is to great which causes them to go boom.
I would say using sch80pvc in a hybrid id the same level of stupididty as using DWV in a pnuematic.
There have been so many hybrids that have failed because of there use of pvc.
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Unread postAuthor: paaiyan » Thu May 08, 2008 9:38 am

There, that makes me feel better. I would NEVER use PVC for a hybrid. I wouldn't use anything less than steel.
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Unread postAuthor: SpudFarm » Thu May 08, 2008 10:11 am

you guys go to much off topid..
there are people that do make pvc hybrids and it was because of them i maked this thread.

rag: it is pretty logic. it is about the same as if you have dropped a rock at the chamber.
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Unread postAuthor: paaiyan » Thu May 08, 2008 10:28 am

Here's something you could do spud. If you test with PVC, find a way to measure the outer circumference of the pipe at intervals, then measure it after each shot, or after every few shots. See if there's any appreciable change.
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Unread postAuthor: SpudFarm » Thu May 08, 2008 10:44 am

you mean like the OD and ID?
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Unread postAuthor: paaiyan » Thu May 08, 2008 10:46 am

Yea, whatever you want to call it. Same difference. Even if there's not DDT, it would be nice to know how much effect there is on the pipe from standard hybrid shots.
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Unread postAuthor: SpudFarm » Thu May 08, 2008 11:25 am

i will use steel.
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Unread postAuthor: MrCrowley » Thu May 08, 2008 2:15 pm

spudfarm wrote:you guys go to much off topid..
there are people that do make pvc hybrids and it was because of them i maked this thread.

When was the last PVC hybrid made? I don't remember one being made this year, unless I missed it. It was probably by noname.

A quick skim appears it was noname back in July last year. So you can't really say people still make PVC hybrids, because they don't. But yeah, your theory seems pretty sound, something I personally over looked when thinking about PVC hybrids.
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Unread postAuthor: SpudFarm » Thu May 08, 2008 2:26 pm

i was thinking it may be the reason to the failiure in the archive

and the PVC hybrids are to "old" for the todays mixes but there will be more PVC hybrids in the world and i may have saved one
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Unread postAuthor: psycix » Thu May 08, 2008 3:37 pm

MrCrowley wrote:When was the last PVC hybrid made?


You never know.
There may be thousands of people who did it not long ago.
The only problem is that we cant know, because we never hear anything from those people again. They dont exist anymore. :roll:
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Unread postAuthor: mark.f » Sat May 10, 2008 8:39 pm

The fact is that PVC is a common hybrid material. I've made a PVC hybrid, noname's made a PVC hybrid, and countless others made PVC hybrids before. I'm not saying that it's advisable, but it's not "retarded". The main reason people have and continue to make them is because they've been built before without failure, notably by DR and other higher-echelon members over at the SGTC when it still existed. There's no getting the idea through to potential hybrid builders, just like there's no getting through to that one pneumatic builder who decided to use DWV cellular core.

My opinion? Use threaded steel fittings. Even if you can't weld, you can join steel fittings with two pipe wrenches and some gas tape. Through personal experience, SCH-40 steel pipe in 3" size is actually cheaper than if you were to build the same system out of SCH-80 PVC. Steel is cheaper, safer, and just cooler.

To the topic, yes, PVC does not handle shock loads very well. Almost all residential and commercial plumbing jobs go to great lengths to protect PVC from fatigue for just this reason. Some sort of recoil absorber would be a good idea to cut down on shock. The actually firing of a hybrid doesn't produce a shock if it's a deflagration, and is actually a smoother and slower burn than an atmospheric pressure combustion cannon.

Lastly, don't group all the PVC hybrid builders in a group and call them idiots. Many of our greatest members have built one before, and many of them would choose steel if they were to build again, due to the new evidence and occurrences of PVC failures (noname's accident, etc.).
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