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Hybrid safety valve

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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Hybrid safety valve

Unread postAuthor: Moonbogg » Thu Jan 01, 2009 8:18 pm

Is there a kind of burst or high flow blowout valve that can be used to ensure chamber pressure doesn't go too hi? I know there are pop valves, but I don't think they would vent the gas fast enough to prevent a dangerous pressure spike.
Maybe a large coupling for a special safety burst disc would work.
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Unread postAuthor: noname » Thu Jan 01, 2009 8:28 pm

If you're worried about the chamber pressure going too high, just make it out of steel.
Other than that, just use a burst disc that's thicker than the firing valve's disc.
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Unread postAuthor: starman » Thu Jan 01, 2009 8:59 pm

Your burst disk is your "safety valve"...another reason not to over do it on its psi setting. Also, having a venting method via a ball valve on your fueling system would be easy to implement. This is a good reason to make sure your burst disk system is up to snuff.

This shouldn't be a concern for you. Any chamber you build should be able to fully contain the combustion you intend to fire.
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Unread postAuthor: Hotwired » Thu Jan 01, 2009 9:02 pm

I'm not seeing the light here.

Yes, when you have a pneumatic running at high pressure it's a good idea to be able to depressurise the chamber through a safety in case something such as a barrel blockage or valve failure occurs which means it's either a bad idea to fire it, a bad idea to fix the problem while it's pressurised or the chamber just won't vent by the normal means.

A hybrid either fires or it doesn't. The pressure change is mostly through heat which if left alone will neutralise itself. If the barrel burst disk fails to burst and there's a more resistant second and automatic valve it won't do anything.

If you do the proper research on the strength of the chamber material there should not be any question of the chamber being able to fail before the burst disk. Or for that matter, the chamber pressure being greater than the cannon can handle.
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Unread postAuthor: Moonbogg » Thu Jan 01, 2009 9:43 pm

Well I am concerned because I want the cannon to be idiot proof. If some stupid kid gets ahold of it and doesn't like to follow directions, hes going to add his own burst disk, or pile them up, then fill the cannon at 10x when its only designed for 2-3x.
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Unread postAuthor: john bunsenburner » Thu Jan 01, 2009 9:53 pm

why would you care...If you know what you are doing and dont give it to a quote on quote "stupid kid " then it is not your concern. If car builders worried about some idiot driving their cars into a wall because they stole them without ever being able to drive it the there would`nt be too many cars driving around now would there. As long as your not the "stupid kid " then there is no problem...
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Unread postAuthor: Lentamentalisk » Fri Jan 02, 2009 1:15 am

Some stupid kid would not know how to make it go... Do you realize just how complicated it is to
1) put in a very strong burst disk
2) meter out the correct amount of propane
3) get a compressor and fill it to exactly the right pressure
4) fire it
Nobody who picks it up, who has not been given a long lesson on how it works, with all of the size stats and filling numbers will even be able to set it off, much less blow them selves up with it. If they do figure out how to set it off, you have much greater concerns than them blowing themselves up, such as them killing other people... Unlike guns, hybrids are idiot proof.
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Unread postAuthor: Moonbogg » Fri Jan 02, 2009 2:00 am

Lentamentalisk wrote:Some stupid kid would not know how to make it go... Do you realize just how complicated it is to
1) put in a very strong burst disk
2) meter out the correct amount of propane
3) get a compressor and fill it to exactly the right pressure
4) fire it
Nobody who picks it up, who has not been given a long lesson on how it works, with all of the size stats and filling numbers will even be able to set it off, much less blow them selves up with it. If they do figure out how to set it off, you have much greater concerns than them blowing themselves up, such as them killing other people... Unlike guns, hybrids are idiot proof.


Excellent points. If someone knows enough about it to actually use it, chances are they will be able to manage to not kill themselves.
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Unread postAuthor: Moonbogg » Fri Jan 02, 2009 2:05 am

I was concerned also becuase aluminum camlocks are only rated to 250. They are the weak link and i'll have to work around them.
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Unread postAuthor: inonickname » Fri Jan 02, 2009 2:25 am

If you know what you're doing it shouldn't be a problem...and why would your burst disk be stronger than the chamber...I'm missing this somewhere..
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Unread postAuthor: starman » Fri Jan 02, 2009 2:46 am

Moonbogg wrote:I was concerned also becuase aluminum camlocks are only rated to 250. They are the weak link and i'll have to work around them.


250 psi is a working rating...actual failure will be much higher. However, I wouldn't recommend building anything more than a 3x hybrid using camlocks. Also, using HGDT, fit no higher rated burst disk than will allow a 300 psi max chamber and barrel pressure. From my studies, this will be somewhere in the 100-150 psi burst range.
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Unread postAuthor: Moonbogg » Fri Jan 02, 2009 3:13 am

starman wrote:
Moonbogg wrote:I was concerned also becuase aluminum camlocks are only rated to 250. They are the weak link and i'll have to work around them.


250 psi is a working rating...actual failure will be much higher. However, I wouldn't recommend building anything more than a 3x hybrid using camlocks. Also, using HGDT, fit no higher rated burst disk than will allow a 300 psi max chamber and barrel pressure. From my studies, this will be somewhere in the 100-150 psi burst range.


Exactly my thoughts! I was liking the looks of 3x with 300psi as a max combustion target value. I used the tool and it looks like you'd really have to use a super heavy round to achieve 300psi. Looks like 330 is about the max the gun would ever see under any circumstance.

What kind of recoil could I expect?? LOL! I bet this is really going to kick some serious ass. Its going to have an advanced combustion layout, built out of 6061-T6. Chamber analysis results just showed 500psi at 2.1 FOS.
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Unread postAuthor: starman » Fri Jan 02, 2009 4:05 am

Moonbogg wrote:What kind of recoil could I expect??


Recoil is going to be dependent on the mass and velocity of your ammo...a burst disk only/no ammo, practically no recoil, a 16 oz can of veggies and you won't be able to hold it.
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Unread postAuthor: Moonbogg » Fri Jan 02, 2009 4:45 am

starman wrote:
Moonbogg wrote:What kind of recoil could I expect??


Recoil is going to be dependent on the mass and velocity of your ammo...a burst disk only/no ammo, practically no recoil, a 16 oz can of veggies and you won't be able to hold it.


Whoa. Yeah I guess there could be like 1,000lbs or so behind that can of veggies. So that would be like getting hit in the chest with 100lbs of force or something like that I think. I'll make sure to have a friend try it first.
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Unread postAuthor: Moonbogg » Fri Jan 02, 2009 4:31 pm

Just got my T-6 camlocks. These things are really impressive. Its so great to be able to buy something so well designed and already made thats such a great fit for the cannon.

Starman if you see this, could you please explain how you made use of the camlocks for your breach loading? I saw a picture somewhere with a barrel sticking through the back of a camlock for spud loading.
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