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Camlock Coupling Pressure

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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Camlock Coupling Pressure

Unread postAuthor: kjjohn » Mon Dec 21, 2009 9:35 pm

I am currently building a hybrid, and I want to know if it is safe to use aluminum camlock coupling for the breech. The chamber will be 2" dia, and the barrel will have a 1.5" bore. Most of the launcher will be constructed from galvanized steel, and HGDT predicted a max pressure of 1100psi upon ignition. The camlock couplings will be 1.5", and most likely constructed from aluminum. Most camlocks I could find were only rated for 250psi (working), but could they withstand the pressure (safely, meaning I could hold on to the gun when it fired) in this hybrid?
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Unread postAuthor: drac » Mon Dec 21, 2009 9:51 pm

Aluminum will be fine for that. However, no hybrid should ever be fired handheld if you value your fingers.
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Unread postAuthor: kjjohn » Mon Dec 21, 2009 9:55 pm

I have seen many hybrids fired handheld (specifically fnord's piston hybrid). Using galv steel, is it really unsafe? I mean, most galv fittings have burst pressures of over 4kpsi, and I will only be producing about 1kpsi.
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Unread postAuthor: starman » Mon Dec 21, 2009 9:56 pm

You should be able to use aluminum cam locks to 3 or 4x. Those things are easily 250 psi capable. If you want to go to higher mixes, go to a steel union or and back to back steel flange setup.
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Unread postAuthor: drac » Mon Dec 21, 2009 9:56 pm

Lemme rephrase that. I wouldn't recommend it, but I have never built one personally. I'm in the process of building one*, but until I garner more experience with hybrids, I'll err on the side of caution. If it's steel, I wouldn't be as weary as with PVC.

*Details coming soon, it's one everyone is sure to love.
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Unread postAuthor: kjjohn » Mon Dec 21, 2009 10:01 pm

starman wrote:You should be able to use aluminum cam locks to 3 or 4x. Those things are easily 250 psi capable. If you want to go to higher mixes, go to a steel union or and back to back steel flange setup.


Is there any other kind of coupling/breech loading method that would be quicker than a union, but be able to withstand up to 1100psi? It doesn't matter if it is not suitable for burst disk loading, this will be a piston hybrid, I just want to have a very quick solution for breech loading.

edit: I found some stainless camlocks rated for the same pressure as the aluminum ones (250psi), but would they be able to withstand more pressure due to their material of construction? They are 316 alloy.
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Unread postAuthor: starman » Mon Dec 21, 2009 10:21 pm

What's heavier... a pound of feathers or a pound of lead. Really, 250 psi is 250psi aluminum or stainless. Really it depends more on what you're going to interface it with.
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Unread postAuthor: kjjohn » Mon Dec 21, 2009 10:26 pm

What do you mean by "interface"? Basically, I am just asking if it would be safe to use the 316 stainless camlock coupling with my design. Just to make things clear: the chamber is 2" dia, the barrel is 1.5", and it will produce between 500 and 1100 psi. I will be using MAPP and pure oxy. The coupling will be 1.5" as well. I am planning on having it be somewhat handheld, so it has to be able to hold in that pressure without blowing off my hand. It will use a piston, not a burst disk.
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Unread postAuthor: SpudBlaster15 » Mon Dec 21, 2009 10:35 pm

I would not use aluminum cam-locks at 1100PSIG. The clamping mechanism is quite strong, but that's really asking a lot from it.

However, since this will be a piston hybrid, you may get away with using them, as the axial stress will not be nearly as high when they are used only to breech load and not to hold a burst disk in place.
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Unread postAuthor: starman » Mon Dec 21, 2009 10:37 pm

kjjohn wrote:What do you mean by "interface"? Basically, I am just asking if it would be safe to use the 316 stainless camlock coupling with my design. Just to make things clear: the chamber is 2" dia, the barrel is 1.5", and it will produce between 500 and 1100 psi. I will be using MAPP and pure oxy. The coupling will be 1.5" as well. I am planning on having it be somewhat handheld, so it has to be able to hold in that pressure without blowing off my hand. It will use a piston, not a burst disk.


Yes I got the details above. The 3 or 4x limit I specified won't be producing anywhere near 500 to 1000 psi, more in the 250 to 350 psi range. I wouldn't plan to take camlocks anywhere near 500 to 1000 psi.

You have to hook your camlock parts up (usually threaded) to something, barrels, chambers, bushings, etc etc. That "hook up" is an interface...and is likely a weak point.
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Last edited by starman on Mon Dec 21, 2009 10:44 pm, edited 1 time in total.
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Unread postAuthor: kjjohn » Mon Dec 21, 2009 10:42 pm

Actually I just revised the specs in HGDT, and I can get it to produce only 800psi while putting out the same velocity.

Sorry if I'm being really repetitive :) , but in your opinion, would this be safe?
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Unread postAuthor: starman » Mon Dec 21, 2009 10:45 pm

kjjohn wrote:Actually I just revised the specs in HGDT, and I can get it to produce only 800psi while putting out the same velocity.

Sorry if I'm being really repetitive :) , but in your opinion, would this be safe?


No. What mix are you attempting?
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Unread postAuthor: kjjohn » Mon Dec 21, 2009 10:52 pm

It will be between 6x and 10x, I'm not sure. If I use a 6x, the chamber will be 2"dia by 24", and if I use anything higher, it will only be 12" long. I am getting fairly consistent output in HGDT by varying the chamber size and mixture this way. The barrel will be 1.5" by 50" either way.
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Unread postAuthor: starman » Mon Dec 21, 2009 11:10 pm

I would be going with steel and welding if at all possible. Any threaded parts smallish....spark plugs etc.
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Unread postAuthor: kjjohn » Mon Dec 21, 2009 11:16 pm

I know that Moonbogg made his Striker without welding. I will probably just go with a 5 or 6x and a larger chamber. I have heard of many people using threaded fittings on these.
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