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oxy vs air & oxy regulator

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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Unread postAuthor: jimmy101 » Thu Jun 04, 2009 1:47 pm

Moonbogg wrote:This is what I have in mind. They are the same looking for both oxy and mapp/propane. It would make a very clean oxy/mapp setup. I just have to make sure to get the fully adjustable ones as many of these friggin mini's come "preset". I assume that means output pressure is fixed and only allows flow control.
Image


A true regulator is a true regulator. Even if it is fixed at a particular pressure it is still a regulator. "Preset" just means it isn't adjustable, which might be OK as long as the preset is at a useable pressure. Any type of setup is also going to need a flow control as well as the regulator since you still need to turn the flow on and off. The on/off control should always be downstream of the regulator. If it is upstream then the regulator often will not work correctly. Indeed, many reg's go way out of regulation when the supply gas is shut off.

You are right though, you don't want anything that attempts to regulate pressure via a flow control like a needle valve. That's an incredibly unsafe way to do it. With low pressure sources (like a propane tank) people often meter without a regulator, they just use a flow control and a gauge. That isn't too bad with a ~120 PSI pressure source like a propane tank since the meter can handle the maximum pressure the propane bottle can generate. It probably is not a good idea with a 2000 PSI (or whatever it is) oxygen tank.
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Unread postAuthor: Technician1002 » Thu Jun 04, 2009 2:01 pm

jimmy101 wrote:Image

A true regulator is a true regulator. Even if it is fixed at a particular pressure it is still a regulator. "Preset" just means it isn't adjustable, which might be OK as long as the preset is at a useable pressure. Any type of setup is also going to need a flow control as well as the regulator since you still need to turn the flow on and off. The on/off control should always be downstream of the regulator. If it is upstream then the regulator often will not work correctly. Indeed, many reg's go way out of regulation when the supply gas is shut off.

You are right though, you don't want anything that attempts to regulate pressure via a flow control like a needle valve. That's an incredibly unsafe way to do it. With low pressure sources (like a propane tank) people often meter without a regulator, they just use a flow control and a gauge. That isn't too bad with a ~120 PSI pressure source like a propane tank since the meter can handle the maximum pressure the propane bottle can generate. It probably is not a good idea with a 2000 PSI (or whatever it is) oxygen tank.


Along that line, the Coleman line of camping lanterns are regulated. If you find one at Goodwill with broken glass or other fault they make very nice compact 0-15 PSI regulators. Coleman used them so as the bottle cools, the lantern does not dim. As a bonus, they are easy to adjust for low light, unlike a valve which is very twitchy at low flow.
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Unread postAuthor: Moonbogg » Mon Jun 08, 2009 10:13 am

Technician1002 wrote:
jimmy101 wrote:Image

A true regulator is a true regulator. Even if it is fixed at a particular pressure it is still a regulator. "Preset" just means it isn't adjustable, which might be OK as long as the preset is at a useable pressure. Any type of setup is also going to need a flow control as well as the regulator since you still need to turn the flow on and off. The on/off control should always be downstream of the regulator. If it is upstream then the regulator often will not work correctly. Indeed, many reg's go way out of regulation when the supply gas is shut off.

You are right though, you don't want anything that attempts to regulate pressure via a flow control like a needle valve. That's an incredibly unsafe way to do it. With low pressure sources (like a propane tank) people often meter without a regulator, they just use a flow control and a gauge. That isn't too bad with a ~120 PSI pressure source like a propane tank since the meter can handle the maximum pressure the propane bottle can generate. It probably is not a good idea with a 2000 PSI (or whatever it is) oxygen tank.


Along that line, the Coleman line of camping lanterns are regulated. If you find one at Goodwill with broken glass or other fault they make very nice compact 0-15 PSI regulators. Coleman used them so as the bottle cools, the lantern does not dim. As a bonus, they are easy to adjust for low light, unlike a valve which is very twitchy at low flow.


I never thought about lanterns. Thats exciting to hear and i'll check it out. Thanks!
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Unread postAuthor: Moonbogg » Tue Jun 09, 2009 5:41 pm

Double post apologies....:

The pre ignition chamber pressures would not exceed 9PSI for a 4x mix. So there would be no high pressure dangers involved with the cannon itself. Any flammable materials in the chamber such as the fan etc, should not burn as the combustion would use all oxygen instantly. Then the spent gasses would be used as the next shot's buffer.
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Unread postAuthor: Technician1002 » Tue Jun 09, 2009 8:06 pm

Moonbogg wrote:Double post apologies....:

The pre ignition chamber pressures would not exceed 9PSI for a 4x mix. So there would be no high pressure dangers involved with the cannon itself. Any flammable materials in the chamber such as the fan etc, should not burn as the combustion would use all oxygen instantly. Then the spent gasses would be used as the next shot's buffer.


Maybe I miss understand the math. I though 4 X was 4 times 1 atm. It would be 4 X atm absolute or 3 BAR on a gauge.. That doesn't compute to 9 PSI in any of my math. :?: :?: :?:
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Unread postAuthor: daberno123 » Tue Jun 09, 2009 8:15 pm

I assume Moonbogg meant 90 psi, which is roughly 4 bar.
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Unread postAuthor: starman » Tue Jun 09, 2009 8:48 pm

daberno123 wrote:I assume Moonbogg meant 90 psi, which is roughly 4 bar.


90 psi is roughly 6 bar above atmospheric pressure.
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Unread postAuthor: daberno123 » Tue Jun 09, 2009 8:53 pm

Thanks starman, my mental math skills have been taken from me by summer! :wink:
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Unread postAuthor: Moonbogg » Tue Jun 09, 2009 9:41 pm

If you start with fresh air and add an additional 3x worth of oxygen, then that would be around 9psi. The nitrogen takes up 80% of the pressure. Pure oxygen only has to be compressed 20% of that pressure. But this is assuming I keep the spent gasses in the chamber as a buffer. I very well may just purge the chamber with o2 so that the o2 is not compressed at all. Then add 5x worth of MAPP which would equal a whopping pre ignition PSI of 1.47 for a full 5x shot.
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Unread postAuthor: starman » Tue Jun 09, 2009 9:56 pm

daberno123 wrote:Thanks starman, my mental math skills have been taken from me by summer! :wink:


No sweat man, I know how the heat can take it out of a guy.... :wink:
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Unread postAuthor: starman » Tue Jun 09, 2009 10:03 pm

Moonbogg wrote:If you start with fresh air and add an additional 3x worth of oxygen, then that would be around 9psi. The nitrogen takes up 80% of the pressure. Pure oxygen only has to be compressed 20% of that pressure. But this is assuming I keep the spent gasses in the chamber as a buffer. I very well may just purge the chamber with o2 so that the o2 is not compressed at all. Then add 5x worth of MAPP which would equal a whopping pre ignition PSI of 1.47 for a full 5x shot.


And just about whatever amount of MAPP you inject will get an ignition so fuel metering becomes almost moot....except that you not put TOO MUCH fuel in. An all O2 chamber actually gives me the jitters thinking about it.

I actually like the idea of starting with fresh air and using the nitrogen "buffer" as a safety factor...then packing appropriate O2 on top of that.
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Unread postAuthor: Technician1002 » Tue Jun 09, 2009 11:32 pm

Moonbogg wrote:If you start with fresh air and add an additional 3x worth of oxygen, then that would be around 9psi. The nitrogen takes up 80% of the pressure. Pure oxygen only has to be compressed 20% of that pressure. But this is assuming I keep the spent gasses in the chamber as a buffer. I very well may just purge the chamber with o2 so that the o2 is not compressed at all. Then add 5x worth of MAPP which would equal a whopping pre ignition PSI of 1.47 for a full 5x shot.


You may get unexpected combustion speed with no nitrogen buffer. It may be a true explosive mixture which is against the forum rules. I mentioned it as a safety concern. It may explode.
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Unread postAuthor: Moonbogg » Wed Jun 10, 2009 12:15 am

Discussing the use of oxidizers isn't against forum rules as far as I am aware. Whats the difference between combustion and explosion? When you say explode, do you mean chamber failure? This cannon will be able to hold at least 2,000psi so I am not too worried about mapp gas and oxygen causing it to explode.
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Unread postAuthor: Technician1002 » Wed Jun 10, 2009 12:22 am

Moonbogg wrote:Discussing the use of oxidizers isn't against forum rules as far as I am aware. Whats the difference between combustion and explosion? When you say explode, do you mean chamber failure? This cannon will be able to hold at least 2,000psi so I am not too worried about mapp gas and oxygen causing it to explode.


The definition of a detonation vs a combustion. The detonation may cause chamber, barrel or other failue.

The sudden and violent release of mechanical, chemical or nuclear energy from a confined space which creates a shock wave that travels at supersonic speeds. Often used interchangeably with explosion.


http://www.chemicool.com/definition/detonation.html
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Unread postAuthor: Moonbogg » Wed Jun 10, 2009 12:31 am

Technician1002 wrote:
Moonbogg wrote:Discussing the use of oxidizers isn't against forum rules as far as I am aware. Whats the difference between combustion and explosion? When you say explode, do you mean chamber failure? This cannon will be able to hold at least 2,000psi so I am not too worried about mapp gas and oxygen causing it to explode.


The definition of a detonation vs a combustion. The detonation may cause chamber, barrel or other failue.

The sudden and violent release of mechanical, chemical or nuclear energy from a confined space which creates a shock wave that travels at supersonic speeds. Often used interchangeably with explosion.


http://www.chemicool.com/definition/detonation.html


Right. The cannon chamber and end caps are going to be so overkill I can't possibly immagine it ever failing. OK i'll spill the chamber specs and tell me what you think.

3" SCH80 6061-T6 chamber x 12" long
1/2" thick 7075-T6 end caps (much stronger than 6061-T6)
secured with 6 #8 machine screws per cap to chamber.

It would take one hell of a blast to cause that beast to break apart. The barrel is 1 1/2" SCH10 6061-T6.
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