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check valve for exhaust

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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check valve for exhaust

Unread postAuthor: JET47 » Fri May 23, 2008 12:11 am

i just thought of something, not sure if it will work though, because i might be a little ignorant of how check valves function.

but it you had a big check valve installed in the back end of a combustion cannon, say, behind the fan, facing inward, would it allow free passage of air at atmospheric pressure but would close when the gun fired, not detracting from its firepower?

i think it wont work because check valves only open in a single direction when sufficient pressure is applied, not the other way, where they close against back pressure.

but i can imagine them being made either way?

does anyone get what im talking about? i know i did a crappy job of explaining
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Unread postAuthor: lockmanslammin » Fri May 23, 2008 12:25 am

Very interesting idea. A check valve requires a certain amount of pressure...or in this case vacuum to open. You would have to have a very light cracking pressure and a very insane fan for it to work. But that doesn't mean it isn't a very interesting idea in a lot of aspects. What if you were to build your own check valve, you could make it very large (same size as chamber) and simply poke it in with your finger when you run the fan.

Also I believe there is a type of check valve that limits flow rate. So it will allow air through it in both directions until to much volume tries going through at once, then it seals like a regular check valve. That would work good if it closed very fast as soon as combustion occurs, otherwise you would be losing power.

But like I said, very interesting idea. Work on it. I'm sure there will be a nice discussion about this one.

Of course, there was probably already a huge discussion on the topic a few months ago.... who knows if its original around this place.

Good luck with it,

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Unread postAuthor: MrCrowley » Fri May 23, 2008 12:26 am

Are you saying that the fan would suck air through the checkvalve? Wouldn't work sorry.
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Unread postAuthor: starman » Fri May 23, 2008 12:33 am

MrCrowley wrote:Are you saying that the fan would suck air through the checkvalve? Wouldn't work sorry.


Yep you need 2-3 lbs of pressure to overcome the spring in a typical check-valve in its flow direction. If you were "airing out" with compressed air it could work nicely...however, not possible with the suck power of an internal computer fan.
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Unread postAuthor: JET47 » Fri May 23, 2008 12:41 am

ok, i wasnt sure which way they worked, looks like its the pressure-makes-them-open-in-one-direction way.

but i was thinking about what lockmanslammin wrote, about the kind that limits flow rate.
so the gun firing makes it close right up, but then as soon as the projectiles out it will open on its own and air can be pulled in by the fan without manually turning a valve or unscrewing a cap.

it would work like, spring is keeping a sealable lid up off its seal, but when pressure is enough at once to push the lid down it makes a seal, kindve like in a piston based pneumatic. and then when the pressure disapates, the lid will be pushed back up off by the spring and the seal disappears.

thinking about it though it would mess up ur air:fuel ratio before firing since the fan is on to mix it up, so u'd still have to rig sumthing to be done manually for venting =/[/quote]
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Unread postAuthor: lockmanslammin » Fri May 23, 2008 12:50 am

good point jet47...

It would mess up the fuel mix.

ok, lets take this idea a little further then.

How about a selenoid operated normally open check valve.
You would have two different momentary buttons. One for venting, that would be wired to only operate the fan, and one for mixing the fuel, that would be wired to close the fan circuit, and power the selenoid that closes the check valve.

Easier than opening a ball valve every time anyways.

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Unread postAuthor: Darkside 6ix » Fri May 23, 2008 12:52 am

very intererting. Alot of people will envy anybody who can pull this off. If this ends up working, combustion cannons will have alot of potential
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Unread postAuthor: MrCrowley » Fri May 23, 2008 12:55 am

pvcpsyco wrote:very intererting. Alot of people will envy anybody who can pull this off. If this ends up working, combustion cannons will have alot of potential

They already do have a lot of potential... :?

Not sure what you are getting at here, seems a bit random. Unless you mean who ever figures out automatic venting will take a huge step closer to semi-automatic combustions.
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Unread postAuthor: clide » Fri May 23, 2008 1:04 am

It probably won't work with a computer fan, but people have used check valves with mattress inflators to vent.

http://www.advancedspuds.com/checkvalve.htm
http://www.spudfiles.com/spudtech_archi ... 17&t=12544

Edit: same as gun as the last link but on Spudfiles
http://www.spudfiles.com/forums/gorts-p ... ter,0.html
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Last edited by clide on Fri May 23, 2008 1:08 am, edited 1 time in total.
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Unread postAuthor: Darkside 6ix » Fri May 23, 2008 1:06 am

kinda, but if you built a fuel intake system for a combustion with the check valve setup and a fan, WHALA! A semi auto. im not all that into combustions, but i still would like to see someone pull this off
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Unread postAuthor: BigGrib » Fri May 23, 2008 2:14 am

Definitely feaseable in my opinion it's have to be a good size dia check valve for venting, and then a couple more maybe 1/4 electric solenoid valves for fueling. maybe used a 555 microcontroller to control timing for fueling firing and venting so that for each pull of the "trigger" it fires vents then reloads and refuels in that order. I would love to collaborate with someone on a project like this. especially since i dont really have the background in electrioncs. it'd definitely be something to pull off.
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Unread postAuthor: jimmy101 » Fri May 23, 2008 10:08 am

Latke's chamber vent system is almost a check-valve like setup.
http://www.burntlatke.com/25cb-testday.html
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The friction is probably too high to act as an automaitc valve so it is operated manually.

It should be possible to build a check valve that would operate at the very low differential pressures that a chamber fan will develop. Perhaps a ping-pong ball in a cage? (Kind of like the self-closing snorkels.) Probably have to fiddle with the design to get it to close tightly for fueling and firing.
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Unread postAuthor: Darkside 6ix » Fri May 23, 2008 10:11 am

Yes, Thats basically a ghetto check valve that has no spring. But i still like that idea.
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Unread postAuthor: THUNDERLORD » Fri May 23, 2008 11:27 am

pvcpsyco wrote:Yes, Thats basically a ghetto check valve that has no spring. But i still like that idea.


Doesn't look ghetto to me. Somewhere someone made a list of "Ghettoness" (a word?) and I think it would need duct tape or something.

Looks like a decent concept and I was thinking about one similar only mounted inside a T.
(Bottom of T to barrel and if it uses a larger motor mounted internally, it would have more room).? 8)
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Unread postAuthor: psycix » Fri May 23, 2008 12:57 pm

Maybe some homemade "flap" valve could approach the idea.
But for normal checkvalves, it wont really work due to the lack of force.
Most checkvalves have got a spring wich causes it to close until enough pressure is applied.
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