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Handheld Hybrid metal fueling probs

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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Handheld Hybrid metal fueling probs

Unread postAuthor: CannonBall » Sun Jul 08, 2007 6:06 am

Hey. just finisched my handheld metal hybrid it look really nice pic's soon.
But my problem is fueling.
Chamber volume is 490 ML
Metervolume is 103 ML
Fuel need by % 3.5333

Ive tryd to fire it up but my problem is if a burst disc is placed and you release gas into the chamber the meter still holds a few psi.
How can i calculate my gas pressure at my meter voume????
I know taking 0.03533333 from 490 = 17.31 ml of gas
Can somebody help me with the calculations :oops:
Cause i can't figure it out when the meter beholds a few psi after injection.

Thanks Patrick :roll:
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Unread postAuthor: sniperjosh » Sun Jul 08, 2007 6:47 am

okay, does ur meter feture two ball valves, and a pressure gauge between these two valves?? - between the propane and the first ball valve there should be a regulator. make sure its setup liek that. Instead of going and confusing urself try this solution, inject 2psi increments into the chamber, and try to ingite. so first u inject 2psi worth, try to ingite, if it doesnt ignite, inject another 2psi, once u get igniton, remember how many injections u did, say it took 8 injections, now u know thats the same as injecting 16psi worth, so then u have a rough idea of what is a suitable mixture, the next step is going slightly higher and lower, keep changing it till u have good instant ignition, and make sure there is minimal smoke left after combustion. now to be perfect once u have ur ball park figure go back to the books and have a play, atleast ull have ur gun working. I love maths its just too late for me lol, so tired :(
remember if ur gonna use numbers and get the perfect setup, ur meter volume and chamber volume calculations need to be spot on also
The gauge is reading something when u inject because u just injected in a shot of gas (slightly presurising the chamber), just add the same amount each time regardless.
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Last edited by sniperjosh on Sun Jul 08, 2007 6:59 am, edited 1 time in total.
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Unread postAuthor: CannonBall » Sun Jul 08, 2007 6:57 am

I just did this calculation....
3x mix = 51 ML gas = 0.51 bar in meter
4x mix = 70 ML gas = 0.7 bar in meter
5x mix = 86.5ML gas = 0.86 bar in meter
6x mix = 103 ml gas = 1 BAR in meter

IF im correct this will be the right calc...
BUT if i inject the gas......
My meter stays at like 0.3 bar at 4xmix so that is 0.4 bar injected right?
How do i solve this problem.
cause i shot i once with a 4x mix Steelbolt 7 grams...and i wasnt impressed it only made a dent in a fire extinguiser. I should have gone threw I think...
Cheers Patrick
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Unread postAuthor: sniperjosh » Sun Jul 08, 2007 7:03 am

dont worry about what ur shooting atm. your main focus is to get a good explosive mixture. Run the launcher witha short barrel and no ammo.
when it ignites take note of the flame exiting the barrel, it should be a healthy blue tip / orange base. after the explosion pump air throught he chamber to rumove the exhaust gas out the barrel, there shouldnt be much, expecially at a 1x (harldy any exhaust smoke). make sure the gun is running healthy. Ignition shoudl always be instant aswell, when its not instant, the mixture isnt perfect. Also, explain to me your metering setup, it doesnt sound the best. Keep in mind ur trying to inject 4.03% propane into the chamber (4.03% of the chamber volume). The meter volume only dictates how much u will need to pressurise the meter, to achieve the 4.03% of the chambers volume.

since ur so commited ot maths... Ur chamber volume = 490ml x 0.0403 (4.03%) = 19.747ml.

19.747ml / 103ml = 0.1918
0.1918 x 14.7psi = 2.818psi meter pressure per mix.

1x = 2.818psi in meter (approx 2.8 )
2x = 5.636psi (approx 5.6)
3x = 8.454psi (approx 8.5)
4x = 11.272psi (approx 11.3)

etc.
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Last edited by sniperjosh on Sun Jul 08, 2007 7:25 am, edited 2 times in total.
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Unread postAuthor: CannonBall » Sun Jul 08, 2007 7:24 am

I use a special gas i need 3.533 procent :lol:
Its 70 butane 30 % propane.
we havent got propane....
But i know what you mean but i only wanna know how
i can calculate it..
0.7bar gas is needed for 4 times mix when i inject it the meter stays about 0.3 bar.... So did i inject the right amount or did i inject 0.4
Cheers Patrick
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Unread postAuthor: sniperjosh » Sun Jul 08, 2007 7:28 am

u injected the right amount :)
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Unread postAuthor: Fnord » Sun Jul 08, 2007 8:28 am

You might want to add a pin-sized hole some where on the chamber, and then weld a piece of pipe nipple on so you can cover the hole with an end cap. when fueling, you can remove the cap and allow the pressure to equailze before adding air.
That way you will get all the pressure out of the meter.

You can calc your meter volume by putting water in the pipe between the valves and measuring that, btw.
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Unread postAuthor: CannonBall » Sun Jul 08, 2007 9:07 am

I already did measure out my meter volume with water... :lol:
So if i wouldnt thighten up the union to let pressure escape.then put in the air it would fire right?

ow i was outside 5 min ago and tested the hybrid put 1 bar gas and let my compressor put some air in the chamber until it reached 3.5 bar it fire with a crap load of force i cant hear right now.. its beeping in my ears.. also the shot produced smoke.. so to much fuel i think.


ow and im considering to make it a gen 2 anyone ideas?
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Unread postAuthor: SpudBlaster15 » Sun Jul 08, 2007 11:58 am

After injecting the fuel, your only goal is to raise the chamber pressure by 4 bar. So, if your gauge reads 0.3 bar after injecting the fuel, add pressure until your gauge reads 4.3 bar. Don't allow the 0.3 bar of fuel to escape the chamber, as this will screw up your fuel mixture.
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Unread postAuthor: Fnord » Sun Jul 08, 2007 12:32 pm

I already did measure out my meter volume with water...

Eh.. I just woke up. I thought I saw something about you couldn't get the volume measured right. oh well.

Allowing gas to escape through the union would let you fire without pressure still in the meter. If what you're doing right now works, you could just stick with that. It would be easier to calc the first way though.

I don't think the fuel ratio caused it to smoke. For some reason my hybrid made more smoke than a musket the first few times I fired it. Stuff in the chamber is probably just burning off.
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Unread postAuthor: CannonBall » Sun Jul 08, 2007 12:47 pm

SpudBlaster15 wrote:After injecting the fuel, your only goal is to raise the chamber pressure by 4 bar. So, if your gauge reads 0.3 bar after injecting the fuel, add pressure until your gauge reads 4.3 bar. Don't allow the 0.3 bar of fuel to escape the chamber, as this will screw up your fuel mixture.


ehmm.... 4x mix and raise 4 bar air? thought it was 3 bar :roll:
How do i post a picture cause it will make it alot easier caus i have 3 ballvalves.. so i put in fuel in meter inject it into chamber..
My shrader valve is between 2 ballvalves so if i inject feul into chamber i close of the one from the meter and let the ballvalve to the chamber open so i dont pressurise the meter.
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Unread postAuthor: CannonBall » Sun Jul 08, 2007 12:59 pm

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Unread postAuthor: SpudBlaster15 » Sun Jul 08, 2007 1:38 pm

Yes, you would add 3 bar. I was thinking in absolute pressures, and thus stated 4 bar rather than 3.
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Unread postAuthor: noname » Sun Jul 08, 2007 1:39 pm

Maybe I'm just dumb and lucky, but I really have no idea what al this "getting the pressure out of the meter" is. I just inject propane a few times, add the correct amount of compressed air, then hook it up to the ignition chamber and fire. As I said in the first part of this post, am I just dumb and lucky?
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Unread postAuthor: CannonBall » Sun Jul 08, 2007 1:40 pm

For more pictures look at hybrid showcase i made a topic
I made a mistake..
Inject fuel it left 0.3 in the meter
and pumped it up to 3 bar... i didnt fire cause i pumped in 2.7 bar :oops:
Tommorow i will try a 0.7 bar injection the pump it up to 3.3 bar that should do the trick 8)
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