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fueling biohazard

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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fueling biohazard

Unread postAuthor: pat123 » Thu May 15, 2008 4:43 pm

last week when drex came over we couldn't get biohazard to shoot. just by roughly measuring the size i got the amount of propane needed to be 45psi. by filling it with water to measure it I got 40psi. we tried it at both and it wouldn't work. :x

after that we started at 60 psi of propane in the meter and tried to fire it. when that didn't work we went down 5 psi and it still didn't work. we continued to go down 5 psi at a time until we got to 5psi. then we just let it all out and pushed the button and it fired. why would it fire with all most no propane in it but it wouldn't when the "right amount" was in it? :?:

are we just missing something obvious?
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Unread postAuthor: DYI » Thu May 15, 2008 4:50 pm

Unless you post the calculations you did to find your meter pressure, we can't help.

If you do that, there's a good chance I'll be able to find your problem, although I don't have any hands-on experience with volumetric fuel meters.
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Unread postAuthor: STHORNE » Thu May 15, 2008 4:55 pm

There could also be an ignition problem. Have you checked that out?
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Unread postAuthor: psycix » Thu May 15, 2008 4:56 pm

Was there still air in your fuel meter when you tried it at the "right" amount of fuel?
Did you vent it properly before fireing off the "way too low" amount of fuel?

Those are my first thoughts of what happened to you.
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Unread postAuthor: pat123 » Thu May 15, 2008 4:59 pm

I am going to measure it again with water to get a more accurate measure but it is about 620in3. I used the program i made http://www.spudfiles.com/forums/hcmp-t13837.html which i am pretty sure is accurate. the meter is 9.4 cubic inches.

I don't think the problem is in the calculations. i think i measured one of them wrong. but since we tried it at 5 psi intervals starting at 0 going to 60 i think something else maybe wrong.
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Unread postAuthor: pat123 » Thu May 15, 2008 5:02 pm

There could also be an ignition problem. Have you checked that out?

I hear it sparking every time

Was there still air in your fuel meter when you tried it at the "right" amount of fuel?
Did you vent it properly before fireing off the "way too low" amount of fuel?
Those are my first thoughts of what happened to you.

we pumped it out with a vacuum pump

edit: Sorry for the double post but they are both different and i didn't read the other two messages before i posted this one.
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Unread postAuthor: DYI » Thu May 15, 2008 5:33 pm

Okay, for this design, the volume of propane needed to fire at 1x is:
[(620ci/95.98 )*100-620]
26ci. (actually 25.9691ci, but we wouldn't want SB15 to be offended :wink: ).

Now, your meter will likely be full of air on the first shot, so on the first shot you would need to fill it to:
{[(26+9.4)/9.4]*14.7}
55psia or 40.7psig.
On the second shot, if the meter is full of propane, you would need:
[(26/9.4)*14.7]
41psia or 26psig.

Remember, this is all for 1x.

At 2x, you would need:
{[(620*2)/95.98]*100-620}
52ci of propane, requiring a meter pressure of 81psig if the meter was full of air or combustion products to start with, or 67psig if the meter was purged with propane beforehand.

Note that these numbers don't take into account the miniscule effect of the air or combustion products that might be in the meter if it wasn't purged.

Judging by these numbers, you couldn't usually exceed 3x without having to dump the meter twice, which complicates things even further. Ever thought of using a chamber pressure meter instead?
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Unread postAuthor: pat123 » Thu May 15, 2008 5:59 pm

Ever thought of using a chamber pressure meter instead?

we are thinking about it but we already have the meter. we probably will. We could use the meter for part of a pnuematic or something.
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Unread postAuthor: drex » Fri May 16, 2008 12:21 pm

i want to use one of DYI's fancy chamber pressure meter instead, but im broke and pats to cheap. :roll: .

pat, lets see if we can't come up with the money and order the parts this weekend?
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Unread postAuthor: SpudFarm » Fri May 16, 2008 4:30 pm

DYI i have decided.. i think i use your meter on my hybrid. seems like big hybrids are hard to fuel. (should be easier to fuel big chambers :? )

i talk to you on MSN about it so i don't hijack this
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Unread postAuthor: pat123 » Fri May 16, 2008 8:39 pm

i talk to you on MSN about it so i don't hijack this


go ahead and talk about it here i would like to know as much about it as you
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Unread postAuthor: LikimysCrotchus5 » Fri May 16, 2008 10:56 pm

DYI wrote:Okay, for this design, the volume of propane needed to fire at 1x is:
[(620ci/95.98 )*100-620]
26ci. (actually 25.9691ci, but we wouldn't want SB15 to be offended :wink: ).

Now, your meter will likely be full of air on the first shot, so on the first shot you would need to fill it to:
{[(26+9.4)/9.4]*14.7}
55psia or 40.7psig.
On the second shot, if the meter is full of propane, you would need:
[(26/9.4)*14.7]
41psia or 26psig.

Remember, this is all for 1x.


At 2x, you would need:
{[(620*2)/95.98]*100-620}
52ci of propane, requiring a meter pressure of 81psig if the meter was full of air or combustion products to start with, or 67psig if the meter was purged with propane beforehand.

Note that these numbers don't take into account the minuscule effect of the air or combustion products that might be in the meter if it wasn't purged.

Judging by these numbers, you couldn't usually exceed 3x without having to dump the meter twice, which complicates things even further. Ever thought of using a chamber pressure meter instead?


Why do you use 95.98? Shouldnt it be 95.8?
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Unread postAuthor: SpudFarm » Sat May 17, 2008 8:23 am

pat123 wrote:
i talk to you on MSN about it so i don't hijack this


go ahead and talk about it here i would like to know as much about it as you


nah it would just go off topic. you can PM me if you want to know.
thanks anyway :)
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Unread postAuthor: DYI » Sat May 17, 2008 6:57 pm

Why do you use 95.98? Shouldnt it be 95.8?


It's a number that others have quoted. I actually get 95.6 when I do the numbers myself. Ask Rag, as I'm sure he'll have the explanation behind the 95.98 number. Regardless of what the correct numbers are, the basis of the equation stays the same, and the results will be very close.
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Unread postAuthor: LikimysCrotchus5 » Sat May 17, 2008 7:17 pm

Ok thanks i was just wondering mif you got that of the hybrid fueling sticky but i couldnt seem to find it.

So pat, have your tried what we have told you?
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