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meter pressure and flexible hose pressure rating?

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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Unread postAuthor: JDP12 » Thu May 03, 2007 12:04 pm

Yea that's what I thought....All that other stuff was really confusing me.

Yea Freefall they are..Because I did a volume measurement with water..So I got an exact volume of both teh chamber and meter pipe-
Chamber=2500mL
Meter pipe= 56.2mL

@Pete Zaria...Yea I'm interested in that garden hose...PM me for details please.
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Unread postAuthor: FeLeX » Thu May 03, 2007 2:21 pm

Alright here we go.
To get chamber volume we do: r*r*pi*length
Asuming that 4" is the diameter and 8" is the length we get: 2*2*3.14*8 so
Chamber volume-100.5 cu.in.
Now to get volume of the propane needed we do 100.5*.04(perfect propane)
Propane volume-4.02 cu.in.
Now to find out the required psi and the rest of the shenanigans we are going to use this formula: p1*v1=p2*v2, where
p1 is the desired psi in the meter;
p2 is atmospheric pressure;
v1 is meter volume required at p1 psi;
v2 is propane volume at 4%;
For the test run we are going to use 90psi and go from there, so we get:
90*x=14.7*4.02;
x=.6566 cu.in. volume of propane required at 90psi;
Now we need to figure out what is the length of a pipe like that would be at 1/2" diameter (.46875) using this formula:
r*r*pi*x=v where x is the length and v is propane volume at 90psi;
.234375*.234375*3.14*x=.6566;
x=3.8;
So the required length of 1/2" ID pipe at 90psi is 3.8 inches.
Now we just need to figure out a psi that would be perfect for 6 inch pipe, asuming that that is how long your pipe is (earlier you said it was about 6 inches).
Lets review our data:
Chamber volume-100.5 cu.in.;
Required propane volume-4.02 cu.in.;
Required propane volume at 90psi-.6566 cu.in.;
Required pipe length at 90psi-3.8";
So now that we know how to work with all that data we can start looking for that perfect psi measurment.
PSI Req. Propane Length

25 2.36 cu.in. 13.7"
40 1.47 cu.in. 8.5"
50 1.18 cu.in. 6.85"
55 1.07 cu.in. 6.2"
57 1.03 cu.in. 6.007"

So as you can see with a pipe that has a diameter of 1/2" and is 6" long you will need 57psi of propane for a perfect 4% mixture.
Notice that this measurmnets will work ONLY if the measurmnets you posted are right, so if you have a 4"x8" chamber and you have a 1/2"x6" pipe then you will need 57psi in that pipe. One more time, will work ONLY if the dimensions you posted are right.

A better way to calculate psi, instead of substituting numbers in:
x*v1=p2*v2 where x is the psi that we are looking for, v1 is the volume of meter pipe, p2 is the atmospheric pressure, and v2 is the propane required by volume.

Lets say I have a 5"x5" chamber and a 1/2"x6" meter pipe;
Chamber Volume-98.125 cu.in.
Meter Volume-(mmmm I gota go catch my bus home Ill finish this when I get back)
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Unread postAuthor: JDP12 » Thu May 03, 2007 2:55 pm

k yea felex, like I said..I'll check when I get home..The only thing is though is that 4.02 cu.in. isn't correct becasue that isn't including the volume of the connections to get ot hte barrel..Can you use the volume somehow or should I just fiddle with it to get the right PSI?

Because I know for sure that the total chamber volume==152.550cu.in

And the meter volume=3.92 cu.in.

So should I just fiddle around with it??

EDIT: I'll just wait till you finish this.
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Unread postAuthor: FeLeX » Thu May 03, 2007 3:30 pm

Well I am not gonna finish that post anymore, because as I can see it you understand how it works now.
The reason it is 4.02 cu.in. is because I was working with the 4"x8" dimension and didn't see your post on the second page with the right volume. Another reason it was 4.02 is because I couldn't put it all together in my head to get the volume (sorry =/) so there was apparently some error. The most important thing is you need to understand how the formulas work and etc.
In case you need some help with that I can explain them throughly.
For now I am just going to work it out for you using the dimensions you gave me.
Chamber Volume-152.55 cu.in.;
Meter Volume-3.92 cu.in.;
152.55*.04=6.102 cu.in. required volume of propane;
Now we can put all this into a formula to get the psi:
p1*v1=p2*v2 where p1 is the psi we are looking for, v1 is the meters volume, p2 is the pressure in the pipe (atmospheric pressure), v2 is the required volume of propane;
Put the values in and you will end up with
p1*3.92=14.7*6.102
p1=22.8psi;
You will be fine with charging it with 25psi since that would be easier to do on a meter. Now the reason our psi values ended up different is because you used different atmospheric pressure.
Bottom line is this: if you measure everything right and gave me the right values then 25psi is what you should use for the best combustion. So yup you were right off the bat, but you know its always good to check.

Good luck man and have fun with your new propane injected gun.
FeLeX
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Unread postAuthor: JDP12 » Thu May 03, 2007 5:32 pm

Okay thanks guys..Just wanted to check..Thanks especially FeLeX for takin time to calculate all that for me..
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Unread postAuthor: sjog » Thu May 03, 2007 8:48 pm

Hey, about that hose. I got hose at McMasters. 1/4 npt fittings ,one end swiveled one end fixed. The fixed end goes on first, ya twist the hose on to the fitting. The swivel end threads on second.300psi the ends are crimped on.Custom lengths, I got one foot. Cost 20$ w/shipping. McMasters is great quick shipping. You can see the hose on my gun L7 gbl
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Unread postAuthor: JDP12 » Thu May 03, 2007 8:51 pm

K...are you talking about like the hose that has braided steel over the plastic inside part?
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Unread postAuthor: sjog » Thu May 03, 2007 9:07 pm

no it's brown. I could'nt find that hose. Steel braid is at plumbers supply
but the threads are not npt something different.


The crack of a golf ball cracking in to a big pine , then flying back at me!!
True story.
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Unread postAuthor: JDP12 » Thu May 03, 2007 9:16 pm

Hmm well that sucks for you sjog..Why weren't you shooting it fast enought to just go through the tree??? Lol just joking :D Good thing you werent hurt.

What's the part number of the pipe??

Would this pipe work?- I have hose barbs- Part # 5304K28
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Unread postAuthor: FeLeX » Thu May 03, 2007 9:48 pm

ilovetoblowthingsup wrote:Okay thanks guys..Just wanted to check..Thanks especially FeLeX for takin time to calculate all that for me..

Awww man its no problem. Message me anytime in case you need more help.
Peace, FeLeX.
PS.
Cant wait to see your gun man.
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Unread postAuthor: JDP12 » Fri May 04, 2007 7:16 am

Yea me too, lol..My parents won't let me shoot it until I get all of my stuff from sgort- propane tank fitting, red chamber fan, golf ball barrel, and spark circuit. :(
They won't even let me use our static guard, which they NEVER use, because "it's expensive and you need to learn patience, its a virtue."

Urghh..Lol
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Unread postAuthor: FeLeX » Fri May 04, 2007 7:58 am

Damn man sounds like my parentals. I just told them to leave me the hell alone and started paying for my guns myself.
Just wondering how much did all that cost you form sgort?
Because I am building a minigun style propane injected spudgun for my friends dad (its his birthday soon) and Ill need all that except the golfball barrel.
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Unread postAuthor: JDP12 » Fri May 04, 2007 9:34 am

Umm 4' golf ball barrel+propane tank fitting+plain old LED fan+ simple spark circuit = $36? I think w/o shipping. The shipping was like $7 something because of the long barrel..The cost w/o the barrel is like..I gotta go to class..I'll tell you in a bit
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Unread postAuthor: FeLeX » Fri May 04, 2007 9:48 am

Dang thats pretty cheap, gotta start shopping there. How long has it been since you ordered that stuff? Oh and did you buy the meter from sgort or did you make one yourself?
PS.
We are talking about the bcarms.com store right?
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Unread postAuthor: JDP12 » Fri May 04, 2007 9:58 am

K update..I didn't order the spark circuit..at least I don't think so... So

fan=$7.99

Propane fitting= $12.99

Golf ball barrel=$15


So i didn't get the spark circuit...so everything without that is only about $21..the circuit is $28.99 but I didn't get it because I figured I can just buy a new BBQ ignitor if mine ever breaks..I've probably clicked it over 50 times now and nothins happened so I decided not to get the circuit.


I ordered them wednesday night (US Central Time) But he had to do a little assembly - glue an adaptor onto the golf ball barrel..

So I think I should get the parts sometime next week..Grrr...
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