Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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sprayandprayboy
- Private 2

- Posts: 36
- Joined: Tue May 24, 2011 11:28 pm
Sun Jun 05, 2011 7:57 pm
hi all im new here. i have a gun that was "spray and pray" but i changed it to propane and it doesnt work

i used the fuel tool
http://www.burntlatke.com/ft_live.html
and it still doesnt work

it was fine as a spray and pray ,this is my first serious gun , my chamber volume is 85 cubic inches ,and my barrel is 32 cubic inches.
any of your help would be very well helpfull
thank you
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ramses
- Staff Sergeant 2


- Posts: 1679
- Joined: Thu May 29, 2008 6:50 pm
Sun Jun 05, 2011 9:46 pm
You may need to change the pressure based on the vapor pressure of propane at whatever temperature.
I would make the meter to work on 50 psi or so, and use an air compressor regulator to maintain that pressure. They were on clearance for $5.00 at Harbor Freight a little while ago, but I think they may have been discontinued. I should have bought more.
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Crna Legija
- First Sergeant 2

- Posts: 2333
- Joined: Sun Jul 20, 2008 5:14 am
- Location: australia
Sun Jun 05, 2011 10:08 pm
whats the volume of your meter? what pressure you filling it to?
'' To alcohol... The cause of, and solution to, all of life's problems.”
--Homer Simpson
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sprayandprayboy
- Private 2

- Posts: 36
- Joined: Tue May 24, 2011 11:28 pm
Mon Jun 06, 2011 1:16 am
I am using like a half of a tank, and my hose is 4 3/8" long not counting the fittings and vaulves and is 3/8" ID, its not working very well, now that i shortened the hose i must blow a little air into the chamber... do u suggest making the hose about 3/4" shorter. thanks o yeah i dont have a regulator should i try to get one

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Crna Legija
- First Sergeant 2

- Posts: 2333
- Joined: Sun Jul 20, 2008 5:14 am
- Location: australia
Mon Jun 06, 2011 2:28 am
sprayandprayboy wrote:I am using like a half of a tank, and my hose is 4 3/8" long not counting the fittings and vaulves and is 3/8" ID, its not working very well, now that i shortened the hose i must blow a little air into the chamber... do u suggest making the hose about 3/4" shorter. thanks o yeah i dont have a regulator should i try to get one

What??????
'' To alcohol... The cause of, and solution to, all of life's problems.”
--Homer Simpson
Add me on ps3: wannafuk, 8/11/11 cant wait
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saefroch
- Staff Sergeant 2

- Posts: 1679
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- Location: U.S.A.- See Map
Mon Jun 06, 2011 5:38 am
sprayandprayboy wrote:half of a tank
Is not a unit of pressure... Please try again

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Crna Legija
- First Sergeant 2

- Posts: 2333
- Joined: Sun Jul 20, 2008 5:14 am
- Location: australia
Mon Jun 06, 2011 12:10 pm
sprayandprayboy wrote:the propane tank is half full
we get that but what pressure are you filling you meter pipe to and how much volume is that pipe?
'' To alcohol... The cause of, and solution to, all of life's problems.”
--Homer Simpson
Add me on ps3: wannafuk, 8/11/11 cant wait
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sprayandprayboy
- Private 2

- Posts: 36
- Joined: Tue May 24, 2011 11:28 pm
Mon Jun 06, 2011 4:47 pm
my meter pipe is the hose it is a high pressure fuel line i dont know how mutch pressure a half full propane tank holds i do not have a regulator, sorry i should have said that my "meter pipe" was a hose.
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saefroch
- Staff Sergeant 2

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Mon Jun 06, 2011 5:11 pm
You've been filling the meter to whatever pressure the tank is? You don't have a gauge on the meter?
Fuel tool says you only need your meter pipe 3.1" long. I HIGHLY recommend manometric fueling, because you will not have potentially massive errors because of a change in temperature.
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Fnord
- First Sergeant 2

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Contact:
Mon Jun 06, 2011 6:21 pm
Uhh, saefroch, I don't think manometric is ideal for a non-airtight gun.
S&P:
As long as you have liquid propane sloshing around in the tank, the pressure inside will be the same (around 120 psi, but varies with temperature).
You don't absolutely need a regulator or a pressure gauge, but it may make life easier. If you could post a picture of your rig that would help us trouble-shoot.
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ramses
- Staff Sergeant 2


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- Joined: Thu May 29, 2008 6:50 pm
Mon Jun 06, 2011 6:30 pm
I HIGHLY recommend volumetric metering with a pressure gauge or regulator over manometric metering, especially for a 1x combustion. Unless you want to have a completely air tight chamber that you fill to precisely 0.62 psi for every shot.
Regulator.
several more
POLAND_SPUD wrote:even if there was no link I'd know it's a bot because of female name

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saefroch
- Staff Sergeant 2

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Mon Jun 06, 2011 7:27 pm
Well I guess I don't understand what "manometric fueling" means. To me, it just means "fueling based on pressure," which would indicate the use of a gauge, but the use of an independent metering volume or pipe is optional. I take it that this term normally refers only to chamber fueling?