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Smaller LPG Tank

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: ramses » Mon Aug 03, 2009 8:35 pm

well if you make the new tank out of steel pipe fittings, there would be no need for a safety valve since they have been tested to 11x. (max peak ~1100psi). but still only fill to around 80%. Fill the tank by weight(use a scale) like they do with CO2 tank. the density of liquid propane is approximately 0.5077 g/cm.
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Unread postAuthor: Technician1002 » Mon Aug 03, 2009 11:09 pm

ramses wrote:well if you make the new tank out of steel pipe fittings, there would be no need for a safety valve since they have been tested to 11x. (max peak ~1100psi). but still only fill to around 80%. Fill the tank by weight(use a scale) like they do with CO2 tank. the density of liquid propane is approximately 0.5077 g/cm.


It is much easier to fill by vent tube. Fill until the vent starts to pick up liquid and shut off the fill and then the vent. Done. Tank can be part of the launcher.
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Vent tube picks up liquid whent the level reaches the end of the tube.
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Unread postAuthor: POLAND_SPUD » Tue Aug 04, 2009 8:59 am

@tech thx that was quite informative


what would I have to do use propane tanks as air reservoirs ?

it would be cool to have a tank that I could fill at home and take somewhere

AFAIK rusting is a problem, what could be done to prevent it ?
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Unread postAuthor: Technician1002 » Tue Aug 04, 2009 11:21 am

POLAND_SPUD wrote:@tech thx that was quite informative


what would I have to do use propane tanks as air reservoirs ?

it would be cool to have a tank that I could fill at home and take somewhere

AFAIK rusting is a problem, what could be done to prevent it ?


First step is remove the old valve and vent the propane outside in a safe location using an air hose. Then vent some more. Then store the tank for a week upside down outside to finish venting.

Next is to pour in some Rustolium paint and shake it around to fully coat the inside and pour the remains out. Leave it inverted and using a muffin fan, a funnel and a piece of 1/2 inch copper pipe, vent the tank for several days until the air exiting the tank no longer smells like fresh paint.
The paint won't dry without fresh air in the tank.

Third add a 3/4 inch to 1/4 inch reducing bushing, 3 way manifold, gauge, relief valve, shut off, and quick coupler.

Remember to invert and blow out on occasion to empty condensation.
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Unread postAuthor: chenslee » Tue Aug 04, 2009 4:25 pm

Cludged this together. The 1/4 npt cross, gauge, and nipple are nearly as big as the 8 cubic inch tank. I didn't model it in, but the open port on the cross is for a safety relief valve.
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Concept of a reduced size refillable LPG tank.
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Unread postAuthor: mark.f » Sun Oct 04, 2009 3:41 pm

Hey, there's been some informative discussion in this thread since I left it (work, school, etc.).

I was actually thinking of some sort of clear sight (rated of course) to check the fluid level when filling. BTW, this tank will be very small when put on the cannon I'm building... no bigger than to last more than a shooting session reliably. I was thinking of using something along the lines of a copper "stub-out" or air chamber, or a length of 3/4" iron pipe.

This cannon is dragging along, though, as I only have a little money left every two weeks to build on. I'm building the barrel today (which is a sleeved type... won't say much more here).
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Unread postAuthor: Technician1002 » Mon Oct 05, 2009 12:50 am

mark.f wrote:Hey, there's been some informative discussion in this thread since I left it (work, school, etc.).

I was actually thinking of some sort of clear sight (rated of course) to check the fluid level when filling. BTW, this tank will be very small when put on the cannon I'm building... no bigger than to last more than a shooting session reliably. I was thinking of using something along the lines of a copper "stub-out" or air chamber, or a length of 3/4" iron pipe.

This cannon is dragging along, though, as I only have a little money left every two weeks to build on. I'm building the barrel today (which is a sleeved type... won't say much more here).


Clear is nice, but getting a reliable seal against metal can be difficult. Plastics and glass may fail under pressure. A pre made solution that can be bolted to the side of a small tank and plumbed in is a site glass for an air conditioning system. Place it at the level you want the top of the liquid and you can see it when it is full.
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Unread postAuthor: mark.f » Mon Oct 05, 2009 7:28 pm

Actually I was looking at a McMaster part... threads into a 1/4" NPT hole. :P
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