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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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Smaller LPG Tank

Unread postAuthor: mark.f » Sun Aug 02, 2009 3:44 pm

This is just a little curiosity thread.

Say you have a tank with liquid propane in it (camping tank, torch tank, bulk tank, etc.). Say you want to mount your gas source to a compact combustion cannon, but don't want a tank that will provide more than 500 shots for your cannon and add all the extra bulk.

I think it is possible to simply construct another, smaller tank from steel pipe fittings or copper tubing (the air chambers / water hammer arrestors seem appropriate), and fill it from the larger tank.

Simply use a torch head / compression fitting combination to get a torch or camping tank down to pipe threads, and then use a quick disconnect combination for filling the smaller tank.

The process would involve filling with the larger tank upside down to allow liquid propane to flow into the smaller tank, until the tank is full.

Any comments/suggestions? I believe the small orifice diameter of the needle valve in the torch head will stop the flow of liquid propane into the smaller tank once the pressures equalize, which would be a problem, but I'm not quite sure.

This is similar to airsoft green gas filling (in that you want liquid propane to fill your 'magazine'), so I don't see any reason why it's not feasible.
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Unread postAuthor: singularity » Sun Aug 02, 2009 3:53 pm

if you use the standard off the shelf torch head the speed at which the LPG transfers will be unbelievably slow. if you modify that same torch head by unscrewing the bottom and removing the restrictor your transfer speeds will be significantly increased however they will not be quite as fast as green gas transfers
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Unread postAuthor: POLAND_SPUD » Sun Aug 02, 2009 4:01 pm

that's a pretty good idea... long time ago I built a BV pneumatic that used propane instead of air... filled it through a fill valve from an old lighter glued inside a nipple... of course I filled it with propane refill tanks for lighters but there are rather expensive and quite a lot of gas leaked during filling so I don't think they are practical
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Unread postAuthor: mark.f » Sun Aug 02, 2009 4:14 pm

Apparently, they sell adapters which go straight from tank threads to NPT threads, which have much more flow than a torch head needle valve. That would be most likely what I would use if speed were my concern.

Apart from speed, though, the orifice diameter might restrict fluid flow as pressure increases... something else to worry about I guess.

EDIT: Good news, just found a 1"-20 (female disposable fuel tank thread) x 1/4" NPT adapter... at Wal-Mart! They sell it as part of a 'Last Measure' fuel adapter which adapts a disposable tank to a large bulk tank thread. It's actually two separate adapters, of which one is the 1"-20x1/4" NPT one.
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Unread postAuthor: chenslee » Mon Aug 03, 2009 9:19 am

250 psi, 8 in^3. 1/8 npt ported, stainless steel. Part is listed for $18.80.

http://www.clippard.com/store/display_d ... u=AVT-24-8

Hell. I might even go this route. Getting rid of the propane tank on my cannon will lighten and tighten it up.

A Mr Heater #F273754 adapter is crucial for adapting a throwaway cylinder to npt pipe threads. I own 3.

To make a feasible system, you are also going to need a couple of ball valves and some npt adapters to go back and forth between 1/4 and 1/8 npt. Some quick disconnects would be tits.

Clippard.com also has other size volume chambers, and their prices are reasonable.

Be aware that though a 250psi rated stainless tank is adequate for LPG, it is NOT an approved container and you will get in a metric crap ton of trouble if you get caught transporting it charged.
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Unread postAuthor: ramses » Mon Aug 03, 2009 9:34 am

yes. I have seen the tank adaptors at harbor freight for ~$5.00
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Unread postAuthor: chenslee » Mon Aug 03, 2009 11:17 am

Sweet! I paid like $13 for mine at Ace Hardware.

Mark, how much was the Walmart adapter? Is it Mr Heater brand?
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Unread postAuthor: Technician1002 » Mon Aug 03, 2009 11:50 am

A word of caution..

Propane expands as it warms up. If a tank is filled 100% with cold propane and then sealed, unsafe pressures will result.

This is the reason that OPD valves are required on tanks now. I had this happen to me. I ran out of propane on winter and took a tank in to be filled (old style POL fitting) They filled the tank. In bringing it home in my car it started venting.

They overfilled the tank.

Proper filling of tanks (Before OPD) was to open the vent. The vent has a tube on it so when the tank is at the proper level, it vents liquid. At that point the filling is supposed to be stopped.

Often service station attendants would close the vent and continue filling. The gas vapor will condense back to a liquid and the tank can be filled 100% where the pump stops filling. This is called Overfill. It is illegal, and unsafe.

Service pressure on a Porpane tank is 240 PSI. The relief valve has a minimum opening pressure of 360 PSI.

The rest of the story.. How I survived..

I smelled the propane start to vent and immediately rolled down the windows while still driving to prevent an explosive mixture and pulled over. I removed the cylinder and opened the vent on the sidewalk and let it vent just to where it stopped venting liquid, closed it, and took it home.

It could have ended much worse and has for some people. This is why OPD valves are now required.

If you build a tank, build in a vent with a space above it and use it to prevent overfilling.

Refillable lighters have this vent. It opens when filling and it's why you stop filling when it starts venting liquid. There is a space above the vent in the tank so you can't fill them 100%. Otherwise lighters exploding in your pocket would be common.

If you remove a valve from a Propane tank, you will find the vent has s tube that extends below the valve so it will vent liquid as the tank is properly filled.
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Valve removed from a propane tank showing the vent tube on the left side of the picture.
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Unread postAuthor: chenslee » Mon Aug 03, 2009 2:04 pm

One of these might work.

Image

At least it would make me feel safer knowing my tank won't Krakatoa on me.
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Unread postAuthor: Technician1002 » Mon Aug 03, 2009 2:14 pm

chenslee wrote:One of these might work.

Image

At least it would make me feel safer knowing my tank won't Krakatoa on me.


Good idea.. The one built into my valve prevented my tank from doing that. A better idea is to design it to fill less than 80% (20% expansion space minimum) and have a safety pressure relief. For propane use about a 300PSI relief valve for safety.
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Unread postAuthor: chenslee » Mon Aug 03, 2009 2:19 pm

I know the pneumatic guys use 100-150 psi's on their cannons to prevent "non-passive end of life failures".

The highest rated relief valve I can find so far is 200psi and it's $19. I know there has to be some out there cheaper.

Also, even warm (less than 100°F) LPG is under 150 psi right?
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Unread postAuthor: chenslee » Mon Aug 03, 2009 2:22 pm

I know the pneumatic guys use 100-150 psi's on their cannons to prevent "non-passive end of life failures".

The highest rated relief valve I can find so far is 200psi and it's $19. I know there has to be some out there cheaper.

Also, even warm (less than 100°F) LPG is under 150 psi right?

There are few on ebay too. http://cgi.ebay.com/Air-Compressor-Safety-Relief-Popoff-Valve-200psi_W0QQitemZ380054701482QQcmdZViewItem

What the heck? I was editing the above and it ended up a new post. Weird.
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Unread postAuthor: Technician1002 » Mon Aug 03, 2009 2:28 pm

chenslee wrote:I know the pneumatic guys use 100-150 psi's on their cannons to prevent "non-passive end of life failures".

The highest rated relief valve I can find so far is 200psi and it's $19. I know there has to be some out there cheaper.

Also, even warm (less than 100°F) LPG is under 150 psi right?

There are few on ebay too. http://cgi.ebay.com/Air-Compressor-Safety-Relief-Popoff-Valve-200psi_W0QQitemZ380054701482QQcmdZViewItem

What the heck? I was editing the above and it ended up a new post. Weird.


Here is the pressure chart..
Check the pressure against the temperature.

Properly removed from the tank, it is possible to use the valve built into all small disposable Propane tanks. Remove the core before brazing them in. Re polish the seat before reassembly. Hydrostat test before use.
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Attachments
Propane.jpg
Propane Vapor Pressure graph
Propane.jpg (37.57 KiB) Viewed 2098 times
PropaneRelief.jpg
Propane Relief Valve on a disposable bottle. It was retained into the design of the Marshmallow Cannon. The spring was trimmed to a lower pressure for use on the modified tank.
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Unread postAuthor: chenslee » Mon Aug 03, 2009 4:03 pm

That T-P chart was what I was thinking of. Thanks. I have one for CO2, but not LPG.

Looks like it will hit 200 psi on a hot hot day, around 110°F, or if left out in the sun. I does not get that hot in my garage, and since it's illegal to transport it won't be baking in my car either.

Then again, propane cannons are technically illegal too, so what the heck.

The Clippard tanks are rated for 250, so I'd put a 250 relief on it and keep it out of the sun. If I needed to transport the thing, I'd just purge the mini tank and take my re-fill rig with me.

This is all tempting since my cannon has an unused slot for an air cylinder that happens to be the same size as that Clippard tank. A custom fuel tank would cut down on a lot of my cannon bulk.
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Unread postAuthor: Technician1002 » Mon Aug 03, 2009 5:27 pm

chenslee wrote: and since it's illegal to transport it won't be baking in my car either.

Then again, propane cannons are technically illegal too, so what the heck.



Transport it empty and fill for the session. Vent to under 50 PSI (keep some to keep water & condensation rust out) and you are good to go.

I've transported empty 1 lb cylinders for outings and filled just for an event, then let them run dry and brought the empties back home.

I've switched to CF bulbs, battery, and inverters so I don't use lanterns much anymore. It is a lot safer.
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Last edited by Technician1002 on Mon Oct 05, 2009 12:43 am, edited 1 time in total.
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