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Mini propane tank

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Mini propane tank

Unread postAuthor: Lockednloaded » Sat Jul 02, 2011 12:13 am

So I've building a smallish hybrid, which presents a problem; the propane tank is just as large as the entire gun. I don't want to have to be carrying around way more propane then I'll ever use in the entire life of the launcher. So I want to transfer some of that Liquid propane into a smaller, more convenient container. So how do y'all recommend I should do/make such a setup? Is it even possible?
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Re: Mini propane tank

Unread postAuthor: Crna Legija » Sat Jul 02, 2011 1:37 am

Lockednloaded wrote:So I've building a smallish hybrid, which presents a problem; the propane tank is just as large as the entire gun. I don't want to have to be carrying around way more propane then I'll ever use in the entire life of the launcher. So I want to transfer some of that Liquid propane into a smaller, more convenient container. So how do y'all recommend I should do/make such a setup? Is it even possible?


you can use a lighter to fill a syringe and meter it that way, ill look for the link
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Unread postAuthor: Lockednloaded » Sat Jul 02, 2011 1:39 am

Well, I'm using a manometric meter
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Unread postAuthor: skishoot » Sat Jul 02, 2011 7:39 am

Have you considered using a small propane tank such as one for a torch? Otherwise you may be able to transfer it if you can connect a propane hose to it with a few valves and make a smaller tank, connect the tank through any type of connection open all valves to fill close and then disconnect.
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Unread postAuthor: DYI » Sat Jul 02, 2011 8:30 am

Well LnL, it isn't all that difficult assuming you can do it outside, and you have a few options. The "nicest" option involves a little bit of expenditure, because what you really want is a container holding the liquid which uses the fittings of your choice, rather than those of the manufacturer's choice.

Firstly, this method is geared toward 1lb tanks for torches. If you have a full-sized tank, siphon valves can be acquired which transfer liquid out of the tank by much the same mechanism that an aerosol can works by.

The method:
1. Build this container, with capability for easy fill. Purge the air from it by filling with water, and blowing the water out with pressurized propane (don't leave it pressurized at this point, the only purpose here is to get the air out).
2. Attach a modified torch valve for high flow to the top of the propane tank.
2. Obtain a few kilograms of dry ice and some liters of methylated spirits.
3. Construct an ice-bath using the dry ice and ethanol (there are several tutorials available on doing this) and use it to cool the propane tank as much as possible ( getting it below its boiling point shouldn't be terribly difficult).
5. Periodically check the pressure level in the tank by venting it into a balloon (or just venting to the atmosphere if you're not in a location where gas buildup is an issue).
6. When the pressure level is confirmed to be almost nothing, take the tank away from the ice bath for a short time and open the valve fully to vent any remaining pressure. Replace the balloon over the outlet and take the tank back to the dry ice bath.
7. Use the dry ice bath to cool your new liquid propane container to below propane's boiling point.
8. At this point, with the cylinder submerged in the dry ice bath and no flammable gases hanging around outside it, it is no longer a significant hazard to drill into the container with a standard twist drill (preferably through the bottom). There could be a short burn when the bit enters the tank if you drill way too fast, but otherwise you're quite safe at this point.
9. With one hole in the bottom of the tank (which you've just drilled) and one in the top (the modified torch fitting), the liquid propane can now be safely poured into your other container. Another hole could be made in the top of the tank to allow for higher flow rate.

You now have your own homemade tank full of liquid propane. Congratulations :lol:

This procedure can, of course, be modified to suit your own preferences. The paramount concern is to not be blown up/incinerated while drilling the hole. With that condition satisfied, everything else is gravy :wink:
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Unread postAuthor: Lockednloaded » Sat Jul 02, 2011 11:52 am

So simple... :?

I understand the ice baths, but I dont understand why I shouldn't be able to pour liquid propane through a high flow tank valve to avoid having to drill through the tank?

EDIT:

Just realized the actual BP of propane, not worth the work...
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Unread postAuthor: SpudBlaster15 » Sat Jul 02, 2011 1:22 pm

Lockednloaded wrote:I understand the ice baths, but I dont understand why I shouldn't be able to pour liquid propane through a high flow tank valve to avoid having to drill through the tank?


Pressure equilibrium.

If propane in a fixed volume container is cooled to below its boiling point at standard pressure, it is no longer capable of responding to a liquid volume change by releasing gaseous phase propane to compensate for the pressure drop. Thus, you need to allow for the introduction of atmospheric air in order to maintain pressure equilibrium and allow the liquid to flow.

There's really no way around creating 2 openings in the tank, short of pulling a hard vacuum on the vessel you plan to fill.
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Unread postAuthor: Fnord » Sat Jul 02, 2011 2:44 pm

Uhh, you could just make a small tank and adaptor out of copper pipe/fittings and hold the large tank upside-down when filling, as you would a butane lighter refill tank.

Unless you have a tank with an anti-siphon tube it'll work just fine. I've done it quite a few times so I don't want any arguments. :wink:
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Unread postAuthor: Technician1002 » Sat Jul 02, 2011 6:03 pm

The upside down tanks used to work in the US until they forced the upgrade from POL valves to the OPD triangle handle valves. The excess flow preventer in the valves prevent dispensing liquid by inverting the tanks. You will need a Forklift or other Liquid delivery tank to deliver liquid to your intended target tank.

One point ot remember is overfilling the smaller tank will make a serious hazard. Porpane changes volume as it warms up. If the tank is overfilled and has no expansion space, the propane will burst the tank. Normally the old style tanks had a bleed valve opened on a siphon extending part way down into the tank. You were supposed to stop filling when the vent sprayed liquid. Many service stations untrained in the safe filling would often think it was just there to purge the air out of the tank. They would wait until it sprayed and then close the vent and continue filling the tank filling the expansion space. This condensed the trapped vapor into a liquid and left no expansion space. Then on the way home (often in the winter) the tank warmed in the car would open the pressure relief valve and spray liquid propane in the car. This safety issue is why they made OPD valves mandentory.
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Unread postAuthor: ilovefire » Sat Jul 02, 2011 7:55 pm

you could just use butane? it still makes for a powerful hybrid
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why make it if it dosent shoot?
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Unread postAuthor: Lockednloaded » Mon Nov 28, 2011 12:13 am

Zeus posted an easier way in the chat, any opinions?
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