This how-to article is about how to make a self-closing fluid chamber, or in other words, an automatic valve, for a pressurized alcohol stove.
Alcohol stoves are ultra-light backpacking stoves, usually made of various types of soda, energy drink and beer cans.
some background information
There are generally two types of DIY alcohol stoves: non-pressurized and pressurized. Non-pressurized is basically a stove with open flame, and easiest to make, pressurized ones have separate chambers where the fluid gasifies under pressure. Most pressurized stoves don’t really have a high pressure, since the pressure is not fully contained. Then there are the high pressure ones, such as the one we have here. This type has a fully contained chamber, creating high gas pressure, and thus the hottest flames. These stoves can get so hot that the aluminum starts glowing red!
I have made numerous stoves before, and if you are interested, you can check out my YouTube videos on how to make various types of these stoves. But a self closing chamber is a concept I have been working on for a while with not much success, until now!
The problem with the high-pressure stoves is that there need to be a convenient way to fill the stove chamber with fuel and then seal it up so it can operate at high pressure. The solution I came up with seems to be simple and reliable. I made a functioning prototype, but haven’t done any field-tests yet!
a quick overview on how the stove is put together
For this prototype, I am using a Venom Energy drink can, with the thicker aluminum core. The cap is from a Rock star energy drink can, but the original cap should also work, but at this point, I haven’t tested that.
The plastic thread is removed from the bottle-neck. The purpose is that the cap can move freely vertically at the top of the bottle-neck.
The can is cut in half at about middle of the can, but the top part does have to be at least as tall as the bottom part.
The orifice (jet) holes are made toward the bottom of the bottle shoulder (or top, when turned up-side down, see images below). I punched the holes, but it’s better to use a tiny drill, since over-punching make the holes too big.
The plastic seal inside the cap needs to be removed, and the cap placed up-side down at bottom, inside the can.
The inside of the cap, and the corresponding surface on top of the bottle-neck need to be completely smooth, for a good seal.
The top part of the can is pressed upside down inside the bottom part of the can, but not all the way down. Stop a few mm before the bottom, so the cap still can move freely vertically. If the top part is pushed too far down, the chamber can’t be filled with fluid,and the stove is basically ruined (the top part can’t be pulled back off the bottom part without destroying either part). One way to prevent the top part from going too far in, is to place temporary spacer on top of the cap.
Once the stove is assembled, the top of the stove needs to be cut down to desired height.
How it works
the theory behind the automatic valve design
OK, that’s how it is put together, now let’s talk about how it actually works. Understanding how it works, you can experiment and improve the stove by trying other types of cans and materials, and do other tweaks.
The cap will be resting at the bottom of the can. When fluid is added from top, into the center of the stove, the chamber, and the cap, will fill up with liquid.
Heet (automobile de-icer) is the preferred fluid. Dump a small amount of the fluid in the stove, enough to flood over the cap, and fill the chamber. Don’t overfill: The fluid in the cap, and in the chamber above the top of the cap, will be burned as stove primer. That also generates heat, but not as much as the heat generated when the jets kick in.
Ignite the fluid. Be careful so you don’t burn yourself. In daylight, you can’t see the flames!
The priming fire will burn up the fuel in the cap, heating up the stove, and the fluid in the chamber. Since the fluid in the cap is consumed, the cap will float up like a boat, and close the gap between the cap and the bottle top, thus closing the chamber.
The fluid in the chamber heats up to the point that it starts gasifying. The pressure in the chamber makes the cap push tighter on the bottle top, increasing the seal effect,
The pressure also starts pushing out he gas through the jet holes. The escaping gas is ignited by the primer fire in the center of the stove. Eventually the primer fire will run out of fluid, since the cap is closed, and die out. The heat generated by the burning gas will continue gasifying and pressurizing the fluid, keeping the jets going.
Hopefully you enjoyed this article! If you have any suggestions, or any questions, please leave a comment below!