Meths Pressure Stove Problems

[markie*mark0]

Built a little pressure meths stove using this walkthrough http://www.britishblades.com/forums/showthread.php?5613-Pictorial-Martyn-s-Mini-Photon-Stove. looks similar to this

But i cant get it to "jet" properly, its made out of two bottoms of energy drink can Ali, bolt in the top, welded together with metal weld. No internal chambers.

I did pack the inside with wirewool to try and get the heat to stay in the meths, but it didnt work so i pulled it out and tried still not worked.

I used 1mm drill bit and tried with 8 holes, not jetting properly, added another 8 so 16 in total still not jetting...


Any tips? Using a new bottle of meths not watered down etc.

 

[Shewie]

That's odd Mark, they usually fire up okay when I've made them.

How tall have you made it? I've just dug one of mine out and it stands at just shy of 40mm, with 8 0.9mm holes drilled around the inside of the rim

 

[markie*mark0]

That's odd Mark, they usually fire up okay when I've made them.

How tall have you made it? I've just dug one of mine out and it stands at just shy of 40mm, with 8 0.9mm holes drilled around the inside of the rim

just over an inch. So similar size to yours.

It gets pressurised ok, but then the jets dont flame up. I've tried a priming pan and got the stove very hot and then its very aggressive, but then the pan runs out and the jets work for a very short time, then they go out.

will try to get a vid asap

 

[Teepee]

I'm at a bit of a loss too. Have you preheated it well? Some of mine take a couple of minutes to prime.

I've made about 6 of that design, all with differeing dimensions and holes and they have all 'jetted'.

Edit;too slow, already answered.

 

[stoviecraig]

Hi Mark,
I've had a bit of a tinker with home made meths stoves as well and i do think that they need a good bit of preheating to fire properly. I've also used loft insulation as a filler inside them to try and 'contain' some of the fuel as well as provide a bit of internal insulation. Seems to work but I would agree with teepee and a couple of minutes priming may be sufficient.

 

[markie*mark0]

just made a quick video, half full with a good splash of meths for pre-heat / priming, jets bloom up nice, but then when the prime runs out so does the jets....

[video=youtube;ecuoN7tvb-M]http://www.youtube.com/watch?v=ecuoN7tvb-M&feature=mfu_in_order&list= UL[/video]

 

[ateallthepies]

Just an idea but maybe that giant bolt is acting as some sort of heat-sink somehow? Try it with a penny instead of the bolt or even light with the hole un-covered?

Steve.

 

[Mastino]

Agree, such a big bolt will actually suck up all the heat. Just a flat top like a penny will do the trick

 

[Hetzen]

I'm only guessing here, but when you get blooming, you're not generating enough heat to maintain the meth boil in the stove.

You're probably going to ruin this stove by trying these methods, but it's a really good process to get a stove that works well, and if you drink as many cans as I do, it's not an expensive outlay to experiment. It's just your time.

I would first try to widen your jet holes. I'm figuring that not enough fuel is burning to transfer their heat back into the can to keep the meth vapourised. Next I would drill further holes. Most of my can stoves have had jets 1cm apart, and a hole size of 1/16 seems to work well.

 

[Hetzen]

You're certainly getting some pressure out of the stove, but I don't think any of that energy is getting back into the can to maintain the meth boil when the prime runs out.

It could be that the holes would work better on the rim instead of the top.

 

[Andy T]

Can i ask what may seem a silly question, when the fuel in the priming pan runs out, and the stove stops working is there still fuel in the stove ? The reason i'm asking is that's one hell of a flame on that stove and it looks like alot of pressure, flames that powerful must really get through some fuel. If you are looking for a lightweight stove thats guranteed to work pm me your addy i'll make you one for free. It may not be as neat but it will work.

 

[Jimmy Bojangles]

Looks to me like the bolt is stoping air getting in to fill the space left be the burning fuel, creating a vacume. Bigger holes may fix this, but I'd try it with the penny trick first, just to confirm that it is the bolt.

Can't see the bolt sucking the heat out, as once it's primed the bolt would have heated up anyway, and if anything should help be holding the heat.

Hope you get it sorted

Mat

 

[wattsy]

You need more holes mate about the same size I normally put 32 holes in mine and they work a treat.

 

[PDA1]

Those jet holes. holes are enormous. I make mine with a push pin or needle. You would need a raging boil to maintain any pressure through those large holes. Try 16 or 32 tiny push pin holes.

 

[ateallthepies]

I really don't think that is the problem PDA1, I use 2mm holes with my .177 airgun pellet stove and get an almost instant bloom and a 3.5 minute vigorous boil with cold 500ml of water using 1 oz of meths.

The pre-heat flame obviously is causing the meths to heat enormously as I rarely see that sort of flame thrower effect, but once out there is no heat to keep the jets supplied with vapour it goes out?? The heat must be going somewhere and that bolt is my guess?

Please remove that bolt Mark and report back?

Steve.

 

[PDA1]

A quick trawl through soda can stove specs shows that most of this type use 1.5 to 2 mm holes (#74 drill bit for the penny stove (1.5 mm) with 5 holes. #80 bit for a 32 jet stove (near 1 mm). The bolt does look a bit on the large size
Question for OP - What size are the holes? How much fuel left in stove when it went out?

 

[PDA1]

http://www.backpacking.net/makegear/photon-stove/

Here are Don Johnston's original instructions for the Photon stove. He expressly recommends very small jet holes.
"The size of the needle is very important because using a larger needle reduces efficiency."

 

[Martyn]

That stove has way more pressure in it than the ones I've made (that's my tutorial you followed). Is your stove hissing after the flame has gone out? The stove is way over-pressurised and once the prime goes out, the stove will too as it no longer has a pilot light to keep it lit and there is so much pressure in the stove, it's just blowing itself out. You need to get the pressure way down. Either by putting more jet holes in it (another 8 at least), or making the jet holes bigger. The idea is to make the stove more powerful than a trangia, but not to compete with a gas stove. That thing looks like a Saturn 5.

From my tutorial....

Less jets = more pressure and bigger flames, more jets = less pressure and smaller flames. It's a compromise, you can play around with the number of jets you use, but I would use at least 20 and less than 36

What you are seeing is the result of only having 8 jets.

You have gone for the high power option, which is fair enough, but there is a point where it just doesnt work as you have found out. Also, the high power option, while very hot, also burns through meths at an alarming rate, making it a fast boiling, but fuel inefficient option. There is no point making an ultralight alcohol stove, if the design of it means you need to carry a gallon of meths to boil a cup of water.

 

[markie*mark0]

Cheers for all your replys guys,

I'm away at the moment so cannot try anything until I get back.

To try and answer some questions:
Jets are around 1mm in size, I tried with 8 and got this result, then I drilled another 8 so total 16 and got a similar result so I autowelded 8 up to start again lol

The stove is still plenty full after the vid, but not hissing... So I'm guessing no heat retention, I'll swap out the bolt and see if that makes a difference and then redrill another 8 holes and bring the pressure down see if it stops blowing the jets out

Will let you all know how I get on

 

[Martyn]

Removing the bolt might help, but because there is too much heat, rather than not enough (think like the element of an electric kettle). Whatever, the stove in the vid is over pressurised and there are 2 reasons why that could happen, either the fuel inside is too hot, or there are not enough places for the fuel vapour to get out, or possibly a combination of both. It might be that even 16 holes isn't enough.

Less jets = more pressure and bigger flames, more jets = less pressure and smaller flames. It's a compromise, you can play around with the number of jets you use, but I would use at least 20 and less than 36

Just keep putting more holes in it until it stays lit.

Just as an experiment, try lighting the stove with no bolt and nothing covering the bolt hole and see if it stays lit? My guess is it will work. Once the fuel boils inside, the escaping gas will be restricted enough for it to jet, even with the big central hole left open. This should prove that you need less pressure/more holes, not more pressure/less holes.