Machined Silent Burner Mini Cap for Optimus Stoves

Something stated, if not understood, questions asked. That's how it works. Statements & questions made in good faith. Opinions & facts both welcome & it gets us there in the end.

Bird has done what I would do. If I don't think something sounds right I'll often ask a question rather that make a challenge.

As seen on Gary's video's on Youtube & from tests done above it makes not a ha'p'oth of difference in practice as Bird suspected

Has anyone tried freezing a cap before swapping it over?

Joking!

 

My tuppenceworth...

With a brass damper I would say it makes very little difference when up to temperature. Where the all-brass caps are king is maintaining vapourisation!

I have machined up a few base-plates/spigots to use standard No.4 and No.5 Inner/Outer caps, from carbon/stainless steel and brass. Brass wins from a flame-maintaining point of view.

The mass/material of the adapter/damper determines: The thermal conductivity to transfer the heat back to the vapouriser; The time it takes for the cap to get up to working temperature (after the priming flame goes out and before the vapouriser cools down); Whether you need a pot on the stove to reflect enough heat down to maintain vapourisation or whether it is self-sustaining.

From experience:

• The thin-walled primus metal/carbon steel caps of the 4200, 4010, Minicap, Midicap variety get up to temperature very quickly and self-sustain happily.
• Home-made carbon steel thin-walled No.4 baseplate/inner/outer caps require a double-prime but work well and sustain well.
• The stainless steel caps of the Unicus variety (thin walls but heavy base/spigot/top) take a while to get up to temperature (double prime) and require a pot to maintain operation, you get a flare-up after a few minutes. The older non-tuneable ones need a little more patience than the newer tuneable ones, same underlying flaw though. Sometimes trouble with higher-power operation in that the flamelets leave the cap and not enough heat goes down to the vapouriser, with the result it eventually fire-balls due to liquid spitting out. Careful, careful, with these.
• My stainless Midicap requires a double prime but when running seems to sustain well.
• The 3D printed stainless steel/bronze infusion caps of the Minicap, Midicap, QS123, QS407 variety take a little more time to get up to temperature but when there maintain it well. They run well without a pot for several minutes (swapping pans/faffing around) but there is a noticeable decrease in simmer performance, as if its running-out-of-steam. A blast on full power gets it running happily again, pot back on and simmer away again. The stainless Unicus caps, it all happens very quickly, you need to watch it like a hawk and get the pan back on.
• The thin-walled brass caps of the Midicap and 4010 do what they do best and get up to temperature quickly and maintain well.
• The heavier-walled brass caps of the Korean No.12 adapter, home-made base/No.4 inner cap, small cap with thick turned base, require either a lot of pre-heating or a bit of time to get up to temperature. They run really well but that mass must be kept hot otherwise fireball. In contradiction to the stainless ones, without a pot keep them at a simmer and it will maintain no problem. Have them blasting away without a pot (lift off to do something for a couple of minutes), the flamelets are off and it allows the mass to cool a little, you notice a gradual decrease in performance...
• With the smaller cap which sits down inside a burner bell, there are little problems, they generally run well.
• With stoves which have a preheat loop (Himalaya, Omni, etc), there are little problems.

One notable experience with materials selection was a spigot I turned up for using No.5 inner/outer caps on one of my No.12 Cookers. First attempt I used 304L stainless as I had it to hand. I could not get it to behave properly, it never ran perfectly for any sustained period of time. On a whim I made one up out of Aluminium Bronze (bearing material, I have some stocks of it), no problems since - same dimensions. I put this down to either the quenching of the vapour stream through the stainless spigot or the lack of thermal conductivity back down the spigot to the loop-vapouriser below. Or a combination of both!

So yes, my vote is where possible to keep it brass or thin walled carbon steel (preferably brass), with as low a mass/geometry as possible.

Certifiable cap-a-holic,
Alec.

 

Alec, That was an extensive explanation and very much appreciated, thank you.
all,
Alec shared examples of how/why longer prime times are required and how some caps result in heat loss... that it's case by case. For an "added" silent burner to maintain or keep the heat IN, is maybe more of a challenge in some cases with "the flame" further away or further is OUT.
The material, the shape/thickness & total mass of various burner parts effect how quickly a stove will heat up (to vaporize) from a cold start, at times in extreme cold.
A burner design works (or not) in less extreme cold but to make heat effectively & efficiently when faced w/cold is the whole point. Wind shield and a pot can be a required part of the equation.
A counterpoint here seems to be only the space that the air is trapped and the vaporizer need to heat as quickly as possible and in some (most?) cases this proves true.

Burners that use prime heat to also begin to heat entire burner will help the process. In some cases it's best to heat beyond the vaporizer (& it won't hurt).
In this case Gary & Joe may have had similar concern and added blind holes in-part as a precaution against potential prime difficulty in cold (we've not heard that exactly, I know).

Hearing "blind holes" gave ME the impression that they perform much like grooves in a vaporizer. Further that, in this case, it's best that the heat of prime flame also begin to heat the area with the holes.
Grooves/blind holes make for more surface area to absorb prime and happens to be less mass/grams but result is it primes quicker/better. thx omc

 

The holes do look very attractive!

Bill, @parramethtrol
Ross ceased everyone's subscriptions a couple of years ago and made all of CCS free.
The new subscriptions only started last year when we moved over to new forum software, which was an expensive process.
I think that the subscription is still the amazing bargain that it has always been.

 

Why do you say that?

Thanks,
Ken in NC

 

I could be totally wrong, (I have been one or two times before), but for parts subjected to frequent heating and cooling, I thought that 360 brass had far too much zinc (and a touch of lead). With both the lead and the zinc subject to off-gassing at temperatures that could be realistically encountered in burner cap temps, I would have thought that a brass with a higher copper content, likely aluminum brass, (or more accurately aluminum bronze) would be the material of choice. My very gifted neighbor makes model engines, and uses 360 for practically everything because it machines like buttah, but avoids it where it is subjected to high temperatures. I know that aluminum brasses are the material of choice in heat exchangers. Also the higher copper content of the aluminum brasses would give better thermal conductivity. When I studied foundry work, they cautioned us against zinc alloys because of the very high toxicity when heated. (See "metal fume fever".) I wouldn't want to be hunched over a bench brazing 360 for the same reasons.

 

agreed, absolute Bargain, still the same price isn't it?

 

@Canuman
Thanks

 

For snwcmpr and anyone else who has the remotest interest in these things, this is a sobering read. I read it some years ago, but it still maintains significant impact: http://www.anvilfire.com/iForge/tutor.php?lesson=safety3/demo.