I'm at it again. This time I made some weird silent burner caps for my SVEA 123. I thought I would use some household items I picked up at the local thrift store for a buck and some brass plates for the same price. Total: $2 for all the brass shown in the next few pics. I'm also writing to present my findings as I went through several sets of candle holders to get to something that worked. The lightbulb finally turned on after I went through my scrap and came up with the weird designs shown below. Here is what one of the candle holders looked liked before I mangled them into the pictures following this first one. I made sure the pieces were made of brass and not steel plated with brass. I ran into one of those as I was working on this and found that silbrazing was next to impossible as I attempted to solder it. Here is the resulting set of burners. The bell-shaped one on the left was the first one I got working. It is made with the candle holder inverted with the stem cut and soldered in. I made others that were a lot larger that did not fit inside the burner basket of my SVEA but rather sat on top. These did not work. The second burner I based sort of on the Radius No. 7. I used the candle drip disc as the top of the burner and stem for the top. The candle holder is in the upright position. Drilling the holes in these were quite the challenge with the angle and the small diameter of the holder. One thing I didn't put in either one is a flame spreader on the inside. On prior iterations I put a dome-shaped spreader inside at the top of the cap thinking that would make a difference in how the cap works. My conclusion is that the cap doesn't really need the spreader as I found the same design in my 111T cap, which doesn't have a spreader on the inside of its burner cap. Here's a better look at the No 7 burner cap. Ok, it looks really weird and probably shouldn't work, but it does. The vapor port on the left burner cap is quite small but I haven't had any trouble pointing the jet into it. I've found that the size really didn't matter unless the burner jet was not lined up properly. Here is the first candle holder burner working well. With some meths priming and a light, it lit nice and blue right away. Now here is the No 7 burner in my SVEA 123. As you can see it has a nice flame pattern even with the drip disc covering up most of it. In this shot you can see the burner vents venting nice blue jets of flame. It makes a slight hissing sound at full flame throttle but nothing near the usual roarer sound. Here it is in low simmer. Usually, at this level of simmer, and with the roarer on, the flame is turning yellow and starts to putter out. With this burner, I can turn the valve down to almost completely closed and it still burns nice and blue. What it is doing is just forming a ring of blue flame around the opening. This is an in-the-dark shot of low simmer. Conclusions: 1. In my prior designs I made burner caps that sat on top of the burner basket. It works until the valve body cools down and then liquid fuel sprays out from the stove jet and quits burning or turns into a fireball. So I had to make the burner cap smaller so it would fit down inside the basket. 2. Even though I made a burner basket that fit down inside the basket, if the flames were not licking the inside walls of the basket, the priming wore off, the stove cooled and vaporization ceased. 3. The burner flame jets must be down near the burner basket to keep it hot, if not, the priming wears off, the jet and valve body cool off and vaporization ceases. What I mean by this is if holes are drilled on top of the burner cap instead of down near the bottom and the sides, vaporization ceases. 4. I tried with and without a flame spreader inside the cap and it made no difference on the size or performance of the flames. So I didn't put any in these two burners. The same is true of the mad hatter burner cap. 5. The inner tube length is very important. If it is too close to the top of the inside of the burner cap, flame performance is poor or non-existent. I made one that didn't even work and burned like a torch for about 5 seconds. I stopped trying to light that right away. I also made a few with a very short inner tube and some with no inner tube and found that the burner caps burned the same with or without the inner tube until you started doing simmering. What would happen is the flame would actually crawl into the burner cap and start the jet on fire. With the tube in place it keeps that from happening. 7. You can make silent burner caps with cheap household brass as long as the size and shape will fit the burner basket. sam
Sam, I think you just found a new hobby. Keep it up and we will all benefit from your experiments. BTW Nice job!
The local PBS radio station has a spot called "We're interested in the way inventive minds work". Me too. A local thrift store has a set of those candle holders ranging from about 8" up to 16" tall for $.25 each....and they've been there for as long as I've been stopping by. I've looked and started to buy but couldn't figure out how to use them. My mind isn't as inventive as yours. Those store seem to always have a brass section full of stuff that can be taken apart to reuse. Thanks for showing that although I can't quite figure out how you put the larger one together or the parts used. Bob
Sam, we can call one of the a mushroom cap and the other a bell cap Earlier you had a tophat cap. More please......
Inventive minds, Hummmm, yes i do wonder if they are wired different? I think they have a bit of the artistic bend to them. make more of these mushroom caps and i'd be pleased to buy one or two from you. I really prefer a silent burner. lance
I like it - mushroom cap and bell cap, although, I do like your first description of mad hatter cap a little better, since it describes how I feel when I'm putting these caps together... sam
Bob, I guess I don't really think of myself as inventive. It's just that when I see a pile of brass or other items, I see burner caps, pot stands, wind screens, fuel tanks, burner rings, stove cases, etc. Really, the one thing I lack that keeps me from 'inventing' more is time. My job just keeps getting in the way!!! I'll put together a step-by-step so you can see how I put the mushroom together. I think that was the funnest one to do. Here is my pile of stove parts. OK, OK I've been a little bit obsessive compulsive about it...
Heya Sam I'm sooooo doing the happy dance. You've done great work here and have succinctly summarized these Truths of Silent Caps above. I agree 100% with your comments. If there was a little "we're not worthy" smiley, I'd be sticking it in here. I have some additional thoughts to share on this most excellent treatise if you don't mind. On #3 above, at least *some* of the flames need to be licking the burner walls. They don't *all* have to, though, as illustrated by this OE Primus 212 burner. On #5 above, you have brilliantly determined that the inner tube controls fuel/air flow and also the back pressure given to the fuel/air jet. If there's not enough clearance, the cap will not work. If too much, then the flame front will move inside the cap and down to the jet. Also called underburn. I've thought that the lip of the inner tube sort of forms a venturi that speeds up the flow of fuel/air due to restriction. Since the velocity is higher at that point than elsewhere in the cap, it acts to prevent the flame front from getting back in the cap even when the overall velocity is low, as in simmering. Because the flow of fuel/air is lower on self-pressurized stoves such as the Primus 70/71, 8R's and Svea 123 (compared to pump-pressurized stoves), I found that I could reduce or eliminate the tendency to underburn with the addition of that little deflector dome on the underside of the minicap. This is an earlier prototype I cut away for illustration. The deflector acts to form that narrow channel of passage between it and the inner tube. I don't use these deflectors on other caps I've made as it seems like the pump driven stoves just don't need them. I suspect that extending the center tube above the top of the inner cap would probably serve the same purpose, but might be a little harder to dial in exactly. As you have pointed out, the cap can be "tuned" by messing about with the center tube height. Anyway, these are my theories about it. Sure doesn't mean they're right. To borrow an expression, "Aren't stoves fascinating?" Thank you so very much for writing up the rules and doing these experiments. 8) Best wishes, Gary
Outstanding work guys!!! I am going to have to try making a silent cap one day when time permits. Thanks for sharing your thoughts, ideas and theories. Cheers, Jeff
Hi Gary, I hadn't thought of the little 'flame spreader' that way before - as a venturi. I've worked on lawn mower and vehicle carburetors and they act on the same principle. That really changes my thinking on these silent burner caps, or at least supports some of my other ideas. You are right, I had to 'fine tune' the inner tube length to find the optimum burn at high and low simmer. I haven't done any measurements as to what that is, it is, for now, just an intuitive feel, but I'm sure there is a scientific method and ratio to tube length and burner hole position. One thing I have figured is that the burner hole position of the highest row must be about 1/3 the length of the way down from the top of the inner tube. Any higher causes problems. I'm sure the venturi concept removes a lot of the 'tuning'. As for 'theories' these are all theories and subject anyone's criticism or correction. I would appreciate that. I'm used to that kind of exchange since I work in a research and laboratory environment constantly performing experiments of one idea or another. As for that Primus burner, that is my next target. I'll be designing something that looks like that. I really like that shape and design. I'm glad you mentioned that not all the flames have to lick the basket - I agree. Thank you Gary sam
Hey Sam, you've OCD on brass items! Whenever you see brass you always see a stove? Man! Thats....that....incurable. With that many brass you can do lotsa fun stuff! Ron
Hi Lads glad to see you Gary ) you are absolutly right with a nature of underburn, some small addition back pressure plays mostly for selfpressurized (low pressure) burner other variants 1)clearance -controls fuel/air ratio in a mixture small clearence can lead to excess of fuel. 2)entire fuel/air jet must enter the inner tube. if the tube is narrow some part of the jet is cutted and burns inside cap. the same takes place then wind blows or cap and jet are not coaxial Grigoriy
Grigoriy, those are the exact experiences I've had while building these caps. I do have a question about what you mean by 'coaxial'. Can you explain this part? thanks, sam
It looks like we have two definitions for underburn here. Gary's under burn is when the vaporized fuel has entered the cap properly but with insufficient inner tube height and venturi size, the actual flame is drawn into the cap continues burning inside and then as the pressure drops further, the actual jet ignites. Maybe we can characterize this a receding back burn or back fire. Grigoriy's under burn is when the vaporized fuel has NOT entered the cap and is ignited underneath. Maybe we can characterize this as pre-ignition since the fuel ignites before entering the tube and cap venturi, as Gary put it. Some thoughts here and another 2 cents (I'm running out of pennies in this economy! ). sam
underburn is underburn. the reason is that flame gets in to a cap. Gary's scenario: good but slow flow inside cap takes place, so fire enters cap through flame holes. My scenario: flow with a defects
That would actually be three flow defects. 1. narrow inner tube (Grigoriy) 2. off-center burner cap (Grigoriy) 3. inner tube height and/or venturi improperly adjusted or sized (Gary)
