H ChrisV: I have a few notions on fuel: Very simply, the hydrocarbon content doesn't define the temperature of the flame: The amount of oxygen (air) mixed with the gas does affect it greatly. I thought Paraffin was cooler than petrol - because my paraffin blow-lamps would not braze, whereas my petrol blow-lamp would. But recently, I rebuilt a paraffin blow-lamp and the flame was MUCH better - as good as the Petrol one.
Butane carries more carbon in its molecules than Propane, so more (denser) fuel. But as the pressure is lower, needs a different matching of sizes to get enough air into the flame for fast (= HOT) combustion. The last few weeks have been too cold (below 10C) in my garage for canister butane blow-lamps to be hot enough on small jobs! - The "reduced pressure" causes the flames to be bigger, more "wooly" and just don't give the focussed heat I need. Propane doesn't worry about temperature above -30C, so is much better in "cooler" climates. The 30% mix canisters you are using will loose most of the propane initially, so the pressure will still drop as the the cannister empties. But initially there won't be the problem I have been having with low-pressure butane canisters in the cold. I only use canister fuel for jobs that will go in a "closed fist" - as the "power" (not temperature) of these blow-lamps is too small for silver soldering anything bigger. Last week I soldered aluminium on the end of a small length of 1 inch channel - but this week I can't solder aluminium on a 5 inch can I am making. The blow-lamp isn't big enough. But I know it is OK when the weather is hotter in summer! (aluminium solder is at about 100 degrees below aluminium melting point. Not the 700 degrees you need for silver solder!).
Propane blow-lamps - because more pressure is available - use smaller jet sizes than Butane blow-lamps - and utilise the higher pressure to get higher velocity gas from the jet - which in turn sucks in MORE air and leads to faster combustion and a hotter, more focussed flame - Ideal for silver soldering. Attached some pics (mock-ups) of some set-ups I use to best apply heat for silver soldering boilers. (I had a problem that the cup-washer on the paraffin blow-lamp fell apart before I got full pressure on this lamp for the demo! - Only 40+ years old! These things are "servicable" items though! - I'll have to cut some leather from a welders gauntlet to make another cup-washer).
Using a horizontal tray of sand and fire-brick, using a vertical tin of sand and fire brick. You can see the 2 types of blow-lamp I use (not hand-held) for pre-heating and that gives me space in the middle for the Propane blow-lamp - using a regulator at 20psi (more and the flame blows-out!). Note the readily available fire extinguisher (To extinguish me if I catch fire!) and the use of extra fire-bricks to enclose the hot job and slow the cooling after soldering.. Both the petrol and paraffin blowlamp will normally get the sides of the boiler a dull red colour, while the Propane blow-lamp applied to the appropriate zone between will get a patch of boiler a decent red to melt silver solder easily. It can't do that without the insulation and 2 extra pre-heating lamps providing more heat. But my left hand cooks inside the leather gauntlet holding the propane blow-lamp! - from the radiant heat from the exposed hot-end of the job. I wear a welder's apron so I don't cook as well!
Watch out that the exhaust from one blow-lamp does not get near the air intake for another blow-lamp, as the flame of that one will be extinguished - with gas going everywhere until it ignites with a WHOOSH! - and sets your clothes on fire. It hasn't happened to me - yet - but I keep the extinguisher handy in case...(!?)
Work safely.
Hope this helps?
K2
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