G'day, When I first tried to pump pressure into this stove I couldn’t get any pressure. I initially put it down to leaking seals. So I pulled it apart, heated and quenched the burner to remove carbon, cleaned the components, replaced the seals and the leather pump cup. When I tried to pump pressure again I still couldn’t get any pressure. So into the bucket of water went the tank and burner. Had to use a compressor to get pressure but once in the water the problem was obvious. One of the vapouriser tubes was cracked, down in the frog where the two tubes came together. The only fix was to re braise the joint and seal the crack. My worry was when I heated the joint the pieces would move out of alignment. The joint was cleaned and fluxed. This is the jig used to support the burner. A piece of 20mm copper tube in the vice to sit the burner in and a modified old test tube holder to keep the alignment true. Filed a piece of 5% silver braise rod and mixed the filings with flux. This was then applied to the joint. (no touching whilst the braise is melted so less chance the tubes will move) Applied heat and waited for the braise to melt. Cleaned up the burner, reassembled and tested the stove. No leaks all finished.
Hi, a really well described and illustrated fettling tutorial. Glasd you got your stove operating once more. Best Regards, Kerophile.
Nice fix, glad you could do it. The 41's are my favorite stove, love the "fatso" tank. I got lucky last Spring and located a silent to go with my roarer burner one. Double love. Duane
Good job, like the 41 I have the noisey burner version called a 42, great stove to have in the car cook kit. Cheers Rob
May I ask. Could it be that the heat and quench may have caused the crack. I say that because you quenched before you dunked it. I have been fairly warned, by several stovies I trust, that heat and quench is not good for brass. The old catalogs show a device to blow air after getting the burner hot. I have a preston loop on a Petromax lantern that I did the heat and quench, and it has micro cracks that were not there before. I do not heat and quench now, I heat and blow compressed air. Ken in NC
Hi, Ken has made a good point. High stresses are induced in the metal of the burner during heat and quench cycles, and this can result in permanent distortion and even cracking of the tubes. The later parts of this thead discuss some of the options open for de-coking blocked burners: https://classiccampstoves.com/threads/ultrasonic-cleaning-of-stove-burners.27409/ Best Regards, Kerophile.
The Primus 41 was a nice stove to work on and I think it will get a lot of work in the future. @snwcmpr ,you are correct in that I can't be sure the quenching didn't cause the crack, but I will say that it was a single crack about 3mm long. Only the very tip was showing above the existing braise. The bottom of the crack I could see looking inside from the bottom. I haven't cleaned many burners but it has crossed my mind when performing this method that it is brutal. However when annealing brass it is the same process, heat and quench??? @kerophile Having said that I have read threads on the pressurised air & heat method and as I have a compressor I intend to peruse this further. I think it will be less stressful on me also as I worry about overheating the burner and having it fall apart. Thanks everyone for the comments.
Hi@ROBBO55. you do not have to quench brass from high temperature after an annealing cycle, air cooling is adequate. http://bisonballistics.com/articles/the-science-of-cartridge-brass-annealing. Some people may water quench brass to save time by cooling an item quickly, but if it is intricately shaped with many changes of section and thickness it will not cool uniformly and the differential stresses can lead to undesirable distortion and cracking. Even with sheet material of uniform thickness you can get severe distortion and bending, which then has to be rectified. The Primus method of burning out petroleum coke is far gentler and more controllable. There are some good posts on CCS of practical set-ups for the method. Remember, that once the coke in the burner tubes is ignited, the reaction is exothermic (heat-producing), so cut down or stop the application of external heat. Good Luck if you try it. Best Regards, kerophile.
A jewelry making instructor showed me a shortcut to annealing copper (and he said brass too). Mark the metal with a black 'Sharpie' pen. Heat the metal and when the mark disappears the metal has had sufficient heat to anneal, and let it air cool. It can be cooled in water after it has air cooled sufficiently.
Thanks @kerophile and @snwcmpr for the advice and clearing up the misconception regarding annealing brass. Much appreciated.
Hi, any of you interested in a 41? One listed now at Tradera. Chance to buy here to a reasonable price, I do not know if this stove is very sought after and popular http://www.tradera.com/item/2939/25...-b-a-hjort-co-fotogenkok-i-harligt-bruksskick
Guess you are right @snwcmpr - better on auction watch. Oh, only swedish buyers @z1ulike - will check better when something appears