I just bought some assorted spares. In the lot was an outer cap for a silent burner. Primus number 4205. I found it in this catalog. Why did they offer both metal and brass? Any thoughts? Vidar
Steel caps have lower material costs but are less sustainable since they turn to rust (even faster at high temperatures). Brass caps should be better (but more expensive). I think brass is also better in coping with rapid temperature changes. Maybe the steel was the 'budget' version?
Hi, I believe that the "Primus Metal" used in these outer caps is not a cheap mild steel or similar alloy. Instead it is a chromium / nickel bearing alloy steel which has heat resistant properties. It was chosen to show superior performance to the brass caps sold previously. The steel caps do not deform and bulge in use, and were much more resistant to melting in the event of under-burn. When first introduced they were more expensive than the brass equivalent which reflects the higher cost of the alloy steel and its pressing/machining costs. Best Regards, Kerophile.
Maybe some other manufacturers had these similar steel caps also... I think that I have Ginge outer caps that have "Heat Resistant" text on them and they handle extensive heat quite well (no discoloration nor rusting after they have been red hot). Also some UK made outer cap that I got in some old stock spare kit from UK had similar type steel outer cap. You can hear from the sound that outer cap gives when hit some small steel rod if it's made from good material(heat resistant) or if it is just from cheap steel that gets rusty.
Hi, you are quite right. It was not long before other stove manufacturers followed the Primus lead, and also intriduced heat resistant silent caps. In this 1930 Primus Con catalogue on p.23 we have mention of the new "NON-MELTING OUTER CAPS" Now obtainable in the new Primus metal, which does not melt even when the burner is "lit back". https://classiccampstoves.com/attachments/1225573577-1930-primus-con-p23-jpg.106953/ The prices of these Primus Metal caps were give in the old pre-decimal currency. Pr. No.4 outer cap 12p Pr. No.5 outer cap 12p Pr. No10 outer cap 14p Brass outer caps 5p So, as I said earlier these alloy caps were sold at a considerably higher price than the older brass designs. Best Regards
On a purely aesthetic level, brass silent burner caps tend to glow red (and turn the flames orange) at simmering levels and the Primus Metal caps don't, I've observed. John
The brass caps have a tighter fit without air leaks. I tend to prefer these but both work fine, much better than the latest no name replacement caps available. Ray
Primus distinguished between silent burner no. 4138 (with Primus Metal outer cap) and no. 4139 (with brass outer cap).
I have notices that 'el cheapo' Indian made soft steel caps that are zinc plated/yellow passivated also turn flame yellow. If I switch cap on same burner to old stock heat resistant steel cap flame will be blue again.
A brass cap burning hot (but burning as normal) for too long will become brittle and you can just press in the perforated section with a fingernail. If you loose the same cap on a hard floor pieces also can come off it. An old used brass cap from a special silent burner can be like this. A quality steel cap will hold up good. Rapid temperature changes is an interesting part of this. A cap – both steel and brass – can glow a bit when a stove is going full tilt. When you then reduce and say you want to just simmer, I find a steel cap to cope best with the change. But this is purely from a using/cooking point of view. All the best, e
Wow, I shouldn't be surprised anymore, but I still do. The knowledge about things in here is so enormous. The cap I got is nos and in very good condition. And I understand that it is a higher priced item. The quality is supreme. There is almost a stainless steel look to it. Now i just need to find a stove to use it on! Vidar
Hi Vidar, I do not know the precise composition of the Primus "special metal" but believe it is a steel with high Chromium and Nickel, and is heat-resistant, so quite likely one of the stainless steel family of alloys. When the Primus special metal was first introduced in the late 1920s, stainless steels were still in their infancy, and although laboratory work had been done, the industrial equipment and processes to make these complex alloys were not yet available. It is likely that the composition of the Primus Metal changed over time and the later production was a true "stainless steel" There is a S. Korean seller who offers matched stainless steel caps and I did try a pair and found them good. They would be particularly useful for marine stoves because of their corrosion resistance. https://classiccampstoves.com/threads/s-korean-silent-burner-caps-stainless-steel.27694/ Best Regrards, George.
@logen @kerophile I have never seen Primus Metal caps with other than some slight surface rust on them; the kind you clean of wit a rag. They behave a bit as hardened steel used for engine parts – there might be a little rust but wipe with an oily rag and the rust is gone. I have seen Primus Metal flake though, flake like you would see on a hard used inner cap from a 111T. I have an old 4200 with a bit of flaking on it. Funny you should mention the Korean cap post – I was looking at that one last night pondering over caps for yet another Radius No 5 without its bits. All the best, e
