Biggest contributor to underburn on this stove is the gap at the joint between outer cap and inner cap rim created by the ‘ramp’ locking arrangement. Flame at the three such gaps around the cap rim flashes back into the burner bell, igniting an ‘underburn’ when the burner is regulated down. The kinetic energy of the vapourised fuel stream at higher output settings prevents blowback and underburn but creates telltale spikes of flame down at the joint near where the gap is greatest at three points. Solution was to apply a fillet of silbraze at those points on the outer gap, blending them in by rubbing the cap joint on a flat abrasive surface. Tendency to underburn at very low settings has been cured. “Final instalment!” I said, but this stove has thrown up some intetesting topics, helped by @gieorgijewski and @Aleks-S
Sorry Duncan, I inadvertently overlooked your sensible suggestion. I still might do as you suggest. Although I gained adequate clearance by tweaking the stowage clamp to cant the stove fuel pipe a bit more inline with a box corner a little more clearance would be the icing on the cake. Thanks.
A Prim-compact shpindle has 1мм thread pitch (20% less than PT-1 and Ogonyok, which has 1,2mm). This partially compensate less sharp taper than of PT-1 and Ogonyok). And with Your add-on it gives far more accuracy for power regulating, which unavailable for other stoves. Great job! And thank You very much for kind words. This is a honor for me. I learn a lot on this site. The language lesson - is lesson for me. "Motion picture" is not in vain so called. I had to add animation, or pictures at least.
The O-ring pump worked ok, but as I described in THIS post in the Fettling Forum it had a certain harshness. I’ve replaced it with one made up from salvaged ‘brassie’ components, incorporating a leather pump cup washer. From this ... ... to this.
What i have read PK - was produced in 3 pumps designs: - Shmell/s - what WE saw at primary photo's, - classic colemans with valve - classic leather pump cup washer
Prim-compact has 2 type of inner cup of a flame spreader. Later of them has a trumpet on the lover end of central tube. Early - not. I suppose it also affects on simmering capability. There are also variations of piston material - brass (early) and aluminium alloy (later).
Alex about simmer /regulation range or easy precision/ truth is: it is big hole valve weak simmer is when - cold (wet - energetic) gas - is heated in burner bottom - proper simmer is when - gas from gas generator - is hot and pour but high pressure i think - secret of that construction is in - "last minute" design changes and someone forget "leave place for" and insert "structure" in gas generator ------------- 1 way generator must be hotter fuel need to be restricted 2 way add something to the generator space - for improving vaporisation surface ----- or 1 and 2 together ---------- it is "setting up" point of works - when "big hole valve" -proper simmer - burner power - pressures - are condition We can change: - entry pressure(tank) connected with - fuel flow / by restricting - raising generator temp. by heat back "repairing" imo - can be importand - in low power mode...
@gieorgijewski @Aleks-S It really just needs: the valve spindle tip to be re-profiled the gaps under the rim of the outer cap filled a larger spirit cup With those modifications the Prim has one of the most controllable regulated burners I know - seriously - and the least prone to underburn. Restricting the fuel flow when the Prim is equipped with a pump that’s not the most efficient is counter-productive. John
Yes - good... ------ My example is controllable regulated too. maybe not "the best" - but is ready for work
I took the Prim Compact along on a hike, and shot a video clip to demonstrate the burner’s controllability. The noise wasn’t the silent burner - in the background was a reservoir overflow, in action after all the rain recently.
Wow what an amazing journey with the Prim Compact and some serious upgrading John. I've been close to buying one on a few occasions but the cheapest on ebay is currently £140 which is simply too much I think.
I know, a crazy, unjustified price for what - unmodified - is a poor stove. Mine was £20 or something like that. Much better stoves, but now also with phenomenally inflated prices, are the Schmel series, the Optimus 8R clones and the Ogonek. Way over the top prices. John
To buy cheap then 140 GBP - you must do some special buy ops in Russia =) Like me and Ian =) But effect of this ops - may be wonderful - see the Ian posts here - many stoves got new life with him after auction in Russia =)
