The topic of how many washers are required around the burner/priming ring/riser 2-layer joint has been discussed in several threads. This thread is intended only to provide a quick, easily identifiable, link into the topic. Basically stoves originally came with one or other of 2 different types of assembly at this 2 layer joint. One was designed to use only one washer, the other was intended to use 2. An additional issue, however, is that wear and tear on some originally 'one washer' joints means that these too sometimes now require 2 to achieve an effective seal. Two photos below show a riser top designed for one washer on the left, and on the right the 2 washer type: And with the spirit/priming ring fitted: The spirit rings themselves are different too: The 'one-washer' spirit ring has a larger diameter central hole with almost no lip to sit a washer into, whilst the central hole in the 2-washer spirit ring is only just sufficient to clear the burner threads and with a nice seating area for a washer under the ring as well as one on top. The key difference between the 2 types of riser tube is that the top surface of the riser designed to use only one washer has a stepped profile, with the lower level being on the outer edge as here: , whilst the 2-washer type has a flat top to the riser wall with a concentric groove machined into it as in the 2nd photo above. The 'one-washer' design was used most extensively by Sievert/Svea on their stoves and on quite a lot of Primus stoves too, as well as in a few other cases. The one further complication is that some Primus stoves with the grooved top risers were originally sent from the factory with only a single washer fitted under a wide hole spirit ring and the whole assembly simply crushed when the burner was tightened to a point where the washer was squeezed up to fill the gap! (See this photo in this thread.) Stoves originally assembled this way are frequent candidates for moving to 2 washers on subsequent re-assembling! Further discussion of the topic can be followed up here and here.
Good summary @igh371 and fine in principle in relation to the ‘one washer’ set-up. To use your photo the distinct ‘step’ between the raised portion of the riser tube and the upper rim of the spirit cup requires some flexibility in the sealing washer to accommodate without a leak under pressure. It may be that the original high asbestos content sealing washers had that sort of flexibility but the modern material (Novus typically) isn’t quite so accommodating I’ve found. Hence my using two on the ‘one washer’ type, born out of experience of not getting a reliable seal otherwise on that arrangement. John
Hi John @presscall , the stepped riser top arrangement doesn't actually require much flexibility in the washer at all. The single sealing washer goes between the riser and ring, pre-positioned as shown in the photo, which provide a more or less flat surface, and the burner itself. The key point of the required pressure seal is between the raised center portion of the riser top and the washer. Strictly speaking the spirit ring doesn't even need to be held that tightly, although in practice it is usually held sufficiently firmly to resist being turned. The only time a particularly malleable washer was needed was in the case of those later Primus stoves where they tried to use a grooved riser top in conjunction with a wide-hole ring, and just torqued the burner down until it was all squashed to fit! Ian
Looks like Burmos was guilty of the same technique Ian, judging by this Burmos 51 I was fettling today. There was one (top) washer in place which had evidently failed and a previous user had slathered exhaust sealant all over the joint in an attempt to make a seal. For good measure they’d slapped the stuff on the taper threads of the burner to tank joint. After the fettle, which included de-soldering the pump tube to silbraze a crack in it (the Burmos Disease I’m beginning to think, having done three such repairs on Burmoses now). Plenty of slack. Top washer installed. Then one beneath to sandwich the cup. Riser tube in place. Once fettled, a good performer.
@igh371 Thank you for the clear and illustrated explanation of the one- and two-washer conundrum. The Australian Aladdin two-burner I mentioned in the earlier thread on this topic, that required one washer to work properly, ended up with “spinning” spirit cups. Cheers Tony
I am hoping to revive this topic from this spring. I am working on a Primus 210 I just received. It is burning well, but I am still struggling to stop the leak at the junction being discussed here. It is the 1 washer type, but still leaks in spite of using a new washer. I seem to struggle with all my Optimus and Primus 3 legged brass stoves. I am never quite sure how tight to turn things. At the moment I have stopped them all from leaking, but it is always a battle. It seems like a poor design to me. Next I will try some stove gasket cement on the 210 and hope for the best. Brad
@BradB On the Primus-type burners, I use either one washer (above the spirit dish) or two (above and below). I tighten to hand tight (no forcing), then tighten further with a neat-fitting spanner. It needs to be snug and tight, but don’t overtighten it and distort the washer(s). After an initial burning, I nip the burner a little tighter. They usually need it after the first burn. A photo of your riser and spirit cup might be useful. Cheers Tony
It is cooling right now. While burning I can see kerosene down at the riser/tank joint. I see that it is a tapered thread without a washer and I am not sure how tight it should be. It is quite wrench tight now. But the kerosene might be following the threads down from the burner. I think when it cools I will put some thread sealant on the tapered thread, just to eliminate that possibility. Of course that is not a solution for a stove meant to be constantly disassembled. If it is indeed coming from the burner, then I will try the second washer underneath. Given the 1 washer design, I am not convinced that it will do much good. But if it worked for others maybe it will work for me. Brad
