@fjfj765 I take your point about not replacing the spring with a new one, improvised or purchased - I don't intend to do that. I trust that the SRV was well designed to function before stove rupture, and understand that the stove is strong and likely to safely deform before rupturing anyways. I realize that the most likely scenario is that I have the original spring and it's working fine, and 600ish grams is a normal amount of force for the spring to take before depressing in a visible way. What I have little perspective on is how to tell whether or not the spring I have in my used stove is the spring that was designed to be there. Without the experience to recognize an unusual spring or a point of comparison, I'd like to get a sense of whether the spring I have is roughly the right strength - from other posts it seems like occasionally used stoves have had the springs swapped in the past. I don't know if the odds of that are closer to 1 in 5 or 1 in 1000. @Fettler I like the idea of getting a new stock fuel cap, both as the most reliable option, and to get a point of comparison for my old spring. I've contacted Katadyn US, and they're going to send me a quote for a new fuel cap tomorrow. @snwcmpr If the "new" cap is new old stock and the rubber in the gasket isn't soft, I have a second viton gasket and pip I could swap in. If I follow through with ordering a new cap, I can ask when they were manufactured. I just read through the exeter_yak post about making NRV springs - it's very impressive! All the more so to make the buckets for the pips to sit in, and then to share the process and the parts with the community.
Assuming you bought the penta wrench from the guy in Taiwan who Berniedawg sold his design to, you can get a new SRV cap from him.
Any cap only needs a pip. The pip is the consumable item. I am not in the camp of buying replacement caps. You still have the same problem, and now you have a non original part.
The Katadyn representative did not know when the replacement caps had been manufactured. My thinking now is that I'll hold off on ordering a replacement until I'm able to look at the spring I currently have while replacing the pip. If it looks like the spring shown in the link below (flat ground ends, coils tighter at one end than the other) I'll probably not replace it, after a lot of advice to that effect in this thread. If curiosity gets the better of me and I order a replacement to check its spring strength, I'll share that value. Either way, I appreciate the knowledge shared here. SVEA 123R Disassembly
@Fettler , my understanding of what @snwcmpr is saying is that the only real problem I had in the first place is replacing the pip/gasket, a "new" replacement cap that was actually manufactured a long time ago would also need to have the pip/gasket replaced. Am I getting that right? I've been doing more reading into anything I can find posted about SRVs here, and I found the spring strength figure I've been looking for, and more: In exeter_yak's second reply to his thread [EY] about Svea 123 SRVs he says: "The computed pressure release based on physical measurement is 63 PSI with a measured compressed spring force of .9 pound and .01463 square inches of pressure seal disk surface (confined by the peaks of the 1/2 toroid machined shape at the bottom of the pressure release component well in the lid)." My first takeaway from that is that I have been ignoring the raised rim or 1/2 toroid in the SRV inside the vent area, which has a larger diameter than the vent hole itself. I of course can't see it from the outside of the cap. I see that it is present, but not dimensioned, in exeter_yak's drawings of the three Sievert lids [DW], and the 1972 Optimus drawing [SR]. Since the rim / toroid is what the pip makes contact with, it would be the correct area to use in calculations, not the diameter of the thru hole to the inside of the tank. With a 600 g spring load, my SRV would then release at 90 psi - definitely better than 134 psi! My second takeaway is that his measured spring force is 0.9 lbs (408 grams) - still significantly lower than my 600. I'd bet his measurement setup was much more precise than mine. I'm going to try to create a more steady way to measure the force it takes to depress my spring, to see if I can spot subtle depression at a lower force. I'm starting to doubt that the intended operation of the SRV is just a little bit of gas "squeeking by" at a significantly lower pressure than the where the spring's force is matched and it begins to move - exeter_yak's calculated 63 psi is very close to the 65 psi design pressure given in Off Belay [SG], and within a rounding error of the 1972 Optimus drawing test range of 64-74 psi [SR]. With fresh nitrile/viton, it seems like the theoritcal release pressure correlates closely with the tested opening of the SRV. It seems like my 90 psi would pass the 100 psi test pressure quoted in Off Belay, but not the 84 psi given in the 1972 internal Optimus QC drawing. [EY] Second reply by exeter_yak on the first page of: Svea 123 Research Project, prelim [SG] 1975 Off Belay, STOVES FOR BACKPACKING, page 6, shared by SNOWGOOSE here: https://classiccampstoves.com/threads/stoves-for-mountaineering-off-belay-1975.12016/
I also improved my setup and saw more subtle movement around 550 grams, plus or minus 20g or so. That puts me at an SRV that would release in the mid to low 80s (psi), which is a level of risk I personally feel comfortable with given that at some point Optimus was using 100 psi as the test pressure.
