This forum seems to be a wonderful group, with plenty of knowledge to share about a fascinating hobby. I'm looking forward to learning from you! This is my first post. I recently purchased an old used Svea 123 for $25 as a project. I felt its long history, its durability, the (potential) shine of the brass, and the roar of the burner would make it a satisfying and useful stove to own, and I'd love to be able to show my friends what came before their MSR Pocket Rockets, Jetboils, and BRS-3000Ts. I also hope the noise brings back fond memories to older cavers at conventions who used similar stoves on expeditions in the past. I took apart the stove and cleaned it up a bit, and ordered a replacement wick, fuel cap gasket, SRV pip, some metal polish and a filed-down penta-bit to access the SRV pip. They haven't arrived yet. In the mean while, I wanted to run a rudimentary test similar to Rob McMillan's setup [RM] to see if the SRV would function in the right ballpark of pressure, aiming for or below the upper limit of 5.2kg/cm2 (74 psi) mentioned in the Optimus document shared by Staffan Rönn [SR]. Using the vent diameter of 0.112 in from Doug Weise's drawing [DW], which looks right to me via ruler (I don't own calipers yet), that gives an area of exposed rubber of 0.00985 in2. The maximum force at which I would expect to feel the pip start to move as the spring compresses would then be 74psi×0.00985 in2 = 0.73 lbs, or 331g. I'll be replacing the pip with a new viton one anyways, so I was not worried about being unable to reseat the dry old pip [AB]. I balanced the SRV on a scale, tared it out, and gently pushed down with the end of a marlinspike, watching the reading until I felt the spring just start to yield, and repeated that maybe a dozen times. It didn't yield until the scale read about 600 grams! That gives a pressure of 134 psi at which the SRV would start to vent, which I'm not comfortable with. The SRV set screw seems to be tightened until the threads are just starting to show, so it doesn't seem to be a case of the screw being too tight. I think the spring must have been replaced in the past with a much heavier one. I have a few questions I'd love to hear yall's opinion on: 1. Does anyone see glaring holes in my thought process, or disagree with my conclusion that I need to replace my SRV spring in order for it to function as a safety device? 2. Did anyone have a batch of SRV springs made and have some spares left? Or perhaps could recommend a model of ballpoint pen that has given a spring that will form a functioning seal, but release somewhere below 74 psi? Otherwise, if the pens in my drawer don't give me a spring that yields before 331 g of force when installed in the SRV and tested as above, I'm looking at a minimum order of 15 springs from thespringstore.com using the part number Pitsligo [P] identified (#PC022-210-7130-SST-0500-CG-N-IN), which comes out to $4/spring for me after shipping (prices must have changed). 3. I'm also interested in how closely the results of rudimentary tests like mine and Rob McMillan's are correlated with the results of higher-end setups that test via compressed air. I searched for but did not find any threads comparing springs yielding to air pressure vs manual depression. Would anyone who owns an SRV tested using a more reliable method mind testing it in a similar way to what I have shown, and post how far off the manual result is versus the compressed air setup? Or send a link to where this has been discussed previously? References for ease of navigation: [DW], [AB] Doug Weise drawing posted by Longilily, and comment posted by Afterburber: Svea 123 SRV [SR] Staffan Rönn, Optimus spec.: Optimus svea 123R disaster [RM] Rob McMillan test setup: SRV Cap Tester/Setter [P] Pitsligo spring part number: SRV Springs
Don't worry about it. The SRV doesn't open that much. The pip will start leaking far before the spring gives way. Even a small leak is enough to vent the built up pressure.
I don't know the answer, but I thought that was one of the best constructed posts asking a question I have seen on this forum, with all the details and references given!
Spot on- when a safety valve of this type releases pressure in use, it's a case of gas creeping between the seal and orifice. The seal, holder and spring won't move a visible amount.
SRV released a couple months ago when I was doing bread on my 123. First time it's happened to me. Years ago, while I had the wick and riser out of a 123, I pressurized it with cap on and was amazed at how much pressure it held, unfortunately I don't recall exact pressure, well over 40psi before SRV released. I'm in the "don't worry bout it" camp too.
Most brass polishes (Brasso, Simichrome, etc) contain ammonia, so please read label carefully. Can cause stress cracks in the fuel tank - not guaranteed to do so, but why risk it?. Yours looks pretty nice as it is. There's a bunch of posts somewhere about what stuff to use in the future if you decide to do so.
I use Mothers Mag Aluminum polish. It smells good and works well. +1 on no ammonia. Why risk it, and it also smells bad.
New fuel cap gasket, prick the jet, and run a tank or two of fuel through it to familiarize yourself with operation and you should be all set. They are impressive when polished. They will not maintain their appearance very long however, unless you are a fanatic about it.
fjfj765, snwcmpr, Blackdog, and Majicwrench - It eases my mind to know that gas can escape well before the spring begins to move in a perceptible way. What keeps me a little bit wary is that when @Rob McMillan did a similar test, his spring moved at around 225-250 grams of force, less than half of the 600ish grams I'm getting. I would still appreciate it if someone with an SRV they know to be functioning is willing to balance it on a scale and press the pip down, and let me know if they get a number closer to mine. Without that, I'll take extra caution to only use the stove for short burns with small cookware. snwcmpr, PWDolkas, fjfj765 - thank you for the advice about ammonia causing stress cracking in brass. I was going to use Simichrome polish after seeing it used in a Youtube video, not knowing it might significantly weaken the metal. Now, I'll avoid ammonia and probably keep the stove as-is (looks-wise) for a while, and look for a safer polish like Mothers Mag & Aluminum if I decide down the road to shine it up. Fettler - I'm definitely looking forward to burning the stove for the first time! Funnily enough, the original wire pricker tool had been lost, and was replaced with a carbide lamp tip cleaner by the previous owner. It seems to me like a good replacement - the wire fits in the jet anyways. That's a good point about needing to frequently re-polish the stove to keep it shining, I'll consider that before spending money to get a safer ammonia-free polish and spending time to use it. Majicwrench - I like your baking setup! Were you happy with how the stove-top bread came out? Paul Lydon and DirtWhiskey , thank you!
@CaverRC , bread turned out fine. BTW, the stove had ran 30 minutes or so before the candle flame at the SRV.
@Majicwrench - The bread looks tasty! Good to know - 30 minutes is a pretty solid run time before the SRV came into play. @snwcmpr - Beautiful flames - they're such a pure blue, and coming out at such a flat angle. Is that the result of running clean fuel at a pretty high pressure? The gasket, pip, and wick arrived today! I swapped out the gasket and wick, but the ebay penta-key still hasn't arrived, so I haven't swapped the pip yet. (It shipped from all the way in Zaporizhzhia, Ukraine. Best wishes to the seller ua.miru, I hope they make it through the war okay.) I did a quick dunk test to make sure the vaporizer had seated well - it had - and noticed a slow leak from the SRV, a bubble every 3 seconds or so, probably from the pip not seating perfectly after I messed around with it. I wanted to see if that translated into enough of a leak to hold a flame with the stove running, and was really eager to fire up the stove for the first time! The stove did great! There didn't seem to be any problem getting to pressure, nor did any candle-flame appear when waving a lighter around the SRV just before shutting off the stove, so the pip must have reseated well enough. I'm really satisfied with it, glad to own it, and am looking forward to getting plenty of use out of it. For all the talk about its jet-engine like roar, it wasn't as loud in person as I had built up in my mind. Here it is bubbling in the dunk test in a bucket full of hot water and a bit of dog hair, priming with alcohol, boiling some water for my dinner, running again, glowing just after shutting off, and acouple of shots from a second run to see if I could get the flames any less yellow / more blue. (I think the software in my phone's camera is exaggerating the reds a bit - they didn't look quite so saturated in real life.). Thanks all for the advice to not let the SRV issue stop me from using the stove! I still may play around with some pen springs to see if I can get one that moves below 331 g of pressure on the scale, and then see if it performs okay if I swap it in the SRV. I'll post updates if so. I would like the mental comfort of an SRV I can trust to vent in case of overpressure.
Do not replace the SRV spring. Leave it be. The SRV is designed to be safe in a wide range of conditions. From bottomed out to all the way loose, it will vent before the tank ruptures. If you feel uncomfortable with the SRV, perhaps you could tighten the penta screw a bit less. That way it'll vent earlier. Again, I would not worry about it. Those founts are silbrazed together, and are very strong. The mode of failure of the founts is usually not dramatic either - the bulging of the bottom is what you see most of the time.
@exeter_yak had some posts about making springs. Pretty detailed. Yes, clean fuel, hot stove, and early version model. (Mid 50s)
i know this sounds crazy, but hear me out. The Svea 123R is still in production. If the concern is about the SRV, a simple solution would be to purchase a replacement fuel cap, thus obviating the need for cannibalising ball point pen springs or spare parts all the way from the Ukraine, and elaborate pressure testing regimens. I mentioned this once on a similar thread, and it went over about as well as if I’d pushed Grandma down the stairs. LOL
