This is kind of an interesting question. The instruction sheet was silent on this? In any case when these stoves were in wide use (because the were the only game in town) I was told they were supposed to “reset”. I was a bit skeptical of this claim, and never saw one reset, ever. I mean maybe that was the intent, but it never seemed to work in practice. Possibly if the rubber or elastomeric was in good condition. Definitely not the way to bet however. The 8R seemed to be prone to setting off the SRV, moreso than the Svea, inherent to the design layout of the fuel tank. What really sealed the deal though, was when Optimus started offering the “Mini-Pump”. Or unsealed the deal really, because users started treating these little stoves like they would a Coleman 2 burner suitcase stove and pumping 20 or 40 strokes into the tank, with predictable result. If you were at this late date to find an old lightly used 8R (or 123) at a garage sale or boot and a Mini-Pump is also included, 10 bucks says the SRV in the cap was probably blown out long ago and put on the shelf. This is very common.
A serviceable SRV can open and seal repeatedly. One which is age hardened is less likely to. An SRV is no different in principle to a NRV, and they reseal multiple times on every occasion the stove is used. The SRV seal is a consumable service part, the same as brake hoses on a car. Even the high-quality material used when new probably should have been replaced after a few years. Many owners were and are ignorant to this fact. Seals need replacing regularly for reliability and safety, same as aformentioned brake hoses. I've deliberately pushed a lot of the petrol stoves I've owned over the years into overpressure to check SRV operation. As I never even bother trying to light a stove without replacing all the service parts first, it's no surprise the SRVs open and reseal as intended. As for the official instructions, no, there is nothing stating a new seal or cap is required if the SRV opens. Some versions of instructions mention that there is a safety valve built into the cap which will release excess pressure, that's it. Edited to add: Expect trouble if fitting a replacement 'new old stock' cap. Unused or not, ozone will have degraded the rubber pip and the stove will not be trustworthy. Replacement of the seal in Viton from a reliable source selling genuine material is the best way for reliability, unless you know when any cap was manufactured....
Exactly why I also recommend learning to service the SRV vs buying a new cap. Experience proves that point.
It’s a bit of stretch to suggest that the current manufacture fuel caps are defective too, but I suppose it’s possible. New as in New is under discussion - to be clear, nobody is suggesting “NOS” or “New Old Stock”. One thing about the DIY cap repair that gives me pause, without pressure testing there is no way to know what PSI the new valve will actually release at. I couldn’t go through the routine only to simply guess (or just hope) upon completion that it is calibrated or adjusted correctly. Might as well do it right. Like mentioned previously some people really enjoy these kinds of challenges, others … do not. To each his own I always say, and more complete info will help guide their decision.
If I recall correctly...... Research here ultimately found it was not imperative to 'set' it to a measured pressure setting.
I wasn't suggesting a cap manufactured within the last year or two would be defective. However, can you provide a link to anywhere selling caps for sale which meet this criteria? I imagine a lot of what is sold is new old stock. Demand isn't exactly high, I'm not sure the owners of the Optimus brand are manufacturing new caps, perhaps they are? I wouldn't presume those linked to on base camp were made this year or last year, although they might be. They could be five years old... in which case they are possibly half way or more through their useful working life. When I first started experimenting with petrol stoves in 2009, a lot of the advice on CCS was 'do not tamper with the SRV'. Being comfortable around pressure vessels due to experience with steam boilers I got on and did my own experiments. Rather than built a test rig like the ones which have appeared on here over the years, I took a lazy option and followed this no-tools procedure: New seal in the SRV. Tighten very slightly. Fire up stove and allow to warm up. If SRV opens before normal operation is reached, tighten further. Carry on and do some cooking with suitably sized vessels. If SRV opens, tighten further. Put too large a vessel on the stove and do some serious cooking. SRV should open. Stove will then function correctly reaching a safe and efficient operating pressure but SRV will vent on overpressure. Not exact but I judged it near enough, especially as I never use oversized vessels.
We are deeply embedded in a "throw it away" society. The need is pushed to upgrade by replacement. The skills of repair, as well as the fortitude to actually consider learning to repair, is being lost, and downplayed, by most of society. Don't be like most. Stand out. Be different. Repair an old stove to original condition.
Couldn't agree more Ken, but there is no point in playing with fire. It needs to be something that you have the confidence and knowledge to do as this part in particular is a safety critical item. Maybe you have that confidence, perhaps I might, but not everybody does. From the OP's posts and questions, I wonder whether they would have that confidence? Nobody is talking about throwing things away, quite the opposite - we are giving advice and encouragement about keeping an old stove in working order. Even if he bought a new cap, he could keep the old one until he is confident to service it.
Contact Katadyn. You can get a new manufacture fuel filler cap for the Svea 123R. My brother got one just recently.
I think there are new ones from Asia being sold on eBay. I bought a “pump cap” a couple of years ago. Works fine.
I'd say a successful wick replacement is a good start! Interestingly there have been several people suggesting replacing the entire cap with a new £15+ item rather than a £1.50 seal, the other disadvantage to the Asian examples at least is the nasty straight knurling. I can't say whether the base camp (one would assume supplied by Katadyn?) is identical in looks to that used on the 8R or not. Nobody advising this has asked about the age of the stove, i.e. which SRV it is fitted with. If it is an older 8R, it will have the SRV with a slotted top. No adjustment possible, no special tools needed. Unscrew SRV cap, remove parts, replace seal, screw back up. Easier than an NRV as no special tool needed and access is better.
I overhauled an Optimus No.8F earlier this evening. These shared the same type of SRV as older 8Rs- I can't remember the date but I don't think it was until the early 1970s that the penta SRV cap appeared on the 8R? Anyway, it indicates how much variation there must have been. There was no adjustment, and the SRV seal was cork. Here's the original, face/reverse/cut in half: It had compressed to an equivalent of winding out an adjustable SRV by 2mm. I couldn't resist firing up the stove before destroying the seal for the photo, and remarkably it made good pressure. Given that the compressive strength of cork bark is likely to vary, and given it is prone to deform quite quickly under the relatively high SRV spring pressure, it shows the design has quite a bit of tolerance. These stoves worked perfectly for a long time before the adjustable SRV was introduced.
Well if it’s all the same, I’d still like to know for myself that it would release at the factory specification. The manufacturer thought it was important enough didn’t they?
I'm pretty sure it's a "plus-or-minus" kind of thing. After all, the original pressure relief for small, self-pressurizing petrol stoves is a steel pin that's pulled through the tank top when the bottom starts to bulge from over-pressurization. Not exactly a precision device. Still, there have been people on this site who have determined safe limits and constructed test fixtures to allow calibration of SRVs. You should be able to find this information via the site's SEARCH function. ....Arch
Only after the existence for half a century of self-pressurising petrol stoves without any means to finely adjust the SRV release pressure. We don't know the reason for Optimus introducing the adjustable SRV cap- was it deemed a vital necessity, or was it due to newly introduced legislation or insurance requirements? Even better, Staffan Rönn posted the original Optimus specifications, which settled things once and for all.
Well, you’re making the point better than I can. It’s true, we don’t know precisely why they did what they did. It may not be a precision device, but it is, at the end of the day, a burning pressurized vessel filled with gasoline. Anyway this is getting off into the weeds here, my point was while we “get off my lawn!” Curmudgeons can lament the advent of a throw-away society, and dearth of DIY repair skills, not everyone is interested in getting off into the weeds. Special tools need purchased, perhaps - the proprietary penta screw, then purchase the innards from a feller in the UK, and then calibrate it to release within some PSI range. Some people just want to camp with Gramps old stove, they don’t want to make a career out of it, that’s all. “Oh, I can just buy a new fuel cap? Great. Let’s do that.” I used to see this in the Old Radio hobby forums. Somebody wanted to get something tuned up again, they sign up to post on a question and some troll with a huge stable of electronic test gear pens up a 12 page missive on what needs to happen, and then a bunch of others jump in and argue, rinse lather repeat. The new guy, with 3 total posts … Eyes glaze over, logs Off, never to return. “Hey where did that new guy go I wonder…”
Well put Mr Fettler! I have always thought that the design with the penta head screw was there as a tamper proof (but serviceable) item for those with the correct tools. Lets make it a positive experience for someone who wants to use grandpa's old stove rather than telling him that he has to be some eco warrior and fettle everything himself! Hope the OP is still tuning in!
Obviously we're all going to operate our own equipment in the way we feel most comfortable. Whether we realize it or not, we're trusting that allegedly new caps were manufactured to the same QC standards as the original equipment. I suspect that these "new" caps are either NOS (in which case I'm suspicious of how the pip may have aged) or are manufactured under a (foreign?) contract with unknown/inconsistent QC. Either way, unless the part is dated, you have no idea how old the rubber pip is, or what material it's made of. We're all engaged in a hobby with highly flammable liquids under a small to moderate amount of pressure. There's no way to guarantee absolute safety. ....Arch
Current production of the 123R is in Romania. Before that it was Taiwan. I don't know when it was moved to Romania, it may have been fairly recently. Katadyn will sell new production caps for the 123 if you ask them. Whether they are of Romanian or Taiwanese origin or the age I can't say. As I said before, my brother bought one a few weeks ago. It was about $11 for the cap and about $13 for shipping to California.
