I've read a lot lately about spring lengths, vent pressures and pentagonal keys for Primus/Optimus/Svea filler caps on petrol (gasoline) stoves. Here's my take on this important topic, and a rustbucket is a crucial part of the tale. First, take a look at this Famos incandescent mantle paraffin (kerosene) lamp, going well ... Here's the heart of that light, the mantle, a delicate tracery of fibres treated with chemicals that incandesce when heated by a ring of blue kero flames Controlling the flames is the wick-raiser knob. A fraction too much height of the wick (its a judgement thing, based on how the flame looks and how the mantle reacts) and here's the result, a nasty overrun, that left unchecked would blacken the lamp chimney, then the ceiling above it, then the rest of the ceiling ... walls ... room That's with a lamp in good health, maintained to a condition that its maker - (Veritas, derived from Ehrich and Graetz, Germany, designs and tooling) - would have been happy to endorse. My point? The stoves we collect, use in the great outdoors (yard, or wherever) still need to be watched in use - whatever the vent pressure the tank filler cap's set at. You can bet that a healthy stove will be obvious, one with a burner or jet blocked or partially obstructed will demonstrate obvious symptoms too. Is it burning right, does it sound right? Sound's like it's choking? Probably is then, so shut down and investigate. Don't rely merely on the tank pressure release valve. Don't let it get so far that it's needed. More pics. Here's an Optimus 80 petrol (gasoline) stove going well, housed in an army surplus case, courtesy of Parra's ebay tip-off. Prior to that shot, I needed to check on the health of the filler cap release valve, which has a pentagon socket. So, I took a hex key ... ... and ground a pentagon on the end I took the valve apart with it ... ... and checked on the state of the spring and the nitrile 'pip' in the valve seat It all checked out. Pressure test? Nah. I haven't seen a CCS post with a definitive pressure release figure yet. A few guesses, sure, quite a variation. Now, if a figure could be established, empirically (experimenting to bursting point) or from long-lost Primus/Optimus/Svea factory sources, is that figure with the stove hot or cold? Or, is it when fresh out of the factory or adjusted for a tank now fifty years old? With a pan on board, or not? What size pan? See what I'm saying? It's not exact. Get a new (old stock, that is) tank filler cap and valve. Will it be up to 'as new' spec though ...??? For myself, I've checked the valve will open and isn't gummed up, or the spring corroded through, so I'm content to carry on and brew up with it. Still fearful? How about this? Yes, it's a rustbucket. It can be used with one hand ... ... or two As a last resort - with no rustbucket available - I recommend a good pair of running shoes. OK, CCS technos, bring it on ... Best wishes, John
Hi John, Informed Consent...that is the essence of your argument. You have considered the factors and made an informed choice. Unfortunately when your stove passes onto its next owner he/she might assume that the safety valve is correctly set at the appropriate release pressure. Caveat Emptor Just my two pennyworth. Best Regards, Kerophile.
You're right of course, George. Now, what's the correct release pressure for that stove? It's an Optimus, so the year's not marked. If I knew the year of manufacture I don't know if Optimus changed the release pressure over the years it was in production. Then again, even if the valve matches up to design spec, maybe a non-destructive test of the tank to check its integrity, given its age, would be best. X-ray photographs, coupled with photomicrography would be thorough. Even with all that and the equivalent of an independent steam boiler test certificate to go with it, it would be an unwise buyer who wouldn't beware - or at least take the basic precautions. I'll leave you to judge whether that should include having a rustbucket and running shoes to hand. Regards, John
I hate to keep singing an old and tired tune --namely "Educate The Newbie"-- but what's the story with having absolutely no literature on Optimus/Svea/Primus SRV design specs? Did all the different factories burn down, taking with them all the different design records, and all the different machining specs? Are all the old employees gone, so that, like Aztec glyphs, the secret of correct SRV pressures have been taken to the grave? Is this the machanical eqivalent of the Irn-Bru formula, that only Mr. Optimus and his daughter (and one other employee, his identity secret) know the correct settings for the SRV, and once each month they gather and build a batch of SRVs to send to our sponsor as replacement parts...? Why is so little actually known about the design and manufacturing standards, and OEM parts specs of these stoves? Alex
Darn good questions you've put there Alex. Incidentally, I apologise for not getting around to measuring up those riser tubes that you were trawling for specs for on CCS a while ago. There's plenty of literature in the CCS reference archives, some of it technical on patents and such, but I don't recall seeing information on tank filler cap pressure release valve specs. Some figures for pressures have been touted around by CCS members but I've seen conflicting figures so I wonder what their sources are. It's possible I've missed locating some data that's there after all, newbie or not. We're dealing, by definition, with old stoves here and as I suggested to George (Kerophile) previously in my tongue-in-cheek response to him, I'd rather make an informed opinion of the state of the stove's general health and not rely on just one component, ie the pressure release valve. Even then, there's still potential to get caught out. No-one could have spotted this one (short of X-raying the tank beforehand) https://classiccampstoves.com/posts/106633 Had that been a petrol (gasoline) self-pressurising stove and not a pumped kero one, the tank would have most likely sprung a leak (rather than burst) before the tank filler pressure release valve operated ... Outdoors, and with an alert stovie, I doubt the consequences would have been too fearsome. Cheers, John
Hello, Doug aka Exeter_Yak has made a pressure release pump that holds the tank cap. You press down and when it hits the pressure it blows the seal. He has been absent as of late. I will try and e-mail him tonight to see if he can give me the pressure settings. Chuck PS Just e-mailed him, Hope I hear from hin soon.
I guess you mean this, chuck? ... Svea 123 Research Project, prelim ... discussed in this topic? https://classiccampstoves.com/posts/109908 Yup, seen it. Great technical achievement to produce an elegant device to establish that the release valve operates at such-and-such a pressure. It remains, for all Doug's work, to ask "what pressure should that be, then?" Stove hot or cold? Valve hot (and hence valve spring hot and at its sloppiest) or cold? Age of stove to be taken into consideration? OR dismantle the release cap, check the bits inside are good, replace the nitrile seal and spring if neither are. Optional, replace the entire cap if you like. I'm saying, that so long as it vents at all, and at a pressure that's not obviously way too low, that's a result then! Incidentally, to Optimus 111B users (the petrol/gasoline one) you need to remember that if the filler cap valve's good/tested/new you need to be sure the NRV is too. In which case, you'll wait a while for anyone on CCS to give you the quote you a release pressure that's not guesswork, I think. Or, replace the 'pip' or entire valve and seal. Or get a kero version of the Optimus. Regards, John
Seems a cold cap on a cold stove would be the critical number to know, as that's what the fettler would be working with while actually setting the pressure on his rehabbed SRV: a room temp SRV in a room (or garage workshop!) temp pressure testing jig. So just to be dense, why not simply index the cap and plug of a new/old stock SRV so that the plug can be reinserted to the exact "factory" setting, disassemble and replace all the rubber so that you know it's good, reassemble to the index marks, and test it in one of those clever test jibs I saw posted a couple months(?) ago? Seems that would at least reveal a release pressure that's in the ballpark. And now I'm concerned: John, why should I be worrying about the NRVs re: the SRVs on my 111Bs? Alex
Seems a cold cap on a cold stove would be the critical number to know, as that's what the fettler would be working with while actually setting the pressure on his rehabbed SRV: a room temp SRV in a room (or garage workshop!) temp pressure testing jig. So just to be dense, why not simply index the cap and plug of a new/old stock SRV so that the plug can be reinserted to the exact %
Drat. Hit "post" before I was done. This is how I meant to continue: So just to be dense, why not simply index the cap and plug of a new/old stock SRV so that the plug can be reinserted to the exact "factory" setting, disassemble and replace all the rubber so that you know it's good, reassemble to the index marks, and test it in one of those clever test jibs I saw posted a couple months(?) ago? Seems that would at least reveal a release pressure that's in the ballpark. And now I'm concerned: John, why should I be worrying about the NRVs re: the SRVs on my 111Bs? Alex
Hi Pitsligo A 111B is a paraffin/kerosene technology stove, which uses petrol/gasoline fuel. If a classic paraffin stove or a 111 of some type which is running on paraffin develops a leak in the NRV, no major problem. You will get a pool of (slightly) smelly fuel, which you really have to provoke to get it to burn. If a 111B or multifuel variant running on petrol develops a leak at the NRV, you have a far more volatile fuel to contend with. Petrol will take a flame far easier than paraffin, and a 5% petrol/air mix is explosive.... Received wisdom with a 111B or multifuel type and petrol is go for it if the stove is designed to use it, but seriously consider replacing at least the pip and spring of the NRV. I'm sure that one of the wiser (was going to say older and wiser, but that's cheeky) heads will be along soon. Cheers
Early Pri.70s... No NRVs, safety fillers or even soldered pins. A little petrol & a similar amount of 'common dog', and you're laughing.
Okay, I get it. Just the usual worries about leakage with petrol vs. leakage with kero. For a minute I thought there was some issue I should worry about, such as the NRV failing dramatically at about the same time as the SRV pops. Yes, NRV overhaul is a biggie when playing with white gas. Thank you! Alex
Unfortunately, it's probably more prosaic than that. I suspect it's for reasons of liability. Optimus, et al never wanted the unwashed masses to be fettling pressure caps -- they wanted us to send it to an official service center or purchase a new one. Even now, with many of the caps no longer made, they're in a similar fix: If they publish a pressure, and a stove ruptures below that, they can expect to pay a lot of money. If they don't provide the info, they're safe. Suppose your stove explodes: "Did you tinker with the safety valve? Then you caused the problem. No? Then the problem was caused by old equipment that should have been replaced." Bottom line is, we're on our own. I tend to test safety valves to make sure they will release, and then try to operate the stove in such a way that a safety valve isn't needed. ....Arch
Ugh. Makes sense, I suppose, when looked at in that light. I must say, though, that I'm surprised nothing has been let slip over the many, many years stoves with SRVs have been in production. I believe it was A&H that, when I asked about SRVs, quoted me 40psi, with quite some certainty. I've heard that 40psi bandied about here, too. Is there any more official source for that, or is it the hard-won and still-disputed knowledge of Master Fettlers?
Due to user (read idiot) error I caused the SRV on my German Military Geniol/Heinze stove to operate when camping in Brecon recently. Unfortunately the resulting projectile stream of paraffin managed to splatter every single cooking item I had brought with me for the weekend. To the accompaniment of much "sympathy" and barely concealed laughter from my camping companions I had to embark on a major washing up session before I could cook anything for dinner. I had totally overfilled the stove leaving little airspace for pressurisation meaning that the stove got up to operating pressure very quickly when pumping but did not maintain it in operation. This stove has both an SRV and a pressure gauge (same as the gauge on a Petromax lamp). As I'm used to giving between 20 and 30 pumps to get up to pressure I initially suspected the gauge as being faulty (not realising at this stage I'd overfilled). The gauge is marked in ATM (atmoshperes) and is redlined at 2 ATM. As I pumped well beyond the 2 ATM I was actually looking at the gauge when I inadvertently "stressed tested" the SRV. This occured at the top of the gauge range at 3 ATM. It might have been slightly over (i.e. the gauge was already on the end stop) but it wouldn't have been by very much. So, assuming the gauge is accurate within a tolerance that we don't need to worry about, then 1 ATM is approx 14.5 psi. Therefore the SRV operated at around 45 psi on this particular stove. Your mileage may vary as the saying goes, and in no way is this meant to provide any definitie guidance. It is merely an observation of an SRV operation event reported here for your interest. I.E. Don't take this as gospel and then blame me if you burn your house down! Cheers, Graham.
4B's i shall not under any circumstances commit to the premis that the manufacterer of a product might know more about their product than the general public but it seems to me that if a gauge should have a "red line" on it then it is intended that that is that maximum allowable presure for that device. To presureize the device by pump strokes or any other measurement beyound that is not only dangerous but in my view(your milage may very) outright foolish. I personelly take the presure gauge to be "gospel" until such time as i have determined it to be "off" due to age or malfunction. Even my newer Coleman devices are pumped to the proper flame not to any predetermined number of pump strokes. I strongly suggest you re-examine your lighting procedures for all flame producing devices. lance
