Hello Graham @Graham Johnson In every SRV filler cap I've disassembled and refurbished so far (about 4 Sievert, 4 Optimus, 1 Primus), I've found that the set screw/insert was screwed as far down into the cap as possible. I've never seen one where the screw/insert was deliberately backed up in any way. Looking at the picture of your Svea 123 cap above... ...I would actually be way more afraid that the set screw might go flying at an inappropriate moment while the stove is in use, followed by the remainder of the SRV assembly, and a flash of gasoline vapor, than I would be afraid of the tank disintegrating. Just my 2 cents... Best, Christina
When I replace the pip in this kind of SRV, I always check the original, non-fettled, position of the screw, and then count the number of turns to extract it from the cap. I then reset it at the same position having replaced the pip with a like pip, and checked the spring for rust and compressibility. My assumption is that the factory would have had the settings to a standard. I've not had one fail. I have a stack of unfettled Svea 123R and Optimus 8R stoves in the shed that will have the factory settings. I'll take some photos of the SRV screws on them. Tony
Thanks for your replies and if I can add the following, I originally thought that exactly reassembled srv would be sufficient, this does not appear to be correct from my simple test results mentioned previously. Both srv that are backed off and secured with thread lock are secure and opened at 90 psi or greater if fully screwed down. This I think is too high and near the original manufacturing test pressure that I think was 100 psi. The 8r srv still has all threads engaged and the 123r srv has about 3 fully engaged threads.
@night_owl is correct. The penta-screw projects too far out by a wide margin. The engineering adage of ‘if it looks right it probably is’ applies. That doesn’t look right. John
Yes I agree about the appearance, but the screw is secured and the operation is correct. If screwed to the normal position the srv did not open until 90 psi, I think this would be dangerous. These srv are crude and old. When testing using scales and pressing directly onto the pip, the results varied drastically. With the screw in normal position 500g of force was needed to open srv, with screw out it lifted at 250g to 300g range. This is why I made the pneumatic test rig to confirm performance
[QUOTE="Graham Johnson, post: 566804, member: … These srv are crude and old…[/QUOTE] So… Your conclusion is the engineers who developed these long lasting, rarely catastrophic, stoves didn’t know what they were doing? And that they allowed defective products to be sold around the world for decades? An open question… Tony
The problem stove 123r is not made in Sweden, possibly an early Chinese or were ever version. These stoves are old and we are forced to fit third party components, so testing is now required as a duty of care. Crude srv compared to srv used in other industries such as process, or boilers. I am open to any help or feedback and do not profess to be a stove expert as many others on here. Just airing my humble observations.
So, you think the company (with a long standing international reputation) does not require a standard? Tony
The company would have had a standard but again these are now old refurbished with third party replacement parts, so the original standard is lost completely. So I feel the obligation to test the srv when refurbished. This is not a slur on the original manufacturers standards in any way. Even NOS srv purchased assembled already require testing in my opinion, they don’t exactly come with a calibration certificate.
Have you seen the many threads and posts about the testing that have been done prior to your joining? We here find it a rare occasion to have to invent the wheel. @kerophile @BernieDawg @exeter_yak @Doc Mark @presscall @Tony Press and others can be searched for posts and threads dating to before I joined. That might help.
Yes, have researched these threads and the subject of srv is ever ongoing. I work in the oil and gas industry, I work with the design and safety of these systems, so over pressure is a common problem. I did get a kind process engineer to work out the formula to equate grams to psi as a cross reference and 250g is close to 50 psi apparently. I do now think that my original 123r base popped out due to overheating due to a stand being used and ultimately the srv original opening pressure being a least 90 or 100 psi as the original 500g opening weight would indicate. Not try to re invent anything, but I like things to work safely.
I can't find where Graham said anything about the engineers not knowing what they are doing. Nor did he say anything was defective that I can find. Certainly old springs, different pips, things are gonna change. Good on ya Graham for coming up with a good way to pressure test them.
Thanks, the test rig was simple and cheap. I couldn’t show the original damaged 123r tank as I had already removed the filler fitting from the tank, as can be seen above soldered to a 1/4 male brass thread reducer on test rig.
Hello Graham It's your stove, and you have to feel (but also, be!) save with it. Still, some remarks in the hope that they might be helpful: When I first started replacing pips in Optimus SRVs of the set screw type (pentagonal, or square), I also counted the number of threads when unscrewing, like @Tony Press . In every case, I found that the set screw had been screwed into the cap as far as possible. In large-scale production of such stoves, I simply cannot imagine every single cap being individually fine-tuned to a particular release pressure. By contrast, I would assume that processes and materials would have been standardized to ensure consistent release pressure in those SRVs. With older forms of SRVs (like the one in your 8R picture), it's even more obvious: There, the inserts are always screwed down right onto the top of the cap. There normally is no gap. My take on this: If the inserts were originally always completely screwed down, then the manufacturers likely used the area of the SRV opening and the specification of the springs to achieve a particular release pressure, but not the number of threads a screw is backed up (which will weaken the maximum pressure the SRV assembly withstands, thread locker or not). Third-party replacement parts may affect things. The way I understand the design of these SRVs, though, the material/elasticity of rubber pips or washers does not affect the way the SRV works. The exception is a hardened and completely non-elastic pip surface, which may lead to earlier release because it won't seal well any more. This is in line with what @exeter_yak has described in the Svea 123 research project thread. I always test refurbished SRVs manually to ensure that they easily open. On one or two occasions, I've found an SRV difficult to manipulate. For me, what helped in these cases was meticulously cleaning and slightly polishing the outer surface of the pip holder and the surface of the canal in the cap. I've seen burrs and sharp edges on pip holders, and any dirt or burr in this area can cause overly high break-loose pressure. By the way, here are gallery pictures of more or less current (Asian) production Svea 123Rs with caps where the set screw looks very much like it's screwed down completely: Svea 123r Katadyn Optimus era 123R Optimus SVEA123R Best, Christina
Thanks for your reply, yes I agree the standard construction on initial assembly would be to assemble as you kindly suggest. But after a single failure and some concerningly high test srv opening pressures, I am merely testing for correct opening pressures. Each of the srv were clean and free from any damage. The only thing that noticeable was that the 123r spring was significantly stronger than the other 2 srv springs. Although each srv is from a different generation of stove. Again I am not trying to discredit anyone or discourage anyone from srv refurbishing.
Possibly a non-original, incorrect spring then? Which would explain the failure of the SRV to open before the tank base deformed, and the need for the screw in such an obviously incorrect position to achieve a sensible opening pressure.
Again thanks for more replies, thanks for the information about springs and it confirms it's a black art indeed spring production. My experience of pressure regulator springs just about confirms that they ideally should not be tampered with. As for the srv screw position being incorrect, if it's absolutely secure and the srv works correctly it fundimentaly cannot be wrong. If people want to make the srv cosmetics look correct that ok, as long as the srv is proven by testing to work correctly.
