I should have added above, that I have a few NOS springs for these NRVs, and if I come across a dodgy looking spring I can replace it. If I recall correctly, I did that once on a stove that I’ve ended up using quite often. Tony
I can appreciate the engineers but as a machinist we made things work. I have stretched springs to work better. We had a saying. "There comes a time when you xxxxx the engineers and go into production." "Too much analysis ends up as paralysis." I will get my own hat and coat.
There is an excellent little book, 'Spring Design and Manufacture', No.19 in the 'Workshop Practice Series', by Tubal Cain (Tom Walshaw). It fully explains everything one needs to know to measure and replicate a spring, or design one from scratch. Measurement of rates, materials, methods, tools, the lot. A good evening's reading for those interested in such matters.
Here's for info a drawing with the pressure settings that were applied to the lids in production. As mentioned earlier, "modern" car gasoline can cause non-linear pressure build up when heated which is why Optimus did not allow car gasoline in self-pressurized stoves such as 123R and 8R. The SRV's may fail to function when pressure rises too fast.
So in round figures that's 65 to 75 psi, but I need to re test the 8r srv again due to the diagram note, that stipulates the test to be done 24 hours after assembly. I guess this allows the spring and the pip to compress or settle into position. Many thanks for this information, greatly appreciated. The diagram looks like a 123 srv possibly, I wonder if all models of stove had a similar setting, it would seem a possibility. The diagram is also dated in the 1970s interesting.
@Staffan Rönn I'm very interested, do you know exactly what it is in modern petrol which makes it behave that way? One would assume the additives, as the warnings pre-date the widespread addition of ethanol to petrol?
Hi @Blackdog I don't know which additives that cause the behavior, but as you point out it's something that occurred before ethanol was added to petrol. What I remember is this (might be a bit foggy): A previous CTO of Optimus told me in the early 1990's that reports of Svea tanks occasionally popping out started coming around the same time as unleaded petrol/gasoline was introduced, so from mid 1970's and on. After investigations and pressure tests the conclusion was that "modern" gasoline/petrol could show a non-linear pressure build up when heated. Sometimes this would result in a pressure build up that was too fast for the SRV to cope with, thus resulting in the bottom popping out. I remember seeing the pressure diagrams from the these tests that he showed me. As a result of the findings Optimus started clearly advising not to use car fuel in the self-pressurized stoves. I'm sure the composition of car fuels have changed a lot since the 1970's, but I don't know anything about the consequences of this development. But the volatility of the fuel and the fact that it's known to be carcinogenic (e.g. vapor/fumes and contact with skin) is enough for me to never ever use car fuel in a camp stove.
Thank you for your reply @Staffan Rönn, much appreciated, I intend to do some further research on the matter as the science of it is fascinating.... I can't help having an enquiring mind! I completely agree however Naptha is obviously cleaner and safer!
The change in gasoline composition since the '70 is well documented in the car collection scene...A lot of car who were running fine are now prone to vapor lock.
Old thread, but I'll add my two bits. All liquids have a non-linear pressure rise with increasing temperature. This includes fuels. How non-linear depends on where on the vapor pressure curve you are operating. As you approach the boiling point and beyond, the pressure rises more rapidly with a small increase in temperature. Perhaps that might explain Optimus' experience as automobile gasoline changed in the '70s and '80s. Perhaps automobile gasoline has additives that exacerbate the non-linear behavior. I use a chemical process simulator at work. I can plot vapor pressure curves for just about any compound or any mixture you can think of over any temperature range you can think of.
