operating pressure for svea 123/r stoves

12:48 a.m. on December 11, 2014 (EST)
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I have two svea 123 stoves. The older one, I bought from REI in 1970, and the younger one,an "r" model bought in 1975, and both going strong.

Here's the question. Has anyone done any research to determine what the operating pressure is of either stove when running full bore, AND, what is the setting of the over pressure valve in the fill cap.

Both of these stoves have seen moderate use, but no real cold weather usage. Neither stove has had an overhaul, although the fill cap gaskets have been replaced.

No one seems to know the answers. If anyone reading can help, I'd sure appreciate it.

Many thanks.

1:14 p.m. on December 11, 2014 (EST)
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Ralph,

It is hard to wear those stoves out. I would not worry about the pressure at all. All of the old brass stoves have a characteristic sound when they are warmed up. I would only be concerned if they don't "sound right." If they don't sound right, after the tank and fuel nozzle have been cleaned, I would replace them.

4:21 p.m. on December 11, 2014 (EST)
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Well, after more than 30 years of use, I am trying to see if there is a correlation between temp, pressure, and the overall "health" of the stove. I agree that anytime the stove doesn't 'sound' right, it should be checked. The tanks on the 'real' svea stoves are very well made and solidly brazed, so overpressure should never be an issue. I have read of vent valves opening and ignighting the gas vapors, but if a short length of tubing was put over the fill cap, and a vent occurred,  it would direct the vapor away from the stove.

Never the less, in 45 years of use, I have never had a vent happen. That spring is pretty stout.

I'm an engineer, so these questions come naturally.  I've done some temperature testing of both the 123 and 123r stoves, and the results are not what I would expect.

Bothe stoves were run on a large metal table outside in 66ºF temp and moderate wind.

Basically,  I ran both stoves full bore, from a full tank (.3 pt) and compared contact temps of the tank, next to the fill cap, and temps at the base of the vaporiser tube. As expected, temps at the base of the vaporiser tube are higher than tank temps. Both stoves run at 210-215 +/- 10ºF at the tube, but only 123-125+/-5ºF at the tank cap.

Running the stove at simmer, raises the tube temp sharply to 230-240+/-10ºF. This is not as expected, except in retrospect, realizing that higher fuel burn causes cooler fuel to be burned faster thus lowering the tube temp, so less fuel burn =hotter fuel.

In both cases, use of a flame spreader to even out hot spots for cooking, raises the temperature of the stove when used at either full burn or simmer due to both reflected heat, and hotter fuel. The svea123 was hotter in this regard at 340ºF versus the 123r at 250ºF.

Granted these numbers are of little value to the average user, it does somewhat ally fears of overheating and venting. Use of a windscreen raised overall temps by 10ºF over severat minutes.

Finally, as fuel was burned, tank pressure appears to rise (more room in the tank to pressurize) since temps gradually increase to 260ºF.

Unfortunately,  I have no way to measure tank pressure at this time. It would be of interest to know what full bore pressure is versus what the vent valve is set at.

Cheers!

7:51 p.m. on December 11, 2014 (EST)
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Ralph, that valve (there are 2 types) is a safety pressure relief valve that should never open if the stove is being operated properly. I have seen several instances of it being released, though, and it is very spectacular. The most spectacular, which I have described here on Trailspace a couple times, was when I was climbing in the Chamonix area, camped in the Biolay campground (now long-gone) in 1964 (my older 231 is from 1955, and a very similar Primus 71L a couple years older than that). A couple of the Irish lads had come back to camp after a late night at the Bar Nat (which no longer exists, though there is a much newer bar in a different location that is mostly a restaurant using the same name, run by a completely different family). Anyway, they were brewing up a bit of tea, sitting in the front of their tent when the valve let loose with a meter or more jet of flame. This created a bit of havoc in the campground, with the lads trapped in their tent (front entrance only, one thing that convinced me that mountaineering tents should have two entrances). Eventually, one Brit footballer (soccer, sorry), gave the stove a boot into the grass (very wet, of course, thanks to the usual summer rains).

I have seen the valve release when someone put one of those aluminum foil windshields around the stove in such a way that heat was reflected back onto the tank. One other cause I have witnessed is using the Optimus pump accessory and giving too many strokes of the pump, so that once the stove was lit, and the tank gaining warmth, the pressure overshot and the leaking fuel ignited, again spectacularly. It only takes 1 or 2 strokes of the pump to provide enough pressure. The idea of the pump is to substitute for the traditional "warmth of your hands" method that we all learned when we got our first Svea, not to provide operating pressure.

According to the instructions that came with the pump, it and the replacement cap (if you had the older cap) will fit the Svea 123 and 123R, and Optimus 8R, 80, 88, 99, and 199. Since I have the Primus 71L, I can tell you it fits the 71L as well (the 71L is a near twin to the 123). The directions that came from Suunto (one of the chain of ownership of Primus, Svea, and Optimus) specify using 5 to 6 pump strokes. I always found 2 strokes as sufficient.

For those who do not know the history, Svea, Primus, and Optimus were originally separate companies, formed in the late 19th Century, though the founding families overlapped through employment and marriages. At various points, the companies combined in various permutations of the names, with Suunto (the Finnish company)being the importer to the US at one point. There are a couple of good reviews of the history available on the Web.

 

1:34 a.m. on December 12, 2014 (EST)
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Bill, Thanks for the info. I was finally able to get hold of a gentleman at A & H Enterprises, which repairs stoves. He told me that the setting on the Svea 123 fill cap pressure relief valve is 30 psi. The stove usually generates (based on temp, fill space in the tank, etc) about 5 psi. He also said that he has seen several of these blow out the base, launching the stove many feet in the air. That bespeaks serious overheating.

11:00 a.m. on December 12, 2014 (EST)
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I should have remembered to suggest contacting A&H. They are the only place you can get parts for the Svea, Primus, and Optimus stoves these days, as far as I have been able to determine. I talked to the Primus people at the Outdoor Retailer Show last summer. There are parts available for the 123 and 123R (I mistyped in my post above - my wife's and my Sveas are 123, not 231, plus we have a 123R and the Primus 71L, all part of our collection of about 25 backpacking stoves - which includes the half dozen puncture-type Bleuets that I ended up with from the Scout Troop I was Scoutmaster of for a number of years when they changed from the Bleuets to the threaded canister stoves and white gas MSR Whisperlites).

8:25 p.m. on December 16, 2014 (EST)
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I've had a embossed case Optimus 8 vent out the SRV on me a few years ago.  I was heating water from a source I was not sure of how safe it was.  I'd heated up two small pots of water, so now I know its limits.  The valve was doing its job.  Also, if the tank/fount gets too hot to hold a hand to for a few seconds, may be getting to hot.  I have not used my 123/R's much, just my collection of 8/8R's. 

Be sure to change the cap gasket and the pip in the SRV if able to access it.  May need the special tool to do that.

Duane

12:43 p.m. on December 17, 2014 (EST)
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Thanks Duane. I plan to get repair kits for both of my 123s. I was thinking that it would be possible to put a length of rubber hose over the fill cap. If the srv did vent, it would vent the vapor where it wouldn't ignite. Since the stove runs at about 5psi and the cap has a 30 psi setting, it's a wonder it vents at all.

7:53 p.m. on December 17, 2014 (EST)
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If you are using the stove per instructions and not doing something dumb, like using an oversize pot to reflect heat down onto the fuel tank of the Svea or Optimus (plus a wraparound aluminum foil windshield to further contain the heat close to the fuel tank), producing significant overheating, you won't have a venting problem. In using our family Sveas and Primus, we have only had one incident, and that was due to overpumping by a huge amount with the Optimus pump (it wasn't one of my family who pumped the over-pressure - keep inexperienced "friends" away from your stove, even if they claim "expert" qualifications). We caught that before lighting the stove, so just some wasted fuel. Adding the rubber hose is probably not going to help, since the fumes will spread and probably get lit by the flames at the burner. A couple of the incidents I have witnessed had the fuel oozing out the safety valve and the fumes lit by the stove flames, which produced more oveheating, resulting in a big jet. But all the incidents I have witnessed or heard reports have involved preventable massive overheating and/or overpressure.

12:24 a.m. on December 18, 2014 (EST)
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Ross and a few others now sell sets of parts that can be used for these small stoves.  Check out eBay if you have not already.  Go under stove parts in the appropriate section.  Since the stove has been fine all these years, all you need is the pip for the SRV and a washer for the cap.  They blame a brownish wick in the tank for using the stove until it has used all the fuel up too many times.  I'm not so sure personally, I think it may be age or ever so little moisture condensation, rotting the wick.  Whose to say.

Duane

12:32 a.m. on December 20, 2014 (EST)
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I have a had a 123R since I bought it new, too many years ago. They are great little stoves and very reliable, as my review on this site attests. As Bill says, don't use a windscreen or a wide pot, or fry pan. I have never used a pump though sometimes prime in the winter with a lighter to heat the tank. I have never had a venting problem. The cap gasket must be in good shape lubed periodically with silicone grease. Duane, the brownish wick can happen if the fuel burns down all the way and the heat in the stove starts to fast the wick. And always keep some fuel in the stove in storage so the wick doesn't dry out.

12:32 a.m. on December 20, 2014 (EST)
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I have a had a 123R since I bought it new, too many years ago. They are great little stoves and very reliable, as my review on this site attests. As Bill says, don't use a windscreen or a wide pot, or fry pan. I have never used a pump though sometimes prime in the winter with a lighter to heat the tank. I have never had a venting problem. The cap gasket must be in good shape lubed periodically with silicone grease. Duane, the brownish wick can happen if the fuel burns down all the way and the heat in the stove starts to fast the wick. And always keep some fuel in the stove in storage so the wick doesn't dry out.

11:12 p.m. on February 19, 2015 (EST)
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I think its possible to use a wind screen without overheating the fuel tank by allowing a decent amount of space between it and the stove. Also, only surround about 2/3rd's of the stove so excess heat does not build up. This still deflects a lot of wind. As alluded to, worst case scenario would be a larger pan on top with the windscreen pulled tightly up to it and completely enclosing all. I have a small scorch buster that I sometimes use with my Svea 123 that only spans the pot supports. No problems thus far.

Incidentally, anyone have an extra of the small pot/cap and original cleaning needle that they would want to sell?

April 2, 2020
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