There are many small upright canister stoves on the market with Western brands on them, and after a while one gets to recognise not just the basic designs used but also, in many cases, the Chinese or Korean factory the stove probably came out of. This stove is not one of those. It is made in Japan and the quality of the stove is uniformly high. The weight is at the lower end of the spectrum, the power output is good, and it has an integrated piezo-igniter system. Its chief claim to fame however is the unique ‘valve’ system used. It does not have the conventional needle valve: it has a miniature pressure regulator instead. We will review the various features in turn, with the pressure regulator given extensive coverage at the end.
The piezo-igniter seems well made. The interesting bit is that the insulated high voltage wire goes up the inside of the burner column to emerge at the top of the burner. You can see a small, bright, pointy bit right at the top of the burner head: that’s the spark gap. This means that the wire and spark gap are well protected from damage. The metal housing around the piezo mechanism itself seems tight and compact. How long the spring mechanism inside the housing and behind the button will last – that I do not know.
It has been claimed that a piezo-igniter (any brand) will only work up to 2,000 – 2,500 meters (6,000 – 8,000 feet). Part of the reason for this is that there is only so much energy in the spark, and if the air and the gas is very cold, the spark may not be able to ionise the gas and break the molecules down. Whether or not this is strictly correct, there is no denying that it might be a smart move to always have a spare lighter (or two) at any altitude.
In use the stove has to be operated slightly differently from other stoves. With a conventional needle valve, you turn the valve off by screwing it in until it comes to a firm stop. With the pressure regulator, there is no firm stop. Instead, you screw the valve in until the flame goes out, then just a little bit further. To start a needle-valve stove, you open the valve from its easily-sensed closed position by a fraction of a turn. With this pressure regulator valve, you have to start winding the valve open and use the piezo many times as you go. Since you can overshoot on the shutting off (no hard stop, remember), it may take a turn or two before gas comes out. This can be rather alarming the first time you experience it (help, it isn’t working!), but it’s something you get used to after a few starts. For the rest of the control range, there is no real difference in behaviour.
Morning tea on the banks of the Colo River, Wollemi NP, Australia.
The power output is claimed to be up to 3,260 W. I think that may be possible with a new canister on a warm day (when the canister pressure is high). Many other canister stoves claim similar power output – but need the same caveat. The claim by Soto that the stove will continue to perform just fine at -5 C (23 F) is seriously misleading however. The claim only works if the canister has an iso-butane/propane mix. If your canister does, then most any upright stove will perform just the same.
Not all brands of canister contain iso-butane: many contain n-butane instead. If your canister has n-butane then, just like any other upright stove on a new canister, it may work at -5 C (23 F) for a while – until the propane in the canister has been almost all used up. Then this stove will die, just like any other upright stove, leaving a canister two-thirds full of n-butane. The claim that owing to the regulator the Soto stove will boil water faster than any other upright stove at -5 C (23 F) flies in the face of basic physics and can be dismissed as marketing spin.
The pot supports are rather cute. You have to slide them up and down to open them out and lock them in position. There is even the word ‘SLIDE’ with a bidirectional arrow stamped on each arm to remind you. The sliding mechanism seems to work just fine. However, I do wish they held the pot a bit further from the burner, because of the CO emission.
CO emission behaviour for the OD-1R stove
The CO emission spikes very high at start-up: almost 300 ppm when measured in the test system we have used for the CO series. It decays steadily, but even after a long time, it is still sitting over 100 ppm. The problem is the usual one of inadequate clearance between the burner and the base of the pot. Vendors often minimise this clearance in order to get slightly higher power output: marketing drive versus customer safety. The graph here shows that CO emission can be reduced by increasing this clearance.
It is worth looking at this problem in slightly more depth. A high level of CO means not enough oxygen (or air) is getting to the flame. Normally most of this air is sucked in through the air holes in the burner column by the high-speed jet of fuel coming out of the jet. The more powerful the jet, the more air gets sucked in. In most stoves the jet is quite small, allowing a high inner pressure P (see next section) to get the right amount of gas coming out – at high speed. But in this case it seems the range for the inner pressure P is lower, owing to design requirement of having the regulator work down to a low canister pressure. The lower pressure drop across the jet requires a large jet hole to get the needed gas flow, which means the jet speed is lower, which means that less air is dragged in through the air holes. To cut a long story short, the design decision to use a fixed regulator with a low output pressure range seems to have resulted in a slightly inadequate amount of air being sucked in, and a higher CO emission.
The instructions do mention The stove can produce carbon monoxide which has no odor and may cause death. The instructions do warn against using the stove in an enclosed space: a warning which should be heeded I think.
The instructions also say NEVER cover the stove with rocks and a windscreen while in use and NEVER surround the unit with wind shields. There is a diagram of the stove with a windshield half way around it and a big cross. I am not sure what ‘cover’ means, but any stove which cannot be used with a windscreen is pretty much useless in the field. I smell lawyers…
The Pressure Regulator – Reviewed
The novel pressure regulator used as the control valve is interesting. This regulator works well as a control valve, but there has been a lot of misleading marketing spin put about by various distributors selling this stove. The claims seem to be based on the marketing claims made by the Soto company – claims which, while not false, do tend to confuse reality. A lack of knowledge at the distributor end has compounded the problem. We will examine what is really going on here.
The control system.
Inside the canister, there is gas pressure, which is a function of the composition of the fuel and the temperature of the canister. This pressure is far too high to go direct into any stove jet: it has to be reduced. This is normally done by the (needle) valve which presents a huge restriction on the gas flow, creating a pressure drop (down to ‘P’). The greater the restriction or pressure drop at the valve, the less pressure there is left to push the gas through the jet, and so the less power comes out of the stove.
In other words, there are two places where the pressure is dropped between the canister and the outer face of the jet (which is at atmospheric pressure): across the control valve and across the jet. If there is a lot of pressure drop across the valve there is little pressure drop across the jet. If there is little pressure across the fixed-size jet there is little flow through it. It is identical to having two resistors in series or two taps on a hose.
It is crucial to understand here that the details of how the pressure is reduced (to P) by the control valve simply do not matter. All that matters is how much pressure is across the jet. A conventional needle valve varies the restriction or pressure drop across itself by varying the area of the hole around the needle in the valve, but this is not the only way this can be done. A more sophisticated diaphragm arrangement can be used for this: one which actually is designed to control the output pressure P per se. This latter is what is done in the Soto stove.
The marketing claim made by Soto is that the stove can maintain a constant power output as the canister pressure varies, and this is technically correct up to a point. The pressure P is regulated, and the flow through the jet depends directly on P. The claims made by some retailers and reviewers imply that the regulator will maintain a constant power output no matter what the pressure in the canister falls to, and this is seriously misleading (or false). The pressure regulator will only work while the canister pressure is high enough: it has to be a fair bit above P to be able to regulate. At this higher canister pressure, it does not matter whether a needle valve or a pressure regulator is used to get P. Below that, canister pressure the power output WILL fall.
The big difference is that using a pressure regulator rather than a needle valve means that P, and hence the flow of gas through the jet, and hence the power output, will be fairly constant despite a falling canister pressure. When using a needle valve, the intermediate P and hence the power output will vary. What the marketing claims do not examine is whether this constant power output matters in practice. I don’t think it matters at all.
If I want high power (to bring water to the boil for instance) I open the valve so the stove is roaring away. If the power output varies a bit – who cares? If I am simmering, I turn the stove right down, but any small variations don’t worry me either because I am usually monitoring dinner fairly closely and may be varying the power output as I go. To be sure, if I was running the stove for half an hour straight there might be some significant changes in the power output which might need correcting – but I never run the stove for that length of time.
The bottom line then is that the stove is nicely built, the piezo igniter works well, and the pressure regulator valve works very smoothly, but the CO emission is a bit higher than I am really comfortable with. The performance in the field does not show any special advantage to the unique pressure regulator valve.
Specifications and Features
|Country of origin||Japan|
|Model||OD – 1R|
|Power output (claimed)||3,260 W|
|Material||Brass, aluminium, stainless steel, plastics|
|Size, packed||78 H x ~55 D mm (3.2 x 2 in)|
|Pot support diameter||110 mm (4.3 in)|
|Weight (claimed)||73 g (2.6 oz)|
|Weight (measured)||72 g (2.6 oz)|
|MSRP||n/a, but retail US$65 has been seen|
- Well made
What’s Not So Good
- High CO emission
- Excessive and misleading marketing spin
Disclosure: The vendor provided this product to the author and/or Backpacking Light at no charge, and it is owned by the author/BPL. The author/Backpacking Light has no obligation to review this product to the vendor under the terms of this agreement.