Many of us will have managed to fit in a few weeks of backpacking this year and some gear might have been having a rough time of it. Beside cleaning, re-proofing and condition checking, think about including an inspection of the O-rings fitted to gas and multi-fuel stoves.
Gas stoves are screwed onto a gas canister valve. An O-ring is incorporated into a groove in the stove’s connector and is compressed when the stove is attached to a gas canister to form a seal and prevent gas escaping from the join. It isn’t often that an O-ring fails and most hikers may never experience it. However they can perish, harden, split or simply be damaged. What is more likely to occur is that they are unseated when the stove is being removed from the canister, then to be potentially dropped and lost. Three Points of the Compass tries to always make a point of checking the O-ring when the stove is unscrewed from a canister, it has not been unusual for me to have to push it back down into its grooved seat. Particular stoves have been more prone to this than others. Some users will put a little silicone grease on the O-ring so that it remains ‘stuck’ to its seat however I do not like to do this as I think it attracts dust and debris, which brings it’s own sealing problems. I recently fitted a new O-ring to my Kovea Spider so took time out to check my other stoves.
A damaged O-ring will not form a good seal and this can manifest itself in an audible continued hiss of escaping gas, with obvious potential for catastrophe. In freezing temperatures O-rings can stiffen and potentially leak fuel. A brief hiss and smell of a little released gas when connecting and disconnecting is normal and to be expected. My Soto Windmaster has two O-rings and gas pressure can build between the two, released with an audible pop when unscrewed/disconnected from the canister, this is normal.
It doesn’t take long to have a quick check of the O-rings fitted to a stove and check for obvious signs of damage. If an O-ring does appear damaged, or possibly the stove is quite old, take the opportunity now to order a replacement. It is a sensible precaution to order a spare or two anyway. Not only do stoves fall out of production and spares become progressively more difficult to source, but a spare can be slipped into a ditty bag ready to replace one damaged or lost while actually on trail. To lose the opportunity to heat water or meals because of the loss of such a simple, small, light, cheap component would-not-be-good!
Annoyingly, manufacturers are poor in including such basic information as the size and specification of O-rings fitted to their stoves on the packaging, in information leaflets, or even on their website. There is poor reason for the latter not to be easily available. Complicated stoves, such as many multi-fuel offerings, have many components and dedicated service kits are sold for these that will include replacement O-rings. These stoves by their very nature are well-made, intended to cross time-zones and be used in extreme conditions and can last many years. Some components will definitely require changing in the stove’s lifetime. Dedicated service kits can remain on sale for some time after a stove has fallen out of production, but not for ever. Again, it makes sense to buy a service kit that includes small and difficult to source spares now rather than ten or twenty years down the road. MSR supplied the response below regarding third-party parts, however it does not address the problem of stoves being withdrawn and a paucity of spares there-on:
“we do not advertise O-ring sizes because we cannot guarantee the quality or materials used in ‘off the shelf’ parts. Some O-rings found in hardware or auto-parts stores use a different grade of elastomer; some are poorly made and have defects on their sealing surfaces that could allow dangerous fuel leaks; some are mislabeled or beyond their shelf life. Safety is always our number one priority, and an incorrect or low-quality O-ring could compromise the safety of your stove; for this reason all replacement stove parts should be purchased from Cascade Designs or from a qualified dealer of MSR products and parts”Mountain Safety Research
O-rings are used in many types of machinery and equipment and are not special ‘back-packing gas stove O-rings’. That said, beside their dimensions, they will be made to a particular specification. Pure rubber becomes brittle with extreme temperature variations, so synthetic rubber is used. Different materials are used for the manufacture of O-rings, such as nitrile, Viton, neoprene and EPDM (ethylene propylene diene monomer). Note that EPDM is not suitable for use with petroleum based fuels so is not used on any multi-fuel or gas stove. Viton (a brand name) rubber O-rings are normally a good choice of replacement but sell at a premium. Standard Viton O-rings do not handle temperatures below -20°C well while standard nitrile O-rings will operate successfully at -35°C.
Because the lindal valves on gas canisters are standard, certified to EN 417, O-rings found on many gas stoves are frequently also standard. Most common is the BS011 O-ring though Primus have used the similar but thicker in diameter BS108 O-ring on some of their stoves. My MSR Pocket Rocket 2, Soto Windmaster, Kovea Spider and almost all of very small stoves such as the BRS 3000-T , Fire Maple Hornet and clones are fitted with the same size BS011 O-ring, no doubt there are exceptions amongst the hundreds of other stove models out there. I show the Fire Maple Hornet here but this stove is effectively the same as the Alpkit Kraku, Robens Fire Midge and Olicamp Ion.
With larger or more complicated stoves, such as the multi-fuel stoves, there are numerous different O-ring requirements so I have only listed the most common sizes here, relevant to my needs. Already mentioned is the Windmaster with two sizes of O-ring. Many Primus stoves also have two sizes of O-ring. Not only that but the dimensions of the pair of O-rings fitted to Primus stoves has changed over the years.
|Reference||Inside diameter (ID)||Outside diameter (OD)||Cross section (CS)|
|Soto Windmaster- large ring||20.5mm||24.5mm||2.00mm|
O-rings can be easily removed with a metal or plastic pick but be careful not to damage the ring if intending to replace it. A wood cocktail stick or toothpick may suffice if need be. I use a titanium toothpick dedicated to the job that does just fine. The thick blunt end on the handle end is just right for easing a new O-ring into a connector head, past the threads. There is absolutely no need to pack this along on trail, it is strictly for home stove maintenance. Once a new O-ring is fitted in a connector and pushed down, spin on a gas canister to make sure that it is firmly seated.
Most stove manufacturers and their regional dealers are more than prepared to sell you the appropriate O-rings, or the larger (and more expensive) service kits for their present range of stoves stoves and some more recently discontinued products too. If an O-ring has failed it may be possible to persuade a manufacturer to supply a replacement under warranty. That doesn’t help you brew a pint of tea and heat a meal halfway up a hill in the middle of a storm however. It might be best to check the condition of a stove prior to it failing on a trip.
When Three Points of the Compass contacted Soto directly regarding replacement O-rings for my Soto Windmaster, an email was received the same day from the US distributer, also copying in the international supplys department in Japan. The latter despatched a package to me within hours and I received it two days later in the UK. My set of replacement O-rings, plus a spare set, were sent gratis. This is excellent service.
It is preferable to buy ‘officially approved’ O-rings from the stove manufacturer. There may be a premium to pay for these, but not always. Replacement ‘official’ O-rings for my Kovea Spider were a grand total of 25 pence each, plus postage. Sourcing official replacements ensures you are getting manufacturer specification, in good condition. Others may choose to simply source their spare or replacement O-rings from a secondary supplier. Manufacturers may also cease to provide spares for withdrawn models of stove and alternative suppliers have to be found and used. Particularly old or rarer stoves can prove problematic in obtaining spares for, though thankfully there remain just a few suppliers for small replacement parts, but these will get progressively harder to source.
Three Points of the Compass includes spare O-rings in the ditty bag carried on trail. The three O-rings taken are two BS011 (one nitrile, one Viton) that will fit almost all small stoves, such as the Kovea Spider, Soto Windmaster, BRS 3000-T, Fire Maple FMS-116T and the Fire Maple Hornet that I carry when using a heat exchanger pot set-up. Also included is the larger size O-ring for the Soto Windmaster. These three O-rings stay in the ditty bag regardless of what stove is being carried, even if using a meths/alcohol stove on trail. I prefer to leave them there rather than take them out and forget to return them, that way I know they will be there should I require one.
This type of maintenance isn’t always possible or practical however. Some manufacturers seem to have delighted in installing O-rings. The fuel pump for the now obsolete Soto Muka was stripped down by one enterprising enthusiast who found that along with a wealth of tiny internal components, there was a grand total of eleven O-rings, some quite miniscule of which only two were the same specification. Field maintenance simply isn’t realistic on such complicated stoves and home repair would be beyond most too, certainly Three Points of the Compass!
It doesn’t end with gas stoves. O-rings are found on other items too, fuel bottles and water filters come to mind. Each with their own vital but vulnerable component. For those people who say that they have never had need to replace an O-ring, have never had one come loose, have never had a problem. I would simply say that my house has never burnt down, but I still have insurance for it.