Saturday, March 25, 2017

The G-Works R1 Gas Saver – Refilling Backpacking Canisters II

Ever notice how expensive the small canisters of gas are?  But the big canisters are cheap by comparison (per gram).  Wouldn't it be nice to pay the big canister rate for small canisters?  Well, you can – with a G-Works Gas Saver adapter.
A G-Works R1 Gas Saver adapter can help one avoid paying the "convenience charge" of small canisters.
I recently walked into a retailer and saw canister gas for $4.95 for 100 grams. Easy math:  $4.95 for 100 grams works out to $0.0495 per gram; that's basically a nickel (five cents) per gram of fuel. OK, so a nickel isn't that much, but why pay more?
A 100 gram canister of gas often retails for $4.95.  That's a nickel per gram.
You know that gas is so much cheaper if you buy the big 440 or 450 g canisters.  For example, at Walmart, I recently saw 440 g canisters for $7.72 or $0.175 per gram.  That's basically two cents per gram, less than half the price of gas when sold in the 100 gram canister.
440 gram canisters for sale for $7.72
Well, I suppose five cents a gram isn't the end of the world, but wouldn't it be nice if you could buy gas for two cents a gram but in the small canisters?  I mean, with the 440 g size, who wants to carry those big, heavy beasts of a canister around for weekend's worth of hiking?  Not me, thank you.

Well, you can pay the big canister rate for small canisters.  Yes, that's right, you can.  You just need a G-Works R1 Gas Saver.  The G-Works Gas Saver basically hooks up two canisters.  When your 100 or 110 g canister runs out, you refill from a 440 or 450 g canister.  Thus, you pay the 440 g rate for the convenient 100 or 100 g size canister.

Custom Filling
You can also custom fill canisters to exactly the amount of gas you need for a given trip.  Say you need approximately 12 ounces of fuel (about 340 g) for a given trip.  Well, gas is only sold in the US in approximately 4, 8, and 16 ounce sizes (roughly 110, 220, and 450 grams respectively).  If you want 12 oz of fuel, you have to buy 16 oz and carry an extra quarter pound of dead weight.  Yes, you could flare off the gas, but that's kind of a waste.

Or, you could carry one 8 oz (about 230 g) and one 4 oz (about 110 g) canister, but remember a 100 g canister of gas weighs 200 g full and 100 g when empty.  In other words, the canister weighs as much as the fuel.  So, by carrying two canisters, you're carrying a lot more steel, and you're really not saving much weight by carrying one 4 oz and one 8 oz canister when compared to carrying a single 440 or 450 g canister.

For example, I took some full canisters, and put them on a scale:
Size Weight when full (g) Weight when full (g)
4 oz 213
8 oz 376
16 oz 622 Difference
Total 589 622 33

The difference between carrying 16 oz of fuel vs. 12 is only 33 g (1.2 oz) because of the weight of the canisters.  The weights between brands of canisters may vary, but these weights should be illustrative.  So, carrying 4 oz less in fuel saves me only about 1 oz in actual weight because of those darned steel canisters.

But what if I custom fill an empty 16 oz canister with 12 oz of fuel?  The weight of the canister does not change, and any reduction in fuel equates to an actual one-to-one reduction in weight.  If I fill with 4 oz less of fuel (113 g), I carry 4 oz less pack weight.  Yes, a bit of fuss to save a quarter pound, but remember that if the average backpacker (who carries something like 80 to 100 items in their backpack) could save just 2 oz on average per item, their pack would weigh on the order of ten pounds less overall.  Ounces are worth shaving wherever you can.  And if you're already using the G-Works adapter to pay the 440 g rate for 110 g canisters, why not not save a few ounces of pack weight while you're at it?

Refilling canisters could be dangerous, very dangerous.  I'm talking about permanent injury, loss of eyesight, disfigurement, and even death.

You will note that I am not a lawyer.  I don't work for any company that could get sued here.  I'm not some ninny in an office who doesn't give a dang about whether you live or die in the back country so long as his company can't be sued.  I am just a fellow lover of the wilderness.  Any warning I give you is realistic and sober.  My warnings are not overblown silliness as are so many of today's legal warnings.  I'm giving it to you straight.  If you ignore me, you're a dumb ass, and I have little sympathy for you.  Don't come crying to me if you didn't heed my warnings.

In my original post on refilling gas canisters, I listed a series of precautions.  Read my original post on refilling gas canisters if you are thinking about refilling canisters of your own.  Please do your homework before you try something like this.  If you do try this, there's a certain danger to it, no matter what.  You're working with highly flammable, explosive gasses.  You've been warned.

Transfer from Like to Like
Not all canisters are created equal.  Some are stronger than others.  When you take canister gas from one canister and transfer it into another, you want to make sure that the receiving canister can handle the resultant pressure.  The ideal way to do this is to "stay within the brand." By "within the brand," I mean transferring Jetboil to Jetboil, Primus to Primus, etc.  If you transfer gas from a larger canister to a smaller canister of the same brand, you already know that the smaller canister can handle the pressure from that blend of gas.  Note:  Some companies, Primus in particular, have different blends:  Summer blend, winter blend, etc.  For companies with different blends, use a donor canister of the same blend as the receiving canister originally held.

If you can't find a donor canister of the same brand as your receiving canister, you can check on the company's website what blend (percentages of propane, isobutane, and n-butane) the canisters held to insure compatibility, but it's best to stay within the brand if you can.  Note that some companies do not publish their blend's percentages and that percentages can change over time.

Basically though, if you transfer from like to like, you minimize the risk that the receiving canister can't handle the pressure.

The Procedure
Custom filling/refilling is actually fairly simple.  I'll list the instructions below.

Before you start, weigh the empty canister.  The weight of the canister + the amount of gas the canister originally contained is the maximum safe total weight of the canister.  For example, if your receiving canister weighs 116 g when empty and originally held 220 g of fuel, then your maximum safe weight is 336 g (116 + 220 = 336).  The amount of fuel your empty canister originally held should be printed on the label of the canister.  If you can't read the label, get a different canister.  Only use canisters in good condition when refilling.
My receiving canister weighs 116 g when empty.
Once you've calculated your maximum safe total weight, do the following:
1.  Place the donor canister into a pan or pot of warm water.  I said warm water, not hot water.  Do not immerse a canister into hot water.  Hot water could cause the internal pressure of the canister to exceed the rating of the canister which could cause the canister to burst.  Do not put the canister in the pan while the pan is on a stove.  What if you left the stove on for a minute and got distracted?  Take the pot off the stove, and then put the canister into the warm (not hot!) water.
2.  Prepare an ice bath in a container that can hold the recipient canister and some water with ice.  You don't want the level of the water to exceed the height of the canister.  Keep the connector and Lindal valve area of the canister dry.
3.  Close the valve on the G-Works Gas Saver adapter.
4.  Screw on the empty receiving canister to the Gas Saver.
5. Take the donor canister out of the warm water, dry it off, and screw the donor on to the other connector on the Gas Saver.
6.  Place the receiving canister into the ice bath taking care to keep water out of the connector and Lindal valve area.
A G-Works Gas Saver properly hooked up with two canisters.
The donor canister is on top.  The receiving canister is on the bottom, in the ice bath.
Take care to keep water out of the connector and Lindal valve area of the receiving canister.
7.  Open the valve on the Gas Saver.

When you open the valve on the Gas Saver, you should hear gas flowing from the full donor canister into the empty receiving canister.

8.  After you've let it run for a minute or so, close the valve, take the receiving canister off the G-Works adapter, and weigh the receiving canister.  While you're weighing the receiving canister, put the donor canister back into the pan of warm (not hot!) water.  Repeat steps 6, 7, and 8 until the receiving canister is full.  Do not exceed the maximum safe fill weight of the canister.
Success!  My canister which weighed only 116 g when empty is now clearly full of gas,
BUT my maximum safe fill weight is 336 g.  I need to vent or burn off 10 g.
If you've over filled the canister, vent the canister outdoors away from any heat sources or open flame using the G-Works Gas Saver with one end attached to the over full canister and the other end not attached to anything.  When there is no canister attached to the other end, opening the valve on the Gas Saver vents the excess gas into the atmosphere.  Alternatively, you can just attach a stove to the over filled canister and burn off the fuel.

That's really all there is to it.  With the above described techniques and the G-Works Gas Saver, you can refill or custom fill smaller, lighter, more convenient canisters using larger, cheaper (per gram) canisters.

Be safe and read all the cautions, please.  This is good stuff, but you do need to be careful.

Take care and happy stoving,


Appendix I – Custom Fuel Blends – DANGER
Danger.  We now depart from anything that might be considered remotely safe.  You're completely on your own here if you do this.  I'm not recommending this to you; I'm just saying it's physically possible.  Just because you can do something doesn't mean that you should.  I have not done this.  It's just too danged dangerous.  Try it at your own risk. And make sure your Life Insurance is all paid up, if you get my drift.  See photos of canister explosions, below.

What am I talking about?  Well, remember my recent post on the other G-Works adapter, the G-Works Propane adapter?  With that propane adapter and the G-Works gas saver adapter combined, you could add propane to a backpacking canister.
Never fill a backpacking gas canister with 100% propane.  

WARNINGS UPDATE, 8 April 2017: David, a chemical engineer, has left a series of remarks down in the comments section, below.  I suggest that you read them in detail if you're thinking of adding extra propane to a backpacking type canister.  Personally, I don't think you should try to add propane, but if you're going to try it, make sure you read, line by line, David's comments, below.

Why would you add propane to a backpacking canister?  Well, for cold weather.  Recall that propane is your best fuel for cold weather. In the US, the most propane content you can get in a backpacking canister is about 25% or 30% depending on whether it's mixed with isobutane or n-butane.  You could boost that percentage to 35% or 40% if you combine the G-Works propane adapter with the Gas Saver adapter.  No, I don't have any photos of this combination.  This is very dangerous and I have not tried it.

If you do add additional propane to your backpacking canisters, add the propane last.  Why?  Well, if you add propane to an empty canister, then, at least for a while, you've got 100% propane in there.  That could be bad, very bad.  Those little lightweight (comparatively) backpacking canisters cannot handle the high pressure of 100% propane.  DON'T DO IT.  I'm not sure you should add propane to a backpacking canister at all, but if you do, add the propane last, after the canister has a factory blended fuel mix in it.
Never fill a backpacking gas canister with 100% propane.  
A stove and pot destroyed by a canister filled with 100% propane.
Note how the canister has burst.
NEVER fill a backpacking type canister with 100% propane.
Backpacking canisters are only strong enough for partial propane mixes, typically 80/20 isobutane/propane or 70/30 n-butane/propane.  Filling a backpacking canister with 100% propane risks an explosion.  Backpacking canisters just aren't strong enough to handle the very high pressures involved with 100% propane.
Never fill a backpacking gas canister with 100% propane.

A stove and pot destroyed by a canister explosion.
NEVER fill a backpacking type canister with 100% propane.


  1. Jim: Good write-up of refilling small containers from large. Using identical or similar blends of butane/propane.

    I'd add a lot more cautions about refilling with any straight propane in order to increase the vapor pressure of the blend.

    - whatever you do to increase vapor pressure at, say, 30F is going to increase vapor pressure at 100F and 120F, which can easily be reached within a windscreen, even on a cold day. Also, during transport in a car, it can get very hot in the sun, could be thoughtlessly placed by a heater outlet, or on the floor above where the exhaust pipe runs. I know, I know, it's so tempting to add another 10% propane but doing so cuts into that safety margin.

    - there's a transient issue as you add 100% propane, wether you initially partially refilled with a 80/20 mix (from a backpacking canister) or from a straight butane (from a horizontal canister). If you add vapor propane, you IMMEDIATELY bring the receiving canister to the donor canister's pressure, and it takes a while for the vapor above to go into solution with the butane-rich liquid below. Even if you add liquid propane through a refilling valve, some of it will immediately flash to vapor (because the receiving canister is below propane's vapor pressure) and, again, you are at propane's vapor pressure, not the vapor pressure of the final blend. Not until you've shaken it around and gotten the vapor in equilibrium with the liquid blend. So, in my mind, you must not add 100% propane if the propane is above the pressure limits of the receiving canister. Looking at blends and their vapor pressures at 50C/122F (DOT criteria), donor propane can't be above 70F/21C. i.e. you can't use warm donor propane.

    - even if you do all the above, you could still inadvertently add too much propane. Let's say you aiming for 70% butane / 30% propane, but got to 40% propane. Now what? It's not just extra mass you can burn or vent off. It's the wrong blend and only burning/venting off 50% or so is going to change the blend much. So you'd have an over-rich canister with a lower max temp rating and while that might be fine for storage and transport during my Alaskan winter, I'm still concerned about the reduced safety margin during use (reflected IR within a windscreen or, hey! have you EVER spilled a pot of pasta? What if that happens UNTO the canister?!?)

    - a way to avoid that transient risk and to provide some margin from getting the mixture wrong, would be to use a green, steel Coleman propane bottle as a transfer vessel. Mix into it (plenty strong enough) and, if you got the mixture right, then fill the backpacking canisters. You'll have to chill it when adding butane blend and super-chill it when adding n-butane, but a chest freezer set on its lowest setting can do that.

    I totally understand the temptation to "improve" the fuel blends, I go winter camping / ski-packing in a place with serious winters, it's rarely over 70F, never over 80F in my summer, and I'm a pretty good chemist, chemical engineer and plumber. And I won't do it.

    What I will do is use Coleman green cylinders of 100% propane in the winter if I'm sledding in (therefore less sensitive to packed weight). Or use a copper or aluminum "Moulder Strip" to provide thermal feedback to 80/20 factory blends to use them down to -15F and lower.

    1. David,

      Thank you very much for your remarks. This without a doubt is the most informative comment I have received here at A.I.S.

      To my chagrin, I hadn't even though about the transient pressures during the filling, only the final pressures. Of course there's going to be transient pressure, particularly if one, God forbid, transfers the 100% propane in gaseous form.

      I have made my warnings stronger in the Appendix; I have increased the number of warnings, and I have added verbiage that refers the reader to your remarks. Hopefully this is enough.

      I could of course never have created the appendix, but I figured that if the idea occurred to me then it could occur to others. I felt it better to write down warnings than to not mention it at all and then have someone blow themselves up simply because they didn't know what they were getting themselves into.

      As for me, I will NEVER add propane to a mix. It's just too dangerous.