Refilling isobutane canisters-how do you know when it is full while still mated?

[Eugene Hollingsworth]

I want a function that can be put in a program or spreadsheet or even a table to reference when filling canisters to know when the recipient is full, while the canisters are mated.

This weekend I recorded the weights of 2 canisters as I alternately filled one, then reversed the process and refilled the other. The resulting graph of the data shows a Sigmoid – like curve. (  https://en.wikipedia.org/wiki/Sigmoid_function  ) I weighed the canisters several times mated and disconnected

Has anyone worked out a reasonably accurate way of knowing when the recipient canister is full without disconnecting it from the donor canister?  The process would be sooo much faster than bleed-disconnect-check-bleed-disconnect-check…

I have a digital scale, some canisters, the G Works Gas Saver. To keep the setup simple and repeatable, while the canisters were mated, I put one on the scale, the other on the desk, which happens to be an inch lower. Also, the donor canisters are variable size and weight, unlike our specific recipient canister.

[Eugene Hollingsworth]

I realized after all that work the table of weights is only valid for those two canisters, one being full, the other being empty.

An overnighter  in the woods would have been more profitable.

[BlackHatGuy]

Not much of a scientist so can’t help you out, sorry.

But after reading your post with all that mating, I felt a strong urge to smoke a cigarette….

[Eugene Hollingsworth]

Ok, we have that out of the way… ??

[Bob Moulder]

I don’t know of a way to do this when using the G-Works Gas Saver setup for transferring isobutane to isobutane.

The only practical way to do this would be to have some sort of in-line meter. Given all the temperature and pressure variables there is no way in heck you’re going to be able to calculate and time it and get the desired amount of transfer within about +/-10g.

Now, if you want to transfer from the cheap butane canisters to a standard isobutane canister you could use one of THESE and place the recipient can on a good scale and either tare the scale to zero or note the weight difference. I have not tried this—I did not buy the transfer gizmo because I don’t really need it—but I think this could prove to be fairly accurate. I’m pretty sure a couple of adapters could be linked together to adapt the “butane” end to work with a standard isobutane canister, but again, I’ve not had the need nor the motivation to have tried it.

If you decide to go the cheap butane route, most of the straight transfer adapters (the ones without the flexible hose) are super easy and quick to attach to/remove from the donor can, so you can quickly put the recipient can with adapter attached onto a scale to check weight… obviously making sure you’ve turned off the valve before doing this, lol. ;^)

This what I do, and I never transfer iso-to-iso, hence no need for the flexi hose adapter.

[Jerry Adams]

I just do it by ear.  Both listening to it as it’s transferring, and shaking the canisters to tell how much there is.  Then disconnect and weigh.

Sometimes the weight change will have been a small amount compared to desired so I’ll know to let it go much longer next time.

Sometimes I’ll be transferring the entire contents which makes it easier.

I don’t need to do more than about 2 or 3 extra unscrewings which isn’t that bad.

I don’t think it’s a good idea to light a cigarette while doing this : )

[Eugene Hollingsworth]

You’re right on Bob – measuring by time / volume just isn’t going to happen.  Motivation: it a neat problem and a practical, if seldom, application. The reason for refilling it bugs me to carry a partial canister or worse a full and partial. Using butane cheaper butane is a bonus.

I hadn’t considered flexible hose adapters when I picked up the G Works Gas Saver – that is probably the best solution – BUT – As long as I’m down this path though, I really want to get a function or method without unscrewing canisters except for the final check(s).  It’s a cool problem and a solution would just be even cooler.

[Jerry Adams]

The flow rate is variable.  It just depends on the temperatures and fullness of the two canisters.

Sometimes it sounds like a lot is flowing, but then I disconnect and measure weight and very little transferred.

Regardless, it only takes 2 or 3 extra disconnects.  And unscrewing, weighing, screwing isn’t that big a deal.

[David Thomas]

My experience is the same as Jerry’s in his first post (#6):

The rate varies a LOT on slight differences of temperature (of course the donor is at room temperature and the recipient is at freezer temperature, but +/- 5 degrees still makes a difference) and fuel blend.

Listening to the transfer happen a few times and you develop a sense of how long it will take.  Counting “one-one-thousand, two-one-thousand, etc” helps quantify that.  If 7 seconds at full open got me 70% of the transfer I wanted, then I’ll need a total of 10 seconds, i.e. an additional 3 seconds to get there.

Disconnecting and re-weighing isn’t hard.  Just ALWAYS HAVE THE TRANSFER VALVE ABOVE the canister you are connecting or disconnecting so the short spurt of fuel is only gas, not liquid.  The first few times you refill, it will take 2 or 3 disconnects and re-weighings.  But after you’ve done a few, stop at your best guess (while counting out loud), reweigh, and then add the last second or two to get there.  I’m usually within 5-10 grams or less with a single disconnect/reweigh.

[David Thomas]

If you always used the same donor and same recipient canisters (size and blend), I can imagine a system in which you balanced the transfer valve on an edge and attached magnets of known weight until it balanced.  Say you start with:

Donor 275 grams, recipient 170 grams + 105 grams of magnets at its center of mass.  275 grams = 275 grams

Then you transfer some fuel, shift magnets around until it is balanced and maybe get
Donor 235 grams, recipient 210 grams + 25 grams of magnets.  You’d know from the magnets going from 105 to 25 grams that you’ve transferred (105-25)/2 = 40 grams of fuel.  So if you you’re aiming to transfer, say, a total of 105 grams, twice that weight of magnets need to move (taken off the recipient + put onto the donor = 210 = 105 x 2.

But with canisters of different sizes, you’d have different lever arms of the fuel in each so I’d have to think about where the magnets should go in that case to make the math as easy as possible.

Or you could use magnets to determine the imbalance both in air and in water.  That and a lot of algebra would give you the density of each canister.  A completely full canister has the same density it did when new.

Conclusion: Accept having to disconnect and reweigh.  Count out loud as you transfer.  Listen by ear to the transferring fluid.  Keep notes as you go.  Pretty soon, you’ll get really close on your first try with only minor topping off or venting needed, if any.

 

[Paul Magnanti]

N.M. Misread the original post…

[Eugene Hollingsworth]

I guess at this point I should get out more and use experience to fill the canisters. Somehow I went down the rabbit hole again.

There is a profitable use of time spurred by this discussion:  I put together a (slightly crude) spreadsheet to substitute numbers over experience knowing how much fuel to carry. Using info gathered here on BPL + burning, boiling, and measuring fuel I know how many grams each of my stoves use in ideal outdoor conditions. Punch in expected liters water per meal, hot lunches or not, number of overnights and bingo! I get a wildly optimistic estimation of fuel to carry. Better this than carrying an extra gallon of when in the BWCA.

[Eugene Hollingsworth]

 

I do spreadsheets because I my coding skills have … vaporized.

 

[Bob Moulder]

For solo 3-season I just figure 11g/day for canister (which I rarely use 3-season) or 50ml/day for denatured alcohol. I don’t do hot lunches, however.

Winter can vary a lot depending upon whether liquid water is available or all water will be obtained by melting snow.

I can fairly confidently declare that I will never again use WG.

 

[Author]

Posts