Refilling Single-Use IsoButane Fuel Canisters

This tutorial will show how I re-use my “Single-Use”, “Disposable”, “Throwaway” isobutane fuel canisters.

There are four main reasons I choose to refill my canisters:

I need canisters available to use on short notice (trips, camping, storms, emergencies, etc.) My closest supplier for isobutane is 23 miles away.
It is difficult to find waste disposal companies that will take the canisters for recycle, so they end up in the landfills.
Refilling the canisters saves money, and who doesn’t like that? For example, JetBoil isobutane 100 canisters cost $5.83 ($5.50 + 6% tax) but can be refilled for $2.35.
It requires less canisters and less storage space

This Instructable has three steps:

Step 1 – Refilling IsoButane “Single-Use” Fuel Canisters For Backpacking, Camping, Hiking, etc.
Step 2 – Single-Use Fuel Canister Android App Calculator (Prototype) & Spreadsheet Tool For Backpacking, Camping, etc.
Step 3 – Explain Effects of Temperature on PSI and Weight

I always weigh new canisters (in grams) at room temperature (75 F) and record the weight on the bottom of each new canister with a sharpie pen. That total weight is then used to calculate how much fuel remains after each use. When I refill that canister later on, I only refill to that weight using the same brand of fuel. (Note: It is important to use scales that can be calibrated and that have Tare functions - otherwise you might be better off just estimating the weight instead.)

The transfer process relies on differences in pressure and gravity. During transfer, you can usually hear the transfer of liquid fuel taking place until the pressure equalizes/stops. In order to fill the "receiving" canister to the same weight as when it was originally purchased you typically will need to purge some fuel vapors from the “receiving canister”.

Note: Working with flamable liquids and gases can be dangerous. User’s assume all risks if they are using this Instructable when handling liquid fuel and gases.

Cautions when refilling canisters

Appropriate safety precautions should always be used and proper safety gear/clothing worn when handling flammable gases.
Working with canister gases should only be done in well ventilated areas and under adult supervision.
When handling flammable gas, recommend all tools & hardware be made of brass to reduce chances of sparking.
The only way to properly measure the amount of fuel in a canister is by weight alone. Canisters should never be over filled beyond the manufacturers original weights (approximately 80% of the canister’s total capacity). It is a good practice to always weigh these canisters when purchased and record the original weights on the canister.
When refilling single-use canisters, recommend only refilling with the same brand/blend of fuel to avoid contamination or adverse results.
While it is legal to refill single-use canisters in the US at this time, it is the individual’s responsibility to follow all local, state and federal laws. Currently, federal law prohibits the transport of refilled single-use canisters in commercial vehicles.

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Step 1: Refilling IsoButane Fuel Canisters for Backpacking, Camping, Hiking, Etc.

To refill isobutane canisters, I use the G-Works Gas Saver Plus (R-2) (Photo Set 1 top right). G-Works Gas Savers are available in two versions: Gas Saver (R-1) & Gas Saver Plus (R-2).

Both designs incorporate a two-way transfer valve – gas vapors flow upward while liquid fuel flows downward. The newer R-2 version has a purge valve that purges fuel vapors from the bottom canister. As a result, the Gas Saver Plus (R-2) should only be used with the printing on it’s side, right-side-up. The Gas Saver (R-1) on the other hand can be used right-side-up or up-side-down.

Both Gas Saver units have a transfer valve that is operated using the attached wire handle. Displaced gas in the "receiving" canister (bottom) rises up through the same small opening from which the liquid fuel drains. Flow ceases as pressure equalizes in the canisters. The size of the canisters doesn’t dictate the direction of liquid fuel flow. The “Donor” canister is always on top and a “Receiver” canister is on the bottom.

On the Gas Saver Plus, the G-vent pressure release port is located on the bottom half and for safety reasons vents to the back side of the valve away from the user.

When transferring it is best to use a level surface for stability. I always attach canister stabilizer legs when transferring isobutane liquid fuel.

This isobutane transfer process is actually safer than refilling a butane lighter, since you use a screw-on valve rather than just holding a tight fit between the lighter and refilling container.

A. When away from home or base station

When away from home, I carry a small scale (Cen-Tech 60332 from Harbor Freight, about $6 on sale; Photo Set 2 top left photo) to keep weight to a minimum. Since the scale platform area is very small and isobutane canisters have rounded port tips, I carry a 7/16” x 0.098 thick grade 8 zinc washer to make it easier to weigh the isobutane canisters (Photo Set 2 & Photo Set 3). The washer helps stabilize the canister when weighing. I place the washer on the scale platform, Tare the scale to zero, and then place the canisters up-side-down on the washer to weigh them.

Normal refill process (Photo Set 2 & Photo Set 3)

Determine how many grams of fuel to transfer

1. Place the thick washer on the scale and Tare the scale (zeros out the weight of washer)

2. Weigh Receiver canister by placing up-side-down on the scale (on washer)

3. Determine how many grams of fuel to transfer by subtracting current weight (step 2) from its full weight

(marked on bottom canister after purchased)

Prepare Receiver canister & Tare scale for fuel transfer

4. Remove the washer & Receiver canister from the scale and set aside

5. Check that the transfer valve is closed on the Gas Saver Plus (fully CW)

6. Place the canister stabilizer legs on the canister

7. Attach Receiver canister to bottom of Gas Saver Plus (Photo Set 2 bottom two photos)

8. Place the Receiver canister with Gas Saver Plus & legs up-side-down on scale and Tare scale to zero (Photo

Set 3 top left)

Transfer fuel

9. Place the Donor canister on a level surface, invert the Receiver canister with Gas Saver Plus, screw on the

Donor canister (Photo Set 3 top right), and set unit upright on canister legs (Photo Set 3 bottom left)

10. Transfer fuel by opening the transfer valve using the wire handle (CCW).

11. After the sound stops or you have transferred enough liquid fuel, close the transfer valve (CW)

12. Invert the canisters so that the Donor canister is on the bottom and unscrew the Donor canister

13. Invert the Receiver canister & Gas Saver Plus and place on scale to determine if enough fuel has transferred

(refer to step 3 calculation).

14. If the transfer process stopped before you were able to transfer the amount needed, purge off some fuel

vapors to allow more fuel to transfer by pressing the purge valve five short bursts (Photo Set 3 bottom right).

15. Repeat steps 9-14 as needed

Wrap up

16. If too much fuel was transferred, purge off using purge valve

17. Place Receiver canister & Gas Saver Plus upright, unscrew Gas Saver Plus, remove stabilizer legs

B. When at home or base station

When at home, I use a typical kitchen scale like the one shown above (Photo set 4 top left).

Normal refill process (Photo Set 4 & Photo Set 5)

Determine how many grams of fuel to transfer

1. Weigh Receiver canister on the scale

2. Determine how many grams of fuel to transfer by subtracting current weight (step 1) from its full weight

(marked on bottom canister after purchased)

Prepare Receiver canister & Tare scale for fuel transfer

3. Remove Receiver canister from the scale and set aside

4. Check that the transfer valve is closed (fully CW) on the Gas Saver Plus

5. Place the canister stabilizer legs on the canister

6. Attach Receiver canister to bottom of Gas Saver Plus (Photo Set 4 bottom two photos)

7. Place the Receiver canister with Gas Saver Plus & legs on scale and Tare scale to zero

Transfer fuel

8. Place the Donor canister on a level surface, invert the Receiver canister with Gas Saver Plus, screw on the

Donor canister (Photo Set 5 top right), and set unit upright on canister legs (Photo Set 5 bottom left)

9. Transfer fuel by opening the transfer valve using the wire handle (CCW).

10. After the sounds stop or you have transferred enough, close the transfer valve (CW)

11. Invert the canisters so that the Donor canister is on the bottom and unscrew the Donor canister

12. Place the Receiver canister & Gas Saver Plus with legs on scale (Photo Set 5 top left) to determine if

enough fuel has transferred (refer to step 2 calculation).

13. If the transfer process stopped before you were able to transfer the amount needed, purge off some fuel

vapors to allow more fuel to transfer by pressing the purge valve five short bursts (Photo Set 5 bottom right).

14. Repeat steps 8-13 as needed

Wrap up

15. If too much fuel was transferred, purge off using purge valve

16. Place Receiver canister & Gas Saver Plus upright, unscrew Gas Saver Plus, remove stabilizer legs

Step 2: Single-Use Fuel Canister Android App Calculator (Prototype) & Spreadsheet Tool for Backpacking, Camping, Etc.

This step will introduce the Single-Use Fuel Canister Tool & Android Calculator App. I designed the app to reliably calculate the fuel level in isobutane/propane fuel canisters and help during the refilling of canisters.

Background

Isobutane/propane canister stoves are widely used: camping, backpacking, survival training, military deployments, etc. In fact, they are so popular that you will have no problem finding them on thru hikes anywhere along the AT. One of the most perplexing problems when using canister stoves is knowing how much fuel is left in a canister when packing. Too little and you could end up running out of fuel; too much and you end up carrying excess weight on long treks.

I tried using a JetBoil Jet Gauge ($20) for measuring the fuel status, but found readings were inconsistent and inaccurate on mine. I do carry it with me in case the batteries in one of my other scales give out. I also looked at using something like the MSR “float” gauge (graphics on sides of canisters), but decided I’m not always near a water source for that to be of much use. I also viewed a video on YouTube on how to use a walking stick with markings to weigh canisters, but I don’t use a walking stick very much anymore. So...

The App – Tool vs Calculator

The app comes in two forms: as a Tool and as an Android Calculator App.

The Tool (Excel spreadsheet) allows users to change values and save the results. The Calculator (Android app) allows users to change values but resets everything after exiting. Since I wouldn’t always have access to my laptop or tablet, I decided I would need an Android app for my smartphone.

I decided to do a prototype before diving in to make a more complicated (robust) Android app. I used an application called Spreadsheet Converter to create a temporary web page from the spreadsheet that could then be converted into an Android app prototype using AppGeyser.

The Excel spreadsheet was designed and tested on a HP laptop (Windows 10) & Samsung tablet and the Android app was tested on a Samsung tablet & Android smartphone. The Spreadsheet can also be used with some other applications such as LibreOffice Calc (seems to work except for the percentage not showing on tip of fuel gauge needle).

During this process I found that Spreadsheet Converter was not as robust as I had hoped and I discovered a software “bug” I could not overcome. That “bug” did not allow the “Description” columns in the “Usage Profiles” and “Refilling Canister Specs” worksheets to be changed by the user after conversion. Regardless, I still went ahead and converted the web page format to a Smartphone Android APK & Tablet Android APK using AppGeyser. The AppGeyser conversion created a couple of cosmetic issues of it’s own – extended bottom lines on some boxes in worksheets. Since this is prototype and the issues were only cosmetic, I decided to go ahead and include the Android app APKs with this Instructable.

Different APK versions were created for a smartphone and a tablet. The smartphone version allows swiping the screen right or left to see all of the information, while the tablet version displays each screen to full width display. Both scroll up and down the same way.

Changeable/selectable information cells are yellow color for user convenience. All other areas of the Tool (spreadsheet cells) and Calculator are protected so that important data or indexing of other sheets aren’t altered accidentally. The light gray areas display info from other sheets.

Included in this step are the Tool and Android app files:

Excel Spreadsheet (Tool, Fuel Canister Tool v5.2.xlsx, CRC32 6F57E392, 51653 bytes)
Smartphone Android app (Calculator, _Phone_Fuel_Canister_Calculator_9062822.apk, CRC32 349C1C17, 13837827 bytes)
Tablet Android app (Calculator, _Tablet_Fuel_Canister_Calculator_9070198.apk, CRC32 2935AF92, 13812687 bytes)

The Photo Sets in this step are of screenshots from various devices I used during testing:

Photo Set 10 – HP Laptop computer – Tool (Excel, spreadsheet)
Photo Set 11 – Sumsung Tab E Tablet – Tool (Excel, spreadsheet)
Photo Set 12 – Sumsung Tab E Tablet – Calculator (Android app – tablet version)
Photo Set 13 – Smartphone – Calculator (Android app – phone version)

Differences between the Tool and Calculator are:

The Calculator allows user changes during use but will reset after closing the application; the Tool can save all changes
The Tool displays fuel gauges on the Calculate Canister Fuel Level & Refill Canister sheets. The gauges also have user changeable thresholds for low (yellow) and very low (red) fuel levels. When using Excel, the fuel gauge needle will display the percent of fuel; when using the spreadsheet in other applications such as LibreOffice 6.0, etc., the percent may not show.
In the Tool, the Descriptions (column 1) of the Calculate Canister Fuel Level & Refill Canister sheets are user changeable, whereas, in the Calculator they are not changeable.

Fuel Canister Calculator Functions

The Trip Planning function was specifically designed for isobutane use. All other functions are designed for both isobutane and propane situations.

Trip Planning

Calculates

(a) Total Fuel needed for trip (grams). Enter:

- Event description

- Number days for that event

- Usage expected per day (grams),

- Reserve fuel preference (grams).

(b) How many canisters would be needed for the most common canister sizes. As the screenshot in Photo

Set 10 shows, in trip planning the choice of canister sizes can be important. Notice that the difference

between 100 vs 110 canisters results in one additional 100 canister for the Trip Planning needs.

Displayed Information

(a) Usage Profile data is shown for three profiles selected by user (from the Usage Profiles sheet) to help in

planning usage per day in trip plan.

Calculate Canister Fuel Level

Calculates

(a) Estimated or actual Fuel in the canister. Enter:

- Full weight (recorded by the user on bottom of canister or the Preferred data at the top of page)

- Net weight (from canister or the Preferred data at the top of page)

- Current weight of the canister & fuel.

- Optional: Empty weight of the canister (defaults to zero)

(b) Days and Boils left for each of Usage Profiles selected by user (from the Usage Profile sheet)

Displayed Information

(a) User is provided two Preferred canister specs (selected by user on Refill Canister Specs sheet)

(b) Displays a red “OVER” message beside fuel calculation when Current weight is higher than Full weight

Refilling Canisters

Calculates

(a) Fuel in the canister. Enter:

- Full weight (auto filled by app from Preferred Receiving Canister user selected on Refill Canister Spec sheet)

- Start weight of the canister & fuel (grams)

- Current weight of the canister & fuel (grams)

(b) Fuel to add to Start weight (grams)

(d) Fuel that has been added (grams)

(e) Cost of Fuel that has been added

(f) Cost fuel per gram of both Receiving & Donor canisters (using data from Refilling Canister Spec sheet)

Displayed Information

(a) Donor & Receiving Canister info (Names at top, rest of specs middle of screen)

(b) Displays a red “OVER” message beside fuel calculation when Current weight is higher than Full weight

Usage Profiles

Calculates

n/a

Displayed Information

(a) Descriptions – NOT changeable by user (column 1)

(b) Usage Per Day – changeable by user (grams – column 2)

User Selectable Information

(a) User selected order of three Profiles to Compare on other sheets (drop down list of 10)

Canister Refill Specifications

Calculates

n/a

Displayed Information

(a) Descriptions – NOT changeable by user (column 1)

(b) Net weight – changeable by user (grams – column 2)

(d) Full weight – changeable by user (grams – column 4)

(f) Cost of canister or refill – changeable by user (dollars – column 5)

User Selectable Information

(a) Donor & Receiving canisters to use for Refill sheet (drop down list of 15)

(b) Preferred canisters to display information on Refill sheet (drop down list of 15)

PSI – Temp – Weight

Mainly a reference sheet to look up Temp vs PSI, Temp vs Weight effects and notes regarding the refilling process (Refer to Step 4).

Future Plans for App…

After using the prototype app for awhile, I’ve decided I’ll probably try creating a more robust app using an Android app Development Suite, time permitting. It should make data entry, list changes, and calculations easier. Some of the issues that bother me about the prototype are (a) the inability to change Descriptions in some tables, (b) it doesn’t allow users to save changes, and (3) the need to grant unnecessary permissions for unneeded/unused resources by AppGeyser. If successful, I’ll post to the Google Play Store.

Step 3: Explain Effects of Temperature on PSI and Weight

At any given temperature, the canister PSI will stay constant independent of the amount of liquid fuel in the canister (Photo Set 15 left). If the temperature remains constant, the PSI only changes as liquid fuel or gas vapors leave the canister. The canister contains gas vapors on the top and liquid fuel on the bottom. If the PSI is too low for the current temperature, some of the liquid fuel will boil to create more gas vapors until it reaches the appropriate PSI. If the temperature drops, some of the gas vapors will revert back to a liquid state and the weight will change accordingly. Depending on the fuel being used, the effects may vary considerably. For example, the change in weights of typical canisters at room temperature and after placing in a freezer for an hour are shown in Photo Set 15 right.

Transferring liquid fuel relies upon various factors: gravity, PSI, etc. We use gravity to exchange liquid fuel from the top canister with gas vapors from the bottom canister.

Purging of excess gas vapors should only be done via the connection ports of the single-use containers using the port itself or hardware attached to the port for that purpose. Never attempt to use the over pressure valve on a single-use canister for purging. Should the over pressure valve become damaged, it could fail later and possibly result in an explosion.

When temperatures of the canisters are kept the same the transfer process is fairly easy to predict and usually requires some purging of the bottom canister to “top off” to the normal fill level (approximately 80% of the canister’s total capacity). Under most circumstances, the canister doesn't need to filled to the original weight when purchased, only to a reasonable level. Obviously, there may be cases where a fill to the original state when purchased will be necessary.

One method for refilling canisters uses temperature to increase the transfer of fuel between canisters. For example, the upper canister might be around 75 F and the lower canister cooled in a freezer to around 0 F. The cooling reduces the PSI in the lower canister (refer to chart above). This results in a higher PSI in the top canister and a lower PSI in the bottom canister. The PSI differential will transfer liquid fuel faster before stopping. In this method of transfer, it is common for too much fuel to be transferred resulting in dangerous over-pressure situations when the temperatures normalize and/or they are stored in hot environments. Be very careful if you use this method of refilling single-use canisters.

Why it’s safer to keep canisters at the same temperature when transferring liquid fuel

When using temperature differentials to transfer liquid fuel, the lower canister must be colder than the upper canister. The colder temperature of the lower canister causes a negative pressure when compared to the upper canister, thus fuel flows faster to the receiving canister. Transferred fuel cools & compresses as it enters to the receiving canister and as long as too much doesn’t transfer in the process everything should be fine. As the compressed fuel and vapor in the receiving canister warm up, the canister pressure increases and may cause over-pressure issues. The final pressure must never exceed the manufacturer’s recommended rating for the canisters.

When transferring using a purge valve, both fuel and vapors stay at the same temperature and only enough vapor is purged from the receiving canister to draw in more liquid fuel to the canister’s original fuel weight. Since the fuel and vapor for both canisters remain at the same temperature, the pressures in both canisters will stay within the manufacturer’s recommended rating for the canisters. Thus, when done properly, purging excess vapor in the receiving canister avoids over-pressure issues.

I hope you find this Instructable useful.