Scott Alpride Airbag Rucksack — Experiments in Mass Reduction

UPDATE I waited for our weather to get colder, and cold soaked the backpack outside at night to 3 degrees fahrenheit, using the single 68 gram cartridge, no hotpacks warming the cartridge, 6.5 hours. The balloon inflated full and taut with satisfactory speed. Due to the balloon being stiff and cold it unfolded out of storage slightly slower then when tested at room temperature. I’ll be using this configuration during skiing at our normal Colorado temperatures, probably packed with a handwarmer or two for insurance. This mod saves a significant 6 ounces under stock configuration. See below for more details.

Shop for Scott Alpride avalanche airbag pack.

Want to run a 30 liter avalanche airbag backpack that weighs about 2268 grams (5 lbs), saving significant weight over many of the rucksacks on the market? Check out my Scott Air Free Alpride 30 mods. Take it to any level that appears practical and safe.

Alpride stock configuration uses two gas cartridges, one carbon dioxide (CO2) and one argon. This results in a super reliable and fast inflation, per European standards. According to the engineer who designed the system, while the 60 gram CO2 cartridge will probably inflate the balloon at ambient temperatures above 23 degrees Fahrenheit, the argon is there “to maintain fast inflation at lower temperatures; also by including the argon the C02 won’t form dry ice because we maintain the pressure inside inside the inflator chamber.”

60 gram CO2 cartridges are readily available as PFD inflators. They fit the Alpride 1/2 inch cartridge port. I made some blockoff plugs for the cartridge ports and bought a few 60 gram PFD cartridges to experiment with. I figured perhaps I could cheat this by using some hand warmer packs to keep the cartridge heated, or perhaps find a slightly larger CO2 cartridge to compensate for lower temps, or both. My experiments were fun, with mixed results.

Quick conclusion is don’t use just one 60 gram CO2 cartridge (no argon) as a weight reduction hack unless you’re ski touring at fairly warm ambient air temperatures, (in my opinion above about 25 degrees F), and even then you should probably pack a few chemical hand warmer packets around the cartridge. If you’re thinking this sounds too iffy and impractical you’re right, so I’m not recommending this hack. But having the option of using only one cartridge in the Alpride still shouts the question, “show me?” What is more, how about a slightly larger CO2 cartridge to compensate for not having the argon? WildSnow.com, here we come.

During decompression, some of the CO2 will freeze in the cartridge at ambient temperatures around negative 5 degrees Celsius (23 F), resulting in a lack of volume for filling the balloon and possibly icing the inflator plumbing with “carbonic ice,” otherwise known as dry ice. What is more, these types of airbag packs work by using the power of the compressed gas to scavenge air volume intake via a venturi valve. Result is that cold ambient air mixes with the CO2, reducing volume. Those are the downsides. To compensate for problems with CO2, the stock Alpride configuration comprises the 60 gram CO2 cartridge we’re experimenting with here as well as a cartridge containing argon gas. The argon obviously provides speed and backup volume, but I’m told also provides added pressure in the plumbing to prevent the formation of dry ice.

Tests and results:

1. At room temperature (around 68 degrees F) using only one OEM cartridge worked well; one 60 gram CO2 cartridge inflated the Alpride balloon to taut pressure plenty quickly.

2. As a torture test, I left the pack outside over frigid Colorado winter night, 8 hours of cold soaking. I then triggered in the morning (using one 60 gram cartridge) at ambient temperature of 25 degrees F (the sun had warmed things up a bit by then). The bag inflated poorly and the cartridge had a chunk of dry ice in it you could hear moving around when shaken. Totally unacceptable.

3. Again testing with just one cartridge, I placed two chemical handwarmer packs around the OEM CO2 cartridge and left the pack outside for 3 hours at 25 degrees F and below. Before triggering, I measured cartridge temperature at 41 degrees, air temperature 25 degrees. Results were poor; bag inflated somewhat but not enough to function.

4. Going truly cowboy, I bought a few 68 gram CO2 cartridges with the correct threading. The stock Alpride cartridge pair weighs 450 grams, while the 68 gram CO2 weighs 278 grams — for a savings of 172 grams (6 ounces). While experimenting I weighed full and empty cartridges and found that my 68 gram cartridges actually held about 70 grams of CO2, which is interesting, as it appears there might be significant variations in how much CO2 cartridges are actually filled with — that requires further study for sure. Overall, this hack seemed to work well and I’ll be using it during my ski tours (with attention to ambient temperatures, and plenty more testing). See below.

This raft of modding and testing resulted in much more than a few trips to our back porch, thus my repacking the Alpride airbag multiple times. A few tips regarding that. 1) Reconfigure the zipper by unhooking the slider, quickly zipping back to the packed position using only one side of the zipper then rehook the slider to start your zipping and packing. 2) Insert an object such as the eraser side of a pencil into the flapper valve on the plumbing so you don’t need three hands while you’re packing. 3) How you pack the balloon isn’t hyper important; don’t roll it up, start folding and stuffing with the side closest to the plumbing. 4) Cock trigger BEFORE installing fresh cartridges, otherwise you’ll get a surprise and spend extra money.

If you have an Alpride and want to experiment for yourself, first task is find a reasonably priced source for PFD cartridges. For the 60 gram units I found these guys, aquamentor.net A six-pack of cartridges costs $80 including shipping, so that’s $13.00 a pop, pretty good. The 68 gram cartridges are harder to find. Please let us know in the comments if you find a source, as they seem to be ideal. If you Google for the 68 gram stuff you can find a few options, especially on Ebay (but beware of the shipping cost markup scam).

I’ve got more cartridges of various persuasions coming. Experiments ongoing. Overall, in my opinion there is a lot of potential for changes to the gas airbag systems that’ll help with weight issues. I’d guess one of the biggest sticking points is the European CE standard, which appears somewhat arbitrary and biased not only for gas systems, is perhaps too strict as to inflation times and even balloon volumes. Result is the usual double edged blade of standards; protecting the consumer, but possibly stifling innovation and improvement. At least we modders can practice our craft and perhaps cut through the B.S.

More weight reduction
Beyond playing around with the gas system of the Alpride, you can do some practical weight stripping that doesn’t compromise safety. Check out some options below:

Check out our unboxing of the Scott Alpride 30 liter airbag backpack.

Shop for Scott Alpride avalanche airbag pack.