I'm off to the alps this year for my first alpine holiday, I will be taking some form of crevasse rescue personal gear. My question is this; can I get away with taking a dmm revolver instead of a pully? The revolvers would have some additional use in rock climbing and are less bulky on the harness. A dedicated pully would probably be more efficient, but more bulky and limited in use elsewhere (for myself at least).
In reply to BStar: Can you get away with it. Sure, I know plenty of people using just biners and no pullies. You just have to make sure you are able to rescue the heaviest person in the group (with his gear on that is). Since you should be training rescues anyways, you should known what you can and can't. If you did not train this, then train. If you can't save everybody, you need something to make sure you can.
fyi, revolver or pulley, considering everything you are carring, there are better ways to get lighter and less bulkier.
In reply to BStar: Revolver efficiency is going to be around 70-75% if the revolver is working perfectly and the rope stays correctly orientated. This is better than a biner but worse than a dedicated pulley.
Apparently, you should put the best pulley on the bottom, the moving pulley. It's much more efficient. The redirect doesn't matter as much (counter intuitive). So if you are going to use a revolver and a pulley, then the revolver would have to be at the anchor side for the greatest efficiency (thus you would want it to be locking). Although one has to factor how much friction is in whatever progress capture you use and therefore a pulley with a smooth autoblock (microtraxion) might practically be more efficient there vs something like a garda hitch.
The microtraxion at 85g, 91% efficiency with an autoblock is pretty sweet, has loads of uses but not all for the trip you are going on. It would work as a beast of an ascender if you are the one that falls down though. It's worth bringing one or two of these. for 170G in weight you'd need no prussiks or pulleys and you'd have a really efficient system. It's spendy though.
That's your crevasse rescue and ascending gear, for less than the weight of one handled ascender. Compared to biners(50-60%) and older pulleys like Fixes(71%) it would be the rolls royce of crevasse rescue pulley systems. The only non reusable thing is the Petzl partner but it's only 56 grams. Everything else you will be carrying already, however you might take a few grams weight pen for a couple of carabiners that are more compatible with the pulleys.
Biners in a hypothetical 3:1: You will need (at least because I'm not taking into account the friction on the lip etc.). 53kg of force to lift your 90kg climber (80kg + 10kg of gear).
With the setup proposed above: 33KG of force to lift the climber.
Once you've added all the other factors you will need all the help you can get.