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Pulleys for crevasse rescue

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Pulleys for crevasse rescue

Postby WyomingSummits » Sun Jan 27, 2013 11:27 pm

Any recommendation on favorite pulleys for crevasse rescue and reasons why? For instance, "x brand is better since you get x ounces in weight reduction with only x reduction in weight capacity".


Thanks for any insight!
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Re: Pulleys for crevasse rescue

Postby Andes6000 » Mon Jan 28, 2013 1:10 am

Check out the petzl ultra legere pulley, i haven't used one so perhaps someone who has can share some insight on that, and always have a tibloc clipped on your harness for self rescue.
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Re: Pulleys for crevasse rescue

Postby WyomingSummits » Mon Jan 28, 2013 1:26 am

Andes6000 wrote:Check out the petzl ultra legere pulley, i haven't used one so perhaps someone who has can share some insight on that, and always have a tibloc clipped on your harness for self rescue.


Thanks, I'll look into it. I will always have prusiks attached to my glacier line with an ascension device attached to my harness. Glacier travel without at LEAST two prusiks ready to go is lunacy.
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Re: Pulleys for crevasse rescue

Postby nartreb » Tue Jan 29, 2013 4:24 am

I've never done a crevasse rescue in the field, but with pulleys in general, a larger-diameter pulley is WAY more effective than a small one. The problem is that a bigger pulley is heavier and takes space on your rack, which stinks since you almost never actually use it. The ultralegere lives up to its name (10g) but has a small diameter, only works with certain 'biners, does not guide the rope and is not self-tending... I'd hesitate to rely on it for crevasse rescue. Could be useful as a second pulley (instead of a bare 'biner) at the hauling side of a 3:1.

I went with cheap pulleys from CAMP ("small mobile"). The comparable Petzl pulleys ("Mini Prusik") are twice the price but half the weight; worth it if you plan to go on crevassed terrain more often than I do. (Not many glaciers here in the East...)
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Re: Pulleys for crevasse rescue

Postby Wastral » Tue Jan 29, 2013 6:55 am

nartreb wrote:I've never done a crevasse rescue in the field, but with pulleys in general, a larger-diameter pulley is WAY more effective than a small one.


100% wrong!
Pulley diameter has little to nothing to do with efficiency as long as the rope/cable in question can bend the radius of the pulley. The larger pulley you used I am sure had a bearing at its center and for this reason was larger. It is the bearing that makes all the difference.

If one wishes to use pully's without bearings for lighter weight, you can partially cheat. :D

Take your standard bearingless cheap pulley and place it in a ziploc baggie full of very fine powdered graphite and then carry it in your pocket/backpack EVERYWHERE for many weeks. This will work the graphite into the bushing of the pulley creating a vastly better slip surface and it will then act just as well as a pulley with a bearing. The problem is that this is NOT a permanent solution and said graphite will likewise work/wear itself OUT of said bushing on your bearingless pulley. Thus, this option requires more upkeep.

For best efficiency with a pulley, buy a pulley with a bearing WITHOUT a shield. IE NO GREASE. Yes, outside detrius can get in, but likewise you can clean it easily as well. Greased bearings while having lower efficiency than bare steel unshielded ball bearing or needle bearing last longer if you are Constantly using them. That is the ONLY reason grease is in the bearings.
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Re: Pulleys for crevasse rescue

Postby pvnisher » Tue Jan 29, 2013 8:57 am

The DMM Revolver. Locking biner with a pulley built right into it.
Get a wiregate revolver for those long extensions to reduce rope drag, and a locking one for crevasse use.
http://dmmclimbing.com/products/locking-revolver/
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Re: Pulleys for crevasse rescue

Postby Andes6000 » Tue Jan 29, 2013 3:14 pm

pvnisher wrote:The DMM Revolver. Locking biner with a pulley built right into it.
Get a wiregate revolver for those long extensions to reduce rope drag, and a locking one for crevasse use.
http://dmmclimbing.com/products/locking-revolver/


I had thought the pulley bit was at the edge of the biner but not the case so looks alright, but it should probably be cleaned quite often. Will give it a try, thanks.
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Re: Pulleys for crevasse rescue

Postby nartreb » Tue Jan 29, 2013 4:40 pm

Wastral, don't take my word for it, take Petzl's:

http://www.petzl.com/en/outdoor/pulleys
Two factors determine a pulley’s efficiency:
- sheave size (the wheel that the rope runs on): the larger the diameter, the greater the efficiency
- bushings and bearings: self-lubricating bushings are efficient. Sealed ball bearings are very efficient and require very little maintenance.


Here's another pulley manufacturer:

http://www.cmi-gear.com/catalog/pulleys/education.asp
In general, larger sheave diameters produce greater pulley efficiencies.


(By the way, that manufacturer actually lists the efficiency of most of their pulleys! Their prices are reasonable, I just wish they'd list weight and size in metric. http://www.cmi-gear.com/catalog/pulleys/micro.asp)

It's pretty simple, the wider the diameter of the sheave, the more torque you have available to overcome bearing friction (plus, less energy loss to rope bend, but that's not much of a factor with climbing rope). You can easily see this for yourself. Set up a difficult task (like pulling a small car on a flat surface with a 2:1 pulley system) and try it with two different-sized pulleys (with the same type of bearing).

The other way to beat friction, of course, is with a better bearing. I would guess that in terms of weight and cost for a given efficiency, ball bearings are close to equivalent to a larger sheave. Of course, a smaller pulley is often more convenient for climbers. Edit: poking around on the CMI site, they have a few models where the size and weight are identical, but the one with a "bearing" (not a "bushing") is about two percentage points more efficient (and about 50% more expensive). These are relatively large-diameter models (~four-inch sheave); I'd guess a bearing would make a more substantial difference on a smaller sheave, since friction would be worse on a smaller sheave. (end edit)

Interesting real-world tests, showing among other things that the Ultralegere is significantly better than a bare 'biner but still far from ideal:
http://www.potomacmountainclub.org/inde ... ew&gid=151%2..

Combining these sources, it looks like a bare 'biner is slightly better than 50% efficient (in other words, hardly working as a pulley at all), the ultralegere gets you to around 70% , a typical climber's pulley might be mid 80s, and a "serious" rescue pulley is in the 90s.
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Re: Pulleys for crevasse rescue

Postby Wastral » Tue Jan 29, 2013 11:51 pm

Since it doesn't seem you have a mechanical engineering degree let me try to put it very simply: Probably fail, but here goes.

Sheave size has no bearing on the subject matter under normal conditions unless you purposefully introduce garbage into the bearing/bushing itself. It matters a lot if you are trying to rotate said pulley from an internal torque as in an electric motor. It would appear that whoever wrote that lazy drivel, lifted that information right from a power sheave company literature. Now, I would LOVE to have an electric motor to haul people out of crevasses, but I will let you carry it along with the generator OK? So, all Sheave diameter increases efficiency information for POWERED applications needs to be discarded. We have to go back to basics of what is happening when we are pulling on the rope in question.

Let me explain. A bit convoluted: Assume the small bushing Petzl/DMM,CMI has is sufficient for rope bend considerations. Its diameter is approx 1.5inches. A 9mm has no problems going over this. A 10.2mm I have is a bit stiff. A bearing DMM prussic minding pulley has a diameter of about 2".

The real deciding factor is can the rope/cable in question actually bend easily around said diameter? If all of your "power" is being used to bend the rope/cable, then your "efficiency" will be lower. IE the DMM "revolver" pulley is WAY too small. Yea, it works in a pinch, but a good portion of your work energy is being used to HEAT the rope due to internal friction of the fibers bending/sliding against one another instead of lift the object. A good rule of thumb is, " If you can easily bend 180 said rope/cable in your hand they any diameter of sheave above this is essentially useless. For this reason, it is better to use 2 identical biners as a pulley than 1 as it creates a larger diameter "pulley" and therefore less inernal heating of the rope.

The difference is maybe 1% between extremely small and a very large sheave under starting conditions and that is only in regards to static friction. Static means the object in question is not moving. Introduce garbage into the bearing and then, yes, Sheave/bearing diameter does matter as you are trying to "crush" rocks. If you are so stupid as to not keep your pully's clean, hey more power to ya. Once the person/object starts moving the efficiency of hauling is no different in regards to sheave size. This is like not cleaning your CAM's. If you are that stupid you deserve everything coming your way and the DARWIN award that ultimately follows.

SO, yes, Petzl can claim higher efficiencies with a larger pulley as technically they are correct though its under 1%. In reality, the static friction inside a bearing/bushing is absurdly small and not even worth contemplating as we are not trying to turn the pulley to create said torque on said rope and lift an object like one does with an electric motor! IE transferring torque from the inside of the sheave through friction to the rope/cable in question. Only when you do this does the diameter (area) of the sheave matter a GREAT DEAL.

PS. Yes, I have read their(Petzle, CMI, BD) reports before and when you practice crevasse rescue you can easily tell the difference between no bearings and bushings. The difference between bushing's and bearings is very small. As far as I am concerned, especially on 2 man rope teams each person must carry 2 pully's that have been at least heavily graphited. A graphited climbers pulley has same efficiency as a greased shielded bearing pulley and for the same weight you can carry nearly double the number of pully's and likewise the money you save can go into buying more gear. If you want the ultimate in efficiecy you use non greased bearings. This grabs you another 5% efficiency. I would use such bearings in my competition engineering projects. You do need to make sure they stay clean.

PPS. The CMI statements are pure drivel as the idiots claim 133% efficient. Sweet, they create energy... :lol: :shock: :shock: :shock:

PPPS. To bring home the Sheave diameter has no bearing, next time you are beside a VERY large crane, you will notice that the DRUM around which the vast majority of the cable is wound is VERY LARGE. WHy? Because the electric/hydraulic motor has to transfer its power to the cable in question. The only way to do this is via friction. Now, look at the block and tackle hoist apparatus coming down and you will notice that its sheaves are much, much, much, smaller than the drum. IE if there was any truth to the matter that one needs a large diameter sheave for higher efficiency you most certainly would see it in large cranes. You do not for the reasons I gave.

Bottom line, Petzl, CMI and whatever idiot wrote their web pages are idiots. Or more likely is that they had to put something on their webpage and technically they can claim what they did. Of course its so insignificant as to be absurd.
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Re: Pulleys for crevasse rescue

Postby nartreb » Wed Jan 30, 2013 4:02 am

So it's "100% wrong" that "a large diameter pulley is way more effictive than a small one", but "the DMM revolver pulley is way too small", have I got that right?

Wake me up when you grow up.
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Re: Pulleys for crevasse rescue

Postby WyomingSummits » Wed Jan 30, 2013 4:35 am

I've never yanked someone out of a crevasse, but I can say with certainty in regard to haul bag applications, that the ultra small pulleys definitely didn't work as well. That being said, past a certain size, I really didn't notice a marked increase in efficiency when using a single pulley configuration. Thanks for the input everyone.
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Re: Pulleys for crevasse rescue

Postby Wastral » Wed Jan 30, 2013 8:35 am

nartreb wrote:So it's "100% wrong" that "a large diameter pulley is way more effictive than a small one", but "the DMM revolver pulley is way too small", have I got that right?

Wake me up when you grow up.


Figures, why do I bother to explain to those who don't wish to learn and then cover their willful ignorance by telling someone else to "grow up". Get a few in every crowd.

Enjoy your willfully ignorant life.
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Re: Pulleys for crevasse rescue

Postby Wastral » Wed Jan 30, 2013 8:49 am

The Chief wrote:WHY are you using pulleys???

A "Z" or 3:1 can be effectively accomplished with...


Try that setup with only 1 person. It ain't gonna work. That is why you carry pulleys. Either you assume the guy can ascend themselves on a new line, or can at least help when a cut in lip(typical) is encountered. Having them ascend is vastly faster then building the 3:1. Assuming you can't do a simple drop loop(2:1) that is. The end result of no pulleys is the guy better not be unconscious. If they are and they can't help, there is no way in hades you are going to get the guy out by yourself as all of your pulling force will be dissipated as friction. This is a valid way to cross glaciers either with or without pulleys. Its a risk like everything else. Typically one just falls in to their waist and easily self extract themselves. One could readily argue that if one is unconscious they probably likewise have broken bones etc making survivability, even if you do extract them, when operating on a 2 man team very low. Its a risk, just like going super light verses light, how much fuel, water, food you carry etc.
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Re: Pulleys for crevasse rescue

Postby asmrz » Wed Jan 30, 2013 4:12 pm

In practical terms you guys are both right.

In my climbing life, I have not had many trips with more than two people on the rope. So in the 70s and 80s we carried prusiks, deadman and a short picket each, thin rope aiders tied into the rope in front of us (ready) and we "wore brown pants" all the way...

These days, I would bring a pulley or two if we go just the two of us. When climbing in threes or more, the rope management and signals between the search guy (the 1st one) and the second and third man are of extreme importance. Knowledge of the "Z" set up helps quite a bit when one goes in. But avoidance is the real story here and if that fails, knowing what to do. When one takes a dive into a big hole (I have on Baker, a bridge broke, a deep fall), things get complicated even if all of us know exactly what to do and have all the right equipment with us.
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Re: Pulleys for crevasse rescue

Postby Fletch » Wed Jan 30, 2013 4:52 pm

I carry a Petzl Mini pulley for crevasse rescue. When we actually had to use it in the field (in Alaska) we used it as a drop setup due to the amount of folks we had and the way the climber fell in.

If this is for Rainier, you can get away with a DMM biner or do as the Chief says. But for AK, I would recommend having three ways to do everything. A pulley can be a good option.
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