Thoughts on balancing "sewing it up" with rope drag.

On that note: are there problems with putting an actual pulley, say this one, in a system that might catch a lead fall? It's rated for 23kN and 5kN WLL (I'm not sure how the forces these numbers represent are exerted). That's the pulley I have, but there are stronger pulleys.

It's probably too fiddly to do in practice; I'm asking out of curiosity more than anything.

David Kerkeslager wrote:

On that note: are there problems with putting an actual pulley, say this one, in a system that might catch a lead fall? It's rated for 23kN and 5kN WLL (I'm not sure how the forces these numbers represent are exerted). That's the pulley I have, but there are stronger pulleys.

It's probably too fiddly to do in practice; I'm asking out of curiosity more than anything.

Decreases the force felt by the faller and increases the force on the belayer making it more likely they drop the climber. Why bother?

Jim Titt wrote:

Decreases the force felt by the faller and increases the force on the belayer making it more likely they drop the climber. Why bother?

To reduce rope drag.

Jim Titt wrote:

Decreases the force felt by the faller and increases the force on the belayer making it more likely they drop the climber. Why bother?

Also increases the peak force on the top piece of gear (if that's where the pulley is).

David Kerkeslager wrote:

To reduce rope drag.

That naturally enough I already knew and there are many other ways to reduce drag, the question was why bother to arrange a system which increases the chances your belayer drops you?

Jim Titt wrote:

That naturally enough I already knew and there are many other ways to reduce drag, the question was why bother to arrange a system which increases the chances your belayer drops you?

But couldn't this be said about *any* measure that decreases rope drag? Less rope drag = more force on the belayer in the case of a fall.

It's also a tradeoff: rope drag is likely to cause a fall. A pulley might increase chances of a fall being a ground fall, but it also decreases chances of falling in the first place. In some cases this might mean a lower chance of ground fall.

Jay Morse wrote:

I'm curious if anyone has experience falling on these biners.  I can only imagine that in a normal situation the belayer would get yanked up extra hard and extra high because of the friction loss causing the fall to be extra long.  Is there really an advantage of using one of these on a short draw vs. just extending and using a normal biner as far as protecting ledge and ground falls?  I'm asking because I like the concept and might buy one, but I'm curious if the math works out in the real world.

I have taken a couple lead falls onto a revolver biner, didn't make any appreciable difference in fall distance. This was on the third of fourth bolt of a route that took a hard 90 degree turn to a crack system. As Jim Titt stated the pulley itself isn't very efficient with a heavier load, the pin is such a small radius for the pulley to rotate on. They do work GREAT for reducing rope drag though, there isn't much load from a rope pulling.

Nick Drake wrote:

They do work GREAT for reducing rope drag though, there isn't much load from a rope pulling.

I do have to wonder how well this statement holds in the real world.  Shouldn't the efficiency of the pulley remain constant over a variety of loads?  Or is the rolling friction of the pulley highly nonlinear at low loads (< 5 lbs)?  I would have thought the nonlinear regime for that would only be at far lower loads.

Nathan Hui wrote:

I do have to wonder how well this statement holds in the real world.  Shouldn't the efficiency of the pulley remain constant over a variety of loads?  Or is the rolling friction of the pulley highly nonlinear at low loads (< 5 lbs)?  I would have thought the nonlinear regime for that would only be at far lower loads.

it sounds like you may be searching for numbers from the engineering world rather than anecdotes from the "real world" (which I would say is about equivalent of a 60-90cm sling for many placements)

Rememer we are talking about drag reduction from the rope sliding through the basket of a biner to a small pulley that can be allowed to rotate. I don't think that it's going to take s high efficiency pulley to make a difference for that particular situation. 

Perhaps an ME can weigh in on this, but I do think diameter of the bearing surface matters significantly as loads increase, but I just stayed at a holiday inn express last night.

Nick Drake wrote:

it sounds like you may be searching for numbers from the engineering world rather than anecdotes from the "real world" (which I would say is about equivalent of a 60-90cm sling for many placements)

Rememer we are talking about drag reduction from the rope sliding through the basket of a biner to a small pulley that can be allowed to rotate. I don't think that it's going to take s high efficiency pulley to make a difference for that particular situation. 

Perhaps an ME can weigh in on this, but I do think diameter of the bearing surface matters significantly as loads increase, but I just stayed at a holiday inn express last night.

True. But understanding the system we use is what is going to push what is possible, and what can be safe enough, rather than just relying on anecdotes.  Alone, anecdotes lead to rules of thumb, which leads to a dogmatic approach to climbing systems.  That, I feel, builds a community of climbers that essentially believe in superstitions, and would be an equivalent of being in the Dark Ages.  But that's just me.

Nathan Hui wrote:

I do have to wonder how well this statement holds in the real world.  Shouldn't the efficiency of the pulley remain constant over a variety of loads?  Or is the rolling friction of the pulley highly nonlinear at low loads (< 5 lbs)?  I would have thought the nonlinear regime for that would only be at far lower loads.

It´s not the efficiency of the pulley that is the problem as such, it is the rope´s characteristics that vary considerably with load, the bend radius and the wrap angle. Fundamentally the coefficient of friction drops with increasing force, the "frictional" resistance decreases with increasing diameter and the resistance is also dependent in a non-linear way to the wrap angle.

I´ll pull out some graphs and explain it better tomorrow.

Rope drag:-

9.5mm rope, tight weave sheath, old but good condition (no furring). 1000g weight on rope (or about 13m of rope hanging below). Efficiency % = Original load/force required to slide through. Angle of bend from straight through.

Revolver 

15°-92% 30°-87% 45°-77% 60°-73% 75°-65% 90°-60%

Wild Country Nitro (a typical modern draw biner).

15°-82% 30°-71% 45°-61% 60°-56% 75°-49% 90°-46%

12mm HMS Karabiner

15°-89% 30°-75% 45°-67% 60°-61% 75°-54% 90°-53%

I also ran a brand new 10mm rope through but the patter is the same, just the values are about 10% higher. There are a couple of design flaws with the Revolver and one is thicker ropes ride off the side of pulley more and drag on the body of the karabiner, with body weight´s or more and thicker ropes this problem becomes considerable making the pulley more or less redundant.

Jim Titt wrote:

There are a couple of design flaws with the Revolver and one is thicker ropes ride off the side of pulley more and drag on the body of the karabiner, with body weight´s or more and thicker ropes this problem becomes considerable making the pulley more or less redundant.

That's why I prefer Petzl Rollclip A to DMM Revolver.

Thanks for the info Jim.

I'm trying to understand the significance of this in terms of how pulling on a the rope is going to feel. If I'm understanding correctly, adding one DMM Revolver to the system dragging 1000g at 90 degrees would be the difference between dragging 1667g and 2173g. And the difference would be greater for larger loads (at least until the rope flattens enough to ride on the side of the pulley as you mentioned). Seems pretty significant.

David Kerkeslager wrote:

Thanks for the info Jim.

I'm trying to understand the significance of this in terms of how pulling on a the rope is going to feel. If I'm understanding correctly, adding one DMM Revolver to the system dragging 1000g at 90 degrees would be the difference between dragging 1667g and 2173g. And the difference would be greater for larger loads (at least until the rope flattens enough to ride on the side of the pulley as you mentioned). Seems pretty significant.

The significance of an extra 500g extra depends entirely on how weak you are . And i wouldn´t place any bets on your second statement being true. 

Jim Titt wrote:

The significance of an extra 500g extra depends entirely on how weak you are .

I'm so weak!   

But also this gets multiplied across the inefficiency of every carabiner in the system, hypothetically? 500g multiplied by 1.21 (the inverse of that 82%) to the power of 10 (10 other carabiners besides your DMM Revolver) would feel like 3364g by the end of the pitch. Probably an extreme example, but I've been known to sew it up this much (weak AND scared!).

Jim Titt wrote:

And i wouldn´t place any bets on your second statement being true. 

Hm, why's that? If a 1000g load feels like 1667g or 2173g depending on carabiner (difference of 506g), wouldn't a 2000g load feel like 3333g or 4546g depending on carabiner (difference of 1013g)?

David Kerkeslager wrote:

Hm, why's that? If a 1000g load feels like 1667g or 2173g depending on carabiner (difference of 506g), wouldn't a 2000g load feel like 3333g or 4546g depending on carabiner (difference of 1013g)?

I thought you mean the the percentages would change under higher loads.

Learn to place less gear, climbing is nicer and faster and you don´t get pumped out that way.

Jim Titt wrote:

Rope drag:-

9.5mm rope, tight weave sheath, old but good condition (no furring). 1000g weight on rope (or about 13m of rope hanging below). Efficiency % = Original load/force required to slide through. Angle of bend from straight through.

Revolver 

15°-92% 30°-87% 45°-77% 60°-73% 75°-65% 90°-60%

Wild Country Nitro (a typical modern draw biner).

15°-82% 30°-71% 45°-61% 60°-56% 75°-49% 90°-46%

12mm HMS Karabiner

15°-89% 30°-75% 45°-67% 60°-61% 75°-54% 90°-53%

I also ran a brand new 10mm rope through but the patter is the same, just the values are about 10% higher. There are a couple of design flaws with the Revolver and one is thicker ropes ride off the side of pulley more and drag on the body of the karabiner, with body weight´s or more and thicker ropes this problem becomes considerable making the pulley more or less redundant.

Another design flaw is that no one ever uses just one Biner on a route. Regardless of what the pulley biner does the drag is still negatively effected by lower drawers

Squeak wrote:

Another design flaw is that no one ever uses just one Biner on a route. Regardless of what the pulley biner does the drag is still negatively effected by lower drawers

That's not really a design flaw, more of just an obvious limitation that nobody expects the revolver to fix. It is supposed to be used strategically on 1 or a few pieces on a pitch where the rope makes the sharpest angle . Obviously if you don't mitigate rope drag on lower pieces, you're still gonna have rope drag, and nobody is saying you won't. However, you might have a little bit less using the revolver.