/ Revolver Krab - Pulley Strength Question

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thedatastream on 05 Apr 2012
I know the screwgate Revolver krabs are rated to 24kN with the gate closed but I can't find any data to say at what load:

1) the pulley stops rotating
2) the pulley becomes irreversebly damaged

I've contacted DMM in parallel but wondered if anyone on here knew?

Cheers
In reply to thedatastream:

Hi,

The pulley stops rotating at around 11.5kN. At this point the Revolver acts as a full strength carabiner - the pulley and its mounting / housing does not compromise the overall integrity of the carabiner.

The pulley bearing can be deformed permanently at forces around 16kN - we have never seen this happen in real life.

Hope that helps

Regards

Simon Marsh

DMM
thedatastream on 05 Apr 2012
In reply to Simon Marsh:

Awesome, thanks Simon
gd303uk - on 05 Apr 2012
In reply to Simon Marsh: Hi Simon i have noticed a small design flaw in the revolver screw gate, ie the load is often not transferred directly over/through the pulley, could this be a cause for concern and the reason the pulley stops working.
cyberpunk - on 07 Apr 2012
In reply to thedatastream: Dont mean to hijack your thread, But I have been using the Revolver alot sports climbing. When I have a project and keep falling at the same place I put a quickdraw there with a Revolver krab. I find that it saves the rope from alot of ware and tare. Also when I put 2 quickdraws on the top of a route I put a quickdraw with a Revolver as again is reduces wear on the rope. Love me Revolver.
gd303uk - on 07 Apr 2012
In reply to cyberpunk: they are good but could be better, and the fact they don't load properly is poor attention to detail really.
Fraser on 07 Apr 2012
In reply to gd303uk:

Short of making a rotating housing in the bottom of the crab for the pulley, which would greatly increase the size and therefore the weight of the whole unit, how do you suggest it might be improved whilst retaining the pulley facility? I must say, the revolver is one of my favourite pieces of kit.
gd303uk - on 07 Apr 2012
In reply to Fraser: shift the centre of gravity , no weight would need to be added just a tweak in the shape of the krab would do this. or make it easier for the rope to pass directly over the pulley, i am not saying they are crap but the fact is the rope does not load directly over/through the pulley , you must admit this is a flaw in the design, as that is the intention of the krabs purpose.
i might add I am not a designer/engineer and am not expected to come up with a solution, I just notice the problem, the solution is for DMM to make.
i have 2 of these and like them. but they can be improved.
Fraser on 07 Apr 2012
In reply to gd303uk:

I'd say that on occasion, the rope doesn't pass directly over the pulley so I can see where you're coming from. This doesn't happen all the time AFAIK, so wouldn't really class it as a design 'flaw'. There will be a reason the pulley is located exactly where it is.

I think we can rest assured that DMM will have tried many profiles before deciding on the current design.
In reply to gd303uk:

This is an interesting thread from DMM's point of view because there is some truth in gd's observations, but the simplistic nature of his statements warrants a reply.

Can you load the Revolver off centre and in a manner whereby the rope seems to be running off the roller - certainly, but it is worth looking at this a bit more closely.

If you were to mark the roller with a horizontal black line and then try to load the roller so that the rope is pulling off centre you will see roller is still rotating uniformly and if you look at the load point of the rope you will see that this is still (primarily) on the roller - the Revolver is still reducing friction and improving efficiency.

It is simple to demonstrate this - just run a heavy load over a Revolver, get the rope to run off centre and pull the load up - repeat with a normal biner. The result is pretty obvious - the weight is far easier to lift with a Revolver no matter how it is loaded - we have demonstrated this a huge number of times at the various events we attend.

Loading off centre is maximised with thick, old single ropes on Revolvers that are unable to move/rotate; it it is minimised on half ropes and modern singles on Revolvers that are able to move or rotate easily. Perfect - no; pretty damn good - yes - and a lot better that using a standard biner in a pulley/friction reducing system.

I'll get some numbers/video sorted to illustrate this.

The comments regarding design are particularly crass - the Revolver was in the design office/tool room/testing stage for about two and a half years and it's development heralded one of the biggest changes in recreational carabiner design (hot forging + I-beaming carabiner backs) seen in the last decade.

The behaviour characteristics of the Revolver under load are far more complex than a standard carabiner - taking a chunk of metal from the very area that is designed to take most load whilst also drilling an axle hole through the same area presented a lot of design challenges. Plus we had to add a rigid steel axle that totally changed how a carabiner behaves under load whilst adding several interacting moving parts that had to perform consistently over a period of years in a very wide range of conditions.

A key design feature - and core to answering the posters comments - was that we needed to make sure that the rope bearing surfaces - the back, the roller and the back/roller intersection all presented a smooth, safe rope bearing radius in all circumstances. This is key because a steeper bottom on the back bar - the ideal way of forcing the rope onto the pulley - could create possible stepped edge issues.

An awful lot of thought + testing went into the design of the Revolver taking into account all sorts of issues/situations/systems/misuse - the shape and geometry are unique and were not predictable by FEA - just the result of a lot of time, knowledge + prototypes.

Nine years on and there is no competitor to the Revolver - nothing has come close or improved on it and this a large testament to Fred and Gethin's design work.

There are no plans to modify the current series of Revolvers, but there is strong demand for a bigger, industrial version of the Revolver with a larger diameter/more efficient roller that will work with larger diameter ropes and this is on (long) list of things to do.

Regards

Simon Marsh

DMM
Fraser on 09 Apr 2012
In reply to Simon Marsh:

Cheers for the detailed, explanatory response, thanks Simon.
gd303uk - on 09 Apr 2012
In reply to thedatastream: > (In reply to gd303uk)
>
> This is an interesting thread from DMM's point of view because there is some truth in gd's observations,

Thanks for your reply Simon, and clearing things up it is much appreciated. DMM is an excellent British company, I am always happy to buy/use your gear and have a rack full that I use regularly.


Regards
Graham

PS
I only know simplistic and crass ;)
Richard Baynes - on 09 Apr 2012
In reply to gd303uk:
> (In reply to thedatastream) > (In reply to gd303uk)

> PS
> I only know simplistic and crass ;)

I thought that was a it harsh too: surely you have to pretend the customer is always right?!


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