TECHNICAL FORUMS > Equipment
a suggestion from a person who has never done a pull thru...
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well, with that admission here goes.......i am familiar with pull downs......pull downs are where the cave has an upper and lower entrance..........the caver(s) enter and pull down a double rope thru a sling or carabiner rigged up top.......two ropes attached by a double grapevine knot, or a single doubled rope is used and its not usually difficult to pull the rope down after everyone has rappeled the pit.......eventually a lower exit is made and beer is consumed shortly thereafter...... i understand that a pull thru is when you enter the lower entrance and pull the rope up from the bottom......or do a pull down to a dead end and then back out the top entrance,....i have never done the latter and it sounds quite intriguingly dangerous!........ not being a part of the english caving scene i am goin to suggest something that may sound old-hat or stupid.......but, here goes anyway......what about using a rounded wheeled device of somesort in the upper rig point.......a carabiner or somesort of metal device is what you are trying to pull the haul cord with the rope attached knot thru......thats whats hard right?.........now, if the carabiner had a "wheeled" device associated with it that had a large enough opening for the knot to easily pass thru the movement when the knot was at the top rig attachment point would have to make the pull thru easier to work???....... :shock: :shock: :shock: :shock: :shock:
Well, unfortunately there are 2 diffierent uses of the term 'pull through' which can understandably lead to confusion if unfamiliar! In the case of the discussions on the best knot / dodgy pull throughs in the Peak District, what we are actually talking about is reaching a belay point / high level passage from the ground which can't be rigged on the way down.
In this case, because you have to pull a knotted rope through the belay, it tends to get stuck- whereas on a 'pull down', it can be rigged without the need for a knot....
So.... There is a large ring bolt or suitable belay at the top of the pitch, but you are at the bottom, needing to get a rope up there and secure. Through the rope at the top is a thin polypropylene cord, which is tied in a loop, coming down from the single upper belay to a pair of bolts a way apart at the bottom, forming an 'A' shape. One end of the caving rope is tied to an end of the poly rope, and the opposite end of the polypro is pulled upon- by magic the caving rope goes up, through the belay and comes back to the bottom where it is tied off to the bolts. Hey presto! the pitch is rigged, prusiked up and abseiled back down, and the caving rope can be pulled the opposite direction and retrieved. You have to make sure you only use the one correct side of the rope!
Does that make sense? :?
Don't see why not - how about something like this?
These sorts of things are advertised as knot passing pullies so would be ideal. I guess people use carabiners because they've often got an old one lying about. If I ever set up a pull thro' then I'll whack a nice user friendly pully on it.....
The petzl pullys are probably not big enough for both the poly prop and the static rope to sit properly and the poly prop could get stuck between the pully and swing cheek :( . There dead expensive so would probably get nicked by less moralistic cavers (90% when it comes to free kit :roll: ). and most importantly - it doesnt provide 2 seperate systems in case of failure - something which if installed by an accountable party (i.e. DCA) would have to be adhered to hence ralphs twin Krab nightmare. :cry:
Erm cant think of anything myself though.
Hang on - what about two concentric rings connected by three spokes. youd attach the outer ring to two chains to two bolts. Thread the inner ring with polyprop. If the inner ring should wear sufficiently to fail the outer ring would be the fail save. and could then be replaced.
Sussed - just need a company to manufacture and distribute them for a retail price under a tenner. :D
underground....thats what i thought was going on!.....bubba we use those type of pulleys in rescue work when knots are involved in the rope, i figured this was something you guys know about and i guessed that the cost and theives would be the problem......they are verrrry expensive........how about this, in that old biner hanging at the top, cut a short length of old narrow pipe that one could thread thru the biner's gate short enough to then slip down to the bottom of the biner where its hanging.....when the knot mass approaches the top you would have a moveable surface for it to ram into, mebbe its(the pipes)ability to rotate would make the passage easier!....:shock:
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