Equipment Report

Distortion and failure of a Lewis Rope Walker

The stainless steel body of the Lewis Rope Walker seems rigid enough for most pitches, yet under the extra pressure placed upon it on the bigger drops it begins to distort. It opens until the sheath sides are pressing tightly against the flexible locking wire on one side and the split (or key) ring on the other.

Recently, in El Sótano, the extreme rigidity of over 1300 feet of rope caused extra sideways pressure which was enough to splay the sheath open to the point where the split ring was forced through the hole in the body. This allowed extra free play on the centre cam and eventually the split ring was levered to an oval shape before being straightened out. Presumably the deformed ring would subsequently either have been forced through the hole or sheared off by the holes' edges.

The failure occurred on the left-foot ropewalker which, in the situation mentioned above, seems to put a high load on the key ring. The point is reached where the whole strength of the ropewalker is entirely dependent upon this small piece of wire which is neither designed for, nor capable of, sustaining the loads thrust upon it.

A modified cam pin, with a larger diameter head solves this problem, allowing the ring to revert to its original purpose (ie. that of preventing cavers from losing the cam pin) instead of acting as a load-bearing time bomb.

With cavers becoming more and more gadget minded, perhaps it is time all new equipment is thoroughly tested to an approved safety standard. The Equipment Committee of B.C.R.A. should be given more facilities and more finance for this purpose instead of letting cavers out as 'guinea pigs'.

J. Eyre

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