In reply to Juan S:
> I don't quite understand how this happens. If I'm reading this right, the Pivot is not auto-locking in guide mode? This doesn't make sense to me. Even with a thin (7.8mm) rope. The physics of how this would happen puzzle me (you have a considerable part of the weight of the climber clamping down the dead rope with all the friction that entails).
> Can I double check you were talking about the DMM pivot on guide mode? And, if you remember more details about your test:
> Was that one or two thin ropes (it should auto-lock with either, but I'm just curious)
> Was the test weight dropped slowly through slow slippage? Or a fast drop?
> Finally, you wouldn't happen to have measured the breaking force required to stop such a fall/slippage?
> My apologies for all the questions!
The loaded rope clamps down on the dead rope and locks it BUT with increasing force the dead rope is squeezed out to the side and in the end the two strands change places, depending on the rope or force either jamming inside the slot or becoming completely free. You can see how this occurs easily by trying a piece of cord instead of a rope.
With bigger ropes this is of little concern as the forces involved have to be quite high but with thin ropes it can occur under bodyweight. Some plates do this worse than others depending on the width and shape of the rope slot.
The weight is slowly lowered onto a single strand.
Once the strands have swapped position the rope is merely running over a karabiner and the plate provides virtually no braking force unless you move your hand to a conventional belaying position.