Self-locking pulley systems
Ascender + pulley at the anchor
When an ascender is incorporated with a pulley at the main anchor point, the rope is stopped from sliding back over the pulley. This is the most efficient type of hauling system as it produces the least friction.
It is limited by the fact that a load cannot be lowered without introducing a lowering system. The hauling system shown in your training materials gives a 3:1 mechanical advantage.
Descender as the locking device
More friction is introduced to the system by the addition of a descender as the locking device. This system is more versatile as it can be converted easily to a lowering system. However, because the system is based around a 2:1 mechanical advantage, a rope that is double the length of the lowering distance is required.
The hauling system in this configuration provides a 6:1 mechanical advantage.
Toggle between the two systems and see how cam grip changes the rope required per metre lifted.
Ascender clamps the load-side rope at the anchor. Highest efficiency — but lowering requires a separate system.
Theoretical MA
3: 1
Real MA
2.77: 1
92% efficient
Input force
0.36kN
to lift 1 kN
Rope per m lifted
3.06m
with cam slip
Cam slip = 2% of each pull is lost to back-creep before the next cycle. Always pair the self-locking system with an independent back-up.
Cam grip ≥ 95% — safe to use