There can be a big difference between the theoretical efficiency of a pulley system and its actual efficiency. Here are test results from the Petzl lab.
Efficiency depending on the device used at the head of the system.
The force required to raise a 100 kg mass was tested under several configurations with different devices at the head of the system and with ropes of various diameters.
Test protocol:
– Ropes tested: 7 mm cord, SEGMENT 8 mm, PUSH 9 mm, CLUB 10 mm, PARALLEL 10.5 mm, AXIS 11 mm, VECTOR 12.5 mm.
– Measurements were made with a constant pull rate of 1.5 meters/minute, on new devices and ropes.
– The results are given for information only; in the field there are numerous variables to take into account (position of haul system elements, rope diameter and construction, hauling speed, hauling smoothness, the haul load…).
Note: pulley efficiency ratings in the Instructions for Use are based on values measured with a simple 1:1 directional.
Hauling efficiency F = xx M is the value obtained with the smallest compatible rope diameter for the device.
The pulley efficiency expressed in % is calculated from this value.
Efficiency is always less than 100%, the efficiency of an ideal pulley (impossible in reality).
Example for MAESTRO S: F = 116 M, efficiency = 86%
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