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.
From Gear In Use 4: Rope Access and Confined Space
1. 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.
– 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…).
SIMPLE DIRECTIONAL (1:1)
|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%
SIMPLE DIRECTIONAL (2:1)
HAUL SYSTEM (3:1)
HAUL SYSTEM (4:1)
HAUL SYSTEM (5:1)
2. 3:1 haul system efficiency depending on the redirect point used
Peace on your Days