Unfortunately, in a cable’s life there will be a time where it experiences fatigue. Sometimes the fatigue will be caused by harsh environmental conditions. Salt water, acids, and other harsh elements will commonly reduce your cable life expectancy. However, there is another reason that your cable may be not lasting as long as you would hope…pulleys and sheaves! Pulleys and sheaves play a significant role in the lifespan of cable. One specific engineering concept, called the D:d ratio, helps extend this cycle life by matching the ideal pulley diameter to a corresponding cable diameter. Here is a closer look at how the D:d ratio functions.

What is the D:d Ratio?
The D:d ratio describes the relationship between pulley diameter and cable diameter, and it is used to maximize cable service life. The uppercase D indicates the pulley diameter, while the lower case d refers to the diameter of the cable, including any jacketing. In other words, the larger the pulley, the higher the D:d ratio. In general, the larger the D:d ratio, the longer the service life of the cable. While the D:d ratio is a highly important consideration, it is to be remembered that this just one of many factors that contribute to cable longevity. You should also evaluate the other aspects of your system if you are experiencing issues with cable fatigue. 

What does this mean?
Pulleys that are too small for a given cable diameter place excess strain on the system by requiring the cable to bend around too small of a radius. This generates fatigue in the cable that will result in eventual failure if not properly addressed. Simply putting the same size cable back on the same size pulley will just repeat the same issue. Despite a smaller pulley often being ideal for space in your application, often choosing the biggest size possible will help you save time and money in the long run as you will not constantly be needing to replace your sheaves and cable.  

What are Some Other Solutions?
Consider selecting a smaller diameter cable for your existing pulleys, as smaller cables are able to bend around tighter radii. Alternatively, you can upgrade your pulleys with the help of QSheaves, Process Sheaves, and eSheaves from Loos & Co., Inc. Cableware Division. QSheaves provides quick turnaround on customizable lifting sheaves, so you no longer have to wait for long lead times from other manufacturers. ESheaves has the OEM replacements you need from Crosby McKissick, and Process Sheaves offers plastic sheaves for processing linear products.

Begin comparing your options on our website here. Alternatively, if you have any questions our team is happy to help! Reach out to us by email through sales@esheaves.com, or by phone at 800.321.LOOS (5667).