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An In-Depth Look at Pulley Efficiency

Introduction

Psyched on longlines but not psyched on tensioning them? Well, you are not alone. Tensioning a longline can be plenty of work. But with the right equipment, it can be a lot less work. The net mechanical advantage and efficiency of a tensioning system is a function of three components primarily: base system pulleys, brake and multiplier pulley. Using inefficient equipment in any of those three categories can profoundly affect your tensioning system’s ability to generate a high mechanical advantage.

 

Equipment

We will look at the efficiency of 11 different pulleys to attain a general idea of how they compare; but the real testing will involve the CAMP double pulleys, which are also branded under a million other names, and the SMC 3" Double PMP's. The SMC PMP pulleys are the best pulleys practical for a longliner, so they will set the ceiling bar for our test. The CAMP doubles are 2 3/8” medium-duty pulleys that are common among slackliners. This test uses two bushing and two bearing CAMP pulleys (they come in both variants). Note that the CAMP doubles are not bottom of the line garbage pulleys. They are midlevel pulleys. Many, many pulleys with worse performance specifications do exist. So if your pulleys are even smaller and crappier than the CAMPs, keep that in mind when reviewing the results of this test.

 

Methods

I summarized the methodology and the differences between the CAMP doubles and SMC PMPs in the following video. With the exception of the 300 lbf tension test, I terminated the test when I reached 100 lbf on the pull strand. Watch the video before continuing.

 

Results

The following photos represent the 100 and 300 lbf efficiency values for 11 common pulleys.

Pulley Efficiency Pulley Efficiency

The following photos represent the results of contrasting the CAMP and SMC pulleys, with no brake, with a GriGri, and with a Pro-Traxion.

Pulley Brake Pulley Brake
Efficiency Values Efficiency Values

The results conclude that switching from the CAMP doubles to the SMC PMPs yielded a 24.8% increase in pulling power with a 5:1 using a GriGri One for a brake. To further contrast, a 7:1 with the CAMP doubles had less pulling power (986 lbf) than a 5:1 with the SMC doubles (1020 lbf) when using a GriGri One for a brake. However, that is partly because the CAMP pulleys seem to do relatively poorly at lower loads compared to the PMPs. Using this test as a formation for a hypothesis, I believe it is valid to conclude that if a slackliner is using relatively poor and crappy pulleys, a 5:1 with the 3” SMC PMPs may outperform that slackliner’s pulleys in a 9:1 combination. Therefore, if you have difficulty tensioning your system, instead of stacking on more pulleys, consider upgrading to the PMPs. You will do less work, and your back will thank you. This is Sayar Kuchenski, a guest author for Slack Science, and I dearly thank you.



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