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For a set of two double pulleys, the force acting on each should be equal to the tension in the rope times the number of ropes connected to the individual pulley if I understand correctly. In this pulley system on mcmaster, it looks as though the force acting on the upper pulley should be 5T (with T being tension) and the force acting on the lower 4T. Can anyone explain why the specs give an effort (which should be the tension) of 85 lbf to give a lifting force of 500 lbf. Why is it not 340 lbf (85*4).

Is my understanding of static pulley systems flawed?

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I am pretty sure you are correct.

I tried to find the mechanical advantage by using a FBD and got it to be 4:1. But just to be sure I poked around the internet a bit and found this great site. The MA is given in section 6-8.3 .

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    $\begingroup$ That link is fabulous. Thanks! $\endgroup$ – A McKelvy Nov 17 '20 at 13:38

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