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Mechanical advantage

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  • Mechanical advantage

    I was asked a question yesterday that I had never considered before. We were using 2 MPD's in a raising exercise of a rescuer in a harness. Both MPD's were rigged as 3:1 Z-rigs. I know that a simple system pulling on another simple system multiplies the mechanical advantage such as a 3:1 pulling on a 3:1 = 9:1. But when the dual systems are attached independently to the load and not pulling on each other then it's just a 3:1 mechanical advantage or would it be considered a 6:1 because both systems compliment each other?

    The temperature dropped into the 40's here this morning and I think it froze my brain. I live in South Louisiana for a reason.

    Thanks,

    Mike

  • #2
    As long as both 3:1 teams are hauling equally, it's a 6:1. When one team resets or just stops pulling, it becomes a 3:1 (as long as one system is pulling).
    I used to be DCFDRescue 2. Forum changover locked me out.

    www.rescue2training.com

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    • #3
      Not sure that I agree with that. I would say the mechanical advantage remains 3:1 although the load is shared between 2 systems. If the total load is 600 pounds you would still need 200 pounds of force to move the load. Think about it like this. If you divide the load between two 3:1 systems, each would have a 300 pound load, and would require 100 pounds on each haul line to move the load. If one person were to grab both haul lines and pull, he would need to apply 200 pounds of pull to move the load. 600:200 = 3:1.

      That was an interesting question and one I have never really thought about before.

      Originally posted by Rescue 2 Training View Post
      As long as both 3:1 teams are hauling equally, it's a 6:1. When one team resets or just stops pulling, it becomes a 3:1 (as long as one system is pulling).
      Last edited by highwire; 01-03-2016, 08:13 PM.

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