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  1. #1
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    Default side by side air bag lifting

    Been arguing this for years -- two lifting bags in tandem --(not stacked) -say a 20 and a 40 -- is the max the weakest one ? so maxed out at 20 - or can you lift 60 -- I always averaged them - so a 40 plus 20 would max out at 30. But that is completely un scientific .Help ?
    ?


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    Quote Originally Posted by slackjawedyokel View Post
    Been arguing this for years -- two lifting bags in tandem --(not stacked) -say a 20 and a 40 -- is the max the weakest one ? so maxed out at 20 - or can you lift 60 -- I always averaged them - so a 40 plus 20 would max out at 30. But that is completely un scientific .Help ?
    There really shouldn't be an argument. Its really just simple math with a few considerations.

    The short answer is, if you have a 40 ton bag and a 20 ton bag, you can lift 60 tons 1 inch. The max height of the lifting system though, is only as high as the smallest bag. So if the 40 ton bag is 13" and the 20 ton is 6", you can only lift up to 6"

    The above answer only applies to when the bags are in tandem.

    If the bags are stacked however, people generally like to say that the lifting potential is only as high as the smaller bag. Which in simple terms and no other variables is true, but really it isnt. That rule only applies if you lift the smallest bag its full inflation. Its just a simple means of teaching without the science behind how the lift works.
    Last edited by BrooklynBravest; 04-15-2014 at 02:58 PM.

  3. #3
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    Quote Originally Posted by BrooklynBravest View Post
    There really shouldn't be an argument. Its really just simple math with a few considerations.

    The short answer is, if you have a 40 ton bag and a 20 ton bag, you can lift 60 tons 1 inch. The max height of the lifting system though, is only as high as the smallest bag. So if the 40 ton bag is 13" and the 20 ton is 6", you can only lift up to 6"

    The above answer only applies to when the bags are in tandem.

    If the bags are stacked however, people generally like to say that the lifting potential is only as high as the smaller bag. Which in simple terms and no other variables is true, but really it isnt. That rule only applies if you lift the smallest bag its full inflation. Its just a simple means of teaching without the science behind how the lift works.
    My concern is ,can you always guarantee that the load is evenly distributed ? -
    ?

  4. #4
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    If you take a 10" x 20" bag and a 10"x10" bag, and place them next to each other. It is the same as having a 10" x 30" bag.

    Not sure if that clarifies anything.

    Basically the bags can only apply lifting force when there is full contact on both sides of the bag. That's why a bag can lift it's rated load 1" and half the full distance. Because it's an inverse relation. As the bag gets bigger the lifting potential diminishes due to the fact that the bag pillows into a ball and less of the bag is able to make contact with the ground and load.

    The bag exerts 116-118 pounds of lift per square inch. Bags are 1 inch thick. So if 10x10" of bag are touching both the ground and load, you can lift 11,600lbs. If you inflate the bag and now only 5x5" of bag are touching the load and ground, you can only lift 2900lbs.

    That said let's take an example.

    You have a frame rail of a truck to lift. The rail is 6" wide.

    You put the 10x20" bag along side the 10x10" bag.

    So you have a 30x10" span of lifting surface.

    We lay that 6" frame rail across it the 30" span. That leaves a 2" overhang of bag space on the sides because the bag is 10" wide and the rail is 6".

    So you have 6x30" of contact with the bag. The area is 180 square inches. 180x116=20,880 lbs.

    If the frame rail had been 10" wide or you got creative with your cribbing, you would be able to theoretically lift the full 10x30 span resulting in 34,800lbs of
    lift.

    Now let's change it slightly. You have a 10x30 bag and a 20x40 bag. Two bags that just don't match up in any direction.

    Put them along side and it's all over the place in size. But let's say we put it so it spans the longest way possible. 70inches long. (30+40)

    We put that 6" rail across. We have a 7" of overhang per side on the one bag and 2" of overhang on the other. The rail is still only touching 6x70". So the area is 420, lift is 48,720. Because any non-contacting bag space regardless how big the bag is, is wasted entirely.

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