Lifting Bag Question

[irons308]

I have a few questions regarding a tandem air bag lift,

If a 70T liftbag and a 40T air bag are placed next to each other is the lifting total 110T for 1 inch, or is there an inherent loss in total lifting force? Would the tandem set-up lift for example only 90T for 1 inch? If so is their a coefficent used?

[jmatthe2]

While I certainly will not claim to be the authority on this here is my take. I would assume the bags will lift the combined amount as they are working independantly of each other. Stack them and you are limited by the smallest bag.

Obvisouly this is assuming the entire surface ara of the bag is being used.

[lutan1]

And remember that you only ever achieve the maximum lifting capacity when fully deflated as they have the most surface area....

[ADSNWFLD]

The 70 ton bad will lift 70 tons (but not at full lift)
You would be limited by the 40 ton bag. Don't use the two bags for anything over 40 tons. If an object is large enough to put the bags side by side you could lift 40 tons per bag, depending on how the load is shared. An example would be lifting a 100 ton machine. The 70 ton bag could be used if the ground is supporting a good % of the load. So the end being lifted doesn't actually weigh the entire 100 tons. The problem is figuring out what part of the machine's weight is.

[jmatthe2]

ADSWFLD - The voice of reason! After taking another look you're right an dI stand corrected.

[irons308]

I did some digging and I found that using the side by side will lift the total 110T, However, as the bags are moved apart the lifting capacity decreases(insert an unknown engineering equation here). I would assume that placing the bags together would give you more lifting surface area, thus simulating a bigger bag if the lift is done simultaneously. Were as if the lift was not done simultaneously the 40T bag would bear the brunt of the lift. The bags maximum lift is for 1", this decreases over the height of the lift as the air column in the bag decreases in area

[scooby0066]

when it comes to lifting bags/cushions their is basically one rule to follow.
though I spend two full days teaching them, I'll brake this down to one simple rule to follow.

air bags/cushion are rated by surface area.

to obtain the rating
you measure the surface area in sq inches and multiply that be the input pressure

WORKING AREA X INPUT PRESSURE = CAPACITY

a example would be

lets say a 6 X 6 bag has a working area of 4.74" X 4.74 " = 22.46 sq inches

multiply that by input pressure, which we will say is 118 psi

your bag lifting capacity would be a maximum of 2,650 pounds at approx one inch

as the bag inflates, it looses surface area, inwhich results in a lower lifting capacity.


if you place bags side by side, say two 32 ton bags
you would have the surface area of both bags, your capacity would be 64 tons

if you stacked two 32 ton bags, you WOULD NOT increase lifting capacity, you would only increase the lifting height advantage. you would only have the surface area of one 32 ton bag contacting the surface you are lifting/pushing, etc.


Sadly, when salesman sell you bags, they are what hey are....salesman. I personally have very limited uses for a 70 ton bag, to put in plain English, they are big, heavy, and clumbsy.

buying multiple bags in the 22 to 40 bags will for the most part, allow you to do more efficiently


Air bags and cushions have many uses, but are the least tool used in training exercises

[FIRECAPT62]

scooby0066 is correct.

You will get the total of both bags.

Total square inched of airbag contacting the surface multiplied by 118 psi is what you can lift. Also note...the total sqaure inches contacting the surface must be the same on both sides of the bag for this rule to work.

If the bag is lying flat on the ground and you are pushing up on an "I" beam then you can only multiply the area that is in contact with the "I" beam.