lift bag air capacity
- Thread starter dferg77
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mwilding
Contributor
At what depth?
Air density doesn't have much to do with it as sea water is relatively incompressible and weighes a constant amount.
Air volume is the issue. You are trying to displace 100 lbs of seawater with a 100 lb bag. So you have to fill it with the volume of air that does so whether it be at 50 feet or 500 feet. Sure it's 10 times denser but it's still the same cubic feet of displacement.
Find out the weight of a cubic foot of seawater and you'll have your answer...
Now back to saving the sharks... FREE THEM ALL!!!
Air volume is the issue. You are trying to displace 100 lbs of seawater with a 100 lb bag. So you have to fill it with the volume of air that does so whether it be at 50 feet or 500 feet. Sure it's 10 times denser but it's still the same cubic feet of displacement.
Find out the weight of a cubic foot of seawater and you'll have your answer...
Now back to saving the sharks... FREE THEM ALL!!!
mwilding
Contributor
well, you are right that the answer will be the same for any depth. However, if the guy asking the question is trying to calculate how much of his tank is going to be used by filling his bag, it has to be normailzed back to 1 ATM...
Salt water is 64 lbs/cuft
Fresh water is 62 lbs/cuft
The task is also important as to how much air you use.
If you are shooting a bag then you just put a puf of air in the bag at depth and let it expand on the way up. It will only be full at the surface.
If you are actually lifting an object then you need enough air in the bag at depth to offset the neg bouyancy of the object.
For lifting you want to use the smallest bag that will lift the object. This way it doesn't get out of control as the gas expands on the way up. You can stay with the bag and vent air as you go up but this is not the best course.
BTW NEVER put yourself under anything being lifted.
Fresh water is 62 lbs/cuft
The task is also important as to how much air you use.
If you are shooting a bag then you just put a puf of air in the bag at depth and let it expand on the way up. It will only be full at the surface.
If you are actually lifting an object then you need enough air in the bag at depth to offset the neg bouyancy of the object.
For lifting you want to use the smallest bag that will lift the object. This way it doesn't get out of control as the gas expands on the way up. You can stay with the bag and vent air as you go up but this is not the best course.
BTW NEVER put yourself under anything being lifted.
Don Burke
Contributor
That would be about 1.6 cubic feet of air at the surface.
at 33 feet, about 3.2
at 66 feet, about 4.8
at 99 feet, about 6.4
at 132 feet about 8
Well, at around 15-20 ft. it takes about 800 lbs. of air to fill up a 1000 lb. lift bag.
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