how much air does it take from your tank for each lift
in a 500 lb lift bag?
GARY S I haven't used it to lift 500 lbs. It doesn't take very much to get it to raise. I was beneath the bag, towing it, and my exhaust bubbles were going inside causing it to rise. It is easily controllable with the dump valve.
KEVEN Y If I were to ask this question my self I would rather turn in my cert cards and never dive again its basic physics or if you must really know.....all of it
Marilyn S I contacted Subsalve. Their reply was "It is a function of depth. Approx. 8 cuft at the surface, 16 cu ft at 33???." This is not to say you should fill it excessively at depth as the air would expand as you go up. And the item you are lifting is a factor as well. If you don't have experience lifting large items I would leave this in the hands of professionals. This is a potentially dangerous situation.
ROY M Depends on the size and type of tank. Low or high pressure, 80-100-130 cubic feet? I can tell you how much I use to fill my 200 lb bag. Using my 133 HP steel tank, filling the 200 lb bag tanks about 250 psi. Really you would need to use cubic feet of air rather than psi. So rough it out would come out to about 5 or 6 cubic feet of air.
KEN B It depends on the weight of the object being lifted the depth etc... The smallest amount of air can begin sending the bag to the surface. You will only put enough air in it to get the object started on the way up... you want a controlled lift - so you don't want to cram the bag full of air... small little puffs in until the object lifts off the bottom. As it rises you need to vent air out of the bag to keep the lift under control. The deeper the bottom started from, the more the air volume will expand on the way up... so it is critically important to control the lift so the item doesn't shoot out of the water like a rocket at the surface. This could cause damage to the item, a boat, another human being etc... and can also result in the item plummeting back to the bottom should it become dislodged or break free.
CANDY H You only need to put in enough to lift it from the bottom then swim it up a several feet and it will take off to the surface as the air expands.
You may want to take a 13 CF tank if you're concerned about using too much of your life support gas.
Salvaging something weighing up to 500# can be dangerous. You should know what you are doing or you can get hurt or worse.