Asahi tank volume.

[Ed B]

Hello. I’m new to this site. I wish I learned of it sooner. A lot of knowledge here. I stumbled on it doing some research of my scuba tanks. Specifically the change in buoyancy from 3500 psi to 500 psi. The suppling vendor found an old memo indicating the tanks are -9lbs at 3500 and become neutral at 500 psi. I did some experimenting and calcs and found that to be close assuming they did not take into account the weight of the valve. I know this thread is old and it looks like the answer is contained in some of the responses. I just want to add more supporting information just incase someone else has a similar need. My tanks are indeed Genesis ST120 and share the same TP number. They also match the dimensions given by the original author of the thread.

 

[Bob DBF]

The only shift in buoyancy should be the change in the weight of the air in the tank, in the case of a 120 that would be about 8.3# from 3500 to 500, around another pound to 0#. If they give the buoyancy as a figure at empty and full it would would be different with and without the valve, giving about another -1# at each end.

One can get more precise with the calculations, but the tank size is nominal so each can vary somewhat off the spec sheet details.

 

[Ed B]

Agreed. Thank you.
Safe diving.

 

[rjack321]

Hello. I’m new to this site. I wish I learned of it sooner. A lot of knowledge here. I stumbled on it doing some research of my scuba tanks. Specifically the change in buoyancy from 3500 psi to 500 psi. The suppling vendor found an old memo indicating the tanks are -9lbs at 3500 and become neutral at 500 psi. I did some experimenting and calcs and found that to be close assuming they did not take into account the weight of the valve. I know this thread is old and it looks like the answer is contained in some of the responses. I just want to add more supporting information just incase someone else has a similar need. My tanks are indeed Genesis ST120 and share the same TP number. They also match the dimensions given by the original author of the thread.

This is correct, no tank chart accounts for the valve but that is a constant so you just end up with the same difference -10 to -1 vs -9 to 0

Air weighs 0.0807 lbs per cf. You can multiple that by the cf of the tank to derive the swing weight for air/nitrox. Trimix obviously weighs less so the starting weight is less and then by the time they are empty the ending weight is the same.