Posted by Murddoc on March 20, 2001 at 17:59:41:
In Reply to: Re: Am I the only one who needs lead with a steel tank? posted by Jeff B on March 20, 2001 at 11:18:43:
Using your numbers,
Full Steel is -6 lead -20 and +16 wetsuit at surface
Full AL is -2,-25 and +16
At 100', Full Steel -6+ -20 +4= -22 lbs
AL -2+ -25 +4= -23
At 100', & 800psi ST -4+ -20 +4= -20
AL +3+ -25 +4= -18
According to your numbers, the AL will loose 5 lbs of air while the Steel will only loose 2 lbs. The only way that would happen is if the steel has 3 lbs more air at 800psi. Which would mean that the steel has approximately 40 cf more air at that time.
Because of the fill pressure differences, to compare apples to apples, we should talk about cf not psi. Otherwise we could say that your air consumption rate is higher with AL than ST tanks (more psi/ min) yet if we compare cf/min, the rates will in fact be the same.
If we compare 100' w/ 70cf used and 25 cf remaining we get:
ST -.5+ -20 +4= -16.5 lbs
AL +3.5+ -25 +4= -17.5
One pound more negative, the same as at the beginning of the dive.
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