- Messages
- 20,561
- Reaction score
- 14,946
- # of dives
- I'm a Fish!
the problem right now is you need to know the brand of tanks they're using. The odds of them using actual HP120's is pretty slim because that would require everyone have DIN valves per regulations, that is why they have skinny necks and the reason the tanks are now rated at 3442 psi with normal valves.
The fun part comes when you have to find out what brand they are using.
Scuba.com has a lot of their information wrong just from what you posted.
no AL80's go from -1.8 to 2.6lbs, they can't, that's just only 50cf of gas.
The AL63's from Luxfer are 2.6lbs positive when empty, but are 2.1lbs empty
Normal Al80's are 1.8 or 1.4lbs negative when full to 4 or 4.4lbs positive when empty. Those are Catalina and Luxfer respectively.
Same goes for steel tanks. If they are using true PST HP120's, then they are 10.3lbs negative full and 1.3lbs negative when empty, but if they are the newer PST E7-120's, then they are -10.5 to 0. If they're using Worthington E7-120's, then they are -11 to -2. If they are Faber F7-120's, then they are -8.8 to +0.7.
So, unfortunately there is literally 0 way to know other than getting the exact tank specs from them. Also, your last statement couldn't be farther from the truth, most steel tanks have somewhat comparable empty buoyancy specs across the manufacturer, so the logic of dropping more weight for larger tanks doesn't work. From PST on the true HP cylinders the opposite is actually true. The HP120's and HP100's are -1.3 when empty, but the HP80 from the same series is -3.3, so with the smaller tank you actually use 2lbs less weight and you can go between the HP100 and HP120 without changing a thing.
This site has the vast majority of tanks on the market.
Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400
The fun part comes when you have to find out what brand they are using.
Scuba.com has a lot of their information wrong just from what you posted.
no AL80's go from -1.8 to 2.6lbs, they can't, that's just only 50cf of gas.
The AL63's from Luxfer are 2.6lbs positive when empty, but are 2.1lbs empty
Normal Al80's are 1.8 or 1.4lbs negative when full to 4 or 4.4lbs positive when empty. Those are Catalina and Luxfer respectively.
Same goes for steel tanks. If they are using true PST HP120's, then they are 10.3lbs negative full and 1.3lbs negative when empty, but if they are the newer PST E7-120's, then they are -10.5 to 0. If they're using Worthington E7-120's, then they are -11 to -2. If they are Faber F7-120's, then they are -8.8 to +0.7.
So, unfortunately there is literally 0 way to know other than getting the exact tank specs from them. Also, your last statement couldn't be farther from the truth, most steel tanks have somewhat comparable empty buoyancy specs across the manufacturer, so the logic of dropping more weight for larger tanks doesn't work. From PST on the true HP cylinders the opposite is actually true. The HP120's and HP100's are -1.3 when empty, but the HP80 from the same series is -3.3, so with the smaller tank you actually use 2lbs less weight and you can go between the HP100 and HP120 without changing a thing.
This site has the vast majority of tanks on the market.
Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400