Differences between tank sizes

[Killerflyingbugs]

Yeah, you people with metric tanks have it easy. The answer to the same question in the context of tanks measured in cubic feet of capacity is not as straightforward.

How so? You can have 2 11L tanks one a 200 bar and one a 300 bar they are the same size tank flooded volume wise, but they are different in how much air they hold. Imperial measured tanks go by the volume of compressed gas, so when you have the same two tanks one would be an 80 cubic ft tank and the other would be a 100 cubic ft tank seems straight forward to me.

 

[DustyC]

Bar is an unit measurement used by countries that haven't been to the moon.

FIFY.

 

[MXGratefulDiver]

What's a bar, and how do you get 232 of them into a cylinder?

A bar is 14.7 psi ... standard atmospheric pressure at sea level. 232 bars is 3410 psi.

... Bob (Grateful Diver)

 

[Storker]

FIFY.

Three small words: Mars Climate Orbiter.

And also: Countries That Don’t Use the Metric System

 

[MXGratefulDiver]

Thanks everyone. I guess what I was trying to ask is will a bigger tank let me dive longer?

Not necessarily ... it's less a function of size than it is of working pressure. I own a variety of cylinders. My LP95's ... which hold 95 cubic feet of gas when filled to working pressure ... are much larger than my HP100's ... which hold 100 cubic feet of gas when filled to working capacity. As with all equipment, there are trade-offs to consider ... such as your local dive shop's ability (or willingness) to fill HP cylinders all the way to their working pressure. Many dive shops can't, or won't ... and a cylinder that's not filled to its specified working pressure isn't giving you its rated volume capacity.

Some years ago I wrote an article that helps explain some of the concepts that you're asking about. You might find it a useful read ... NWGratefulDiver.com

... Bob (Grateful Diver)

 

[Storker]

I doubt that any steel tanks in Sydney are 200 bar tanks. They are more likely to be 232 bar as this is what all the common steel ones sold in Australia are now and have been for at least 15 years.

I've seen 200 bar tanks at vacation ops here in Europe, and I occasionally see them on our version of Craigslist, so they're not quite phased out in the part of Europe I know. New tanks are either 232 or 300 bar, though. 300 bar tanks are more negative than 232s and can be nice in a single tank rec setup, but for anything bigger than 12L singles they just get too heavy.

I use 10L 300 bar, since I generally have no issues getting 300 bar fills, and I save a little weight compared to, say, a 12L 232 or a 15L 200.

 

[tech_diver]

While I was working at a dive store years ago, a browsing customer asked me how many PSI a Spare Air can hold. I told him 3000 PSI and he said, "Wow! That little tank holds as much air as one of those big ones." Sadly, he actually did mean air, not pressure.

 

[_Ralph]

Yeah, you people with metric tanks have it easy.

My tanks don't develop a split personality when I refer to them as 16L or HP130... 12L/HP100 .... 15L/LP95 etc....

Just start using metric, the tank doesn't care

_R

 

[Lorenzoid]

How so? You can have 2 11L tanks one a 200 bar and one a 300 bar they are the same size tank flooded volume wise, but they are different in how much air they hold. Imperial measured tanks go by the volume of compressed gas, so when you have the same two tanks one would be an 80 cubic ft tank and the other would be a 100 cubic ft tank seems straight forward to me.

Well, just one example I'm familiar with is a so-called "LP85." One would think it holds exactly 85 cf of gas at some standard "low" (whatever that means) working pressure. But a manufacturer's "LP85" might happen to hold 82.9 cf at 2640 psi, which is the allowed "10% overfill" above its "Service Pressure" of 2400 psi. Confusing enough? The names given to tanks by their manufacturers are marketing names and do not always give the consumer enough information to know their true capacity. Rather, you generally need to consult a sheet with the tank specs. The "10% overfill" thing adds unnecessary complexity. A "LP85" at 3500 psi holds roughly the same 100 cf as a "HP100" at 3500 psi. Now, since metric tank names refer to their "water volume," you know from the name of the tank exactly what gas volume it will hold at any given pressure by one simple multiplication. To answer the OP's question, yes, you can reliably count on a tank labeled "15L" being able to hold more gas than a tank labeled "12L" at any given pressure.

 

[KevinNM]

Three small words: Mars Climate Orbiter.

ExoMars Schiaparelli lander. Because stopping your landing sequence 3km in the air is almost the same as landing safely. Other than the part where you explode in a giant fireball on impact...