Air cylinders

[CuzzA]

That depends on depth and whether you're diving enriched air. Again, "generally" speaking, when diving air you may hit your NDL, when diving EAN you may hit your air reserve first. OR depending on the profile, they may be the same which would be ideal.

Too many variables though that depend on depth and mix. I recall seeing a chart that shows the sweet spot for EAN. I'll see if I can find it.

http://www.scubadiving.com/training/basic-skills/practical-guide-nitrox

 

[ZzzKing]

If yo have a choice of having an lp95 or a hp100 and you can only get a 3000 psi fill, in your area, you are way short of having a full tank with the hp100 and have another 10-15% in the lp95. a lp95 at about 3000 psi is about 108 cuft.

If you are doing your own fills, you can pump them up to whatever you want. If you are looking to others to fill them, you should make sure they will overfill them. There are no places in this part of the country that will, that I am aware of. The service pressure of those LP95's is 2400 and you will have 95 cuft of gas. Don't count on being able to get 108 unless you already know a shop that will do it for you.

I will concede slightly on my point of tank weight. Perhaps I should have clarified that because most people who use steel tanks do so for the higher capacity of the bigger tanks so the extra weight is something to consider.

The little steel 80's might be a good choice for a smaller diver. They are shorter and lighter out of the water / heavier in the water.

 

[Bob DBF]

The service pressure of those LP95's is 2400 and you will have 95 cuft of gas. .

The LP95 holds 95 cuft at 2640#, 2400 +10%, so it holds 86 cuft at 2400#. You will find tanks with a + rating calculate the volume with the +, and hold less at the actual service pressure.


Bob

 

[ZzzKing]

Excellent point Bob. Thanks for clarifying that.

 

[NAM001]

If you are doing your own fills, you can pump them up to whatever you want. If you are looking to others to fill them, you should make sure they will overfill them. There are no places in this part of the country that will, that I am aware of. The service pressure of those LP95's is 2400 and you will have 95 cuft of gas. Don't count on being able to get 108 unless you already know a shop that will do it for you.



The little steel 80's might be a good choice for a smaller diver. They are shorter and lighter out of the water / heavier in the water.

The point was not about getting an over fill it was about getting a fill that when cooled ends up at 3000. leaving you short with a hp tank and being overfull on a lp tank. Depending where yo are from you cant count on getting a full fill on an hp tank. LIke wise many shops do not look at a tank and lps are often filled like al 80's. Many hp users have to remind tha tank minkey that it is a hp tank.

 

[ZzzKing]

And my point was not to buy a tank based on the assumption that you will be getting overfills. An overfill that cools to the proper pressure at 70 degrees is not an overfill. Filling a LP tank to 3000psi+ IS an overfill and the shops around here don't do that.

The solution to under filling an HP tank is to check it before you leave and make them complete the fill if necessary after explaining to them what the 3442 that is stamped on the side means. If their setup can't fill to that pressure, you either live with it or find a new shop. Or you can buy your own compressor and do whatever you want.

 

[NAM001]

And my point was not to buy a tank based on the assumption that you will be getting overfills. An overfill that cools to the proper pressure at 70 degrees is not an overfill. Filling a LP tank to 3000psi+ IS an overfill and the shops around here don't do that.

The solution to under filling an HP tank is to check it before you leave and make them complete the fill if necessary after explaining to them what the 3442 that is stamped on the side means. If their setup can't fill to that pressure, you either live with it or find a new shop. Or you can buy your own compressor and do whatever you want.

I was not suggesting that, rather than the inablility to get a full fill with a 3500 psi tank. and the high probibility of getting an overfill of an lp tank from the filler filling it like it was an al 80

 

[ZzzKing]

We may be saying the same thing, then.

 

[NAM001]

We may be saying the same thing, then.

I think so.

 

[Diving Dubai]

Okay - if I may simplify things

Because I'm 200 bar would be 2900psi and 232 bar 3400psi

AL 80 is 11 litres

(all approximate)

I am (or started out as) a metallurgist For the record form a professional standpoint I don't agree with overfills. just stamp the working pressure on the tank and fill to that. However I appreciate that number over overfills carried out vs failure rate means it's pretty safe.

Our shops tend to fill, leave to cool then top off.

AL 80 as stated already are relatively inexpensive and easy to maintain hence their predominate use as rentals.

On Land if you have an AL and Steel tank of the same size the steel will always be lighter - NOT to be confused with buoyancy where the AL will be more buoyant.

Because steels get a higher pressure fill you get more gas.

As tanks get larger an AL is not only much heavier in on land but also heavier than a steel underwater (less buoyant) a 120cf is roughly equivalent to a steel 15l I know which one I'd prefer on my back - having used both

Steel needs a little more care to maintain. i.e. you really do need to wash them especially the boot at the bottom which can trap salt water which will corrode the cylinder - steel tanks do not have flat bases like AL

Steels can come in a "lightweight" version. We use Faber lightweights here as we want a little weight saving given our thinner exposure suit requirement. If you're diving dry all the time then you might have a normal thickness steel.

If an AL 80 suits your diving then a 10l steel will hold slightly more gas but be lighter - great for those with a smaller build

As Peter rightly points out - when you start carrying lots of cylinders then you would want to have AL otherwise you'd be really negative. I use a Steel 15l for back gas but my deco and back up gas side slings are all S50 or S40 AL.