steel 80, or 100?

[neophyte]

This is something I have to chine in on ,I trained on al 80's, after cert. my instructor loaned me hp 104,s for about 10 dives, { I fell in love} Then all of a sudden he started letting me use LP 95,s {without telling me} You go from a 3200 psi fill to a 26 or 2700 psi fill .
He says volume is the key , that basicly it,s the same tank if you breath it right
consumsion rate
Now I'm looking at some steel 130,s 3445 psi ,tested @5000psi
Big $
I,m still confused ,I'm comfortable with the hp I love the big # on the spg but if I learn to control my breathing , will the lp's serve me just as well?

Your instructor is exactly right that volume is the key. Controlling your breathing doesn't enter into it as far as differences between the tanks is concerned.

An LP95 with a rated pressure of 2664 holds 95 cubic feet feet of gas when it is filled to a pressure of 2664 PSI.

An HP100 with a rated pressure of 3442 holds 100 cubic feet of gas when it is filled to a pressure of 3442 PSI.

How many cubic feet of gas you have to breathe is what matters for bottom time.

This page
http://www.diveriteexpress.com/gas/steel.shtml
does a great job (in my opinion) of explaining the qualities of various tanks. If you scroll down to where it says "Variable Capacity of Cylinders" there's a chart that shows how much gas several common tanks will hold at a few different pressures.

For whatever it's worth, when I finally buy myself a tank I'll be getting an HP119; if all I can get is 3000 PSI I'll still have 107 cubic feet of gas.

Hopefully that's helpful. I remember how confused I was the first time I rented an LP tank and was told it was full when it didn't even have the 3000 PSI I was used to with AL 80s.

 

[UnixSage]

I've considered purchasing 100's but everyone I dive with has 80's, my thinking was that I'd just be coming up with extra air.

Assumptions:
Stressed diver SAC rate 1cf/min
1 min to sort out problem at depth
30ft/min assent rate from depth to 15fsw
3min Saftey stop at 15fsw

If at 132 feet one diver has a problem starts sharing air:
1 Min to sort out the problem
((132/32.8)+1)*1=5cf
3.9 Minutes to assend from 132fsw to 15fsw average depth 73.5fsw
((73.5/32.8)+1)*3.9=12.6cf
3 Min safety stop at 15fsw
((15/32.8)+1)*3=4.3cf

So one diver needs 5+12.6+4.3=21.9cf
So for two divers to do a safe assent from 132fsw would need 44cf
on a 3000psi 80cf tank the turn pressure would be 1600psi
2100psi if you add 500psi on top

Those big tanks are not that big when you put it that way. 1cf/min may be high for some but might be low for others. If you skip the saftey stop and assend at 60ft/min you cut this in half also so it all depends on how you look at it YMMV

 

[ScubaMike14]

Assumptions:
Stressed diver SAC rate 1cf/min
1 min to sort out problem at depth
30ft/min assent rate from depth to 15fsw
3min Saftey stop at 15fsw

If at 132 feet one diver has a problem starts sharing air:
1 Min to sort out the problem
((132/32.8)+1)*1=5cf
3.9 Minutes to assend from 132fsw to 15fsw average depth 73.5fsw
((73.5/32.8)+1)*3.9=12.6cf
3 Min safety stop at 15fsw
((15/32.8)+1)*3=4.3cf

So one diver needs 5+12.6+4.3=21.9cf
So for two divers to do a safe assent from 132fsw would need 44cf
on a 3000psi 80cf tank the turn pressure would be 1600psi
2100psi if you add 500psi on top

Those big tanks are not that big when you put it that way. 1cf/min may be high for some but might be low for others. If you skip the saftey stop and assend at 60ft/min you cut this in half also so it all depends on how you look at it YMMV

Math! I hate math!

Um....er.......Beavis, I'm confused?

Mike Rushton

 

[paulthenurse]

Math! I hate math!

Um....er.......Beavis, I'm confused?

Mike Rushton

Math simplified...

Great big enormous tanks with oodles o' air = good!
Teeny weeny ittsy bittsy tanks= not good!
Two wigged out divers on one 'Teeny weeny ittsy bittsy' tank = Really freakin' bad!

I don't get why I never pulled an A in math is school?

 

[Cold_H2O]

I think of it this way ~
IS THERE EVER A SITUATION WHERE TOO MUCH AIR IS A BAD THING?

I have yet to hear a diver state.. "Dang, look at all my extra air. I wish I didn't have so much."

Air ~ Diving ~ MORE IS GOOD ~ LESS IS BAD.
No math needed just clear thinking.

 

[pgdive]

Here is some clarification on some of the things being discussed here.

The Din/Yoke question. HP tanks are DIN because the actual yoke (The metal u-shaped piece on the regulator first stage) on many regulators can not handle the higher pressure. As an example even the newer Scubapro regs (as well most older regs) are not rated to the 3442psi of the Pressed Steel and Worthington tanks. If you look at some of the real old regs, that yoke is paper thin. It would be very scary if they were attached to a HP tank.

Almost all newer compressors are capable of filling the HP tanks. This was a problem in the past but most of the compressors now can go up past 4000psi (Most go to 4500). Now whether or not you get a good fill on the HP, is dependent on the how long you want to wait for your tank. Fast fills =Short Fills.

I guess my own personal opinion on tank size is to get the right size tank for the type or diving you are going to be realistically doing. Don’t worry about what you might do years down the road and then be stuck with something that is too heavy and unpleasant to dive with now. Obviously I have access to more tanks than the average diver; everything from single 65’s to double 130’s and everything in between. What I find myself using for the majority of the diving that I do is HP 100 (With a pony bottle if I’m going deeper than 60ft’ ish).The last thing that I want to be doing is lugging a 130 up down the rocks at Magnolia or Cathedral. Dive a lot, get comfortable in the water, get your SAC rate down and don’t worry about it. I have friends that can go out to the U-853 with two 100cf and a 30cf pony and do two nice easy 20 minute dives with plenty of air left over. For a brand new diver it should be a long time before the dives that you are doing require anything larger than a single 100 or 120 (If you have the height for it) and a pony bottle.

Just my 2 cents

Paul

 

[UnixSage]

Math! I hate math!

Um....er.......Beavis, I'm confused?

Mike Rushton

For two divers to safely assend from 130fsw it takes about 40cf of air. The math was to show where the figures come from. It was suprising to me how fast it added up.. I learned a new respect for going deep.

 

[scubastew]

100s !!

 

[douglasville diver]

Thanks for all the info and the link from scubamike

 

[localdivah]

Another consideration in the DIN vs. Yoke is how much you plan on diving locally vs. abroad. Most of the common resort areas, with the exception of Europe or the Middle East favor yoke valves on tanks. What that means is that if you go DIN on your regulator and tanks at home, you need to either get a $60 DIN-to-yoke adapter that mates to the reg first stage, or just a totally separate 1st stage. I went the second route, and find it a bit of a pain in the ***, since I dive away from home a lot.

However, I got my wife's setup in DIN and she NEVER dives cold water, so I should have just gotten her a yoke setup.

Ditto the convertible valves that give you the option of diving either DIN or yoke on them. Paul at PG hooked me up with one at a good price, so now I have an extra tank on yoke if any new buddies need a loaner.