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Martin2
07-21-2008, 12:05
I know there's a similar thread tight now, but I didn't want to hijack his. Here's the overview:
"original hydro looks to be 1965 recent hydro 3-07 and vis. 4-08. this tank has been tumbled and cleaned. it has a brand new k valve installed and 2100 psi when i hooked the regs up the other day to make sure every thing was working properly."
I don't really need a larger tank as I dive with my husband and surface with more air than I need as it is. Thoughts?

Rileybri
07-21-2008, 12:07
what are they asking for it??

Martin2
07-21-2008, 12:18
what are they asking for it??

$70.00

Rileybri
07-21-2008, 12:21
what are they asking for it??

$70.00

That is not a bad price with the K valve and recent maintence work done to it! I got mine with a J valv and new burst disck and current vis/Hyd for 40 full to give yo uand idea. If $70 is not going to hit you hard I would probably get it!

Martin2
07-21-2008, 12:33
That's what I was thinking. I'll have to drive a bit to get it, but I think it will make a nice addition to our collection.

mike_s
07-21-2008, 12:34
what are they asking for it??

$70.00


$70 isn't a bad price for it if the tank is in good condition, considering it's in recent hydro and vis and has been cleaned and has a new valve. A new valve would run $40 to $50 bucks on average for a K valve at most shops...

note that it's most likely a 2250psi rated tank and is old and not one that you'd do 'cave fills' on (over filling).

but there is nothing wrong with a steel 72, especially for someone with low air consumption compared to your dive partner.

Martin2
07-21-2008, 12:50
note that it's most likely a 2250psi rated tank and is old and not one that you'd do 'cave fills' on (over filling).

Hmmm...I may rethink this then. We already have some AL80s. I don't care about overfilling and actually prefer that they don't overfill my tanks, but 2250 would be quite a bit less air (that I admittedly don't need).

I was just hoping for a slightly smaller tank and to drop a bit of weight off my belt. Sounds like this will do that, but I will lose a fair amount of air. Not an issue now while my DH uses our AL80s, but may be an issue when we find him a steel tank. He wants a larger one to help balance our consumption.

Rileybri
07-21-2008, 12:58
note that it's most likely a 2250psi rated tank and is old and not one that you'd do 'cave fills' on (over filling).

Hmmm...I may rethink this then. We already have some AL80s. I don't care about overfilling and actually prefer that they don't overfill my tanks, but 2250 would be quite a bit less air (that I admittedly don't need).

I was just hoping for a slightly smaller tank and to drop a bit of weight off my belt. Sounds like this will do that, but I will lose a fair amount of air. Not an issue now while my DH uses our AL80s, but may be an issue when we find him a steel tank. He wants a larger one to help balance our consumption.

Dont swet it I use a this same tank with AL80 divers and unless they have an amazing SAC rate I have not found it to be an issue. As a matter of fact on the two wreck dives I did recently I was first in and last out with 33 min of BT at 65' and 750 psi on the boat after! Get it!!!

Martin2
07-21-2008, 13:09
If DH uses a steel 130, will it still be plenty of air? I have a good SAC rate, but I'll be ticked if I have to shorten a dive because I'm out of air!

Rileybri
07-21-2008, 13:13
If DH uses a steel 130, will it still be plenty of air? I have a good SAC rate, but I'll be ticked if I have to shorten a dive because I'm out of air!

Well I would have to say no it wont be, but then again a St120 is much bigger than a 72 or an AL80. I ilke the &2 because of its prozimity in size and air to an (most people I dive with are using) with negative bouyency to boot!

Martin2
07-21-2008, 13:15
That's why I am attracted to it. But I'm a little concerned that I'll be sorry once we get him his steel tank. We'll see. Thanks for all of your insight. Chances are I'll probably get it. Could be a while before we get him another tank anyway.

Rileybri
07-21-2008, 13:23
That's why I am attracted to it. But I'm a little concerned that I'll be sorry once we get him his steel tank. We'll see. Thanks for all of your insight. Chances are I'll probably get it. Could be a while before we get him another tank anyway.


Well the 120 is in a different league. He would have to call his dive not you as you will have the smaller tank. Worst case is you can easly turn the tank around for what you got it for if it does not work out St72 are quite popular!

Martin2
07-21-2008, 13:26
That's why I am attracted to it. But I'm a little concerned that I'll be sorry once we get him his steel tank. We'll see. Thanks for all of your insight. Chances are I'll probably get it. Could be a while before we get him another tank anyway.


Well the 120 is in a different league. He would have to call his dive not you as you will have the smaller tank. Worst case is you can easly turn the tank around for what you got it for if it does not work out St72 are quite popular!

Good thought--I'll pitch it to him that way! And it will be great for dives where he doesn't need or want to carry the 120. And if it means that I have to upgrade to a HP 80 at some point, that could probably be arranged.

CompuDude
07-21-2008, 13:30
note that it's most likely a 2250psi rated tank and is old and not one that you'd do 'cave fills' on (over filling).

Hmmm...I may rethink this then. We already have some AL80s. I don't care about overfilling and actually prefer that they don't overfill my tanks, but 2250 would be quite a bit less air (that I admittedly don't need).

I was just hoping for a slightly smaller tank and to drop a bit of weight off my belt. Sounds like this will do that, but I will lose a fair amount of air. Not an issue now while my DH uses our AL80s, but may be an issue when we find him a steel tank. He wants a larger one to help balance our consumption.

"2250" is not less air. That's the working pressure of the tank. That means that in a 72 cubic foot tank, you have 72 cubic feet of gas when you fill it up to 2250psi.

For an Aluminum 80 (which is misnamed), you have 77.4 cubic feet of gas when you fill it up to 3000 psi.

So as you can see, the capacities of the two tanks are fairly close (72 vs. 77.4), they just work with different pressure ratings to reach their rated capacity.

At 2250 psi in your steel 72, you DO have less gas than you have with an aluminum 80 at 3000 psi, simply because it's a slightly smaller tank. But not so much less as you might think if you just look at 2250psi compared to 3000 psi... they're just not comparable numbers, since the actual sizes of the tanks are different.

MSilvia
07-21-2008, 13:30
2250 would be quite a bit less air
Not necessarily. 2250 might be quite a bit less PRESSURE than you have in a 3000 psi 80 cubic foot tank, but the 72 will be full at that pressure, while the 80 will be almost 1/3 emptied. The volume of air represented by a given pressure varies among different kinds of tanks. What you should be comparing is the rated capacity, not the service pressure.

Martin2
07-21-2008, 13:39
I knew someone would jump in with the math for me at some point. The issue isn't the 72 vs the AL80. It is when my DH gets either the 120 or 130 that he's been wanting. I have the rated capacity of the 80s we own and the steel tank he's wanting (from the ST website). Any idea what the rated capacity should be for the 72?

Martin2
07-21-2008, 13:41
I just realized that my post makes it sound like I can't or won't do the math. I can and will do it for myself, I'm just a bit too busy at work to focus on it. It doesn't come as easily to me yet that I can do it while multi tasking. I'll need to take some time tonight and sit down with the numbers. Still leaves the question of the rated capacity on the 72 though. Anyone know?

MSilvia
07-21-2008, 13:51
As far as I know, it's 71. 2 cubic feet with a '+' rating... which means it can be filled to 2475 psi...10% more than its rated 2250. Without the '+' the tank has 64.7 cf at its rated 2250 psi.

Martin2
07-21-2008, 13:57
OK, now I'm confused. So maybe I should take a step back and do some additional homework. Tanks all hold roughly the cubic feet that they're called (80's hold silghtly less than 80, etc). Which is why the 72 vs the 80 would not be any significant difference, especially with the SAC difference. My confision comes in the the HP tanks then. Does a HP 80 hold more air than a LP 80 (both steel)? If so, how do I account for that difference. If not, what is the difference? Help!

MSilvia
07-21-2008, 14:08
Does a HP 80 hold more air than a LP 80 (both steel)? If so, how do I account for that difference. If not, what is the difference? Help!
No... they both hold about 80. The difference is that they are full at different pressures. Also, the size, buoyancy and weight characteristics are different.

Mfgr: PST E7-80
Service pressure: 3442
Actual air capacity: 80
Outer diameter: 7.25
Length: 20
Empty weight: 28
Buoyancy Empty: -2.5
Buoyancy Full: -8.5

Mfgr: PST LP-80
Service pressure: 2400 +10%
Actual air capacity: 80.6
Outer diameter: 7.25
Length: 24
Empty weight: 34
Buoyancy Empty: -1
Buoyancy Full: -7

Mfgr: Faber 80
Service pressure: 2400 +10%
Actual air capacity: 78
Outer diameter: 7.25
Length: 24
Empty weight: 30
Buoyancy Empty: -1.7
Buoyancy Full: -7.55

Mfgr: Faber 80
Service pressure: 3180 +10%
Actual air capacity: 80
Outer diameter: 7.25
Length: 19.88
Empty weight: 32.5
Buoyancy Empty: -7.22
Buoyancy Full: -13.22

There's a good tank comparison table at http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

Martin2
07-21-2008, 14:26
Makes sense, thank you. Basically it is putting the same amount of air in a smaller space, yes?

MSilvia
07-21-2008, 14:36
Makes sense, thank you. Basically it is putting the same amount of air in a smaller space, yes?
Yeah, that's pretty much it. I'm glad the explaination helped.

You might find this post helpfull too... http://forum.scubatoys.com/201916-post19.html

Martin2
07-21-2008, 14:41
Thank you for your help. I'm still leaning toward getting the 72, but more for the size than anything else. I'm hoping it will follow the sizing of most 72s and be a few inches shorter than my AL80s. That alone is a nice benefit when you're 5'3".

MSilvia
07-21-2008, 14:44
I dive with old LP72s myself, and I really like them.

BSea
07-21-2008, 14:51
Thank you for your help. I'm still leaning toward getting the 72, but more for the size than anything else. I'm hoping it will follow the sizing of most 72s and be a few inches shorter than my AL80s. That alone is a nice benefit when you're 5'3".I'm not trying to talk you out of that 72 because I have 4 & think they are great tanks. But you might consider a high pressure steel 80 which should help you with getting a lot of lead off your belt compared to an AL 80. 1st it's about 4 pound lighter, and about 5 pounds less buoyant. That's about 9 pounds of lead you won't need.

Edit: And the 80 is about 6 inches shorter. Even shorter than the 72. This is a popular tank for women at the LDS that i use.

Martin2
07-21-2008, 15:08
Thank you for your help. I'm still leaning toward getting the 72, but more for the size than anything else. I'm hoping it will follow the sizing of most 72s and be a few inches shorter than my AL80s. That alone is a nice benefit when you're 5'3".I'm not trying to talk you out of that 72 because I have 4 & think they are great tanks. But you might consider a high pressure steel 80 which should help you with getting a lot of lead off your belt compared to an AL 80. 1st it's about 4 pound lighter, and about 5 pounds less buoyant. That's about 9 pounds of lead you won't need.

Edit: And the 80 is about 6 inches shorter. Even shorter than the 72. This is a popular tank for women at the LDS that i use.

True. But it costs quite a bit more at the moment as well. 250 or so with the discount, I think.

mike_s
07-21-2008, 15:19
Makes sense, thank you. Basically it is putting the same amount of air in a smaller space, yes?


that's pretty much it....

don't confuse PSI with volume.

a LP95 (LP= Low Pressure) at 2400psi is about the same volume as a HP100 at 3442psi.



so don't worry that this steel 72 at 2250psi is less air. yes it's a little less, but that's only by volume.

the "pro's" of having this tank is that it is a small tank and more negative bouyant which means you don't have to wear as much led weight.

steel 72's are great tanks. They have prob been in use longer than about any other tank used by divers. If it wasn't a great tank then you wouldn't see them anymore. The reason they are cheaper is that they are older and sometimes people want a larger capacity tank (such as 100cf)

BSea
07-21-2008, 15:20
True. But it costs quite a bit more at the moment as well. 250 or so with the discount, I think.Cost is a factor. I guess from your statement about the size being a plus that it might be more of an issue than the cost.

Besides, he's getting a big new shiny tank from ST....you should too. :)

Seriously though, If you go on many diving trips where you drive, and take your tanks. Be aware that some places won't fill that 72, or any tank that old. I've never had a problem getting mine filled, but just so you know.

There was a thread earlier, that had a post by an owner of a dive shop, and he said he won't fill tanks over 20 years old. I can't find it right now. If I find it again, I'll post it back here.

mike_s
07-21-2008, 15:36
There was a thread earlier, that had a post by an owner of a dive shop, and he said he won't fill tanks over 20 years old. I can't find it right now. If I find it again, I'll post it back here.


lots of shop owners who are clueles....

lots that don't fill old aluminum tanks because of the 6351 aluminum allow problem and apparently dont know the difference between an old aluminum tank and an old steel tank... :smilie40:

BSea
07-21-2008, 15:41
There was a thread earlier, that had a post by an owner of a dive shop, and he said he won't fill tanks over 20 years old. I can't find it right now. If I find it again, I'll post it back here.


lots of shop owners who are clueles....

lots that don't fill old aluminum tanks because of the 6351 aluminum allow problem and apparently dont know the difference between an old aluminum tank and an old steel tank... :smilie40:
I think it has more to do with clueless employees. So the owner makes a blanket rule so "Gilligan" doesn't have to think.

Martin2
07-21-2008, 15:46
One would hope that at least the shop affiliated with the commercial dive school here would know better, but I'll certainly call and ask. Very good point.

As far as his shiny new tank vs mine, he isn't getting his yet either. Maybe for his birthday later this year. Or Christmas. We'll work it out, I'm sure.

Rileybri
07-21-2008, 16:54
So all of this talk about ST72's got my mind going so I went down to my LDS to let them know I would be joining them on an invitational dive next month. wile I was there I checked in with my DI/DM about his stash of 20+ ST72's. To make a long story short he is giving me what will be my 2nd ST72 for the price of doing a hydro on it next year!!!! Not a bad deal if you ask me!!!!!!


LONG LIVE THE ST72!!!!!!!!

MSilvia
07-21-2008, 17:01
Sweet deal Bri! At this rate, folks are going to be paying you to take their gear!

CompuDude
07-21-2008, 19:24
don't confuse PSI with volume.

a LP95 (LP= Low Pressure) at 2400psi is about the same volume as a HP100 at 3442psi.
I think you meant, an LP95 at 2640psi is about the same as an HP100 at 3442... pesky plus ratings!

captain
07-21-2008, 21:17
note that it's most likely a 2250psi rated tank and is old and not one that you'd do 'cave fills' on (over filling).

Hmmm...I may rethink this then. We already have some AL80s. I don't care about overfilling and actually prefer that they don't overfill my tanks, but 2250 would be quite a bit less air (that I admittedly don't need).

I was just hoping for a slightly smaller tank and to drop a bit of weight off my belt. Sounds like this will do that, but I will lose a fair amount of air. Not an issue now while my DH uses our AL80s, but may be an issue when we find him a steel tank. He wants a larger one to help balance our consumption.

Al 80 at 3000psi 77 cu/ft, steel 72 at 2500 72 cu/ft, 5 cu/ft not enought to worry about. plus the steel 72 is 5# negative full and 0 to 1# positive empty. You can take weight off.

captain
07-21-2008, 21:18
So all of this talk about ST72's got my mind going so I went down to my LDS to let them know I would be joining them on an invitational dive next month. wile I was there I checked in with my DI/DM about his stash of 20+ ST72's. To make a long story short he is giving me what will be my 2nd ST72 for the price of doing a hydro on it next year!!!! Not a bad deal if you ask me!!!!!!


LONG LIVE THE ST72!!!!!!!!

You ain't wrong.