hp steel tank ?

[SDAnderson]

hey guys, very new to the scuba board, but i have a good amount of diving under my belt. I am starting to look at scuba tanks and am leaning towards the hp 100 119 or 130. I thought i had a good understanding of tanks, but today when i went into the scuba shop near my house, and asked for a price on a hp steel tank the guy tried to sell me on lp or al(i knew that part would happen). His reason for lp or al was strange to me and was not something i have ever heard before. He said i would not be able to get a fill on a hp steel b/c no dive shop can pump to 5500psi, he was telling me that working pressure on a hp steel is 3442, but that they should be filled to 5500 psi to get there full advertised volume. Did i just find the one random dive shop guy who didn't know about hp steels, or am i missing something?
thanks for all the help

I find it hard to believe that this conversation actually took place.

Buying a tank:

1. The only thing aluminum has going for it is price. If you've got the budget, buy steel.
2. Buy the biggest tank you can comfortably carry. Better too much air than not enough.
3. Buy as high pressure as you can, with the following caveat: HP cylinders need a compressor that can fill to 3500 psi. Most can, but if you live in a remote area you should find out if your shop can handle the load.
4. Painted tanks are going to get banged up. Don't buy the pretty colors unless you can live with what will become an ugly tank.
5. Put a DIN/K convertible valve on it. No matter what the future holds for you, it will meet your needs.
6. If it's got a flat bottom, it doesn't need a boot.

 

[Splash-X]

Regardless of the % the tank was filled, my point was/is the statment that I beleive this "pro" for HP over LP is incorrect:

"The advantages are higher safety at a given fill pressure, greater capacity at a legal fill pressure, easier to find an LDS that will fill them to more than 2640psi and in a few cases slightly lighter weight."


Having a higher PSI rating doesn't specificaly make it "safer". If you were trying to fill a LP tank to 3200psi thats one thing but apples to apples, 100cuft (LP @ 2600PSI) of gas vs 100cuft (HP @ 3200PSI) of gas, that statment to me just seems inaccurate. Maybe I'm wrong?

 

[WD8CDH]

Remember, I said at a given fill pressure (not rated pressure), so an HP tank at 2640psi will be safer than an LP tank at 2640psi. And of course, an HP tank at 3442psi will be safer than an LP tank at 3442psi.

 

[WD8CDH]

Quote:
Originally Posted by WD8CDH
But personally, I would rather dive small doubles than ANY 8" diameter single.

What are your reasons? I am currently deciding on the HP100 or HP130.

Because I like the mass of the tanks closer to my body. Less bulk, easier to maneuver, easier to get thru tight spaces. Less tendency to turn "Turtle".

 

[WD8CDH]

Originally Posted by WD8CDH
The advantages are higher safety at a given fill pressure, greater capacity at a legal fill pressure, easier to find an LDS that will fill them to more than 2640psi and in a few cases slightly lighter weight.

Are you sure about that?

A LP100 rated at 2600PSI has 100cuft of gas when it has 2600PSI. A HP100 rated at 3200PSI has 100cuft of gas when filled to 3200PSI. (give or take some PSI for your exact tank rating)

You wouldn't need to fill a LP tank any greater than 2600PSI to have 100cuft so your point of having a higher legal capacity is moot as far as my knowledge goes (don't call me an expert). 100cuft = 100cuft, the PSI needed to achieve 100cuft is lower in a LP.

If I'm wrong, correct me please.

Give a choice between a LP and a HP I would select a LP as any shop can easily fill to the capacity where you often get short changed on a HP as some banks don't carry the needed pressure for that,

You are correct but I was comparing LP vs. HP of the same PHYSICAL size, not the same rated capacity.

Like comparing an LP100 vs. an HP130. Both would have about the same PHYSICAL size and if both were filled to the same pressure, both would hold the same cubic feet of air even though their RATED capacity is different. And obviously, if both were filled to the same psi, the HP tank would have a higher safety margin.

So, except for cost, I see no advantage of having an LP100 over an HP130.

 

[ronhend]

I just got a hp 130 and drove it last weekend for the first time.

I really like it, lots of air and no weight required at all.

Only drawback is it is kind of heavy on land.

More air is a good thing

Ron

 

[Splash-X]

You are correct but I was comparing LP vs. HP of the same PHYSICAL size, not the same rated capacity.

Like comparing an LP100 vs. an HP130. Both would have about the same PHYSICAL size and if both were filled to the same pressure, both would hold the same cubic feet of air even though their RATED capacity is different. And obviously, if both were filled to the same psi, the HP tank would have a higher safety margin.

So, except for cost, I see no advantage of having an LP100 over an HP130.

So would a LP100 vs a LP130 (physical size aside).... to have only 100cuft in a LP130 you would need far less PSI than what the tank is rated to carry.

The only valid point I see is that a 100cuft LP tank is roughly the same physical size as a HP130 but even that varies by manufacturer. I'm not trying to step on toes or anything.

 

[Puffer Fish]

So would a LP100 vs a LP130 (physical size aside).... to have only 100cuft in a LP130 you would need far less PSI than what the tank is rated to carry.

The only valid point I see is that a 100cuft LP tank is roughly the same physical size as a HP130 but even that varies by manufacturer. I'm not trying to step on toes or anything.

Ignore the rated pressure for a minute...

A worthington LP 108 is 26 inches tall and 8 inches in diameter.. and weights 43 lbs.

A worthington HP130 is 25.5 inches tall and 8 inches in diamter.. and weights 43 lbs.

If you fill them to the same pressure.. say 2640 (the rated pressure fro the LP tank)..

The LP has 108 cubic ft.

The HP has 100 cubic ft...

But the HP was an inch shorter (slightly smaller actual volume).

Fill the HP to 3,000 (something almost any shop can do) and you have 113.

Buy a Faber FX 133, and you are now 101 versus 108 at the same pressure, and a tiny bit lighter.

Only difference is that you have a tank rated to go to 3442 psi, so if you do find a place with higher pressure fills... you can use it.

I got my high pressure tanks on sale, so the cost issue was in the other direction.. with them being cheaper.

 

[WD8CDH]

So would a LP100 vs a LP130 (physical size aside).... to have only 100cuft in a LP130 you would need far less PSI than what the tank is rated to carry.

The only valid point I see is that a 100cuft LP tank is roughly the same physical size as a HP130 but even that varies by manufacturer. I'm not trying to step on toes or anything.

Yes, the HP130 would only need 2640 psi to hold 100 CF of air. And you are correct that it varies from manufacturer to manufacturer and to a lesser extent from tank to tank. It's hard to be EXACT when not all of the tank manufacturers publish the actual internal volume of the tank (usually in cubic inches for US tanks or liters in Europe) to more precisely calculate capacity at different pressures but you can come close from rated capacity. It's interesting that the Aluminum SCUBA tank manufacturers publish internal volume. Here on the Catalina site it is listed as Water Capacity:
SCUBA Cylinders

I do know for a fact that Faber makes an HP140 and an LP108 that are spec'd within .01" of each other in length and the same diameter that both have a rated internal water capacity of 1037 cu. in. Those two tanks would be almost indistinguishable from each other visually and by how they dive or carry. They would both hold the same amount of air at a particular pressure. They are probably made with the same dies on the same stamping machine. The only real difference is the HP tank is made from a higher strength steel alloy and is probably heat treated differently.

So other than price wouldn't you select the same physical size tank that holds the same air at 2640 psi but could be filled to a higher pressure legally and hold more air when filled to it's maximum legal pressure?