steel tanks: LP or HP?

[mrdiver]

This has probably been discussed to death, but I am looking for brief but sincere opinions on this subject...I personally feel that the HP steel tanks are the way to go, but I am open to any opinions...Also, does the air contained in steel tanks 'age' or otherwise become 'stale' over time? A friend told me that the reason he doesnt use steel tanks is because the air 'tastes' bad...He told me that one has to use the air promptly after filling to avoid the 'steel taste' problem...He said that a steel tank cannot be left filled too long because it will go bad....Any comments?

 

[Uncle Pug]

mrdiver once bubbled...
I personally feel that the HP steel tanks are the way to go

Your choice.

I used to use HP but went to LP when I started mixing gases.

LP allows you to get better usage from your supply cylinders as well as fill off of a bank without having to pump it up so often.

As far as air going stale... nah.

 

[large_diver]

Some basic thoughts:

HP:
- For certain models, can be lighter (dry land weight) than LP steel or AL tanks of the same volume.
- Must use DIN valve
- May be difficult to get complete fill, especially if you are in a hurry.
- Some large HPs are VERY negatively buoyant when full

LP:
- Among heaviest (dry land weight) vs. HP and AL
- Easiest to get complete fill (2640 PSI) and possible to overfill
- DIN or yoke
- In general, more negatively buoyant than AL but less negative than HP of the same size

 

[NJdiver85]

When deciding on HP vs LP, consider where you will most likely get the tanks filled. For example, my LDS (where I will get my tanks filled 95% of the time) can consistenly fill an HP tank to 3500 PSI with no problem. In fact, his compressor is able to go up to 3700. For an LP tank, the same LDS will also provide a complete fill (to 2640 PSI), but will NOT overfill the tank. This removed one of the benefits of getting an LP tank. In addition, once the LP tank lost its + rating, it would be filled to 2400 PSI only. The HP tank maintains its 3500 PSI rating.

 

[notabob]

tbg once bubbled...
In addition, once the LP tank lost its + rating, it would be filled to 2400 PSI only. The HP tank maintains its 3500 PSI rating.

Well, not necessarily. A + rating can be re-stamped after the initial mfg's hydro expires if you find a hydro station that is willing to do the little bit of extra calculations that are required to re-stamp it. Also, Faber HP tanks still use the + ratings. 3180+ is the service pressure in those, and 3498 w/10% overfill.

You can find a bunch of tank statistics from various mfgs here:

http://www.scubadiving.com/gear/27tanktips/stats.shtml

-Roman.

 

[ScubaDan]

I am new to diving so about the PST 104's are they 104 filled to 2400 or to there + rating at 2640

 

[notabob]

ScubaDan once bubbled...
I am new to diving so about the PST 104's are they 104 filled to 2400 or to there + rating at 2640

All LP tanks' rated pressure is at 2640psi (i.e. includes the 10% overfill). So if a tank loses its + rating for whatever reason, its max volume can only be 90% of its initial rating. In case of the 104 it'll drop to 93.6 ft3 if the + rating is lost. Hope this helps.

-Roman.

 

[Soggy]

What is required to get an overfill (meaning above the 2640 pressure rating)? A local shop was telling me that the LP rating is ridiculously low and that they are routinely filled above 3000 psi in the UK and by cavers. Do you need to do a modification on the burst disk or just find a sympathetic dive shop?

 

[NJdiver85]

Sympathetic dive shop. In cave country, the dive shops do it because that is what the divers are demanding. In other parts of the country, New Jersey in my case, few are demanding an overfill. So if I walk in and ask for it, the reply is "we just don't do that."