Why choose LP tanks over HP Steel tanks?

[Kohanbash]

Hi all
I am a recreational cold water diver looking to extend my bottom time (I dont need comments to improve SAC, etc..). I have mostly used AL80's, and have used LP steel on ocasion.

I am thinking about getting an HP100 steel tank.

Is there a reason people choose LP tanks over HP (besides cost)?

Thanks

 

[Bob DBF]

All my LP tanks are more negatively buoyant than my HP. Weight off the belt.

As availability of HP fills, not usually an issue to me, but on boats with quick fills mine is always good and HP tanks are short fills.

I like steel and usually buy when I can find a good deal regardless of pressure. I do like to find Faber MP tanks, but that's just me.


Bob

 

[Marie13]

Interesting about the fills. I have local friends who tell me they have trouble getting LP fills. HP fills are not a problem (I have HP80s, will be getting a pair of HP100s before next season).

 

[Bob DBF]

Interesting about the fills. I have local friends who tell me they have trouble getting LP fills.

Now that just dosent make sense to me. Seems as if a shop could hit 3500#, stopping at 2400, or 2640#, would be a peice of cake.


Bob

 

[JackD342]

Agreed, feels like there is a miscommunication somewhere on the LP fills. Unless the trouble your friends have is getting the LP 2400 tanks filled higher than service pressure to 3000 or more.... but that would never happen, right?

Two technical reasons for LP, both real, but not easily quantifiable:

• Higher pressures put more stress, wear, and tear on your regulator. Same reason you turn your air on slowly rather than quickly.
• How cold and how deep are you diving? There are a lot of contributing factors that can add up to a regulator freezing. One is depth, with added air density. Another is starting pressure - your 1st stage gets colder reducing air from 3500 psi to 140 than it does reducing from 2400 to 140. Of course if applicable, you also have the option of underfilling HP tanks on shallower cold dives, and maxing them out on deeper dives which hopefully are in less cold conditions.

One other note - many LP steel tanks have a + rating that allows them to be filled 10% over service pressure. This requires an additional check at the 5 year interval hydro test, and sometimes is not easy to obtain. I had a hydro tester in the past that just refused to even consider it. Others may have trouble obtaining the proper test spec for the + rating. If your tank has the REE number stamped on it, then it doesn't need to be found elsewhere.

 

[Marie13]

Now that just dosent make sense to me. Seems as if a shop could hit 3500#, stopping at 2400, or 2640#, would be a peice of cake.

Bob

It’s other places besides my shop. If you’re only getting fills at the shop, no problem. Try at some of the quarries, nope.

 

[BRT]

It’s other places besides my shop. If you’re only getting fills at the shop, no problem. Try at some of the quarries, nope.

I simply don't believe this.

 

[JackD342]

One other thought - I suppose someone with an assembly line fill station with multiple whips filling multiple cylinders at the same time may be resistant to anything other than their "standard" fill.
I have the pressure regulator on my fill station set for 3000 so I can't overfill a tank by mistake. For lower pressures, I have to pay closer attention, and for some folks that might mean hand holding your tank through the fill by itself instead doing it in a batch. To finish the thought, for higher pressures I need to do a little more too - raise the limit on the pressure regulator, and then back it down again after.​

 

[BRT]

One other thought - I suppose someone with an assembly line fill station with multiple whips filling multiple cylinders at the same time may be resistant to anything other than their "standard" fill.
I have the pressure regulator on my fill station set for 3000 so I can't overfill a tank by mistake. For lower pressures, I have to pay closer attention, and for some folks that might mean hand holding your tank through the fill by itself instead doing it in a batch. To finish the thought, for higher pressures I need to do a little more too - raise the limit on the pressure regulator, and then back it down again after.​

Which would mean that they couldn't fill AL80's too.

 

[MichaelMc]

Now that just dosent make sense to me. Seems as if a shop could hit 3500#, stopping at 2400, or 2640#, would be a peice of cake.
Bob

My recent record for rental LP tanks is they come at 2250, despite + rated. The shops explanation, about their own tanks, was they do not always come back from hydro with + ratings. Which did not really explain things in my mind. My only thought is they have few Nitrox whips, and put them at set pressures they do not want to change. So LP 2400+ gets lumped with ST 72s. Faber stamping 'do not overfill' in all caps likely does not help, though the rentals were born before that.