High Pressure Vs Low Pressure Steel tanks

[Topbodz]

Just wondering the advantages of Low Pressure tanks.

Who (cave dives, deep divers...) prefers Low pressure

Read a thread on it (from SB) yesterday but it didn't clear things up

other that the fact that you can overfill them...

Is there other reasons to go with low pressure....

thanks

 

[Bob DBF]

Cave divers can carry around 40% more air in the same tank by over filliing it, and the tanks can take it.
The advantage becomes obvious.

I am not a cave diver so I don't over fill the tank, much. I got it because the one I ran across was cheap. In addition, the weight of the tank will drop lead off your belt. Last but not least, I dive a vintage double hose regulator and the service pressure of the tank is in the pressure range of what the regulator will take so that I can use the regulator with a larger gas supply than the old steel 72's.



Bob
---------------------------------
I may be old, but I’m not dead yet.

 

[Topbodz]

Thanks Bob!

I also read that its best for gas blending such a partial pressure fills... Not understanding that part, is it problematic to blend gas in a HP tank?

Cave divers can carry around 40% more air in the same tank by over filliing it, and the tanks can take it.
The advantage becomes obvious.

I am not a cave diver so I don't over fill the tank, much. I got it because the one I ran across was cheap. In addition, the weight of the tank will drop lead off your belt. Last but not least, I dive a vintage double hose regulator and the service pressure of the tank is in the pressure range of what the regulator will take so that I can use the regulator with a larger gas supply than the old steel 72's.



Bob
---------------------------------
I may be old, but I’m not dead yet.

 

[TwoCards]

Low pressure tanks can generally be had for less money and in areas where overfilling is a common practice (north Florida) they will give you as much or more air as their HP counterparts. I live in N Florida but ended up with 3442 psi (hp) tanks for a couple reasons. I wanted higher capacity tanks than al 80's as I'm a little heavy on air usage. I considered LP tanks as they would work fine for me now, but if I move or dive in other areas it’s unlikely I would be able to get them overfilled. For example two comparable in size tanks are the lp 85 and hp100. An HP 100 gives you 80 cu ft of air at a 2640 psi which is close to the 85 cu ft of air you get in an lp85 filled to the same pressure. Most shops would stop there with an LP tank, but the hp 100 can be filled to its rated pressure and have 100 cu ft of air. So the way I figure is I can always get at least 3000 psi in my hp tanks at any shop which is still more than an lp tank and when I do get full fills I have significantly more air than an lp of similar size filled to its rated pressure. Check out this link for some more info on hp vs lp

 

[Hatul]

I only have HP tanks, and one issue is that I always have to prod the shop to get a good fill. If I don't it's common to come out with 3200 psi fill and even less on boats. I think part of the problem is more heating in filling the HP tank and it takes longer to fill.

 

[Colliam7]

Just wondering the advantages of Low Pressure tanks. . . . other that the fact that you can overfill them... Is there other reasons to go with low pressure....thanks

While overfilling is often given as a reason to go with LP cylinders, a second reason occasionally cited is that some people report having difficulty getting 'full' HP fills - they can get fills to ~3000 psi but apparently some fill stations don't have the equipment, or willingness, to fill beyond that pressure. I have never encountered such a problem in the eastern US, but a few others apparently have. I have routinely been able to get fills to 3500psi (and beyond) in shops in NC, FL, AL, etc.

I also read that its best for gas blending such a partial pressure fills... Not understanding that part, is it problematic to blend gas in a HP tank?

It is NOT problematic to blend gas in a HP cylinder. HOWEVER, the standard supply cylinders of oxygen and helium that are used in most blending operations have a working pressure of 2400psi, so blending gas in a HP cylinder may require use of a booster pump. Some fill operators consider use of a booster pump with oxygen to be inappropriate or unsafe. I do not. We routinely boost when filling with 100% O2, or with helium, as the available pressure in our oxygen and helium supply cylinders decreases. In addition, there are some operators who will simply not fill a cylinder with 100% to a pressure above 2400 psi, because of the fact that a booster pump is needed. For backgas cylinders, that really isn't an issue.

The choice of LP vs HP is probably better made on the basis of weight, buoyancy and trim characteristics, that 'fill-ability'.

 

[lowviz]

Colliam7,

-OP may be referring to filling from HP cylinders via transfill whip.

In that case, LP's are easier to mix than HP's would be...

 

[Colliam7]

OP may be referring to filling from HP cylinders via transfill whip.

He may, but his post didn't indicate that.

In that case, LP's are easier to mix than HP's would be...

Absolutely, simply based on pressure differences.

I guess we are both left to speculate on what he meant by:

I also read that its best for gas blending such a partial pressure fills

I confess, I usually don't think of 'gas blending' in the context of using a transfill whip and a HP cylinder.

 

[lowviz]

....//.....I confess, I usually don't think of 'gas blending' in the context of using a transfill whip and a HP cylinder.

In a pinch, there is usually a way to transfill the mix you want as long as you have one or two full HP cylinders to top up the pressure. The fill order matters. Nothing worse than charging in the wrong order and ending up "can't get there from here". Wrote a program for this, just spin the dials, would gladly share if it wasn't for the legal issues involved.

No magic, can be done with a calculator also...

 

[Jax]

Just wondering the advantages of Low Pressure tanks.

Who (cave dives, deep divers...) prefers Low pressure

Read a thread on it (from SB) yesterday but it didn't clear things up

other that the fact that you can overfill them...

Is there other reasons to go with low pressure....

thanks

Topbodz, one thing that should register in your consideration is "Do I have an LDS that can fill my HP steel to 3442?"

Most small LDS have compressor that will fill to 3000psi.

As far as I know, there is one LDS in Phoenix area that will / can fill a bottle to 3442.

Therefore, I always have a fill of 3000psi, which cools to 2700 psi, which is 2700/3442 * 100cf = 78cf . . . so that inability to fill to capacity makes my 100s into 80's.