Slinging a Tank

[Dr. Lecter]

I just grabbed a bunch of recently hydro/vized LP72s for $45 each. Finding cheap 6.9" bands for doubling them up looks like it would be harder, though. Tiny doubles have their place...I don't want to lug double 130s for every dive, and sometimes I don't want to squeeze them through certain restrictions.

LP tanks have the benefit of holding X amount of gas at a lower pressure...and some people will overfill them, giving you X+Y in the same sized package. Downsides are: heavier than HP tanks generally (LPs have a heavier sidewall from what I understand) and not everyone will overfill them. The LP72s, for example, are rated for 2250psi but supposedly only hold 72 if they have their + rating of 2475psi. Mine don't but should, and will after next hydro. In the meantime, I'm happy to fill them to 2500...but true cave fills aren't something that seems popular for LP72s and I'm not interested in joining the bleeding edge of cave fill innovation.

 

[nv]

I just grabbed a bunch of recently hydro/vized LP72s for $45 each. Finding cheap 6.9" bands for doubling them up looks like it would be harder, though. Tiny doubles have their place...I don't want to lug double 130s for every dive, and sometimes I don't want to squeeze them through certain restrictions.

LP tanks have the benefit of holding X amount of gas at a lower pressure...and some people will overfill them, giving you X+Y in the same sized package. Downsides are: heavier than HP tanks generally (LPs have a heavier sidewall from what I understand) and not everyone will overfill them. The LP72s, for example, are rated for 2250psi but supposedly only hold 72 if they have their + rating of 2475psi. Mine don't but should, and will after next hydro. In the meantime, I'm happy to fill them to 2500...but true cave fills aren't something that seems popular for LP72s and I'm not interested in joining the bleeding edge of cave fill innovation.

How do they compare to standard and HP tanks?

I dive HP80s. A little confused - are you saying an LP80 will carry the same as an HP80 - different being psi, and naturally the cylinders are different sizes?

 

[rambaldi]

How do they compare to standard and HP tanks?

I dive HP80s. A little confused - are you saying an LP80 will carry the same as an HP80 - different being psi, and naturally the cylinders are different sizes?

If filled to the designed pressure an LP80 and an HP80 carry the same amount of gas. The HP80 is filled to a higher psi, the internal volume of the tank is smaller.

 

[nv]

If filled to the designed pressure an LP80 and an HP80 carry the same amount of gas. The HP80 is filled to a higher psi, the internal volume of the tank is smaller.

So the benefit comes into play with the additional psi put into LP tanks. Other than that I can't see any other benefit; I assume that they are larger than their steel and standard counter parts

 

[rambaldi]

So the benefit comes into play with the additional psi put into LP tanks. Other than that I can't see any other benefit; I assume that they are larger than their steel and standard counter parts

There are other benefits, such as less stress on a compressor (doesn't have to run to as high a pressure). The internal volume is larger but due to the lower expected pressures different steels or thicknesses could be used for the tank walls.

 

[Crass3000]

As far as LP vs. HP.... My understanding is that some shops can't supply the high pressure do to the fact that they don't have a booster. People just don't use steel tanks up north as much as on the coasts as far as I have seen. Almost everybody dives AL80s. I'm just happy if I get 3000psi.

Edit: The first time I tried slinging a pony it didn't go so well. First dive of the season and overtasked with navigation and dragging a flag. I ended up getting a BP/W soon after and found the position of the D rings a lot easier to attach to. Once you get used to slinging a bottle you really don't notice them much. I normally sling a 40cuft as a redundant pony but will be taking a class where they want me to have an 80cuft on back, sling another 80cuft for backgas, and my 40cuft as a high O2 deco mix. Kind of a strange setup but with a little practice slinging bottles really becomes second nature. The instructor just doesn't want to push us toward any sort of rigging so as to save us money and become more aware of what we like before we invest more money. I think I may be heading to sidemount but want to get used to doubles on back so I know the differences. Sidemount just seems like a good match for caving but at this point what do I know?????????

 

[Dr. Lecter]

Let's go to the stats:

X7 Steel 80

3442psi

7.25"wide

19.7"tall

28lbs empty

- 9.0lbs full : - 3.0lbs empty

Worthington doesn't make a LP 80, but the LP85 is very close to it:

Description	LP Series 27 (no longer available)	LP Series 77	LP Series 85	LP Series 95	LP Series 108	LP Series 121
Model	LP27	LP77	LP85	LP95	LP108	LP121
Service Pressure	2400+ psi	2400+ psi	2400+ psi	2400+ psi	2400+ psi	2400+ psi
True Capacity @ 2640 psi	27.0 cu ft	77.0 cu ft	82.9 cu ft	93.3 cu ft	108.6 cu ft	120.0 cu ft
Buoyancy* FULL	- 3.0 lbs.	- 6.8 lbs.	- 7.1 lbs.	- 10.1 lbs.	- 10.7 lbs.	- 11.1 lbs.
Buoyancy* EMPTY	- 1.0 lbs.	- 1.0 lbs.	- 0.7 lbs.	- 3.0 lbs.	- 2.6 lbs.	- 2.0 lbs.
Weight EMPTY	11.9 lbs.	32.5 lbs.	36.8 lbs.	41.9 lbs.	45.9 lbs.	49.9 lbs.
Outside Diameter	5.5 in.	7.25 in.	7.25 in.	8.00 in.	8.00 in.	8.00 in.
Cylinder Length	14.5 in.	23.2 in.	24.7 in.	23.7 in.	26.5 in.	29.2 in.

The LP tank that gives you closest to 80cf will be the same diameter as an HP 80, easier to get full fills on, and have somewhat better buoyancy characteristics (unless you need to sink a big neoprene drysuit and thick undergarment), but is 5" longer and almost 10lbs heavier out of the water. If it doesn't get a plus rating for whatever reason, its fill pressure will result in less than the stated capacity (i.e. an LP 85 tank gets less than 85cf if filled to its regular rated pressure of 2400psi). If, however, you have a shop that does cave fills, you may be able to get 130cf+ of gas into a relatively tiny tank. It depends on what the local shop practices are.

 

[waterpirate]

There is no advantage 1 way or the other except cost. lp 72's are the f100 of scuba tanks, built to last and plenty of them available on the used market. I bought my double 72's banded and manifolded in hydro for 250.00 a set. That is close to the cost of a new manifold.
Eric

 

[chrpai]

LP72(+) makes perfect sense for a friend of mine because he can fill them up to 3000psi whenever he wants. (87cf) They are relatively small and lightweight and he doesn't need a weightbelt when diving it.

The dive shop I go to has this phobia with 72's and I'd only get 2250 (65cf) if I could get a fill at all. 2/3 of the time my LP95's only get filled to 2400psi and I have to remind them yet again to put a few hundred more psi in it.

I think the reason that John thinks tiny doubles makes sense is because he's a technical diver that mostly dives doubles. It solves his problem of not having to switch his regulators and wing back and forth between single and doubles. That works for him. But the part I have a problem with is suggesting it's a good solution for recreational divers. For me, as a guy who only dives single tank, it's easier and cheaper to add the (40cf) pony for redundancy. The DIR rigged tank slung on the side works well for me and I don't need a new solution.

 

[DaleC]

Don't forget the risk of too little air reserved if a shutdown is required at the max depth/duration point of the dive. You might be ready to turn with your reserve volume when a failure occurs and by the time you isolate you have less than that reserve to ascend with.