LP vs HP tanks on doubles...

[ianr33]

Al 80 doubles are great for warm water. Cheap and light as a feather (compared to 104's )
With a 3mm wetsuit I use 6 pounds of weight plus a 6 pound backplate,not much weight to carry.

Using 2 deco gases they hold enough for 20 minutes at 200 feet,just an easy way to dive.

 

[Van Isle]

I've just finished researching and buying a set of doubles and a wing; I feel your pain! The information one can get on the internet is incredibly biased and is based on a poster's geographic location, type of diving, air consumption, fills and mixes available.

It is important to talk to the divers doing the diving you want to do in the area you want to do it.

For me, PNW cold water deco dives with less than 30 minutes of deco, in a dry suit, one deco gas, led me to HP 100s. I'm not afraid of the weight of the bigger tanks, despite being 5'8", but I did want a doubles set that I could and would dive all the time to get bottom time in the rig on lots of recreational shore dives prior to fundies/tech training. If I ever get to bigger, badder dives, I'll get 130s. No big deal. If I move to cave country to do huge penetrations I'll get what works there, LP 104s or whatever is gospel. Getting trimix fills is easy here: there are boosters around, I can get partial pressure blends, 32% is banked for "standard" trimix mixes. If that's not the case where you are maybe LP tanks make it easier to get the right mixes, I don't know. Again, that's why you need to talk with divers doing your dives in your area. Good luck!

VI

 

[iztok]

Why is everyone saying that it is easier to get mixes in LP vs. HP?

This would only be the case if they are both filled to their marked filling pressure. But as soon as one fills both to the same pressure there is the same story.

LP95 and say HP 119 (or 120) have about the same internal volume and at the same pressure hold the same amount of gas. Filling either one with the gas mix is equally problematic. Now if one would compare LP95 and HP100 then story might be different. However LP proponents usually talk about serious overfill to and above HP pressure.

All else being equal I would rather overfill HP tank to 4000 then LP tank to 4000.

 

[Van Isle]

Why is everyone saying that it is easier to get mixes in LP vs. HP?

This would only be the case if they are both filled to their marked filling pressure. But as soon as one fills both to the same pressure there is the same story.

I haven't heard of this before this post, but I'm guessing it might be true in cases where there is neither a booster readily available nor large banks of high pressure helium and O2, so it would be therefore easier (i.e. have sufficient gas at sufficient pressure) to get partial pressure fills in an LP tank assuming final fill of 2400psi vs HP 3445psi.

But this is just a guess.

VI

 

[iztok]

I haven't heard of this before this post, but I'm guessing it might be true in cases where there is neither a booster readily available nor large banks of high pressure helium and O2, so it would be therefore easier (i.e. have sufficient gas at sufficient pressure) to get partial pressure fills in an LP tank assuming final fill of 2400psi vs HP 3445psi.

But this is just a guess.

VI

As I said if we talk about filling to nominal pressure of LP vs nominal pressure of HP. However they are equal when it comes to same pressure fills.

 

[sean_nc]

I dive double Faber 95's. Recently a cave shop asked us what we wanted filled in the tanks. My new dive buddy said "pump em up to 4k" (I thought he was joking, the shop didn't). Which the shop did. When we got in the water, my computer read 3860psi. Hmmm. 3860psi = 139cu' of air each tank. That's alotta stinkin air in a set of LP tanks. Try that magic with HP tanks. Now granted, I wouldn't ask for 4k fills. But a cold 3600 is very common.

Not trying to pick on you Superlyte but this logic has never made sense to me.

1. If you continuously overfill any tank and use up the safety margin you run a real risk of problems.

2. Why not just get the same tank with a different steel that is rated to hold the pressure? Safer way to hold the same amount of gas.

3. If your local shop wants to pump the tanks that high I don't want to be around. I know shops have been doing it for years but I see no reason to risk it when I can get the right tank and do it safely.

4. If it's as safe as everyone says why not "Try that magic" with an HP and fill that 3442 up to 5163?

 

[UCFKnightDiver]

Not trying to pick on you Superlyte but this logic has never made sense to me.

1. If you continuously overfill any tank and use up the safety margin you run a real risk of problems.

2. Why not just get the same tank with a different steel that is rated to hold the pressure? Safer way to hold the same amount of gas.

3. If your local shop wants to pump the tanks that high I don't want to be around. I know shops have been doing it for years but I see no reason to risk it when I can get the right tank and do it safely.

4. If it's as safe as everyone says why not "Try that magic" with an HP and fill that 3442 up to 5163?

Find me an HP tank that holds in excess of 130 cuft of gas and I will, and it has been happening for years with no failures and tanks are still passing hydro's with no problem, not seeing the issue here.

 

[iztok]

Find me an HP tank that holds in excess of 130 cuft of gas and I will, and it has been happening for years with no failures and tanks are still passing hydro's with no problem, not seeing the issue here.

HP 130 at 3860psi (pressure you mentioned) holds 147 cuft.

 

[elan]

I think there is a tank made by Faber which holds 146 cuf at 3500 if I'm not mistaken.

 

[UCFKnightDiver]

HP 130 at 3860psi (pressure you mentioned) holds 147 cuft.

I don't believe I mentioned any pressure of 3860psi.