Double HP100s for Cave or NOT??

[Curt Bowen]

And a small $3.95 a month could help it stay in business so you and others can retrieve this valuable information

No I'm not a Scuba Board sales rep

 

[xiSkiGuy]

Here is the argument against these tanks:

"Double steel HP100s position too much weight on the upper part of your body, and you will be struggling to maintain horizontal trim during cave diving, as compared to double LP85s. The preferred LP85s are lighter, and can be overfilled 10%, providing nearly the same amount of gas as the HP100s. The LP85s are longer (avoiding excessive weight toward the divers head) thereby enabling the cave diver to better maintain the necessary horizontal trim. Skilled cave divers who use double steel HP100s are essentially non-existent".

Whomever wrote that doesn't know very much about tanks or cave fills. LP85s hold 85cf with the 10% overfill (ie. at 2400psi + 10% or 2640psi). But none of that really matters when getting your tanks filled in cave country. A typical 3600psi fill on those LP85s will give you almost 116cf per tank. A 3600psi fill on those X7-100s will give you a little less than 105cf per tank. You will cover how to determine tank volume at a given pressure and matching dissimilar tank volumes during your cavern/intro class.

LP85s are a more common tank in cave country, but they aren't necessarily better than X7-100s. Whether the 100s will make you overly head heavy is an individual issue, and not a blanket fact. LP85s are longer than X7-100s and may trim out better for some people (especially taller people).

Somehow I doubt X7-100s are the mark of an unskilled cave diver.

 

[Mr. Bubble]

"At the end of the dive (when your trying to do your decompression stops) with almost empty tanks you will be floating like a cork."

I don't think that will be a problem. They remain negative when empty as well.

 

[xiSkiGuy]

I am facing a learning curve with both a new dry suit purchase (my first) AND new (my first) doubles set. The responses on this thread have removed my doubts concerning the HP100s.

I'm sure this goes without saying, but be sure you get very comfortable with your new gear before taking cavern!

 

[Curt Bowen]

"At the end of the dive (when your trying to do your decompression stops) with almost empty tanks you will be floating like a cork."

I don't think that will be a problem. They remain negative when empty as well.

You missed the point. Yes the tanks might always be negative if they are not attached to you in your bouyant drysuit.

 

[tonka97]

I'm sure this goes without saying, but be sure you get very comfortable with your new gear before taking cavern!

I am planning to take cavern using my jacket BC/single tank; maybe will use new dry suit if it works out OK in pool trial.

 

[Meng_Tze]

Somehow I doubt X7-100s are the mark of an unskilled cave diver.

Maybe it should be.

"Inability to be able to dive with X7-100's opposed to good diving characteristics with other tanks is a sign of an unskilled diver"

(and that was a joke before I get killed here)

 

[rjack321]

Maybe it should be.

"Inability to be able to dive with X7-100's opposed to good diving characteristics with other tanks is a sign of an unskilled diver"

(and that was a joke before I get killed here)

Actually you aren't too far off the mark. HP100s are one of the easier doubled cylinders to dive with. Compared to say HP119s or even more challenging HP80s. If you struggle in HP100s you might need more practice/experience overall.

Or just different tanks. Skill can make up for some equipment difficulties, but not all.

 

[tonka97]

LP85s hold 85cf with the 10% overfill (ie. at 2400psi + 10% or 2640psi). But none of that really matters when getting your tanks filled in cave country. A typical 3600psi fill on those LP85s will give you almost 116cf per tank. A 3600psi fill on those X7-100s will give you a little less than 105cf per tank.

Is it considered safe to fill a LP steel 85 cf '2640 psi max rated tank' up to 3600 psi?

Is it just an issue of possibly blowing the burst disk, without danger of bodily injury?

 

[Brewone0to]

Overfilling an 85 by 10% does not "provide nearly the same amount of gas as the HP100s". It provides 85cft. You have to overfill them to a bit over 3100psi to get 100 cft. That's about a 30% overfill. Not that that is a big deal, just an inaccuracy. I've dove a set of 85s filled to 4000 before.

I get my HP100's overfilled by 20% as well.
Thats right at 4200psi, but it gives me
240 cu ft if it's a sidemount kinda day.