Cave fills?

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Brett Hatch

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I currently do (strictly rec) single-tank dives in the Monterey area with HP100 steel tanks filled to ~3442 psi. I have heard that filling LP tanks (2400 psi or 2640 with the + rating) up to ~3500 psi is very common in some places of the world, such as Florida cave country. The result is a smaller tank containing a lot more gas than my HP100's. It's my understanding that this practice is safe for divers (read: nearly no more risk vs diving an HP tank at the same pressure). Rather, it is the tank filling operator who takes on additional risk, since there is a non-zero chance of tank failure during the fill.

My primary LDS's operators don't do this. Are there any dive operators in the Bay Area who do these "cave fills"? If so, I might consider picking up some LP85's (or similar).

Thanks.
 
it isn't a lot more. i have some faber lp tanks and yes you get a few more CF overfilling a lp85 compared to a hp100, but honestly it isn't a huge difference. if you want a lot more gas, switch to doubles, either backmount or sidemount. it makes a little more sense if you are running large LP tanks like double 108s or larger for greater amount of backgas without going to multiple stages, but it really isn't necessary for most diving in the area.
 
I think there is a difference in the discussion of cave fills as to whether you are trying to excape bying additional equipment and maximizing the equipment you have because you can not take more. example if you want to do a radical cave fill for a single tank, dont,,,,, buy a second larger tank. If yo uare in a cave then you pack those tanks to the statistical max and go for it. My lp85's have been over 4k in the sun but not over 4k from the fill. Im not reall confy with that but it happened. a pair of lp 85's at 4k is about 240 cuft. Basically a 3rd tank worth,,, of which you have about 200 you can use and still maintain a good IP reg pressure provide for a buddy and inflate a wing with a load. the weight is reasonable compared to double 104's or 108's for another 50 cuft or so. Im no expert but as far as I know you dont do cave fills on hp tanks. I have nothing to back that up with other than word of mouth. the LP's are ideal for things like that. You fill slow and carefully adn things have been over all without incident. I have also seen people fill al80's to over 4k to do deep bounce dives to 200 ft pluss. Crazy IMO but they do it. I normally fill my al95's to about 3300 or so at the pump and they cool a bit to about 3200. lots of air for local lakes etc. either way it is a lot more air than any al 80 or should I say al 77. at about 3k or so my lp95's are about 108's quite often i use a lpl 120 @ 3200 and dive all day on it. over filled YES but as far cry from a 4k fill.
 
Doubles are on the horizon, but I'm not quite ready for that plunge. I have been diving wet, and have my first a drysuit coming in the mail this week. My goal is to get completely comfortable with diving dry before taking on another big gear change like going for doubles. Maybe I'll be ready by the end of the year or so. In the mean time, it seems that swapping to an over-filled LP tank requires no gear other gear or skill adjustments, just a matter of finding the right operator and some tanks.

@runsongas do you get your LP tanks cave filled locally?

Also yes, I agree that 108's would be nice. Taking a look at the cylinder specs, they seem to be about the same size, weight, and buoyancy characteristics as my HP100's.

edit: posted at the same time as KWS...
 
sad to say but most shops i get fills from dont even know they are filling a LP tank so they pump it to 32oo like a al80 and Im good with that. mums the word.
 
Doubles are on the horizon, but I'm not quite ready for that plunge. I have been diving wet, and have my first a drysuit coming in the mail this week. My goal is to get completely comfortable with diving dry before taking on another big gear change like going for doubles. Maybe I'll be ready by the end of the year or so. In the mean time, it seems that swapping to an over-filled LP tank requires no gear other gear or skill adjustments, just a matter of finding the right operator and some tanks.

@runsongas do you get your LP tanks cave filled locally?

Also yes, I agree that 108's would be nice. Taking a look at the cylinder specs, they seem to be about the same size, weight, and buoyancy characteristics as my HP100's.

edit: posted at the same time as KWS...


i have a couple of OMS 120's that I think are actually 125's or so at 2640.
 
i have a couple of OMS 120's that I think are actually 125's or so at 2640.

Sounds like the OMS 121, listed 6th-from-last on Huron's cylinder spec page.
 
Does cave filling a lp steel tank reduce it's lifespan?
 
I have LP50s for sidemount. My experience in the Monterey area is most shops fill them to 2650. One filled to 2200 or 2400 and had to be questioned about whether they saw the + rating. As a gentle way of asking if they knew what they were doing.

I've had casual conversations about the statistical safety of cave fills on LP tanks when such things came up. But not asked them explicitly to do it. I don't know their rules or liability and I'm not doing anything where I can't just surface or take more or bigger tanks.
 
https://www.shearwater.com/products/perdix-ai/

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