Wassup with Cave Fills?

[NW Dive Dawg]

So...... wassup with "Cave Fills" ??? Is it simply that in cave country that shops are totally OK with any risk associated with over-filling tanks? Why can't we get the exact same PSI in the same tanks for Open Water fills? Or is it that folks with their own compressors are just overfilling because they know that the tolerances have a large safety factor built-in?

 

[formernuke]

 

[Lorenzoid]

There's a lot to unpack here--for those who dare--but I'll start with the terminology. Shops in north Florida "cave country" will commonly fill steel tanks generously if that's what you request, and they will do so without regard to whether you plan to dive in a cave or poke about the OW spring basin. The term "cave fill" is sort of a misnomer.

 

[OTF]

While we're asking the cave fill questions:

I understand the somewhat accepted practice of routinely overfilling LP steel tanks, but what's the thinking on overfilling HP steels? Especially tanks like the PST 3500's which are relatively thin? Are HP steels rated with the same conservatism as LP steels or less?

 

[Still Kicking]

Bottom line: steel tanks have a very wide safety margin and a long track record of being overfilled with few failures, and DOT has a very lax (almost non-existent) enforcement program for scuba fill stations. Given this, many shops in cave country choose to turn a blind eye to the working pressure ratings on steel tanks. YMMV.

I think HP steels get pumped to 4000 psi but I am not 100 percent on that -- a Florida local will correct me if I am wrong.

 

[Nemrod]

"Cave fills" are not new and are routine in some areas of Florida. It only pertains to LP steels best I knew but I guess the practice has morphed to the HP steels as well. Nobody is cave filling aluminum tanks but I have gotten a few and when I hooked up my reg and the spg needle spun off I did not know whether to run or be happy! And yet some of these stores will not fill an aluminum tank that is older than 15 years.

 

[boulderjohn]

So why are cave fills not available for open water, NDL divers? For the most part, because they really aren't needed. If you are staying within NDLs, getting that extra gas shouldn't do you a whole lot of good.

I own a set of LP 85s that I expressly bought for sidemount cave diving, and they have had cave fills for that reason. I also use them backmounted for OW, NDL dives. The South Florida shop I use for fills used to give me something close to cave fills on many occasions, and I used to get back on the boat after a long OW dive with oodles of air. This past year (I am only there in the winter), procedures changed, and I no longer get those big fills. They still overfill them a tad (about 2900 usually), but I am still getting back on the boat with oodles of gas.

It is to a large degree also true of typical OW tech dives. I have done such dives in South Florida using LP 108s, and I absolutely could not get them filled past their rated pressure; in fact, the shop I used then often would not even fill them to their rated pressure. It was still enough gas for the dives we did.

 

[Marie13]

Some dive shops in the Midwest who have owners experienced in tech diving will fill LP steels to 3000. I’d prefer more, but I’ll take what I can get!

 

[tursiops]

Some dive shops in the Midwest who have owners experienced in tech diving will fill LP steels to 3000. I’d prefer more, but I’ll take what I can get!

I wonder if they stop at 3000 because that is all their compressor (optimized for AL80s) will do?

 

[Marie13]

I wonder if they stop at 3000 because that is all their compressor (optimized for AL80s) will do?

They’ll fill HP steels to service pressure - 3442. These are not what I refer to as “warm water shops.”