Tank question

[Josh Levinson]

My girlfriend and I are looking into cave diving courses this summer, and so I've got a question. She dives with twin LP 98s and finds them too heavy. She's thinking about getting a pair of HP 80 cf steel tanks. Is that a good idea? Thanks.


Josh

 

[roakey]

By "too heavy" do you mean too negative in the water or too heavy walking to the water?

If too heavy walking to the water you may have to move to 80s, but it's not optimal solution on several levels, but it'll have to do if she can't schlep the heavier cylinders. Another option is just for her to get stronger. I know some small women that stomp 104s around.

Also make sure you realize the impact of her going to 80s on your dive time as a team. Read my reply in http://www.scubaboard.com/t7661/s.html and understand that the smaller cylinders will probably be the limiting factor for the team.

Roak

 

[Trog]

I agree with Roakey.

The 80's have a nasty boancy tendency as well. They get floaty at around 2,000 psi. Not a good thing for any deco, or silt situations. So your looking at adding V or P weights, and that negates some of the benefits of the smaller tanks.

Trog

 

[Divesherpa]

If you do your training in Florida, your low pressure cylinders will be pumped beyond where your high pressure cylinders would be. She may have to go with LP 80's, But if that's the case, her remaining gas supply would always be what turned the dive.

Cheers

 

[Darian Dunn]

Is there a "standard" tank size?

It sounds like people are using everything from al80s to Steel 104s (set up in doubles of course).

I also understand that you (I) should get the same thing as your buddy, but I have not found that buddy as of yet.

 

[BILLB]

Divesherpa made a statement that I know is too true. LP steel tanks will get pumped to pressures far in excess of the manufacture's rating. I know this is nothing new for the cavers but my question is this: What makes the cavers so different that they can fill there LP's to 3000 PSI and then more and feel safe about it?

I have never heard of a tank failure in cave diving but this practice surely must have a negative impact on the life of the tank.

Also, my cave certified friend have indicted to me at HP steel tanks are not recommended for cave diving. I can understand the need for LP's on boats with tired old compressors but why in cave diving? Is it the bouyancy profiles.

If the lady wants to take dead weight off her back and keep the volume, then PST HP100 are the tanks she needs. My wife uses then and loves them (she is small in size too). PST HP 100's are 29.6 pounds when full (3500 psi). LP 104's are abou 44 pounds (which is the cloest thing I have on record for steel 98's). Faber LP 95's are 40 pounds.

 

[Divesherpa]

Here is the best part about filling in cave country. If you meet someone who had a PST 104 fail hydro, please let me know. There are tanks down here that have been pumped to 4,000 psi for years on a semi-daily basis which have no problem with hydro. Some friends in the UK say they put 4,000 psi in the OMS tanks there because they are rated higher.

In cave diving the high pressure tanks aren't dove for two main reasons. 1 is buoyancy issues, but the main reason is that all steel tanks are pumped to what the high pressure tanks are filled to and beyond in some places, making a LP 80 basically the same as a HP 120.

As to diving the same tanks as your buddy, this isn't critical. Being close is great, but not overly critical. After more reading and instruction on cave diving procedures, you will understand more about 1/3's and when to turn a dive due to gas supply (the most common reason for us to turn a dive).
cheers