I want to get a new tank but there is so much to choose from im not really sure what tank best fits me. I am diving an AL80 right now that I borrowed from my father. It does work fine and I guess I could get one just like it but looking around I have many options I never considered. Aluminum or steel, HP or LP, yoke or DIN. I have a DIN 1st stage with a yoke adapter so I could use a DIN valve but what is better about a DIN valve over a yoke. I also just started drysuit diving and would like to shed a few pounds so mabey a steel tank would be a good idea. If I got a HP tank could I get fills higher than 3000PSI? My LDS only had AL80 with yoke valves with the plug you can pull out to make it a DIN valve in stock. So when I asked him all these questions he kept pointing me in that direction. Not to say he is wrong but I am not sure if he was just trying to tell me what I wanted to hear or if he was telling me the truth. Any opinions?
Hello DUI.
You've asked some good questions. Ones that many divers begin to ask as they get more involved in diving and decide to purchase their own gear.
The selection of a tank is usually based on the needs of the diver. Factors such as total gas needs, SAC rate, ballast needs, trim and buoyancy needs are to be considered.
Lets look at the issues you raised.
Aluminum vs Steel : Most divers were trained using Aluminum 80s. They are durable, less expensive, thicker, and more positive (they float more) when empty.
Steel tanks are more expensive, more resistant to damage, have a higher potential volume capacity, are more negative at the end of the dive, but are more prone to rust.
The selection for most divers when comparing steel vs aluminum usually centers around the need for more breathing gas and the ability to take the weight normally worn on a weight belt or integrated BC and displace it to the tank where it will rest closer to your center of gravity. If you are doing relatively short dives in relatively shallow water then an aluminum tank should fill your needs. If you are doing deeper dives or require more bottom time then a steel tank may be more suitable.
HP vs LP : This issue has been discussed quite a bit and I would suggest doing a search using those words to see what the resident experts have to say. Briefly,
the difference in LP and HP revolves around the ability to overfill the tank as well as the density of the walls of the tank. A HP tank is usually filled to its rated pressure. So that a HP 100 has 100 cu ft of gas at 3442 psi. These tanks are not usually over pressurized. Divers have chosen to overfill LP tanks beyond their rated pressure. Whether this is right or wrong has also been discussed by the resident experts and their opinions both pro and con are worth reading. So that a LP 95 has 95 cu ft of gas at 2400 psi. A diver would have more gas in the cylinder if they filled it to 3000 psi for example.
Some concerns that divers have had regarding HP tanks is that not all fill shops have the ability to put 3442 psi of gas in a tank or are used to just filling all tanks to 3000 psi. This means that the HP tank would not be full. For LP tanks, not all fill stations will fill the tank beyond its rated pressure. Thus if they fill it to 2400 psi, you still have 95 cu ft of gas in a Steel 95 for example. I am not advocating one over the other, just discussing the thought process that divers go through when selecting between the two.
DIN vs Yoke : My understanding is that is has been thought that a DIN connection is a more secure connection since the 1st stage is threaded into the valve as opposed to placed over the valve in a yoke connection. It is also my understanding after reading the posts in the Regulator section that this is a subjective approach, with both connections proving to be equally successful in accomplishing their goals. The difference may come in dealing with higher pressures. Most of the technical divers that I know use DIN connections with yoke adapters for when they travel abroad. This way your 1st stage is able to accommodate either set up. Tank valves with the yoke plug seem to be more common these days and seem like a reasonable idea. The goal again is that it gives you more options depending on how you have your gear configured or might want it configured in the future. I think the person in the dive shop was telling you the truth.
Hope this helps and I look forward to reading the input from other posters.
Anyway I'm down to 8 pounds of lead now.
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