Tanks, Valves and More!
By Ken Kollwitz
Have you ever wondered why there are so many different types of Scuba cylinders and which one might be the best for you? It is just like your gear, it all depends on the type of diving you do. I have 18 Scuba cylinders (steel and aluminum) and it’s not because I like to collect them. I do know people with more. It can be a problem storing them and making sure the hydros and VIP’s are current. My tanks are basically grouped into 4 categories; tech, beach / camping, solo / deep and boat diving. I have different cylinders for different types of diving I do, just like my gear. Now I know money doesn’t grow on trees (only at weddings and special events), so the idea here is to think ahead of what type of diving you may want to do. Just like your gear. As you continue diving you may find that 1 tank will not fit all occasions. If you want to use Nitrox for longer dives, why limit yourself to a small cylinder? If you have a large cylinder, why limit yourself to only boat or easy beach dives (unless that is what you like) because of the weight of the tank? Some of the best beach dives require a long walk or hike (not for everyone). As you can see there are a few things to consider when buying a Scuba cylinder, not to mention that steel and aluminum cylinder have different buoyancy characteristics. Before buying a Scuba cylinder, it is a great idea to do a little research. You can do research by asking your local dive shops, using the internet, asking other divers and going to the Scuba shows in Long Beach.
Aluminum and steel cylinders can be made out of different alloys. Cylinders also come in many sizes (72, 80, 95,100,120, etc.) and have different working pressures (working pressure, 2250, 2400, 3000, 3500, etc.). Aluminum tanks generally are 3000 psi or less and steel are 3500 psi or less, it all depends on the tank. The tanks that are 3500 psi usually have D.I.N. valves, which require your regulator 1st stage to have a different style connector on it. Keep the fill pressure in mind; some boats only fill to 3000 psi.The working pressure is stamped along the top of the tank as well as the alloy its made of , the manufacturer, the hydro date, D.O.T. (Dept. of Transportation) approved and more. As per D.O.T. requirements, Scuba cylinders are required a hydro test every 5 years and as per the Scuba industry are required a V.I.P. once a year.
Here are some things to consider when buying a Scuba tank. Cheapest is not always the best. Aluminum 80’s are usually the least expensive and are tall and very buoyant at the end of a dive. Because of there length, they seem to either hit you in the head (1st stage) or your behind (bottom of tank) if you have a short torso. You will also need more weight, because they are more buoyant. Also they usually do not last (years) as long as a steel tanks. Aluminum cylinders are great for pony tanks, side slung deco tanks, auxiliary air or argon tanks. They also work well as your main tank if you are tall, they are usually less expensive and are easy to find. Steel tanks are more expensive, last longer (years), have higher fill pressures, are more durable, and have better buoyancy characteristics. They can also help with your center of balance and help you maintain better neutral buoyancy (the most important dive skill to master). Steel tanks will also let you take some weight off your weight belt or your weight intergraded B.C.
As far as care of a Scuba cylinder; you should store in a cool dry place, laying down if possible (this can be hard for storage reasons) and wash good after use. Try to avoid standing tanks up unless they are being held or strapped down. If they fall over they could hurt someone or something. Also never let them sit without any air in them.
Here is some information on tank valves. There are 3 main valve types that you will see. The older J valve (still some around) which has a manual twist knob opposite the main on/off knob. The extra knob was made to pull down by a wire for an emergency; you could then get about 300psi extra (if it worked right). The K valve which is on most tanks today, have just an on/off valve. They come in a regular yoke style (fits most standard 1st stages), or a D.I.N. style, which fits D.I.N. (mainly high pressure) setup 1st stages. There is also a new style K valve now. It has a removable insert so it can be setup for a normal style or D.I.N. style 1st stage. Also on every valve you will find what looks like a pipe plug with a small hole in it. This is for the burst disc. The burst disc is a flat thin piece of metal (different sizes for different fill pressures) made to burst if the pressure in the tank becomes too great. It is a safety device. If the tank is full and becomes to hot (sitting in sun or hot car) the pressure inside the tank will increase dramatically and can blow the burst disc (I have seen this happen once).
Here is some extra information. CAUTION –Do not use Luxfer 6351 alloy aluminum 80’s (stamped on tank) Scuba cylinders that have not been visually inspected and eddy-current tested and then properly documented. These cylinders were made in the U.S. from 1972-mid 1988. Some shops will not even fill these tanks. If you think you might have one go to Luxfer website and check press releases and technical bulletins. If you like math, here is a formula you can do sometime to see how much air you really have in your tank. Let’s say your tank fill pressure is 3500psi and the boat only fills to 3000psi and you have a steel 80, how much air do you have? Take the gauge fill pressure (3000psi) and divide it by the tank fill pressure (3500psi), multiply that by the cubic feet of the tank (80) and you come out with 68.5 cubic feet. You now have less air then a steel 72 tank. This is one reason why, 1 tank doe’s not fit all diving.
This article is based on information I have acquired over the years. I am not a cylinder or gear expert. I am only trying to provide some information that may be useful to some people (I hope).