OCEANCO Ltd

Your choice involves price, tank capacity, tank construction, tank size and weight, tank buoyancy, tank pressure and tank manufacturers.
If you are a new diver and not sure of what to choose, you can be certain that if you buy a new tank and you don't fill a tank beyond its legal capacity you don't have to worry about safety. There are no dangerous tanks sold. Your main consideration other than price should be to carry the right amount of air for your needs. Women are generally smaller than their dive partners and so do not use as much air. They can, therefore, carry smaller tanks. Sumo wrestlers or other divers in that size range would need to carry larger tanks in order to stay submerged as long as their dive partners. Keep in mind that a dive team needs to surface when the first diver depletes his/her air supply. So consider the size of your tank as compared to the air supply used by the other divers you will usually dive with.

What's a good size tank to get?

The most commonly used tank is the "Standard Aluminum 80" (AL80) that actually holds about 77 cubic feet of gas at 3000 psi. This is plenty of gas for the experienced air diver, and usually the no decompression dive time is what limits the dive. The most consistent complaint about the AL80 is its poor buoyancy characteristics. It is very positively buoyant near the end of the dive, which means that you have to start your dive with too much weight, yet sometimes you are still struggling to stay neutral at your safety stop.

If you usually return to the boat with 800 psi or more of gas in an AL80, then you might consider a smaller tank such as the Aluminum 63 or low-pressure steel 66 (LP66). One big advantage of using a smaller tank is that you will use less air carrying a smaller tank because of the reduced resistance in the water. So, for example, if you actually use 60 cubic feet of air on a particular dive, carrying an AL80, you would probably only have used 55 cubic feet if you were carrying an AL63. Another advantage of the smaller tank is less weight to carry and haul up the boat ladder. Many women prefer these compact and lightweight tanks for sport diving.

On the other hand, if your gas consumption is sometimes the limiting factor on your bottom time, you might choose a larger tank like the low-pressure steel 95 (LP95), or high-pressure steel 100 (HP100). The aluminum 100 is the largest aluminum tank available. The steel tanks usually carry more air for their weight than the aluminum.

An excellent compromise solution, if 80 cubic feet of gas is enough, but you don't want to deal with the additional weight and buoyancy hassles of the larger tanks, is the low-pressure steel tanks.

Special considerations when selecting a tank for Nitrox.

Selecting a Tank for Sport Diving with Nitrox is a whole different ballgame. Nitrox divers are more often limited by the volume of their tank, because they tend to stay down longer. Nitrox divers usually select one of the larger capacity tanks to take advantage of their longer bottom times available to them.

The first thing to consider is your budget. Aluminum tanks are less money than steel tanks when you consider dollars versus cubic feet. You can see that immediately by dividing the cost of the tank by the number of cubic feet of air that the tank holds. The least expensive tank considering the dollars per cubic feet would be the 3,000 psi, 80 cu.ft. aluminum. Bear in mind that this tank does not really hold 80 cubic feet of air but really holds 77 cubic feet. If you check our tank comparison charts you will see the actual capacity of the various tanks.

If you keep your tank clean and do not allow it to become completely empty you don't run much risk of corrosion. Compressed air as used by a scuba diver has zero moisture in it. AS long as a tank has some pressure inside it will keep out ambient air. An empty tank will allow outside air to enter the tank, carrying water vapor and possibly starting corrosion.

The other main reason for a tank to fail its hydro test is metal fatigue caused by the expansion and contraction of the tank as it is filled and emptied during use. Although you can't see it, the tank stretches when it is filled to full pressure and returns to normal as the air is breathed out. The more often this is done, the sooner the tank will become too weak to use. Steel tanks hold up better under use than do aluminum tanks.

Areas of the country where there is a lot of cave diving will sometimes have dive shops and divers who will fill steel tanks beyond their legal capacity. I'm not talking about the 10% overfill that is allowed on steel tanks. I'm talking about filling 2640 psi steel tanks to 3500 psi or filling 3500 psi tanks to 4500 psi. Besides being illegal, the extra pressure puts added stress on the tank walls causing the tank to weaken before it normally would causes damage to the regulator and gauges.

Steel versus aluminum is a consideration for commercial divers, instructors, gear rental shops and others who use a tank many times a week. For the average sport scuba divers this is not so important because the number of times they usually use a tank during each year will not greatly affect the tank. But this is an important thing to remember when you are tempted to purchase a used tank. It might look tempting to buy a used tank in a pawn shop or flea market or even a dive shop or from an instructor. You look at the hydro date and see that it needs inspection and figure if you add the cost of the inspection to the low price of the tank you will have a bargain. It will be no bargain if the tank fails the hydro test because the strength of the tank has been depleted by frequent use.

Check our tank comparison tables to see the difference in buoyancy (full and ampty) of the tank you are considering. That is important when you figure in the buoyancy of your body during the dive. If you are going to be diving in warm water with a very thin covering that has no buoyancy you will be fairly neutral in the water. If you are diving in cold water with a dry suit or a thick wet suit, you may want to get a tank that is heavier in the water so you won't have to wear so much weight on your belt or in your BCD weight pockets.

If you are not sure of what tank to choose, don't hesitate to ask for advice from the dive shop. Most dive shops will have someone who is knowledgeable to help you. Feel free to call us toll free at 888-925-6789 during business hours (eastern standard time) for information. We are happy to talk to you even if you don't buy from us.

The terms high pressure and low pressure relate to the comparison of pressures between different types of tanks. Even low pressure, which is usually 2640 psi is high enough pressure to be expremely dangerous if not used properly.

The main diffence to a diver is that a high pressure tank will hold more air for its physical size than will a low pressure tank. In order to do this, the high pressure tank usually must have thicker walls, adding to its weight so what you gain in size you give up in weight.

Also, keep in mind that tanks rated 3500 psi and above usually come with a DIN valve rather than the common K (yoke) valve adapter found on most American regulators. We provide our high pressure tanks with a combination valve that can be used with either a DIN or K valve type regulator.

Low pressure tanks generally will last many more years than high pressure tanks because of the lesser stress on the tank walls. They are also more commonly used by NITROX divers as being more convenient for some methods of filling. The low pressure will also put less stress on your regulator and other equipment that is connected to your air supply.

One of the most common questions we get from divers is concerning the true meaning of the 10% overfill on tanks. Here are the facts.
Aluminum tanks never get an overfill. It is only used on steel tanks.
The overfill on steel tanks is only allowed on tanks that have a + sign stamped after the date of their most recent hydro test. The first date on a tank is the legally required test done by the manufacturer before he sells the tank.
If there is a + sign after the date it means that the tank may be filled to a pressure 10% higher than the pressure stamped on the tank.
If there is no + sign after the latest date on the tank, the tank may only be filled to the exact pressure stamped on that tank.
It is possible that a tank will not get that + sign after its second or third hydro test. That will tell you that the tank has been used a lot and can only be filled to the pressure stamped on it.