Features Of Scuba Dive Tanks

Information On Scuba Tank Markings, Tank Valves, And Burst Disks

Sep 12, 2008

Because scuba tanks carry the life-sustaining air during a scuba dive, there are many aspects of a scuba diving tank a scuba diver needs to know.

The last test date is the date the filling station will look for to check the tank is within test and safe to fill.

Testing station stamp identifies the testing station. Some divers put bogus dates on their tanks in an attempt to get them filled. The use of the test station stamp eliminates this problem.

Test pressure is used when testing the tank and is higher than the working pressure. If there is some temptation to fill to this higher test pressure, forget it. The test pressure is just for testing. It is filled to this pressure under a controlled situation and only for a short period.

Water Capacity relates to the size of the tank. It could be expressed in kilograms or litres, as one litre of water weighs one kilogram. The two most common tank sizes are the 88 cubic foot that has a water capacity of 11.2 litres. The 62 cubic foot tank has a water capacity of 8.6 litres.

There may also be the date manufactured, type of material, the empty tank’s weight and, in Australia, the relevant Australian Standard.

Tanks come with two types of valves. They acquired their names from the path the airway takes through the valve.

In the newer valves the path has no close resemblance to the letters, but the names have stuck. The most common in Australia is the K valve. This is a straight on-off valve.

The other type is the J valve that has a reserve system. The air in the tank holds a spring-loaded stem off a seat until the pressure drops to around 2000 kPa. At this point the spring closes the valve stopping the airflow. A lever beside the tank is then used to fully open the valve.

With the modern use of pressure gauges, buddy pairs, alternate air supplies, and dive computers, J valves are rarely used. If using a tank with a J valve with modern equipment, always put the reserve lever down in the ‘dive’ position.

A tank valve should not be turned off with excessive force; it only needs a small nip to stop the flow. Too much pressure can wear the seat. In some situations the seat can be worn so much that when the valve is opened the stem does not clear the seat completely and the airway is not fully open.

With the fancy coloured scuba equipment available there is a temptation to paint tanks. Any painting must be done with extreme caution, as it is not a simple matter of slapping on a new coat. Heat based paint or strippers can change the metal properties of a scuba tank. Usually a good scrub with soap and water will lift the appearance.

Buying Secondhand Tanks

Be wary when buying a second hand tank. It may look perfect outside but inside could be corroded. Or the valve might need a good overhaul. A tank should undergo a hydrostatic test before purchase.

Burst Disk

This is a safety valve built into the valve assembly. It is designed as the weakest point so if overfilled, or if the tank heats up, it will burst and release the pressure.

Scuba tanks, though heavy and tough, are a complex item of scuba gear. For information on the use of scuba tanks, refer to Using Scuba Diving Tanks

The copyright of the article Features Of Scuba Dive Tanks in Scuba Diving is owned by Bruce Iliff. Permission to republish Features Of Scuba Dive Tanks in print or online must be granted by the author in writing.