A scuba cylinder is important in storing and in delivering the right amount of breathing pressure to divers by adjusting the demand valve of a diving regulator. These scuba diving tanks are required to undergo a cylinder test or cylinder testing from time to time. This cylinder test is to ensure that the cylinder is functioning properly when in use.
Cylinder testing times differ from some countries to another. The scuba cylinder test is categorized into two main parts which are the visual inspection which is conducted every 2.5 years and the hydrostatic testing that is recommended every five years in the European Union. In some countries such as Norway, a visual and hydrostatic test is demanded after 3 years from the date the tank was manufactured and again, a continuous testing of the scuba tank every 2 years. In Australia, scuba tanks are tested every 12 months thereafter.
The visual cylinder test is done by a certified dive shop. During the visual inspection of the scuba cylinders, the examination of the interior and exterior parts is conducted by a properly trained technician in the field. The inspectors open the diving tank and check it inside out. They will check for possible presence of corrosions and physical damages. The diving cylinder is considered to fail the visual test if a dent is detected that is greater than 2mm, the wall thickness was reduced to greater than 25% of its original measure, if the thickness of the wall is no longer visible, a great amount of tread damage is noted and if the weight of the cylinder without the valve has been less than 95% of the weight that is recorded on the cylinder's stamp.
Scuba dive tanks which fail this test will be subjected to pressure testing and will be fixed before allowing it to be used again. If the device passes the visual scuba cylinder test, a sticker will be stamped on it proving that the scuba tank is safe to be refilled and reused. Scuba shops will not refill tanks whose stickers which are out of date.
This cylinder testing is commonly done by pressurizing the scuba tank cylinders. This process will evaluate the flexing capacity of the tank walls. This hydrostatic testing is performed by replacing the valve with special testing connection and by loading the tank with water under pressure. The scuba cylinder is placed under water. A certain amount of pressure will be administered to the liquid. The level of water increases as the tank is being pressurized. This is how scuba cylinder technicians measure the amount of the tank's expansion. If the tank will not meet the specification requirement of safety, it fails the test.
Another usual way of determining if the tank fails the cylinder test is when the valve threads go off making a loud noise. There are also incidents when during cylinder testing, the bottom of the cylinder bursts open which takes place because of corrosion. Only scuba cylinders which pass this test will be stamped with a current test paper with the name of the cylinder testing company, the year and month of testing. The scuba diving tanks which were not successful during inspection, will not be given the stamp and will never be refilled with air again.