Hydrostatic Tank Testing, this is what happens.Everyday life is full of rules and regulations and the scuba industry sure has it's fair share. When it comes to hydrostatic tank testing the regulations are more than important, they are crucial.Each country has it's own set of guidelines, which govern the use, maintenance and transportation of pressure vessels, which scuba cylinders are one of. These laws are pretty similar because a pressure vessel is the same wherever you are and the things that go wrong can only be safely checked in certain ways. In the US the Department of Transportation sets the rules and regulations in respect to the maintenance and use of scuba cylinders and they require hydrostatic tank testing every five years. In other countries it is less, Australia require scuba cylinders to be hydrostatically tested every year. What is Hydrostatic Tank TestingA hydrostatic test is the most common way in which a scuba tank is tested for any leaks or flaws.During a hydrostatic tank test a qualified technician fills your scuba tank with an incompressible liquid, water is there weapon of choice, which is the safest, if the tank does fail and ruptures whilst under pressure it will not explode like pressurised air would. The test pressure exerted is 5/3 the normal pressure stamped on the side of your tank. So if your tanks standard fill is 3,000 psi, they will pressurise it to 5,000 psi with water. How do they do Hydrostatic Test my Scuba Tank?Your scuba tank is first filled with water from a high pressure water pump and then submerged into a sealed chamber, which is also filled with water.The sealed chamber is connected to a calibrated burette for measuring. Your scuba cylinder is then pressurised to it's test pressure and held there for a maximum of 30 seconds. The water pressure inflates your scuba tank which expands and forces the water out of the sealed chamber into the calibrated burette. After 30 seconds the total amount of water that has spilled into the burette is recorded, this is called the Total Expansion. Now as the pressure in your scuba tank is released and your tank deflates, it shrinks back to almost it's normal or pre-pressure size. The water that was in the burette is allowed to return to the main chamber, but not all of the water will return as your scuba tank has been stretched. the stretching is called Permanent Expansion and the difference between the Total Expansion and the Permanent Expansion is called the Elastic Expansion, lot's of expansion here. There is a formula used to determine the percent expansion which is: Percent Expansion = (Permanent Expansion / Total Expansion) x 100 Your scuba cylinder is condemned when the Percent Expansion exceeds the predetermined limits set for your particular cylinder. Once your scuba tank has passed the hydrostatic tank testing, it will be cleaned and dried. The outside of the cylinder will then be stamped with the current month and year, and will allow the tank to be refilled for another 5 years before another hydro test is required. Why do we need to Hydrostatic Test our Cylinders?The hydrostatic tank test ensures that your scuba cylinder can safely hold it's rated pressure, after all we don't want our scuba tank exploding on us , a bit like wearing a missile on our back! Well not quite, but I guess you get the picture as to why it is important.How do I know what all the markings on my scuba tank are for? Easy have a look here. If you are interested to know more about Scuba Tanks then click here this will tell you all you need to know. |
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