Scuba tanks are often taken for granted, and overlooked as an integral piece of diving equipment. They are seen as disposable, single use, dull and grey, and are often indistinguishable from one another. However, we rely on our tanks every dive to provide the very essential air we breathe. To dive safely, we should at the very least know the differences between tanks, the safety checks when inspecting our tanks, and the regulations and testing of tanks.
First of all, each tank should have several markings around the tank neck providing the specific details of each tank. These should include the area of manufacture, the material, the working pressure, the serial code, and the hydrostatic pressure test dates. It’s important to know the material of your tank as this will affect its weight throughout the dive. Common aluminium tanks (3AL) actually lose weight throughout a dive as we use up the air from within, typically losing around 2 kg of negative buoyancy. This means divers generally have to carry additional weight with them when using aluminium tanks to stay in control of their buoyancy when approaching the surface to complete their safety stop on low air. Steel tanks (3AA) on the other hand maintain their weight throughout the dive and therefore extra weight is not always necessary.
While studying the details inscribed on the tank, it’s also important to remember to check the tanks hydrostatic pressure test dates. This highlights when the tank was previously tested for its safety and structural integrity by a certified technician. During the test, a tank’s valve is removed and the tank is filled with water inside a special hydro compression barrel where it is pressurised to 140% of its working pressure. The tanks expansion under pressure is measured by water displacement, the amount of which determines a pass or a fail. Upon passing the test, the date is inscribed on the neck and the tank is certified for the next 5 years (or less depending on local laws and regulations). Please remember to always check test dates and only dive on safe and certified tanks!
Tank valve systems also change between tanks. Yolk systems are all fitted with an O ring and require yolk regulators to clamp over the valve to create a seal. Alternatively, DIN tank valves allow DIN regulators to screw into the tank valve for a tighter and more robust attachment. DIN regulators all have their own O ring, and are often used in colder, more strenuous diving where the likelihood of freezing or impact is increased (e.g. Tech, Ice, Cavern, and Cave). Both systems are reliable and used worldwide, yet it is important to know which is which, and how each tank valve and regulator interact.
As few people own their own tank due to travel and transportation difficulties, it’s a good idea to always check a rental tank before setting up your scuba equipment. Firstly you want to make a note of its material, and check the tank is within 5 years or less of its previous hydrostatic pressure test dates. Also make sure it has the right tank valve for your regulators, and that either the tank (yolk) or your regulators (DIN) have an intact O ring. Always check the tank over for any dents or deformities in a visual inspection. Once satisfied it appears in good shape, remember to open the tank valve momentarily to clear any dust or debris before attaching your regulators.
After you’ve done all your checks and you’re happy with your tank, assemble your equipment and you’re good to go diving with the assurance your tank is safe to use. Although heavy, and dull, we truly couldn’t dive without scuba tanks, so try to show a little appreciation and thank the tank!