By Alec Peirce and Selene Muldowney
Hey Divers – Alec Peirce again with more tech tips!
We are here to make diving a little more fun and a little easier.
We are talking about scuba tanks today; most folks believe that tanks are the most vital part of diving. Certainly, they are very important since it gives you the air you need to breathe. They can however, give you problems if not taken care of. Some folks do not own their tanks and instead rent them for about $15 a day. Others buy their own tanks and have to fill them for about $10 per dive. Divers who travel overseas generally rent them.
Sometimes there is some confusion about tanks as they can appear to be somewhat mysterious. There is nothing mysterious – an aluminum bottle that gets filled with filtered, compressed air is the standard scuba tank today. Pretty much what you will find anywhere in the world is the 80 cubic foot aluminum tank. Safe to use and meets all government standards. This particular tank is made by Catalina, one of the biggest tank manufacturers in the world. There are not many companies that make tanks as it is a big investment.
Let’s look at this tank: two tests must be performed on a regular basis to every scuba tank. The first one is called a Visual Inspection, which is unique to scuba. Other pressure cylinders do not need this test. The reason it is unique to scuba is because it is a marine sport taking place next to water and salt water is hard on tanks. Also, sorry to say this, but divers are not known to be very careful about their equipment.
What is involved in an annual Visual inspection?
Tanks need to be checked regularly to make sure they are safe to use so are inspected every twelve months by a qualified scuba tank inspector. The inspector looks at it inside and out, looking for corrosion and other problems. If there are problems sometimes you may be able to get it fixed. If the tank is safe to use the inspector places a sticker on it otherwise the tank could be scrapped.
The inspector opens the tank and removes the valve, standard on high pressure devices. One exception is that scuba valves include an internal dip tube. The dip tube is needed because scuba cylinders are used in water and in an upside-down position, any water inside the tank will run down the cylinder into the tank valve causing corrosion. The dip valve blocks water from entering the tank valve – it is a great idea.
The inspector then checks the valve, there are two O rings – a big O ring that seals the neck and a small one that seals the face. Always replace them as they cost just a couple of dollars. The inspector already looked at the outside of the tank to make sure there are no scratches or dents and removed any tank boot to look under it. They inspect the threads very carefully to make sure that over a period of time under sustained pressure they have not corroded. We use a special device that is highly magnified to check it all very carefully.
Next they look inside the tank with a special light called a visual inspection light that essentially throws shadows on the walls. We look to make sure the sides are smooth and clean. If we find any black particles or white powder we have to clean it out. This is simple but does require training. Once that is all done and the inspector is satisfied it is re-assemble and pressurized to an appropriate pressure. They then attach a sticker to the tank with the name of the company that did the visual inspection and the date. This is a fairly inexpensive test.
What is involved in a 5 year hydrostatic test?
The other test that must be done every five years it is called the hydrostatic test. The government regulations and training are complicated and not worth the money for a local dive shop to do so tanks go to large professional testing facilities. Tanks are stripped down and taken to a hydrostatic test station to measure the tanks metal elasticity. Every time you fill a tank it changes size. The test checks the elasticity of the tank is within acceptable amounts. Once the test is completed and passes, they stamp data into the tank metal. Every five years it is stamped so you can see the complete history of the tanks hydrostatic tests.
These are two tank tests – both very important, are relatively inexpensive and exist to keep your diving safe. It is well worth the price.
Hope you found this subject interesting and looking forward to seeking you soon,
Please check out the many wonderful videos produced by Alec Peirce and enjoy them as much as we have! The wealth of knowledge he shares from both learning from experience and learning from mistakes, has helped many divers become safer divers as well as more active in our sport!