Why do divers need scuba cylinders and tank valves?
Scuba Cylinders and Tank Valves have a similar purpose and function which is to supply the diver with a breathing gas while he's diving. The compressed high-pressure air is safely stored in a cylindrical metal container usually on the diver's back attached to the buoyancy jacket. The valve is attached to the neck of the scuba tank and its main purpose is to control the air flow from the cylinder to the first stage of the regulator.

What are the common sizes and materials for scuba cylinders ?
Scuba cylinders are available in a variety of air capacities, pressure ratings and sizes. The most common sizes for scuba tanks are 8, 10, 12, and 15 litres (water capacity). You may wonder how long 12 litres of compressed air inside a scuba cylinder will last underwater. There are many factors that influence the rate of air consumption, but generally a 12 litre tank of air is about the same amount of air as a walk-in wardrobe. The air pressure increases as it is compressed inside the tank during the filling process, most typically to 200 bar or 3000 psi. Scuba cylinders are made of Aluminum or Steel and both types are subject to regulations of government agencies. Aluminum cylinders usually corrode slower than steel cylinders but generally steel tanks hold a similar quantity of air in a smaller cylinder at higher pressures.

What markings are commonly found on the neck of a scuba cylinder ?
The regulating agencies require cylinder manufacturers to stamp specific information onto the cylinder neck. These markings should indicate the type of material that the cylinder is made of and also the maximum pressure that is permitted inside the cylinder - working pressure. Additional markings could include an identification serial number, dates of all hydrostatic pressure tests and a symbol that might identify the cylinder manufacturer or distributor.

What's the difference between a DIN valve and a yoke valve ?
The K-valve is a simple on/off valve and usually made from chrome-plated brass. Cylinder valves can be identified as a yoke assembly or DIN (Deutschees Institut fuer Normung). The yoke valve is more commonly used by recreational divers globally with the DIN system being a popular screw type assembly in many European countries. Both valve assemblies require an O-ring to secure an air tight seal so this should be checked as part of your equipment setup routine.

What is a burst disk and what's its purpose ?
A burst disk is usually made from copper and adds a safety feature to the valve. The purpose of burst disks is to relieve cylinder over pressurization of the cylinder during the filling process or if it is exposed to excessive heat. If the pressure inside the tank gets too high the burst disk will rupture and release the pressurized air before the cylinder would explode.

What are general safety guidelines and maintenance recommendations for handling scuba cylinders ?
Scuba cylinders are cylindrical shaped to increase their structural strength which makes them heavy and unstable especially when they are standing upright. Always secure unattended and upright tanks or lay them down horizontally and block the cylinder when transporting them in your car. Rinse cylinders and valves with fresh water after the dive and store them away from direct sunlight. The best way to keep moisture out of the scuba tank is not to let it drain completely and always leave around 20 bar of air inside. Have it refilled if the air remains inside for more than six months as it can turn stale. An annual visual inspection inside the cylinder and periodic hydrostatic pressure testing by a trained technician will check for early signs of internal corrosion and always follow the manufacturer's guidelines.