In open-circuit SCUBA systems, a variety of gas mixtures are used, and the breathing gas is expelled out of the circuit after each breath.
Closed-circuit systems are employed when oxygen is the sole gas used. They recycle the spent gas from the diver by filtering carbon dioxide and returning unused oxygen.
The gas cylinder is a storage vessel constructed of steel or aluminum that allows gas (commonly air, though other gas mixtures are frequently used) to be stored at high pressure. SCUBA gas cylinders are visually inspected annually and hydrostatically tested every five years to ensure they are not compromised by corrosion, defects or fatigue.
A pillar valve is screwed into the neck of the cylinder, allowing the air to be released from the cylinder. Once opened, high-pressure gas is allowed to flow to a low-pressure environment. This allows the valve to work in both directions for filling the gas cylinder and then using the gas cylinder. Because the gas released from the pillar valve is at high pressure, the attachment of a regulator is required to make the gas usable for breathing. Pillar valves are equipped with a burst disc that allows gas to escape in the event of over-pressurization.
Types of Pillar Valves
Pillar valves used in open-circuit SCUBA are yoke-valves and DIN valves, each differentiated by how a regulator attaches to the body of the valve.
Article Written By David Chandler
David Chandler has been a freelance writer since 2006 whose work has appeared in various print and online publications. A former reconnaissance Marine, he is an active hiker, diver, kayaker, sailor and angler. He has traveled extensively and holds a bachelor's degree from the University of South Florida where he was educated in international studies and microbiology.