Storage Cylinders

Storage Cylinders

(a) Low-pressure Cylinders

Most military aircraft at one time used a low-pressure oxygen system in which the gaseous oxygen was stored under a pressure of ap­proximately 450 psi in large steel cylinders painted yellow. These cylinders were so large for the amount of oxygen they carried that they never became popular in civilian aircraft, and even the military has stopped using these systems.

(b) High-pressure Cylinders

Today, almost all gaseous oxygen is stored in green painted steel cylinders under a pressure of between 1,800 and 2,400 psi. All cylinders ap­proved for installation in an aircraft must be ap­proved by the Department of Transportation (DOT) and may be of either the DOT 3AA 1800 or the DOT 3HT 1850 type.

Both types of cylinders must be hydrostatically tested to 5/3 of their working pressure, which means that the DOT 3AA cylinders are tested with water pressure of 3,000 psi every five years and stamped with the date of the test. DOT 3HT cylinders must be tested with a water pressure of 3,083 psi every three years, and these cylinders must be taken out of service after 15 years, or after they have been filled 4,380 times, whichever comes first.

All oxygen cylinders must be stamped near the filler neck with the approval number, the date of manufacture, and the dates of all of the hydros­tatic tests. It is extremely important before servic­ing any oxygen system that you ensure that all cylinders are proper for the installation and that they have all been inspected within the ap­propriate time limit.

Oxygen cylinders may be mounted permanently in the aircraft and connected to an installed oxygen plumbing system, or for light aircraft where oxygen is needed only occasionally, they may be carried as a part of a portable oxygen system. The cylinders for either type of system must meet the same requirements, and should be painted green and identified with the words AVIATORS BREATH­ING OXYGEN written in white letters on the cylinder.

9.2.2 Regulators: It is the oxygen regulator that determines the type of system we have. There are two basic types of regulators in use, and in each type we have variations. For low-demand systems, such as are used in the smaller piston-engine powered general aviation aircraft, we normally use a con­tinuous flow regulator that allows oxygen to flow from the storage cylinder regardless of whether the user is inhaling or exhaling. Continuous flow systems are not economical of the oxygen, but their simplicity and low cost make them desirable when the demands are low. The emergency oxygen systems that drop the mask to the pas­sengers of large jet transport aircraft in the event of cabin depressurization are also of the con­tinuous flow type.