Conversion. Beverage containers to aviation oxygen cylinders. With the outside and inside of non-shatterable oxygen cylinder for high altitude flying complete, several rigorous tests are applied to guarantee safety. Every cylinder off the production line of the metal division of a large Eastern rubber factory is hydrostatically tested at 800 pounds pressure, twice the pressure maintained in the cylinder under normal use, to test the strength of the welding. It is then given air test at 400 pounds pressure as shown above. Here, an attendant is placing a cylinder into a steel compartment filled with water before the pressure is applied. By means of a hand crank, the inspector rotates at all points. Firestone, Akron, Ohio. Sourced from the Library of Congress.