To what fraction of the service pressure should DOT 3A, 3AA, or 3AL cylinders be tested?

The correct fraction for testing DOT 3A, 3AA, or 3AL cylinders is 5/3 of the service pressure. This means that during the hydrostatic testing process, these cylinders are filled with water and subjected to a pressure that is 5/3 times their rated service pressure to ensure their integrity and safety under working conditions. This testing method is designed to identify any weaknesses or failures in the cylinder's material or construction by ensuring it can withstand pressures greater than those it would typically encounter in service.

Testing at this higher fraction is a standard practice to guarantee that the cylinders remain safe for operational use, thereby minimizing the risk of failure during normal service. The use of a fraction greater than 1, such as 5/3, is essential to provide a safety margin and account for any potential deterioration over time. This rigorous testing helps maintain safety standards and compliance with regulatory requirements for gas cylinders.