Inspections and tests on regulators and relief valves are a Department of Transportation (DOT) compliance rule. The sections within the DOT manual stating the rule include 192.351 through 192.359, 192.751, 192.479, 192.481, 192.739, and 192.741. Keep in mind; these rules are the minimum required tests. Your company or governing regulatory agency may be more stringent and require more detailed testing. You must also keep in mind that the manufacturer of your equipment will provide guidelines pertaining to maintenance of the equipment. These tests are not only required for safe, reliable service to your customers, but the results could also be used in any legal proceeding for documentation purposes.