Modern "code" safety relief valves are not designed to operate continuously, as required in locomotive service. Locomotive style valves are designed for locomotive service. Our Consolidated type pressure relief valves are made to the original Consolidated design, and have the same reliability and durability as the originals. Consolidated did not recertify its locomotive style safety valves in the 1950s due to the lack of demand resulting from the demise of the steam locomotive. Though our pressure relief valves are identical to the original design, they are not National Board certified safety valves, as it is not economically feasible to have National Board recertify the design due to the small quantities required by steam locomotives today. If your jurisdiction requires a "code" safety valve, a practical solution is to install a "code" valve set at MAWP, as the "high pop," and a Strasburg Rail Road pressure relief valve, set at 5 PSI below MAWP, as the "low pop." This avoids lifting and wearing out the "code" safety valve.