Current through Register Vol. 54, No. 44, November 2, 2024
Section 3a.27 - Different working pressures(a) At least one safety valve on each boiler must be set at or below the maximum allowable working pressure. All other valves may be set within a range of 3% above the maximum allowable working pressure. The range of setting of all of the saturated steam valves on the boiler may not exceed 10% of the saturated steam valve set at the highest pressure.(b) When a boiler system is comprised of boilers with different maximum allowable working pressures having minimum safety valve settings varying more than 6% and connected so that steam flows toward the lower pressure boiler, the boiler system must meet one of the following requirements:(1) A check valve must be installed in the steam line to protect the lower pressure boilers.(2) Additional safety valves on the low-pressure side of the boiler system must protect lower pressure boilers and meet the following requirements: (i) The additional safety valve capacity must be based on the maximum amount of steam that can flow into the low-pressure system.(ii) Additional safety valves must have at least one valve set at a pressure that is not greater than the lowest maximum allowable pressure.(iii) Other valves must be set within a range of not more than 3% above the lowest allowable pressure.