D.C. Mun. Regs. tit. 12, r. 12-E1014
Insert a new Section 1014 in the Mechanical Code to read as follows:
General. Each unfired pressure vessel shall be protected by safety and relief valves and shall be provided with indicating and controlling devices to ensure its safe operation. These valves and devices shall be so constructed, located and installed that they cannot readily be rendered inoperative.
Safety valves. The relieving capacity of safety valves shall be such as to prevent pressure in the vessel from rising to more than ten percent (10%) above the maximum allowable working pressure, taking into account the effect of static head. Safety valve discharge shall be carried to a safe place.
Type of safety valve. Each pressure vessel safety valve shall be of the direct spring-loaded type, having a substantial lever- lifting device so that the disk can be lifted from its seat by the spindle not less than ? th the diameter of the valve when the pressure of the vessel is seventy-five percent (75%) of that at which the safety valve is set to open.
Marking. Every pressure vessel valve shall be marked "ASME" or "National Board Standard," and shall bear the following information:
Prohibited safety valves. Safety valves having either the seat or disk of cast iron shall not be used.
Multiple safety valves. If more than one safety valve is used, the discharge capacity shall be taken as the combined capacity of all valves.
Pressure relief in unfired pressure vessels. For vessels in which pressure is not generated but is derived from an outside source, each safety valve shall be so connected to the vessel, vessels or system which it protects as to prevent pressure from rising beyond the maximum allowable pressure in any vessel protected by the safety valve.
Pressure relief in other than unfired pressure vessels. For vessels in which pressure may be generated, the safety valve or valves shall be connected directly to the vessel that is to be protected or to a pipe line leading to the vessel. The internal cross-sectional area of the pipe line shall be not less than the nominal area of the safety valve or valves used, and without any intervening valve between the vessel and the safety valve or valves protecting it.
Pressure relief escape pipe. When an escape pipe is used, it shall be full- sized and fitted with an open drain to prevent liquid from lodging in the upper part of the safety valve, and no valve of any description shall be placed on the escape pipe between the safety valve and the atmosphere.
Escape pipe fittings. When an elbow is placed on an escape pipe, it shall be located close to the safety valve outlet or the escape pipe shall be securely anchored and supported. When two or more safety valves are placed on one connection, this connection shall have a cross-sectional area at least equal to the combined area of these safety valves.
Freeze protection. Each safety valve which is exposed to a temperature of 32 °F (0 °C) or less shall have a drain at least ? inch (9.5 mm) in diameter at the lowest point where water can collect.
Spring adjustment. Safety- valve springs shall not be adjusted to carry more than 10 percent greater pressure than that for which the springs were made.
Valve testing. Each safety valve shall be tested at least once every day by raising the disk from its seat.
Valve sizing. Safety valves for compressed air tanks shall not exceed 3 inches (75 mm) in diameter and shall be sized for the maximum flow of free air that can be supplied, as determined in Section VIII, Division 1, Part UG, paragraph UG-133, "Determination of Pressure Relief Requirements" in the ASME Code.
Use of rupture disks. Rupture disks or heads used for supplemental protection of pressure vessels shall be designed to fail at a pressure above the safety or relief valve setting.
Multiple vessels. When two or more unfired pressure vessels that are allowed different pressures are connected to a common source of pressure, all safety valves shall be set at a pressure not exceeding the lowest vessel working pressure allowed.
D.C. Mun. Regs. tit. 12, r. 12-E1014