.24 Power Boiler — Existing Installation: Safety Valve.

A. A weighted-lever safety valve or a safety valve having a cast iron seat or disc:

(1) May not be used after October 15, 1975; and

(2) Shall be replaced by a direct, spring-loaded, pop-type valve that complies with the requirements of the ASME Code, Section I.

B. A boiler shall have at least one safety valve.

C. A boiler shall have at least two safety valves if the boiler has:

(1) More than 500 square feet of water-heating surface; or

(2) An electric power input of more than 500 kw.

D. A safety valve shall be:

(1) Connected to the boiler, independent of any other steam connection;

(2) Attached:

(a) As close as possible to the boiler, without unnecessary intervening pipe or fittings; and

(b) With no valve of any type between the safety valve and the boiler; and

(3) Installed in a manner that protects walkways and platforms from discharges.

E. If an escape pipe is used:

(1) There may not be a valve of any type between a safety valve and the atmosphere;

(2) It shall be:

(a) At least the full size of the safety valve discharge; and

(b) Fitted with an open drain to prevent water from lodging in the upper part of a safety valve or escape pipe;

(3) If a safety valve escape pipe has an elbow, the:

(a) Elbow shall be located near the safety valve outlet; or

(b) Escape pipe shall be anchored and supported securely.

F. A boiler shall have sufficient safety valve capacity to discharge all steam the boiler can generate without allowing pressure to rise more than:

(1) 6 percent above the highest pressure to which any valve is set; and

(2) 6 percent above the maximum allowable working pressure.

G. Settings.

(1) At least one safety valve on a boiler shall be set at or below the maximum allowable working pressure.

(2) Additional valves shall be set not more than 3 percent above the maximum allowable working pressure.

(3) The range of settings of all safety valves on a boiler may not exceed 10 percent of the highest pressure to which any valve is set.

H. When two or more boilers, operating at different pressures and safety valve settings, are interconnected, the lower pressure boilers or interconnected piping shall have safety valves of sufficient capacity to prevent over-pressure, considering the maximum generating capacity of all boilers.

I. A boiler supplied with feedwater directly from a water main without the use of feeding apparatus other than a return trap, may not have a safety valve set at a pressure greater than 94 percent of the lowest pressure obtained in the supply main feeding the boiler.

J. Relief Capacity.

(1) The relief capacity of a safety valve shall be tested by one of the following:

(a) An accumulation test (unless the valve is located on a boiler having a superheater or reheater), performed by shutting off all other steam-discharge outlets from the boiler and forcing fires to the maximum. The safety valve relief capacity shall be sufficient to prevent increased pressure in excess of 6 percent of the maximum allowable working pressure.

(b) Measuring the maximum amount of fuel that can be burned, and computing the corresponding evaporative capacity on the basis of the heating value of the fuel, as outlined in the appendix of the ASME Code, Section I.

(c) Measuring the maximum amount of feedwater that can be evaporated.

(2) When either method in §J(1)(b) or (c) is used, the sum of the safety valve capacities shall equal or exceed the maximum evaporative capacity of the boiler.

(3) If relief capacity is insufficient, additional valves shall be provided.