(1) The maximum allowable working pressure of standard boilers shall be determined by the applicable sections of the codes under which they were constructed and stamped. The maximum allowable working pressure on the shell of a nonstandard boiler or drum shell shall be determined by the strength of the weakest section of the structure computed in accordance with formulas provided by the national board of boiler and pressure vessel inspectors or any other nationally recognized engineering authority.

(2) Each power boiler having not more than five hundred square feet of water-heating surface shall have at least one approved safety valve. Each boiler having more than five hundred square feet of water-heating surface shall have two or more approved safety valves.

(3) The safety valve capacity of each power boiler shall be that which will discharge all the steam that can be generated by the boiler without allowing the pressure to rise more than six percent above the highest pressure any valve is set, and in no case to more than six percent above the maximum allowable working pressure.

(4) Power boilers equipped with one safety valve shall have the safety valve set at or below the maximum allowable working pressure. If additional valves are used, the highest pressure setting on additional valves shall not exceed the maximum allowable working pressure by more than three percent.

(5) When two or more power boilers operating at different pressures and safety valve settings are interconnected, the lower pressure boilers or interconnected piping shall be equipped with safety valves of sufficient capacity to prevent overpressure, considering the generating capacity of the boiler with the lowest allowable pressure.

(6) All power boilers shall have a water-feed supply which will permit the boilers being fed at any time while under pressure.

(7) Power boilers that are fired with solid fuel not in suspension and having more than five hundred square feet of water-heating surface shall have at least two means of feeding water. Each source of feeding shall be capable of supplying water to the boiler at a pressure of six percent higher than the highest setting of any safety valve on the boiler, and one such source of feeding shall be steam-operated.

(8) Power boilers fired by gaseous, liquid, or solid fuel in suspension and having less than five hundred square feet of water-heating surface may be equipped with a single source of feeding water if:

(a) Means are provided for immediate shutoff of heat release;

(b) The boiler furnace and fuel system do not retain sufficient stored heat to cause damage to the boiler if the water-feed supply is interrupted.

(9) Power boilers that have a water-heating surface of not more than one hundred square feet shall not have water-feed piping and connection to the boiler smaller than one-half inch pipe size. For boilers having a water-heating surface of more than one hundred square feet, the water-feed piping and connection to the boiler shall not be less than three-fourths inch pipe size. The feed water shall be introduced into a boiler in such a manner that the water will not be discharged directly against surface-exposed gases of high temperature or to direct radiation from the fire or near any riveted joints of the furnace sheets or shell. The water-feed pipe shall be provided with a check valve near the boiler and a valve or cock between the check valve and the boiler. When two or more boilers are fed from a common source, there shall be a regulating valve on the branch to each boiler between the check valve and the source of supply. In all cases where returns are fed back to the boiler by gravity, a check valve and stop valve shall be on each return line, the stop valve placed between the boiler and the check valve, and both shall be located as close to the boiler as practicable.

(10) Fire-actuated plugs, if used, shall conform to the requirements of the A.S.M.E. boiler and pressure vessel code for power boilers.

(11) No outlet connections, except for damper regulator, feed-water regulator, low-water fuel cutout, drains, or steam gauges, shall be placed on the piping that connects the water column or gauge glass to the boiler. The water column shall be provided with a drain valve of at least three-fourths of an inch pipe size.

(12) Each power boiler, except forced flow steam generators designed to operate without a fixed water level, shall have at least one water-gauge glass; except that boilers operated at pressures over four hundred PSI shall be provided with two water-gauge glasses which may be connected to a single water column or connected directly to the drum, in which case they shall conform to A.S.M.E. requirements. The gauge-glass connections and pipe connections shall not be less than one-half inch pipe size. Each water-gauge glass will be fitted with a drain cock or valve. When the boiler operating pressure exceeds one hundred PSI, the glass will be fitted with a globe or gate-valved drain.

(13) The lowest visible part of the water-gauge glass shall be at least two inches above the lowest permissible water level, which level shall be that at which there will be no danger of overheating any part of the boiler when in operation at that level. This subsection (13) does not apply to forced flow steam generators which are designed to operate without a fixed water level.

(14) Each power boiler shall have a steam gauge, with dial range not less than one and one-half times the maximum allowable working pressure, connected to the steam space or to the steam connection to the water column. The steam gauge shall be connected to a siphon or equivalent device of sufficient capacity to keep the gauge tube filled with water and so arranged that the gauge cannot be shut off from the boiler except by a cock placed near the gauge and provided with a tee or lever handle arranged to be parallel to the pipe in which it is located when the cock is open.

(15) Each power boiler shall be provided with a one-fourth inch nipple and globe valve connected to a steam space for the exclusive purpose of attaching a test gauge when the boiler is in service so the accuracy of the gauge may be ascertained.

(16) Steam-gauge connections shall be suitable for the maximum allowable working pressure and steam temperature; if the temperature exceeds four hundred degrees Fahrenheit, brass or copper pipe or tubing shall not be used.

(17) When a steam-gauge connection longer than eight feet becomes necessary, a shutoff valve may be used near the boiler if the valve is of the outside-screw-and-yoke type and is locked open when the boiler is in operation. The line shall be of ample size with provisions for free blowing.

(18) Each steam-discharge outlet, except a safety valve, shall be fitted with a stop valve located as close as practicable to the boiler. When such outlets are over two-inch pipe size, the valve used on the connection shall be the outside-screw-and-yoke rising spindle type to indicate, at a distance, the position of its spindle, whether it is closed or open. The wheel may be carried either on the yoke or attached to the spindle.

(19) When power boilers provided with manholes are connected to a common steam main, the steam connection from each boiler shall be fitted with two stop valves having ample free-blow drain between them. The discharge of this drain shall be visible to the operator while manipulating the valves and shall be piped clear of the boiler setting. The stop valve shall consist preferably of one automatic nonreturn valve set next to the boiler and a second valve of the outside-screw-and-yoke type; or two valves of the outside-screw-and-yoke type may be used.

(20) Each power boiler shall have a blow-off pipe fitted with a valve or cock. All fittings and pipe shall conform to the applicable section of the A.S.M.E. boiler and pressure vessel code.

(21) Provisions shall be made for the expansion and contraction of steam mains connected to power boilers by providing substantial anchorage at suitable points so undue strain shall not be transmitted to the boiler. Steam reservoirs shall be used on steam mains when heavy pulsations of the steam currents cause vibration of the boiler shell plates.

(22) All power boilers heated with gas, oil, or mechanical firing, except stoker- or hand-fired coal-burning units which are constantly attended, shall be provided with an automatic low-water fuel cutout and with an automatic fuel-regulating control, controlled by boiler pressure.

(23) All cases not specifically covered by this article shall be treated as new installations or may be referred to the director for instructions concerning the requirements.