N.Y. Comp. Codes R. & Regs. tit. 12, § 14-9.9 – Valve capacity.

(a) The minimum safety valve or safety relief valve relieving capacity for other than electric boilers, waste heat boilers, organic fluid vaporizer generators, and forced-flow steam generators with no fixed steam and waterline, when provided in accordance with section 14-9.5(c) of this Subpart shall be determined on the basis of the pounds of steam generated per hour per square foot of boiler heating surface and waterwall heating surface, as given in the following table:

(1) The required steam relieving capacity in lb/hr of the safety relief valves on a high-temperature water boiler shall be determined by dividing the maximum output in Btu/hr at the boiler nozzle obtained by the firing of any fuel for which the unit is designed, by 1000.
(2) Any economizer which may be shut off from the boiler, thereby permitting the economizer to become a fired pressure vessel, shall have one or more safety relief valves with a total discharge capacity, calculated from the maximum expected heat absorption in Btu/hr, as determined by the manufacturer, divided by 1000. This absorption shall be stated in the stamping.
(3) The required relieving capacity in pounds per hour of the safety or safety relief valves on a waste heat boiler shall be determined by the manufacturer. When auxiliary firing is to be used in combination with waste heat recovery, the maximum output shall include the effect of such firing in the total required capacity. When auxiliary firing is to be used in place of waste heat recovery, the required relieving capacity shall be based on auxiliary firing or waste heat recovery, whichever is higher.
(4) The minimum safety valve or safety relief valve relieving capacity for electric boilers shall be 3½ lb/hr/kw input.
(5) Organic fluid vaporizer generators require special consideration as given in the ASME Code.

Minimum pounds of steam per hour per square foot of surface

Boiler heating surface

	Hand-fired	Stoker-fired	Oil, gas, or pulverized-fuel-fired	Hand-fired	Stoker-fired	Oil, gas, or pulverized-fuel-fired
Fire-tube boilers	5	7	8	8	10	14
Water-tube boilers	6	8	10	8	12	16

Note: When a boiler is fired only by a gas having a heat value not in excess of 200 Btu per cubic foot, the minimum safety valve relieving capacity may be based on the values given for hand-fired boilers above.

(b) In many cases a greater relieving capacity of safety valves will have to be provided than the minimum specified by this Subpart and in every case the requirements of this section shall be met.
(c) The heating surface shall be computed as follows: Heating surface, as part of a circulating system in contact on one side with water or wet steam being heated and on the other side with gas or refractory being cooled, shall be measured on the side receiving heat. Boiler heating surface and other equivalent surface outside the furnace shall be measured circumferentially plus any extended surface. Waterwall heating surface and other equivalent surface within the furnace shall be measured as the projected tube area (diameter × length) plus any extended surface on the furnace side. In computing the heating surface for this purpose, only the tubes, fireboxes, shells, tubesheets, and the projected area headers need be considered, except that for vertical firetube steam boilers, only that portion of the tube surface up to the middle gage cock is to be computed. The minimum number and size of safety valves required shall be determined on the basis of the aggregate relieving capacity and the relieving capacity marked on the valves by the manufacturer. Where the operating conditions are changed, or additional heating surface such as water screens or waterwalls is connected to the boiler circulation, the safety valve capacity shall be increased, if necessary, to meet the new conditions. The additional valves required on account of changed conditions may be installed at the boiler outlet or on the steam line between the boiler and the main stop valve except when the boiler is equipped with a superheater or other piece of apparatus, in which case they may be installed on the steam pipes between the boiler drum and the inlet to the superheater or other apparatus, provided that the steam main between the boiler and points where a safety valve or valves may be attached has a cross-sectional area at least three times the combined areas of the inlet connections to the safety valves applied to it.
(d) If the valve capacity cannot be computed or if it is desirable to prove the computations, it may be checked in any one of the three following ways, and if found insufficient, additional capacity shall be provided:
1. (1) By making an accumulation test, that is, by shutting off all other steam-discharge outlets from the boiler and forcing the fires to the maximum. The safety valve equipment shall be sufficient to prevent an excess pressure beyond that specified in section 14-9.9(e) of this Subpart. This method should not be used on a boiler with a superheater or reheater or on a high-temperature water boiler.
2. (2) By measuring the maximum amount of fuel that can be burned and computing the corresponding evaporative capacity upon the basis of the heating value of the fuel (see section 14-9.9[a] of this Subpart).
3. (3) By determining the maximum evaporative capacity by measuring the feedwater. The sum of the safety valve capacities marked on the valves shall be equal to or greater than the maximum evaporative capacity of the boiler. This method shall not be used on high-temperature water boilers.
(e) The valve capacity for each boiler shall be such that the valve or valves will discharge all the pressure that can be generated by the boiler without allowing the pressure to rise more than six percent above the highest pressure at which any valve is set and in no case to more than six percent above the maximum allowable working pressure. The maximum capacity of a boiler shall be determined by the manufacturer and shall be based on the capacity of the fuel-burning equipment, on the air supply, draft, etc.