.21 Power Boiler — Existing Installation: Boiler Feed System.

A. A boiler shall have a feed supply which permits it to be fed at any time while under pressure.

B. A boiler having more than 500 square feet of water-heating surface shall have at least two means of feeding, as follows:

(1) One means shall be an approved feed pump, injector, or inspirator;

(2) The other source may be directly from a water main, at a pressure 6 percent greater than the set pressure of the safety valve having the highest setting.

C. A boiler conforming to the ASME Code, PG-61.1, and fired by gaseous, liquid, or solid fuel in suspension may have a single feed supply provided that means are furnished for the immediate shutoff of heat input if the water feed is interrupted.

D. Feedwater shall be fed into a boiler so that it will not be introduced:

(1) Near a riveted joint of a shell or furnace sheet; or

(2) Directly against a surface exposed to:

(a) A product of combustion, or

(b) Direct radiation from the fire.

E. Feed Pipe.

(1) Feed pipe shall have a:

(a) Check valve near the boiler; and

(b) Valve or cock between the check valve and the boiler.

(2) When two or more boilers are fed from a common source, the branch to each boiler shall have a valve between the check valve and source of supply.

(3) The inlet of a globe valve on a feed pipe shall be under the disc of the valve.

F. Returns.

(1) When a return is fed back to a boiler by gravity, each return line shall have, as close as practicable to the boiler, a:

(a) Check valve; and

(b) Stop valve placed between the boiler and the check valve.

(2) It is recommended that no stop valve be placed in the supply and return pipe connection of a single boiler installation.

G. Deaerating Heater. When a deaerating heater is:

(1) Not used, the recommended minimum temperature for feedwater is 120F to avoid creating localized stress.

(2) Used, the recommended minimum feedwater temperature is 215F, so that dissolved gases can be released completely.