A-A-50558 Valves, Pressure Regulating, Steam No S/S DocumentThis commercial item description covers steam pressure regulating valves that transform steam from a specified initial pressure to a specified final reduced discharge pressure or range of pressures. The specified inlet steam pressures range from 15 pounds per square inch gage psig to 1,500 psig 103 kiloPascals gage kPagage to 10,343 kPagage. The steam pressure regulating valves covered by this commercial item description are intended for transforming steam from a specified initial pressure to a specified final reduced discharge pressure or range of pressures in steam systems.

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A-A-50558

Class 900 - 900 psig (6205 kPa(gage)) WSP at 750°F (399 C). Class 1200 - 1200 psig (8274 kPa(gage)) WSP at 750°F (399 C). Class 1500 - 1500 psig (10,343 kPa(gage)) WSP at 750°F (399 C).

Sizes (inches nominal pipe size): 1/4 (8 mm), 3/8 (10 mm), 1/2 (15 mm), 3/4 (20 mm),

1 (25 mm), 1-1/2 (40 mm), 2 (50 mm), 2-1/2 (65 mm), 3 (80 mm), 4 (100 mm), 5 (125 mm),

6 (150 mm), 8 (200 mm), 10 (250 mm) and 12 (300 mm).

Sizes (inches outside diameter): 14 (355.6 mm) and 16 (406.4 mm).

3. SALIENT CHARACTERISTICS.

3.1 Description. The pressure reducing valves shall automatically reduce the specified initial steam pressure to the specified final reduced pressure or pressure range, at all conditions of flow between the minimum and maximum flow specified, without hunting, cycling, fluttering, or chattering. The motion of operating parts shall be smooth, non sticking, and free of perceptible backlash. The valves shall be fully adjustable over the specified operating range, without the replacement of springs or diaphragms. Unless otherwise specified (see 7.2), the valves shall be designed to permit replacement of readily removable parts without removal of the bodies from the line. All parts necessary for satisfactory operation of the valves shall be supplied.

3.1.1 Type I. Type I valves shall consist essentially of valve body and diaphragm, bellows, or piston-operated valve, loaded by means of a spring, weight and lever, air dome, or air tank. The valves shall be completely self-contained, direct-operated valves, controlled by the steam pressure within the reduced-pressure chamber of the valve body without the use of external piping.

3.1.2 Type II. Type II valves shall consist essentially of valve body, main valve with a

spring-loaded diaphragm or piston-operator, and a pilot valve with a spring-loaded diaphragm operator. The valves shall be completely self-contained, pilot-operated valves, controlled by means of an intermediate steam pressure supplied by the pilot valve, built integral with, or rigidly attached to the body of the main valve. The pilot valve shall be controlled by the pressure within the reduced-pressure chamber of the main valve.

3.1.3 Type III. Type III valves shall consist essentially of valve body and a diaphragm, or bellows operator, loaded by means of a spring, weight and lever, air dome, or air tank. The diaphragm or bellows chamber shall be provided with a tap for the connection of the feeler pipe, but the feeler pipe will not be required with the valve. The valves shall be direct operated, controlled by the reduced-steam pressure by means of the external feeler pipe connected at some point in the reduced-pressure line on the downstream side of the valve.

3.1.4 Type IV. Type IV valves shall consist essentially of a main valve with a spring-loaded diaphragm operator, a pilot valve with a spring or weight and lever-loaded diaphragm operator, and any necessary restricting or throttling valves. The diaphragm chambers of the main and pilot valves shall be provided with taps for the connection of feeler and control piping, but the feeler and control piping will not be required with the valve. The main valve shall be controlled by the