In General:

The pressure reducing valve’s function is to reduce and control a pressure downstream of the valve in accordance with a manually set spring tension. If the downstream pressure exceeds the set pressure, the valve closes dead tight, due to its self-centering ball-plug on a soft seat.
The valve is primarily designed for service with hazardous gases. The valve body is constructed of ASTM A105 forged steel to meet the recommendations of The Chlorine Institute for Class IV piping. The upper valve body has provisions for a vent connection so that, in the event of a ruptured diaphragm, the fluid may be vented to an appropriate area. All materials in the flow section of the valve are specifically suited to the flow medium specified. Seat and plug are housed in a completely removable capsule for cleaning or capacity changes