MSS - Manufacturers Standardization Society of the Valve and Fittings Industry.
Scope
This Standard Practice applies to valves for gen-eral liquid and gas service that effect valve closure by means of a resilient diaphragm sealing against a weir or a diaphragm acting in conjunction with a separate or integral disk-member sealing against a seat@ having equal sealing capability in either flow direction@ and having diaphragms being essentially made of elastomeric or plastic material or combinations thereof. This Standard Practice defines the following categories of valves: a) Class 125 or 150 Valves; b) Standard Valves; c) Valves for Special (Low Pressure) Applications. The purchaser@ when referencing the Standard@ shall also specify the appropriate category as listed above. This Standard Practice covers the following: a) Pressure-Temperature Ratings and Design requirements; b) Commonly Used Diaphragm Pressure Limitations; c) Body@ Bonnet@ and Bolting Materials; d) Commonly Used Face-to-Face Dimensions for Flanged Valves; e) Body End Connections and Wall Thicknesses; f) Actuator Application Requirements; g) Tests; h) Marking.