MSS - Manufacturers Standardization Society of the Valve and Fittings Industry.
Scope
SCOPE AND FIELD OF APPLICATION This Standard Practice covers stainless-steel-lined@ cast@ or fabricated bonnetless@ low pressure knife gate valves that are designed and manufactured to serve as a ??Double Block and Bleed??(1) single valve system in pipelines. These valve types shall have flanged body designs compatible with ASME B16.5 flanges for NPS 2 (DN 50) through NPS 24 (DN 600)@ ASME B16.47 Series A flanges for NPS 26 (DN 650) through NPS 36 (DN 900). The valves identified in this Standard Practice are intended for use in applications where shock loadings are not encountered. Applications at conditions other than those specified in Section 3 require special design consideration. The valves identified in this Standard Practice are intended for use in applications where a ??Double Block and Bleed?? type of isolation is required@ and where two individual isolation valves with a removable or drain-containing spool piece between them is typically used. NOTE: (1) For the purpose of this Standard Practice@ ??Double Block and Bleed?? refers to a valve (or valve application) with two seating surfaces that@ in the closed position@ provide a seal against pressure from both ends of the valve with a means of venting/bleeding the cavity between the seating surfaces.