This Standard Practice establishes requirements and criteria for 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" 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 new SP-154 are intended for use in applications where shock loadings are not encountered and 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: 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, provides a seal against pressure from both ends of the valve with a means of venting/bleeding the cavity between the seating surfaces.