CSA B64 Series:21

1 Scope 1.1 This Standard covers atmospheric vacuum breakers (AVB). 1.2 In this Standard, “shall” is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with each Standard in the Series; “should” is used to express a recommendation or that which is advised but not required; and “may” is used to express an option or that which is permissible within the limits of the Standards in the Series. Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material. Notes to tables and figures are considered part of the table or figure and may be written as requirements. Annexes are designated normative (mandatory) or informative (non-mandatory) to define their application. 1.3 This Standard is written in SI units, which are the units of record for the purposes of this Standard. For conversion tables, see Annex A of CSA B64.0. Vacuum is expressed in pressure below ambient. All pipe sizes are shown as nominal pipe sizes (NPS).