BACKFLOW PREVENTER APPARATUS

摘要

BACKFLOW PREVENTER APPARATUS A back flow preventer apparatus designed for connection between a supply pipe having liquid under pressure and a service pipe, the backflow preventer apparatus comprising a pair of check valves in series and defining a zone therebetween, a relief valve operable upon a change in differential pressure across the upstream check valve, and a vacuum breaker operable upon a drop in pressure in the zone to a predetermined pressure supply above atmospheric pressure. The differential pressure operable relief valve, when opened upon certain operating conditions, causing the zone to drain to atmosphere. The vacuum breaker operates independent of supply pipe pressure or service pipe pressure but solely on a drop in pressure in the zone.