Series 805Y wye-pattern design double check valve assembly backflow preventers consist of two independently operating poppet type check valves. Each check valve is spring loaded to maintain a minimum of 1 PSIG differential pressure across the check in a no-flow condition. In normal flow conditions the checks open an amount corresponding to the flow rate. During a backflow (backpressure) situation the seat discs close and seal to prevent any flow reversal. Sizes 3/4 to 2 inch (805Y, 805YB, 805YS, 805YR) include two spring-loaded, Y-pattern bronze check valves, two bronze shut-off valves and four test cocks for field testing. All valves are threaded type and the unit is shipped completely assembled.