This check seat fits the 2 1/2 - 3" Watts 909 Series reduced pressure detector assembly (RPDA) backflow preventers. This seat will fit either the first or second check assembly. To remove the old seat, loosen 1/4 turn and pull straight up. To install new seat, push straight down and tighten 1/4 turn. Be sure to lube the O-Ring before installing. Does NOT include parts for the bypass assembly. No special tools are required for servicing. Genuine Watts replacement parts.