The Relief Valve Rubber Repair Kit is compatible with the 2-1/2 in-6 in Model 375, 375A, 375AST, 475, and 475V Reduced Pressure Principle Backflow Preventer. Repair Kit components include one Upper Plunger O-Ring, one Diaphragm, one Seal Ring, one Relief Valve Seat O-Ring, and one Relief Valve O-Ring. The accessories within the kit allow you to speed up repairs, while lowering maintenance costs and extending the product life. The Zurn® Wilkins portfolio offers long-lasting protection from back siphonage and backpressure of contaminated water into the potable water supply.