The 2" Wilkins 975XL Reduced Pressure Zone backflow preventer was introduced in 1993 to replace the earlier model 975. The 975XL features removable seats, while the original 975 did not have removable seats. All other parts will interchange between the 975 and 975XL models. The checks are a poppet style and are not self contained and there is spring pressure against the covers. The relief valve is a piston style with an internal sensing line. This device does not meet low lead laws introduced in 2014. A lead free version is available, known as the 975XL2. A seat removal tool is required for seat service.