The 1 1/2" Wilkins 950XL Double Check Valve Assembly was designed to replace the original 950 and 950A models. The difference in the 950XL was the plastic replacable seats. The 950XL is a two cover, wye pattern design. The checks are a poppet style and are not self contained and there is spring pressure against the covers. The body is of bronze construction. A seat removal tool is required for seat service.