Abstract: A check valve assembly is disclosed which is inserted in a fluid flow conduit leading from a source of fluid flow to a mechanism utilizing the fluid flow. The check valve assembly comprises a housing having an inlet port and an outlet port that communicate with a central chamber in the housing, and a valve disposed in the central chamber adapted to permit fluid flow from the inlet port through the chamber to the outlet port and prevent fluid flow from the outlet port through the chamber to the inlet port. The housing comprises a first attachment piece associated with the inlet port and adapted to be attached to the fluid flow conduit leading from the source of fluid flow, and a second attachment piece associated with the outlet port and adapted to be attached to one of several adapter elements. Various types of adapter elements are disclosed which include sections for connecting the adapter element to the second attachment piece and to the fluid flow conduit leading to the mechanism utilizing the fluid flow.