a unitized check valve assembly comprises : a valve body having a bore therethrough , the bore having an inlet and an outlet , a valve disk engaging said body at said outlet , a valve retainer engaging the body and surrounding the valve disk and the outlet ; a first biasing member in compression between the body and the valve retainer ; and a second biasing member in compression between the body and the valve disk . the flow passage between the valve seat and the valve is continuous around the circumference of the valve . in a preferred embodiment , the valve body and the valve disk each have a mating surface , the mating surfaces define an interface therebetween , and the interface comprises a portion of a spherical surface .