Abstract: The invention relates to a combination valve and back pressure valve which in one embodiment performs as a two-way check valve, and in another embodiment performs as a back pressure valve. The invention contains both apparatus and method claims. The valve includes a cylindrical member having an inlet port and an outlet port, with a bore therethrough. A valve sleeve is disposed within the bore. A valve stem is also slidably disposed within the bore. A selective dis-attachment assembly is incorporated into the valve and includes pre-selected shear pistons.