A high pressure rotary shear valve assembly comprising: a stator device defining a substantially planar stator face and at least two or more stator channels in fluid communication with said stator face at corresponding stator ports, said stator face being composed substantially of one of a metallic material and a ceramic material; and a rotor assembly including: a rotor device having a substantially planar rotor face defining one or more rotor channels, said rotor face being composed substantially of one of a metallic material and a ceramic material, a tribological coating disposed atop at least one of said rotor face and said stator face, the rotor device defining a proximal facing contact surface oriented opposite the rotor face, wherein said rotor device comprises a valve shaft, configured for rotation about a rotational axis of the valve assembly, a head portion disposed at a distal end of the valve shaft, the head portion defining a distal seating surface configured to seat the rotor device thereon, a compliance assembly including a compliant element (44, 50) having a contact surface, the compliant element defining a proximal facing surface oriented opposite the contact surface and in supportive abutting contact with the contact surface of the rotor device and the distal seating surface of said head portion, wherein said compliant element orients the substantially planar rotor face substantially parallel to and substantially flush against the substantially planar stator face of the stator device; and wherein said rotor device is rotatably mounted about the rotational axis in a manner enabling fluid-tight, selective relative rotation between the rotor face and the stator face, at a rotor-stator interface, between two or more rotor positions. a stator device defining a substantially planar stator face and at least two or more stator channels in fluid communication with said stator face at corresponding stator ports, said stator face being composed substantially of one of a metallic material and a ceramic material; and a rotor assembly including: a rotor device having a substantially planar rotor face defining one or more rotor channels, said rotor face being composed substantially of one of a metallic material and a ceramic material, a tribological coating disposed atop at least one of said rotor face and said stator face, the rotor device defining a proximal facing contact surface oriented opposite the rotor face, wherein said rotor device comprises a valve shaft, configured for rotation about a rotational axis of the valve assembly, a head portion disposed at a distal end of the valve shaft, the head portion defining a distal seating surface configured to seat the rotor device thereon, a compliance assembly including a compliant element (44, 50) having a contact surface, the compliant element defining a proximal facing surface oriented opposite the contact surface and in supportive abutting contact with the contact surface of the rotor device and the distal seating surface of said head portion, wherein said compliant element orients the substantially planar rotor face substantially parallel to and substantially flush against the substantially planar stator face of the stator device; and a head portion disposed at a distal end of the valve shaft, the head portion defining a distal seating surface configured to seat the rotor device thereon, a compliance assembly including a compliant element (44, 50) having a contact surface, the compliant element defining a proximal facing surface oriented opposite the contact surface and in supportive abutting contact with the contact surface of the rotor device and the distal seating surface of said head portion, wherein said compliant element orients the substantially planar rotor face substantially parallel to and substantially flush against the substantially planar stator face of the stator device; and wherein said rotor device is rotatably mounted about the rotational axis in a manner enabling fluid-tight, selective relative rotation between the rotor face and the stator face, at a rotor-stator interface, between two or more rotor positions.