A choke valve is a type of control valve that has a restriction orifice that is used in oil and gas production wells to control the flow of good fluids being produced. The purpose is to reduce the pressure drop across the valve at the maximum flow rate either to eliminate cavitation or to reduce the intensity of the damage to the valve. The rate of flow is determined only by the ambient pressure on the upstream side of the valve.
A diffuser plate is a disk that has many small holes drilled in it that are installed downstream of the piping system. It is used to reduce the pressure drop across the control valve and creates backpressure between the valve and plate.