Nowadays, the application of mechatronic systems in various aspects and industries such as military, aerospace, manufacturing automation, CNC machining equipments, petroleum and gas industries, civil equipments and etc. are wide spread. Combination of hydraulic and electronic devices in a control system needs some parts to connect them, which is an electro hydraulic servo valve. A hydraulic valve is used to direct and control flow or pressure of a hydraulic flow. An electro hydraulic servo valve which consists of electromagnetic hydraulic sections is response of converting low power electric signal to hydraulic signals that can control hydraulic devices with high speed and accuracy. Flapper-nozzle electro hydraulic servo valves with dry torque motor and force feedback system have wide spread use in any applications, because of their high accuracy and speed. These valves consist of delicate and precise parts that have critical material selection and manufacturing procedures. If these parameters are not selected appropriately, may defect accuracy and stability of the whole system. Pilot valves which compound of electromagnetic and hydraulic sections have important role in servo valves structure because of their sensitive parts. In the present work, manufacturing process of a pilot valve of a commercial electro hydraulic flapper-nozzle servo valve with dry torque motor is studied. In the first chapter all types of noted valves is introduced and structure and various structures and mechanism of these valves are explained. Then, structure of a two-stage flapper-nozzle servo valves with force feedback system is explained and the role of each part is mentioned. In the second chapter, mathematical relations of electromagnetic, mechanical and hydraulic sections of a servo valve is brought and effects of some critical parameters on performance of servo valve, is shown. Since the reverse engineering method was chosen to extract manufacturing procedure of a servo valve, a two-stage flapper-nozzle servo valve was selected. In third and fourth chapters, properties and specifications of each part are studied. Firstly, on each part chemical analysis was done to discover the material used to make it and its metallurgical properties. Chemical analysis was performed on EDX SERON-TECH AIS-2100 machine. EDX method does not report exact results for elements with atomic number less than 4. SEM photography of machined surfaces, hardness and roughness tests was done for each parts of valve. Finally, with gathering the results of pervious tests and technical references, for each parts proper material and manufacturing procedure selection was suggested. For process selection of each part, some criteria such as quantity, surface roughness and dimensional tolerance are vital. Keywords: Electro Hydraulic Servo Valve(EHSV), Feedback Spring, Flexure Tube, Manufacturing Process
