Finite Element and Experimental Validation of Stiffness Analysis of Precision Feedback Spring and Flexure Tube of Jet Pipe Electrohydraulic Servovalve M. Singaperumal*, Somashekhar. S. Hiremath* R. Krishna Kumar** *Precision Engineering and Instrumentation Laboratory **Manufacturing Engineering Section Indian Institute of Technology Madras Chennai - 6000 36 (India). Abstract Electrohydraulic servovalve has a major part to play in feedback control system. The feedback spring and flexure tube elements are identified as more critical spring elements in servovalve operation. If these elements are properly designed with respect to stiffness, automatically dynamic performance of the servovalve is improved. Hence an attempt has been made to predict the stiffness of these elements by finite element method. The solid model of these components are carried out in IDEAS-Master module and simulated with appropriate boundary conditions. Also an experimental prototype model is designed and fabricated to test these precise components .The obtained results are validated with FEM results. The FEM gives complete behavior of these components. Results related to stress concentration areas due to loading are also included in the paper. Key words: jet pipe, servovalve, solid model, stiffness and simulation. 1. INTRODUCTION Fluid power control, that is the transmission and control of energy by means of a pressurized fluid, is an old and well recognized discipline. The growth of fluid power has accelerated with our desires to control ever increasing quantities of power and mass with higher speeds and greater precision. More specifically, where precise motion control is desired and space and weight are limited, the convenience of high power-to-weight ratio makes hydraulic servomechanisms the ideal control elements. The demand to achieve more accurate and faster control at high power levels, especially in the areas of machine tools, primary flight controls, and automatic fire control produced an ideal marriage of hydraulic servomechanisms with electronic signal processing. Information could be transuded, generated, and processed more easily in the electronic medium than as pure mechanical or fluid signals, while the delivery of power at high speeds could be accomplished best by the hydraulic servo. This marriage of electronics and hydraulics into electrohydraulic servomechanisms created both a solution to an existing class of control problems and a demand for a whole new strain of components [1]. An electrohydraulic servo valve is a transducer. It transforms an electrical signal into hydraulic power. This is not done directly. An intermediate conversion to mechanical motion is first made by means of an electromagnetic torque motor and this is then used to stroke the mechanical control element of the valve. Originally, solenoids were used to directly move the spool, but this requires a relatively long stroke. It also requires large forces to overcome friction and flow forces. In order to ensure sufficiently low time constants, except for very small systems, therefore, it is necessary to use the torque motor to drive the pilot stage or hydraulic amplifier which in turn strokes the power spool [2]. A very wide range electrohydraulic flow control valves have been employed and comprehensive reviews been published by Shute and Turnbull [3] and [4]. A varied range of designs have been described by Himmler [5]. The modern valve is a two-stage device, invariably employing feedback from the second stage to the first stage, which is controlled by an electric torque motor. The analyzed valve is a two-stage jet pipe electrohydraulic flow control servovalve, converts an electrical signal to precise proportional hydraulic flow. The jet pipe servo valve serves to convert pressure energy into the kinetic energy of a jet and directs this jet towards two closely spaced receiver holes in the receiver block [6]. When the jet of oil strikes the flat receiver block, its kinetic energy is recovered in the form of pressure. If the stream is directed exactly halfway between the receiver holes, the pressure in the two holes will be equal; the differential pressure, therefore, is zero. As the jet pipe is deflected, more oil will be directed at one hole than the