SERVO VALVES 1 SERVO VALVE A SERVO VALVE

SERVO VALVES 1

SERVO VALVE A SERVO VALVE IS A DIRECTIONAL VALVE IT MAY BE INFINITELY POSITIONED TO PROVIDE CONTROL OF BOTH THE AMOUNT AND THE DIRECTION OF FLUID FLOW. A SERVO VALVE COUPLED WITH PROPER FEEDBACK SENSING DEVICES PROVIDES VERY ACCURATE CONTROL OF THE POSITION, VELOCITY OR ACCELERATION OF AN ACTUATOR. 2

CONVENTIONAL DIRECTIONAL VALVE T B P A 3

SERVO VALVE - Compare with a Proportional Valve Based on Control Method PROPORTIONAL VALVE SERVO VALVE Pressure , flow, Direction control by electrical signal Controller & Amplifier is used Pressure, flow, Direction control by electrical signal Controller & Amplifier is used 4

SERVO VALVE - Compare with a Proportional Valve Based on Application PROPORTIONAL VALVE SERVO VALVE For general electrical control system. Open loop or Closed loop circuit High Accuracy, High Frequency applications. Closed loop circuit 5

PROPORTIONAL VALVES & SERVO VALVES OPEN LOOP & CLOSED LOOP Open Loop circuit : SLOW FAST Accuracy, Response : POOR Controllability : GOOD Cost : LESS Controller controls the hydraulic valve according to the input signal which is given from the controller to the valve. 6

PROPORTIONAL VALVES & SERVO VALVES Closed Loop Circuit : CONSTANT SPEED According to the requirement of speed or position or pressure , input signal is given and compared with output value through a sensor and necessary adjustments are made. Input signal and output values are compared and differences are corrected. This gives high accuracy & high Response ( Feed back Control System ) 7

SERVO VALVE Control method in a Proportional Valve 8

SERVO VALVE Control method in a Proportional Valve By Providing Spool between Magnetic Solenoid and Spring it is possible to control Hydraulic energy. 9

ELECTRO-HYDRAULIC TWO STAGE SERVO VALVE ARMATURE NULL ADJUST MAGNET UPPER POLEPLATE LOWER POLEPLATE FLAPPER NOZZLE COIL FEEDBACK SPRING BUSHING SPOOL INLET ORIFICE P A R B INLET FILTER 10

ELECTRO-HYDRAULIC TWO STAGE SERVO VALVE MAGNET Graphic Symbol R P A B Side Sectional View P R 11

SERVO VALVE - OPERATION No Signal to Valve Service R P 12

SERVO VALVE - OPERATION Signal applied to torque motor & spool about to move. Service R P 13

SERVO VALVE - OPERATION Equilibrium condition with signal applied. Service R Service P 14

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ELECTRO-HYDRAULIC THREE STAGE SERVO VALVE PILOT VALVE SLEEVE L. V. D. T SPOOL Drain Port A P B R 17

SERVO PILOT PROPORTIONAL VALVE Input Voltage PILOT VALVE SERVO AMPLIFIER SPOOL SPRING L. V. D. T R A P B Pilot Pr. Port 18

MECHANICAL SERVO VALVE STYLUS SLEEVE SPOOL Drain Port T A P B Pilot Pr. Port 19

SERVO VALVE - Compare with a Proportional Valve Based on Function PROP. VALVE According to required function many types of valves are available - Prop. Pr. Ctrl. Vv - Prop. Flow Ctrl. Vv - Prop. Pr. & Flow Control Valve - Prop. Dir. & flow Control Valve. SERVO VALVE Construction same as Dir. Valve. Type of feedback sensor, function of the servo valve is determined. Use pr. Sensor and give feedback, then become pr. Control Servo Valve. 20

SERVO VALVE - Compare with a Proportional Valve Based on Function PROP. VALVE Rated flow same as Conventional valve for Pr. Control & flow control Valve. For Dir. Control depends on accuracy and frequency response. Rated flow gives flow at 10 ~ 30 Kg/Cm 2 pr. Diff. SERVO VALVE To get high frequency response, high pressure response should be given. Generally 70 Kg/Cm 2 of pres. Diff. Is given. Rated flow indicates flow at pr. drop of 70 Kgf /Cm 2 Take care about power loss & heat generation. 21

+2 0 -2 -4 -110 -6 -90 -8 -70 -50 -30 -10 5 10 20 30 50 100 ( Degrees ) 38 L/min 63 L/min Phase Lag Amplitude Ratio ( Gain ) ( d. B ) FREQUENCY RESPONSE 200 Frequency ( Hz ) 22

SERVO VALVE - Compare with a Proportional Valve Performance comparison 23

SERVO VALVE - Most Sensitive to Contamination Application Cleanli. Filter ness Stds. General Hydraulic System NAS 12 20 ~ 30 ab Proportional Valve & Flow Control Valve to control small flow SERVO VALVE NAS 11 10 ab. NAS 7 5 ab. 24