SERVO VALVES

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 .

CONVENTIONAL DIRECTIONAL VALVE B A P

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

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

PROPORTIONAL VALVES & SERVO VALVES OPEN LOOP & CLOSED LOOP Open Loop circuit : 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. SLOW FAST

PROPORTIONAL VALVES & SERVO VALVES Closed Loop Circuit : 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 ) CONSTANT SPEED

SERVO VALVE Control method in a Proportional Valve

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

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

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

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

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

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

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

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

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

Based on Function - Compare with a Proportional Valve PROP. VALVE SERVO VALVE - Compare with a Proportional Valve Based on Function PROP. VALVE SERVO 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. 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.

Based on Function - Compare with a Proportional Valve SERVO VALVE PROP. VALVE SERVO 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/Cm2 pr. Diff. To get high frequency response, high pressure response should be given. Generally 70 Kg/Cm2 of pres. Diff. Is given. Rated flow indicates flow at pr. drop of 70 Kgf /Cm2 Take care about power loss & heat generation.

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

Performance comparison SERVO VALVE - Compare with a Proportional Valve Performance comparison

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