1. SERVO VALVES

2. 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 .

3. CONVENTIONAL DIRECTIONAL VALVEB A P

4. 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

5. 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

6. 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

7. 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

8. SERVO VALVE
Control method in a Proportional Valve

9. 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.

10. 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

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

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

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

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

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

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

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

20. 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.

21. 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.

22. 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 )

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

24. 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.