Download SERVO VALVE

SERVO VALVES
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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
.
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CONVENTIONAL DIRECTIONAL VALVE
T
B P
A
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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
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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
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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.
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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 )
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SERVO VALVE
Control method in a Proportional Valve
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SERVO VALVE
Control method in a Proportional Valve
By Providing Spool between Magnetic Solenoid
and Spring it is possible to control Hydraulic
energy.
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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
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ELECTRO-HYDRAULIC TWO STAGE SERVO VALVE
MAGNET
Graphic Symbol
R
P
A B
Side Sectional View
P R
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SERVO VALVE - OPERATION
No Signal to Valve
Service
Service
R
P
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SERVO VALVE - OPERATION
Signal applied to
torque motor &
spool about to
move.
Service
Service
R
P
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SERVO VALVE - OPERATION
Equilibrium
condition with
signal applied.
Service
R
Service
P
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15
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ELECTRO-HYDRAULIC THREE STAGE SERVO VALVE
PILOT VALVE
SLEEVE
L.V.D.T
SPOOL
Drain
Port
A
P
B
R
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SERVO PILOT PROPORTIONAL VALVE
Input
Voltage
PILOT VALVE
SERVO
AMPLIFIER
SPOOL
SPRING
L.V.D.T
R
A
P
B
Pilot Pr. Port
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MECHANICAL SERVO VALVE
STYLUS
SLEEVE
SPOOL
Drain
Port
T
A
P
B
Pilot Pr.
Port
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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.
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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/Cm2 pr. Diff.
SERVO VALVE
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.
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+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 ) ( dB )
FREQUENCY RESPONSE
200
Frequency ( Hz )
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SERVO VALVE
- Compare with a Proportional Valve
Performance comparison
Type of valve.
Item.
Pressure
difference and
rated flow.
Hysterisis.
Repeatability.
Proportional valve.
High
Standard. performance
Servo valve.
10
Kgf / Cm2
15 ~ 30
Kgf / Cm2.
70
Kgf / Cm2.
Less 5%.
Less 1%.
1 ~ 3%.
Less 1 %.
Less 1%.
Less 0.5 %.
Gain
at
6 ~ 10 Hz. 20 ~ 40 Hz. 70 ~ 150 Hz.
Frequ
– 3db.
-ency
response Phase
at
6 ~ 9 Hz. 15 ~ 45 Hz. 150 ~170 Hz.
o
90 .
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SERVO VALVE
- Most Sensitive to Contamination
Application
CleanliFilter
ness
Stds.
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.
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