tmhp51 servomechanisms (ht2012) lecture 04 - liu iei · pdf filemagnus sethson @liu.se lecture...
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Magnus [email protected]
Lecture 04TMHP51 Servomechanisms (HT2012)
Sensors for feedbackServo-Valve internalsMulti-stage Valves
1
1
The Servo Valve
2
760 SeriesServovalves
ISO 10372 Size 04
The actual flow is dependentupon electrical command signaland valve pressure drop.Theflow for a given valve pressuredrop can be calculated usingthe square root function forsharp edge orifices:
ΔpQ = QN
ΔpN
Q [gpm] = calculated flowQN [gpm] = rated flowΔp [psi] = actual valve
pressure dropΔpN [psi] = rated valve
pressure drop
760 SERIES SERVOVALVES
The 760 Series flow controlservovalves are throttle valvesfor 3-, and preferably 4-wayapplications.They are a highperformance, two-stage designthat covers the range of ratedflows from 1 to 15 gpm at1000 psi valve drop.The output stage is a closed center,four-way, sliding spool.The pilotstage is a symmetrical double-nozzle and flapper, driven by adouble air gap, dry torquemotor. Mechanical feedback ofspool position is provided by a
cantilever spring.The valvedesign is simple and rugged fordependable, long life operation.
These valves are suitable forelectrohydraulic position,speed, pressure or force con-trol systems with high dynamicresponse requirements.
Principle of operationAn electrical command signal(flow rate set point) is appliedto the torque motor coils andcreates a magnetic force whichacts on the ends of the pilotstage armature.This causes a
deflection of armature/flapperassembly within the flexuretube. Deflection of the flapperrestricts fluid flow through onenozzle which is carried throughto one spool end, displacingthe spool.
Movement of the spool opensthe supply pressure port (P) toone control port while simulta-neously opening the tank port(T) to the other control port.The spool motion also appliesa force to the cantilever spring,creating a restoring torque onthe armature/flapper assembly.
Once the restoring torquebecomes equal to the torquefrom the magnetic forces, thearmature/flapper assemblymoves back to the neutralposition, and the spool is heldopen in a state of equilibriumuntil the command signalchanges to a new level.
In summary, the spool positionis proportional to the inputcurrent and, with constantpressure drop across the valve,flow to the load is proportionalto the spool position.
2
VALVE FEATURES
➣ 2-stage design with dry torque motor
➣ Low friction double nozzle pilot stage
➣ High spool control forces
➣ High dynamics
➣ Rugged, long-life design
➣ High resolution, low hysteresis
➣ Completely set-up at the factory
➣ Optional fifth port for separate pilot supply
➣ Intrinsically safe or flameproof valve versions are available
760 SERIESTWO STAGE SERVOVALVES
This catalog is for users with technicalknowledge.To ensure that all necessarycharacteristics for function and safety of the
system are given, the user has to check thesuitability of the products described here.In case of doubt, please contact Moog Inc.
Intrinsically safe valve versions are available for use in hazardous locations.Specific models are certified to FM,ATEX, CSA, and TIIS standards. Contact the factoryfor details.
3
Servovalveswith integrated ElectronicsD791 and D792 Series
Q [l/min] = max. flow!p [bar] = valve pressure drop
with QAK [cm2] = spool drive areapX [bar] = pilot pressure
The pilot pressure pX has to be atleast 15 bar above the returnpressure of the pilot stage.
D791 and D792 SeriesThree stage servovalves
Principle of operationAn electrical command signal (setpoint, input signal) is applied tothe integrated control amplifierwhich drives a current throughthe pilot valve coils. The pilot valveproduces differential pressure inits control ports. This pressuredifference results in a pilot flowwhich causes main spool dis-placement.The position transducer which isexcited via an oscillator measuresthe position of the main spool(actual value, position voltage).
This signal then is demodulatedand fed back to the controlamplifier where it is comparedwith the command signal. Thecontrol amplifier drives the pilotvalve until the error betweencommand signal and feedbacksignal is zero. Thus, the position ofthe main spool is proportional tothe electrical command signal.
Q Q ppN
N= !
! p 2,5 10 QA
pX-2
K" # # !
The actual flow depends on theelectrical command signal andthe valve pressure drop, and maybe calculated using the squareroot function for a sharp-edgedorifice.The flow value Q calculated inthis way should not exceed anaverage flow velocity of 30 m/s inports P, A, B and T.
Q [l/min] = calculated flowQN [l/min] = rated flow!p [bar] = actual valve pressure
drop!pN [bar] = rated valve pressure
drop
Operational features
❒ Electrical position feedback with pressure isolated positiontransducer (LVDT), no wear
❒ Integrated SMD electronics with false polarity protection❒ Optional external pilot supply and return connections via fifth
and sixth port in valve body❒ Low threshold and hysteresis, excellent null stability❒ Preadjusted at factory
4
If large flow rates with high valvepressure drops are required, anappropriate higher pilot pressurehas to be chosen to overcome theflow forces. An approximate valuecan be calculated as follows:
The valves D791 and D792 Seriesdescribed in this catalogue havesuccessfully passed EMC testsrequired by EC Directive. Pleasetake notice of the respectivereferences in the electronicssection.
Our quality management systemis certified in accordance withDIN EN ISO 9001.
This catalogue is for users withtechnical knowledge. To ensurethat all necessary characteristicsfor function and safety of thesystem are given, the user has to
check the suitability of theproducts described here.In case of doubt please contactMoog.
The flow control servovalves D791and D792 Series are throttle valvesfor 3-way and preferably 4-wayapplications. These three stageservovalves have been especiallydeveloped for such demandingapplications where high flow ratesand at the same time extremedynamic performance require-ments must be met. The design ofthese valves is based on the wellknown D079 Series. The inte-grated electronics has beenreplaced by a new design applyingSMD technology. The valves are
offered with pilot valves of D761or D765 Series, optional standardresponse or high response versionsare available. Series D791 can de-liver rated flow up to 250 l/min,Series D792 is available with ratedflow up to 1000 l/min.These valves are suitable for pres-sure or force control, position andvelocity control systems with highdynamic response requirements.
4
Source:
F1 servo valve, 93gram, 3.5kW power control
5
MOOG Inc
5
Source:
Two-Stage Servo Valve
6
6
Source:
P A T B
Classical Nozzle-Flapper Controlled Servo Valve
7
7
Source:
T B P A
3 stage Servovalve D792with Pilot valve D765 Series
8
Three Stage Servo Valve
8
The Torque Motor
9
9
Torque Motor
10
TORQUE MOTOR
➣ Charged permanent magnets polarize the polepieces.
➣ DC current in coils causes increased force in diagonallyopposite air gaps.
➣ Magnetic charge level sets magnitude of decentering forcegradient on armature.
HYDRAULIC AMPLIFIER
➣ Armature and flapper rigidly joined and supported by thin-wallflexure sleeve.
➣ Fluid continuously flows from pressure PS, through both inletorifices, past nozzles into flapper chamber, through drain orificeto tank T.
➣ Rotary motion of armature/flapper throttles flow through one nozzle or the other.
➣This diverts flow to one end of the spool.
Æ
Spool at Null Feedback Spring Spool
Bushing
Spool Dispaced to Left
Ps T T Ps
A B
Ps T T Ps
A B
T
PS PS
ARMATURE
FLEXURESLEEVE
FLAPPER
INLETORIFICE
PermanentMagnetFlux
PermanentMagnetAttractiveForce
Coil Flux
Torque toRotateArmature
N
S
N
S
N
S
➤➤
➤➤
N
N
S
S
UpperPolepiece
PermanentMagnet
Armature
Coil
N
S
Lower Polepiece
NOZZLE FLAPPER SERVOVALVE OPERATION
VALVE SPOOL
➣ Spool slides in bushing (sleeve) or directly in body bore.
➣ Bushing contains rectangular holes (slots) or annular groovesthat connect to supply pressure PS and tank T.
➣At “null” spool is centered in bushing; spool lobes (lands) justcover PS and T openings.
➣ Spool motion to either side of null allows fluid to flow from PS
to one control port and from other control port to T.
16
TORQUE MOTOR
➣ Charged permanent magnets polarize the polepieces.
➣ DC current in coils causes increased force in diagonallyopposite air gaps.
➣ Magnetic charge level sets magnitude of decentering forcegradient on armature.
HYDRAULIC AMPLIFIER
➣ Armature and flapper rigidly joined and supported by thin-wallflexure sleeve.
➣ Fluid continuously flows from pressure PS, through both inletorifices, past nozzles into flapper chamber, through drain orificeto tank T.
➣ Rotary motion of armature/flapper throttles flow through one nozzle or the other.
➣This diverts flow to one end of the spool.
Æ
Spool at Null Feedback Spring Spool
Bushing
Spool Dispaced to Left
Ps T T Ps
A B
Ps T T Ps
A B
T
PS PS
ARMATURE
FLEXURESLEEVE
FLAPPER
INLETORIFICE
PermanentMagnetFlux
PermanentMagnetAttractiveForce
Coil Flux
Torque toRotateArmature
N
S
N
S
N
S
➤➤
➤➤
N
N
S
S
UpperPolepiece
PermanentMagnet
Armature
Coil
N
S
Lower Polepiece
NOZZLE FLAPPER SERVOVALVE OPERATION
VALVE SPOOL
➣ Spool slides in bushing (sleeve) or directly in body bore.
➣ Bushing contains rectangular holes (slots) or annular groovesthat connect to supply pressure PS and tank T.
➣At “null” spool is centered in bushing; spool lobes (lands) justcover PS and T openings.
➣ Spool motion to either side of null allows fluid to flow from PS
to one control port and from other control port to T.
16
10
Torque Motor & Flapper-Nozzle Operation
11
OPERATION
➣ Electrical current in torque motor coils creates magneticforces on ends of armature.
➣ Armature and flapper assembly rotates about flexure sleevesupport.
➣ Flapper closes off one nozzle and diverts flow to that end ofspool.
➣ Spool moves and opens PS to one control port; opens other control port to T.
➣ Spool pushes ball end of feedback spring creating a restoringtorque on the armature/flapper.
➣ As feedback torque becomes equal to torque from magneticforces, armature/flapper moves back to centered position.
➣ Spool stops at a position where feedback spring torqueequals torque due to input current.
➣ Therefore, spool position is proportional to input current.
➣ With constant pressures, flow to load is proportional tospool position.
DPL
PS
T T
A B
Valve Respondingto Change inElectrical Input
N
S
N
S
PS PS
PS
Flow to Actuator
PS
T TPS
A B
Valve ConditionFollowing Change
N
S
N
S
PS PS
N S
OperationOperationOperation
17
TORQUE MOTOR
➣ Charged permanent magnets polarize the polepieces.
➣ DC current in coils causes increased force in diagonallyopposite air gaps.
➣ Magnetic charge level sets magnitude of decentering forcegradient on armature.
HYDRAULIC AMPLIFIER
➣ Armature and flapper rigidly joined and supported by thin-wallflexure sleeve.
➣ Fluid continuously flows from pressure PS, through both inletorifices, past nozzles into flapper chamber, through drain orificeto tank T.
➣ Rotary motion of armature/flapper throttles flow through one nozzle or the other.
➣This diverts flow to one end of the spool.
Æ
Spool at Null Feedback Spring Spool
Bushing
Spool Dispaced to Left
Ps T T Ps
A B
Ps T T Ps
A B
T
PS PS
ARMATURE
FLEXURESLEEVE
FLAPPER
INLETORIFICE
PermanentMagnetFlux
PermanentMagnetAttractiveForce
Coil Flux
Torque toRotateArmature
N
S
N
S
N
S
➤➤
➤➤
N
N
S
S
UpperPolepiece
PermanentMagnet
Armature
Coil
N
S
Lower Polepiece
NOZZLE FLAPPER SERVOVALVE OPERATION
VALVE SPOOL
➣ Spool slides in bushing (sleeve) or directly in body bore.
➣ Bushing contains rectangular holes (slots) or annular groovesthat connect to supply pressure PS and tank T.
➣At “null” spool is centered in bushing; spool lobes (lands) justcover PS and T openings.
➣ Spool motion to either side of null allows fluid to flow from PS
to one control port and from other control port to T.
16
11
The Servo System
12
12
Servo System
13
DesignAreospace LLC
13
Direct Drive Pilot Stage
14
14
Source:
15
Single Stage Servo Valve
15
Source:
Fieldbus connector X4
Fieldbus connector X3
Status LEDs
Digital electronics
Position transducer (LVDT)
Valve connector X1
Service connector X10
Spool
Bushing
Linear force motor
Ports
Single-Stage Servo Valve
16
MOOG D636 Single-Stage Servo Valve
16
Source:
force of the linear force motor is proportional to the coil
C@B9>7C§56653D§@B539C5§C@??<§=?F5=5>D§5F5>§1719>CD§�?G§
Permanent magnets Centering springs
Bearing Coil Armature Screw plug
Permanent Magnet Linear Force Motor
17
17
Permanent Magnet Linear Force Motor Operation
18
LINEAR FORCE MOTOR
➣ A linear force motor is a permanent magnet differential motor.
➣ The motor consists of a coil, pair of high energy rare earthmagnets, armature, and centering springs.
➣ Without a current being applied to the coil, the magnets andsprings hold the armature at equilibrium.
➣ When current is applied to the coil with one polarity, the flux in one of the air gaps surrounding the magnets is increased,cancelling out the flux in the other.
➣ This dis-equilibrium allows the armature to move in thedirection of the stronger magnetic flux.
➣ The armature is moved in the opposite direction by changing the polarity of the current in the coil.
VALVE SPOOL
➣ Spool slides in bushing (sleeve) or directly in body bore.
➣ Bushing contains rectangular holes (slots) or annular grooves that connect to supply pressure PS and tank T.
➣ At “null,” spool is centered in bushing; spool lobes (lands)just cover PS and T openings.
➣ Spool motion to either side of null allows fluid to flow fromPS to one control port, and from other control port to T.
OPERATION
➣ An electrical signal corresponding to the desired spool positionis applied to the integrated electronics and produces a pulsewidth modulated (PWM) current in the linear force motor coil.
➣ The current causes the armature to move which then directlyactivates the spool.
➣ The spool moves and opens pressure P to one control port,while the other control port is opened to tank T.
➣ The position transducer (LVDT), which is mechanically attachedto the spool, measures the position of the spool by creating anelectrical signal that is proportional to the spool position.
➣ The demodulated spool position signal is compared withthe command signal, and the resulting electrical error drivescurrent to the force motor coil.
➣ The spool moves to its commanded position and the spoolposition error is reduced to zero.
➣ The resulting spool position is thus proportional to thecommand signal.
DIRECT DRIVE SERVO-PROPORTIONAL VALVE OPERATION
S NN S
N S S N
Directionof Armature
N S S N
S NN S
Permanent Magnets Centering Springs
Coil Armature
P A T B X
19
LINEAR FORCE MOTOR
➣ A linear force motor is a permanent magnet differential motor.
➣ The motor consists of a coil, pair of high energy rare earthmagnets, armature, and centering springs.
➣ Without a current being applied to the coil, the magnets andsprings hold the armature at equilibrium.
➣ When current is applied to the coil with one polarity, the flux in one of the air gaps surrounding the magnets is increased,cancelling out the flux in the other.
➣ This dis-equilibrium allows the armature to move in thedirection of the stronger magnetic flux.
➣ The armature is moved in the opposite direction by changing the polarity of the current in the coil.
VALVE SPOOL
➣ Spool slides in bushing (sleeve) or directly in body bore.
➣ Bushing contains rectangular holes (slots) or annular grooves that connect to supply pressure PS and tank T.
➣ At “null,” spool is centered in bushing; spool lobes (lands)just cover PS and T openings.
➣ Spool motion to either side of null allows fluid to flow fromPS to one control port, and from other control port to T.
OPERATION
➣ An electrical signal corresponding to the desired spool positionis applied to the integrated electronics and produces a pulsewidth modulated (PWM) current in the linear force motor coil.
➣ The current causes the armature to move which then directlyactivates the spool.
➣ The spool moves and opens pressure P to one control port,while the other control port is opened to tank T.
➣ The position transducer (LVDT), which is mechanically attachedto the spool, measures the position of the spool by creating anelectrical signal that is proportional to the spool position.
➣ The demodulated spool position signal is compared withthe command signal, and the resulting electrical error drivescurrent to the force motor coil.
➣ The spool moves to its commanded position and the spoolposition error is reduced to zero.
➣ The resulting spool position is thus proportional to thecommand signal.
DIRECT DRIVE SERVO-PROPORTIONAL VALVE OPERATION
S NN S
N S S N
Directionof Armature
N S S N
S NN S
Permanent Magnets Centering Springs
Coil Armature
P A T B X
19
Neutral Actuated
18
Valve Performance
19
19
Flow Charateristics
2020
STEP rESPoNSE
Time [ms]
Stro
ke [%
]
0
25
50
75
100
0 5 10 15 20
�"�!%���)§"�# ��#�
Frequency [Hz]
Phas
e la
g [d
egre
es]
Am
plit
ude
rati
o [d
B]
10 1001 10000
- 30
- 60
- 90
- 120
- 150
+/– 25%
+/– 90%
+/– 10%
+/– 05%
-12
-9
-6
-3
0
3
PrESSurE SigNAl CurVE(valve with zero lap)
-4Command signal [%]
-3 -2 -1 0 1 2 3 4
[%]
p AB p P
Δ
VAlVE Flow SigNAl CurVE(valve with zero lap)
-80
-60
-40-20
0
20
10080
60
40
Command signal [%]
[%]
-100 1006020-20-60
MOOG D636 Characteristics21
21
Nozzle-Flapper Servo Valve Performance
224
-10
-6
-2
+2
0
-4
-8Am
plitu
de R
atio
(dB
)
Phas
e la
g (d
egre
es)
10020 30070 5005030 200 1000
20
40
60
80
100
120
Frequency (Hz)Frequency Response
of 1, 2.5, and 5 gpm Servovalves
10
±100%±40%
3000 psi DTE-24at 100˚F (38˚C)Rated Current:
-10
-6
-2
+2
0
-4
-8Am
plitu
de R
atio
(dB
)
Phas
e la
g (d
egre
es)
10020 30070 5005030 200 1000
20
40
60
80
100
120
Frequency (Hz)Frequency Response
of 10 gpm Servovalves
10
±100%±40%
3000 psi DTE-24at 100˚F (38˚C)Rated Current:
-10
-6
-2
+2
0
-4
-8Am
plitu
de R
atio
(dB
)
Phas
e la
g (d
egre
es)
10020 30070 5005030 200 1000
20
40
60
80
100
120
Frequency (Hz)Frequency Response
of 1, 2.5, and 5 gpm Servovalves
10
3000 psi DTE-24at 100˚F (38˚C)Rated Current:
±100%±40%
-10
-6
-2
+2
0
-4
-8Am
plitu
de R
atio
(dB
)
Phas
e la
g (d
egre
es)
10020 30070 5005030 200 1000
20
40
60
80
100
120
Frequency (Hz)Frequency Response
of 10 gpm Servovalves
10
3000 psi DTE-24at 100˚F (38˚C)Rated Current:
±100%±40%
Typical CharacteristicCurves with ±40% and ±100%input signal, measured at 3,000pilot or operating pressure.
Standard Valves
High and Super High Response Valves
Model…Type 760-………Mounting Pattern ISO 10372 - 04 - 04 - 0 - 92Valve Body Version 4-way
2-stage with spool–bushing assemblyPilot Stage Nozzle/Flapper, HighflowPilot Connection Optional, Internal or External XRated Flow (±10%) at !pN = 1,000 psi
Standard [gpm] 1.0 2.5 5.0 10.0 15.0High Response [gpm] 1.0 2.5 5.0 10.0 15.0
Response Time @ 3000 psi Standard [ms] 6 6 6 10 16
High Response [ms] 4 4 4 7 13
Threshold* [%] 0.5
Hysteresis* [%] 3.0
Null Shift at !T = 100˚F [%] < 2.0
Null Leakage Flow* max. [gpm] 0.40 to 0.61
Pilot Leakage Flow* max. [gpm] 0.26
Spool Drive Area Standard [in2] .076
High Response [in2] .053
Super High Response [in2] .025
-10
-6
-2
+2
0
-4
-8Am
plitu
de R
atio
(dB
)
Phas
e la
g (d
egre
es)
10020 30070 5005030 200 1000
20
40
60
80
100
120
Frequency (Hz)Frequency Response
of 15 gpm Servovalves
10
±100%±40%
3000 psi DTE-24at 100˚F (38˚C)Rated Current:
-10
-6
-2
+2
0
-4
-8Am
plitu
de R
atio
(dB
)
Phas
e la
g (d
egre
es)
10020 30070 5005030 200 1000
20
40
60
80
100
120
Frequency (Hz)Frequency Response
of 15 gpm Servovalves
10
3000 psi DTE-24at 100˚F (38˚C)Rated Current:
±100%±40%
* Measured at 3,000 psi pilot or operating pressure
760 SERIESTECHNICAL DATA
22
LVDTLinear Variable Differential Transformer
23
23
LVDT, Linear Variable Differential Transformer
24
Source: Design News Inc.
24
Source:
LVDT
13
14
9
12
10
11
S2-8
2200pFpF
680
S2-71K5
R6100K
10K
S2-1
S2-2
S2-3
S2-4
S2-5
S2-6
10K
10K
6.8nF
6.8nF
15nF
15nF
47nF
47nF
TP2
DEMODULATORSECONDARYAMPLIFIER
PHASE ADJUSTMENT CIRCUIT
OSCILLATOR
+1
+1 TP3
SECONDARYSIGNAL
TEST POINT
ADJUST FOR MINIMUMPHASE DIFFERENCE
SECONDARYDEMOD
TEST POINT
LEAD
LAG
VAC2
Front Panel
2
(P.C.B.)
(P.C.B.)
LVDT Phase & Oscillation Circuit
25
25
Jet-Pipe Pilot Stage
26
26
Jet-Nozzle Pilot Stage
27
SERVOJET® PILOT STAGE
➣ The ServoJet® pilot stage consists mainly of torque motor, jetpipe, and receiver.
➣ A current through the coil displaces the jet pipe from itsneutral position.This displacement, combined with the specialshape of the nozzle, directs a focused fluid jet from bothreceivers towards one receiver.
➣ The jet now produces a pressure difference in the controlports.
➣ This pressure difference results in a pilot flow, which in turncauses a spool displacement.The pilot stage drain is throughthe annular area around the nozzle to tank T.
OPERATION
➣ An electrical command signal (flow rate set point) is applied tothe integrated position controller which drives the valve coil.
➣ The current through the coil displaces the jet pipe from itsneutral position.
➣ The displacement of the jet directs the flow to one end ofthe spool.
➣ Spool moves and opens P to one control port, while theother control port is open to tank T.
➣ The position transducer (LVDT), which is excited via anoscillator, measures the position of the main spool (actualposition voltage).
➣ The signal for the actual position of the spool is thendemodulated and fed back to the controller, where it iscompared with the command signal.
➣ The controller drives the pilot valve until the error betweencommand signal and spool position feedback signal is zero.
➣ Thus, the position of the main spool is proportional to theelectrical command signal.
SERVOJET® SERVO-PROPORTIONAL VALVE OPERATION
VALVE SPOOL
➣ Spool slides in bushing (sleeve) or directly in body bore.
➣ Bushing contains rectangular holes (slots) or annular grooves that connect to supply pressure PS and tank T.
➣ At “null,” spool is centered in bushing; spool lobes (lands)just cover PS and T openings.
➣ Spool motion to either side of null allows fluid to flow fromPS to one control port, and from other control port to T.
X T A P B T2 Y
Annular Area
Nozzle Receiver
JetPipe
18
SERVOJET® PILOT STAGE
➣ The ServoJet® pilot stage consists mainly of torque motor, jetpipe, and receiver.
➣ A current through the coil displaces the jet pipe from itsneutral position.This displacement, combined with the specialshape of the nozzle, directs a focused fluid jet from bothreceivers towards one receiver.
➣ The jet now produces a pressure difference in the controlports.
➣ This pressure difference results in a pilot flow, which in turncauses a spool displacement.The pilot stage drain is throughthe annular area around the nozzle to tank T.
OPERATION
➣ An electrical command signal (flow rate set point) is applied tothe integrated position controller which drives the valve coil.
➣ The current through the coil displaces the jet pipe from itsneutral position.
➣ The displacement of the jet directs the flow to one end ofthe spool.
➣ Spool moves and opens P to one control port, while theother control port is open to tank T.
➣ The position transducer (LVDT), which is excited via anoscillator, measures the position of the main spool (actualposition voltage).
➣ The signal for the actual position of the spool is thendemodulated and fed back to the controller, where it iscompared with the command signal.
➣ The controller drives the pilot valve until the error betweencommand signal and spool position feedback signal is zero.
➣ Thus, the position of the main spool is proportional to theelectrical command signal.
SERVOJET® SERVO-PROPORTIONAL VALVE OPERATION
VALVE SPOOL
➣ Spool slides in bushing (sleeve) or directly in body bore.
➣ Bushing contains rectangular holes (slots) or annular grooves that connect to supply pressure PS and tank T.
➣ At “null,” spool is centered in bushing; spool lobes (lands)just cover PS and T openings.
➣ Spool motion to either side of null allows fluid to flow fromPS to one control port, and from other control port to T.
X T A P B T2 Y
Annular Area
Nozzle Receiver
JetPipe
18
27
The Jet-Pipe Function
28
DesignAreospace LLC
28
