Fluid Power Devices Circuits

HYDRAULIC CONTROL DEVICES & CIRCUITS

FLUID POWER DEVICES & CIRCUITS CIRCUITS

FLUID POWER – DEVICES & CIRCUITS

RANA SAHA DEPARTMENT DEPARTMENT OF MECHANICAL ENGINEERING JADAVPUR JADAVPUR UNIVERSITY KOLKATA – 700 032 [email protected]


THE SYSTEM ACCESSORIES

Voltage

EHP

ELECTRIC MOTOR

Current

rpm

lpm

IHP

HHP PUMP

Torque

CONTROL DEVICES

Pressure

RESERVOIR

rpm or m/s

lpm

HHP

OHP ACTUATOR LOAD

• Power Supply Pressure • Controller • Sensors • DAS • PC Interface

AUTOMATIC CONTROL

Torque/ Force



Hydraulic fluids


Reservoir In addi additi tion on to hold holdin ing g the the supp supply ly of flui fluid d needed to ensure that all lines and components are completely filled with fluid at all times, the reserv reservoir oir has four four other other functi functions ons:: 1. It separates entrained air. air. Dwell time in the rese reserv rvoi oirr prov provid ides es oppo opport rtun unit ity y for for air air bubb bubble less in the fluid luid to rise rise to the the top top and and burs burstt on the the surf surfaace. 2. It dissipates pressure pressure pulses. Circ Circui uits ts with ith sev several ral actua tuators tors and ran random dom actua tuatio tion of the these actu actuat ator orss can can have have sign signif ific ican antt pres pressu sure re puls pulses es in the the retu return rn line line.. OffOff-li line ne filt filtra rati tion on elim elimin inat ates es the the infl nfluence of thes hese pulses on the filter, because they they are are diss dissip ipat ated ed by the the rese reserv rvoi oirr. 3. It 3. It provides cooling. 4. It 4. It traps contaminant. If the the rese reserv rvoi oirr has has to trap trap contaminant, the filtration is not working corre orrecctly tly. The rese reserv rvoi oirr doe does tra trap conta ontam mina inant when when the filter filter bypas bypasses ses..



Pumps Positive Displacement

Non Positive Displacement Centrifugal

Variable

Fixed

Axial Propeller

Vane Gear

Mixed Flow

Internal Internal External (Crescent) (Gerotor)

Piston

Vane

Screw

Balanced

Radial

Unbalanced

Axial

Piston

Swash Plate

Radial

Bent Axis

Axial Rotating Cylinder Block

Bent Axis

Swash Plate Rotating Swash Plate

Classification of Pumps


GEAR PUMP

•

For relatively low level of pressure (about 140 to 180 bar or 14 to 18 MPa) • Very simple, reliable, relatively cheap and less dirt sensitive • In order to prevent cavitation, the pressure at the suction side of the pump should not exceed 0.1 to 0.2 bar (10 to 20 kPa) below atmospheric pressure (minimim absolute pressure: 0.8 bar or 80 kPa).



GEAR PUMP – DETAILS


VANE PUMP

Variable •Maximum

Fixed

pressure: about 200 bar. •Pulse free delivery and low level of noise. •The amount of eccentricity determines the displacement displacement of the pump. pressure at the suction side of the pump •In order to prevent cavitation, the pressure should not exceed 0.1 to 0.2 bar (10 to 20 kPa) below atmospheric pressure (minimim absolute pressure: 0.8 bar or 80 kPa).



AXIAL PISTON PUMP Fixed •

Workingpressure above aprox. 250 bar. • This type of pump can be driven in both directions. Rotating Swash Plate •

Can operate without valves because the rotating barrel has a determined suck and pressure zone. • Normally this pump has 5, 7, 9 or 11 pistons.

Rotating Barrel


AXIAL PISTON PUMP – CYLINDER VALVE PLATE DETAILS



Variable •The angle of the

swashplate determines the stroke of the pistons and therefore the amount of displacement of the pump. •Normally the swashplate is adjusted by a hydraulic cilinder built inside the pumphousing.


Valves Pressure Control

Pressure Relief

Flow Control

Fixed

Direction Control Check Valve Shuttle

Pressure Reducing Sequence Unloading

Variable Two Way Pressure Compensated Deceleration

Counterbalance

Valve Functions Classification

Three Way Four Way



PRESSURE RELIEF VALVE Single Stage


PRESSURE RELIEF VALVE Pilot Operated (2 Stage)



PRESSURE RELIEF VALVE AS AN UNLOADING VALVE •

•

•

The pi pillot ope perrat ateed pr preess ssur uree rel elie ieff val alve ve is ap appl plie ied d in sy syst stem emss with a considerable amount of flow. It's task is to limit the pressure in the system on an acceptable value value.. The pilot val alv ve is adjusted at 150 bar. The pressure below the main valve is equal to the press ssu ure above the main valve, for exam ex ampl plee 10 100 0 ba barr (d (det eter ermi mine ned d by th thee lo load ad on th thee hy hydr drau auli licc mo moto tor) r).. The sp spri ring ng on th thee ma main in va valv lvee (a (abo bout ut 1 to 5 ba bar) r) ke keep epss th thee va valv lvee in thee cl th clos osed ed po posi siti tion on.. As lo long ng as th thee pr pres essu sure re in th thee sy syst stem em do does es no nott increase the adjusted pressure, the pump flow goes to the hydr hy drau auli licc mo moto torr. Whe hen n th thee hy hydr drau auli licc mo moto torr is ov over erlo load aded ed,, th thee pressure will increase and the pilot valve will open. From that mom mo ment on th thee pr preess ssur uree ab abo ove th thee ma main in val alv ve is lim imit iteed on 15 150 0 bar. Howe Ho weve verr, th thee pu pump mp fl flow ow ca cann nnot ot be dr drai aine ned d by th thee sm smal alll th thro rott ttle le in th thee by by--pa pass ss ca cana nall, so the pr preess ssur uree be bellow th thee mai ain n val alv ve wil illl incr in crea ease se wit ith h th thee sp spri ring ng pr pres essu sure re of ab abou outt 1 to 5 ba barr (t (the he pr pres essu sure re below the main valve will increase to 151...155 bar). Then the main valve opens and the majority of the pump flow will be drai dr aine ned d by th thee ma main in va valv lve. e.


SEQUENCE SEQ UENCE VALVE



COUNTER BALANCE VALVE


FLOW CONTROL

Fixed



PRESSURE COMPENSATED FLOW CONTROL VALVE


CHECK VALVES

Pilot – operated check valve



SHUTTLE VALVE


DIRECTION CONTROL VALVE

Method of actuation: • Manual • Electrical - Sole Soleno noid id - Force/T Force/Torque orque Motor




Actuators Rotary

Linear

Symmetric

Limited rotation

Continuous rotation Gear

Vane Asymmetric

Vane

Piston

Single Acting

Piston Fixed Unidirectio tional

Double Acting

Bidirectional

Variable

Classification of Actuators Actuators and their Symbols



A typical linear actuator details


ACCUMULATORS

An accumulator accumulator is a container container in which fluid is is stored under pressure pressure as a source of power. Functions: 1.Auxiliary power source to supplement the pump 2.Emergency power source in case of power failure to operate critical circuit functions 3.Hydraulic shock absorber for circuits where sudden impact loads, quick stops, or reversals with heavy loads are a characteristic of the system



INTENSIFIERS

Converts low-pressure fluid power into higher-pressure fluid power. Intensifiers (also called boosters) are used to multiply forces when a great force is needed through a relatively short distance. Hydraulic presses, riveting machines, and spot welders are typical applications. •

•

•


Some Basic Hydraulic Circuits

Basic Hydraulic Circuit - Linea inear r - Rota Rotarry • Regenerative Circuit • Counterbalance Circuit • Hydraulic Circuit with Speed Control - Meter Meter-I -In n - Meter Meter-O -Out ut • Sequence Circuit • Accumulator Circuit • Intensifier Circuit •


FLUID POWER DEVICES & CIRCUITS CIRCUITS RETRACT EXTEND

Linear Actuator (Hydraulic Cylinder)

Directional Control Valve A

P

B

T

Pressure Relief Valve

Pressure Gauge

Pump

Suction Strainer

BASIC HYDRAULIC CIRCUIT-1 CIRCUIT-1 Reservoir


Rotary Actuator (Hydraulic Motor)

A P

B T

BASIC HYDRAULIC CIRCUIT-2 CIRCUIT-2


FLUID POWER DEVICES & CIRCUITS CIRCUITS RETRACT EXTEND

A

P

B

T

REGENERATIVE CIRCUIT (Extension stroke)


Counter balance Valve

COUNTERBALANCE CIRCUIT



Pressure Compensated Flow Control Valve

SPEED CONTROL CIRCUIT (METER-IN)


Pressure Compensated Flow Control Valve

SPEED CONTROL CIRCUIT (METER-OUT)



Sequence Valve

SEQUENCING CIRCUIT

FLUID POWER DEVICES & CIRCUITS CIRCUITS Accumulator 2 way, Solenoid operated DCV

4 way, Solenoid operated DCV

ACCUMULATOR CIRCUIT (AUXILIARY POWER SOURCE)



Intensifier (Booster Cylinder)

INTENSIFIER CIRCUIT (High speed, low pressure approach followed by low speed high pressure piercing operation)


A TYPICAL ELECTROHYDRAULIC CONTROL SYSTEM



Suggested Reading: P ower.. Prentice Hall. • Pease, D.A. Basic Fluid Power •

Merritt, H. E. (1967), Hydraulic Control Systems. Wiley, Wiley, New York.

•

Esposito, A.; Fluid Power (with Application). 2003

Sullivan, James A., 1998, Fluid Power Theory and Applications, Fourth Edition, Prentice-Hall International •

• Yeaple,

Frank, 1996, Fluid Power P ower Design Handbook, Third Edition, Marcel Dekker, Inc., N.Y. N.Y.

Thank Than k You… You…

Fluid Power Devices Circuits

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