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DIRECTION CONTROL VALVE
- 2. INTRODUCTION Directional controlvalves • Asthe name implies directional control valves are used to control the direction of flow in ahydraulic circuit. Theyare used to extend, retract, position or reciprocate hydraulic cylinder and other components for linear motion. • Valvescontains ports that are external openings for fluid to enter and leave via connecting pipelines • Thenumber of ports on adirectional control valve (DCV) isusually identified by the term “way”.Forexample, avalve with four ports isnamed asfour-way valve 2
- 3. Classificationof Directional control valves 1. According to type of construction: • Poppet valves • Spoolvalves 2. According to number of working ports: • Two-way valves • Three – way valves • Four- wayvalves. 3. According to number of Switchingposition: • Two– position • Three – position 4. According to Actuatingmechanism: • Manual actuation • Mechanical actuation • Solenoid ( Electrical ) actuation • Hydraulic ( Pilot )actuation • Pneumatic actuation 3
- 4. Poppetvalves Directional poppet valves consists of a housing bore in which one or more suitably formed seating elements ( moveable ) in the form of balls, conesare situated. When the operating pressure increases the valve becomesmore tightly seatedin this design. Themain advantage of poppet valvesare; • No Leakageasit provides absolutesealing. • Longuseful life, asthere are no leakageof oilflows. • May be used with even the highest pressures,asno hydraulic sticking(pressure dependent deformation ) and leakagesoccursin thevalve. Thedisadvantages of these valvesare; • Largepressure lossesdue to shortstrokes • Pressurecollapse during switching phasedue to negative overlap ( connectionof pump, actuator and tank at the sametime). 4
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- 6. spoolvalves • Thespool valve consistsof aspool which is acylindrical member that haslarge- diameter lands machined to slide in avery close- fitting bore of the valve body. • Thedegree of sealing depends on the sizeof the gap,the viscosity of the fluidand especially on the level ofpressure. • Theamount of leakageis primarily dependent on the gapbetween spool and housing. Henceasthe operating pressure increases the gapmust be reducedor the length of overlap increased.Theradial clearance is usually lessthan 20μ. 6
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- 8. DCVFLOWPATHTERMINOLOGY 8 Valve Type Valve Use 2 way On oroff functionsfor fluidsupply 3 way Singleactingcylinders& uni- directionalmotors 4 way Doubleactingcylinders,bi-directional motors 5 way Pneumaticsystemswith dual air pressure Theabove description referto thetotal numberof directions in which a fluidcan travelthrougha directional control valve
- 9. DCVFLOWPATHTERMINOLOGY • 2POSITION • 3POSITION • 4POSITION Thepositions referto which direction thefluidhappens to going when a valve is shifted 9
- 10. DCVSCHEMATICSYMBOLS Thebasicvalve symbol is ablank envelope. DCV‘Shaveatleast two envelops which corresponds with 2 position valve. A3 position valve will havethree envelope and soforth. 10
- 11. Arrows are added to indicate adirection that fluid cantravel through the valve in that position. Eacharrow crossing represents two ports .Theabove example indicates four ports. 11
- 12. 3wayvalve 12 2wayvalve Thelittle ‘T’Emblem represents blocked port The arrow indicate one inlet port and one outlet port
- 13. 4 WAY3 POSITIONDCV Thecutaway diagram showshow aspool canconnect and disconnect passages 13
- 14. WORKING •If spool is shifted to right ,portAis connected to the port which is being fed by the pump,port P .At the sametime port BISconnected tothe tank port T . •Thefluid from the port Pflows through the port Aand tankTreceives the fluid from portB 14
- 15. •If the spool is shifted to left ,the spool connects port Pwith port B, and port A withport Twhich givesareversal of the previous flowpath 15
- 16. DCVOPERATORS •An operator is adevice that physically movesaspool or poppet. •Manual operators such as the push button,handlever,and foot pedal use human power foractuation. •Mechanical operators useamachine component to contact aroller or ball bearing. •Pilot operators useafluid to movethe spool. •Asolenoid useselectro-mechanical force to move aspool orpoppet. 16
- 17. SOLENOIDOPERATION •Asolenoid is an electrical-mechanical device that takes electrical energy and produces alinear force in the direction ofvalve spool. •When solenoid is energized ,the air gapis closed quickly and aforce isdeveloped in the direction of the valve spool. •Aspring holds the spool against the solenoid pushpin when the solenoid is de- energized. 17
- 18. DETENTS(OPERATOR) •Detents are usedto hold avalve spool inplace. •Theykeep the spool from moving due to vibration or possibly from gravity where the valve is placed in an uprightposition. •Theabove fig showsaball and spring typedetent 18
- 19. SUBPLATEMOUNTED4 WAYVALVES •Subplate or sub basemounting is convenient way of attaching aDCVto a system and reducing the time required to replace it should the need arise. •TheDCVis held into place by four fasteners and asealis made with Orings. The time savingsis in to having toremove pipe connections 19
- 20. PIGGY-BACKDCV •Piggy-backingis aterm used to describe two valvesconnected asaUnit wheresmall valve controls the operation of largervalve. •This arrangement makesused of the powerful force of fluid in order to actuate a largeflow DCV . 20
- 21. CENTERCONDITIONS • OPENCENTER •In open- center circuit, all ports are open to each other in the center position. When the valve is in open center position, the pump flow is directed to the tank at atmospheric pressure. •At the sametime the actuator canbe moved freelyby applying an external force. Open center valve help to prevent heatbuildup. 21
- 22. CLOSEDCENTER •In closed center DCVall ports are closed to each other.Hence the actuator connected to ports Aand Bis hydraulically locked and cannot be movedby an external force . •This not only waste pump design power but promotes wear and shortens pump life.Also the temperature of oil is raised due to heat buildup in the system. Thispromotes oil oxidation , viscosity drop, which further raises the wear of parts and increased leakage. 22
- 23. TANDEMCENTERED • In the center configuration, the working portsAand Bare blocked , and the pump port Pis connected to tank portT . •Thetandem center also results in alocked actuator . However,italso unloads the pump at atmosphericpressure. •Theapplication of this design may be to hold acylinder or fluid motor under load23.
- 24. FLOATINGCENTERED •In this position the pump port is blocked and the two working ports Aand Bare connected to tank port T .Sincethe working ports Aand Bare connected to tank T , the actuator can be moved freely without any external force and hence the name floating. •The pump produce flow at the high pressure setting of the pressure relief valve, which builds up heat in the circuit. Hence this center configuration is used only in special case. 24
- 25. APPLICATIONOFCVIN AUTOMATIC TRANSMISSION •Control valves can also react to changesin pressure. This simple shift valve is held at the end of its bore by spring tension and blocks the fluid under pressure at portA. •Thelarger differential area at port Cis subject to governor pressure and asvehicle road speed increases, the increasing pressure forces the valve to the left and allows fluid to flow acrossfrom port Ato port B.Thiscan be directed to operate the next clutch or servo and change the transmission to ahigherratio. •Asroad speed falls and governor pressure diminishes, the spring moves the valve back to cut off the fluid supply and the transmission downshifts. 25
- 26. APPLICATIONSIN AUTOMOTIVEAREA 26 • Control valvesare applied in each area where hydraulic controland actuation tasksoccur. • In the automotive area, Supply,control and regulating of actuations for automated manual transmissions (AMT), double clutch transmissions (DCT),continuous variable automatic transmissions (CVT)or automatic transmissions (AT). • Control of automated clutch actuations in hybrid drives. • Control of differentiallocks.
- 27. C0NCLUSION 27 • Directional control valve is used to direct the supply of oil to theactuator in ahydraulic system. • Directional control valvesare essentially usedfor distribution ofenergy in afluid power system.Theyestablish the path through which afluid traverses agiven circuit. For example they control the direction ofmotion of ahydraulic cylinder ormotor. • Thesevalvesare usedtocontrol the start, stop and changein direction of flow of pressurizedfluid.
- 28. REFERENCE 28 • JagadheeshaT-fluid power control systems-hydraulics control inmachine tools(chpter2) • Maher yahyasallom,Zahurrin samad-MAGNETO-RHEOLOGICAL DIRECTIONALCONTROLVALVE-Date:21May2011 • V .JSonavane,T .JRane,P .CGawade-DESIGNANDANAL YSISOFGLOBEV AL VE ASCONTROLV AL VEUSINGCFDSOFTTWARE-Date:16July2012
- 29. THANKYOU 29