1. BASIC HYDRAULICCIRCUIT

2. Basic Hydraulic Circuits 3. Structure of a hydraulic system This simplified block diagram shows the division of hydraulic systems into a signal control section and a hydraulic power section. This signal control section is used to activate the valves in the power control section. 4. Hydraulic power section The diagram of the hydraulic powersection is complemented in thiscase by a circuit diagram to allowcorrelation of the various functiongroups; the power supply sectioncontains the hydraulic pump anddrive motor and the components forthe preparation of the hydraulicfluid. The energy control sectionconsists of the various valves used toprovide control and regulate theflow rate, pressure and direction ofthe hydraulic fluid. This drivesection consists of cylinders orhydraulic motors, depending on theapplication in question. 5. Simple Hydraulic CircuitA simple openThe equivalentcenter hydraulic circuit circuit schematic 6. Interaction of components The animations show the sequences in a basic hydraulic circuit in simplified form - the actuation and spring return of the final control element (4/2-way valve), the advance and return of the drive component (double acting cylinder) and the opening and closing of the pressure relief valve. 7. Interaction of components (Animation) 8. Interaction of components (Animation) 9. Interaction of components (Animation) 10. Interaction of components (Animation) 11. Interaction of components (Animation) 12. Interaction of components (Animation) 13. Interaction of components (Animation) 14. Interaction of components (Animation) 15. Circuit diagram: Return flow filter An oil filter situated in thereturn line to the tank hasthe advantage that thefilter is thus easy tomaintain. Adisadvantage, however, isthat contamination isremoved from thehydraulic fluid only after ithas passed through thehydraulic components. This configuration is oftenused. 16. Circuit diagram : Pump inlet filter With thisconfiguration, the pump isprotected fromcontamination. The filteris, on the other hand, lesseasily accessible. If these filters have a toofine mesh, suctionproblems and cavitationeffects may occur.Additional coarse filtersupstream of the pump arerecommended. 17. Circuit diagram: Pressure linefilter Pressure filters can beinstalled selectivelyupstream of valves whichare sensitive tocontamination; this alsoenables smaller mesh sizesto be used. A pressure-resistanthousing is required, whichmakes this configurationmore expensive. 18. Circuit diagram: Contamination indicator It is important that the effectivenessof a filter can be checked by acontamination indicator. Thecontamination of a filter ismeasured by the pressure drop; asthe contamination increases, thepressure upstream of the filterincreases. The pressure acts on aspring- loaded piston. As thepressure increases, the piston ispushed against a spring. There are a number of differentdisplay methods. Either the pistonmovement is directly visible or it isconverted into an electrical or visualindication by electrical contacts. 19. Circuit diagram: Hydraulic powerunit The illustration showsthe detailed circuitsymbol for a hydraulicpower unit. Since this is ancombination unit, adot/dash line is placedaround the symbolsrepresenting theindividual units. 20. Pressure relief valve (1) In this designincorporating a poppetvalve, a seal is pressedagainst the inlet port P by apressure spring when thevalve is in its normalposition. In this situation, forexample, an unloadedpiston rod is executing anadvance stroke and theentire pump delivery isflowing to the cylinder. 21. Circuit diagram: Pressure reliefvalve (2) As soon as the forceexerted by the inletpressure at A exceeds theopposing spring force, thevalve begins to open. In this situation, forexample, the piston rod isfully advanced; the entirepump delivery is flowing atthe preset system pressureto the tank. 22. PRV used to limit system pressure This illustration shows apressure relief valve withina basic hydraulic circuit(used to control a doubleacting cylinder). The resistances at theoutlet (tank line, filter)must be added to the forceof the spring in thepressure relief valve. Seealso the animationInteraction ofcomponents (at page 7). 23. PRV used to limit system pressure This illustration shows the same circuit as the previous illustration, but with the cut-away view of the PRV replaced by the appropriate circuit symbol. 24. (1A) Circuit without brake valve(Animation) One application of pressurerelief valves is as brake valves;these prevent pressure peakswhich may otherwise occur asthe result of mass moments ofinertia when a directionalcontrol valve is suddenly closed.The animation shows an(incorrect) circuit in schematicform in which the working lineon the exhaust side hasfractured due to the absence of abrake valve. The next animation shows thecorrect circuit. 25. Circuit without brake valve(Animation) 26. Circuit without brake valve(Animation) 27. Circuit without brake valve(Animation) 28. Circuit without brake valve(Animation) 29. (2) Circuit diagram: Brake valve This illustration shows thecorrect circuit for the problem intopic 1A. This circuitincorporates not only a brakevalve on the piston-rod side butalso a non-return valve on theinlet side via which oil can betaken in from a reservoir duringthe vacuum phase following theclosure of the directional controlvalve. The following animation showsthe events which occur in thetwo working lines. 30. Circuit with brake valve(Animation) The animation (2a) showsin schematic form thebehavior of the PRV duringthe braking phase, while(2b) shows the behavior ofthe non-return valve(NRV) in the supply lineand (2) shows the twoevents together insummary. The necessity of the brakevalve can be demonstratedby the precedinganimation. 31. [2a] Circuit with brake valve (Animation) 32. [2b] Circuit with brake valve (Animation) 33. Thank you