jj512basichydrauliccircuit-121222093438-phpapp01

8/12/2019 jj512basichydrauliccircuit-121222093438-phpapp01

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BASIC HYDRAULIC CIRCUIT


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Hydraulic power sectionThe 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.


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Simple Hydraulic Circuit

A simple opencenter hydraulic circuit

The equivalentcircuit schematic


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Interaction of componentsThe animations show thesequences in a basichydraulic circuit insimplified form - the

actuation and springreturn of the final controlelement (4/2-way valve),the advance and return ofthe drive component

(double acting cylinder)and the opening andclosing of the pressurerelief valve.


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Interaction of components(Animation)


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Circuit diagram: Return flow filter An oil filter situated in thereturn line to the tank hasthe advantage that thefilter is thus easy to

maintain. A disadvantage,however, is thatcontamination is removedfrom the hydraulic fluidonly after it has passed

through the hydrauliccomponents.This configuration is oftenused.


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Circuit diagram : Pump inlet filter With this configuration,the pump is protectedfrom contamination. Thefilter is, on the other hand,

less easily accessible.If these filters have a toofine mesh, suctionproblems and cavitationeffects may occur. Additional coarse filtersupstream of the pump arerecommended.


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Circuit diagram: Pressure linefilter

Pressure filters can beinstalled selectivelyupstream of valves whichare sensitive to

contamination; this alsoenables smaller mesh sizesto be used. A pressure-resistanthousing is required, whichmakes this configurationmore expensive.


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Circuit diagram: Contaminationindicator

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.


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Circuit diagram: Hydraulic powerunit

The illustration showsthe detailed circuitsymbol for a hydraulic

power unit.Since this is ancombination unit, adot/dash line is placedaround the symbolsrepresenting theindividual units.


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Pressure relief valve (1)In this designincorporating a poppet valve, a seal is pressedagainst the inlet port P by a

pressure spring when the valve is in its normalposition.In this situation, forexample, an unloadedpiston rod is executing anadvance stroke and theentire pump delivery isflowing to the cylinder.


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Circuit diagram: Pressure reliefvalve (2)

As soon as the forceexerted by the inletpressure at A exceeds theopposing spring force, the valve begins to open.In this situation, forexample, the piston rod isfully advanced; the entire

pump delivery is flowing atthe preset system pressureto the tank.


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PRV used to limit system pressureThis illustration shows apressure relief valve withina basic hydraulic circuit(used to control a double

acting 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).


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PRV used to limit system pressure

This illustration showsthe same circuit as theprevious illustration,

but with the cut-away view of the PRVreplaced by theappropriate circuit

symbol.


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(1A) Circuit without brake valve(Animation)

One application of pressurerelief valves is as brake valves;these prevent pressure peaks

which may otherwise occur asthe result of mass moments of

inertia when a directionalcontrol valve is suddenly closed.The animation shows an(incorrect) circuit in schematicform in which the working lineon the exhaust side has

fractured due to the absence of abrake valve.The next animation shows thecorrect circuit.


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Circuit without brake valve(Animation)


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(2) Circuit diagram: Brake valveThis illustration shows thecorrect circuit for the problem intopic 1A. This circuitincorporates not only a brake

valve on the piston-rod side but

also a non-return valve on theinlet side via which oil can betaken in from a reservoir duringthe vacuum phase following theclosure of the directional control

valve.

The following animation showsthe events which occur in thetwo working lines.


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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 brake valve can be demonstratedby the precedinganimation.


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[2a] Circuit with brake valve(Animation)


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[2b] Circuit with brake valve(Animation)


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jj512basichydrauliccircuit-121222093438-phpapp01