Hydraulic Systems Basics

12Hydraulic SystemsAccurate diagrams of hydraulic circuits are essentialto the technician who must diagnose and repairpossible problems. The diagram shows how thecomponents will interact. It shows the technician howit works, what each component should be doing andwhere the oil should be going, so that he candiagnose and repair the system.There are two types of circuit diagrams.Cutaway Circuit Diagrams show the internalconstruction of the components as well as the oil flowpaths. By using colors, shades or various patterns inthe lines and passages, they are able to show manydifferent conditions of pressure and flow.The other type of diagram is the Schematic CircuitDiagram.Schematic Circuit Diagrams are usually preferredfor troubleshooting because of their ability to showcurrent and potential system functions. A schematicdiagram is made up of consistent geometric symbolsfor the components and their controls andconnections.Schematic symbol systems:I.S.O. International Standards Organization.A.N.S.I. American National Standards InstituteA.S.A American Standards AssociationJ.I.C. Joint Industry ConferenceA combination of these symbols are shown in thismanual. There are difference between the systemsbut there is enough similarity so that if youunderstand the symbols in this manual you will beable to interpret other symbols as well.Hydraulic ReservoirsReservoirs are pictured as either an open squaremeaning it is a vented reservoir, or a closed reservoirmeaning that it is a pressurized reservoir. Everysystem reservoir has at least two lines connected toit, and some have many more. Often the componentsthat are connected to it are spread all over theschematic. Rather than having a lot of confusinglines all over the schematic, it is customary to drawindividual reservoir symbols close to the component.Similar to the ground symbol in some wiringschematics. The reservoir is usually the onlycomponent to be pictured more than onceToro University Technical Training

Hydraulic SystemsHydraulic Lines13LinesA hydraulic line, tube, hose or any conductor thatcarries the liquid between components is shown as aline. Some lines have arrows to show direction of oilflow, and lines may be shown as dashed lines toshow certain types of oil flow.There are lines that cross other lines but are notconnected, there are several ways to show lines thatare not connected. Lines that are connected areshown with a dot or sometime just as two linescrossing. If the schematic shows a specific symbol toshow lines that are not connected then anything elseis connected.PumpsHydraulic PumpsThere are many basic pump designs. A simple fixeddisplacement pump is shown as a circle with atriangle that is pointing outward. The triangle pointsin the direction that the oil will flow. If the pump isreversible or is designed to pump in either direction,it will have two triangles in it and they will pointopposite of each other indicating that oil may flow inboth directions. An arrow through the pump showsthat it is a variable displacement pump.Hydraulic MotorsHydraulic MotorsHydraulic motor symbols are circles with triangles,but opposite of a hydraulic pump, the triangle pointsinward to show the oil flows in to the motor. Onetriangle is used for a non-reversible motor and twotriangles are used for a reversible motor. An arrowthrough a motor shows that it is a variable speedmotor.Toro University Technical Training

14Hydraulic SystemsCheck Valves and Relief ValvesCheck ValvesA check valve is shown as a ball in a V seat. Whenoil pressure is applied to the left side of the ball, theball is forced into the V and no oil can flow. When oilpressure is applied to the right side of the ball, theball moves away from the seat and oil can flow pastit. A by-pass check is a one way valve with a springon the ball end of the symbol. This shows thatpressurized oil must overcome the spring pressurebefore the ball will unseat.Relief ValvesA relief valve is shown as a normally closed valvewith one port connected to the pressure line and theother line connected to the reservoir. The flowdirection arrow points away from the pressure lineand toward the reservoir. When pressure in thesystem overcomes the valve spring, pressure isdirected through the valve to the reservoir.Control ValvesControl ValvesA control valve has envelopes (squares) thatrepresent the valve spool positions. There is aseparate envelope for each valve position and withinthese envelopes there are arrows showing the flowpaths then the valve is shifted to that position. All theport connections are drawn to the envelope thatshows the neutral position of the valve. We canmentally visualize the function of the valve in anyposition. A valve that has parallel lines drawn outsideof the valve envelopes shows that this valve iscapable of infinite positioning. This valve usuallyoperated between the positions shown. An exampleof this type of valve would be a flow priority valve or apressure regulating valve.Valve actuatorsThe valve spools can be controlled a variety of ways.The top picture (A) shows the symbol for a levercontrol. The middle picture (B) shows the symbol fora pedal control (foot operated). The lower control (C)is an electric solenoid.Toro University Technical Training

Hydraulic SystemsCylinders15Hydraulic CylindersA cylinder symbol is a simple rectangle representingthe barrel. The rod and piston are represented by atee that is inserted into the rectangle. The symbolcan be drawn in any position.MiscellaneousFilters and CoolersFilters, strainers and heat exchangers (coolers) areshown as squares that are turned 45 degrees andhave port connections at the corners. A dotted line90 degrees to the oil flow indicates a filter or astrainer. A solid line 90 degrees to the oil flow with 2triangles pointing out indicates a cooler. The symbolfor a heater is like that of a cooler, except thetriangles point inward.Flow ControlsThe basic flow control is a representation of arestrictor. If the restrictor is adjustable a slantedarrow will be drawn across the symbol.Valve EnclosuresWhen you see an enclosure outline, that indicatesthat there are several symbols that make up acomponent assembly such as a valve body or valvestack. The enclosure outline appears like a box andis broken with dashes on all sides.Toro University Technical Training

16Hydraulic SystemsComplete Hydraulic SchematicHere we have a simple hydraulic schematic using thesymbols that we discussed and how they are used ina complete schematic. You can see that we have ahydraulic pump which gets it’s fluid from thereservoir, pulls the fluid through the filter than sendsit to the valve. The valve directs the oil to thehydraulic cylinder.Toro University Technical Training

Hydraulic Systems17LIFTThe key to understanding complex schematics is to break them down into their individual circuits. If you aretroubleshooting a lift/lower problem, you don’t need to be looking at the cutting drive or steering circuits.This schematic is from the Reelmaster 5200/5400-D Service Manual. As you can see, in the Service Manual,we provide a information on where the flows and pressures are in different modes of operation to make theschematic easier to understand. There is also usually a written explanation of the circuit operation in theManual.Toro University Technical Training

18Hydraulic SystemsHydrostatic TransmissionsThere are three distinct types of hydrostatic drive systems currently used in turf mowing equipment.To begin to understand hydrostatic drive units, lets start by looking at the various types and configurations ofhydrostatic transmissions.Pump with Remote Wheel MotorsHydrostatic Systemwith remote mountedpumpIn-Line Pump and MotorThe first type is a hydrostatic system which consistsof a hydrostatic pump with a remotely mountedmotors. In this type of hydrostatic system thehydrostatic pump is mounted by, and driven by, theunits engine. The pump is connected to the drivemotor by hoses or steel lines. These motors can bemounted directly to the wheels or to a drive axle.A different type of hydrostatic drive system is aninline pump and motor system. In this system themotor and pump are constructed as a single unit, thiseliminates the necessity of high pressure drive linesbetween the pump and the motor. This unit isnormally mounted to a drive axle or transaxle.Toro University Technical Training

Hydraulic SystemsU-type TransmissionWhy Different Systems?19A similar version is the U-type transmission. In thistype of system the pump and motor are constructedas a common component with the pump usuallylocated above the motor.All three systems work well in their designedapplications. The remote motor design works wellwhen there is no transmission or transaxle, or whenthe location of the engine and the drive system callfor such a configuration. The U type hydrostaticsystem is more compact while the inline hydrostaticsystem is usually easier to repair and maintain.We will be using the inline hydrostatic pump andmotor system in this session for illustration purposes.A hydrostatic drive consists of a hydrostatic pump,which pumps oil to a drive motor. The mostsignificant feature of a hydrostatic system is thepump. The pump is a variable displacement pump.This means that the output of the pump can bevaried and is not controlled only by the engine RPMlike a fixed displacement pump. This requires that thepump be a piston pump.Toro University Technical Training

20Hydraulic SystemsComponentsLet’s look at the components that make up a complete hydrostatic drive system.Piston Group AssemblyThe pump consists of the following components:Piston group assemblyThis rotating piston group is mounted to the inputshaft and is driven by the engine. It consists of apiston block with numerous precision machinedbores which house the pump pistons. The smallpump pistons consist of the piston and the pistonslipper. The slipper is usually a brass or aluminumcomponent which is connected to the piston andmoves the pistons when the pump is operating.Swash PlateSwash plateThe piston slippers pivot and slide against ahardened washer called a thrust washer. The thrustwasher is located in the swash plate. The swashplate pivots on two support pins and controls thepump output. As the operator moved the tractioncontrol pedal to increase travel speed the swashplate angle increases.Piston Group OperationAs the piston group spins the pistons are moved inand out of their bores and they pump oil. As we sawin the previous slides the quantity of the oil beingpumped is controlled by the angle of the swash plate.As long as the swash plate is kept in the neutralposition, no oil will be pumped. As the operatormoves the traction control pedal the angle of theswash plate increases, this in turn increases thepiston travel. As the piston travel increases theamount of oil pumped increases and the travel speedchanges.Toro University Technical Training

Hydraulic Systems21Charge pumpCharge PumpWhile the transmission is in operation there is aconstant loss of oil (by design) within thecomponents of the pump and motor. For example,holes in the end of each piston allow a small amountof oil to form a cushion between the slipper’s faceand the thrust washer. This oil must be continuouslyreplenished. Built in to the system is pump called acharge pump. This pump can be a gear pump, or agerotor pump. Both of these pumps are fixeddisplacement. Fixed displacement means that thepump’s output is fixed by the RPM of the engine. Itcannot be varied except by increasing or decreasingthe speed of the engine. Excessive oil not requiredby the drive circuit opens the charge relief valve andflows back to the reservoir.Charge CircuitOil is lost during use through designed in leakage areas. Replenishes lost oil used for:CoolingLubricationHydrostatic Lubrication As the drive pressure increases so doesthe lubrication pressureLubricationPressureDrivePressurePistonToro University Technical TrainingOne piston is shown here illustrate the principle thatthe drive pressure increases so does the lubricationpressure for the piston slipper and swash platesurface.

22Hydraulic SystemsOn a remote hydrostatic motor type system thehydrostatic motors can be a gear motor, gerotormotor or a piston type motor as shown here. Onsome designs a single motor is used to drive adifferential transaxle. Another design uses individualmotors for each wheel, either driving the wheelsdirectly or through a planetary gear drive.MotorsPiston MotorGear MotorGerotor MotorWhen the motor is built as part of the completeassembly like an inline or U type system the motor isa piston type motor very similar the piston pumpexcept that the swash plate is usually a fixed swashplate. Being fixed the stroke of the pistons remainconstant. The motor’s speed of rotation can not bechanged except by changing the volume of oil that itreceives from the pump. Remember that a givencolumn of oil will cause the motor to turn at a givenspeed. More oil will in-crease the motor speed. Lessoil will slow it down.Overall OperationAs the engine turns the pump rotating group, thepistons run on the swash plate which is in the neutralposition. With the swash plate in neutral there is nomovement of the pistons so no oil is being pumped.As the operator moves the traction control pedal theswash plate angle increases and the pump pistonsbegin to displace oil. This oil is directed to the pumpsection and the unit moves.Toro University Technical Training

Hydraulic Systems23When the operator needs to change directions thetraction pedal is moved back to the neutral positionand than moved to the reverse position. In thereverse position the swash plate moves in theopposite direction as it did in the forward direction. Inthis position the oil is pumped to the opposite side ofthe motor and the unit moves in reverse.Here is the closed loop circuit of an inline hydrostatictransmission shown in a schematic view.Directional charge checksDirectional charge check valves are incorporated intothe charge circuit to direct the charge pump output tothe low pressure side of the drive circuit. The oil willflow into the low pressure side to replace the oil lostthrough normal leakage. The oil in the high pressureside closes the remaining charge check valve so thatno high pressure oil can bleed off into the chargecircuit.Toro University Technical Training

24Hydraulic SystemsCharge Flow – GM300Simple items often overlookedHere is a view of the closed loop main circuit andcharge circuit within the inline hydrostatictransmission from a Groundsmaster 300 Series.The hydrostatic transmission will provide trouble freeoperation if it is serviced and maintained properly.There are, however, a few simple items that are oftenoverlooked when poor performance is evident.1. The “ no-load” engine RPM. setting is too slow.2. Worn, loose or misadjusted linkage is notposi-tioning the swash plate actuating arm farenough, even though the traction control pedal orhand lever is fully pushed.3. The tow or bypass valve is partially open, lettingoil bypass in the main system.4. The hydraulic oil filter or inlet line is not tightenedsufficiently; air is being drawn in past the filter sealinto the charge pump, and then into the main circuit.Air in the hydraulic system will cause cavitation anddamage the rotating components.IMPORTANT: The “tow valve” is not to be used fortowing long distances, but should be used only to getthe machine out of the way or onto a trailer. Towingover a distance will cause the traction circuit to runout of oil because charge pump is not running.Toro University Technical Training

Hydraulic Systems25Hydraulic Hoses and FittingsHydraulic HosesHydraulic hoses are subject to extreme conditionssuch as, pressure differentials during operation andexposure to weather, sun, chemicals, hightemperature operating conditions or mishandlingduring operation or storage. Hoses that move duringoperation are more susceptible to these conditionsthan others.\Before disconnecting or performing any work on ahydraulic system, all pressure in the system must berelieved by stopping the engine and lowering orsupporting the implement.Inspect hoses frequently for signs of deterioration ordamage. Check hoses for leakage and replace whenleaks are found.Keep body and hands away from pin hole leaks ornozzles that eject hydraulic fluid under pressure. Usepaper or cardboard, not hands, to search for leaks.Hydraulic fluid escaping under pressure can havesufficient force to penetrate the skin and do seriousdamage. If fluid is injected into the skin, it must besurgically removed within a few hours by a doctorfamiliar with this type of injury or gangrene mayresult.Hose BookToro University Technical TrainingWhen replacing a hydraulic hose, be sure that thehose is straight (not twisted) before tightening thefittings. This can be done by observing the imprint onthe hose. Using two wrenches, hold the hose straightwith one wrench and use the other wrench to tightenthe hose swivel nut to the fitting. Use proceduresshown in the Toro Hydraulic Hose Servicing Manual,Part No. 94813SL.

26Hydraulic Systems\O-ring Face Seal (ORFS FittingsMake sure both threads and sealing surfaces arefree of burrs, nicks, scratches, or any foreignmaterial.Make sure the O-ring is installed and properly seatedin the groove. It is recommended that the O-ring bereplaced any time the connection is opened.Lubricate the O-ring with a light coating of oil.SAE O-ring (Non-adjustable)SAE Straight thread O-ring Port Fittings (NonAdjustable)1. Make sure both threads and sealing surfaces arefree of burrs, nicks, scratches, or any foreignmaterial.2. Always replace the O-ring seal when this type offitting shows signs of leakage.3. Lubricate the O-ring with a light coating of oil.4. Install the fitting into the port and tighten it downuntil finger tight.5. Tighten the fitting to the correct torque.SAE O-ring Port (Adjustable)SAE Straight thread O-ring Port Fittings(Adjustable)1. Make sure both threads and sealing surfaces arefree of burrs, nicks, scratches, or nay foreignmaterial.2. Always replace the O-ring seal when this type offitting shows signs of leakage.3. Lubricate the O-ring with a light coating of oil.4. Turn back the jam nut as far as possible. Makesure the back up washer is not

gear pump is a positive displacement pump, meaning that whenever the pump is turning the pump must pump oil. If pump flow is totally blocked, sudden failure of the pump or other component will occur. As the gears in the pump rotate, suction is created at the inlet port o