SERVICE TRAINING - BTP Hydraulics

1 HYDRAULIC SYSTEMSSERVICE TRAININGTABLE OF CONTENTSBASIC HYDRAULIC SYSTEMS .. Pumps ..10 Vane MOTORS ..13 HYDRAULIC SYSTEMS ..14 HYDROSTATIC SYSTEMS ..18 CONTROL HYDRAULIC TERMS ..22 June 2004- 2 -Basic Hydraulic SystemsBASIC HYDRAULIC SYSTEMSP urpose:This handout covers the most common questions about Cat hydraulic systems. It will explain thedifferent hydraulic systems, components, and methods of is a light, viscous liquid used as a lubricant or for power transfer in a hydraulic system. Mostcommon oils are refined from naturally occurring crude oil. The properties of the oil can be changedeither in the refining process or by using additives. Like most other liquids, oil is a virtuallyincompressible substance. Therefore, it transmits power instantaneously in a hydraulic system.

2 Theprimary functions of oil in a hydraulic system include: Power transmission Lubrication Sealing CoolingViscosity Oil becomes thin as the temperature rises and thickens as the temperature lowers. If the viscosity ofthe oil is too low, the oil may leak past seals and joints. If the viscosity is too high, sluggish operationmay be the result and extra power is needed to push oil through the system. Viscosity of oil isexpressed by the Society of Automotive Engineers (SAE) numbers 5W, 10W, 20W, 30W, 40W, higher the viscosity number, the thicker the oil. Most hydraulic systems use 10W oil. Petroleum OilPetroleum oil is the most common type of oil used in hydraulic systems. It is refined from naturallyoccurring crude oil found in the earth s crust. It can maintain a constant volume under high pressure,compressing only 1% for every 2000 psi.

3 The molecular chains of petroleum oil are random in means that at extreme high or low temperatures, petroleum oil can break down in the system overa long range of 2004- 3 -Basic Hydraulic SystemsSynthetic OilSynthetic oil is a lubricant that is manufactured without the use of crude oils for base stock. Theprocess of making synthetic oil involves chemical reactions with specific materials to produce acompound with planned and predictable properties. Synthetic oils are specifically blended with ahigher viscosity index than petroleum oils. Viscosity index is a measurement of a fluid s change inthickness depending upon changes in the temperature. This enables synthetics to operate in extremeheat and cold better than petroleum oils. The molecular chains in synthetic oil are consistent in length,enabling a close estimate to be made about the properties of synthetic oil.

4 Synthetic oils have nosignificant advantage in normal temperature ranges or at standard change OilBiodegradable oil is a fluid based on biodegradable vegetable oil. It is recommended when hydraulicmachines have to operate in environmentally sensitive areas such as forests, parks, golf courses, lakes,and agriculture. If spilled, biodegradable oil is able to biodegrade and will not cause damage to thesoil, water, environment, or nature. The fluid properties of biodegradable oil are typically inferior tomost petroleum and synthetic based 2004- 4 -Basic Hydraulic SystemsVALVESD irectional Control ValveA directional control valve directs the supply of oil to an actuator. A directional control valve consistsof a body with internal passages, which are connected and disconnected by a moveable valve of the valve is the valve spool.

5 The valve spool consists of lands and grooves. The lands blockoil flow through the valve body, while the grooves allow oil to flow around the spool and through thevalve body. There are two basic types of directional control valves; open center valves and closedcenter 2004- 5 -Basic Hydraulic SystemsOpen Center ValvesOpen center valves permit oil to flow through the valve at all times. In NEUTRAL the open centerpassage allows oil to flow from the supply back to the tank at low pressure. When the valve is shifted,oil flows from supply to an actuator. The returning oil from the actuator flows back through the valveto the tank. The valve can be shifted in the opposite direction, allowing it to be supplied to theopposite side of the center hydraulic systems are always supplying a relatively high flow.

6 This enables the hydraulicsystem to quickly respond when the valve is shifted. Advantage: Fast responseDisadvantage: Partial shift causes partial flow to the tank and the actuator, which generates more heat Control may not be as precise Typically requires a larger oil coolerJune 2004- 6 -Basic Hydraulic SystemsClosed Center ValvesClosed center valves operate similar to open center valves, except in NEUTRAL. Closed center valvesblock the flow from the pump to the tank in NEUTRAL. When the valve is shifted oil flows only tothe actuator with a full or partial shift. When the valve is centered, flow through the valve valves are typically used with a variable displacement pump to provide flow on : Flow only to circuit activated Generates less heat than open center valves More precise flow controlDisadvantage: Requires high flow relief valve or variable displacement pump Slower response when activatedJune 2004- 7 -Basic Hydraulic SystemsHYDRAULIC PUMPSH ydraulic pumps are used to create flow of the oil in a hydraulic system.

7 Various designs are used forpumps including: Gear Vane Gerotor PistonAll pumps produce flow. Pressure is created as a result of system 2004- 8 -Basic Hydraulic SystemsINLET OILOUTLET OILHOUSINGDRIVE GEARIDLER GEARHOUSINGOUTLETRING GEARCRESCENTDRIVE GEARINLETGear PumpsA gear pump develops flow by carrying fluid between the gear teeth and the housing. There are twotypes: external and internal. External gear pumps have two gears in mesh fitted inside a gear pumps ( crescent pumps) also use two gears, but one gear rotates inside the : Simpler system Compact design Handles debris well Long life Low costDisadvantages: Fixed displacement Input speed must be increased to get more flow output High horsepower drawWhere Used: Engine oil pumps Transmission pumps Lower pressure hydraulic systemsJune 2004- 9 -Basic Hydraulic SystemsOUTERGEARINNERGEARG erotor PumpsA gerotor pump is similar to an internal pump except that the inner gear sets inside the outer gear, andthe outer gear turns slower than the inner gear on some designs.

8 Other designs have a fixed outer gearand the inner gear walks around in the outer gear (Also known as a hand-metering unit). Advantages: Compact design Low costDisadvantage: Fixed displacement Input speed must be increased to get more output Lower pressure range than other pumpsWhere Used: Steering systems Some engine oil pumpsJune 2004- 10 -Basic Hydraulic SystemsINLET PORTROTOROUTLETPORTVANESCAMRINGVane PumpsThe operation of a vane pump works by a rotor driven by a drive shaft that turns inside an oval camring. Vanes are fitted to the rotor slots and follow the surface of the ring as the rotor turns. The fluidis forced between the vanes and is carried out to the other side of the pump. Vane pumps are eitherfixed or variable displacement. Variable displacement pumps are not as robust as fixed displacementpumps and are seldom used in mobile hydraulic applications.

9 Fixed displacement pumps that use twoinlet and outlet ports are balanced, which increases the pump : Versatile design Unbalanced pumps are able to be variable displacement pumps QuietDisadvantages: Cannot handle as high pressures as other designs Does not tolerate contamination wellWhere Used: Wheel loader hydraulic system Scraper hydraulic systemJune 2004- 11 Basic Hydraulic SystemsCAM RINGCAM FOLLOWERPISTONVALVEINTAKEEXHAUSTFIXED DISPLACEMENTINTAKEEXHAUSTVARIABLE DISPLACEMENTCONTROL LEVERRETAININGPLATESWASHPLATESWASHPLATES LIPPERPISTONBARRELASSEMBLYDRIVESHAFTP iston PumpsPiston pumps operate by a piston reciprocating in a bore as the pump rotates. The piston draws fluid inas it retracts and expels fluid as it moves forward. Piston pumps can be either radial or axial, and bothstyles can be fixed or variable displacement.

10 Fixed displacement axial piston pumps operate by using afixed position swashplate to control the output of the pistons. Variable displacement axial pistonpumps vary displacement by varying the angle of the swash plate. Radial piston pumps are typicallyvariable displacement and vary their displacement by moving a reaction ring to increase or decreasepiston travel. Advantages: Capable of high speeds and high pressures Variable displacement capability Reduced horsepower drawDisadvantages: More complex than vane or gear pumps Tightly machined surfaces demand clean hydraulic fluid High initial cost Does not tolerate contamination wellWhere Used: Hydraulic Excavator hydraulic system Track Type Loader Hydrostatic drive system Backhoe Loader hydraulic systemJune 2004- 12 -Basic Hydraulic SystemsHYDRAULIC MOTORSH ydraulic motors closely resemble hydraulic pumps in construction.