MAGM 262Mr. ConradoHydraulic Fundamentals - 2

The Hydraulic SystemThe basic hydraulic system has seven partsPumpLines and connectorsCylinder or MotorCheck valveReservoirControl ValveRelief Valve

Hydraulic pumpThe pump moves the hydraulic fluidPumps create flow not pressureCome in positive fixed displacement and variable displacementFix displacement Moves the same amount of fluid every rotationVariable displacement The amount of fluid discharged can be changed and controled.

Lines and ConnectionsCarry the fluid from the pump to where the work will be done and back.Come in various sizes and shapesAre a major source of repair

Cylinders and motorsDo the work the system was designed for.Convert hydraulic force into mechanical motion.CylindersConvert hydraulic force into recipricating motionCan be single acting or double actingMotorsConvert hydraulic force into rotary motion

The Check ValveA simple one way valve which uses a poppet to control fluid flow.Can be used to controlFluid directionCircuit pressures

The ReservoirIs the storage container for the hydraulic fluidMaintains constant supply of fluid to the pumpHelps in fluid filtrationActs as a heat sink and is a major part of the fluid heat dissipation system.

Control ValvesControl valves are used to control the pressure, direction and volume of oil flow in hydraulic systems.There are three types of control valvesPressure controlDirection controlVolume Control

Relief ValvesHydraulic systems are designed to operate at certain pressures. Relief valves are built into the system as a protection device.

Pressure through the Orifice Effect

Hydraulic FundamentalsThe Orifice EffectIn hydraulics it is common to use the term pump pressure. However the pump does not produce pressure only flow. When flow is restricted pressure is created.In the system we have here the pump is producing a flow of 1gallon per minute but note that do to the lack of any restriction the system pressure is zero.

Hydraulic FundamentalsAn orifice offers a restriction to pump flowWhen oil flows through the orifice, pressure is created on the upstream side of the orifice.In this example it could be stated that a pressure of 30 psi is needed to send a flow of 1GPM through this orifice.

Hydraulic FundamentalsOil flow to tank or reservoir blockedA positive displacement pump will continue to pump 1 GPM of oil into the system. When the system is full pressure develops throughout the system. The two gauge readings will be the same.Pressure will continue to increase until flow is diverted to another tank or circuit. This is usually done with a relief valve. If this was not done pressure would continue to rise until there was a failure in the system.

Hydraulic FundamentalsRestriction in SeriesThere are two basic types of circuits, series and parallel.Relief valves in this circuit (Orifices can also be arrange in this configuration) offer a resistance that is similar to resistors in an electrical system.Oil must flow through each resistance before it returns to the tank. The total resistance is equal to the sum of all the individual resistances.

Hydraulic FundamentalsRestriction in ParallelIn a parallel circuit system fluid will take the path of least resistance.Here the pump supplies oil for each of the three circuits.Circuit one has the highest priority and circuit three has the lowest.When the pump supplies oil the passages to the left of all circuits is being filled and pressurized. When this pressure reaches 30psi circuit one opens and begins to fill.One circuit one reaches 60psi circuit two opens and begins to pressurizeWhen circuit two reaches 90psi circuit three opens and begins to fill.

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