Basic Hydraulic SystemsBasic Hydraulic Systemsinin

Construction PlantConstruction Plant

John HoldenJohn Holden

Construction MachinesConstruction Machines

Construction machines use hydraulics to move heavy loads. Hydraulics can be used to move a

heavy Load, with a small force.

All of these machines use hydraulic pressure to move cylinders that operate buckets, booms,

blades and raise bodies.

Typical machines include:

Excavators.

Loading Shovel

Dump trucks.

Bulldozer

Pascal's LawPascal's Law

• The amount of pressure in the liquid The amount of pressure in the liquid is equal to the force, with respect to is equal to the force, with respect to the area being acted upon.the area being acted upon.

• The pressure always act at right The pressure always act at right angles to the surfaceangles to the surface

Pascal’s LawPascal’s Law

Pascal’s LawPascal’s Law

• Force is equal to area multiplied by Force is equal to area multiplied by pressurepressure

F = P x AF = P x A

• Pressure is equal to force divided by areaPressure is equal to force divided by area

P = P = FF AA

Hydraulic BasicsHydraulic Basics• Hydraulic pumps create Hydraulic pumps create flowflow - not pressure. - not pressure.

• Resistance to flow creates Resistance to flow creates pressurepressure. .

• Flow determines actuator speed. Flow determines actuator speed.

• Pressure determines actuator force. Pressure determines actuator force.

• Fluid under pressure takes the path of least Fluid under pressure takes the path of least resistance. resistance.

• When fluid moves from an area of high When fluid moves from an area of high pressure to an area of low pressure pressure to an area of low pressure (pressure drop) without performing useful (pressure drop) without performing useful work, heat is generated. work, heat is generated.

Basic Hydraulic SystemBasic Hydraulic System

Hydraulic TankGear Pump

Main Relief Valve

Return Filter

Direction Control Valve

Actuator

Hydraulic Tank

Gear Pump

Main Relief Valve

Return Filter

Actuator

Direction Control Valve

Hydraulic PumpHydraulic Pump

Gear Pump Vane Pump

Piston Pump

PosPump.exe

GearPump.exe

Piston PumpPiston Pump

Variable DisplacementVariable Displacement

Hydraulic RamsHydraulic Rams

Double Acting Double Acting

End CapPort Piston Rod Port

Piston Seal Cylinder Gland Seal Rod EyeDblCyl.exe

Double Acting RamDouble Acting Ram

• Double acting rams can exert force in Double acting rams can exert force in two directions. two directions.

• Under the influence of hydraulic Under the influence of hydraulic pressure the piston rod of a double pressure the piston rod of a double acting ram will both extend and acting ram will both extend and retract. retract.

Hydraulic RamsHydraulic Rams

Single Acting Ram

VentPort

Single Acting Ram

• Single acting rams can exert force in Single acting rams can exert force in only one direction. Under the only one direction. Under the influence of hydraulic pressure the influence of hydraulic pressure the piston rod of a single acting ram will piston rod of a single acting ram will extend.extend.

• The piston rod can only be retracted The piston rod can only be retracted by the influence of some external by the influence of some external force (usually the weight of the load force (usually the weight of the load or the machine itself ). or the machine itself ).

Displacement RamDisplacement Ram

• A displacement ramA displacement ram is a form of single acting ram. is a form of single acting ram.

• Pumping fluid into the port will fill the space Pumping fluid into the port will fill the space around the piston rod, as there is a seal between around the piston rod, as there is a seal between the gland and the rod the oil is contained.the gland and the rod the oil is contained.

• pumping further fluid into the cylinder will displace pumping further fluid into the cylinder will displace the volume of the piston rod and it will extend.the volume of the piston rod and it will extend.

Multistage Telescopic RamMultistage Telescopic Ram

• Multistage telescopic rams are most Multistage telescopic rams are most commonly single acting. commonly single acting.

• A telescopic cylinder is used to A telescopic cylinder is used to obtain a longer stroke length from a obtain a longer stroke length from a given closed length.given closed length.

SnglCyl2.exe

Relief ValvesRelief Valves

Direct ActingDirect Acting

Pilot Operated Relief ValvePilot Operated Relief Valve Relief ValvesRelief Valves

Closed Open

Blocked Oil Filter Blocked Oil Filter

Bypass Valve

AccumulatorsAccumulators

•Energy Storage

•Emergency supply

•Dampen pressure changes

•Surge control

•Thermal expansion

•Shock absorber in Suspension systems

Diaphragm AccumulatorDiaphragm Accumulator

NitrogenDiaphrag

m

Oil

Piston AccumulatorPiston Accumulator

Nitrogen

Oil

Piston

Bladder AccumulatorBladder Accumulator

Nitrogen

Oil

Bladder