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