1. Basic Hydraulic Systems in Construction Plant
John Holden

2. Construction Machines
Construction machines use hydraulics to move heavy loads. Hydraulics can be used to move a heavy Load, with a small force.
Typical machines include:
Loading Shovel
Dump trucks.
Bulldozer
Excavators.
All of these machines use hydraulic pressure to move cylinders that operate buckets, booms, blades and raise bodies.

3. Pascal's Law
The amount of pressure in the liquid is equal to the force, with respect to the area being acted upon.

4. Pascal’s Law
The pressure always act at right angles to the surface

5. Pascal’s Law Force is equal to area multiplied by pressure F = P x A
Pressure is equal to force divided by area
P = F A

6. Hydraulic Basics Hydraulic pumps create flow - not pressure.
Resistance to flow creates pressure.
Flow determines actuator speed.
Pressure determines actuator force.
Fluid under pressure takes the path of least resistance.
When fluid moves from an area of high pressure to an area of low pressure (pressure drop) without performing useful work, heat is generated.

7. Basic Hydraulic System
Actuator
Actuator
Direction Control Valve
Direction Control Valve
Return Filter
Main Relief Valve
Return Filter
Main Relief Valve
Gear Pump
Gear Pump
Hydraulic Tank
Hydraulic Tank

8. Hydraulic Pump
Gear Pump
Vane Pump
Piston Pump

9. Piston Pump

10. Variable Displacement

11. Hydraulic Rams Double Acting Port Piston Rod Port End Cap Piston Seal
Cylinder
Gland Seal
Rod Eye

12. Double Acting Ram
Double acting rams can exert force in two directions.
Under the influence of hydraulic pressure the piston rod of a double acting ram will both extend and retract.

13. Hydraulic Rams
Single Acting Ram
Vent
Port

14. Single Acting Ram
Single acting rams can exert force in only one direction. Under the influence of hydraulic pressure the piston rod of a single acting ram will extend.
The piston rod can only be retracted by the influence of some external force (usually the weight of the load or the machine itself ).

15. Displacement Ram A displacement ram is a form of single acting ram.
Pumping fluid into the port will fill the space around the piston rod, as there is a seal between the gland and the rod the oil is contained.
pumping further fluid into the cylinder will displace the volume of the piston rod and it will extend.

16. Multistage Telescopic Ram
Multistage telescopic rams are most commonly single acting.
A telescopic cylinder is used to obtain a longer stroke length from a given closed length.

17. Relief Valves
Direct Acting

18. Pilot Operated Relief Valve
Relief Valves
Pilot Operated Relief Valve
Closed
Open

19. Blocked Oil Filter
Bypass Valve

20. Accumulators Energy Storage Emergency supply Dampen pressure changes
Surge control
Thermal expansion
Shock absorber in Suspension systems

21. Diaphragm Accumulator
Nitrogen
Diaphragm
Oil

22. Piston Accumulator
Nitrogen
Piston
Oil

23. Bladder Accumulator
Nitrogen
Bladder
Oil