1. Muhajir Ab. Rahim School of Mechatronic Engineering
Hydraulic Systems
Muhajir Ab. Rahim
School of Mechatronic Engineering

2. The Basic Hydraulic System
Consist of these components
A fluid, usually oil
A tank, or reservoir, to hold a supply of fluid
Fluid conditioning devices to keep the fluid clean and cool
A prime mover, usually an electric motor or engine, to drive the pump
A pump, to cause the fluid to flow
Conductors, usually pipe or tubing, to carry the fluid
Valving, to control fluid flow, direction and pressure
One or more actuators, usually cylinders or hydraulic motors, to do the work

3. Hydraulic Fluid
Water?
Evaporates, freezes, leaks, rust parts, poor lubricant
Petroleum oil

4. Viscosity Viscosity is a measure of oil’s resistance to flow.
It is determined under laboratory conditions by measuring the time required for a specific amount of oil at a specific temperature to flow through a small opening.
The higher the viscosity, the longer it takes.
High viscosity= thick, Low viscosity= thin
Viscosity index is a measure of how much the viscosity changes when the oil is heated.
High viscosity index, if the viscosity change very little. (good quality- lubricant capability remains constant)

5. Pour, Flash and Fire Points
Pour point is the lowest temperature at which a given oil will flow enough to be useful
Flash point is the temperature at which oil will flash, or light briefly if touched with a flame
Fire point is the temperature at which a given oil, if touched with a flame, will catch fire and stay lit for at least five seconds.
The auto-ignition temperature is the level of heat at which a given oil will catch fire by itself.

6. Functions of Hydraulic Fluids
Transmit force to the actuators doing work of the system
Conduct heat away from moving parts
Lubricate moving parts to reduce heating, lessen wear, and increase efficiency

7. Desired characteristics of hydraulic fluids
Appropriate viscosity
Lubricating ability
Freedom from damaging chemicals
Resistance to foaming
Fire resistance
Oxidation resistance
*Additives are used to achieve desired characteristics in hydraulic fluid

8. Contaminants Contaminants in hydraulic fluid are a major source of
problems in system operation
The three principle sources of contaminants are;
Newly installed components
Air entering the tank
System operation, generating chemicals, gum, sludge, varnish and moisture

9. Hydraulic Reservoir (Tank)
The functions of a tank are
Store fluid
Protect fluid
Provide means for checking fluid level
Provide means for adding fluid
Cooling
Remove contaminants

11. Strainer is used to block large contaminant particles from entering the system
Baffle is a wall in the tank, to disrupt the flow between return line and pump inlet line (for more even fluid temperature and more thorough settling of contaminants to the tank bottom)
Magnetic plug is used to attract metal particles. (should be removed and cleaned periodically)

12. Tank Schematic Diagram
Tank with immersed strainer
Tank with strainer in pump inlet line
Tank with strainer in pump inlet line, filter in return
Tank with pump inlet line

13. Pump The purpose of pump is to cause fluid flow
The motor or engine that drives a pump is called a prime mover
The most common type of pump is the external gear pump
Positive-displacement pumps mean that fluid must be moved when the pump is running

15. Pump Schematic Diagram
MOTOR
STRAINER
TANK
System schematic showing location of the pump and motor

16. Pressure Relief Valves
A pressure relief valve
has two functions:
Set a maximum operating pressure level for the system
Protect system components such as the pump, valves, and lines from overpressure.

17. System schematic showing location of the pressure relief valve
PUMP
PRESSURE RELIEF VALVE
MOTOR
STRAINER
TANK
System schematic showing location of the pressure relief valve

18. Pressure Reducing Valve
The purpose of pressure reducing valve is to regulate or limit pressure for an individual circuit branch or actuator

19. M System schematic showing location of the pressure reducing valve
PUMP
PRESSURE RELIEF VALVE
MOTOR
STRAINER
TANK
System schematic showing location of the pressure reducing valve

20. Directional Control Valve
The purpose of directional control valve is to deliver fluid to an actuator at the proper port at the appropriate time.
A way is a flow path through a valve.
A port is an opening in the valve body.
A position is a specific setting of a spool which determines flow paths.
Directional control valves are described by specifying the number of ways, the number of positions, the means by which the valve is operated, and for 3-ways valves, whether open or closed center.

22. PRESSURE REDUCING VALVE DIRECTIONAL CONTROL VALVEM
PUMP
DIRECTIONAL CONTROL VALVE
MOTOR
PRESSURE RELIEF VALVE
STRAINER
ACTUATOR
TANK
System schematic showing location of the directional control valve and actuator

23. Actuator
Device which converts fluid energy into mechanical force and motion.
Cylinder is used to produce motion in a straight line, which we call linear motion.
Rotary actuator (hydraulic motor) is used to convert hydraulic energy into rotating motion about an axis.

25. Quiz A hydraulic system is said to have a mechanical
advantage of 40. If the input piston, with a
12 inch radius, has a force of 65 pounds pushing
downward a distance of 20 inches, find
i. the volume of fluid that has been displaced
ii. the upward force on the output piston
iii. the radius of the output piston
iv. the distance the output piston moves