Hydraulics is the area of engineering that deals with liquid flow and pressure. There are two types of hydraulic systems: hydrostatic systems, where there is no fluid flow; and hydrodynamic systems, where fluid is flowing. In hydrostatic systems, Pascal's law states that pressure is transmitted equally throughout the confined fluid. In hydrodynamic systems, pressure drops along the length of hydraulic lines. Hydraulic systems use hydraulic fluids to transmit force via pressure and flow through components like pumps, valves, actuators and reservoirs to perform work.

1. Hydraulics

2. Hydraulics
An area of engineering
science that deals with
liquid flow and pressure

3. Hydraulic Fluids
 Liquid pumped through a hydraulic system
 Petroleum-based or synthetic oil
 Serve four major functions:
1. Power transmission
2. Lubrication of moving parts
3. Sealing of spaces between moving parts
4. Heat removal
 Relatively Incompressible!

4. Two Types or Conditions of
Hydraulic Systems
Hydrostatic
Hydrodynamic

5. Hydrostatics -
a “No Flow” Scenario
 “Static” means “stationary” or “non flowing” in
a hydraulic system
 Hydraulic systems are considered static when
there is no flow
 Pascal’s Law (for hydrostatics):
 a pressure applied to a confined hydrostatic fluid
is transmitted with equal intensity throughout the
fluid
 Same pressure all throughout!

6. Hydrodynamics –
a “Flow” scenario
 “Dynamic” means “moving” or “flowing” in a
hydraulic system
 Hydraulic systems are considered dynamic
when there is flow
 Pascal’s Law does not apply!
 Pressure does not have equal intensity in a
flowing dynamic system
 Pressure drops along the length of a hydraulic line
in flowing systems

7. Flow and Pressure
 Flow, Q
 volume flow rate
 amount of fluid moving through system per
unit time
 Pressure, P
 force per unit area of fluid moving through
a system
Area
Force
Pressure 
A
F
P 

8. Mechanical Advantage
 Ideal mechanical advantage (IMA)
 Assumes no frictional losses
 Calculated as ratio of output force to input force
 Actual mechanical advantage (AMA)
 always less than ideal
 difficult to calculate
F
F
input
output
IMA 

9. Application of Pascal’s Law in
a Simple Hydrostatic System
How much force must you exert on piston A to lift a load on piston
B of 500 lbs? What is the ideal mechanical advantage of this
system?

10. Problem Solving
Step 1: Determine the pressure in
the system using information about
piston B
Known Unknown
A = 500 in2 P=?
F = 500 lb
Equation No algebra needed
Substitution & Solution
STEP 2: Use the pressure
calculated in STEP 1 and information
about piston A to calculate force
Known Unknown
A = 1.0 in2 F=?
Equation and algebra:
Substitution & Solution
1psi
in
lb
1
500in
500lb
P 2
2



(A)
A
F
(A)P 
A
F
P  PA
F 
2
in
lb
1
psi
1
P 

  1.0lb
1.0in
in
lb
1
PA
F 2
2









A
F
P 

11. Problem Solving
Step 3: Determine the ideal mechanical advantage (IMA) of
the system using information from STEPS 1 & 2
Known Unknown
F(input) = 1 lb IMA=?
F(output) = 500 lb
Equation No algebra needed
Substitution & Solution
500
1.0lb
500lb
IMA 

F(input)
F(output)
IMA 

12. A Hydraulic System

13. Tank/Reservoir
 Storage device which is open and not
pressurized
Filter

14. Pumps
 Positive displacement
pump (Gear Pump): a
specific amount of fluid
passes through the pump
for each rotation
 Centrifugal pump (Vane
Pump): no specific
amount of fluid flow per
rotation; flow depends on
speed of blades

15. Accumulators
 Storage device which is closed and is
under pressure

16. Valves
 Check Valve  Directional Control

17. Linear Actuators
Use hydraulic power to move linearly
Single Acting Double Acting

18. Rotary Actuators
Use hydraulic power to rotate
Single-Vane Double-Vane

19. Applications
 Robotics
 Oil systems in vehicles (e.g. brakes)
 Presses
 Heavy equipment
 Wood splitter
 Aircraft control systems

20. The Hydraulic Trainer
Motor
Pump
Return line
from reservoir
Pressure line
Pressure Regulator
In-line
Pressure
Gauge
Flow Control Valve
Check Valve
Actuators
Directional Control Valve
Inline-Tee
Return line
Connections
Supply line
Connections