Hydraulic and Pneumatic
Transmission
Chapter 1 Introduction to fluid power
Objectives:
The purpose of this chapter is to describe:
1. Operation of hydraulic systems.
2. Power elments, actuators, control components and
Ancillary components .
3. fluid power diagram and symbols
Upon completing this chapter, you should be able to:
1. Explain the operation of the various types of elements.
2. Identify the graphical symbols used for elements.
3. Understand the advantages and disadvantages of fluid
power.
1.1 Transmission and transmission classification
1.1.1 Transmission
A whole machine consists of a prime mover, a transmission
section, a control section and a end-use device(working
machine).
Prime
mover
Transmission
section
End use
device
Control
section
The commonly used prime movers are electric motors,
gasoline engines and diesel engines.
1.1.2 classification
According to working media, the transmission mechanism
can be classified as mechanical transmission, electric
transmission and fluid transmission.
1.1 Transmission and transmission classification
1.1.3 FLUID POWER DEFINITION
Fluid power is that energy transmitted and controlled by means
of a pressurized fluid, either liquid or gas.
The fluid transmission can be classified as hydrostatics
transmission, hydrodynamics transmission, pneumatics
transmission and viscosity transmission.
1 Several words: Fluid power
Hydraulic transmission
Hydrostatic transmission
Hydrodynamic transmission
2 History of fluid power
In the seventeen century, Pascal put forward the principle
of fluid power
In the eighteen century, the first press was manufactured
1.1 Transmission and transmission classification
Before electrical power was developed , fluid power had
being used to drive hydraulic equipment such as cranes,
presses, winches, extruding machines, hydraulic jacks,
shearing machines, and riveting machines.
The modern era of fluid power is considered to have begun
in 1906 when a hydraulic system was used for elevating and
controlling guns on the battleship USS Virginia.
During and after World War II the aviation and aerospace
industry provided the impetus for many advances in fluid
power technology .
Today fluid power is used extensively in practically every
branch of industry.
19
1.2 Theory of hydraulics
and hydraulic system
18
16
17
1.2.1 Theory of hydraulics
Figure1.1 Principle of operation of
grinding machine’s hydraulic system
1-tank; 2-filter; 3,12,14-return line; 11
4-pump; 5-spring; 6-steel ball;
7-relive valve; 8,10-pressure line;
9-manually actuated directional
control valve ;
11,16-hand lever;
13-throttle valve;
15-directional valve;
17-piston; 18-cylinder;
19-work table.
15
16
(b)
15
14
13
9
12
(c)
11
9
7
10
8
6
5
4
3
2
1
(a) 1→2→4→9→13→15 → 18(left)
18(right)→15→1
The work table moves to right.
(b)1→2→4→9→13→15 → 18(right)
18(left)→15→1
The work table moves to left.
(c)1→2→4→9→1
The work table stops.
The pump unloads
Valve 13—throttle valve,
which is used for speed
control.
Valve 5—relive valve,
which is used to
maintain the system
pressure constant.
1.2 Theory of hydraulics and hydraulic system
1.2. 2 COMPONENTS OF HYDRAULIC SYSTEM
(1) A power component(pump) which forces the liquid
through the system, and converts mechanical power to fluid
power.
(2)Actuators (Cylinders or motors) which convert fluid
power to linear or rotary mechanical power.
(3)Control components : including valves, which control
the direction, pressure and rate of flow. Directional valve 15 is
a control component.
(4)Ancillary hydraulic components: Filters, regulators,
pipes, reservoirs, etc.
1.2 Theory of hydraulics and hydraulic system
8
1.2.3 fluid power diagram and symbols
check valve
7
6
relieve valve
5
cylinder
4
pump
3
motor
2
1
1.3 Advantage and disadvantage of fluid power
1.3.1 The advantages of fluid power
(1) High horsepower, low weight ratio. Hydraulic
components are compact and lightweight .
(2)Easy, accurate controlling ,reversible, infinitely variable
speed and load control completely automatic operations.
(3)Accurate position control for linear and rotary elements,
and variable speed control.
(4)Power linkage where kinematic linkage is impractical,
convenient method of power transmission over long distance.
(5)Reduction of wear by the self-lubrication action of the
transmission medium.
1.3 Advantage and disadvantage of fluid power
(6) simplicity, safety, great flexibility, reliability and
economy.
(7) Standardization. The fluid power industry has
established design and performance standards for hydraulic
and pneumatic products.
1.3.2 Some of the major disadvantages of hydraulic systems
(1) Impairment of system operation by contamination
(2) Hydraulic fluid leakage
(3) Fire hazards with flammable hydraulic fluids
(4) Hydraulic lines can burst, possibly resulting in injuries
to people due to high-speed oil jets and flying pieces of metal,
if proper design is not implemented.
(5) Adequate oil filtration must be maintained