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Hydraulic Systems Civil Engineering (CE) Notes | EduRev

Civil Engineering (CE) : Hydraulic Systems Civil Engineering (CE) Notes | EduRev

``` Page 1

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 63
Module 5: Hydraulic Systems
Lecture 1
Introduction
1. Introduction
The controlled movement of parts or a controlled application of force is a common
requirement in the industries. These operations are performed mainly by using electrical
machines or diesel, petrol and steam engines as a prime mover. These prime movers can
provide various movements to the objects by using some mechanical attachments like
screw jack, lever, rack and pinions etc. However, these are not the only prime movers.
The enclosed fluids (liquids and gases) can also be used as prime movers to provide
controlled motion and force to the objects or substances. The specially designed enclosed
fluid systems can provide both linear as well as rotary motion. The high magnitude
controlled force can also be applied by using these systems.  This kind of enclosed fluid
based systems using pressurized incompressible liquids as transmission media are called
as hydraulic systems. The hydraulic system works on the principle of Pascal’s law which
says that the pressure in an enclosed fluid is uniform in all the directions. The Pascal’s
law is illustrated in figure 5.1.1. The force given by fluid is given by the multiplication of
pressure and area of cross section. As the pressure is same in all the direction, the smaller
piston feels a smaller force and a large piston feels a large force. Therefore, a large force
can be generated with smaller force input by using hydraulic systems.

Figure 5.1.1 Principle of hydraulic system

Page 2

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 63
Module 5: Hydraulic Systems
Lecture 1
Introduction
1. Introduction
The controlled movement of parts or a controlled application of force is a common
requirement in the industries. These operations are performed mainly by using electrical
machines or diesel, petrol and steam engines as a prime mover. These prime movers can
provide various movements to the objects by using some mechanical attachments like
screw jack, lever, rack and pinions etc. However, these are not the only prime movers.
The enclosed fluids (liquids and gases) can also be used as prime movers to provide
controlled motion and force to the objects or substances. The specially designed enclosed
fluid systems can provide both linear as well as rotary motion. The high magnitude
controlled force can also be applied by using these systems.  This kind of enclosed fluid
based systems using pressurized incompressible liquids as transmission media are called
as hydraulic systems. The hydraulic system works on the principle of Pascal’s law which
says that the pressure in an enclosed fluid is uniform in all the directions. The Pascal’s
law is illustrated in figure 5.1.1. The force given by fluid is given by the multiplication of
pressure and area of cross section. As the pressure is same in all the direction, the smaller
piston feels a smaller force and a large piston feels a large force. Therefore, a large force
can be generated with smaller force input by using hydraulic systems.

Figure 5.1.1 Principle of hydraulic system

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 2 of 63
The hydraulic systems consists a number of parts for its proper functioning. These
include storage tank, filter, hydraulic pump, pressure regulator, control valve, hydraulic
cylinder, piston and leak proof fluid flow pipelines. The schematic of a simple hydraulic
system is shown in figure 5.1.2. It consists of:
• a movable piston connected to the output shaft in an enclosed cylinder
• storage tank
• filter
• electric pump
• pressure regulator
• control valve
• leak proof closed loop piping.
The output shaft transfers the motion or force however all other parts help to control the
system. The storage/fluid tank is a reservoir for the liquid used as a transmission media.
The liquid used is generally high density incompressible oil. It is filtered to remove dust
or any other unwanted particles and then pumped by the hydraulic pump. The capacity of
pump depends on the hydraulic system design. These pumps generally deliver constant
volume in each revolution of the pump shaft. Therefore, the fluid pressure can increase
indefinitely at the dead end of the piston until the system fails. The pressure regulator is
used to avoid such circumstances which redirect the excess fluid back to the storage tank.
The movement of piston is controlled by changing liquid flow from port A and port B.
The cylinder movement is controlled by using control valve which directs the fluid flow.
The fluid pressure line is connected to the port B to raise the piston and it is connected to
port A to lower down the piston. The valve can also stop the fluid flow in any of the port.
The leak proof piping is also important due to safety, environmental hazards and
economical aspects. Some accessories such as flow control system, travel limit control,
electric motor starter and overload protection may also be used in the hydraulic systems
which are not shown in figure 5.1.2.

Figure 5.1.2 Schematic of hydraulic system
Page 3

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 63
Module 5: Hydraulic Systems
Lecture 1
Introduction
1. Introduction
The controlled movement of parts or a controlled application of force is a common
requirement in the industries. These operations are performed mainly by using electrical
machines or diesel, petrol and steam engines as a prime mover. These prime movers can
provide various movements to the objects by using some mechanical attachments like
screw jack, lever, rack and pinions etc. However, these are not the only prime movers.
The enclosed fluids (liquids and gases) can also be used as prime movers to provide
controlled motion and force to the objects or substances. The specially designed enclosed
fluid systems can provide both linear as well as rotary motion. The high magnitude
controlled force can also be applied by using these systems.  This kind of enclosed fluid
based systems using pressurized incompressible liquids as transmission media are called
as hydraulic systems. The hydraulic system works on the principle of Pascal’s law which
says that the pressure in an enclosed fluid is uniform in all the directions. The Pascal’s
law is illustrated in figure 5.1.1. The force given by fluid is given by the multiplication of
pressure and area of cross section. As the pressure is same in all the direction, the smaller
piston feels a smaller force and a large piston feels a large force. Therefore, a large force
can be generated with smaller force input by using hydraulic systems.

Figure 5.1.1 Principle of hydraulic system

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 2 of 63
The hydraulic systems consists a number of parts for its proper functioning. These
include storage tank, filter, hydraulic pump, pressure regulator, control valve, hydraulic
cylinder, piston and leak proof fluid flow pipelines. The schematic of a simple hydraulic
system is shown in figure 5.1.2. It consists of:
• a movable piston connected to the output shaft in an enclosed cylinder
• storage tank
• filter
• electric pump
• pressure regulator
• control valve
• leak proof closed loop piping.
The output shaft transfers the motion or force however all other parts help to control the
system. The storage/fluid tank is a reservoir for the liquid used as a transmission media.
The liquid used is generally high density incompressible oil. It is filtered to remove dust
or any other unwanted particles and then pumped by the hydraulic pump. The capacity of
pump depends on the hydraulic system design. These pumps generally deliver constant
volume in each revolution of the pump shaft. Therefore, the fluid pressure can increase
indefinitely at the dead end of the piston until the system fails. The pressure regulator is
used to avoid such circumstances which redirect the excess fluid back to the storage tank.
The movement of piston is controlled by changing liquid flow from port A and port B.
The cylinder movement is controlled by using control valve which directs the fluid flow.
The fluid pressure line is connected to the port B to raise the piston and it is connected to
port A to lower down the piston. The valve can also stop the fluid flow in any of the port.
The leak proof piping is also important due to safety, environmental hazards and
economical aspects. Some accessories such as flow control system, travel limit control,
electric motor starter and overload protection may also be used in the hydraulic systems
which are not shown in figure 5.1.2.

Figure 5.1.2 Schematic of hydraulic system
NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 3 of 63
2. Applications of hydraulic systems
The hydraulic systems are mainly used for precise control of larger forces. The main
applications of hydraulic system can be classified in five categories:
2.1 Industrial: Plastic processing machineries, steel making and primary metal
extraction applications, automated production lines, machine tool industries,
paper industries, loaders, crushes, textile machineries, R & D equipment and
robotic systems etc.
2.2 Mobile hydraulics: Tractors, irrigation system, earthmoving equipment,
material handling equipment, commercial vehicles, tunnel boring equipment, rail
equipment, building and construction machineries and drilling rigs etc.
2.3 Automobiles: It is used in the systems like breaks, shock absorbers, steering
system, wind shield, lift and cleaning etc.
2.4  Marine applications: It mostly covers ocean going vessels, fishing boats and
navel equipment.
2.5 Aerospace equipment: There are equipment and systems used for rudder
control, landing gear, breaks, flight control and transmission etc. which are used
in airplanes, rockets and spaceships.

3. Hydraulic Pump
The combined pumping and driving motor unit is known as hydraulic pump. The
hydraulic pump takes hydraulic fluid (mostly some oil) from the storage tank and delivers
it to the rest of the hydraulic circuit. In general, the speed of pump is constant and the
pump delivers an equal volume of oil in each revolution. The amount and direction of
fluid flow is controlled by some external mechanisms. In some cases, the hydraulic pump
itself is operated by a servo controlled motor but it makes the system complex. The
hydraulic pumps are characterized by its flow rate capacity, power consumption, drive
speed, pressure delivered at the outlet and efficiency of the pump. The pumps are not
100% efficient. The efficiency of a pump can be specified by two ways. One is the
volumetric efficiency which is the ratio of actual volume of fluid delivered to the
maximum theoretical volume possible. Second is power efficiency which is the ratio of
output hydraulic power to the input mechanical/electrical power. The typical efficiency of
pumps varies from 90-98%.
The hydraulic pumps can be of two types:
• centrifugal pump
• reciprocating pump
Page 4

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 63
Module 5: Hydraulic Systems
Lecture 1
Introduction
1. Introduction
The controlled movement of parts or a controlled application of force is a common
requirement in the industries. These operations are performed mainly by using electrical
machines or diesel, petrol and steam engines as a prime mover. These prime movers can
provide various movements to the objects by using some mechanical attachments like
screw jack, lever, rack and pinions etc. However, these are not the only prime movers.
The enclosed fluids (liquids and gases) can also be used as prime movers to provide
controlled motion and force to the objects or substances. The specially designed enclosed
fluid systems can provide both linear as well as rotary motion. The high magnitude
controlled force can also be applied by using these systems.  This kind of enclosed fluid
based systems using pressurized incompressible liquids as transmission media are called
as hydraulic systems. The hydraulic system works on the principle of Pascal’s law which
says that the pressure in an enclosed fluid is uniform in all the directions. The Pascal’s
law is illustrated in figure 5.1.1. The force given by fluid is given by the multiplication of
pressure and area of cross section. As the pressure is same in all the direction, the smaller
piston feels a smaller force and a large piston feels a large force. Therefore, a large force
can be generated with smaller force input by using hydraulic systems.

Figure 5.1.1 Principle of hydraulic system

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 2 of 63
The hydraulic systems consists a number of parts for its proper functioning. These
include storage tank, filter, hydraulic pump, pressure regulator, control valve, hydraulic
cylinder, piston and leak proof fluid flow pipelines. The schematic of a simple hydraulic
system is shown in figure 5.1.2. It consists of:
• a movable piston connected to the output shaft in an enclosed cylinder
• storage tank
• filter
• electric pump
• pressure regulator
• control valve
• leak proof closed loop piping.
The output shaft transfers the motion or force however all other parts help to control the
system. The storage/fluid tank is a reservoir for the liquid used as a transmission media.
The liquid used is generally high density incompressible oil. It is filtered to remove dust
or any other unwanted particles and then pumped by the hydraulic pump. The capacity of
pump depends on the hydraulic system design. These pumps generally deliver constant
volume in each revolution of the pump shaft. Therefore, the fluid pressure can increase
indefinitely at the dead end of the piston until the system fails. The pressure regulator is
used to avoid such circumstances which redirect the excess fluid back to the storage tank.
The movement of piston is controlled by changing liquid flow from port A and port B.
The cylinder movement is controlled by using control valve which directs the fluid flow.
The fluid pressure line is connected to the port B to raise the piston and it is connected to
port A to lower down the piston. The valve can also stop the fluid flow in any of the port.
The leak proof piping is also important due to safety, environmental hazards and
economical aspects. Some accessories such as flow control system, travel limit control,
electric motor starter and overload protection may also be used in the hydraulic systems
which are not shown in figure 5.1.2.

Figure 5.1.2 Schematic of hydraulic system
NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 3 of 63
2. Applications of hydraulic systems
The hydraulic systems are mainly used for precise control of larger forces. The main
applications of hydraulic system can be classified in five categories:
2.1 Industrial: Plastic processing machineries, steel making and primary metal
extraction applications, automated production lines, machine tool industries,
paper industries, loaders, crushes, textile machineries, R & D equipment and
robotic systems etc.
2.2 Mobile hydraulics: Tractors, irrigation system, earthmoving equipment,
material handling equipment, commercial vehicles, tunnel boring equipment, rail
equipment, building and construction machineries and drilling rigs etc.
2.3 Automobiles: It is used in the systems like breaks, shock absorbers, steering
system, wind shield, lift and cleaning etc.
2.4  Marine applications: It mostly covers ocean going vessels, fishing boats and
navel equipment.
2.5 Aerospace equipment: There are equipment and systems used for rudder
control, landing gear, breaks, flight control and transmission etc. which are used
in airplanes, rockets and spaceships.

3. Hydraulic Pump
The combined pumping and driving motor unit is known as hydraulic pump. The
hydraulic pump takes hydraulic fluid (mostly some oil) from the storage tank and delivers
it to the rest of the hydraulic circuit. In general, the speed of pump is constant and the
pump delivers an equal volume of oil in each revolution. The amount and direction of
fluid flow is controlled by some external mechanisms. In some cases, the hydraulic pump
itself is operated by a servo controlled motor but it makes the system complex. The
hydraulic pumps are characterized by its flow rate capacity, power consumption, drive
speed, pressure delivered at the outlet and efficiency of the pump. The pumps are not
100% efficient. The efficiency of a pump can be specified by two ways. One is the
volumetric efficiency which is the ratio of actual volume of fluid delivered to the
maximum theoretical volume possible. Second is power efficiency which is the ratio of
output hydraulic power to the input mechanical/electrical power. The typical efficiency of
pumps varies from 90-98%.
The hydraulic pumps can be of two types:
• centrifugal pump
• reciprocating pump
NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 4 of 63
Centrifugal pump uses rotational kinetic energy to deliver the fluid. The rotational energy
typically comes from an engine or electric motor. The fluid enters the pump impeller
along or near to the rotating axis, accelerates in the propeller and flung out to the
periphery by centrifugal force as shown in figure 5.1.3. In centrifugal pump the delivery
is not constant and varies according to the outlet pressure. These pumps are not suitable
for high pressure applications and are generally used for low-pressure and high-volume
flow applications. The maximum pressure capacity is limited to 20-30 bars and the
specific speed ranges from 500 to 10000. Most of the centrifugal pumps are not self-
priming and the pump casing needs to be filled with liquid before the pump is started.

Figure 5.1.3 Centrifugal pump

Page 5

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 63
Module 5: Hydraulic Systems
Lecture 1
Introduction
1. Introduction
The controlled movement of parts or a controlled application of force is a common
requirement in the industries. These operations are performed mainly by using electrical
machines or diesel, petrol and steam engines as a prime mover. These prime movers can
provide various movements to the objects by using some mechanical attachments like
screw jack, lever, rack and pinions etc. However, these are not the only prime movers.
The enclosed fluids (liquids and gases) can also be used as prime movers to provide
controlled motion and force to the objects or substances. The specially designed enclosed
fluid systems can provide both linear as well as rotary motion. The high magnitude
controlled force can also be applied by using these systems.  This kind of enclosed fluid
based systems using pressurized incompressible liquids as transmission media are called
as hydraulic systems. The hydraulic system works on the principle of Pascal’s law which
says that the pressure in an enclosed fluid is uniform in all the directions. The Pascal’s
law is illustrated in figure 5.1.1. The force given by fluid is given by the multiplication of
pressure and area of cross section. As the pressure is same in all the direction, the smaller
piston feels a smaller force and a large piston feels a large force. Therefore, a large force
can be generated with smaller force input by using hydraulic systems.

Figure 5.1.1 Principle of hydraulic system

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 2 of 63
The hydraulic systems consists a number of parts for its proper functioning. These
include storage tank, filter, hydraulic pump, pressure regulator, control valve, hydraulic
cylinder, piston and leak proof fluid flow pipelines. The schematic of a simple hydraulic
system is shown in figure 5.1.2. It consists of:
• a movable piston connected to the output shaft in an enclosed cylinder
• storage tank
• filter
• electric pump
• pressure regulator
• control valve
• leak proof closed loop piping.
The output shaft transfers the motion or force however all other parts help to control the
system. The storage/fluid tank is a reservoir for the liquid used as a transmission media.
The liquid used is generally high density incompressible oil. It is filtered to remove dust
or any other unwanted particles and then pumped by the hydraulic pump. The capacity of
pump depends on the hydraulic system design. These pumps generally deliver constant
volume in each revolution of the pump shaft. Therefore, the fluid pressure can increase
indefinitely at the dead end of the piston until the system fails. The pressure regulator is
used to avoid such circumstances which redirect the excess fluid back to the storage tank.
The movement of piston is controlled by changing liquid flow from port A and port B.
The cylinder movement is controlled by using control valve which directs the fluid flow.
The fluid pressure line is connected to the port B to raise the piston and it is connected to
port A to lower down the piston. The valve can also stop the fluid flow in any of the port.
The leak proof piping is also important due to safety, environmental hazards and
economical aspects. Some accessories such as flow control system, travel limit control,
electric motor starter and overload protection may also be used in the hydraulic systems
which are not shown in figure 5.1.2.

Figure 5.1.2 Schematic of hydraulic system
NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 3 of 63
2. Applications of hydraulic systems
The hydraulic systems are mainly used for precise control of larger forces. The main
applications of hydraulic system can be classified in five categories:
2.1 Industrial: Plastic processing machineries, steel making and primary metal
extraction applications, automated production lines, machine tool industries,
paper industries, loaders, crushes, textile machineries, R & D equipment and
robotic systems etc.
2.2 Mobile hydraulics: Tractors, irrigation system, earthmoving equipment,
material handling equipment, commercial vehicles, tunnel boring equipment, rail
equipment, building and construction machineries and drilling rigs etc.
2.3 Automobiles: It is used in the systems like breaks, shock absorbers, steering
system, wind shield, lift and cleaning etc.
2.4  Marine applications: It mostly covers ocean going vessels, fishing boats and
navel equipment.
2.5 Aerospace equipment: There are equipment and systems used for rudder
control, landing gear, breaks, flight control and transmission etc. which are used
in airplanes, rockets and spaceships.

3. Hydraulic Pump
The combined pumping and driving motor unit is known as hydraulic pump. The
hydraulic pump takes hydraulic fluid (mostly some oil) from the storage tank and delivers
it to the rest of the hydraulic circuit. In general, the speed of pump is constant and the
pump delivers an equal volume of oil in each revolution. The amount and direction of
fluid flow is controlled by some external mechanisms. In some cases, the hydraulic pump
itself is operated by a servo controlled motor but it makes the system complex. The
hydraulic pumps are characterized by its flow rate capacity, power consumption, drive
speed, pressure delivered at the outlet and efficiency of the pump. The pumps are not
100% efficient. The efficiency of a pump can be specified by two ways. One is the
volumetric efficiency which is the ratio of actual volume of fluid delivered to the
maximum theoretical volume possible. Second is power efficiency which is the ratio of
output hydraulic power to the input mechanical/electrical power. The typical efficiency of
pumps varies from 90-98%.
The hydraulic pumps can be of two types:
• centrifugal pump
• reciprocating pump
NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 4 of 63
Centrifugal pump uses rotational kinetic energy to deliver the fluid. The rotational energy
typically comes from an engine or electric motor. The fluid enters the pump impeller
along or near to the rotating axis, accelerates in the propeller and flung out to the
periphery by centrifugal force as shown in figure 5.1.3. In centrifugal pump the delivery
is not constant and varies according to the outlet pressure. These pumps are not suitable
for high pressure applications and are generally used for low-pressure and high-volume
flow applications. The maximum pressure capacity is limited to 20-30 bars and the
specific speed ranges from 500 to 10000. Most of the centrifugal pumps are not self-
priming and the pump casing needs to be filled with liquid before the pump is started.

Figure 5.1.3 Centrifugal pump

NPTEL – Mechanical – Mechatronics and Manufacturing Automation

Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 5 of 63
The reciprocating pump is a positive plunger pump. It is also known as positive
displacement pump or piston pump. It is often used where relatively small quantity is to
be handled and the delivery pressure is quite large. The construction of these pumps is
similar to the four stroke engine as shown in figure 5.1.4. The crank is driven by some
external rotating motor. The piston of pump reciprocates due to crank rotation. The piston
moves down in one half of crank rotation, the inlet valve opens and fluid enters into the
cylinder. In second half crank rotation the piston moves up, the outlet valve opens and the
fluid moves out from the outlet. At a time, only one valve is opened and another is closed
so there is no fluid leakage. Depending on the area of cylinder the pump delivers constant
volume of fluid in each cycle independent to the pressure at the output port.

Figure 5.1.4 Reciprocating or positive displacement pump

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