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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