PPT: Hydraulic Machines | Fluid Mechanics for Mechanical Engineering PDF Download

 Page 1


                                            
 
 
 
HYDRAULIC SYSTEMS 
 
1. Introduction 
Hydraulic systems are used for transmission of power through the medium of 
hydraulic oil. The hydraulic system works on the principle of Pascal’s law which 
says that “ the pressure in a  fluid at rest is transmitted uniformly in all 
directions” .   
The fluid medium used is hydraulic oil, which may be mineral oil or water or 
combinations. This area is also known as oil hydraulics.  
The power transferred is  
Power = Pressure x flow rate in the tubes or hoses.  
The schematic of a simple hydraulic system is shown in the figure below. It 
consists of: 
? a movable piston connected to the output shaft in an enclosed cylinder 
? storage tank containing hydraulic fluid 
? filter which is in suction line of pump inside the tank or on tank inlet line. 
? Electric motor /  Diesel or petrol engine which is the primary source of  power 
? Hydraulic pump driven by motor or engine  
? Pressure control valve  
? Leak proof closed loop piping. 
? Direction control valve which controls the direction of  fluid flow so as to 
change the direction of motion of a linear or rotary actuator 
? Actuator – A cylinder for linear movement  or a hydraulic motor for rotary 
actuation of  load  
 
 
Page 2


                                            
 
 
 
HYDRAULIC SYSTEMS 
 
1. Introduction 
Hydraulic systems are used for transmission of power through the medium of 
hydraulic oil. The hydraulic system works on the principle of Pascal’s law which 
says that “ the pressure in a  fluid at rest is transmitted uniformly in all 
directions” .   
The fluid medium used is hydraulic oil, which may be mineral oil or water or 
combinations. This area is also known as oil hydraulics.  
The power transferred is  
Power = Pressure x flow rate in the tubes or hoses.  
The schematic of a simple hydraulic system is shown in the figure below. It 
consists of: 
? a movable piston connected to the output shaft in an enclosed cylinder 
? storage tank containing hydraulic fluid 
? filter which is in suction line of pump inside the tank or on tank inlet line. 
? Electric motor /  Diesel or petrol engine which is the primary source of  power 
? Hydraulic pump driven by motor or engine  
? Pressure control valve  
? Leak proof closed loop piping. 
? Direction control valve which controls the direction of  fluid flow so as to 
change the direction of motion of a linear or rotary actuator 
? Actuator – A cylinder for linear movement  or a hydraulic motor for rotary 
actuation of  load  
 
 
                                            
 
 
 
1.1 Applications of Hydraulic Systems 
The chief advantage that hydraulic systems derive is from the high pressures that 
can be applied leading to high force or toque by the actuating piston or motor.  
Pressures normally used in Industry are 140 bar (140 kgf/ cm
2
 ˜14 MPA ˜ 2000 
psi). But in some specific applications in machine tools and aerospace, 350 bar 
(35 MPa or 5000 psi) is also common.  
Example: Consider an actuator with a 10 cms diameter piston. If the pressure 
applied on the piston is 140 bar, Force that the piston rod delivers  
= F = Pressure x Area =  140 * p/4* 10
2
 = 10,996 Kgf = 108 KN.  
ie nearly 10 Tons of load can be applied using a 10 cms dia cylinder. If the 
pressure is 350 bar, load will be 25 Tons.  
Similarly high torques can be applied with a small sized motor compared to an 
electric motor. The high Power / Weight ratio of the hydraulic actuators is the 
prime reason for use of hydraulics.   
 
1.2 Application areas: 
Hydraulic systems are generally used for precise control of larger forces. The 
main applications of hydraulic system can be classified in five categories: 
 
 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. 
 
 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. 
 
 Automobiles: brakes, shock absorbers, steering system, wind shield, lift 
and cleaning etc. 
 
 Marine applications: Controls in ocean going vessels, fishing boats and navel 
equipment. 
 
 Aerospace equipment: R udder control, landing gear, breaks, flight control 
and transmission, rocket motor movement 
 
Page 3


                                            
 
 
 
HYDRAULIC SYSTEMS 
 
1. Introduction 
Hydraulic systems are used for transmission of power through the medium of 
hydraulic oil. The hydraulic system works on the principle of Pascal’s law which 
says that “ the pressure in a  fluid at rest is transmitted uniformly in all 
directions” .   
The fluid medium used is hydraulic oil, which may be mineral oil or water or 
combinations. This area is also known as oil hydraulics.  
The power transferred is  
Power = Pressure x flow rate in the tubes or hoses.  
The schematic of a simple hydraulic system is shown in the figure below. It 
consists of: 
? a movable piston connected to the output shaft in an enclosed cylinder 
? storage tank containing hydraulic fluid 
? filter which is in suction line of pump inside the tank or on tank inlet line. 
? Electric motor /  Diesel or petrol engine which is the primary source of  power 
? Hydraulic pump driven by motor or engine  
? Pressure control valve  
? Leak proof closed loop piping. 
? Direction control valve which controls the direction of  fluid flow so as to 
change the direction of motion of a linear or rotary actuator 
? Actuator – A cylinder for linear movement  or a hydraulic motor for rotary 
actuation of  load  
 
 
                                            
 
 
 
1.1 Applications of Hydraulic Systems 
The chief advantage that hydraulic systems derive is from the high pressures that 
can be applied leading to high force or toque by the actuating piston or motor.  
Pressures normally used in Industry are 140 bar (140 kgf/ cm
2
 ˜14 MPA ˜ 2000 
psi). But in some specific applications in machine tools and aerospace, 350 bar 
(35 MPa or 5000 psi) is also common.  
Example: Consider an actuator with a 10 cms diameter piston. If the pressure 
applied on the piston is 140 bar, Force that the piston rod delivers  
= F = Pressure x Area =  140 * p/4* 10
2
 = 10,996 Kgf = 108 KN.  
ie nearly 10 Tons of load can be applied using a 10 cms dia cylinder. If the 
pressure is 350 bar, load will be 25 Tons.  
Similarly high torques can be applied with a small sized motor compared to an 
electric motor. The high Power / Weight ratio of the hydraulic actuators is the 
prime reason for use of hydraulics.   
 
1.2 Application areas: 
Hydraulic systems are generally used for precise control of larger forces. The 
main applications of hydraulic system can be classified in five categories: 
 
 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. 
 
 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. 
 
 Automobiles: brakes, shock absorbers, steering system, wind shield, lift 
and cleaning etc. 
 
 Marine applications: Controls in ocean going vessels, fishing boats and navel 
equipment. 
 
 Aerospace equipment: R udder control, landing gear, breaks, flight control 
and transmission, rocket motor movement 
 
                                            
 
 
 
1.3 Advantages and Disadvantages of Hydraulic systems 
 Advantages of  Hydraulic systems  
 
? High power to weight ratio  compared to electrical systems  
? Allows easy control of speed and position, and direction  
? Facilitates stepless power control 
? Allows combination with electric controls 
? Delivers consistent power output which is difficult in pneumatic or 
mechanical drive systems 
? Performs well in hot environment conditions 
 
Compared to Pneumatics:  
? Much stiffer (or rigid) due to incompressible fluid  
? Better speed of response 
? Better lubricity (less friction)  and rust resistance  
? Low maintenance cost. 
 
Disadvantages 
 
• Material of storage tank, piping, cylinder and piston can be corroded 
with the hydraulic fluid. Therefore one must be careful while selecting 
materials and hydraulic fluid. 
• Structural weight and size of the system is more which makes it unsuitable 
for the smaller instruments. 
• Small impurities in the hydraulic fluid can permanently damage the 
complete system. Therefore suitable filter must be installed. 
• Leakage of hydraulic fluid is also a critical issue and suitable 
prevention method and seals must be adopted. 
•   Hydraulic fluids, if not disposed properly, can be harmful to the    
      environment. 
 
 
 
 
Page 4


                                            
 
 
 
HYDRAULIC SYSTEMS 
 
1. Introduction 
Hydraulic systems are used for transmission of power through the medium of 
hydraulic oil. The hydraulic system works on the principle of Pascal’s law which 
says that “ the pressure in a  fluid at rest is transmitted uniformly in all 
directions” .   
The fluid medium used is hydraulic oil, which may be mineral oil or water or 
combinations. This area is also known as oil hydraulics.  
The power transferred is  
Power = Pressure x flow rate in the tubes or hoses.  
The schematic of a simple hydraulic system is shown in the figure below. It 
consists of: 
? a movable piston connected to the output shaft in an enclosed cylinder 
? storage tank containing hydraulic fluid 
? filter which is in suction line of pump inside the tank or on tank inlet line. 
? Electric motor /  Diesel or petrol engine which is the primary source of  power 
? Hydraulic pump driven by motor or engine  
? Pressure control valve  
? Leak proof closed loop piping. 
? Direction control valve which controls the direction of  fluid flow so as to 
change the direction of motion of a linear or rotary actuator 
? Actuator – A cylinder for linear movement  or a hydraulic motor for rotary 
actuation of  load  
 
 
                                            
 
 
 
1.1 Applications of Hydraulic Systems 
The chief advantage that hydraulic systems derive is from the high pressures that 
can be applied leading to high force or toque by the actuating piston or motor.  
Pressures normally used in Industry are 140 bar (140 kgf/ cm
2
 ˜14 MPA ˜ 2000 
psi). But in some specific applications in machine tools and aerospace, 350 bar 
(35 MPa or 5000 psi) is also common.  
Example: Consider an actuator with a 10 cms diameter piston. If the pressure 
applied on the piston is 140 bar, Force that the piston rod delivers  
= F = Pressure x Area =  140 * p/4* 10
2
 = 10,996 Kgf = 108 KN.  
ie nearly 10 Tons of load can be applied using a 10 cms dia cylinder. If the 
pressure is 350 bar, load will be 25 Tons.  
Similarly high torques can be applied with a small sized motor compared to an 
electric motor. The high Power / Weight ratio of the hydraulic actuators is the 
prime reason for use of hydraulics.   
 
1.2 Application areas: 
Hydraulic systems are generally used for precise control of larger forces. The 
main applications of hydraulic system can be classified in five categories: 
 
 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. 
 
 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. 
 
 Automobiles: brakes, shock absorbers, steering system, wind shield, lift 
and cleaning etc. 
 
 Marine applications: Controls in ocean going vessels, fishing boats and navel 
equipment. 
 
 Aerospace equipment: R udder control, landing gear, breaks, flight control 
and transmission, rocket motor movement 
 
                                            
 
 
 
1.3 Advantages and Disadvantages of Hydraulic systems 
 Advantages of  Hydraulic systems  
 
? High power to weight ratio  compared to electrical systems  
? Allows easy control of speed and position, and direction  
? Facilitates stepless power control 
? Allows combination with electric controls 
? Delivers consistent power output which is difficult in pneumatic or 
mechanical drive systems 
? Performs well in hot environment conditions 
 
Compared to Pneumatics:  
? Much stiffer (or rigid) due to incompressible fluid  
? Better speed of response 
? Better lubricity (less friction)  and rust resistance  
? Low maintenance cost. 
 
Disadvantages 
 
• Material of storage tank, piping, cylinder and piston can be corroded 
with the hydraulic fluid. Therefore one must be careful while selecting 
materials and hydraulic fluid. 
• Structural weight and size of the system is more which makes it unsuitable 
for the smaller instruments. 
• Small impurities in the hydraulic fluid can permanently damage the 
complete system. Therefore suitable filter must be installed. 
• Leakage of hydraulic fluid is also a critical issue and suitable 
prevention method and seals must be adopted. 
•   Hydraulic fluids, if not disposed properly, can be harmful to the    
      environment. 
 
 
 
 
                                            
 
 
 
1.4 Relative advantages of different power transmission systems:  
Each type of power transmission and control system has specifically suitable application 
areas. However, we can make some general comparisons between them.  
Fluid power and Electrical are good at transmitting power over long distances, and also better 
controllable compared to mechanical devices. Electrical devices are the cheapest. Hydraulic 
systems have better power/weight ratio. In terms of cost, electrical would be the cheapest.   
Following table gives a relative comparison of Hydraulic, pneumatic and Mech / EM systems .    
H – Hydraulic;  P – Pneumatic  M – Mechanical/Electromechanical;  E – Electrical  
Property Best Good Fair 
Torque/Inertia H P M 
Power /weight H,P - M 
Rigidity H M P 
Dirt vulnerability E,M - H,P 
Speed of response E H M. P 
Compactness E H M,P 
Ability to work in 
adverse conditions 
- P,M,H E 
Relative cost M,E H,P - 
 
1.5  Hydraulic fluids:  
The general requirements of fluids in power transmission are :  
1. Low cost 
2. Non-corrosive 
3. Have infinite stiffness 
4. Good lubrication properties 
5. Store well without degradation  
6. Non-toxic 
7. Non-inflammable 
8. Properties remain stable over wide range of temperatures.   
 
Page 5


                                            
 
 
 
HYDRAULIC SYSTEMS 
 
1. Introduction 
Hydraulic systems are used for transmission of power through the medium of 
hydraulic oil. The hydraulic system works on the principle of Pascal’s law which 
says that “ the pressure in a  fluid at rest is transmitted uniformly in all 
directions” .   
The fluid medium used is hydraulic oil, which may be mineral oil or water or 
combinations. This area is also known as oil hydraulics.  
The power transferred is  
Power = Pressure x flow rate in the tubes or hoses.  
The schematic of a simple hydraulic system is shown in the figure below. It 
consists of: 
? a movable piston connected to the output shaft in an enclosed cylinder 
? storage tank containing hydraulic fluid 
? filter which is in suction line of pump inside the tank or on tank inlet line. 
? Electric motor /  Diesel or petrol engine which is the primary source of  power 
? Hydraulic pump driven by motor or engine  
? Pressure control valve  
? Leak proof closed loop piping. 
? Direction control valve which controls the direction of  fluid flow so as to 
change the direction of motion of a linear or rotary actuator 
? Actuator – A cylinder for linear movement  or a hydraulic motor for rotary 
actuation of  load  
 
 
                                            
 
 
 
1.1 Applications of Hydraulic Systems 
The chief advantage that hydraulic systems derive is from the high pressures that 
can be applied leading to high force or toque by the actuating piston or motor.  
Pressures normally used in Industry are 140 bar (140 kgf/ cm
2
 ˜14 MPA ˜ 2000 
psi). But in some specific applications in machine tools and aerospace, 350 bar 
(35 MPa or 5000 psi) is also common.  
Example: Consider an actuator with a 10 cms diameter piston. If the pressure 
applied on the piston is 140 bar, Force that the piston rod delivers  
= F = Pressure x Area =  140 * p/4* 10
2
 = 10,996 Kgf = 108 KN.  
ie nearly 10 Tons of load can be applied using a 10 cms dia cylinder. If the 
pressure is 350 bar, load will be 25 Tons.  
Similarly high torques can be applied with a small sized motor compared to an 
electric motor. The high Power / Weight ratio of the hydraulic actuators is the 
prime reason for use of hydraulics.   
 
1.2 Application areas: 
Hydraulic systems are generally used for precise control of larger forces. The 
main applications of hydraulic system can be classified in five categories: 
 
 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. 
 
 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. 
 
 Automobiles: brakes, shock absorbers, steering system, wind shield, lift 
and cleaning etc. 
 
 Marine applications: Controls in ocean going vessels, fishing boats and navel 
equipment. 
 
 Aerospace equipment: R udder control, landing gear, breaks, flight control 
and transmission, rocket motor movement 
 
                                            
 
 
 
1.3 Advantages and Disadvantages of Hydraulic systems 
 Advantages of  Hydraulic systems  
 
? High power to weight ratio  compared to electrical systems  
? Allows easy control of speed and position, and direction  
? Facilitates stepless power control 
? Allows combination with electric controls 
? Delivers consistent power output which is difficult in pneumatic or 
mechanical drive systems 
? Performs well in hot environment conditions 
 
Compared to Pneumatics:  
? Much stiffer (or rigid) due to incompressible fluid  
? Better speed of response 
? Better lubricity (less friction)  and rust resistance  
? Low maintenance cost. 
 
Disadvantages 
 
• Material of storage tank, piping, cylinder and piston can be corroded 
with the hydraulic fluid. Therefore one must be careful while selecting 
materials and hydraulic fluid. 
• Structural weight and size of the system is more which makes it unsuitable 
for the smaller instruments. 
• Small impurities in the hydraulic fluid can permanently damage the 
complete system. Therefore suitable filter must be installed. 
• Leakage of hydraulic fluid is also a critical issue and suitable 
prevention method and seals must be adopted. 
•   Hydraulic fluids, if not disposed properly, can be harmful to the    
      environment. 
 
 
 
 
                                            
 
 
 
1.4 Relative advantages of different power transmission systems:  
Each type of power transmission and control system has specifically suitable application 
areas. However, we can make some general comparisons between them.  
Fluid power and Electrical are good at transmitting power over long distances, and also better 
controllable compared to mechanical devices. Electrical devices are the cheapest. Hydraulic 
systems have better power/weight ratio. In terms of cost, electrical would be the cheapest.   
Following table gives a relative comparison of Hydraulic, pneumatic and Mech / EM systems .    
H – Hydraulic;  P – Pneumatic  M – Mechanical/Electromechanical;  E – Electrical  
Property Best Good Fair 
Torque/Inertia H P M 
Power /weight H,P - M 
Rigidity H M P 
Dirt vulnerability E,M - H,P 
Speed of response E H M. P 
Compactness E H M,P 
Ability to work in 
adverse conditions 
- P,M,H E 
Relative cost M,E H,P - 
 
1.5  Hydraulic fluids:  
The general requirements of fluids in power transmission are :  
1. Low cost 
2. Non-corrosive 
3. Have infinite stiffness 
4. Good lubrication properties 
5. Store well without degradation  
6. Non-toxic 
7. Non-inflammable 
8. Properties remain stable over wide range of temperatures.   
 
                                            
 
 
 
Many types of fluids are used ranging from water, mineral oils, vegetable oils, synthetic 
and organic liquids. Water was the first liquid used and is very cheap. But its 
disadvantages are – freezes easily, rusts metal parts, boils and relatively poor lubricant.  
Mineral oils are far superior in these properties. Its success also lies in  – the ease with 
which their properties can be changed with additives.  
 
Additives used are - various chemicals like phenols and amines, chlorine and lead 
compounds, esters, organo-metallic compounds, for change in properties such as:  
1. Antioxidants 
2. Corrosion inhibitor 
3. Rust inhibitor 
4. Anti-foam 
5. Lubrication improver 
6. Pour point depressant 
7. Viscosity index improver.   
1.6 FILTERS 
When hydraulic fluids are contaminated, hydraulic systems may get damaged and malfunction   
due to clogging and internal wear . They require filtration to remove contaminants.  
Filters are classified as  
i. Reservoir filters:  
ii. Line filters 
iii. Off-line filters 
iv. Other cleaning equipment 
1. Reservoir filters: These may be installed in the reservoir at the pump suction port 
or in the return line cleaning the liquid returning to the port.  
Suction type filter consists of a core rolled up with a filter paper and submerged in 
working fluid. Typically they use 100 micron filter papers.  
Return filters or either mounted on the reservoir or in the lines.  
Filtration ratings in return lines vary from 10 micron to 35 micron, lower micron 
rating being used for higher pressures.  
2. Line filters: These are installed when high filtration is required and are used to 
avoid high suction at the reservoir filters. These are used with a separate line 
connection.  Filter selection depends upon pressure, flow rate and filtration rating.  
3. Off-line filters: These filters clean fluids in a reservoir using a dedicated pump 
and filter separate from the line.   These are used when higher cleaning level is 
required.   
4. Other equipment include air breather (filtering out dust in the air), oil filling port 
or magnetic separator to absorb iron powders in reservoir.