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VISHWAKARMA GOVT. ENGG. COLLEGE
INDUSTRIAL TRAINING REPORT
BASIC OF HYDRAULIC SYSTEM
Assembly and testing
SUBMITED BY
REEGAL K. PATEL
VISHAWAKARMA GOVERNMENT ENGINEERING COLLEGE, CHANDKHEDA.
ENROLLMENT NO. : 120170119009
DEPARTMENT OF MECHANICAL ENGINEERING
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I confirm that this report is my own personal work and that all material other than my own is
properly referenced.
Student’s Name: PATEL REEGAL KANUBHAI
Student’s Signature:
Date : 26/05/2015
MOBILE NO. 94287 38947
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Acknowledgement
Apart from the efforts of me, the success of any project depends largely on the encouragement and
guidelines of many others. I take this opportunity to express my gratitude to the people who have been
instrumental in the successful completion of this project.
I would like to show my greatest appreciation to Mr. HARISHCHANDRA PATIL. I can’t say thank
you enough for their tremendous support and help. I feel motivated and encouraged every time I attend
thier meeting. Without thier encouragement and guidance this project would not have materialized.
The guidance and support received from all the members who contributed and who are contributing to
this project, was vital for the success of the project. I am grateful for their constant support and help.
STUDENT SIGNATURE
(REEGAL K. PATEL)
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ABOUT BOSCH REXROTH
Bosch Rexroth India Ltd. is one of the leading specialists in drive and control technology. The company supplies tailored solutions for driving, controlling and moving. Bosch Rexroth is a partner for industrial applications (machinery applications and engineering and factory automation), mobile applications and renewable energies, and is thus a supplier choice of customers for high quality hydraulic, pneumatic and mechatronic components and systems. Established in 1975, Bosch Rexroth India serves customers through manufacturing facilities at Ahmedabad and a customized unit in Bangalore with widespread sales and service offices, as well as dealers’ network all over India. Bosch Rexroth India offers its customers all drive and control technologies such as Industrial Hydraulics, Mobile Hydraulics, Pneumatics, Linear Motion and Assembly Technology, Electric Drives and Control. Rexroth is a reliable partner for its customers, supporting their production of safe and efficient machines and thereby contributing to the economical use of natural resources. The company is accredite d to ISO 9001:2008, ISO 14001:2004, OHSAS18001:1999 certification. It offers:
Manufacture of hydraulic valves, blocks, cylinders and power units in Ahmedabad. Customizing unit in Bangalore for power units, pneumatic panels, cabinets and cylinders, cutting and
assembly line for linear motion products.
Multi-disciplinary know-how is the basis for innovative solutions that are used as components or customized systems. Because Rexroth offers a complete range of drives and controls. Rexroth technology is used in all branches of industry. Its comprehensive service offerings fortify Rexroth's leading position worldwide as a partner for machine and system manufacturers.
Economical, precise, safe, and energy efficient: drive and control technology from Bosch Rexroth moves
machines and plants of any size. The company bundles global application experience in the market
segments of mobile applications, plant construction and engineering, factory automation, and
renewable energies to develop innovative components as well as tailored system solutions and services.
Bosch Rexroth offers its customers hydraulics, electric drives and controls, pneumatics, drive
technology, and linear motion and assembly technology all from one source. With locations in over 80
countries, more than 37,500 associates generated a sales revenue of approximately EUR 6.5 bn in 2012.
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Contents 1.Introduction to Hydraulics: ...............................................................................................................5
Effect of Temperature on Viscosity: ......................................................................................................6
2.Basic Symbols: .................................................................................................................................7
3.Hydraulic Pumps: ........................................................................................................................... 12
BASIC DESIGN OF PUMPS .............................................................................................................. 12
External gear pumps: ............................................................................................................. 14
Internal gear pumps:.............................................................................................................. 15
Vane pump:........................................................................................................................... 15
Variable Displacement Vane Pump: ............................................................................................ 15
Axial piston pumps: ............................................................................................................... 16
Bent axis: .................................................................................................................................. 16
Swashplate: .............................................................................................................................. 17
Major aspects in the selection of pumps ..................................................................................... 18
4.Non return valves: ......................................................................................................................... 20
5.Pressure control valve: ................................................................................................................... 22
Classification: ............................................................................................................................... 22
Pressure relief valve: ..................................................................................................................... 22
Pressure reducing valves ............................................................................................................... 23
Flow control valve: .................................................................................................................... 24
6.Directional control valve ................................................................................................................ 25
Classification: ............................................................................................................................... 25
Spool directional valve: ................................................................................................................. 27
Direct operated valves ............................................................................................................... 28
Pilot operated directional control vales: ..................................................................................... 29
Poppet directional valves: ............................................................................................................. 30
Difference between spool directional valve and poppet valve: ........................................................ 31
7.Cylinder......................................................................................................................................... 32
Properties: ................................................................................................................................ 32
Cylinder types: .......................................................................................................................... 32
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1.Introduction to Hydraulics:
Mass:
A weight force is created by mass on the ground in the gravity.
Force:
According to the newton’s law,
Force = mass*acceleration
F = m*a
Pressure (P):
If a force acts perpendicularly to a surface and acts on the whole surface then the force F divided by the
area of the surface A is the pressure P.
P = F/A
Work (W):
Work is a product of distance covered s and the force F which acts in the direction of the displacement
W = F*s.
The SI unit for the work is the Joule
1 J = 1 Nm = 1 Ws.
Pascal’s law:
The basic idea behind any hydraulic system is very simple: force applied at one point is transmitted to
another point using and incompressible fluid, which is almost always going to be a type of oil. In some
systems, such as brake systems in a car, multiply the process. A major part of hydraulics is Pascal’s
principle:
Changes in pressure at any point in an enclosed fluid at rest are transmitted undiminished to all
points the fluid and act in all directions.
Bernoulli’s Law for incompressible fluids:
H = z + p/ρg + v2/2g (fluid is flowing with a significant difference in height between source & sink)
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Where H=total head pressure, v= fluid velocity, g= force of gravity, z= the height of the fluid source,
p=fluid pressure & ρ=fluid density
p0 = p + v2/2 (fluid height is insignificant)
Where p0 = total system pressure, p= static pressure v= flow velocity
Viscosity:
Viscosity is a quantitative measure of a fluid’s resistance to flow.
Dynamic (or Absolute) Viscosity:
The dynamic viscosity(η) of a fluid is a measure of the resistance it offers to relative shearing motion.
η= F/ [A×(u/h)]
η= τ /(u/h) N-s/m²
Kinematic Viscosity :
It is defined as the ratio of absolute viscosity to the density of fluid.
ν= η/ρ m²/s ; ρ= density of fluid
Effect of Temperature on Viscosity:
The viscosity of liquids decreases with increase the temperature.
The viscosity of gases increases with the increase the temperature.
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2.Basic Symbols:
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3.Hydraulic Pumps:
BASIC DESIGN OF PUMPS The main types of hydraulic pumps which operate on the displacement principle are outlined below:
1. External gear pump
Volume is created between the gears and housing walls.
V=m*z*b*h*
m= module, z= number of gears, b= width of gears, h= height
of gears
2. Internal gear pump
Volume is created between the gears, housing and spacing
Hydraulic Pumps
Gear
External gear
pump
Internal gear pump
Gear ring
pump
Vane
Single chamber
Double chamber
Piston
Radial piston
Ecentric cylinder
block
Ecentric shaft
Axial piston
Swashplate
Bent axis
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element.
V= m*z*b*h*
m= module, z= number of gears, b= width of gears, h= height of
gears
3. Ring gear pump
The rotor has one gear less than on the internally geared stator.
Planetary movement of the rotor.
V= z*(Amax-Amin)*b
z= number of gears, b= width of gears
4. Screw pump
The displacement chamber is formed between threads
and housing.
𝑉 =
4(𝐷2−𝑑2) ∗ 𝑠 ∗ 𝑐
C<1
The correction factor c especially takes the interlocking of
threads of both spindles into consideration.
5. Single chamber vane pump
Volume is created between the circular stator, rotor and
vanes.
V= 2**b*e*D
b= vane width
6. Double chamber vane pump
Due to the twin cam forms of the stator, two displacement
processes occur per revolution.
𝑉 =
4(𝐷2 −𝑑2)∗ 𝑘 ∗ 𝑏
b= vane width, k = vane stroke per revolution
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7. Radial piston pump with eccentric cylinder block
The pistons rotate within the rigid external ring.
Eccentricity ‘e’ determines the stroke of the pistons.
𝑉 =
4(𝑑𝑘
2) ∗ 2𝑒 ∗ 𝑧
z= number of piston
8. Radial piston pump with eccentric shaft
The rotating eccentric shaft causes radially oscillating
piston movement to be produced.
𝑉 =
4(𝑑𝑘
2) ∗ 2𝑒 ∗ 𝑧
z= number of piston
External gear pumps: External pumps are used in large numbers in mobile hydraulics.
Features:
- Relatively high pressure for low weight
- Low cost
- Wide range of speeds - Wide temp./viscosity range
Function:
Gear is connected via coupling with the drive.
Gears are positioned in such way by the bearing blocks that the
gears mesh on rotation with the minimum clearance.
Fluid is fed into the gear chambers and via pressure port of the
pump into the hydraulic system. Hence a prerequisite for the pump
to function is that the gear chambers are sealed to such an extent
that fluid can be transported with as little loss as possible.
Important parameters
Displacement volume 0.2 to 200 cm3
Max. pressure up to 300 bar (size dependent)
Range of speeds 500 to 6000 rpm
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Internal gear pumps: The most important feature of internal gear pumps is the very low noise level. Hence they are primarily
used in industrial hydraulics and in vehicles which operate in an enclosed space.
Function
The gear rotor is connected to the drive. When the gear rotor and internal gear rotate , the space
between the gears increases. The pump “sucks”.
This increase in space occurs over an angle about 120˚. Hence the disp lacement chamber is filled slowly.
When the chambers are full, the fluid is transported without change in volume to the pressure port.
Important parameters
Displacement volume 3 to 250 cm3
Operating pressure up to 300 bar (dependent on size)
Range of speed 500 to 3000 rpm (dependent on size)
Vane pump:
Function:
1- As the rotor rotates and fluid enters the pump, centrifugal force, hydraulic pressure, and/or
pushrods push the vanes to the walls of the housing. The tight seal among the vanes, rotor, cam, and
side plate is the key to the good suction characteristics common to the vane pumping principle.
2. The housing and cam force fluid into the pumping chamber through holes in the cam. Fluid enters
the pockets created by the vanes, rotor, cam, and side plate.
3. As the rotor continues around, the vanes sweep the fluid to the opposite side of the crescent
where it is squeezed through discharge holes of the cam as the vane approaches the point of the
crescent. Fluid then exits the discharge port.
Variable Displacement Vane Pump:
In variable displacement the discharge of pump can be changed by varying the eccentricity between
rotor and pump cam-ring. As eccentricity increases pump discharge increases. With decrease in
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eccentricity discharge decreases and oil flow completely stop when rotor becomes concentric to pump
cam ring.
Axial piston pumps: These consists of a number of pistons which are caused to reciprocate by the relative rotation of an
inclined plate or by angling the piston block.
There are two types of axial piston pumps:
1. Bent axis
2. Swashplate
Bent axis:
1- Bent axis piston Pumps have a rotating cylinder containing parallel pistons arranged radially around
the cylinder centre line.
2- The pressure in the fluid causes the pistons to reciprocate over a stroke based on the relative angle of
the shaft and cylinder.
3- The motion of the pistons results in the rotation of the shaft.
4- The cylinder is driven by an shaft which is arranged at an angle to thecylinder axis.
5- The shaft includes a flange with a mechanical connection to each piston.
6- The greater the angle of the cylinders to the shaft axes the longer the pistons stroke and the less the
rotation speed per unit fluid flow rate.
Features:
Typical displacements to 500 cm3/hr
Typical pressures to 350 bar
No through shaft option (multiple assemblies not possible)
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High overall efficiency
Compact package.
Swashplate:
1- Swash plate pumps have a rotating cylinder containing pistons.
2- A spring pushes the pistons against a stationary swash plate, which sits at an angle to the cylinder.
3- The pistons suck in fluid during half a revolution and push fluidout during the other half.
4- It contains two semi-circular ports.
5- These ports allow the pistons to draw in fluid as they move toward the swash plate and discharge it as
they move away.
6- For a given speed swash platepumps can be of fixed displacement like this one, or variable by having
a variable swash plate angle.
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Major aspects in the selection of pumps
1- Flow rate requirement 2- Operating speed
3- Pressure rating 4- Performance
5- Reliability 6- Maintenance
7- Cost and Noise 8- Fluid Type
ASSEMBLY :-
a group of machine parts,
especially one forming a self-contained,
independently mounted unit.
What to assemble ?
Company assmbel the diff. parts in a housing
of metal where diff. type
Rings
Spring
Spring sheet
Spool
Controlling parts of valves etc.
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Nut & bolt for fixing.
Washer
Different valves have a diff. parts to assemble as per requirement of function
of valve.
Now
the classification of hydraulics valves.
note: in bosch reorth sanad, each screw driver
work on pneumatic system and other small riveting machine etc. also work on
its.
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Sign.
4.Non return valves: They have the task to allow the flow in one direction only.In the other direction the flow is prevented
from flowing usually by a conical or spherical element (poppet valves).There are also spool valves but
they do not seal so well.The element is pressed to the seat by a spring force.Usually needs metallic
surfaces with very accurate machining.Valve seats with elastic surface did not prove to be very good.
Important parameters
Sizes: 6 to 150 flow: up to 15000 L/min operating pressure: up to 315 bar
cracking pressure : without spring ;
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0.5;1.5;3 or 5 bar
Pilot-operated check valves:
With an outside pressure the valve can be opened again.There is a piston with a larger surface which is
operated with a lower pressure than the closing pressure the valve can be opened.Main application:
holding of loads and when desired, sinking.
Pilot operated check Pilot operated check
valve without drain portvalve with drain port
Sandwich type check valve:
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5.Pressure control valve:
Classification: • pressure relief valves
• pressure reducing valves
• pressure sequence valve
Pressure relief valve: Has the task to limit the pressure in a hydraulic system or in a part of the system.
The pressure can rise in a hydraulic system if:
- the flow rate from the pump is larger than the flow rate through the actuator
- the volume of a closed system is reduced
- the load of the actuator rises
- heat is introduced into a closed system
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- the hydraulic resistance of the system rises
Direct operated pressure relief valve:
The valve which is screwed into a housing or a control block comprises sleeve, spring, adjustment
mechanism, poppet with damping spool and hardened seat.
The spring pushes the poppet on to its seat. The spring force can be steplessly adjusted by means of the
rotary knob. The pressure is thus also set accordingly.port p is connected to the system. Pressure in the
system acts on the poppet surface. If pressure lifts the poppet from its seat, the connection to the port
is opened. The poppet stroke is limmited by a pin in the damping bore.
Pilot operated:
Direct operated valves are limited as the flow increases due to the space required for the control spring.
A Large flow requires a large poppet or spool diameter. The area and hence the spring force increases
proportionally to the diameter squared.
In order to keep the space required for these valves down to a sensible level, pilot operated valves are
used for large flows. They are used to limit the operating pressure or limit and unload the operating
pressure by means of solenoid operation.
1 - Main valve 2 - Pilot valve
3 – Main spool 4 - 5 - 11 - Throttle
6 - 7 - 13 - Operation line
8 - Valve body 9 - Spring
15 - Discharging
Pressure reducing valves In contrast to pressure relief valves which affect the input pressure,
pressure reducing valves are used to infulence the output pressure.
Pressure relife valve
Direct operated
Pilot operated
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The reducing of input pressure or the maitenance of output pressure is achieved at a set value, which is
below the charging pressure available in the main circuit. It is thus possible to reduce the pressure in
one part of the system to a level lower than system pressure.
Flow control valve: Flow control valves are used to keep a set flow constant regardless of pressure variations. This is
achieved in that in addition to adjustment throttle an adjustment moving throttle is built into the
system, which operates as a control throttle and at the same time as a comparison element in the closed
loop control circuit.
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6.Directional control valve
Classification: 1. Spool valves or poppet valves
2. Switching or continuously adjustable valves
3. Number of ports and positions
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4. The kind of governing and positioning unit
Directional valves
Spool va lves
Direct operated
Manually Operated
Mechanically Operated
Hydraulically Operated
Pneumatically Operated
Electrically Operated
Pi lot operated
Electro-hydraulically
Poppet va lves
Direct operated
Manually operated
Mechanically operated
Hydraulically operated
Pneumatically operated
Electrically operated
Pi lot operated
Electro-hydraulically
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Spool directional valve:
Directional spool valves in which a moving spool is situated in the valve housing.
When the control spool is moved, it connects or separates the annular channels in the
housing.
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Directional spool valves are sealed along the clearance between the moving spool and the
housing.
The degree of sealing depends on the clearance, the viscosity of fluid and especially on
the level of pressure.
Amount of leakage is dependent on the clearance between spool and the housing. Hence
in theory, the clearance must be reduced or the length of overlap increased as the
operating pressure increases.
There are two subdivisions in directional spool valves
1. Direct operated valves
2. Pilot operated valves
Direct operated valves
Direct operated directional spool valves “imply that they are directional spool valves the control spools
of which may be operated directly by solenoid, pneumatic/hydraulic forces or by a mechanically acting
device without any intermediate amplification.
Electrical operation:
This type of operation is the most common, due to the automatic processes required in industry.
Solenoid is used as controller in this operation. solenoid controls the movement of spool.
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Manually operated directional control valve:
The spool is fixed rigidly to the operating mechanism and follows its movement.
The spools is returned by springs, which push the spool
back to its original position once the operating force
has been removed. If a detent is fitted and the spool
cannot be returned by centring springs, the spool
position is fixed by the detent and can then only be
changed again by means of an operation.
Pilot operated directional control vales:
There are two models in the pilot operated valves.
1. Spring centred
2. Pressure centred
Spring centred model
On the spring centred model, the main control spool is held in centre position by the springs.
Both spring chambers are thus connected in neutral position via the pilot valve with the tank at zero
pressure. Thus the centre position for the pilot valve is fixed.
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Pressure centred model
In the centre position of pressure centred valves both control chambers are connected with the control
pressure. The main control spool is held in the centre position by the effect of the pressurised surfaces
of spool centring bush and centring pin.
Poppet directional valves: Directional poppet valves are direction valves in housing bore of
which one or more suitably formed seating elements in the form
of balls, poppets or plates are situated. With this design as
operating pressure increases, the valve becomes more tightly
sealed.
Main features of directional poppet valves are:
No leakage
Long idle times possible, as there are no leakage oil
flows and throttle clearances which could float
Isolating function without additional isolating
elements
Large pressure drop due to short strokes
Loss of performance due to incomplete balancing of pressures on the valve axis.
1 – ball2 – spring3 – poppet, 4 –
housing 5 – lever 6 – operating pin, 7 –
ball8 - poppet
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Difference between spool directional valve and poppet valve:
Spool directional valve Poppet valve 1.spool is used as a closing element in spool
directional valve
1. ball or poppet is used as a closing element in
poppet valve
2. Annular clearance is always there. 2. No clearance is there.
3. Leakage flow is continuously present between
P and L
3. No Leakage flow is there.
4. low pressure drop as compare to poppet valve 4. high pressure drop
5. Need relatively large displacements because a
positive overlap is needed for sealing.
5. Need smaller displacements to let fluid through.
6. Design for low pressure as compared to
poppet valve and high flow.
6. Design for high pressure and lesser flow
compared to spool valve.
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7.Cylinder
Properties:
The cylinders have to be good quality steel with close tolerances.There have to be good sealing both at
the piston rod and at the cylinder.With time dirt may come in and damage the surfaces. This has to be
possibly reduced.In this case, the leakage will increase all the time.
Cylinder types:
Single acting: Double acting piston:
work can be done only in one direction Work is done in both directions
Plunger
Plunger
Piston
Piston rod on both sides
Telescopic
Telescopic
Fast moving
Fast moving
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Testing :-
the trial of the quality of
valves for proper condition which is
required for functioning at certion
condition and cheked out error in it if it is
present.
In a testing process each test batch have
a separate power pack applied and
testing is done by them
Now valve which have to be test is set in
a fix condition after that the flows pipe
are connected with it then start the
testing of valve
Valve is testing for diff. condition
Diff. switching postion
Leakage in valve etc. are checked there.
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Testing require very small time and its
give accurate result by test batch testing.
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