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.