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1. ON –LINE LECTURE
By
Dr. R. C. Salunkhe
Assistant Prof.
Deptt. of FMPE, CAET, Godhra
Course Code : FMPE-3.5.2
Course Title : Tractor Systems and Controls
Topic : Hydraulic System
for
B. Tech Students of CAET Godhra
Semester: 5th

2. Hydraulic System
 It is a mechanism in a tractor to raise,
hold or lower the mounted or semi-
mounted equipments by hydraulic
means.
 All tractors are equipped with hydraulic
control system for operating three point
hitch of the tractor.
It also used for tilting hydraulic trailer.
Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra

3. Principle of Operation
The working principle of hydraulic system is
based on Pascal’s law.
This law states that the pressure applied to
an enclosed fluid is transmitted equally in all
directions.
Small force acting on small area can produce
higher force on a surface of larger area.

4. Components of hydraulic system
(i) Hydraulic pump
(ii) Hydraulic cylinder and piston
(iii) Hydraulic tank
(iv) Control valve
(v) Safety valve
(vi) Hose pipe and fittings and
(vii) Lifting arms.
Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra

5. (i) Hydraulic pump
• In hydraulic system, positive displacement pumps are
used.
• These pumps give high pressure and low discharge.
• These pumps are categorized as (a) reciprocating
pump and (b) Rotary pump.
• In automobile hydraulic system rotary pumps are
used as its required less space.
• There are several types of hydraulic pump, such as
gear pump, plunger pump, vane pump, and screw
pump. Gear pump is widely used in tractors.
• Gear pump can flow a bigger amount of oil, compared
to plunger pump.
• The oil pressure in the pump varies from 150 to 200
kg/cm2.
Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra

6. (i) Gear pump
 This kind of pump consists of
two gears fitted in a single
housing.
 One gear acts as driving gear
and the other as driven.
 The high speed operation of
the gears generate partial
vacuum and due to that
draws oil from the reservoir
through the intake, sucks
between the teeth and force
towards the discharge port.
 These kinds of pump are
largely utilized on agricultural
machines.

7. (ii) Hydraulic cylinder:
• The cylinder converts the hydraulic power to
mechanical power for doing various jobs.
• It is a bigger size cylinder, fitted with a piston
and a connecting rod.
• It is also called Ram cylinder.
• The connecting rod transmits power from the
piston to the lifting arms.
• Piston moves in the hydraulic cylinder and
causes reciprocating motion in the cylinder.
• The lifting arms are raised by the hydraulic
pressure while raising the implement but it is
lowered by its own weight.
Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra

8. (iii) Hydraulic tank (Reservoir):
• Hydraulic tank is used for storing hydraulic oil
for the system.
• In some tractors, transmission chamber itself
works as a hydraulic tank and same oil is
used for transmission system as well as
hydraulic system.
• In some tractors separate tank is used as
hydraulic oil reservoir.
Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra

9. (iv) Control valve:
• It is a type of valve, which controls the
movement of hydraulic oil to have desired
direction and magnitude.
• Thus control valve is to perform three
functions:
(a)To change the direction of lifting,
(b) To change the power of lifting and
(c) To change the speed of lifting.
The control valve is operated by hand lever.
Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra

10. (v) Safety valve or Relief valve:
• It protects the system from high pressure.
• The valve is set for slightly higher than the
working pressure.
• In case the pressure increases beyond the
working pressure, the relief valve opens
allowing the fluid to pass onto the reservoir.
• Also, piston reaches its extreme positions;
the relief valve opens to bypass the oil.
Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra

11. Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra
Working of hydraulic system
As shown in Fig.7.1 (a), when operating lever is at neutral
position, control valve restrict the further movement of oil
towards cylinder. Due to this oil is trapped between pump
and control valve which result into increase the oil
pressure beyond the working pressure and relief valve gets
open and oil is directed towards the reservoir.

12. Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra
For raising the implement, operating lever shifted to lifting position as shown
in Fig. In this position, control valve allows the flow of oil towards hydraulic
cylinder with high pressure. As the result the piston of cylinder moved in
outward direction, which in turn, raises the lifting arms. The lifting arms are
attached with implements and hence implement get raised gradually. When
the piston reaches its extreme positions; again the pressure on the oil starts
increasing beyond working pressure and when it reaches to pre-set value,
the relief valve opens and bypass the oil to the reservoir and implements
remain in raised condition.
Working of hydraulic system

13. Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra
For lowering the implement, operating lever shifted to lowering position as shown in
Fig. 7.1(c). In this position, control valve restrict the flow of oil coming from pump and
allows the cylinder oil back to reservoir. Due to self weight of implement and hence
there is no pressure on the oil in the cylinder, piston moves in inward direction and
pushes the oil from cylinder to back to reservoir. Due to this implement get lowered.
Again in this condition also oil is trapped between pump and control valve which
result into increase the oil pressure beyond the working pressure and relief valve gets
open and oil is directed towards the reservoir.
Working of hydraulic system

14. Types of hydraulic system
(a) Open centre valve and (b) Closed centre valve
(a) Open Centre Valve
In open centre type, when valve is kept in neutral
position, the outlet port remains closed but inlet port
remains open and fluid can pass through the centre of
the valve to the reservoir again as shown in Figure.

15. (b) Closed Centre Valve
In case of closed centre valve, both inlet and outlet
ports remain closed in its neutral position. A lever is
provided to close or open the ports of the valve. ‘O’
rings are used for sealing the valve body to prevent
the leakage. It is shown in Figure.

16. Valves used in hydraulic system
Hydraulic valves are the controller of the
hydraulic systems. These are used to control the
pressure, direction, and volume of the hydraulic
fluid in the hydraulic systems.
• Major Functions of Hydraulic Valves
– To control the pressure in the hydraulic system,
– To direct the fluid for conducting required work,
– To control the flow of the fluid in the hydraulic circuit
to protect the system from damages or breakdowns,
– To control the sequence in which hydraulic fluid will
flow to different circuits,
– To control the direction of flow, etc.

17. Types of Hydraulic Control Valves
On basis of the functions meant for, three
kinds of valves are used in hydraulic systems
namely
(i) Pressure control valves,
(ii) Volume control valves, and
(iii) Directional control valves.

18. (i) Pressure Control Valve: Pressure Relief Valve
 A pressure relief valve is one of the most common
pressure regulating valves.
 They are used to limit the pressure to a safe level. The
valve remains closed during normal operation but when
pressure reaches to upper limit it opens and allows the
hydraulic fluid to move towards the reservoir.
 This upper limit of pressure is known as ‘Cracking
Pressure’.

19. (ii) Volume Control Valve
 Volume control valves are used to control the flow
volume of the fluid in the hydraulic system.
 One type of such valve controls the volume through a
metering orifice and another through division of flow in
two or more circuits as shown in Figure.

20. (iii) Direction Control Valve: Spool Type Valve
These valves control the direction of the fluid flow in
the hydraulic system.
The rotary and spool valves are used for this purpose.
Two kinds of spool valves are used: (i) open centre;
and (ii) closed centre. The following figure shows two
positions of the sliding spool are: (i) left and (ii) right.

21. Methods of Hydraulic Control
The hydraulic system of the tractor is controlled by
three important methods.
 Position control :
• In this method, constant depth of operation is
maintained by automatic adjustment of draft of
tractor.
• The system the control valve can be operated directly
by the driver to raise lower or hold an implement,
mounted on the linkage at any chosen height.
• It is used on level ground with homogeneous soil
condition.
• It is used for light agricultural operations (where
required depth of operation is about 5 to 7 cm)
operation like weeding, planting and sowing.

22.  Draft control :
• In this control, the implement is set for particular
draft (drawbar pull) rather than depth.
• The hydraulic control valve reacts to changes in the
loading in either the top or lower links which are due
to changes in the draft or pull required by the
implement. If any implement goes too deep its draft
increases. This increase is sensed through the top link
or lower links. The control system then raises the
implement until the draft is back to the present level.
• It is used on undulating ground with heterogeneous
soil condition.
• It is used for heavy agricultural operations (where
required depth of operation is more than 8-10 cm)
operation like ploughing and harrowing.

23. Mixed control:
• It is a combination of position control and
draft control.
• It is done by blending both controls by the
response though an interlink mechanism.
• In which, desired depth of ploughing is
maintained within close limits and the daft is
also controlled for better traction to avoid
slipping of tire.

24. Design Problems on Hydraulic
System
Write:
Practical No. 7- Hydraulic System
Assignment no.1- Design Problems on Clutch
System
Prepared by: Dr. R. C. Salunkhe, Assi. Prof. Deptt. of FMPE, CAET,AAU, Godhra

25. Thank you