Hydraulic System of Tractor

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Hydraulic

Power

basics

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Pascal’s Law

Pressure exerted at any point on

a confined liquid is

a confined liquid is transmi

transmitted

tted

undiminished in all directions.

(3)

Pascal’s Law

Pressure exerted at any point on

a confined liquid is

a confined liquid is transmi

transmitted

tted

undiminished in all directions.

(4)

Pascal's law

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Hydrau

lic

T

erms

H

Hyyddrraauulliic c PPiissttoon n SShhaafft t PPSSII P

Pnneeuummaattiic c SSttrrookke e CChheecck k vvaallvve e SSppooool l vvaallvvee P Puummp p SSeeaal l RRoocckksshhaafft t CCyylliinnddeer r Hydraulic Hydraulic motor motor Single-acting acting Double-acting acting Input / Input / Output Output

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Hydraulic

T

Tool

ool or

or equipment

equipment power

powered

ed

by the movement of fluid

under

under pr

pressure.

essure. Example

Examples

s

are brakes, jacks & tractor

lifts.

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Pneumatic

Tool or equipment

powered

or

supported

by

the

movement

of

compressed air.

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PSI

Pounds per Square Inch

determines amount of force

GPM

Gallons per Minute

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Pressure applied to piston “A” is

transferred equally to a piston of the

same size “B” because PSI is the

same throughout the system.

Basic

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If the surface area of piston “B” is 10

times the surface area of piston “A”,

then the force applied to piston “A” is

multiplied 10 times as the force exerted

on piston “B”. PSI is equal throughout

hydraulic

advantage

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Input / Output

Force input on a hydraulic

system or component results

in transfer of power to output

of force by the system or

component.

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Pump

Functions

in

a

hydraulic system by

pressurizing

and

moving fluid from one

part of the system to

another.

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Hydraulic pumps are usually one

of four types:

PISTON

GEAR

VANE

INTERNAL ROTOR

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Piston Pumps

• _{Work well at PSI’s of 2000 or more}

• _{Single piston pump used in bottle jacks}

• _{Require several pistons working together to}

generate enough volume for tractor applications

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Gear Pumps

•

Work well at 1500 PSI and

below

•

Work with a minimum of

moving parts

•

Less expensive to manufacture

than piston type pumps

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Gear

Pump

driven gear

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Hydraulic Motor

Receives power from

moving fluid to transfer

hydraulic

power

to

mechanical

rotating

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Cylinder

Piece of equipment that

transfers

hydraulic

power into mechanical

movement in one or two

directions only.

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Single-acting

Refers to a hydraulic

cylinder that works in

one direction only.

Double-acting

Refers to a hydraulic

cylinder that pushes

and pulls.

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Single-acting cylinder

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Double-acting Cylinder

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Piston

Internal component of a

hydraulic cylinder that is

moved in a linear motion by

the action of fluid introduced

into the cylinder.

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Shaft

The polished round bar that

is

extended

from

and

retracted into a hydraulic

cylinder.

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Stroke

The length of movement that a

hydraulic cylinder is capable

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Seal

Found

in

hydraulic

components; function is to

keep fluid from leaking

between moving and

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Check Valve

Restricts flow of fluid to only

one direction; allows pressure

to build up or be maintained.

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Spool Valve

Controls direction of flow of

fluid in a hydraulic system to

cause the different parts of

the system to function.

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The first hydraulic power lift

for a tractor was introduced

in 1935 by John Deere. This

unit only had two positions,

up and down, but the

hydraulic action cushioned

the

lowering

of

the

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Rockshaft

Rotating shaft on a modern

tractor powered by an internal

hydraulic cylinder; used to

transfer

power

to

the

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INTRODUCTION

Normally, a hydraulic system with reference to a tractor is considered to be a unit responsible for lifting and lowering an agricultural implement.

The draft control and weight transfer has become an inevitable function of the hydraulic system.

In the hydraulic system the fluid is confined inside pipe lines, reservoir and cylinders. When pressure is applied at any point, the force is transferred by the fluid throughout the system which is utilized to lift the implements and do other jobs with minimum of effort.

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The reason for selecting the hydraulic system of power transfer is due to its merits over the

mechanical means of power transfer which are enumerated below:

The hydraulic system is simpler than the mechanical linkage system because fluid power can be routed around corners with less problems.

 _{The system is flexible enough, allow the point}

of application to move to any location with respect to the source of power generation, which is almost constant in the case of the mechanical system.

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 _{In comparison to input heavy forces can be}

controlled simply by increasing the size of the cylinder.

_{Because of self lubrication, wear and tear is less}

and hence the system is economical to operate.

 _{A good range of speed of operation is possible.}

_{A hydraulic system is safer than a mechanical}

system as the moving parts are minimized.

Though the system is preferred but can’t be called a perfect system without any drawbacks. The efficient operation require a regular cleanliness to avoid rusting, corrosion, dirt and other foreign materials.

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Parts of hydraulic system

Hydraulic system fitted with the following basic components are:

 _Reservoir  _Pump

 _{Relief valve}  _{Control valve}

 _{Cylinder and piston}  _{Filter or strainer}

 _{Operating lever}  _Distributor

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Reservoir

It is contains sufficient oil to move the

piston for lifting the load.

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Pump

It forces the fluid from the reservoir

to the cylinder

.

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Relief Valve

It protect the system from high pressure.

The valve is set for slightly higher than

the working pressure. In case the pressure

increase beyond the working pressure, the

relief valve opens allowing the fluid to

pass on the reservoir. Also when the

piston reaches its extreme position, the

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Control Valve

The control valve is used to allow the

operator to direct the flow of fluid

either from the pump to the cylinder

or from the cylinder to the reservoir.

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Cylinder

The cylinder convert the hydraulic power

to mechanical power for doing the

various jobs.

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Hydraulic Valves

A hydraulic system is never complete without

valves. These valves vary in shape and

function, but ultimately control the circuit by

regulating the pressure, direction and volume

of oil flow. Based on their function, they can

be divided into the following categories –

1. Directional-control valves

2. Pressure-control valves or safety valves

3. Volume-control valves

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Hydraulic system can be broadly divided into two major system –

1. Open-centre-system 2. Closed-centre system

The open-centre-system uses a constant-flow pump with an open-centre spool valve so that when oil is not flowing to the cylinder, it can pass onto the reservoirs.

In the case of the close-centre the pump is of variable flow type and the spool valve is close-centre type. In the neutral position the pump stops pumping oil.

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Implement Control

The tractor with a built-in lift system is connected to the implement through a specific type of mechanical linkage termed as three-point linkage and the system is known as mounted system. The implement is connected to the tractor hydraulic through three points – two bottom links and one top link. Both the bottom links are connected to two lift arms through lift links. The lift arms are directly mounted on a rock shaft which is further connected to the piston rod.

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Any movement of the piston rod. Any movement of the piston is transferred to the bottom links. The top link is used for connecting the third hitch point of the implement and is adjustable for maintaining the implement level and suction angle. Load sensing for the draft control can also be done through the top link which is spring loaded. In some tractors the lower links are spring loaded for draft sensing. Depending upon the soil condition and type of operation the mounted implement can be controlled either by position control or draft

control.

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Position Control

The lever position on the quadrant directly represents the corresponding position or depth of the implement. Therefore in position control it is possible to present the working depth. Therefore normally the position control is used for weeders, planting and sowing machines, sprayers and for transportation of the implement.

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Draft

Control

Under this system of control, the implement is set for a particular draft (drawbar pull) rather than depth. In varied soil conditions the implement automatically takes more or less depth to maintain the predetermined draft.

Most of the indigenous tractors possess a draft control system in addition to the position control.

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Mixed Position and Draft Control

It is also possible in some Tractor (viz. HMT, Ford, etc) to suitable blend the response through an interlink mechanism so that a desired depth of ploughing is maintained within close limits and draft control too is allowed to function for better traction.

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Maintenance and repair of hydraulic system

For successful operation of any hydraulic system, cleaning and periodic maintenance is very essential. If the operator is alert and keeps the machine clean, refills clean oil, replaces or clean the filter regularly, keeps the tubes and rubber hose tight and protects the system from dust and other contaminants, the system will undoubtedly work efficiently with less trouble.

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Continuously

Most of the troubles arise because of dirty or improper grade of oil in use. Low oil level also is a cause of a number of troubles. Normally, the following defects may arise:

1. System may not work at all.

2. System may work slowly but fail to lift under load.

3. Sinking of load may take place. 4. Cylinder movement may be jerky. 5. System may get hot and foaming.

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Continuously

While diagnosing the trouble, one should check whether system is defective due to the pump or some other component. If the pump is fitted outside, it can be observed and its sound can be listened to, but if it is fitted inside, the flow pressure can be checked at the delivery of the pump. The pump can either produce insufficient discharge or can create insufficient pressure. The reasons for low volume and low pressure are enumerated below.

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