Tractor hydraulics

Tractor Hydraulics

Content

IntroductionWorking principleWhy Hydraulic systemParts of hydraulic systemTypes of hydraulic system

(a) Based on centre system

(b)Based on controlMaintenance and repair

Introduction

A unit responsible for lifting and lowering an agricultural implement

Function-draft control and weight transferFluid is confined inside pipelines, reservoir and cylindersHydraulic pumps transfer the fluid from the reservoir to

the hydraulic system. This transfer raises the energy level of the fluid by increasing its pressure. The motor provides the power source for the pump

Working principle

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 direc tions. Small force acting on small area can produce higher force on a surface of larger area.

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Why hydraulic system

Simpler than mechanical linkage systems

System is flexible enough

Power can be engaged or disengaged using a simpler valve

Input heavy forces can be controlled easily

A good range of speed operation is possible

Is safer than mechanical system

Parts of hydraulic system

ReservoirPumpValvesFluidMotorHoseFilterCylinderAccumulator

Reservoir

It 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 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.Schema


Relief valve

Relief valves are used in hydraulic systems to limit the system pressure to a specific set level. If this set level is reached, the pressure relief valve responds and feeds the excess flow from the system back to the tank


Control valves

Control valve is a type of valve, which controls the movement of hydraulic oil to have desired direction, magnitude and speed of lifting. This helps to determine speed of movement for the actuators.


Hydraulic motor

A hydraulic motor converts hydraulic energy into mechanical energy: a rotating shaft. It uses hydraulic pressure and flow to generate torque and rotation.


Hydraulic Hose

Hydraulic hose is specifically designed to convey hydraulic fluid to or among hydraulic components, valves, actuators, and tools. It is typically flexible, often reinforced and usually constructed with several layers of reinforcement since hydraulic systems frequently operate at high or very high pressures.


Hydraulic filter

Hydraulic filters are used to protect your hydraulic system components from damage due to contamination of oils caused by particles


Hydraulic accumulator

A hydraulic accumulator stores fluid under pressure

Accumulators can take a specific amount of fluid under pressure and store it. The fluid is then released when it´s required to perform a specific task in the hydraulic system

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Types of hydraulic systems

Open centre system

Close centre system

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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 system at two bottom links and one top link. Both the bottom links are connected to two lift arms thro ugh lift links. The lift arms are directly mounted on a rockshaft, which is further connected to the piston rod. Any movement of the piston is trans ferred 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.

Position control

In this system, constant depth of ploughing is maintained by automatic adjustment of draft of tractor. In this 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.

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 position control

Mixed position and draft control

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

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 protect the system from dust and other contaminants, the system will undoubtedly work efficiently with less trouble

Engineering

Tractor hydraulics