unit 2.pdf

FARM TRACTOR Tractor is a self-propelled power unit having wheels or tracks for operating agricultural implements and machines including trailers. Tractor engine is used as a prime mover for active tools and stationary farm machinery through power take-...

FARM TRACTOR Tractor is a self-propelled power unit having wheels or tracks for operating agricultural implements and machines including trailers. Tractor engine is used as a prime mover for active tools and stationary farm machinery through power take-off shaft (PTO) or belt pulley. CLASSIFICATION OF TRACTORS Tractors can be classified into three classes on the basis of structural-design: (i) Wheel tractor: Tractors, having three of four pneumatic wheels are called wheel tractors. Four- wheel tractors are most popular everywhere. (ii) Crawler tractor: This is also called track type tractor or chain type tractor. In such tractors, there is endless chain or track in place of pneumatic wheels. (iii) Walking tractor (Power tiller): Power tiller is a walking type tractor. This tractor is usually fitted with two wheels only. The direction of travel and its controls for field operation is performed by the operator, walking behind the tractor. On the basis of purpose, wheeled tractor is classified into three groups: (a) General purpose tractor: It is used for major farm operations; such as ploughing, harrowing, sowing, harvesting and transporting work. Such tractors have (i) low ground clearance (ii) increased engine power (iii) good adhesion and (iv) wide tyres. (b) Row crop tractor: It is used for crop cultivation. Such tractor is provided with replaceable driving wheels of different tread widths. It has high ground clearance to save damage of crops. Wide wheel track can be adjusted to suit inter row distance. (c) Special purpose tractor: It is used for definite jobs like cotton fields, marshy land, hillsides, garden etc. Special designs are there for special purpose tractor. TRACTOR COMPONENTS A tractor is made of following main components: (1) I. C. engine, (2) Clutch (3) Transmission gears (4) Differential unit (5) Final drive (6) Rear wheels (7) Front wheels (8) Steering mechanism (9) Hydraulic control and hitch system (10) Brakes (11) Power take-off unit (12) Tractor pulley and (13) Control panel. Every tractor is fitted with an I. C. engine, the engine may be carburettor type or diesel type but nowadays almost all the tractors are diesel tractors. SELECTION OF TRACTOR Selection of tractor depends upon following factors: (1) Land holding: Under a single cropping pattern, it is normally recommended to consider 1 hp for every 1 hectares of land, in other words, one tractor of 20-25 hp is suitable for 20 hectares farm. (2) Cropping pattern: Generally, less than 1.0 hectare/hp have been recommended where adequate irrigation facilities are available and more than one crop is taken. So, a 30-35 hp tractor is suitable for 25 hectares farm. (3) Soil condition: A tractor with less wheel base, higher ground clearance and low overall weight may work successfully in lighter soil but it will not be able to give sufficient depth in black cottonsoil. (4) Climatic condition: For very hot zone and desert area, air cooled engines are preferred over water- cooled engines. Similarly for higher altitude, air cooled engines are preferred because water is liable to be frozen at higher altitude. (5) Repairing facilities: It should be ensured that the tractor to be purchased has a dealer at nearb y place with all the technical skills for repair and maintenance of machine. (6) Running cost: Tractors with less specific fuel consumption should be preferred over others so that running cost may be less. (7) Initial cost and resale value: While keeping the resale value in mind, the initial cost should not be very high; otherwise, higher amount of interest will have to be paid. (8) Test report: Test report of tractors released from farm machinery testing stations should be consulted for guidance. 1. Front wheel 2. Fuel tank cap 3. Accelerator pedal 4. Brake pedal 5. Steering wheel 6. Hydraulic control lever 7. Turn signal lamp 8. Lift arm 9. Rear tire 10. Instrument panel 11. Clutch pedal 12. Step 13. Seat 14. Rear axle housing 15. Side clearance 16. Engine hood 17. Fan cover 18. Muffler 19. Fuel tank 20. Throttle lever 21. Main speed change lever 22. Fender Fig. 1 Components of tractor CONTROL BOARD OR DASH BOARD OF A TRACTOR The control board of a tractor generally consists of: (1) Main switch (2) Throttle lever (3) Decompression lever (4) Hour meter (5) Light switch (6) Horn button (7) Battery charging indicator (8) Oil pressure indicator and (9) Water temperature gauge. TRACTOR TYRES AND FRONT AXLE TYRES: The tyres are available in many sizes with the ply ratings as 4, 6 or 8. The ply rating of tyres indicates the comparative strength of tyres. The higher the rating, the stronger are the tyres. The tyres size 12—38 means, that the sectional diameter of tyres is 12" and it is mounted on a rim of 38" diameter. The inflation pressure in the rear wheels of the tractor varies between 0.8 to 1.5 kg/cm2. The inflation pressure of the front wheel varies from 1.5 to 2.5kg/ cm2. Useful life of the pneumatic tyres under normal operating condition may be about 6000 working hours for drawbar work. FRONT AXLE: Front axle is the unit on which front wheel is mounted. This wheel is an idler wheel by which tractor is steered in various directions. The axle is a rigid tubular or I-section steel construction pivoted at the centre. There are various adjustments of front wheel. Hitching system of Tractor Drawn Implements Tractor drawn implements possess higher working capacity and are operated at higher speeds. These implements need more technical knowledge for operations and maintenance work. Tractor drawn implements may be a) Trailed type b) Semi-mounted type and c) Mounted type. a) Trailed type implement: It is one that is pulled and guided from single hitch point but its weight is not supported by the tractor. b) Semi-mounted type implement: This type of implement is one which is attached to the tractor along a hinge axis and not at a single hitch point. It is controlled directly by tractor steering unit but its weight is partly supported by the tractor. c) Mounted type implement: A mounted implement is one which is attached to the tractor, such that it can be controlled directly by the tractor steering unit. The implement is carried fully by the tractor when out of work. SOME IMPORTANT TERMS CONNECTED WITH TRACTORS Wheelbase: Wheel base is the horizontal distance between the front and rear wheels of a tractor, measured at the ground contact. Ground clearance: It is the height of the lowest point of die tractor from the ground surface, the tractor being loaded to its maximum permissible weight. Track: Track is the distance between the two wheels of the tractor on the same axle, measured at the point of ground contact. Turning space: It is the diameter of the smallest circle, described by the outermost point of the tractor, while moving at a speed, not exceeding 2 km/hr with the steering wheels in full lock. Cage wheel: It is a wheel or an attachment to a wheel with spaced cross bars for improving the traction of the tractor in a wet field. It is generally used in paddy fields. POWER TILLER It is a prime mover in which the direction of travel and its control for field operation is performed by the operator walking behind it. It is also known as hand tractor or walking type tractor. The conceptof power tiller came in the world in the year 1920. Japan is the first country to use power tiller on large scale. In Japan, the first successful model of power tiller was designed in the year 1947. Production of power tiller rapidly increased during the year 1950 to 1965. Power tiller was first introduced in India in the year 1963. Power tiller is a walking type tractor. The operator walks behind the power tiller, holding the two handles of power tiller in his own hands. Power tiller may be called a single axle walking type tractor, though a riding seat is provided in certain designs. Average size of holding in India is about 2.5 Power tiller hectares. There are 89% of total land holdings of less than six hectares. Under such conditions, power tiller may be useful as a power unit. Components of power tiller: A power tiller consists of the following main parts: (1) Engine (2) Transmission gears (3) Clutch (4) Brakes (5) Rotary unit. All the power tillers are fitted with an I. C. engine. At present, most of the power tillers are fitted with diesel engine. The makes like Kubota, Mitsubishi, and Sarachi have used diesel engine in India. Operation: The main clutch is a lever on the handle. The lever can be shifted to on or off position while operating in the field. When the lever is shifted to on position, the power from the engine is transmitted through the main clutch to the various parts of the power tiller. When the lever is shifted to off position the power from the engine is cut-off from the rest of the transmission. Power transmission in power tiller: For operation of power tiller, the power is obtained from the IC Engine, fitted on the power tiller. The engine power goes to the main clutch with the help of belt or chain. From main clutch, the power is divided in two routes, one goes to transmission gears, steering clutch and then to the wheel. The other component goes to the tilling clutch and then to the tilling attachment. The flow diagram for transmission of power is given below: Transmission gear Steering clutch Wheels Engine Main clutch Tilling clutch Tilling attachment V- belt is usually used to transmit power from the engine to the main clutch, because V-belt has very high efficiency and it works as a shock absorber also. Main clutch: Power goes from the engine to the main clutch. Clutch may be: (i) Friction clutch or (ii) V-belt tension clutch. Friction clutch is generally used for bigger power tiller. Usually, it is a dry type multiple disc clutch.V-belt tension clutch is used for small power tillers. The main functions of clutch in a power tiller are: (i) to transmit engine power to transmission gears and (ii) to make power transmission gradual and smooth. Transmission gears: Transmission box consists of gears, shafts and bearings. The speed change device may be; (a) gear type or (b) belt type. Brakes: All power tillers have some braking arrangement for stopping the movement. Most of the power tillers use inner side expansion type brake. Wheels: Usually 2 to 4 ply pneumatic tyres are used in power tillers. The pressure of the tyre ranges from 1.1 to 1.4 kg/cm2. Steering cutch lever: Steering clutch is provided on the grip of the right and left handles. When (he left side is gripped, power is cut-off on left side of the wheel and the power tiller turns to the left. Similarly, when the right side is gripped, the power tiller turns to the right.  FUEL & FUEL SYSTEM PROPERTIES OF FUEL Fuel is a substance consumed by the engine to produce energy. The common fuels for internal combustion engines are: 1. Petrol 2. Power kerosene 3. High speed diesel oil 4. Light diesel oil. The important properties of these fuels are given below: S.No Name of fuel oil A. P. I. Specific Calorific value degree Gravity kcal/kg B.T.U./lb (i) Light diesel oil (L.D.O.) 22 0.920 10300 18600 (ii) High speed diesel oil (HSD) 31 0.820 10550 19000 (iii) Power kerosene 40 0.827 10850 19500 (iv) Petrol 63 0.730 11100 20000 QUALITY OF FUEL The quality of the fuel mainly depends upon the following properties: 1. Volatility of the fuel 2. Calorific value of the fuel 3. Ignition quality of the fuel Volatility: Volatility of fuel has considerable effect on the performance of the engine by affecting the following: (i) Ease of starting the engine. (ii) Formation of vapour lock in the fuel system, (iii) Accelerating characteristics of the engine, (iv) Distribution of fuel in multi-cylinder engine. In I. C. engine, all the liquid fuel must be converted into vapour fuel before burning. High speed diesel oil is most difficult to vapourise. Vaporizing temperature of high-speed diesel oil is higher than that of the petrol, hence the petrol vaporizes quicker than diesel oil in the engine cylinder. This helps in easy starting of petrol engines. Calorific value: The heat liberated by combustion of a fuel is known as calorific value or heat value of the fuel. It is expressed in kcal /kg of the fuel. The heat value of a fuel is an important measure of its worth, since  this is the heat which enables the engine to do the work. Ignition quality: Ignition quality refers to ease of burning the oil in the combustion chamber. Octane number and cetane number are the measures of ignition quality of the fuel. Detonation (Knocking): Detonation or engine knocking refers to violent noises, heard in an engine, giving a pinging sound during the process of combustion. It occurs during the process of combustion of the mixture within the cylinder after the ignition has taken place. It is an undesirable combustion and results in sudden rise in pressure, a loss of power and overheating of the engine. It is caused by improper combustion chamber, high compression pressure, early ignition timing, improper fuel and inadequate cooling arrangement. Pre-ignition: Burning of air-fuel mixture in the combustion chamber before the piston has reached the top dead centre is called pre-ignition. Pre-ignition occurs when the charge is fired too far ahead of the top dead centre of the piston due to excessive spark advance or excessive heat in the cylinder. FUEL SUPPLY SYSTEM IN SPARK IGNITION ENGINE The fuel supply system of spark ignition engine consists of: (i) Fuel tank (ii) Fuel filter (iii) Sediment bowl (iv) Fuel lift pump (v) Carburettor (vi) Fuel pipes (vii) Inlet manifold In some spark ignition engine, the fuel tank is placed above the level of the carburettor. The fuel flows from the fuel tank to the carburettor under the action of gravity. There are one or two filters between the fuel tank and the carburettor. A transparent sediment bowl is also provided to hold the dust and dirt of the fuel. If the tank is below the level of the carburettor, a lift pump is provided in between the tank and the carburettor for forcing fuel from the tank to the carburettor of the engine. The fuel comes from the fuel tank to the sediment bowl and then to the lift pump. From there the fuel goes to the carburettor through suitable pipe. From the carburettor, the fuel goes to the engine cylinder, through the inlet manifold of the engine.  Fuel system of spark ignition engine. CARBURETTOR: The process of preparing an air-fuel mixture away from the cylinders of an engine is called carburetion and the device in which this process take place is called carburettor. Principle of carburettor: The basic principle of all carburettor design that when air flows over the end of a narrow tube or jet containing liquid, some liquid is drawn into the air stream. The quantity of liquid drawn into the air stream increases as the speed of air flow over the jet increases and also the quantity is greater if the jet is made larger. Carburettor with pump feed to fuel reservoir Diaphragm type fuel pump Function of Carburettor: The main functions of the carburettor are: (i) To mix the air and fuel thoroughly (ii) To atomise the fuel (iii) To regulate the air-fuel ratio at different speeds and loads and (iv) To supply correct amount of mixture at different speeds and loads. FUEL SYSTEM OF DIESEL ENGINE During engine operation, the fuel is supplied by gravity from fuel tank to the primary filter where coarse impurities are removed. From the primary filter, the fuel is drawn by fuel transfer pump and is delivered to fuel injection pump through second fuel filter. The fuel injection pump supplies fuel under high pressure to the injectors through high pressure pipes. The injectors atomise the fuel and inject it into the combustion chamber of the engine. The fuel injection pump is fed with fuel in abundance. The excess fuel is by-passed to the intake side of the fuel transfer pump through a relief valve. The main components of the fuel system in diesel engine are: (1) fuel filter (2) fuel lift pump (3) fuel injection pump (4) atomizers and (5) high pressure pipe. Cylinder  Injector  Fuel → injection → → Diesel Fuel Filter Tank → Fuel lift pump Filter pump  Two conditions are essential for efficient operation of fuel system: (i) The fuel oil should be clean, free from water, suspended dirt, sand or other foreign matter, (ii) The fuel injection pump should create proper pressure, so that diesel fuel may be perfectly atomized by injectors and be injected in proper time and in proper quantity in the engine cylinder. Fuel should be filtered before filling the tank also. If these precautions are followed, ninety per cent of diesel engine troubles are eliminated. Layout of fuel supply in diesel engine FUEL LIFT PUMP (FEED PUMP OR TRANSFER PUMP) It is a pump, which transfers fuel from the fuel line to the fuel injection pump. It is mounted on the body of fuel injection pump. It delivers adequate amount of fuel to the injection pump. The pump consists of: (I) body (2) piston (3) inlet valve and (4) pressure valve. The valves are tightly pressed against their seats by springs. The piston is free to slide in the bore. The fuel contained in the space below the piston is forced to flow through secondary fuel filter to the injection pump. At the same time downward movement of the piston creates a depression in the space above the piston which, causes the fuel to be drawn in the transfer pump from the fuel tank through the inlet valve and the primary filter. FUEL INJECTING PUMP It is a pump, which delivers metered quantity of fuel to each cylinder at appropriate time under high pressure. Tractor engines may use two types of fuel injection pump: (i) Multi-element pump and (ii) Distributor (Rotary) type pump. Fuel Injector: It is the component, which delivers finely atomized fuel under high pressure to the combustion chamber of the engine. Modern tractor engines use fuel injectors, which have multiple holes. Main parts of injector are: nozzle body and needle valve. The nozzle body and needle valve are fabricated from alloy steel. The needle valve is pressed against a conical seat in the nozzle body by a spring. The injection pressure is adjusted by adjusting the screw. FUEL INJECTION SYSTEM Diesel fuel is injected in diesel engine through injectors with the help of fuel injection pump. The system using injectors, fuel injection pump, fuel filter, and fuel lines is called fuel injection system. The main functions of fuel injection system are: (i) To measure the correct amount of fuel required by engine speed and load, (ii) To maintain correct timing for beginning and end of injection, (iii) To inject the fuel into the combustion space against high compression pressure. (iv) To atomise the fuel for quick ignition. Process of fuel injection in diesel engine is of two types: (i) Air injection (ii) Solid injection. Air injection: In this process, the engine uses compressed air to force the fuel into the cylinder. It is a bulky system and hence it is not considered very suitable for vehicles and tractors. It is mostly used on heavy-duty stationary engines. Solid injection: A high-pressure pump is used for forcing the fuel into the combustion chamber. COMBUSTION CHAMBER A combustion chamber is a space inside the engine, where the combustion of fuel takes place. In diesel engine, the fuel is atomized, vaporized and burnt inside combustion chamber, whereas in spark ignition engine, atomization of fuel takes place in the carburettor and vaporization occurs in carburettor as well as the inlet manifold. Combustion chamber is classified as: (a) Direct injection chamber (b) Indirect injection chamber TURBOCHARGER It is a turbo-compressor driven by the exhaust gases of the engine to supply air under pressure to the cylinders of the engine. Turbocharger is useful because the power output of a diesel engine can be increased by supplying compressed air to the engine cylinders. If more air is delivered to the cylinders the fuel charge can also be increased and will release more energy. The turbocharger consists of a centrifugal compressor with impellers and a gas turbine unit. The compressor impeller and the turbine wheel are rigidly fixed on a common shaft. Compressor impeller draws air from the atmosphere and delivers it to the intake manifold and from there it goes to the engine cylinders thus improving the volumetric efficiency of the engine. FUEL FILTER It is a device to remove dirt from fuel oil. Solid particles and dust in diesel fuel are very harmful for giving a fine degree of filtration. Fuel injection equipment in diesel engines is extremely sensitive to dirt and solid particles present in fuel. A filter is used to remove the dirt and solid particles from the fuel to ensure trouble- free fuel supply. It consists of a hollow cylindrical element contained in a shell, an annular space being left between the shell and the element. The filtering element consists of metal gauge in conjunction with various media such as packed fibres, woven cloth, felt, paper etc. These filters are replaced at certain intervals, specified by the manufacturer. Usually there are two filters in diesel engine: (1) Primary filter and (2) Secondary filter. The primary filter removes water and coarse particle of dirt from the fuel. The secondary filter removes fine sediments from the fuel. Fuel filter for diesel engine GOVERNOR Governor is a mechanical device designed to control the speed of an engine within specified limit used on tractor or stationary engines for: (v) Maintaining a nearly constant speed of engine under different load conditions (vi) Protecting the engine and the attached equipments against high speeds, when the load is reduced or removed. Tractor engines are always fitted with governor. There is an important difference in principle between the controls of a tractor engine and that of a motor car. In case of motor car, the fuel supply is under direct control of the accelerator pedal, but in tractor engine, the fuel supply is controlled by the governor. The operator changes the engine speed by moving the governor control lever. A governor is essential on a tractor engine for the reason that load on the tractor engine is subjected to rapid variation in the field and the operator cannot control the rapid change of the engine speed without any automatic device. For example, if the load on the tractor is reduced, the engine would tend to race suddenly. If the load is increased, the engine would tend to slow down abruptly. Under these circumstances, it becomes difficult for the operator to regulate always the throttle lever to meet the temporary changes in the engine load. A governor automatically regulates the engine speed on varying load condition and thus the operator is relieved of the duty of constant regulating the throttle lever to suit different load conditions.  COOLING SYSTEM A system, which controls the engine temperature, is known as a cooling system. NECESSITY OF COOLING SYSTEM The cooling system is provided in the IC engine for the following reasons: The temperature of the burning gases in the engine cylinder reaches up to 1500 to 2000°C, which is above the melting point of the material of the cylinder body and head of the engine. (Platinum, a metal which has one of the highest melting points, melts at 1750 °C, iron at 1530°C andaluminium at 657°C.) Therefore, if the heat is not dissipated, it would result in the failure of the cylinder material. Due to very high temperatures, the film of the lubricating oil will get oxidized, thus producing carbon deposits on the surface. This will result in piston seizure. Due to overheating, large temperature differences may lead to a distortion of the engine components due to the thermal stresses set up. This makes it necessary for, the temperature variation to be kept to a minimum. Higher temperatures also lower the volumetric efficiency of the engine. REQUIREMENTS OF EFFICIENT COOLING SYSTEM The two main requirements of an efficient cooling system are: 1. It must be capable of removing only about 30% of the heat generated in the combustion chamber. Too much removal of heat lowers the thermal efficiency of the engine. 2. It should remove heat at a fast rate when the engine is hot. During the starting of the engine, the cooling should be very slow so that the different working parts reach their operating temperatures in a short time. TYPES OF COOLING SYSTEM There are two types of cooling systems: (i) Air cooling system and (ii) Water-cooling system. AIR COOLING SYSTEM In this type of cooling system, the heat, which is conducted to the outer parts of the engine, is radiated and conducted away by the stream of air, which is obtained from the atmosphere. In order to have efficient cooling by means of air, providing fins around the cylinder and cylinder head increases the contact area. The fins are metallic ridges, which are formed during the casting of the cylinder and cylinder head The amount of heat carried off by the air-cooling depends upon the following factors: (i) The total area of the fin surfaces, (ii) The velocity and amount of the cooling air and  (iii) The temperature of the fins and of the cooling air. Air-cooling is mostly tractors of less horsepower, motorcycles, scooters, small cars and small aircraft engines where the forward motion of the machine gives good velocity to cool the engine. Air-cooling is also provided in some small industrial engines. In this system, individual cylinders are generally employed to provide ample cooling area by providing fins. A blower is used to provide air. Advantages of Air-Cooled Engines Air cooled engines have the following advantages: 1. Its design of air-cooled engine is simple. 2. It is lighter in weight than water-cooled engines due to the absence of water jackets, radiator, circulating pump and the weight of the cooling water. 3. It is cheaper to manufacture. 4. It needs less care and maintenance. 5. This system of cooling is particularly advantageous where there are extreme climatic conditions in the arctic or where there is scarcity of water as in deserts. 6. No risk of damage from frost, such as cracking of cylinder jackets or radiator water tubes. WATER COOLING SYSTEM It serves two purposes in the working of an engine: a) It takes away the excessive heat generated in the engine and saves it from over heating. b) It keeps the engine at working temperature for efficient and economical working.  The water cooling system is used in the engines of cars, buses, trucks, etc. In this system, the water is circulated through water jackets around each of the combustion chambers, cylinder, valve seats, and valve stems. The water is kept continuously in motion by a centrifugal water pump which is driven by a V-belt from the pulley on the engine crankshaft. After passing through the engine jackets in the block and cylinder heads. The water is passing through the radiator. In the radiator, the water is cooled by air drawn through the radiator by a fan. Usually, the fan and water pump are mounted and driven on a common shaft. After passing through the radiator, the water is drained and delivered to the water pump through a cylinder inlet passage. The water again circulated through the engine jackets. This cooling system has four types of systems: (i) Direct or non-return system, (ii) Thermo-Syphone system, (iii) Hopper system and (iv) Pump/forced circulation system. Though the present tractor has a forced circulation system, it is still worthwhile to get acquainted with the other three systems. Force Circulation Water Cooling System This system is similar in construction to the thermo-syphone system except that it makes use of a centrifugal pump to circulate the water throughout the water jackets and radiator. The water flows from the lower portion of the radiator to the water jacket of the engine through the centrifugal pump. After the circulation water comes back to the radiator, it loses its heat by the process of radiation. This system is employed in cars, trucks, tractors, etc. Parts of Liquid Cooling System The main parts in the water-cooling system are: (i) water pump, (ii) fan, (iii) radiator and pressure cap, (iv) fan belt (v) water jacket, (vi) thermostat valve, (vii) temperature gauge and (viii) hose pipes. Water Pump This is a centrifugal type pump. It is centrally mounted at the front of the cylinder block and is usually driven by means of a belt. This type of pump consists of the following parts: (i) body or casing, (ii) impeller (rotor), (iii) shaft, (iv) bearings, or bush, (v) water pump seal and (vi) pulley. The bottom of the radiator is connected to the suction side of the pump. The power is transmitted to the pump spindle from a pulley mounted at the end of the crankshaft. Seals of various designs are incorporated in the pump to prevent loss of coolant from the system. Fan The fan is generally mounted on the water pump pulley, although on some engines it is attached directly to the crankshaft. It serves two purposes in the cooling system of an engine. (a) It draws atmospheric air through the radiator and thus increases the efficiency of the radiator in cooling hot water. (b) It throws fresh air over the outer surface of the engine, which takes away the heat conducted by the engine parts and thus increases the efficiency of the entire cooling system. Radiator The purpose of the radiator is to cool down the water received from the engine. The radiator consists of three main parts: (i) upper tank, (ii) lower tank and (iii) tubes. Hot water from the upper tank, which comes from the engine, flows downwards through the tubes. The heat contained in the hot water is conducted to the copper fins provided around the tubes. An overflow pipe, connected to the upper1 tank, permits excess water or steam to escape. There are three types of radiators: (i) gilled tube radiator, (ii) tubular radiator (Fig. b) and (iii) honey comb or cellular radiator (Fig. c) Type of radiators Gilled tube radiator: This is perhaps the oldest type of radiator, although it is still in use. In this, water flows inside the tubes. Each tube has a large number of annular rings or fins pressed firmly over its outside surface.  Tubular radiator: The only difference between a gilled tubes radiator and a tubular one is that in this case there are no separate fins for individual tubes. The radiator vertical tubes pass through thin fine copper sheets which run horizontally. Honey comb or cellular radiator: The cellular radiator consists of a large number of individual air cells which are surrounded by water. In this, the clogging of any passage affects only a small parts of the cooling surface. However, in the tubular radiator, if one tube becomes clogged, the cooling effect of the entire tube is lost. Thermostat Valve It is a kind of check valve which opens and closes with the effect of temperature. It is fitted in the water outlet of the engine. During the warm-up period, the thermostat is closed and the water pump circulates the water only throughout the cylinder block and cylinder head. When the normal operating temperature is reached, the thermostat valve opens and allows hot water to flow towards the radiator (Fig. 8.5a). Standard thermostats are designed to start opening at 70 to 75°C and they fully open at 82°C. High temperature thermostats, with permanent anti-freeze solutions (Prestine, Zerex, etc.), start opening at 80 to 90°C and fully open at 92°C. Types of thermostat There are three types of thermostats: (i) bellow type, (ii) bimetallic type and (iii) pellet type. Bellow type valve: Flexible bellows are filled with alcohol or ether. When the bellows is heated, the liquid vaporizes, creating enough pressure to expand the bellows. When the unit is cooled, the gas condenses. The pressure reduces and the bellows collapse to close the valve. Bimetallic type valve: This consists of a bimetallic strip. The unequal expansion of two metallic strips causes the valve to open and allows the water to flow in the radiator. Pellet type valve: A copper impregnated wax pellet expands when heated and contracts when cooled. The pellet is connected to the valve through a piston, such that on expansion of the pellet, it opens the valve. A coil spring closes the valve when the pellet contracts. PRESSURE COOLING SYSTEM In the case of the ordinary water-cooling system where the cooling water is subjected to atmospheric pressure, the water boils at 212°F. But when water is boiled in a closed radiator under high pressure, the boiling temperature of water increases. The higher water temperature gives more efficient engine performance and affords additional protection under high altitude and tropical conditions for long hard driving periods. Therefore, a pressure-type radiator cap is used with the forced circulation cooling system.  The cap is fitted on the radiator neck with an air tight seal. The pressure-release valve is set to open at a pressure between 4 and 13 psi. With this increase in pressure, the boiling temperature of water increases to 243°F (at 4 psi boiling tap 225°F and 13 psi boiling temperature 243°F). Any increase in pressure is released by the pressure release valve to the atmosphere. On cooling, the vapours will condense and a partial vacuum will be created which will result in the collapse of the hoses and tubes. To overcome this problem the pressure release valve is associated with a vacuum valve which opens the radiator to the atmosphere. ANTI-FREEZE SOLUTIONS In order to prevent the water in the cooling system from freezing, some chemical solutions which are known as anti-freeze solutions are mixed with water. In cold areas, if the engine is kept without this solution for some time, the water may freeze and expand leading to fractures in the cylinder block, cylinder head, pipes and/or radiators. The boiling point of the anti-freeze solution should be as high as that of water. An ideal mixture should easily dissolve in water, be reasonably cheap and should not deposit any foreign matter in the jacket pipes and radiator. No single anti-freeze solution satisfies all these requirements. The materials commonly used are wood alcohol, denatured alcohol, glycerine, ethylene, glycol, propylene glycol, mixtures of alcohol and glycerine and various mixtures of other chemicals. SERVICING & CLEANING OF COOLING SYSTEM For smooth and trouble-free service, the cooling system should be cleaned at periodic intervals to prevent the accumulation of excessive rust and scale. The commercial cleaning compounds available must be carefully used in accordance with the manufacturers' instructions. A general cleaning procedure is outlined below. If a considerable amount of scale and rust has accumulated, it may not be possible that cleaning alone will remove it. In that case, the radiator and engine water jackets must be flushed out with special air pressure guns. Cooling System Cleaning Procedure It involves the following steps. 1. Drain the system by opening the drain cocks. Prepare a solution of washing soda and water, with a ratio of 1 kg soda to 10 litres of water. Fill up this solution in the radiator and engine block and run the engine on idle load for 8 to 10 hours. Drain this solution and flush the system with clean water. 2. In case the scale formulation is bard and cannot be completely removed with washing soda, another cleaning agent can be prepared with 40 parts of water, 5 parts of commercial hydrochloric acid and 1 part of formaldehyde. This solution is allowed to remain in the system for 2 to 3 hours at normal load. Afterwards this could be drained and the system flushed with clean water. 3. Pressure flushing: In this the air pressure is used to both agitate and circulate the water through the cooling  system. (a) Straight flushing: Connect the lead-away hose to the water outlet connection on the engine. Insert the flushing gun in the hose attached to the water pump inlet connection. Turn on the water until the water passages are filled and the release the air in short blasts, allowing the water to fill the engine after such blasts. (b) Reverse flushing: Before making connections for reverse flushing the thermostat should be removed from the cooling system. The procedure for this is outlined below: (i) Radiator: Disconnect the top hose of the radiator from the engine and attach a lead-away hose to the radiator. Disconnect the bottom of the radiator from water pump and attach the flushing gun. Connect water and air hoses to the gun. Turn on the water and fill the radiator to the top. Release the air in short blasts and allows the water to fill the radiator between each blast. Continue the operation until the water from the lead-away hose is clear, (ii) Engine: Connect the lead-away hose to the inlet of the water pump and the flushing gun to the water outlet of the pump on the cylinder head. Follow the same procedure. LUBRICATION SYSTEM I. C. engine is made of many moving parts. Due to continuous movement of two metallic surfaces over each other, there is wearing moving parts, generation of heat and loss of power in the engine lubrication of moving parts is essential to prevent all these harmful effects. PURPOSE OF LUBRICATION Lubrication produces the following effects: (a) Reducing friction effect (b) Cooling effect (c) Sealing effect and (d) Cleaning effect. (a) Reducing frictional effect: The primary purpose of the lubrication is to reduce friction and wear between two rubbing surfaces. Two rubbing surfaces always produce friction. The continuous friction produce heat which causes wearing of parts and loss of power. In order to avoid friction, the contact of two sliding surfaces must be reduced as far as possible. This can be done by proper lubrication only. Lubrication forms an oil film between two moving surfaces. Lubrication also reduces noise produced by the movement of two metal surfaces over each other. (b) Cooling effect: The heat, generated by piston, cylinder, and bearings is removed by lubrication to a great extent. Lubrication creates cooling effect on the engine parts. (c) Sealing effect: The lubricant enters into the gap between the cylinder liner, piston and piston rings. Thus, it prevents leakage of gases from the engine cylinder. (d) Cleaning effect: Lubrication keeps the engine clean by removing dirt or carbon from inside of the engine along with the oil. Lubrication theory: There are two theories in existence regarding the application of lubricants on a surface: (i) Fluid film theory and (ii) Boundary layer theory. (i) Fluid film theory: According to this theory, the lubricant is, supposed to act like mass of globules, rolling in between two surfaces. It produces a rolling effect, which reduces friction. (ii) Boundary layer theory: According to this theory, the lubricant is soaked in rubbing surfaces and forms oily surface over it. Thus, the sliding surfaces are kept apart from each other, thereby reducing friction. TYPES OF LUBRICANTS Lubricants are obtained from animal fat, vegetables and minerals Lubricants made of animal fat, does not stand much heat. It becomes waxy and gummy which is not very suitable for machines. Vegetable lubricants are obtained from seeds, fruits and plants. Cottonseed oil, olive oil, linseed oil and castor oil are used as lubricant in small Simple machines. Mineral lubricants are most popular for engines and machines. It is obtained from crude petroleum found in nature. Petroleum lubricants are less expensive and suitable for internal combustion engines. A good lubricant should have the following qualities: 1. It should have sufficient viscosity to keep the rubbing surfaces apart 2. It should remain stable under changing temperatures. 3. It should keep lubricated pans clean. 4. It should not corrode metallic surfaces. ENGINE LUBRICATING SYSTEM The lubricating system of an engine is an arrangement of mechanism and devices which maintains supply of lubricating oil to the rubbing surface of an engine at correct pressure and temperature. The parts which require lubrication are: (i) cylinder walls and piston (ii) piston pin (iii) crankshaft and connecting rod bearings (iv) camshaft bearings (v) valves and valve operating mechanism (vi) cooling fan (vii) water pump and (viii) ignition mechanism. There are three common systems of lubrication used on stationary engines, tractor engines and automobiles: (i) Splash system (ii) Forced feed system and (iii) Combination of splash and forced feed system. SPLASH SYSTEM In this system, there is an oil trough, provided below the connecting rod. Oil is maintained at a uniform level in the oil trough. This is obtained by maintaining a continuous flow of oil from the oil sump or reservoir into a splash pan, which has a depression or a trough like arrangement under each connecting rod. This pan receives its oil supply from the oil sump either by means of a gear pump or by gravity. A dipper is provided at the lower end of the connecting rod. This dipper dips into to oil trough and splashes oil out of the pan. The splashing action of oil maintains a fog or mist of oil that drenches the inner parts of the engine such as bearings, cylinder walls, pistons, piston pins, timing gears etc. Splash lubrication system This system is usually used on single cylinder engine with closes crankcase. For effective functioning of the engine, proper level of oil maintained in the oil pan. Lubrication depends largely upon the size of oil holes and clearances. This system is very effective if the oil is clean and undiluted. Its disadvantages are that lubrication is not very uniform and when the rings are worn, the oil passes the piston into combustion chamber, causing carbon deposition, blue smoke and spoiling the plugs. There is every possibility that oil may become very thin through crankcase dilution. The worn metal, dust and carbon may be collected in the oil chamber and be carried to different parts of the engine, causing wear and tear. FORCED FEED SYSTEM In this system, the oil is pumped directly to the crankshaft, connecting rod, piston pin, timing gears and camshaft of the engine through suitable paths of oil. Usually, the oil first enters the main gallery, which maybe a pipe or a channel in the crankcase casting. From this pipe, it goes to each of the main bearings through holes. From main bearings, it goes to big end bearings of connecting rod through drilled holes in the crankshaft. From there, it goes to lubricate the walls, pistons and rings. There is separate oil gallery to lubricate timing gears. Lubricating oil pump is a positive displacement pump, usually gear type or vane' type. The oil also goes to valve stem and rocker arm shaft under pressure through an oil gallery. The excess oil comes back from the cylinder head to the crankcase. The pump discharges oil into oil pipes, oil galleries or ducts, leading different parts of the engine. This system is commonly used on high- s pee d multi-cylinder engine in tractors, trucks and automobiles. Forced feed lubrication system COMBINATION OF SPLASH AND FORCED FEED SYSTEM In this system, the engine component, which are subjected to very heavy load are lubricated under forced pressure, such as main bearing connecting rod bearing and camshaft bearing. The rest of the parts like cylinder liners, cams, tappets etc. are lubricated by splashed oil. Oil pump: Oil pump is usually a gear type pump, used to force oil into the oil pipe. The pump is driven by the camshaft of t engine. The lower end of the pump extends down into the crankcase which is covered with a screen to check foreign particles. A portion of the oil forced to the oil filter and the remaining oil goes to lubricate various part of the engine. An oil pressure gauge fitted in the line, indicates the oil pressure in the lubricating system. About 3 kg/sq cm (45 psi) pressure is developed in the lubrication system of a tractor engine, [f the oil pressure gauge indicates no pressure in the line, there is some defect in the system which must be checked immediately. Lubricating oil pump is a positive displacement pump. OIL FILTER: Lubricating oil in an engine becomes contaminated with various materials such as dirt, metal particles and carbon. Oil filler removes the dirty elements of the oil in an effective way. It is a type of strainer using cloth, paper, felt, wire screen or similar elements. Some oil filter can be cleaned by washing, but in general old filters are replaced by new filters at specified interval of time prescribed by manufacturers. Wearing of parts, oil consumption and operating cost of an engine can be considerably reduced by proper maintenance of oil filters. Oil pressure gauge: Oil pressure gauge is used to indicate the oil pressure in the oil lines. It serves to warn the operator of any irregularity in the system. Crankcase breather: The engine crankcase is always fitted with some kind of breather, connecting the space above the oil level with the outside atmosphere. The purpose of the breather is to prevent building up pressure in the crankcase. Relief valve: Relief valve is provided to control the quantity of oil circulation and to maintain correct pressure in the lubricating system. TROUBLES IN LUBRICATION SYSTEM There are a few common troubles in lubrication system such as: (1) Excessive oil consumption (2) Low oil pressure and (3) Excessive oil pressure- Excessive oil consumption: When there is excessive oil consumption in the engine, the reasons arc : (a) more oil goes to combustion chamber and gets burnt (b) some leakage occurs in some part of - the line and (c) loss of oil in form of vapour through ventilating system. Oil can enter the combustion chamber throughrings and cylinder walls, worn piston rings and worn bearings. Low oil pressure: Low oil pressure can result due to: (i) weak relief valve spring (ii) worn oil pump (iii) cracked oil line (iv) obstruction in the oil lines (v) very thin oil and (vi) worn out bearings. Care should be taken to remove these defects as far as possible to increase the oil pressure in the lubricating system. Sometimes defective oil pressure indicator shows low oil pressure. This should be checked. Excessive oil pressure: Excessive oil pressure may result due to : (i) stuck relief valve (ii) strong valve spring (iii) clogged oil line and (iv) very heavy oil. These defects should be removed to reduce the excessive oil pressure in the lubricating system. Sometimes defective oil pressure indicator records high oil pressure. Care should be taken to check this defect. CARE AND MAINTENANCE OF LUBRICATION SYSTEM The following are few suggestions for good lubrication system: A good design of oil circulation system should be chosen. Correct grade of lubricant ensures long and trouble-free service. Oil should be maintained at desired level in the oil chamber. Oil should be cleaned regularly and after specified period of use, old filters should be replaced by new filters. Connections, pipings, valves and pressure gauge should be checked regularly. Oil should be changed regularly after specified interval of time. Before putting the new oil, the crankcase should be cleaned and flushed well with a flushing oil. Precautions should be taken to keep the oil free from dust and water.  Hydraulic System of Tractor: It is a mechanism in a tractor to raise, hold or lower of mounted or semi-mounted equipments by hydraulic means. All tractors are equipped with hydraulic control system for operating three-point hitch of the tractor. BASIC COMPONENTS OF HYDRAULIC SYSTEM The basic components are: (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. Operation: The hydraulic pump draws up oil from the oil reservoir and sends it to the control valve under high pressure. From the control valve, the oil goes to the hydraulic cylinder to operate the piston, which in turn, raises the lifting arms. The lifting arms are attached with implements. The hydraulic pump is operated by suitable gears, connected with engine. There are two types of arrangements for storing hydraulic oil in the system: (i) There is a common oil reservoir for hydraulic system and the transmission system in some tractors, (ii) There is a special tank for hydraulic oil. It is separate from the transmission chamber. Hydraulic pump: 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 Hydraulic cylinder: 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. Hydraulic tank: 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 there for hydraulic oil. Control valve: Control valve is a type of valve, which controls the movement of hydraulic oil to have desired direction, magnitude and speed of lifting. Thus, the control valve is to perform three functions: (1) to change the direction of lifting (2) to change the power of lifting and (3) to change the speed of lifting. Oil filter: It is small filter, located at a convenient position in the passage of the oil. HITCH AND CONTROL BOARD OF TRACTOR HITCH For the efficient and safe tractor operation, implements are to be hitched properly. Implements can be of Trailed, Semi-mounted and Mounted type. Implements can be hitched in two ways: (a) Drawbar hitch and (b) Three-point linkage. Drawbar hitch: Drawbar is a device by which the pulling power of the tractor is transmitted to the trailing implements. It consists of a crossbar with suitable holes, attached to the lower hitch links. It is fitted at the rear part of the tractor. Three-point linkage: It is a combination of three links, one is upper link and two are lower links (lift arm, operated by hydraulic system), the links articulated to the tractor and the implements at their ends in order to connect the implement to the tractor. Advantage of three-point linkage: (1) Easy control of working implements (2) Quick setting of implements (3) Automatic hydraulic control of implements such as position control, draft control etc. (4) Good balancing of attached implements. 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 through 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 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. Weight transfer: Rear part of the tractor is heavier than the front part to get higher tractive efficiency. However, sufficient weight on the front axle is also required to facilitate easy steering and to compensate the effect due to weight transfer. When the load is pulled, the tendency of front axle is to become light by losing some weight and the same adds to the rear axle. The higher the pull, the greater is the weight transfer. Mathematically this can be represented by: where the line of pull is always assumed to be parallel to the ground.