Unit 5 Temperature Regulators of Cooling System

A device used for supporting the necessary temperature in the cooling system of automobiles and tractors is called the temperature regulator. When the temperature of the water in the cooling system is less than 70°C the cooling system operates with the temperature regulator closed. The water is circulated by water pump only through the cylinder head, block and regulator housing. A by-pass in the regulator housing returns the water to the water.

The temperature of the water being above 70°C, the cooling system operates with the temperature regulators open. The water is allowed to flow into the radiator permitting maximum cooling capacity of the system to be used. Therefore the temperature regulators may be called the "watchdogs" of the cooling system.

However, very often, regulators are unjustly accused of causing an engine to overheat. Usually the first thought is to remove them at first sign of overheating. Don't jump to this conclusion. Overheating can result from a number of defects and incorrect operating procedures.

First, you should remove radiator cap and insert a reliable thermometer into the water to be sure that the temperature, gauge is correct. If the thermometer indicates that the engine is overheating, a systematic check should be made to determine the cause.

Begin with an inspection of radiator core by looking for signs of scale or dirt. Using soft water and a rust inhibitor recommended by the machine's manufacturer will greatly reduce scale and rust deposits in the system.

Free flow of air through radiator fins and around, engine is equally essential to adequate cooling. Inspect radiator core fins to see if they are damaged or bent or simply plugged with mud. A loose .fan belt or bent fan blades is also a common cause of overheating. Operating a diesel engine at continuous overload is another.

If, after checking these items, cause of overheating is not found, you must remove the temperature regulators. If the engine still overheats with the regulators removed, they are not the cause of the trouble and should be reinstalled. If the engine runs at normal operating temperatures with the regulators removed, they are at fault and new regulators should be installed. It is not recommended that the engine should be operated any longer than necessary with the regulators removed.

In most cases, overheating can be prevented by observing all the measuring instruments and by regular checking all the systems of the engine.

UNIT 6

NON-METALLIC MATERIALS

In machihes and machinery.

How quickly polymers have come into our life! Some people even have thought that with the discovery of polymers natural materials will lose their importance for man. Indeed, chemists have created a great variety of synthetic materials. There is no doubt now that these materials surpass some natural substances in lightness, strength, chemical durability and elasticity. Everybody knows adhesives and lubricants with synthetic polymer basis to be better for some purposes than the natural glues and oils.

Very often synthetic materials take place of metals because their properties are higher than those of metals. However, poly­mer materials would not be able to compare with metals as electri­city and heat conductors. On the other hand, polymers are better insulators of electricity, some of them providing the best heat insulation.

Polymers being very cheap materials is also a well known fact. It should be noted that they are produced from the by-products of oil refining, natural gas, oil, coal farming waste and timber pulp.

The advantages of synthetic materials are used by the scientists and designers in the construction of automobiles, tractors, cranes and other machinery. Different kinds of plastics having been obtain­ed, it became possible to decrease the weight and the size of ma­chines, mechanisms and devices. Such parts as numerous gears, glass holders, bodies and covers of carburettors, plafonds, win­dow glasses, steering wheels, buttons of different devices, hand­les and tubes are manufactured from plastics obtained on the ba­sis of thermoplastic resins. A new kind of synthetic rubber has made the service life of motor tyres longer.

Textolite is an excellent insulating material for electric equipment. Glass plastics can operate under high temperatures. They are strong and offer resistance to heat, water, oil, acids and alkalis. Car bodies are now made of glass plastics.

UNIT 7

TWO-CYCLE DIESEL ENGINES

The idea of a two-cycle engine is to complete the cycle in only two strokes of the piston, that is, in only one revolution of the crankshaft. Thus a two-cycle engine running at the same speed as a four-stroke engine will have twice as many power strokes. The two-stroke cycle is particularly adaptable to the diesel system.

Now let's see what happens in a typical two-cycle diesel engine. This engine uses a rotary blower which takes in air from the atmosphere and delivers it, at a low pressure, to an air chamber. There are two valves in the cylinder head, as in a four-cycle engine, but both are exhaust valves, instead of one inlet and one exhaust. There is a row of holes, or ports, in one cylinder wall. These inlet ports are covered by the piston and therefore closed most of the time. But they are uncovered when the piston nears the bottom of its stroke. The ports are connected to the blower outlet by the air chamber.

Suppose the piston is at the bottom of its stroke. The intake ports are open; so are the exhaust valves. Air is being drawn in through the inlet ports and is pushing the exhaust gases left from the previous cycle out through the exhaust valves. When the piston is raised about a quarter of the way up, the exhaust valves will close and the inlet ports will be covered. Now there are no exhaust gases in the cylinder. It is full of fresh air. The rest of the upward stroke is an ordinary compression stroke. Just before the piston reaches its top position /"top dead centre"/ the fuel is sprayed into the chamber full of hot compressed air. Ignition and expansion take place just as in the four-stroke engine, and piston starts down on its power stroke. When the piston is three quarters of its way down, the exhaust valves open and the spent gases go out. The piston goes down and uncovers the inlet ports. The fresh air is again blown into the cylinder. Just as before, this helps to get the exhaust gases out. The cylinder is full of fresh air again. The piston reaches its bottom position and the cycle is complete, all in one revolution.

We can see that compression and power stroke are not much different from those in four-cycle engines. But the exhaust and intake actions take place more or less Simultaneously.