Lubrication System

The lubrication system of modern airplanes is on the whole independent and mounted entirely іn the engine.

The lubrication system is relatively simple in design and operation but its function is of vital importance. The principal purposes of the lubrication system are:

to supply oil to various points in the engine;

to reduce friction between moving parts;

to cool the areas with which the lubricant comes in contact.

The lubrication systems are different in design. The reciprocating engine has an innumerable number of rotating and moving parts that require lubrication. The lubricating oil is also used to cool the cylinder walls, which attain a very high temperature. As a result, a heavy oil must be used to withstand the high temperatures and oil consumption is relatively high.

In comparison, the gas-turbine engine has considerably less rotating parts to lubricate and none of the oil is in contact with the parts of the engine heated by combustion. Therefore, the lubrication systems of the gas-turbine engines are rather simple arrangements. The units requiring lubrication are the main bearings and the gears in the accessory section. The purpose of the lubrication system is to provide an adequate supply of clean oil to the above mentioned parts at the right temperature.

The friction resulting from such metal-to-metal contact would cause a loss of power, rapid wear of surfaces and a temperature rise.

There are two basic types of lubrication systems: the dry sump and wet sump types. Some engines utilize a combination of the dry and wet sump types, while others are lubricated entirely with a dry sump type. Wet sump engines store lubricating oil in the engine proper, while dry sump engines use an internal tank mounted in the aircraft structure for oil storage purposes. The lubrication system comprises two subsystems: the pressure system, which supplies oil to the engine, and the scavenge system which returns the used oil to the tank.

The main units of a typical lubrication system are:

reservoir or tank for oil storage;

oil coolers;

pressure and scavenge pumps;

centrifuges for removing air bubbles from oil;

one or more oil filters;

flow dividers;

different valves, drain cocks, manometers, thermometers and pipelines.

Oil tank for aviation gas-turbine engines may be separated from the engine, be attached to the engine or be a structural part of the engine. In general, they are constructed of light-weight welded sheet metal and shaped to fit the location in which they are to be placed.

Different types of oil coolers are used. They may be either simple oil radiators with ram-air cooling or be of the type which utilizes fuel as the cooling medium.

An oil pump incorporates two main elements: a pressure pump and a scavenge pump. The pressure pump delivers oil to various points in the engine where lubrication is necessary. Scavenge pumps are similar to pressure pumps in design. They are used to drain oil from sumps and other drainage points and for returning the oil though the oil cooler to the tank. Oil filters or strainers are constructed in many designs. The main purpose of a filter is to remove all foreign particles from the lubricant.

Oil from the aircraft tank is delivered to the inlet of the pressure pump. Then it is pumped through a filter to the moving parts of the engine which need lubrication (compressor and turbine bearings, etc.). Oil from various bearings drains into a sump, from which it is picked up by scavenge elements and returns back to the tank. The pump system is provided with a pressure regulator which prevents supply of excess pressure to the inlet of the pump. A check valve in the line leading to the engine prevents the oil tank from forcing oil into the engine when it is shut down. Oil systems for present turbojet engines incorporate one main pressure pump and some, six, as a rule, scavenge pumps.

Exercise 2. Give derivatives of the following verbs, use both suffixes and prefixes. Translate the formed words.

To lubricate, to cool, to depend, to relate, to design, to operate, to reduce, to move, to result, to power, to utilize, to combine, to store, to use, to press, to turn, to serve, to divide, to differ, to drain, to regulate, to provide, to prevent, to lead, to present.

 

Exercise 3. These words from the text can be used as verbs and nouns. Translate them and give other words from the dictionary of such a kind.

Pump, air, design, function, supply, point, contact, result, cause, power, rise, use, turn, filter, flow, fuel, oil, present.