galyatova_v_n_lelet_i_a_angliyskiy_yazyk

The parts, which make up the operating mechanisms of an engine, may be divided into two groups: the group, which forms the drive mechanisms, and the group, which forms the actuating mechanisms. The source of power for the operating mechanisms of an engine is the crank­ shaft.

A drive mechanism may be of the gear, chain or belt type. The gear type is the most common. A combination of gears and chains is used as the driving mechanism in some engines. A separate drive mechanism, which is used to transmit power for the operation of engine valves, is generally called the camshaft drive or timing mechanism. Camshaft drives are designed to maintain the proper relationship between the speeds of the crankshaft and the camshaft.

In order for the valves (intake, exhaust, fuel injection, air starter) to operate, there must be a change in the type of motion. In other words, the rotary motion of the crankshaft and drive mechanism must be changed to a reciprocating motion. The group of parts, which causes the valves of an engine to operate, is generally called the valve actuating mechanism. It may include the cams, cam followers, push rods, rocker arms, and valve springs. In some engines, the camshaft is so located that the need for push rods is eliminated. In such cases, the cam follower is a part of the rocker arm.

There is a considerable variation in the design and arrangement of the parts of operating mechanisms found in different engines. The size of an engine, the cycle of operation, the cylinder arrangement, and other factors govern the design and arrangement of the components as well as the design and arrangement of the mechanisms.

Exercise I.

Answer the questions

1.What is the principal function of the operating mechanisms?

2.What types of drive are used in the operating mechanisms?

3.What are the camshaft drives designed for?

4.What valves are operated by the actuating mechanism?

5.What are the parts of this mechanism?

6.In what case does this mechanism not include push rods?

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V

Exercise II.

Speak of the Operating Mechanisms.

Exercise III.

Read and translate text В in written form.

Text B.

Pumps

A pump is a machine used to raise liquids from a low point to a high point. A pumping system on a ship consists of suction piping, a pump and discharge piping. Every pump has a power end, which may be a steam turbine or an electric motor and a liquid end where the liquid en­ ters or leaves the pump. The typical characteristics for the pump are the suction head and the discharge head. The suction head is the pressure of the liquid entering the pump or the difference in the level of liquid with respect to the level of the pump on the suction side. The discharge head is the pressure of the liquid leaving the pump or the level of liquid with respect to the level of the pump on the discharge side.

There are three main classes of pumps in marine use: displacement, axial flow and centrifugal. Displacement pumps can be either reciproca­ ting or rotary. The operating principle of the reciprocating displacement pump is the following. As the piston moves upwards suction takes place below the piston and liquid is drawn in, while the discharge valve is closed. Above the piston liquid is discharged and the suction valve is closed. As the piston travels down the operations of suction and dis­ charge occur on opposite sides.

A relief valve is always fitted between the pump suction and dis­ charge chambers to protect the pump against excessive pressure.

The rotary displacement pumps operate by means of rotary parts which trap the liquid at the suction side and force it through the dis­ charge outlet. According to the type of rotary elements there are rotary vane displacement pumps, gear displacement pumps and screw dis­ placement pumps.

An axial flow pump uses a screw propeller to axially accelerate the liquid. The outlet passages and guide vanes are arranged to convert the velocity increase of the liquid into a pressure.

In a centrifugal pump liquid enters the center of the impeller and flows radially out between the vanes. A diffuser or volute is then used to

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convert most of the kinetic energy in the liquid into pressure. There are single-entry or double-entry centrifugal pumps.

Various valves are fitted to the pumps. These include the follo­ wing: globe valves, non-return or check valves; relief valves.

Starting (the centrifugal pump and axial flow pump)

1.Open the suction check valve wide, operating at the same time the air vent on the top side.

2.Close the air vent as soon as liquid flows out of it.

3. Start the motor leaving the discharge valve closed.

4.Check that direction of rotation is as indicated by the arrow.

5.Slowly open the discharge check valve until operating re­ quirements are reached.

6.Check on the ammeter that power requirements do not exceed the motor possible rating.

7.Check tightness of the packing gland. Leaks must be reduced to a few drops which is required to prevent harmful heating of the packing’s and the shaft.

During operation the pump output is to be controlled by ope­ rating on the discharge valve and never on the suction valve which must always remain wide open.

Exercise IV.

Put 10 questions to the text.

Exercise V.

Translate into Russian paying attention to Infinitive constructions.

1.The work is considered to be fulfilled in a week.

2.Turbo-charging is known to increase the engine power greatly.

3.The highest powered installation is expected to produce more than 30,000 bhp.

4.The main fact of choosing this engine for propulsion power is said to be reliability.

5.The main and crankpin bearings were found to be in ex­ tremely good condition with no signs of wear.

6.Cleaning the lower parts is likely to be difficult, especially in the region of fire hole ring.

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7.Such an arrangement has proved to produce optimum mixing conditions between gas and air.

8.We know this engine to have good starting conditions.

9.This method of lubricating allows friction to be decreased to a minimum.

10.They reported the ship to have been launched this week.

Exercise VI.

Translate into English.

1.Приводные механизмы используются для передачи энергии.

2.Чтобы исключить загрязнение масла продуктами сгорания, оно должно находиться в отдельном танке.

3.Насосы применяются для того, чтобы прокачивать жид­ кость.

4.В шатуне просверлено отверстие, для того чтобы подавать охлаждающее масло в поршень.

5.Для того, чтобы выпускать воду из системы, установлены спускные клапана.

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Text А.

Engine Cooling Systems

A great amount of heat is generated within an engine during opera­ tion. Combustion produces the greater portion of this heat; however, compression of gases within the cylinders and friction between moving parts add to the total amount of heat developed within an engine.

Of the total heat supplied to the cylinder of an engine by the bur­ ning fuel, only one-third is transformed into useful work; an equal amount is lost to the exhaust gases, and approximately 30 to 35 percent of the heat of combustion must be removed in order to prevent damage to engine parts. The greater portion of the heat, which may produce harmful results, is transferred from the engine through the medium of water; lubricating oil, air, and fuel are also utilized to aid in the cooling of the engine. All methods of heat transfer are utilized in keeping engine parts and fluids (air, water, fuel, and lubrication oil) at safe operating temperatures.

The cooling system may be of the open or closed type. In the open system, the engine is cooled directly by salt water. In the closed system fresh water, (or an antifreeze solution) is circulated through the engine. The fresh water is then cooled by salt water. In marine installations the closed system is the type commonly used.

The cooling system of an engine may include such parts as pumps, coolers, engine passages, water manifolds, valves, expansion tank, pi­ ping, strainers, connections, and instruments. Design and location of parts may differ considerably from one engine to another.

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Exercise I.

Answer the questions.

1.What are the sources of the heat generated in an engine?

2.How much heat is transformed into useful work?

3.How many percent of the heat must be removed from the engine by means of cooling?

4.What fluids are utilized for cooling purposes in an engine?

5.What parts does the water cooling system of an engine include?

Exercise II.

Speak of the Engine Cooling Systems.

Exercise III.

Read and translate text В in written form.

Text B.

Heat Exchangers

The type of heat exchangers most used in marine work is of tubular form. The principles of construction and operation are same for the two applications of cooling jacket water and cooling lubricating oil. A stack of thin walled tubes is supported by spacer plates within a cylindrical casing. The ends of the tubes communicate with header boxes so that the secondary fluid (sea water) can enter one of these and leaves the after flowing through the tubes..

The primary fluid (fresh, water or lubricating oil) flows through the cylindrical casing over the outside of the tubes giving up heat to the sea water. The header boxes can be removed and the tube stack withdrawn for cleaning.

The rate at which heat is transferred from the primary to the secon­ dary fluid depends upon the total surface area of the tubes, their radial thickness, the conductivity of the material, the heat transfer coefficient from the primary fluid to the tube surface and from the tube surface to the secondary fluid.

The chief troubles of heat exchangers are fouling and corrosion. The former decreases heat transmission, while the latter usually results in temporary repairs being made by plugging the damaged tubes redu­ cing the heat transmission surfaces of the cooler.

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Regular inspection and cleaning of heat exchangers is essential in the interests of maintaining the efficiency of cooling systems. Sea water is the main source of deposits and for this reason it is usually circulated through the tubes as the bores can be cleaned by mechanical means using rods and brushes, rotating or power driven if necessary.

If deposits of hard scale are formed then chemical cleaning is ne­ cessary. When deposits on the outside of the tubes from fresh water take place chemical cleaning is the only possible way to remove them. The method used is to soak the tube stack in a weak acid solution containing corrosion inhibitors.

Exercise IV.

Put 10 questions to the text.

Exercise V.

Translate into Russian paying attention to Adverbial Clauses.

1.Burning of the piston crowns can take place if cooling is not effective.

2.Forced cooling is necessary as it provides permissible tem­ perature of engine parts.

3.Reliable operation of an engine is provided as effective forced cooling is maintained.

4.The use of sea water can decrease the reliability of an engine because even a slight leakage of it leads to corrosion of engine parts.

5.An oil cooling system includes an oil cooler so that oil can be cooled with sea water.

6.The degree of cooling an engine must not be too high in order that heat loss would be smaller.

7.The middle temperature of a cooling substance must be as high as possible so that the engine operation would be eco­ nomical.

8.Natural ventilation of heat is not enough as long as an engine is under operation.

9.Wear of engine parts is increased rapidly as soon as lubrica­ ting oil film between friction parts is destroyed.

10.Successful operation of any engine depends upon the removal of excess heat from the cylinders, pistons, valves, etc., so as to keep the temperatures of these parts within allowable limits.

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Exercise VI.

Translate into English.

1.Втулки цилиндра могут охлаждаться морской или пресной водой, в то время как поршни обычно охлаждаются маслом.

2 .Воздух не используется для охлаждения двигателей боль-

шо й м о щ н о с т и , т. к. эффективность такого охлаждения низка.

3.Самым удобным охлаждающим веществом для морских ди­ зелей является морская вода, потому что не требуются танки для хранения и холодильники.

4.Эффективность охлаждающей системы морской водой уменьшается, как только на внутренних частях двигателя образует­ ся накипь.

5.Необходимо принудительное охлаждение, с тем чтобы поддерживать допустимую температуру головки (днища) поршня.

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Text A.

Lubricating Oil Systems

It is important not only that the proper type of lubricant be used, but also that the lubricant be supplied to the sliding or rolling parts in proper quantities, at the proper temperature, and that provisions be made to remove any impurities which enter the system. The engine lubricating systems are designed to fulfill these requirements, as the life and reli­ ability of the engine depend on good lubrication.

Most conventional marine diesel engines use three separate lubri­ cating systems. They are the following: (I) the crankcase oil with its pump, filter and cooler used for the crankshaft, connecting rod and cam­ shaft bearings, and for piston cooling; (2) the cylinder oil and the cylin­ der lubricators adjusted to meter a specific number of drops per minute;

(3) the valve-gear centralized lubricating system in which lubricant is drained separately in order to prevent contamination of the crankcase oil by leaking fuel, injector cooling water, or exhaust gas.

2-cycle and 4-cycle diesel engines are supplied with lubricating oil under pressure to all bearings and moving parts. Therefore, such systems are called pressure-lubricating systems whose essential parts are the fol­ lowing: (I) Tanks and sumps used to hold the oil that is continuously circulated. (2) Lubricating oil pumps, which provide pressure for forcing "the oil through the oil passages and the bearings. Maximuni system pressure is set by a relief valve. It must be adequate to provide the re­ quired oil flow through bearing clearances. The lube oil pumps are driven by chains or gears from the crankshaft, or by extension of the crankshaft or camshaft. They are located either inside or outside the crankcase.

When a centrifuge or oil-treatment system is installed to niaintain clean lubricating oil, additional pumps are required to deliver oil to the treating equipment. (3) Lubricating oil circulating in the engine picks up friction heat from the bearings, heat from oil-cooled pistons, and also heat transferred from the combustion space to the oil film on the cylin­ der walls. This heat is removed by contact with water-cooled surfaces in the oil cooler of shell-and-tube construction.

No matter what system of filtering is employed, filters should pro­ vide the required flow rate at an acceptable pressure drop. Mechanical straining is usually accomplished by a fine-mesh screen.

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