MEOclassIIexamnotes

The timing diagram shows the closing and opening of the valves. The working cycle is illustrated as a ‘P - V’ diagram (pressure-volume). The line ‘l – l’ represents atmospheric line. The piston is considered to have just moved over the ‘top dead centre’ and is on its way down. The air inlet is already open and because of the partial vacuum created when the piston moves towards its bottom position, fresh air is sucked into the cylinder. This process is represented in the 'p-v' diagram by the line ‘1-2’ which is termed suction line. This movement of the piston is called 'Suction Stroke". After the piston has moved over bottom dead centre, the suction valve closes and the volume of air in the cylinder is compressed during the course of the up stroke of the piston. This is represented by the line ‘2-3’ in the above diagram and termed as compression line. This movement of piston is compression stroke. The ignition takes place at point 3 and combustion continues for th...

Material Requirements. The material should retain its greatest strength at high temperatures. No tendencies to air harden. Critical temperature above 800*C. No tendency of high temperature scaling. Hot and cold corrosion resistant. Able to be forged and machined easily. Capable of consistent and reliable heat treatment. Most diesel engines use an Austenitic heat-resisting alloy steel. The seating surface can be stellited. Typical heat treatment:  Heat up to 950*C and cool in air to give a Brinnel Hardness of 269. Surface Treatment: Surface treatment is frequently used to improve or modify valve steel characteristics. Chrome-cobalt-tungsten alloy available in various grades of hardness is widely used. The hardness when deposited is in the order of 375 to 425 Brinnel. The valve head is treated to more than 430*C to reduce contraction stresses. The value face is now sweated by an oxyacetylene flame and the alloy deposited continually by welding (1.02 mm to 1.52 m...

An engine indicator consists of a small bore cylinder containing a short stroke piston which is subjected to the same varying pressure that takes place inside the engine cylinder during one cycle of operations.  This is done by connecting the indicator cylinder to the top of the engine cylinder in the case of single-acting engines, or through change over cocks and pipes leading to the top and bottom ends of the engine cylinder in the case of double-acting engines. The gas pressure pushes the indicator piston up against the resistance of a spring, a choice of specially scaled springs of different stiffness being available to suit the operating pressures within the cylinder and a reasonable height of diagram. A spindle connects the indicator piston to a system of small levers designed to produce a vertical straight-line motion at the pencil on the end of the pencil lever, parallel (but magnified about six times) to the motion of the indicator piston. The “pencil” is often a b...

Following Procedure has to be followed when opening Liner Inform company and take permission.Take immobilisation certificate from port state control. Read the manual and have a tool box meeting with everyone involved in the job. Discuss the complete procedure. Prepare important tools and spares required for overhauling liner as given in the manual Prepare risk assessment and make sure all personal safety equipment are used Shut starting air for Main Engine and display placards Engage turning gear Open indicator cocks for all the cylinders Stop main lube oil pump and switch off the breaker Once the engine jacket temperature comes down, shut the inlet water valve for the unit to be overhauled Keep other units in Jacket preheating system to maintain the jacket temperature Drain the jacket water of the concerned unit from exhaust v/v and liner. Shut the fuel oil to the particular unit whose liner is to be removed Dismount the cylinder head using dedicated lifting tools Dis...

At a star-delta start of electric motors it is often considered necessary to limit the compression work of the machine at the starting moment in order to reduce the starting torque of the electric motor.  Usually, a solenoid valve is used in a by-pass arrangement which in the starting up phase short circuits the discharge side to the suction side of the compressor.  At the same time, a non-return valve must be fitted in the discharge line to the condenser preventing the return flow of discharge gas to the compressor. When the electric motor has reached its max. number of revolutions per minute, a switch takes place from star to delta start.  The solenoid valve is closed and the compressor now works under normal conditions.

Acid content inside a system can emulsify with the compressor oil to form an aggressive oil sludge that reduces lubrication properties. This can lead to serious compressor damage. Sludge can also cause a variety of other problems in a system, such as blockages of strainers, expansion valves and other tiny passage