Cylinder cover and it's mountings of 2 stroke marine diesel engine

The cylinder cover seals the top portion of the cylinder liner and carries mountings necessary for engine operation. 
The cylinder cover acts as a gas-tight seal thereby forming an enclosed chamber where combustion can take place without escaping gases.
It is subjected to gas forces during combustion, thermal stress, pressure fluctuations during the entire cycle and bending stresses.
The cylinder cover is made of 0.6% carbon steel having a UTS - 400 to 500 N/mm2 which has a good tensile strength to withstand high pressure and temperatures. It also has good fatigue strength to withstand pressure fluctuations in cylinders.

The mountings of the cylinder cover :

Safety Valve:

  • A safety valve is fitted in each cylinder cover.
  • When the pressure inside the cylinder increases above the maximum allowed peak pressure, the safety valve lifts and releases the excess pressure.
See the cross-section view of the safety valve:

Fuel valve:

  • The fuel valve, known as a fuel injector is fitted on the cylinder cover by two holding down bolts.
  • The fuel valves atomized the high-pressure fuel supplied by the fuel pump and inject it into the cylinder.
  • In this fuel valve, fuel oil is circulated when the engine is on standby.
  • When the engine has started the circulation of oil will stop and the pressurized oil is supplied to the cylinder.
  • The fuel valve consists of a valve body, valve head and union nut.
  • The non-return valve, thrust spindle with thrust spring and spindle guides area assembled inside the valve body.
  • The spindle guide complete consist of spindle guide, nozzle, thrust piece and cut off shaft.
  • The spindle guide is assembled with a press-fit, cut off shaft is pressed against the tapered valve seat of the spindle guide by the action of the thrust spring.
  • This spring pressure is transmitted through the slotted thrust foot, The thrust spring determines the opening pressure of the valve.
  • The non-return valve consists of housing, thrust piece, slide and spring. The non-return valve is assembled with a press fit.
  • The slide of a non-return valve is present by the spring against the tapered valve seat inside the non-return valve.
  • In this position, the head of the slide uncovers a small-bore arranged for circulation purposes in the trust piece.

Indicator Valve:

  • Indicator valves are fitted in each cylinder. It is a double-seated valve with a spring-loaded closing face.
  • The combustion chamber of the cylinder is connected to the valve through a bore. It is used for taking indicator cards.
  • The indicator valves are kept open while turning the engine or blowing through the engine with air.
  • Any accumulation of oil or water in the cylinder will be expelled through the indicator valve when blown through with the air.
  • This will indicate the cylinders which are having problems. The engine should not be turned with a turning gear motor without opening the indicator valves.

Air Starting Valve:

  • The starting air valve is fitted on a cylinder cover. It is controlled by control air from the starting air distributor. It is kept in closed position by spring.
  • When the main starting valve is open, the starting air pipe up to the starting valve is pressurized.
  • The control air from the air distributor acts on the piston of the starting valve. The starting valve opens and the air flows from the starting air pipe to the cylinder.
  • After starting the space above the air piston is vented through the vent pipe of the air distributor.

Exhaust Valve:

  • Exhaust valve is fitted in the central bore of the cylinder. It is attached to the cylinder cover by four studs and nuts and forms a gas tight seal.
  • The burnt exhaust gases in the cylinder are expelled through the exhaust valve to the exhaust manifold.
  • The valve seat is fitted to the bottom of the valve housing.
  • The valve spindle passes through the spindle guide fitted in the bore of the valve housing.
  • The valve spindle is made from nimonic alloy, a family of nickel- based high temperature low creep material. A vane wheel is fitted to the valve spindle at the bottom part, which rotates the spindle while the engine is running.
  • The air piston and the hydraulic piston are mounted at the top of the spindle.
  • The air piston is locked to the spindle by a two piece conical ring. It keeps the valve closed and acts like a spring.
  • The hydraulic piston opens the exhaust valve when the oil under pressure acts on top of the piston.
  • A high pressure pipe connects the hydraulic cylinder on top of the exhaust valve and the actuator mounted on top of the camshaft.
  • Oil is supplied to the hydraulic actuator through a non return valve. The exhaust valve cam mounted in the camshaft controls the timing of the exhaust valve.
  • The exhaust valve is water cooled. The cooling water flows from the bottom through the bore in the valve housing and discharged from the top of the valve housing.

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