First of all, we should know about Cylinder cover which is also known as Cylinder head is tightened down against the top of the cylinder liner by means of nuts and studs. The nuts are tightened by means of hydraulic jacks. It seals the top end of the cylinder space. Sealing between the cylinder cover and cylinder liner is obtained by means of a sealing ring which is made of mild steel. A cooling water space around the cylinder cover is formed by a cooling jacket which mounted on the lower part of the cylinder cover. Another cooling water space is made around the valve seat when the valve is installed. The cylinder head is made of one piece and is provided with bores for mountings such as exhaust valve, fuel valves, air starting valve, safety valve, indicator valve, and rocker arm which are explained below in a brief sense.
Exhaust Valve:
It is the hottest part of the cylinder cover. It is fitted in the central bore of the cylinder cover/head. By using four studs and nuts, it is attached to the cylinder cover and forms a gas-tight seal. The exhaust in the cylinder is 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 of the nimonic type. 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 as a spring. The hydraulic piston opens the exhaust valve when the oil under pressure acts on top of the piston. The hydraulic cylinder on top of the exhaust valve and the actuator mounted on top of the camshaft are connected by a high-pressure pipe. Oil is supplied to the hydraulic actuator through a non-return valve. The timing of the exhaust valve is controlled by the exhaust valve cam mounted in the camshaft. The exhaust valve is water-cooled. The cooling water flows from the bottom through bores in the valve housing and discharged from the top of the valve housing.
Relief Valve:
It is fitted in each cylinder cover. When the pressure inside the cylinder increases above the maximum allowed peak pressure the relief valve lifts and releases the excess pressure.
Fuel Valve:
The fuel valves which are also known as fuel injectors are fitted on cylinder cover by two holding down bolts. The fuel valves atomize 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 in 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 guide are assembled inside the valve body. The spindle guide consists of a spindle guide, nozzle, thrust piece, and cut-off shaft. The spindle guide is assembled with the press fit. The cut-off shaft is pressed against the tapered valve seat of the spindle guide by the action of the thrust spring. The spring pressure is transmitted through the slotted thrust foot. The thrust spring determines the opening pressure of the valve. The non-return valve consist of housing, thrust piece, slide, and spring. The non-return valve is assembled with press fit. The slide of the non-return valve is pressed 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 thrust 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 turning gear motor without opening the indicator valves.
Air Starting Valve:
The starting valve is fitted on the cylinder cover. It is controlled by control air from the starting air distributor. It is kept in the closed position by a 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.
Rocker Arm:
A valve rocker is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet to open it. One end is raised and lowered by a rotating lobe of the camshaft while the opposite end acts on the valve stem. When the camshaft lobe raises the surface of the arm, the within presses down on the valve stem, opening the valve. When the surface of the arm is permitted to return (thanks to camshaft rotation), the inside rises, along the valve spring to shut the valve. Because of the rocker arms, excessive mass especially at the lever ends limits the engine’s ability to reaches high operating speeds.
Authored by: Cdt. Swapnil Pawar, TMI
