When the cam lobe reaches the maximum height, the valve opens fully. The other end of the rocker arm’s tip moves downward and the inlet valve opens against the spring’s tension. When the tappet moves up, it pushes the push-rod and one end of the rocker arm upwards. As the camshaft turns, the cam lobe brings the tappet upward. Overhead Valve MechanismĪs the name says in this mechanism valves are placed overhead on the combustion chamber. Additional rotation of the cam triggers the tappet to move downwards and the valve is stopped by the tension of the valve spring. When the cam lobe attains the maximum height, the valve opens completely. When the camshaft rotates the cam, the lobe opens the valve directly through the tappet against the spring’s tension. In this mechanism as shown in the figure, the inlet valve is placed on the side of the cylinder valve. It is generally used in two-stroke engines. This valve is placed in such a way that suction pressure opens the inlet valve and closes the exhaust valve and exhaust pressure closes the inlet valve and opens the exhaust valve. It covers the passages and allows air or charge to flow in one direction only. In this valve, a mechanical strip is hinged at one end. The valve timing diagram of both petrol and diesel engine is discussed below: The valve timing diagram of the Petrol Engine Modified valve timings improve the Volumetric efficiency of the engine. And valves are the mechanical mechanism which has some delay, so valve timing is arranged to overcome this delay. In actual practice the timing of opening and closing is varied slightly to get the best output on the proper flow of fuel and exhaust gases. As we know the valve opens or closes at the end of the stroke but this is theoretical timing. The valve timing diagram is a graphical representation of opening and closing timing and duration of valves with respect to the crank rotation. The exhaust valve is made of a steel alloy of silicon and chromium which has good resistance to heat. The function of the exhaust valve is to remove the burnt fuel i.e., exhaust gases out of the combustion chamber so that fresh charge can come in. As fuel coming in is at a lower temperature so inlet valve is usually made of nickel-chromium alloy steel. When the inlet valve closes it seals the combustion chamber tightly and restricts more fuel to come in. The Inlet valve is provided for the intake of fuel into the combustion chamber. This mechanism is run by the crankshaft with the help of a timing chain for desired opening and closing of the valve. These valves are actuated by a cam and follower mechanism. One of them is an inlet valve which is used to restrict and allow the flow of fuel into the combustion chamber.Īnother valve is known as the exhaust valve which is used for the exit flow of exhaust gases. These are provided to regulate the flow of fuel and gases in or out of the combustion chamber. Types of Engine Valves: Valve Timing Diagram & Valve Operating Mechanism : Engine valves are mechanical components that are provided on the head of the combustion chamber of an internal combustion engine. Types of Engine Valves: Valve Timing Diagram & Valve Operating Mechanism What is an Engine Valve?
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