So last time I explained how the spark plug operated. Today I am going to tell about the valves in the engine. The valves, though seem small and inconsequential, play quite an important role in the engine. A lot of times people ask what controls the inflow and outflow of air and fuel into the chamber above the pistons or how is a specific quantity of air fuel mixture administrated into this chamber? The answer is the valves.
The valves commonly called 'The Poppet Valves' are attached to long rod which pushes it down called the stem. First the stem pushes the inlet valve down which lets in the air fuel mixture. then the spring to which the inlet valve is attached retracts the stem and so the valve closes. The speed of this process is usually determined by the speed of the pistons.
The faster the pistons move the quicker the valves will open and close. Now the piston compresses the mixture. As the mixture is compressed the spark plug initiates a spark which ignites this mixture. Now the outlet valve opens and the heat generated escapes out.
The same cycle is repeated again.
Now the problem arises in racing or fast cars. The piston movement in those is extremely fast and thus the spring is not able to retract the stem and the valve quickly (This situation is called valve float). Thus, such cars are equipped with special type of valves called Desmodromic Valve, which being closed by a positive mechanical actions instead of a spring, are able to close quickly, thus facilitating fast and efficient closing and opening of the valve. This picture should you help you understand more clearly.
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