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What is Poppet Valve ?

What is a Poppet Valve ?

 
A Poppet Valve is a valve in an engine primarily used for controlling the time and quantity of fuel entering the engine. A poppet valve is also known as Mushroom Valve. Poppet Valves are generally used in automobile engines. The poppet valve is a simple and effective design used mainly for 2/2 and 3/2 functions. It has good sealing characteristics and can often be the choice for a supply shut off valve. A poppet seal has a butt action against a raised edged aperture. The poppet seal will give long life and supply to the port assists the spring to hold the poppet shut.
Valves are based either on the poppet principle or slide principle. In poppet valves, a ball, a cone or a disc is pressed by a spring against the seat of passage. The high pressure per unit area which is created, means that valves of this kind provide a very efficient seal.
The below is a pictorial representation of Poppet Valve –
The valve stem moves up and down inside the passage called guide, which is fitted in the engine – block. The head of the valve is called as valve face and is generally ground to have a 45 degrees angle, so as to fit properly on the valve seat in the block and prevent leakage.
A valve spring with a spring retainer aids the return of valve after operation. When the cam rotates, the taper is lifted, thereby lifting the valve to open. in the closed position of the valve a slight clearance is necessary between the valve tappet and the stem. This gap is known as valve tappet clearance. 
This gap allows for the expansion of the valve stem and other parts in the valve operating mechanism as the engine becomes heated. In the construction, the valve seat and inserts are pressed into the cylinder block. These inserts reduce wear and tear thereby preventing leakage and frequent replacing of the valve.

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