Types of Engine Valves –
The valves are nothing but the gates for opening and closing the inlet and exhaust passages in the cylinder. The engine valves are broadly classified into three types. They are as follows –
- Rotary Valve
- Sleeve Valve
- Poppet Valve
Rotary Valve –
Rotary valve has a hollow shaft which runs in the housing attached to the cylinder head. The hollow shaft has two ports, one is inlet port and the other is exhaust port. At the time of suction stroke, the inlet port meshes with the intake manifold and at the time of exhaust stroke, the exhaust port meshes with the exhaust manifold. These valves function very quickly but subjected to greater wear. Rotary valves are found unsuccessful because of escaping of gasses and gumming up of its system.
Sleeve Valve –
Engine cylinder liner has inlet port and exhaust port cut in it. Another sleeve has inlet and exhaust openings. At the time of inlet, the inlet port of sleeve meshes with the inlet opening of the cylinder and at the time of exhaust, the exhaust port of the sleeve meshes with the outlet opening of the cylinder. The sleeve which has inlet and exhaust ports move up and down and also rotates with the suitable mechanism. Due to greater wear in the sleeves these valves are not in use.
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 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.