Valves (Intake And Exhaust)DESCRIPTION
The word valve indicates a device that regulates the passage of a fluid: permitting it, partializing it or preventing it, depending on the case. The valves can be controlled automatically or by a control system. The valves are unidirectional if they allow the passage of the fluid in one direction only. The best known, are housed in the cylinder head in the number of two or four for each cylinder (however, there are also engines that employ three or even five valves!) and regulate the flow of gases entering and coming out: they can be intake or exhaust valves. They are controlled by one or two camshafts or other parts (often only a rocker arm or a tappet for each valve). A spring retrieves each valve: usually it is of a helical type but often are used two different diameter springs coaxially arranged.