Reed valve

Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face. Modern versions often consist of flexible metal or composite materials (fiberglass or carbon fiber).

Reed valves, normally a leather flap covering a hole, are amongst the earliest form of automatic flow control for liquids and gases. They have been used for thousands of years in water pumps and for hundreds of years in bellows for high-temperature forges and musical instruments such as church organs and accordions. In nature, heart valves operate in a somewhat similar fashion.

Reed valves are used in some reciprocating compressor designs, and in the pumping element of some musical instruments, large and small.

Reed valves are commonly used in high-performance versions of the two-stroke engine, where they control the fuel-air mixture admitted to the cylinder. As the piston rises in the cylinder a vacuum is created in the crankcase beneath the piston. The resulting pressure differential opens the valve and the fuel-air mixture flows into the crankcase. As the piston descends, it raises the crankcase pressure causing the valve to close to retain the mixture and pressurize it for its eventual transfer through to the combustion chamber. The Swedish motorcycle company Husqvarna produced a two-stroke, 500 cc displacement single cylinder engine with a reed-valve controlled intake, one of the biggest in using this arrangement. Reed valves in two-stroke engines have been placed in the intake ports and also in controlling the intake to the crankshaft space.

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Wikipedia