When the operation of the engine, the crankcase vapors by the trachea, the check valve is sucked into the cylinder, small air filter and fresh air through the valve chamber cover into the crankcase. The role of the check valve is to prevent too large a degree of vacuum of the engine at low speed low load intake pipe to suck out the oil from the crankcase. The crankcase ventilation unidirectional valve, is composed mainly by the valve, the valve body, the valve seat and the spring. Engine during idling to a degree of vacuum in intake pipe, the check valve being sucked on the seat, the crankcase exhaust gas through valve orifice into the intake pipe; with the engine load is increased, the decline in the degree of vacuum of the intake manifold, the valve spring outwards under the force to open the top, when ventilation is gradually increased; engine heavy load when the valve is fully open, ventilation rate, and thus update the crankcase air.

(2) the general formula
Only with a rubber hose the crankcase intake pipe linking ventilation generally forced ventilation. This ventilation mode structure is relatively simple, just piping connections, in the middle do not need other components connected to apply to some small engines. The gasoline engine crankcase general formula forced ventilation device. The upper part of the air filter with the air intake hose, used to pass to the inlet valve chamber cover, tappet chamber cover a trachea through to the carburetor.
The work of the engine, the crankcase gases inhaled via a tracheotomy carburetor, filtration of fresh air from the air cleaner through the air intake hose, valve chamber cover added to the crankcase.