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A crankcase ventilation system (CVS) removes unwanted gases from the crankcase of an internal combustion engine. The system usually consists of a tube, a one-way valve and a vacuum source (such as the inlet manifold). The unwanted gases, called "blow-by", are gases from the combustion chamber which have leaked past the piston rings. Early ...
Manifold vacuum, or engine vacuum in a petrol engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere. Manifold vacuum is an effect of a piston's movement on the induction stroke and the airflow through a throttle in the intervening carburetor or throttle body leading to the intake manifold. It is a ...
A crankcase is the housing in a piston engine that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/air mixture passing through the crankcase before entering the cylinder(s). This design of the engine does ...
The CVH is known for producing excessive sludge if the service schedule is ignored or if poor quality oil is used. The cause is the design of the crankcase ventilation circuit, which Ford revised several times over the engine's lifetime but never completely cured. Due to this, camshaft and tappet wear problems are common.
An oil catch can is fitted in line of the crank case breather system. It is placed in between the breather outlet and the intake system. As the crank vapors pass through the catch can the oil droplets, un-burnt fuel, and water vapor condense and settle in the tank. This stops them from reaching the intake and causing the issues mentioned above.
Day cycle engines are crankcase scavenged and port timed. The crankcase and the part of the cylinder below the exhaust port is used as a pump. The operation of the Day cycle engine begins when the crankshaft is turned so that the piston moves from BDC upward (toward the head) creating a vacuum in the crankcase/cylinder area.
The Citroën 2CV boxer-twin engine took advantage of this pumping effect to maintain a partial vacuum inside the crankcase, in order to reduce oil leaks when an oil seal malfunctions. This was achieved by using a one-way valve (a leather or rubber flap over a hole in the crankcase), to let air escape the crankcase but not enter it. [5]
It may be made up of more than one diverging cone depending on requirements. The vacuum wave arrives in the cylinder during the transfer cycle and helps suck in fresh mixture from the crankcase into the cylinder, and/or prevent the suction of exhaust gases into the crankcase (due to crankcase vacuum). [3]