PCV - LAP Electrical Ltd

What The PCV System Does

In gasoline engines small amounts of combustion gases seep past the piston rings into the crankcase.
These crankcase blow-by gases contain undesirable hydrocarbon air pollutants. To prevent these vapours from escaping into the atmosphere, while allowing proper ventilation of the crankcase- the positive crankcase ventilation (PCV) system is used.

How The PCV "Closed" System Functions

Beginning with the 1964 model year, California law required that new gasoline powered cars sold in that state be equipped with a "closed" PCV system. This became a federal requirement for 1968 and later model year gasoline powered cars. In addition, California law requires 1955 through 1960 model year gasoline cars to be so equipped whenever "transferred" from one person to another.

The closed PCV system is similar in operating principle to the open system, except... fresh air enters the closed system from the clean air side of the air cleaner or a seperate PCV breather filter on the inside periphery of the air cleaner, or in the line from the rocker arm cover to the air cleaner.

The closed system is more effective in preventing air pollution than the open system because it is completely encased. If pressure builds up in the crankcase on an engine with the closed system, such as with plugged PCV valve hose or fittings, the blow-by gases will be forced into the air cleaner. This happens because all other outlets are sealed. When these vapours pass through the air cleaner, they are mixed with fresh air and routed via the carburetor and intake manifold, back into the combustion chamber to be burned.

Design Features Of PCV Valves

All PCV Valves are designed to rigid specifications. For example, case-hardened metering surfaces of PCV valves are held to tolerances of 1/7 of a thousandth of an inch (.0005"). That's a sixth of the thickness of a human hair.

Also, every PCV valve is flow-checked in production to be sure it meets air flow requirements. This is necessary because the PCV valve air flow does not go through the carburetor but acts as a calibrated air bleed into the intake manifold.

The heat treatment of all PCV Valve metering surfaces and the plunger reduce surface wear. Thus every PCV valve maintains its closely held tolerances during its useful life.

Most PCV valve assemblies consist of a coil spring, plunger, a connector assembly and a body assembly which are crimpled together. The valve dimensions, spring and internal dimensions are specifically designed to produce the desired air flow requirements which are shown on a flow curve.