Positive Crankcase Ventilation Valve: Description and Operation

OPERATION
The PCV valve contains a spring loaded plunger. This plunger meters the amount of crankcase vapors routed into combustion chamber based on intake manifold vacuum.

Engine Off Or Engine Backfire - No Vapor Flow:

When the engine is not operating, or during an engine backfire, the spring forces the plunger back against the seat. This prevents vapors from flowing through the valve.

High Intake Manifold Vacuum - Minimal Vapor Flow:

When engine is at idle or cruising, high manifold vacuum is present. At these times, manifold vacuum is able to completely compress spring and pull plunger to top of valve. In this position, there is minimal vapor flow through the valve.

Moderate Intake Manifold Vacuum - Maximum Vapor Flow:

During periods of moderate intake manifold vacuum, the plunger is only pulled part way back from the inlet. This results in maximum vapor flow through the valve.