Emission System: Emissions-Evaporative: Valve-PCV: Operation

Fig 1: Typical Closed Crankcase Ventilation System

Courtesy of DAIMLERCHRYSLER CORP.

A typical enclosed crankcase ventilation system is shown in Fig 1.

The PCV system operates by engine intake manifold vacuum. Filtered air is routed into the crankcase through the air cleaner hose. The metered air, along with crankcase vapors, are drawn through the PCV valve (4) and into a passage in the intake manifold. The PCV system manages crankcase pressure and meters blow by gases to the intake system, reducing engine sludge formation.

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

Fig 2: Engine Off or Engine Backfire - No Vapor Flow

Courtesy of DAIMLERCHRYSLER CORP.

When the engine is not operating or during an engine pop-back, the spring forces the plunger back against the seat. This will prevent vapors from flowing through the valve.

Fig 3: High Intake Manifold Vacuum - Minimal Vapor Flow

Courtesy of DAIMLERCHRYSLER CORP.

During periods of high manifold vacuum, such as idle or cruising speeds, vacuum is sufficient to completely compress spring. It will then pull the plunger to the top of the valve. In this position there is minimal vapor flow through the valve.

Fig 4: Moderate Intake Manifold Vacuum - Maximum Vapor Flow

Courtesy of DAIMLERCHRYSLER CORP.

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