What does this PCV valve cutaway diagram show?

It shows two cross-section views of a PCV valve: one during low speed operation with high manifold vacuum, and one during high speed operation with low manifold vacuum, with flow arrows from the crankcase and/or rocker arm cover to the intake manifold.

Where does the flow through the PCV valve come from and go to?

Flow enters from the crankcase and/or rocker arm cover and exits to the intake manifold.

How does manifold vacuum relate to engine speed in this diagram?

The diagram labels low speed operation as high manifold vacuum and high speed operation as low manifold vacuum.

How does the PCV valve position differ between low and high speed operation?

In the low speed/high vacuum view, the spring-loaded plunger is drawn toward the intake manifold side, restricting flow; in the high speed/low vacuum view, the plunger sits with the spring extended, allowing more flow to the intake manifold.

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PCV Valve Cutaway Diagram – Low vs High Speed Operation (Ford Bronco)

PCV valve flow cross-section: low speed high vacuum vs high speed low vacuum crankcase ventilation

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PCV valve operation cutaway showing flow from crankcase/rocker cover to intake manifold. Low-speed (high manifold vacuum) restricts flow; high-speed (low vacuum) opens it wider.

AI caption October 2005 · Photo 138 of 277

This document is a schematic cutaway illustration showing the internal operation of a PCV (Positive Crankcase Ventilation) valve under two engine operating conditions. Two cross-section views of the valve are stacked vertically. In both views, flow arrows enter from the left, labeled 'FROM CRANKCASE AND/OR ROCKER ARM COVER,' pass through the valve body containing a spring-loaded plunger, and exit to the right toward an arrow labeled 'TO INTAKE MANIFOLD.' The top illustration is captioned 'LOW SPEED OPERATION—HIGH MANIFOLD VACUUM,' showing the valve plunger pulled toward the manifold side by strong vacuum, restricting flow. The bottom illustration is captioned 'HIGH SPEED OPERATION—LOW MANIFOLD VACUUM,' showing the plunger positioned so the spring is extended, allowing greater flow through the valve. A reader can learn from this diagram how the PCV valve's internal tapered plunger and spring modulate crankcase vapor flow into the intake manifold depending on manifold vacuum level and engine speed. The document contains no year, make, model, engine, or part number information — it is a generic PCV valve operation diagram uploaded to a 1992 Ford Bronco gallery.

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Frequently asked questions

What does this PCV valve cutaway diagram show?: It shows two cross-section views of a PCV valve: one during low speed operation with high manifold vacuum, and one during high speed operation with low manifold vacuum, with flow arrows from the crankcase and/or rocker arm cover to the intake manifold.
Where does the flow through the PCV valve come from and go to?: Flow enters from the crankcase and/or rocker arm cover and exits to the intake manifold.
How does manifold vacuum relate to engine speed in this diagram?: The diagram labels low speed operation as high manifold vacuum and high speed operation as low manifold vacuum.
How does the PCV valve position differ between low and high speed operation?: In the low speed/high vacuum view, the spring-loaded plunger is drawn toward the intake manifold side, restricting flow; in the high speed/low vacuum view, the plunger sits with the spring extended, allowing more flow to the intake manifold.