Crank case ventilation pipes in Corolla EE-100 XE

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Crank case ventilation pipes in Corolla EE-100 XE

The corolla XE 98 model (2E engine) has two pipes in tappet cover for crankcase ventilation. First pipe is directly connected to the intake but the second pipe is through a valve in tappet cover (called 'positive crankcase ventilation 'PCV' valve). What is the purpose of that valve?? That is a one way valve but what is its use ??

Gari.pk User 5173 asked on 26 Jul 2010 13:27:40 pm

1 Answer

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Mohsin - on 26 Jul 2010 13:27:52 pm

"The valve is simple, but actually performs a complicated control function. An internal restrictor (generally a cone or ball) is held in "normal" (engine off, zero vacuum) position with a light spring, exposing the full size of the PCV opening to the intake manifold. With the engine running, the tapered end of the cone is drawn towards the opening in the PCV valve, restricting the opening proportionate to the level of engine vacuum vs. spring tension. At idle, the intake manifold vacuum is near maximum. It is at this time the least amount of blow by is actually occurring, so the PCV valve provides the largest amount of (but not complete) restriction. As engine load increases, vacuum on the valve decreases proportionally and blow by increases proportionally. Sensing a lower level of vacuum, the spring returns the cone to the "open" position to allow more air flow. At full throttle, there is nearly zero vacuum. At this point the PCV valve is nearly useless, and most combustion gases escape via the "breather tube" where they are then drawn in to the engine's intake manifold anyway"
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