How PCV Flow Changes With Engine Speed & Load?

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PCV Flow Change:

The flow of a PCV valve is calibrated for a selected engine application. For the system to function normally, therefore, the PCV valve must adjust the flow as operating conditions change.


Engine OFF:

When the engine is off, the spring inside the valve pushes the pintle shut to seal the crankcase and stop the escape of any residual vapors into the atmosphere.


Engine ON:

When the engine starts, the vacuum within the manifold pulls on the pintle and sucks the PCV valve open. The pintle is pulled up against the spring and moves to its highest position. But the tapered shape of the pintle doesn’t allow maximum flow during this position. Instead, it restricts flow therefore the engine will idle smoothly.



The same thing happens during deceleration when the intake vacuum is high. The pintle is pulled all the high to scale backflow and minimizes the effect of blowby on diesel emissions.


Engine Cruising:

When the engine is cruising under light load and at part throttle, there’s less intake vacuum and fewer pull on the pintle. this permits the pintle to slip down to a mid-range position and permit more airflow.



Under high load or hard acceleration conditions, intake vacuum drops, even more, allowing the spring inside the PCV valve to push the pintle valve even lower to its maximum flow position. If blowby pressure builds up faster than the PCV system can handle it, the surplus pressure flows back through the breather hose to the air filter and is sucked into the engine and burned.


Engine Backfire:

In the event of an engine backfire, the sudden rise in pressure inside the manifold blows back through the PCV hose and slams the pintle shut. This prevents the flame from traveling back through the PCV valve and possibly igniting fuel vapors inside the crankcase.

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