PCV Valve Purpose?
PCV Valve Purpose? I was thinking about it today, and I can't come up with a good reason for the PCV valve. Obviously it's a check valve that only lets air through one way, but the air is only going to flow through the valve one direction anyways when there in vacuum in the intake manifold. So what is the PCV valve stopping from going the other way, and when? Just curious, that's all.
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Joined: Apr 2002
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From: Cincinnati, Ohio
The PCV sucks out the blowby gases that get past the rings and into the crankcase. From that standpoint it could be considered an emissions device. There are two big benefits to keeping one. If the gases aren't evacuated the oil gets saturated with contaminents and the effective life of the oil is greatly reduced. The other reason is you will get a nasty smell from the engine bay if you just vent to the atmosphere.
I dont think thats what he's asking... He wants to know why, if there is always positive pressure coming from the case, is there a check valve, and not just a piece of hose.... basically, why would there be pressure coming from the intake?
Originally Posted by HawkFanatic
I dont think thats what he's asking... He wants to know why, if there is always positive pressure coming from the case, is there a check valve, and not just a piece of hose.... basically, why would there be pressure coming from the intake?
I know the purpose of the PCV system, to ventilate the crankcase using engine vacuum, but why is there a check valve? What is the valve stopping that could go from the intake into the valve covers? Or... as said, why not just get rid of the valve and use a straight through piece of hose. Maybe the PCV valve is some sort of restrictor?
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Joined: Apr 2002
Posts: 1,755
Likes: 2
From: Cincinnati, Ohio
O.K. you forced me to do some reading. The valve varies flow. At idle when blowby is minimal it pulls the least from the crankcase. At WOT when there is little or no vacuum and maybe some crankcase pressure the valve will open internally to flow the most. The system can also be overwhelmed as those that use catch cans know. Backfire and possible explosion was the reason for a one way valve. The forced induction crowd know that it is really not that good of a check valve though and almost everybody adds an additional one way check valve.
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