<VV> Fwd: PVC Valves Explained?

[jay m]

On 4/13/2013 10:01 PM, Matt Nall wrote:
>   <jaysplace at laserpubs.com>
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> A standard PCV valve has a spring-loaded restrictor, to limit flow at
> high manifold vacuum and allow greater flow at low manifold
> vacuum/higher engine load.
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>   Jay!!  How did you figure this out???  gggg
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> A PC Valve is a ONE WAY CHECK VALVE......  if the are clean.. they rattle????
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oh, yes - it also functions as a check valve. And if it isn't totally 
gummed solid, it will rattle.
But they also have the low/high flow rate function as well.
uh - that is, in my experience and reading,  "normal" PCV valves do.
Dunno what kind of bastard devices were put on Corvairs.

>   The ONE WAY  is to prevent Crankcase Explosions caused by carb Backfires!!!
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> Early units had a just an orifice....with a plunger to clean!!... but many pan gaskets and valve cover / valley cover gaskets were lost!! ggg
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>    Yes there is a difference in orifice size  depending on the engine..and the amount of blowby  expected under normal conditions...but you can enlarge the orifice,  lower the throttle opening and richen the idle Mixture to compensate.
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>    Sadly , a Fixed orifice  allows only so much flow... and with vacuum being highest at idle.. it only gets worse as vacuum falls off...  High Throttle openings....
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> Someone talked about a VENT  being needed to be a "True  PCV  system"......  BS!  A VENT  is what lets Moisture into the crankcase...but we need one for when blowby volume is higher than what the PC valve can flow...
no- look at what blowby consists of - some unburned hydrocarbons, some 
burned hydrocarbons.
Burned hydrocarbons mostly consist of CO2 and H2O - water vapor.

The vent hose goes to the air cleaner so that excess blowby can escape 
the crankcase and be cycled back through the motor.
And so when the PCV actually tries to suck more than there's blowby 
present, you pull fresh air (which will have some water vapor present, 
of course) into the crankcase to purge some of the fumes from the crankcase.

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>    Exhaust powered systems, normally used by drag racers,   can pull enough volume  to cause a negative pressure... there by causing better ring seal..and use no vents!

some racers do use pumps to pull a partial vacuum in the crankcase - I 
doubt it affects ring seal, but it reduces windage loss substantially.
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> Kevin Willson's setup
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> http://corvaircenter.com/phorum/file.php?1,file=27129,filename=HEADERS.JPG
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> http://corvaircenter.com/phorum/file.php?1,file=27131,filename=blowby.jpg
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-- 
Jay