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  #891  
Old 11 Hours Ago
kitabel kitabel is offline
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Originally Posted by bustert View Post
allow vehicles to ford deep water without water intrusion
How would it do that? PCV valve is not a 1-way valve, it's always open (the area depends on engine vacuum).
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  #892  
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Originally Posted by kitabel View Post
PCV valve is not a 1-way valve
I thought it was.
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  #893  
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It's only a one way valve with the assist from vacuum to close it.
Without vacuum, it's a loose open fit to atmosphere.
Of course, pressure exerted from outside - in can also force it closed to a one way valve.
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  #894  
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Thanks for that; interesting.
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  #895  
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Transpose that thought to someone opening the oil cap with the engine shut down.
At rest, the system inside should be at atmosphere.
Else, the breather is stuck closed and not allowing pressure to equalize.
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  #896  
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Originally Posted by Hippysmack View Post
It's only a one way valve with the assist from vacuum to close it.
Without vacuum, it's a loose open fit to atmosphere.
Of course, pressure exerted from outside - in can also force it closed to a one way valve.
Here we go again. Vacuum and pressure are two sides of the same coin. PCV valves allow one way flow, out from the crankcase. There's air flow because there's a pressure differential. Some valves have more "preload" than others needing more pressure differential before they allow flow.

Vacuum or pressure depends on your perspective. If you were in the crankcase while the pistons are coming down you'd see atmospheric pressure outside (relatively) as a vacuum.
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It's always open.
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Originally Posted by Tomcatt View Post
Vacuum and pressure are two sides of the same coin. PCV valves allow one way flow, out from the crankcase. There's air flow because there's a pressure differential. Some valves have more "preload" than others needing more pressure differential before they allow flow.

Vacuum or pressure depends on your perspective. If you were in the crankcase while the pistons are coming down you'd see atmospheric pressure outside (relatively) as a vacuum.
I see what you are getting at.
But the source of air movement usually gets top billing.

In consideration of stop motion of a piston raised from the bottom to the top and vise versa.

The term “vacuum” is used to describe the zone of pressure below atmospheric pressure.
Vacuum is a negative gauge pressure, usually referenced to the existing standard barometric pressure where the equipment will operate.

If you are looking from inside out and watching pressure go out the breather hose, it could be perceived as vacuum (or other source) from the atmosphere sucking the air from the engine. \\
However, atmosphere cannot move without opposing forces affecting it.

Piston downstroke, by default, is the catalyst that moves air out of the engine starting when the piston is fully topped out so we label the offending party as positive pressure.


Piston upstroke, by default, is the catalyst that pulls air into the engine starting when the piston is fully bottomed out.
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This is a Ford F-150 PCV valve.
The source that opens and closes it is different than the Sportster but the operation of it is expressed.
Notice the notations.
The vacuum line is installed on the top nipple and the hose is ran from the carb / intake (negative pressure is the source affecting the valve).
The bottom portion is installed into the valve cover.
(the cover over the breathing system in this instance).

At idle, it shows high intake vacuum and low CC pressure flow.
At that point, the pressure is pulling on top of the disc.
There is still however some portion of flow thru the PCV at idle since the top disc does not fully seal to the top of the housing.
The disc rises toward the top position due to higher intake vacuum pressure.

As speed increases, vacuum lowers and the disc does also.
However, at acceleration there is lower intake vacuum and higher CC pressure flow (higher windage in the CC).

Only during a backfire through the intake / carb does the valve fully close (positive pressure is the source affecting the valve).
At that point, the pressure is pushing on top of the disc.

Now notice the location of the spring. It is below the disc, not attached to it.
Therefore, the disc will not fully close off CC pressure unless there is a positive force pushing the disc from above.
With the engine shut down, there is no force to close the disc down.
This will equalize pressure between atmosphere and the CC just as Sporty breathers do.
It takes a pressure source (either positive or negative) to turn it into anything more than a decoration.

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