You seem to have a mental block regarding the meaning of the word "vacuum". Anything less than atmospheric pressure = vacuum. There are various levels of vacuum, ranging from one you can't feel (fraction of an "Hg) to a full vacuum that would give you a big hickey.... 30"Hg. So the answer is yes.... it is possible for the PCV valve configuration to put the crankcase at a pressure that is less than atmospheric. The fact that any air at all flows from the breather at atmospheric pressure, into the valve cover demonstrates that the crankcase is at a pressure lower than atmospheric. If its at less than atmospheric, by definition it is under vacuum.

 

For all practical purposes there is no reason to say the pcv system puts the crankcase under a vacuum. It is so minute it makes no difference at all and it will just confuse people.

 

Actually, it make very little difference at all. That's why it surprises me that thread after thread you always raise the issue, and make an absolute, but incorrect statement that the PCV system doesn not put the crankcase under vacuum.
Simply stated, is does put the crankcase under vacuum, under certain operating conditions.

 

imo the crankcase is under vacum. a good test to se if your pcv system is working right is to take a small pice of paper an put it over the end of the fresh air hose with the engine running, if it stays on the end of the hose the crankcase has a slight vacum and is working properly. as injuneer stated anything less than atmospheric pressure is vacum.

 

 

Possibly "only" at an idle and it would depend on the engine. As engine RPM increase, piston ring blow-by increases and the PVC system can no longer keep up. End result, hot oily gases build-up in the crankcase (pressurize) and possibly blow-out under pressure if not properly ventilated. Hence the need for crankcase breathers, or vacuum pump. Additionally, the vacuum pumps help mitigate the effects of crankshaft windage.

Check-out these tech artices on crankcase vacuum pumps, which supports my position.

http://www.dragstuff.com/techarticles/vacuum-pumps.html

http://www.gzmotorsports.com/vacuum-pump-guide.html

WD

 

i agree with you on all points, i was just trying to give an example of how the cankcase is under vacum at idle. not much but there is one. imo breathers and vacum pumps are very usefull in a high compression engine that has more than average blow by.