Description of Krank vents and Catch cans

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Joined: Sun Feb 08, 2015 5:05 am

Description of Krank vents and Catch cans

Postby Justin » Sun Feb 08, 2015 11:48 pm

I was trying to figure out what Krank vents and catch-cans were today by searching etc. after a while I got a vague idea, but thought some hand sketches might help me, which they did. I think I understand how these devices work now.

I decided to take it a step further and draw the sketches up on PC, then maybe post to Wiki.

Do you think the following descriptions and attached diagrams make sense? More importantly are they correct? . . . The numbered descriptions go with the numbered sketches.

1) Low load, the crankcase vapors are pulled into the plenum thru the PCV valve. This valve meters the flow so there is not so much flow that it affects engine operation.

2) As the load increases, blow-by also increases, possibly overrunning the PCV valve, . . . the excess blow-by vents into the intake

3) Once the load increases to the point that the plenum pressure is greater than the crankcase (atmosphere), then the PCV closes. . . . At that point ALL of the blow-by exits out the vent tube to the intake.

4) If the PCV is bad, and leaks, it could allow boost pressure to leak into the crankcase, causing even more flow out the other side into the intake. Could the crankcase become pressurized? That would only seem possible if the blow-by and boost leak is so great that it overpowers the vent tube.

5) The addition of a catch can in the vent tube could clean up the vapors, keeping the intake, turbo, and intercooler line cleaner.

6) If the catch can is vented to atmosphere, then that would eliminate all the contamination from the intake, but would be going directly into the air we breath.

7) The installation of Krant vents creates a vacuum in the crankcase during low loads (because the vent tube is now closed).
There is a claim that this could possibly increase power by placing a vacuum on the underside of the piston. That would make sense when considering the power stroke and intake stroke, because the vacuum would pull the piston down. It seems though that advantage would be eliminated during the compression and exhaust stroke when the piston is moving back up.
One sure benefit of a vacuum in the crankcase would be that it would be nearly impossible for oil to leak out of seals from crankcase to atmosphere under these conditions.

8) Under boost, the Krank vent equipped engine would act similar to condition 3 above, except that the upper Krank vent is certain not to leak like the stock PCV might.

9) & 10) no diagrams . . . Catch cans could be installed with Krank vents, similar to 5) and 6) above

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