Oil seal vacuum tolerance

[EngJW]

We are installing a postive crankcase ventilation system on an old engine. The pcv valve creates a vacuum in the crankcase of about 7 inches of water. We are concerned about the effect of vacuum on seal performance, and if this vacuum is enough to draw dirt into the engine. The catalogs I have only specify the maximum positive pressure. Can anyone help?

Thanks,
John Woodward

 

[Onno]

1 atm. of differential pressure over a surface produces a force of 100 kg/m^2. So, depending on the dimensions and construction of the seal you can make an evaluation of the force. In my experience overpressure can have very different effects on seals if they are used in vacuum appliances. This is logical since all the forces are loading the seal in an opposite way.
7 inches of water can be absolute or relative. Relative this under-pressure does not produce a big force.
However 7 inches water absolute nearly produces the full force : 100 kg/m^2.
Finally: if the seala leaks due to a vacuum load it "definitely" will take in dirt (or whatever else is available for mass transport).