CDR Valve

[Garbage_Mechan]

There will be vacuum if the air filter is plugged.
That is what the little plastic graduated air filter restriction gauge indicates on many diesel engines, especially equipment where filters plug up often.

 

[Thewespaul]

It regulates blowby by pulling crankcase pressure into the intake so you're not blowing your dipstick out and causing oil leaks.

 

[Garbage_Mechan]

But once again the CDR does not go a dang thing under normal operations except be a connector between manifold and crankcase. A hose or tube would do the same thing.

 

[Macrobb]

Yup; under normal conditions, you could just hook it up with a piece of hose.

Seriously... there's no metering going on here - engine creates blow by(lots of it); it pulls oil droplets along with it, at which point they get sucked into the intake manifold and burned.
IDIs have massive ring gaps, meaning massive blow by no matter what. New engines will have blow by, old ones will have it. I noticed no real difference between one pre-rebuild 7.3 idi and post-rebuild, even though pre-rebuild it used about 1 quart every 60 miles, and post-rebuild it didn't use any noticeable amount of oil.
There was still a ton of blowby going through the CDR, and there was still oil droplets attached to it.

(Note: I had also installed a brand new CDR on it, pre-rebuild, before I understood why it doesn't matter at all).

also, vacuum:
Diesels do create vacuum - an engine is an air pump. The vacuum, however, should be relatively low unless the incoming air is restricted. The more restriction, the more vacuum and the less power the engine makes.
You aren't going to be getting enough to run anything with(and the lower the vacuum the better), which is why you have a mechanical vacuum pump.