Folks, besides my Diesel Chief Engineer License, I am also a Steam C/E......and when working around steam you must learn a bit about Vacuum.....

When evacuating something like a condenser, or in this case the Car's Vacuum System (Engine Controls, Brake Assist, AC Climate control, Door Locks, etc.)....if the system is tight you will have a large volume of atmosphere pumped from the system, gradually diminishing until your maximum vacuum is attained, probably about 25-26 in/hg......if you are pumping from a good, tight system there should be very little atmosphere to be removed after this point.....However if you have leaks, whatever the volume of atmosphere that the leak or leaks will allow, will continue to be pumped (evacuated) from the system....

I don't know if this was a design consideration at MB, (the discharge of the vacuum pump to the crankcase) but.....on larger Diesels it's a good idea to maintain a very slight positive pressure within the crankcase....this helps to eliminate some of the contributing factors that will allow a crankcase explosion to occur.....large Diesels also have explosion doors that will rapidly relieve internal pressures in an attempt to minimize structural failure and shrapnel....I have experienced 1 (one) crankcase explosion and an associated fire....and I never want to see another......

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG