<E30> brake booster vacuum lines

[Rob Ellis <aellis@xxxxxxxxxxxxxxxx>]

My brake booster has a vacuum line that runs to a valve then splits in 
two: one goes to the intake manifold, the other meets with the rubber 
intake boot then goes to the manifold.

Can someone explain what the valve does?  Why is the system setup this way?

I'm trying to understand this so I can do some troubleshooting:  my car 
makes a whirring/buzzing noise on the first cold startup of the day.... 
then the brake boost kicks in (takes about 5-10seconds of driving).  I 
also seem to have a mysterious vacuum leak despite ALL new gaskets and 
rubber... except for these booster hoses.  Maybe the two are related?

Thanks for any info,
Rob

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