Update: FYI still out of stock.

I have a question. For the turbo diesel 300D brake booster vacuum hose, the two nipple check valve type, the nipple with the white ring base (0.6 coded) will freely pass air when blowing through it or drawing on it.
The second nipple, black base, and farthest from the brake booster ( 0.5 coded) does not pass air freely (or at all by mouth) either way. I have two of these assemblies and they act the same.

How does the system work? How does the check valve interact with each individual nipple?? In other words,what is the mechanical function of each nipple having different restriction codes?



Thanks. I am trying to figure this out academically.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD