vacuum check valve

[Hemersam]

I discovered the check valve (the thing is colored black and blue) on my '78 280SE which is in the vacuum line to the door locks is bad.  I bought a new one at the MB dealership yesterday; it is colored black and white. Like a dummy (I know, I know), I didn't ask which way it goes in the vacuum line, i.e., does the white part face the manifold end or the firewall end of the line? Or does it make any difference? Appreciate an answer.
Hemersam
I'm trying to learn about all this "stuff." Really, I am.   

[koan]

Black and white (with a red stripe?) valves are not the same as blue and black valves.

Blue and black seal completely one way. The other has a controlled "leak", where vacuum needs to be applied quickly but released slowly (or the other way round), used in ignition and emission systems

Black to source of vacuum , blue to door lock reservoir (through firewall).

koan

[Hemersam]

  Koan: Thanks a bunch for replying, but now I'm confused. The MB dealership gives me the wrong check valve (I should be surprised?)?  The old one in my car is black/blue, but the new one is black/white (NO red strip). I think I'll take the thing back to the dealership and buy the right one from one of the local suppliers (whose one is black/blue). Frustrating, yet another reason to avoid dealerships if at ALL possible!  Thanks for your info; you guys are great!
Hemersam
Garland, Texas, USA

[craigb]

When fitting one i just sucked on each end and you will soon know which way stops air etc. ie. you want to be able to suck to the manifold.

[koan]

Well maybe the standard one way vacuum vale is now black and white without a stripe.

I haven't bought one for a few years but the black/white/red item was about 5 times the price of the black/blue item.

Did the M-B supplied item have a part number?

Might be able to find out if the old part supercedes to what you were given.

koan

[Hemersam]

  Koan: the invoice shows the following: 11OG 123-800-00-78 (I think that's correct). Does this help identify anything?  I notice that some parts websites show the part to look exactly like my old one (black/blue). Confusing.
Hemersam   

[koan]

It looks like the valve is correct. I can't find the part number here but AutoHausaz show your valve and the blue/black with the same description. By those descriptions black/white/red must be a metered valve - meaning it "leaks" one way.

koan