# Check valve direction questions.



## The A1 and A2 German (Nov 18, 2002)

After yeilds & searches, and reading through other car forums I'm more confused then ever. I've always been under the impression the arrow on a check valve goes towards the motor...yet reading....others are saying not the case and the arrow points away. Wtf......I just did my B5's vac system and ALL arrows are towards (to) motor. I'm attempting to redo my check valve on my brake booster with a AC Delco 90304535, do cars vary on this issue? I'm trying not only to find this out, but aswell find if that arrow on that check valve goes towards the motor, or towards the bb?

You can see a picture in Google Images: Ac Delco 90304535


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## TBT-Syncro (Apr 28, 2001)

think of it this way and its easy. a brake booster should never see boost, only vacuum.

so take the check valve and blow in to it. The orientation that you can blow through it should always face away from the brake booster.


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## The A1 and A2 German (Nov 18, 2002)

Yes, but I don't have the cv and have to order it, it the nipples are on the wrong side I can't use it.


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## BLSport (Dec 24, 2005)

The arrow on a check valve points in the direction of flow, so it would point away from the brake booster.


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## The A1 and A2 German (Nov 18, 2002)

Just an update. 

It appears in all cases, the arrow always points toward the motor. 

So this works perfect, as it places the nipples ( for accessories) on the boost and vacuum side, so what ever plugs into them would be able to read both. If placed on the other side of the diaphragm, you'd only read vacuum.


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## waabaah (Jun 24, 2006)

Update: NOT all check valves point towards motor and one should not think this way. 

I know what you mean but others may not. What happens if the hose runs parrallel or the hose loops around. 

Like said, that arrow is air flow direction. Like a one way street. Think of a two lane road. (Boost and vacuum). Now pretend that 2 lane road comes up to a one way road. Depending on direction of one way road will tell you if you need to turn around or if you can continue driving down the road. 

In the case of the brake booster, brake booster works off vacuum. It should never see boost. So arrow should point towards the vacuum source.


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