Posted this in the tech forum but did not get much back:

What does the vacuum line that I have outlined in yellow do? I tried to change it out to a Samco vacuum line but, it appears to have a check valve in the line at the red X. (That is probably why it has an arrow and "eng" written on the hose. )

Anyone change this line out and remove/replace the check valve?

Maybe I will just buy an extra from Lokey next time and try to take it apart and replace the check-valve into the Samco line.

 

Brake booster. That's the reason for the check valve. It only needs vacuum.

 

What's a "brake booster"?

 

I gave you an answer within 30 min of your orig posting..........

 

Still trying to see if anyone has changed the line out. . . Does not look like it.

 

That hose has a check valve that maintains a vacume on your brake master cylinder so that you dont have to pump the pedal to get the brakes to work......

 

So then it holds a certain pressure so that the brakes work... Interesting. I guess any pressure over a set limit and it "purges" itself, but in what direction? Toward the plenum or away from it? (must be away from it, no?)

 

No, it only lets the brake booster see vacuum. When your car is idling it creates vacuum that that helps "power" your brakes when at partial and low throttle.(This is over simplifying it so no one give me a long explaination) The check valve only lets the "brake booster" see vacuum. If it saw boost it would make it more difficult it hit your brakes. Kinda like not using a 1:1 FPR. As boost goes up the injector has to overcome the positive manifold pressure. Check valves are kind of like one way valves they only let air flow in one direction and when it reverts back it closes down the "flap". These are used very often in Turbocharging a NA car such as a Honda where if the ECU sees positive pressure or boost it will throw a code and go into limp. You install these check valves to fight this problem.