I am slowly. Working my way into a f/I build. Thinking turbo build. I have an 03 sss. With vacuum brakes and the eletric assist unit on the booster. What check valve are you using to prevent the brakes from being boosted? I know many say its internal. But I want a little extra insurance.

 

Most brake boosters already have a valve that holds vacuum in the booster when engine is not running. If you think about it, how does it stop air from going into the booster when engine shuts off? The vacuum line where it connects to the booster actually connects to a plastic valve. That valve prevents air from going into the booster. Keep reading if you want to know why and how it is done.

Compare that to what you are asking about. "Vacuum" is one of those things that does not actually exist. What actually is happening it that the brake booster has almost all of its air removed. The outside air is trying to get into the booster to equalize the pressure. It cannot get in when engine is running, because the engine intake manifold has less air in it at idle, and the brake booster is connected to the intake manifold. They both have about the same air pressure(almost 0psi). If you open the throttle on the engine, that creates a large leak in the intake manifold, outside air pressure pushes in, driving the intake pressure up. The brake booster cannot allow that to happen, otherwise you have no power assist. That means that it already has a device that stops the engine from pushing air into the booster.
If you have a device that pressurizes the intake manifold to a higher level than atmosphere, the brake booster already has a device to prevent the high pressure from entering it.

Something to keep in mind, suction does not exist(just ask your wife), it is actually air being forced into a space that does not have enough air in it.

 

i use these 1 way valves from this place

Aluminum One-Way Check Valve 10mm Barbed

 

Never ran one with any of my boosted setups. Whats it matter if the booster gets boosted? You wont be on the brakes AND on the throttle at the same time. Brake stands done properly engage the brakes then rev the engine up, so the booster starts in vacuum so the pedal has minimal effort