F 150 4WD Pickup V8-281 4.6L VIN W EFI (1997)
Vacuum Brake Booster Check Valve: Description and Operation
The power brake booster check valve.
1. Is located on the front of the power brake booster.
2. Is positioned between the power brake booster and the power brake booster hose.
3. Closes when the engine is turned off.
4. Is part of the power brake booster, and is not replaced separately.
5. In the closed position, traps engine vacuum in the power brake booster.
6. Reserve vacuum allows several power assisted brake applications with the engine off.
The function of the power brake booster check valve is to allow manifold vacuum to enter the power brake booster and prevent the escape of vacuum in
case manifold vacuum is lost during sustained full throttle operation.
