Since the hydraulic pressure cause greater valve movement, the valve admits higher air pressure in the power cylinder that results in stronger braking action.
Vacuum Brakes
In this system, when brakes are applied, air gets exhausted from the cylinder head, while air pressure acts on the pistons rear side to exert a pull on the rod attached to the piston.
If the brake valve is closed, the pressure is equal on both sides of the piston and no pull is exerted.
Controlled, Stab and Downhill Braking
Also referred as squeeze braking, controlled braking method means applying the brakes maximally to the point of not locking the wheels. When using control method, try to avoid turning the steering wheel. If steering is absolutely necessary, release the brakes until the tires gain traction. You should do this if the wheels begin to slide.
Stab braking means using the brakes hardly and releasing them the moment the wheels lock up. After this releasing, it will pass a second before the wheels start to roll, so you should stay off the brakes long enough. When the wheels start rolling, apply the brakes again.
