What happens when the shuttle valve is placed in the ON position?

What happens when the shuttle valve is placed in the ON position?

• A. Ventilates the hydraulic system
• B. Applies static pressure to the brakes
• C. Releases pressure from the brakes
• D. Engages the parking brake

Answer: (B)

A shuttle valve serves as a pressure selector that feeds the brake line from whichever pressure source is active. When it is ON, it routes hydraulic pressure to the brake lines, so brake fluid is held at a higher, steady pressure and the brakes are applied. This is why you’ll see the brakes engaged when the valve is ON—the system maintains static pressure in the brake circuit to push the pistons and clamp the brakes. It doesn’t vent or release pressure, and it doesn’t actuate a parking brake by itself. The idea behind this arrangement is to keep braking available by maintaining pressure in the line, even if one source drops off, the other can still supply the brakes through the valve.

A shuttle valve serves as a pressure selector that feeds the brake line from whichever pressure source is active. When it is ON, it routes hydraulic pressure to the brake lines, so brake fluid is held at a higher, steady pressure and the brakes are applied. This is why you’ll see the brakes engaged when the valve is ON—the system maintains static pressure in the brake circuit to push the pistons and clamp the brakes. It doesn’t vent or release pressure, and it doesn’t actuate a parking brake by itself. The idea behind this arrangement is to keep braking available by maintaining pressure in the line, even if one source drops off, the other can still supply the brakes through the valve.