Park brake valves are located in the brake lines between the master cylinders and the brakes. They are used to hold pressure in the brakes on an aircraft as a way of preventing the aircraft from moving when grounded. Park brake valves have two inlet ports or fittings connected to the upstream master cylinders and two outlet ports or fittings connected to the downstream brakes. They are actuated by way of a control arm that is mechanically attached by a rod or a cable to the cockpit.
The pilot’s linear movement of the rod or cable causes rotation of the control arm which rotates the park brake valve’s internal camshaft. This motion of the camshaft opens or closes internal poppets. The poppets allow two-way flow when the valve is in the open position and one-way flow, only from inlet to outlet, when the valve is in the closed position.
The basic park brake valve functionality is as described above. However, additional features are often built into or added onto the park brake valve to meet customer requirements. A micro switch or proximity sensor is a common addition that provides feedback to let the pilot know the position of the control arm.
Thermal relief valves are also commonly added to allow for pressure relief of the brake hydraulics. The heat generated during a stop can migrate into the system when the aircraft is parked. This prevents the brakes from being inadvertently pressurized beyond their design limits.

Park brake valves are located in the brake lines between the master cylinders and the brakes. They are used to hold pressure in the brakes on an aircraft as a way of preventing the aircraft from moving when grounded. Park brake valves have two inlet ports or fittings connected to the upstream master cylinders and two outlet ports or fittings connected to the downstream brakes. They are actuated by way of a control arm that is mechanically attached by a rod or a cable to the cockpit.
The pilot’s linear movement of the rod or cable causes rotation of the control arm which rotates the park brake valve’s internal camshaft. This motion of the camshaft opens or closes internal poppets. The poppets allow two-way flow when the valve is in the open position and one-way flow, only from inlet to outlet, when the valve is in the closed position.
The basic park brake valve functionality is as described above. However, additional features are often built into or added onto the park brake valve to meet customer requirements. A micro switch or proximity sensor is a common addition that provides feedback to let the pilot know the position of the control arm.
Thermal relief valves are also commonly added to allow for pressure relief of the brake hydraulics. The heat generated during a stop can migrate into the system when the aircraft is parked. This prevents the brakes from being inadvertently pressurized beyond their design limits.