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.
Spring loaded accumulators maintain pressure on the brakes. Park brake valve accumulators are used in applications where the aircraft may be parked during the day and are needed to maintain that brake pressure overnight. Typically, ambient air temperature decreases at night, which would cause a corresponding pressure decrease of the brake pressure. The park brake valve accumulator is intended to prevent the brake pressure from falling below the limits needed to hold the aircraft.
Park brake valves may also have pressure switches installed that electrically close when the brake pressure reaches a certain value. This can be set to illuminate a light in the cockpit as feedback for the pilot. Less common is a pressure transducer, which is used to determine the actual pressure in the brake system.
APPLICATIONS: General aviation, light jets, turboprop passenger and cargo aircraft.
FEATURES AND ATTRIBUTES:
• Anodized housing – corrosion protection
• Stop pins for control arm – allows for precise open and closing position of control arm
• Made in America
• Thermal relief valve
• Proximity switch
• Micro switch
• Pressure transducer
• Pressure switch
Operating Temperature (F)
-65° to 275°F
60° to 90° angle
Multiple fluids MIL-PRF-5606, MIL-PRF-83282 and MIL-PRF-87257
0.5 lb to 5.5 lb