ratchet valve

A valve normally used in the wing-flap system to retain pressure in the flap-actuating cylinder, thereby preventing the flaps from drooping while they are up when the airplane is on the ground and from creeping while they are down when the airplane is in flight. The valve is installed in the wing-flap system between the actuating cylinder and the selector valve. A typical ratchet valve has three spring-loaded adjustable valves as shown in the illustration. Ports A and D are connected to the selector valve, and ports B and C to the actuating cylinder. Valves E and F are primarily relief valves, whereas valve G is a temperature-expansion relief valve. When the selector is in the up position, fluid under pressure from the selector valves enters port A and unseats valves E and F. The fluid can then flow out through port B to the actuating cylinder and move the flaps up. Fluid from the opposite end of the actuating cylinder enters port C and flows around valve F, out through port D, and to the return line through the selector valve. When the flaps reach the full up position, valve E seats. Even though the pressure applied at port A decreases through a leak-type selector valve, the pressure will be retained in the actuating cylinder by valve E; hence, the flaps remain up. When the selector valve is placed in the down position, fluid under pressure enters port D, opens valves E and F, and flows out through port C to the actuating cylinder. Return fluid enters port B and flows around valve E and out through port A to the return line.