All About Aircraft Hydraulic System Actuators

Hydraulic systems are extremely important for many aircraft, ensuring that they have sufficient power to deploy landing gear, extend flight surfaces, operate cargo doors, and carry out other such processes that require high amounts of strength. In order for the hydraulic system to conduct such actions, they rely on numerous hydraulic actuators which serve to transform the energy of fluid pressure into a mechanical force. In this blog, we will provide a brief overview of hydraulic system actuators, allowing you to become familiar with the most common types and their roles.

A standard actuating cylinder consists of its housing, pistons, piston rods, and seals. The piston operates in a polished bore, and there may be multiple ports on the component that will permit fluid to enter and exit the bore. During operation, the piston is capable of moving forward and backward within the bore, and the piston rod moves in and out of the housing through its open end. The seals are important for preventing fluid leakage, as any pressure loss will cause the hydraulic system to lose its functionality. Actuating cylinders may come in the form single-action and double-action types, meaning that they either can produce powered movement in one direction or two.

With a single-action actuating cylinder, pressurized fluids enter the assembly from the inlet side and begin to push against the piston face. This force causes the piston to shift right, and air will vent out of the spring chamber as the spring is compressed. The movement of the piston will cause the piston rod to shift as well, ensuring that an actuation is carried out. As the fluid pressure is lessened, the force of the compressed spring will cause the piston and piston rod to return to their resting state, also causing fluids to be forced out of the assembly.

Double-action aircraft actuators have two ports, and their operation is managed by a four-way selector valve. If the selector valve is set to the “ON/EXTEND” position, then pressurized fluids will enter the left port of the assembly. As a result, the piston will extend outwards to the right. When the selector valve is set to the “RETRACT” position, however, fluids will enter from the right and cause the piston to be forced out left. When hydraulic actuators have piston rods that operate as discussed, they are considered linear actuators.

Rotary actuators are capable of reaching arc lengths that are 90°, 180°, 360°, or 720° based on their configuration. For aircraft, rotary actuators are most commonly used for nose wheel steering mechanisms when in the form of a rack and pinion actuator. With such types, a long piston has one side machined into a rack so that it can rotate the output shaft while engaged to a pinion. As fluids enter one side of the actuator, the other side will be connected to the return.

Hydraulic motor variations that are piston-type are the most common for hydraulic systems. While similar to hydraulic pumps, the hydraulic motor transforms hydraulic energy into a rotary force. Such motors may be an axial inline or bent-axis type, though the fixed-displacement bent-axis type is the most common. Hydraulic motors may be used for numerous aircraft operations, and examples include the activation of leading edge slats, trailing edge flaps, and the stabilizer trim.

The hydraulic system is very beneficial for aircraft, ensuring an ease of control for numerous flight surfaces and devices. When you are in need of reliable hydraulic actuator components and other aircraft parts, look no further than Fulfillment by ASAP. Fulfillment by ASAP is a premier supplier of aviation, NSN, and electronic parts that have been sourced from top global manufacturers that we trust. As you explore our offered components, we invite you to take advantage of our provided RFQ services in order to receive competitive quotes for your comparisons. Get started today and see why customers choose to rely on Fulfillment by ASAP for all their operational needs.


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