Hydraulic Drives and Actuators

Description A hydraulic drive consists of three major parts: The generator (such as a hydraulic pump) driven by an electric motor, a combustion engine or a windmill (this guides and controls the system) and an actuator (such as a hydraulic motor or a hydraulic cylinder) to drive the machinery.

Advantages It uses 'incompressible' fluid which results in a greater, more efficient & consistent work or power output A leakage in a hydraulic system is easier to spot during ground maintenance operations compared to a pneumatic system leakage. Hydraulic fluid operates very well in a very hot working environment, it is able to sustain its airworthiness viscosity, density & fluid temperature even if it subjected under extreme heat.

Disadvantages Hydraulic fluid is highly corrosive to most of the aircraft materials. Due to the heavy loads experienced in a typical hydraulic system, structural integrity is a must which also means higher structural weight for the aircraft in addition to the weight of its hydraulic lines, pumps, reservoirs, filters, etc. Hydraulic system is susceptible to contaminations & foreign object damage. Mishandling and constant exposure to hydraulic fluid and its gas fumes without proper equipment and precautions is a health risk. If disposed improperly, a hydraulic fluid is an environmental hazard.

Different Types of Hydraulic Motors Hydraulic gear motors - Epicyclic gear motor Hydraulic vane motors - Balanced vane motor Hydraulic Piston motors - Axial piston motor -Radial piston motor Part-turn actuators - Rotary actuator - Rack and pinion actuator

Hydraulic Geared Motors Gear motors and axial piston motors are high speed motors. If your operation requires a lower speed, you can reduce the output speed of the shaft by using gears. The operating pressure of gear motors is usually quite low: between 100 and 150 bar. Modern gear motors, however, are capable of operating at continuous pressures of up to 250 bar. Key features of gear motors:Low weight and size Relatively high pressures Low cost Wide range of speeds Wide temperature range Simple and durable design Wide viscosity range

Epicyclic Gear Motors Epicyclic gear motors are also called orbit motors, gear ring motors or gerotor motors. Unlike gear motors, the orbit motor has very low oil leakage. The motor can produce large torques at very slow speeds (approximately 5 rpm). Key features of epicyclic gear motors, gear ring, orbit or ge-rotor motors are: Low oil leakage High torque at low speeds Large displacement volume Relatively small size Low noise level

Parameters for gear motors Typical parameters for a gear motor are: Displacement volume: 3 to 100 cc Maximum pressure: up to 250 bar Range of speeds: 500 to 4,000 rpm Maximum torque: up to 400 Nm Typical parameters for a epicyclic motor are: Displacement volume: 10 to 1,000 cc Maximum pressure: up to 250 bar Range of speeds: 5 to 1,200 rpm Maximum torque: up to 4,000 Nm

Hydraulic Vane Motors Hydraulic vane motors are used in both industrial applications, such as screw-drive and injection molding, and mobile applications, such as agricultural machinery. Hydraulic vane motors have less internal leakage than gear motors and are therefore better suited for lower speeds: about 100 rpm minimum. The maximum operating pressure of hydraulic vane motors is between 100 and 140 bar, and they're used in both hydraulics and pneumatics. Key features of hydraulic vane motors are: Low noise level Low flow pulsation High torque at low speeds Simple design Easy serviceability Vertical installation friendly

Parameters for vane motors Typical parameters for vane motors are: Displacement volume: 9 to 214 cc Maximum pressure: up to 230 bar Range of speeds: 100 to 2,500 rpm Maximum torque: up to 650 Nm

Part Turn Actuators Part-turn actuators are mainly used for bunker slides, opening butterfly valves, and for push, pull, lift and mix operations. This type of actuator, also known as a rotary actuator, can only rotate left or right over an angle of 300°. They operate at pressures around 70 bar. Part-turn actuators are much smaller than cylinders and do not have any external moving parts. Part-turn actuators are very simple in design. There are two versions: one has two wings on the axle, and the other one has two internal dividers. This construction brings the swivel bracket back to around 120° and doubles the torque. The first version is prone to a low, continuous leakage rate along the wing. This means that, during operation, the rotary actuator must be under constant pressure in order to perform properly.