Hydraulic Motors and Rotary actuators
Explanation:
Hydraulic motors are powered by pressurized hydraulic fluid and transfer rotational kinetic energy to mechanical devices. Hydraulic motors, when powered by a mechanical source, can rotate in the reverse direction, and act as a pump.
Hydraulic rotary actuators use pressurized fluid to rotate mechanical components. The flow of fluid produces the rotation of moving components via a rack and pinion, cams, direct fluid pressure on rotary vanes, or other mechanical linkage. Hydraulic rotary actuators and pneumatic rotary actuators may have fixed or adjustable angular strokes, and can include such features as mechanical cushioning, closed-loop hydraulic dampening (oil), and magnetic features for reading by a switch.
Motor type is the most important consideration when looking for hydraulic motors. The choices include axial piston, radial piston, internal gear, external gear, and vane. An axial piston motor uses an axially mounted piston to generate mechanical energy. High-pressure flow into the motor forces the piston to move in the chamber, generating output torque. A radial-piston hydraulic motor uses pistons mounted radially about a central axis to generate energy. An alternate-form radial-piston motor uses multiple interconnected pistons, usually in a star pattern, to generate energy. Oil supply enters the piston chambers, moving each individual piston and generating torque. Multiple pistons increase the displacement per revolution through the motor, increasing the output torque. An internal gear motor uses internal gears to produce mechanical energy. Pressurized fluid turns the internal gears, producing output torque. An external gear motor uses externally mounted gears to produce mechanical energy. Pressurized fluid forces the external gears to turn, producing output torque. A vane motor uses a vane to generate mechanical energy. Pressurized fluid strikes the blades in the vane, causing it to rotate and produce output torque.
Additional operating specifications to consider include operating torque, pressure, speed, temperature, power, maximum fluid flow, maximum fluid viscosity, displacement per revolution, and motor weight. The operating torque is the torque that the motor is capable of delivering, which depends directly on the pressure of the working fluid delivered to the motor. The operating pressure is the pressure of the working fluid delivered to the hydraulic motor. The fluid is pressurized by an outside source before it is delivered to the motor. Working pressure affects operating torque, speed, flow, and horsepower of the motor. The operating speed is the speed at which the hydraulic motors’ moving parts rotate. Operating speed is expressed in terms of revolutions per minute or similar. The operating temperature is the fluid temperature range that the motor can accommodate. Minimum and maximum operating temperatures are dependent on the internal component materials of the motor, and can vary greatly between products. The power the motor is capable of delivering is dependent on the pressure and flow of the fluid through the motor. The maximum volumetric flow through the motor is expressed in terms of gallons per minute, or similar units. The maximum fluid viscosity the motor can accommodate is a measure of the fluid’s resistance to shear, and is measured in centipoise (cP), a common metric unit of dynamic viscosity equal to 0.01 poise or 1 mP. The dynamic viscosity of water at 20°C is about 1 cP (the correct unit is cP, but cPs and cPo are sometimes used). The fluid volume displaced per revolution of the motor is measured in cubic centimetres (cc) per revolution, or similar units. The weight of the motor is measured in pounds or similar units.
