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Electro-hydraulic actuators (EHAs), replace hydraulic systems with self-contained actuators operated solely by electrical power. EHAs eliminate the need for separate hydraulic pumps and tubing, because they include their own pump, [ 1 ] simplifying system architectures and improving safety and reliability.
A pneumatic actuator is similar to a hydraulic one but uses a gas (usually air) instead of a liquid. [8] [9] Compared to hydraulic actuators, pneumatic ones are less complicated because they do not need pipes for the return and recycling of the working fluid. On the other hand, they still need external infrastructure such as compressors ...
Hydraulic motors usually have a drain connection for the internal leakage, which means that when the power unit is turned off the hydraulic motor in the drive system will move slowly if an external load is acting on it. Thus, for applications such as a crane or winch with suspended load, there is always a need for a brake or a locking device.
The CP system generates large power losses if the machine works with large variations in load pressure and the average system pressure is much lower than the pressure setting for the pump regulator. CP is simple in design, and works like a pneumatic system. New hydraulic functions can easily be added and the system is quick in response.
A servo valve receives pressurized hydraulic fluid from a source, typically a hydraulic pump. It then transfers the fluid to a hydraulic cylinder in a closely controlled manner. Typically, the valve will move the spool proportionnaly to an electrical signal that it receives, indirectly controlling flow rate.
A fluid coupling consists of three components, plus the hydraulic fluid: The housing, also known as the shell [5] (which must have an oil-tight seal around the drive shafts), contains the fluid and turbines. Two turbines (fanlike components): One connected to the input shaft; known as the pump or impeller, [5] or primary wheel input turbine. [5]
The motor may be attached to the end of the actuator. The drive motor is of typical construction with a solid drive shaft that is geared to the drive nut or drive screw of the actuator. Compact linear actuators use specially designed motors that try to fit the motor and actuator into the smallest possible shape.
A hydraulic cylinder is the actuator or "motor" side of this system. The "generator" side of the hydraulic system is the hydraulic pump which delivers a fixed or regulated flow of oil to the hydraulic cylinder, to move the piston. There are three types of pump widely used: hydraulic hand pump, hydraulic air pump, and hydraulic electric pump.