Hydraulic system

Posted on Feb 5, 2014

A hydraulic or hydrostatic drive system or hydraulic power transmission is a drive or transmission system that uses hydraulic fluid under pressureto drive machinery. The term hydrostatic refers to the transfer of energy from flow and pressure, not from the kinetic energy of the flow. Such a system basically consists of three parts.

Hydraulic system
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The generator (e. g. a hydraulic pump, driven by an electric motor, a combustion engine or a windmill ); valves, filters, piping etc. (to guide and control the system); the motor (e. g. a hydraulic motor or hydraulic cylinder ) to drive the machinery. Pascal`s law is the basis of hydraulic drive systems. As the pressure in the system is the same, the force that the fluid gives to the surroundings is therefore equal to pressure x area. In such a way, a small piston feels a small force and a large piston feels a large force. The same counts for a hydraulic pump with a small swept volume, that asks for a small torque, combined with a hydraulic motor with a large sweptvolume, that gives a large torque. By throttling the fluid between generator part and motor part, or by using hydraulic pumps and/or motors with adjustable swept volume, the ratio of the transmission can be changed easily. In case throttling is used, the efficiency of the transmission is limited; in case adjustable pumps and motors are used, the efficiency however is very large. In fact, up to around 1980, a hydraulic drive system had hardly any competition from other adjustable (electric) drive systems. Nowadays electric drive systems using electric servo-motors can be controlled in an excellent way and can easily compete with rotating hydraulic drive systems. Hydraulic cylinders are in fact without competition for linear (high) forces. For these cylinders anyway...

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