Advantages of Hydraulic Control

There are many unique features of hydraulic control compared to other types of control. These are fundamental and account for the wide use of hydraulic control. Some of the advantages are the following:

1. Heat generated by internal losses is a basic limitation of any machine. Lubricants deteriorate, mechanical parts seize, and insulation breaks down as temperature increases. Hydraulic components are superior to others in this respect since the fluid carries away the heat generated to a convenient heat exchanger. This feature permits smaller and lighter components. Hydraulic pumps and motors are currently available with horsepower to weight ratios greater than 2 hp/lb. Small compact systems are attractive in mobile and airborne installations.

2. The hydraulic fluid also acts as a lubricant and makes possible long component life.

3. There is no phenomenon in hydraulic components comparable to the saturation and losses in magnetic materials of electrical machines. The torque developed by an electric motor is proportional to current and is limited by magnetic saturation. The torque developed by hydraulic actuators (i.e., motors and pistons) is proportional to pressure difference and is limited only by safe stress levels. Therefore hydraulic actuators develop relatively large torques for comparatively small devices.

4. Electrical motors are basically a simple lag device from applied voltage to speed. Hydraulic actuators are basically a quadratic reson.amcc from flow to speed with a high natural frequency. Therefore hydrauliic actuators have a higher speed of response with fast starts, stops, and spee:d reversals possible. Torque to inertia ratios are large with resulting high acceleration capability. On the whole, higher loop gains and bandwudths are possible with hydraulic actuators in servo loops.

5. Hydraulic actuators may be operated under continuous, intermit tenit, reversing, and stalled conditions without damage. With relief valwe protection, hydraulic actuators may be used for dynamic breaking. Larg

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