Of the hydrokinetic devices, the scoop-trimming and scoop-control units require that a mechanical motion be imparted to the scoop tubes for control, and some device must be furnished to provide this motion. This may be a hand crank on a manual control system. Simple mechanical systems are often used—a typical example is a weighted float with a rope connected to the scoop tube, controlling level in a tank. However, most installations utilize electric, electrohydraulic, hydraulic, or pneumatic actuating devices. It is not surprising that the pipeline and refinery industries use electrohydraulic actuators similar to those used on valves. The electric utility industry prefers pneumatic or electric damper operators. The only criterion for actuator selection is compatibility with the other elements of the control system.

The leakoff devices require a signal to the control valve. At present, this is standardized as a hydraulic-pressure signal, although special transducers would permit the use of other types of signals. The hydrodynamic devices are available with manual level control (which could be adapted to actuators) or with closed-loop constant-pressure or constant-temperature systems. All hydroviscous drives utilize oil pressure applied to a piston to "clamp" or vary the spacing of the disks. This hydraulic pressure may be varied by almost any type of signal, provided that the proper servos are utilized. Thus the signal may be electric, hydraulic, or pneumatic.

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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