Hydraulic clutches are equipment drive assemblies that contain hydraulically actuated components for connecting two shafts so that they can either be locked together and spin at the same speed, or decoupled and spin at different speeds. They deliver a higher torque per unit volume than other types of clutches and provide fast response times and smooth engagement. Hydraulic clutches transmit force from one point to another using an incompressible fluid such as oil that powers a piston. Engaging a hydraulic clutch transfers power from an engine to devices such as a transmission and drive wheels. Disengaging a hydraulic clutch stops the power transfer, but allows the engine to continue turning. Hydraulic clutches are self-regulating and require less maintenance than many other systems. 

Specifications for hydraulic clutches include torque rating, power, rotational speed, and maximum pressure. Spring-return clutches require power to engage. Spring-actuated clutches require power to disengage. A variety of engagement methods are available. Non-contact clutches uses methods such as magnetic fields and eddy currents. Friction clutches generate friction between contact surfaces. Wrap spring clutches transmit torque from the input to the output through a wrapped spring that uncoils to disengage the clutch. Hydraulic clutches with teeth engage only during stops or at slow speeds. Oil shear clutches achieve drive engagement through the viscous shear of transmission fluid between the clutch plates. Other plate-based clutches control torque with compression springs. Sprags, steel wheels that tip in one direction to wedge between inner and outer races, are clutches that can often transmit more torque than other slip or overrunning devices. Ball detent clutches feature a slip mechanism in which, upon overload, seated balls are dislodged and overcome springs or air pressure engagement. Similarly, pawl clutches overcome spring or air pressure engagement and rotate out of their detent. With roller detent clutches, rollers that are held in place by springs wedge between the inner and outer races to engage the clutch. 

Selecting hydraulic clutches requires an analysis of measurements and mounting configurations. Important measurements include diameter, the cross-sectional width of the assembly; length, the dimension along the axis of rotation; and weight. Shaft configurations can be in-line along the axis of the load, parallel but offset from the axis, or perpendicular (right angle) to the axis. Drive and load connections for hydraulic clutches often use shafts that attach to bores or flanges. With some drive shafts that attach to bores, the output is a drive component such as a pulley, gear, or sprocket. Often, these types of hydraulic clutches are designed to accept several different drive components.  

Industrial or general-purpose hydraulic clutches are designed for a wide variety of power transmission applications. Specialized devices are available for aerospace, automotive, heavy transport, marine, military, and off-road applications. Some hydraulic clutches are designed for use with web tension control, automation, or robotics systems. Other devices are designed for use with conveyor drives and pump motor drives. Power take off clutches (PTO) are typically used with heavy equipment such as dump trucks, snowplows, and tractors.


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