Pneumatic clutches are equipment drive assemblies that contain pneumatic 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. Pneumatic clutches transmit force from one point to another using compressed air or other gases. Engaging a pneumatic clutch transfers power from an engine to another device such as a transmission and/or drive wheels. Disengaging a pneumatic clutch stops the power transfer, but allows the engine to continue turning.
Pneumatic Clutch Engagement
All pneumatic clutch operation requires some form of spring assistance to couple with a shaft. The two types of spring assistance are spring-actuated clutches, which require power to engage and spring-return clutches, which require power to disengage.
Pneumatic clutch systems are available with a variety of engagement technologies. 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. Pneumatic 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 pneumatic 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.
Pneumatic Clutch Specifications
Selecting pneumatic 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 pneumatic clutches often use shafts that attach to bores or flanges. With some drive shafts that attach to a bore, the output is a drive component such as a pulley, gear, or sprocket. Often, these types of pneumatic clutches are designed to accept several different drive components.
Features and Options of Pneumatic Clutches
A number of support features, many of which are application dependant, are important options to consider when selecting between the myriad pneumatic clutches available. Some of the more common options include adjustable torque, which is used primarily with slip clutches and torque limiters. Users can adjust the torque at which the clutch disengages or slips. Zero backlash clutches allow no play or backlash during the engagement of the load and no load disengagement during a direction reversal. Bi-directional clutches can be set-up to rotate in either direction. A pneumatic clutch with automatic re-engagement uncouples with the load when the torque rises beyond a certain point, but then re-engages when it returns to an acceptable level. Slip indication devices can move a pin radially when an overload occurs, or send an electrical signal to the drive motor. Finally, pneumatic clutches with a feedback system provide an electrical or electronic signal for monitoring parameters such as position, speed, torque, lockup, or slip status.
An industrial pneumatic clutch is 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 pneumatic 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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