Pneumatic clutches transfer power from one part of a power transmission driveline to another using compressed air or other gas as an operating fluid. Engaging a pneumatic clutch transfers power from an engine to down-train devices such as a transmission and drive wheels. Disengaging a pneumatic clutch stops the power transfer, but allows the engine to continue turning. Pneumatic clutches are superior in their thermal capacity. Air clutches do not generate heat during extended periods of engagement. Pneumatic clutches can be designed to direct air across the clutch plates for cooling. Pneumatic clutches have several other advantages when used in a moving system: Pneumatic clutches transfer power from one part of a power transmission driveline to another using compressed air or other gas as an operating fluid. Engaging a pneumatic clutch transfers power from an engine to down-train devices such as a transmission and drive wheels. Disengaging a pneumatic clutch stops the power transfer, but allows the engine to continue turning. Pneumatic clutches are superior in their thermal capacity. Air clutches do not generate heat during extended periods of engagement. Pneumatic clutches can be designed to direct air across the clutch plates for cooling. Pneumatic clutches have several other advantages when used in a moving system: 

• Source Availability—Pneumatic clutches use air to operate. Air is very abundant and free, so it is easy to restock the clutch system.
• Safety—Because pneumatic clutches run on air, safety hazards are significantly reduced. There are few fires because air is non-flammable, and leakages in the clutch system do not create a hazard for the environment.
• Cost Effectiveness—The initial cost of manufacturing a pneumatic clutch system is lower. Plastics, zinc, and aluminum are affordable materials that are commonly found in pneumatic clutch systems.
• Cleanliness—Air is relatively clean. Pressurized air constantly forces out dirt or debris in the system. Thanks to the limited amount of tubes, the clutch system can be easily disassembled and cleaned.

Specifications

Important specifications to consider while selecting a pneumatic clutch include but are not limited to:

• Torque Rating—The maximum torque rating for the clutch should equal or exceed the application's requirement. 
• Power—The maximum power rating for the clutch.
• Speed—The maximum rotary speed rating. This specification applies only to rotary clutches.
• Maximum Pressure—The maximum pressure for a pneumatic clutch.
• Shaft Configuration—Clutch may be mounted in-line, parallel, or right angle.
• Drive/Load Connection:
  • In-line Shafts—The drive and the load have shafts that attach to a through-bore. 
  • Through Shaft—The drive shaft attaches to a bore and the load is driven through the outer diameter. 
  • Shaft—Pulley/Gear/Sprocket—The drive shaft attaches to a bore and the output is a drive component such as a pulley, gear, or sprocket. These clutches are often designed to accept different drive components. 
  • Flange—The clutch is mounted to the object in motion via a flange.

Several pneumatic clutch engagement methods are available, including:

• Noncontact—Braking action is achieved through a non-contact technology such as a magnetic field, eddy currents, etc. 
• Friction—Friction between contact surfaces transmits power. This is the most common configuration.  
• Toothed—Toothed contact surfaces transmit power without slipping or heat generation. Teeth are engaged only when stopped or running at a slow speed (< 20 rpm). 
• Wrap Spring—A coiled spring wraps downward onto the rotating element. The device is disengaged when the spring is uncoiled via a control tang at its end. 
• Oil Shear—Braking action is engaged via the viscous action of the shearing of transmission fluid. 

Features

Additional capacities can be added to pneumatic clutches. These features help customize the unit to meet special or unique requirements. Typical features and options include:

• Adjustable Torque—Adjustable torque is used primarily for slip clutches and torque limiters. Users can adjust the torque at which the clutch disengages or slips.
• Zero Backlash—There is no play or backlash during the engagement of the load and no load disengagement during a direction reversal. 
• Washdown Capable—The housing is rated for washdown cleaning.
• Bi-directional—Devices can be set up to rotate in either direction.
• Automatic Re-engagement—The clutch re-engages the load when the torque drops to an acceptable level.
• Slip Indication—Slip indication can move a pin radially when an overload occurs or send an electrical signal to the drive motor. 
• Feedback—Feedback provides an electrical or electronic signal for monitoring parameters such as position, speed, torque, lockup, or slip status. 

Compressed air is usually clean and easy to handle. The simplicity of pneumatic clutches leads to much more accurate torque control compared to mechanical clutches. When combined with pneumatic brakes, the brake/clutch packages provide reduced braking distances, and are often used in larger, heavier vehicles like buses. Air-actuated clutches transmit higher torques than similar sized electric or mechanical clutches, but not quite the torque achievable by a hydraulic clutch. Pneumatic clutch actuation is selected for its simplicity and efficiency in moving disengagement force from the operator’s position to the clutch location. 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. Pneumatic clutches make sense to use in many applications by providing a light weight, relatively low maintenance actuation system.

Related Information

CR4 Community—Hydraulic Clutch

Image credit:

Andantex USA, Inc.