Whittaker Survival Capsules Employ Formsprag Clutches For Extra Safety
Survival capsules are lowered from offshore rigs with winch systems that contain overrunning clutches capable of withstanding extreme shock loads. Whittaker Corporation, La Mesa, Calif., selected Formsprag® overrunning clutches manufactured by the Industrial Power Transmission Division of Dana Corporation for use on some models of the U.S. Coast Guardapproved capsules.
Produced in 14-, 36/38-, 50-, and 54-man-capacity models, the Whittaker survival capsules are impact resistant and totally enclosed for protection against fire and the environment.
They are equipped with air, water, food, and other survival gear, and are propelled by diesel engines. They also have pumps that can provide a continuous exterior water bath in the event of fire on the water surface.
The capsules are supported on rigs above the ocean surface by electric winches and platforms. The winch cable is attached to the capsule at a single point with an onload/ offload hook. This single-point attachment eliminates the need for fore and aft connections, and speeds launch and recovery during emergencies and drills.
The winch consists of a singlegrooved cable drum driven by an electric motor through a gear reducer and an overrunning clutch. The input shaft from the gear reducer runs through and is keyed to the clutch's inner race. A weight-set band-type brake can be used to hold the outer race of the clutch during raising and stowage.
An overrunning clutch consists basically of cylindrical inner and outer races with a full complement of precision-machined sprags filling the annular space between the races. Each sprag is essentially a strut that transmits power from one race to the other by a wedging action when either race is rotated in the driving direction. Rotation in the other direction frees the sprags and the clutch is disengaged, or overruns. In standard clutch designs either race may be the driving member or the driven member.
When the band-type brake securing the sprag clutch's outer race is released, the gear reducer, shaft, clutch, and drum assembly are free to turn, allowing the capsule to descend to the water. A centrifugal brake attached to the gear reducer's input shaft limits the lowering speed to within safe parameters.
For hoisting, the band brake on the clutch's outer race is set and the clutch's inner race overruns the outer race as the drive shaft turns the drum to raise the capsule. Since the sprag clutch permits rotation in one direction only, when the band brake is set, the clutch serves as a safety backstop during hoisting.
Transient shock load protection is provided by the Formsprag PCE™ (Positive Continuous Engagement) sprag design. It prevents sprag rollover and permanent clutch damage that can occur during overload.
With the PCE design, projections on the front and back flanks of each sprag provide positive sprag-tosprag abutment during overloading to prevent damage and allow the unit to continue to function.
Another feature of these overrunning clutches is the "Free-Action" sprag retainer. It spaces and positions each sprag uniformly, yet allows independent movement of each sprag while under load. Each sprag adapts automatically to varying annular space conditions, resulting in uniform engagement and load distribution of all sprags at all times.
Ultra-hard Formchrome® sprags, exclusive with Formsprag clutches, provide extra-long life, maximum wear resistance and lower maintenance costs.
The U.S. Coast Guard requires a service factor of 6:1 for safety equipment.
The long life and consistent performance provided by the "Free- Action" retainer and Formchrome wear resistance combined with the shock load protection of PCE sprags enables the Formsprag overrunning clutch to meet this stringent requirement, providing added safety for Whittaker's survival capsules.
For further information on Whittaker survival capsules, Circle 46 on Reader Service Card For more information on Formsprag overrunning clutches, Circle 47 on Reader Service Card
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