The lip seal degradation on a large coal-fired power plant’s oil-lubricated holdbacks was experiencing problems. To prevent airborne contaminants from reaching internal seals and parts lip seals were designed. It became difficult for maintenance crews to keep up with the required lip seal lubrication schedule with multiple inclined and overland coal conveyor systems located throughout the facility. The resulting lip seal degradation led to an increase in costly downtime.

To solve the problem, new grease-filled Formsprag LLH (Long Life Holdback) models were installed as replacements to older Formsprag and competitive oil-lubricated units. The facility manager expects a significant improvement in productivity since maintenance will not be required on the new LLH units as they already use grease lubrication (grease used for both internal lube and grease labyrinth seal areas).

LLH Series backstopping clutches are designed for use on conveyor head shafts, bucket elevators, or any other machinery where reverse rotation must be positively prevented. LLH units come ready to install and are equipped with a one-piece, quickly detachable torque arm.

A variety of LLH model sizes are utilized at the facility with torque capacities ranging from 4,000 to 700,000 lb.ft. (952000Nm) and maximum overrunning speeds from 130 to 400 RPM. The largest units are mounted on two conveyor systems with 60” wide belts that move 1,100 tons/hr on each belt.

Highlights

• Oil lubed LLH holdback replaced with grease lubricated models
• Reduced maintenance and downtime
• Eight older Formsprag and competitor units replaced
• Torque capacities ranging from 4,000 to 700,000 lb.ft. (952000Nm)
• Maximum overrunning speeds from 130 to 400 RPM