Machine Design

Pneumatic Lubricators

The increased use of manifolding, complex valves, and miniature components have increased the difficulty of transmitting lubricants to pneumatic components. The problem is to get enough oil to the components without flooding them. Even in a straight line, oil particles with diameters larger than about 80 ∝in. tend to coalesce within about 25 ft from the lubricator. They form pools in the bottom of the line, and must depend on the sweeping action of the air to reach their intended destination.

Manifolds and complex valves contribute to this coalescing action by inserting restrictions and turbulent areas in the flow path. Smaller components use less air, so oil particles take longer to reach their destination.

But these difficulties are not insurmountable. Flow paths that are too tortuous or lengthy for a direct-flow lubricator may present no problem to a recirculating flow lubricator. And pulse lubricators are available for still more difficult applications. Direct-flow lubricators spray a mist of oil directly into the air line. They are inexpensive, and can adequately lubricate most pneumatic systems if air lines are reasonably straight, do not exceed about 25 ft in length, and include no sections where air must rise vertically. Oil particles emitted from direct-flow lubricators have diameters ranging from 0.4 ∝in. to 0.02 in. About 96 to 97% of these particles are larger than 80 ∝in., and tend to coalesce on air lines fairly rapidly. Recirculating-flow lubricators are similar to direct-flow lubricators, except that they recirculate misted oil past a baffle and into the bowl. Large particles remain in the bowl because of their mass, and medium particles coalesce on the baffle. As a result, particles injected into the air stream have diameters ranging from 0.4 to 80 ∝in. These smaller particles can traverse up to 100 ft of straight pneumatic line. Recirculating-flow lubricators cost about the same as comparable direct flow models, but cannot be refilled under pressure. Pulse lubricators do not spray an oil mist into the line, but instead inject a small, accurately measured amount of liquid oil directly into a pneumatic actuator. Because the injection point is at the actuator, the length and complexity of the pneumatic line leading to the actuator is irrelevant. The amount of oil directed to each actuator can be controlled individually to match actuator requirements. Pulse lubricators are mechanically more complex and more costly than either direct-flow or recirculating-flow lubricators.

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