Machinery's Handbook, 31st Edition
Lubrication Delivery Methods 2517 Manual gun delivery systems are commonly known as grease guns and oil guns. These hand-dispensing devices are capable of delivering lubricant at pressures exceeding 15,000 psi (103 MPa), and must be used with extreme caution if the bearing seal is not to be compromised—especially when lubricating from a remote located grease nipple. Bearings manually lubricated with grease and oil guns are lubricated with significantly more lubricant and less frequent applications than automatic centralized lubricated bear- ings. Manual lubrication results in a high degree of bearing fluid friction and a significant lower life expectancy. Single point lubricators are self-contained automatic dispensing units that house a lubricant reservoir and can dispense oil or grease to a single bearing or a small number of bearings through a manifold system. Earlier versions of the grease units employed a spring-loaded follower plate that dispensed against a bearing back pressure through a controllable bleed valve; while oil units used gravity (also known as gravity units) to allow oil to drip through a bleed valve at a controlled rate onto a brush or wick device touching the moving shaft or part. Both unit types are refillable and are still available. Modern-day versions are mostly one-time-use units that employ programmable controlled battery op- erated positive displacement pumps, or electrochemical gas expandable bellows to move the lubricant to the bearing. Centralized total loss systems employ a pump that can be automatically or manually activated to pump oil (solid or mist) or grease to a series of metering valves mounted at the lubrication point, or in a manifold device piped to the bearing point. These systems are capable of delivering a metered amount of lubricant on a cyclic basis to many hundreds of lubricant points simultaneously. Because the lubricant is not reclaimed at the bearing point, the pump reservoir must be filled with lubricant on a regular basis. This lubrication system is the most common type of found on industrial equipment. Centralized oil recirculating systems are designed to continually pump a metered amount of oil through each bearing point. The oil is channeled back to the reservoir through a filter system and pumped out again through the distribution system. Self contained bath and splash installations are “pick-up” type systems that employ oil in a reservoir filled to an engineered level that covers the lowest submersed gear teeth. As the gear moves it picks up the oil and transfers lubricant as each gear engages and disen- gages. Higher rpm speed causes the lubricant to be splashed high into the gearbox cavity so that is is distributed to all the internal devices. Contamination Control Before an oil lubricant gets to perform its lubrication function at the bearing point, it must often go through a torturous handling process where the oil must be transferred multiple times before it eventually resides in the final application reservoir. The lubricant is shipped from the refinery to the blending station, to the manufacturer’s bulk storage tank, to the supplier’s storage tank, to the barrel or pail, to the user’s storage facility, to the maintenance department, and finally to the machine’s reservoir. If the transfer equipment and storage tanks/devices are not dedicated to this exact lubricant type and scrupulously clean, and the oil is not filtered at every transfer point, the virgin oil will be contaminated when placed in the equipment reservoir. In a study performed by the National Research Council of Canada on bearing failure in primary industries it was found that 82 percent of wear-induced failure was particle- induced failure from dirty lubricants, with the greatest wear caused by particles whose size equaled the oil film thickness. Perhaps the greatest contamination enemy for bear - ings is the ever present silt and its abrasive properties. Fig. 13 shows the Macpherson curve, which depicts the contaminant effect on roller bearing life based on contaminant micron size.
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