Machinery Lubrication

Machinery Lubrication March-April 2020

Machinery Lubrication magazine published by Noria Corporation

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www . machinerylubrication.com | March - April 2020 | 31 ML Figure 3. Circulating system components. Figure 2. Oil flow through a circulating system. The Essential Function: Oil Flow e essential function of a circulating system is to deliver the prescribed flow of oil into the bearing. e oil is collected from the bearing, as suggested by the name "circulating oil system." e oil is filtered and cooled (if necessary) while passing through the lubrica- tion system. e path the oil follows is shown in Figure 2. It begins with the oil coming into the reservoir through piping connected to an overflow port at the bearing. e bearing is located at a higher elevation than the system, so the oil flows by gravity. Fluid spills over the baffle in the reservoir. Larger contaminants tend to settle on the side of the baffle where the oil enters. e suction created by the pump draws the fluid into the piping. A strainer traps large particles before the oil enters the pump. e motor drives the pump to create flow and pressure. Next, the oil is routed through a filter to remove fine particles so they do not reach the bearing. e oil then flows to the bearing. Finally, excess fluid is directed back into the reservoir through a bypass valve. In its simplest form, a circulating oil system may not require any type of control other than its power supply. e system forms a loop and functions without interruption until a filter replacement is necessary. e features inherent to a circulating oil system are shown in Figure 3. Determining System Requirements Each application of a circulating system is unique. e bearing manufacturer should be consulted for the specific flow rate, system pressure, fluid type and operating temperature. e user specifies the connecting piping size, line distances, elevation to the bearing, surrounding temperature, power availability and safety considerations. Instruments and electronic controls can be added to cope with demanding environments or provide active feedback to the operator. For instance, warnings and fail-safes can ensure that any variances are detected and action is taken before the lubrication of the bearing is compromised. Such precautions may be warranted if the bearing is started and stopped as part of its normal operation, the load or rota- tion speed varies, the temperature fluctuates, or it is in a particularly dirty environment. Some bearings must operate without interruption, which requires that the circulating oil system do the same. Redundancy can be built into the system. Dual filters with separate piping and control valves enable the filter to be changed while the flow of oil is diverted. A built-in second pump and motor can serve as a backup so the system remains operational during service or major component replacement. Matching Components to the Requirements Consider the following factors when specif ying a circulating oil system: Flow Rate If the system is supplying more than one bearing, the flow rate must equal the sum of the requirements. Flow into the bearing is controlled through the use of a needle valve at the delivery point. e pump and motor are sized to the maximum required flow rate plus a small contin- gency factor. e pump supplies oil at a constant rate. Any flow in excess of what the bearing can accept is diverted back into the lube skid's reservoir by a bypass relief valve located near the fluid outlet. Pressure A typical operating pressure is 35 pounds per square inch (psi) or less. Specialized applications may require higher pressures, such as a system designed to suspend a bearing in lubricant during startup to avoid metal-to-metal contact. e maximum amount of pressure is 1 2 3 4 5 6 8 7

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