Machinery Lubrication

Machinery Lubrication July Aug 2013

Machinery Lubrication magazine published by Noria Corporation

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Page 29 of 60

AUTOMATIC LUBRICATION LUBRICANTS Systems Technology INTERMITTENT OIL AND GREASE FLOW OIL, OIL MIST AND AIR/OIL Series Progressive System Continuous Oil-Circulation System Oil-Mist Lubrication System Air/Oil Lubrication System Dual-Line Lubrication System Single-Line Parallel System Flow meter (volume transducer) Yes, but not suitable for low-volume flow Yes No No No-flow switch Yes, sensitive to viscosity and temperature Yes No No Flow-monitoring switch Yes, sensitive to oil flow and temperature Yes No No Inductive flow switch Yes, with material limitations No No Yes Thermistor flow switch Yes, but narrow temperature range Yes Possible Yes Push-button flow switch Possible but not recommended Yes No No Magnetic-field flow switch Yes No No Yes Optical flow sensor No, due to pressure limitations Yes Possible Yes Flow confirmation sensors and their applications cated. Even though a flow meter can be used in intermittent-flow systems, it is more suitable for oil-circulation systems. No-Flow Switches A no-flow switch is designed solely for continuous-flow or semicontinuous-flow lubrication systems. It is implemented by an electrical contact switch that is activated by a plunger under spring force. In normal conditions, the continuous lubricant flow pushes the plunger away from the electrical switch, countering the spring force on the plunger. When the lubricant flow stops, the spring force drives the plunger toward the electrical switch and eventually pushes the switch closed. The closed switch can either set off an alarm or directly shut off the machinery being protected. A typical no-flow switch does not need a controller or electrical device to protect the machinery and is popular on large gas compressors where direct protection is desired. A no-flow switch can be installed close to the lube point, but there still will be a short tube connecting the outlet from the no-flow switch to the lube point inlet. 28 July - August 2013 | Flow-Monitoring AC Switches Most flow-monitoring switches are intended for checking the flow in an oil-circulation system. However, there are also certain models available for intermittent oil flow. Keep in mind that different flow rates with lubricant viscosity variations will require different models to suit the application. Inductive Flow Switches An inductive flow switch is designed to sense the intermittent flow from a dispensing device. The flow detector utilizes an inductive sensor to monitor the movement of a check ball driven by lubricant flow. The flow sensor can be subjected to pressure up to 3,000 psi. A grease-flow sensor with flow sensitivity of 0.016 cc and above per shot is currently available. However, the flow of 0.03 cc per cycle from an injector in a single-line parallel system will not be recognized because the force from the lubricant flow is not high enough to overcome the biasing spring force. The spring force is adjustable to compensate for the lubricant's viscosity.

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