Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/359954
40 July - August 2014 | www.machinerylubrication.com By michael Schilling BeArINg lUBrICAtIoN A A nuclear plant recently experienced wire wooling on the journal bearings and shaft of one of its feed water pumps. This was detected by the color of the oil turning black during a post-maintenance accep- tance run. The equipment did not have any form of filtration installed but just a rough strainer in the reservoir. The pump was turned off, and the strainer inspected. The pump in question has a double volute design, which assures radial balance. It has specially constructed bearing housings that contain the thrust (outboard end) and radial (coupling end) bearings. The radial bearing is a split- sleeve journal bearing. The thrust bearing combines a split-sleeve journal bearing with a pivoted shoe bearing, thrust disc and locating ring. Oil Lube System The oil lubrication system furnishes lubricant under pressure to the pump and motor bearings. The lubricant for the motor is an ISO 32 grade turbine oil and is compatible with the lubricant required for the pump. For this design, the pump bearing housings are furnished with an oil deflector. The oil deflector has a nose ring that inserts between the labyrinth seal cast in the bearing housing and the pump shaft. There is also an outer ring that overlaps a lip, which is cast into the upper and lower bearing housings. The tight clearance between the oil deflector and pump shaft minimizes water intrusion as well as oil leakage. During normal operation, all oil is supplied by the shaft-driven gear pump, while a motor-driven auxiliary oil pump is on standby. The pump's lubrication system configuration is designed to start the motor-driven auxiliary oil pump when the main pump's oil pressure falls below 7 pounds per square inch (psi). The intent in this configuration is to provide suffi- cient lubrication to the pump bearings in the event the shaft-driven gear pump fails while the pump is in normal operation. The motor is a 7,000-horsepower hori- zontal induction unit that is connected to the pump via a flexible coupling. The pump's rotating assembly (including impellers, shaft, wear rings, wire wooling Bearing Failure: A Case study Left to Right: Pump Outboard (Journal) - Bottom Half Pump Outboard (Journal) - Top Half Pump Outboard - Journal Section of the Shaft Examples of inadequate foreign material exclusion practices on oil piping removed from the system