Which statement is true about plain bearings?

Which statement is true about plain bearings?

• A. They require intermittent lubrication
• B. They operate without oil
• C. They must be continuously lubricated by pressure oil
• D. They can run without oil for short periods

Answer: (C)

Plain bearings rely on a continuous oil film to keep the bearing surface and the journal apart. This film is maintained by oil pressure from the pump, and it must be present under all operating conditions; if the pressure drops, the film collapses and metal-to-metal contact occurs, leading to rapid wear and overheating. That’s why the true statement is that they must be continuously lubricated by pressure oil. Intermittent lubrication, running without oil, or only brief oil-free periods would allow the film to break down and cause damage. Some systems do supplement lubrication with splash oil, but the fundamental requirement in standard plain bearing operation is a continuous oil pressure supply.

Plain bearings rely on a continuous oil film to keep the bearing surface and the journal apart. This film is maintained by oil pressure from the pump, and it must be present under all operating conditions; if the pressure drops, the film collapses and metal-to-metal contact occurs, leading to rapid wear and overheating. That’s why the true statement is that they must be continuously lubricated by pressure oil. Intermittent lubrication, running without oil, or only brief oil-free periods would allow the film to break down and cause damage. Some systems do supplement lubrication with splash oil, but the fundamental requirement in standard plain bearing operation is a continuous oil pressure supply.