What’s the first instrument you check after starting the engine on your airplane? Most likely, it’s the oil pressure gauge. Proper oil pressure is critical to a happy reciprocating engine, and the oil pressure gauge shows us whether the oil is doing its job—lubricating and cooling bearing surfaces where parts are rapidly rotating and sliding past each other.
The gauge displays oil pressure in pounds per square inch (psi). The normal operating range is shown as a green arc.
The oil pressure gauge is connected to a pressure-sensing mechanism such as a Bourdon tube. A Bourdon tube is a flattened tube that is fixed and sealed on one end and unfixed on the other. As fluid or pressure is applied to one end of the tube, the unfixed portion straightens out, then curls back when pressure is reduced—picture a New Year’s Eve noisemaker and you get a general idea. A pointer is attached to the moving portion of the tube through a linkage of small shafts and gears, and that’s what you read on the gauge as increases or decreases in oil pressure.
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