Where is oil pressure measured in a Piston Engine?
The oil pressure measured is that pressure provided BY the pump and available TO the lubrication system. Oil pressure is monitored and displayed so that any failure of a bearing, such as the main bearings and big-end bearings, which will reduce the resistance to flow and consequently reduce the pressure, will be made known by either a drop in indicated oil pressure and/or warned of by a "low oil pressure" warning light. Scavenge pumps which return oil to the oil tank will/should always have a greater volumetric capacity than a supply pump, to ensure oil available for the pressure pump, the pressure not being critical. Oil sumps are not usually pressurised (except in 2-Stroke engines) and it is volume to the inlet side of the pump which counts. Therfore "(A) On the output side of the pressure pump" is the correct answer.