An aircraft engine often comprises a pressure regulating valve (PRV) designed to maintain fluid pressure, for instance lubricating oil in a main oil supply circuit, within a desired pressure range when the engine is operating. A PRV can also be designed to avoid excessive oil feed during engine start-up and shutdown at locations having a pressure seal, for instance bearing cavities. Pressure seals are provided to mitigate oil leaks between two components where at least one moves relative to the other. These pressure seals are often not entirely efficient when they operate below a minimum pressure. This situation can occur during engine start-up and engine shutdown, for instance when the rotational speed of the engine is under idle speed. The PRV then initially diverts the pressurized oil coming from the main oil supply circuit to a location upstream an oil supply pump until the pressure, for instance the pressure in a bearing cavity, is sufficient for the pressure seals to operate efficiently. The main bypass outlet is closed afterwards and should remain closed when the aircraft engine is above idle speed since an aircraft engine then generates enough pressure for the pressure seals to operate efficiently. Some situations, however, could cause the oil pressure to temporarily decrease down to a very low value during a flight, for instance when the aircraft is subjected to a negative “g” event. A negative-g event can occur during an inverted flight or in some other circumstances during a flight, such as during the moments immediately following a water load release by a firefighter aircraft. During a negative-g event, air bubbles can enter the main oil supply circuit through the supply pump, thereby reducing the oil pressure. This could cause some PRVs to open the main bypass outlet and possibly increase the time required for the oil pressure to recover. Room for improvements thus exists in the design of a PRV.