Aviation Technical English for aircraft maintenance engineers (Авиационный технический английский язык для студентов-авитехников)

70 d) The displacement of oil from the variable pitch propeller and other automatic controlling devices. The  hot pot  forms a separate compartment within the tank. Its purpose is to reduce the time taken to raise the temperature of the oil when starting the engine from cold by restricting the quantity of oil in circulation when the oil is cold and viscous. The hot pot consists of a cylinder of metal fitted above the oil outlet to the engine, thus the oil must be inside the hot pot to be able to reach the pressure pump. When starting, the level of oil in the hot pot drops, uncovering a ring of small diameter ports. These ports offer a great resistance to the flow of cold thick oil so that very little passes to the inside of the hot pot. The oil is returned from the engine to the inside of the hot pot and is re-circulated. As the hot oil is returned to the tank some of its heat raises the temperature of the walls of the hot pot. The oil in the immediate vicinity is heated and thins so that the ports offer less resistance to the flow of the thinner oil, and progressively more and more oil is brought into circulation. The oil is filtered by the suction filter before passing to the pressure pump. When feathering propellers are fitted, the lower ring of feed ports to the hot pot is placed above the bottomof the tank; this provides a feathering reserve of oil even if the main tank has been emptied through the normal outlet, as would occur if the main feed pipeline was to develop a leak or completely fail. The scavenge oil returning to the tank is passed by an internal pipeline over a de-aerator plate to the inside of the hot pot. The plate separates the air from the oil to reduce frothing. The tank is vented through the crankcase breather to prevent oil losses during excessive frothing conditions. *www.aircraftspruce.ca/catalog/pdf/13-08714.pdf (05.10.2018). THE PRESSURE PUMP The pump consists of two deep toothed spur gears rotating in a close fitting pump casing and driven via the accessory housing. Oil is carried by either side of the casing in the space between the gear teeth, and is made to flow. The outlet side of the pump is enclosed and restriction to flow is