A method for continuous purification of motor lubricant oil comprising - circulating lubricant oil between a motor lubricant oil tank and a motor; - transporting contaminated lubricant oil from said motor lubricant oil tank in a cleaning loop, said transport in said cleaning loop comprising - adding at least one liquid separation aid to contaminated lubricant oil; - supplying contaminated lubricant oil with said liquid separation aid to a three-phase centrifugal separator; - discharging said contaminated lubricant oil with said separation aid at an inlet device of the three-phase centrifugal separator, wherein said inlet device comprises a central conical receiving structure arranged around the axis of rotation R of the three-phase centrifugal separator, said structure comprising a central receiving zone for receiving the oil and separation aid and inlet channels for directing the lubricant oil with said separation aid from said receiving zone to the separation space of the three phase centrifugal separator, wherein the inlet channels extend from the periphery of the receiving zone and spiral down the outer surface of said conical receiving structure; - smoothly accelerating the incoming oil with separation aid by guiding it via said inlet channels of the inlet device to the separation chamber of the three-phase centrifugal separator; - continuously separating contaminants from said lubricant oil in the separation space of the three-phase centrifugal separator and continuously discharging a first liquid phase comprising purified lubricant oil from a liquid light phase outlet of the separator, continuously discharging a second liquid phase comprising solid contaminants from a liquid heavy phase outlet of the separator and continuously discharging a sludge phase from a sludge outlet by the aid of a conveyor screw of the three-phase separator; and - transporting said first liquid phase comprising purified oil back to the lubricant oil tank. - circulating lubricant oil between a motor lubricant oil tank and a motor; - transporting contaminated lubricant oil from said motor lubricant oil tank in a cleaning loop, said transport in said cleaning loop comprising - adding at least one liquid separation aid to contaminated lubricant oil; - supplying contaminated lubricant oil with said liquid separation aid to a three-phase centrifugal separator; - discharging said contaminated lubricant oil with said separation aid at an inlet device of the three-phase centrifugal separator, wherein said inlet device comprises a central conical receiving structure arranged around the axis of rotation R of the three-phase centrifugal separator, said structure comprising a central receiving zone for receiving the oil and separation aid and inlet channels for directing the lubricant oil with said separation aid from said receiving zone to the separation space of the three phase centrifugal separator, wherein the inlet channels extend from the periphery of the receiving zone and spiral down the outer surface of said conical receiving structure; - smoothly accelerating the incoming oil with separation aid by guiding it via said inlet channels of the inlet device to the separation chamber of the three-phase centrifugal separator; - continuously separating contaminants from said lubricant oil in the separation space of the three-phase centrifugal separator and continuously discharging a first liquid phase comprising purified lubricant oil from a liquid light phase outlet of the separator, continuously discharging a second liquid phase comprising solid contaminants from a liquid heavy phase outlet of the separator and continuously discharging a sludge phase from a sludge outlet by the aid of a conveyor screw of the three-phase separator; and - transporting said first liquid phase comprising purified oil back to the lubricant oil tank. - adding at least one liquid separation aid to contaminated lubricant oil; - supplying contaminated lubricant oil with said liquid separation aid to a three-phase centrifugal separator; - discharging said contaminated lubricant oil with said separation aid at an inlet device of the three-phase centrifugal separator, wherein said inlet device comprises a central conical receiving structure arranged around the axis of rotation R of the three-phase centrifugal separator, said structure comprising a central receiving zone for receiving the oil and separation aid and inlet channels for directing the lubricant oil with said separation aid from said receiving zone to the separation space of the three phase centrifugal separator, wherein the inlet channels extend from the periphery of the receiving zone and spiral down the outer surface of said conical receiving structure; - smoothly accelerating the incoming oil with separation aid by guiding it via said inlet channels of the inlet device to the separation chamber of the three-phase centrifugal separator; - continuously separating contaminants from said lubricant oil in the separation space of the three-phase centrifugal separator and continuously discharging a first liquid phase comprising purified lubricant oil from a liquid light phase outlet of the separator, continuously discharging a second liquid phase comprising solid contaminants from a liquid heavy phase outlet of the separator and continuously discharging a sludge phase from a sludge outlet by the aid of a conveyor screw of the three-phase separator; and - transporting said first liquid phase comprising purified oil back to the lubricant oil tank.