Method of purifying contaminated oil from particles suspended in the oil in a centrifugal separator

A method of purifying contaminated oil from particles suspended there in by means of a liquid separation aid having a density larger than that of the oil and being dispersed in the contaminated oil in order to make the particles more easily separable from the oil, the method comprising

• supplying said contaminated oil and said liquid separation aid into a separation chamber of a rotating centrifugal rotor,
• separating in said separation chamber the particles and the liquid separation aid from the oil by centrifugal force,
• discharging purified oil from the separation chamber through a central light phase outlet thereof and
• discharging separated particles together with separated liquid separation aid from the separation chamber through a heavy phase outlet of the separation chamber, situated radially outside said central light phase outlet,
• pre-charging the separation chamber, before supplying a substantial amount of contaminated oil thereinto, with a starting liquid, which is heavier than the oil and insoluble therein, in an amount such that a layer of the starting liquid forms a liquid seal in the centrifugal rotor, covering said heavy phase outlet,
• supplying thereafter said contaminated oil and said liquid separation aid into the separation chamber, and
• discharging from the separation chamber through said heavy phase out-5 Jet at least part of said starting liquid and particles together with liquid separation aid, separated from the oil.