It is a machine used (mainly) on board of sea-going vessels to remove dirt (sludge) from the fuel. Separators are also used in the petro-chemical and dairy industry.
It is used to clean the fuel or lube oils for a ship. Fuel for a ship is called fuel oil. The quality of fuel or lube oil is often not very good for various reasons. The full name of a separator is a mineral oil separator. Not to be confused with an oily water separator (see next question). When fuel oil is delivered to a ship, it first goes into a settling tank. That's where the first separation actually starts, i.e. due to gravity heavy particles sink to the bottom of the settling tank. The oil is then pumped into the separator where it is purified. It then goes into a day tank and from there to the main engine. See figure 1.
Dirty water (e.g. water from the mineral oil separator!) can be dumped into the ocean if it goes through an oily water separator. This machine separates the water from the oil so that it can be released safely into the ocean.
It uses centrifugal force (the opposite of centripetal force). An electromotor supplies the power. The electromotor rotates a worm wheel. The worm wheel shifts the force through a worm on the horizontal bowl spindle. This rotates the separator bowl. The bowl consists of a number of bowl discs where light components such as oil and heavier components such as water and sludge (sand, rust, dirt, etc.) are separated by using centrifugal force. The lighter component is pushed inwards while heavier components are pushed outwards.
A separator can operate as a purifier or as a clarifier. In most cases separators will operate as purifiers. A purifier separates three phases: solid particles (sludge) and two insoluble liquids (oil and water). A purifier is mainly used when sludge has to be separated from oil together with smaller quantities of water from sludge.
A clarifier separates two phases: solid particles (sludge) from a liquid (oil). In that case the water outlet is simply blocked by using a level ring to seal it off. In case there is some water it will be removed together with the sludge.