How A Centrifuge Works

The SE range of centrifugal oil cleaners are capable of removing water and all "heavier than oil" particle contamination from oils. Designed for use with, vegetable oil, gear oil, and lubricating/sump oil, the centrifuges will work more efficiently if the oil is heated prior to filtration to reduce the viscosity to a level similar to lubricating oil at normal engine operating temperature, this is particularly important when used with vegetable oil.

The SE range of oil cleaning centrifuges consist of two sections - the centrifuge body and the rotor. Used in conjunction with a pump of the correct pressure, dirty oil enters the side of the centrifuge housing via the pipe work assembly and travels up through the hollow centre spindle. At the top of the spindle, a baffle distributes the oil uniformly into the centrifuge rotor. Because the rotor spins at about 8000 rpm, the oil quickly accelerates to a very high speed. The resulting centrifugal forces of up to 2000 times that of gravity force any heavier than oil contaminants such as soot, fat, grease and water outward onto the inside of the rotor cover wall where it consolidates into a dense cake material. Clean oil leaves the rotor through the propulsion jets and enters the body section where it can drain through the mounting bracket. It is the oil pressure alone that drives the centrifuges.

For cleaning of lubrication oil that has been used in a combustion engine, please note that whilst the centrifuge will remove all heavier-than-oil particles, it will not reverse changes that have occurred to the oil at a molecular level - for example the black colour of used engine oil is not only caused by carbon deposits i.e. soot (which will be removed) but by a change in the molecular structure of the oil caused by the combustion of hydrocarbons around and within it, and this colouring cannot be removed by using a centrifuge alone.

The purpose of a centrifuge.

A Centrifuge is an oil cleansing device, it is not intended to purify foul oil in one pass, but to remove the contaminants from oil that cannot be removed by the lowest rating of washable filter (this being 80 micron), and particles that are too small to be removed by any filter (smaller than 1 micron), by combining washable filters with a centrifuge you can eliminate the need for disposable filter elements.

Number of passes required.

A centrifuge is not designed to purify oil in a single pass, unless the oil is very clean. The speed at which the centrifuge separates contaminants from oil is determined by the cleanliness of the main body of oil and the RPM (not the RPM alone). The centrifuge rotor is driven by jets of oil propelled out from the rotor, creating a propulsion force away from the outer wall of the centrifuge, without the jets the rotor will not spin, so to spin at all it needs to pass oil at a rate of about 3 lpm... if your oil is heavily contaminated then a large proportion of the oil will go straight through the centrifuge to provide the propulsion, and only a small amount of contamination will be separated in the initial pass/es, if your centrifuge fails to remove anything after repeated passes then your oil may need to be filtered to a better standard beforehand.

Multiple passes (up to 3) may be required to gain the highest purity when sub-micron contamination is present. The centrifuge will require emptying of contaminants periodically, although regularity will depend upon how contaminated your oil is and the size of centrifuge being used, the better you strain your oil beforehand, the longer the centrifuge will operate before cleaning is required. Oil should be pre-filtered to a maximum particulate size of 250 microns prior to being pumped into the centrifuge.

Particulate separation.

A Centrifuge will remove heavier-than-oil particles, but it will find it more difficult to separate any particles if the main body of oil is heavily contaminated with material of the same specific gravity, in this case the oil will require more than one pass, or for the oil to be filtered to a better standard before pumping into the centrifuge, the cleaner the main body of oil is, or gets, the faster the rate of separation will be.

Liquid separation.

A Centrifuge will remove heavier-than-oil liquids by the same means as it removes particles, but it will not remove "miscible" liquids, for example liquids that have the same "Specific Gravity" as the oil, or contaminants that are bonded to the oil molecules chemically. It is worth noting particularly with liquids that the maximum capacity of the centrifuge rotor cap (where dirt is held) is approximately 295 Grams, if you pump a lot of water, glycerol, or animal fat through the centrifuge then it will become full very quickly and this will prevent further separation.

Results and fine tuning.

Centrifuges take a bit of getting used to, some people expect too-much-too-soon and get frustrated without investigating their problems properly. Most problems are experienced by those who use a centrifuge for purifying waste vegetable oil, and are mostly caused by excessive animal-fat in the oil (this is white in colour at room temperature) Animal Fat makes the oil cloudy and, being almost the same SG as the oil, makes it extremely difficult to separate. We recommend passing a small amount of oil through an ion-exchange or cellulose media to determine if any cloudiness is caused by animal fats.