The expeller consists of a pressing box or cage sur-rounding a horizontal shaft mounted with a series of worms. At the feeding end of the cage there is an opening through which the meal is fed into the expeller. At the discharge end of the cage there is cone which practically restricts the passage. The rotation of the horizontal shaft causes the meal to push forward by its screw action, thereby increasing the internal pressure and thus squeezing the oil. The internal pressure of the expeller is regulated by the perforated box, while the cake passes out through the opening around the cone.

The expeller is a self contained unit which has its own heating kettle and an arrangement for automatic feeding. The expeller requires no attention after setting so long as proper temperature and moisture content of the seed meal is regulated. The meal as it passes through the expeller becomes hotter by liberation of frictional heat.
For the satisfactory extraction of different oil seeds the design of the worms plays a very important role. High grade steel worms possess great resisting power for pressure and abrasion, thus resulting in their long life.

Oil expellers are designed to operate at pressures LOW and HIGH. Low pressure expellers remove only a portion of oil in the seed meal and generally have very high capacities ranging from 30-80 M.T of seed per day of 24 hours. They are used in combination with their high pressure expellers or with solvant extraction plants or to extract the maximum oil from high oil containing seeds from which complete extarction at a stretch is not generally possible. High pressure expellers produce at one stretch all the possible extraction oil from the seed meal. High pressure expellers operate at a pressure of 2.5-3.0 ton per square inch and have low capacities.