The reduced the power is transmitted to spindle ,the screw in the spindle will spin , that will push the oil crop forward unendingly . Due to the space between the pressing tank and the screw become smaller and smaller , then the density of the oil crop will be bigger ,at last the pressure increased . During the pressing , the frictional force produced the heat . So the machine got the pressure and the heat , which will destroy the cell of the oil crop , oil will overflow ,the cake will be pushed out of the machine . When the overflowed the oil pass by the filer , the vacuum pumping will pump the air out of the cask , there will be a subatmospheric pressure inside the cask . The oil flow into the cask , the scraps will be left outside .