Hence, in modern installations, the first expression of those seeds is carried out in so-called cage (clodding) presses, consisting of hydraulic presses provided with circular boxes or cages, into which the meal is filled.
These cages or boxes are either constructed of metal staves held together by a number of steel rings, or consist of one cylinder having a large number of perforations.
The presses having perforated cylinders, although presenting mechanically a more perfect arrangement, are not preferable to the press cages formed by staves, as the holes become easily clogged up by the meal, when the cylinder must be carefully cleaned out.
Modern improvements, with a view to cheapening of cost, effect the transport of the cages from one press battery to another on rails.
In order to dispense even with the charging of the presses by hand, in some systems the cages are first charged in a preliminary press, from which they are transferred mechanically by a swinging arrangement into the final press.