An excellent modification of the screw-press was invented and patented by Mr. Daniel Dunn, of Pentonville, which is adapted to a variety of uses ; the following is a description :—Instead of the simple lever, consisting of a long straight bar, which requires so large a space to move it in, the patentee uses a compound lever (much like those employed in the ordinary printing press), by which means the same power is obtained in a much more compact apparatus.. Fag. l represents an elevation of the complete press, and Fig. 2 a plan of the improved part of the machine ; the like letters in each figure den ' similar parts. a is the bed of the press b 6 of massive oak; b b the cheeks or side g; c the head ; d the nut fixed into the head, through which the screw e is turned ; f is the platten ; g the goods, together with the press-boards or metal plates between them. Thus far the press is like others ; but instead of having a large screw-head, with apertures, for the insertion of a long lever bar, that part of the screw is squared, and on it is fixed a circular metallic plate or wheel A, with a double row of ratchet-teeth; one of the rows of teeth project horizontally from the periphery, the other vertically, as will be understood upon examining both figures. i is the handle of the compound lever, which, being formed into a circular eye at the farthest extremity, is thereby fixed upon, and traverses up and down the fulcrum k, which is an upright bar firmly bolted to one of the cheeks of the press. To alter the power according to circumstances, the curved end of the handle i is perforated with several holes, to receive a key or bolt, which fastens the other portion 1 of the compound lever to it (best seen in Fig. 2); the extremity of I is hooked or notched so as to take bold of the teeth of the ratchet-wheel, and it has a plate screwed on to it at o to prevent it from falling off. To support the compound lever at the required elevation, a.stout pin is passed into a hole, of which there are a series made for the purpose in the side cheek. In operating with this press, the goods are laid upon the bottom board in the usual manner ; the platten f is then brought down by turning• the ratchet-wheel round by band. The pressure is then given by pulling back the handle i in the direction, and to the position, shown by dotted lines in Fig. 2 ; by repeatedly moving the handle in this way, the ratchet-wheel is drawn round by the lever, which causes the screw to descend and to force the platten against the goods : during this operation it will occasionally be necessary to let the lever descend upon the fulcrum, by taking out the supporting pin, and putting it into the next hole beneath. When it is required to unscrew the press, the hooked end of the lever 1 is placed in contact with the circle of teeth on the upper sur face of the ratchet-wheel ; the lever being then pulled the reverse way, the screw is raised, and the pressure taken off.
A very substantial and practical standing press has been made by Mr. J. L. Ponchee, type-founder, of Holborn : it is particularly designed for the use of bookbinders, stationers, and printers; the arrangement dispensing with the long inconvenient lever, as in Mr. Dunn's. It is represented in the following per spective outline. There is little in its structure that varies essentially from other presses of the kind ; the head, bed, cheeks, screw, and nut, may be regarded as the same. The chief novelty consists in employing, in addition to these parts, a toothed wheel b, fixed on the axis of the screw, and operating upon it by the small pinion c turned by the lever d, which fits on the square end of the axis of c, whereon it is shifted at every fresh pull The power of the preen, when brought down to the work, may thus be increased in proportion to the difference of the diameters between the large wheel and the little pinion; the slow operation of the press at this time is of little consequence. This press stands in but little room, considering its mechanical efficacy, and it is manu factured at a low price.
The foregoing are sufficient examples of the construction of screw presses ; we shall therefore proceed to give a description of a moat ingenious, cheap, and effective press, in whioh all the other mechanical powers are brow ht into operation; viz. the wheel and axle, lever, wedge, inclined plane, and ey. It is one of the inventions of Mr. Ewings, a talented member of e London Mechanics' Institution, who obtained for it Dr. Fellowes's annual prize of ten pounds. This press, which is applicable to the packing of goods, pressing of juice from fruits, oil from seeds, or other purposes to which the screw-press is usually applied, consists of a frame-work, and two or more block's or beams, between which the articles to be subjected to pressure are to be placed ; and these vary in form, size, and material, according to the purposes for which they are intended. Mr. EwinFs does not claim any novelty in the construction of
these parts, but only in his method of producing the pressure, which is effected by bringing together the pieces that act on the articles to be pressed by wedges ; these are forced in by levers (in the manner represented by the fol lowing figures 1 and 2), in both of which the same letters of reference represent similar parts. a is the base of the press, furnished at each end with ratchet notches b 6, which constitute the fulcrums of the levers h h; c is the top of the press, supported by the frames d d; and e e are the pieces acting on the goods, either downwards, upwards, or both, according u the pressure may be required : in $g. 1 it is represented acting upwards; and in /V. 2 it is repre sented acting both ways ffff are friction rollers, between which the wedges g g are projected. A cord is fixed to a hook on the end of one of the levers, and passing over a pulley k, on the end of the other, is attached to a small drum 1, wluch is furnished with a ratchet-wheel and pall, and is turned by a winch We have seen other modifications of Mr. Ewings's press, but we have selected the above as best calculated to show the principle of its action. Amongst the advantages of this press have been noticed the simplicity and economy of its construction, as it may be made by almost any person accus tomed to handle carpenters' or smiths' tools, of very cheap materials ; and also the facility with which its power may be varied : it may be diminished or increased to any extent, simply by changing the form of the wedges; but the drawing,* exhibit its various applications and mode of operation so obviously as to preclude the necessity of further remarks.
We shall now proceed to the consideration of those presses wherein the power applied is communicated through the medium of an incompressible fluid.
The hydrostatic, or water press, as it is sometimes called, was first brought into a practical form by the late Mr. Joseph Bramah, and was patented by him in 1796. Since this period it has undergone many new improvements in the constructive department, which, although they have not sensibly added to its mechanical energy, have materially added to its convenience, by rendering its operation more easy and certain. The following diagram is explanatory of the principle upon which it acts. a represents the foundation plate of the machine, and b the head-plate, connected together by four strong standards cc; the latter should be of wrought iron; and the whole of the utmost strength and solidity, to resist the entire force of the press, which is exerted upon the goods placed between the follower d and the head of the press. The piston or ram e, (which supports the follower and goods) moves up and down in a very massive hollow cylinder f, bored very accurately at its upper part to fit the ram, and at its lower end somewhat widened, as shown by the dotted lines, to admit a small quantity of water, which is forced into it by a small force-pump g, along the pipe h. Just above that part of the cylinder where the water discharges itself in a minute crevice, an annular cavity is formed around the cylinder, wherein is fitted a folding collar of leather, which presents a thin edge both to the ram and to the cylinder, to render the junction between them water-tight, which it does most effectually by the action of the pressure itself. The top of the cylinder where the ram emerges from it, is provided with a stuffing box, well packed, and secured by a covering, plate. Now if we suppose the area of the valve by which the water is admitted into the cylinder to be one-eighth of an inch (as usual), and the power applied thereto by the lever of the pump to be a ton, and the area of the section of the ram to be 64 inches, we have 64 x 64 = 4096 tons applied to the goods in this press, according to the known laws of the pressure of fluids, as explained under the article HYDROSTATICS The power mentioned is unnecessarily great for the general purposes of a press ; but it it obvious that it may be reduced to any required extent by altering the propor tions of the lever, the valve of transmission, and the ram ; and it is equally obvious that the power may, by other modifications, be increased to an indefinite extent.