HKB
paddle-wheel fixed in the stern of the vessel, of which drawings are annexed to the specification; but it was not until 1795 that he patented his Hydrostatic or Hydraulic Press.
Though the principle on which the Hydraulic Press is founded had long been known, and formed the subject of much curious speculation, it remained unproductive of results until a comparatively recent period, when the idea occurred of applying it to mechanical purposes. A machine of the kind was indeed proposed by Pascal, the eminent philosopher, in 1664, but more than a century elapsed before the difficulties in the way of its construction were satisfactorily overcome. Bramah's machine consists of a large and massive cylinder, in which there works an accurately-fitted solid piston or plunger. A forcing-pump of very small bore communicates with the bottom of the cylinder, and by the action of the pump-handle or lever, exceeding small quantities of water are forced in succession beneath the piston in the large cylinder, thus gradually raising it up, and compressing bodies whose bulk or volume it is intended to reduce. Hence it is most commonly used as a packing-press, being superior to every other contrivance of the kind that has yet been invented; and though exercising a prodigious force, it is so easily managed that a boy can work it. The machine has been employed on many extraordinary occasions in preference to other methods of applying power. Thus Robert Stephenson used it to hoist the gigantic tubes of the Britannia Bridge into their bed,[2] and Brunel to launch the Great Eastern steamship from her cradles. It has also been used to cut bars of iron, to draw the piles driven in forming coffer dams, and to wrench up trees by the roots, all of which feats it accomplishes with comparative ease.
The principal difficulty experienced in constructing the hydraulic press before the time of Bramah arose from the tremendous pressure exercised by the pump, which forced the water through between the solid piston and the side of the cylinder in which it worked in such quantities as to render the press useless for practical purposes. Bramah himself was at first completely baffled by this difficulty. It will be observed that the problem was to secure a joint sufficiently free to let the piston slide up through it, and at the same time so water-tight as to withstand the internal force of the pump. These two conditions seemed so conflicting that Bramah was almost at his wit's end, and for a time despaired of being able to bring the machine to a state of practical efficiency. None but those who have occupied themselves in the laborious and often profitless task of helping the world to new and useful machines can have any idea of the tantalizing anxiety which arises from the apparently petty stumbling-blocks which for awhile impede the realization of a great idea in mechanical invention. Such was the case with the water-tight arrangement in the hydraulic press. In his early experiments, Bramah tried the expedient of the ordinary stuffing-box for the purpose of securing the required water tightness' That is, a coil of hemp on leather washers was placed in a recess, so as to fit tightly round the moving ram or piston, and it was further held in its place by means of a compressing collar forced hard down by strong screws. The defect of this arrangement was, that, even supposing the packing could be made sufficiently tight to resist the passage of the water urged by the tremendous pressure from beneath, such was the grip which the compressed material took of the ram of the press, that it could not be got to return down after the water pressure had been removed.