Note 98 — Chapter VIII · JAMES NASMYTH

Compare Nasmyth’s sketch, Fig. 23, with Fig. 24, which was taken from the model of his first hammer now in the South Kensington Museum (Exhibit No. 1571). The description of it in the catalog is as follows:

“It consists of a base plate with a large central opening through which projects the top of the anvil, so that a blow on the anvil is not transmitted to the base plate. On the plate are secured two standards which form guides for the hammer-head or tup, and also support an overhead cylinder, the piston of which is connected with the tup by a piston rod passing through the bottom of the cylinder. Steam is admitted to this cylinder by a stop valve in the form of a slide, and then by a slide valve on the front of the cylinder, which by a hand lever can be moved so as to let steam in below the piston and so raise the heavy tup. When it is lifted to a height proportionate to the energy of the blow required, the steam is by the slide valve permitted to escape and the hammer falls upon the forging placed on the anvil. The cylinder is therefore only single-acting, but the top is closed, and a ring of holes communicating with the exhaust pipe is provided at a little distance down inside. In this way an air cushion is formed which helps to start the piston downwards when a long stroke is being taken, and also the steam below the piston is permitted to escape when the tup has been lifted as high as it can safely go. Soon after its invention the steam hammer was greatly increased in power by accelerating the fall of the tup by admitting steam above the piston in the downstroke and so changing it into the usual double-acting steam hammer.” Cat. Machinery Collection, Part II, p. 255.

[99] Autobiography, p. 242.