LAMB'S ENGINES. 349
the other. The available capacity of the chamber, that is the whole volume of its upper part less the volume of the circular part of the piston, is filled and emptied once in each revolution ; the pump is therefore single-acting. When in its lowest position the piston allows free communication to exist for an instant between the suction and delivery pipes, which, however, with a tolerably quick motion might not greatly injure its action. Between the end sufaces of b and d there is lower pairing, but that between their outer surfaces (those shown in the section) is higher, which of itself renders it difficult to keep the joint tight. The pump requires no valves, none at least for the usual purposes.
Plate XV. Fig. 1. Lamb's steam-engine * (patented 1842). This machine was intended to work with air or gas as well as steam, or to be used as a pump. If the very indistinct description of the inventor can be trusted our figure represents its essential parts. The mechanism is a reduced turning slider-crank, the block c being omitted ; its general formula is therefore (C" 3 'P- L ) d c. The coupler b is again the piston, the frame d the chamber. The special formula is therefore (C^P- 1 -)* c. On account of the omission of c, the higher pairing between b and d which we have already described in 76 (Figs. 269 and 270), is used at 3, which almost destroys the possibility of that joint being steam-tight. The inventor rectifies this by the use of some additional closing piece, the nature of which he does not make clear, and which we have therefore omitted. The tightness of this joint is not, however, important if only leakage could be prevented between the circular walls of the chamber and the piston where they are in contact, for Lamb uses the steam both within and without the annular piston. Tn the position shown there is on the left between the piston and the outer wall of the chamber a considerable space, while between the inner side of the piston and the inner wall of the chamber an opening into which steam is admitted is just beginning to show itself. The action here begins when the outer space is just half full and the crank at the top of its stroke. The steam in the two complementary spaces within and beyond b is allowed to escape freely. As the crank rotates the slot at 3' moves up and down the fixed diaphragm in d, exactly as the pin 3 and block c in the last
- See as to this and the following machine, Repertory of Patent Inventions, 1843.
Enlarged series, vol. 1, p. 98.
