420 KINEMATICS OF MACHINERY.
ing purposes, and also as a fire-pump ; it has also been used in England as a hydraulic motor* (chamber- wheel turbine), and serves often as a gas-pump in gas-works. It has thus been successfully applied to three of the several applications of chamber- wheel gear before enumerated.
So far as the originality of the invention goes if we may speak at all of the " invention " of what is really only a special form of the Pappenheim chamber-gear Eepsold was not the first to use it, for in France Lecocq obtained a patent for a similar rotary pump in 1832 ; f he called it a "pump with two pistons revolving on one another."
100.
Dart's or Behrens' Chamber-wheel Gear. Plate XXXVI. Fig. 2
In the American section of the last Paris Exhibition there were two applications of the chamber- wheel train shown in Fig. 2, PL XXXVI.; they were invented by Behrens and exhibited by Dart and Co.J The two pump-wheels are here again one-toothed, as in the last case. They are fixed at their sides to circular discs (not shown in our engraving) and this renders it possible to remove altogether the portions of them below the teeth, i.e., the root cylinders. The place of the latter is taken by the cylinders q and c 2 , which are fixed to the chamber. These have cylindric hollows, q r and n s, the contact of which with the points of the teeth, as the latter revolve, is sufficient to render unnecessary the additional contact of the flanks of the teeth. In our figure these are shown so as also to work together, mp being a curtate epitrochoid, described by the point o. In practice the point o is left a little clear of the curve (by rounding it off) in order to prevent the compression of fluid in the triangular space op q. So soon as the point p reaches q, o has got to the same place, and passes downwards from q to r. The point of the tooth of "b, therefore, works closed against q r, while its root t moves always in contact
- Practical Mech. Journal, 1855-6, vol. xviii., p. 28.
t Propagation Industrielle, vol. iii., 1868, p. 182.
J Propagation Industrielle, vol. ii., 1867, p. 116. Engineering, Apr. 4, 1875, pp. 368-9. .
