Page:The Kinematics of Machinery.djvu/441

 REPSOLIfS PUMP. 419

the Hamburg firm of Eepsold. This well-known machine, which excited great attention in its time, is a chamber-wheel train, the pump wheels of which have one tooth only. Pig. 1, PL XXXVI. is a schematic representation of it. The profiles of the teeth beyond the pitch circles are here epicycloids, as m gr and nt, and within them hypocycloids as ms and nr, both obtained, as in ordinary set wheels, by rolling upon and within the pitch circles (primary centroids) the equal describing circles (auxiliary cen- troids) IT and W v The portion su of the profile, added at the root of the teeth, is a part of the path of the point t of the wheel I relatively to a ; the hypocycloidal arc m s corresponds to the roll- ing of W l through the arc m v. The points of the teeth tp and q Gr are cylindrical, as are also the corresponding surfaces between their flanks, exactly as in the case of common spur wheels. With the profile forms here described the delivery of the pump is not absolutely uniform, for the whole profile of the wheel does not pass continuously through the point of contact. The want of uniformity is so small that it may fairly be neglected; all that is necessary, however, to prevent it entirety is to use in the tooth faces at m q, n t, &c., such a form as makes the whole profile a con- tinuous curve as e.g. a circular arc and using for the roots of the teeth the corresponding enveloping form.

The pump-wheels of Eepsold's machine are commonly described as "eccentrics of special form" or something of. the kind; it is clear, however, from what has just been said, and a glance at the figure makes it still more evident, that each of them is simply a spur-wheel with one tooth. The point and root cylinders of the teeth slide upon one another, so that wear must unavoidably take place at first, as in the Eoot's blower Fig. 2, PL XXXIV. It is therefore difficult to retain a tight joint where these parts of the wheels are in contact, and the pump is therefore most suitable for working with low pressures. The wings EG and FH of the chamber must be greater than semicircles in order to prevent com- munication between the suction and delivery pipes behind the wheels. Eepsold has used packing strips of leather in them.* The volume of fluid delivered per revolution is almost exactly equal to that of the tooth-ring.

Eepsold's pump is used in mining operations, generally for drain-


 * Berliner Verhandlungen, 1844, p. 208.

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