Page:The Kinematics of Machinery.djvu/436

 414 KINEMATICS OF MACHINERY.

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Payton's Water Meter. Plate XXXV. Fig. 1.

Fig. 1, PL XXXV. is a schematic outline of a water meter exhibited in the English department of the Paris Exhibition of 1867.* It is a two-toothed chamber- wheel train, the profiles of its wheel teeth being involutes of circles. The line (and normal) of contact NN makes in our figure an angle of 15 to the line of centres ; it is necessary to make this angle small in order that the contact may last sufficiently long, The involutes touching in op extend from m to q and from r to n ; within m and r circular arcs of any convenient radius (so long as they do not interfere with the contact) continue the profiles to the bosses of the wheels. The backs of the teeth have for their profiles curves which are very nearly parallel to the involutes and which must lie very close to them in order not to disturb the contact, in order, i.e. that the back of one tooth may not foul the point of the opposite one. It is for this reason that the teeth have received their peculiar scoop-shaped form.

Here again a quantity of water, contained in the space behind each tooth, is returned every revolution, so that the delivery of the water, as in Fabry's machines and one of Root's, is discontinuous. This can be seen also from the fact that the point of contact does not traverse the whole profile continuously. The volume of water actually passing through the meter per revolution is again very nearly equal to that of the tooth-ring cylinder.

"Whether good workmanship is of itself sufficient so completely to prevent leakage that the apparatus can make an accurate water meter can only be determined by experience. The instrument, unquestionably a very simple one, seems to have been very rapidly received into favour in England.


 * The Engineer, Feb. 1868, p. 92. (< Epicycloidal Water-meter.")