PA PP EN HELM CHAMBER- WHEELS. 405
wheels must remain in close contact. The shafts of the wheels pass beyond the chamber, and are kinematically connected by two equal spur-wheels, a^ and \. If now one of the axes that of a, for in- stance be caused to revolve, the other will turn with equal angular velocity in the opposite direction. If the turning take place in the direction of the arrows in Fig. 1, and the lower opening be connected with a reservoir of water, then as the wheels revolve the spaces between their teeth will be filled with water, which they will transfer from one side of the chamber to the other. On account of the contact between the teeth where they gear together at m n no water can pass backwards, so that it must be driven onwards through the delivery-pipe. The machine may therefore serve as a pump, and for this purpose offers the advantages that it has neither valves nor any motions but rotary ones.
FIG. 278.
There is no difficulty in so forming the teeth of a and b that their profiles are always in contact in at least one point somewhere in the neighbourhood of mn, and that the point of contact passes continuously through the whole profiles as they move. Under the supposition that this is the case as it is in Fig. 1 no water can pass back from the upper to the lower part of the chamber between a and I. The amount of water passing through the ma<tjine is then directly proportional to the number of revolutions of the wheels. If these move uniformly, the water is delivered in a con- tinuous stream, on which account the machine might be well suited for a fire-pump.
The volume of water delivered by the pump per revolution is equal to the contents of the spaces* of both wheels, or as the volume of the teeth may in this case be considered the same as the volume of the spaces, is approximately equal to the contents of a
- A " space " is the volume enclosed between the sides of two consecutive teeth,
and limited above and below by the point and root cylinder of the teeth.
