A construction of this sort has been carried out by Ober-Bergrath Althaus in the tanning mill at Vallendar near Ehrenbreitstein. The essential parts of the arrangement can be seen in [Fig. 118]. A E A is an ordinary reaction wheel with four curved revolving pipes and a fall of 124 ft., and B B is a larger wheel with floats which is set in rotation by the water issuing from A. A. Since the two wheels turn in opposite directions, they must be connected together by a special form of wheel-work. The outer wheel affords the additional advantage of serving at the same time as a fly-wheel, thereby giving a more uniform rate of motion to the whole machinery.
Fig. 118.
Turbines are variously constructed, but all have curved floats or buckets against which the water acts by its impulse or reaction in flowing either outward from a 1 central chamber, 2 inward from an external casing, 3 from above downward, and, 4 from below; these constructions are either divided into outward, vertical or central discharge wheels.
Turbines may also be divided into reaction turbines, or those actuated substantially by the water passing through them (their buckets moving in a direction opposite to that of the flow); impulse turbines or those principally driven by impact against their blades or buckets (the buckets moving with the flow); and combined reaction and impulse wheels which include the best modern types of turbines. In reaction turbines the wheel passages are designed to be always full and therefore the water under pressure; in the impulse turbine the passages are not usually full.
Fig. 119.
Turbines in which the water flows in a direction parallel to the axis are called parallel flow turbines—or journal turbines.
The turbine-dynamometer is a device used for measurings or testing the power delivered by turbines (whence its name).
Fourneyron’s Turbine. This is, in its latest form, when properly constructed, the nearest perfect of the horizontal water-wheels. It revolves either in the air or under water, and may be either high or low pressure. For the low-pressure wheel, the water enters the flume from the open reservoir, with free surface, as in Fig. 119. For high pressure, the reservoir is boxed up and the water brought in at the side through a pipe, as shown in [Fig. 124], page 136. The first is for low and the second for high falls.