File:Vertical Section of Holyoke Testing-Flume.jpg

The flume occupies the lower part of a substantial building; the main features are shown in Fig. 77. The walls of the wheel pit (D - D), which is 20 feet square, are built of stone masonry, and lined with brick laid in cement. The water is admitted to it from the head canal through a trunk or penstock, and vestibule, which are not shown in the figure. Over an opening in the floor of the wheel pit, the wheel W tor be tested is set in place, the water discharged from it finding its way through a large opening into the tailrace C, 35 feet long and 20 feet wide; and finally over a sharp-crested weir at A, into the lower canal. The whole head h available for testing may be from 4 to 18 feet for the smaller wheels, and from 11 to 14 feet for large wheels, up to 300 horsepower. The measuring capacity of the weir, which may be used to its full length, 20 feet (and then would have no end contractions), is about 230 cubic feet per second. The head h becomes known in any test by observations of the water level in two glass tubes communicating with the respective bodies of water W and C. The water in channel C, which is a channel of approach for the weir A, communicates (at a point some distance back of the weir) by a lateral pipe with the interior of a vessel open to the air, in a side chamber. Water rises in this vessel, and finally remains stationary at the same level as that of the surface in the channel of approach. A hook gage being used in connection with this vessel, observations and readings are taken, from which the value of H, or head on the weir, may be computed, for use in the proper weir formula for the discharge q. Fig. 77 shows a turbine in position for testing, with a vertical shaft—the ordinary case. Upon the upper end of the shaft is secured a cast-iron pulley P, to the rim of which the Prony brake is fitted for purposes of test.