24 



and by means of the gate in the overflow wall can be made to rise level 

 with the overflow crest and the quantity delivered is regulated by adjusting 

 the orifice. The pressure on the orifice is regulated and kept more or less 

 constant by the overflow wall. The excess water passes over the overflow 

 wall and also through the regulating gate into the downstream compart- 

 ment and from there into the pipe. By proper adjustment of the gate the 

 water level may be kept fairly constant. When the gate is entirely closed 

 the excess water will pass over the overflow and increase the pressure on 

 the orifice and the accuracy of the measurement will depend on the quan- 

 tity of water passing over and the length of the overflow crest. A moderate 

 increase in pressure will not affect the accuracy very greatly, for instance a 

 1-inch increase in pressure will increase the volume delivered by 6 per cent. 

 It would be feasible to use a weir plate in place of the miners' inch plate, 

 but with a weir plate the quantity delivered could not be adjusted and the 

 accuracy would be affected to a much greater extent by an increase in 

 depth of water on the crest. 



Fig. 18 shows a similar box used in southern California. It differs from 

 the previous one in that instead of delivering the water through an orifice 

 adjustable in size by a slide, it is delivered through a number of openings 

 varying in size and each closed by a slide gate. In the illustration the 

 three smaller orifices are opened and the fourth one closed. The water 

 passes through the orifices into a basin formed by two half sections of pipe 

 cemented to the box and connected at the bottom to the private pipe of the 

 orchardist. 



Miners' inch box and takeout from pressure pipe line. 



To deliver water from a pipe under pressure and measure it by miners' 

 inches the same form of construction could be used as for a weir box (Fig. 

 11), using a miners' inch plate instead of the weir plate. This form of 

 miners' inch box is shown in Fig. 19 which illustrates a box used in south- 

 ern California. In this case the orifice is 5 inches high and is regulated by 

 two slides. The pressure on the center of the orifice is 4 inches, which gives 

 a depth of water of only \\/ 2 inches from the upper edge of the orifice to 

 the water level. The height of the orifice is too great in proportion to 

 the pressure. 



Miners' inch box with overflow wall for canals or flumes. 



The use of an overflow to regulate the head on the opening can be ap- 

 plied to miners' inch boxes installed in earth ditches or in flumes very 

 much in the same manner as for pipe lines. Fig. 20 illustrates the con- 

 struction of the device. It consists of a section of flume divided into two 

 compartments by the parallel overflow crest wall in between. The compart- 

 ment which forms part of the supply ditch is open at both ends and the 

 flow can be checked or regulated by flashboards. The other compartment 

 forms the box from which the water is taken out through the orifice in the 

 side wall. The flow into the box is regulated by a gate and the excess passes 

 over the crest of the overflow wall back into the canal. The crest of the 

 overflow should be 8 inches above the center of the opening and must be 

 of sufficient length to dispose of the excess without increasing the depth 

 of water to a great extent. 



