Cablegation: I. Cable Controlled Plugs in Perforated Supply Pipes for Automatic Furrow Irrigation
ABSTRACT A single pipe line served both the transmission and distribution functions at the head of a furrow ir-rigated field. Pipe size was selected to be slightly less than full when carrying the flow rate available on the ex-isting grade. Orifices were drilled in the pipe 30 ° from vertical toward the furrow side. Water was forced out of these orifices by a plug in the pipe. Position and move-ment of the plug were controlled by attaching it, with a cable through the pipe, to a reel at the inlet end with its rotation rate governed by a geared down, 12 v DC elec-tric motor, regulated in turn by a rheostat. A computer model predicted, and field tests corrobo-rated, that orifices near the plug had highest flows, with flow diminishing in orifices further upstream to zero flow at a distance determined by total flow, orifice size and spacing, and slope of the pipeline. As the plug passes a specific orifice, moving downstream at speeds from 3 to 6 m/h, flow begins at the maximum rate then decreases with time until the flow ceases. Effects on flow times and rates from orifices of varying orifice size, total water supply rate and plug speed, and of using multiple plugs and sleeving, are illu-strated and discussed.