What is the purpose of an irrigation standpipe commonly used in agriculture, and how does it work?

Question

I live in a primarily agricultural area and I see standpipes located in virtually every piece of ag land, yet I have no idea what purpose they serve or how they work. I have a guess but I would like be aware of how these things work so I don't inadvertantly make a fool of myself sometime while talking to a farmer.

Answer 1

Standpipes are attached to pressure-fed systems to allow output valves to be positioned at a convenient height. Standpipes are attached to gravity-fed piped water systems for cheap water control. Irrigation ditches below the level of the supply water are plumbed with pipes that have an upward-facing ell on the end. Water spills out of the ell and into the irrigation ditch. To shut off the flow you stick a piece of pipe into the ell that is long enough so that its top is above the supply level.

Answer 2

Center pivot irrigation apparatus:

An electrically controlled water powered reversible center pivot irrigation apparatus is disclosed. The apparatus includes a multiplicity of water-carrying conduits flexibly connected to each other and supported at intervals by self-propelled supports. Each of the self-propelled supports includes a water powered sprinkler which turns a drive shaft for propulsion of the support. An electrically controlled transmission designates the direction in which the support travels and mechanical linkages, operable in either direction of movement of the apparatus, control the flow of water from the conduits to the sprinklers depending upon the relative position between adjacent conduits.