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On-farm pipe networks are classified as open (low head) or closed (pressurized) depending on whether the system is open to the atmosphere. Both types of pipelines can be laid on the ground surface or buried. Surface pipes have the advantage (over buried pipes) of portability, while buried lines can be placed below the tillage zone where damage by farm machinery, vehicles, vandals, etc., is minimized. When buried above the frost depth, provisions for draining buried pipelines are required.
Pipelines have several advantages over open channels. Well-constructed pipelines eliminate seepage and evaporation losses, avoid weed problems, and are normally safer than open channels, since humans and equipment cannot fall into the water stream. Pipelines also permit the conveyance of water uphill against the normal slope of the land and, unlike the open channel, can be installed on non-uniform grades. The use of buried pipe eliminates pad construction for open channels, allows use of the most direct routes from the water source to fields, and minimizes the loss of productive land (since crops can be planted up to or over the pipelines). Portable pipe systems laid on the soil surface can be removed while cultural operations are in progress. Open channels may, however, be more economical than pipelines when land is flat and flows are large.
Because low head pipelines are open to the atmosphere, heads in these pipelines seldom exceed 15m (50 ft). The standpipe provides head regulation, water release, vacuum relief, and air release. Open pipelines are not generally used with application systems that require more than 6m (20 ft) of head.
Pressurized pipelines normally supply application systems that require more than 6m (20 ft) of head. Pressurized pipelines are not open to the atmosphere and do not contain structures such as standpipes. Pressure regulating, check, air release, and vacuum relief valves are used instead of standpipes and pump stands to provide flow and pressure control as well as to protect the pipeline.
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