. Bulletin of the Department of Agriculture. Agriculture; Agriculture -- United States. WOOD PIPE FOR CONVEYING IRRIGATION WATER. 15 SPILLWAYS. As a precaution against damage that might result from accidental stoppage of the pipe and to facilitate quick emptying in case of acci- dent, spillways should be provided near the intake to siphons on irrigation systems where it is feasible to do so. AIR VALVES. At every summit of a wood-pipe line, an air valve or chimney should be placed. This is to allow air to enter so as to prevent a vacuum and liability of collapse when the pipe is emptied, a
. Bulletin of the Department of Agriculture. Agriculture; Agriculture -- United States. WOOD PIPE FOR CONVEYING IRRIGATION WATER. 15 SPILLWAYS. As a precaution against damage that might result from accidental stoppage of the pipe and to facilitate quick emptying in case of acci- dent, spillways should be provided near the intake to siphons on irrigation systems where it is feasible to do so. AIR VALVES. At every summit of a wood-pipe line, an air valve or chimney should be placed. This is to allow air to enter so as to prevent a vacuum and liability of collapse when the pipe is emptied, as well as to permit the escape of air that may accumulate at such points. Of the various types of air valves on the market one in common use is illustrated by figure 4. A valve of this kind remains open until closed by internal water pressure, and by means of an angle valve air that accumu- lates while the pipe is in service may be released by Where practicable, iron pipes open at the top are carried to a point above the hydraulic gradient in preference to the use of air valves at sum- mits. Air valves and chimneys are usually connected to wood pipe by means of cast saddles, which are held in place by steel bands (PI. Ill, fig. 1). BLOW-OFFS. Blow-offs are attached near the bottom at low points of the wood pipes in a man- ner similar to that of attaching chimneys, and a sufficient number should be pro- vided so that every section of the pipe line may be drained and flushed out. Ordinary gate valves are usually employed for this purpose, the size to use being dependent on conditions. In lines where a large amount of silt is liable to accumulate, such valves should be of large size. On the 84-inch pipe of the Pueblo, Kocky Ford Irrigation Co. the 6-inch blow-offs operating under a head of 75 feet would completely clog up with grass, leaves, and debris. To clean the pipe it was necessary to cut a number of holes through it. These were made 30 inches square. New blow-off gat
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