Figure 5.25. Hand-moved system: 1) pump, 2) mainline, 3) lateral.
The use of hoses reduces the number of laterals that are needed, and so, the system costs are less than for permanent systems. Problems can arise with the plastic hoses. The system is reliable for orchards but operators may have difficulties in managing the system in field crops.
Hand-Moved Systems. These are designed to be moved by hand. The lateral is usually in aluminum or plastic pipe between 50 mm and 100 mm in diameter and 9 to 12 m long, so that it can be moved easily by one person. The laterals remain in position until irrigation is complete. The pump then is stopped and the lateral disconnected from the mainline, drained, dismantled, moved by hand to the next point on the mainline, and reassembled. Usually, the lateral is moved between one and four times each day. It gradually is moved around the field until the whole field is irrigated (Fig. 5.25).
Systems may have two or more laterals to irrigate large areas. They are connected to the mainline using valve couplers. This allows irrigation to continue while one of the laterals is being moved. In some cases, when the sprinklers are used to germinate new plantings, to leach salts, or to supplement rainfall, the whole system including pump and mainline is moved from field to field.
Hand-moved sprinklers are used to irrigate a wide range of field and orchard crops. Their capital cost is low and they are simple to use. However, they require a large labor force, often working in wet, muddy, and uncomfortable conditions.
Towed Systems. To alleviate labor requirements, laterals (aluminium or plastic) can be mounted on wheels or skids and towed across the submain to their new settings. Towed systems are used for large fields.
Sprinkler-Hop Systems. Sprinklers are placed only at every second or third position along the laterals. When the irrigation depth has been applied, the sprinklers are disconnected and moved or "hopped" along the lateral to the next position. This is done without stopping the flow in the lateral because each sprinkler connection is fitted with a special valve that automatically stops the flow when the sprinkler is removed. After the two or three hops are complete, the lateral is moved to the next position. Normally only one lateral move or one sprinkler hop is required each day.
Side-roll or wheel-line systems use an aluminium or galvanized steel lateral as the axle of a large (1.5 to 2.0 m diameter) wheel. The wheels are spaced 9-12 m apart and allow the lateral to be rolled from one irrigation setting to the next. A small internal combustion engine normally is used to roll the whole lateral. The pipes must be strong, and rigid couplings are used to carry the high torque loads. The engine often is located in the middle of the lateral to reduce the torque. The small rotary sprinklers, spaced 9 to 12 m apart, are mounted on a special weighted swivel assembly to make sure they are always in an upright position after each move.
The mainline is laid along the side of the field. When irrigating, the lateral remains in one place until the water has been applied. The pump then is stopped and the lateral uncoupled from the mainline and drained (to reduce the weight) and rolled to the next position using the engine. A flexible hose connection to the hydrant allows the lateral to be moved over two or three sets with supply from the same hydrant.
This system is best suited to large flat rectangular areas growing low field crops. In heavy soils, the wheels may become bogged down in the mud.
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