12.2.1: Types of Systems

Moved-lateral sprinkler systems are composed of a lateral that is periodically repositioned across the field. The lateral consists of individual pieces of pipe connected with a coupler and latching system. Individual pieces of pipe are often referred to as a joint, a length, or a section of pipe. The simplest sprinkler system is a hand-move system where the lateral joints are carried from set to set by hand and the lateral is reassembled at the new set (Figure 12.2a and 12.2b). In some cases, aluminum pipe is used for the mainline (Figure 12.2c). In other cases, the mainline is buried and risers with hydrants are connected to the lateral (Figure 12.2d). While these systems are versatile, they require considerable labor, especially if the soil surface remains muddy after irrigation or the soil surface is not protected by the crop. Moving laterals is also difficult when crops are tall. Moving the lateral is much easier when the soil is covered such as with grass or alfalfa. Once the lateral reaches a field boundary it must be disassembled and transported to the next location to be irrigated. The lengths of pipe, sprinkler types and nozzle sizes are usually the same for all joints of the lateral to avoid confusion when repositioning the lateral. The substantial effort required to move the lateral promotes large application depths per irrigation to minimize the number of moves.

Figure 12.2. Handmoved sprinkler system. (Photos a and b are courtesy of USDA-NRCS. Figures c and d were adapted from Turner and Anderson, 1980)

Hand-move irrigation systems are the cheapest to buy and maintain. Maintenance involves replacing gaskets used to seal adjoining lengths of pipe—usually replaced biennially or triennially. Sprinklers and nozzles should also be replaced periodically. Sprinkler replacement depends on the amount of annual use; however, sprinklers often last more than five years. The pipe has a long life; thus, investment and maintenance costs are small while labor requirements are quite high. In some cases, hand-move systems are used for special purposes such as leaching salts during the off-season where surface methods are used during the irrigation season. Hand-move systems are extremely portable so they can be used on fields where supplemental irrigation is not required every season.

To alleviate the labor of carrying laterals, several mechanical adaptations were developed to reposition the lateral to the next set. One method uses a tractor, or other power source, to pull the lateral across the field from one set to another. This type of system is called a towline, skid-tow or drag-line system. The components and plan view of the system as shown in Figure 12.3. As shown in the plan view, the pipeline is towed in a zigzag fashion across the field. The lengths of pipe are held together with tow-line couplers that connects two lengths of pipes. Connecting pins were used within the coupler to allow quick disassembly when relocating laterals to the starting set. A skid pan held the pipe above the soil and protected the drain that was included in the coupler. The pipeline is supported by devices, called outriggers or stabilizers, that are clamped onto the pipeline to prevent the lateral from twisting during movement which prevents sprinkler risers from tipping over and breaking. Wheels were also used as shown in Figure 12.3 to provide stability; thus, some systems are called wheel-tow systems. To reduce abrasion on the aluminum pipe—especially for rough terrain—steel skid pans can be clamped at the midpoint of the joints to carry the pipe above the soil.

Figure 12.3. Tow-line sprinkler system and components. (Diagram of tow-line with wheel stabilizers is courtesy of Turner and Anderson, 1980. Plan view of field and tow-line system is adapted from Turner and Anderson, 1980.)

Tow-line systems work well on low-growing crops where the lateral pipe can slide freely across the soil and crop surface. The pipe must be pulled between the rows when the system is used for row crops. This is easily done for low-growing crops such as soybeans or grain sorghum. For tall crops, such as corn, the tractor will flatten one or two rows of corn when the pipe is pulled. Sometimes producers plant a few rows of a low-growing crops in the alley where the pipe is pulled. Others plant the tow alley to a permanent grass. In any case there will be a loss of production area for tall crops. The end cap and hitch shown in Figure 12.3 are installed on both ends of the lateral. The lateral is connected to the mainline using a flexible hose.

Tow-line systems are more expensive to purchase and maintain than hand-move systems. The same pipe and sprinklers are needed as for hand-move systems, but stabilizers and couplers increase investment cost. Friction between the soil and the pipe often causes wear that shortens the life of tow-line systems. Less labor is needed to move laterals from one set to the next than for hand-move systems; however, more time is needed to disassemble and reposition the pipeline once the lateral reaches the field boundary.

The third type of moved-lateral systems is the side-roll, wheel-move, wheel-line, or hand-roll system. With this system wheels are clamped directly onto the lateral pipeline (Figure 12.4c). Pipe used on side-roll systems is usually thicker walled than for hand-move or towline systems. The joints of the lateral are rigidly fastened—sometimes using gears between joints—to remain connected while applying torque when moving the system. The pipeline is moved by rotating the pipeline directly or in some cases to a drive shaft that runs parallel to the lateral. For mechanically powered systems torque is applied by an engine located on a chassis (Figure 12.4b) located either at one end of the lateral or along the center of the lateral where access is convenient. The engine slowly turns the pipeline or drive shaft, and the wheels rotate across the field. Hand-roll systems do not have an engine and the wheels are rotated by hand. The clearance below side-roll systems is typically about 3 feet but can be as much as 6 or 8 feet for special large diameter wheels. Sometimes braces are needed to keep the lateral in place after moving. Some alignment by hand to straighten laterals may be needed after moving. Sprinkler levelers (Figure 12.4d) include a swivel that kept sprinklers vertical if the pipeline did not rotate to the perfect angle. All moved-lateral systems should be drained prior to moving as demonstrated with the drain shown in Figure 12.4d for side-roll systems.

Figure 12.4. Side-roll sprinkler system and components. (The plan view shown in drawing a is adapted from Turner and Anderson, 1980. Picture c is courtesy of Rain for Rent and picture d is courtesy of Wade Rain, Inc.).