Figure 1. Schematic of layout for a cable tow traveler. Travel lanes are 180 to 330 feet apart depending on sprinkler capacity and diameter of coverage.
*Formula used to compute total water applied when using a gun type traveler.
The acres of cropland that can be irrigated per week will depend on the sprinkler capacity (gpm), the amount of total irrigation to be applied per acre (inches per acre), and the number of hours per week the machine is operated. In operating the machine, the machine is initially positioned 60 to 100 feet from the end of the field. The cable is attached to an anchor on the other end of the field. One end of the hose is attached to a hydrant on the main line and the other end is attached to the traveler. There should be about 30 feet of hose behind the machine at the start. The water is turned on and the sprinkler operates for 30 to 45 minutes before the machine is put in gear to begin its travel through the field. This irrigates the end of the field. After traveling the length of the field, the machine stops and the sprinkler is operated 30 to 45 minutes to irrigate that end of the field. Figure 1 shows a typical layout for a cable-tow traveler.
Figure 1. Schematic of layout for a cable tow traveler. Travel lanes are 180 to 330 feet apart depending on sprinkler capacity and diameter of coverage.
There are several United States and foreign manufacturers of hose drag sprinklers. Some companies offer a variety of sizes of machines with different hose sizes and lengths. Other companies offer a more limited range of machine sizes. Some machines are designed for small turf uses and others for larger agricultural applications.
At least one manufacturer offers a hose-pull traveler that has small sprinklers or spray nozzles mounted on a boom rather than using one- or two-gun sprinklers. The small sprinklers operate at lower pressure than gun sprinklers. They do, however, have a higher instantaneous application rate. This higher rate can result in runoff and erosion on soils that have a slow intake rate.
In operation, the hose-drag traveler is somewhat similar to the cable-tow traveler. With low growing crops, the sprinkler cart will travel over the crops and no travel lane is required. Lane spacing is a function of sprinkler capacity or length of the boom.
The hose winds onto the drum as the sprinkler cart is pulled in. Once the sprinkler cart reaches the drum, the entire machine can be moved. The machine is moved from lane to lane with a tractor. The sprinkler cart and hose are pulled out from the machine by a tractor. Some of the machines have a 360 degree turntable on which the drum is mounted. (With the turntable machine, it is possible to irrigate fields on either side of the machine.)
The length of field that can be irrigated is equal to the hose length plus 60 to 120 feet. Spacing between lanes will depend on sprinkler diameter. Normal spacing is 70-80 percent of sprinkler diameter. Sprinklers can be operated in a part- or full-circle mode. The area directly in front of the sprinkler cart is usually left dry. Normal sprinkler pressure is in the range of 60 to 100 psi.
The amount of irrigation applied to an area at one time can be varied by adjusting cart travel speed. Lane spacing and sprinkler capacity are also variables. The total acreage of land that can be irrigated per week will depend on the amount of irrigation applied per acre, the number of hours per week the machine is operated, and sprinkler capacity. Figure 2 shows a typical layout for a hose-drag traveler.
Figure 2. Schematic of layout for a hose drag traveler. Travel lanes are 100 to 330 feet apart depending on sprinkler capacity and diameter coverage.
Most cable-tow and hose-drag machines have speed compensation that adjusts the travel speed of the machine or sprinkler cart through the field to insure that it is uniform as more cable or hose builds up on the cable drum or hose drum.
The travelers were originally designed for irrigating fresh water onto cropland. However, several hose-drag travelers have been used recently to land apply nutrient-rich effluent (wastewater). Effluent that contains limited amounts of solids can be applied with water drive machines, but if any appreciable amount of solids is present, auxiliary engine drives should be used.
The hose-drag traveler is adaptable to odd-shaped fields and varying row lengths. Both machines are transportable and can easily be moved to other fields.
The introduction of the boom sprinkler for the hose-drag traveler waa an attempt to reduce energy requirements. However, this machine is best adapted to flat topography, low growing crops, and high infiltration rate soils. The machine is not easily transported between farms. Also, the boom sprinkler is not well adapted for land application of nutrient-rich effluent that contains an appreciable amount of solids.
There are several ways that growers can reduce energy requirements for travelers. These include using larger hose on the machine, uaing shorter lengths of hose, using larger supply pipe, and using lower pressure at the sprinkler. However, there are trade- offs on each of these energy-saving methods. The major trade-off is higher initial cost for system components that must be balanced against savings in energy. Using lower presaure at the sprinkler can result in reduced irrigated area (wetted diameter), larger droplet size, and potentially, more soil compaction and runoff.
As an example, consider a properly tuned diesel engine connected to a properly matched pump. For each 16- to 17.5- horsepower of engine horsepower, one gallon of diesel fuel will be consumed per hour. An average figure is 16 horsepower (Hp) per gallon of fuel. By using methods to reduce pump pressure, such as larger diameter main line, larger hose on the machine, or lower sprinkler pressure, it is possible to reduce horsepower requirements and, therefore, fuel consumption.
Table 1 gives data for pressure (head) requirements for hose-drag travelers supplied by one manufacturer. The comparison shown in Table 1 assumes:
Two hose sizes, 4.0-inch ID and 4.5- inch ID, and two main line sizes, 6- inch ID Class 200 PVC pipe and 8-inch ID Class 200 PVC pipe, are used. The 4-inch ID hose is 1250 feet long and the 4.5-inch ID hose is 1300 feet long. The main line is 3000 feet for both the 6-inch and 8-inch.
The difference in purchase price between the two travelers is approximately $3700. The difference in installed cost between the 6-inch and 8 inch ID main line pipe is approximately $1.50 per foot or $4500. Assuming a machine life of 12 years and 10 percent interest,the annual difference in ownership cost between the 4-inch ID hose and 4.5- inch ID hose machine is $543.00.
Assuming a pipe life of 25 years and 10 percent interest, the annual difference in ownership between the 6-inch and 8-inch ID main line pipe is S496.00. To justify purchasing the larger hose or larger pipe, the fuel savings should at least equal the additional ownership cost.
Fuel cost (savings) are computed based on the energy required to deliver the required flow rate at the desired operating pressure. To compute horsepower (HP) requirements, use the formula shown below.
Horsepower =
After assuming a certain efficiency pump, compute horsepower requirements and fuel consumption. Table 2 gives horsepower requirements and fuel consumption for three pump efficiencies, based on 16.66 water horsepower per gallon of diesel fuel for the four combinations of traveler sizes and supply pipe sizes.
Figuring the farm cost of diesel fuel at $.90 per gallon and the traveler operating 584 hours per year (6 inches of irrigation on 75 acres of cropland), the fuel savings between the smaller hose and smaller pipe size and the larger hose and larger pipe size would be approximately S725.00 per year for the 65 percent efficient pump. The annual difference in cost of ownership of the two systems is S1039.00. Therefore, the fuel savings do not cover the additional cost of ownership. Also, fuel costs are paid annually whereas the initial investment is an up-front cost.
Similar comparisons can be made for other machines and hose sizes.