12.5: Travelers

A semi-automated sprinkler system was developed in the 1960’s to reduce labor and to adjust application depths to match soil and crop requirements. The early versions consisted of rotating booms mounted on a cart that was periodically moved. That design was replaced with a towable cart that could be pulled continuously across the field to provide a moving sprinkler system. Initially the travelers were pulled by winding up cable on a cart. The other end of the cable was anchored at the end of the travel lane. Big guns were developed that operated at high pressures but could throw water hundreds of feet. Utilization of traveler systems has decreased in the United States to about 2% of the sprinkler irrigated land. However, systems are utilized more extensively internationally.

Figure 12.16. Soft-hose traveler irrigation system. (Photos at top are courtesy of Yüzüak Irrigation Sprinklers.)

A modern cable-tow, or softhose, traveler is shown in Figure 12.16. Water is supplied to the traveler with a flexible hose, called a lay-flat hose. The hose is looped behind and to the side of the traveler when positioning the cart to the edge of the field. This avoids interference with the cart when moving toward the center of the field. This style of traveler is pulled by a winch that rolls cable from the field boundary toward an anchor—often the tractor used to reposition the cart for subsequent irrigations. The water source can also be in the middle of the field. This allows a hose that is half the length of the cable. The effective diameter of the cable reel increases as cable is rewound on the cart. This could cause variable speed of movement as the cart moves along the towpath. Special controls are used to vary the speed of the cable winch to provide uniform speed of travel. The traveler stops when it reaches the anchor point. The hose is then drained and rewound onto the hose reel. The cart is then located at the edge of the next towpath and the process repeats. Guns apply water beyond the edge of the traveler set as shown in Figure 12.16.

Later designs of travelers eliminated the cable and used a fortified hose to drag the sprinkler cart along the path (Figure 12.17). Hoses were designed to supply water to the cart and with enough tensile strength to pull the sprinkler cart through the field. This eliminates the need for a cable to move the gun through the field. The sprinkler cart is smaller than the cart for the soft-hose traveler; therefore, less effort is needed to move the gun across the field. These hoses are generally polyethylene and are referred to as hard hoses because they are quite rigid. Hose diameter can be as big as six inches and the length can be up to 2,000 feet; however, most systems use hose smaller than five inches. Manufacturer recommendations should be carefully followed when selecting the hose diameter and length to have adequate strength and to minimize friction loss. The hard-hose traveler requires less time to reposition to the next set than a soft-hose traveler because the hose is rewound onto the reel as the sprinkler cart is towed across the field. Additionally, the hard hose is not drained during rewinding which prevents the hose from collapsing as it is rewound onto the cart. The hose-reel cart is generally equipped with a lift to carry the sprinkler cart while repositioning the system or for storage. Once a set has been irrigated the sprinkler cart is lifted with the primary cart and the system is repositioned for the next set. In many cases the hose reel can be rotated in place to irrigate the set opposite of the one just completed. The host cart is slowly pulled from the hose reel to the far end when positioning for the next set. The diameter of the coiled hose on the reel increases as the hose is rewound, increasing the effective diameter of the hose reel. Just like with cable tow systems, the change of diameter can cause a variation of travel speed along the towpath; therefore, these travelers must adjust the speed of rotation of the reel to maintain a constant sprinkler cart velocity.

Figure 12.17. Hard-hose traveler diagram with photo of a traveler with a gun (photo a is courtesy of Cadman Power Equipment) and with large boom (photo b is courtesy of Bauer Group).

Recently a large boom has become available which replaces the big gun (Figure 12.17b). The advantage of the boom, which does not rotate, is that uniform application of water is more achievable, and less pressure is required to apply water across the set (Peters and McMoran, 2008). Friction loss in the hose remains the same as for a gun with equal flow; however, the operating pressure is less. Wind effects are also diminished with a boom configuration.

All travelers have slope limitations. Slope along the towpath changes the effort required to transport the gun. Slope perpendicular to the towpath may cause the cart to slide downslope. Slope also affects the acceptable application rate to avoid runoff. Manufacture recommendations should be followed regarding slope.

The traveler has little clearance and the hose and/or cable must be pulled across the soil surface. Therefore, the traveler operates along a travel lane. This is often a grass or alfalfa strip for row crops so that the hose can move easily.

The big gun does not make a complete circle during operation (Figure 12.18). The gun is designed to operate over an arc and then it automatically reverses to the starting position of the arc. The arc and starting position should be set according to the manufacturer's recommendations to provide uniform irrigation. If the arc is too large, excess water will be applied near the lane where the traveler is towed.

Figure 12.18. Operational characteristics of a big gun traveler