Irrigation Fundamentals

Part 6, Sprinkler Systems, Soft and Hard Hose Travelers

By Ed Butts, PE, CPI

In this continuing series on irrigation practices and techniques we have so far reviewed terms and definitions, crop use, soil properties, and basic types of irrigation. Last month, we introduced Big Gun irrigation and a sample design. This month, expanding that topic, we will outline soft hose and hard hose traveler systems.

Traveling Sprinkler Systems

Soft hose and hard hose (or reel irrigation) systems—also called traveling gun or simply traveler systems—consist of a single large sprinkler head, generally an equivalent to a Nelson Model 150 or 200 Big Gun®. They spray water over a portion of a circular pattern as the gun automatically and systematically moves through the field.

Traveling sprinklers were originally developed to significantly reduce labor with a minimum of initial investment for large acreage as an alternative to more expensive center pivot systems and to irrigate unusual or irregular-shaped fields. Travelers are capable of irrigating both regularly and irregularly shaped fields with run distances up to one-half mile (2640 feet). Traveling Big Gun sprinklers are capable of high uniformity application of water when the proper sprinkler flow rate, operating pressure, and travel lane spacings are selected.

As opposed to a solid set or portable Big Gun system, these sprinklers are placed on traveling machines or carts, with a soft, flexible rubber or hard, relatively stiff polyethylene water hose attached to and feeding the machine or cart.

A soft hose, also called a cable-tow traveler, is designed to travel twice the length of the hose. A hard hose, or hose-pull, traveler length is limited to the length of the hose stored on the reel. Thus, a soft hose traveler equipped with 660 feet of hose is designed for a run of 1320 feet (one-quarter mile). A hard hose traveler or reel with the same length of hose is limited to a run of 660 feet.

The run length can vary with the actual length of hose extracted from the reel or the reel can be rotated to double the total run length to 1320 feet without moving the reel. Either machine uses a small engine or is powered by the pressure and flow of incoming water that drives an inline turbine, piston, or bellows mechanism to retrieve the cart for a hard hose reel or propel the machine forward for a soft hose traveler.

Hose for both styles of travelers is stored on the reel during transfer to another set. A purge pump is often incorporated on the machine to purge and drain the hose for retrieval and transport by attaching the pump to a PTO (power take-off) from a nearby tractor. The travelers can be relocated and re-positioned, wherever necessary, so long as they remain connected to a source of pressurized water to drive the sprinkler head and machine when powered by water.

In instances with low supply pressure, an onboard engine-driven booster pump can be used to raise sprinkler pressure from a lower inlet pressure. Although they will work effectively on any shape or type of field, these sprinklers are often best suited for irregular-shaped fields, leased or rented ground, difficult-to-reach areas, and fields that cannot be otherwise irrigated because of obstructions like ditches, power lines, trees, roads, streams, or buildings.

Hard Hose and Soft Hose Travelers Compared

The following comparisons can be made between the hard hose or reel traveler and the soft hose or cable-tow traveler.

• A reel traveler can usually be moved in a shorter amount of time because there is no hose to reel in and no cable to unwind.
• A reel traveler will require more pressure to operate at the same GPM and hose length because the friction loss through the less expandable hard hose and associated drive mechanism horsepower is usually greater.
• A reel traveler is usually more expensive in capital costs but is usually capable of irrigating more acreage because less time is required to reposition, and it can irrigate twice the acreage per position by using rotation of the reel.
• Only the amount of hose that is needed must be wound off a reel traveler, whereas all hose of a soft hose machine must be wound off the reel and stretched out into a loop behind the machine so water can flow through the entire hose length without experiencing pressure-losing kinks in the hose. This makes the hard hose machine easier to use on short runs.
• Unlike a soft hose traveler, a hard hose traveler does not require a set end anchor, such as a tractor or imbedded earth anchor at the end of each run to which the cable is attached during the run to pull the machine toward the anchor.
• The hose on a hard hose machine is generally pulled in a relatively straight line. On a soft hose machine, the drag hose is pulled out behind the machine into a long return loop to the center fed hydrant. In areas with obstructions or impediments, this could cause more damage to the soft hose from kinks or uneven pull stress on the machine.
• A narrow travel lane for the gun cart is the only lane required for a hard hose traveler. A wider travel lane is required for the soft hose machine and to accommodate the looped radius of the soft hose.
• Both hard hose and soft hose systems use a large and long sprinkler hose and drive mechanism. Thus the pump operating pressure is usually higher as additive friction losses can build pump discharge pressures up to 150 psi. This requires more horsepower and thus more energy consumption, up to twice as much than a comparable center pivot or solid set Big Gun system.
• Labor and dedicated tractor requirements for traveling gun systems are considerably higher than with a stationary Big Gun or center pivot system as both traveler systems must be moved and reconfigured between sets. When earth anchors are unavailable, soft hose travelers often require tying up a tractor to use as the cable dead-man anchor. Hard hose travelers require a tractor with adequate drawbar horsepower to relocate the heavier reel between sets, usually through mud, and to pull the hose cart out to the beginning end of the run.

The distance or spacing between travel lanes for any given sprinkler size, including Big Guns, is largely determined by local wind conditions and uniformity requirements. High winds tend to distort or modify the sprinkler pattern into an egg-shaped or oval coverage pattern. Therefore, if possible, the direction of gun travel should be set at right angles (90°) to the prevailing wind.

While the continuous movement of this irregular sprinkler pattern improves applying water uniformly, it is essential to use closer spacings between travel lanes to ensure proper overlap to water-intense or critical crops. A part-circle sprinkler should be used when it is desirable to leave a dry path in front of the traveler or cart to prevent bogging down in mud from the sprinkler’s applying water to the ends of the field, without excessive overthrow beyond the field’s boundary and to adjust the arc of the sprinkler to compensate for excessive wind.

This is often a critical factor for the heavier and unbalanced pull exerted on a soft hose traveler than the lighter gun cart used on a reel. A full-circle sprinkler should be used when the lowest possible application rate is desired since the application rate of a traveling sprinkler is governed by the sprinkler flow rate, lane spacing, and the degree of sprinkler coverage or arc.

When using a part-circle sprinkler to maintain a dry travel path in front of the cart or machine, adjust the area of the circle not watered to the smallest possible remaining arc, with 60° to 90° the generally accepted limits. This will usually provide a sprinkler coverage between 300° to 270°, respectively. This will also provide nearly as low an application rate as is obtained with a full-circle sprinkler at the same performance.
The application rate of a part-circle sprinkler is greater than for a full-circle sprinkler of the same capacity, increasing in accordance to the proportion of circle covered.

For example, the application rate of a sprinkler covering one-half of a circle (180°) is double that of a full-circle sprinkler operating at 360°.

Pressure Requirements and Trajectories

As the applied pressure at the Big Gun nozzle increases, the stream velocity through the nozzle also increases, causing the stream to be broken into smaller, finer droplets and enabling the stream to be carried to a farther distance. Because of the continuous traveling movement of the sprinkler, the same exact area is not covered twice and is therefore not over-watered. In addition, a relatively constant distribution uniformity is generally maintained over a broad range of pressures.

Selecting the proper operating pressure, like the gun’s trajectory angle, is mostly a consideration of providing droplet conditions that are suitable for the needs and condition of the crop and soil to be irrigated. General recommendations for nozzle pressure at a traveling Big Gun to achieve the most desirable droplet conditions are shown in Table 1.

For the most part, general recommendations for the application of Big Gun sprinklers should adhere to the guidelines that were outlined in Part 5 (WWJ, September) of this series.

The benefit of using an adjustable trajectory angle Big Gun is to enable the operator to lower the trajectory angle to fight higher winds and conversely raise the trajectory angle with low wind conditions. The higher trajectories maximize the distance of throw and allow the stream droplets to reach a nearly zero horizontal velocity before descending to the ground from gravity. The lower trajectories tend to fight wind better—however, the radius of throw is reduced.

Therefore, travel lane spacing must be considered as a principal design factor as the stream has less opportunity for effective breakup, so the effects on soil should also be considered. Higher operating pressures (90 to 110 psi) should always be used for lower trajectory (18° and 21°) Big Gun sprinklers. The use of lower trajectory angles generally results in better wind-fighting ability but reduced throw distances. The degree of throw reduction depends upon the nozzle flow rate, but in general, the throw distance is reduced almost 3% with each 3° drop in the trajectory angle. A small secondary nozzle is often used with Big Gun sprinklers to improve coverage from inadequate stream breakup and to provide better coverage at a closer radius from the head.

Soft Hose Travelers

Soft hose, cable-tow, or “Water Winch” systems (Figure 1) use a flat style of flexible rubber drag hose that is stored on a hose cart between

sets and during relocation to a different site. The hose is pulled along the irrigation lane by a water- or engine-powered cable winch that

stores steel cable affixed to a stationary anchor at the end of the field. Because the gun is directly attached to the machine and

Figure 1. Soft hose traveler.

moved separately by the cable, water or drag soft hoses are flexible and collapsible and are like fire hoses since they don’t require the tensile strength needed to reel in a heavy gun cart.

Drag hoses are pulled behind the machine as it moves or travels along the irrigation lane. Storage of hose between sets can be done by using a horizontal or vertical hose storage reel. An example of a horizontal storage reel is shown in Figure 1.

In recent years, soft hose travelers have been declining in use, largely replaced by hard hose or reel irrigation systems which are easier to set up and move and more flexible to use. However, many soft hose systems are still in use on established or smaller fields, particularly those with very narrow lane spacing such as berries and vines, and as inexpensively purchased used equipment.

A cable-tow traveler consists of a large sprinkler mounted directly to and above the traveler along with a large and flexible length of soft, pliable rubber hose, one end of which is attached to the traveler and the other end to a pipe or hydrant supplying water from the water source. The machine propels itself through the field by progressively winding and reeling in a steel cable onto a drum or pulley mounted on the traveler.

Figure 2. Hard hose traveler.

Power to propel the cable winch is generally provided by an onboard water motor, water piston (bellows), water turbine, or auxiliary internal combustion engine usually powered from propane, gasoline, or diesel fuel. The depth of water application depends on the sprinkler output (flow rate), lane spacing, sprinkler coverage in degrees, and speed of travel—the only easily modifiable field parameter. The travel speed is varied by changing the winding or retraction speed of the cable winch but typically averages around 1 to 6 feet per minute, which translates to between 3 inches to ½-inch of net water depth applied per run, respectively.

Hose sizes are available in diameters from 2½ inches to 6 inches and typical lengths that range from 330 feet to 1320 feet, with 660 feet the most common for quarter-mile runs. The maximum length of run is twice the length of the hose, assuming the hose is connected to a supply pipe or hydrant in the center of the length of the run, the most common configuration The cable-tow hose is flat when not in use and is stored
by winding it onto a horizontal or vertical hose reel on the machine between sets.

The cable used to propel the machine is a multi-strand, high-strength aircraft type of steel cable, in typical sizes between ¼-inch to ⅜-inch. It must be attached to an immovable object or anchor at the edge of the field or end of the run for partial runs. A tractor can be used for this purpose, or alternatively, a deadman earth anchor can be installed at the end of each travel lane.

Figure 3. Hard hose traveler in operation.

The cable-tow traveler is a versatile machine and can be used on a variety of crops and field sizes and slopes. For most crops (except low-growing crops like peanuts), an alleyway of sufficient width is required to accommodate both the machine and the wide radius hose loop that must be pulled behind the machine. This alley or travel lane may be as little as 6 feet in width for smaller machines or as much as 16 feet wide for larger machines. The travel lanes must be kept clear of rocks and other materials that could damage the hose or impede travel of the winch.

Hard Hose “Reel” Irrigators

Hard hose or “reel” irrigators (Figure 2) are set up in one area and allowed to operate for a certain amount of time, then moved to water a different area. Hard hose systems work with sturdy polyethylene plastic hoses that are reeled onto a large vertical hose reel, pulling the sprinkler cart along the irrigation lane where watering is necessary. They are reeled and powered by water turbine, piston, or bellows drives or a small engine mounted on the hose reel, which drives a hydraulic powered system that slowly rotates the reel to gradually roll up and pull in the heavy and bulky hard hose while retrieving the gun cart and sprinkler at the end of the hose.

As with a soft hose traveler, the speed of retraction can be adjusted to apply different amounts or equivalent depth of water to the field. The hose-pull traveler has three main components: a large reel mounted on a two- or four-wheel cart, a separate cart with a large volume Big Gun type of sprinkler mounted on the cart, and a large diameter and long length of semi-rigid polyethylene hose.

The trailer-mounted hose reel is parked at the end or in the middle of a travel lane. Water is fed through the entire length of hose to the sprinkler cart. The sprinkler, mounted on the cart, is pulled inwards toward the reel by the hose as it is wound onto the trailer-mounted hose reel (see Figure 3).

Available hose sizes range from 1½ inches to 5 inches inside diameter and the length varies from 150 feet to 300 feet. Smaller reel irrigators for flow rates between 3 GPM to 100 GPM (1-inch to 2-inch diameter with 300 feet to 600 feet of hose) are often used for grass areas of 2 acres up to 10 acres such as athletic fields, golf courses, parks, and lawns. Larger reels (≥2½-inch hose) are typically used for larger acreage to irrigate truck crops, vegetables, turf, pasture grasses, and to apply wastewater and slurry.

Due to the long required turning radius of polyethylene hose, these units generally use a large diameter of reel to wind the hose and therefore have a high profile and a potential of overturning—with some of the larger machines as much as 12 feet in height. This height tends to make the unit top-heavy and more apt to tip over on uneven ground.

_____________________

This concludes this insert in this series on irrigation fundamentals and techniques. Next month, we will continue this series with a discussion on center pivot and lateral move systems.

Until then, work safe and smart.

Ed Butts, PE, CPI, is the chief engineer at 4B Engineering & Consulting, Salem, Oregon. He has more than 40 years of experience in the water well business, specializing in engineering and business management. He can be reached at epbpe@juno.com.