South Carolina Irrigation Pages
Traveling Gun Systems
Traveling gun systems are quite aptly named. These systems consist of a wheeled cart with a large sprinkler (more commonly called a "gun" or "big gun"), the main traveler machine with a hose reel, and an irrigation hose. The wheeled cart (called a gun cart) is pulled either by a cable or a hard irrigation hose during operation. The "gun" travels while irrigating, hence the term "traveling gun."
The flexibility and portability of the traveling gun make it the only real solution in some instances. Irrigating smaller acreages (10 to 30 acres) is generally cost prohibitive with a center pivot, so if drip irrigation is not an option for the crop in question then the traveling gun quickly becomes the best irrigation method.
Hard Hose Traveling Guns
The speed at which the hose reel pulls the gun cart in - as well as the flow rate - determines the amount of water applied during irrigation.
Hard hose travelers come in sizes from 4 acre systems with less than 1 inch diameter hose to 100+ acre systems with 5 inch diameter hose. The hose is a black polyethylene high pressure hose that will last for many years. Repair couplings are available for the hose if a crack should appear during normal use. A good rule of thumb for hose replacement involves counting the number of repair couplings - if the hose has 5 couplings then it is time to replace the hose.
The sprinklers or "guns" are typically large sprinklers with nozzles of 1 inch diameter or larger, although the very small (2 and 5 acre) systems may use a common brass impact sprinkler. The gun nozzles can be changed to provide more or less flow within reason - a traveler designed for a flow of 300 gpm will lose too much pressure to friction losses to operate properly if a flow of, say, 400 gpm is attempted. Traveler hose size and length play a large role in the maximum flow rating of a traveler.
Engine Drive or Turbine Drive?
There are several "drive" or reel-in power systems for traveling guns, but two are more common than the others. The first is called turbine drive. This method places a small turbine on the traveler that is chained or geared to the hose reel. A portion (or all) of the irrigation water flows through this turbine on the way to the gun. The flow of the water pushes vanes or paddles on the turbine, which in turn powers the hose reel. The advantage of this system is obvious - the traveler reels in the gun cart any time water is moving through the system. If the pump is running the system should be operating properly. This is a common and well-proven design that works quite well with normal irrigation water. The solids content of animal waste lagoon effluent can plug the small openings and clearances in a turbine drive, so in that case an engine driven system would be a more appropriate choice (although new systems now offer a choice of a "slurry turbine").
The engine drive system is a fairly simple system. A small gasoline engine (generally 5 hp) is mounted on the traveler. This engine is chained or geared to the hose reel and is operated during irrigation to reel in the gun cart. There are no close clearances inside the piping, so this system is ideal for slurries and effluent application. The drawback of this system is two-fold:
One other advantage to the engine-driven system is a smaller machine pressure loss than a turbine-drive system, since no pressure is lost to reel in the hose. This can mean a slightly higher maximum flow rate for an engine-driven machine with the same hose size, length, and gun.
Another power type is a water-powered system called bellows-drive. This system was used by various manufacturers in the past but seems to be rare on new larger traveling guns today. It is currently used on small (4 to 10 acre) hard hose travelers in many instances.
During operation water fills a diaphram or "bellows," which in turn expands. During expansion this bellows pushes a lever that in effect "ratchets" the hose reel one "click," reeling the hose in a slight amount. The expansion of the bellows then trips a valve that releases the water inside it. This allows the bellows to contract (usually with the help of a spring). The valve allowing the water to exit the bellows then shuts and the process begins again.
Since the bellows water is "dumped" after each cycle a hose is generally attached to the bellows outlet to allow this water to drain out some distance (10 to 20 feet) from the machine, which prevents muddying the area around the machine.
Click here to see pictures of the various traveler drive types
Cable-Tow or Soft Hose Travelers
The terms Cable-Tow and Soft-Hose both refer to the same type of traveling gun. These traveling gun systems are similar to the hard hose systems with the following differences:
(3) The entire machine (which is much smaller than a comparable hard hose machine) usually travels across the field instead of a simple gun cart. Each machine has a cable winch powered either by a water turbine or a gasoline engine. During traveler set up the cable is unrolled and attached to an anchor point such as a tree or stationary tractor. The winch pulls in the cable during irrigation, pulling the machine along and dragging the irrigation hose behind (hence the term "drag hose").
Click here to see a soft-hose traveler with a
separate gun cart
Some cable-tow machines have a hose reel included as an integral part of the machine for convenience during transport, while others have a completely separate hose reel on a trailer. Cable-tow machines are generally less much less expensive than hard hose machines, but the setup time and labor required is greater. Hard hose machines seem to have a longer service life than comparable cable-tow machines.
Traveling guns are operated in "lanes" - that is, one "lane" or section is irrigated, then the system is moved to the next "lane" or section. The actual distance between these lanes depends on the diameter of throw of the sprinkler, which depends in turn on the sprinkler operating pressure and nozzle size. A typical spacing between lanes is 70% of the diameter of throw of the gun or sprinkler, but this recommendation can vary with manufacturer.
Click here to see a typical traveling gun lane
Some larger hard hose machines have what is known as a "turntable." This device allows the user to pivot the hose reel on the undercarriage. Using this option a user could set the traveler up and irrigate on one side of the traveler. When the traveler has completed that irrigation "pull" the hose reel can then be turned 180 degrees on the turntable and another "pull" be made on the other side of the machine. This option is quite useful in fields where the total length of the field is longer than the traveler's irrigation hose. On fields where the irrigation hose is as long or longer than the field's longest pull this option is unnecessary.
The following formula will help the user determine the amount of water applied during an irrigation pull:
inches = (1.605 x GPM) / (LSP x TSPD)
GPM is the flow rate in gallons per minute, LSP is the spacing between "lanes" in feet, and TSPD is the traveler reel-in speed in feet per minute. As an example, consider a traveler that has a flow rate of 200 gpm, a lane spacing of 180 feet, and a travel speed of 3 feet per minute:
inches = (1.605 x 200gpm) / (160 feet x 3 feet per minute)
= 321 / 480 = 0.67 inches
Most users will apply at least 1 inch of water per pass - or more if the soil properties, slope and groundcover conditions will accept the water without runoff.
Time of Operation and Flow Rate
Most traveling guns systems are designed to operate 60 to 90 hours per week. Irrigating for these long periods allows a smaller traveler to be used to cover more acreage, which in turn means a lower initial cost for the equipment. Travelers can be sized to irrigate the required acreage in 40 hours each week or less, but the cost of the system per acre is quite high in these cases and can make the system economically unfeasible.
The labor required to keep a traveling gun irrigating 8 to 12 hours per day can be considerable, so the user should first evaluate the labor time available before deciding on the irrigation time. In many instances a single, long "pull" with the traveler may take 7 to 10 hours to apply the necessary amount of water, so in these cases the labor requirement would be simply setting up the traveler once each day, checking on its progress several times during irrigation, and turning the system off. Moving the system two and three times per day (most often due to shorter "pulls") increases the labor need substantially.
A table is provided below that shows time of irrigation per week, amount of water applied, and flow rate required to accomplish that irrigation amount in the specified time frame. The table is based on an application efficiency of 75%. Larger flow rates mean larger machines, larger piping, and larger pumps, all of which mean a more expensive system.
Conversion Note: 1 acre = 0.4047 hectare; 1" (1 inch) = 2.54 cm; 1 PSI (1 pound per square inch) = 6.895 KPa or 0.06895 bar; 1 gallon per minute (1 gpm) = 3.78 liter per minute.