Pivot: Questions & Answers

Yes. The pivot rotates continuously when it is irrigating. Each tower moves in short intermittent steps to maintain its alignment.

400m long pivots are the most common length. With an end gun operating a 400m pivot could effectively irrigate up to 140 acres under good wind conditions. A 500m pivot can cover up to 220 acres in low wind conditions.

Longer pivots are normally between 400m (1320ft.) and 500m (1650ft.) Even longer pivots are in use but in these cases the soil infiltration rate must be given extra consideration. Long pivots apply a large amount of water at the far end and the soils ability to adsorb it is a critical issue.

The irrigation water is supplied to the system through a stationary “pivot point”. The pivot point is set on a permanent concert pad and does three things. It supplies the water for the spans, it supplies the electricity to the motors and controls as well as anchors the pivot in place. As the anchor point the pivot system rotates around the pivot point to maintain its’ proper location in the field.

One man can monitor 12 or more systems. If automated control centers are established any numbers of pivot systems can be monitored from one location.

Pivots operate best on level ground. However mildly sloping or rolling land can also be irrigated by center pivots. However terrain with sharp breaks such as an arroyo must be avoided. Also care should be given on rolling terrain to assure that rises can be cleared by the pivot spans.

Almost all field and row crops can be irrigated by a center pivot. This includes tall crops such as sugar cane which utilize high clearance center pivots. Orchards and trellised crops do not lend themselves to center pivot irrigation.

Soils are a major consideration when apply center pivot machines. Sand, sandy loams, loam, and silt loams are considered good pivot soils. Sandy clay loam, clay loam, and silty clay are considered marginal soils and sandy clay, clay, and silty clay soils are considered to be soils that must be viewed with extreme caution.

In a 160 acre square field the pivot without an end gun will irrigate 126 acres or 79% of the area. The addition of an end gun could add from 10 to 14 additional acres. On larger farms with multiple installations the pivots may be “nested” which would reduce the unirrigated area to about 7%.

Rutting is a function of soil type. Many sand or sandy loams show little rutting. As the content of silt or clay increases in the soil more rutting will occur. On pure clay soils the rutting will be severe.

It depends on the crop. Most field crops are planted in a straight line. Row crops are also planted in a straight line and normal farming practices are followed. A few growers use circular planting and farming practices, but it is not required.

A common center pivot depreciation schedule calls for a 15 year useful life. However a large factor on useful life is the quality of the irrigation water. Corrosive waters can cause span failure in 5 years or less. With good quality water and optimum conditions 25 years of operation is not uncommon.

Energy saving sprays or other low pressure devices are most commonly used. There are several choices. Most operate on drop pipes which place the sprays closer to the crop to reduce wind drift. The spray heads operate on 10 to 15 PSI.

Operating pressure refers to water pressure that is required for proper operation of the irrigation system. This includes the discharge pressure at the spray head as well as internal friction losses in the system and field elevation changes. On level ground operating pressures run from 25 to 30 PSI on average length pivots

There is a speed control dial in the main pivot control panel. Pivot rotation speeds can vary from several days to less than one day.

The amount of water applied by the system will be set by the pivot designer and will include information on crop, soil and weather conditions. The grower may control the amount and how long it takes to apply the water by adjusting the speed of rotation.

Irrigation uniformity is a measure of how evenly the water is applied to the field. If every part of the field receives exactly the same amount of water the uniformity is 100%. Center pivots are one of the most efficient irrigators now in use. Efficiencies above 90% are most common.

Safety is a high priority in center pivot design. Much attention is paid to the proper grounding of each system. Complete instructions are included in the Wade Rain Center Pivot Owners’ Manual and Dealer Manual. In addition all major electrical components are manufactured to meet UL electrical safety standards as well as NEC and ASABE codes.

Crop clearance below the span is 9.5 feet as measured from the bottom tread of the floatation tires. This is adequate clearance for a normal corn crop. For taller crops a high rise model is available with a 12.5 foot clearance.

Each tower has its own alignment control system. This control activates whenever the adjacent tower on the down stream side moves ahead of the inboard tower. This causes the tower to engage and realign itself.

Soils and terrain are a limiting factor in the use of center pivots. In most cases the terrain should be level with sandy to loamy soils. Also any structures or other obstacles in the field must be removed or otherwise accounted for.

Center Pivots offer fully mechanized irrigation which applies water at a very high uniformity with a frequency that can be matched to the crops consumptive need. It is an excellent low labor irrigation tool.

The cost per acre for a pivot varies directly with its length. Short pivots have a very high cost per acre and longer pivots cost much less. On a 1/4 mile long pivot that irrigates 126 acres the installed cost may average between $75,000.00 and $80,000.00, plus freight. This would place the cost per acre at between $595.00 and $635.00 per acre.

Yes, an installation crew with a boom truck and other equipment is required to install the system and the wiring must be completed by a licensed electrician. All servicing of the electrical systems should be done by a licensed electrician.

The pivot is fully hot dipped galvanized with a minimum thickness of 3.15 mil. With good quality irrigation water the protective finish will last for many years. However in some areas where very caustic irrigation water is used corrosion may occur much sooner.

Yes, towable pivots are available. They can be towed in a straight line between pivot points. Towable machines require special gear boxes on the tower trucks and modifications to the pivot point.

Wade Rain pivots come equipped with 1-1/2 HP motors as standard. 3/4 HP motors are available for lighter applications.

If the pivot stops rotating or misaligns for any reason the safety system will automatically shut down the electrical operation and stop the machine. An overwatering switch is also available that will shut off the water supply at the same time.

Yes, There is a directional control switch in the main control panel. Simply set the switch in the forward or reverse position.

Yes, The pivot can be run with or without water.

Yes, A fertilizer injector can be connected to the water supply

Used properly a center pivot system can offer very high crop yield. The amount of increase depends on the efficiency of the previously used irrigation system. A cost analysis of the farm in question will answer just how large that increase may be. In almost all cases the cost vs. return results more than justify the addition of a center pivot.

A big gun is a large volume sprinkler that has a long radius of throw. It is placed on the end tower of the pivot to extend the irrigated area beyond the last tower of the pivot. It requires a booster pump on the end tower to increase the water pressure.

Near the pivot point one spray covers a small area and it has a low discharge rate. As the line extends toward the far end each watering outlet covers a larger amount of acreage. Therefore along the line the water volume of each spray gets progressively larger.