Linear Move Systems

Figure 5. A Linear Move system.  Notice the concrete water supply channel (and the fact that the system spans both sides of the channel).

All of the points listed for center pivots can be easily applied to linear move systems with two exceptions - travel path and water inlet.

A linear move system does just what its name implies - it moves in a linear or straight line path.  One design of linear move system covers the entire width of the field and waters the entire field in one pass.  This would be synonymous with the "windshield wiper" pivot mentioned above - after the irrigation cycle is completed the machine is located at the far end of the field that was irrigated.   To start the next irrigation cycle on the driest area of the field, the linear move machine must be "run dry" back to the original starting point, which adds wear and tear.

Another type of linear move design involves installing a linear move machine that only covers one-half of the width of the field.  This system irrigates one-half of the field in one pass.  At the end of this pass, the machine is rotated 180 degrees (manually with the help of the motorized towers) and is set up to return down the other side of the field, watering the other half.  This system most closely resembles the full-circle center pivot system in that the machine ends the irrigation cycle at its original starting point.  The drawback to this system is that there is some labor requirement to re-orient the system at each end of the field.

The water supply for the linear move obviously cannot be supplied by a central pivot point such as that used for the center pivot.  One method of water supply involves the use of a flexible "drag hose" that is attached to an underground piping system.  The drag hose system utilizes attachments to riser points similar to those used for traveling gun systems.  Depending on the length of run of the system, the attachment point may need to be moved between two or three supply points (or remain attached to a single point) during one pass.  This adds to the labor requirement, but not substantially.

The other option involves a natural (Figure 6) or concrete (Figure 5 above) ditch or channel with a suction assembly extending into the ditch from the linear move machine.  This removes the labor of moving the inlet hose, but adds water losses due to evaporation, and in the case of the natural channel, seepage into the ground. 

Certain soil types will require a concrete or lined channel to prevent large seepage losses.  This water supply option may or may not be viable depending on the topography of the field.  In either of these options a pump is placed on the machine itself and travels with the system.     

Figure 6. A linear move system drawing water from a natural channel. (image source unknown)