Portable systems (with or without fixed, buried mainline)

Both the lateral and mainline are assembled from portable quick-couple pipes. Sprinklers are mounted on the portable lateral pipes (Figure 1). Pipes are uncoupled and moved by hand between each set (Figure 2).

This type of system is extremely labour intensive. In a large field, a team of labourers will be fully employed moving pipes. The portable lightweight pipes used, are easily damaged. Rubber seals in the connections are also not expected to last long (Figure 3).

Regular inspections to identify leaks and damaged pipes are required. The system can only be used in open fields. Portable systems cannot be used with taller crops as damage is likely to occur when sprinkler lines are moved.

Sprinklers are mounted directly onto each second or third lateral pipe. Between each movement of the lateral the hydrant valve is closed, each coupling disconnected, and the water in the pipe allowed to drain. The placing and alignment of pipes are very important. If laterals are not properly aligned, the resulting sprinkler spacing will be uneven and poor water distribution will occur.

For smaller fields sighting rods can be placed in pairs on the side of the field. In larger fields it is normal to draw furrows, which act as a placement guide, making certain that laterals are correctly spaced and aligned (Figure 4).

Portable sprinkler systems are often cheaper than other types of sprinkler systems. The cost of regularly replacing damaged pipes and high labour costs do, however, lead to very high running costs.

A wide variety of portable systems equipment is available (Figure 5). Different makes and types of pipe are, however, seldom compatible.

Care should be taken when ordering equipment that the correct type of coupling, size, and manufacturer, are quoted. Each manufacturer of portable irrigation pipes will supply a full range of equipment that can be assembled on-site to build an irrigation system.

Regular maintenance is important. The farmer should check pipe seals and inspect pipes for damage at least once every week.

When a fixed, buried mainline is used, slightly less labour is needed as there are fewer lines to disconnect and move. The mainline is also protected and should last for up to 20 years. Additional costs are incurred as hydrant valves are required at regular intervals along the length of the mainline.

This series is published with acknowledgement to the ARC Agricultural Engineering for the use of their manuals. Visit www.arc.agric.za for more information.