Hop-along and dragline systems are designed to reduce labour requirements on portable systems. Each time the lateral is moved, several movements of the sprinkler can be made before the next lateral move. This allows the labour team which moves the lateral to perform other tasks during the day. The lateral on dragline or hop-along systems is only moved once per day. During the day individual sprinklers can be moved by a single person.

This part-time use of labour can bring about considerable savings on labour costs. In schemes where small-scale farmers have adjoining small plots, they can cooperate to move laterals early in the morning, and then each farmer can work his own field for the rest of the day. In larger systems, the bulk of the labour required to move laterals can do other work for most of the day.

For these labour-saving systems, the sprinkler is connected by means of a riser valve (also known as a riser coupler) attached to the lateral. Sprinklers or dragline connections are then simply plugged directly into the line. A riser is secured in the riser valve by means of a bayonet or latch-type connection. Most riser valves used in South Africa have latch connections.

With fixed lateral systems, all laterals needed to operate the system are permanently buried. Only the sprinkler (and fitted dragline) is moved. This saves considerably on the amount of labour needed to operate the system. Sprinklers are often evenly distributed throughout the system. This reduces the flow through any single lateral and allows smaller diameter pipes to be used in the distribution system.

Sighting line

In the example (dragline) shown, the final lateral serves 2 or 3 sprinklers (depending on the sprinkler positions in the cycle of movement). In a conventional portable system, the same line would need to be capable of serving 10 sprinklers. All of the sprinkler connections are by means of riser valves.

As the flow rate through draglines increases, friction losses can increase to the extent that it is no longer feasible to fit draglines to sprinklers. The difficulty of moving dragline-coupled sprinklers in tall crops, or crops which can be damaged by dragging the hose through the field could also prevent draglines being used. In such cases, fixed laterals are used with hop-along sprinkler move systems.

Fixing the position of dragline sprinklers in the field is very important. An error in placement in the order of 10% of the sprinkler spacing will seriously affect the way in which the spray patterns of sprinklers overlap. This will change the system distribution and the whole irrigation process will be less efficient.

The added advantage of hop-along systems on fixed laterals are the accurate fixing of the sprinkler placement position. It becomes possible to use more complex triangular spacings and to optimise sprinkler spacings to use the maximum possible spacing which gives a good overall distribution pattern.

Without portable pipes or draglines, which are easily damaged, this type of system is expected to last for at least 15 years before equipment will need replacing. Depending on laterals used, the type of standpipe, and sprinkler spacings, hop-along systems can be cheaper than an equivalent dragline system.

Solid set systems

• 

Solid set systems are normally used with automated control systems. They are used on dense crops such as sugar cane, where moving sprinklers is very difficult. They can, however, also be used on other high value crops. Solid set systems will usually cost in the order of 3 times the cost of hop-along or dragline systems.

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.