First look: Weta irrigator

Meet the Weta irrigator, a revolutionary new dairy effluent irrigator by AgFirst Engineering.

Developed to address the environmental challenges faced by New Zealand dairy farmers, the Weta irrigator has been developed by AgFirst Engineering director Davieth Verheij and his Te Awamutu team.

AgFirst Engineering is involved in all things water and waste water, with specialist engineers working throughout the country and overseas. Davieth particularly specialises in water supply and dairy effluent system design, supply, and build projects.

“The key design considerations for the development of the Weta irrigator were clear,” says Davieth.

“Kiwi farmers need their effluent irrigator to have high capacity and low intensity, application uniformity/accuracy and last but not least, to be low maintenance and user-friendly.

“Why is this important? Dairy effluent is nutrient rich. It is essential to apply effluent at the right time, with the correct application rate (intensity in mm/hr) and application depth (total loading in mm). Failure to do so results in a nutrient loss.

Adequately sized dairy effluent storage (ponds/large tanks) have been a large a focus over the past decade. Storage provides the ability to defer irrigation. However, it still needs to be applied to land—a task that requires the greatest amount of management and which will be the decider as to whether your effluent system is making you money or costing you money.

So what does a travelling irrigator need to achieve to overcome these challenges? Travel speed selection must be accurate, and the irrigator must be able to maintain its travel speed. This assures average application depth/rate is uniform, and therefore, the nutrient application is uniform.

The length of grass, length/size of drag hose, and whether the irrigator is on the flat, going uphill or downhill, all affect the travel speed of conventional travelling irrigators. The irrigator must have high capacity (flow and pressure) to achieve large wetted widths. This means fewer irrigator shifts as a greater area is being captured at one time. To achieve this capacity, large diameter drag hose is required and there must be as little restriction through the irrigator as possible. The irrigator winch system must be strong, low maintenance, and efficient to provide the energy required to drag the larger heavier hose and ensure selected travel speed is maintained.


“We have developed ‘the what’ by knowing ‘the why’. The result is the Weta irrigator.”

The Weta irrigator uses an inline turbine and hydraulically powered winch system. Traditional irrigator winch drums are driven by rotating booms, cams, spring loaded teeth, gearboxes, chains, bearings, and pulleys. The Weta’s turbine directly rotates a hydraulic pump significantly decreasing maintenance and greasing.

A speed sensor mounted on the winch rope continuously measures travel speed. The travel speed is operator selected in m/hr by a simple dial or digital display.

The Weta’s solar-powered speed controller monitors travel speed and controls a turbine bypass valve and fail-safe shut off valve. The turbine bypass valve is what controls the travel speed. Once the selected travel speed has been achieved, the remaining effluent flow is bypassed around the turbine direct to the rain gun nozzle. If the irrigator slows down (due to a hill or increased drag on the hose), the speed regulation valve adjusts to put more flow through the turbine to provide the additional energy required to maintain travel speed. The result is a uniform application of nutrients.

The Weta irrigator can achieve wetted widths of up to 100m with application depths from 1mm to 25mm. The rain gun can be operated in full, half, or even part circles, providing huge flexibility.

Features include a 3T rated Dyneema winch rope, GPS proof of placement, built-in anti-siphon system, travel speed, and pressure sensing for fail-safe automatic shut off.

Innovative features associated with the Weta irrigator

  • Energy-efficient, turbine-powered hydraulic winch system delivers maximum winch capacity with minimum maintenance. No need for a gearbox, shear pins, chains, sprockets, bearings, cams, and bushes.
  • A speed control system senses the achieved speed of the winch rope retrieval and adjusts turbine flow to maintain a constant speed.
  • An end of run and lack of travel fail-safe shut off valve is incorporated in the irrigator.
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