08 Aug
Constructing and testing a novel hops sprayer a work in progress
Posted by Super User

In 2013 we decided to try to build an alternative to a radial airblast sprayer for hops. Before you run out and build one, know that this is still just a prototype and there are bugs to work out. And who knows, it might still be workable…

Hop bines are trained around twine lines and grown an average 5.5m (~18ft) high. Each line supports two or more bines and, when mature, the line becomes a dense column of foliage as much as 0.5m (~2ft) in diameter. Hopyards, both organic and conventional, use radial airblast sprayers to apply products to the foliage. However, the profile of the radial airblast boom does not match the profile of the target crop. The nozzles at the top of the sprayer have to spray a target 5.5m (~18ft) away, while those at the side spray a target 0.5m (~2ft) away. Additionally, the air from the fan must be calibrated to carry the spray to the highest point on the hop bine, which means it is excessive for the length of bine directly adjacent. With this in mind, it was theorized that a more efficient sprayer design would feature a vertical boom to position each nozzle as close to the target as possible.

We would build “the Hopsprayer“.

Beyond the obvious requirements of operator safety and being mechanically sound, the design and construction of the Hopsprayer was guided by four principles:

The Hopsprayer should be less expensive than a conventional 3-point hitch airblast sprayer or small trailed airblast sprayer, making it cost-effective for Ontario’s small-acreage operations (~$4,000.00 CAD).

The Hopsprayer should be constructed of over-the-counter parts that require minimal modification and no special machining or tools to assemble.

The Hopsprayer should have the capacity to operate in the same conditions as an airblast sprayer (i.e. moderately uneven terrain, reasonable ground speeds, and through any configuration of hopyard trellising).

The Hopsprayer should achieve comparable or better spray coverage along the entire length of the hop bine, both on the upper and lower surfaces of the leaves.

Key Structural Components

In order to make construction as simple as possible, it was decided to build the sprayer from a commercially-available three-point hitch horizontal boom sprayer. After removing the horizontal boom, several concepts were examined for mounting nozzles on a dynamic vertical boom. The key requirement was that the vertical boom could be raised incrementally, and nozzles activated sequentially, to match the height of the hop bine as it grew taller over the growing season.

The boom itself went through several redesigns, each dismissed for reasons of excessive weight, lack of structural stability, or concerns about operator safety when raising and lowering (or even folding and unfolding) the boom. Finally, it was decided to use a commercially-available 6m (~20ft) sliding aluminium ladder. This had the advantage of being strong, light, easy to mount, and the hollow rungs were ideal for running spray lines from one side of the boom to the other. Plus, with the addition of a marine hand winch, the ladder could easily be extended to any height.

Regarding the nozzles, several nozzle bodies and tips were considered, but the Arag Microjet had several advantages over conventional nozzle-body-and-tip configurations. The Microjet has a mixing valve built into the nozzle body which allows the operator to turn individual nozzles off, as well make minor changes to the spray quality emitted from each unit. Further, the brass nozzle body bends 90° before terminating in a threaded male connection, ideal for fixing to the ladder and attaching spray lines.

From this point, it was a matter of positioning the key components and finding appropriate mounting hardware.