Challenging the 0.5m convention – Spring ’19 edition
Despite all the advances in technology during the past 20 years, one sprayer specification that hasn’t changed is the dominance of the 50cm nozzle spacing. But it is now beginning to face questions and challenges.
If you are looking to buy a new or replacement sprayer it likely to equipped with nozzles spaced at 50cm. But how many operators ever question the nozzle spacing on offer?
When given a choice, however, operators do seem will to break with convention. Horsch Leeb, for example, reports about 70% of its machines sold in the UK go out equipped with the 25cm spacing option.
There is, however, also the much less well-known 33.3cm, which can offer significant advantages and with very few modifications.
Murray Allan, who runs Spraytrac, based at Boroughbridge, Yorkshire has been championing 33.3cm spacings for more than three decades.
“The main benefit is improved efficacy, with lower drift. If you look at the retention advice of the ASABE droplet size classification it shows fine to medium droplets give ‘very good’ and ‘good’ retention. My own and customer’s experience with 33.3cm nozzle spacings and 80° nozzles support this,” he explains.
What’s wrong with 50cm?
The main difficulty, suggests Murray, is at 50cm the outlets are too far apart – and to bridge the gap and create the necessary overlap, it requires the use of a 110° fan angle. “The problem is that these nozzles create fine droplets on the edges of the fan, which are prone to drift,” he explains.
“To get the absolute best out of the application we need to shift to a finer, more controlled, spray quality for when it’s required. And this can be done only by narrowing the distance between the nozzles and increasing the momentum behind each droplet,” he explains.
Appliance of science
A 33.3cm spacing needs to operate with nozzles producing an 80° fan angle, at a 50cm boom height. By introducing another nozzle per metre you will be also increasing the liquid rate by a third, so this means we need to come down a nozzle size to maintain the same volume.
While this does mean using a finer nozzle, which could increase drift, other factors need also to be considered.
“Moving to an 80° nozzle increases the droplet size, but now there are three nozzles in the equation, and very importantly an extra 3 bar pressure/m. The laws of physics determine a narrower angle also produces fewer fines on the edge of the fan and is much less prone to drift from the outside, compared with a 110° fan,” explains Murray.
This, he adds, is clearly illustrated on the pictures below:
The 80° nozzle (A) produces a larger droplet with fewer fines at the edges. These are far less prone to drift compared with the 110° fan (B).
The video below shows the impact of each nozzle type, by switching between the two.