Principal facts of spray nozzle technology


  Nozzle types and spray geometries           Coverage
  Overlapping in Broadcast Spraying      Nozzle maintenance

Nozzle types and spray geometries



 

Atomization


The atomization process breaks liquids down into droplets. Most of the nozzles used in agriculture rely on hydraulic atomization resulting from fluid pressure in combination with the orifice effect of the nozzle tip. Those two factors accelerate the flow velocity of the medium to be atomized. This converts potential energy into kinetic energy (= speed). The release of tension experienced by the liquid as it emerges from the nozzle tip produces an initially flat lamella of liquid that soon loses its stability and becomes wavy. That gives rise to strings of liquid that disintegrate into droplets of various size.
 
 

Specification of Lechler nozzles


The performance data of Lechler agricultural spray nozzles are stated in accordance with international standards and include the following information:

  • type of nozzle
  • spray angle
  • tip size

Lechler nozzles are ISO color-coded, with each different color corresponding to a defined flow rate. The latter is also reflected in the nozzle size, e.g., -05 stands for a flow rate of 0.5 US gallons per minute, or 1.89 l/min at 2.81 bar, or 1.94 l/min at 3.0 bar (color: brown). The material indicator for color-coded nozzles is either “S” for stainless steel or “C” for ceramic.

 

Coverage


The theoretical coverage of a given nozzle is chiefly determined by the spray angle and the spray height, i.e., the distance between the nozzle and the target surface. Depending on the height of the nozzle and its size, the spray angle and accuracy of distribution can depend to a certain extent on the spray pressure. Hence, the recommended spray pressure at the nozzle tip and the minimum spray height for a specific nozzle spacing are two prerequisites for the uniform distribution of liquid within the spray pattern.
 
Theoretical coverage as a function of spray height and spray angle (data in table based on water):
 

 
* Parenthesized data: major difference between effective and theoretical coverage.
 
Due to the physically unavoidable effect of spray-jet droop, the effective coverage may fall short of the theoretical coverage listed in the above table, especially in cases involving low spray pressure and substantial spray height.

 

Overlapping in Broadcast Spraying


Most broadcast spraying with boom sprayers is executed with flat-jet nozzles. Multiple-overlapping ensures that the liquid is uniformly distributed across the entire working width of the boom. Thanks to their large spray angles of 120° and 90°, high-precision nozzles by Lechler are particularly well-suited to the job.
 

Flat spray nozzles


With a view to avoiding mutual interference, the spray planes of flat spray nozzles have an offset of 5°-10° with respect to the boom axis. In the case of Lechler diaphragm check valves used in conjunction with Lechler's TWISTLOC / MULTIJET bayonet caps, the offset is adjusted automatically.
Lechler offers a special nozzle aligner (order no. 065.231.02) for systems with threaded caps.
 

Hollow cone nozzles


Hollow cone nozzles should be arranged such that their coverage pattern yields minimal overlap at the target-surface plane.

 

 

 

Nozzle maintenance


The proper, uniform application of plant protection chemicals requires well-functioning nozzles.
Consequently, all nozzles should be washed out with clear water after each use to prevent any accumulation of deposits in the nozzle feed lines and in the nozzles themselves.
Manual cleaning of nozzles should be restricted to the use of cleaning brushes (order no. 06A.D30.56.00) to avoid damaging the exit orifice rims of the nozzles.
The best way to avoid clogging is to ensure that all strainers and screen inserts serving the nozzles or other parts of the apparatus are properly selected.
The flow-rate tables for nozzles of different types and sizes include references to recommended nozzle strainers.
The strainer setup on the plant protection equipment should have decreasing mesh widths (i.e., increasing mesh number) from the filling screen to the nozzle strainer.
 

 

Spray tip materials


Most agricultural spray nozzles are made of plastic (POM), stainless steel, ceramic and, in some cases, brass.
All these materials are resistant to known plant protection chemicals, and all with the exception of brass are resistant to liquid fertilizers.
Plastic is conspicuous for high precision, resistance to wear and very good price-performance ratios.
Stainless steel is the material of choice for high mechanical loads.
Ceramic nozzles are the most wear-resistant of all and therefore recommended for their extremely long service lives and high areaspecific performance.
 

Düsenverschleiß


Even properly used nozzles wear down in time and eventually have to be replaced.
The rate of wear depends on such factors as spray pressure, abrasiveness of the sprayed liquid, and the material of which the nozzle is made.
Improper cleaning and handling can damage the nozzle nozzles and therefore must be avoided.
An easy way to determine how badly worn a nozzle tip may be is to gauge its flow rate with the aid of a calibration container, a stop watch and a pressure gauge fitted on a nozzle body on the spray boom. With such a setup, one compares the flow rate through a used nozzle with that of a new one of equal size.
If the flow rate through a used nozzle is found to exceed that of a new spray tip by more than 10 %, it should be replaced.
All data shown in the tables of this catalogue state the flow rates of new nozzles. Nozzles fitted on a spray boom can also be checked through on a test bench (patternator) to determine their condition with regard to cross distribution. The quality of cross distribution and changes in flow rate can be interdependent with regard to the calculated coefficient of variation (CV).
 
The wear resistance of the nozzle material increases in the following order:
  • brass
  • stainless steel
  • plastic
  • ceramic

 

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