The Parts of a Sprayer

Tank. This is usually made of non-corrosive plastic material such as polyethylene or reinforced fibreglass. Some sprayers have an extra tank on the front of the tractor, which reduces the time spent travelling from farm to field. A transfer pump is used to move the liquid to the main tank. It also keeps the contents of the front tank well mixed while spraying the chemical from the rear tank.

Figure 13.1 Steering systems for trailed sprayers.

Plate 13.5 Mounted sprayer with a 1,200 litre tank and 18 m spraybar.

Pump. Power take-off driven, it may be of the roller vane, piston or diaphragm type. Roller vane pumps are little used now because of corrosion and lubrication problems. Multi-diaphragm pumps are in common use. Pump size will vary with type of sprayer. Typical pump outputs are:

• 1,000 litre mounted sprayer with a diaphragm pump - 150 litres per minute.

• 2,000 litre trailed model with a six-cylinder diaphragm pump - 230 litres per minute.

• 2,500 litre self-propelled model with a six-cylinder diaphragm pump - 300 litres per minute.

Sprayer pumps should run at the standard 540 rpm power take-off speed. Operating press­ure is one of the factors determining appli­cation rate and when pressure is increased droplet size will be reduced. Small droplets will drift, even in light wind, and this must be avoided.

Roller vane pumps ( seeFigure 13.2) are relatively inexpensive to make and maintain. With outputs of 15-20 litres/min and operating at 2-10 bar pressure they are more suited to compact sprayers for turf care and amenity use. A roller vane pump consists of a rotor offset to one side of its hous­ing with a number of rubber, nylon or steel rollers, or vanes, in grooves around the outside of the rotor. The rollers are thrown outwards against the housing when the pump rotates and liquid is drawn into the pump at the position where the rotor is furthest from the casing. The liquid is carried round between the rollers until it reaches the discharge point. Here the rotor is very close to the housing, the rollers are pushed, in turn, fully into their slots and the liquid is pumped from the outlet.

Figure 13.2 A roller vane pump.

Piston pumps ( seeFigure 13.3) with working pressures of up to 40 bar and outputs of 200 litres/minute or more are positive displacement pumps, with the piston delivering the same volume on each stroke. The pump works in a similar way to the piston in an engine with inlet and outlet valves and rings to prevent loss of liquid between the piston and cylinder wall. Output can be increased by using a pump with more than one cylinder. An accumulator or air bottle can be included in the circuit to even out delivery by reducing the pulsing effect of the piston. Piston pumps are the most expensive type of pump used for sprayers.

Diaphragm pumps with a maximum operating pressure of about 20 bar and outputs ranging from 10-200 litres/minute are used on many current models of sprayer. These pumps may have a single diaphragm or as many as six units working in line for high output machines. The pump shown in Figure 13.3 has a diaphragm connected to a piston which moves up and down in a cylinder. On the downward stroke the diaphragm suction closes the outlet valve and opens the inlet valve, and liquid is drawn into the pump chamber. On the upward stroke pressure closes the inlet valve and opens the outlet valve, forcing the liquid out of the cham­ber into the sprayer system.

Figure 13.3 A piston diaphragm pump.

Diaphragm pumps, or piston diaphragm pumps as they are more commonly known, run at high speeds and, like piston pumps, there can be a problem with pulsing on one- and two-cylinder pumps, but this is overcome by includ­ing an air bottle in the system. Pulsing is not a problem with high output multiple diaphragm pumps. This type of pump is simple to maintain and will not be damaged if accidentally run dry.

Centrifugal pumps with a high-speed impeller are high-output and high-pressure pumps suit­able for spraying pesticides and liquid fertil­isers. Although not often used on sprayers, they are suitable for the high-speed transfer of liquid from a back-up tank at the front of the tractor to the rear sprayer tank and for filling the sprayer from a water bowser. Centrifugal pumps can operate at low pressure and will not be damaged if they run dry.

Relief valve. An adjustable relief valve is included in the pump circuit to control working pressure. It is one of the factors which determines the applica­tion rate. The relief valve also returns excess chemical, not required by the nozzles, back to the tank, and agitates the tank contents, keeping them well mixed.

Filters. These are a vital part of the sprayer circuit. The nozzles have very small holes which will easily block if particles of dirt are allowed to reach them. The location, and number, of filters varies with different sprayers.

There are usually four stages of filtration. The first is a filter basket in the filler, the second is in the suction line before the liquid enters the pump, the third is in the delivery line from the pump and final filtration is frequently included in each nozzle. Sprayers with self-fill hoses will have a filter unit at the end of the suction pipe. All filters must be kept clean.

Spraybar. The spraybar and nozzles are made of non-corrosive material, usually plastic or stainless steel, supported by a light but strong metal frame. Spray bar or boom widths of 12 to 24 m are the most popular but some trailed sprayers nave booms up to 50 m wide. Depending on its width, the boom will have between three and eight sections, which are hydraulically folded for transport. Vertical boom adjustment is pro­vided for different crop and target heights.

The spray boom is mounted on a suspension system designed to keep it parallel with the ground, to reduce boom bounce and to over­come the tendency for the boom to swing back­wards and forwards, or yaw, on rough ground. Any unwanted boom movement will alter the position of the nozzles in relation to the spray target, causing overdosing or missed strips.

A break-back device is built into the spraybar hinge points. This allows the bar to swing backwards, preventing damage if it hits an obstruction.

Isolating taps, controlled from the tractor cab, enable the driver to turn off any section of the spray boom. This is useful when less than a full boom width is required, especially when spray­ing alongside field margins.

Plate 13.6 Multi-head nozzles can be rotated to give an instant change of nozzle type or size.

Nozzles. Sprayer nozzles are made from plastic. They are colour coded according to their output, and classified by an International system as very fine, fine, medium, coarse and very coarse. Most pesticides require fine, medium or coarse nozzles, and the most suitable nozzle for a particular product is usually stated on the con­tainer label.

Flat fan nozzles with a flat triangular spray pattern are commonly used on boom sprayers. Fan angles can range from 80 to 110 degrees.

Cone nozzles are similar but can produce either a hollow or solid cone spray pattern. However, they are prone to drift. Hollow cone nozzles are used with air-assist sprayers which have a curtain of air to give good spray coverage in dense crops.

Air-induction or twin-fluid nozzles use low pres­sure air supplied into the nozzle to assist in the atomisation of the liquid.

Air inclusion nozzles use an a venturi system to produce larger droplets with air bubbles which reduce drift but are still retained on the leaf.

Deflector nozzles produce a wide-angle coarse spray pattern and are more commonly used for the application of liquid fertilisers.

Many sprayers have a multi-head nozzle holder which can be rotated to change the size or type of nozzle used.

A check valve controlled by the pressure in the spray line prevents chemical drip when the sprayer is switched off. The check valve also ensures full delivery from the nozzle when spraying re-starts.

Mixing devices. Most sprayers have either a chemical induction probe or an induction hopper operated by the sprayer pump for adding the chemical to the water. The chemical probe is placed in the con­tainer and the required amount of chemical is drawn from it into a small measuring tank on the sprayer. The chemical is then transferred to the main tank and thoroughly mixed with the water by pumping the contents around the system.

An induction or mixing hopper (see Plate 13.7) is used in conjunction with the pump and the main sprayer tank. The required amount of chemical is poured into the hopper tank - pro­tective clothing must be worn - and after closing the hopper lid a valve is opened so that the pump sucks the contents into the tank.

Plate 13.7 The chemical mixing hopper on this sprayer can also be used to wash chemical containers.

Powders, tablets and dissolvable bags of chemical are added to the hopper after opening a valve to partly fill it with water. When mixed, the contents are sucked into the sprayer tank. A supply of clean water is carried on the sprayer and this is used to flush the mixing hopper and wash out the chemical container before moving off to the field.

Some sprayers have a pump operated self-filling suction hose used to pump water into the tank from a water bowser or other suitable water source. This overcomes the need to travel to and from the farm every time the tank is empty. However, a self-fill hose must not be used to fill a sprayer tank from livestock drink­ing troughs, ponds, streams, etc. where pollu­tion from spray chemicals might occur.

Many farmers now use a self-contained water bowser with a pump and a secure chemical store which holds enough water to re-fill the tank several times. However, the power take-off or engine driven bowser pump may only be used for water.

An alternative system is a mixer tank consist­ing of a large water tank on wheels complete with a power take-off or engine driven pump and chemical induction equipment used to take ready mixed chemical to the sprayer. The tank is filled with water and chemical at the farm and the contents are agitated while it is towed to the field, ready for transfer to the sprayer. However, a water bowser, used in conjunction with the induction hopper on the sprayer, is preferred by many sprayer operators.

Figure 13.4a A spray nozzle with an anti-drip diaphragm valve.

Figure 13.4b Types of spray nozzle tip.

Plate 13.8 The clean water container for rinsing the mixing hopper on this sprayer also provides water for flushing the sprayer when work is completed, and for hand washing.

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