GB2234692A - Electrotsatic spray head. - Google Patents

Abstract

An electrostatic spray charging head includes means (20) to support a spray-charging electrode (30) forward of a hydraulic spray nozzle (50) arranged to spray in a horizontal direction, in which the support means (20) includes upright surface features (22, 23) to trap incident spray liquid for dispersal with gravity assisted flow while the electrode (30) is of uprightly elongated form. Conveniently the electrode is embedded in an upright housing basally formed as a knife edge (34). The electrode and any housing may be open at the base.

Description

ELECTROSTATIC SPRAYING This invention relates to the spraying of electrically charged sprays of agricultural liquids.

With increasing regulation of agricultural spraying precision in application is more and more important. Electrical leakage in the region where the charge is applied to the liquid reduces the efficiency of the charging action and can mean that the apparent spray conditions are not achieved. Such leakage is not always readily identified by the user.

Hydraulic spray devices are well-established for the production of uncharged agricultural liquid sprays and many users prefer such devices for charged sprays. Accordingly spray charging heads have been proposed which are usable with such existing spray nozzles.

It is an object of the invention to produce electrically charged hydraulic sprays in a reliable and predictable manner.

According to the invention there rs provided an electrostatic spray charging head including means to support a spray-charging electrode forward of an hydraulic spray nozzle arranged to spray in a horizontal direction, in which the support means includes upright surface features to trap incident spray liquid for dispersal with gravity assisted flow and in which the electrode is of uprightly elongated form.

Conveniently the electrode is embedded in an upright housing basally formed as a knife edge.

Conveniently the electrode, together with any housing, is open at the base.

Preferably the electrode is of inverted U-form providing opposed inward surfaces between which spray travels for charging and an electrical connection on the top of the inverted U-form.

Preferably the support means is cranked downwardly towards the electrode to assist flow of incident spray liquid to dispersal.

Conveniently the upright surface features include at least one of grooves and bars.

According to a particular aspect of the invention there is provided a spray charger including a sprayhead as defined above and a charging electrode power supply including means to trip supply of power to said electrode if the current drawn is excessive and means to vary the value for excessive current trip.

Advantageously the charger includes means to indicate at least one value of current and voltage supply to the electrode.

Conveniently said indication means simply shows adequate and inadequate supply values.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a spray charging head in assembled and "exploded" form, and Figures 2, 3 and 4 show a circuit for a spray charging head power supply.

Figure 1 shows a head for electrically charging a horizontally directed spray from a conventional hydraulic spray nozzle, indlcated in outline at 50, conveniently secured thereto by nozzle holder 10 of a clamp ring 11 and clamp screw 12.

Extending forwardly, in the tense of the spray, from the nozzle holder 10 is a support 20 for an electrode 30.

Support 20 includes a pair of side members 21, preferably downwardly cranked as at 26, attached, by bonding, welding or other suitable means, to clamp ring 11. Members 21 are formed with one or more upright features such as 22 and 23, which trap incident liquid, such as spray returning to the support, and encourage gravity assisted flow to disperse incident spray to reduce the possibility of electrical leakage.

At the forward ends of the side members 21 is attached, again by bonding, welding or other suitable means, an upright electrode housing 24, 25. The housing is of sandwich construction so that an electrode 30 is embedded in the housing by the assembled parts 24, 25 to expose only the inwardly facing surface.

The electrode 30 is conveniently of inverted U-form with, at the top, an electrical connection 31 extending to a high-voltage terminal 32 to which a suitable high-voltage connector 33 can be attached. The lower parts of housing 24, 25 and side members 21, indicated at 27, 28 and 29, are formed to produce a basal knife edge 34 when assembled. This knife edge assists in the shedding of incident liquid which has flowed, under gravity assistance, down the upright housing and the cranked side members. The use of solidly-formed features to disperse liquid, such as items 22 and 23 and the basal knife-edge 34, avoids the spiky features proposed hitherto which can easily be broken or cause injury if not properly designed. Such features have been proposed because points and spikes are conventional high-voltage discharge means.

Suitable materials and construction will be readily apparent. Thus plastics, preferably tough and having a smooth surface and lower water absorption, for the support and electrode housing with brass for the electrode are appropriate.

The lower part of the electrode 30, in the illustrated embodiment, is open to reduce the risk of liquid collection but in some arrangements the electrode can be of closed loop form but with the same general shape of parallel upright sides.

Air assistance can be applied to the spray if required, particularly when the closed loop is used. A closed loop is also suitable when high hydraulic pressures are used.

High voltage supply is indicated by HTA, HTB. HTA is a conductor while HTB can be a conductor or a conductive path via conductive spray liquid L supplied to the nozzle 50. The polarity can be chosen to suit ambient conditions. Negative polarity for HTA can be better in some conditions.

In general no more than three to six kilovolts of potential are needed at a current of a few tens of microamperes (say 30 to 60 pA) so the risk of a dangerous shock is minimised, but safety precautions may still be needed.

A power supply is indicated at 40 in Figure 1. This contains any suitable electrical arrangement to convert a low potential supply LV, of say 10 to 200 volts, to the high potential for HTA, HTB. It is an important operational feature of the invention that the power supply provides an indication of the manner in which the spray charging is operating. Indicator 41 can show when an overload occurs, possibly due to excessive electrical leakage. Indicators 42, 43 can show a correct, excessive or inadequate operating potential and indicators 44, 45 a correct, excessive or inadequate operating current in GO/NO GO manner.

In this way an operator can easily be assured of proper operation without requiring great technical knowledge. A control 46 can be provided to set different operating potentials and/or currents by reference to various intended spraying actions, and at the same time set the appropriate indicator conditions. If required meters rather than GO/NO GO indicators may be used.

In use of electrostatically charged sprays for horticulture a number of spray "charging" heads as described above can be assembled with horizontally directed sprayheads onto a mast or other structure mounted on a trolley which is moved in a controlled manner, throuh a greenhouse or like structure for the cultivation of crops. For convenience the sprayheads can be divided into groups and each group supplied by a separate power supply. Typically three or four sprayheads are supplied by each supply.

Figures 2,3 and 4 show in more detail a power supply suitable for the controlled supply of electrical potential to such an assembly of spray "charging" heads. The current in high tension supplies HT1, HT2, respectively from each of two high voltage supplies PS1, PS2, conveniently Brandenburg Model 695, is monitored by respective paths starting with differential amplifiers U41, U42 supplied with current signals from respective potential dividers in the high potential return paths at the power supplies. Trouble signals are provided by trip indicators HV1 and HV2. Similar arrangements will be apparent to those skilled in the art to produce appropriate trouble signals for other parts of the circuit or for the power supply arrangement of Figure 1.

Claims (11)

1. An electrostatic spray charging head including means to support a spray-charging electrode forward of an hydraulic spray nozzle arranged to spray in a horizontal direction, in which the support means includes upright surface features to trap incident spray liquid for dispersal with gravity assisted flow and in which the electrode is of uprightly elongated form.

2. A head according to Claim 1 in which the electrode is embedded in an upright housing basally formed as a knife edge.

3. A head according to Claim 1 in which the electrode and any housing Is open at the base.

4. A head according to Claim 1 in which the electrode is of inverted U-form providing opposed inward surfaces between which spray travels for charging and an electrical connection on the top of the inverted U-form.

5. A head according to Claim 1 in which the support means is cranked downwardly towards the electrode to assist flow of incident spray liquid to dispersal.

6. A head according to Claim 1 in which the upright surface features include at least one of grooves and bars.

7. A spray charging arrangement including a head according to Claim 1 or any dependent claim and a charging electrode power supply including means to trip supply of power to said electrode if the current drawn is excessive and means to vary the value for excessive current trip.

8. A spray charging arrangement according to Claim 7 including means to indicate at least one value of current and voltage supply to the electrode.

9. A charger according to Claim 8 in which said indication means simply shows adequate and inadequate supply values.

10. An electrostatic spray charging head substantially as herein described with reference to Figure 1 of the accompanying drawings.

11. A spray charging arrangement substantially as herein described with reference to Figure 1 or Flgures 1 to 4 of the accompanying drawings.