THE DIMENSIONAL CHANGE OF FAN NOZZLE TIP ORIFICES IN CONSEQUENCE OF WEAR PROCESS

István Sztachó-Pekáry
Department of Horticultural Machinery, Kecskemét College, Hungary

ABSTRACT

The dimensions of fan spray nozzle tips have been determined before and after a wear test of fifty-hour by a measuring microscope. The design, nominal capacity, and the material have influenced the dimensional change of the tips through wear. The percentage increase of the characteristic dimensions, the quotients of minor/major axis and the area of nozzle tip orifices were determined. The regression diagrams and equations of the dimensional changes vs. nominal capacity were worked out. It has been found that the percentage of dimensional changes of Standard Flat Spray Tip types is less than the dimensional changes of Extended Range Flat Spray Tip types.

Key words: dimensional change, nozzle tips, sprayer, wear test.

INTRODUCTION

Pesticides must be applied properly to achieve satisfactory weed, disease, and insect control. Pesticide container labels indicate the recommended application rates for best results. However, proper application can be achieved only if the pesticide equipment performs properly, and is calibrated and operated correctly. Application accuracy is directly affected by how well each component of the sprayer performs. Spray nozzles are important in metering, atomizing and controlling the distribution of spray over the spray swath. Changes in these functions of a nozzle can influence the efficiency and effectiveness of the chemicals applied.

There has been considerable interest in nozzle wear rates and there have been several publications regarding the wear rates of various nozzles for different operating conditions. First Wilson [5] measured the percentage increase in flow rates through brass discs after spraying various carriers used with fungicides at pressure of 2760 kPa. He used 120 g·dm^-3 of carrier/water and found flow rate increased from 1.8% to 48% measurement of the initial flow rate after spraying 30 minutes. Wooten [6] measured the effects of flowable and wetable powder formulations of an herbicide (diuron) on the wear rates of nozzles with fan tips. His results showed that the wetable powder formulation caused faster wear than the flowable formulation. He also showed much faster wear with brass than stainless steel tips.

The literature on nozzle wear rates indicates considerable differences among reported results. Much of the difference in nozzle wear rates is due to the different operating conditions used when testing nozzles. Factors which influence nozzle wear include spraying pressure, duration of test; type and concentration of materials used in the spray mixture; time of use of abrasive before it is changed during the test, and type of nozzle and size, shape, and material of the orifice. There is a considerable need for reliable information on wear rates of nozzles. Reed [2] also reported that wear rate of an 8001 brass fan spray tip was greatly influenced by spray pressure. For example, the relative wear life was five times longer at 138 kPa than at 414 kPa. A comparison of relative wear between 8001 stainless steel and brass fan spray tips showed that stainless steel had 9.5 times longer life when the operating pressure was 138 kPa but only 4.0 times longer life when operated at 414 kPa.

The usage of fan nozzle tips is very common both in agriculture and industry. The objectives of this research were firstly, to develop equipment for a wear test for nozzles; secondly to determine the characteristic features and the dimensional change in nozzle orifices after the test process.

MATERIALS AND METHODS

Characterizing parameters of the tested fan nozzles

Fan-pattern nozzles are widely used in agricultural and industrial applications. For the purpose of the research the nozzles with the following tips of TeeJet^® made by Spraying System Co. (USA) were chosen. The marking on the tips is shown in figure 1:

Nozzle Type Series:

TP Standard Flat Spray Tip
XR Extended Range Flat Spray Tip
Spray Angle:
80°
110°
Orifice Nominal Capacity (× 0.1 Gallons – 0.38 liters per minute rated at 40 PSI – 276 kPa):
02
04
06
08
Material:
brass (–)
polymer (P)
stainless steel (S)
ceramic (K)

The geometrical dimensions of the tested tips

The list and the geometric dimensions of selected nozzles for the experiment are classified along with type series, nominal capacities, materials, spray angles and measured orifice dimensions of the tips. Three pieces of every single tip of each type were tested; the total number of tested tips was 144. All the tested nozzle tip orifices were approximately elliptical; their original 2a major and 2b minor axes (fig. 2) were measured with a microscope with its own ocular scale and micrometer screw. The data are presented in table 1, the mean dimensions of the same three tips of each nozzle tip type were used for the test. There was very little variation in dimensions of orifices for tips with the same nominal capacity and material. The quotient of minor/major axes b/a, the eccentricity and the discharge area A of the tips have also been determined. The A discharge area of the tips can be determined by the following formula:

(1)

Different dimensions of major and minor axes were measured at nozzles with different nozzle tip types and materials, but with the same nominal capacities. Groups were created of nozzle tip types in order to compare according to type, material and spray angle (fig. 3, fig. 4 and fig. 5). The most equable eccentricity was given by the nozzle tips XR 80xx VS. The character of tips TP 110xx VP was akin. The eccentricity of ceramic tips has been different from all the other types (tab. 1).

It was found that the orifice area of the different nozzle tips increased linearly by the nominal capacity, according to the discharge equation (fig. 3, fig. 4, fig. 5 and fig. 6). The figures are assembled to show the differences between the investigated materials, spray angles and nozzle tip types. It was also found that the largest variance of dimensions of TP type series was at the nominal capacity 08, especially with TP 8008 VS and TP 11008 VP, respectively. At the XR type series the largest variance was found with tips XR 8008 VS and XR 11008 VK (tab. 1).

Equipment and procedure

A test stand was constructed in order to determine nozzle wear rates. Phot. 1 shows the test stand constructed to wear the nozzle tips typically as in the application of pest control agents. The test stand consists of an approx. 200 dm³ tank with a pumping system to recirculate the mixture of water and abrasive through the nozzles. Up to six nozzles can be mounted on each of the three pipes at the top of the tank. Quick Teejet^® nozzle assemblies (Spraying Systems Co.) were used so that the spray tips could be rapidly removed and its flow rates with water and dimensions by microscope could be measured. To supply the liquid to the nozzles, a diaphragm type pump was used; model ANNOVI REVERBERI AR 503, driven with a belt drive from a 1.2 kW motor. A bypass flow tube and a pressure regulator were used to maintain the desired pressure at the nozzle tips and to return excess flow to the tank. Both a mechanical and an injector agitation system were used [4]. The duration of the test procedure was fifty hour.

The rating spray pressure during the tests was 276 kPa. This pressure was selected because it is the pressure of the nominal capacities of the tested nozzles. A mixture containing 0.06 kg of kaolin clay per liter of water was used in testing all of the nozzles [7]. The used type of kaolin clay is similar to carriers that have been used in wetable-powder pesticide formulations. Due to wear from the abrasives, the mixtures were changed at certain times specified by the next equation:

(2)

where T – the usage time of mixture, h
M – constant, V – the volume of the mixture, dm³
Q_b – the total discharge of the 18 nozzles, dm³ h^-1

The mixtures were changed at specific times calculated with M = 300 [3].

THEORETICAL ANALYSIS OF THE INCREASE OF GEOMETRICAL DIMENSIONS

Three nozzle tips of each tip type (tab. 1) were tested. Before and after the fifty-hour test procedure all the orifices of nozzle tips were measured. Then, the mean of three measured dimensions of the same tips were taken into consideration.

Inspection of orifices of some popular fan-pattern nozzles used to apply pesticides indicated that orifice walls at the ends of the major axis were perpendicular to the plane of the orifice. But, orifice walls at the ends of the minor axis were curved, expanding outward with increasing upstream distance. Therefore orifice wear in the Y-direction is expected to be smaller than in the X-direction (fig. 2). According to Ozkan’s report [1] and our former experiences [4] it had been indicated that the width of spray pattern of worn fan-pattern nozzles did not change, but the flow rate increased in the center of the pattern. Thus, changes in elliptical orifice size are considered only for the X-direction in the subsequent developments. The same observations were found after our fifty-hour wear procedure. Photo 2 shows the nozzle tip orifice of TP 8002 BRASS before and after the fifty-hour test process.

According to this observation further calculations were made with substitution a₁ = a₀, where the subscripts are: (0) before and (1) after the test process, respectively.

The percentage increase of minor axe b_% is:

(3)

after conversion:

(4)

To calculate the percentage increase of quotient b/a, defined k₀ as and k₁ as

(5)

after conversion:

(6)

The percentage increase of orifice area A_% is:

(7)

Replacing equation (1) into equation (6):

(8)

It can be seen that equations (8) and (6) have the same formula as equation (4). Therefore,

(9)

It was found that the percentage increase of the quotient k_% and the percentage increase of orifice area A_% are identical to b_%. The percentage increases of the minor axis vs. the nominal capacity are shown by fig. 7, fig 8, fig 9 and fig 10. The same figure shows the regression curve and equation fitted at the measured points.

RESULTS OF THE WEAR TESTS

The dimensional increase of the different nozzle tips

Out of the Standard Flat Spray Tips the bronze material tips with nominal capacity 02 and spray angle 110° (TP 11002 BRASS, fig. 8) had the largest dimensional increase after the test process, on the average 72%. The next measured dimension increase was observed also on bronze material tips with nominal capacity 02 and spray angle 80° (TP 8002 BRASS, fig. 7), on the average 67%. They were followed by the stainless steel (S) and the polymer (P) material tips with nominal capacity 02, having average dimensional increase 50% and 42%, respectively.

Out of the Extended Range Flat Spray Tips the polymer material tips with nominal capacity 02 and spray angle 110° (XR 11002 VP, fig. 9) had the largest dimension increase after the test process, on the average 110%. The next measured dimension increase was observed on the stainless steel tips with nominal capacity 02 and spray angle 80° (XR 8002 VS), on average, 49%.. They were followed by the ceramic (K) material tips with nominal capacity 02 with 10% average dimensional increase.

Comparing of Standard Flat Spray Tips type (TP) and Extended Range Flat Spray Tips type (XR)

After the investigation above the wear property of the two type series of tips made from the same materials (P and S) and with the same sprays angle and nominal capacity was also analyzed. Our measured data showed that the increase of the nozzle tip orifice areas of Standard Flat Spray Tips was less than the increase of the nozzle tip orifice areas of the Extended Range Flat Spray Tips.

SUMMARY AND CONCLUSIONS

Comparing the measured data of a fifty-hour wear procedure has determined the character and the quantity of dimensional change of different flat spray nozzles with special regard to design, material and nominal capacity.

From the measured data of the orifice change of different types of nozzles, the following conclusions can be drawn:

1. The orifice area of the different nozzle tips increased linearly by the nominal capacity.

2. A fifty-hour wear process changes only the dimension of the minor axis of the elliptical nozzle tip orifices.

3. The percentage increase of quotient k_% and the percentage increase of orifice area A_% are identical to the percentage increase of the minor axe b_%..

4. The orifice dimension of nozzle tips with the lowest nominal capacity has the highest percentage increase; the higher the nominal capacity of a nozzle tip is, the lower the exponential increase of its dimension will be.

5. The orifice of the Standard Flat Spray tips made of brass has the largest increase of their dimensions.

6. The orifice of the Extended Range Flat Spray Tips made of polymer has the largest increase of their dimensions.

7. The percentage change of the dimensions of Standard Flat Spray Tips is smaller than then those of the Extended Range Flat Spray Tips with the same material, nominal capacity and spray angle.

REFERENCES

1. Ozkan H. E., Reichard D. L., Sweeney J. S., 1992. Effect of orifice wear on spray patterns from fan nozzles. Transaction of the ASAE 35(4), 1091-1096.

2. Reed T., Ferrazza J., 1984. Wear life of agricultural nozzles. ASAE Paper No. AA84-001, St. Joseph. Mich., ASAE.

3. Reichard D. L., Ozkan H. E., Fox R. D., 1991. Nozzle wear rates and test procedure. Transaction of the ASAE 34(6), 2309-2316.

4. Sztachó-Pekáry I., 2004. The effects of fan nozzles orifice wear on flow rate and spray pattern. Progress Agric. Eng. Sci., Akadémia Kiadó, (Budapest) Sample Issue, 7-29.

5. Wilson J. D., 1943. Relative abrasion to spray nozzle discs by various fungicidal ingredients. Ohio Agric. Experim. Sta. Bull. 28(222), 10.

6. Wooten O. B., 1963. Effects of diuron on wear of spray nozzles. USDA/ARS 42-91 Bull. 8.

7. Zhu H. Brazee R. D., Reichard D. L., Fox R. D., Krause C. R., Chapple A. C., 1995. Fluid velocity and shear in elliptic-orifice spray nozzles. Atomization and Sprays 5(3), 343-356.

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