A re-examination of the disk flow regulator*

Bull. Org. mond. Sante' 1971, 44, 847-854Bull. Wld Hlth Org. A Re-examination of the Disk Flow Regulator* D. B. WEATHERS,1 J. W. TAYLOR 2 & J. A. JENSEN 3 It is important in residual spraying programmes for malaria eradication that a uniform deposit of insecticide should be applied to the walls ofdwellings. The uniformity ofapplica- tion with hand compression sprayers is greatly enhanced if a disk flow regulator is used, but this device has not been popular for field use as its properties alter after afew days' use. This study explains the mode of action of the device and discloses that swelling of the disk caused by the DDT formulation is the primary cause of the gradual reduction of output. The needfor proper mating of the disk with the nozzle tip is explained, and the 9504E-type tip is described as best suited for the desired spray output. Use of the disk flow regulator is recommended because it permits uniform spray application and reduces nozzle-tip erosion. INTRODUCTION It is important in residual spraying for malaria control that the recommended deposit of insecticide for walls of dwellings be adhered to as closely as possible. Excessive application is wasteful, whereas insufficient application may be inadequately effective. The hand compression sprayer used in malaria programmes does not give a uniform deposit unless some means of controlling its output is provided, because the output of the spray nozzle decreases as the sprayer pressure decreases. Compensation by the sprayman can improve the uniformity of applica- tion but such measures are difficult to control. Mechanical pressure regulators have been used to some extent but their design is complex and they require frequent cleaning and maintenance. The disk flow regulator (DFR), however, is a simple device that will maintain a constant spray discharge rate and swath width with a drop in tank pressure of as much as 40 lbf/in2 (2.8 kgf/cm2). This device has been described adequately by Lonergan & Hall (1959a, 1959b) and Hall & Taylor * From the US Department of Health, Education, and Welfare, Public Health Service, Health Services and Mental Health Administration, Center of Disease Control, Technical Development Laboratories, Savannah, Ga. 31402, USA. This study was accomplished as part of a contractual agreement between the Center for Disease Control and the United States Agency for International Development. I Research Chemical Engineer, CDC, Technical Devel- opment Laboratories. ' Mechanical Engineering Technician, CDC, Technical Development Laboratories. 3 Engineer Director, CDC, Technical Development Laboratories. (1962). The commercial unit 4 has been assessed in field trials, notably by Acheson & Roy 6 in Togo, Fitzjohn & Stevens 6 in Nigeria, Thomson & Taylor (unpublished data, 1966) in Guatemala, and Kolta & Kuo in Egypt.7 These field studies have confirmed laboratory results and they show that the DFR, when used with the proper nozzle tip, controls the spray flow within narrow limits although the sprayer pressure ranges from 55 lbf/in2 to 25 lbf/in2 (3.9-1.8 kgf/cm2). The spray pattern was poor, however, and the spray angle was less than desired and decreased as the time of use increased. The disks used in these tests failed to retain their regulatory property after several days of use. Spraymen also noted that the droplet size increased and that the hissing sound normally associated with spraying was absent. These effects seemed unnatural and undesirable. The disk regulator, therefore, has not been popular in spraying programmes. This study was undertaken to explain how the disk functions and to determine: (1) the degree of 'Produced by H. D. Hudson Manufacturing Co., Chicago, Ill., USA. Use of trade names is for information only and does not constitute endorsement by the Public Health Service or the US Department of Health, Education, and Welfare. a Acheson, M. & Roy, L. (1967) A field and laboratory trial of a disc flow regulator. Unpublished document WHO/ Mal/67.599. I Fitzjohn, R. A. & Stevens, P.A. (1963) Field tests of rubber disc regulators on compression sprayers. Unpublished document WHO/Mal/377. 7Kolta, S. & Kuo, C. (1970) A field and laboratory trial of disc flow regulators and Even-spray nozzle tips. Unpub- lished document WHO/Mal/70.709. 2697 847- 9 848 D. B. WEATHERS, J. W. TAYLOR & J. A. JENSEN improvement provided by the disk regulator over unregulated flow; (2) the reasons for deterioration in performance of the disk; (3) the proper disk-tip combination to minimize deficiencies in perform- ance; and (4) whether the use of the disk regulator is justified in spite of its imperfections. DEFICIENCIES OF THE PRESENT SYSTEM The nozzle tip used almost exclusively in malaria control at present is the CHSS 8002 flat-fan tip, made of hardened stainless steel.' This tip is designed to produce a flat, fan-shaped spray with an angle of 80°, at a flow rate of 757 ml/min (0.2 US gal/min) at 40 lbf/in2 (2.8 kgf/cm2). Spraying techniques for the various malaria programmes are based on these specifications. However, the actual tank pressures recommended in using the hand-compression sprayer range between 55 lbf/in2 and 25 lbf/in2 (3.9-1.8 kgf/ cm2). Under these conditions the spray output and fan angle vary from about 900 ml/min to 600 ml/min and from 840 to 750, respectively. Therefore, the deposit on the wall will vary unless the sprayman can compensate for the continually changing output and swath width. It is doubtful whether such com- pensatory measures can be applied in practice to produce a satisfactorily uniform spray deposit. In fact, spraymen in both WHO- and USAID-spon- sored malaria programmes are carefully trained to maintain a constant spraying speed and swath width when spraying a surface with insecticide. Under these conditions, the deposit on the wall must vary in direct proportion to the variation in nozzle output. As the discharge rate varies ± 150 ml/ min, or ±20%, from the nominal rate of 757 ml/min, the deposit on the surfaces sprayed must also vary by approximately this amount. THE DISC FLOW REGULATOR - ITS FUNCTION AND PERFORMANCE Fig. 1 shows the regulator assembly, its parts (a, b), and the shape of the disk, with (d) and without (c) pressure applied. The location of the disk assembly in the nozzle body is shown in Fig. 2. Note that the disk opening becomes smaller when the disk is compressed by the tank pressure (Fig. id), and this change is directly proportional to the applied pressure. The disk functions until the pressure in the spray tank drops below about 20 lbf/in2 (1.4 kgf/ 1 This and other nozzle tips referred to in this paper are manufactured by Spraying Systems Co., Bellwood, Ill., USA. cm2), and maintains a constant pressure of 9-11 lbf/ in2 (0.63-0.77 kgf/cm2) (in combination with a 9504 nozzle tip) between the disk and the nozzle tip. The efficacy of the DFR in controlling spray performance is shown in Fig. 3. When the standard 8002 flat-fan tip is used, the unregulated flow drops from 900 ml/min to 600 ml/min, and the fan angle decreases from 840 to 750 as the sprayer pressure decreases from 55 lbf/in2 to 25 lbf/in2 (3.9-1.8 kgf/ cm2), the normal operating range of the sprayer. In contrast, when the 9504 tip is used with the DFR, a nearly constant flow of 730-705 ml/min and a fan angle of 79-76° is maintained over the same pressure range. Fig. 3 also shows that the pressure at the nozzle tip is maintained at 10± 1 lbf/in2 (0.70 kgf/cm2). Although the tip pressure begins to fall at about 30 lbf/in2 (2.1 kgf/cm2) in the sprayer, the flow rate holds until the sprayer pressure falls below 20 lbf/in2 (1.4 kgf/cm2)-the critical pressure for the DFR-9504 tip combination. The curves in Fig. 3 illustrate that although the DFR is in effect a flow regulator, it controls flow by maintaining a constant pressure at the nozzle tip and is thus actually a pressure regulator. RETAINER DISC HOLDER (b) (C) (d) Fig. 1. Construction of the disk flow regulator. A RE-EXAMINATION OF THE DISK FLOW REGULATOR Fig. 2. Construction of the nozzle-DFR assembly. 40 30 TANK PRESSURE (LBF/IN2) Fig. 3. Regulation of flow by the disk flow regulators. 849 90 801 ~-J aC CD 1000 900 F z 800 ° X 700 5001 8002 TIP 9504 -DFR N\9504WITITR-ElEDFR ___ _- ___$- -- - -e--- - -_,. 0-f - _e I-LU~ II l0 9 a 60 20 701 600l 850 D. B. WEATHERS, J. W. TAYLOR & J. A. JENSEN Table 1. Changes in disk weight after soaking Initial Weight after Percentage Weight after PercentageSoaking medium Dnisk weight 185 hours change in drying in air chaninSoakingmedi no. (g) (g) weight fr2days chne inh 5% DDT 1 0.1527 0.1810 + 18.5 0.1792 + 17.4 2 0.1485 0.1770 + 19.2 0.1747 + 17.6 Water-Triton X-100 1 0.1 555 0.1 540 - 0.96 0.1541 - 0.90 2 0.1475 0.1465 - 0.68 0.1460 - 1.0 Water 1 0.1595 0.1575 - 1.3 0.1574 - 1.3 2 0.1584 0.1572 - 0.76 0.1560 - 1.5 Matching of regulator and nozzle tip The low pressure at the nozzle tip produced by the DFR makes it necessary to use a tip with an orifice larger than that of the 8002 standard tip in order to attain the desired 757 ml/min (0.2 US gal/min) flow rate. The 8004 tip has been used most extensively in previous work. However, the 8004 tip, like the 8002, produces an 800 fan only at a pressure of 40 lbf/in2 (2.8 kgf/cm2), and, because of the low tip pressure, the fan angle produced with the DFR was less than the desired 800. A special tip, Hudson No. 153-400, which produces a wider fan when used with the DFR, was evaluated in the field but was found to be unsatisfactory.' Laboratory studies have shown that the 9504 flat-fan or the 9504E (Evenspray) tip is the preferred tip for use with the DFR. Observations on changes in disk properties One of the principal objections to the DFR reported in the various field trials has been that after the disk has been used for some time, it gradually loses its ability to control the flow and that the output of a particular disk-tip combination decreases from day to day. This phenomenon has been generally ascribed to a " set" in the rubber disk since partial recovery of flow occurs if the disk is not used for a short period. It has also been assumed that some of the reduction in flow rate might be due to accumulation of the DDT formu- lation under or around the rubber disk within its holder. We thought that the gradual deterioration in the 1 Acheson, M. & Roy, L. (1967) A field and laboratory trial of a disc flow regulator. Unpublished document WHO/ Mal/67.599. flow-control properties of the disk might be due to changes in the disk other than a physical " set " of the rubber; for example, it could be due to a chemical action of the DDT slurry. To test this theory, we removed 6 disks from their holders and carefully weighed them. Then we soaked 2 of them in distilled water, 2 in distilled water with 1 % Triton X-1001 detergent added, and 2 in 5% DDT (pre- pared from 75% water dispersible powder) for a total of 185 hours. The disks were periodically removed, rinsed in water, dried, and weighed. The results of this test are shown in Table 1. As can be seen, the disks soaked in the DDT formulation showed a substantial weight increase. This increase, which totalled about 19% after 185 hours, was apparently continuing when the test was stopped, and was a permanent increase as indicated by the weights obtained 20 days later. The disks were also noticeably swollen in appearance. The disks soaked in water or in the water-detergent mixture were essentially unchanged. A subsequent test was undertaken to determine the magnitude of dimensional changes in the disks caused by the DDT formulation and the effect of these changes on disk performance. The flow rates and flow patterns of 12 disks were measured, all with the same 9504 nozzle tip, and the disks were then weighed. Disk thickness and diameter and orifice diameter were also measured. Eight of the disks were then soaked in the 5% DDT formulation and 4 were soaked in distilled water for 5 hours per day. After each day's soaking, the disks were rinsed and dried, then reweighed and measured. After reinstalling the disks in their holders and checking 1 Produced by Rohm & Haas Co., Philadelphia, Pa.,'USA. A RE-EXAMINATION OF THE DISK FLOW REGULATOR Table 2. Changes in disk properties after soaking Flow rate of disk-tip combination at 40 lbf/in2 Percentage changes in disk measurements(ml/min) Disc no. Initial Final Percentage Weight Thickness Diameter Orifice rate rate change Wih Thcns Damtr diameter D DT-soaked 1 726 707 - 2.6 + 11.7 + 2.9 - 1.0 + 2.5 2 729 725 - 0.55 + 11.0 + 3.7 - 1.7 + 2.5 3 745 712 - 4.4 + 14.4 + 5.1 0 + 2.5 4 752 760 + 1.1 + 15.9 + 4.4 - 0.7 + 2.5 5 789 742 - 6.0 + 11.4 + 4.4 - 1.3 0 6 779 743 - 4.6 + 11.7 + 2.9 0 0 7 805 769 - 4.5 + 13.6 + 6.0 + 1.4 + 2.5 8 768 723 - 5.9 + 13.8 + 5.9 + 0.7 + 2.5 Water-soaked 9 812 819 + 0.86 - 1.8 - 1.5 - 1.5 0 10 760 800 + 5.3 - 0.9 - 2.2 - 2.2 0 11 791 812 + 2.7 - 0.7 - 1.5 - 1.5 0 12 728 760 + 4.4 + 0.01 + 0.7 + 0.7 0 their flow rates, the disks were removed from the holders and dried in air overnight. At the end of the test, flow patterns were again determined. The total soaking time for each of the disks was 69 hours. The results of this test (shown in Table 2) again indicate that soaking in the DDT formulation increased the weight of the disks as well as their thickness, but changes in both disk diameter and orifice diameter were insignificant. Dimensional changes of the water-soaked disks were small, but it is interesting that the disk weight and thickness decreased slightly. Changes in flow rates of the disks after soaking appeared to correlate inversely with changes in weight and dimensions, with the DDT-soaked disks showing generally decreased flow rates and water-soaked disks increasing in flow. Although not shown in the table, a slight decrease in fan angle was noted for the DDT- soaked disks as opposed to a slight increase for those soaked in water. It should be noted that the DDT used in these tests was produced to meet Specification No. PHS/NCDC-1-102, which is used for all DDT purchased by USAID. No effort was made to determine whether the effects noted were due to DDT, per se, or to impurities or other constituents of the 75% DDT formulation. However, a limited test using a 5% slurry made from p, p'-DDT more than 99% pure did produce weight gains in 2 disks of approximately the same magnitude as those reported. DFR performance under simulatedfield conditions Five nozzle tips each of the 9504 and 9504E types were paired with DFRs and then the initial spray pattern was assessed at 40 lbf/in2 (2.8 kgf/cm2). The flow rates of all tips were obtained in the range of 20 Ibf/in2 to 60 Ibf/in2 (1.4-4.2 kgf/cm2) in 10-lbf/in2 (0.7 kgf/cm2) increments. The combi- nations were attached to a multiple outlet sprayer manifold. A 5% DDT water dispersible powder suspension was discharged through the tips at 40 lbf/in2 and in 5 seconds " on " and 5 seconds " off" cycles. A total of 25 US gal (94.6 litres) of spray passed through each tip in a 4-hour period totalling 1500 cycles. This simulated one day of field spraying. At the end of this period, all tips and disks were rinsed with water without brushing or mechanical cleaning. Flow rates of the combinations were then measured at 10-lbf/in2 increments from 20 lbf/ in2 to 60 lbf/in2, and the disks were air-dried over- night. This measurement was repeated the following morning to detect any "recovery" of the disks. Spray patterns were determined only after the passage of 112.5 US gal (425 litres) and 212.5 US gal (804 litres) of spray, the equivalent of 1 and 2 weeks of field spraying. 851 D. B. WEATHERS, J. W. TAYLOR & J. A. JENSEN QUANTITY OF 5% DDT DISCHARGED (US GAL) U-0 01189 Fig. 4. Changes in flow rates with use: 9504 tip-DFR assembly. Dashed line: initial results; solid line: after recovery for 16 h (except as noted). 800 750 9- -J W 650 600 L 60 50 40 30 20 TANK PRESSURE (LBF/IN2) *o0 01190 Fig. 5. Changes in flow regulation by the disk flow regulator with use. Solid line: initial; dashed line with squares: after use for 1 week; dashed line with triangles: after use for 2 weeks. 852 - 03 m -J cm M U- co -J W C= 31: C) -J LL. U- 700 A RE-EXAMINATION OF THE DISK FLOW REGULATOR 853 Fig. 4 shows the changes in flow rate at 40 lbf/in2 (2.8 kgf/cm2) of the 9504-DFR combinations as the test progressed. The flow rates after either overnight or weekend " recovery " of the disks when they were dried in air are also shown on this graph. Fig. 5 illustrates how the disk regulates the flow over the sprayer pressure range of 60-20 lbf/in2 (4.2-1.4 kgf/cm2) when it is new and also after it has been used for 1 and 2 weeks of simulated field spraying. Although the flow rate of the DFR does diminish with use, and although only part of this loss can be regained by not using the disk for a while, the DFR still provides excellent flow control at the reduced rate (Fig. 4 and 5). Also, the reduction in flow rate after 2 weeks' use is only about 12% of the initial flow rate, and some recovery of flow rate occurs if the disk is not used for a short period. This compares very favourably with the variation in flow of about 38% found with the unregulated 8002 tip as the sprayer pressure falls from 55 lbf/in2 to 25 lbf/in2 (3.9 kgf/cm2 to 1.8 kgf/cm2) in normal operation. The distribution patterns of the 9504- DFR and 9504E-DFR combinations, not repro- duced here, showed very little change with use and were generally superior to that obtained with the unregulated 8002 tip. The 9504E (Evenspray) produced a very even distribution of flow across the fan width. Reduction of nozzle tip erosion The 9504 tip when used with the DFR has a flow rate approximately equal to that of an unregulated 8002 tip at 40 lbf/in2 (2.8 kgf/cm2). However, because the 9504 has a larger orifice, the liquid velocity through the orifice is lower. and this should reduce abrasion of the orifice by the spray material. To determine the magnitude of any reduction in tip erosion, we ran a test with a slurry of 8 lb of Hi-Sil 2331 per 50 US gal of water at a pressure of40 lbf/in2 (3.63 kg per 189 litres at 2.8 kgf/cm2), and followed the method described by Jensen et al. (1969). Ten 9504 and ten 9504E tips were assessed for flow rates and spray distribution patterns; then they were paired with DFRs and installed in the test equipment. After the passage of each 10 US gal (37.8 litres) of slurry and up to a total of 100 US gal (378.5 litres), flow rates and patterns were again obtained for each tip. A similar test was then run using 3 tips of each type without the DFR. 1 Produced by PPG Industries, Pittsburgh, Pa., USA. This is a severe erosion test and a CHSS-8002 tip under the same conditions would be expected to show an increase in flow rate of 5-6 %. The results of the test appear in Table 3. Flow rates for the 9504 and 9504E tips run without the DFR increased by an average of 2.3% and 3.2%, respectively, whereas the flow rates for both types of tips run with the DFR increased by only 1.4%. These results indicate that the useful field life of the 9504 tip used with the DFR would be substantially greater than that of the present 8002 tip. Distribution patterns for the tips remained essentially unchanged after the erosion test. Table 3. Erosion test with 100 US gallons of Hi-Sil 233 slurry Flow rates at 40 Ibf/in2 (ml/min) a Type of tip a Initial Final % Increase 9504 without DFR 1 444 1 478 2.3 9504E without DFR 1 446 1 493 3.2 9504 with DFR 1 443 1 464 1.4 9504E with DFR 1 450 1 471 1.4 a Data for the tips without DFRs are averages for 3 tips and those for tips with DFRs are averages for 10 tips. DISCUSSION AND CONCLUSIONS The results of this study indicate that the disk flow regulator (DFR) is a useful device that improves uniformity of application of insecticide when used with the hand compression sprayer. The DFR has certain deficiencies, but these have generally been over-emphasized and its really useful properties, which have not been stressed, are discussed below. The DFR controls flow by maintaining a uniform pressure at the nozzle tip that is necessarily lower than the sprayer pressure. For this reason a nozzle tip must be selected that will produce the desired output and fan angle at the reduced tip pressure. It has been found that the 9504E tip is the preferred tip for use with the disk flow regulator at present available. The lower tip pressure results in a reduction of the normal " hissing " sound of the spray and a slightly larger droplet size. However, because the velocity of the droplets is reduced there is less bounce-off from the surface being sprayed. Also, because fewer fine particles are generated, drift losses are reduced. 854 D. B. WEATHERS, J. W. TAYLOR & J. A. JENSEN The reduction in output of the disk with use is apparently due to absorption of DDT by the disk rather than to build-up of DDT between the disk and its holder. Some deposits were found in a few of the DFRs used in the simulated field spraying, but there was no correlation between DDT build-up and performance. The rate of flow through the disk improves again if the disk is not used for some time. Erosion of the nozzle tip is reduced when the DFR is used because the velocity of the spray through the orifice is lower, and because the orifice is larger. The disk now available gives in a flow rate slightly less than the desired 757 ml/min and the flow gradually decreases with use. Therefore, if a deposit of exactly 2 g/m2 of spray material is desired on the surfaces sprayed, either the disk must be modified to provide the desired flow in- crease, or spraymen must be taught to compensate for the lower output. RESUMt NOUVELLE tTUDE DU RtGULATEUR DE DEBIT A DISQUE Le regulateur de debit a disque est un dispositif simple, fait de caoutchouc synthdtique moule et placd dans une monture de cuivre. Employe avec le bec de buse appro- prie, il permet d'obtenir, du pulverisateur a pression prealable actionne manuellement couramment utilise dans les programmes d'eradication du paludisme, un debit d'insecticide relativement constant. Cette regularite de ddbit rend possible I'application, sur les murs des habitations, d'une couche d'insecticide plus uniforme que ne le permettent les methodes et le materiel actuel- lement en usage. Plusieurs essais pratiques, ainsi que des recherches en laboratoire, ont prouve l'utilite du regulateur a disque, mais ils ont aussi fait apparaitre certains inconvenients, en particulier une legere dimi- nution du ddbit qui s'accentue progressivement 'a l'usage. La presente etude a eu notamment pour objectif de rechercher les raisons de ce phenomene, d'essayer de choisir le bec de buse le mieux adapte a l'emploi du regulateur a disque, ainsi que d'etudier en laboratoire le fonctionnement de l'association bec de buse-rdgulateur de ddbit en simulant les conditions dans lequelles se ddroulent les operations de pulverisation. I1 ressort de ces travaux que c'est l'association du modele existant de regulateur de debit a disque et d'un bec de buse de type 9504E (acier trempe inoxydable) qui donne les meilleurs resultats. On a 6galement trouve que la reduction du debit provenait d'un gonflement du disque dui ii l'absorption d'un ou plusieurs des com- posants de la suspension de DDT a 5% generalement utilisee dans les programmes d'eradication du paludisme. Les avantages que presente le regulateur de debit a disque - debit constant, reduction des 6claboussures et de 1'eparpillement dans l'air du liquide projete, et prolongation de la duree du bec de buse - en com- pensent les inconvenients et son utilisation est a recom- mander. REFERENCES Hall, L. B. & Taylor, J. E. (1962) Bull. Wld Hlth Org., 27, 279-281 Jensen, J. A., Taylor, J. W., & Pearce, G. W. (1969) Bull. Wld Hlth Org., 41, 937-940 Lonergan, R. P. & Hall, L. B. (1959a), Bull. Wid Hlth Org., 20, 955. Lonergan, R. P. & Hall, L. B. (1959b) Bull. Wld Hlth Org., 20, 961