UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA SPRAYING EQUIPMENT FOR PEST CONTROL O. C. FRENCH BULLETIN 666 May, 1942 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Fundamental mechanics of sprayers 3 Atomization of spray liquid 3 Pump types and their characteristics 4 Pressure regulators 5 Nozzles, guns, and rods 7 Pressure and its effects 9 Pressure losses in hose and rods 13 Agitation 13 Portable power sprayers 17 Engine-powered sprayers 17 Power-take-off sprayers 18 Traction-driven sprayers 19 Sprayer tanks 19 Transport trucks and wheel equipment 19 Towers 21 Mixing plants and refilling equipment 24 Stationary spray plants 24 Object of the stationary system 24 Pump and mixing plant 26 Piping design 26 Installation of pipe lines 30 Rate of spraying 31 Original cost of stationary systems 32 Advantages and limitations of stationary spray systems 32 Portable pipe-line systems 32 Objective of portable systems 32 The portable pipe line 33 Methods of using portable pipe-line systems 33 Merits and limitations of portable pipe-line systems 34 Air atomizing sprayers 34 Development and use 34 Types of equipment 34 Atomizing characteristics of air-type sprayers 37 Weed sprayers 39 Requirement of equipment 39 Pumps for weed sprayers 39 Booms and nozzles 40 Acknowledgments 42 SPRAYING EQUIPMENT FOR PEST CONTROL 1 O. C. FKENCH 2 Nearly every commercially grown fruit, nut, and vegetable crop in California requires some treatment for the control of pests. Spraying is still the most widely used method, especially with fruits and nuts. That spraying costs are an important item can be shown from the fol- lowing conservative estimates : 8 Total fruit and nut acreage, 1939 1,505,550 Total value of these crops, 1939 $154,793,000 Estimated expense of spraying, 1939 $ 10,000,000 This estimated spraying cost covers labor, materials, and depreciation on equipment, but not dusting or fumigation. Since the annual spraying program requires such a sizable portion of the grower's time and money, this publication will explain certain funda- mentals of modern spraying equipment. Although much information is available on effective chemicals for sprays, the greatest problem in prac- tical field spraying is the proper use of mechanical methods of applying the chemicals to plants. Regardless of the crop being protected or the pest being controlled, there are three fundamental requirements for the equipment: (1) to obtain complete coverage of the tree or plant; (2) to apply the spray during the most effective period; and (3) to obtain these results at a minimum cost. No one special method will assure all growers of these results. What is satisfactory for one condition may prove ineffectual for another. FUNDAMENTAL MECHANICS OF SPRAYERS Atomization of Spray Liquid. — The purpose of any sprayer is to atomize a liquid or a liquid containing solids into droplets and to apply this finely divided spray to plant, fruit, or leaf surfaces. Obviously, the object of producing a spray in order to wet a surface is to obtain ade- quate coverage with a minimum of material. The atomization of a liquid into practical sprays is accomplished by several methods, the most common of which is direct hydraulic pressure forcing the liquid through a nozzle and causing it to disintegrate into droplets. Another method of producing sprays is to use a high- velocity air stream striking either a 1 Eeceived for publication August 5, 1941. 2 Lecturer in Agricultural Engineering and Assistant Agricultural Engineer in the Experiment Station. 3 Data for acreage and total value of crops from California Cooperative Crop Ee- porting Service. [3] 4 University of California — Experiment Station jet of liquid or a coarsely atomized liquid. This process is merely the reverse of discharging a jet of liquid at high velocity into still air. Pump Types and Their Characteristics. — With the exception of pumps used for knapsack sprayers, such as the compressed-air and diaphragm types, all spray pumps are essentially similar as to basic principles. The knapsack compressed-air sprayer utilizes a simple air-displacement pump mounted inside a small cylindrical tank. Air within the tank is compressed until a pressure of 50 to 75 pounds per square inch is ob- tained. When the discharge nozzle is opened, the air pressure forces liquid out of the nozzle. Obviously, spraying pressure will be constantly changing with this equipment: as the liquid level decreases, the air expands and its pressure decreases. For this reason the compressed-air sprayer of the knapsack type is not suitable where uniform spraying pressure is desired. Constant-pressure pumps for knapsack sprayers are of two types, plunger and diaphragm, both of which are positive-displacement types. Such pumps are fitted with a small air chamber to maintain uniform pressure. Though the pumps may be mounted either inside or outside the tank, the tank does not have to withstand any pressure ; it is merely a supply tank for the pump. The operator must pump continuously while spraying. Uniform pressure of from 50 to 75 pounds per square inch can, however, be maintained with this type of pump. Knapsack types of sprayers are suitable only for low-growing crops. Pumps for power sprayers are of the displacement, single-acting, reciprocating type. They are available in a wide range of sizes and capacities, and for working pressures up to 1,000 pounds per square inch, or even higher. The capacity of a reciprocating pump depends upon five things : (1) number of cylinders; (2) diameter of cylinder; (3) length of stroke; (4) number of strokes of plunger per unit of time; and (5) volumetric efficiency of the pump (defined as the actual volume discharged divided by the plunger displacement). All manufacturers now rate their pumps as to maximum capacity in gallons per minute at a given pressure. The volumetric efficiency of reciprocating pumps used on modern power sprayers when new or in good repair should be 90 per cent or higher. Very little leakage, therefore, should occur past the valves or plunger packings. Manufacturers have carried on much research, during recent years, to improve the life of plunger packing and valves. With the tendency toward increased working pressure and also toward in- creased concentration of certain chemicals used in insecticides and fun- gicides, the problem of maintaining the life of cylinder walls, plunger packing, and valves is difficult. Bul. 666] Spraying Equipment for Pest Control 5 All modern power-spray pumps are equipped with ball-type valves. Corrosion-resistant valve seats and balls, usually of hardened stainless steel, are used. The present design of valve-seat assemblies avoids the use of any gaskets; this eliminates a source of leak that formerly was troublesome. Two types of plunger displacement mechanisms are in use today : a plunger fitted with an expanding type of packing known as the plunger cup (this type of packing moves with the plunger) ; and a plunger oper- ating through stationary packing which serves as the cylinder wall of the displacement chamber. The relative merits of the two systems are controversial; neither is free from wear caused by handling abrasive chemicals under high pressure. Plunger cups are now generally con- structed of molded rubber and fabrics. In operation the cup edges ex- pand against the cylinder walls on the pressure stroke ; this seals and prevents leakage past the cup. The prevention of leakage or blow-by depends on the condition not only of the packing but also of the surface of the cylinder walls. Most cylinder walls are now coated with acid-resist- ant porcelain to retard corrosion and abrasion. Abrasion causes little grooves in the cylinder walls ; and when these occur, even new plunger packings cannot prevent leakage. Plungers of outside-pack types are made of stainless steel, since the plunger surface must remain free of corrosion if leakage is to be prevented. The stationary or outside type of packing may be adjusted so tightly as to score the plunger ; a slight leakage will indicate that the packing is not so tight as to cause scoring. The reciprocating motion of displacement plungers may be obtained by several different mechanisms, the most common being crankshaft and connecting rods (fig. 1) ; eccentric and connecting rods (fig. 2) ; and Scotch-yoke assembly (fig. 3). The only difference between the crankshaft and eccentric is in the diameter of crank pins : with a crank- shaft the diameter of the pin is less than the throw; with an eccentric the pin diameter is greater than the throw. Since the Scotch-yoke assembly permits the operation of two opposed plungers from one reciprocating mechanism, sprayers using this system are built with either two or four cylinders. Whether the cylinder should be vertical or horizontal is largely controversial. Improvement of lubrication systems by enclosing working parts, to afford protection from dust and provide more nearly self -oiling systems, has been a notable advancement in the service of spray pumps. Likewise the use of high-grade metals and designing for easy accessibility of valves and plungers has materially simplified maintenance. Pressure Regulators. — A pressure regulator on a spray pump has a threefold function: (1) it is a safety device; (2) it maintains uniform University of California — Experiment Station Fig. 1. — Triplex vertical-type spray pump with crankshaft and connecting rods. < m& b 1 -J!™ / t«l " *> ■ ~ w?*** i ■ ■' MB 3 c m% Fig. 2.— -A horizontal-type pump with eccentrics (a), connecting- rod drive, and movable plunger-cup packings (ft). Arrows c and d indicate suction and discharge valves respectively. pressure at the spray nozzle; and (3) it allows the pump to operate at greatly reduced load when no material is being discharged. The principle on which regulators operate is either a spring-loaded diaphragm or a plunger which, if the pressure of liquid exceeds the resistance offered by Bul. 666] Spraying Equipment for Pest Control the compression spring, will lift a ball valve and permit excess liquid to by-pass to the supply tank (fig. 4). By the use of a check valve between the diaphragm or plunger and the pump discharge line, the regulator becomes a partial unloading device as well as a pressure-relief valve. To function sensitively and positively, both the relief -valve ball and the check-valve ball must fit perfectly in their seats. If the check valve were removed, the regulator would function merely as a relief valve. For good operating conditions, some liquid should by-pass through the regulator €)aL*^ If . ,.** Fig. 3. — Pump using Scotch-yoke drive (a) with horizontal opposed plungers and stationary outside-type packing (b). while spraying is in progress. If no liquid is by-passing, then the dis- charge of the guns is too great for the capacity of the spray pump. Nozzles, Guns, and Bods. — Most of the nozzles commonly used, either as an integral part of spray guns or as an attachment on spray rods, are known as the eddy-chamber type. In these, liquid flows at high velocity through a vortex plate with spiral or tangentially arranged channels, which sets up a whirl in an eddy chamber. This whirl tends to break up the stream of liquid before it is discharged through the nozzle orifice. Some of the eddy-chamber nozzles are so designed that the depth of the chamber can be varied by means of an adjustable plunger (fig. 5). The commonly known "short spray gun" utilizes this type of nozzle. Varia- tion of the depth of the eddy chamber changes the angle of spray cone emitted from the nozzle orifice. A shallow chamber will produce a wide- angle cone of spray ; a deep chamber, a narrow-angle cone. If the eddy- chamber depth is increased sufficiently, a jet-type stream will be emitted 8 University of California — Experiment Station from the nozzle disk. The symmetry of spray cones is affected by irregu- larly worn disk orifices or unsymmetrically shaped vortex openings. That is, one side of the cone may contain most of the spray, or the spray may be streaked. Spray cones lose their symmetry at a short distance from the nozzle orifice, usually within 3 feet, because of air-current disturbances ; IOCK WASHER VALVJ CAGE STAINLESS STEF L SAIL NITRALlOy VALVE SEAT OVERFLOW TO SANK PLUNGER Fig. 4. — Spray-pump pressure regulators: A, diaphragm-type regulator; B, plunger-type regulator. for this reason the type of spray pattern produced is of minor impor- tance except for nozzles operated within approximately 3 feet of the object, such as the nozzles used on bamboo rods for tree spraying or on booms for vegetable and weed sprayers. Two types of spray patterns are produced by cone sprays : either a ring or a solid-pattern type. The ring- type pattern is produced by a hollow-cone spray ; the solid or disk pat- tern by a solid-cone spray (fig. 6). The latter pattern is obtained with a vortex or whirl plate having, besides the vortex openings, a central orifice directly in line with the spray-disk orifice and of approximately Bul. Q6Q] Spraying Equipment for Pest Control the same diameter. Addition of a central orifice in the vortex plate simply fills the center of the spray cone ; hence the term "solid cone." Pressure and Its Effects. — Pressure has been much discussed as to its SHUTOFF DISK AJUSTABLE PLUNGER SHUTOFF SEAT VORTEX PLATE RUBBER WASHER CAP NOZZLE BODY VORTEX PLATE CAP RUBBER WASHER EDDY CHAMBER A B Fig. 5. — Common eddy-chamber type spray nozzles: A, variable-depth type B, fixed-depth type. M v-;-' -V^V\ ;v":i. :0 Av '•;<*: •'.'.r/r, ■j?a ;- : -:^-.- ,: V'^' A B Fig. 6. — Ideal spray patterns: A, ring-type pattern produced by a hollow-cone spray; B, disk type obtained with a solid cone. The patterns are representations of cross sections of a spray stream. effect on the operation of guns and nozzles, and upon the success and failure of spraying. To determine how pressure affects the common spray- gun equipment, tests were made with a short gun adjusted for both close- and long-range spraying with pressures varying from 200 to 1,000 pounds per square inch. The gun was rigidly mounted to discharge hori- 10 University of California — Experiment Station zontally over a grid work of uniformly spaced cans so that the carry of the spray droplets could be measured. The point where a maximum quan- tity of spray was collected, called the maximum-quantity point, was chosen as an index of the carry. The results appear in figure 7. As shown by curve A of figure 7, the distance the spray droplets carried increased rapidly with increased pressures up to 600 pounds per square 35 30 25 20 15 10 B 200 400 600 800 1,000 PRESSURE AT NOZZLE IN POUNDS PER SQUARE INCH Fig. 7. — The effect of pressure on distances spray droplets carry: curve A for a short gun adjusted for close-range spraying; curve B for short guns adjusted for solid-stream or long-range spraying. inch; but pressures from 600 to 1,000 pounds per square inch caused little increase of carry. The actual distances of carry shown in the figure cannot be directly applied to other nozzles. The characteristic shape of curve A can be generalized, however, to include all nozzles that produce wide-angle cone sprays. Curve B of figure 7 shows that with a nozzle producing a solid spray stream, the maximum quantity of spray carries much farther than with wide-angle cone sprays. Carrying distance increases with pressure very much as in wide-angle cone sprays up to 800 pounds per square inch. Pressures above 800 pounds actually decreased the carrying distance. Bul. 666] Spraying Equipment for Pest Control 11 This break can be explained in that an increase of pressure finally causes the entire stream to be broken into small droplets, and as such lack suffi- cient momentum to carry. The latter fact also explains why cone sprays do not increase in carry much above pressures of 600 pounds. Figure 8 shows how pressure affects the size of spray droplets pro- duced by a typical nozzle producing a hollow-cone-type spray. The data were obtained by using a 0.4 per cent mixture of slaked-process lime and ~5oC ?5o" 5TJ0 5t50 IjOOO" PRESSURE AT NOZZLE IN POUNDS PER SQUARE INCH Fig. 8. — The effect of pressure on spray-droplet diameters as discharged from a nozzle giving a hollow-cone type of spray. water. Spray droplets from a short gun, carefully collected on clean glass slides, were measured with a microscope. The results show that to reduce the average diameters of droplets by one half, one must increase the pressure by four times. According to these tests, to secure additional distance of carry one should increase the rate of discharge of a nozzle by changing to a larger disk orifice instead of increasing the pressure : a pressure increase di- minishes droplet diameters so that the drops tend to travel a shorter distance. The use of pressures of 450 to 600 pounds in place of 250 to 400 has proved advantageous in most kinds of orchard spraying : it has speeded up spraying operations without requiring additional man-hours of labor and, if handled properly, without requiring any increase in the quantity of spray material. With higher pressures the liquid is broken into many X University of California — Experiment Station more droplets, a condition that tends to give a more uniform coverage at a more rapid rate. To be sure, an operator handling a larger quantity of spray per unit of time must be more alert, or wastage will result. There is apparently one exception to the use of high pressures — that of calyx spraying. According to field experience and some experiments, one ob- tains a better deposit of lead arsenate in calyx cups by using pressures of 200 to 400 pounds and solid-cone sprays. The reason, apparently, is that larger spray droplets traveling at low velocity penetrate and remain in the calyx cups better than finely atomized sprays at higher velocity. Contrary to popular belief, with a given nozzle and a constant pressure, decreasing the size of disk orifice does not decrease the size of the spray droplets. Pressure is the primary factor controlling the degree of atomi- zation: high pressure produces small droplets; low pressure, large droplets. The various factors and their influence on nozzle operation 4 are briefly summarized below. Disk-orifice diameters affect : 1. Diameter of spray cone (the smaller the orifice the smaller the cone). 2. Carry (carrying distance increases with diameter) . 3. Quantity of discharge. Pump-pressure increases cause : 1. Smaller spray droplets. 2. Increased carry of droplets (with pressures up to 800 pounds per square inch). 3. Increased included angle of spray cone. Eddy-chamber depth increases cause : 1. Increased carry. 2. Increased output. 3. Decreased atomization. 4. Decreased included angle of spray cone. Vortex-opening size increases cause : 1. Increased carry. 2. Increased output. 3. Decreased atomization. 4. Decreased included angle of spray cone. Irregularities of disk orifice cause unsymmetrical spray cones and irregular spray patterns. Increasing the thickness of disk decreases the included angle of the spray cone. *Davies, Cornelius, and G. R. "B. Smyth-Homewood. Investigations on machinery used in spraying. Jour. Southeast. Agr. Col. [Wye, Kent, England] No. 34:39-62. 1934. Bul. 666] Spraying Equipment for Pest Control 13 Pressure Losses in Hose and Bods. — The loss of pressure between the pump and spray nozzle occurs mainly in the hose when short guns or multiple-nozzle guns are used. Loss of pressure in bamboo rods may be large ; for example, losses in a 10-foot bamboo rod lined with %-inch pipe and equipped with shut-off valve are shown in the following tabulation : Pounds per Gallons per square inch minute discharge pressure loss 1.0 4.2 1.5 10.0 2.0 19.0 2.5 31.0 3.0 47.0 3.5 66.0 4.0 90.0 4.5 •. 120.0 Many spray operators now employ bamboo rods with double nozzles hav- ing %4-inch disk orifices which at 250 pounds' pressure will discharge 4.25 gallons per minute ; this causes a pressure loss of 100 pounds per square inch in the rod itself. Unfortunately, bamboo rods are all lined with %-inch pipe or tubing and were never designed for capacities greater than 2 to 3 gallons per minute. If more than these amounts are extensively used, larger-diameter rods should be obtained. Pressure loss is caused by friction of the liquid against the inside sur- face of the hose or rod. The magnitude of this loss varies with the square of the velocity of flowing liquid, the length of hose or rod, and the roughness of the inside surface of the hose, couplings, and rods. Figure 9 shows average pressure losses for various sizes of hose with different volumes of liquid flowing. Tables 1, 2, and 3 give approximate rates of discharge of short guns, multiple-nozzle rods, and bamboo rods. By means of these tables and figure 9 one may estimate the pressure loss to be ex- pected in hose lines equipped with various nozzles. Agitation. — Some type of agitation is provided in all power sprayers and in most hand sprayers, to insure that a uniform concentration of supply material will be maintained in the supply tank from full to empty. 5 The common means of agitation in power-spray tanks are two or more paddles, either propeller or flat type (fig. 10), mounted on a shaft running lengthwise of the tank. The shaft is driven either by chain and sprockets or by gears from the spray pump. Agitator shafts are usually so arranged that the paddles sweep within % inch of the bottom of the tank. Requirements for agitation vary, of course, with different types of spray mixtures used. Oil sprays and particularly tank-mix oil 5 Borden, Arthur D. Oil sprays for deciduous fruit trees by the tank-mixture method. California Agr. Exp. Sta. Cir. 345:1-16. 1938. 14 University of California — Experiment Station TABLE l Average Kates of Discharge of a Short Gun Adjusted for Long-Range Spraying* Pressure at gun in pounds Gallons per minute discharge using disks with the given sizes of orifice per square inch 3/64 inch 4/64 inch 5/64 inch 6/64 inch 7/64 inch 8/64 inch 200 300 0.64 0.79 0.91 1.02 1.13 1.10 1.32 1.55 1.72 1.90 1.70 2 06 2.40 2.89 2.94 2.40 2.90 3.40 3.75 4.12 3.33 4.15 4.75 5.30 5.80 4.10 5.05 400 5.75 500 6.40 600 7.00 * Short guns adjusted for close-range spraying will deliver approximately 5 to 10 per cent less volume than that shown in the table. TABLE 2 Average Rates of Discharge of a Multiple-Nozzle Gun Having Three or More Nozzles Pressure at gun in pounds per Gallons per minute per nozzle with vortex plates having no central orifice — for disk sizes given Gallons per minute per nozzle with vortex plates having also central orifice of same diameter as disk sizes given square inch 3/64 inch 4/64 inch 5/64 inch 6/64 inch 3/64 inch 4/64 inch 5/64 inch 6/64 inch 200 0.64 0.79 0.92 1 03 1.13 1.25 1.53 1.77 2.00 2.17 1.61 1.97 2.27 2.57 2.80 2.13 2.60 3.00 3.40 3.70 0.67 0.83 0.97 1.08 1.17 1.37 1.67 1.93 2.17 2.37 1.81 2.23 2.57 2.87 3.17 2.41 300 3.00 400 3.47 500 3.87 600 4.23 TABLE 3 Average Rates of Discharge of a Double-Nozzle 10-Foot Bamboo Rod Pressure at base of rod in pounds Gallons per minute for nozzles having vortex plates without central orifice — for disk sizes given Gallons per minute per nozzle with vortex plates having also central orifice of same diameter as disk sizes given per square inch 3/64 inch 4/64 inch 5/64 inch 6/64 inch 7/64 inch 3/64 inch 4/64 inch 5/64 inch 6/64 inch 7/64 inch 200 0.98 1.15 1.28 1.40 1.50 1.45 1.75 2.00 2.20 2.40 1.80 2.15 2.42 2.70 2.90 2.20 2.64 3.00 3.32 3.60 2.50 2.92 3.30 3.70 3.95 1.42 1.75 2.00 2.20 2.40 2.05 2.45 2.80 3.10 3.40 3.20 3.90 4.50 5.00 5.50 3.72 4.60 5.30 5.90 6.40 4.40 300 5.40 400 500 6.10 6.80 600 7.45 Bul. 666] Spraying Equipment for Pest Control 15 6 z ■k ^ ^ % 3< u / V / >" " < -U- / / / <0 ' 1 / / / f / Q. / f y J t / / z 70 I 4 1 / (A / t f / / O 50 f J / 1 --/ z 40 o / J / a / / / -7— u. / f / ' / ,tl / f / / / LOSS PER 50 FT. LENGTH 1 NCLU UINO hi 1 1 INCb llllll 3 4 GALLON 9 910 S PER Ml 2 NUT 3 E A s Fig. 9. — Friction losses in different sizes of spray hose at various rates of flow. Fig. 10. — An assortment of fiat blades and one common propeller type of agitator. sprays require the most violent agitation. Obstructions in the sprayer tank such as pipes, braces, and filler screens tend to produce quiet spots and to reduce the effectiveness of agitation. With some spray mixtures in which the suspended materials tend to separate, such as lead arsenate, oil, and soap, it is necessary to reduce the amount of agitation. The power requirement varies approximately as the 2.9 power of the speed of rotation of the agitators; if, for example, an agitator shaft 16 University of California — Experiment Station turning 100 revolutions per minute were speeded up to 125 the power re- quirements would be increased ( ) 29 = 1.91 times. Power consump- tion will vary directly with the depth of liquid above the agitators. For the same degree of mixing, propeller-type paddles require a higher speed of rotation than square-end flat paddles. Agitation in cylindrical-bottom tanks requires shaft speeds and horsepower only 80 and 50 per cent, re- iOO 350 400 450 PERIPHERAL SPEED OF AGITATORS IN FEET PER MINUTE 500 Fig. 11. — Curves showing the relation of tank depth and energy consumption at various agitator-shaft speeds to give a uniform mixture of spray oil and water. The chart is designed for semiflat-bottom tanks, 50 inches long, and flat-blade agitators. The ratio B is determined by dividing the total tip width of agitator blades in inches by length of tank in inches. The horsepower input for any given set of conditions is obtained by multiplying the indicated value from the chart scale by the given tank length in inches divided by 50 inches. For cylindrical-bottom tanks, shaft speeds can be determined by multiplying the indicated value from the chart scale by 0.80. Values for horsepower should be multiplied by 0.50. spectively, of that required in the semiflat-bottom tanks. For certain spray mixtures, the square-end agitators tend to whip an excess of air into the liquid when the tank is nearly empty ; this will cause the pump to operate inefficiently. The results of tests on requirements for agitating tank-mix oil sprays have been plotted in figure 11, by which one can estimate speed, energy consumption, and flat-blade equipment for any sprayer tank. To use this chart for cylindrical-bottom tanks, multiply the speeds indicated by 80 per cent, since agitation is more effective than in semiflat-bottom tanks. Bul. 666] Spraying Equipment for Pest Control 17 For example, the following typical problem is to be solved by the use of figure 11 : With a cylindrical-bottom tank 38 inches wide, 57 inches long, 7 inches above the bottom, and liquid level 36 inches above the agitator shaft, find the speed required to agitate the oil-spray mixture, the size and number of the flat blades, and the energy consumption. Solution : The maximum length of blades can be only 13 inches in order to clear the bottom of the tank. Choosing a ratio R of total blade-tip width to tank length of 0.42, and reading the chart horizontally (dotted line) at the 36-inch depth to E, 0.42 on the solid vertical line, one finds that the peripheral speed of the blade tip must be 500 feet per minute, or a shaft speed of 147 revolutions per minute with a 13-inch blade. 6 Since the chart is based on a semiflat-bottom tank, multiplying the speed by 80 per cent results in a speed of 118 revolutions per minute or 336 feet per minute tip speed. To find the energy consumption, follow vertically up- ward on the chart from 336 feet per minute to the broken line R, 0.42, thence horizontally to the horsepower scale, which indicates approxi- mately 0.22 horsepower. The tank length is 57 inches, so this value must 57 be multiplied by — , since the chart is based on a tank length of 50 inches, 50 57 hence 0.22 X — = 0.25 horsepower. The ratio of blade-tip width to 50 tank length was chosen as 0.42, or 24 inches (0.42 X 57 = 24) of blade width. One must use either three 8-inch-width or four 6-inch-width flat blades. The results of this example then are as follows : Speed = 118 revolutions per minute ; horsepower = 0.25 ; number of blades t= three of 8-inch width. The width of the tank may be disregarded since its effect upon agitation is slight. | /4-0" % VI ZX/Z' p/cn/( p/o/form f/oor 7 fanti /?o./*, to # = 500 ft. of % -in. pipe, at 5 g.p.m. = 4.6 X 5 23 E to F = 150 ft. of y 2 -in. hose, at 5 g.p.m. = 18 X 3 54 Total pressure loss 147 The pressure available at gun F will be 600 - 147 = 453 pounds per square inch. Likewise, pressures at guns H, J, L, and N can be com- puted ; they are 463, 487, 482, and 458 lbs. per square inch respectively. The dead-end, gridiron plan for pipe lines has proved most popular and practicable in California. With this layout (fig. 22) the main extends centrally through the orchard with laterals at right angles and on both sides of the main. Ordinarily, no provision is made for draining the pipe 30 University of California — Experiment Station lines ; if freezing is apt to occur, some method of draining must be pro- vided. It is usually simple to find, in the system, a low point where a drain can be installed. A practical plan for hydrants is to locate a riser with valve near the base at every second tree along the laterals. This method allows the popu- lar "long-pattern" system of spraying to be practiced (fig. 23). The laterals should be so spaced that not more than 130 feet of hose is re- quired to spray each block unless the sprayman has a helper. One man can handle up to 130 feet of %-inch hose unless a high covercrop is en- countered, since during spraying actually only one half of the hose need be pulled. K> o q o o o o o c*-d oaooaaaa o o o o o o o o dto a o o o o o o a -J /HYDRANT fo o o o o t$*R*fMW\^@f&w^ o o o o o c o o o ©m € o o ooo a & o o -o o o o o o o o o OOGOOGOOO ©IIS? o o o o OOOOOGOOO o o o K3 O Fig. 23. — Diagram illustrating "long-pattern" system of spraying from stationary pipelines. With this plan, hydrants are located close to the trunks of the trees. The sprayman begins at tree 1 and follows the path indicated by arows until the block is completed. Another plan is to place the hydrant valves directly on laterals and below the ground level. This method eliminates the extra ditching and pipe required where hydrants are placed by tree trunks. Since the hy- drant is located in the center space between four trees, a plan of spraying can be used (fig. 24) whereby more trees can be sprayed from one hydrant than with the long-pattern system ; thus fewer hydrants are required, and less time will be lost in removing and attaching the spray hose. "With this plan, hydrant valves must be uncovered after each tillage operation between sprays, a situation that ordinarily will not occur more than twice during a spray season. Installation of Pipe Lines. — Pipe lines may be placed on the surface of the ground, overhead, or buried in the ground. Of these arrangements, the last is probably most desirable. The pipes can be laid deep enough to permit cultivation over them without injury. Hydrant valves above ground should be placed close to trunks of trees; those underground should be deep enough to escape damage from tillage implements. The trenches for pipe lines can usually be dug by power equipment with con- siderable saving in costs. Bul. 666] Spraying Equipment for Pest Control 31 For the stationary systems, galvanized iron pipe is recommended. Per- manent pipe lines should be installed with the same care as any plumbing job. All threads should be painted with a good pipe compound. Plenty of unions should be used throughout the system so that future repairs can be more readily made. Shut-off valves should be placed on each lateral directly off the main. Hydrant valves with bleeders, commonly known as stop-and-waste types, are best to use because they save time in discon- necting the spray hose. One should test the complete system for leaks o o o o o o o o o o < o Q Q Q O O O O O oooooooo OOOOQOOO oooooooo o o o o O oo o O O G O o o o o OOOOOOOO oooooooo Oooooooo LATERALS • HYDRANTS oooooooo oooooooo o o-o o o o o o oooooooo o o o a O o o o » O O Q O } o o o o ) o o oo OOOOOOOO OOOOOOOO o o Q o o o o o o o o Fig. 24. — Diagram showing a method of spraying when hydrants are located directly on laterals, below ground, and in the center space between four trees. before covering any of the pipes. The life of underground pipes is often questioned. Since certain soils and the resulting solutions may rapidly corrode pipes, a prediction of expected life is difficult. Many systems have been in service over twenty years. Recently an orchardist in Santa Clara County removed a piping system twenty-seven years old. This pipe was in good enough condition to be used again for a stationary system : the threaded end sections were merely cut off, and the pipe rethreaded. Before planning a stationary underground system one should observe other buried pipes in the vicinity to determine whether corrosion is apt to be serious. Present spray materials do not seriously injure the inside surfaces of pipes. Bate of Spraying. — On a stationary system covering 48 acres of pears, time studies were made for one complete spray season in order to deter- mine the man-hour requirement and the rate of spraying. The long- 32 University of California — Experiment Station pattern system of spraying was used in this orchard, with six to seven spraymen at work. A total of nine sprays were applied during the season on the acreage, excepting one application that covered only one half of the orchard. To spray this acreage 233 hours was required, the rate being 1.75 acres per hour; and 2,165 or an average of 5.3 man-hours per acre was used. According to records for individual blocks, an average of 40 minutes was required for a man to spray 22 trees with an average of 4.5 gallons of material per tree. The time required for moving the spray hose from one hydrant to another averaged 3 minutes. This represents 7 per cent of time lost from having to move to each hydrant. As shown by other time and cost studies, the total cost of operating stationary plants is generally 15 to 30 per cent less than for portable sprayers. Original Cost of Stationary Systems. — The cost of the pumping unit of the stationary plant should not be greater than for the portable spray- ers that would be required for the same acreage. On large-acreage instal- lations, the cost of the pumping plant per acre will usually be less for stationary systems than for portable equipment. Pipe-line costs will vary, but in general will run from $25.00 to $40.00 per acre. Advantages and Limitations of Stationary Spray Systems. — Station- ary spray systems have certain advantages : 1. Timeliness of spray applications. 2. High annual duty of pumping plant equipment. 3. Relative unimportance of soil conditions. 4. Easier spraying on hillsides. 5. Lower operating costs. The limitations are : 1. Such systems are economically feasible only in long-lived or- chards such as of pears and apples, which require several sprays per season. 2. The initial investment is high. 3. It is difficult to cover the tops of trees. 4. The use of spray towers is generally impracticable. PORTABLE PIPE-LINE SYSTEMS Objective of Portable Systems. — Portable pipe-line spraying has been used in several California orchards during recent years in order that spraying might be done even when ground conditions would not permit the use of portable sprayers and when the orchard did not justify in- stallation of stationary systems. With this system, a portable sprayer is used as a semistationary plant. The sprayer can be located on a road Bul. 666] Spraying Equipment for Pest Control 33 along the edge of the orchard and can supply spray material to a pipe line laid on the ground surface through a section of the orchard. Connections for spray hose are located at intervals along the line. After spraying a block of trees, the pipe and sprayer are moved to another block. The Portable Pipe Line. — The size of pipe used for portable lines must necessarily be limited to % inch because of the labor involved in moving. Since the pipe must be small, usually not more than two men can spray from one line because of excessive friction losses. Ordinarily the pipe line is made up by connecting 20- to 22-foot lengths of pipe together either with sleeve couplings or with unions. Two lengths can be readily moved as a unit by two men. Connections for spray hose are spaced approximately at every fourth or sixth tree along the line. These hose connections consist of a hydrant valve with male pipe threads on one end and male hose threads on the other, attached into a tee in the line. Some growers have built up their pipe lines by using "quick detach- able" hose couplings for risers as well as at every second joint in the line in order to reduce the time required for moving the pipe. It is doubtful whether the time saved will offset the additional cost of the special couplings. Unions need not be used for the joints to be disconnected ; sleeve cou- plings will serve instead. It is considerably easier, however, to start the threads of a union, particularly where a long length of pipe must be handled. Special light-weight wrenches to fit the unions can be handled faster than the pipe wrenches necessary where sleeves are used. Methods of Using Portable Pipe-Line Systems. — The plan of spraying with the portable pipe system depends somewhat on the tree spacing and upon the accessibility of roadways on which the portable sprayer can be located. Some growers, for example, have found it desirable to place the line at every eighth tree row and to have hydrants at every sixth tree along the line, each hydrant thus serving 48 trees. Another plan is to place the pipe line at every eighth tree row and to locate hydrants at every fourth tree. The hydrant then serves 32 trees. The number of trees sprayed from one hydrant depends, of course, on the length of hose line used. Since this system is usually practiced where soil conditions are soft, hose lines should probably be not more than 100 to 125 feet long in order that the effort of dragging the hose may be kept low. Plans for spraying blocks from portable-line hydrants resemble the one illustrated in fig- ure 24. Operators often find it advantageous to have a refilling truck for servic- ing the sprayer and also to have one or two men besides the spraymen to help move the pipe. 34 University of California — Experiment Station Merits and Limitations of Portable Pipe-Line Systems. — With the portable pipe method of spraying, a grower with a portable sprayer can get his spraying done on schedule when ground conditions may be too wet to pull the sprayer through the orchard. The system costs much less than a stationary system. The main disadvantages are the labor involved in moving the pipe line, the rather large losses in pressure experienced if long lengths of pipe are required, and the difficulty of covering the tops of large trees. AIR ATOMIZING SPRAYERS Development and Use. — Power sprayers using a high-velocity air stream for atomizing and applying dilute liquid spray material have been available for many years ; their use, however, has been limited be- cause they lack the flexibility of hydraulic sprayers. More recently, air atomizing equipment has been developed for applying concentrated liquid sprays. During the period 1930-1932 a serious infestation of grape leafhoppers occurred in the San Joaquin Valley. This pest was satisfac- torily controlled by the application of small quantities of pyrethrum oil atomized and conveyed to the vines with air. Two types of power sprayers were developed to atomize concentrated oil spray by use of air. One type, utilizing compressed air, atomized the liquid like a paint sprayer; the other used a blower that produced a high-velocity air stream into which the oil was sprayed from an atomizing nozzle. The principle of air atomiz- ing sprayers is to dilute the particles of concentrated spray with air instead of water, at the same time utilizing the air stream to carry the small droplets of spray to the plant surface. The quantity of liquid required for this principle of spraying varies from 2 to 4 gallons per acre for grapes, up to as much as 12 to 25 gallons per acre for tree crops. The small amount of liquid required per acre permits a sprayer unit considerably lighter than ordinary hydraulic sprayers. Much time is saved because refills are less frequently required. Continued experimental work has extended the use of concentrated liquid sprayers to several fields of pest and fungus-disease control, such as the application of dormant oil on deciduous trees and of tartar emetic (with sugar) for citrus thrips. Types of Equipment. — In applying concentrated liquid sprays, three types of sprayers have been used successfully, namely compressed air, blower or fan type, and airplane. The compressed-air sprayer has an air compressor driven by a gasoline engine. The size of air compressor will depend on the number of nozzles desired ; ordinarily a displacement of 5 cubic feet per minute per nozzle is satisfactory. A compressor capable of displacing 10 cubic feet of free air per minute will furnish sufficient air at 80 pounds' pressure per square Bul. 666] Spraying Equipment for Pest Control 35 inch to operate two nozzles like the one illustrated in figure 25. For such a compressor a 4-horsepower engine is adequate. Each nozzle is provided with two %-inch hose lines, one for compressed air and the other (an oil- resistant type) for liquid. Liquid containers ordinarily are mounted high enough on the sprayer to permit liquid to flow to the nozzles by gravity. A pressure slightly less than atmospheric will occur at the exit of the liquid line because of the high velocity of air flowing across the liquid jet. Compressed-air sprayers have generally been used by operating the individual nozzles by hand (fig. 26, A). In a few instances, however, nozzles have been fitted on a boom for certain truck-crop work. This type of sprayer is limited to low-growing plants such as vines or truck crops. The blower or fan type of sprayer utilizes the principle of fixed nozzles, ■q sfop cocKs v -/?7y t ^&^ ^| PF L A , Fig. 30.- -Two types of nozzles that deliver the flat-fan type of spray. (From Bul. 634.) - 0.80 0.60 0.40 0.20 60 60 100 GALLONS PER ACRE Fig. 31. — A chart showing required discharge per nozzle to give desired quantity per acre at various field speeds. If nozzles are spaced 18 inches apart on the boom, multiply the indicated discharge per nozzle by 1.5 ; if spacing is 2 feet, multiply by 2.0. 42 University of California — Experiment Station and the quantity of spray desired per acre. Nozzles that deliver spray at an included angle of 60° should be spaced 1 foot apart ; 80°, 18 inches apart ; 90°, 2 feet apart. Wider spacing of nozzles is desirable ; the cost is then smaller and larger orifices lessen the danger of clogging. Figure 31 has been prepared as an aid in the selection of nozzles for any given boom, and of different field speeds for various quantities of spray per acre. The chart is designed for nozzle spacing of 1 foot. For 18-inch spacing, multiply the discharge per nozzle by 1.5 j for 2-foot spacing, multiply by 2.0. Manufacturers of nozzles can furnish several sizes of disks, usually listed as to the diameter of the disk orifice in standard twist-drill num- ber. Before going into the field, a boom must be calibrated so that the pressure may be adjusted to discharge the exact amount of material desired ACKNOWLEDGMENTS The author is grateful to all who have aided in preparing this bulletin, especially H. B. Walker, Roy Bainer, J. P. Fairbank, G. F. MacLeod, and A. M. Boyce. The following firms were helpful in supplying illustrations : Hardie Manufacturing Company, Friend Manufacturing Company, and the John Bean Manufacturing Company. 20m-5.'42(871S)