ET-149 June 1939 
 
 United States Department of Agriculture 
 Bureau of Entomology and Plant Quarantine 
 
 LABORATORY SPRAYING AND WASHING APPARATUS 
 
 By Robert D. Chisholm. 
 Division of Insecticide Investigations 
 
 In the study of spray residues under laboratory conditions 
 it is necessary to have a means whereby the sprays may be applied 
 on plants, glass plates, and other surfaces and also a means for 
 simulating the washing effect of rain. One of the methods often 
 employed for this purpose includes the use of a paint sprayer, which 
 atomizes the spray by means of compressed air. The equipment neces- 
 sary is expensive, considering the combined cost of the paint 
 sprayer, air compressor, and control valves. Also it is not readily 
 portable. 
 
 Apparatus has been developed which is of low cost and is 
 readily portable. Furthermore, it permits the use of a wide vari- 
 ety of spray nozzles to produce sprays of varying character and 
 thus more nearly duplicate sprays as they are used in the field. 
 The same equipment used for applying spray mixtures may also be 
 used to simulate the washing effect of rain by merely substituting 
 water for the spray mixture. 
 
 Description and Operation of Apparatus 
 
 To operate the apparatus, cocks D and F are closed and cock 
 C is opened, after which the spray mixture is poured into the 
 percolator (A), and the motor (G) is started. The spray mixture 
 flows from the percolator into the gear pump (B), from which it is 
 forced back into the bottom of the percolator through a tube at- 
 tached to cock C. This tube is closed at the end, and near its 
 end it has two holes of 1/16" diameter, which are drilled at right 
 angles to each other. This arrangement produces vigorous agitation 
 of the spray mixture and reduces foaming and swirling to a minimum. 
 By partly closing cock C the pressure in the system is increased. 
 Constant pressures up to 50 pounds per square inch may be maintained 
 by a simple adjustment of cock C. Higher pressures are obtainable 
 by increasing the speed of the pump. The spray nozzle (E) is 
 operated by opening cock D. To clean the apparatus, cock F is 
 opened and the excess spray is discharged. This is followed by 
 sufficient clear water to remove the last trace of the spray 
 mixture . 
 
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 Since the capacity of the gear pump is far greater than the 
 output from the spray nozzle, it is evident that this apparatus is 
 essentially a device for the continuous removal of a portion of a 
 uniform flow of a spray mixture which is under constant pressure. 
 The device is constructed of standard parts, is portable, and may 
 by used anywhere that electricity is available. The type of spray 
 delivered may be varied through a wide range by means of changes in 
 the pressure, location of the spray nozzle in relation to the ob- 
 ject to be sprayed, and the use of various types of nozzles. In 
 this way sprays may be applied under hydrostatic pressure in a 
 manner which closely duplicates field spraying. Furthermore, the 
 same apparatus may be used to simulate the effect of rain on spray 
 residues by simply substituting water for the spray mixture. 
 
 The spraying apparatus may be used in various ways, one of 
 which is illustrated in figure 1. This shows a spray hood which 
 contains apparatus for rotating glass plates through the spray. 
 
 The spray hood is in the form of a cube with one face omitted, 
 each dimension being 4 feet. It is assembled from sections made of 
 lumber 2 inches square and covered with galvanized iron. The sec- 
 tions are bolted together. The galvanized iron in the bottom is 
 in the form of a pan 4' x 4' x 2" and has a 1" pipe flange in one 
 corner to accommodate a drain pipe. The galvanized iron on the 
 sides extends on the inside to the bottom of the pan. 
 
 The device for rotating objects through the spray is mounted 
 on a 1" X 12" board placed diagonally in the hood. It is raised 
 above the pan by means of cleats in order to allow the removal of 
 the excess liquids through the drain. The rotating device consists 
 of a turntable (J), to which is attached a support (H) for a rack 
 (I) . Power is transmitted to the turntable by a motor (K) by means 
 of belts and pulleys which reduce the speed of the rack to 2 r.p.m. 
 This speed may be varied by changes in the sizes of the pulleys. 
 The rack consists of eight metal rods 9 inches in length, which are 
 attached to the top of the support. A Parrot paper clip is attached 
 to the end of each rod to hold the glass plates in a vertical 
 position. The plates are supported in the clips by means of 3- 
 sided prisms, with a saw cut in the top edge into which the bottom 
 edge of the glass plate is fitted. The glass plates are 5" x 7" 
 photographic plates, with one corner ground to provide a space for 
 identification marks. 
 
 The support and rack may be removed and a circular table 
 substituted in cases where it may be desirable to spray plates 
 while they are in a horizontal position or to spray potted plants 
 or other material. 
 
 When in operation, the pulleys, motor, and turntable are 
 protected from the spray by means of a metal cover. 
 
Figure 1. — Laboratory spraying and washing apparatus. 
 The necessary pipes and fittings are shown. The 
 appeiratus is mounted on a portable wooden base. 
 
 Parts of apparatus for producing spray: 
 
 A. Glass percolator, 2-liter capacity. 
 
 B. Gear pump, 3/8", with 6" pulley. 
 G. Cock, 3/8", to control pressure. 
 
 D. Cock, 1/4.", to control nozzle. 
 
 E. Vermorel spray nozzle. 
 
 F. Cock, 3/8", to drain apparatus. 
 
 G. Motor, I/-4 hp., 1,725 r. p. m., with 2" pulley. 
 
 Parts of apparatus for rotating glass plates: 
 H. Support for the rack. 
 I. Rack for holding glass plates. 
 J . Turntable . 
 K. Small motor. 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 08537 0863 
 
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