LIBRARY 
 ^TATE PLANT BOARD 
 
 ET-180 September 1941 
 
 United States Department of Agriculture 
 Bureau of Entomology and Plant Quarantine 
 
 A DUST GUN FOR LABORATORY EXPERIMENTS WITH INSECTICIDES 
 
 By F. H. Harries, Division of Truck 
 Crop and Garden Insect Investigations 
 
 The equipment described herein was designed for applying 
 small weighed quantities of derris and pyrethrum dusts according to 
 a technic employing a spray gun that was used previously in testing 
 liquid preparations of the same materials. The apparatus was 
 operated by compressed air and consisted of a dust-delivery mech- 
 anism mounted on a common type of laboratory spray gun for the 
 purpose of utilizing the air-valve control lever of the sprayer 
 (fig. 1, A). This assembly was connected to a reducing valve and 
 pressure gauge on a compressed-air line by a section of air hose. 
 
 The duster attachment (B) consisted of a short delivery 
 tube mounted on a cylindrical housing containing an air-driven 
 wheel and a fine-toothed disc. The dust delivery tube was made of 
 two short sections of 1/4-inch brass pipe joined by a brass tee 
 attached to the dust cylinder. The dust cylinder was 3-1/2 inches 
 in diameter and 3/4 of an inch in length and was fashioned on a 
 lathe from a large bronze bearing. The inside diameter of the 
 cylinder was cut slightly larger for a distance of about 3/8 of 
 an inch from one end, and a tightly fitting disc of sheet copper 
 was pressed in against the flange formed by the difference in 
 diameter and soldered in place to form a partition. The inside 
 diameter was also cut slightly larger for a distance of about 1/16 
 of an inch from each end of the cylinder to form flanges for 
 receiving the front and back cover plates (D and F) . Plates closing 
 the ends of the dust cylinder were made of heavy sheet copper and 
 were held in place by nuts on the end of a stationary steel shaft 
 placed through the center of the housing. 
 
 The wheels were made from discs of sheet copper and were 
 mounted on a bronze sleeve or bearing fitted to turn freely on the 
 steel shaft. The sleeve extended through a hole of slightly larger 
 diameter in the partition and was equipped with outside threads for 
 mounting the toothed wheels. These were clamped rigidly to the 
 sleeve on opposite sides of the diaphragm by means of thin lock 
 nuts on both sides of each disc. Small vanes were fashioned along 
 the edge of the drive wheel (C) by cutting in about 1/4 of an inch 
 
- 2 - 
 
 at 1/8-inch intervals and twisting these sections at right angles 
 to the plane of the disc. Teeth of the dust wheel (E) were made 
 in the same way. except that the cuts were made just deep enough 
 at l/16~inch intervals to give the sections a slight twist and 
 roughen the edge of the disc. 
 
 Two small copper tubes, fastened with solder, passed through 
 a plug in the delivery tube to divide the air stream. One of these 
 tubes was led through a small hole in the top of the cylinder and 
 was bent to direct the compressed air against the blades of the 
 drive v/heel . Holes v/ere cut in the back plate (D) to permit escape 
 of the air. The other tube was extended beyond the brass tee in 
 the delivery tube to produce a suction at the top of the dust cham- 
 ber, where air was admitted through two small holes bored in the 
 housing (F) . The end of this tube was soldered over and then 
 partially opened with a needle to make a smaller opening, so that 
 the greater portion of the air would pass through the other tube 
 and be used in spinning the wheels. 
 
 The insecticidal dust was introduced through a hole in the 
 front plate that was opened by unscrewing a m.etal cap. The dust was 
 carried upward on the teeth of the disc and by the agitation of the 
 air produced by revolutions of the dust wheel, then it was taken 
 through the brass tee into the delivery tube by suction and expelled 
 by compressed air. It was apparently unnecessary to clean the 
 reservoir or dust chamber between operations, but the cleaning 
 could easily be done by removing the front plate and dust wheel. 
 A slight residue was left in the delivery tube after applying each 
 dust charge, and this was removed with a small brush. The rate of 
 dust delivery was regulated by adjusting the reducing valve to 
 determine the pressure of the compressed air. This control also 
 permitted the delivery of dusts of different physical properties 
 at about the same rate. The present apparatus gave a more complete 
 dispersal and more uniform delivery of the entire dust charge than 
 other types of equipment tested. 
 
A. SIDE VIEW OF GUN ASSEMBLY 
 
 \MP^4 
 
 '^-fc"'- ■"- 
 
 li^ 
 
 B. CROSS SECTION 
 
 SHOWING DETAILS 
 
 c. 
 
 DRIVE 
 WHEEL 
 
 D. 
 
 BACK 
 
 PLATE 
 
 HOLES 
 FOR ESCAP 
 OF AIR 
 
 AIR JET ^i 
 
 BACK 
 PLATE-*!! 
 
 
 DUST 
 WHEEL 
 
 LOCATION OF 
 HOLES FOR 
 ADMITTING 
 AIR 
 
 ragtjre 1. — Diagram of the dust gun showing details of construction. 
 
UNIVERSITY OF FLORIDA 
 
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 3 1262 09240 9357