September 1966 



COMMERCIAL FISHERIES REVIEW 



COMPRESSOR UNIT: A diesel-powered air compressor which delivered 315 cubic feet 

 per minute (free air rating) was set up on the east shore of the study area. This unit supplied 

 air at about 80 pounds per square inch pres- 

 sure on 18 -second cycles, i.e., 9 seconds 

 "on" time followed by 9 seconds "off" time. 

 A pressure tank of 200 -gallon capacity, with 

 pressure valve and gauge, was installed at the 

 outlet of the compressor. The tank helped 

 cool the air through expansion and a large 

 radiation surface. 



Operation during warm weather produced 

 air of extremely high temperature; therefore, 

 additional cooling was needed to prevent soft- 

 ening or melting the plastic pipe. From the 

 regulated pressure tank, 120 feet of copper 

 water tubing 1-inch diameter was spiraled 

 loosely into about 5 -foot coils. The air was 

 directed from the pressure tank to this tubing, 

 which was hung on a rod so that the coils were 

 submerged below the surface of the water. 

 The "radiator" sufficiently cooled the air to 

 a temperature compatible with the semirigid 

 plastic pipe. The temperature of the air en- 

 tering the rigid pipe after flowing through the 

 cooling coil never exceeded 76 F. even in 



80° F. weather. Constant maintenance, such as oil changes and greasing, is needed onadiesel 

 unit which is to be kept in operation for extended periods of time. A 160 -cubic foot per min- 

 ute standby compressor was kept on the site for emergency use and was connected so that the 

 unit could be operated to ensure constant air flow when the main compressor was not func- 

 tioning. 



Fig. 4 - Reeling out liose and chain. 



Bee 



of three 



ause of the excessive noise 

 walls and a roof, was built 



of the compressor unit, a plywood structure, consisting 

 over the unit (fig. 5). Since the installation obstructed 

 the east shore of the river, a lighted 

 sign was posted on the river bank to 

 inform boat traffic of the obstruction. 

 As the main compressor unit consumed 

 about 80 gallons of diesel fuel every 

 24 -hour period, a 27 5 -gallon fuel sup- 

 ply was hooked directly to the com- 

 pressor engine to reduce the number 

 of refueling operations. 



After the pipe was installed, the 

 compressor unit was started to pre- 

 vent silt from entering or clogging the 

 holes in the plastic pipe and the pres- 

 sure was slowly brought up to the desired 

 80 pounds per square inch. During early operation, the air curtain was a solid and continu- 

 ous stream of readily visible bubbles (fig. 6). As the study progressed the initial holes tended 

 to close, because of the burrs left on the inside of the pipe during drilling. To correct this, 

 SCUBA divers punched holes with a fine pin at 2 -inch rather than 6 -inch intervals. This di- 

 ameter (0,02 inch) was about double that of the No. 80 drill. The close-spaced holes produced 

 a much more vigorous, uniform, and probably more effective curtain (fig. 7). Unfortunately, 

 as the study went on, even the larger holes became partially plugged and the action was re- 

 duced. 



Fig. 5 - Equipment installation. 



