automatically correct the height of the spray bar, as thischange occurs.The uniform application of asphalt prime and tackcoat is essential.Transverse spread should not beallowed to vary more than 15 percent, and thelongitudinal spread should not vary more than 10percent. To ensure the correct application, you mustcalibrate the distributor before it is used. Then thetransverse and longitudinal spread rate variations shouldbe checked periodically to determine when thedistributor is operating within these limits. A procedurefor checking these spread variations in the field has beenstandardized by ASTM D 2995, published by theAmerican Society for Testing and Materials.FILLING TANKS AND DISTRIBUTORS.—Always use a manhole strainer when filling tanks anddistributors unless you are filling them with emulsions.When you do not want material to enter the pump andcirculating system, ensure the intake valve lever is in theUP position. When the tank is full of hot bitumen thatFigure 16-34.-Proper angling of nozzles.coverage.This height varies according to the nozzlemay set upon entering a cold pump, you should heat thespacing of the spray bar. Under heavy wind conditionsor depending on the nozzle spacing, it maybe necessaryto lower the bar farther down so that the surface onlyreceives double coverage.On some distributors, as asphalt is sprayed (and theload lightens), the truck rear springs of the truck rise,raising the distributor and changing the height of thespray bar. Mechanical devices are usually available thatpump and circulating system before starting to circulatethe bitumen to prevent it from freezing in the pump. Aportable burner is available to use if the pump is cold.When you are filling lines using a pump, always usea strainer in the filling line except when using emulsions.Be sure that all connections between the distributor andsource of supply are tight. Because air leaks reducevacuum and slow down the heavier bitumens, it may beFigure 16-35.-Spray bar height and coverage.16-29
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