Asphalt distributors are used to apply prime or tack coats on a surface in preparation for paving. They are available in either truck mounted or trailer models and are considered the most important piece of equipment on any asphalt surface treatment project.^[1] It consists of an insulated tank with a heating system, a spray bar and unique control system.

Application of a prime or tack coat by the distributor is an exact science that requires sophisticated equipment to ensure it produces a uniform spray.

Contents 1 History 2 Features/How it Works 2.1 Circulating System 2.2 Spray Bar 2.3 Controls 2.4 Trailer Units 3 Common Manufacturers 4 Additional Photos 5 References

[edit] History

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[edit] Features/How it Works

Asphalt distributors are equipped with tank capacities ranging from 800 to 5,500 gal and are capable of handling products ranging from light cold applications of emulsified asphalt to heavy asphalt cements heated to spraying viscosity.^[2] At the back end of the tank a spray bar with nozzles is attached. Spray bars can cover surfaces from six to 30 feet depending on boom width and pump capacity.^[3] Most distributors are also equipped with hand sprayers to reach areas not covered by the spray bar or for subsealing rigid slabs of pavement.

[edit] Circulating System

An engine driven pump powers the circulating system. It enables the filling of the distributor tank, circulates material from the tank, to the spray bar, and onto the surface. It is also capable of drawing excess material back from the bar, to the tank, and into an outside holding source.^[4]

[edit] Spray Bar

It is essential that the spray bar have constant pressure along the entire length for equal output from all nozzles. The methods to maintain pressure can vary between make and model, some control pressure with variable pump speed while others use constant pump speed and a pressure relief valve. The correct pump speed neither atomizes nor distorts the spray fan, whereas non-uniform pressure will result in streaking on the surface being sprayed. Pressure that is too high can also be detrimental, this is why each manufacture provides pump speed and pressure charts for determining the discharge in volume per minute for each nozzle size.^[5]

It is also extremely important to have the correct size nozzle for the type and grade of asphalt, as well as the proper application rate. The angle of the long axis of each nozzle opening must be adjusted to ensure that the spray fans do not interfere with one another. While angles may vary between make and model they usually range between 0.26 and 0.52 radians or 15 to 30 degrees.^[6]

Height of the bar must be uniform throughout spraying and cannot be so high that wind distortion can occur. For optimal results the spray bar should not exceed 0.5 in. This height must be maintained even as the load lightens. In order to restrict variance in height some models tie the frame to the springs of the vehicle, while others control this with mechanical controls.^[7]

[edit] Controls

The control system on an asphalt distributor is extremely important because it enables every aspect of the vehicle to be monitored and controlled from the operator’s cab. It consists of a valve system that controls the flow of material, a pump tachometer, or a pressure gauge to register pump output, and a bitumeter.^[8]

The bitumeter measures the rate of travel in distance (feet) per minute. It is made of a rubber wheel attached to a retractable frame, which rotates to measure the exact rate of travel. A cable is connected to the wheel and displays the data in the operator’s cab. The bit wheel must be checked often to ensure it is clear of debris or results will be inaccurate.^[9]

[edit] Trailer Units

Trailer asphalt distributors can come with or without an insulated tank. Without, they can be used as a stationary pump to transfer liquid bitumen from an asphalt melter to the storage tanks in a dedrumming setup.^[10] They can also be fixed with a spray bar and towed behind a unit with a tank to apply a surface coat of asphalt.^[11]

Trailer units with insulated tanks operate on the exact same process as truck mounted asphalt distributors. However, most trailers are considerably smaller than their truck mounted counterparts.

[edit] Common Manufacturers

• Chevrolet
• Ford
• Freightliner
• GMC
• International
• Peterbilt
• Rosco
• Sterling
• Western Star

[edit] Additional Photos

[edit] References

1. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 314-315
2. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 314-315
3. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 314-315
4. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 315-316
5. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 315-316
6. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 315-316
7. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 315-316
8. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 316-317
9. ↑ Asphalt Institute. The Asphalt Handbook: Manual Series No. 4 (MS-4), 1989 Ed. Pg. 316-317
10. ↑ Equipment Used in Bituminous Operations. Global Security. 2008-09-23.
11. ↑ Equipment Used in Bituminous Operations. Global Security. 2008-09-23.