necessary to preheat the circulating system to ensure that the first material to enter the pump is not to be chilled sufficiently  to  stop  the  pump.  A  portable  burner  is available for this purpose. An opening in the circulating system housing at the rear, near the bottom of the housing,  is  provided  for  the  burner. Normally, 150 gallons per minute (gpm) is the best loading speed. Light materials or heavy materials at spraying temperature may be loaded at faster pump speeds.  Check  the  filling  line  as  well  as  the  pump discharge  strainer  periodically  and  clean  as  needed. When the distributor is to be filled with hot bitumen, proceed cautiously if there is any moisture in the tank or if  emulsion  was  used  in  the  previous  load  because foaming could occur. A liquid compound, Dow Corning DC-200, can be used to prevent foaming. HEATING  BITUMEN  IN  THE  DISTRIBU- TOR.— When you are heating bitumen in a distributor with  low-pressure  atomizing  burners,  using  clean, moisture-free  fuel  is  important;  therefore,  use  kerosene, fuel oil, or diesel fuel.  DO NOT USE GASOLINE. To start the blower, disengage the engine clutch, engage the blower drive clutch, then engage the engine clutch. Air pressure should be sufficient to raise the air relief  valve  slightly.  Excessive  engine  speed  will  raise the relief valve too much. The correct air pressure to use is 1 1/2 to 2 psi. Fuel pressure should not be excessive. High fuel pressure will make the needle valve adjustments more sensitive. The correct fuel pressure to use is 10 to 20 psi. Pressure is determined by a relief valve, located under the fuel tank. An adjusting screw and locknut are inside  the  dome-shaped  cap. Do not light the burners unless you are sure the flues are covered with 6 inches of material the full length of the tank. On tanks having high-low flues, it is necessary to cover only the lower flue when using the lower burner. Open the stack cover. To light the burners, you should turn the air butterfly valves to the START position, light the torch, and hold it under the burner tip. Then turn the valve about one-half turn. The burner should ignite immediately. If it does not, turn off the needle valve and wait until the gas is exhausted from the flues, then try again. NOTE: The correct amount to turn the needle valve is  determined  by  the  fuel  pressure.  Experience  is  the only way you can determine the correct amount for a particular unit. At  first,  the  flame  will  be  yellow  and  smokey. Adjust the fuel valve so that the flame is bright orange with slight color in the exhaust. More adjustment to the fuel will be needed as the flues and tank contents heat up. WARNING When the burner goes out, you should turn off the fuel valve immediately and do NOT attempt  to  relight  until  the  gas  vapors  are exhausted  from  the  flues. For larger flames, increase the air butterfly valve opening and the fuel valve opening in equal increments. Always keep a mix that produces an exhaust that has a slight color. The nozzle of the burner is adjustable for the amount of secondary air desired. Light the burner and turn this nozzle until you secure the type of flame you desire. Further adjustment is not necessary. Do NOT leave the burners unattended. Do NOT heat to a temperature over the maximum spraying temperature recommended by the supplier. To shut off the burners, turn the fuel off before stopping the blower or turning off the air. Spraying Correct spraying cannot be obtained unless the bitumen  is  heated  to  the  proper  spraying  temperature. When using 1/8-inch nozzles, set the governor from 120 to 180 gpm for a 12-foot spray bar. In the NCF, a rule of thumb for GPM is 10 gallons per minute for every foot  of  bar  length.  Example:  10-foot  bar  length  = 10 GPM. Higher pump speeds cause excessive fogging of the spray. Lower pump speeds cause the bitumen spraying fan, as shown in figure 16-33, to sag with heavy edges. Also, when the fans have heavy edges, the cause could be that the material is too cold or the pump speed is too slow. At the end of the day, be sure to flush out the pump and circulating system. Performing this easy draining and   cleaning   operation   prevents   the   pump   and circulating system from clogging up because of bitumen setting up and hardening in the system. Attachments Some areas cannot be reached with the spray bar; therefore, it is sometimes necessary to apply asphalt by another means. In such cases, spraying can be done by hand with a spray hose and gun, as shown in figure 16-30