Lesson 6/Learning Event 4
pump adjustments. It is very important that the asphalt being used is at the prescribed mixing
temperature before the tests begin. The procedure for calibrating by the pump output method is
as follows:
a. Determine the approximate pump setting (Figure 25) from the METERING PUMP
CAPACITY CHART (Table 19). As determined in Step 5-1, the required feeding
rate is 9.3 lbs per rev. By interpolating on the chart, it is found that the setting
required to deliver this rate is 60.3.
b. Set the pump to 60.3 and take a weight sample (Figure 26). The procedure for taking
a weight sample is as follows:
Obtain two test buckets of approximately 25 gallons each.
Weigh one test bucket and record the weight.
Place the other test bucket under the sample pipe.
With the control valve in the test position, run the pump until the sample pipe
begins to discharge asphalt. Stop the pump and allow the pipe to drip for one (1)
minute. Remove the test bucket and discard the asphalt.
Place the weighed bucket under the sample pipe and record the revolution counter
reading.
Run the pump until the test bucket is between 1/2 and 3/4 full. Stop the pump and
allow the sample pipe to drip for one (1) minute.
Weigh the sample and subtract the weight of the bucket to obtain the weight of
the asphalt.
Record the revolution counter reading and subtract the reading at the beginning of
the test to obtain the number of revolutions run.
Divide the weight of the asphalt by the number of revolutions to determine the lbs
per rev being delivered.
NOTE: Always allow the sample pipe to drip for one (1) minute before
weighing the test bucket. Be sure to weigh the test bucket before each
test, as asphalt clinging to the sides of the bucket will change its weight.
c. Adjust the metering pump setting as necessary and take another weight sample
following the procedures outlined above to check for accuracy.
d. Continue this procedure until the output of the pump is equal to the required lbs per
rev for the mix.
NOTE: When the weight sample equals the required lbs per rev, make at
least one final weight sample to insure accuracy.
Step 11. Determine the Initial Cold Feed Settings.
(1) The percentage of each aggregate stockpile used in the aggregate blending operation
(Table 12) serves as a guide in determining the initial cold
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