Lesson 6/Learning Event 4
Due to the many variables encountered, such as weight per cubic foot, shape of particles, and
aggregate gradation, it would be extremely difficult to make charts that would give the flow for
all types of aggregate at a given gate opening. It is more satisfactory and accurate to calibrate
the feeder gates for the material used on each job. The steps taken in feeder gate calibration are:
(1) Fills the gradation unit bins with hot, dried aggregate. Insure that the level of aggregate
remains above the telltales while making the test.
(2) Weigh the test buckets and mark the height on each bucket. Number the buckets and
position them under the test chutes.
(3) Set all four apron feeder gates at the 8" opening and run the feeders for two or three
revolutions with the test gate levers in the "RUN" position.
(4) Stop the feeders and turn the test gate lever to the "TEST" position.
(5) Take the revolution counter reading and record it on the calibration work sheet (Table
(6) Run the apron feeders until the test buckets are filled to approximately 3" from the top.
Run continuously until the desired amount of material is in the test buckets.
CAUTION: Do not over-fill the test buckets or the material will have to be discarded and
the test run again.
(7) Stop the apron feeders and again record the revolution counter reading. The number of
revolutions run is determined by subtracting the first counter reading from the last counter
reading (Table 16).
(8) Weigh each test bucket carefully and subtract the weight of the bucket. The weight of
each size material is divided by the number of revolutions run, giving the lbs. per rev. flow for
an 8" gate opening for each size of aggregate (Table 9).
(9) Repeat and take the average of three tests at 3 different gate openings for accuracy. This
is time consuming but may facilitate adjustments during plant operations.
(10) Lift all spring clamps away from the indicator spring (Figure 24). Each coil of the
spring represents one pound per revolution. Stretch each spring from the 8" end until the gate
pointer is over the coil corresponding to the pounds per revolution obtained in the tests. Each
spring must be stretched uniformly over the entire 8" scale. Lock the springs by releasing the
spring clamps at the 8" mark.
(11) Check the setting by running one or two weight samples at other gate openings below
the 8" mark.
NOTE: If the actual feeder delivery does not quite match the reading on the indicator
spring, make the final adjustment of the spring at the nearest spring lock before moving