5. Operation
38
PNEG-2116
Bucket Elevator
In-Service Belt Tension
If the belt tracks properly and does not slip when the elevator is operating at maximum capacity, then the
belt is sufficiently tensioned. Tension adjustment, however, must wait until the entire installation is
complete and material (the product; grain, etc.) can be conveyed to and from the elevator.
1. While observing all prudent safety precautions, posted or otherwise, examine the belt as it passes
over the head pulley
WHILE
the elevator is under load. The pulley should track properly. Belt slip is
most often detected by observing the bearing setscrews on the head and tail shafts while counting
the number of revolutions of pulley in the same period of time, typically 30 or 60 seconds.
IMPORTANT:
Since the head pulley is lagged and its effective diameter is larger compared to the boot
pulley, head pulley rotation speed will be slightly slower than the boot pulley even if there
is no belt slip.
If the belt is slipping and all other conditions appear to be normal, adjust the take-up.
a. If the elevator has a screw take-up, adjust the acme screws evenly to force the pulley downward
and increase belt tension.
(OR)
b. If the elevator has a posi-guide gravity take-up, adding ballast to the weight box will increase belt
tension. The ballast should be spread evenly throughout the box for best results. Be sure to
reinstall the weight box cover to prevent rainwater from accumulating in the weight box. See
.
2. Verify that belt speed closely approximates that specified on the drawings. If it does not, check the
drive system, especially if all drive components were not furnished by InterSystems. Among the
points to consider are:
a. If the elevator includes a chain drive, compare the number of teeth of the drive and driven
sprocket. Verify that the resultant ratio, taken together with the reducer’s output speed, will
produce the specified final pulley RPM.
If the elevator includes a V-belt drive, compare the pitch diameters of the drive and driven
sheaves. Verify that the resultant ratio taken together with the reducer’s output speed will
produce the specified final pulley RPM.
b. Whether the elevator employs direct coupled, chain, or belt drive, you must verify that the motor's
speed and the reducer’s reduction ratio will produce the required output speed to produce the
specified final pulley RPM.
c. If no other problem is uncovered, check to see that the drive components are not slipping on the
shafts. Sometimes during field assembly, the keys are inadvertently left out.
3. If the belt speed matches the specified value and the elevator does not seem to be handling the
specified capacity, review the factors set forth in elevator intake
. The elevator will not operate at maximum capacity if material does not flow freely into
and out of the elevator.
4. Verify that the belt continues to track the center of the head and boot take-up pulleys. If it does not,
check to see if the material being fed into the elevator is entering at an angle from one side or the
other and forcing the belt to one side of the pulley. This condition, if it occurs, must be corrected.
Continual lateral pressure on the belt can cause the belt edge to rub against the elevator structure.
At the very least, the belt will wear rapidly. More serious than wear, a fire and/or explosion can occur
if belt friction generates sufficient heat.
5. After the elevator has operated for a period of time, the take-up may require readjustment to
compensate for mechanical belt stretch. Depending upon the amount of mechanical stretch, the belt
may even have to be shortened and respliced.
