Wood’s Powr-Grip MRTARC811LDC - Manual (Page 33)

Rev 2.0/7-12 31 MRTA8-DC: #35076RC
V
ACUUM
S
WITCH
A
DJUSTMENT
Vacuum Switch Function 25
A vacuum switch controls the vacuum pump and the vacuum lift light (see OPERATING
FEATURES for location of vacuum switch). When the power switch located on the lifter is in the
ON position ( ), activating the apply function engages the vacuum pump, which evacuates the
vacuum pads. After the lifter attains a vacuum level sufficient for lifting the maximum load
weight (hereafter, “minimum lifting level”), the vacuum switch automatically turns off the pump
and turns on the lift light.
26 In order to maintain sufficient vacuum, the vacuum switch
automatically turns on the pump and turns off the lift light again before vacuum decreases to a
level that is lower than the minimum lifting level.
Conditions Requiring Readjustment
At the factory, the vacuum switch is set to maintain the minimum vacuum level specified for Load
Capacity (see SPECIFICATIONS). However, shipping vibrations or shocks, normal wear, or other
conditions may adversely affect this adjustment. Periodically verify the switch adjustment by
comparing how the vacuum pump and the vacuum lift light function in relation to the vacuum
level registered on the vacuum gauge, as follows:
• If the pump
turns off and the lift light turns on before vacuum attains the minimum lifting level,
it is likely that the air filter’s element is dirty. Any filter element that obstructs airflow
must be replaced (refer to A
IR
F
ILTER
M
AINTENANCE
preceding). Otherwise, the pump would
turn off at vacuum levels that are not sufficient to lift the maximum load weight.
• If the pump turns off but the lift light does not turn on after vacuum attains the minimum lifting
level, the light bulb may be burned out. The bulb should be replaced when necessary.
Otherwise, the operator might wait unnecessarily for the lift light to turn on, after the lifter
has already attained sufficient vacuum to lift the maximum load weight.
• If the pump does not turn off and the lift light does not turn on after vacuum increases to a
level much higher than the minimum lifting level, the vacuum switch may be adjusted to
maintain a lower vacuum level. Otherwise, the pump would continue to run unnecessarily
after the lifter has attained sufficient vacuum to lift the maximum load weight.
• If the pump does not turn on and the lift light does not turn off before vacuum decreases to a
level lower than the minimum lifting level, the vacuum switch must be adjusted to
25
Lifters equipped with a Dual Vacuum System have 2 vacuum switches. Directions are the same for these lifters except that
each vacuum switch must be tested and adjusted individually. When you are evaluating vacuum system functions under
Conditions Requiring Readjustment, remember that each vacuum switch corresponds with one vacuum gauge and one vacuum
circuit. After you have removed the cover from the control enclosure, you can trace the vacuum lines to determine which
components are connected to one another.
26
When using the lifter at high elevations, reduced atmospheric pressure may prevent the vacuum generating system from
attaining the vacuum level set at the factory. This causes the pump to run continuously. If the ability to lift the maximum load
weight is not required, the operator can adjust the vacuum switch to maintain a lower vacuum level, allowing the pump to cycle
normally. However, be advised that lifting capacity decreases proportionally with decreasing vacuum, based on the
vacuum level specified for the Load Capacity (see SPECIFICATIONS). For example, if a lifter's Load Capacity is rated at 16" Hg
[-54 kPa], lifting capacity decreases by 6.25% for each inch of Hg subtracted from (or for each 3.4 kPa added to) the vacuum
level.
Always maintain a minimum vacuum level of 10" Hg [-34 kPa], regardless of the vacuum level specified for the
original Load Capacity. In addition, lifter markings should be adjusted to reflect the revised Load Capacity and the vacuum gauge
should be marked to indicate the revised minimum lifting level.