Consider the following real-world scenario
that occurred at a wood products plant:
A company had severe shock and
leakage problems on a piece of mobile
equipment. The pump was also being
changed at intervals of once per month.
There was an adjustment on the pump
(called a compensator), which limited the
maximum system pressure. A relief valve in
the system was used as an extreme safety
device and a shock absorber. The recom-
mended settings for the compensator and
relief valve were 1,500 and 1,750 pounds
per square inch (PSI), respectively. When
the stacker started and stopped, the pres-
sure gauge needle spiked to the maximum
of 3,000 PSI, vibrated and then settled in
at 1,800 PSI. This indicated that the
compensator and relief valve were both set
too high. After the compensator and relief
valve were reset to the recommended
settings, the pressure went up momen-
tarily to 1,750 PSI (relief setting) before
settling in at 1,500 PSI (compensator
setting). The difference in the force exerted
on the 10-inch boom cylinder (78.54
square inches of area) with the relief valve
at 3,000 PSI and at 1,750 PSI was 98,175
pounds. Once the pressures were properly
set, the shock was eliminated and the life
of the pump was increased. After the
clamps and O-rings were replaced, the
leakage stopped as well.
Mistake #2:
Lack of Accumulator and
Hydraulic Safety Procedures
When a machine is repaired, the pump's
electric drive motor is turned off and
lockout/tagout procedures are performed.
The pressure gauge is rarely checked
before work is begun on or around the
machine. Accumulators store hydraulic
energy in the form of pressurized fluid.
Most systems contain an automatic or
manual dump valve that will allow the
high-pressure fluid in the accumulator to
dump to the tank, permitting the pressure
to drop to zero. The automatic dump
By Al Smiley, GPM Hydraulic Consulting
ML
www.machinerylubrication.com
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July - August 2016
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