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Ultrasound is a great technology for
trouble shooting internal hydraulic leaks, blockages, and bypasses.
Georgia Pacific in Brunswick, GA using their
Ultrawave SDT170 found an internal leak on a grappler hydraulic stop
valve. The grappler is used to transport tons of timber through the
mill and hydraulic leaks on these rams can interrupt timber loading,
stopping other parts of the plant.
Purpose of Ultrasonic test:
Determine location of fluid bypass
or internal leakage of hydraulic components. Reduce equipment downtime
by limiting disassembly and repair to only defective components.
Hypothesis:
Properly holding hydraulic cylinder
stop valves will produce no sound as heard by detection equipment.
Defective valves will produce a continual “hissing noise” as the fluid
leaks past the valve/valves.
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Overview of Grapple and Close up of four
cylinders (one was leaking) |
Test Procedure:
Position grapple bucket in working
platform so that all four stop valves can be reached with detection
equipment. With electric hydraulic pump pressurizing system, have
operator close grapple.
Ensure SDT Ultrasonic Detector is
set to the US sensor setting (internal leak setting). Position the SDT
contact probe on the stop valve body and then instruct operator to
pressurize system once again by continuously forcing the grapple into
the closed position. Observe the amplitude bar scale and value on the
SDT Detector. Note: An amplitude fluctuation
of approximately twenty decibels indicates a properly seating,
non-leaking stop valve.
With SDT headphones, listen for
either a continual or fluctuating hissing sound. A continual hissing
sound combined with a constant amplitude value means that the
stop valve is leaking pressure.
Test Results:
One of the four stop valves was
found to have no fluctuation in amplitude value or sound.
Test validation:
All four stop valves were manually
tested by removing the return oil lines and pressurizing the hydraulic
cylinder and stop valves. With the system operating at approximately
eighteen hundred PSI, a substantial amount of oil could be seen leaking
from the suspected valve. No leaks were observed from the other three
valves.
Inspection of the leaking valve
revealed broken (clipped) “O” rings around the valve body. The stop
valve was replaced with a newly rebuilt valve that when tested also
leaked. The valve was removed and found to have suffered from clipping
of the “O” ring seal. Inspection of the valve block revealed a sharp
entrance edge that may possibly clip the “O” ring during valve
installation.
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