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.

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.