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Leak Detection for Hydraulic Systems

Current Procedures

Two different procedures to verify hydraulic system integrity include visual inspection and pressure decay testing. A visual inspection is sometimes used after the system has been pressurized with hydraulic fluid. A technician walks around operating equipment looking for leaking hydraulic fluid. Using air for over pressure decay leak testing is another way to confirm the integrity of the hydraulic system. If the test fails, finding the leak may involve using a water dunk tank or a spray solution looking for bubbles around valves, fittings, hoses, lines, etc.

UL101 Test Procedures

  1. Select UL101 Receiver, Headset, Mini Concentrator, and 1-Inch Acoustic Tip from case.

  2. Attach Mini-Concentrator and plug in headset to UL101 Receiver.

  3. Test battery by moving output switch to headset only position. If meter needle is below the 5-10 (½ scale) of the meter, replace the battery. Return output switch to headset/meter position.

  4. Turn gain switch to ½ gain (half moon); adjust potentiometer knob between 1 and 2.

  5. Begin at one end of the HVAC system. Point the UL101 receiver in the direction of the refrigerant lines and fittings and walk along while scanning with the receiver.

  6. A leak is indicated by a jump in the meter and a loud rushing sound through the headset.

  7. Once a leak is detected, pinpoint by switching the Mini-Concentrator attachment with the 1-Inch Acoustic Tip. Adjust the potentiometer down to locate the exact source of the leak.

  8. Indicate the location by marking the leak, and repair. Verify repairs with UL101.


The UL101 is much faster and more effective at locating hydraulic fluid system leaks, even during peak operation. Technicians do not have to feel around operating machinery or failed parts with their hands to find leaks or spray down components with soap and water solution looking for bubbles to find leaks. Ultrasound Leak Detection is not hindered by facility operation noise and, therefore, less guess work is involved in leak isolation. This allows the company to focus more on production and less time on quality control inspections, warranty rework and infield repairs. Additional uses of the UL101 include using the provided solid probe attachment to listen for ultrasound. Pressing the tip of the solid probe (attached to the UL101 receiver) against a valve, the user can easily hear the valve functioning and determine its operating condition, such as leak by.

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