I .— KEEPING THEM RUNNING
Page 73
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with Ron Cater Locating an air leak in the pneumatic system of a large vehicle is a tedious process when using traditional methods. In general, vehicles have to be moved to a quiet spot where an operator with very keen hearing may possibly trace the leak. Failing this, painting the air lines with a soap solution until a telltale bubble reveals the fault, has often been the only method available. But now by using .a Dawe Type 1873 Ultrasonic Leak Detector, the job can be considerably simplified.
The detector is a simple handheld device, no bigger than a large torch, designed to provide on-site location of air or gas leaks in both pressure and vacuum pipe systems and vessels. Such leaks, I am told, generate a broad spectrum of ultrasonic
energy sound energy of a frequency too high to be heard by the human ear—in the 40 kHz region. This energy can be detected by a suitable microphone, amplifier and indicator, even in the presence of considerable audible noise from other sources.
In operation the detector is positioned to obtain a maximum meter reading or audible headphone signal. The leak is then in the direction indicated by the detector and may be accurately located by following through. No great experience or special operator training is required. •
The amount of ultrasonic energy generated by the leak depends on the velocity of the escape, which in turn depends on the pressure in the system and the dimensions of the orifice. Amplifier sensitivity is adjusted by means of a volume control knob to give a convenient output level, whatever the leak's energy level. The sensitivity range is sufficient to search comfortably in close proximity to a high-velocity leak or as much as 45 ft from an orifice of 0.01 in diameter at a pressure of less than 10Ib /in2 Where there is sufficient pressure, an orifice as small as 0.002in. diameter can be located.
The device is made and marketed by Dawe Instruments Ltd., Concorde Road, Western Avenue, London, W3.