TESTING FOR EXTERNAL GAS LEAKAGE WITH THE STANDARD PROBE

Testing For Internal Leaks with Contact Probe

TM-1-1500-335-23 Nondestructive Inspection Methods Manual
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T.O. 33B-1-1 5-86 5.6.3.1 TESTING FOR EXTERNAL GAS LEAKAGE WITH THE STANDARD PROBE. NOTE Use of the earphones is mandatory in areas where the background noise might interfere with hearing noise from the speaker. Use of the earphones is recommended for all tests. a. Connect the probe to the instrument. b. If in a noisy area, wear the earphones and attach the earphone connector to the instrument. c. Set the volume control to its minimum position. NOTE During this step, the probe should be pointed away from the assembly to be tested and away from any other possible leak sources. If no background noise is audible or the meter indicator does not move past zero, replace the batteries and repeat the check for background noise and meter indication movement. If noise and meter indication movement is still not noted, the instrument is not functional and must be repaired or replaced. Repair should be performed by the PMEL. d. Turn the instrument on and increase the volume control until the meter indication moves slightly ahead from zero and a slight background noise is heard from the speaker or the earphones. e. Use a 500-milliliter polyethylene bottle (NSN 6640-314-2097). Hold it about arm's length away from the probe with the bottle nozzle facing the probe opening. Rapidly squeeze the bottle and note the meter reading. The meter reading should be at least 70. If it does not, the instrument is not functioning properly and must be turned into the PMEL for repair and calibration. f. Search for leaks by pointing the probe at the test assembly and moving the probe around suspected leak areas. Note fluctuations in meter readings and volume from the speaker or earphones. When fluctuations are noted, maximize the meter reading by moving the probe and pointing it straight at the suspected leak area. The leak will generally be located in front of the probe when the meter reading and volume is at a maximum. g. To locate the leak, attach the rubber extension to the probe. This increases the directional response characteristics of the probe. Keep the probe pointed in the direction where the meter indication and noise is maximized and move the probe toward the test assembly. Where the extension tip meets the test assembly with maximum meter reading and noise is the leak location. It may be necessary to lower the volume control to keep the meter reading on scale as the probe is moved closer to the test assembly. NOTE Under certain conditions background noise detected by the instrument can prevent the detection of relevant leakage. This background noise can result from many types of air movement (wind, running of air motors or air cooled motors, running aircraft engines, operating pneumatic systems, etc.). h. The leakage rate may be estimated by moving the probe away from the leak to the maximum detection distance (leakage just indicated, slight increase in meter indication and noise level from normal

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