Xmic
24/01/05
MAN-095-0001 Revision B
© Palmer Environmental Ltd 2005
Page 18
noise can be heard further away on metal than on plastic. Also bear in mind that the
further you go from a leak noise source the more difficult it is to pinpoint that leak
noise accurately.
Background noise can interfere with leak detection. Traffic and machinery noises can
travel for considerable distances through both air and ground material and often
occur in the same frequency bands as leak noise. Sometimes it is necessary to use
leak detection techniques at night when interfering noises are less.
It is very important to adopt a methodical approach when using any instrument for
acoustic leak detection. It is necessary to practice the technique in order to
distinguish between different sounds, recognising background or interfering noises,
so that they can be eliminated. It is also essential that other (non-leakage) system
noise sources such as consumer draw-off or partially closed valves be eliminated by
logical site inspection practices prior to any excavation taking place.
Hand probe
For normal soft ground surfaces the single pointed extension rod should be
connected - do not over-tighten the screw thread. For direct contact with
underground fittings via access covers it may be necessary to use the second
extension rod. To do this, remove the single rod and connect the extension rod -
replacing the pointed rod again. If the rods have been over-tightened, spanner slots
allow easy removal.
Surveying
The leak location can be narrowed down by listening at accessible contact points
such as meters, hydrants, valves and stop-taps. These provide good points of sound
pick-up, particularly if the pipe is metallic. Use the hand-probe/extension rod to
listen at these points.
If there are no accessible contact points or if the pipe is of non-metallic material, use
the microphone foot for listening, placing the foot over the pipe route in the area of
the suspected leak. Move along the pipe route listening at each accessible pipefitting