The method comprises the following steps - introducing a low amplitude air pressure transient into the drainage and vent
system of a building in order to propagate a
pressure wave from a fitting (6) into a stack (1) and the network of the drainage
system; - recording the passage of said transient by means of an air pressure
transducer (7) located near the fitting (6) or introduction area of the transient; - recording the successive pressure reflections of the transient from each drain
pipe (2) of the network of the drainage
system; - establishing a pressure versus
time signature recorded by the pressure
transducer (7) and sending those signals to a central
data acquisition system; - the pressure transient is propagated throughout the network at an acoustic velocity and is reflected by each and every
pipe termination of the network so as to establish a characteristic
reflection coefficient for each
pipe termination; - said characteristic
reflection coefficient is compared with testing results performed initially in a perfect network with no dry trap defects or leakage's and in case a different signature of the pressure trace is recorded, the point of diversion will be determined at the time at which the reflection from the altered pipe end termination arrives at the air pressure
transducer so that the comparison of this defect trace with the stored
defect free signature yields that time and, as the
wave speed is known, the determination of the distance from the pressure transducer to the defective trap or seal.