Sonic signalling transducer

A method and apparatus for detecting a leak in a pipeline and initiating, at the leak location, a sonic signal in the stream fluid, the signal being of a magnitude and character to be detected at remote upstream and downstream stations for location of the leak by known computations based on the time differential between the arrival times of the signals at the remotely spaced stations.

BACKGROUND OF THE INVENTION 
A primary object of the invention resides in the provision of a ferret-type 
leak detector including means for signaling the presence of a leak as the 
ferret passes thereover with improved means for the generations of sonic 
signals within the fluid stream for detection at stations both upstream 
and downstream of the leak aperture and comparison of the differential of 
signal arrival times for determining the leak location. 
Another object is to provide a ferret of the type which houses leak 
detection apparatus with means for generation of sonic signals in opposite 
directions through a fluid stream while utilizing major structure of the 
detection ferret as components of the sonic signal generator. 
A further object is to provide a fluid pipeline leak detector ferret with 
improved means operable in response to a leak detector signal to actuate a 
pressurized gas driven transducer for generation of sonic waves which 
travel in opposite directions within the fluid stream for detection at 
stations up and downstream of the leak. 
Other objects and advantages will become apparent to persons skilled in the 
art upon examination of the drawings and the following description.

DETAILED DESCRIPTION 
As shown in the drawings, leak detection ferret 10, disposed within a 
pipeline 12, comprises an elongate body portion which includes a cylinder 
defining element 14 and a piston forming element 16. The downstream (arrow 
direction) end portion of element 14 is externally provided with a 
plurality of radially extending axially spaced baffles 18 of lessor 
diameter than pipeline 12. Adjacent the outermost baffle 18 is packing 
element 22 having circumferential portions in light fluid sealing contact 
with the pipeline inner wall surface. A bore 24 extends axially through 
element 22 and the head of cylinder 14 and check valve 26, normally biased 
open by a helical spring 28, extends into a compression chamber 30 formed 
between the valved end of cylinder 14 and the downstream end of piston 
forming member 16. 
The upstream end of piston forming member 16 is provided with a plurality 
of radial baffles 32 similar to baffles 18, above described, and with a 
trailing packing element 34. An axially extending passageway 36 exposes 
one side of differential sensor 38 to upstream fluid pressures while 
passageway 40 exposes the opposite side of sensor 38 to fluid pressures 
within a bounded area between the packing elements 22 and 34. Electronics 
associated with sensor 38, all enclosed within piston forming element 16, 
includes an amplifier 42, a solenoid actuating circuit 44, a recorder 46 
and battery supplies 47 and 48. 
The opposite end of element 16 has concentrically disposed therein a 
pressurized gas cartridge 50, a gas release valve 52 and a solenoid 54, 
connected by conduit 56 to circuit 44 for actuation by an amplified signal 
from sensor 38 to effect substantially instantaneous release from 
cartridge 50 of the pressurized gas, such as Co.sub.2. A bore 58 conducts 
the released gas into chamber 30. The piston end of element 16 and the 
open end of cylinder 14 are provided with spaced circumferential channels 
in which are disposed sealing rings, such as rings 51 and 59, which may be 
O-rings. The piston head radially projects outwardly in the area of ring 
59 for contacting engagement at the end of the piston stroke with and 
inwardly projecting radial portion of cylinder 14 in the area of ring 51. 
In operation, as ferret 10 passes over a leak such as shown at 62, the 
differential between the upstream fluid pressure applied through 
passageway 36 to one side of sensor 38 and the reduced pressure due to the 
leak in the bounded fluid between packing elements 22 and 34 as applied to 
the opposite side of sensor 38 initiates a signal indicative of the leak. 
That signal, fed through amplifer 42 to circuit 44, energizes solenoid 54 
to trigger valve 52 open with resultant rapid release of the compressed 
gas through bore 58 into chamber 30, closing valve 26 and driving the 
piston head of element 16 and the closed end of cylindrical element 14 
apart. Packing elements 22 and 34 are thus rapidly driven in down and 
upstream directions to generate oppositely directed sonic waves in the 
stream fluid. The initial gas pressure in cartridge 50 may be selected to 
result in blocking elements 22 and 34 driven apart at a rate to insure 
generation of sonic waves of relatively long wavelength. Low frequency 
sonic waves travel appreciably farther through liquid than do those of 
higher frequencies. 
Chamber 30 is preferably of small volume for maximum pressure application 
to the head of piston 16 and to the end wall cylinder 14 following release 
of the pressurized gas from cartridge 50. 
As ferret 10 moves downstream with the pressurized fluid in pipeline 12 the 
upstream pressure urges packing element 34, hence piston 16 to the right 
as viewed in FIG. 1. Since the fluid stream is blocked from flowing around 
element 34, and element 22 is subjected to some degree of back pressure 
from the stream, even with valve 26 open, the stream exerts oppositely 
directed forces on the piston and cylinder assembly to urge the piston 
into the cylinder sufficiently to maintain chamber 30 at a small size 
required to insure that upon release of the pressurized gas elements 22 
and 34 will be driven apart by very high applied forces. 
The gas is released into chamber 30 as a step function with a fourier 
integral spectrum ranging from maximum at d.c. to .omicron. at .omega. = 
.omicron..omicron.. The step must be maintained long enough that the loss 
of high frequencies at the receiving end does not prevent the step from 
reaching approximately full value, as shown in FIG. 2. 
Thus, the driving force of released gas, after instantly closing valve 26, 
continues the step function shown in FIG. 2 to cause cylinder 14 and 
piston 16, hence blocking members 22 and 34 to be propelled apart by a 
pulsed surge sufficient to establish sonic signals which are clearly 
distinguishable from normal pipe noises, when received at spaced stations 
after a time delay as in FIG. 2.