Patent Description:
Fire hydrants are commonly connected to fluid systems, such as municipal water infrastructure systems and water mains, through stand pipes. Because these fluid systems are typically partially or entirely located underground, it can be difficult to detect leaks within the fluid systems. Additionally, it can be difficult to access these fluid systems for monitoring. Fire hydrants can provide convenient above-ground access to the fluid systems. Leaks within the fluid systems can send vibrations through the fluid system and up stand pipes to the fire hydrants. These vibrations propagating through the stand pipes and fire hydrants can be monitored to detect leaks within the connected fluid system. However, fire hydrants can be subjected to other sources of vibration such as wind, rain, ambient noise from loud passing vehicles, or direct contact such as pedestrians bumping into fire hydrants or bicyclists leaning their bicycles against fire hydrants. These sources of background noise can trigger false alarms or make it more difficult for a potential leak to be detected.

<CIT> discloses an oil filler cap that can determine engine speeds from sensed vibrations. It discloses the use of a data logger and associated vibration sensor, and an oil filler cap which can include a vibration sensor and can also include a mounting point for a data logger. The vibration senso is coupled to an engine speed determination module determining engine speed from a value of the sensed vibration.

<CIT> discloses a leak detection sensor that includes a transducer, the transducer including a base, a piezoelectric layer, and a conductive layer and at least two leads connected to the transducer. A method of making a leak detection sensor includes obtaining a transducer, the transducer including a base, a piezoelectric layer, and a conductive layer; and effecting a mounting hole such that the mounting hole is defined in the transducer.

<CIT> discloses a transmitter and a water system or distribution protection device, such as a fire hydrant protection device. The water system protection device inhibits an unauthorized individual from accessing water from a water system device, such as a fire hydrant. The transmitter transmits a first signal when the water system protection device is tampered with. One or more sensing devices are provided that sense when the water system protection device has been tampered with, and cause the transmitter to transmit the first signal.

<CIT> discloses an outdoor fire hydrant which may be used to extinguish a fire. It discloses an outdoor fire hydrant receiving a firefighting device to extinguish fire, including an enclosure wherein a supply pipe to supply fire water is installed. The fire hydrant comprises an earthquake sensor for detecting an earthquake, to control the cylinder selection valve to allow the cylinder selection valve to supply the fire water to the cylinder supply line when the earthquake occurs.

The features and components of the following figures are illustrated to emphasize the general principles of the present disclosure. The drawings are not necessarily drawn to scale. Corresponding features and components throughout the figures may be designated by matching reference characters for the sake of consistency and clarity.

The present disclosure can be understood more readily by reference to the following detailed description, examples, drawings, and claims, and the previous and following description. However, before the present devices, systems, and/or methods are disclosed and described, it is to be understood that this disclosure is not limited to the specific devices, systems, and/or methods disclosed unless otherwise specified, and, as such, can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

The following description is provided as an enabling teaching of the present devices, systems, and/or methods in its best, currently known aspect. It will also be apparent that some of the desired benefits of the present disclosure can be obtained by selecting some of the features of the present disclosure without utilizing other features.

As used throughout, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "an element" can include two or more such elements unless the context indicates otherwise.

As used herein, the terms "optional" or "optionally" mean that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

The word "or" as used herein means any one member of a particular list and also includes any combination of members of that list. Further, one should note that conditional language, such as, among others, "can," "could," "might," or "may," unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain aspects include, while other aspects do not include, certain features, elements and/or steps.

Disclosed is a hydrant assembly and associated methods, systems, devices, and various apparatus. The hydrant assembly can comprise a fire hydrant and a vibration sensor. It would be understood by one of skill in the art that the disclosed hydrant assembly is described in but a few exemplary aspects among many. No particular terminology or description should be considered limiting on the disclosure or the scope of any claims issuing therefrom.

<FIG> is a perspective view of a hydrant assembly <NUM> comprising a fire hydrant <NUM> and a vibration sensor <NUM> (shown in <FIG>) in accordance with one aspect of the present disclosure. The fire hydrant <NUM> can comprise a barrel <NUM>, a nozzle cap <NUM>, and a bonnet <NUM>. The barrel <NUM> can define a top barrel end <NUM> and a bottom barrel end <NUM> disposed opposite from the top barrel end <NUM>. The barrel <NUM> can be substantially tubular, and the barrel <NUM> can define a barrel axis <NUM> extending from the top barrel end <NUM> to the bottom barrel end <NUM>. In the present aspect, the barrel axis <NUM> can be substantially vertically aligned wherein the barrel axis <NUM> is aligned with the force of gravity.

The barrel <NUM> can comprise a top flange <NUM> disposed at the top barrel end <NUM> and a base flange <NUM> disposed at the bottom barrel end <NUM>. The base flange <NUM> can be fastened to a stand pipe flange <NUM> of a stand pipe <NUM> of a fluid system (not shown), such as a water main for example and without limitation. The base flange <NUM> can be fastened to the stand pipe flange <NUM> by a plurality of fasteners <NUM>. A bonnet flange <NUM> of the bonnet <NUM> can be attached to the top flange <NUM> of the barrel <NUM>, such as with a plurality of fasteners (not shown) similar to the fasteners <NUM>. The bonnet <NUM> can comprise an operation nut <NUM>, or "op nut", which can be rotated to open and close a main valve (not shown) positioned at the bottom barrel end <NUM> or below in the stand pipe <NUM> in order to respectively supply or cut off pressurized water flow to the fire hydrant <NUM>.

The barrel <NUM> can define one or more nozzles 140a,b. The nozzle cap <NUM> can be screwed onto the nozzle 140a to seal the nozzle 140a. With the nozzle cap <NUM> sealing the nozzle 140a, pressurized water cannot escape through the nozzle 140a when the main valve (not shown) is in an open position. The nozzle cap <NUM> can define a cap nut <NUM> which can be turned, such as with a wrench, to tighten or loosen the nozzle cap <NUM> on the nozzle 140a.

<FIG> is a perspective rear view of the nozzle cap <NUM> of the fire hydrant <NUM> of <FIG>. The nozzle cap <NUM> comprises a cap body <NUM> and a cap cover <NUM>. The cap body <NUM> defines a first body end <NUM> and a second body end <NUM> disposed opposite from the first body end <NUM>. The cap cover <NUM> is attached to the first body end <NUM> of the cap body <NUM>. The cap body <NUM> defines a threaded bore <NUM> extending into the cap body <NUM> from the second body end <NUM> to an inner wall <NUM> of the cap body <NUM>. The threaded bore <NUM> defines a cap axis <NUM> of the cap body <NUM>, and the cap axis <NUM> extends from the first body end <NUM> to the second body end <NUM>.

The threaded bore <NUM> defines internal threading <NUM>, and the threaded bore <NUM> can be screwed onto the nozzle 140a (shown in <FIG>) to mount the nozzle cap <NUM> on the nozzle 140a by rotating the nozzle cap <NUM> about the cap axis <NUM>. In the present aspect, the internal threading <NUM> can be straight threading that does not taper from the second body end <NUM> towards the inner wall <NUM>. In other aspects, the internal threading <NUM> can be tapered threading that tapers from the second body end <NUM> towards the inner wall <NUM>. A gasket <NUM> can be positioned adjacent to the inner wall <NUM>, and the gasket <NUM> can be configured to form a seal with the nozzle 140a (shown in <FIG>) when the nozzle cap <NUM> is screwed onto the nozzle 140a in a sealed position. As described below with respect to <FIG> and <FIG>, the gasket <NUM> can be selected based on its thickness, measured axially along the cap axis <NUM>, to alter a rotational indexing of the nozzle cap <NUM> relative to the nozzle 140a.

<FIG> is a front view of the nozzle cap <NUM> of <FIG> with the cap cover <NUM> (shown in <FIG>) removed from the cap body <NUM>. The cap body <NUM> can define a cavity <NUM> extending inwards into the cap body <NUM> from the first body end <NUM> to the inner wall <NUM>. In the present aspect, the cavity <NUM> can extend axially inward relative to the cap axis <NUM>, shown extending out of the page. The inner wall <NUM> can separate the cavity <NUM> from the threaded bore <NUM> (shown in <FIG>). The cap body <NUM> can define a circumferential wall <NUM> which partially encloses the cavity <NUM> and extends circumferentially around the cavity <NUM> relative to the cap axis <NUM>. A cavity opening <NUM> to the cavity <NUM> can be defined at the first body end <NUM>, and a cavity gasket <NUM> can extend around the cavity opening <NUM>. The cavity gasket <NUM> can be configured to seal with the cap cover <NUM> to enclose and seal the cavity <NUM>.

The circumferential wall <NUM> can define external scallops 316a,b. The external scallops 316a,b can extend radially inward into the circumferential wall <NUM> relative to the cap axis <NUM>. Each of the external scallops 316a,b can respectively be enclosed by an antenna cover 318a,b, and an antenna strip 320a,b can be enclosed within each of the external scallops 316a,b between the respective antenna cover 318a,b and the circumferential wall <NUM>.

The nozzle cap <NUM> can comprise a battery pack <NUM> and a printed circuit board ("PCB") <NUM>, each disposed within the cavity <NUM>. The PCB <NUM> can be attached to a mounting bracket <NUM> which can be secured within the cavity <NUM> by a pair of fasteners <NUM>.

As shown, the nozzle cap <NUM> of the fire hydrant <NUM> also comprises the vibration sensor <NUM> of the hydrant assembly <NUM>, and the vibration sensor <NUM> can be disposed within the cavity <NUM>. The vibration sensor <NUM> can define a sensor axis <NUM> which can be perpendicular to the cap axis <NUM>. The vibration sensor <NUM> can be attached to the circumferential wall <NUM>, and the vibration sensor <NUM> can extend radially inward from the circumferential wall <NUM> and into the cavity <NUM> with respect to the cap axis <NUM>.

The battery pack <NUM>, the PCB <NUM>, the vibration sensor <NUM>, and the antenna strips 320a,b can be connected together in electrical communication. The vibration sensor <NUM> can be configured to detect leaks within the fluid system (not shown) by monitoring vibrations travelling up the stand pipe <NUM> (shown in <FIG>) and through the fire hydrant <NUM> (shown in <FIG>) when the nozzle cap <NUM> is mounted on the nozzle 140a (shown in <FIG>). Vibration patterns within the fluid system can indicate the presence of leaks within the fluid system. The vibration sensor <NUM> can produce voltage readings when the vibration sensor <NUM> experiences vibrations. These voltage readings can be processed by the PCB <NUM> to determine whether leaks are present, and a signal can be transmitted outwards from the nozzle cap <NUM> by the antenna strips 320a,b to convey whether leaks have been identified within the fluid system.

<FIG> is a perspective view of one example aspect of the vibration sensor <NUM> of <FIG> wherein the vibration sensor <NUM> is a piezoelectric vibration sensor. Piezoelectric vibration sensors are described in greater detail in <CIT>, which is hereby incorporated by reference in its entirety.

The vibration sensor <NUM> can comprise a base <NUM>, at least one piezoelectric crystal <NUM>, and a plurality of calibration masses <NUM>. The calibration masses <NUM> can be distributed circumferentially around the base <NUM>. In the present aspect, the calibration masses <NUM> can be integrally formed with the base <NUM>; however in other aspects, the calibration masses <NUM> can be separate components which can be attached to the base <NUM>, such as with a glue, adhesive, mastic, epoxy, or another method such as welding, brazing, soldering, or any other attachment method for example and without limitation. In the present aspect, the calibration masses <NUM> can extend axially outward from each side of the base <NUM> with respect to the sensor axis <NUM>. A notch <NUM> can be defined between each pair of adjacent calibration masses <NUM>, and the calibration masses <NUM> can vibrate independently from one another.

The piezoelectric crystal <NUM> can be attached to the base <NUM>, and the piezoelectric crystal <NUM> can be disposed radially inward from the calibration masses <NUM> with respect to the sensor axis <NUM>. In some aspects, an additional piezoelectric crystal (not shown) can be attached to the opposite side of the base <NUM>. In the present aspect, the piezoelectric crystals <NUM> can be bonded to the base <NUM> with a conductive adhesive. In other aspects, the piezoelectric crystals <NUM> can be attached to the base <NUM> through other suitable means such as double-sided tape, various glues, various coatings including elastomeric and silicon coatings among others, pure adhesives, or by a fastener.

In the present aspect, a fastener <NUM> can extend through the base <NUM> and piezoelectric crystals <NUM>. The fastener <NUM> defines a threaded end <NUM>, and a spacer <NUM> can be fit over the fastener <NUM> between the base <NUM> and the threaded end <NUM>. According to the invention, the threaded end <NUM> defines a first sensor end <NUM> of the vibration sensor <NUM>, and a second sensor end <NUM> is defined by the calibration masses <NUM>, opposite from the first sensor end <NUM>. The sensor axis <NUM> extends through the fastener <NUM> and the vibration sensor <NUM> as a whole from the first sensor end <NUM> to the second sensor end <NUM>.

The threaded end <NUM> threadedly engages a threaded hole <NUM> (shown in <FIG>) defined by the circumferential wall <NUM> (shown in <FIG>) to attached the vibration sensor <NUM> to the cap body <NUM> (shown in <FIG>). With the vibration sensor <NUM> attached to the cap body <NUM>, and the nozzle cap <NUM> (shown in <FIG>) attached to the nozzle 140a (shown in <FIG>), the vibration sensor <NUM> can detect vibrations from the fluid system (not shown) and convert the vibrations to a voltage signal. When the vibration sensor <NUM> is exposed to vibrations, the calibration masses <NUM> can oscillate axially relative to the base <NUM> which can produce internal stresses within the piezoelectric crystal <NUM>. Stresses within the piezoelectric crystal <NUM> can produce a voltage signal which can then be interpreted by the PCB <NUM> (shown in <FIG>) to determine if leaks are present within the fluid system.

<FIG> is a front detail view of the hydrant assembly <NUM> focusing on the nozzle 140a and the nozzle cap <NUM> with the cap cover <NUM> of the nozzle cap <NUM> shown in transparency with the underlying components shown in dashed lines. Experimentation has revealed that the signal-to-noise ratio detected by the vibration sensor <NUM> is generally optimized when the sensor axis <NUM> is aligned with the barrel axis <NUM> of the barrel <NUM> of the fire hydrant <NUM>, such as when vertically aligned relative to the direction of gravity as shown in the present aspect.

The cap cover <NUM> can define indicia <NUM>, which can align with the circumferential placement of the vibration sensor around the circumferential wall <NUM>. For example, in the present aspect, the vibration sensor <NUM> can be positioned in a six-o-clock position wherein the sensor axis <NUM> is vertically aligned, and the vibration sensor <NUM> is positioned at the bottom of the nozzle cap <NUM>. The indicia <NUM> can also be positioned in the six-o-clock position so that the indicia <NUM> is approximately centered over the vibration sensor <NUM>. In the present aspect, the indicia <NUM> can be the ECHOLOGICS logo which can be approximately centered over the vibration sensor <NUM>; however, in other aspects, the indicia <NUM> can define any combination of words, numbers, and/or symbols to indicate the circumferential position of the vibration sensor <NUM> along the circumferential wall <NUM>. For example, in some aspects, the indicia could be a line extending across the cap cover <NUM> which can be positioned parallel to the sensor axis <NUM> or an arrow indicating the preferred vertical alignment. Because a user cannot see into the cavity <NUM> in the present aspect, the indicia <NUM> can be configured to notify a user of the placement of the vibration sensor <NUM> along the circumferential wall so that the nozzle cap <NUM> can be optimally oriented when attaching the nozzle cap <NUM> to the nozzle 140a. In other aspects, some or all of the cap cover <NUM> can comprise a transparent material configured to provide a view of the orientation of the vibration sensor <NUM> within the cavity <NUM>.

<FIG> is a front detail view of the hydrant assembly <NUM> focusing on the nozzle 140a and the nozzle cap <NUM> which demonstrates various potential positions 600a-h for the vibration sensor <NUM> (shown in <FIG>) and the sensor axis <NUM>, as shown by the dashed lines in the shape of the vibration sensor <NUM>. The cap cover <NUM> is shown without the indicia <NUM> (shown in <FIG>) for clarity. The exemplary potential orientations for the sensor axis <NUM> are shown as 301a-d.

Sensor axis 301a can correspond to the vertical orientations of the twelve-o-clock position 600a and the six-o-clock position 600e. In these positions, the sensor axis 301a is vertically aligned in parallel to the barrel axis <NUM> of the fire hydrant <NUM>. These positions generally provide an optimal signal-to-noise ratio, as described above. In these positions, an angle defined between the sensor axis 301a and the barrel axis <NUM> can equal zero degrees, and therefore, this angle is not shown or labelled.

Sensor axis 301c corresponds to the horizontal orientations of the three-o-clock position 600c and the nine-o-clock position <NUM>. In these positions, the sensor axis 301c is horizontally aligned, and the sensor axis 301c can be perpendicular to the barrel axis <NUM>. An angle Ac defined between the sensor axis 301c and the barrel axis 101can equal ninety degrees. Experimentation generally shows that the signal-to-noise ratio is least desirable when the vibration sensor <NUM> (shown in <FIG>) is in a horizontal orientation with the sensor axis 301c perpendicular to the barrel axis <NUM>, which is vertical.

The sensor axis 301b corresponds to the positions 600b,f, and the sensor axis 301d corresponds to the positions 600d,h. The sensor axes 301b,d can be oblique to the barrel axis <NUM>. The sensor axis 301b can define an angle Ab with the barrel axis <NUM>, and the sensor axis 301d can define an angle Ad. In these positions, the angles Ab,Ad can be acute angles measuring less than ninety degrees. In these aspects, the signal-to-noise ratio is generally superior to that of the horizontal orientations of positions 600c,g but generally inferior to the signal-to-noise ratio of the vertical orientations of positions 600a,e. The signal-to-noise ratio improves as the angles Ab,Ad decrease to zero degrees, wherein the sensor axes 301b,d align with the barrel axis <NUM>.

The demonstrated positions 600a-h are merely exemplary and should not be viewed as limiting. The vibration sensor <NUM> (shown in <FIG>) can be oriented at any angle around the cap axis <NUM>, shown extending out of the page. The sensor axis <NUM> can be perpendicular to the cap axis <NUM> regardless of potential orientation or rotational indexing of the nozzle cap <NUM>.

Rotational indexing of the nozzle cap <NUM> relative to the nozzle 140a can be primarily dictated by the torque required to form a seal between the nozzle cap <NUM> and the nozzle 140a via the gasket <NUM> (shown in <FIG>). For example, in an aspect wherein the internal threading <NUM> (shown in <FIG>) of the threaded bore <NUM> (shown in <FIG>) is right-handed threading, the nozzle cap <NUM> can be tightened onto the nozzle 140a by rotating the nozzle cap <NUM> in a clockwise direction about the cap axis <NUM> relative to the viewing angle shown. For example, in some aspects, the torque required to form a seal may naturally place the vibration sensor <NUM> (shown in <FIG>) in one of the less desirable positions, such as position 600c. In such a case, if the nozzle cap <NUM> is backed off to place the vibration sensor <NUM> in the desirable twelve-o-clock position 600a, the seal between the nozzle cap <NUM> and the nozzle 140a may be compromised, and the nozzle cap <NUM> can leak. Conversely, a user can attempt to overtighten the nozzle cap <NUM> towards the desirable six-o-clock position 600e; however, the user may not be able to fully rotate the nozzle cap <NUM> to vertically align the vibration sensor <NUM> and achieve optimal signal-to-noise ratio. Additionally, overtightening the nozzle cap <NUM> can make the nozzle cap <NUM> difficult to remove, such as in the case of an emergency where firemen may need to open the nozzle 140a.

One solution is to alter a gasket thickness T (shown in <FIG>) of the gasket <NUM> (shown in <FIG>) to adjust the rotational indexing of the nozzle cap <NUM> relative to the nozzle 140a. By increasing the gasket thickness T of the gasket <NUM>, the rotational indexing of the nozzle cap <NUM> can be rotated counter-clockwise about the cap axis <NUM> with respect to the viewing angle shown in aspects wherein the internal threading <NUM> (shown in <FIG>) is right-handed threading. For example, if the vibration sensor <NUM> (shown in <FIG>) is in position 600b when the nozzle cap <NUM> is torqued to the required specification to seal the nozzle 140a, the nozzle cap <NUM> can be removed, and the gasket <NUM> can be replaced with another gasket <NUM> having a larger gasket thickness T so that the vibration sensor <NUM> can be placed in the twelve-o-clock position 600a when the nozzle cap <NUM> is torqued to the required specification.

Conversely, a thinner gasket <NUM> can be used to rotate the rotational indexing of the nozzle cap <NUM> in the clockwise direction about the cap axis <NUM> with respect to the viewing angle shown. For example, if the vibration sensor <NUM> is in position 600d when the nozzle cap <NUM> is torqued to the required specification to seal the nozzle 140a, the nozzle cap <NUM> can be removed, and the gasket <NUM> can be replaced with another gasket <NUM> having a smaller gasket thickness T so that the vibration sensor <NUM> can be placed in the six-o-clock position 600e when the nozzle cap <NUM> is torqued to the required specification.

Rather than changing the gasket thickness T of the gasket <NUM>, similar results can be achieved by positioning shims between the gasket <NUM> and the inner wall <NUM> (shown in <FIG>), and a pack of shims of varying thicknesses can be included with an installation kit for the nozzle cap <NUM>. In some aspects, the shim could be attached to the inner wall <NUM> with an adhesive sealant to prevent leaks between the shim and the inner wall <NUM>. In other aspects, two gaskets <NUM> can be utilized, and the shim can be positioned between the two gaskets <NUM> to prevent leaks between the shim and the inner wall <NUM>. The necessary thickness of the shims can be calculated based on the thread pitch of the internal threading <NUM> (shown in <FIG>) using the following formula: <MAT> wherein θ equals the desired angle of rotational correction in degrees, TPI is the threads-per-inch pitch of the internal threading <NUM>, and shim thickness is measured in inches. For example and without limitation, if the internal threading <NUM> defines a thread pitch of <NUM> TPI, then each clockwise <NUM>-degree rotation of the nozzle cap <NUM> translates the nozzle cap <NUM><NUM>" along the cap axis <NUM> towards the nozzle 140a. In order to alter the rotational indexing of the nozzle cap <NUM> counterclockwise by ninety degrees, a <NUM>" shim can be added between the gasket <NUM> and the inner wall <NUM>. The same formula can be utilized to determine the necessary increase or decrease in gasket thickness T (shown in <FIG>) to achieve the desired rotational indexing of the nozzle cap <NUM>.

In some aspects of the nozzle cap <NUM>, two vibration sensors <NUM> can be attached to the nozzle cap <NUM> at a ninety-degree offset from one another along the circumferential wall <NUM> (shown in <FIG>). In such an aspect, the nozzle cap <NUM> would only have to be overtightened or backed off by a maximum of forty-five degrees to position one of the two vibration sensors <NUM> in one of the vertical orientations: the twelve-o-clock position 600a or the six-o-clock position 600e. In such aspects, the nozzle cap <NUM> can comprise an accelerometer to determine which of the two vibration sensors <NUM> is more optimally oriented when taking readings. In some aspects, the gasket <NUM> can comprise a soft, compressive material, such as a soft rubber like neoprene, which can allow for a greater range of adjustment to the rotational indexing compared to a harder material, such as a hard rubber.

<FIG> is a cross-sectional side view of the barrel <NUM> and nozzle cap <NUM> of <FIG> taken along line <NUM>-<NUM> shown in <FIG>. In the aspect shown, the vibration sensor <NUM> can be in the six-o-clock position, and the sensor axis <NUM> can be vertically aligned in parallel with the barrel axis <NUM>. Each of the barrel axis <NUM> and the sensor axis <NUM> can be perpendicular to the cap axis <NUM>.

As shown and previously described, the gasket <NUM> can define the gasket thickness T, and the gasket <NUM> can be positioned between the inner wall <NUM> of the cap body <NUM> and a nozzle end <NUM> of the nozzle 140a. The vibration sensor <NUM> can also be screwed into the threaded hole <NUM> defined by the circumferential wall <NUM> to secure the vibration sensor <NUM> to the circumferential wall <NUM>.

In other aspects, the vibration sensor <NUM> can be positioned within the bonnet <NUM> (shown in <FIG>) of the fire hydrant <NUM> (shown in <FIG>) or within the barrel <NUM> (shown in <FIG>) of the fire hydrant <NUM>. In such an aspect, the sensor axis <NUM> can be vertically aligned parallel with the barrel axis <NUM> of the barrel <NUM>. Improvement in the signal-to-noise ratio for the vibration sensor <NUM> can be attributed to aligning the direction of oscillation of the calibration masses <NUM> (shown in <FIG>) with the direction of vibration propagation. The calibration masses <NUM> can oscillate substantially axially along the sensor axis <NUM> of the vibration sensor <NUM>. The vibrations can originate within the fluid system and then travel substantially vertically up the stand pipe <NUM> (shown in <FIG>) to the fire hydrant <NUM>. By vertically aligning the sensor axis <NUM> parallel to the barrel axis <NUM>, the calibration masses <NUM> can be ideally positioned to oscillate upwards and downwards, which makes the vibration sensor <NUM> more sensitive to the vibrations propagating up the stand pipe <NUM> to the fire hydrant <NUM>.

During experimentation, vibration sensors were installed on a fire hydrant attached to a <NUM>-inch ductile iron water main at a test facility. Vibration sensors were positioned in both vertical and horizontal orientations, and the vibration sensors took readings while water was flowed from valves to simulate leaks in the water main. Across the frequency range <NUM>-<NUM>, the vertically oriented sensor demonstrated an average 3dB increase in signal strength relative to the horizontally oriented sensor. Further testing was conducted wherein individuals clapped and yelled in proximity to the fire hydrant to measure sensitivity to airborne background noise, and the vibration sensors in the vertical orientation were found to be less sensitive to background noise. Across the frequency range <NUM>-<NUM>, the vertically oriented sensor demonstrated an average 8dB increase in signal-to-noise ratio when comparing the leak simulation to airborne noise.

Further testing was conducted with fire hydrants to determine if the increase in signal-to-noise ratio would offer improved performance in detecting leaks. Vibration sensors in both horizontal and vertical orientations were attached to two separate fire hydrants while leaks of varying sizes were simulated by opening valves in the attached water infrastructure systems. In sixteen out of seventeen conditions tested, the vertically oriented sensors yielded correlations of higher strength than the horizontally oriented sensors, which demonstrates a higher likelihood that the vertically oriented sensors would detect the leak in a real world scenario.

Claim 1:
A nozzle cap (<NUM>) for a fire hydrant, the nozzle cap comprising:
a cap body (<NUM>), the cap body (<NUM>) defining a cap axis (<NUM>) extending from a first body end of the cap body (<NUM>) to a second body end of the cap body (<NUM>), the cap body (<NUM>) defining a threaded bore (<NUM>) extending into the cap body (<NUM>) from the second body end (<NUM>) to an inner wall (<NUM>) of the cap body (<NUM>) with internal threading (<NUM>) arranged to engage a nozzle of a said fire hydrant, wherein the cap axis (<NUM>) defines an axis of rotation around which the internal threading (<NUM>) of the cap body (<NUM>) rotates; and
a vibration sensor (<NUM>) attached to the cap body (<NUM>), the vibration sensor (<NUM>) defining a sensor axis (<NUM>) extending from a first sensor end (<NUM>) of the vibration sensor (<NUM>) to a second sensor end (<NUM>) of the vibration sensor (<NUM>), the vibration sensor (<NUM>) comprising a fastener (<NUM>) with a threaded end (<NUM>), the threaded end (<NUM>) defining the first sensor end (<NUM>) of the vibration sensor (<NUM>), the second sensor end (<NUM>) being defined by calibration masses (<NUM>) of the vibration sensor (<NUM>), wherein the second sensor end (<NUM>) is opposite from the first sensor end (<NUM>), wherein the threaded end (<NUM>) is arranged to threadedly engage a threaded hole (<NUM>) defined by a circumferential wall (<NUM>) of the cap body (<NUM>) so to attach the vibration sensor (<NUM>) to the cap body (<NUM>),
wherein the sensor axis (<NUM>) extends through the fastener (<NUM>) and the vibration sensor (<NUM>) from the first sensor end (<NUM>) to the second sensor end (<NUM>), wherein the sensor axis (<NUM>) is aligned perpendicular to the cap axis (<NUM>).