Abstract:
A sensor unit detects an open vacuum interface valve coupled to a gravity sump that is pneumatically coupled to an air relief tube of a vacuum sewage system. The sensor unit includes an open valve sensor, a communication device, a processor and a power source. The open valve sensor is affixed to the air relief tube. The processor is in electronic communication with the open valve sensor and the communication device. The processor is configured to read a sensed value from the open valve sensor and cause the communication device to transmit an alarm signal when the sensed value meets predefined criteria. The power source provides power to the open valve sensor and to the communication device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to valve sensor systems and, more specifically, to a sensor system for detecting faulty valves in a vacuum sewer system. 
         [0003]    2. Description of the Prior Art 
         [0004]    Vacuum sewer systems are commonly used in areas without a substantial natural gradient that allows gravity flow of sewage to a treatment plant. Such systems are often used in beachside and island residential areas because in such areas most houses are topographically nearly as low as or lower than the elevation of the sewage treatment plant. 
         [0005]    In a vacuum sewer system, as shown in  FIG. 1 , sewage flows by gravity from a home  10  into a collection pit  20  (a single collection pit may connect several homes to a vacuum sewer system), that includes a sump  22 . Located above the sump  22  is a vacuum interface valve  24  that is pneumatically controlled and operated. As the sewage level rises in the sump, air trapped in sensor pipe pushes on a diaphragm in a controller coupled to the vacuum interface valve  24 , which causes the valve to open when the sewage reaches a predetermined level. When the vacuum interface valve  24  opens, differential air pressure between the collection pit  20  and a sewage main  30  propels the sewage through a suction tube  26  and through the valve  24  into the sewage main  30 , which is kept under a vacuum. An air relief tube  40  is provided to allow air inflow into the collection pit  20  while the vacuum interface valve  24  is open. 
         [0006]    The sewage flows through the sewage main  30  into a collection tank  52  at a vacuum station  50 . Sewage pumps transfer the sewage from the collection tank  52  to the wastewater treatment facility or nearby gravity manhole. Differential air pressure is the driving force in vacuum sewer systems. Typically, vacuum sewer lines are kept under a vacuum of −50 kPa to −70 kPa created by the vacuum pump  52  located at the vacuum pump station  50 . This pressure differential provides the energy required to open the vacuum interface valves and to transport the sewage. 
         [0007]    For various reasons, a vacuum interface valve  24  can get stuck in an open, or partially open position. When this occurs, air can flow freely from the air relief tube  40  into the sewage main  30 . This causes a loss of vacuum in the sewage main  30 , which results in the vacuum pump  52  over working and wasting energy. 
         [0008]    In a vacuum sewer system in which many different collection pits are serviced by a common sewage main, a stuck open valve is usually detected when the vacuum pump at the vacuum station cycles “on” an unusually high number of times during a given hour. Once a stuck valve is detected, a technician has to shut off each leg of the system along the main until the leaking valve is detected. This can be quite time consuming and costly, as it takes at least one hour to detect the existence of a faulty valve and it can take several hours to determine which valve on the line is faulty. It can also leave many homes on the line without sewer service while their systems are being shut down during the leak detection process. 
         [0009]    It has been proposed to retrofit existing vacuum interface valves with underground electronic valve position detection switches. However, doing so would require digging to the valve level to install such switches and also would require installing electrical power systems and underground communication systems that are coupled the switches. Thus, installing such switches would be both difficult and costly. 
         [0010]    Therefore, there is a need for a detection system for faulty vacuum interface valve that can quickly detect a faulty valve, but that can be installed without requiring access to the inside of a collection pit. 
       SUMMARY OF THE INVENTION 
       [0011]    The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a sensor unit for detecting an open vacuum interface valve coupled to a gravity sump that is pneumatically coupled to an air relief tube of a vacuum sewage system. The sensor unit includes an open valve sensor, a communication device, a processor and a power source. The open valve sensor is in pneumatic communication with the interior of the air relief tube. The processor is in electronic communication with the open valve sensor and the communication device. The processor is configured to read a sensed value from the open valve sensor and cause the communication device to transmit an alarm signal when the sensed value meets predefined criteria. The power source provides power to the open valve sensor and to the communication device. 
         [0012]    In another aspect, the invention is a system for detecting an open vacuum interface valve coupled to a gravity sump of in a vacuum sewage system. The system includes a plurality of sensor units and at least one monitoring station. Each sensor unit of the plurality of sensor units includes at least one air relief tube pressure sensor coupled to an interior portion of the air relief tube, at least one ambient pressure sensor disposed outside of the air relief tube, a communication device and a processor in electronic communication with the air relief tube pressure sensor, the ambient pressure sensor and the communication device. The processor is configured to read a first pressure from the air relief tube pressure sensor and a second pressure from the ambient pressure sensor periodically, calculate a difference between the first pressure and the second pressure, cause the communication device to transmit an alarm signal to a network when the difference meets predefined criteria, a memory that stores identifying data that is uniquely associated with the sensor unit and wherein the alarm signal includes the identifying data and a power source for providing power to the air relief tube pressure sensor, the one ambient pressure sensor and the communication device. At least one monitoring station receives the alarm signal. The monitoring station includes a computer configured to correlate the identifying data with the sensor unit and to display an identification of which sensor unit that has detected an open vacuum interface valve. 
         [0013]    In yet another aspect, the invention is a method for detecting an open vacuum interface valve coupled to a gravity sump coupled to a vacuum sewage system, in which a pressure drop is detected inside of an air relief tube coupled to the vacuum sewage system, in which the pressure drop is associated with the open vacuum interface valve. When the pressure drop is sustained for a predetermined amount of time, then a signal is transmitted to a monitoring station. The signal includes data that identifies the open interface valve. 
         [0014]    These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic diagram of a prior art vacuum sewer system. 
           [0016]      FIG. 2  is a schematic diagram of a sensor mesh of a valve fault detection system. 
           [0017]      FIG. 3  is a schematic diagram of an air relief tube with a valve fault sensor affixed thereto. 
           [0018]      FIG. 4  is a schematic diagram of a valve fault sensor. 
           [0019]      FIG. 5A  is a front elevational view of a valve fault sensor. 
           [0020]      FIG. 5B  is a side elevational view of the valve fault sensor shown in  FIG. 5A . 
           [0021]      FIG. 6  is a schematic diagram of a valve fault detection system. 
           [0022]      FIG. 7  is a flow chart showing one representative method of operation of a valve fault sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. Unless otherwise specifically indicated in the disclosure that follows, the drawings are not necessarily drawn to scale. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” Also, as used herein, “global computer network” includes the Internet. 
         [0024]    As shown in  FIG. 2 , one embodiment is a system  100  for detecting an open vacuum interface valve coupled to a gravity sump of in a vacuum sewage system. Each of a plurality of sensor units  110  is coupled to an above-ground portion of a different air relief tube  40  in the vacuum sewage system. Each sensor unit  110  is configured to detect when a vacuum interface valve is stuck open. Each sensor unit  110  is configured to communicate data regarding the current state of the air relief valve associated with its air relief tube  40  to a relay station  130  or a central monitoring station. 
         [0025]    Detection may occur in one of several ways. For example, as shown in  FIG. 3 , in one embodiment a sensor unit  110  is configured to detect a pressure differential between the inside of a relief tube and the ambient pressure. When the inside of the relief tube has a sustained lower pressure than ambient pressure for a predetermined period, the pressure sensor (or the central monitoring station receiving data from the sensor unit  110 ) determines that the valve is stuck open. In another embodiment, the sensor detects sound inside of the relief tube and if the sound inside of the tube corresponds to the sound made by an open valve for a predetermined amount of time, the system determines that the valve is stuck open. 
         [0026]    Returning to  FIG. 2 , in one representative embodiment each sensor unit  110  includes a wireless communications device that allows it to communicate automatically with a relay station  130 . When the relay station receives data from a sensor unit  110 , it transmits the data to a central monitoring station for further processing. 
         [0027]    As shown in  FIGS. 4 ,  5 A and  5 B, a sensing unit  110  configured to sense pressure can include several components, including a pressure transducer  114  that is couplable to the inside of an air relief tube  40  to determine an internal air pressure. This may be done either by placing the pressure transducer through a hole drilled in the air relief tube  40 , or by coupling an external pressure sensor to a tube that is in communication with the interior of the air relief tube  40 . 
         [0028]    A processor  118  receives the internal air pressure from the pressure transducer  114  determines if a pressure drop that is characteristic of a stuck open valve has occurred. In another embodiment, the processor merely collects the pressure data and transmits it to the central monitoring station where the determination of whether the valve is stuck open is made. If a sufficient pressure drop is sensed, the processor  118  determines if the pressure drop lasts for a period of time that would indicate that the valve is stuck open (i.e., when the pressure drop is sustained for longer that the pressure drop expected from a normal emptying of the sump). A memory  120  stores the data from the pressure transducer and a unique identification of the sensor (which can be used to identify the location of the stuck open valve by pairing the unique identifications of all sensors with locations in a sump location database), along with any necessary program data. In an alternative embodiment, the sensing unit could include a microphone configured to sense sound inside of the air relief tube and a signal processor to determine if the sound corresponds to the sound made by a stuck open valve. 
         [0029]    An ambient pressure transducer  126  (as shown in  FIG. 5B ) can be added in one embodiment to determine the ambient air pressure outside of the air relief tube. In this embodiment, a differential between pressure transducer  114  and pressure transducer  126 , can be used to determine if the valve is stuck open. This embodiment would be more expensive to produce; however, it would compensate for sudden changes in ambient pressure. 
         [0030]    A communications device, such as a mesh network transceiver  124  (e.g., a Zigbee® mesh network transceiver) or a networking radio, transmits data from the sensor unit  110  to the central monitoring station. If a mesh network transceiver  124  is used, then the sensor units  110  work together to form a mesh network, which can cover a wide distance, yet expend relatively little power. A power source, such as a battery  122  (e.g., a lithium ion battery) or a solar power cell, powers the transducers, the processor and the communications device. The sensing unit  110  may be placed in a protective housing  112  with a gasket  116  used to prevent air leakage into the air relief tube when in use. 
         [0031]    As shown in  FIG. 6 , the individual sensing units  110  can form a mesh network that eventually communicates with a relay station  130 . Alternately, a network of radio repeater hubs can be employed to form a network. The relay station  130  communicates data received from the network to a central monitoring station  140 . This may be done in several ways, including transmission via a wireless network, transmission via a satellite communication system, transmission via land lines, transmission via a global computer network, or one of the many other ways of transmitting data between stations. 
         [0032]    As shown in  FIG. 7 , in one method of determining whether to send an alarm corresponding to a stuck open valve, a timer is started  200 , the pressure inside of the air relief tube is sensed  202 . A test  208  is performed to determine if the pressure is less than a predetermined threshold corresponding to the pressure that would exist when the valve is open. If the pressure is less than the threshold, then the current value of the timer is compared  210  to a time threshold to determine if the valve has been open continuously for an amount of time that would indicate that the valve is stuck open. If the result is that the valve is stuck open, then an alarm is issued  212 . The alarm, which identifies the stuck open valve, may be displayed on an alarm screen, sent directly to a technician, or both. The alarm would be coupled with a display indicating which valve was stuck open, thereby allowing a technician to identify the stuck open valve easily. 
         [0033]    While the sensed data may be evaluated locally by the processor, it may also be transmitted to the central monitoring station to be evaluated there. In this case, the sensed data, a timestamp and a sensor unit are all transmitted to the central monitoring station. The central monitoring station could periodically poll each of the sensor units, or the sensor units could be programmed to upload the data to the central monitoring station on a periodic basis. It is also possible that both a central monitoring station evaluation and a local evaluation are performed to increase reliability of the system. 
         [0034]    A similar method could be employed if another quality of the air relief tube is being sensed to determine if the valve is stuck open. For example, if a sound sensor is being used, the system could compare the sound being sensed to a characteristic of the sound that would be expected if the valve were stuck open. In such a system, the sensed sound could be transformed (using well known signal processing techniques, such as with a digital signal processor) into a frequency domain representation and this representation can be compared to a frequency domain representation of the sound made by an open valve. If the representations are the same, or within a predetermined margin of each other, for a period of time that would indicate that the valve is stuck open, then an alarm will be issued. The sound sensor could also be configured to detect a higher sound volume than normal (or a higher volume than normal of certain frequency components of the sound in the air relief tube). 
         [0035]    The above described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.