Abstract:
An expansion tank which comprises a tank having a predetermined volume capacity; an expandable diaphragm in the tank, partitioning tank volume into a liquid-containing portion for holding liquid and a gas-containing portion for holding a gas under a pressure that defines a normal pressurized gas volume when the liquid-containing portion holds a predetermined liquid volume; and a proximity sensor mounted to the tank at the gas-containing portion thereof and adapted to emit an alarm signal when volume of the gas-containing portion is reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of U.S. Ser. No. 11/500,219 filed on Aug. 8, 2006. 
     
     FIELD OF INVENTION 
       [0002]    This invention relates to expansion tanks in hydronic systems and the like. More particularly, this invention relates to predictive sensors in expansion tanks that are part of hydronic systems and the like. 
       BACKGROUND OF INVENTION 
       [0003]    Hydronics refers to the use of water as a heat transfer medium in heating and cooling systems. Hydronic systems are commonly utilized in heating, ventilating and air conditioner (HVAC) applications. Typical hydronic systems include a circulating heat transfer medium loop, associated valves, a radiator, a pump, and a boiler or chiller to implement the desired heat transfer. A water loop hydronic system also must include at least one expansion tank to accommodate a varying volume of the heat transfer liquid, such as water, inasmuch as the liquid volume contracts and expands as it cools and heats. The expansion tanks utilize an elastomeric diaphragm pressurized with compressed gas such as air to accommodate the variations in liquid volume by further gas expansion or compression, and help control pressure in the hydronic system. 
         [0004]    Expansion tanks usually include a diaphragm to hold the excess liquid and a compressed gas portion for controlling over-all system pressure. When the diaphragm is overexpanded due to an excessive system pressure or a gas leak from the tank, the diaphragm can burst necessitating a costly system shut-down for repair. It would be advantageous to detect not only system failures such as a rupture of the diaphragm but also a condition wherein the diaphragm has been overly expanded and is likely to burst unless remedial steps, e.g., reduction in system pressure by draining, are timely taken. 
         [0005]    Accordingly, it is an object of the present invention to provide an expansion tank having excessive diaphragm movement alarm means mounted thereto for monitoring expansion of the diaphragm within the expansion tank. 
         [0006]    The term “diaphragm” as used herein and in the appended claims denotes an elastomeric deformable web or membrane that spans the tank and is secured to the sidewall of the tank ( FIG. 8 ) or an elastomeric bladder suspended in the tank ( FIG. 2 ) and adapted to hold a liquid. In either case, the web or membrane, as well as the bladder, partitions the tank interior into two compartments or portions—a closed, gas-containing portion for the containment of a gas under pressure and a liquid-containing portion for the holding of a portion of the liquid that expands from the system. 
         [0007]    It is a further object of this invention to provide an expansion tank system and method of use which includes an expansion detector that does not damage the diaphragm in the expansion tank. 
         [0008]    It is also an object to provide an expansion tank having a sensor element which is able to detect potential diaphragm failure modes, i.e. tank flooding and/or over-extension of a tank diaphragm. 
         [0009]    It is yet another object to provide an expansion tank alarm system in module form so that it may be readily installed or replaced through a tank coupling. 
         [0010]    These and other objects and advantages of the apparatus and method aspects of the present invention will be apparent to those skilled in the expansion tank art. 
       SUMMARY OF THE INVENTION 
       [0011]    Expansion tanks embodying the present invention are capable of detecting a potential failure condition in an expansion tank due to an abnormal deflection of the tank&#39;s diaphragm in a hydronic system, loss of counterbalancing gas pressure in the tank, and the like. 
         [0012]    In particular, an expansion tank of the present invention comprises a tank having a predetermined volume capacity and an expandable diaphragm in the tank. The expandable diaphragm partitions the tank volume into a liquid-containing portion for holding a liquid and a gas-containing portion for holding a gas under a pressure that defines a normal pressurized gas volume when the liquid-containing portion of the tank holds a predetermined liquid volume. A proximity sensor is mounted to the tank at the gas containing portion thereof and is adapted to emit an alarm signal when the gas containing portion is reduced as a result of diaphragm expansion. 
         [0013]    A wide variety of proximity sensors, capable of detecting expansion of the diaphragm mounted in the tank can be utilized. Illustrative are the capacitive proximity sensors such as a dielectric type capacitive proximity sensor, a conductive type capacitive proximity sensor, and the like, mechanical proximity sensors such as stain gages and the like, electromechanical proximity sensors, and the like. 
         [0014]    As stated hereinabove, the diaphragm can be an elastomeric, deformable web or membrane that partitions the tank interior, or an elastomeric bladder mounted in the tank that defines the liquid-containing portion of the tank. 
         [0015]    A method aspect of the present invention is directed to monitoring the size of an expandable diaphragm situated in an expansion tank and comprises the steps of detecting by means of a proximity sensor the presence of an expansion tank diaphragm in the vicinity of a predetermined tank wall portion and generating an alarm in response to a signal received from the proximity sensor. 
         [0016]    The proximity sensor can be mounted to the tank in several ways, depending upon the type of proximity sensor utilized. In the case of the capacitive proximity sensors, these sensors can extend into the gas-containing portion of the tank through an appropriate coupling, or these sensors can detect the presence of the expanded diaphragm through a sight glass and the like provided in the tank wall. In the case of a mechanical or electromechanical proximity sensor, at least a portion of the sensor extends into the gas-containing portion of the tank. The mechanical or electromechanical proximity sensors are activated by physical contact with the diaphragm. 
         [0017]    The proximity sensors contemplated by the present invention are also capable of detecting a flooding condition within the tank, that is, the condition when the diaphragm has burst and liquid in the expansion tank has encroached into the gas-containing portion of the tank. 
         [0018]    Expansion tanks equipped with a diaphragm proximity sensor according to the present invention are also suitable for use in municipal water and sewage handling systems, power wash systems, reverse osmosis systems, fuel handling systems, fire protection systems, and the like where fluctuations in system pressure of a liquid must be accommodated. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the drawings. 
           [0020]      FIG. 1  is a schematic illustration of a closed-loop hydronics system that utilizes an expansion tank embodying the present invention; 
           [0021]      FIG. 2  is an enlarged elevational view of the expansion tank shown in  FIG. 1 . 
           [0022]      FIG. 3  is a schematic illustration of an air separation and expansion tank detail of a hydronics system, the expansion tank being provided with a bladder type diaphragm; 
           [0023]      FIG. 4  is a schematic illustration of a hydropneumatic expansion tank embodying the present invention and utilizing a diaphragm in the form of an elastomeric web that partitions the tank volume into a gas-containing portion and a liquid containing portion; 
           [0024]      FIG. 5  is a schematic illustration of an electromechanical proximity sensor mounted in the wall of an expansion tank at flooding conditions; 
           [0025]      FIG. 6  is a schematic illustration of an electromechanical proximity sensor mounted in the wall of an expansion tank; 
           [0026]      FIG. 7  is a schematic illustration of another type of electromechanical proximity sensor; 
           [0027]      FIG. 8  is a schematic illustration of an expansion tank embodying the present invention and under normal operating conditions; 
           [0028]      FIG. 9  is a schematic illustration of an expansion tank embodying the present invention and under abnormal, excessive system pressure condition; and 
           [0029]      FIG. 10  is a schematic illustration of an expansion tank embodying the present invention and showing a ruptured diaphragm as well as a flooded condition. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0030]    The invention described herein is, of course, susceptible of embodiment in many forms. Shown in the drawings and described hereinbelow in detail are preferred embodiments of the present invention. It is to be understood, however, that the present disclosure is an exemplification of the principles of this invention but does not limit this invention to the illustrated embodiments. 
         [0031]    Referring to  FIGS. 1 and 2 , a closed loop heating system  12  includes expansion tank  10  equipped with proximity sensor  11  and alarm module  20  mounted to tank  10 . Proximity sensor  11  preferably is a dielectric type capacitive proximity sensor such as Model C1ALLAN1-P, commercially available from Stedham Electronics Corporation, Reno, Nev. 89502, U.S.A. Boiler  14  supplies hot water which is circulated through radiators  13  and  16  by pump  26  via lines  15 ,  17 ,  18  and  19 . Line  24  is in fluid flow communication with line  15  as well as with bladder-type diaphragm  21  in expansion tank  20 . Excess system water  23  is held within bladder-type diaphragm  21 . System pressure, typically about 12 to about 30 pounds per square inch gage (psig) is maintained by reason of pressurized gas within gas-containing portion  22 . Tank  10  is also equipped with air charging valve  27  for adjusting air pressure in the gas-containing portion  22 . 
         [0032]      FIG. 3  illustrates a hydronics installation. Floor mounted, vertical expansion tank  30  is equipped with suspended bladder  32  that holds excess system water  34 . Pressure gage  36  monitors system water pressure. Air charging valve  38  is provided on tank  30  for pressurization of gas-containing portion  40  of tank  30 . Proximity sensor  42  is mounted to tank  30  and monitors conditions within the gas-containing portion  40 . If bladder  32  expands beyond a predetermined limit due to an abnormal increase in system pressure or an air leak in gas-containing portion  40 , proximity sensor  42  detects such an expansion and emits a signal that energizes an appropriate alarm so that system water pressure can be relieved before excessive stress or bursting pressure is reached within bladder  32 . If overexpansion of bladder  32  is due to an air leak from gas-containing portion  40 , additional air pressure can be supplied through air charging valve  38 . 
         [0033]    Air separator  45  is provided in feed line  47  that communicates via water line  49  with the input or suction side of a pump (not shown). Expansion tank  30  and its bladder  32  are, in turn, in fluid flow communication with water line  49  via line  51 . Tee connection  53  is provided in line  54  to facilitate connection with another, parallel expansion tank if desired. System pressure relief valve  56  is also provided in communication with water line  49 . 
         [0034]      FIG. 4  illustrates a typical installation of a vertical, floor mounted expansion tank  58  that is provided with proximity sensor  60  mounted to tank  58  in the region that defines gas-containing portion  62  within tank  58 . Membrane  64  partitions tank  58  into a gas-containing portion  62  and liquid containing portion  66 . Tank  58  also has an air charging valve  68  and inspection port  59 . 
         [0035]    Liquid-containing portion  66  is in fluid flow communication with a water system via line  67 . Pressure gage  69  in line  67  monitors system water pressure. 
         [0036]      FIG. 5  illustrates a flooding condition in expansion tank  10 . Bladder-type diaphragm  21  has burst and water held within the liquid-containing portion  23  has entered gas-containing portion  22 . Proximity sensor  11  mounted to tank detects the approaching water level, emits an alarm signal that, in turn, energizes alarm module  20  equipped with audible alarm  81  as well as with visual indicator light  82  and on/off/reset button  84 . Remote alarm capabilities can be incorporated as well, if desired. 
         [0037]      FIG. 6  illustrates electromechanical proximity sensor  70  equipped with alarm module  90  mounted in the wall of an expansion tank. Proximity sensor  70  extends into the gas-containing portion of the tank and alarm module  90  associated with sensor  70  is situated outside the expansion tank. 
         [0038]    Proximity sensor  70  includes a float  77  mounted at the distal end of arm  76  which forms an integral, substantially L-shaped piece  73  with arm  74  that carries a magnet  75  at the distal end thereof. The L-shaped piece  73  is pivotably mounted at  72  to bar  71  supported by housing  98 . When float  77  is moved upwardly either by an expanding bladder or the buoyant force exerted on float  77  by a rising water level, magnet  75  approaches and closes contact points  94  and  96  in housing  98 , thereby closing the alarm circuit in alarm module  90 . This alarm circuit includes, in addition to contact points  94  and  96 , leads  101  and  102 , a power source such as battery  85 , audible alarm  81 , visual alarm  82 , and on/off/reset button  84 . 
         [0039]      FIG. 7  depicts another proximity sensor suitable for use in practicing the present invention. 
         [0040]    In this particular embodiment float  107  is affixed to the distal end of a wire spring  109  mounted in a conductive sleeve  111  but electrically isolated therefrom. Leads  119  and  121  are connected, respectively, to wire spring  109  and conductive sleeve  111  and to the same alarm module as that shown in  FIG. 6 . Wire spring  109  is held in place inside conductive sleeve  111  by epoxy disc  117 . The alarm circuit is closed and an alarm signal emitted when float  120  is urged upwardly either by an expanding diaphragm or a rising water level and wire spring  109  which contacts conductive sleeve  111 . 
         [0041]      FIGS. 8 ,  9  and  10  illustrate the position of the diaphragm in an expansion tank under various conditions. In  FIG. 8  expansion tank  130  is shown under normal operating conditions, the liquid  132  held in tank  130  occupying about 40 percent of tank volume, pressurized gas  134  occupying about 60 percent of tank volume and being separated from liquid  132  by diaphragm  136 . In this particular example the system water pressure is in the range of about 12 to about 30 psig and is counterbalanced by pressurized gas  134 . Proximity sensor  140  is mounted in the wall of tank  130 . Alarm module  142  associated with sensor  140  is on the outside of the tank  130 . 
         [0042]    When the system water pressure rises ( FIG. 9 ), more of liquid  132  occupies the tank volume and diaphragm  136  becomes distended, shifting proximity sensor  140  upwardly and energizing the alarm. Similarly, when diaphragm  136  has burst, rising water level in tank  130  maintains proximity sensor  140  in an upwardly position as shown in  FIG. 10 . 
         [0043]    Under normal operating conditions in a hydronics system, the liquid volume in the expansion tank is about 40 percent of total tank volume and the pressurized gas or air volume is about 60 percent of total tank volume. An alarm condition occurs when the diaphragm is distended to near its maximum tensile or burst strength. The latter, of course, is dependent on the material of construction and thickness of the diaphragm. Expansion tank diaphragm are butyl rubber, natural rubber, nitrile rubber, and the like. 
         [0044]    Preferably, the proximity sensor is positioned at or in the expansion tank so that an alarm signal is emitted when the gas-containing portion of the tank has been reduced by at least about 40 percent of normal value. 
         [0045]    The emitted alarm signal can be processed in a variety of ways. As described hereinabove, the alarm signal can be utilized to energize an audible alarm or a visual alarm. The alarm signal can also be transmitted to a remote site having a centrally located monitor or data logger that can receive alarm signals from more than one expansion tank in a hydronics system or systems. The choice of a particular expansion tank monitoring arrangement depends largely on the size of the involved hydronic system or systems involved.