Abstract:
A flow detection sensor has a manifold with an inlet on a bottom surface and an outlet on a side surface. A movable partial blockage rests near the bottom surface of the manifold and is movable upward in response to a flow of liquid from the inlet to the outlet. A sensor detects the position of the movable partial blockage within the manifold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is related to U.S. non-provisional utility application titled, “TANKLESS WATER HEATER,” which was filed on even date herewith; and inventor Robert E. White, III. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the field of sensing the flow of a liquid and more particularly to a highly sensitive liquid flow detector. 
   2. Description of the Related Art 
   Liquid flow detectors are often used to detect the flow of water in water heaters. Electrically operated water heaters generally are known in the prior art and have numerous common features. The most common water heater used today is a water heater having a storage tank. In this, a supply or tank of water is pre-heated by an electric heating element or combustion of fossil fuel so that hot water is available shortly after a hot-water spigot is opened. Storage-tank water heaters waste energy in that there is substantial energy lost by radiation and conduction of the hot water stored in their storage tank, sometimes 40 or 50 gallons. The radiated energy also taxes air conditioning systems. Several attempts have been made to reduce this waste, including enhanced insulation for reducing radiated heat lost and using timers to disable the heating elements during night hours. 
   Recently, tankless, or instantaneous, heaters have been deployed for heating water on demand. There are several major advantages in tankless water heaters. The first is, because there is no pre-heated water, there is very little energy loss due to heat radiated from the pre-heated water. Second, the tankless water heaters are smaller, requiring fewer raw materials and requiring fewer resources in shipment. Third, the tankless water heaters occupy less space in homes, apartments, retail outlets, warehouses etc. 
   Several U.S. patents cover various aspects of tankless water heaters. U.S. Pat. No. 3,351,739, issued to Eckman has a tankless water heater with staged energization of electrical heating elements and a high temperature cutout switch. 
   U.S. Pat. No. 3,795,789, issued to Malzoni has a tankless water heater with a flow switch and electric heating elements. 
   U.S. Pat. No. 4,604,515, issued to Davidson and U.S. Pat. No. 4,638,147, issued to Dytch et al. include a solid state switch to control electrical current to the heating elements. Dytch mounts the solid state switch on a wall of the heating chamber, thereby cooling the switch while recovering generated heat. Dytch also teaches locating a temperature sensor at the outlet of the heater. 
   U.S. Pat. No. 5,479,558 to White, Jr., et al describes a flow-through tankless water heater with a flow switch. The flow switch has an arm and a ball joint, but requires significant water flow to energize the flow switch. 
   U.S. Pat. No. 6,552,283 to Cabrera describes a flow-switch. The flow switch has a floating magnetic set of balls that have a specific gravity higher than water yet will float upwardly in a pipe when water flows, thereby coming into proximity with a magnetic switch and energizing the heating elements. The floating set of magnetic balls must be retained within the pipe to prevent them from flowing out of the water heater. Unfortunately, this requires screens within the flow of water which, in many circumstances, corrode or clog during use. 
   GB 471,730 to Shepherd describes a flow switch for a tankless water heater. The flow switch of this patent has a plunger in a cylinder that, when water flows, is pushed downward, activating a mercury switch to power the heating elements. This switch uses a spring to urge the plunger back into the resting mode, thereby removing power from the heating elements. The use of a spring is problematic, in that the spring can break or corrode, thereby resulting in continuous power to the heating elements. 
   None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. What is needed is a liquid flow detector that detects a small amount of liquid flow and has limited components that are exposed to the liquid, reducing failure due to corrosion and clogging. 
   SUMMARY OF THE INVENTION 
   It is an objective of the present invention to provide a flow sensor that will detect the flow of a liquid such as water. 
   It is a further objective of the present invention to provide a flow sensor that will detect very small amounts of flow. 
   It is a further objective of the present invention to provide a flow sensor that has few moving parts exposed to any liquid, reducing corrosion and contaminate build-up. 
   In one embodiment, a flow detection sensor is disclosed including a manifold with an inlet on a bottom surface, an outlet on a side surface and a magnetic sensor situated on an upper surface. A plunger rests on the bottom surface of the manifold and has an imbedded magnet. The plunger partially obstructs the flow of a liquid from the inlet when the liquid is still and lifts upwardly within the manifold to a closer proximity with the magnetic sensor when the liquid flows, whereas the magnetic sensor detects the closer proximity of the imbedded magnet and changes electrical state. 
   In another embodiment, a method of detecting a flow of a liquid is disclosed including providing a flow sensor with a manifold that has an inlet on a bottom surface, an outlet on a side surface and a magnetic sensor situated on an upper surface. A plunger movable within the manifold has an imbedded magnet and rests on the bottom surface of the manifold, partially obstructing the flow of liquid from the inlet when the liquid is still. The method continues with the start of flow of the liquid at which time the plunger rises within the manifold to a closer proximity with the magnetic sensor. Correspondingly, the magnetic sensor detects a magnetic field of the imbedded magnet and changes its output from a first state indicative of no flow to a second state indicative of the flow. 
   In another embodiment, a flow detection sensor is disclosed including a manifold with an inlet on a bottom surface and an outlet on a side surface. A movable partial blockage rests near the bottom surface of the manifold and is movable upward in response to a flow of liquid from the inlet to the outlet. A sensor detects the position of the movable partial blockage within the manifold. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be best understood by those having ordinary skill in the art by reference to the following detailed description when considered in conjunction with the accompanying drawings in which: 
       FIG. 1  illustrates an exploded view of a flow sensor of the present invention. 
       FIG. 2  illustrates a cross sectional view of a flow sensor of the present invention. 
       FIG. 3  illustrates a cross sectional view of a flow sensor of the present invention during water flow. 
       FIG. 4  illustrates a pictorial view of a tankless water heater of the present invention. 
       FIG. 5  illustrates a pictorial view of an enclosure of a tankless water heater of the present invention. 
       FIG. 6  illustrates a schematic diagram of a tankless water heater of the present invention. 
       FIG. 7  illustrates a schematic diagram of a tankless water heater of a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Throughout the following detailed description, the same reference numerals refer to the same elements in all figures. 
   Referring to  FIG. 1 , an exploded view of a flow sensor of the present invention will be described. The flow sensor  1  detects minute volumes of water flowing in from the inlet pipe (elbow)  20  and out the outlet pipe  8  (not visible in  FIG. 1 ). The flow of water is detected by a plunger  10  (a movable partial obstruction) that is held by gravity on an edge of the inlet pipe  20  (or on the bottom surface of the flow sensor manifold  4 ) when no water flow occurs. When water flow begins, the plunger  10  rises within the flow sensor manifold  2 , approaching a magnetic sensor  3 . In the preferred embodiment, the plunger  10  has a stem  29  that rests in the inlet pipe  20  and helps prevents the plunger  10  from exiting the inlet pipe  20  as it rises. In the preferred embodiment, the plunger  10  has a magnet  11  that, when in proximity of the magnetic sensor  3 , energizes the magnetic sensor  3 , either opening a circuit or closing a circuit or changing the impedance of the magnetic sensor&#39;s  3  output. The magnetic sensor  3  is held in place by, for example, threads, a fitting  12  and a washer  14 , thereby preventing leakage of water. The fitting  12  is adapted to the flow sensor manifold  2  by any way known in the industry. Although other configurations and mountings of the sensor are equally anticipated, it is preferred to use a threaded mounting such that the sensor  3  is adjustable within the flow sensor manifold  2 , thereby providing a range of flow volume trigger points. For example, if the magnetic sensor  3  is lowered close to the plunger  10 , the flow sensor  1  triggers at a very slight amount of flow. Likewise, if the magnetic sensor  3  is raised away from the plunger  10 , the flow sensor  1  triggers at a higher amount of flow. 
   There are many types of magnetic sensors  3  known in the industry including reed relays, inductors and Hall Effect sensors. The magnetic sensor  3  is preferably a magnetic switch that is in one state (e.g., off) in absence of a magnetic field and in another state (e.g., on) in presence of a magnetic field. Other magnetic sensors  3  work equally as well. For example, an inductive sensor includes a coil of wire that changes impedance corresponding to the proximity of a magnetic material (ferrous material) such as iron or steel. With such a sensor, circuitry is added to operate the solid state relay (discussed later) in response to an impedance change. 
   Referring to  FIG. 2 , a cross sectional view of a flow sensor of the present invention is described. In this figure, no water (fluid) is flowing through the inlet pipe  20  through the flow sensor manifold  2  and out the outlet pipe  8 . The plunger  10  is, therefore, resting by forces of gravity on the rim of the input pipe  20 , though in other embodiments, the plunger  10  rests on any other suitable surface, including a lower surface of the flow sensor manifold  2 . 
   The plunger  10  has a magnet  11  for magnetically engaging with the magnetic sensor  3 , though the magnetic sensor  3  is not energized in this mode since water (fluid) is not flowing and the plunger  10  with magnet  11  is outside of the range of influence of the magnetic sensor  3 . In other words, the magnetic sensor  3  is not stimulated by the magnet  11  because the magnet  11  is outside the range of operation of the magnetic sensor  3 . Many factors influence the engagement of the magnetic sensor  3  with the magnet  11 , including the strength of the magnet  11 , the distance between the magnet  11  and the magnetic sensor  3  and the sensitivity of the magnetic sensor  3 . For the flow sensor  1  of the present invention to operate, these parameters are selected such that the magnetic sensor  3  is in a first state when there is no flow and the plunger  10  is held by gravity against the input pipe  20  or bottom area of the manifold  2  and the magnetic sensor  3  is in a second state when there is flow and the plunger  10  is lifted away from the input pipe  20  of bottom area of the manifold  2  by the flow. In some embodiments, the magnetic sensor  3  is a normally open switch that closes in proximity to a magnet. In other embodiments, the magnetic sensor  3  is a normally closed switch that opens in proximity to a magnet. In still other embodiments, the magnetic sensor  3  has a variable impedance or resistance that changes proportionally to the proximity to the magnet. 
   In some embodiments, a lip  7  is formed in the wall of the flow sensor manifold  2  partially blocking the output pipe  8  so that the plunger  10  doesn&#39;t lift out of its seat (input pipe  20 ) and move into the output pipe  8  or clog the output pipe  8 . In preferred embodiments, the plunger  10  has a stem  29  that extends downward into the inlet pipe  20 , thereby holding the plunger upright and helping to prevent the plunger  10  from escaping the flow sensor manifold  2 . 
   In some embodiments, an anti-vacuum tube  13  is drilled or formed in the stem  29  of the plunger  10  to assist in the insertion of the magnet  11 . In the preferred embodiment, the magnet  11  is press-fit into the plunger  10 , and without the anti-vacuum tube  13 , air caught when inserting the magnet  11  can create pressure that can work to push the magnet  11  out of the plunger  10 . The anti-vacuum tube  13  eliminates this pressure. In alternate embodiments, the magnet  11  is installed into the plunger  10  in a vacuum environment or the magnet  11  is bonded to the plunger  10  with an adhesive. The fitting  12  and washer  14  are shown for completeness. 
   Referring to  FIG. 3 , a cross sectional view of a flow sensor of the present invention during water flow will be described. In this figure, water (fluid) is flowing through the inlet pipe  20  through the flow sensor manifold  2  and out the outlet pipe  8 . The plunger  10  is, therefore, lifted by the flow, off the rim of the input pipe  20 . 
   As the plunger  10  rises in response to the flow of liquid from the inlet pipe  20  to the outlet pipe  8 , the magnet  11  of the plunger  10  magnetically engages with the magnetic sensor  3 . The magnetic sensor  3  is thereby stimulated by the magnet  11  because the magnet  11  is now within the range of operation of the magnetic sensor  3 . 
   Again, in some embodiments, a lip  7  is formed in the wall of the flow sensor manifold  2  partially blocking the output pipe  8  so that the piston  10  doesn&#39;t lift out of its seat (input pipe  20 ) and move into the output pipe  8  or clog the output pipe  8 . 
   Referring to  FIG. 4  a pictorial view of a tankless water heater utilizing the flow sensor  1  previously described is shown. In this embodiment, the components are mounted and secured to a chassis panel  23 . Water enters the tankless water heater  30  through an input conduit  19  and inlet pipe fitting  20 , entering the flow sensor manifold  2 . The magnetic sensor  3  detects magnetic flux when water flows and the plunger  10  with magnet  11  (not visible) rises into its proximity. The magnetic sensor  3  is coupled to a solid state relay  4 , signaling it to energize. The solid state relay  4  is controlled by the magnetic sensor  3  and a thermocouple  32 . The magnetic sensor  3  energizes the solid state relay  4  when water flows and the thermo-couple  32  controls the amount of current flowing through the solid state relay  4  based upon the output water temperature. Solid state relays are well known in the industry and often used in electric water heaters of all types. 
   When a hot water tap connected to the tankless water heater  30  is opened and water flows, the cold water flows out of the flow sensor manifold  2  and into a first heater manifold  25 , through a first heating chamber  15 , through connecting pipes  17  into a second heating chamber  16  and into a second heater manifold  26  before exiting the tankless water heater  30  through an outlet pipe  27 . Within the first heating chamber  15  is a first heating element  5  and within the second heating chamber  16  is a second heating element  6 . 
   When water flows, the flow sensor  1  detects such and the magnetic sensor  3  signals the solid state relay  4  to close, thereby providing electric current to the heating elements  5 / 6 . The heating elements are, preferably, standard, submersible, electric heating elements as known in the industry. As the water is heated, the thermocouple  32  measures the water temperature at the outlet of the tankless water heater  30 . If the temperature rises above a predetermined level, the solid state relay  4  is signaled to reduce the current to one or both of the heating elements  5 / 6 , thereby regulating the output temperature. 
   In some embodiments, thermal safety switches  33 , in thermal conductivity with the heating chambers  15 / 16  monitor the temperature of the chambers  15 / 16  and, if a high-temperature threshold is exceeded, power is interrupted to the heating elements  5 / 6 , preventing overheating, excessive pressure and other related problems. 
   Also shown for completeness is a power terminal block  9 . Normally, 220V AC household power is provided by three wires, two hot legs and a neutral. The power terminal block  9  connects the incoming power to the various components of the tankless water heater  30 . Details of these connections are shown in  FIGS. 6 and 7 . 
   Referring to  FIG. 5 , a pictorial view of an enclosure of a tankless water heater of the present invention will be described. The inlet  19  passes through a cover  24  of the enclosure. The chassis panel  23  is covered by the cover  24 . The outlet and power connections are not visible. 
   Referring to  FIG. 6 , a schematic diagram of the electrical connections of a first embodiment of the present invention is shown. One leg of the AC power  50  enters the tankless water heater  30  through the solid state relay  4 . Although shown as AC, in some countries, DC power is used. It is preferred that the AC voltage be 220V at 50 or 60 Hz, though any voltage and frequency can be used. In this embodiment, the solid state relay  4  is controlled by input  56  from the water flow sensor  1  and input  58  from the temperature sensing thermo-couple  32 . When water is flowing, the water flow sensor  1  signals the solid state relay  4  to close or start the flow of current through the series path between its power output  54 , through the thermal safety switches  33 , through the heating elements  5 / 6  and back to the other leg of the AC power  52 . As current flows, the heating elements  5 / 6  heat the water. The thermocouple  32  detects the output temperature of the tankless water heater  30  and as it reaches the desired temperature, signals the solid state relay  4  to reduce the current flowing through the heating elements  5 / 6 . In some embodiments, the solid state relay  4  continuously varies the current through the heating elements  5 / 6  depending upon the water temperature detected by the thermocouple  32 . In other embodiments, the solid state relay  4  varies the current in steps (e.g., 100%, 90%, 80%, etc). In some embodiments, the solid state relay  4  is only capable of switching the current on or off. 
   The thermal safety switches  33  are normally closed thermal switches that open if the temperature of the heating chambers  15 / 16  exceed a specified temperature, for example 140 degrees Fahrenheit. Thermal safety switches  33  are known in the industry and usually consist of a bi-metallic disc that, when heated over a threshold temperature, deform and interrupts the flow of electricity. 
   Referring to  FIG. 7 , a schematic diagram of the electrical connections of a second embodiment of the present invention is shown. As in the first embodiment, one leg of the AC power  50  enters the tankless water heater  30  through the solid state relay  4 . Although shown as AC, in some countries, DC power is used. It is preferred that the AC voltage be 220V at 50 or 60 Hz, though any voltage and frequency can be used. In this embodiment, the solid state relay  4  is controlled by input  56  from the water flow sensor  1  and input  59  from the control panel  60 . When water is flowing, the water flow sensor  1  signals the solid state relay  4  to close or start the flow of current through the series path between its power output  54 , through the thermal safety switches  33 , through the heating elements  5 / 6  and back to the other leg of the AC power  52 . As current flows, the heating elements  5 / 6  heat the water. 
   In this embodiment, the thermocouple  32  measures the output temperature of the tankless water heater  30  and provides a proportional electrical signal  58  to a control panel  60 . Such control panels are known in the industry. In some embodiments the control panel  60  includes a mechanism to set the water temperature to a desired value such as 105 degrees Fahrenheit. In some embodiment the control panel also includes a display to indicate the water temperature setting. As the water temperature reaches the set temperature, the control panel signals the solid state relay  4  through its output  59  to reduce the current flowing through the heating elements  5 / 6 . In some embodiments, the solid state relay  4  continuously varies the current through the heating elements  5 / 6  depending upon the water temperature detected by the thermo-couple  32 . In other embodiments, the solid state relay  4  varies the current in steps (e.g., 100%, 90%, 80%, etc). In some embodiments, the solid state relay  4  is only capable of switching the current on or off. 
   As in the first embodiment, the thermal safety switches  33  are normally closed thermal switches that open if the temperature of the heating chambers  15 / 16  exceed a specified temperature, for example 140 degrees Fahrenheit. Thermal safety switches  33  are known in the industry and usually consist of a bi-metallic disc that deform and interrupts the flow of electricity when heated above a threshold temperature. 
   Equivalent elements can be substituted for the ones set forth above such that they perform in substantially the same manner in substantially the same way for achieving substantially the same result. 
   It is believed that the system and method of the present invention and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely exemplary and explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.