Patent Publication Number: US-2013228177-A1

Title: Cpap humidifier tank control valve

Description:
BACKGROUND 
     The present disclosure relates generally to Continuous Positive Airway Pressure (CPAP) machines, and more particularly to refilling humidifier tanks for CPAP machines. 
     Sleep apnea is a sleeping disorder characterized by pauses in breathing during sleep. Patients with sleep apnea often benefit from nighttime respiratory assistance with a CPAP machine. CPAP machines are most commonly used for home treatment of sleep apnea, but also can be used for hospital patients who are ill or for newborn infants. CPAP machines work by continuously flowing pressurized air through a patient&#39;s throat to keep the airway open. The CPAP air is usually drawn from the surrounding atmosphere and consequently, can be quite dry. Some CPAP machines include a humidifier for adding moisture to the pressurized air, but conventional CPAP humidifiers are less than ideal. 
     SUMMARY 
     A respiratory humidifier includes a tank, an air inlet, an air outlet, and a control valve. The tank stores liquid. The air inlet opening is located on the tank and fluidly connects the tank to an air pump. The air outlet opening is located on the tank and fluidly connects the tank to an air mask. The control valve is attached to the air outlet opening and defines both an air outlet passageway and a liquid inlet passageway. The control valve includes a shut-off mechanism for blocking the liquid inlet passageway when liquid in the tank reaches a level. 
     A CPAP humidifier system includes an air pump, a humidifier tank, a control valve, and an auxiliary reservoir. The humidifier tank has an air inlet opening and an air outlet opening. The air inlet opening is fluidly connected to the air pump, and the air outlet opening is fluidly connected to an air mask. The control valve is attached to the air outlet opening and defines both an air outlet passageway and a liquid inlet passageway. The auxiliary reservoir is fluidly connected to the liquid inlet passageway for providing liquid to the humidifier tank. 
     A method of providing humidified air to a user includes pumping air and flowing pumped air to a humidifier tank to form humidified air. The method further includes flowing humidified air from the humidifier tank through a control valve to a mask and flowing liquid from an auxiliary tank through the control valve to the humidifier tank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a CPAP humidifier system in accordance with the present disclosure. 
         FIG. 2  is perspective view of a humidifier tank having a control valve. 
         FIG. 3  is a vertical cross sectional view of the humidifier tank and control valve of  FIG. 2 . 
         FIG. 4A  is a vertical cross sectional view, and  FIG. 4B  is a horizontal cross sectional view, of a first embodiment of a control valve. 
         FIG. 5A  is a vertical cross sectional view, and  FIG. 5B  is a horizontal cross sectional view, of a second embodiment of a control valve. 
         FIG. 6A  is a vertical cross sectional view, and  FIG. 6B  is a horizontal cross sectional view, of a third embodiment of a control valve. 
         FIG. 7A  is a vertical cross sectional view,  FIG. 7B  is a horizontal cross sectional view, and  FIG. 7C  is a vertical cross sectional view of a fourth embodiment of a control valve. 
         FIG. 8A  is a vertical cross sectional view,  FIG. 8B  is a horizontal cross sectional view, and  FIG. 8C  is an exploded cross sectional view of a fifth embodiment of a control valve. 
         FIG. 9  is an exploded cross sectional view of a sixth embodiment of a control valve. 
         FIG. 10A  is an exploded cross sectional view, and  FIG. 10B  is an assembled cross sectional view, of a seventh embodiment of a control valve. 
         FIG. 11A  is an exploded cross sectional view, and  FIG. 11B  is an assembled cross sectional view, of an eight embodiment of a control valve. 
         FIG. 12  is a vertical cross sectional view of a humidifier tank having a drop in control valve. 
         FIG. 13A  is a side view, and  FIG. 13B  is a front view, of a flexible auxiliary liquid reservoir. 
         FIG. 14A  is a side view of a first embodiment of an auxiliary liquid reservoir and electric pump. 
         FIG. 14B  is a side view of a second embodiment of an auxiliary liquid reservoir and electric pump. 
         FIG. 14C  is a side view of a third embodiment of an auxiliary liquid reservoir and electric pump. 
         FIG. 14D  is a side view of a fourth embodiment of an auxiliary liquid reservoir and electric pump. 
     
    
    
     DETAILED DESCRIPTION 
     Some CPAP machines incorporate humidifiers for adding moisture to CPAP air. Conventional CPAP humidifier tanks are designed to hold only enough water for about eight to ten hours of CPAP use (e.g. a few ounces of water) and therefore, requires liquid refilling on a daily basis. The present disclosure proposes use of an auxiliary liquid reservoir connected to a CPAP humidifier tank by a control valve. The auxiliary reservoir holds anywhere from three days to three weeks worth of liquid and therefore, negates the need for daily refills of the CPAP humidifier tank. The control valve regulates flow of liquid from the auxiliary reservoir to the CPAP humidifier tank based on a level of liquid within the humidifier tank. The proposed CPAP humidifier system is described in detail below with reference to  FIGS. 1-14D . 
       FIG. 1  is a schematic view of CPAP humidifier system  10  in accordance with the present disclosure. CPAP humidifier system  10  includes air pump  12 , water tank  14 , air conduit  16 , base  18 , heater  20 , first plug  22 , second plug  24 , pump air outlet  26 , tank air inlet  28 , tank air outlet  30 , tank liquid inlet  32 , control valve  36  liquid conduit  38  having first end  40  and second end  42 , auxiliary reservoir  44 , humidified air conduit  48  having first end  50  and second end  52 , and mask  54 . Air pump  12  pumps air through humidifier tank  14  for increasing humidity of the air before it is delivered to user U. Humidifier tank  14  is connected to auxiliary reservoir  44  through control valve  36 , which regulates an amount of liquid within humidifier tank  14 . 
     In the depicted CPAP humidifier system  10 , air pump  12  is positioned next to humidifier tank  14 . Air conduit  16  connects a side of air pump  12  to an adjacent side of humidifier tank  14 . Both air pump  12  and humidifier tank  14  rest on top of base  18 , which is usually in contact with a floor or other surface in a room. Heater  20  is located between a bottom of humidifier tank  14  and a top of base  18 . First plug  22  electrically connects air pump  12  to a power source (e.g. an outlet) and second plug  24  electrically connects heater  20  (through base  18 ) to a power source (e.g. an outlet). Air pump  12  includes pump air outlet  26  and humidifier tank  14  inlets tank air inlet  28 , which are fluidly connected to one another by air conduit  16 . Humidifier tank  14  further includes tank air outlet  30  and tank liquid inlet  32 , which are commonly located at a top of humidifier tank  14 . 
     When activated or “turned on”, air pump  12  uses electrical energy supplied by first plug  22  to pressurize ambient air. The pressurized air is pumped from air pump  12  to humidifier tank  14 . More specifically, pressurized air exits pump air outlet  26  and travels through air conduit  16  to tank air inlet  28 . When activated or “turned on”, heater  20  uses electrical energy supplied by second plug  24  to vaporize liquid (e.g. turn water into steam). The pressurized air mixes with the vapor to form humidified air within humidifier tank  14 . This humidified air then exits humidifier tank  14  at tank air outlet  30  for use by user U. 
     Control valve  36  is attached to commonly located tank air outlet  30  and tank liquid inlet  32 . Liquid conduit  38  fluidly connects auxiliary reservoir  44  to humidifier tank  14 . More specifically, liquid conduit  38  includes first end  40  attached to control valve  36  and second end  42  attached to auxiliary reservoir  44 . A top of control valve  36  is attached to first end  50  of humidified air conduit  48 , and a bottom of control valve  36  is attached to tank air outlet  30  and tank liquid inlet  32 . Humidified air conduit  48  fluidly connects humidifier tank  14  to mask  54 . More specifically, humidified air conduit  48  includes first end  50  attached to control valve  36  and second end  52  attached to mask  54 . Mask  54  is configured to be secured to a face of user U. 
     Liquid is stored within auxiliary reservoir  44  for supplying liquid to and refilling humidifier tank  14 . Auxiliary reservoir  44  can take many different forms (e.g. flexible or rigid, associated with an electric pump or using gravity, etc.). Fluid flows out of auxiliary reservoir  44 , through liquid conduit  38 , and through control valve  36  to liquid inlet  32  of tank humidifier  14 . For example, auxiliary reservoir can hold between about 0.125-1 gallon (4.73 milliliters-3.8 liters) of fluid, while humidifier tank  14  can hold between about 2-10 ounces (54.1-295.7 milliliters) of fluid. Accordingly, auxiliary reservoir  44  of CPAP humidifier system  10  requires refilling far less frequently than conventional CPAP systems possessing only a tank humidifier and lacking an auxiliary reservoir  44 . Humidified air flows out of tank air outlet  30 , through control valve  36 , through adaptor  46 , and through humidified air conduit  48  to mask  54  for inhalation by user U. With CPAP humidifier system  10 , it is possible to flow both liquid and humidified air through control valve  36  simultaneously. Control valve  36  defines both an air passageway and a liquid passageway as described in more detail below. 
       FIG. 2  is perspective view of humidifier tank  14  having control valve  36  attached to first end  50  of humidified air conduit  48 . Humidifier tank  14  includes tank air inlet  28 , tank air outlet  30 , tank liquid inlet  32 , top  56 , bottom  58 , four walls  60 , and liquid L. Control valve  36  includes top portion  62 , bottom portion  64 , liquid inlet port  66 , shut-off mechanism  68 , and air vents  70 . Control valve  36  is attached to humidifier tank  14  to mange liquid intake from an auxiliary reservoir (e.g auxiliary reservoir  44  in  FIG. 1 ), while simultaneously allowing a flow of humidified air to first end  50  of humidified air conduit  48 . 
     In the depicted embodiment, humidifier tank  14  is transparent to show its interaction with control valve  36 . Humidifier tank  14  is a substantially rectangular box and includes top  56 , opposite bottom  58 , and four side walls  60 . Tank air inlet  28  is an opening located on one side wall  60  of humidifier tank, and is fluidly connected to an air pump (e.g. air pump  12  in  FIG. 1 ). In the depicted embodiment, tank air outlet  30  and tank liquid inlet  32  are a single opening located on top  56  of humidifier tank  14 , which is surrounded by a raised collar (e.g. see collar  72  in  FIG. 3 ). For alternative embodiments, tank air outlet  30  and tank liquid inlet  32  are separate openings and one or both of these openings can be located on side wall  60  of humidifier tank  14 . In a conventional CPAP system, a tank air outlet is directly connected to a humidified air conduit, and there is no tank liquid inlet or control valve. In the presently described embodiment, control valve  36  is attached to tank air outlet  30  to repurpose this space into both tank air outlet  30  and tank liquid inlet  32 . 
     Control valve  36  includes top portion  62 , and an opposite bottom portion  64 . Top portion  62  has first end attached to first end  50  of humidified air conduit  48  and a second end extending through tank air outlet  30  and tank liquid inlet  32 . Bottom portion  64  extends from its attachment to top portion  62  near tank air outlet  30  and tank liquid inlet  32  down into humidifier tank  14 . Liquid inlet port  66  projects from a side of top portion  62  for connection to a liquid conduit (e.g. first end  40  of liquid conduit  38  from  FIG. 1 ). Shut-off mechanism extends  68  from a bottom of bottom portion  64  and is in contact with liquid L within humidifier tank  14 . Vents  70  are oblong openings extending vertically along bottom portion  62 . 
     Pressurized air flows into humidifier tank  14  from tank air inlet  28 . Liquid flows from liquid port  66 , through top portion  62  (extending through tank liquid inlet  32 ) and bottom portion  64  downwardly into humidifier tank  14 . Liquid L collects on bottom  58  of humidifier tank  14  and is contained by side walls  60 . Pressurized air within humidifier tank  14  mixes with vapor to form humidified air. The humidified air flows into vents  70  in bottom portion  62 , upwardly through upper portion  60  (extending through tank air outlet  30 ) and to first end  50  of humidified air conduit  48 . The design of control valve  36  allows the outward flow of humidified air can to occur simultaneously with the inward flow of liquid. When liquid L within humidifier tank  14  reaches a set level, shut-off mechanism  68  is activated to slow or halt the inward flow of liquid L through control valve  36 . In the depicted embodiment, shut-off mechanism  68  includes a float arm and a seal. Alternative designs for control valve  36  including alternative shut-off mechanisms  68  are contemplated and discussed in detail below with reference to  FIGS. 4A-12 . 
       FIG. 3  is a vertical cross sectional view of humidifier tank  14  having a control valve  36  with humidified air conduit  48  removed. Humidifier tank  14  includes tank air inlet  28 , tank air outlet  30 , tank liquid inlet  32 , top  56 , bottom  58 , walls  60 , and liquid L. Control valve  36  includes top portion  62 , bottom portion  64 , liquid inlet port  66 , shut-off mechanism  68 , and air vents  70 . Humidifier tank  14  further includes collar  72 . Control valve  36  further includes neck  74 , shoulder  76 , body  78 , O-rings  79 , seal  80 , arm  82  having first end  84  and second end  86 , and float  88 . Control valve  36  defines air passageway  90  having inlet  92  and outlet  94 , and liquid passageway  96  having inlet  98  and outlet  100 . Control valve  36  simultaneously allows a flow of humidified air to through air passageway  90  and a flow of liquid through liquid passageway  90 . 
     Substantially horizontal top  56  of humidifier tank  14  includes a vertically raised collar  72 , which defines a common, circular, opening for both tank air outlet  30  and tank liquid inlet  32 . A central portion of control valve  36  extends through collar  72  such that top portion  62  is located vertically above collar  72  and outside of humidifier tank  14  while bottom portion  64  is located vertically below collar  72  and inside of humidifier tank  14 . Upper portion  62  of control valve  36  can be further divided into neck  74  and shoulder  76 . Shoulder  76  and neck  74  can be manufactured as individual items and later joined to from upper portion  62 , or they can be manufactured as a single piece. Neck  74  is the topmost portion of upper portion  62  and is sized to mate with (e.g. fit inside of) a humidifier conduit (such as first end  50  of humidifier conduit  48  shown in  FIG. 2 ). Shoulder  76  has a top end attached to neck  74 , and a bottom end abutting a top of collar  72 . Shoulder  76  has a diameter larger than neck  74  and collar  72  such that a bottom end of shoulder  76  rests on top of collar  72  and prevents control valve  36  from falling into humidifier tank  14 . Liquid inlet port  66  extends into a side of shoulder  76 . 
     Neck  74 , shoulder  76 , and body  78  are substantially cylindrical, coaxial and vertically stacked in series. In alternative embodiments, neck  74 , shoulder  76 , and body  78  are rectangular and offset from each other. As shown in  FIG. 3 , shoulder  76  has a largest relative diameter, neck  74  has a middle sized relative diameter, and body  78  has a smallest relative diameter. Body  78  extends vertically from upper portion  62  to lower portion  64  of control valve  36 . A top end of body  78  is attached to a bottom end of shoulder  76  and forms a lip. Body  78  has a diameter smaller than both shoulder  76  and collar  72 , such that body  78  extends through collar  72  into humidifier tank  14 . An outside surface of body  78  and an inside surface of collar  72  can form a light interference fit. Body  78  is the “fitting portion” of control valve  36 . One or more o-rings  79  can be located at a top end of body  78  for providing frictional contact between an outer surface of body  78  and an inside surface of collar  72 . Located more toward a center of body  78  are a plurality of oblong air vents  70  for receiving air into control valve  36 . A bottom end of body  78  is located at lower end  64  of control valve  36  is attached to shut-off mechanism  68 . 
     As shown in  FIG. 3 , each portion of shut-off mechanism  68  is in contact with liquid L. In the depicted embodiment, shut-off mechanism  68  be further divided into seal  80 , arm  82 , and float  88 . Seal  80  is a spherical ball located inside of an opening in the lower end of body  78 . Arm  82  extends horizontally from a lower end of body  78  at a location near seal  80 . More specifically, arm  82  extends from a first end  84  secured to a lower end of body  78  to second end  86  spaced a horizontal distance away from seal  80 . Seal  80  can be made of a resilient material such as rubber or the like. In the depicted embodiment, arm  82  is substantially rectangular and second end  86  is surrounded by substantially cylindrical float  88 . As indicated by its name, float  88  is configured to float such that a top of float  88  is located above a surface of liquid L. Float  88  can be made of a light weight material having a density less than water. In alternative embodiments, float  88  is a hollow structure. 
     Control valve  36  defines substantially cylindrical air passageway  90 . Air passageway  90  is defined by wall that extends through body  78 , shoulder  76 , and neck  74  of control valve  36 . Inlet  92  of air passageway  90  is located centrally on body  78  near air vents  70 . Outlet  94  of air passageway  90  is located at a top end of neck  74 . Humidified air from humidifier tank  14  flows into inlet  92  of air passageway  90  through air vents  70 . Humidified air flows upwardly from inlet  92  along air passageway  90  to outlet  94  in order to exit humidifier tank  14  (air leaves tank air outlet  30  through control valve  36 ). As described with reference to  FIG. 1 , humidified air conduit  48  is attached to control valve  36  for conducting humidified air from humidifier tank  14  to mask  54  for use by user U. More specifically, first end  50  of humidified air conduit  48  is attached to neck  74 , such that outlet  94  of air passageway  90  is fluidly connected to mask  54 . Air passageway  90  is continuously open during both inspiration and exhalation of user U. 
     Control valve  36  also defines substantially cylindrical liquid passageway  96 . Liquid passageway  96  is defined by wall that extends through shoulder  76  and body  78  to shut-off mechanism  68  of control valve  36 . Inlet  98  of liquid passageway is located centrally within shoulder  76  near liquid inlet port  66 . Outlet  100  of liquid passageway  96  is located at lower portion  64  or bottom end of body  78  near shut-off mechanism  68 . Liquid flows from a conduit attached to a liquid reservoir (such as liquid conduit  38  and liquid reservoir  44  from  FIG. 1 ) into inlet  98  of liquid passageway  96  through liquid inlet port  66 . Liquid flows downwardly from inlet  98  along liquid passageway  96  to outlet  100  in order to enter humidifier tank  14  (liquid enters tank liquid inlet  32  through control valve  36 ). In the depicted embodiment, liquid passageway  96  is located concentrically within air passageway  90  although other configurations are contemplated (e.g. see  FIGS. 4A-12 ). 
     Shut-off mechanism  68  is located at outlet  100  of liquid passageway  96 . In the depicted embodiment, outlet  100  of liquid passageway  96  is slightly expanded in relation to the rest of liquid passageway  96  and seal  80  is located in this expanded portion of outlet  100 . As shown in  FIG. 3 , when liquid L levels are relatively high in humidifier tank  14 , float  88  causes arm  82  to raise and form an acute angle with liquid passageway  96 . When arm  82  is raised it pushes seal  80  upwardly into, and forms a seal with, outlet  100  of liquid passageway  96 . Liquid will flow into inlet  98  and fill passageway  96 , but not exit outlet  100  due to seal formed by arm  82  and seal  80 . In other words, shut-off mechanism  68  shuts off the flow of liquid into humidifier tank  14  when liquid level L reaches a set level. The contrast is also true. 
     As liquid L is depleted from vaporization, float  88  will move downwardly with a surface of liquid L. The lowered float will cause arm  82  to drop and form a perpendicular angle or an obtuse angle with liquid passageway  96 . Once arm  82  drops, it no longer forces seal  80  against outlet  100  and seal  80  can drop down out of its sealing arrangement with liquid passageway  96 . Liquid will be free to flow out of outlet  100  and into humidifier tank  14  to replenish the depleted liquid L level. Accordingly, shut-off mechanism  68  responds to a level of liquid L in tank  14  by either blocking or allowing incoming liquid flow. The control over liquid influx is independent of air flowing out of control valve  36 . Liquid can be flowing through control valve  36  or blocked, but humidified air is continuously free to flow out of humidifier tank  14 . Control valve  36  can take many forms as described below with reference to  FIGS. 4A-11 . 
       FIG. 4A  is a vertical cross sectional view, and  FIG. 4B  is a horizontal cross sectional view, of a first embodiment of control valve  36 A. Control valve  36 A includes top portion  62 A, bottom portion  64 A, liquid inlet port  66 A, shut-off mechanism  68 A, air vents  70 A, neck  74 A, shoulder  76 A, body  78 A, seal  80 A, arm  82 A having first end  84 A and second end  86 A, and float  88 A. Control valve  36 A defines air passageway  90 A having inlet  92 A and outlet  94 A, and liquid passageway  96 A having inlet  98 A and outlet  100 A. Humidified air can pass continuously through air passageway  90 A while shut-off mechanism  68 A controls flow of liquid out of liquid passageway  96 A. 
     Control valve  36 A of  FIGS. 4A-4B  is similar to control valve  36  of  FIGS. 1-3 , and like numerals indicate like components. Like control valve  36 , control valve  36 A is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 A differs from control valve  36  in that liquid passageway  96 A is placed to one side of air passageway  90 A, and seal  80 A is triangular. The similarities and differences between control valve  36 A and control valve  36  are described in further detail below. 
     Upper portion  62 A of control valve  36 A can be further divided into neck  74 A and shoulder  76 A. Neck  74 A is the topmost part of upper portion  62 A, and has a bottom end attached to a top end of shoulder  76 A. A bottom end of shoulder  76 A is attached to a top end of body  78 A. Neck  74 A, shoulder  76 A, and body  78 A are substantially cylindrical and vertically stacked in series. Shoulder  76 A has a largest relative diameter, neck  74 A has a middle sized relative diameter, and body  78 A has a smallest relative diameter. Body  78 A extends vertically from upper portion  62 A to lower portion  64 A of control valve  36 A. Located toward a center of body  78 A is a plurality of oblong air vents  70 A for receiving air into control valve  36 A. A bottom end of body  78 A is located at lower end  64 A of control valve  36 A and is attached to shut-off mechanism  68 A. Shut-off mechanism  68 A can be further divided into seal  80 A, arm  82 A, and float  88 A. Seal  80 A is a triangular protrusion attached to first end  84 A of arm  82 A. Arm  82 A extends horizontally from body  78 A at a lower portion  64 A of control valve  36 A. More specifically, arm  82 A extends from first end  84 A secured to the lower portion of body  78 A to second end  86 A spaced a horizontal distance away from first end  84 A. In the depicted embodiment, arm  82 A is substantially rectangular and substantially cylindrical float  88 A extends upwardly form its attachment to second end  86 A. 
     Control valve  36 A defines substantially cylindrical air passageway  90 A and substantially cylindrical liquid passageway  96 A. Air passageway  90 A is defined by one or more walls that extend vertically through body  78 A, shoulder  76 A, and neck  74 A of control valve  36 A. Inlet  92 A of air passageway  90 A is located on body  78 A near air vents  70  toward lower end  64 A of control valve  36 A. Outlet  94 A of air passageway  90 A is located at a top end of neck  74 A and is enlarged in comparison to the rest of air passageway  90 A. Liquid passageway  96 A is defined by one or more walls that extend through shoulder  76 A and body  78 A to shut-off mechanism  68 A of control valve  36 A. Inlet  98 A of liquid passageway extends horizontally into shoulder  76 A from liquid inlet port  66 A at one side. Once within shoulder  76 A, liquid passageway  96 A makes an approximately right angled turn to extend vertically through one side of body  78 A. Outlet  100 A of liquid passageway  96 A is located at lower portion  64 A or bottom end of body  78 A near shut-off mechanism  68 A. Air passageway  90 A is several times wider than liquid passageway  96 A. As shown in  FIG. 4B , liquid passageway  96 A is located within air passageway  90 A, but liquid passageway  96 A is located off to one side of air passageway  90 A. 
     Shut-off mechanism  68 A is located at outlet  100 A of liquid passageway  96 A. When control valve  36 A is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), float  88 A will float on a top surface of the liquid. The flotation of float  88 A causes arm  82 A to assume a raised position such that it extends horizontally across outlet  100 A of liquid passageway  96 A. First end  84 A of arm  82 A will form an approximately right angle with liquid passageway  100 A and push seal  80 A upwardly into outlet  100 A of liquid passageway to prevent liquid from exiting control valve  36 A. Liquid will flow into inlet  98 A and fill passageway  96 A, but not exit outlet  100 A due to seal formed by arm  82 A and seal  80 A. As liquid within the humidifier tank evaporates, float  88 A will move downwardly along with a surface of depleted liquid. The lowered float  88 A will cause arm  82 A to drop and form an obtuse angle with liquid passageway  96 A. Once arm  82 A drops, it no longer forces seal  80 A against outlet  100 A so seal  80 A can move downwardly out of its sealing arrangement with liquid passageway  96 A. Liquid will be free to flow out of outlet  100 A and into the humidifier tank to replenish the depleted liquid level. Accordingly, shut-off mechanism  68 A responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 5A  is a vertical cross sectional view, and  FIG. 5B  is a horizontal cross sectional view, of a second embodiment of control valve  36 B. Control valve  36 B includes top portion  62 B, bottom portion  64 B, liquid inlet port  66 B, shut-off mechanism  68 B, air vents  70 B, neck  74 B, shoulder  76 B, body  78 B, seal  80 B, arm  82 B and float  88 B. Control valve  36 B defines air passageway  90 B having inlet  92 B and outlet  94 B, and liquid passageway  96 B having inlet  98 B and outlet  100 B. Humidified air can pass continuously through air passageway  90 B while shut-off mechanism  68 B controls flow of liquid out of liquid passageway  96 B. 
     Control valve  36 B of  FIGS. 5A-5B  is similar to control valve  36  of  FIGS. 1-3  and control valve  36 A of  FIGS. 4A-4B , and like numerals indicate like components Like control valve  36 , control valve  36 B is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 B differs from control valve  36 A in that liquid passageway  96 B is concentric with air passageway  90 B, and arm  82 B and float  88 B are contained within lower portion  64 B of control valve  36 B. The similarities and differences between control valve  36 B and control valves  36  and  36 A are described in further detail below. 
     Upper portion  62 B of control valve  36 B can be further divided into neck  74 B and shoulder  76 B. Neck  74 B is the topmost part of upper portion  62 B, and has a bottom end attached to a top end of shoulder  76 B. A bottom end of shoulder  76 B is attached to a top end of body  78 B. Neck  74 B, shoulder  76 B, and body  78 B are substantially cylindrical and vertically stacked in series. Shoulder  76 B has a largest relative diameter, neck  74 B has a middle sized relative diameter, and body  78 B has a smallest relative diameter. Body  78 B extends vertically from upper portion  62 B to lower portion  64 B of control valve  36 B. Located toward a center of body  78 B is a plurality of air vents  70 B for receiving air into control valve  36 B. A bottom end of body  78 B is located at lower end  64 B of control valve  36 B and is attached to shut-off mechanism  68 B. Shut-off mechanism  68 B can be further divided into seal  80 B, arm  82 B, and float  88 B. Seal  80 B is a triangular protrusion attached to a center of arm  82 B. Arm  82 B is substantially rectangular and located wholly within body  78 B at lower portion  64 B of control valve  36 B. Located centrally within body  78 B just below a center of arm  82 B is spherical float  88 B. 
     Control valve  36 B defines substantially cylindrical air passageway  90 B and substantially cylindrical liquid passageway  96 B. Air passageway  90 B is defined by one or more walls that extend vertically through body  78 B, shoulder  76 B, and neck  74 B of control valve  36 B. Inlet  92 B of air passageway  90 B is located on body  78 B near air vents  70 B toward lower end  64 B of control valve  36 B. Outlet  94 B of air passageway  90 B is located at a top end of neck  74 B and is enlarged in comparison to the rest of air passageway  90 B. Liquid passageway  96 B is defined by one or more walls that extend through shoulder  76 B and body  78 B to shut-off mechanism  68 B of control valve  36 B. Inlet  98 B of liquid passageway extends horizontally into shoulder  76 B from liquid inlet port  66 B at one side. Near a central location of shoulder  76 B, liquid passageway  96 B makes an approximately right angled turn to extend vertically through body  78 B. Outlet  100 B of liquid passageway  96 B is located at lower portion  64 B or bottom end of body  78 B near shut-off mechanism  68 B. Air passageway  90 B is several times wider than liquid passageway  96 B. As shown in  FIG. 5B , a majority of liquid passageway  96 B (the vertically extending portion in body  78 B) is located concentrically within air passageway  90 A. 
     Shut-off mechanism  68 B is located at outlet  100 B of liquid passageway  96 B. When control valve  36 B is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), float  88 B will float on a top surface of the liquid. The flotation of float  88 B pushes upwardly on arm  82 A which lodges seal  80 B into outlet  100 B of liquid passageway  96 B to prevent liquid from exiting control valve  36 B. Liquid will flow into inlet  98 B and fill passageway  96 B, but not exit outlet  100 B due to seal formed by float  88 B, arm  82 B, and seal  80 B. As liquid within the humidifier tank vaporizes, float  88 B will move downwardly along with a surface of depleted liquid. The lowered float  88 B will allow arm  82 B to drop away from outlet  100 B of liquid passageway  96 B. Once arm  82 B drops, it no longer forces seal  80 B against outlet  100 B. Liquid will be free to flow out of outlet  100 B and into the humidifier tank to replenish the depleted liquid level. Accordingly, shut-off mechanism  68 B responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 6A  is a vertical cross sectional view, and  FIG. 6B  is a horizontal cross sectional view of a third embodiment of control valve  36 C. Control valve  36 C includes top portion  62 C, bottom portion  64 C, liquid inlet port  66 C, shut-off mechanism  68 C, air vents  70 C, neck  74 C, shoulder  76 C, body  78 C, seal  80 C, arm  82 C having first end  84 C and second end  86 C, and float  88 C. Control valve  36 C defines air passageway  90 C having inlet  92 C and outlet  94 C, and liquid passageway  96 C having inlet  98 C and outlet  100 C. Humidified air can pass continuously through air passageway  90 C while shut-off mechanism  68 C controls flow of liquid out of liquid passageway  96 C. 
     Control valve  36 C of  FIGS. 6A-6B  is similar to control valve  36  of  FIGS. 1-3 , control valve  36 A of  FIGS. 4A-4B , and control valve  36 B of  FIGS. 5A-5B , and like numerals indicate like components. Like control valve  36 , control valve  36 C is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 C differs from control valve  36 A in that outlet  100 C of liquid passageway  96 C is located on a side of body  78 C and seal  80 C is pin-shaped. The similarities and differences between control valve  36 C and control valves  36 ,  36 A, and  36 B are described in further detail below. 
     Upper portion  62 C of control valve  36 C can be further divided into neck  74 C and shoulder  76 C. Neck  74 C is the topmost part of upper portion  62 C, and has a bottom end attached to a top end of shoulder  76 C. A bottom end of shoulder  76 C is attached to a top end of body  78 C. Neck  74 C, shoulder  76 C, and body  78 C are substantially cylindrical and vertically stacked in series. Shoulder  76 C has a largest relative diameter, neck  74 C has a middle sized relative diameter, and body  78 C has a smallest relative diameter. Body  78 C extends vertically from upper portion  62 C to lower portion  64 C of control valve  36 C. Located toward a lower portion  64 C are air vents  70 C forming oblong openings into body  78 C for receiving air into control valve  36 C. A bottom end of body  78 C is located at lower end  64 C of control valve  36 C and is attached to shut-off mechanism  68 C. Shut-off mechanism  68 C can be further divided into seal  80 C, arm  82 C, and float  88 C. Seal  80 C is pin-shaped having a tip end and opposite flat end, and is located within body  78 C. The tip end of seal  80 C is located near a center of body  78 C, while the flat end of seal  80 C is in contact with first end  84 C of arm  82 C. Arm  82 C extends horizontally from body  78 C at lower portion  64 C of control valve  36 C. More specifically, arm  82 C extends from first end  84 C secured to the lower portion of body  78 C to second end  86 C spaced a horizontal distance away from first end  84 C. In the depicted embodiment, arm  82 C is substantially rectangular and substantially cylindrical float  88 C extends upwardly form its attachment to second end  86 C. 
     Control valve  36 C defines substantially cylindrical air passageway  90 C and substantially cylindrical liquid passageway  96 C. Air passageway  90 C is defined by one or more walls that extend vertically through body  78 C, shoulder  76 C, and neck  74 C of control valve  36 C. Inlet  92 C of air passageway  90 C is located on body  78 C near air vents  70 C toward lower end  64 C of control valve  36 C. Outlet  94 C of air passageway  90 C is located at a top end of neck  74 C and is enlarged in comparison to the rest of air passageway  90 C. Liquid passageway  96 C is defined by one or more walls that extend through shoulder  76 C and body  78 C. Inlet  98 C of liquid passageway  96 C extends horizontally into shoulder  76 C from liquid inlet port  66 C at one side of control valve  36 C. Once within shoulder  76 C, liquid passageway  96 C makes an approximately right angled turn to extend vertically down one side of body  78 C. Outlet  100 C of liquid passageway  96 C is an opening extending through body  78 C and out of control valve  36 C on the same side of body  78 C as inlet  98 C of liquid passageway  96 C. In the depicted embodiment, outlet  100 C is located centrally along body  78 C above vents  70 C and not far beneath liquid inlet port  66 C. Air passageway  90 C is several times wider than liquid passageway  96 C. As shown in  FIG. 6B , liquid passageway  96 C is located to one side of air passageway  90 C in a thickened portion of a wall defining body  78 C. 
     When control valve  36 C is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), float  88 C will float on a top surface of the liquid. The flotation of float  88 C causes arm  82 C to assume a raised position such that it extends horizontally across the bottom end of body  78 C at lower portion  64 C of control valve  36 C. Arm  82 C will form an approximately right angle with body  78 C and push upwardly on vertical pin seal  80 C. More specifically, first end  84 C of arm  82  will push upwardly on the flat end of seal  80 C. This upward movement of seal  80 C causes the pin end to slide past and block outlet  100 C of liquid passageway to prevent liquid from exiting a side of control valve  36 C. Liquid will flow into inlet  98 C and fill passageway  96 C, but not exit outlet  100 C due to seal formed by arm  82 C and seal  80 C. As liquid within the humidifier tank vaporizes, float  88 C will move downwardly along with a surface of depleted liquid. The lowered float  88 C will cause arm  82 C to drop and form an obtuse angle with liquid passageway  96 C. Once arm  82 C drops, it no longer forces the pin end of seal  80 C past outlet  100 C. Seal  80 C moves downwardly out of its sealing arrangement with outlet  100 C of liquid passageway  96 A. Liquid will be free to flow out of outlet  100 C and into the humidifier tank to replenish the depleted liquid level. Accordingly, shut-off mechanism  68 C responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 7A  is a vertical cross sectional view,  FIG. 7B  is a horizontal cross sectional view, and  FIG. 7C  is a vertical cross sectional view of a fourth embodiment of control valve  36 D. Control valve  36 D includes top portion  62 D, bottom portion  64 D, liquid inlet port  66 D, shut-off mechanism  68 D, air vents  70 D, neck  74 D, shoulder  76 D, and body  78 D. Control valve  36 D defines air passageway  90 D having inlet  92 D and outlet  94 D, liquid passageway  96 D having inlet  98 D and outlet  100 D, and vacuum air vent  102 D. Humidified air can pass continuously through air passageway  90 D while shut-off mechanism  68 D controls flow of liquid out of liquid passageway  96 D. 
     Control valve  36 D of  FIGS. 7A-7C  is similar to control valve  36  of  FIGS. 1-3 , control valve  36 A of  FIGS. 4A-4B , control valve  36 B of  FIGS. 5A-5B , and control valve  36 C of  FIGS. 6A-6B , and like numerals indicate like components. Like control valve  36 , control valve  36 D is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 D differs from control valve  36  in that liquid passageway  96 D and vacuum air vent  102 D are placed to one side of air passageway  90 A, and vacuum air vent  102  forms shut-off mechanism  68 D. The similarities and differences between control valve  36 D and control valves  36 ,  36 A,  36 B, and  36 C are described in further detail below. 
     Upper portion  62 D of control valve  36 D can be further divided into neck  74 D and shoulder  76 D. Neck  74 D is the topmost part of upper portion  62 D, and has a bottom end attached to a top end of shoulder  76 D. A bottom end of shoulder  76 D is attached to a top end of body  78 D. Neck  74 D, shoulder  76 D, and body  78 D are substantially cylindrical and vertically stacked in series. Shoulder  76 D has a largest relative diameter, neck  74 D has a middle sized relative diameter, and body  78 D has a smallest relative diameter. Body  78 D extends vertically from upper portion  62 D to lower portion  64 D of control valve  36 D. Located between a center of body  78 D and lower portion  64 D are a plurality of air vents  70 D openings for receiving air into control valve  36 D. A bottom end of body  78 D is located at lower end  64 D of control valve  36 D 
     Control valve  36 D defines substantially cylindrical air passageway  90 D, substantially cylindrical liquid passageway  96 D, and substantially cylindrical vacuum air vent  102 D. Air passageway  90 D is defined by one or more walls that extend vertically through body  78 D, shoulder  76 D, and neck  74 D of control valve  36 D. Inlet  92 D of air passageway  90 D is located on body  78 D near air vents  70 D toward lower end  64 D of control valve  36 D. Outlet  94 D of air passageway  90 D is located at a top end of neck  74 D and is enlarged in comparison to the rest of air passageway  90 D. Liquid passageway  96 D is defined by one or more walls that extend through shoulder  76 D and body  78 D to lower end  36 D control valve  36 D. Inlet  98 D of liquid passageway extends horizontally into shoulder  76 D from liquid inlet port  66 D at one side of control valve  36 D. Once within shoulder  76 D, liquid passageway  96 D makes an approximately right angled turn to extend vertically downward through one side of body  78 D. Outlet  100 D of liquid passageway  96 D is located at lower portion  64 D or bottom end of body  78 D. Vacuum air vent  102 D is located next to liquid passageway  96 D and follows the same trajectory through control valve  36 D. Air passageway  90 D is several times wider than liquid passageway  96 D. As shown in  FIG. 4B , liquid passageway  96 D is located to one side of air passageway  90 D and is adjacent vacuum air vent  102 D. 
     Extending along with liquid passageway  96 D is air vent  102 . Like liquid passageway  96 D, vacuum air vent  102 D is defined by one or more walls that extend through shoulder  76 D and body  78 D to lower end  36 D control valve  36 D. An inlet of vacuum air vent  102 D is located at lower portion  64 D or bottom end of body  78 D right next to outlet  100 D of liquid passageway  96 D. Vacuum air vent  102 D extends vertically upward through one side of body  78 D alongside liquid passageway  96 D. Once within shoulder  76 D, vacuum air vent  102 D makes an approximately right angled turn to its outlet located at liquid inlet port  66 D adjacent inlet  98 D of liquid passageway  96 D. In the depicted embodiment, shut-off mechanism  68 D is vacuum air vent  102 D, which functions as a vacuum seal to regulate the flow of liquid through control valve  36 D. 
     To use control valve  36 D, a liquid conduit (such as liquid conduit  38  shown in  FIG. 1 ) should additionally include an air conduit. The dual fluid conduit is attached to liquid inlet port  66 D and provides liquid to liquid passage  96 D while simultaneously providing for air to escape out of vacuum air vent  102 D. When control valve  36 D is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), a top surface of liquid will touch both outlet  100 D of liquid passageway  39 D and outlet of vacuum air vent  102 D. Since air cannot escape from the humidifier tank through vacuum air vent  102 D, liquid is prevented from exiting outlet  100 D of liquid passageway  96 D. As liquid within the humidifier tank vaporizes, a top surface of liquid will no longer be in contact with outlet  100 D of liquid passageway  96 D and the inlet of vacuum air vent  102 D. Since air can escape from tank through vacuum air vent  102 D, liquid will be free to flow out of outlet  100 D and into the humidifier tank to replenish the depleted liquid level. Accordingly, vacuum air vent  102 D functions as shut-off mechanism  68 D that responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 8A  is a vertical cross sectional view,  FIG. 8B  is a horizontal cross sectional view, and  FIG. 8C  is an exploded vertical cross sectional view, of a fifth embodiment of control valve  36 E. Control valve  36 E includes top portion  62 E, bottom portion  64 E, liquid inlet port  66 E, shut-off mechanism  68 E, neck  74 E, shoulder  76 E, body  78 E, seal  80 E, arm  82 E having first end  84 E and second end  86 E, float  88 E. Control valve  36 E defines air passageway  90 E having inlet  92 E and outlet  94 E, and liquid passageway  96 E having inlet  98 E and outlet  100 E. Control valve  36 E further includes tube  104 E having first end  106 E and second end  108 E, and valve block  110 E having top  112 E, bottom  114 E, first cavity  116 E, second cavity  118 E, and pin  120 E. Humidified air can pass continuously through air passageway  90 E while shut-off mechanism  68 E controls flow of liquid out of liquid passageway  96 E. 
     Control valve  36 E of  FIGS. 8A-8C  is similar to control valve  36  of  FIGS. 1-3 , control valve  36 A of  FIGS. 4A-4B , control valve  36 B of  FIGS. 5A-5B , control valve  36 C of  FIGS. 6A-6B , and control valve  36 D of  FIGS. 7A-7C , and like numerals indicate like components. Like control valve  36 , control valve  36 E is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 E differs from control valve  36  in that valve  36 E is formed in discrete pieces, tube  104 E connects upper portion  62 E to lower portion  64 E, and seal  80 E is triangular. The similarities and differences between control valve  36 E and control valves  36 ,  36 A,  36 B,  36 C, and  36 D are described in further detail below. 
     Upper portion  62 E of control valve  36 E can be further divided into neck  74 E and shoulder  76 E. Neck  74 E is the topmost part of upper portion  62 E, and has a bottom end attached to a top end of shoulder  76 E. A bottom end of shoulder  76 E is attached to a top end of body  78 E. Neck  74 E, shoulder  76 E, and body  78 E are substantially cylindrical and vertically stacked in series. Shoulder  76 E has a largest relative diameter, neck  74 E has a middle sized relative diameter, and body  78 E has a smallest relative diameter. Body  78 E extends vertically downwards from shoulder  76 E a relatively short distance. Lower end  64 E of control valve  36 E is spaced a distance from lower end of body  78 E by tube  104 E. A first end  106 E of tube  104 E extends into a lower end of body  78 E and a second end  108 E of tube  104 E is attached to valve block  110 E. Second end  108 E of tube  104 E extends through top  112 E and into first cavity  116 E of valve block  110 E. Shut-off mechanism  68 E, including seal  80 E, arm  82 E and float  88 E, is attached to bottom  114 E of valve block  110 E. Seal  80 E is a triangular protrusion attached to first end  84 E of arm  82 E. Seal  80 E extends upwardly into second cavity  118 E on bottom  114 E of valve block  110 E. Arm  82 E extends horizontally from bottom  114 E of valve block  110 E at lower portion  64 E of control valve  36 E. More specifically, arm  82 E extends from first end  84 E secured to the bottom  114  of valve block  110  to second end  86 E spaced a horizontal distance away from first end  84 E. In the depicted embodiment, arm  82 E is substantially rectangular and substantially cylindrical float  88 E extends upwardly form its attachment to second end  86 E. 
     Control valve  36 E defines substantially cylindrical air passageway  90 E and substantially cylindrical liquid passageway  96 E. Air passageway  90 E is defined by one or more walls that extend vertically through body  78 E, shoulder  76 E, and neck  74 E of control valve  36 E. Inlet  92 E of air passageway  90 E is located at a bottom end of body  78 E. Outlet  94 E of air passageway  90 E is located at a top end of neck  74 E and is enlarged in comparison to the rest of air passageway  90 E. Liquid passageway  96 E is defined by one or more walls that extend through shoulder  76 E and body  78 E, as well as by tube  104 E, and first and second cavities  114 E,  116 E extending through valve block  110 E. Inlet  98 E of liquid passageway extends horizontally into shoulder  76 E from liquid inlet port  66 E at one side. Once within shoulder  76 E, liquid passageway  96 E makes an approximately right angled turn to extend vertically through one side of body  78 E. Liquid passageway  96 E continues from body  78 E, through the length of tube  104 E and through first cavity  116 E and second cavity  118 E of valve block  110 E. Outlet  100 E of liquid passageway  96 E is located at second cavity  118 E of valve block  110 E near bottom  114 E and shut-off mechanism  68 E. Air passageway  90 E is several times wider than liquid passageway  96 E, but liquid passageway  96 E is about twice as long as air passageway  96 E. As shown in  FIG. 8B , liquid passageway  96 E is located next to air passageway  90 E with liquid passageway  96 E being located to one side of air passageway  90 E. 
     Control valve  36 E is assembled by inserting first end  106 E of tube  104 E into liquid passageway  96 E defined in body  78 E, and by inserting second end  108 E of tube  104 E into liquid passageway  96 E defined in first cavity  116 E of valve block  110 E. Shut-off mechanism  68 E is secured to bottom  114 E of valve block  110 E by snapping first end  84 E or arm  82 E into attachment with valve block  110 E or by passing pin  120 E through openings in both arm  82 E and valve block  110 E. Shut-off mechanism  68 E is located at outlet  100 E of liquid passageway  96 E. 
     When control valve  36 E is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), float  88 E will float on a top surface of the liquid. The flotation of float  88 E causes arm  82 E to assume a raised portion such that it extends horizontally across outlet  100 E of liquid passageway  96 E. First end  84 E of arm  82 E will form an approximately right angle with liquid passageway  100 E and push seal  80 E upwardly into outlet  100 E of liquid passageway to prevent liquid from exiting control valve  36 E. Liquid will flow into inlet  98 E and fill passageway  96 E, but not exit outlet  100 E due to seal formed by arm  82 E and seal  80 E. As liquid within the humidifier tank evaporates, float  88 E will move downwardly along with a surface of depleted liquid. The lowered float  88 E will cause arm  82 E to drop and form an obtuse angle with liquid passageway  96 E. Once arm  82 E drops, it no longer forces seal  80 E against outlet  100 E. Seal  80 E moves downwardly out of its sealing arrangement with liquid passageway  96 E. Liquid will be free to flow out of outlet  100 E and into the humidifier tank to replenish the depleted liquid level. Accordingly, shut-off mechanism  68 E responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 9  is an exploded cross sectional view of a sixth embodiment of control valve  36 F. Control valve  36 F includes top portion  62 F, bottom portion  64 F, liquid inlet port  66 F, shut-off mechanism  68 F, neck  74 F, shoulder  76 F, body  78 F, seal  80 F, arm  82 F having first end  84 F and second end  86 F, float  88 F. Control valve  36 F defines air passageway  90 F having inlet  92 F and outlet  94 F, and liquid passageway  96 F having inlet  98 F and outlet  100 F. Control valve  36 F further includes tube  104 F having first end  106 F and second end  108 F, pin cavity  122 F, pin  124 F, and flap  126 F. Humidified air can pass continuously through air passageway  90 F while shut-off mechanism  68 F controls flow of liquid out of liquid passageway  96 F. 
     Control valve  36 F of  FIG. 9  is similar to control valve  36  of  FIGS. 1-3 , control valve  36 A of  FIGS. 4A-4B , control valve  36 B of  FIGS. 5A-5B , control valve  36 C of  FIGS. 6A-6B , control valve  36 D of  FIGS. 7A-7C , and control valve  36 E of  FIGS. 8A-8C , and like numerals indicate like components. Like control valve  36 , control valve  36 F is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 F differs from control valve  36  in that valve  36 F is formed in discrete pieces, tube  104 F connects upper portion  62 F to lower portion  64 F, seal  80 F is triangular, and float  88 F includes flap  126 F. The similarities and differences between control valve  36 F and control valves  36 ,  36 A,  36 B,  36 C,  36 D, and  36 E are described in further detail below. 
     Neck  74 F is the topmost part of upper portion  62 F and extends vertically upward from shoulder  76 F. Liquid inlet port  66 F also extends vertically upward from shoulder  76 F parallel to neck  74 F. Shoulder  76 F extends horizontally between a bottom of neck  74 F and liquid inlet port  66 F and a top of body  78 F. Neck  74 F and body  78 F are substantially cylindrical and vertically stacked, but neck  74 F is offset to one side of body  78 F. Body  78 F extends vertically downwards from neck  74 F and shoulder  76 F a relatively short distance. Lower end  64 F of control valve  36 F is spaced a distance from lower end of body  78 F by tube  104 F. A first end  106 F of tube  104 F extends into a lower end of body  78 F, and a second end  108 F of tube  104 F is attached to shut-off mechanism  68 F. Pin hole  122 F extends upwardly into second end  108 F of tube  104 F, and pin  124 F extends upwardly from first end  84 F of arm  82 F. Pin  124 F is snapped into pin hole  122 F to attach arm  82 F to tube  104 F. Seal  80 F is a triangular protrusion attached to first end  84 F of arm  82 F next to pin  124 F. Seal  80 F extends upwardly into second end  108 F of tube  104 F. Arm  82 F extends horizontally from first end  84 F to second end  86 F spaced a horizontal distance away from first end  84 F. In the depicted embodiment, arm  82 F is substantially rectangular and substantially rectangular float  88 F extends upwardly form its attachment to second end  86 F. In the depicted embodiment, float  88 F is molded as an open structure and then assembled into a box by moving flap  126 F to snap into place as a top that defines hollow internal space of float  88 F. 
     Control valve  36 F defines substantially cylindrical air passageway  90 F and substantially cylindrical liquid passageway  96 F. Air passageway  90 F is defined by one or more walls that extend vertically through body  78 F, shoulder  76 F, and neck  74 F of control valve  36 F. Inlet  92 F of air passageway  90 F is located at a bottom end of body  78 F. Outlet  94 F of air passageway  90 F is located at a top end of neck  74 F and is enlarged in comparison to the rest of air passageway  90 F. Liquid passageway  96 F is defined by one or more walls that extend through shoulder  76 F and body  78 F, as well as by tube  104 F. Inlet  98 F of liquid passageway  96 F extends vertically downward from liquid inlet port  66 F through shoulder  76 F and through one side of body  78 F. From body  78 F, liquid passageway  96 F continues the length of tube  104 F. Outlet  100 F of liquid passageway  96 F is located second end  108 F of tube  104 F. Air passageway  90 F is wider than liquid passageway  96 F, and liquid passageway  90 F is longer than air passageway  90 F. 
     Control valve  36 F is assembled by inserting first end  106 F of tube  104 F into liquid passageway  96 F defined in body  78 F. Shut-off mechanism  68 E is secured to tube  104 F by snapping pin  124 F into its mating relationship with pin hole  122 F. So assembled, shut-off mechanism  68 F is located at outlet  100 F of liquid passageway  96 F. When control valve  36 F is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), float  88 F will float on a top surface of the liquid. The flotation of float  88 F causes arm  82 F to assume a raised position such that it extends horizontally across outlet  100 F of liquid passageway  96 F. First end  84 F of arm  82 F will form an approximately right angle with liquid passageway  100 F and push seal  80 F upwardly into outlet  100 F of liquid passageway  96 F to prevent liquid from exiting control valve  36 F. Liquid will flow into inlet  98 F and fill passageway  96 F, but not exit outlet  100 F due to seal formed by arm  82 F and seal  80 F. As liquid within the humidifier tank evaporates, float  88 F will move downwardly along with a surface of depleted liquid. The lowered float  88 F will cause arm  82 F to drop and form an obtuse angle with liquid passageway  96 F. Once arm  82 F drops, it no longer forces seal  80 F against outlet  100 F. Seal  80 F moves downwardly out of its sealing arrangement with liquid passageway  96 F. Liquid will be free to flow out of outlet  100 F and into the humidifier tank to replenish the depleted liquid level. Accordingly, shut-off mechanism  68 F responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 10A  is an exploded cross sectional view, and  FIG. 10B  is an assembled cross sectional view, of a seventh embodiment of control valve  36 G. Control valve  36 G includes top portion  62 G, bottom portion  64 G, liquid inlet port  66 G, shut-off mechanism  68 G, neck  74 G, shoulder  76 G, body  78 G, seal  80 G, arm  82 G having first end  84 G and second end  86 G, float  88 G. Control valve  36 G defines air passageway  90 G having inlet  92 G and outlet  94 G, and liquid passageway  96 G having inlet  98 G and outlet  100 G. Control valve  36 G further includes tube  104 G having first end  106 G and second end  108 G, and flange  126 G, nipple  128 G, cavity  130 G, and seal housing  132 G. Humidified air can pass continuously through air passageway  90 G while shut-off mechanism  68 G controls flow of liquid out of liquid passageway  96 G. 
     Control valve  36 G of  FIGS. 10A-10B  is similar to control valve  36  of  FIGS. 1-3 , control valve  36 A of  FIGS. 4A-4B , control valve  36 B of  FIGS. 5A-5B , control valve  36 C of  FIGS. 6A-6B , control valve  36 D of  FIGS. 7A-7C , control valve  36 E of  FIGS. 8A-8C , and control valve  36 F of  FIG. 9 , and like numerals indicate like components. Like control valve  36 , control valve  36 G is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 G differs from control valve  36  in that valve  36 G is formed in discrete pieces, tube  104 G extends through liquid inlet port  66 G, and through body  78 G to shut-off mechanism  68 G, and valve  80 G is rectangular. The similarities and differences between control valve  36 G and control valves  36 ,  36 A,  36 B,  36 C,  36 D,  36 E, and  36 F are described in further detail below. 
     Upper portion  62 G of control valve  36 G can be further divided into neck  74 G and shoulder  76 G. Neck  74 G is the topmost part of upper portion  62 G, and has a bottom end attached to a top end of shoulder  76 G. A bottom end of shoulder  76 G is attached to a top end of body  78 G. Liquid inlet port  66 G is an opening extending horizontally into shoulder  76 G. Neck  74 G, shoulder  76 G, and body  78 EG are substantially cylindrical and vertically stacked in series. When viewed in vertical cross section, neck  74 G, shoulder  76 G, and body  78 G are rectangular in shape. Shoulder  76 G has a largest relative diameter, neck  74 G has a middle sized relative diameter, and body  78 G has a smallest relative diameter. Body  78 G extends vertically downwards from shoulder  76 G to lower end  64 G of control valve  36 G. One vertical side of body  78 G is closed, but an opening extends into the opposite vertical side of body  78 G for receiving air. 
     Tube  104 G is a flexible conduit that extends through control valve  36 G from liquid inlet port  66 G to shut off mechanism  68 G. A first end  106 G of tube  104 G extends horizontally through liquid inlet port  66 G. Once through shoulder  76 G, tube  104 G curves vertically downward to extend through body  78 G. Second end  108 G of tube  104 G cooperates with shutoff mechanism  68 G at lower end  64 G of control valve  36 G. Bottom end of body  78 G has horizontally extending flange  126 G. Nipple  128 G extends vertically upwards from a center of flange  126 G for receiving second end  108 G of tube  104 G. Cavity  130 G extends into a side of flange  126 G for coupling with arm  82 G. Shut-off mechanism  68 G, including seal  80 G, arm  82 G and float  88 G, is attached to flange  130 G at a bottom end of body  78 G. Seal  80 G is substantially rectangular and housed within a bottom end of a substantially rectangular seal housing  132 G. First end  84 G of arm  84 G cooperates with cavity  130 G to attach arm  82 G to flange  126 G. First end  84 G of arm  82 G extends horizontally through an upper end of seal housing  132 G. Second end  86 G of arm  82 G is attached to float  88 G. Accordingly, arm  82 G extends from first end  84 G to second end  86 G spaced a horizontal distance away from first end  84 G. In the depicted embodiment, arm  82 G is substantially cylindrical and substantially rectangular float  88 G extends form its attachment to second end  86 G. 
     Control valve  36 G defines substantially cylindrical air passageway  90 G and substantially cylindrical liquid passageway  96 G. Air passageway  90 G is defined by one or more walls that extend vertically through body  78 G, shoulder  76 G, and neck  74 G of control valve  36 G. Inlet  92 G of air passageway  90 G is the opening located at a bottom end of body  78 G. Outlet  94 G of air passageway  90 G is located at a top end of neck  74 G. Liquid passageway  96 G is defined mostly by tube  104 G. Inlet  98 G of liquid passageway  98 G extends horizontally into shoulder  76 G from liquid inlet port  66 G at one side. Once within shoulder  76 G, liquid passageway  98 G makes an approximately right angled turn to extend vertically through body  78 G. Liquid passageway  98 G continues the length of tube  104 G to second end  108 G, which is attached to nipple  128 G. Liquid passageway  98 G extends through a center of nipple  128 G to outlet  100 G located at bottom end of flange  126 G. Outlet  100 G of liquid passageway  96 G is located at shut-off mechanism  68 G. Air passageway  90 G is several times wider than liquid passageway  96 G. As shown in  FIG. 10B , liquid passageway  96 G is located within air passageway  90 G when both are extending through body  78 G. 
     Control valve  36 G is assembled by inserting second end  108 G of tube  104 G through liquid inlet port  66 G and body  78 G. Second end  108 G of tube  104 G is attached to nipple  128 G on flange  108 G, and first end  106 G of tube  104 G extends out of liquid inlet port  66 G. Shut-off mechanism  68 G is secured to body  78 G by snapping first end  84 G or arm  82 G into attachment with opening  130 G in flange  126 G. Seal  80 G is placed the bottom end of seal housing  132 G, and first end  84 G of arm  82 G extends through the upper end of seal housing  132 G. Float  88 G is secured to second end  86 G of arm  82 G. So assembled, shut-off mechanism  68 G is located at outlet  100 G of liquid passageway  96 G. 
     When control valve  36 G is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), float  88 G will float on a top surface of the liquid. The flotation of float  88 G causes arm  82 G to assume a raised portion such that it extends horizontally across outlet  100 G of liquid passageway  96 G. First end  84 G of arm  82 G will form an approximately right angle with liquid passageway  100 G and pull seal housing  132 G including seal  80 G upwardly toward outlet  100 G of liquid passageway to prevent liquid from exiting control valve  36 G. Liquid will flow into inlet  98 G and fill passageway  96 G/tube  104 G, but not exit outlet  100 G due to seal formed by arm  82 G and seal  80 G. As liquid within the humidifier tank evaporates, float  88 G will move downwardly along with a surface of depleted liquid. The lowered float  88 G will cause arm  82 G to drop and form an obtuse angle with liquid passageway  96 G. Once arm  82 G drops, it no longer forces seal  80 G against outlet  100 G. Seal  80 G moves downwardly out of its sealing arrangement with liquid passageway  96 G. Liquid will be free to flow out of outlet  100 G and into the humidifier tank to replenish the depleted liquid level. Accordingly, shut-off mechanism  68 G responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 11A  is an exploded cross sectional view, and  FIG. 11B  is an assembled cross sectional view, of an eighth embodiment of control valve  36 H. Control valve  36 H includes top portion  62 H, bottom portion  64 H, liquid inlet port  66 H, shut-off mechanism  68 H, neck  74 H, shoulder  76 H, body  78 H, seal  80 H, arm  82 H having first end  84 H and second end  86 H, and float  88 H. Control valve  36 H defines air passageway  90 H having inlet  92 H and outlet  94 H, and liquid passageway  96 H having inlet  98 H and outlet  100 H. Control valve  36 H further includes tube  104 H having first end  106 H and second end  108 H, and valve block  110 H having top  112 H, bottom  114 H, cavity  116 H, and pin  120 H. Humidified air can pass continuously through air passageway  90 H while shut-off mechanism  68 H controls flow of liquid out of liquid passageway  96 H. 
     Control valve  36 H of  FIGS. 11A-11B  is similar to control valve  36  of  FIGS. 1-3 , control valve  36 A of  FIGS. 4A-4B , control valve  36 B of  FIGS. 5A-5B , control valve  36 C of  FIGS. 6A-6B , control valve  36 D of  FIGS. 7A-7C , control valve  36 E of  FIGS. 8A-8C , control valve  36 F of  FIG. 9 , and control valve  36 G of  10 A- 10 B, and like numerals indicate like components. Like control valve  36 , control valve  36 H is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 H differs from control valve  36  in that valve  36 H is formed in discrete pieces, tube  104 H extends through liquid inlet port  66 H, and through body  78 H to shut-off mechanism  68 H, and valve  80 H is rectangular. The similarities and differences between control valve  36 H and control valves  36 ,  36 A,  36 B,  36 C,  36 D,  36 E,  36 F, and  36 G are described in further detail below. 
     Upper portion  62 H of control valve  36 H can be further divided into neck  74 H and shoulder  76 H. Neck  74 H is the topmost part of upper portion  62 H, and has a bottom end that receives a top end of shoulder  76 H. A bottom end of shoulder  76 H is attached to a top end of body  78 H. Shoulder  76 H and body  78 H can be integrally formed. Liquid inlet port  66 H is an opening or window extending into one side of shoulder  76 H. Neck  74 H, shoulder  76 H, and body  78 EH are substantially cylindrical and vertically stacked in series. Shoulder  76 H has a largest relative diameter, neck  74 H has a middle sized relative diameter, and body  78 H has a smallest relative diameter. Body  78 H extends vertically downwards from shoulder  76 H to lower end  64 H of control valve  36 H. The bottom end of body  78 G is open for receiving air. 
     Tube  104 H is a rigid conduit that extends through control valve  36 H from liquid inlet port  66 H to shut off mechanism  68 H. First end  106 H of tube  104 H extends horizontally through liquid inlet port  66 H, and is trapped between a top end of shoulder  78 H and a bottom end of neck  74 H. Once through shoulder  76 H, tube  104 H curves vertically downward to extend through body  78 H. Second end  108 H of tube  104 H cooperates with shutoff mechanism  68 H at lower end  64 H of control valve  36 H. Shut-off mechanism  68 H, including seal  80 H, arm  82 H and float  88 H, is attached to valve block  110 H, which is suspending from tube  104 H. Second end  108 H of tube  104 H extends through top  114 H and into cavity  116 H of valve block  110 H. Seal  80 H is substantially rectangular and housed within valve block  110 H near bottom  114 H. Arm  82 H extends horizontally from valve block  110 H at lower portion  64 H of control valve  36 H. More specifically, arm  82 H extends from first end  84 H secured to the bottom  114 H of valve block  110 H by pin  120 H, to second end  86 H spaced a horizontal distance away from first end  84 H. In the depicted embodiment, arm  82 H is substantially cylindrical and substantially rectangular float  88 H is attached to second end  86 J. 
     Control valve  36 H defines substantially cylindrical air passageway  90 H and substantially cylindrical liquid passageway  96 H. Air passageway  90 H is defined by one or more walls that extend vertically through body  78 H, shoulder  76 H, and neck  74 H of control valve  36 H. Inlet  92 H of air passageway  90 H is the opening located at a bottom end of body  78 H. Outlet  94 H of air passageway  90 H is located at a top end of neck  74 H. Liquid passageway  96 H is defined mostly by tube  104 H. Inlet  98 H of liquid passageway  98 H extends horizontally into shoulder  76 H from liquid inlet port  66 H at one side. Once within shoulder  76 H, liquid passageway  98 H makes an approximately right angled turn to extend vertically through body  78 H. Liquid passageway  98 H continues the length of tube  104 H to second end  108 H, which is attached to cavity  116 H of valve body  110 H. Liquid passageway  98 H extends through cavity  116 H to outlet  100 H located in valve body  110 H. Outlet  100 H of liquid passageway  96 H is located at shut-off mechanism  68 H (seal  80 H and arm  82 H). Air passageway  90 H is several times wider than liquid passageway  96 H. As shown in  FIG. 11B , liquid passageway  96 H is located within air passageway  90 H when both are extending through body  78 H. 
     Control valve  36 H is assembled by inserting second end  108 H of tube  104 H through liquid inlet port  66 H and body  78 H. Top end of shoulder  76 H is then inserted into the bottom end of neck  74 H, thereby trapping first end  98 H of tube  104 H between a bottom end of neck  74 H and a top end of shoulder  76 H at liquid inlet port  66 H. First end  98 H of tube  104 H should extend horizontally out of liquid inlet port  66 H. Second end  108 H of tube  104 H is secured to shut-off mechanism  68 H. Shut-off mechanism  68 H is secured to body  78 H by inserting second end  108 H of tube  104 H into cavity  116 H of valve body  110 H. Seal  80 G is inserted into valve block  110 H near liquid outlet  100 H. First end  84 H of arm  82 H is secured to valve body  110 H by pin  120 H or other suitable means of attachment. Float  88 H is secured to second end  86 H of arm  82 H. So assembled, arm  82 H and seal  80 H form shut-off mechanism  68 H located at outlet  100 H of liquid passageway  96 H. 
     When control valve  36 H is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), float  88 H will float on a top surface of the liquid. The flotation of float  88 H causes arm  82 H to assume a raised portion such that it extends horizontally across outlet  100 H of liquid passageway  96 H. First end  84 H of arm  82 H will form an approximately right angle with liquid passageway  96 H and pull seal  80 H upwardly toward outlet  100 H of liquid passageway  96 H to prevent liquid from exiting control valve  36 H. Liquid will flow into inlet  98 H and fill passageway  96 H/tube  104 H, but not exit outlet  100 H due to seal formed by arm  82 H and seal  80 H. As liquid within the humidifier tank evaporates, float  88 H will move downwardly along with a surface of depleted liquid. The lowered float  88 H will cause arm  82 H to drop and form an obtuse angle with liquid passageway  96 H. Once arm  82 H drops, it no longer forces seal  80 H against outlet  100 H. Seal  80 H moves downwardly out of its sealing arrangement with liquid passageway  96 H. Liquid will be free to flow out of outlet  100 H and into the humidifier tank to replenish the depleted liquid level. Accordingly, shut-off mechanism  68 H responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 12  a vertical cross sectional view of humidifier tank  14 I having drop in control valve  36 I. Humidifier tank  14 I includes tank air inlet  28 I and collar  72 I. Control valve  36 I includes top portion  62 I, bottom portion  64 I, liquid inlet port  66 I, shut-off mechanism  68 I, neck  74 I, shoulder  76 I, seal  80 I, air passageway  90 I having inlet  92 I and outlet  94 I, and liquid passageway  96 I having inlet  98 I and outlet  100 I, tube  104 I having first end  106 I and second end  108 I, nipple  128 I, seal housing  132 I, and retainer  133 I. Control valve  36 I simultaneously allows a flow of humidified air to through air passageway  90 I and a flow of liquid through liquid passageway  96 I. 
     Control valve  361  of  FIG. 12  is similar to control valve  36  of  FIGS. 1-3 , control valve  36 A of  FIGS. 4A-4B , control valve  36 B of  FIGS. 5A-5B , control valve  36 C of  FIGS. 6A-6B , control valve  36 D of  FIGS. 7A-7C , control valve  36 E of  FIGS. 8A-8C , control valve  36 F of  FIG. 9 , control valve  36 G of  FIGS. 10A-10B , and control valve  36 H of  FIGS. 11A-11B , and like numerals indicate like components. Like control valve  36 , control valve  36 I is configured to be inserted into tank air outlet  30  of humidifier tank  14 . Control valve  36 I differs from control valve  36  in that valve  36 I lacks body  78 , tube  104 I extends through liquid inlet port  66 I to shut-off mechanism  681 , and float  80 I doubles as a seal. The similarities and differences between control valve  36 I and control valves  36 ,  36 A,  36 B,  36 C,  36 D,  36 E,  36 F,  36 G, and  36 H are described in further detail below. 
     Humidifier tank  14 I includes a vertically raised collar  72 I, which defines a common, circular, opening for both tank air outlet  30 I and tank liquid inlet  32 I. Upper portion  62 I of control valve  36 I extends around collar  72 I such with some of upper portion  62 I located vertically above collar  72 I. Upper portion  62 I of control valve  36 I can be further divided into neck  74 I and shoulder  76 I. Neck  74 I, shoulder  76 I are substantially cylindrical and vertically stacked in series. Neck  74 I is the topmost portion of upper portion  62 I and is sized to mate with (e.g. fit inside of) a humidifier conduit (such as first end  50  of humidifier conduit  48  shown in  FIG. 2 ). Shoulder  76 I has a top end attached to neck  74 I, and a bottom end surrounding collar  72 I. Shoulder  76 I has a diameter larger than neck  74 I and collar  72 I and is configured to fit over collar  72 I. An outside surface of collar  72 I and an inside surface of neck  74 I can form a light interference fit. Liquid inlet port  66 I extends into a side of shoulder  76 I. 
     Tube  104 I is a flexible conduit that extends through control valve  36 I from liquid inlet port  66 I to shut off mechanism  68 I. First end  106 I of tube  104 I extends horizontally through liquid inlet port  66 I. Once through shoulder  76 I, tube  104 I curves vertically downward through the bottom open end of shoulder  76 I and into tank  14 I. Second end  108 I of tube  104 I cooperates with shutoff mechanism  68 I at lower end  64 I of control valve  36 I. Nipple  128 I extends vertically upwards from a valve housing  132 I to receive second end  108 GI of tube  104 GI. In the embodiment depicted, second end  108 I of tube  104 I extends over nipple  128 I thereby securing tube  104 I to shut-off mechanism  64 I. Opening or window  701  extends into a side of seal housing  132 I to allow fluid follow into seal housing  132 I. Seal housing  132 I has an interior cavity for housing seal  80 I, which doubles as a float. Retainer  133 I is attached to and extends across a bottom of seal housing  132 I to retain float or housing seal  80 I. Retainer  133  can also function as a ballast to help control buoyancy and positioning of seal housing  132 I within a tank. Both seal  80 I and seal housing  132 I can be substantially rectangular, cylindrical, or any other suitable shape. 
     Control valve  36 I defines substantially cylindrical air passageway  90 I and substantially cylindrical liquid passageway  96 I. Air passageway  90 I is defined by one or more walls that extend vertically through shoulder  76 I and neck  74 I of control valve  36 G. Inlet  92 I of air passageway  90 I is the opening located at a bottom end of shoulder  76 I. Outlet  94 I of air passageway  90 I is located at a top end of neck  74 I. Liquid passageway  96 I is defined mostly by tube  104 I. Inlet  98 I of liquid passageway  96 I extends horizontally into shoulder  76 I from liquid inlet port  66 I at one side. Once within shoulder  76 I, liquid passageway  98 I makes an approximately right angled turn to extend vertically out of the bottom end of shoulder  96 I and into tank  14 . Liquid passageway  98 I continues the length of tube  104 I to second end  108 I, which is attached to nipple  128 I. Liquid passageway  98 I extends through a center of nipple  128 I to outlet  100 I located within seal housing  132 I. Outlet  100 I of liquid passageway  96 I is located at shut-off mechanism  68 I. Air passageway  90 I is several times wider than liquid passageway  96 I, and liquid passageway  96 I is several times longer than air passageway  90 I. As shown in  FIG. 12 , liquid passageway  96 I is located within air passageway  90 I when both are extending through shoulder  76 I. Control valve  36 I is assembled by inserting second end  108 I of tube  104 I through liquid inlet port  66 I and into tank  14 I. Second end  108 I of tube  104 I is attached to nipple  128 I on seal housing  132 I, and first end  106 I of tube  104 I extends out of liquid inlet port  66 I. Float seal  80 I is placed the bottom end of seal housing  132 I to function as shut-off mechanism  68 I for outlet  100 I of liquid passageway  96 I. 
     When control valve  36 I is placed in a humidifier tank where liquid levels are relatively high (see  FIG. 3 ), float seal  80 I will float on a top surface of the liquid. The flotation of float seal  80 I pushes float seal  80 I upwardly in seal housing  132 I toward outlet  100 I of liquid passageway  96 I to prevent liquid from exiting control valve  36 I. Liquid will flow into inlet  98 I and fill passageway  96 I/tube  104 I, but not exit outlet  100 I due to seal formed by float seal  80 I. As liquid within the humidifier tank evaporates, float seal  80 I will move downwardly along with a surface of depleted liquid. The lowered float seal  80 I will drop downwardly within seal housing  132 I and no longer press against outlet  100 I. Liquid will be free to flow out of outlet  100 I and into humidifier tank  14 I to replenish the depleted liquid level. Accordingly, shut-off mechanism  68 I responds to a level of liquid in humidifier tank by either blocking or allowing incoming liquid flow. 
       FIG. 13A  is a side view, and  FIG. 13B  is a front view, of flexible auxiliary liquid reservoir  134 . Depicted in  FIGS. 13A-13B  is auxiliary liquid reservoir  134  having grommets  136  for cooperating with hooks  138  on wall  140 . Also shown are body  142 , reservoir liquid outlet  144 , conduit inlet  146 , and liquid conduit  148 . Auxiliary liquid reservoir  134  is an alternative reservoir for providing liquid to a CPAP humidifier tank. 
     Auxiliary liquid reservoir  134  is similar to auxiliary reservoir  44  shown in  FIG. 1 . A top of auxiliary liquid reservoir  134  includes apertures or grommets  136  for receiving hooks  138  extending from wall  140 . In alternative embodiments, hooks  138  are attached to a movable stand or any other suitable furniture or surface. Body  142  of auxiliary liquid reservoir  134  is flexible, and can be formed from flexible plastic or the like. Body  142  may resemble an IV bag and contains a volume of liquid L. Liquid L may also include additives such as medicines or aroma therapy. Reservoir liquid outlet  144  is located at a bottom of body  142  and can include a quick connect fixture. Conduit inlet  146  is secured to reservoir liquid outlet  144  and can include a quick connect fixture for easily connecting and forming a fluid connection between auxiliary liquid reservoir  134  and liquid conduit  148 . 
     Auxiliary liquid reservoir  134  of  FIGS. 13A and 13B  functions similarly to auxiliary liquid reservoir  44  of  FIG. 1 . Liquid L flows from auxiliary reservoir  134  through fluid conduit  148  to a control valve and humidifier tank to replenish liquid in the humidifier tank (e.g. see liquid conduit  38  connecting auxiliary reservoir  44  to control valve  36  and humidifier tank  14 ). If liquid L contains medication or aroma, then the medication or aroma is also added to the humidifier tank through a control valve. Auxiliary liquid reservoir  134  is hung by grommets  136  a vertical distance about a humidifier to allow gravity to urge liquid L out of auxiliary liquid reservoir  134  through liquid conduit  148  to a control valve and humidifier tank. As described below with reference to  FIGS. 14A-14D , auxiliary liquid reservoir can alternatively be attached to a pump. 
       FIG. 14A  is a side view of a first embodiment of auxiliary liquid reservoir  142 A and electric pump  152 A. Depicted in  FIG. 14A  are auxiliary liquid reservoir  134 A, body  142 A, reservoir liquid outlet  144 A, conduit inlet  146 A, liquid conduit  148 A, connecting conduit  150 A, electric pump  152 A, and electric plug  154 A. Auxiliary liquid reservoir  134 A is equipped with electric pump  152 A for pumping liquid L from auxiliary reservoir  134 A to a CPAP humidifier tank. 
     Auxiliary liquid reservoir  134 A is similar to auxiliary reservoir  44  shown in  FIG. 1 . Body  142 A of auxiliary liquid reservoir  134 A is pliable but sturdy, can be formed from plastic, and contains liquid L. Reservoir liquid outlet  144 A is located at a bottom of body  142 A. Connecting conduit  150 A is attached to, and fluidly connects, reservoir liquid outlet  144 A to a side of electric pump  152 A. Auxiliary liquid reservoir  134 A is placed side-by-side with electric pump  152 A. Conduit inlet  146 A of liquid conduit  148 A is attached to a top of electric pump  152 A. Liquid conduit  148 A is intended to fluidly connect electric pump  152 A to a control valve secured into a humidifier tank. When connected to a power source such as an outlet, electric plug  154 A provides power to electric pump  152 A. In alternative embodiments, electric plug  154 A is omitted and electric pump  152 A includes a battery as a power source. 
     Auxiliary liquid reservoir  134 A of  FIG. 14A  functions similarly to auxiliary liquid reservoir  44  of  FIG. 1 . Liquid L flows out of auxiliary reservoir  134 A at reservoir liquid outlet  144 A, and through connection conduit  150 A to electric pump  152 A. Electric pump  152 A pumps liquid L through conduit inlet  146 A and along fluid conduit  148 A to a control valve and humidifier tank to replenish liquid in the humidifier tank (e.g. see liquid conduit  38  connecting auxiliary reservoir  44  to control valve  36  and humidifier tank  14  of  FIG. 1 ). Auxiliary liquid reservoir  134 A is associated with electric pump  152 A to negate the need for gravity in flowing liquid L. In contrast to auxiliary liquid reservoir  134  shown in  FIGS. 13A-13B , auxiliary liquid reservoir  134 A can be placed anywhere and need not be hung vertically above a CPAP humidifier tank to function as intended. As described below with reference to  FIGS. 14B-14D , auxiliary liquid reservoir  134 A can be attached to electric pump  152 B in a variety of other ways. 
       FIG. 14B  is a side view of a second embodiment of auxiliary liquid reservoir  142 B and electric pump  152 B. Depicted in  FIG. 14B  are auxiliary liquid reservoir  134 B, body  142 B, reservoir liquid outlet  144 B, conduit inlet  146 B, liquid conduit  148 B, connecting conduit  150 B, electric pump  152 B, and electric plug  154 B. Auxiliary liquid reservoir  134 B is equipped with electric pump  152 B for pumping liquid L from auxiliary reservoir  134 B to a CPAP humidifier tank. 
     Auxiliary liquid reservoir  134 B is similar to auxiliary liquid reservoir  44  of  FIG. 1  and auxiliary liquid reservoir  134 A of  FIG. 14A . Body  142 B of auxiliary liquid reservoir  134 B is pliable but sturdy, can be formed from plastic, and contains liquid L. In the depicted embodiment, auxiliary liquid reservoir  134 A is an “off the shelf” gallon jug of water. Reservoir liquid outlet  144 B is located at a top of body  142 B. Connecting conduit  150 B is attached to, and fluidly connects, reservoir liquid outlet  144 B to a bottom of electric pump  152 B. In the embodiment depicted, connecting conduit  150 B extends into body  142 B of auxiliary liquid reservoir  134 B. Electric pump  152 B is located vertically above auxiliary liquid reservoir  134 B and a bottom of electric pump  152 B can be in contact with a top of auxiliary liquid reservoir  134 B. Conduit inlet  146 B of liquid conduit  148 B is attached to a top of electric pump  152 B. Liquid conduit  148 B is intended to fluidly connect electric pump  152 B to a control valve to a humidifier tank. When connected to a power source such as an outlet, electric plug  154 B provides power to electric pump  152 B. In alternative embodiments, electric plug  154 B is omitted and electric pump  152 B includes a battery as a power source. 
     Auxiliary liquid reservoir  134 B of  FIG. 14B  functions similarly to auxiliary liquid reservoir  44  of  FIG. 1  and auxiliary liquid reservoir  134 A of  FIG. 14A . Liquid L is pulled out of auxiliary reservoir  134 B at reservoir liquid outlet  144 B by connection conduit  150 A and into electric pump  152 A. Electric pump  152 B pumps liquid L through conduit inlet  146 B and along fluid conduit  148 B to a control valve and humidifier tank to replenish liquid in the humidifier tank (e.g. see liquid conduit  38  connecting auxiliary reservoir  44  to control valve  36  and humidifier tank  14  in  FIG. 1 ). Auxiliary liquid reservoir  134 B is associated with electric pump  152 B to negate the need for gravity in flowing liquid L to a CPAP humidifier tank. In contrast to auxiliary liquid reservoir  134  shown in  FIGS. 13A-13B , auxiliary liquid reservoir  134 B can be placed anywhere and need not be hung vertically above a CPAP humidifier tank to function as intended. As described below with reference to  FIGS. 14C-14D , auxiliary liquid reservoir  134 B can be attached to electric pump  152 B in a variety of other ways. 
       FIG. 14C  is a side view of a third embodiment of auxiliary liquid reservoir  142 C and electric pump  152 C. Depicted in  FIG. 14C  are auxiliary liquid reservoir  134 C, body  142 C, reservoir liquid outlet  144 C, conduit inlet  146 C, liquid conduit  148 C, connecting conduit  150 C, electric pump  152 C, and electric plug  154 C. Auxiliary liquid reservoir  134 C is equipped with electric pump  152 C for pumping liquid L from auxiliary reservoir  134 C to a CPAP humidifier tank. 
     Auxiliary liquid reservoir  134 C is similar to auxiliary liquid reservoir  44  of  FIG. 1 , auxiliary liquid reservoir  134 A of  FIG. 14A , and auxiliary liquid reservoir  134 B of  FIG. 14B . Body  142 C of auxiliary liquid reservoir  134 C is pliable but sturdy, can be formed from plastic, and contains liquid L. In the depicted embodiment, auxiliary liquid reservoir  134 B is an “off the shelf” bottle of water. Reservoir liquid outlet  144 C is located at a bottom of body  142 C. Connecting conduit  150 C is attached to, and fluidly connects, reservoir liquid outlet  144 C to a top of electric pump  152 C. In the embodiment depicted, connecting conduit  150 C extends upwardly into body  142 C of auxiliary liquid reservoir  134 C. Electric pump  152 C is located vertically below auxiliary liquid reservoir  134 C and a top of electric pump  152 C can be in contact with a bottom of auxiliary liquid reservoir  134 C. Conduit inlet  146 C of liquid conduit  148 C is attached to a top of electric pump  152 C next to auxiliary liquid reservoir  164 C. Liquid conduit  148 C is intended to fluidly connect electric pump  152 C to a control valve attached to a humidifier tank. When connected to a power source such as an outlet, electric plug  154 C provides power to electric pump  152 C. In alternative embodiments, electric plug  154 C is omitted and electric pump  152 C includes a battery as a power source. 
     Auxiliary liquid reservoir  134 C of  FIG. 14C  functions similarly to auxiliary liquid reservoir  44  of  FIG. 1 , auxiliary liquid reservoir  134 A of  FIG. 14A , and auxiliary liquid reservoir  134 B of  FIG. 14B . Liquid L flows out of auxiliary reservoir  134 C at reservoir liquid outlet  144 C by connection conduit  150 C and into electric pump  152 C. Electric pump  152 C pumps liquid L through conduit inlet  146 C and along fluid conduit  148 C to a control valve and humidifier tank to replenish liquid in the humidifier tank (e.g. see liquid conduit  38  connecting auxiliary reservoir  44  to control valve  36  and humidifier tank  14  in  FIG. 1 ). Auxiliary liquid reservoir  134 C is associated with electric pump  152 C to negate the need for gravity in flowing liquid L to a CPAP humidifier tank. In contrast to auxiliary liquid reservoir  134  shown in  FIGS. 13A-13B , auxiliary liquid reservoir  134 C can be placed anywhere and need not be hung vertically above a CPAP humidifier tank to function as intended. As described below with reference to  FIG. 14D , auxiliary liquid reservoir  134 C can be attached to electric pump  152 C in other ways. 
       FIG. 14D  is a side view of a fourth embodiment of auxiliary liquid reservoir  142 D and electric pump  152 D. Depicted in  FIG. 14D  are auxiliary liquid reservoir  134 D, body  142 D, reservoir liquid outlet  144 D, conduit inlet  146 D, liquid conduit  148 D, connecting conduit  150 D, electric pump  152 D, and electric plug  154 D. Auxiliary liquid reservoir  134 D is equipped with electric pump  152 D for pumping liquid L from auxiliary reservoir  134 D to a CPAP humidifier tank. 
     Auxiliary liquid reservoir  134 D is similar to auxiliary liquid reservoir  44  of  FIG. 1 , auxiliary liquid reservoir  134 A of  FIG. 14A , auxiliary liquid reservoir  134 B of  FIG. 14B , and auxiliary liquid reservoir  134 C of  FIG. 14C . Body  142 D of auxiliary liquid reservoir  134 D is pliable but sturdy, can be formed from plastic, and contains liquid L. In the depicted embodiment, auxiliary liquid reservoir  134 D is an “off the shelf” bottle of water. Reservoir liquid outlet  144 D is located at a top of body  142 D. Connecting conduit  150 D is attached to, and fluidly connects, reservoir liquid outlet  144 D to a top of electric pump  152 D. In the embodiment depicted, connecting conduit  150 D extends upwardly from electric pump and then downwardly into body  142 D of auxiliary liquid reservoir  134 D. Electric pump  152 D includes a space for supporting auxiliary liquid reservoir  134 D, such that a top electric pump  152 D can be in contact with a bottom of auxiliary liquid reservoir  134 D. Conduit inlet  146 D of liquid conduit  148 D is attached to a top of electric pump  152 D next to auxiliary liquid reservoir  134 D. Liquid conduit  148 D is intended to fluidly connect electric pump  152 D to a control valve attached to a humidifier tank. When connected to a power source such as an outlet, electric plug  154 D provides power to electric pump  152 D. In alternative embodiments, electric plug  154 D is omitted and electric pump  152 D includes a battery as a power source. 
     Auxiliary liquid reservoir  134 D of  FIG. 14D  functions similarly to auxiliary liquid reservoir  44  of  FIG. 1 , auxiliary liquid reservoir  134 A of  FIG. 14A , auxiliary liquid reservoir  134 B of  FIG. 14B , and auxiliary liquid reservoir  134 C of  FIG. 14C . Liquid L is pulled out of auxiliary reservoir  134 D at reservoir liquid outlet  144 D by connection conduit  150 D and into electric pump  152 D. Electric pump  152 D pumps liquid L through conduit inlet  146 D and along fluid conduit  148 D to a control valve and humidifier tank to replenish liquid in the humidifier tank (e.g. see liquid conduit  38  connecting auxiliary reservoir  44  to control valve  36  and humidifier tank  14  in  FIG. 1 ). Auxiliary liquid reservoir  134 D is associated with electric pump  152 D to negate the need for gravity in flowing liquid L to a CPAP humidifier tank. In contrast to auxiliary liquid reservoir  134  shown in  FIGS. 13A-13B , auxiliary liquid reservoir  134 D can be placed anywhere and need not be hung vertically above a CPAP humidifier tank to function as intended. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.