Patent Publication Number: US-6988332-B2

Title: Air driven liquid pump

Description:
FIELD OF THE INVENTION 
   The present invention relates to the general field of maple sap collecting equipment and is particularly concerned with an air driven pump. 
   BACKGROUND OF THE INVENTION 
   Since the days of the colonists, in the Northern United States and Canada, maple syrup and related sugar products have been manufactured by tapping maple sap from hard maple trees ( Acer Saccharinum ) typically in late winter or early spring. Heat is then applied from an open fire or confined flame against the bottom of a vaporizer tank or tub within which the maple tree sap is placed to concentrate the sap and produce maple syrup. 
   Indeed, maple sap containing 2% to 3% sugar as it comes from the tree has no maple flavor and no color. The characteristic flavor and maple color result from the reactions that occur when the maple sap is evaporated and concentrated to the syrup form by boiling. 
   Typically, the maple sap is fed into an upwardly open flue pan supported over a wood or coal fire and collecting the concentrated maple syrup which failed to be evaporated by the evaporation process. Evaporators of every type are used to manufacture maple sugar, sorghum and similar types of syrup or sugar products. 
   Maple syrup sugar producers are typically individuals or families working in so-called “sugar shacks” sometimes with limited electrical power. Maple sap is typically carried from the maple tree to the sugar shack either by conventional methods using horses to carry the sap collected in buckets through the sometimes rugged terrain leading to the shack or through a more modern method using hydraulic lines fluidly coupled both to the maple tree at one end and to a collecting vessel adjacent the sugar shack. 
   When the more modem method using fluid tubes or lines is favored, the maple sap emanating from the trees, commonly referred to as maple water, is carried through the hydraulic line towards the sugar shack by gravity. Although a negative pressure or vacuum is created in the hydraulic line, the vacuum is used essentially for extracting the sap from the maple tree as opposed to being used for carrying the sap towards the sugar shack. 
   Accordingly, sugar shacks are typically located at a low level terrain relative to the trees being sapped. However, even in ideal situations wherein the sapped trees are all located above the sugar shack, there sometimes exists a situation wherein the hydraulic line, because of the rugged terrain, must travel at a level lower than that of the sugar shack. 
   Hence, in such situations, maintaining proper flow of the sugar water to the sugar shack becomes problematic. Accordingly, there exists a need for providing a suitable method of somehow pumping the maple water located at a level underneath a sugar shack to a level higher than the latter so that the sap collecting system may continue to use gravity to induce flow of the maple water towards the sugar shack. 
   Several types of mechanical pumping mechanisms for transferring fluid from a lower to a higher level are known and are in wide use. Two of the most common types of pumps are the so-called dynamic or momentum-change pumps and the so-called positive displacement pumps. 
   Dynamic pumps add momentum to a fluid by means of rapidly moving blades, fans or the like. As the fluid moves through open passages and discharges into a diffuser section, its momentum is increased and its velocity converted into an increased pressure. Dynamic pumps include rotodynamic or rotary type pumps such as axial flow, centrifugal or radial exit flow and mixed flow pumps. They also include so-called injector pumps, fluid activated types such as gas lift and hydraulic ram pumps and electromagnetic pumps. 
   Positive displacement pumps all generally have some types of moving boundary that forces fluid to move by volume changes. The fluid is admitted through an inlet into a cavity, which then closes, and the fluid is squeezed through an outlet. Common examples of positive displacement pumps include reciprocating and rotary types. Reciprocating types use a plunger, a piston or diaphragm as the moving boundary. Rotary types use one or more sliding vanes, helical screws, gears or the like. 
   Such conventional pumps require several moving components having a relatively large mass or density. These components are subject to relative large accelerations and frictions require costly and time-consuming maintenance and are also prone to wear and vibrations. Typically, they also require elaborate lubrication, cooling and control systems involving additional components. Also, they usually typically require some means for priming the system prior to effective operation and are subject to damage due to neglect by the operator. 
   Accordingly, they are not well-suited to being used in the specific context of maple sap hydraulic lines. They are also not suitable for many other types of contexts requiring a relatively simple yet effective means of locally increasing the level of a liquid in a hydraulic system subjected to a vacuum. Accordingly, there exists a need for a maple sap collecting line pumping system. 
   SUMMARY OF THE INVENTION 
   It is general object of the present invention to provide an improved air driven liquid pump that can be used maple sap collecting line pumping system or any other suitable context. 
   In accordance with the present invention, there is provided an air driven liquid pump for pumping a target volume of liquid emanating from a liquid inlet duct into a liquid outlet duct, both the liquid inlet and outlet ducts being subjected to at least a partial air vacuum, the liquid inlet and outlet ducts being fluidly coupled together respectively upstream from the liquid pump and downstream from the liquid pump by a by-pass duct extending therebetween, the liquid pump comprising: a reservoir having a reservoir wall enclosing a reservoir chamber; a liquid inlet aperture extending through the reservoir wall for fluid coupling to the liquid inlet duct; a liquid outlet aperture extending through the reservoir wall for fluid coupling to the liquid outlet duct, the liquid outlet aperture being in fluid communication with an outlet level inside the reservoir chamber located below the liquid inlet aperture and corresponding to a predetermined lower threshold value of the volume of the liquid within the reservoir chamber; an air aperture extending through the reservoir wall for pneumatically coupling the reservoir chamber with the atmospheric air located exteriorly to the reservoir; a liquid inlet valve operationally coupled to the liquid inlet aperture, the liquid inlet valve being operable between a liquid valve open configuration and a liquid valve closed configurations for respectively allowing and preventing the flow of a fluid through the liquid inlet aperture; an air valve operatively coupled to the air aperture, the air valve being operable between an air valve open configuration and an air valve closed configurations for respectively allowing and preventing the flow of air through the air aperture; a volume responsive first actuating means for selectively moving the liquid inlet valve to the liquid valve closed configuration and the air valve to the air valve open configuration upon the volume of liquid within the reservoir reaching a predetermined upper threshold value; a volume and pressure responsive second actuating means for selectively moving the liquid inlet valve to the liquid valve open configuration and the air valve to the air valve closed configuration upon the volume of liquid within the reservoir reaching the predetermined lower threshold value and the pressure differential between the air pressure inside and outside the reservoir reaching a predetermined differential threshold; whereby with the liquid inlet valve in the liquid valve open configuration and the air valve in the air valve closed configuration the liquid is allowed to flow into the reservoir chamber for filling the latter while the pressure inside the reservoir chamber is lowered by the at least partial air vacuum at a level lower then that of the atmospheric pressure outside the reservoir so as to create a pressure differential therebetween, when the volume of liquid within the reservoir chamber reaches the predetermined upper threshold value the first actuating means opens the air valve allowing the air pressure inside the reservoir chamber to rise so as to pump out the liquid inside the reservoir chamber through the liquid outlet aperture and, the first actuating means also substantially simultaneously; closes the liquid inlet valve so as to prevent liquid flow into the reservoir and so as to maintain the at least partial vacuum in the liquid inlet duct through the by-pass duct for maintaining the liquid inlet valve in the liquid valve closed configuration while the liquid is being pumped out of the reservoir chamber, when the volume of liquid inside the reservoir chamber falls to the lower threshold value, the air now allowed to flow out of the reservoir chamber through the liquid outlet aperture lowers the pressure inside the reservoir chamber to the predetermined differential threshold allowing the second actuating means to move the liquid inlet valve to the liquid valve open configuration and the air valve to the air valve closed configuration for a new cycle to begin. 
   Typically, the liquid pump further comprises a float component mounted within the reservoir chamber for buoyantly moving within the reservoir chamber according to the level of liquid contained therein, the float component allowing selective opening and closing of the liquid inlet valve depending on the level of liquid contained in the reservoir chamber. 
   Conveniently, the liquid pump further comprises a float component mounted within the reservoir chamber for buoyantly moving within the reservoir chamber according to the level of liquid contained therein, the float component allowing selective opening and closing of the air valve depending on the level of liquid contained in the reservoir chamber. 
   Typically, the liquid pump further comprises a float component mounted within the reservoir chamber for buoyantly moving within the reservoir chamber according to the level of liquid contained therein, the float component allowing selective opening and closing of the liquid inlet valve depending on the level of liquid contained in the reservoir chamber; the liquid inlet valve including a liquid valve seat, the float component including a liquid valve sealing plate for abuttingly and sealingly contacting the liquid valve seat when the level of liquid contained within the reservoir chamber reaches the predetermined upper threshold value. 
   Conveniently, the float component includes a float component buoyant section pivotally attached to the reservoir wall by a pivotable float arm, the liquid valve sealing plate being mechanically coupled to the float arm, the liquid valve sealing plate being configured, sized and positioned so as to abuttingly and sealingly contact the liquid valve seat when the level of liquid contained within the reservoir chamber reaches the predetermined upper threshold value. 
   Typically, the reservoir wall includes a wall upper segment, the liquid inlet aperture extending through the wall upper segment, the float arm being pivotally attached to the wall upper segment; the float arm including an arm actuating segment and a substantially perpendicular arm spacing segment, the liquid valve sealing disc being mounted on the arm actuating segment. 
   Conveniently, the liquid pump further comprises a float component mounted within the reservoir chamber for buoyantly moving within the reservoir chamber according to the level of liquid contained therein, the float component allowing selective opening and closing of the air valve depending on the level of liquid contained in the reservoir chamber; the air valve including an air valve seat and an air valve sealing plate for abuttingly and sealingly contacting the air valve seat when the air valve is in the air valve closed configuration; the float component being adapted to move the air valve sealing plate away from the air valve seat when the level of liquid contained within the reservoir chamber reaches the predetermined upper threshold value. 
   Typically, the air valve includes an air valve actuating arm, the air valve actuating arm being attached adjacent a longitudinal end thereof to the air valve sealing plate, the air valve actuating arm having an opposed distal end thereof extending into the reservoir chamber for contacting the float component and allowing the latter to move the air valve sealing plate away from the air valve seat when the level of liquid contained within the reservoir chamber reaches the predetermined upper threshold value. 
   Conveniently, the reservoir wall includes a wall upper segment, the air inlet aperture extending through the wall upper segment, the float arm being pivotally attached to the wall upper segment; the float arm including an arm actuating segment and a substantially perpendicular arm spacing segment, the air valve actuating arm being adapted to contact the arm actuating segment. 
   Typically, the air valve includes an air valve body mounted across the wall upper segment, the air inlet aperture being in fluid communication with an air valve flow channel extending through the air valve body; the air valve actuating arm being slidably inserted within an air valve arm receiving channel also extending through the air valve body. 
   Conveniently, the liquid pump further comprises a reservoir spacing tube extending from the liquid outlet aperture to the outlet level. 
   Typically, the reservoir wall includes a wall upper segment and a wall lower segment, the liquid outlet aperture extending through the wall upper segment; the reservoir spacing tube establishing fluid communication between the liquid outlet aperture and the outlet level, the outlet level being positioned substantially adjacent to the wall lower segment. 
   Conveniently, the reservoir spacing tube is provided with a relatively small vacuum aperture extending therethrough for facilitating the outflow of the air contained within the reservoir chamber as the latter is being filled by the liquid. 
   Typically, the liquid pump further comprises a chamber drain for allowing selective drainage of the liquid contained in the reservoir chamber. 
   Conveniently, the chamber drain prevents drainage of the liquid contained in the reservoir chamber when a predetermined level of vacuum is present is the reservoir chamber and allows drainage of the liquid contained in the reservoir chamber when the vacuum level within the reservoir chamber is lower then the predetermined level of vacuum. 
   Typically, the reservoir wall includes a wall lower segment, the chamber drain including a drainage aperture extending through the wall lower segment and a drain valve; the drain valve including a drain valve seat and a drain valve ball mounted within perforated ball enclosure for movement selectively in and out of sealing engagement with the drain valve seat depending on the pressure differential between the air pressure in and out of the reservoir chamber. 
   In accordance with the present invention, there is also provided a method for pumping maple sap emanating from a maple tree through a liquid inlet duct into an liquid outlet duct having a portion thereof located at a higher level then the liquid inlet duct, the method using a liquid pump comprising: a reservoir having a reservoir wall enclosing a reservoir chamber; a liquid inlet aperture extending through the reservoir wall for fluid coupling to the liquid inlet duct; a liquid outlet aperture extending through the reservoir wall for fluid coupling to the liquid outlet duct, the liquid outlet aperture being in fluid communication with an outlet level inside the reservoir chamber located below the liquid inlet aperture and corresponding to a predetermined lower threshold value of the volume of the liquid within the reservoir chamber; an air aperture extending through the reservoir wall for pneumatically coupling the reservoir chamber with the atmospheric air located exteriorly to the reservoir; a liquid inlet valve operationally coupled to the liquid inlet aperture, the liquid inlet valve being operable between a liquid valve open configuration and a liquid valve closed configurations for respectively allowing and preventing the flow of a fluid through the liquid inlet aperture; an air valve operatively coupled to the air aperture, the air inlet valve being operable between an air valve open configuration and an air valve closed configurations for respectively allowing and preventing the flow of air through the air aperture; a volume responsive first actuating means for selectively moving the liquid inlet valve to the liquid valve closed configuration and the air valve to the air valve open configuration upon the volume of liquid within the reservoir reaching a predetermined upper threshold value; a volume and pressure responsive second actuating means for selectively moving the liquid inlet valve to the liquid valve open configuration and the air valve to the air valve closed configuration upon the volume of liquid within the reservoir reaching the predetermined lower threshold value and the pressure differential between the air pressure inside and outside the reservoir reaching a predetermined differential threshold; the method comprising the steps of: 
   hydraulically coupling the liquid inlet duct to the liquid inlet aperture and the liquid outlet duct to the liquid outlet aperture; providing a by-pass duct for fluidly coupling the liquid inlet and outlet ducts respectively upstream and downstream from the liquid pump; 
   creating a vacuum in the liquid inlet and outlet ducts. 
   Advantages of the present invention include that the proposed pumping system allow a liquid flowing through a partially or fully vacuumed hydraulic circuitry to be raised against the action of gravity to a higher level. 
   Also, the proposed system is specifically designed to be used in various settings including settings wherein electrical or other types of energy are scarce. More specifically, the proposed pumping system is designed so as to be usable without external sources of energy outside that created by the vacuum in the hydraulic circuitry. 
   Furthermore, the proposed pumping system is designed so as to be reliable without requiring elaborate maintenance with a minimal amount of moving parts, thus being less subject to friction, wear and vibration. 
   Still furthermore, the proposed pumping system is designed so as to be manufacturable using conventional forms of manufacturing so as to provide a pumping system that will be economically feasible, long-lasting and relatively trouble-free in operation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be disclosed, by way of example, in reference to the following drawings in which: 
       FIG. 1 : in a schematic elevational view, illustrates part of a pumping system in accordance with an embodiment of the present invention, the pumping system being shown fluidly connected to collecting ducts and attached to a schematized maple tree; 
       FIG. 2 : in a cross-sectional view, illustrates some of the components part of the pumping system shown in  FIG. 1 , the components being shown as a negative pressure is being built in the hydraulic circuitry and a small quantity of maple sap enters the pumping system container; 
       FIG. 3 : in a cross-sectional view, illustrates some of the internal components of the pumping system shown in  FIGS. 1 and 2  as the level of liquid within the container rise while the air inlet valve part of the system remains in a closed configuration; 
       FIG. 4 : in a cross-sectional view, illustrates some of the components of the pumping system shown in  FIGS. 1 through 3  as the level of water within the container continues to rise and the air inlet valve remains in a closed configuration; 
       FIG. 5 : in a cross-sectional view, illustrates some of the components of the pumping system shown in  FIGS. 1 through 4  as the level of water within the container has risen to a level such that the air inlet valve is open and the liquid inlet valve is closed; 
       FIG. 6 : in a cross-sectional view, illustrates some of the components of the pumping system shown in  FIGS. 1 through 5  as the emptied container presents a closed air inlet valve and an open liquid inlet valve. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , there is shown in a schematic partial view, an air driven liquid pump in accordance with an embodiment of the present invention generally designated by the reference numeral  10 . The liquid pump  10  is shown fluidly coupled to a hydraulic circuitry used for carrying maple sap emanating from maple trees such as schematically represented and identified by the reference numeral  12  to a sugar shack (not shown but located at a higher level than the liquid pump  10  and arbitrarily located in a direction towards the left hand side of  FIG. 1 ). It should be understood that the liquid pump  10  could be used in other contexts and with other types of hydraulic circuitry without departing from the scope of the present invention. 
   The liquid pump is typically used for pumping a target volume of liquid, such as maple sap, emanating from a liquid inlet duct  14  into a liquid outlet duct  16 . Both the liquid inlet and outlet ducts  14 , 16  are subjected to at least a partial air vacuum. The air vacuum is created by a vacuum pump typically located adjacent to or in a sugar shack (not shown). The vacuum pump (not shown) is calibrated and used for extracting the maple sap from maple trees such as the maple tree schematically represented and indicated by the reference numeral  12 . 
   The outlet duct  16  is typically fluidly coupled to another segment of the hydraulic circuitry which may or may not incorporate another liquid pump  10 , or to a maple sap collecting tank located inside or adjacent to the sugar shack (not shown). The liquid inlet and outlet ducts  14 ,  16  are fluidly coupled together respectively upstream and downstream from the liquid pump  10  by a bypass duct  18  extending therebetween. In  FIG. 1 , the flow direction of the maple sap within ducts  14 ,  16  is indicated schematically by the thinner arrows  20 , while the flow direction of air within ducts  14 ,  16  and  18  created by the vacuum pump is indicated schematically by the thicker arrows  22 . 
   The hydraulic circuitry, including the liquid pump  10 , is typically maintained above the ground surface  24  by a corresponding circuitry supporting system. The circuitry supporting system may take any suitable form without departing from the scope of the present invention. In the embodiment shown in  FIG. 1 , the circuitry supporting system includes supporting cables  26  attached to the ducts  14 ,  16  and/or  18  using conventional cable-to-duct attachment rings  28 . The supporting cables  26  are typically suspended to the maple trees  12  by forming a loop around the tree truck thereof, the loop being typically secured by a cable attachment clap  30 . 
   Referring now more specifically to  FIG. 2 , there is shown some of the components of the liquid pump  10 . The liquid pump  10  includes a tank or reservoir  32  for collecting the maple sap or liquid  34 . The reservoir  32  has a reservoir wall enclosing a reservoir chamber  36 . 
   Although the reservoir  32  is shown in the Figures as having a substantially parallelepiped-shaped configuration, it should be understood that the reservoir  32  could have other configurations without departing from the scope of the present invention. 
   Typically, the reservoir wall includes a wall upper segment  38 , a wall lower segment  40  and a wall peripheral segment  42  extending therebetween. 
   The liquid pump  10  also includes a liquid inlet aperture  44  extending through the reservoir wall for fluid coupling to the liquid inlet duct  14 . In the embodiment shown throughout the Figures, the liquid pump  10  includes a conventional inlet fitting such as a substantially L-shaped inlet fitting  46  for fluidly coupling the liquid inlet duct  14  to the reservoir chamber  36 . It should however be understood that other types of coupling could be used without departing from the scope of the present invention. 
   The liquid pump  10  also includes a liquid outlet aperture  48  extending through the reservoir wall for fluid coupling to the liquid outlet duct  16 . The liquid outlet aperture  48  is in fluid communication with an outlet level inside the reservoir chamber  36  located below the liquid inlet aperture  44  and corresponding to a predetermined lower threshold value of the volume of the liquid within the reservoir chamber  36 . 
   In the embodiment shown throughout the Figures, the liquid outlet aperture is put into fluid communication with the outlet level  50  by a reservoir spacing tube  52  extending from the liquid outlet aperture  48  to the outlet level  50 . Typically, although both the liquid inlet and outlet apertures  44 ,  48  extend through the wall upper segment  38  while the outlet level  50  is positioned substantially adjacent to the wall lower segment  40 . 
   In the embodiment shown throughout the Figures, a conventional outlet fitting such as is substantially rectilinear outlet fitting  54  is inserted into the liquid outlet duct  16  for fluidly coupling the reservoir chamber  36  to the liquid outlet duct  16 . Again, it should be understood that other coupling means could be used without departing from the scope of the present invention. Also, other means could be used for establishing fluid communication between the liquid outlet aperture  48  and the outlet level  50 . For example, the liquid outlet aperture  48  could be located substantially adjacent to the wall lower segment  40  instead of through the wall upper segment  38 . 
   The liquid pump  10  further includes an air aperture  56  extending through the reservoir wall for pneumatically coupling the reservoir chamber  36  with the atmospheric air located exteriorly through the reservoir  32 . Typically, all though by no means exclusively, the air aperture  56  extends through the upper wall segment  38 . 
   The liquid pump  10  further includes a liquid inlet valve  58  operationally coupled to the liquid inlet aperture  44 . The liquid inlet valve  58  is operable between the liquid valve open configuration, shown in  FIGS. 2 through 4  and  6 , and a liquid valve closed configuration, shown in  FIG. 5 , for respectively allowing and preventing the flow of the fluid  34  through the liquid inlet aperture  44 . 
   The liquid pump  10  still further includes an air valve  60  operatively coupled to the air aperture  56 . The air valve  60  is operable between an air valve open configuration, shown in  FIG. 5 , and an air valve closed configuration, shown in  FIGS. 2 through 4  and  6 , for respectively allowing and preventing the flow of air through the air aperture  56 . 
   The liquid pump  10  further includes a volume responsive first actuating means for selectively moving the liquid inlet valve  58  to the liquid valve closed configuration and the air valve  60  to the air valve open configuration upon the volume of liquid within the reservoir  32  reaching a predetermined upper threshold value. The liquid pump  10  is still further provided with a volume and pressure responsive second actuating means for selectively moving the liquid inlet valve  58  to the liquid valve open configuration and the air valve  60  to the air valve closed configuration upon the volume of liquid within the reservoir reaching the predetermined lower threshold value and the pressure differential between the air pressure inside and outside the reservoir  32  reaching a predetermined differential threshold. 
   Typically, the liquid pump  10  includes a float component  62  mounted within the reservoir chamber  36  for buoyantly moving within the reservoir chamber  36  according to the level of liquid  34  contained therein. The float component  62  allows selective opening and closing of the liquid inlet valve  58  depending on the level of liquid  34  contained within the reservoir chamber  36 . Typically, the liquid pump  10  includes another float component  62  (not shown) or the same float component  62  is also used for allowing selectively opening and closing of the air valve  60  depending on the level of liquid  34  contained in the reservoir chamber  36 . 
   Typically, the liquid inlet valve  58  includes a liquid valve seat  64 . Also, the float component  62  includes a liquid valve sealing plate  66  for abuttingly and sealingly contacting the liquid valve seat  64  when the liquid  34  contained within the reservoir chamber  36  reached the predetermined upper threshold value. 
   Typically, the float component  62  includes a float component buoyant section  68  pivotally attached to the reservoir wall by a pivotable float arm  70 . The liquid valve sealing plate  66  is mechanically coupled to the float arm  70 . The liquid valve sealing plate  66  is configured, sized and positioned so as to abuttingly and sealingly contact the liquid valve seat  64  when the level of liquid  34  contained within the reservoir chamber  36  reached the predetermined upper threshold value. 
   In the embodiment of the invention shown throughout the Figures, the float arm  70  is pivotally attached to the wall upper segment  38 . Also, the float arm  70  includes an arm-actuating segment  72  and a substantially perpendicular arm spacing segment  74 . The liquid valve-sealing disc  66  is mounted on the arm-actuating segment  72 . 
   Typically, although by no means exclusively, the arm actuating segment  72  is pivotally attached to an arm-mounting base  76  by an arm hinge pin  78 . The arm-mounting base  76  is, in turn, attached to the wall upper segment  38  through the use of a conventional fastening means, such as a screw  80  or the like. Also, the float component buoyant section  68  is typically attached to the arm spacing segment  74  by a buoyant section-to-arm attachment segment  82 . 
   The air valve  60  includes an air valve seat  84  in an air valve sealing plate  86  for abuttingly and sealingly contacting the air valve seat  84  when the air valve  60  is in the air valve closed configuration. The float component  62  is adapted to move the air valve sealing plate  86  away from the air valve seat  84  when the level of liquid  34  contained within the reservoir chamber  36  reaches the predetermined upper threshold value. 
   Typically, the air valve  60  further includes an air valve-actuating arm  88 . The air valve-actuating arm  88  is attached adjacent to a longitudinal end thereof to the air valve sealing plate  86 . The air valve actuating arm  88  has an opposed distal end thereof extending into the reservoir chamber  36  for contacting the float component  62  and allowing the latter to move the air valve sealing plate  86  away from the air valve seat  84  when the level of liquid contained within the reservoir chamber  36  reaches the predetermined upper threshold value. 
   Typically, the air valve  60  further includes an air valve-actuating arm  88 . The air valve-actuating arm  88  is attached adjacent to a longitudinal end thereof to the air valve sealing plate  86 . The air valve actuating arm  84  has an opposed distal end thereof extending into the reservoir chamber  36  for contacting the float component  62  and allowing the latter to move the air valve sealing plate  86  away from the air valve seat  84  when the level of liquid contained within the reservoir chamber  36  reaches the predetermined upper threshold value. The air valve-actuating arm  88  is typically provided with an arm abutment tip  90  adapted to contact the arm-actuating segment  72 . 
   As illustrated more specifically in  FIG. 3 , the air valve  60  typically includes an air valve body  92  mounted across the wall upper segment  38 . The air inlet aperture  56  is in fluid communication with an air valve flow channel  94  extending through the air valve body  92 . The air valve actuating arm  88  is slidable inserted within an air valve arm-receiving channel  96  also extending through the air valve body  92 . The reservoir spacing tube  52  is preferably provided with a relatively small vacuum aperture  98  extending therethrough for facilitating the outflow of the air contained within the reservoir chamber  36  as the latter is being filled by the liquid  34  and, when the sap is being sucked up, allows the mixing of air within the sap therefore reducing the weight of the sap column and therefore increasing the hight at which the sap coulb be sucked up. 
   Referring back to  FIG. 2 , there is shown that the liquid pump  10  typically further includes the chamber drains  100  for allowing selective drainage of the liquid  34  contained within the reservoir chamber  36 . Preferably, the chamber drains  100  prevents drainage of the liquid  34  contained in the reservoir chamber  36  when a predetermined level of vacuum is present in the reservoir chamber  36  and allows drainage of the liquid  34  contained in the reservoir chamber  36  when the vacuum level within the reservoir chamber  36  is lower than the predetermined level of vacuum. 
   In the embodiment shown throughout the Figures, the chamber drain  100  includes a drainage aperture  102  extending through the wall lower segment  40  and a drain valve  104 . The drain valve  104  includes a drain valve seat  106  and a drain valve ball  108  mounted within the perforated ball enclosure  110  for movement selectively in and out of sealing engagement with the drain valve seat  106  depending on the pressure differential between the air pressures in and out of the reservoir chamber  36 . 
   IN use, with the liquid inlet valve  58  in the liquid valve open configuration and the air valve  60  in the air valve closed configuration, the liquid  34  is allowed to flow into the reservoir chamber  36  for filling the latter while the pressure inside the reservoir chamber  36  is lower by the at least partial air vacuum at a level lower than that of the atmospheric pressure outside of the reservoir  36  so as to create a pressure differential therebetween. 
   When the volume of liquid  34  within the reservoir chamber  36  reaches the predetermined upper threshold value, the first actuating means opens the air valve  60  allowing the air pressure inside the reservoir chamber  36  to rise so as to pump out the liquid  34  inside the reservoir chamber  36  through the liquid outlet aperture  48 . Simultaneously, the first actuating means also closes the liquid inlet valve  58  so as to prevent liquid flow into the reservoir  32 , and so as to maintain the at least partial vacuum in the liquid inlet duct  14  through the bypass duct  18  for maintaining the liquid inlet valve  58  in the liquid valve closed configuration while the liquid is being pumped out of the reservoir chamber  36 . 
   When the volume of liquid  34  inside the reservoir chamber  36  falls to the lower threshold value, the air now allowed to flow out of the reservoir chamber  36  through the liquid outlet aperture  48  lowers the pressure inside the reservoir chamber  36  to the predetermined threshold allowing the second actuating means to move the liquid inlet valve  58  to the liquid valve open configuration and the air valve  60  to the air valve closed configuration for a new cycle to begin. 
     FIGS. 2 through 6  illustrate the configuration of some of the components of the liquid pump  10  during various operational stages of a pumping cycle.  FIG. 2  illustrates the liquid inlet valve  58  in the liquid valve open configuration and the air valve  60  in the air valve closed configuration. The air pressure within the reservoir chamber  36  is lower than that outside the reservoir  32  because of the vacuum provided by the vacuum pump (not shown) located typically downstream adjacent or inside the sugar shack (also not shown). The vacuum created by the vacuum pump induces extraction of the maple sap from the maple trees. The extracted maple say then flows through the action of the gravitational force through the liquid inlet duct  14  and through the inlet fitting  46  into the reservoir chamber  36 , as indicated by the flow and droplets  34 . 
   The vacuum also creates a suction in the drainage aperture  102  causing the valve ball  108  to move according to arrow  112  to the drain valve closed configuration preventing the liquid  34  contained within the reservoir chamber  36  from being drained therefrom. The liquid  34  emanating from the liquid inlet duct  14  is hence allowed to accumulate within the reservoir chamber  36 . 
     FIG. 3  illustrates an operational stage wherein the level of liquid  34  within the reservoir chamber  34  has risen to a position such that the arm-actuating segment  72  contacts the abutment tip  90 . However, the components of the air valve  60  are calibrated so that the force generated by the atmospheric pressure acting on the air valve sealing plates  86  prevent the air valve  60  from being opened until the level of liquid  34  within the reservoir chamber  36  reaches the predetermined upper threshold value. As indicated by arrows  114 , since the bottom of the reservoir spacing tube  52  is now emerged into the accumulating volume of liquid  34 , the air contained within the reservoir chamber  36  is allowed to escape through the vacuum aperture  98 . 
     FIG. 4  illustrates an operational stage wherein the level of liquid  34  within the reservoir chamber  36  is approaching the upper threshold value. Typically, although by no means exclusively, the upper threshold value is reached when the level of liquid  34  within the reservoir chamber  36  reaches ¾ of the height of the tank or reservoir chamber  36 . 
   The arm actuating section  72  imparts an increasing pressure on the air valve-sealing disc  86  through the air valve-actuating arm  88 . However, the atmospheric pressure outside the reservoir  32  still counterbalances the force generated by the float component buoyant section  68  allowing the air valve  60  to remain in a closed configuration. Also, the liquid inlet valve  58  still allows entry of liquid inside the reservoir chamber  36 . 
     FIG. 5  illustrates an operational stage wherein the level of liquid  34  within the reservoir chamber  36  has reached the upper threshold value. The position of the flow to component buoyant section  68  has caught the float arm actuating segment  72  to exert pressure on the abutment tip  90 , such that the air valve sealing disc  86  is lifted from the air valve seat  84 , allowing an inflow of atmospheric air schematically illustrated and indicated by arrows  116 , the flow from the exterior of the reservoir  32  into the reservoir chamber  36  through the air valve flow channel  94 . 
   This sudden inflow of atmospheric air, in turn, suddenly increases the air pressure within the reservoir chamber  36  creating a downward force, schematically illustrated and indicated by arrows  118 , causing the liquid  34  having accumulated into the reservoir chamber  36  to flow outwardly through the reservoir spacing tube  52  in the outlet fitting  54  towards the liquid outlet duct  16 , as indicated by arrows  120 . 
   Simultaneously, the position of the float component buoyant section  68  has also moved the float arm actuating segment  72  in such a position that the liquid valve sealing disc  66  attached thereto now sealing contacts the liquid valve seat  64  hence preventing further inflow of liquid  34  within the reservoir chamber  36 . 
   Closing of the liquid inlet valve  58  also allows the vacuum within the hydraulic circuitry located upstream from the liquid pump  10  to be maintained through the bypass duct. Maintenance of the vacuum within the upstream hydraulic circuitry, in turn, allows the liquid valve sealing disc  66  to be suctioned so as to remain in the liquid valve closed configuration until the liquid  34  within the reservoir chamber  36  has been emptied out of the latter. 
     FIG. 6  illustrates an operational stage wherein the reservoir chamber  36  has been emptied from the liquid  34  initially contained therein. As the liquid  34  emptied out of the reservoir chamber  36 , the level of liquid  34  within the reservoir chamber  35  eventually reaches a position lower than that of the outlet level  50 . Once the outlet level  50  is reached, air begins to be suctioned out of the reservoir spacing tube  52  by the vacuum in the hydraulic circuitry. 
   The air valve flow channel  94  is calibrated so that the outlet flow of air through the reservoir spacing tube  52  is greater than the inflow of air through the air valve flow channel  94 . Accordingly, the air pressure within the reservoir chamber  36  decreases. As the vacuum rebuilds within the reservoir chamber  36 , the suction provided by the vacuum at the liquid valve seat  64  is no longer sufficient to hold the air valve sealing disc  66  thereagainst, hence allowing the float arm  70  to pivot downwardly. Downward pivotal movement of the float arm actuating segment  72 , in turn, allows the air valve  60  to move towards the air valve closed configuration and the liquid inlet valve to open, initiating a new pumping cycle. 
   When the sap collecting operation is terminated, the vacuum pump is shut off allowing the pressure within the hydraulic circuitry, including the reservoir  32 , to rise to the level of the atmospheric pressure. As the pressure within the reservoir chamber  36  rises, suction on the valve ball  108  decreases, allowing the latter to fall as is indicated by arrow  122 , hence opening the drain valve  104 . Liquid remaining within the reservoir chamber  36  is allowed to flow, as indicated by arrows  124 , through drain valve apertures  126  to prevent liquid remaining in the reservoir chamber  36  from potentially freezing therein.