Abstract:
A filler unit for automatically topping up a battery cell ( 14 ) includes a float vessel ( 16 ) for containing the liquid to be dispensed and a float valve assembly ( 34 ) for establishing a predetermined substantially constant head of liquid in the vessel ( 16 ). A baffle plate ( 40 A) in the vessel ( 16 ) is spaced sufficiently close to a wall of the vessel ( 16 ) to define a capillary passage between the wall and the baffle plate ( 40 A), with at least that surface of the baffle plate ( 40 A) which defines the capillary passage being hydrophilic. In use, the replenishment water is able to flow from the vessel ( 16 ) to the cell ( 14 ) under gravity along a flowpath until such time as the water level in the cell ( 14 ) has risen to a desired level. This creates a pressure equilibrium in the flowpath which causes the flow from the vessel ( 16 ) to the cell ( 14 ) to cease automatically.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a filler unit for automatically topping up a container with liquid, and in particular to a battery filler unit for automatically topping up battery cells with electrolyte in the form of purified water to compensate for losses due to electrolysis and evaporation. 
     One such battery filler unit consists of a vessel which may be positioned immediately above a battery cell and supplied with water in a manner which maintains a constant head in the vessel. An orifice in the bottom of the vessel communicates with a downpipe which extends downwards from the orifice into the top portion of the cell. Water flows from the vessel to the cell under gravity along a flow path defined by the orifice and the downpipe thereby adding to the electrolyte and causing the level of the electrolyte to rise progressively until the lower end of the downpipe becomes submerged below the level of the electrolyte. 
     The orifice forms a continuous air seal by action of surface tension in the water being dispensed. As the lower end of the downpipe becomes submerged, air in the downpipe becomes trapped, and a condition is set up for pressure equilibrium in the flow path causing flow from the vessel to the cell to cease. 
     In one improvement of a battery filler unit a baffle plate is introduced and spaced close to the bottom of the vessel to form a capillary passage which operates in tandem with the orifice to improve the quality of the seal at the head of the downpipe. This improvement forms the subject of U.S. Pat. No. 4,544,044. Resistance to the flow of water under the baffle plate is known to be dependent on the physical dimensions underneath the baffle plate. Problems can sometimes arise when these surface characteristics undergo variations sufficient to interfere with the correct flow of the replenishment water. One method which has been used to help alleviate the problem has been to vary the clearance between adjacent faces formed by the bottom of the vessel and the lower surface of the baffle plate appropriately so as to preserve the requisite flow rate. 
     An obvious disadvantage of this measure is that the capillarity diminishes with increased spacing, leading to a corresponding sacrifice in the efficacy of the airseal with an increase in through flow and uneven filling of the cells of a multi-celled battery. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a filler unit for use in dispensing a liquid into a container to top up the container to a predetermined desired level, the container being divided by level sensing means into a first pressurizable chamber and a second vented chamber, and the filler unit including a vessel for containing the liquid to be dispensed, means for establishing a predetermined substantially constant head of liquid in the vessel, an outlet orifice defined in the wall of the vessel, a baffle in the vessel spaced sufficiently close to the wall to define a capillary passage between the wall and the baffle, wherein the outlet orifice communicates directly with the pressurizable chamber, with at least that surface of the baffle which defines the capillary passage being hydrophilic, the unit being intended for iocation relative to the container, such that in use the liquid is able to flow from the vessel to the container under gravity along a flowpath having a hydrophilic portion defined by the capillary passage and the orifice into the pressurizable chamber until such time as the liquid level in the container has risen to the desired level within the lower end of the pressurizable chamber to trap air therein, thereby to create a pressure equilibrium in the flowpath which causes the flow from the vessel to the container to cease automatically. 
     In a preferred form of the invention, the level sensing means comprises a downpipe which terminates short of the base of the container and defines the first pressurizable chamber and divides the container into the first and second chambers, and the orifice is formed in a base wall of the vessel, with the downpipe extending downwardly from the orifice. 
     Advantageously, at least the capillary passage-defining surface of the baffle plate is hydrophilic by virtue of it being subjected to a surface treatment which serves to increase the wettability thereof. 
     By the term “hydrophilic” is meant that the capillary passage is capable of establishing the flowpath within a period of time not exceeding 15 seconds, wherein the capillary passage is substantially dry prior to the establishment of the flowpath. 
     Typically, the various components making up the filler unit, and in particular the baffle plate and the vessel, are injection moulded from a plastics material, such as polypropylene, with the resultant surface of the components having a gloss finish which is inherently hydrophobic, the baffle plate being hydrophilic by virtue of it being subjected to a surface treatment which serves to increase the wettability thereof. 
     The surface treatment may include the step of coating at least the operatively lower surface of the baffle plate with a hydrophilic substance, with the coating being sufficiently insoluble to withstand at least initial contact with condensate from the container, which in the case of a lead-acid battery, includes dilute sulphuric acid. 
     The hydrophilic substance typically includes group II metal salts, which are preferably a calcium and/or a magnesium salt such as calcium magnesium carbonate, and which are functionally insoluble in dilute sulphuric or battery acid. 
     More typically, the salts are chosen from the group comprising calcium carbonate, calcium hydroxide and calcium magnesium carbonate, or dolomite (CaMg(CO 3 ) 2 ). 
     Other possible hydrophilic substances or wetting agents include calcium chloride, calcium hypochlorite, and magnesium hydroxide, although the wetting effect in respect of these agents is in most cases reduced as they are functionally neutralized in respect of wetting effect in diluted sulphuric or battery acid. 
     In an alternative form of the invention, the plastics material from which the baffle plate is injection moulded is pre-mixed with a predetermined quantity of a granular filler which may be a finely divided suspended filler which is exposed on the operatively lower surface of the baffle plate. 
     Conveniently, the injection moulded baffle plate is subsequently treated with an acid so as to dissolve the exposed filler on the operatively lower surface of the plate, thereby defining pockets which provide a wettable surface. This surface may then be treated with a suitable surfactant such as a detergent or sodium bisulphate to encourage the wetting process. 
     The filler is preferably a group II metal salt. More preferably, the group II metal salt is soluble in hydrochloric acid, and may be in the form of calcium magnesium carbonate. 
     The surface treatment may also be achieved by surface oxidization of the injection moulded plastics components. 
     Physical surface-altering treatments such as flame or corona treatment may also be used. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross-sectional side view of a prior art filler unit in use on a battery cell in which flow has progressed partly through the filler unit, 
     FIG. 2 shows a cross-sectional side view of a filler unit of the invention in use on a battery cell in which flow is proceeding normally into the cell, and 
     FIG. 3 shows a perspective view of a set of filler units of the invention installed on a multi-cell battery connected to facilitate a filling operation. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     The battery cell filling arrangement  10  of FIG. 1 comprises a filler unit  12  located uppermost in a battery cell  14 . The filler unit  12  includes a float vessel  16  having a base  18  positioned on top of a battery lid  20  of the battery cell  14 . A downpipe or level sensing pipe  22  extends into the interior of the cell, and has a lowermost opening  24  which is positioned a suitable distance away from a plate assembly  25 , to divide the cell into a pressurizable chamber  26  within the downpipe and a non-pressurizable chamber  27  surrounding the downpipe and venting to atmosphere. 
     The filler unit  12  further comprises a water feed arrangement including a pair of feed tubes  28  coupled to opposed spigot arms  29  of a T-duct  30 , the central vertical duct  32  of which delivers replenishment water to the float vessel  16 . A float valve assembly  34  is located within the float vessel  16  for providing a predetermined substantially constant head therein. The float carries a central pin valve  36  adapted to mate with a valve seat  32 A defined at the lowermost opening of the central duct  32 . 
     A central outlet  38  is defined in the base  18  at the head of the downpipe  22 , and a disc-shaped injection moulded baffle plate  40  is located immediately above the base  18  so as to define a capillary passage  42  which progressively broadens in cross-section from the outer periphery of the baffle plate  40  towards the central orifice  38 . Replenishment water enters the feed tubes  28  via a suitable pressurized water feed arrangement and passes through the central duct  32 , the valve  36 , and around and directly beneath the float valve assembly  34 , causing it to float upwardly within the float vessel  16 . 
     During normal operation, and as is clear from FIG. 2, the replenishment water flows inwardly through the capillary passage  42  into the mouth of the orifice  38 , where it provides an air seal at the head of the downpipe  22  through action of the surface tension in the replenishment water  44 . The water flows into the battery cell  14  along a filamentary flow path  45  which lies substantially along the central axis of the downpipe  22  and into the battery cell  14  to raise the electrolyte level to a level indicated at  46 . The lower opening  24  in the downpipe becomes sealed as the electrolyte or water in the battery cell  14  is replenished. The air pressure within the downpipe  22  rises progressively by virtue of the head “h” as the level  46  of water is approached. The increase in air pressure shuts off the flow of water through the orifice  38  and capillary passage  42 . This in turns raises the water level in the float vessel, and results in the valve  36  mating with the valve seat  32 A and closing off the flow of replenishment water into the filler unit at the central duct  32  as the float valve assembly  34  rises. 
     During the battery charging process, various released gases pass through the filler unit  12  via venting ducts  52  where the liquid fraction of the spray or mist forms a condensate  56 , with the gaseous discharge exiting via the path  54 . The condensate then flows across the upper surface of the float and downwardly into the capillary passage  42 . A portion of the liquid condensate trickles back into the battery cell  14  via the central orifice  38 , whilst the remainder is retained within the confines of the filler unit  12 . The condensate thus provides progressive wetting of the walls of the capillary passage constituted by the underside of the baffle plate  40  and the upper surface of the base  18  of the vessel. 
     The filler unit of FIG. 1 is assembled from components formed in a conventional plastics injection moulding process, as a result of which the flow of replenishment water  44  will proceed up until the FIG. 1 stage, where it just reaches the entrances of the capillary passage  42 . This tends to occur in particular when the filler unit has just been installed, and is dry. The reason for this is that the injection moulded plastic surfaces tend to be hydrophobic, or non-wetting, which means that non-pressurized flow through the capillary passage  42  does not normally occur. The only way of inducing flow under these conditions is to increase the spacing within the capillary passage. This would have the resultant effect of reducing or even nullifying the capillarity of the passage  42 , thereby seriously compromising the progressive air seal which the capillary passage provides, leading to possible overtopping. 
     It has been found that this problem can be addressed by altering surface wetting characteristics of the hydrophobic plastic material from which the baffle plate is formed. 
     The surface wetting characteristics of certain plastics, such as ABS plastics, can be temporarily enhanced by the application of surfactants such as domestic detergents. The wetting characteristics of these detergents are not always satisfactory when applied to other more economically produced plastics such as polypropylene, of which lasting wettability can be particularly difficult to achieve in the short term without additional treatment. In one form of the invention, the polypropylene plastic from which the baffle plate  40 A is injection moulded is supplemented as follows. 
     When manufacturing a master batch of plastics material for injection moulding the baffle plate component, calcium magnesium carbonate is mixed with polypropylene plastic so that there is an even dispersion throughout the body of the suspended calcium magnesium carbonate, with a suitable density appearing near the surface thereof. The procedure typically used is to mix a 40% calcium carbonate-filled polypropylene “modified plastic” or “modified polypropylene”, which is purchased from the supplier, with pure polypropylene in the required ratio to obtain, say, 8% of calcium carbonate by mass. The modified plastic is formulated in a complicated extrusion process, but once suspended in plastic, further dilution can be performed by the moulder simply by mixing the required ratio of pure polypropylene. 
     The particles at the surface interface are optionally dissolved by immersing the injection moulded product in hydrochloric acid for a suitable period of time. Alternatively, the particles may be dissolved naturally by extended exposure to acidic electrolyte after installation and subsequent to commencement of operation on a container such as a battery. Dissolution of the surface-based calcium carbonate particles gives rise to a corresponding number of tiny pockets, thereby making it wettable and promoting capillarity. The surface is not merely allowed to dry, as it would be difficult to revitalize the wetting properties merely by adding water. For this reason, a small quantity of detergent and sodium bisulphate is applied to the surface before it is allowed to dry. 
     Other methods of providing capillarity include treatment with surfactants such as calcium chloride, calcium hypochlorite and magnesium hydroxide. The wetting effect is, in most cases, seriously reduced when the component is then brought into contact with diluted sulphuric acid, which is typically present in the condensate, or the sodium bisulphate which is applied to the surface. 
     An improved method of treatment is to immerse the injection moulded polypropylene baffle plate component in a slurry of finely divided calcium magnesium carbonate, and boiling the component for ten minutes within the slurry. The component then becomes covered with a thin layer of calcium and/or magnesium salt which bonds to the polypropylene surface. Whilst not strong enough to withstand rough handling, the coating provides an effective wetting agent and promotes capillarity when applied to the baffle plate  40 A and the base of the valve vessel  16 . The coating generally remains effective when brought into contact with diluted sulphuric acid and sodium bisulphate of the type typically encountered. 
     With reference to FIG. 2, the filler unit  12 A has been assembled from components taken directly from an injection moulding process, except the baffle plate  40 A which is boiled in a calcium magnesium carbonate slurry prior to assembly. The baffle plate optionally contains between zero and 40% of calcium magnesium carbonate. When first brought into service under conditions in which pre-wetting of the capillary passage has not occurred, the flow of replenishment water  44  will proceed into the capillary passage  42 , even though it may be a narrow passage, virtually immediately or with a minimal period of delay, and will thereafter advance via the orifice  38  into the cell  14  within a period not exceeding 15 seconds. The air seal provided by the baffle plate  40 A in this arrangement is excellent, notwithstanding that only the plate  40 A is wetting, whilst the surface of the base  18  of the vessel  16  need only be partially or even non-wetting. 
     Upon permanent installation on the battery cell  14 , the filler unit  12 A is subjected to periodic ingress of electrolyte mist or spray, forming condensate  56 , as was previously outlined. Some of the condensate  56  is returned to the cell  14  via the capillary passage  42 , whilst a small portion is retained on the surface of the baffle plate  40 A, assisted to some extent by the presence of calcium and/or magnesium salts which adhere to the plastics material surface of the baffle plate  40 . This results, over an extended period of time, (weeks to months), in corrosive penetration of the condensate into the outer surface of the baffle plate  40 , thereby naturally enhancing the wettability thereof. 
     Generally, after the condensate  56  has commenced wetting of the surface of the baffle plate  40 , it will sustain wetting even if the filling and coating provided by the treatment process is consumed or lost. 
     Wetting can optionally be promoted by means of surface oxidization of the various plastics materials components, through brief application of a suitably adjusted flame, or by corona discharge treatment, or by a variety of other processes which nullify the naturally hydrophobic characteristic of specified injection moulded plastics materials, to turn them into hydrophilic characteristics. 
     In the case of battery filler usage, it should be borne in mind that these processes may introduce substances onto the surfaces of the plastics materials components which may interfere with the proper operation of the battery cells, and these must therefore be avoided. For example, the use of calcium/magnesium carbonate, sodium bisulphate and detergents, in the small quantities employed, is not incompatible with the proper operation of lead-acid batteries. On the other hand, the use of chlorides, even in small quantities, is not compatible with the proper operation of lead-acid batteries. 
     FIG. 3 illustrates a single point battery filling system  60  installed on a twelve cell battery  62 , in which the filler units  84  correspond to the filler unit  12  of FIG. 1, and  12 A of FIG.  2 . The filling system  60  is shown connected to facilitate a filling operation, the filling system  60  including a water reservoir  64  positioned above the twelve cell battery  62  to permit at least a portion of the water volume  66  to flow by gravity to the filler units  84 . While flow by gravity is a preferred method for bringing replenishment water to the filler units  84 , any form of pressurisation of the water sufficient to provide flow into the filler units  84  can be used. 
     The water reservoir  64  has an outlet tube  70  connected to a control valve  72 , which is in turn connected, by another length of tube  74 , to a disconnectable coupling comprising an upper section  76  and a lower section  78 . The upper section  76  and the lower section  78  may be parted by an operator in attendance and reconnected when required. 
     The lower section  78  of the disconnectable coupling connects to a tee  82  via another length of tube  80 . The tee  82  connects to two similar banks comprising six filler units  84  interconnected by five stub tubes  90 , and terminated by a stopper  92 . 
     A filling procedure is initiated by connecting the upper section  76  to the lower section  78  of the disconnectable coupling and by opening the control valve  72 . Provided there is a sufficient volume of water  66  in the reservoir  64 , water will flow from the reservoir  64  to the filler units  84  and into the cells  94  of the battery  62  to replenish any water lost from the electrolyte within the cells through normal use of the battery  62 . 
     The volume of water  66  within the reservoir  64  is maintained by adding sufficient water to the reservoir via an access port  68 . Water may be added at intervals or continuously to the reservoir  64  from a suitable source of supply. 
     The filling procedure is terminated by closing the control valve  72 . The disconnectable coupling may be opened immediately or after a suitable period of time determined by the operator in attendance, by parting the upper section  76  from the lower section  78 . Any continuous inflow of water to the reservoir  64  is typically interrupted when the volume of water  66  in the reservoir  64  begins to exceed a predetermined amount after the outflow has been stopped. 
     The disconnectable coupling comprising upper section  76  and lower section  78  may be of a type which provides automatic closure of their respective flow paths upon disconnection, and automatic opening upon connection, thereby assisting in minimising or even eliminating any water spillage. 
     Upon initiation of the filling procedure a portion of the water volume  66  runs along the flow paths defined by the tubes in the direction indicated by the arrows  96 , filling the entire flow path from the reservoir outlet tube  70  to the stoppers  92  with water. The tubes  86 ,  88  and  90  and stoppers  92  correspond to the feed tubes  28  defined in FIG. 1, and therefore replenishment water will begin to flow into the respective float vessels  16  of the respective filler units  12 . 
     The twelve battery cells  94  correspond to twelve containers, each equivalent to the container  14  shown in FIG. 1, and therefore replenishment water will be ready to flow into the twelve battery cells  94 . 
     If the filler units  84  are assembled from components formed in a conventional plastics injection moulding process the flow of replenishment water into the battery cells  94  may be subject to some delay due to the hydrophobic nature of the capillary passage  42  as illustrated in FIG.  1 . However, if the filler units  84  are assembled from components including a baffle plate  40 A which has been suitably treated to make its surface hydrophilic, the flow of replenishment water will proceed almost without any delay. 
     A delay as may be experienced through the use of untreated components will in no way reduce the usefulness of the filling system in normal application, but can prove inconvenient when attempting to reduce the filling time period by terminating the filling procedure earlier such as in a situation where the operator has available a limited period of time to attend to a series of filling systems in a multi-system installation. 
     There will always be a varying degree of hydrophilic/hydrophobic reaction within a range of examples of typical filler units. It is therefore unlikely that two or more units on a given battery will have identical characteristics. It is self-evident, therefore, that any attempt to reduce filling time by simply disconnecting the water earlier will result in the filling rates of the individual battery cells  94  of battery  62  not being equal. 
     This variation in hydrophilic/hydrophobic reaction is almost entirely neutralised if all twelve filler units  84  are assembled from components including a baffle plate  40 A which has been suitably treated to make its surface hydrophilic. 
     The invention extends to the use of filler units having multiple level sensing pipes or other level sensing arrangements which divide the cell into pressurizable and non-pressurizable chambers.