Patent Publication Number: US-2021162321-A1

Title: Degassing Electrorheological Fluid

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of, and claims priority to, U.S. application Ser. No. 16/118,884, filed Aug. 31, 2018, which claims priority to U.S. provisional patent application No. 62/552,555, titled “DEGASSING ELECTRORHEOLOGICAL FLUID” and filed Aug. 31, 2017, all of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     Electrorheological (ER) fluids typically comprise a non-conducting oil or other fluid in which very small particles are suspended. In some types of ER fluid, the particles may have diameters of 5 microns or less and may be formed from polystyrene or another polymer having a dipolar molecule. When an electric field is imposed across an ER fluid, the viscosity of the fluid increases as the strength of that field increases. This characteristic of ER fluids can be used to control flow in a system containing an ER fluid. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the invention. 
     In some embodiments, a system may include an output manifold that may be in fluid communication with a reservoir and that may include multiple discharge ports. Each of the discharge ports may be configured to discharge electrorheological fluid into a housing. A recovery manifold may be in fluid communication with the reservoir and may include multiple recovery ports. Each of the recovery ports may be configured to receive the electrorheological fluid from a housing. A gas remover may be positioned to extract gas from the electrorheological fluid received from the recovery ports. 
     In some embodiments, a method may include connecting a housing to a fluid system containing an electrorheological fluid. The fluid system may include a gas remover. After connecting the housing to the fluid system, the electrorheological fluid may be pumped through the housing and the gas remover. After pumping the electrorheological fluid through the housing and through the gas remover, the housing may be disconnected from the fluid system. 
     Additional embodiments are described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements. 
         FIG. 1A  is rear lateral top perspective view of an ER fluid housing according to some embodiments. 
         FIG. 1B  is a top view of the ER fluid housing of  FIG. 1A . 
         FIG. 1C  is a partially schematic area cross-sectional view taken from the plane indicated in  FIG. 1B . 
         FIG. 1D  is an enlarged portion of the view of  FIG. 1C . 
         FIG. 2A  is a lateral top perspective view of an ER fluid housing according to certain additional embodiments. 
         FIG. 2B  is a top view of the ER fluid housing of  FIG. 2A . 
         FIGS. 2C through 2E  are partially schematic area cross-sectional views taken from the planes indicated in  FIG. 2B . 
         FIG. 3A  is a block diagram of a fluid system according to some embodiments. 
         FIG. 3B  is a perspective view of the gas remover from the fluid system of  FIG. 3A . 
         FIG. 3C  is a side cross-sectional view from the plane indicated in  FIG. 3B . 
         FIGS. 4A through 4G  are block diagrams showing operations using the system of  FIG. 3A . 
         FIG. 5A  is a block diagram of a fluid system according to further embodiments. 
         FIG. 5B  is a block diagram of the gas remover from the fluid system of  FIG. 5A . 
         FIGS. 6A through 6E  are block diagrams showing operations using the system of  FIG. 5A . 
         FIG. 7  is a block diagram of a fluid system according to additional embodiments. 
         FIGS. 8A through 8E  are block diagrams showing operations using the system of  FIG. 7 . 
         FIGS. 9A through 9E  are block diagrams showing a system, and operations of that system, according to yet additional embodiments. 
         FIGS. 10A through 11B  are block diagrams showing systems, and operations of those systems, according to yet further embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is rear lateral top perspective view of an ER fluid housing  10  according to some embodiments. Housing  10  includes a main body  11  and two fluid chambers  12  and  13 . Chambers  12  and  13  are bounded by flexible contoured walls  14  and  15 , respectively, that extend upward from a top side of main body  11 . As explained in more detail below, a channel within main body  11  connects chambers  12  and  13 . Chambers  12  and  13  and the connecting channel may be filled with ER fluid using sprues  16  and  17 . After filling, sprues  16  and  17  may be sealed and housing  10  used as a component of an article of footwear. In particular, housing  10  may be incorporated into a sole structure and chambers  12  and  13  placed under a support plate. ER fluid may then be allowed to flow between chambers  12  and  13  when it is desired to adjust a shape of the sole structure. Flow from chamber  13  to chamber  12  may decrease a height of a central region  19  of chamber  13  relative to main body  11  and simultaneously increase a height of a central region  18  of chamber  12 . Flow in the opposite direction will have the opposite effect. When central portions  18  and  19  achieve desired heights, further height change can be stopped by energizing electrodes in the connecting channel. Energizing those electrodes increases viscosity of ER fluid in that channel and prevents further flow of ER fluid between chambers  12  and  13 . 
       FIG. 1B  is a top view of housing  10 . The location of channel  20  that connects chambers  12  and  13  is indicated with small broken lines. A pair of opposing electrodes are positioned within channel  20  on bottom and top sides and extend along a portion  21  indicated in with large broken lines.  FIG. 1C  is a partially schematic area cross-sectional view taken along the plane indicate in  FIG. 1B . Gray shading is used in  FIG. 1C  to indicate regions that will contain ER fluid once housing  10  is filled. As seen in  FIG. 1C , chambers  12  and  13  have bellows shapes created by folds in walls  14  and  15 .  FIG. 1D  is an enlargement of the region indicated in  FIG. 1C .  FIG. 1D  shows additional details of channel  20  and of electrodes  22  and  23  respectively covering the top and bottom walls of channel  20  along portion  21 . In some embodiments, channel  20  may have a maximum height h between electrodes of 1 millimeter (mm), an average width (w) of 2 mm, and a length along a flow path between chamber  12  and  13  of at least 200 mm. 
     Exemplary material for housing  10  and chambers  12  and  13  includes thermoplastic polyurethane (TPU). Exemplary material for electrodes  22  and  23  includes 0.05 mm thick, 1010 nickel plated, cooled rolled steel. Additional details of housing  10  and of other types of similar housings can be found in the U.S. Provisional Patent Application 62/552,548 filed Aug. 31, 2017, titled “Footwear Including an Incline Adjuster”, which application is incorporated by reference herein. 
       FIG. 2A  is a lateral top perspective view of an ER fluid housing  50  according to certain additional embodiments.  FIG. 2B  is a top view of housing  50 . Housing  50  includes a main body  51  and six fluid chambers. Chambers  52   a  through  52   c  are located on one side of housing  50 , and chambers  53   a  through  53   c  are located on an opposite side. Chambers  52   a  through  52   c  and  53   a  through  53   c  are bounded by flexible contoured walls  54   a  through  54   c  and  55   a  through  55   c , respectively, that extend upward from a top side of main body  51 . Chambers  52   a  through  52   c  and  53   a  through  53   c  are connected by channels  60 . 1  through  60 . 5 , which channels are located in main body  51  and are indicated in  FIG. 2B  with small broken lines. Opposing electrodes are positioned within channel  60 . 3  on bottom and top sides and extend along a portion  61  indicated in  FIG. 2B  with large broken lines. 
     Chambers  52   a  through  52   c , chambers  53   a  through  53   c , and channels  60 . 1  through  60 . 5  may be filled with ER fluid using sprues  66  and  67 . After filling, sprues  66  and  67  may be sealed and housing  50  used as a component of an article of footwear. In particular, housing  50  may be incorporated into a sole structure and chambers  52   a  through  52   c  and  53   a  through  53   c  placed under a support plate. ER fluid may then be allowed to flow from chambers on one side (e.g., chambers  53   a  through  53   c ) to chambers on the other side (e.g., chambers  52   a  through  52   c ) to adjust a shape of the sole structure. Flow from chambers  53   a  through  53   c  to chambers  52   a  through  52   c  may decrease heights of central regions  59   a  through  59   c  of chambers  53   a  through  53   c , respectively, relative to main body  51  and simultaneously increase heights of central regions  58   a  through  58   c  of chambers  52   a  through  52   c , respectively. Flow in the opposite direction will have the opposite effect. Height change can be stopped by energizing electrodes in channel  60 . 3  to prevent further flow of ER fluid. 
       FIG. 2C through 2E  are a partially schematic area cross-sectional views taken from the planes indicate in  FIG. 2B .  FIG. 2E  is enlarged relative to  FIGS. 2C and 2D . Gray shading is used in  FIGS. 2C through 2E  to indicate regions that will contain ER fluid once housing  50  is filled. The structure of chambers  53   a  and  53   b  is similar to that of chamber  53   c , although chamber  53   a  is of slightly smaller diameter. The structure of chamber  52   a  is similar to that of chambers  52   b  and  52   c . The structure of channels  60 . 1 ,  60 . 4 , and  60 . 5  is similar to that of channels  60 . 2  and  60 . 3 , although channels  60 . 1 ,  60 . 2 ,  60 . 4 , and  60 . 5  lack electrodes. As seen in  FIGS. 2C and 2D , chambers  52   a  through  52   c  and  53   a  through  53   c  have bellows shapes created by folds in walls  54   a  through  54   c  and  55   a  through  55   c .  FIG. 2E  shows additional details of channel  60 . 3  and of electrodes  62  and  63  respectively covering the top and bottom walls of channel  60 . 3  along portion  77 . In some embodiments, channel  60 . 3  may have a maximum height h between electrodes of 1 mm, an average width w of 2 mm, and a length along a flow path between chambers  52   c  and  53   c  of at least 270 mm. The maximum height h (between top and bottom walls) and average width w of channels  60 . 1 ,  60 . 2 ,  60 . 4 , and  60 . 5  may have the same dimensions as the maximum height and average width, respectively, of channel  60 . 3 . 
     Exemplary material for housing  50  and chambers  52   a  through  52   c  and  53   a  through  53   c  includes TPU. Exemplary material for electrodes  22  and  23  includes 0.05 mm thick, 1010 nickel plated, cooled rolled steel. Additional details of housing  50  and of other types of similar housings can be found in the U.S. Provisional Patent Application 62/552,551 filed Aug. 31, 2017, titled “Incline Adjuster With Multiple Discrete Chambers”, which application is incorporated by reference herein. 
     When using ER fluid in a housing such as housing  10  or housing  50 , it is beneficial to remove air from that fluid. If bubbles can form in the ER fluid of such a housing during operation, the device incorporating the housing may malfunction. The electrical field strength required to arc across an air gap is approximately 3 kilovolts per millimeter (kV/mm). In at least some applications employing a housing such as housing  10  or housing  50 , this field strength may be less than a typical field strength needed to achieve sufficient viscosity in ER fluid within a channel to stop flow. If bubbles form and arcing occurs, the electrical field across a channel may collapse. If the electrical field were to collapse in this manner, flow through a channel would be allowed at the precise time it is desirable to inhibit flow. 
     It can be difficult to remove air from ER fluid used to fill a housing such as is described above. The dimensions with the chambers and channels are relatively small, and there are numerous locations within those channels and chambers where bubbles may collect during filling. These difficulties may be compounded when attempting to produce such housings in quantity, as time-consuming and labor-intensive degassing procedures can significantly increase production costs. 
     Various embodiments include systems and methods for removing air from ER fluid used to fill ER fluid housings. In at least some such embodiments, a system provides a source of degassed ER fluid that may be circulated through one or more housings. Multiple housings can be connected to the system and processed simultaneously. A reservoir of degassed ER fluid supplies the housings. The degassed fluid is pumped into each housing though an inlet. The incoming fluid displaces ER fluid that is already in the housing and that may still contain air. The displaced ER fluid exits each housing and is recovered by the system. The recovered ER fluid is then degassed and returned to the reservoir. By continuously pumping degassed ER fluid through each housing for a period of time, air within each housing is removed. 
     An example of an ER fluid that may be used in the herein-described embodiments is sold under the name “RheOil 4.0” by ERF Produktion Würzberg GmbH. That particular ER fluid has a dynamic viscosity at 25° C. of 35 mPa*s and a kinematic viscosity at 25° C. of 34 mm 2 /s. 
       FIG. 3A  is a partially schematic block diagram showing a fluid system  100  according to some embodiments. In  FIG. 3A  and subsequent figures, system  100  and other systems, as well as methods for using such systems, are described by reference to examples involving one or more housings  10 . However, the systems and methods described herein could be used to fill a single housing  10 , to fill one or more housings  50 , to fill one or more housings of another type, and/or to fill combinations of housings of different types. 
     System  10  includes a reservoir  101 . Reservoir  101  is a tank that holds ER fluid  110 . In at least some embodiments, a reservoir has an internal volume that is substantially greater than an internal volume of a fluid housing processed by the system that includes that reservoir. As but one example, housings such as housings  10  and  50  may have internal volumes that are able to hold ER fluid of approximately 22 milliliters and 24 milliliters, respectively. Conversely, a reservoir such as reservoir  101  may have an internal volume that holds at least 10 liters of ER fluid. 
     A gas remover  102  is positioned within tank  101 . Incoming ER fluid  110  that is recovered from housings  10  being processed with system  100  is received through an intake conduit  103  and injected into gas remover  102 . Gas remover  102  removes air entrained from the incoming fluid and exhausts the removed air through a vent tube  104 . An end  139  of vent tube  104  is positioned above the surface of ER fluid  110  to avoid dissolution of exhausted air in ER fluid  110 . Degassed ER fluid  110  exits gas remover  102  from an outlet  105 . In some embodiments, and as discussed in more detail below, gas remover  102  may be a centrifugal flow bubble remover. 
     Reservoir  101  is connected to a vacuum source  106  by a vacuum line  107 . A valve  111  may be opened to connect vacuum source  107  to the interior of reservoir  101 , and closed to isolate the reservoir  101  interior from the vacuum source  107 . When the valve  111  is open, vacuum source  107  maintains a sub-atmospheric pressure PSA in the headspace  108  between the top of reservoir  101  and the surface of fluid  110  within reservoir  101 . Pressure PsA is lower than an ambient atmospheric pressure PA in the environment of system  100  outside reservoir  101 . In at least some embodiments, PSA is 24 millibars or lower. Vacuum source  106  may include a vacuum pump that runs continuously when activated. In some embodiments, a pump of vacuum source  106  may receive a signal from a pressure sensor  112  within reservoir  101  and be configured to begin pumping when PSA increases to a first value (e.g., a first percentage of a desired PsA) and to continue to pump until PSA reaches a second value (e.g., a second, lower, percentage of the desired PsA). In some embodiments, vacuum source  106  may comprise a separate vacuum tank that is maintained within a desired pressured range by a vacuum pump, with the vacuum tank connected to headspace  108 . 
     ER fluid  110  flows from reservoir  101 , through a supply conduit  114 , to an output manifold  117 . Output manifold  117  is in fluid communication with a plurality of discharge ports  118 . For convenience, only two discharge ports  118  are shown. Wavy line interruptions in the representation of manifold  117  indicate the presence of additional portions of manifold  117  and additional discharge ports  118  that have been omitted from the drawings for convenience. Each discharge port  118  includes a corresponding port supply line  119 , corresponding a port valve  120 , and a corresponding discharge fitting  121 . In some embodiments, each discharge fitting  121  may be a tapered rubber tube that fits within a housing inlet (e.g., one of sprues  16  or  17 ) and that can form a fluid seal around the housing inlet. Supply lines  119  in some embodiments may be formed from flexible tubing. Valve  120  may be used to start and stop flow from a corresponding discharge fitting. 
     System  100  also includes a recovery manifold  124 . Recovery manifold  124  is in fluid communication with a plurality of recovery ports  125 . For convenience, only two recovery ports  125  are shown. Wavy line interruptions in the representation of manifold  124  indicate the presence of additional portions of manifold  124  and additional recovery ports  125  that have been omitted from the drawings for convenience. Each recovery port  125  includes a port recovery line  126 , a corresponding port valve  127 , and a corresponding recovery fitting  128 . In some embodiments, each recovery fitting may be a tapered rubber tube, of the same dimensions as a discharge fitting, that fits within a housing outlet (e.g., one of sprues  16  or  17 ) and that can form a fluid seal around the housing outlet. A bypass  122  connects manifolds  117  and  124 . A valve  123  of bypass  122  may be opened or closed to allow or prevent flow through bypass  122 . 
     Wavy line interruptions in the representations of supply lines  119  and recovery lines  126  indicate additional lengths in those lines that have been omitted from the drawings for convenience. As explained in more detail below, those additional lengths may be used during some operations to invert orientations of connected ER fluid housings. Each pair of a discharge port  118  and a recovery port  125  can be used to connect an ER fluid housing to system  100 , thereby placing the internal volume of the connected housing into fluid communication with gas remover  102 , ER fluid reservoir  101 , and other system components (when appropriate valves are open and pump(s) operating). In the drawings, only two discharge port/recovery port pairs are shown for system  100  and for systems in other embodiments. In some embodiments, system  100  and/or systems according to other embodiments may have at least 5, at least 10, or at least 20 discharge port/recovery port pairs. 
     Recovery manifold  124  is connected to a pump  131  by a conduit  130 . Pump  131  provides the pumping action for system  100 . In particular, pump  131  creates a pressure and a flow rate at output  132  that is sufficient to inject ER fluid  110  into gas remover  102  at sufficiently high speeds for gas remover  102  to operate. The output of gas remover  102  provides the pressure within reservoir  101  to pump ER fluid  110  through conduit  114 , manifold  117 , ports  118 , connected ER fluid housings, ports  125 , manifold  124 , and conduit  130 . 
     Conduits  114  and  130  may include respective valves  133  and  134  that may be closed to isolate reservoir  101  from other system components. Outlet  105  and vent conduit  104  of gas remover  102  may include respective check valves  137  and  136  to prevent backflow into gas remover  102 . Check valve  137  may also provide back pressure on output  105  to facilitate operation of gas remover  102 . 
       FIG. 3B  is a perspective view of gas remover  102 .  FIG. 3C  is a side cross-sectional view of gas remover  102  from the plane indicated in  FIG. 3B . Gas remover  102  has a central bore  140  that includes a generally cylindrical first section  141 , a tapered second  142 , and a generally cylindrical third section  143  having a diameter smaller than the diameter of section  141 . Sections  141 ,  142 , and  143  are concentric. ER fluid  110  enters through one or more injection ports  144 . Ports  144  are configured to inject ER fluid  110  tangentially around the outer perimeter of section  141  to create a swirling flow, as indicated by the approximately helical broken line. The centrifugal force of the swirling flow causes the heavier ER fluid  110  to move toward the wall of bore  140  and the lighter air in ER fluid  101  to move toward the center of bore  140 . As the swirling flow of ER fluid  110  is forced through tapered section  142 , an air column collects in the center of bore  140  and is forced backward and out of gas remover  102  through vent port  104 . Degassed ER fluid  110  is forced forward and out of gas remover  102  through outlet  105 . In some embodiments, ER fluid  110  may flow through gas remover  102  at a rate of between 10 and 50 liters/minute, and may have an outlet pressure in the range of 0.1 to 1 MPa. 
     In some embodiments, gas remover  102  may be a bubble remover such as is described in U.S. Pat. No. 5,240,477, which patent is incorporated by reference herein. Such bubble removers are commercially available and manufactured by Opus Systems Inc. of Tokyo, Japan. 
     Operation of system  100  is shown in  FIGS. 4A through 4G . In  FIGS. 4A through 4G , states of valves are indicated by the symbols shown in the legends of each drawing figure. In particular, a closed valve is indicated by an “X” and an open valve is indicated by an arrow. On and off states of pump  131  and vacuum source  106  are indicated by added text labels.  FIGS. 4A and 4B  show operations to connect housings to, and initially fill housings with ER fluid from, system  100 . In  FIG. 4A , a discharge fitting  121  is placed into an inlet (e.g., a sprue  17 ) of a housing  10 , and the corresponding valve  120  is opened to allow ER fluid  10  from system  100  to fill the housing. The valve  120  is allowed to remain open until ER fluid  110  begins to emerge from the housing outlet (e.g., from a sprue  16 ), at which point the valve  120  is closed. As shown in  FIG. 4B , a fitting  128  of a recovery port  125  is then placed into the housing outlet, and the valves  120  and  127  corresponding to the fittings placed in the housing are opened. The operations of  FIGS. 4A and 4B  are then repeated for additional housings. During the operations of  FIGS. 4A and 4B , pump  131  is on, vacuum source  106  is off, valves  133  and  134  are open, and valve  111  is closed. ER fluid  110  is flowing through system  110 , as indicated by arrows. Valve  123  of bypass  122  is open so as to prevent pump  131  from having insufficient input flow while housings are being connected. 
     In a subsequent operation shown in  FIG. 4C , after all housings have been connected, valve  123  of bypass  122  is closed to cause maximum flow of ER fluid  110  through connected housings  10 . ER fluid  110  is then continuously pumped through connected housings  10  for first time interval T 1 . In some embodiments, T 1  may have a duration of e.g., 5 minutes. During interval T 1 , degassed ER fluid  110  flows from manifold  117  into, and through, each connected housing  10 . This flow gathers bubbles that may have formed within housings  10  during initial filling and carries those bubbles out of the housing. Recovered ER fluid  110  from each of the housings  10  flows into manifold  124  and is driven by pump  131  back to gas remover  102 . Gas remover  102  exhausts those bubbles into headspace  108  through vent  104  and outputs degassed ER fluid  110  into reservoir  101  through output port  105 . 
     During a portion of interval T 1 , and as shown in  FIG. 4D , connected housings  10  may be inverted in the vertical plane. In some embodiments, supply lines  119  and  126  have sufficient length to facilitate this inversion. Inversion may use gravity to help dislodge bubbles out of regions that may be partially shielded from flow and into regions receiving a stronger flow, thereby allowing such bubbles to be carried away. 
     After interval T 1 , bypass valve  123  is opened and valves  120  and  127  are closed. Each of housings  10  is then removed and reconnected to system  110  in a reverse manner. For example, if fittings  121  and  128  were respectively located in sprues  17  and  16  of a housing  10  during interval T 1 , fitting  121  is placed into sprue  16  and fitting  128  is placed into sprue  17 . After reconnection, the valves  120  and  127  of the reconnected fittings are opened. After each of the housings has been reconnected in this manner, and as shown in  FIG. 4E , bypass valve  123  is closed. ER fluid  110  is then continuously pumped through connected housings  10  for second time interval T 2 . Interval T 2  may have a duration that is the same as, or that is shorter or longer than, the duration of interval T 1 . During interval T 2 , degassed ER fluid  110  flows from manifold  117  into, and through, each connected housing  10  in a reverse direction relative to the flow during interval T 1 . This flow gathers bubbles that may have been captured in an internal housing region that is more shielded from flow in one direction, but which is less shielded from flow in the opposite direction. Recovered ER fluid  110  from each of the housings  10  again flows into manifold  124  and is driven by pump  131  back to gas remover  102 . Gas remover  102  again exhausts bubbles into headspace  108  through vent  104  and outputs degassed ER fluid  110  into reservoir  101  through output port  105 . 
     During a portion of interval T 2 , and as shown in  FIG. 4F , connected housings  10  may again be inverted in the vertical plane. 
     After interval T 2 , bypass valve  123  is opened and the housings are removed from system  100 . As each housing is removed, valves  120  and  127  corresponding to the fittings  121  and  128  removed from that housing are closed. The inlets and outlets of each removed housing may then be sealed by, e.g., RF welding across each sprue. 
     Additional series of the operations of  FIGS. 4A through 4F  may then be performed for additional sets of housings  10 . After removal of the housings at the end of a final series of those operations, and as shown in  FIG. 4G , pump  131  is turned off and valves  134  and  133  are closed. Additional ER fluid  110  may be added to reservoir  101  through a feed opening (not shown) to replace ER fluid that remains in the housings  10  that were filled during the operations of  FIGS. 4A through 4F . After sealing that feed opening, valve  111  is opened and vacuum source  106  is turned on. Headspace  108  is then maintained at PSA during a third interval T 3 . In some embodiments, interval T 3  may have a duration of at least 30 minutes, at least 1 hour, or at least 4 hours. While exposed to pressure PSA, dissolved air or minute bubbles that may have escaped removal by gas remover  102  are drawn out of EF fluid  110 . At the conclusion of interval T 3 , vacuum source  106  is turned off, valve  111  is closed, and system  100  is then available to perform further series of the operations of  FIG. 4A through 4F . 
       FIG. 5A  is a partially schematic block diagram showing a fluid system  200  according to some further embodiments. Like system  100 , system  200  includes a gas remover  202 . In system  200 , however, gas remover  202  is a different type of gas remover and is located outside of reservoir  101 . Other elements of system  200  are the same as elements of system  100 . Elements of system  200  that are the same as elements of system  100  are identified with the same reference numbers used in  FIGS. 3A  through  4 G, and previous descriptions of details of those elements apply in connection with system  200 . 
       FIG. 5B  is a block diagram of gas remover  202 . Gas remover  202  of system  200  is an ultrasonic bubble remover. Gas remover  202  includes a reactor chamber  270  into which ER fluid  110  is pumped by pump  131 . During operation of system  200 , the ER fluid  110  pumped into chamber  270  may have been discharged from connected housings and include gas for removal. A “barbell” horn  271  is partially immersed in ER fluid  110  within chamber  270 . A transducer  272  is attached to the other end of horn  271 , with transducer  272  connected to a separate generator (not shown) that drives transducer  272 . Ultrasonic processors such as gas remover  202  are commercially available. One example of such a processor is the ISP-3000 Industrial-Scale Ultrasonic Liquid Processor provided by Industrial Sonomechanics, LLC of New York, N.Y., US. When gas remover  202  is turned on, ultrasonic energy from horn  271  forces gas out of ER fluid  110  within chamber  270 . One or more vents  273  in chamber  270  may allow removed air to escape. In some embodiments, gas remover  202  may utilize a Full-wave Barbell Horn (FBH) with an output tip diameter of 35 mm, operated at the ultrasonic amplitude of 100 micro-meters peak-to-peak, and operated at a frequency of approximately 20 kHz. 
     System  200  may be used in operations similar to the operations described in connection with system  100  and  FIGS. 4A through 4G . In a first set of operations, ER fluid housings may be connected to, and initially filed with ER fluid from, system  200 . Except for the performance of such operations using system  200  instead of system  100 , the operations to connect and initially fill ER fluid housings using system  200  are the same as the operations described in connection with  FIGS. 4A and 4B . 
     In a subsequent operation shown in  FIG. 6A , after all housings have been connected, valve  123  of bypass  122  is closed to cause maximum flow of ER fluid  110  through connected housings  10 . ER fluid  110  is then continuously pumped through connected housings  10  for first time interval T 1 . In some embodiments, T 1  may have a duration of e.g., 5 minutes. During interval T 1 , degassed ER fluid  110  flows from manifold  117  into, and through, each connected housing  10 . Recovered ER fluid  110  from each of the housings  10  flows into manifold  124  and is driven by pump  131  back to gas remover  202 . Gas remover  202  removes bubbles from the recovered ER fluid  110  and outputs degassed ER fluid  110  into reservoir  101 . During a portion of interval T 1 , and as shown in  FIG. 6B , connected housings  10  may be inverted in the vertical plane. 
     After interval T 1 , bypass valve  123  is opened and valves  120  and  127  are closed. Each of housings  10  is then removed and reconnected to system  200  in a reverse manner similar to that described above in connection with system  100 . After reconnection, the valves  120  and  127  of the reconnected fittings are opened. After each of the housings has been reconnected in this manner, and as shown in  FIG. 6C , bypass valve  123  is closed. ER fluid  110  is then continuously pumped through connected housings  10  for second time interval T 2 . Interval T 2  may have a duration that is the same as, or that is shorter or longer than, the duration of interval T 1 . During interval T 2 , degassed ER fluid  110  flows from manifold  117  into, and through, each connected housing  10  in a reverse direction relative to the flow during interval T 1 . Recovered ER fluid  110  from each of the housings  10  again flows into manifold  124  and is driven by pump  131  back to gas remover  202 . Gas remover  202  again removes bubbles and outputs degassed ER fluid  110  into reservoir  101 . During a portion of interval T 2 , and as shown in  FIG. 6D , connected housings  10  may again be inverted in the vertical plane. 
     After interval T 2 , bypass valve  123  is opened and the housings are removed from system  200 . As each housing is removed, valves  120  and  127  corresponding to the fittings  121  and  128  removed from that housing are closed. The inlets and outlets of each removed housing may then be sealed by, e.g., RF welding across each sprue. Additional series of the operations of  FIGS. 6A through 6D  (including initial connection and filling operations similar to those of  FIGS. 4A and 4B ) may then be performed for additional sets of housings  10 . After removal of the housings at the end of a final series of those operations, and as shown in  FIG. 6E , pump  131  is turned off and valves  134  and  133  are closed. Additional ER fluid  110  may be added to reservoir  101  through a feed opening (not shown). After sealing that feed opening, valve  111  is opened and vacuum source  106  is turned on. Headspace  108  is then maintained at PSA during a third interval T 3 . In some embodiments, interval T 3  may have a duration of at least 30 minutes, at least 1 hour, or at least 4 hours. At the conclusion of interval T 3 , vacuum source  106  is turned off, valve  111  is closed, and system  200  is then available to perform further series of the operations of  FIG. 6A through 6D . 
       FIG. 7  is a partially schematic block diagram showing a fluid system  300  according to some additional embodiments. Like systems  100  and  200 , system  300  includes a gas remover  302 . In system  300 , however, gas remover  302  comprises a series of filters  381  through  385 . Each of filters  381  through  385  extends completely across the interior of reservoir  101 . ER fluid  110  entering reservoir  101  through inlet  391  must therefore pass through each of filters  381  through  385  before reaching outlet  392 . Entrained bubbles in ER fluid  110  are captured by one of filters  381  through  385  and ultimately rise to headspace  108 . Although the embodiment of  FIG. 7  shows gas remover  302  having five filters, in other embodiments additional or fewer filters may be included. In some embodiments, each of the filters may be a 10 micron mesh filter. In other embodiments, one or more of the filters may be a different size filter. In some such embodiments, for example, a coarser filter may be used near inlet  391  and a finer filter may be used near outlet  392 . 
     Other elements of system  300  are the same as elements of systems  100  and  200 . Elements of system  300  that are the same as elements of previously-described systems are identified with the same reference numbers used above, and previous descriptions of details of those elements apply in connection with system  300 . 
     System  300  may be used in operations similar to the operations described in connection with systems  100  and  200 . In a first set of operations, ER fluid housings may be connected to, and initially filed with ER fluid from, system  300 . Except for the performance of such operations using system  300  instead of system  100 , the operations to connect and initially fill ER fluid housings using system  300  are the same as the operations described in connection with  FIGS. 4A and 4B . 
     In a subsequent operation shown in  FIG. 8A , after all housings have been connected, valve  123  of bypass  122  is closed to cause maximum flow of ER fluid  110  through connected housings  10 . ER fluid  110  is then continuously pumped through connected housings  10  for first time interval T 1 . In some embodiments, T 1  may have a duration of e.g., 5 minutes. During interval T 1 , degassed ER fluid  110  flows from manifold  117  into, and through, each connected housing  10 . Recovered ER fluid  110  from each of the housings  10  flows into manifold  124  and is driven by pump  131  back to reservoir  101  and gas remover  302 . Gas remover  302  removes bubbles from the recovered ER fluid  110  and provides degassed ER fluid  110  in reservoir  101  near outlet  392 . During a portion of interval T 1 , and as shown in  FIG. 8B , connected housings  10  may be inverted in the vertical plane. 
     After interval T 1 , bypass valve  123  is opened and valves  120  and  127  are closed. Each of housings  10  is then removed and reconnected to system  300  in a reverse manner similar to that described above in connection with system  100 . After reconnection, the valves  120  and  127  of the reconnected fittings are opened. After each of the housings has been reconnected in this manner, and as shown in  FIG. 8C , bypass valve  123  is closed. ER fluid  110  is then continuously pumped through connected housings  10  for second time interval T 2 . Interval T 2  may have a duration that is the same as, or that is shorter or longer than, the duration of interval T 1 . During interval T 2 , degassed ER fluid  110  flows from manifold  117  into and through each connected housing  10  in a reverse direction relative to the flow during interval T 1 . Recovered ER fluid  110  from each of the housings  10  again flows into manifold  124  and is driven by pump  131  back to reservoir  101  and gas remover  302 . Gas remover  302  again removes bubbles and provides degassed ER fluid  110  at the outlet  392  of reservoir  101 . During a portion of interval T 2 , and as shown in  FIG. 8D , connected housings  10  may again be inverted in the vertical plane. 
     After interval T 2 , bypass valve  123  is opened and the housings are removed from system  300 . As each housing is removed, valves  120  and  127  corresponding to the fittings  121  and  128  removed from that housing are closed. The inlets and outlets of each removed housing may then be sealed by, e.g., RF welding across each sprue. Additional series of the operations of  FIGS. 8A through 8D  (including initial connection and filling operations similar to those of  FIGS. 4A and 4B ) may then be performed for additional sets of housings  10 . After removal of the housings at the end of a final series of those operations, and as shown in  FIG. 8E , pump  131  is turned off and valves  134  and  133  are closed. Additional ER fluid  110  may be added to reservoir  101  through a feed opening (not shown). After sealing that feed opening, valve  111  is opened and vacuum source  106  is turned on. Headspace  108  is then maintained at PSA during a third interval T 3 . In some embodiments, interval T 3  may have a duration of at least 30 minutes, at least 1 hour, or at least 4 hours. At the conclusion of interval T 3 , vacuum source  106  is turned off, valve  111  is closed, and system  300  is then available to perform further series of the operations of  FIG. 8A through 8D . 
     In some embodiments, a system may be configured to treat ER fluid with a vacuum while that system is pumping ER fluid through a gas remover and through ER fluid housings.  FIGS. 9A through 9E  show operations in a system  400  according to one such embodiment. System  400  is similar to system  100 , but with several additional components added. In addition to reservoir  101 , system  400  includes a second reservoir  401 . Reservoirs  101  and  401  are connected by a transfer conduit  495 . A valve  496  in conduit  495  is actuatable by a solenoid  497  to open and close conduit  495 . Reservoir  401  is connected by a conduit  493  to an input of a second pump  488 , with conduit  492  connecting the output of pump  488  to manifold  117 . Valve  494 , as well as valves  434  (replacing valve  134  of system  100 ) and  411  (replacing valve  111  of system  100 ) are actuatable by respective solenoids  485 ,  487 , and  486 . A computer operated controller  498  is configured to control solenoids  485  through  487  and  497 , and is further configured to activate and deactivate pump  132 , pump  488 , and vacuum source  106 . Controller  498  may include a processor and memory storing instructions that, when executed by the processor, cause the processor to perform operations such as are described herein. Controller  498  is also communicatively coupled to a fluid level sensor  490  in reservoir  401 . A float  491  of sensor  490  rises and falls with the level of ER fluid  110  in reservoir  110  and outputs a signal, based on the position of float  491 , indicative of the level of ER fluid  110  present in reservoir  401 . Float-operated fluid level sensors are known in the art. 
     Manifolds  117  and  124  are similar to manifolds  117  and  124  of previously described embodiments. Manifold  117  includes discharge ports  118  and manifold  124  includes recovery ports  125 , although only valves  120  and  127  of ports  118  and  125  are marked in  FIGS. 9A through 9E . Other elements of system  400  that are the same as elements of systems  100 ,  200 , and  300  are identified with the same reference numbers used in  FIGS. 3A through 4G , and previous descriptions of those elements apply in connection with system  400 . 
     System  400  may be used to perform operations similar to those described in connection with  FIGS. 4A through 4F . Unlike system  100 , however, system  400  fills connected housings with degassed ER fluid  110  from reservoir  401 . Fluid is pumped from reservoir  401  to manifold  117  by pump  488 . Recovered ER fluid  110  that is received in manifold  124  is pumped by pump  132  through gas remover  102  and into reservoir  101 . At the same time, vacuum source  106  is activated and pressure PSA is maintained within reservoir  101 . While ER fluid  110  is being pumped to gas remover  102  and into reservoir  101 , and while pressure PsA is being maintained in reservoir  101 , valve  496  is closed. 
       FIG. 9B  shows system  400  after multiple series of operations similar to those of  FIGS. 4A through 4F  have been performed. Reservoir  401  is almost depleted and reservoir  101  is almost full. In response to a signal from sensor  490  indicating that the fluid level within reservoir  401  has dropped to a predetermined level, controller  498  places system  400  into a reservoir-to-reservoir transfer mode. Additional details of this mode are shown in  FIG. 9C . Controller  498  has turned off vacuum source  106  and pumps  132  and  488 . Controller has closed valves  434 ,  411 , and  494 , and has opened valve  496 , by actuating the corresponding solenoids. Controller  498  may also cause reservoir  101  to be vented to atmospheric pressure by actuating a solenoid of a separate vent valve (not shown) in reservoir  101 . As a result, ER fluid  110  stops flowing between valve  494  and valve  434  through manifolds  117  and  124  and connected housings. Fluid flows from reservoir  101  into reservoir  401 . In some embodiments, and as indicated in  FIG. 9C , reservoirs  101  and  401  are positioned so that ER fluid  110  may flow by gravity alone. In other embodiments, a separate transfer pump may be interposed in conduit  495  and controlled by controller  498 . 
     Controller  498  maintains system  400  in the reservoir-to-reservoir fluid transfer mode until the level of ER fluid  110  in reservoir  401  reaches a second predetermined level, as shown in  FIG. 9D . In response to receiving a signal from sensor  490  indicating that the second predetermined level is reached, and as shown in  FIG. 9E , controller  498  returns system  400  to the filling mode. In particular, controller  498  closes valve  496  and opens valves  434 ,  412 , and  494  by actuating the corresponding solenoids, closes the valve venting reservoir  101  to atmospheric pressure, turns on vacuum source  106 , and turns on pumps  132  and  488 . 
     As can be appreciated from the above discussion, system  400  is a modification of system  100  to treat ER fluid with a vacuum while pumping ER fluid through a gas remover and through ER fluid housings. This modification includes, e.g., addition of a second reservoir to receive degassed ER fluid from the first reservoir when the level of degassed ER fluid within the second reservoir drops to a certain level. As can be appreciated by persons skilled in the art, after such persons have the benefit of the teachings provided herein, systems  200  and  300  could be modified in a similar manner.  FIGS. 10A and 10B  are block diagrams of a system  500  reflecting such a modification of system  200 .  FIG. 10A  shows system  500  in a normal operating mode while pumping ER fluid  110  through connected housings.  FIG. 10B  shows system  500  in a reservoir-to-reservoir transfer mode. System  500  operates in a manner similar to that described for system  400 , except that controller  498  also deactivates gas remover  202  when in the reservoir-to-reservoir transfer mode. 
       FIGS. 11A and 11B  are block diagrams of a system  600  reflecting a modification of system  300 .  FIG. 11A  shows system  600  in a normal operating mode while pumping ER fluid  110  through connected housings.  FIG. 11B  shows system  600  in a reservoir-to-reservoir transfer mode. System  600  operates in a manner similar to that described for system  400 , except that controller  498  also opens a valve  651  in a conduit  699  when in normal operating mode so that ER fluid  110  will flow across filters  381  through  385 . Controller  498  opens and closes valve  651  by actuating a corresponding solenoid  652 . Conduit  699  may include a one-way valve  659  to prevent flow through conduit  699  in the wrong direction. In some embodiments, conduit  699  may include an additional pump (not shown) to help fluid flow in the proper direction. If included, such a pump could be turned on by controller  498  when valve  651  is open and turned off by controller  498  when valve  651  is closed. In some embodiments, conduit  699  may be omitted. 
     Embodiments include, without limitation, the following variations on the systems and methods described above.
         In some embodiments employing a centrifugal flow bubble remover such as that described in connection with  FIGS. 3A and 3C , the bubble remover may be located outside of a reservoir.   In some embodiments, a fluid system may include multiple different types of gas removers that operate simultaneously. Such embodiments include, without limitation, systems using a centrifugal flow bubbler remover and an ultrasonic bubble remover, systems using a centrifugal flow bubble remover and one or more filters, systems using an ultrasonic bubble remover and one or more filters, and systems using a centrifugal flow bubbler remover, an ultrasonic bubble remover, and one or more filters.   In some embodiments, one or more of the operations described in above may be omitted. As one example, pumping ER fluid through housings in a reversed direction may be omitted. As another example, inverting housings may be omitted, or housings may only be inverted a single time (e.g., inverted during flow in one direction through housings, but not when flow through reverse direction is performed). The order of certain operations described above may be varied.   In some embodiments, vacuum operations such as those described in connection with  FIGS. 4G, 6E, and 8E  may not be performed.   In some embodiments, a system may lack a bypass between manifolds. In some such embodiments, a pump is only turned on when all housings are connected and ER fluid is able to flow through those connected housings. Prior to initial connection of those housings to such a system, those housings may be separately filled from another source of ER fluid.       

     The foregoing description of embodiments has been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit embodiments of the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments. The embodiments discussed herein were chosen and described in order to explain the principles and the nature of various embodiments and their practical application to enable one skilled in the art to utilize the present invention in various embodiments and with various modifications as are suited to the particular use contemplated. Any and all combinations, subcombinations and permutations of features from herein-described embodiments are the within the scope of the invention.