Abstract:
This invention relates to a check valve ( 19 ) for use in an ink supply line ( 13 ) of an ink jet printing system ( 1 ) between an ink reservoir ( 11 ) and an inkjet printhead ( 3 ) so as to prevent de-priming of the printhead upon the latter being subjected to impact loads or the like. Specifically, the improvement of this invention comprises a one-piece check valve ( 37 ) of an elastomeric material having a flapper valve ( 43 ) movable between a closed position in which the flapper valve blocks the backflow of ink and an open position in which ink is free to flow past the check valve member to the printhead. The flapper valve ( 43 ) is defined by a slot ( 49 ) separating the flapper valve from the outer margin ( 41 ) of the check valve ( 37 ) and the flapper valve is integrally joined to the outer margin by a hinge portion ( 45 ) so as to enable movement of the flapper valve between its open and closed positions.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to ink jet printing, and, more specifically, to ink jet printing systems used to imprint packages or cartons with various indicia as the packages are conveyed past an ink jet printhead at a printing station positioned along a conveyor path. Such inkjet printing systems are oftentimes used to imprint shipping information, bar codes, lot numbers and other production or shipping information on overcartons or secondary packaging in a production packaging line or the like. The printhead of such inkjet printing systems is typically supplied with ink from an ink supply remote from the printhead by means of appropriate ink tubes or lines. 
     Because the printheads are located in close proximity to the cartons (or other objects to be imprinted) as they are conveyed past the printhead if a carton is not properly positioned on the conveyor line, the carton may come into contact with the printhead as the carton is conveyed therepast. In some applications, the cartons are conveyed past the printhead with considerable speed (up to 150 feet/minute or more) and the cartons are heavy. Upon the printhead being hit by one of these heavy cartons being conveyed at such speeds, a considerable impact or shock load is imparted to the printhead. It is known that such impact loads can cause the printhead to de-prime. 
     It is believed that upon the above-described shock load being imparted to the printhead, a back pressure or shock wave is generated within the ink supply line which travels at extremely high speed through the ink supply line toward the ink reservoir. This shock wave can so reduce the pressure within the ink supply line as to de-prime the printhead. More specifically, and especially with capillary ink feed systems, it is believed that the shock wave may generate back pressures in the ink supply system sufficient to break the meniscus of the ink in the ink orifices of the printhead thus de-priming the printhead. Such de-priming of the printhead is a serious problem. 
     In the event the printhead de-primes, the printhead will not print until it again is primed with ink. If cartons conveyed past the printhead in a production packaging line are not imprinted, the cartons must be removed from the production line and must either be manually marked or, after the printhead is re-primed, must be positioned on the conveyor line so as to be again conveyed past the printhead for being properly imprinted by the printhead. This, of course, can cause major problems on a production line using such ink jet printing systems. 
     In addition, it is a time consuming process to re-prime a printhead during which time the packaging line on which the printing system is installed must be shut down. Of course, it is highly undesirable and costly to shut down a production packaging line. In addition, with certain ink jet printing systems, special inks are required to prime the printheads. These special priming inks are expensive and are time consuming to use. 
     It has long been a goal for such ink jet print systems, and particularly for capillary ink feed systems, to lessen the tendency of the printhead to de-prime. One way of reducing the tendency of the printhead to de-prime has been to incorporate a check valve in the ink supply line between the ink reservoir and the printhead. Upon a back pressure or shock wave being generated in the printhead and traveling back through the ink supply line, and upon this back pressure or shock wave encountering the check valve, the check valve will close thus preventing the shock wave from traveling to the ink supply. However, it has been found that the incorporation of prior art check valves (as hereinafter described in detail), in the ink supply circuit has not abated the tendency of the printhead to de-prime. It is believed that movement of the check valve member from its open to its closed position can sometimes generate a region of low pressure within the ink supply system which can cause a pressure differential of sufficient magnitude to result in de-priming of the printhead. 
     Still further, the incorporation of a check valve in the ink supply system has other draw backs. First, if the check valve is normally closed, upon initiating flow of ink to the printhead (which is usually in pulses rather than in a steady state flow), the normally closed check valve will require a higher pressure to initially open the check valve (referred to as a cracking pressure). Further, such check valves are susceptible to contamination from particles in the ink such that an accumulation of such contamination particles may adversely affect the operation of such check valve. Still further, the incorporation of such a check valve in the ink supply lines causes a flow restriction that may adversely affect the flow of ink to the printhead and may increase the response time of the ink supply system to the printhead. 
     As noted, prior art printheads have used check valves in the past. As shown in FIG. 10 of the drawings, a first embodiment of such a prior art check valve is shown which has been used with a capillary ink supply system for an ink jet printhead. This prior art check valve, as indicated in its entirety at  101 , has a valve body  103  having an inlet  105  and an outlet  107  with a check valve chamber  109  therewithin. A check valve member, as indicted at  111 , is provided in chamber  109  which is movable from a closed position in which the downstream face of the check valve member is in sealing engagement with the downstream face of the chamber  109  surrounding inlet  105  so as to block the backflow of ink from chamber  109  into inlet  105 . Upon the check valve member  111  being subjected to normal flow via the inlet  105  from the ink supply to the printhead, the flow will cause the check valve member  111  to shift from its above-described closed position to an open position within chamber  109  in which ink may flow around the periphery of the check valve member  111  and to be discharged from the outlet  107  for flowing to the printhead. In such prior art check valves, the check valve member  111  was typically made of a flexible, resilient elastomer, such as a suitable silicone rubber material or the like, and the check valve member has a diameter somewhat less than the inner diameter of chamber  109  such that the check valve member is free to move within the chamber between its open and its closed positions. As shown, with the check valve member  111  in its open position, the ink is free to enter the chamber  109  on the downstream face of check valve member  111  and to flow around the periphery of the check valve member and to flow to outlet  107 . 
     It will be appreciated that the average flow rate of ink through the above-noted check valves to the printhead is very low (e.g., about 0.5 ml./min.). Moreover, the size of such check valves is small. For example, the diameter of the check valve member  111 , as shown in FIG. 8 may only be about 0.110 inches. Referring again to the check valve shown in FIG. 7, upon a shock wave (back pressure pulse) traveling from the printhead to the check valve, the shock wave will travel through the outlet  107  and will enter chamber  109 . There, the back pressure or shock wave will act against the entire upstream face of valve member  111  thus causing the member to move axially within chamber  109  to its closed position. However, upon the valve member moving within the chamber from its open to its closed position, the volume of the chamber on the upstream side of the valve member expands greatly and thus generates a low pressure void within the valve chamber. This in turn lowers the pressure within the ink supply line upstream from the check valve and within the printhead. This low pressure may be sufficient to overcome the meniscus force of the ink within the ink orifices of the printhead and thus may result in de-priming of one or more orifices of the printhead. Thus, even with the presence of such check valve in the ink supply system, the check valve did not eliminate the de-priming problem and may even be a cause of printhead de-priming. 
     In an effort to overcome the shortfalls of the check valve shown in FIG. 10, a second embodiment of a prior art check valve, as shown in FIG. 11, has been used with such ink jet printing systems in an effort to further minimize the tendency of the printhead to de-prime upon the printhead being struck by a carton, as above-described. In this other embodiment of a prior art check valve, the check valve, as indicated in its entirety at  201 , has a valve body  203  having an ink inlet  205  and an ink outlet  207  with a check valve chamber  209  therebetween. Similar to valve  101  heretofore described, check valve  201  has an elastomeric check valve member  211  disposed in chamber  209  for blocking back flow from the chamber to inlet  205  when the check valve member  211  is in its closed position. In addition, a part spherical or a conical support  213  is provided at the downstream side of the chamber and the support has an apex  215 . Support  213  is of open construction so that ink may flow through the support to the outlet  207 . Check valve member  211  is disposed between the downstream face of chamber  209  and support  213  such that the center of the downstream face of the check valve member is engageable by apex  215  of support  213 . Check valve member  211  is normally of a flat, planar shape. However, upon installation of check valve member  211  in chamber  209 , the check valve member is deformed into a convex configuration, as shown in FIG. 11, in which the outer margins of the downstream face of the check valve member are in sealing contact with the downstream end of chamber  209  so as to block the flow of ink from inlet  205  to outlet  207 . Upon a slight pressure differential within chamber  209  so as to cause ink to flow from inlet  205  to outlet  207 , the apex  215  is engaged by the check valve member and the outer margins of the check valve member are caused to flex inwardly away from the sides of chamber  209  and the upstream face of the check valve member moves clear of the inlet face of the chamber thereby to enable ink to flow to outlet  207 . 
     Upon a shock wave being generated in the printhead (in the manner above described), the shock wave will enter chamber  209  via outlet  207  and will act against the concave upstream face of valve member  211  facing conical support  213 . This causes the valve member to shift toward its closed position and the outer edges of the check valve member move outwardly so as to sealingly engage the walls of chamber  209  and to check the backflow of the ink. 
     It will be appreciated that the check valves of FIGS. 10 and 11 are not drawn to the same scale. Specifically, check valve  201  shown in FIG. 11 has a considerably larger cross section than check valve  101  shown in FIG.  10 . For example, the diameter of check valve member  211  is about three (3) times the diameter of check valve member  111 . As a result of this larger size, the check valve member also allows a low pressure zone to be formed within chamber  209  which can result in de-priming of the printhead. Further, check valve  201  is also susceptible to contamination particles interfering with operation of the check valve, and valve  201  still requires a cracking pressure to initiate ink flow. 
     There has been a long-standing need for a check valve for use in an ink jet ink supply system, which more effectively prevents de-priming of the printhead, which requires less cracking pressure, which is less susceptible to ink contamination particles interfering with operation of the check valve, and which has a faster response time than prior check valves. 
     BRIEF SUMMARY OF THE INVENTION 
     Among the several objects and features of the instant invention may be noted the provision of a check valve which may be readily incorporated within the ink supply system of a capillary ink supply for an ink jet printing system between the ink supply reservoir and the ink jet printhead which reliably prevents de-priming of the printhead upon the printhead being subjected to an impact or shock load, such as upon the printhead being hit by a package conveyed therepast. 
     The provision of such a check valve which has a minimum cracking pressure and which has a minimum response time such that the check valve has little or no adverse affect on the normal operation of the ink supply system. 
     The provision of such a check valve which is not adversely sensitive to deposits of contamination particles which may accumulate within the check valve over an extended period of service. 
     The provision of such a check valve which is of simple and low construction, and which is reliable in operation. 
     Other objects and features of this invention will be in part apparent and in part pointed out hereinafter. 
     This invention is a check valve for use in an ink supply line of an ink jet printing system between an ink reservoir and a inkjet printhead so as to prevent de-priming of the printhead upon the latter being subject to impact loads or the like. The check valve has a body having an inlet adapted to be connected to and ink reservoir, an outlet adapted to be connected to the printhead, a chamber within the housing between the inlet and the outlet, and a check valve member within the chamber movable between a closed position in which ink back flow from the chamber into the inlet is prevented and an open position in which ink from the inlet may flow to the outlet and thence to the printhead. Specifically, the check valve member is an elastomeric member having a flapper valve portion movable between a closed position in which the flapper valve blocks the backflow of ink from the chamber into the inlet and an open position in which ink is free to flow past the check valve member from the inlet to the outlet. The flapper valve portion is defined by a curved slot separating the flapper valve from the outer margin of the check valve member. The flapper valve is integrally joined to the outer margin by a hinge portion so as to enable movement of the flapper valve relative to the outer margin of the check valve member between its open and closed positions. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is an elevational view of an inkjet printhead positioned proximate a conveyor along which objects (cartons) to be printed by the printhead are conveyed past the printhead with the printhead being supplied ink from an ink reservoir via an ink supply line; 
     FIG. 2 is an exploded perspective view of the print engine of the printhead having multiple ink jet orifices therein and illustrating a check valve of the present invention installed in the ink supply line proximate the print engine for preventing de-priming of the orifices upon the printhead being subjected to an impact load or the like; 
     FIG. 3 is an enlarged side elevational exploded view of the check valve of the present invention illustrating an inlet fitting, and outlet fitting, and a check valve member interposed therebetween; 
     FIG. 4 is a view taken along line  4 — 4  of FIG. 3 illustrating a flapper-type check valve member of the present invention; 
     FIG. 5 is a side elevational view of the check valve member shown in FIG. 4 with the flapper valve (as shown in solid lines) in its closed position in which the upstream face of the flapper valve is in sealing engagement with the structure (shown in phantom) of the fitting housing forming the inlet bore of the check valve thereby to prevent back flow of ink from the printhead to the ink supply and an open position (as shown in dotted lines) in which the flapper valve is hingedly moved away from the fitting structure thus allowing ink to flow from the inlet bore to the printhead; 
     FIG. 6 is an exploded perspective view of the check valve of the present invention; 
     FIG. 7 is a longitudinal cross sectional view of the check valve of the present invention; 
     FIG. 8 is a longitudinal cross sectional view of still another embodiment of a check valve of the present invention having a “duckbill” or reed-type valve member with the valve member in its closed position; 
     FIG. 9 is a view similar to FIG. 8 showing the “duckbill” valve member in its open position; 
     FIG. 10 is a longitudinal cross sectional view of a first prior art check valve heretofore used with printheads; and 
     FIG. 11 is a longitudinal cross sectional view of another embodiment of a prior art check valve heretofore used with printheads. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more specifically to FIG. 1, an inkjet printing station, as generally indicated at  1 , is shown in which an inkjet printhead  3  is positioned proximate a conveyor line  5  which conveys objects O (cartons) past printhead  3  so that the printhead may inkjet print indicia on the objects as the objects are conveyed past the printhead. The objects O to be imprinted are cartons and the cartons are conveyed in the direction “out of the paper”, as shown in FIG.  1 . It will be noted that the printing face of the printhead is in close proximity to the face of the carton to be imprinted. As described in the co-assigned U.S. patent application Ser. No. 08/728,744 filed Oct. 11, 1996, the printhead may be mounted on a resilient mount  7  so as to allow the printhead to be engaged by a carton conveyed along the path of the conveyor. The printhead has spring guides  9  which are engaged by the carton such that the printhead is moved from an inward initial position to a printing position with the printing face of the printhead being resiliently held in a desired printing position with respect to the surface of the carton to be printed. However, because the cartons may vary in size and because the cartons may be mis-positioned on the conveyor, in some instances the cartons contact the printhead at such speed and with such force that the printhead is subjected to high impact loads which may de-prime the printhead, as described in the Background of this Invention. Print station  1  further comprises an ink supply or reservoir, as indicated at  11 , and ink is supplied to printhead  3  from the ink supply by means of an ink supply line  13 . 
     Referring now to FIG. 2, the print engine, as indicated at  15 , of printhead  3  is shown to have a plurality of ink jet printing orifices  17  for emitting ink jet droplets in a controlled fashion for imprinting indicia on cartons O in the conventional manner. Ink supply line  13  has a check valve of the present invention as indicated generally at  19 , installed therein adjacent print engine  15  for preventing the back flow of ink to the reservoir which may cause de-priming of the orifices  17  of the print engine upon the printhead being subjected to impact loads as upon being struck by a carton or the like conveyed past the printhead. Preferably, check valve  19  is housed within printhead  3 . 
     The print engine herein shown uses a so-called capillary ink supply system, but it will be understood that other types of print engines are also subject to de-priming and the check valve  19  of the present invention (as will be hereinafter described) may be used with such other ink jet printing systems to prevent de-priming. 
     Referring now to FIG. 3, check valve  19  of the present invention is shown to comprise an inlet fitting  21  and an outlet fitting  23 . These fittings are preferably molded of a suitable synthetic resin material, such as Delrin or Acetron GP. Inlet fitting  21  has an inlet bore  25  and a nipple end  27  which is adapted to be sealably inserted into ink supply line  13  so that ink from ink reservoir  11  may flow to printhead  3 . Likewise, outlet fitting has an outlet bore  29  and a similar nipple end  31  so that the outlet fitting may be operably connected to print engine  15  so as to supply ink to the various ink jet orifices  17 . It will be appreciated that the inlet and outlet bores  25  and  29 , respectively, are of relatively small diameter (e.g., 0.081 inches). It will be appreciated that outlet bore  29  may have an inwardly converging upstream end, as indicated at  32 , for receiving ink from the inlet fitting. 
     As shown in FIG. 6, with the inlet and outlet fittings  21  and  23  assembled, a check valve body, as indicated in the entirety at  33 , is formed with the latter having a check valve chamber  35  therewithin. Inlet fitting  21  is sealed relative to check valve fitting  23  when assembled by means of an O-ring  36   a  received in an O-ring groove  36   b  formed in inlet fitting  23 . Within check valve chamber  35 , a check valve member  37  is sealingly secured relative to the check valve body. As shown in FIGS. 3 and 5, inlet fitting  21  has a recess  39  (also referred to as the upstream end face of check valve chamber  35 , namely the end face of the chamber toward the ink supply) formed therein which receives check valve member  37 . Check valve member  37  is preferably a one piece elastomeric member having an outer marginal portion  41  and an inner tongue or flapper valve portion  43  integral with the outer marginal portion and attached thereto by a hinge portion  45  for permitting angular hinged movement of the flapper valve portion  43  relative to the outer marginal portion  41  between a closed position (as shown in solid lines in FIG. 5) in which the upstream face  47  of the flapper valve in is sealing engagement with the inlet fitting so as to block the flow of ink from inlet bore  25  into check valve chamber  35  and an open position (as shown in dotted lines in FIG. 5) in which the upstream face  47  of flapper valve portion  43  is spaced from the inlet fitting proximate the outlet of bore  25  so as to enable the flow of ink from the inlet bore into the check valve chamber. As shown in FIG. 6, upon flapper valve portion moving to it open position, the flapper valve will be at least in part received in the conical converging section  32  of outlet bore  29  of the outlet fitting. 
     It will be appreciated that flapper valve  43  is formed integrally with outer portion  41  via hinge portion  45  and that the flapper valve is separated from the outer portion by a slot  49 . Preferably, slot  49  is of a generally U-shaped configuration such that the flapper valve is also of U-shaped configuration. However, within the broader scope of this invention, the flapper valve may be of shapes other than a U-shaped configuration. For example, flapper value may be rectangular or even of triangular shape. Hinge portion  45  is located at the open end of the U-shaped slot  49 . Further, slot  49  is preferably of sufficient width such that the outer edges of flapper valve portion  43  are clear of (do not touch) the inner edges of outer portion  41 . With a slot of such width, the operation of the check valve has been found to be less susceptible to dirt or other particles in the ink and thus the check valve of the present invention reliably operates even under conditions of high particle contamination. Since flapper valve portion  43  is formed (cut) from a generally flat (planar) blank of elastomeric sheet material, it will be appreciated that the flapper valve as a memory such that the flapper valve is resiliently biased to return to its flat planar (closed) position upon removal of an opening force (e.g. the flow of ink to the printhead). 
     As noted, the check valve  19  of the present invention is of relatively small size. For example, the assembled check valve is only about 1.2 inches in length and has an outside diameter of about 0.375 inches. The diameter of check valve member  37  is about 0.25 inches and the part circular shaped flapper valve portion  43  has a diameter of about 0.12 inches. The thickness of the check valve member  37  is about 0.024-0.025 inches. Preferably, slot  49  is about 0.02 inches in width. As noted, check valve member is preferably of a suitable elastomer material, such as silicone rubber, ASTM 9668, without fabric reinforcement. The silicone elastomer may preferably, but not necessarily, have a durometer rating of about 50±5 on the Shore A scale. 
     In operation, with the check valve  19  of the present invention installed in the ink supply line  13  between in reservoir  11  and print engine  15 , flapper valve  43  is in its normally closed to its open position (as shown in dotted lines in FIG.  5 ). Upon ink being drawn to printhead orifices  17 , as by capillary action or the like, the flow of ink from ink supply  11  to printhead  3  is indicated. Because of the resilient construction of check valve member  37 , and particularly because of the low stiffness of hinge  45 , flapper valve requires very little force to move it from its closed to its open position. As noted above, this force required to open the check valve is sometimes referred to as the “cracking force” for the check valve. With the very low flowrates of ink drawn from the ink supply to the printhead and under the very low pressure differentials generated by the capillary flow of ink, flapper valve  43  is readily opened with very low cracking force and with very little resistance to the flow of the ink. Flapper valve  43  will remain open so long as ink continues to flow to the printhead in the normal manner, even at the above-noted low flow rates which may, for example, range from to slightly more than 0 to about 4 ml./min. It will be further appreciated that if the flow to the printhead is in pulses rather than a steady state flow, the flapper valve of the check valve of the present invention will not unduly impede or restrict such flow of ink to the printhead. 
     In the event the printhead  3  is subjected to an impact or shock load, as, for example, may be caused by the printhead being struck by a carton O being conveyed along conveyor  5 , such impact or shock force may form a back pressure or shock wave in the ink within the orifices  17  and within the ink supply line proximate the printhead. This back pressure or shock wave will be transmitted at relatively high speed through the ink supply line  13  back toward ink supply  11 . As noted, check valve  19  of the present invention, is installed in ink supply line  13  (preferably relative near printhead  3 ) so as to prevent the transmission of this back pressure or shock wave from de-priming orifices  17  of ink which will, in turn, prevent printhead from printing. 
     With flapper valve  43  in its open position (as shown in dotted lines in FIG.  5 ), upon the back pressure or shock wave traveling through ink supply line  13  from the printhead to the check valve, upon the back pressure or shock wave entering check valve chamber  35 , this back pressure will act against the side of the flapper valve member  43  facing the printhead (referred to as the downstream face of the flapper valve), and this back pressure or shock wave will exert a force on the flapper valve that results in the near instant closing of the flapper valve against face  39  of the check valve chamber thus blocking the back flow of ink from the printhead into inlet  25 . In this manner, the generation of a negative pressure in the ink supply line between the printhead and the check valve sufficient to result in the de-priming of the inkjet printing orifices  17  of the printhead, even when the printhead is subjected to very high shock or impact loads, is effectively presented. 
     Referring now to FIGS. 8 and 9 illustrate another embodiment of the check valve or the present invention wherein the primary difference between the embodiment of FIGS.  3 - 7  and FIGS. 8 and 9 is the construction and operation of the valve member. Thus, the embodiment of FIGS. 8 and 9 is illustrated in its entirety by reference character  59  and corresponding parts of the embodiment of FIGS. 8 and 9 having a similar construction and operation to the components of the embodiments of FIGS.  3 - 7  are indicated by similar, but “primed” reference characters and thus the function and construction of these similar parts will not be herein separately described. With regard to the differences between the check valve  59  of FIGS. 8 and 9 and the check valves  19 , as described above in regard to FIGS.  3 - 7 , valve member  37 ′ is a so-called “duckbill” or reed valve. Specifically, valve  37 ′ comprises a unitary member molded of suitable silicone elastomer, such as ASTM 9668. The valve member  37 ′ has a base flange  61  which is sealably secured within check valve chamber  35 ′ and a tubular body  63  extending downstream from flange  61 . The downstream end of valve member  37 ′ tapers to a closed end  65  with a slit  67  between the upper and lower valve sections  69   a ,  69   b . The valve sections  69   a ,  69   b  are molded so as to be normally closed. That is, the valve sections  69   a ,  69   b  are molded such that slit  67  is normally closed. Due to the elongate construction of valve sections  69   a ,  69   b  and due to the fact that the valve member  37 ′ is molded of a suitable elastomer, as described above, the valve member, and particularly the valve sections  69   a ,  69   b , are flexible. 
     In operation, upon the pressure within valve the valve sections  69   a ,  69   b  of valve  59  increasing even by a relatively small amount above the downstream pressure, as may be caused by a pulse of ink being caused to flow from ink supply  11  to printhead  3  at the above-noted very low flow rates and at very low pressure differentials (e.g., less than one inch of water pressure), the increased pressure within the valve sections  69   a ,  69   b  causes the valve sections to at least in part deform thereby to result in slit  67  opening to thus allow ink to flow from within the valve member into the valve chamber  35 ′ downstream from valve member  37 ′ and to flow to printhead  3 . Upon a back pressure or shock wave emanating from printhead  3 , the back pressure or shock wave will flow into check valve chamber  35 ′ on the outside of the check valve sections  69   a ,  69   b  and will force the sections from their above-described open position in which slit  67  is open to a closed position in which slit  67  is closed thereby to prevent the back flow of ink through the check valve  59  toward the ink supply. It will be appreciated that it requires very little force (i.e., back pressure or shock wave) to effect closing of the valve sections  69   a ,  69   b  (which are molded in a normally closed position and which must be held in their open position by a nominal positive pressure within the valve members as ink flows from the ink supply to the printhead). Thus, valve member  59  will react very quickly to move from its open to its closed position upon being subjected to a back pressure or a shock wave from the printhead. Likewise, valve  59  exhibits a very low cracking pressure and offers little flow restriction and thus does not unduly impede the flow of ink to the printhead. Contamination particles within the ink have little adverse affect on the closing or opening of valve  59  due to the very flexible nature of valve sections  69   a ,  69   a  and due to the flexible nature of the outer ends of the valve sections and the slit to accommodate dirt particles and yet to effectively close the check valve  59 . 
     In view of the above, it will be seen that the several objects and features of this invention are achieved and other advantageous results attained. 
     As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.