Abstract:
An emitter comprising: a plurality of inlet apertures through which liquid enters the emitter; a manifold flow channel into which liquid that passes through the apertures flow; an elastic diaphragm that seats on the manifold flow channel; an outlet aperture through which liquid that enters the emitter exits the emitter; wherein liquid that enters the inlet apertures displaces only a portion of the diaphragm from the manifold channel so that the liquid can leave the manifold channel and flow through the emitter to reach the outlet aperture.

Description:
BACKGROUND 
     Irrigation systems that deliver water, often containing plant nutrients, pesticides and/or medications, to plants via networks of irrigation pipes are very well known. In many such irrigation networks, water from an irrigation pipe is delivered to the plants by “emitters” or “drippers”, hereinafter generically referred to as emitters, which are connected to or installed along the length of the pipe. Each emitter comprises at least one inlet or an array of inlets through which water flowing in the pipe enters the emitter and an outlet through which water that enters the emitter exits the emitter. The emitter diverts a relatively small portion of water flowing in the pipe and discharges the diverted water to irrigate plants in a neighborhood of the location of the emitter. 
     Generally, to control rate of water discharge by the emitter, the emitter comprises an elastic diaphragm and/or a water flow and pressure reduction channel, a “labyrinth channel” or “labyrinth” through which water that enters the emitter must flow to reach the emitter outlet. The labyrinth channel is a high resistance flow channel along which pressure of water flowing through the emitter drops relatively rapidly with distance along the labyrinth channel. The pressure drop from a relatively high water pressure at the emitter inlet, to a relatively low discharge pressure, generally a gauge pressure equal to about zero, substantially at or near the emitter outlet. The labyrinth channel generally comprises a tortuous “obstacle” flow path that generates turbulence in water flowing in the labyrinth to reduce water pressure and discharge of water by the emitter. Usually, the obstacle path comprises a configuration of baffles that impede and introduce turbulence into water flow. 
     The elastic diaphragm operates to control liquid flow so that it is substantially independent of inlet pressure for a range of pressures typically encountered in irrigation applications and is equal to a flow rate between about 0.5 and 12 liters per hour (l/h). The diaphragm is usually seated on a support shelf and is located between the inlet and the outlet and constrains water that enters the emitter inlet to pass through the labyrinth to reach the emitter outlet and flow out of the emitter. The diaphragm is responsive to pressure of the entering water, and as pressure of the entering water increases, the diaphragm undergoes increasing distortion. The distortion operates to increase resistance to liquid flow through the dripper with increase in distortion. In some emitters, the distortion increases resistance to water flow through the emitter with increase in inlet pressure by increasing a length of the labyrinth through which liquid is constrained to flow to reach the outlet. Some emitters are formed having an outlet reservoir into which water that flows through the labyrinth empties, and from which water exits the emitter and additionally or alternatively, the increase in resistance may be accomplished by changing a dimension of an outlet reservoir to increase resistance of liquid in the outlet reservoir to exit the reservoir. 
     An emitter having a flow regulated so that it is substantially independent of inlet liquid pressure is referred to as a regulated emitter. 
     Labyrinths and various other liquid flow channels in emitters have a tendency to become blocked by particulate matter, such as dirt, debris or agglomerations of plant nutrients that may be carried by liquid that flows through the emitter during plant irrigation from irrigation pipes in which the emitters are mounted. In addition, emitter outlets and flow channels have a tendency to get clogged with dirt and debris that are sucked back into the emitters by water and/or air backflow. Water and/or air backflow typically occurs when supply of water to irrigation pipes providing water to plants in a field or hothouse is turned off and pressure in the pipes falls. For subsurface drip irrigation (SDI) pipes, which are buried in the ground or a growing medium, particulate matter in the surrounding soil or growing medium tends to be drawn into and clog emitters in the pipes when water pressure in the pipes falls. For above surface drip irrigation, backflow tends to clog emitters by drawing into the emitters particulate matter in mud and dust in environments in which the emitters often are located. 
     To reduce a probability of particulate matter carried by liquid flowing in irrigation pipes from entering and clogging emitters mounted in the pipes, emitters are generally designed having various types of inlet filtering configurations. The inlet filters tend to prevent particulate matter greater than a given size that may be carried by irrigation liquids in the pipes from entering the emitters. Internal liquid flow channels of the emitters are formed sufficiently large so that particulate characterized by a size less than the given size that are passed by the filters do not clog the channels. To reduce a probability that dirt and debris is sucked back into emitters when water pressure is reduced in the pipes emitters have been designed to seal themselves against back flow when pressure in an irrigation pipe in which they are installed is reduced. Such drippers, commonly referred to as “anti-siphon” or “non-return” emitters, are usually configured having an elastic diaphragm that sets on and seals an inlet orifice of the emitter. 
     U.S. Pat. No. 6,027,048, the disclosure of which is incorporated herein by reference, describes a regulated non-return agricultural emitter comprising a filter configuration, a labyrinth, and an elastic diaphragm that seals the emitter against “backflow”. The inlet configuration comprises two relatively long inlet channels that “are relatively larger in width than those of conventional emitter units”. Each inlet channel has an array of “filter baffles” along its length and is “undercut” in an outside surface of the emitter so that it is partially covered with a lip that runs along the length of the channel. The baffles and lip operate to prevent particulate matter in liquid carried by an irrigation pipe in which the emitter is installed and that might clog the emitter from entering the inlet channel. The two inlet channels communicate via a coupling channel to a “single restricted inlet” through which liquid from the irrigation pipe in the inlet channels enters the emitter. An elastic diaphragm operates to regulate liquid flow through the emitter. To provide a non-return function, the diaphragm seals the single restricted inlet when water pressure in the irrigation pipe is reduced below a desired threshold pressure. 
     The patent notes that the use of “inflow paths which are relatively larger in width than those of conventional emitter units” aids in “minimizing the dangers of blockage”, and are “of particular significance where, as in the emitter unit specifically described and illustrated, a non-return valve construction is provided for. With such a construction, only a single restricted inlet . . . into the emitter unit is available, and such a restricted inlet could not accommodate adequate filtering means.” 
     U.S. Pat. No. 5,615,838, the disclosure of which is incorporated herein by reference, describes integrated emitters, referred to as in-line emitters, that have a non-return feature and optionally provides a regulated flow of water. In an embodiment of the invention, a flexible membrane closes the emitter to flow into or out of the emitter when inlet pressure to the emitter falls below a minimum pressure. The membrane optionally functions to control a length of a labyrinth through which water flows responsive to inlet pressure to regulate flow of water provided by the emitter. 
     SUMMARY 
     An aspect of some embodiments of the invention relates to providing a regulated non-return emitter suitable for mounting inside an irrigation pipe and comprising a relatively simple configuration. 
     An aspect of some embodiments of the invention, relates to providing the emitter with a relatively simple filtering configuration. 
     In an embodiment of the invention, the emitter comprises a relatively long manifold flow channel formed on an internal surface of the emitter. The manifold communicates with a plurality of inlets through which liquid from an irrigation pipe comprising the emitter enters into the manifold and the emitter. 
     An elastic diaphragm seats on the manifold channel and constrains liquid that enters the manifold via the inlets to flow through a labyrinth before debauching into an outlet reservoir from which the liquid exits the emitter. 
     According to an aspect of some embodiments of the invention, the manifold channel comprises a raised rim on which the diaphragm seats to seal at least a portion of the channel and constrain thereby the liquid to flow through the labyrinth. 
     According to an aspect of some embodiments of the invention, an array of protuberances, hereinafter referred to as “registration buttons”, on the internal emitter surface on which the manifold channel is formed, position the diaphragm so that it seats on the labyrinth and forms a wall of the labyrinth. 
     In an embodiment of the invention, the diaphragm deforms responsive to inlet pressure of liquid that enters the inlets to regulate liquid flow through the emitter by changing dimensions of the outlet reservoir. 
     There is therefore provided in accordance with an embodiment of the invention an emitter comprising: a plurality of inlet apertures through which liquid enters the emitter; a manifold flow channel into which liquid that passes through the apertures flow; an elastic diaphragm that seats on the manifold flow channel; an outlet aperture through which liquid that enters the emitter exits the emitter; wherein liquid that enters the inlet apertures displaces only a portion of the diaphragm from the manifold channel so that the liquid can leave the manifold channel and flow through the emitter to reach the outlet aperture. 
     Optionally, the emitter comprises a labyrinth that receives liquid that has flowed in the manifold channel. Optionally, the emitter comprises a regulation reservoir that receives liquid that flows through the labyrinth. Optionally, the emitter is configured so that displacement of the diaphragm decreases volume of the regulation reservoir. 
     In some embodiments of the invention, the diaphragm seats on the labyrinth to constrain liquid to flow through the labyrinth. 
     In some embodiments of the invention, the emitter comprises first and second parts that sandwich the diaphragm between them. Optionally, the first part is formed having the manifold channel. Optionally, the emitter has a feed flow channel formed in the first part that receives liquid that exits the manifold channel and directs flow of the received liquid in a direction to enter the labyrinth. Optionally, the diaphragm covers a first portion of the feed flow channel leaving a second portion uncovered. Optionally, the received liquid exits the feed flow channel via the second portion of the feed flow channel to enter the labyrinth. Optionally, when the diaphragm is displaced from the manifold channel, it is displaced from at least a portion of the first portion of the feed flow channel. 
     In some embodiments of the invention, the first part is formed having a plurality of protuberances on which the diaphragm rests. Optionally, when the diaphragm is displaced from the manifold channel some of the liquid that exits the manifold channel flows between protuberances to reach the feed flow channel. 
     In some embodiments of the invention, the second part is formed having the labyrinth. 
     In some embodiments of the invention, the second part is formed having the reservoir chamber. 
     There is further provided in accordance with an embodiment of the invention, an emitter comprising: a first part having formed therein a manifold flow channel having first and second regions; a second part having formed therein a labyrinth; and an elastic diaphragm sandwiched between the first and second parts so that the diaphragm is maintained pressed by the second part to the first region of the manifold flow channel. Optionally, liquid enters the manifold flow channel via a plurality of apertures. Optionally, the second part is formed having a regulation reservoir, and wherein the diaphragm is located between the reservoir and the second region of the manifold flow channel. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
       Non-limiting examples of embodiments of the present invention are described below with reference to figures attached hereto. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same symbol in all the figures in which they appear. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
         FIG. 1A  shows a schematic exploded view of a regulated non-return emitter comprising an emitter housing, an elastic diaphragm, and a housing insert (rotated out of position for convenience of presentation), in accordance with an embodiment of the invention; 
         FIG. 1B , shows a schematic perspective view of the emitter housing shown in  FIG. 1A  from a direction opposite that from which the housing is shown in  FIG. 1A , in accordance with an embodiment of the invention; 
         FIG. 1C  schematically shows the diaphragm shown in  FIG. 1A  seated in the emitter housing, in accordance with an embodiment of the invention; 
         FIG. 1D  schematically shows a perspective view of the emitter shown in  FIG. 1A  completely assembled, in accordance with an embodiment of the invention; 
         FIG. 2A  schematically shows the assembled emitter shown in  FIG. 1D  mounted in an irrigation pipe in accordance with an embodiment of the invention; 
         FIG. 2B  schematically shows a view of the emitter in  FIG. 2A  cutaway to show flow patterns of liquid in the emitter, in accordance with an embodiment of the invention; 
         FIG. 2C  schematically shows another view of the emitter in  FIG. 2A  cutaway to show flow patterns of liquid in the emitter, in accordance with an embodiment of the invention; 
         FIG. 2D  schematically shows the emitter housing shown in  FIG. 1A  and flow patterns of liquid along a bottom surface of the emitter, in accordance with an embodiment of the invention; 
         FIG. 2E  schematically shows a view of the emitter cutaway to show flow of liquid through a labyrinth of the emitter, in accordance with an embodiment of the invention; and 
         FIG. 2F  schematically shows a view of the emitter cutaway to show the elastic diaphragm shown in  FIG. 1A  sealing the emitter against backflow, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1A  shows a schematic, exploded, perspective view of an emitter  20  configured to be inserted inside an irrigation pipe, divert liquid flowing in the pipe and emit the diverted liquid from the pipe to irrigate plants, in accordance with an embodiment of the invention. Emitter  20  optionally comprises a housing  22 , an elastic diaphragm  50  and a housing insert  60 . In the perspective of  FIG. 1 , internal features and surfaces of housing  22  and housing insert  50  are shown. 
     Housing  22  is formed having an optionally rectangular diaphragm recess  23  defined by a bottom internal surface  24 , relatively long, optionally mirror image, edge surfaces  25 , and relatively short edge surfaces  26  and  27 . Long edge surfaces  25  are surfaces of, optionally mirror image, side support shelves  28 . Short edge surfaces  26  and  27  are surfaces of end support shelves  29  and  30  respectively. 
     Bottom internal surface  24  is formed having an optionally straight manifold flow channel  32  that communicates with a linear array of distinct inlet apertures  33  though each of which liquid flowing in an irrigation pipe in which the emitter is mounted may separately enter the emitter. Each distinct inlet aperture  33  thus defines a separate fluid flow path between an external surface  36  of the emitter and the manifold flow channel  32  which is arranged such that all liquid passing through the emitter must pass through the manifold flow channel  32 . The manifold channel is rimmed with a raised rim  34  which rises above the bottom internal surface  24 . Each inlet aperture  33  is characterized by a size that tends to prevent particulate matter that may clog the emitter flow channels from entering the emitter. The inlet apertures are, optionally, formed by a plurality of parallel ribs  35  that are optionally substantially perpendicular to the length of manifold flow channel  32  and separated by, optionally equal width, spaces  43 . The ribs depend towards manifold flow channel  32  from an external surface  36  of housing  22  shown in a  FIG. 1B .  FIG. 1B , schematically shows a perspective view of housing  22  from a direction opposite that from which housing  22  is shown in  FIG. 1A . Spaces  43  t between the ribs intersect manifold flow channel  32 . The size of each inlet aperture  33  is defined by a space  43  between ribs  35  and the width of manifold flow channel  32 , i.e., the inlet aperture size is substantially equal to a projection of the space between two adjacent ribs  35  on a space defined by the width of the manifold flow channel. In accordance with an embodiment of the invention, the width of manifold channel  32  is larger than the width of each space  43  so that particulate matter that may pass through a space  43 , in general would not clog the manifold flow channels. 
     Bottom surface  24  ( FIG. 1A ) is also optionally formed having a linear feed flow channel  38  that is optionally parallel to manifold inlet channel  32 . Feed flow channel  38  extends in a direction towards end shelf  30  from a region  41  alongside a manifold channel  32  to beyond the manifold channel  32  and into cranny  39  formed in the end shelf. An array of registration buttons  40 , configured as protuberances, each spaced apart from the manifold flow channel  32 , surrounds manifold and feed channels  32  and  38  in a portion of bottom surface near end shelf  30 . Registration button  40  and manifold rim  34  rise about bottom surface to about a same height. 
     Elastic diaphragm  50  is shaped to seat in diaphragm recess  23  of housing  22  and has a rectangular shape with long edges  52 . When seated in the diaphragm recess, the diaphragm is framed by long edge surfaces  25  and short edge surfaces  26 , and  27 .  FIG. 1C  schematically shows diaphragm  50  seated in diaphragm recess  23  ( FIG. 1A ). 
     It is noted that when diaphragm  50  is positioned in the diaphragm recess, the diaphragm covers features on bottom surface  24  except for a portion  37  of feed flow channel  38  that is located in cranny  39 . Portion  37  of the feed flow channel in the cranny is hereinafter referred to as a feed channel outlet port  37 . 
     Housing insert  60  has an inside surface  62  and is shaped to be inserted into housing  22  so that portions of the inside surface seat on support shelves  28 ,  29  and  30 . Inside surface  62  of housing insert  60  is formed having a labyrinth  64  that empties into an internal “regulation reservoir”  70  and is connected to a labyrinth inlet channel  65  having a labyrinth inlet port  66 . Labyrinth  64  may be any suitable labyrinth known in the art and is optionally a labyrinth similar to a labyrinth described in PCT Patent Application IB2006/052473, the disclosure of which is incorporated herein by reference. Regulation reservoir  70  is formed having a “trickle channel”  72  and a regulation reservoir outlet channel  74  discussed below. 
     Housing insert  60  is flipped 180° about an axis  90  relative to its orientation in  FIG. 1A  to be inserted into housing  22 . When the housing insert  60  is properly inserted into housing  22 , the insert is supported by support shelves  28 ,  29  and  30  and labyrinth inlet port  66  ( FIG. 1A ) of the insert is located over cranny  39  and feed channel outlet port  37  ( FIG. 1A  and  FIG. 1C ) of housing  22 . To secure housing insert  60  in the housing, any of various methods and or materials known in the art may be used. For example, insert  60  may be bonded in housing  22  by ultrasonic welding or by gluing. 
     With housing insert  60  securely in place in housing  22 , diaphragm  50  is sandwiched between the insert and the housing, pressing firmly on inside surface  62  of insert  60  and rim  34  and registration buttons  40  on bottom internal surface  24  of housing  22 . By being pressed snugly to inside surface  62  of insert  60  the diaphragm provides a top wall for labyrinth  64  that substantially seals the labyrinth against leakage of liquid where the diaphragm covers the labyrinth. 
       FIG. 1D  schematically shows a perspective view of emitter  20  completely assembled with insert  60  flipped and seated in housing  22 . In the perspective of  FIG. 1D , an outside top surface  68  of housing insert  60  is shown. The top surface is optionally curved to match a curvature of an irrigation pipe in which emitter  20  is intended to be installed so that it may be bonded to an inside surface of the pipe. Top surface  68  is optionally formed having an outside liquid reservoir  76  that communicates with regulation reservoir  70  ( FIG. 1A ) via regulation reservoir outlet channel  74 . Liquid exits an irrigation pipe in which emitter  20  is installed from outside liquid reservoir  76 . 
       FIGS. 2A-2E  schematically illustrate operation of emitter  20  when mounted in an irrigation pipe  100  in which liquid, indicated by a block arrow  102  for irrigating plants is flowing, in accordance with an embodiment of the invention.  FIG. 2A  schematically shows the irrigation pipe partially cutaway to show the emitter mounted therein. 
     In  FIG. 2B  emitter  20  is cutaway to show a cross section of the emitter in a plane AA indicated in  FIG. 2A . Plane AA bisects emitter  20  along the length of manifold flow channel  32 . A portion, indicated by wavy arrows  104 , of liquid  102  flowing in irrigation pipe  100  is diverted into emitter  20  and flows into manifold flow channel  32  through spaces  43  between ribs  35 , which define inlet apertures  33  of the emitter. Liquid  104  that enters manifold flow channel  32  is substantially prevented from exiting the manifold channel in a first region, indicated by a bracket  106 , of the channel opposite labyrinth  64  because in that first region insert  60  presses diaphragm  50  snuggly onto rim  34  of the manifold channel thereby sealing the channel in that region against egress of liquid. 
     However, in a second region, indicated by a bracket  110 , of manifold channel  32 , opposite regulation reservoir  70 , diaphragm  50  is not constrained to remain pressed against rim  34 . As a result, in second region  110  of manifold channel  32 , when pressure of liquid  104  that enters the manifold channel exceeds a predetermined threshold pressure, the pressure pushes diaphragm  50  off of rim  34  of the manifold channel. The threshold pressure is determined, inter alia, by properties of material from which diaphragm  50  is produced, dimensions of the diaphragm, dimensions of the rim  34  and dimension of regulation reservoir  70 . Diaphragm  50  and regulation reservoir  70  may be configured using any of various methods and materials known in the art to provide a desired threshold pressure. Optionally, the threshold pressure is substantially zero. 
     As diaphragm  50  is lifted off rim  34 , liquid  104  flows out of second region  110  of channel  32  filling a space  112  that its pressure creates between the diaphragm and housing  22 . The flow of liquid out of the manifold channel  32  in second region  110  is schematically represented in  FIG. 2B  by arrows  114  and generates a flow of liquid indicated by wavy arrows  115  in the manifold channel towards second region  110 . Liquid  114  that flows out of manifold channel  32  exits the manifold channel under diaphragm  50  to flow in substantially all directions in space  112  between diaphragm  50  and bottom surface  24  of housing  22 , eventually to flow into feed flow channel  38 . Optionally, space  112  overlies at least region  41  ( FIG. 1A ) of feed flow channel  38  as shown in a  FIG. 2C . 
       FIG. 2C  schematically shows a cross section of emitter  20  along a plane BB indicated in  FIG. 2A  in which diaphragm  50  is lifted off rim  34  by pressure of liquid  104  ( FIG. 2B ) flowing into emitter  20  and liquid flowing out of manifold channel  32  enters feed flow channel  38 . In  FIG. 2C , and in  FIG. 2D  that follows, liquid flowing towards feed flow channel  38  from space  112  is schematically represented by block arrows  120 .  FIG. 2D  schematically shows housing  22  and bottom internal surface  24  of the housing, and in the figure, arrows  120  schematically indicate flow of liquid from manifold channel  32  to feed flow channel  38  by various flow routes. As indicated in  FIG. 2D , some of the flow routes to feed flow channel  38  pass around registration buttons  40 . 
     Liquid that enters feed flow channel  38  flows along the feed flow channel to feed flow outlet port  37  ( FIGS. 1A ,  1 C,  2 D) from where it exits the feed flow channel. The exiting fluid flows upwards from the outlet port along cranny  39  ( FIGS. 1A ,  1 C,  2 D) to flow into labyrinth inlet channel  65  via labyrinth inlet port  66  ( FIGS. 1A ,  2 B) and therefrom into labyrinth  64 . In  FIG. 2B  fluid flowing upwards from outlet port  37  along cranny  39  and into inlet port  66  is schematically represented by a block arrow  126 . Liquid that flows into labyrinth  64  wends it way through the labyrinth to enter regulation reservoir  70 . Arrows  128  in  FIG. 2B  schematically represent liquid flowing through the labyrinth and into regulation reservoir  70 . 
     Details of liquid flow into and through labyrinth  64 , in accordance with an embodiment of the invention are shown in  FIG. 2E . The figure schematically shows a cross section of emitter  20  along a plane CC indicated in  FIG. 2A  showing labyrinth  64 , labyrinth inlet channel  65  and its inlet port  66 . Liquid, indicated by arrows  130 , from feed flow channel  38  ( FIG. 2C ,  FIG. 2D ) flows upwards along cranny  39  ( FIGS. 1A ,  1 C) of housing  22  to labyrinth inlet port  66  and enters labyrinth inlet channel  65 . Liquid  130  then flows into labyrinth inlet channel  64  and meanders its way through the labyrinth to debauch into regulation reservoir  70 . From the regulation reservoir the liquid flows into outlet reservoir  76  shown in  FIGS. 2A-2C  and exits irrigation pipe  100  via orifice  101 . 
     Resistance to flow of liquid into regulation reservoir  70  from the labyrinth and from the regulation reservoir into outlet reservoir  76  is a function of displacement of diaphragm  50  away from bottom internal surface  24  of housing  22  and into the regulation reservoir and increases with the displacement. The displacement in turn is a function of inlet pressure of liquid entering emitter  20  that operates to lift the diaphragm off rim  34  and into the regulation reservoir and increases with increasing pressure. By suitably determining dimensions of regulation reservoir  70  and elasticity and thickness of diaphragm  50 , resistance to liquid flow through regulation reservoir  70  is determined, in accordance with an embodiment of the invention, to increase substantially linearly with increase in inlet pressure. As a result, the diaphragm operates to regulate flow of liquid from irrigation pipe  100  through emitter  20  and flow rate of liquid from the irrigation pipe that passes through emitter  20  and exits the irrigation pipe is substantially independent of inlet pressure. Trickle channel  72  ( FIG. 1A ) functions to maintain liquid flow through emitter  20  for inlet pressures that are so large that diaphragm  50  is pressed against reservoir outlet channel  74  and would in the absence of the trickle chamber seal the outlet channel. 
     Diaphragm  50  also operates to seal emitter  20  against backflow of liquid into emitter  20  and when liquid pressure in irrigation pipe  100  drops below the threshold pressure the diaphragm relaxes to seat on rim  34  and seal the emitter against backflow of and possible concomitant suction of debris into the emitter ( FIG. 2F ). 
     In the description and claims of the present application, each of the verbs, “comprise” “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily an exhaustive listing of members, components, elements or parts of the subject or subjects of the verb. 
     The invention has been described with reference to embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the described invention and embodiments of the invention comprising different combinations of features than those noted in the described embodiments will occur to persons of the art. For example, the features of housing insert  60 , may be formed in a housing for an emitter in accordance with an embodiment of the invention and the features of housing  22  may be incorporated in an insert. Manifold flow channel  32  and/or feed flow channel  38 , which are shown as rectilinear may be curved. The scope of the invention is limited only by the claims.