Abstract:
Drip irrigation apparatus including a main water flow channel having associated therewith along a length thereof a plurality of pressure-controlled drip irrigation emitter units and at least one secondary water flow channel extending generally parallel to the main water flow channel and receiving water from at least one of the plurality of pressure-controlled drip irrigation emitter units, the at least one secondary water flow channel having water outlets disposed along the length of the main water flow channel, intermediate the plurality of pressure-controlled drip irrigation emitter units.

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application is related to U.S. Provisional Patent Application Ser. No. 60/732,611, filed Nov. 1, 2005 and entitled DRIP IRRIGATION APPARATUS, the disclosure of which is hereby incorporated by reference and priority of which is hereby claimed pursuant to 37 CFR 1.78(a) (4) and (5)(i). 
     FIELD OF THE INVENTION 
     The present invention relates to drip irrigation apparatus and methods of manufacture thereof. 
     BACKGROUND OF THE INVENTION 
     The following patent publications are believed to represent the current state of the art: 
     U.S. Pat. Nos. 4,177,946; 4,285,472; 4,430,020; 4,473,191; 4,534,515; 4,874,132; 5,106,021; 5,615,838; 6,027,048; 6,206,305 and 6,382,530. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide improved drip irrigation apparatus and methods of manufacture thereof. 
     There is thus provided in accordance with a preferred embodiment of the present invention drip irrigation apparatus including a main water flow channel having associated therewith along a length thereof a plurality of pressure-controlled drip irrigation emitter units and at least one secondary water flow channel extending generally parallel to the main water flow channel and receiving water from at least one of the plurality of pressure-controlled drip irrigation emitter units, the at least one secondary water flow channel having water outlets disposed along the length of the main water flow channel, intermediate the plurality of pressure-controlled drip irrigation emitter units. 
     In accordance with a preferred embodiment of the present invention the at least one secondary water flow channel includes at least one of a weeping hose and a sweat irrigation hose. Preferably, the at least one secondary water flow channel has associated therewith at least one pressure reducing pathway, having outlets which correspond to the water outlets. 
     There is also provided in accordance with another preferred embodiment of the present invention drip irrigation apparatus including a main water flow channel having associated therewith along a length thereof a plurality of pressure-controlled drip irrigation emitter units, at least one secondary water flow channel extending generally parallel to the main water flow channel and receiving water from at least one of the plurality of pressure-controlled drip irrigation emitter units and at least one pressure-reducing pathway associated with each of the at least one secondary water flow channel and distributed therealong, the at least one pressure-reducing pathway having outlets disposed along the length of the main water flow channel, intermediate the plurality of pressure-controlled drip irrigation emitter units. 
     In accordance with a preferred embodiment of the present invention the outlets are defined by welding. Preferably, the at least one pressure reducing pathway includes a series of discrete labyrinths each having an inlet and an outlet. Additionally, the discrete labyrinths are realized by embossing of the at least one secondary water flow channel. Alternatively, the discrete labyrinths are realized by attaching discrete labyrinth elements to the at least one secondary water flow channel. 
     In accordance with another preferred embodiment of the present invention the at least one pressure reducing pathway includes a generally continuous series of non-mutually communicating labyrinths, each having an inlet and an outlet. Preferably, the non-mutually communicating labyrinths are realized by embossing of the at least one secondary water flow channel. Additionally or alternatively, the inlet faces the at least one secondary water flow channel and the outlet faces away from the at least one secondary water flow channel. 
     In accordance with yet another preferred embodiment of the present invention the at least one pressure reducing pathway includes a generally continuous labyrinth, having multiple inlets and multiple outlets. Preferably, the multiple outlets are generally evenly spaced on either side of each of the multiple inlets. Additionally or alternatively, two of the multiple outlets are provided for each of the multiple inlets. As a further addition or alternative, the multiple inlets face the at least one secondary water flow channel and the multiple outlets face away from the at least one secondary water flow channel. 
     In accordance with still another preferred embodiment of the present invention at least one of the plurality of pressure-controlled drip irrigation emitter units includes a low pressure leakage prevention feature. Preferably, at least one of the plurality of pressure-controlled drip irrigation emitter units includes an inlet aperture, a raised wall having a rim, the raised wall and the rim surrounding the inlet aperture and an elastic element operative to be displaced when water pressure in the main water flow channel exceeds a predetermined threshold, and to be in sealed engagement with the rim of the raised wall when water pressure in the main water flow channel does not exceed the predetermined threshold. Additionally or alternatively, at least one of the plurality of pressure-controlled drip irrigation emitter units includes two mutually sealed portions. 
     In accordance with a further preferred embodiment of the present invention a first one of the two mutually sealed portions includes a circumferential raised elongate portion and an internal raised elongate portion extending between two sections of the at least one pressure-reducing pathway, and a second one of the two mutually sealed portions includes a circumferential elongate recess and an internal elongate recess, the two mutually sealed portions being sealed by engagement of the raised elongate portions with the elongate recesses. Preferably, the raised elongate portions have a generally triangular cross section, and the elongate recesses have a generally rectangular cross section. Additionally or alternatively, the two mutually sealed portions are sealed ultrasonically. 
     In accordance with a yet further preferred embodiment of the present invention the two mutually sealed portions are sealed ultrasonically along the raised elongate portions and the elongate recesses. Preferably, at least one of the two mutually sealed portions and the at least one pressure reducing pathway is not deformed by ultrasonic sealing of the raised elongate portions and the elongate recesses. Additionally or alternatively, dimensions of at least one of the two mutually sealed portions and the at least one pressure reducing pathway are not changed by ultrasonic sealing of the raised elongate portions and the elongate recesses. 
     In accordance with a still further preferred embodiment of the present invention the at least one pressure reducing pathway maintains its functionality even when sealing between inwardly facing sides of the two mutually sealed portions is incomplete. Preferably, the first one of the two mutually sealed portions includes a circumferential raised wall and an internal raised wall having a protrusion therebetween, the protrusion being operative to at least partially prevent particular matter from flowing into the at least one pressure reducing pathway. 
     In accordance with an additional preferred embodiment of the present invention the raised wall includes a non-circular wall, and the rim is configured such that at a predetermined threshold pressure across the elastic element, the elastic element transitions from generally complete circumferential disengagement with the rim to generally complete circumferential engagement with the rim. Preferably, the rim is configured such that at a second predetermined threshold pressure across the elastic element, the elastic element transitions from generally complete circumferential engagement with the rim to generally complete circumferential disengagement with the rim. Additionally or alternatively the rim of the non-circular wall is non-planar. 
     In accordance with another preferred embodiment of the present invention the main water flow channel is defined by welding of one elongate edge of a sheet to an interior location therealong. Preferably, the at least one secondary water flow channel is defined by welding of another elongate edge of the sheet to a labyrinth defining strip which is welded to the sheet at an exterior location therealong. 
     In accordance with yet another preferred embodiment of the present invention the main water flow channel is defined by welding of first and second elongate edges of a first sheet at a seam location. Preferably, the at least one secondary water flow channel is defined by welding of a first elongate edge of a second sheet to the first elongate edge of the first sheet at the seam location and by welding a second elongate edge of the second sheet to a labyrinth defining strip which is welded to the first sheet at an exterior location therealong. 
     In accordance with still another preferred embodiment of the present invention the main water flow channel is defined by an elongate tube. Preferably, the at least one secondary water flow channel is defined by welding of a first elongate edge of a sheet to the elongate tube at a first exterior location therealong and by welding of a second elongate edge of the sheet to a labyrinth defining strip which is welded to the elongate tube at a second exterior location therealong. Alternatively, the at least one secondary water flow channel is defined by welding of a first elongate edge of a sheet to the elongate tube at a first exterior location therealong and by welding of a second elongate edge of the sheet to the elongate tube at a second exterior location therealong, the sheet having a labyrinth defining strip welded at a surface thereof which faces an exterior surface of the elongate tube. 
     As a further alternative, the at least one secondary flow channel is defined by a second elongate tube surrounding the elongate tube, the second elongate tube having welded at a first location of an interior surface thereof a labyrinth defining strip and being welded at a second location of the interior surface thereof to an outer surface of the elongate tube. 
     In accordance with a further preferred embodiment of the present invention the main water flow channel has welded at an interior location therealong at least one of the plurality of pressure-controlled drip irrigation emitter unit. Preferably, the at least one secondary water flow channel includes material having at least one of weeping hose functionality and sweat irrigation functionality. 
     There is further provided in accordance with a further preferred embodiment of the present invention a pressure-controlled drip irrigation emitter element including a water inlet, an inlet control chamber receiving water from the water inlet via an inlet aperture, a pressure reducing pathway receiving water from the inlet control chamber, an outlet control chamber receiving water from the pressure reducing pathway, an elastic element separating the inlet control chamber and the outlet control chamber and a non-circular wall surrounding the inlet aperture and having a rim, the rim being configured such that at a predetermined threshold pressure across the elastic element, the elastic element transitions from generally complete circumferential disengagement with the rim to generally complete circumferential engagement with the rim. 
     There is additionally provided in accordance with an additional preferred embodiment of the present invention a pressure-controlled drip irrigation emitter element including a water inlet, an inlet control chamber receiving water from the water inlet via an inlet aperture, a pressure reducing pathway receiving water from the inlet control chamber, an outlet control chamber receiving water from the pressure reducing pathway and an elastic element separating the inlet control chamber and the outlet control chamber, the inlet control chamber, the outlet control chamber and the pressure reducing pathway being defined by ultrasonic sealing of first and second emitter element portions in a manner such that the dimensions of the pressure reducing pathway are not affected. 
     In accordance with a preferred embodiment of the present invention the inlet aperture is surrounded by a non-circular wall having a rim, the rim being configured such that at a predetermined threshold pressure across the elastic element, the elastic element transitions from generally complete circumferential disengagement with the rim to generally complete circumferential engagement with the rim. Preferably, the rim is configured such that at a second predetermined threshold pressure across the elastic element, the elastic element transitions from generally complete circumferential engagement with the rim to generally complete circumferential disengagement with the rim. 
     In accordance with another preferred embodiment of the present invention the rim of the non-circular wall is non-planar. Preferably, one of the first and second emitter element portions includes a raised elongate portion and another of the first and second emitter element portions includes a corresponding elongate recess, the raised elongate portion and the elongate recess being ultrasonically welded together. Additionally or alternatively, the raised elongate portion has a generally triangular cross section and the elongate recess has a generally rectangular cross section. 
     In accordance with still another preferred embodiment of the present invention the one of the first and second emitter element portions also includes an internal raised elongate portion extending between two sections of the pressure-reducing pathway, and the another of the first and second emitter element portions also includes a corresponding internal elongate recess, the internal raised elongate portion and the internal elongate recess being ultrasonically welded together. Preferably, the internal raised elongate portion has a generally triangular cross section and the internal elongate recess has a generally rectangular cross section. 
     In accordance with yet another preferred embodiment of the present invention the pressure reducing pathway maintains its functionality even when sealing between inwardly facing sides of the two mutually sealed portions is incomplete. Preferably, one of the first and second emitter element portions includes a circumferential raised wall and an internal raised wall having a protrusion therebetween, the protrusion being operative to at least partially prevent particular matter from flowing into the pressure reducing pathway. 
     There is also provided in accordance with another preferred embodiment of the present invention a pressure-controlled drip irrigation emitter element disposed along an interior wall of a water supply tube including a water inlet coupled to the interior wall of the water supply tube, an inlet control chamber receiving water from the water inlet via an inlet aperture, a pressure reducing pathway receiving water from the inlet control chamber, the pressure reducing pathway being separated from the interior wall of the water supply tube, an outlet control chamber receiving water from the pressure reducing pathway via a pressure reducing pathway outlet passage and an elastic element separating the inlet control chamber and the outlet control chamber, the pressure reducing pathway outlet passage extending from the pressure reducing pathway, along a pathway extending between the emitter element and the interior wall of the water supply tube, and to the outlet control chamber. 
     In accordance with a preferred embodiment of the present invention the inlet aperture is surrounded by a non-circular wall having a rim, the rim being configured such that at a predetermined threshold pressure across the elastic element, the elastic element transitions from generally complete circumferential disengagement with the rim to generally complete circumferential engagement with the rim. Preferably, the rim is configured such that at a second predetermined threshold pressure across the elastic element, the elastic element transitions from generally complete circumferential engagement with the rim to generally complete circumferential disengagement with the rim. 
     In accordance with another preferred embodiment of the present invention the rim of the non-circular wall is non-planar. Preferably, the inlet control chamber, the outlet control chamber and the pressure reducing pathway are defined by ultrasonic sealing of first and second emitter element portions in a manner such that the dimensions of the pressure reducing pathway are not affected. Additionally or alternatively, the first and second emitter element portions includes a raised elongate portion and another of the first and second emitter element portions includes a corresponding elongate recess, the raised elongate portion and the elongate recess being ultrasonically welded together. 
     In accordance with yet another preferred embodiment of the present invention the raised elongate portion has a generally triangular cross section and the elongate recess has a generally rectangular cross section. Preferably, the one of the first and second emitter element portions also includes an internal raised elongate portion extending between two sections of the pressure-reducing pathway, and the another of the first and second emitter element portions also includes a corresponding internal elongate recess, the internal raised elongate portion and the internal elongate recess being ultrasonically welded together. Additionally or alternatively, the internal raised elongate portion has a generally triangular cross section and the internal elongate recess has a generally rectangular cross section. 
     In accordance with a further preferred embodiment of the present invention the pressure reducing pathway maintains its functionality even when sealing between inwardly facing sides of the two mutually sealed portions is incomplete. Preferably, one of the first and second emitter element portions includes a circumferential raised wall and an internal raised wall, having a protrusion therebetween, the protrusion being operative to at least partially prevent particular matter from flowing into the pressure reducing pathway. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
         FIG. 1  is a simplified, general schematic illustration of drip irrigation apparatus constructed and operative in accordance with a preferred embodiment of the present invention; 
         FIGS. 2A and 2B  are simplified pictorial illustrations of first and second sides of a first portion of a drip irrigation emitter element useful in the drip irrigation apparatus of  FIG. 1 ; 
         FIGS. 3A and 3B  are simplified pictorial illustrations of first and second sides of a second portion of the drip irrigation emitter element useful in the drip irrigation apparatus of  FIG. 1 ; 
         FIG. 4  is a first simplified exploded view illustration of the drip irrigation emitter element of  FIGS. 2A-3B ; 
         FIG. 5  is a first simplified assembled view illustration of the drip irrigation emitter element of  FIG. 4 ; 
         FIG. 6  is a second simplified exploded view illustration of the drip irrigation emitter element of  FIGS. 2A-5 ; 
         FIG. 7  is a second simplified assembled view illustration of the drip irrigation emitter element of  FIG. 6 ; 
         FIG. 8  is a simplified sectional illustration of the drip irrigation emitter element of  FIGS. 2A-7 , taken along section lines VIII-VIII in  FIG. 5 , the drip irrigation emitter element being placed inside a drip irrigation line of the general type shown in  FIG. 1 ; 
         FIG. 9  is a simplified sectional illustration of the drip irrigation emitter element of  FIGS. 2A-7 , taken along section lines IX-IX in  FIG. 5 , the drip irrigation emitter element being placed inside a drip irrigation line of the general type shown in  FIG. 1 ; 
         FIG. 10  is a simplified sectional illustration of the drip irrigation emitter element of  FIGS. 2A-7 , taken along section lines X-X in  FIG. 5 , the drip irrigation emitter element being placed inside a drip irrigation line of the general type shown in  FIG. 1 ; 
         FIGS. 11A ,  11 B,  11 C and  11 D are simplified illustrations of a problem in the operation of prior art pressure-controlled anti-leakage drip irrigation emitters,  FIG. 11A  being a simplified not-to-scale pictorial illustration,  FIGS. 11B and 11C  being sectional illustrations taken along respective section lines XIB-XIB and XIC-XIC in  FIG. 11A , and  FIG. 11D  being a superposition of portions of  FIGS. 11B and 11C ; 
         FIGS. 12A ,  12 B,  12 C and  12 D are simplified illustrations of a solution to the problem in the operation of prior art pressure-controlled anti-leakage drip irrigation emitters as shown in  FIGS. 11A-11D ,  FIG. 12A  being a simplified not-to-scale pictorial illustration,  FIGS. 12B and 12C  being sectional illustrations taken along respective section lines XIIB-XIIB and XIIC-XIIC in  FIG. 12A , and  FIG. 12D  being a superposition of portions of  FIGS. 12B and 12C ; 
         FIGS. 13A ,  13 B,  13 C and  13 D are generally to-scale simplified illustrations which correspond to  FIGS. 12B and 12C  in the context of the drip irrigation emitter element of  FIGS. 2A-10 ,  FIGS. 13A and 13B  showing a first operative orientation of the drip irrigation emitter element and  FIGS. 13C and 13D  showing a second operative orientation of the drip irrigation emitter element; 
         FIGS. 14A ,  14 B,  14 C and  14 D are simplified illustrations of another solution to the problem in the operation of prior art pressure-controlled anti-leakage drip irrigation emitters as shown in  FIGS. 11A-11D ,  FIG. 14A  being a simplified not-to-scale pictorial illustration,  FIGS. 14B and 14C  being sectional illustrations taken along respective section lines XIVB-XIVB and XIVC-XIVC in  FIG. 14A , and  FIG. 14D  being a superposition of portions of  FIGS. 14B and 14C ; 
         FIGS. 15A ,  15 B,  15 C and  15 D are generally to-scale simplified illustrations which correspond to  FIGS. 14B and 14C  in the context of the drip irrigation emitter element of  FIGS. 2A-10 ,  FIGS. 15A and 15B  showing a first operative orientation of the drip irrigation emitter element and  FIGS. 15C and 15D  showing a second operative orientation of the drip irrigation emitter element; 
         FIGS. 16A ,  16 B,  16 C and  16 D are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with a preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 ; 
         FIGS. 17A ,  17 B,  17 C and  17 D are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with another preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 ; 
         FIGS. 18A ,  18 B,  18 C and  18 D are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with yet another preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 ; 
         FIGS. 19A ,  19 B,  19 C and  19 D are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with still another preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 ; and 
         FIGS. 20A ,  20 B,  20 C and  20 D are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with a further preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to  FIG. 1 , which is a simplified, general schematic illustration of drip irrigation apparatus constructed and operative in accordance with a preferred embodiment of the present invention.  FIG. 1  shows a main water flow channel  100  having disposed at longitudinally spaced locations therealong, typically separated from each other by approximately one meter, a plurality of pressure-controlled drip irrigation emitter elements  102 , which preferably include a low pressure leakage prevention feature. Each drip irrigation emitter element  102  provides a pressure-compensated liquid flow output to a secondary water flow channel  104 , which extends generally parallel to main water flow channel  100 , via a pressure-compensated emitter element output aperture  106  formed in a common wall  108 , joining main water flow channel  100  and secondary water flow channel  104 . 
     At least one longitudinally spaced secondary water flow channel labyrinth  110  communicates with secondary water flow channel  104  and provides a reduced pressure output at multiple water outlets  112  which communicate with the outside of the secondary water flow channel  104 . Preferably a plurality of inlets  114  are provided to the at least one longitudinally spaced secondary water flow channel labyrinth  110  along the length thereof. Outlets  112  and inlets  114  are typically defined by welding or by other manufacturing techniques. Typically water outlets  112  are separated from each other by 10 cm. Alternatively, secondary water flow channel  104  may be a weeping hose, such as a weeping hose of the type described in U.S. Pat. No. 5,299,885, the content of which is incorporated herein by reference, or such as an Aquapore weeping hose commercially available from Aquapore Moisture Systems, Inc. of Pheonix, Ariz. Alternatively, secondary water flow channel  104  may be any type of hose suitable for sweat irrigation. 
       FIG. 1  includes five enlargements showing five alternative labyrinth structures. An enlargement designated by Roman numeral I shows the at least one longitudinally spaced secondary water flow channel labyrinth  110  implemented as a series of discrete labyrinths  116 , each having an inlet  118  and an outlet  120 . The discrete labyrinths  116  may be realized by embossing of the secondary water flow channel  104  or alternatively by attaching discrete labyrinth elements to the secondary water flow channel  104 . 
     An enlargement designated by Roman numeral II shows the at least one longitudinally spaced secondary water flow channel labyrinth  110  implemented as a generally continuous series of non-mutually communicating labyrinths  122 , each having an inlet  124  and an outlet  126 . The generally continuous series of non-mutually communicating labyrinths  122  may be realized by embossing of the secondary water flow channel  104 . 
     An enlargement designated by Roman numeral III shows the at least one longitudinally spaced secondary water flow channel labyrinth  110  implemented as a generally continuous labyrinth  128 , having multiple inlets  130  and outlets  132 . Preferably, the outlets  132  are generally evenly spaced on either side of each inlet  130 . Typically two outlets  132  are provided for each inlet  130 . 
     An enlargement designated by Roman numeral IV shows the at least one longitudinally spaced secondary water flow channel labyrinth  110  implemented as a generally continuous series of non-mutually communicating labyrinths  142 , each having an inlet  144  facing the secondary water flow channel  104  and an outlet  146  facing in an opposite direction, away from the secondary water flow channel  104 . The generally continuous series of non-mutually communicating labyrinths  142  may be realized by embossing of the secondary water flow channel  104 . 
     An enlargement designated by Roman numeral V shows the at least one longitudinally spaced secondary water flow channel labyrinth  110  implemented as a generally continuous labyrinth  148 , having multiple inlets  150  facing the secondary water flow channel  104  and multiple outlets  152  facing in an opposite direction, away from the secondary water flow channel  104 . Preferably, the outlets  152  are generally evenly spaced on either side of each inlet  150 . Typically two outlets  152  are provided for each inlet  150 . 
     Reference is now made to  FIGS. 2A and 2B , which are simplified pictorial illustrations of first and second sides of a first portion of a drip irrigation emitter element useful in the drip irrigation apparatus of  FIG. 1 , to  FIGS. 3A and 3B , which are simplified pictorial illustrations of first and second sides of a second portion of the drip irrigation emitter element useful in the drip irrigation apparatus of  FIG. 1 , to  FIG. 4 , which is a first simplified exploded view illustration of the drip irrigation emitter element of  FIGS. 2A-3B , to  FIG. 5 , which is a first simplified assembled view illustration of the drip irrigation emitter element of  FIG. 4 , to  FIG. 6 , which is a second simplified exploded view illustration of the drip irrigation emitter element of  FIGS. 2A-5 , to  FIG. 7 , which is a second simplified assembled view illustration of the drip irrigation emitter element of  FIG. 6 , and to  FIGS. 8 ,  9  and  10 , which are simplified sectional illustrations of the drip irrigation emitter element of  FIGS. 2A-7  when placed inside a drip irrigation line of the general type shown in  FIG. 1 . 
     Turning initially to  FIGS. 4-7 , water from main water flow channel  100  ( FIG. 1 ) passes a water filtering grid  200 , as indicated by an arrow  201 , and through an inlet aperture  202 , which aperture is surrounded by a raised wall  204 . When the pressure of the water in main water flow channel  100  exceeds a predetermined threshold, preferably 0.5 Atmospheres, the water displaces a generally rectangular planar elastic element  206 , which, in the absence of such pressure, lies in sealed engagement with a rim  208  of raised wall  204 . 
     An inlet control chamber  209  is defined by rim  208 , a surface  210  and generally rectangular planar elastic element  206 . Displacement of generally rectangular planar elastic element  206  from sealed engagement with rim  208  allows water to flow through aperture  202  into inlet control chamber  209 , as described further hereinbelow with reference to  FIGS. 13A-13D , along surface  210 , as indicated by arrows  211 , and via a longitudinal recess  212  formed in surface  210  to an inlet  214  of a labyrinthine passageway  216 . The structure of the labyrinthine passageway  216  is seen from additional consideration of  FIGS. 2A and 3B  which illustrate facing, mutually sealed sides  220  and  222  of respective portions  224  and  226  of a drip irrigation emitter element  230 , useful as the drip irrigation emitter element  102  ( FIG. 1 ). 
     Portions  224  and  226  of drip irrigation emitter element  230  are sealed together at a circumferential raised elongate portion  232  to which is connected an internal raised elongate portion  234 , which extends between two sections  236  and  238  of pressure-reducing labyrinthine passageway  216 . Elongate portions  232  and  234  extend from side  222  of portion  226  and sealingly engage correspondingly located elongate recesses  242  and  244  formed on side  220  of portion  224 . Preferably, elongate portions  232  and  234  have a generally triangular cross section as seen in the enlarged portion of  FIG. 6 , and recesses  242  and  244  have a generally rectangular cross section as seen in the enlarged portion of  FIG. 4 . 
     The labyrinthine passageway  216  is defined by a series of tooth-like protrusions  250  which extend from a surface  251  and have a top surface  252 . In the assembled drip irrigation emitter element  230 , when elongate portions  232  and  234  are sealed to respective elongate recesses  242  and  244 , surfaces  210  and  252  lie in mutually touching, preferably sealed engagement. Preferably, the sealing is effected ultrasonically and the dimensions of the circumferential raised elongate portion  232 , the internal raised elongate portion  234  and corresponding recesses  242  and  244  are such that ultrasonic sealing thereof does not deform or affect the dimensions or mutual engagement of surfaces  210  and  252  and particularly does not affect the dimensions of the labyrinthine passageway  216 . 
     It is appreciated that sealing between internal elongate portion  234  and corresponding elongate recess  244  is provided such that in the event of incomplete sealing between surfaces  210  and  252 , water will not bypass much of the labyrinthine passageway  216  from section  236  to section  238  and from the region lying between surface  210  and elastic element  206  to section  238 . 
     The water flows through the labyrinthine pathway  216  to a labyrinthine pathway outlet  260  and the water pressure is correspondingly reduced by about 0.4 Atmospheres, typically from a line pressure of 0.5 to 4 Atmospheres. 
     Reference is now made additionally to  FIGS. 8-10 , which illustrate a side  270 , shown with particular clarity in  FIG. 3A , of portion  226  of element  230 , being sealed to an interior wall surface  272  of a water supply pipe  274 , useful as main water flow channel  100  ( FIG. 1 ). 
     As seen in  FIGS. 3A ,  4  and  5 , a circumferential raised wall  280  and an internal raised wall  282  define respective rims  284  and  286  which are heat welded to interior wall surface  272  ( FIG. 8 ). 
     Water passes through labyrinthine pathway outlet  260  and enters a chamber  290 , from which it exits via an outlet  292  and enters an outlet control chamber  294 , formed at side  222  of portion  226  and sealed by generally rectangular planar elastic element  206 . Elastic element  206  is supported by a surface  296  which surrounds outlet control chamber  294 . 
     As seen particularly in  FIGS. 8-10 , generally rectangular planar elastic element  206  governs water flow through an outlet  300  of outlet control chamber  294 , as a function of the line pressure applied to generally rectangular planar elastic element  206  at a surface  302  thereof, which surface engages rim  208 . Outlet  300  is typically in the form of a circular hole. Preferably, a shallow slot  304 , which is seen with particular clarity in  FIGS. 3B and 6 , is provided in communication with the outlet  300 , to assist in providing efficient pressure responsive flow control of water passing through the outlet  300 . 
     Water passing through outlet  300  enters a volume  310 , defined between a surface  312  of side  270  and surface  272  of water supply pipe  274 , and then passes to a volume  314 , defined between a surface  316  of side  270  and surface  272  of water supply pipe  274 , via a partial obstruction  320 . The partial obstruction  320  is provided for helping to prevent particulate matter from passing back from volume  314  into volume  310 . 
     Water leaves volume  314  via an opening  322  formed in water supply pipe  274 , which opening corresponds to pressure-compensated emitter element output aperture  106  ( FIG. 1 ). 
     Reference is now made to  FIGS. 11A ,  11 B,  11 C and  11 D, which are illustrations of a problem in the operation of prior art pressure-controlled anti-leakage drip irrigation emitters,  FIG. 11A  being a simplified not-to-scale pictorial illustration,  FIGS. 11B and 11C  being sectional illustrations taken along respective section lines XIB-XIB and XIC-XIC in  FIG. 11A , and  FIG. 11D  being a superposition of portions of  FIGS. 11B and 11C . 
     Reference is made to prior art pressure-controlled anti-leakage drip irrigation emitters which employ a non-square, rectangular elastic element  380  which is secured along its non-square, rectangular periphery and a circular raised wall  382  surrounding an inlet aperture  384 . When the liquid pressure underlying the rectangular elastic element  380  is such that an underside surface  386  of the elastic element  380  barely touches portions  388  of the top surface  390  of wall  382 , which lie closest to an edge of the elastic element  380 , the underside surface  386  does not touch portions  392  of the top surface  390  which lie further from an edge of the elastic element  380 . This can be seen with particular clarity in  FIGS. 11B and 11C  as well as in the superposition of  FIGS. 11D . 
     The present inventors have understood that this constitutes a problem in pressure-controlled anti-leakage drip irrigation emitters, since there exists a range of pressures at which the inlet aperture is not fully open or fully closed by the elastic element  380 , resulting in a leakage situation. Furthermore, the circumferentially incomplete contact between the elastic element  380  and top surface  390  of wall  382  surrounding the inlet aperture  384  inhibits sealing of the inlet aperture at even lower pressures, inasmuch as any contact between the elastic element  380  and any location on top surface  390  increases the amount of force required to establish further and full contact. Accordingly, the level of fluid pressure underlying the elastic element  380  required to achieve sealing of the inlet aperture is much lower than would otherwise be required to seal the inlet aperture, and undesired leakage occurs following termination of water supply to the drip irrigation line and following initial supply of water to the drip irrigation line. 
     Reference is now made to  FIGS. 12A ,  12 B,  12 C and  12 D, which are illustrations of a solution to the problem in the operation of prior art pressure-controlled anti-leakage drip irrigation emitters as shown in  FIGS. 11A-11D  and discussed hereinabove,  FIG. 12A  being a simplified not-to-scale pictorial illustration,  FIGS. 12B and 12C  being sectional illustrations taken along respective section lines XIIB-XIIB and XIIC-XIIC in  FIG. 12A , and  FIG. 12D  being a superposition of portions of  FIGS. 12B and 12C . 
     As seen in  FIGS. 12A-12D , a non-circular raised wall  400  surrounds an inlet aperture  402 . In this case, in accordance with a preferred embodiment of the present invention, when the liquid pressure underlying a rectangular elastic element  406  is such that an underside surface  408  of the elastic element  406  barely touches portions  410  of the top surface  412  of wall  400 , which lie closest to an edge of the elastic element  406 , the underside surface  408  simultaneously or nearly simultaneously also barely touches portions  414  of the top surface  412  which lie further from an edge of the elastic element. This can be seen with particular clarity in  FIGS. 12B and 12C  as well as in the superposition of  FIG. 12D . 
     The present inventors have understood that this solves the problem in prior art pressure-controlled anti-leakage drip irrigation emitters which was discussed above with reference to  FIGS. 11A-11D , by greatly reducing or eliminating the range of pressures at which the inlet aperture is not fully open or fully closed by the elastic element  380 , resulting in a leakage situation. Furthermore, the circumferentially complete contact between the elastic element  406  and top surface  412  of wall  400  surrounding the inlet aperture  402  enhances sealing of the inlet aperture. Accordingly, the level of fluid pressure underlying the elastic element  406  required to achieve sealing of the inlet aperture can be higher than would otherwise be required to seal the inlet aperture in the prior art. Thus, sealing takes place following termination of water supply to the drip irrigation line at a higher line pressure and thus enables efficient use of the drip irrigation line over a greater range of variation of height than was possible in the prior art. Any leakage that occurs, takes place over a substantially shorter period following termination of water supply to the drip irrigation line, and over a shorter period following initial supply of water to the drip irrigation line, than in the prior art. 
     Reference is now made to  FIGS. 13A ,  13 B,  13 C and  13 D, which are generally to-scale simplified illustrations which correspond to  FIGS. 12B and 12C  in the context of the drip irrigation emitter element of  FIGS. 2A-10 ,  FIGS. 13A and 13B  showing a first operative orientation of the drip irrigation emitter element and  FIGS. 13C and 13D  showing a second operative orientation of the drip irrigation emitter element. 
       FIGS. 13A and 13B  are generally to-scale simplified illustrations which correspond to  FIGS. 12B and 12C  in the context of the drip irrigation emitter element of  FIGS. 2A-10 . The non-circular configuration of the inlet aperture  402  ( FIGS. 12A-12D ) can be seen by considering the separations between portions of the rim  208  in respective  FIGS. 13A  ( 410  in  FIG. 12B) and 13B  ( 414  in  FIG. 12C ), which represent mutually perpendicular cross-sections of the drip irrigation emitter element. The indicated angles illustrate the angular engagement between the elastic element  206  and rim  208  of the wall  204  of the inlet aperture  202 . 
       FIGS. 13A and 13B  show the drip irrigation emitter element in a closed operative orientation in which surface  302  of elastic element  206  lies in sealed engagement with rim  208 , thereby preventing the flow of water from inlet aperture  202  into inlet control chamber  209 .  FIGS. 13C and 13D  show the drip irrigation emitter element in an open operative orientation in which surface  302  of elastic element  206  is displaced from sealed engagement with rim  208 , thereby allowing the flow of water from inlet aperture  202  into inlet control chamber  209 . 
     Transition of the drip irrigation emitter element from the closed operative orientation of  FIGS. 13A and 13B  to the open operative orientation of  FIGS. 13C and 13D  occurs when the water pressure in main water flow channel  100  ( FIG. 1 ) exceeds a predetermined threshold preferably of 0.5 Atmospheres. Transition of the drip irrigation emitter element from the open operative orientation of  FIGS. 13C and 13D  to the closed operative orientation of  FIGS. 13A and 13B  occurs when the water pressure in main water flow channel  100  ( FIG. 1 ) drops below a predetermined threshold preferably of 0.2 Atmospheres. 
     Reference is now made to  FIGS. 14A ,  14 B,  14 C and  14 D, which are simplified illustrations of another solution to the problem in the operation of prior art pressure-controlled anti-leakage drip irrigation emitters as shown in  FIGS. 11A-11D ,  FIG. 14A  being a simplified not-to-scale pictorial illustration,  FIGS. 14B and 14C  being sectional illustrations taken along respective section lines XIVB-XIVB and XIVC-XIVC in  FIG. 14A , and  FIG. 14D  being a superposition of portions of  FIGS. 14B and 14C . 
     As seen in  FIGS. 14A-14D , a non-circular raised wall  460  having a non-uniform wall height, surrounds an inlet aperture  462 . It is appreciated that the inlet aperture  462  is typically of somewhat smaller dimensions than that of  FIGS. 2A-10  and  12 A- 13 B. The wall  460  is configured to be lowest at portions  464  of a top surface  466  of wall  460 , which lie closest to an edge of an elastic element  470  and highest at portions  472  of the top surface  466  of wall  460 , which lie furthest from an edge of the elastic element  470 . 
     In this case, in accordance with another preferred embodiment of the present invention, when the liquid pressure underlying the rectangular elastic element  470  is such that an underside surface  474  of the elastic element  470  barely touches portions  464  of the top surface  466  of wall  460 , the underside surface  474  simultaneously or nearly simultaneously also barely touches portions  472  of the top surface  466 . This can be seen with particular clarity in  FIGS. 14B and 14C  as well as in the superposition of  FIG. 14D . 
     The present inventors have understood that this embodiment also solves the problem in prior art pressure-controlled anti-leakage drip irrigation emitters which was discussed above with reference to  FIGS. 11A-11D , by greatly reducing or eliminating the range of pressures at which the inlet aperture is not fully open or fully closed by the elastic element  380  ( FIGS. 11A &amp; 11B ), resulting in a leakage situation. Furthermore, the circumferentially complete contact between the elastic element  470  and top surface  466  of wall  460  surrounding the inlet aperture  462  enhances sealing of the inlet aperture. Accordingly, the level of fluid pressure underlying the elastic element  470  required to achieve sealing of the inlet aperture can be higher than would otherwise be required to seal the inlet aperture in the prior art, and any leakage that occurs takes place over a substantially shorter period following termination of water supply to the drip irrigation line and over a shorter period following initial supply of water to the drip irrigation line than in the prior art. This enables efficient use of the drip irrigation line over a greater range of variation of height than was possible in the prior art. 
     Reference is now made to  FIGS. 15A ,  15 B,  15 C and  15 D which are generally to-scale simplified illustrations which correspond to  FIGS. 14B and 14C  in the general context of the drip irrigation emitter element of  FIGS. 2A-10 , but having a somewhat smaller inlet aperture  202 . The non-circular configuration of the inlet aperture  202  and its non-uniform wall height ( FIGS. 14A-14D ) can be seen by considering the separations between and variations in height of portions of the rim  208  in  FIGS. 15A and 15C  ( 464  in  FIG. 14B ) and in  FIGS. 15B and 15D  ( 472  in  FIG. 14C ), which represent mutually perpendicular cross-sections of the drip irrigation emitter element. The indicated angles in  FIGS. 15A and 15B  illustrate the angular engagement between the elastic element  206  and rim  208  of the wall  204  of the inlet aperture  202 . 
       FIGS. 15A and 15B  show the drip irrigation emitter element in a closed operative orientation in which surface  302  of elastic element  206  lies in sealed engagement with rim  208 , thereby preventing the flow of water from inlet aperture  202  into inlet control chamber  209 .  FIGS. 15C and 15D  show the drip irrigation emitter element in an open operative orientation in which surface  302  of elastic element  206  is displaced from sealed engagement with rim  208 , thereby allowing the flow of water from inlet aperture  202  into inlet control chamber  209 . 
     Transition of the drip irrigation emitter element from the closed operative orientation of  FIGS. 15A and 15B  to the open operative orientation of  FIGS. 15C and 15D  occurs when the water pressure in main water flow channel  100  ( FIG. 1 ) exceeds a predetermined threshold of preferably 0.5 Atmospheres. Transition of the drip irrigation emitter element from the open operative orientation of  FIGS. 15C and 15D  to the closed operative orientation of  FIGS. 15A and 15B  occurs when the water pressure in main water flow channel  100  ( FIG. 1 ) drops below a predetermined threshold of preferably 0.2 Atmospheres. 
     Reference is now made to  FIGS. 16A ,  16 B,  16 C and  16 D, which are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with a preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 . 
       FIGS. 16A-16D  show drip irrigation apparatus of the general type shown in  FIG. 1 , and more particularly of the type shown in enlargements II and III in  FIG. 1 .  FIGS. 16A-16D  show drip irrigation apparatus of the type shown in enlargement II of  FIG. 1 , formed of an elongate sheet of plastic  500  to which drip irrigation emitter elements  502 , preferably of the type described hereinabove with reference to  FIGS. 2A-10 , are welded. 
     One elongate edge of sheet  500 , designated by reference numeral  504 , is welded to an interior location of the sheet  500 , which is designated by reference numeral  506 , thereby to define a main water flow channel  508  which corresponds to main water flow channel  100  ( FIG. 1 ). 
     An opposite elongate edge of sheet  500 , designated by reference numeral  510  is welded at an exterior location of sheet  500 , which is designated by reference numeral  512 , to a secondary water flow channel labyrinth-defining strip  514 , which is also welded to sheet  500 , so as to define a secondary water flow channel  516 , and a secondary water flow channel labyrinth  518 . 
     Alternatively, strip  514  may have weeping hose functionality and/or sweat irrigation functionality, and in such a case, need not define a labyrinth. 
       FIG. 16A  is a partially sectional, partially pictorial illustration, taken at arrows A-A in the general schematic illustration of  FIG. 1  and along the section lines A-A in enlargement II of  FIG. 1 , which section lines pass through a water inlet  520  of the drip irrigation emitter element  502 , which allows water to flow from main water flow channel  508 . 
       FIG. 16B  is a partially sectional, partially pictorial illustration, taken at arrows B-B in the general schematic illustration of  FIG. 1  and along the section lines B-B in enlargement II of  FIG. 1 , which section lines pass through a water outlet  522  of the drip irrigation emitter element  502 , which allows water to flow into the secondary water flow channel  516 . 
       FIG. 16C  is a partially sectional, partially pictorial illustration, taken at arrows C-C in the general schematic illustration of  FIG. 1  and along the section lines C-C in enlargement II of  FIG. 1 , which section lines pass through a water inlet  524  of the secondary water flow channel labyrinth  518 , which allows water to flow from the secondary water flow channel  516  into the secondary water flow channel labyrinth  518 . 
       FIG. 16D  is a partially sectional, partially pictorial illustration, taken at arrows D-D in the general schematic illustration of  FIG. 1  and along the section lines D-D in enlargement II of  FIG. 1 , which section lines pass through a water outlet  526  of the secondary water flow channel labyrinth  518  which allows water to flow from the secondary water flow channel labyrinth  518  to the atmosphere. 
     Reference is now made to  FIGS. 17A ,  17 B,  17 C and  17 D, which are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with another preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 . 
       FIGS. 17A-17D  show drip irrigation apparatus of the general type shown in  FIG. 1 , and more particularly of the type shown in enlargements II and III in  FIG. 1 .  FIGS. 17A-17D  show drip irrigation apparatus of the type shown in enlargement II of  FIG. 1 , formed of an elongate sheet of plastic  530  to which drip irrigation emitter elements  532 , preferably of the type described hereinabove with reference to  FIGS. 2A-10 , are welded. 
     The elongate edges of sheet  530 , designated by reference numerals  534  and  536 , are welded together at a seam  538 , thereby to define a main water flow channel  540  which corresponds to main water flow channel  100  ( FIG. 1 ). 
     An elongate edge  542  of an additional elongate sheet of plastic  544  is welded at seam  538  to edge  534  of sheet  530 . Alternatively, elongate sheet  544  may incorporate material having weeping hose functionality and/or sweat irrigation functionality. An opposite elongate edge  546  of sheet  544  is welded at an exterior location of sheet  530 , which is designated by reference numeral  548 , to a secondary water flow channel labyrinth-defining strip  550 , which is also welded to sheet  530 , so as to define a secondary water flow channel  552 , and a secondary water flow channel labyrinth  554 . Alternatively, strip  550  may have weeping hose functionality and/or sweat irrigation functionality, and in such a case, need not define a labyrinth. 
       FIG. 17A  is a partially sectional, partially pictorial illustration, taken at arrows A-A in the general schematic illustration of  FIG. 1  and along the section lines A-A in enlargement II of  FIG. 1 , which section lines pass through a water inlet  556  of the drip irrigation emitter element  532 , which allows water to flow from main water flow channel  540 . 
       FIG. 17B  is a partially sectional, partially pictorial illustration, taken at arrows B-B in the general schematic illustration of  FIG. 1  and along the section lines B-B in enlargement II of  FIG. 1 , which section lines pass through a water outlet  558  of the drip irrigation emitter element  532 , which allows water to flow into the secondary water flow channel  552 . 
       FIG. 17C  is a partially sectional, partially pictorial illustration, taken at arrows C-C in the general schematic illustration of  FIG. 1  and along the section lines C-C in enlargement II of  FIG. 1 , which section lines pass through a water inlet  560  of the secondary water flow channel labyrinth  554 , which allows water to flow from the secondary water flow channel  552  into the secondary water flow channel labyrinth  554 . 
       FIG. 17D  is a partially sectional, partially pictorial illustration, taken at arrows D-D in the general schematic illustration of  FIG. 1  and along the section lines D-D in enlargement II of  FIG. 1 , which section lines pass through a water outlet  562  of the secondary water flow channel labyrinth  554  which allows water to flow from the secondary water flow channel labyrinth  554  to the atmosphere. 
     Reference is now made to  FIGS. 18A ,  18 B,  18 C and  18 D, which are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with yet another preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 . 
       FIGS. 18A-18D  show drip irrigation apparatus of the general type shown in  FIG. 1 , and more particularly of the type shown in enlargements II and III in  FIG. 1 .  FIGS. 18A-18D  show drip irrigation apparatus of the type shown in enlargement II of  FIG. 1 , formed of an elongate tube of plastic  570 , to an interior wall of which are welded drip irrigation emitter elements  572 , preferably of the type described hereinabove with reference to  FIGS. 2A-10 . The plastic tube  570  defines a main water flow channel  574  which corresponds to main water flow channel  100  ( FIG. 1 ). 
     An elongate edge  576  of an elongate sheet of plastic  578  is welded to tube  570  at an exterior location therealong, designated by reference numeral  580 . An opposite elongate edge  582  of sheet  578  is welded to a secondary water flow channel labyrinth-defining strip  584 , which is welded to tube  570  at an exterior location therealong, designated by reference numeral  586 , so as to define a secondary water flow channel  588 , and a secondary water flow channel labyrinth  590 . 
     Elongate sheet  578  may alternatively incorporate material having weeping hose functionality and/or sweat irrigation functionality. Strip  584  may alternatively have weeping hose functionality and/or sweat irrigation functionality and in such a case, need not define a labyrinth.  FIG. 18A  is a partially sectional, partially pictorial illustration, taken at arrows A-A in the general schematic illustration of  FIG. 1  and along the section lines A-A in enlargement II of  FIG. 1 , which section lines pass through a water inlet  592  of the drip irrigation emitter element  572 , which allows water to flow from main water flow channel  574 . 
       FIG. 18B  is a partially sectional, partially pictorial illustration, taken at arrows B-B in the general schematic illustration of  FIG. 1  and along the section lines B-B in enlargement II of  FIG. 1 , which section lines pass through a water outlet  594  of the drip irrigation emitter element  572 , which allows water to flow into the secondary water flow channel  588 . 
       FIG. 18C  is a partially sectional, partially pictorial illustration, taken at arrows C-C in the general schematic illustration of  FIG. 1  and along the section lines C-C in enlargement II of  FIG. 1 , which section lines pass through a water inlet  596  of the secondary water flow channel labyrinth  590 , which allows water to flow from the secondary water flow channel  588  to the secondary water flow channel labyrinth  590 . 
       FIG. 18D  is a partially sectional, partially pictorial illustration, taken at arrows D-D in the general schematic illustration of  FIG. 1  and along the section lines D-D in enlargement II of  FIG. 1 , which section lines pass through a water outlet  598  of the secondary water flow channel labyrinth  590 , which allows water to flow from the secondary water flow channel labyrinth  590  to the atmosphere. 
     Reference is now made to  FIGS. 19A ,  19 B,  19 C and  19 D, which are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with still another preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 . 
       FIGS. 19A-19D  show drip irrigation apparatus of the general type shown in  FIG. 1 , and more particularly of the type shown in enlargements IV and V in  FIG. 1 .  FIGS. 19A-19D  show drip irrigation apparatus of the type shown in enlargement IV of  FIG. 1 , formed of an elongate tube of plastic  600 , to an interior wall of which are welded drip irrigation emitter elements  602 , preferably of the type described hereinabove with reference to  FIGS. 2A-10 . The plastic tube  600  defines a main water flow channel  604  which corresponds to main water flow channel  100  ( FIG. 1 ). 
     An elongate edge  606  of an elongate sheet of plastic  608  is welded to tube  600  at an exterior location therealong, which is designated by reference numeral  610 . An opposite elongate edge  612  of sheet  608  is welded to tube  600  at another exterior location therealong, designated by reference numeral  614 , thereby defining a secondary water flow channel  616 . Welded to an interior facing surface of sheet  608  is a secondary water flow channel labyrinth-defining element  618 , which defines a secondary water flow channel labyrinth  620 . 
     Elongate sheet  608  may alternatively incorporate material having weeping hose functionality and/or sweat irrigation functionality, and in such a case, element  618  may be omitted. 
       FIG. 19A  is a partially sectional, partially pictorial illustration, taken at arrows A-A in the general schematic illustration of  FIG. 1  and along the section lines A-A in enlargement IV of  FIG. 1 , which section lines pass through a water inlet  622  of the drip irrigation emitter element  602 , which allows water to flow from main water flow channel  604 . 
       FIG. 19B  is a partially sectional, partially pictorial illustration, taken at arrows B-B in the corresponding schematic illustration of  FIG. 1  and along the section lines B-B in enlargement IV of  FIG. 1 , which section lines pass through a water outlet  624  of the drip irrigation emitter element  602 , which allows water to flow into the secondary water flow channel  616 . 
       FIG. 19C  is a partially sectional, partially pictorial illustration, taken at arrows C-C in the general schematic illustration of  FIG. 1  and along the section lines C-C in enlargement IV of  FIG. 1 , which section lines pass through a water inlet  626  of the secondary water flow channel labyrinth  620 , which allows water to flow from the secondary water flow channel  616  to the secondary water flow channel labyrinth  620 . 
       FIG. 19D  is a partially sectional, partially pictorial illustration, taken at arrows D-D in the general schematic illustration of  FIG. 1  and along the section lines D-D in enlargement IV of  FIG. 1 , which section lines pass through a water outlet  628  of the secondary water flow channel labyrinth  620 , which allows water to flow from the secondary water flow channel labyrinth  620  to the atmosphere. 
     Reference is now made to  FIGS. 20A ,  20 B,  20 C and  20 D, which are simplified sectional illustrations of drip irrigation apparatus constructed and operative in accordance with a further preferred embodiment of the present invention, taken at locations indicated by respective arrows A, B, C and D in the general schematic illustration of  FIG. 1 . 
       FIGS. 20A-20D  show drip irrigation apparatus of the general type shown in  FIG. 1 , and more particularly of the type shown in enlargements IV and V in  FIG. 1 .  FIGS. 20A-20D  show drip irrigation apparatus of the type shown in enlargement IV of  FIG. 1 , formed of an inner elongate tube of plastic  650 , to an interior wall of which are welded drip irrigation emitter elements  652 , preferably of the type described hereinabove with reference to  FIGS. 2A-10 . The plastic tube  650  defines a main water flow channel  654  which corresponds to main water flow channel  100  ( FIG. 1 ). 
     An outer elongate plastic tube  656 , which may be extruded over inner elongate tube  650 , defines with an outer surface of inner elongate tube  650  a secondary water flow channel  658 . Tube  656  may or may not be joined to tube  650 . 
     Welded to an interior facing surface of tube  656  is a secondary water flow channel labyrinth-defining element  660 , which defines a secondary water flow channel labyrinth  662 . Tube  656  may alternatively incorporate material having weeping hose functionality and/or sweat irrigation functionality, and in such a case, element  660  may be omitted. 
       FIG. 20A  is a partially sectional, partially pictorial illustration, taken at arrows A-A in the general schematic illustration of  FIG. 1  and along the section lines A-A in enlargement IV of  FIG. 1 , which section lines pass through a water inlet  664  of the drip irrigation emitter element  652 , which allows water to flow from main water flow channel  654 . 
       FIG. 20B  is a partially sectional, partially pictorial illustration, taken at arrows B-B in the general schematic illustration of  FIG. 1  and along the section lines B-B in enlargement IV of  FIG. 1 , which section lines pass through a water outlet  666  of the drip irrigation emitter element  652 , which allow water to flow into the secondary water flow channel  658 . 
       FIG. 20C  is a partially sectional, partially pictorial illustration, taken at arrows C-C in the general schematic illustration of  FIG. 1  and along the section lines C-C in enlargement IV of  FIG. 1 , which section lines pass through a water inlet  668  of the secondary water flow channel labyrinth  662 , which allows water to flow from the secondary water flow channel  658  to the secondary water flow channel labyrinth  662 . 
       FIG. 20D  is a partially sectional, partially pictorial illustration, taken at arrows D-D in the general schematic illustration of  FIG. 1  and along the section lines D-D in enlargement IV of  FIG. 1 , which section lines pass through a water outlet  670  of the secondary water flow channel labyrinth  662 , which allows water to flow from the secondary water flow channel labyrinth  662  to the atmosphere. 
     It is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.