Abstract:
An irrigation sprinkler including a base defining an axis, a pressurized water inlet mounted onto the base, a nozzle, communicating with the inlet, and providing a pressurized water stream which is generally outwardly directed relative to the axis and a water stream deflector for engaging the pressurized water stream and deflecting at least part of the water stream azimuthally with respect to the axis, the deflector including a first pressurized water stream engagement surface and a second pressurized water stream engagement surface downstream of the first engagement surface, the first engagement surface having a pressurized water stream directing configuration arranged to direct a first portion of the stream impinging thereon, which does not exceed a predetermined quantity, onto the second surface and to direct at least a second portion of the stream impinging thereon, which at least a second portion exceeds the predetermined quantity, not onto the second engagement surface.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to irrigation sprinklers and more particularly to sprinklers, which are driven for rotation about a vertical axis by an output water stream which impacts on a sprinkler element. 
       BACKGROUND OF THE INVENTION 
       [0002]    Various types of impact sprinklers are known in the art. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention seeks to provide an improved irrigation sprinkler. 
         [0004]    There is thus provided in accordance with a preferred embodiment of the present invention an irrigation sprinkler including a base defining an axis, a pressurized water inlet mounted onto the base, a nozzle, communicating with the inlet, and providing a pressurized water stream which is generally outwardly directed relative to the axis and a water stream deflector for engaging the pressurized water stream from the nozzle and deflecting at least part of the water stream generally azimuthally with respect to the axis, the water stream deflector including a first pressurized water stream engagement surface and a second pressurized water stream engagement surface downstream of the first pressurized water stream engagement surface, the first pressurized water stream engagement surface having a pressurized water stream directing configuration arranged to direct a first portion of the pressurized water stream impinging on the first pressurized water stream engagement surface, which does not exceed a predetermined water stream quantity, onto the second pressurized water stream engagement surface and to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface, which at least a second portion exceeds the predetermined water stream quantity, not onto the second pressurized water stream engagement surface. 
         [0005]    Preferably, the nozzle is selectable to provide a selectable water stream quantity which may be less than, equal to or greater than the predetermined water stream quantity. 
         [0006]    In accordance with a preferred embodiment of the present invention, the pressurized water stream directing configuration of the first pressurized water stream engagement surface includes at least one vane which divides the pressurized water stream into the first portion of the pressurized water stream and the at least a second portion of the pressurized water stream. Additionally, the at least one vane includes a plurality of vanes, which divide the pressurized water stream into the first portion of the pressurized water stream and a plurality of second portions of the pressurized water stream. Alternatively or alternatively, the at least one vane has a generally triangular cross section. 
         [0007]    Preferably, the second pressurized water stream engagement surface has at least one water stream bypass aperture formed therein and the first pressurized water stream engagement surface is arranged to direct the at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface through the at least one water stream bypass aperture. 
         [0008]    In accordance with a preferred embodiment of the present invention, the second pressurized water stream engagement surface is configured to be impinged upon generally only by the first portion of the pressurized water stream and the first pressurized water stream engagement surface is arranged to direct the at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface away from the second pressurized water stream engagement surface. 
         [0009]    Preferably, the pressurized water stream directing configuration of the first pressurized water stream engagement surface includes at least one channel through which passes the pressurized water stream. In accordance with a preferred embodiment of the present invention, the at least one channel includes a pair of vanes which are joined by an integrally formed top plate. Additionally or alternatively, the at least one channel has an at least partially curved cross section. In accordance with a preferred embodiment of the present invention, the at least one channel has a generally triangular cross section. 
         [0010]    In accordance with a preferred embodiment of the present invention, the first pressurized water stream engagement surface includes at least one vane which divides the pressurized water stream into the first portion of the pressurized water stream and the at least a second portion of the pressurized water stream, the second pressurized water stream engagement surface has at least one water stream bypass aperture formed therein by at least one vane, the first pressurized water stream engagement surface is arranged to direct the at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface through the at least one water stream bypass aperture and the at least one vane which defines the at least one water stream bypass aperture and the at least one vane which divides the pressurized water stream on the first pressurized water stream engagement surface are formed as generally collinear continuations of each other. 
         [0011]    Preferably, the irrigation sprinkler also includes at least one intermediate vane spanning both the first and the second pressurized water stream engagement surfaces and joining the at least one vane which define the at least one water stream bypass aperture and the at least one vane which divides the pressurized water stream on the first pressurized water stream engagement surface. 
         [0012]    In accordance with a preferred embodiment of the present invention, the second pressurized water stream engagement surface downstream of the first pressurized water stream engagement surface is curved. Preferably, the first pressurized water stream engagement surface is generally planar and the second pressurized water stream engagement surface downstream of the first pressurized water stream engagement surface is curved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
           [0014]      FIGS. 1A ,  1 B,  1 C and  1 D are simplified isometric illustrations, taken from four different viewpoints, of an assembled sprinkler constructed and operative in accordance with a preferred embodiment of the present invention; 
           [0015]      FIGS. 2A and 2B  are simplified exploded view illustrations, taken from two different viewpoints, of the sprinkler of  FIGS. 1A-1D ; 
           [0016]      FIGS. 3A and 3B  are simplified side view illustrations of a hammer element forming part of the sprinkler of  FIGS. 1A-1D ,  2 A &amp;  2 B,  FIGS. 3A &amp; 3B  being mutually rotated by 180 degrees; 
           [0017]      FIGS. 3C and 3D  are simplified isometric illustrations of the hammer element of  FIGS. 3A and 3B , taken from two different viewpoints; 
           [0018]      FIGS. 3E ,  3 F and  3 G are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 3A ; 
           [0019]      FIGS. 3H ,  3 I,  3 J and  3 K are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 3A ; 
           [0020]      FIGS. 4A and 4B  are simplified side view illustrations of an alternative hammer element suitable for forming part of the sprinkler of  FIGS. 1A-1D ,  2 A &amp;  2 B,  FIGS. 4A &amp; 4B  being mutually rotated by 180 degrees; 
           [0021]      FIGS. 4C and 4D  are simplified isometric illustrations of the hammer element of  FIGS. 4A and 4B , taken from two different viewpoints; 
           [0022]      FIGS. 4E ,  4 F and  4 G are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 4A ; 
           [0023]      FIGS. 4H ,  4 I,  4 J and  4 K are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 4A ; 
           [0024]      FIGS. 5A and 5B  are simplified side view illustrations of a further alternative hammer element suitable for forming part of the sprinkler of  FIGS. 1A-1D ,  2 A &amp;  2 B,  FIGS. 5A &amp; 5B  being mutually rotated by 180 degrees; 
           [0025]      FIGS. 5C and 5D  are simplified isometric illustrations of the hammer element of  FIGS. 5A and 5B , taken from two different viewpoints; 
           [0026]      FIGS. 5E ,  5 F and  5 G are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 5A ; 
           [0027]      FIGS. 5H ,  5 I,  5 J and  5 K are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 5A ; 
           [0028]      FIGS. 6A and 6B  are simplified side view illustrations of another hammer element suitable for forming part of the sprinkler of  FIGS. 1A-1D ,  2 A &amp;  2 B,  FIGS. 6A &amp; 6B  being mutually rotated by 180 degrees; 
           [0029]      FIGS. 6C and 6D  are simplified isometric illustrations of the hammer element of  FIGS. 6A and 6B , taken from two different viewpoints; 
           [0030]      FIGS. 6E ,  6 F and  6 G are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 6A ; 
           [0031]      FIGS. 6H ,  6 I,  6 J and  6 K are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 6A ; 
           [0032]      FIGS. 7A and 7B  are simplified side view illustrations of yet another hammer element suitable for forming part of the sprinkler of  FIGS. 1A-1D ,  2 A &amp;  2 B,  FIGS. 7A &amp; 7B  being mutually rotated by 180 degrees; 
           [0033]      FIGS. 7C and 7D  are simplified isometric illustrations of the hammer element of  FIGS. 7A and 7B , taken from two different viewpoints; 
           [0034]      FIGS. 7E ,  7 F and  7 G are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 7A ; 
           [0035]      FIGS. 7H ,  7 I,  7 J and  7 K are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 7A ; 
           [0036]      FIGS. 8A and 8B  are simplified side view illustrations of still another hammer element suitable for forming part of the sprinkler of  FIGS. 1A-1D ,  2 A &amp;  2 B,  FIGS. 8A &amp; 8B  being mutually rotated by 180 degrees; 
           [0037]      FIGS. 8C and 8D  are simplified isometric illustrations of the hammer element of  FIGS. 8A and 8B , taken from two different viewpoints; 
           [0038]      FIGS. 8E ,  8 F and  8 G are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 8A ; 
           [0039]      FIGS. 8H ,  8 I,  8 J and  8 K are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 8A ; 
           [0040]      FIGS. 9A and 9B  are simplified side view illustrations of still another hammer element suitable for forming part of the sprinkler of  FIGS. 1A-1D ,  2 A &amp;  2 B,  FIGS. 9A &amp; 9B  being mutually rotated by 180 degrees; 
           [0041]      FIGS. 9C and 9D  are simplified isometric illustrations of the hammer element of  FIGS. 9A and 9B , taken from two different viewpoints; 
           [0042]      FIGS. 9E ,  9 F and  9 G are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 9A ; 
           [0043]      FIGS. 9H ,  9 I,  9 J and  9 K are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 9A ; 
           [0044]      FIGS. 10A ,  10 B &amp;  10 C are respective simplified front view, top view and back view illustrations of the sprinkler of  FIGS. 1A-3B , showing water flows therethrough when a relatively small nozzle is employed; 
           [0045]      FIG. 10D  is a simplified sectional illustration taken along lines D-D in  FIG. 10A ; 
           [0046]      FIGS. 11A ,  11 B &amp;  11 C are respective simplified front view, top view and back view illustrations of the sprinkler of  FIGS. 1A-3B , showing water flows therethrough when a relatively small nozzle is employed; 
           [0047]      FIG. 11D  is a simplified sectional illustration taken along lines D-D in  FIG. 11A ; and 
           [0048]      FIG. 11E  is a simplified sectional illustration taken along lines E-E in  FIG. 11A . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0049]    Reference is made to  FIGS. 1A ,  1 B,  1 C and  1 D, which are simplified isometric illustrations, taken from four different viewpoints, of an assembled sprinkler constructed and operative in accordance with a preferred embodiment of the present invention, and to  FIGS. 2A and 2B , which are simplified exploded view illustrations, taken from two different viewpoints, of the sprinkler of  FIGS. 1A-1D . 
         [0050]    As seen in  FIGS. 1A-2B , the sprinkler comprises a sprinkler body  102  including a riser portion  104 , a forward nozzle mounting portion  106 , a rearward nozzle mounting portion  108  and a bridge portion  110 . 
         [0051]    Riser portion  104  preferably includes a generally hollow cylindrical portion  112 , a top flange portion  114  and a bottom threaded portion  116 . 
         [0052]    Forward nozzle mounting portion  106  preferably includes a radially extending and upwardly extending generally hollow cylindrical portion  122 , which communicates with the interior of generally hollow cylindrical portion  112 , and a pair of nozzle mounting protrusions  124  on an upwardly and radially outward edge of cylindrical portion  122 . 
         [0053]    Rearward nozzle mounting portion  108  preferably includes a radially extending and upwardly extending generally hollow cylindrical portion  132 , which communicates with the interior of generally hollow cylindrical portion  112 , and a pair of nozzle mounting protrusions  134  on an upwardly and radially outward edge of cylindrical portion  132 . 
         [0054]    Bridge portion  110  preferably includes a pair of upwardly extending arms  142  and  144 , which support a joining portion  146  defining a flange  148  having a central aperture  150  which is spaced from a corresponding recess  152  along a vertical axis  154 . Underlying flange  148  there are provided a plurality of, typically four, spring mounting protrusions  156 . 
         [0055]    As seen most clearly in  FIGS. 2A &amp; 2B , mounted on riser portion  104  are multiple elements, which are here described in physical descending order from the element which lies below and against top flange portion  114 . A sand protection sleeve  162  encloses a compressed thrust spring  164 . A thrust spring seat  166  underlies spring  164  and overlies and partially surrounds a top flange  168  of a threaded connector base  170 . Connector base  170  is formed with an outer threaded bottom portion  172 , which serves for mounting of the entire sprinkler. A plurality of washers, typically including a two rubber washers  174  and  176  and an intermediate low friction washer  178 , are retained about riser cylindrical portion  112  by an apertured retaining cap  180 , which is threaded onto bottom threaded portion  116  of riser  104 . 
         [0056]    A selectable size forward nozzle  190  is replaceably mounted onto forward nozzle mounting portion  106  and retained thereon by engagement with nozzle mounting protrusions  124 . 
         [0057]    A selectable size rearward nozzle  192  is replaceably mounted onto rearward nozzle mounting portion  108  and is retained thereon by engagement with nozzle mounting protrusions  134 . Alternatively a plug (not shown) may replace the selectable rearward nozzle  192 . 
         [0058]    A vertical hammer mounting shaft  196  is preferably mounted along vertical axis  154  and extends through aperture  150  and is seated in recess  152 . Disposed about shaft  196  is a hammer sand protection sleeve  198  and a drive spring  200 , which is mounted at one end thereon onto four spring mounting protrusions  156 . 
         [0059]    A hammer  210  is rotatably mounted onto shaft  196 . Various embodiments of hammers are described hereinbelow in detail. A spray diffuser  212  may optionally be mounted on hammer  210 . 
         [0060]    Reference is now made to  FIGS. 3A and 3B , which are simplified side view illustrations of a hammer element  300  forming part of the sprinkler of  FIGS. 1A-2B ,  FIGS. 3A &amp; 3B  being mutually rotated by 180 degrees, and to  FIGS. 3C and 3D , which are simplified isometric illustrations of the hammer element of  FIGS. 3A and 3B , taken from two different viewpoints. Reference is also made to  FIGS. 3E ,  3 F and  3 G, which are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 3A , and to  FIGS. 3H ,  3 I,  3 J and  3 K, which are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 3A . 
         [0061]    As seen in  FIGS. 3A-3K , hammer  300  preferably includes a generally central hub portion  302  that defines a cylindrical sleeve portion  304  which is preferably sized to rotatably accommodate vertical hammer mounting shaft  196 . Hub portion  302  also preferably defines a plurality of, typically four, spring mounting protrusions  306 . 
         [0062]    Extending generally forwardly from hub portion  302  is a deflector mounting arm  308  from which extends a deflector  310 . Deflector mounting arm  308  also preferably includes an attachment recess  312  and aperture  314  for optional mounting thereon of spray diffuser  212 . 
         [0063]    Extending generally rearwardly from hub portion  302  is a balancing arm  316 . 
         [0064]    Reference is now particularly made to deflector  310  and to  FIGS. 3E-3K . It is a particular feature of the present invention that deflector  310  includes a first pressurized water stream engagement surface  320 , which receives a water stream from the forward nozzle  190 , and a second pressurized water stream engagement surface  322 , downstream of the first pressurized water stream engagement surface  320 , wherein the first pressurized water stream engagement surface  320  has a pressurized water stream channeling configuration arranged: 
         [0065]    to direct a first portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  320 , which does not exceed a predetermined water stream quantity, onto the second pressurized water stream engagement surface  322 , and 
         [0066]    to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  320 , which second portion exceeds the predetermined water stream quantity, not onto the second pressurized water stream engagement surface  322 . 
         [0067]    Preferably, the second pressurized water stream engagement surface  322  has at least one, and typically two, water stream bypass apertures  324  formed therein and the first pressurized water stream engagement surface  320  is arranged to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  320  through the water stream bypass aperture or apertures  324 . 
         [0068]    It is also a particular feature of the present invention that the first pressurized water stream engagement surface  320  is preferably formed with two mutually spaced generally parallel upstanding vanes  330 , having parallel mutually facing surfaces and non parallel opposite surfaces, which divide surface  320  into preferably three water engagement sub-surfaces  332 ,  334  and  336 . In the illustrated embodiment, the width of each of water engagement sub-surfaces  332 ,  334  and  336  is generally identical, however, alternatively, the individual sub-surfaces  332 ,  334  and  336  may have different widths. Alternatively, the number of vanes  330  provided may be more or less than two. 
         [0069]    Preferably vanes  330  have a generally truncated triangular cross section and have increased thickness from a stream incoming edge  340  of first pressurized water stream engagement surface  320  to a stream exiting edge  342  of the first pressurized water stream engagement surface  320 . Preferably vanes  330  each have a tapered stream facing edge  344 . 
         [0070]    First water stream engagement surface  320  is preferably generally flat except for a short tapered portion adjacent incoming edge  340 . 
         [0071]    Both the first and second water stream engagement surfaces  320  and  322  are defined by side walls  350  and  352 , which join first and second water stream engagement surfaces  320  and  322  and define an open space therebetween. 
         [0072]    It is a further particular feature of the present invention that the second pressurized water stream engagement surface  322  is preferably formed with two mutually spaced generally parallel upstanding vanes  360  which divide surface  322  into preferably three water engagement sub-surfaces  362 ,  364  and  366 . 
         [0073]    In the illustrated embodiment, the width of each of water engagement sub-surfaces  362 ,  364  and  366  is generally identical, however, alternatively, the individual sub-surfaces  362 ,  364  and  366  may have different widths. Alternatively, the number of vanes  360  provided may be more or less than two. 
         [0074]    Preferably vanes  360  have a generally uniform thickness from a stream incoming edge  370  of second pressurized water stream engagement surface  322  to a stream exiting edge  372  of the second pressurized water stream engagement surface  322 . Preferably vanes  360  each have a tapered stream facing edge  374 . 
         [0075]    Second water stream engagement surface  322  is preferably generally curved, faces generally oppositely to first water stream engagement surface  320  and includes a generally flat portion  376  adjacent incoming edge  370 , which extends into a generally curved portion  378 , adjacent stream exiting edge  372 . 
         [0076]    It is an additional particular feature of the present invention that preferably water engagement sub-surfaces  362  and  366 , on opposite sides of water engagement sub-surface  364 , are formed with apertures extending nearly all along generally curved portion  378  and preferably along a downstream part of flat portion  376 . 
         [0077]    Reference is now made to  FIGS. 4A and 4B , which are simplified side view illustrations of a hammer element  400  forming part of the sprinkler of  FIGS. 1A-2B ,  FIGS. 4A &amp; 4B  being mutually rotated by 180 degrees, and to  FIGS. 4C and 4D , which are simplified isometric illustrations of the hammer element of  FIGS. 4A and 4B , taken from two different viewpoints. Reference is also made to  FIGS. 4E ,  4 F and  4 G, which are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 4A , and to  FIGS. 4H ,  4 I,  4 J and  4 K, which are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 4A . 
         [0078]    As seen in  FIGS. 4A-4K , hammer  400  preferably includes a generally central hub portion  402  that defines a cylindrical sleeve portion  404  which is preferably sized to rotatably accommodate vertical hammer mounting shaft  196 . Hub portion  402  also preferably defines a plurality of, typically four, spring mounting protrusions  406 . 
         [0079]    Extending generally forwardly from hub portion  402  is a deflector mounting arm  408  from which extends a deflector  410 . Deflector mounting arm  408  also preferably includes an attachment recess  412  and aperture  414  for optional mounting thereon of spray diffuser  212 . 
         [0080]    Extending generally rearwardly from hub portion  402  is a balancing arm  416 . 
         [0081]    Reference is now particularly made to deflector  410  and to  FIGS. 4E-4K . It is a particular feature of the present invention that deflector  410  includes a first pressurized water stream engagement surface  420 , which receives a water stream from the forward nozzle  190 , and a second pressurized water stream engagement surface  422 , downstream of the first pressurized water stream engagement surface  420 , wherein the first pressurized water stream engagement surface  420  has a pressurized water stream channeling configuration arranged: 
         [0082]    to direct a first portion of the pressurized water stream impinging on the first pressurized water stream  420 , which does not exceed a predetermined water stream quantity, onto the second pressurized water stream engagement surface  422 , and 
         [0083]    to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  420 , which second portion exceeds the predetermined water stream quantity, not onto the second pressurized water stream engagement surface  422 . 
         [0084]    Preferably, the second pressurized water stream engagement surface  422  has at least one, and typically two, water stream bypass apertures  424  formed therein and the first pressurized water stream engagement surface  420  is arranged to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  420  through the water stream bypass aperture or apertures  424 . 
         [0085]    It is also a particular feature of the present invention that the first pressurized water stream engagement surface  420  is preferably formed with two mutually spaced generally parallel upstanding vanes  430 , having parallel mutually facing surfaces and non parallel opposite surfaces, which divide surface  420  into preferably three water engagement sub-surfaces  432 ,  434  and  436 . In the illustrated embodiment, the width of each of water engagement sub-surfaces  432 ,  434  and  436  is generally identical, however, alternatively, the individual sub-surfaces  432 ,  434  and  436  may have different widths. Alternatively, the number of vanes  430  provided may be more or less than two. 
         [0086]    Preferably vanes  430  have a generally truncated triangular cross section and have increased thickness from a stream incoming edge  440  of first pressurized water stream engagement surface  420  to a stream exiting edge  442  of the first pressurized water stream engagement surface  420 . Preferably vanes  430  each have a tapered stream facing edge  444 . 
         [0087]    First water stream engagement surface  420  is preferably generally flat except for a short tapered portion adjacent incoming edge  440 . 
         [0088]    Both the first and second water stream engagement surfaces  420  and  422  are defined by side walls  450  and  452 , which join first and second water stream engagement surfaces  420  and  422  and define an open space therebetween. 
         [0089]    It is a further particular feature of the present invention that the second pressurized water stream engagement surface  422  is preferably formed with two mutually spaced generally parallel upstanding vanes  460  which divide surface  422  into preferably three water engagement sub-surfaces  462 ,  464  and  466 . 
         [0090]    In the illustrated embodiment, the width of each of water engagement sub-surfaces  462 ,  464  and  466  is generally identical, however, alternatively, the individual sub-surfaces  462 ,  464  and  466  may have different widths. Alternatively, the number of vanes  460  provided may be more or less than two. 
         [0091]    Preferably vanes  460  have a generally uniform thickness therealong from a stream incoming edge  470  of second pressurized water stream engagement surface  422 . Preferably vanes  460  each have a tapered stream facing edge  471 . 
         [0092]    Second water stream engagement surface  422  is preferably generally curved, faces generally oppositely to first water stream engagement surface  420  and includes a generally flat portion  472  adjacent incoming edge  470 . Only water engagement sub-surface  464  extends into a generally curved portion  474 . 
         [0093]    Thus it is appreciated that, as distinct from the embodiment described hereinabove with reference to  FIGS. 3A-3K , in the embodiment of  FIGS. 4A-4K , the water engagement sub-surfaces  462  and  466  have respective stream exiting edges  476  and  478 , which are relatively close to and downstream of stream incoming edge  470  and water engagement sub-surface  464  has a stream exiting edge  480  which is much further downstream thereof. 
         [0094]    Reference is now made to  FIGS. 5A and 5B , which are simplified side view illustrations of a hammer element  500  forming part of the sprinkler of  FIGS. 1A-2B ,  FIGS. 5A &amp; 5B  being mutually rotated by 180 degrees, and to  FIGS. 5C and 5D , which are simplified isometric illustrations of the hammer element of  FIGS. 5A and 5B , taken from two different viewpoints. Reference is also made to  FIGS. 5E ,  5 F and  5 G, which are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 5A , and to  FIGS. 5H ,  5 I,  5 J and  5 K, which are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 5A . 
         [0095]    As seen in  FIGS. 5A-5K , hammer  500  preferably includes a generally central hub portion  502  that defines a cylindrical sleeve portion  504  which is preferably sized to rotatably accommodate vertical hammer mounting shaft  196 . Hub portion  502  also preferably defines a plurality of, typically four, spring mounting protrusions  506 . 
         [0096]    Extending generally forwardly from hub portion  502  is a deflector mounting arm  508  from which extends a deflector  510 . Deflector mounting arm  508  also preferably includes an attachment recess  512  and aperture  514  for optional mounting thereon of spray diffuser  212 . 
         [0097]    Extending generally rearwardly from hub portion  502  is a balancing arm  516 . 
         [0098]    Reference is now particularly made to deflector  510  and to  FIGS. 5E-5K . It is a particular feature of the present invention that deflector  510  includes a first pressurized water stream engagement surface  520 , which receives a water stream from the forward nozzle  190 , and a second pressurized water stream engagement surface  522 , downstream of the first pressurized water stream engagement surface  520 , wherein the first pressurized water stream engagement surface  520  has a pressurized water stream channeling configuration arranged: 
         [0099]    to direct a first portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  520 , which does not exceed a predetermined water stream quantity, onto the second pressurized water stream engagement surface  522 , and 
         [0100]    to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  520 , which second portion exceeds the predetermined water stream quantity, not onto the second pressurized water stream engagement surface  522 . 
         [0101]    Preferably, the second pressurized water stream engagement surface  522  has at least one, and typically two, water stream bypass apertures  524  formed therein and the first pressurized water stream engagement surface  520  is arranged to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  520  through the water stream bypass aperture or apertures  524 . 
         [0102]    It is also a particular feature of the present invention that the first pressurized water stream engagement surface  520  is preferably formed with two mutually spaced generally parallel upstanding vanes  530 , having parallel mutually facing surfaces and non parallel opposite surfaces, which divide surface  520  into preferably three water engagement sub-surfaces  532 ,  534  and  536 . In the illustrated embodiment, the width of each of water engagement sub-surfaces  532 ,  534  and  536  is generally identical, however, alternatively, the individual sub-surfaces  532 ,  534  and  536  may have different widths. Alternatively, the number of vanes  530  provided may be more or less than two. 
         [0103]    Preferably vanes  530  have a generally triangular cross section and have increased thickness from a stream incoming edge  540  of first pressurized water stream engagement surface  520  to a stream exiting edge  542  of the first pressurized water stream engagement surface  520 . Preferably vanes  530  each have a tapered stream facing edge  544 . 
         [0104]    First water stream engagement surface  520  is preferably generally flat except for a short tapered portion adjacent incoming edge  540 . 
         [0105]    Both the first and second water stream engagement surfaces  520  and  522  are defined by side walls  550  and  552 , which join first and second water stream engagement surfaces  520  and  522  and define an open space therebetween. 
         [0106]    It is a further particular feature of the present invention that the second pressurized water stream engagement surface  522  is preferably formed with two mutually spaced generally parallel upstanding vanes  560  which divide surface  522  into preferably three water engagement sub-surfaces  562 ,  564  and  566 . 
         [0107]    In the illustrated embodiment, the width of each of water engagement sub-surfaces  562 ,  564  and  566  is generally identical, however, alternatively, the individual sub-surfaces  562 ,  564  and  566  may have different widths. Alternatively, the number of vanes  560  provided may be more or less than two. 
         [0108]    Preferably vanes  560  have a generally uniform thickness from a stream incoming edge  570  of second pressurized water stream engagement surface  522  to a stream exiting edge  572  of the second pressurized water stream engagement surface  522 . Preferably vanes  560  each have a tapered stream facing edge  574 . 
         [0109]    Second water stream engagement surface  522  is preferably generally curved, faces generally oppositely to first water stream engagement surface  520  and includes a generally flat portion  576  adjacent incoming edge  570 , which extends into a generally curved portion  578 , adjacent stream exiting edge  572 . 
         [0110]    It is an additional particular feature of the present invention that preferably water engagement sub-surfaces  562  and  566 , on opposite sides of water engagement sub-surface  564 , are formed with apertures extending nearly all along generally curved portion  578  and preferably along a downstream part of flat portion  576 . 
         [0111]    Reference is now made to  FIGS. 6A and 6B , which are simplified side view illustrations of a hammer element  600  forming part of the sprinkler of  FIGS. 1A-2B ,  FIGS. 6A &amp; 6B  being mutually rotated by 180 degrees, and to  FIGS. 6C and 6D , which are simplified isometric illustrations of the hammer element of  FIGS. 6A and 6B , taken from two different viewpoints. Reference is also made to  FIGS. 6E ,  6 F and  6 G, which are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 6A , and to  FIGS. 6H ,  6 I,  6 J and  6 K, which are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 6A . 
         [0112]    As seen in  FIGS. 6A-6K , hammer  600  preferably includes a generally central hub portion  602  that defines a cylindrical sleeve portion  604  which is preferably sized to rotatably accommodate vertical hammer mounting shaft  196 . Hub portion  602  also preferably defines a plurality of, typically four, spring mounting protrusions  606 . 
         [0113]    Extending generally forwardly from hub portion  602  is a deflector mounting arm  608  from which extends a deflector  610 . Deflector mounting arm  608  also preferably includes an attachment recess  612  and aperture  614  for optional mounting thereon of spray diffuser  212 . 
         [0114]    Extending generally rearwardly from hub portion  602  is a balancing arm  616 . 
         [0115]    Reference is now particularly made to deflector  610  and to  FIGS. 6E-6K . It is a particular feature of the present invention that deflector  610  includes a first pressurized water stream engagement surface  620 , which receives a water stream from the forward nozzle  190 , and a second pressurized water stream engagement surface  622 , downstream of the first pressurized water stream engagement surface  620 , wherein the first pressurized water stream engagement surface  620  has a pressurized water stream channeling configuration arranged: 
         [0116]    to direct a first portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  620 , which does not exceed a predetermined water stream quantity, onto the second pressurized water stream engagement surface  622 , and 
         [0117]    to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  620 , which second portion exceeds the predetermined water stream quantity, not onto the second pressurized water stream engagement surface  622 . 
         [0118]    Preferably, the second pressurized water stream engagement surface  622  has at least one, and typically two, water stream bypass apertures  624  formed therein and the first pressurized water stream engagement surface  620  is arranged to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  620  through the water stream bypass aperture or apertures  624 . 
         [0119]    It is also a particular feature of the present invention that the first pressurized water stream engagement surface  620  is preferably formed with two mutually spaced generally parallel upstanding vanes  630 , having parallel mutually facing surfaces and non parallel opposite surfaces, which divide surface  620  into preferably three water engagement sub-surfaces  632 ,  634  and  636 . In the illustrated embodiment, the width of each of water engagement sub-surfaces  632 ,  634  and  636  is generally identical, however, alternatively, the individual sub-surfaces  632 ,  634  and  636  may have different widths. Alternatively, the number of vanes  630  provided may be more or less than two. In this embodiment, vanes  630  are joined by an integrally formed top plate  638 , thereby defining a water flow channel  639  between vanes  630  and top plate  638 . 
         [0120]    Preferably vanes  630  have a generally truncated triangular cross section and have increased thickness from a stream incoming edge  640  of first pressurized water stream engagement surface  620  to a stream exiting edge  642  of the first pressurized water stream engagement surface  620 . Preferably vanes  630  each have a tapered stream facing edge  644 . 
         [0121]    First water stream engagement surface  620  is preferably generally flat except for a short tapered portion adjacent incoming edge  640 . 
         [0122]    Both the first and second water stream engagement surfaces  620  and  622  are defined by side walls  650  and  652 , which join first and second water stream engagement surfaces  620  and  622  and define an open space therebetween. 
         [0123]    It is a further particular feature of the present invention that the second pressurized water stream engagement surface  622  is preferably formed with two mutually spaced generally parallel upstanding vanes  660  which divide surface  622  into preferably three water engagement sub-surfaces  662 ,  664  and  666 . 
         [0124]    In the illustrated embodiment, the width of each of water engagement sub-surfaces  662 ,  664  and  666  is generally identical, however, alternatively, the individual sub-surfaces  662 ,  664  and  666  may have different widths. Alternatively, the number of vanes  660  provided may be more or less than two. 
         [0125]    Preferably vanes  660  have a generally uniform thickness from a stream incoming edge  670  of second pressurized water stream engagement surface  622  to a stream exiting edge  672  of the second pressurized water stream engagement surface  622 . Preferably vanes  660  each have a tapered stream facing edge  674 . 
         [0126]    Second water stream engagement surface  622  is preferably generally curved, faces generally oppositely to first water stream engagement surface  620  and includes a generally flat portion  676  adjacent incoming edge  670 , which extend into a generally curved portion  678 , adjacent stream exiting edge  672 . 
         [0127]    It is an additional particular feature of the present invention that preferably water engagement sub-surfaces  662  and  666 , on opposite sides of water engagement sub-surface  664 , are formed with apertures extending nearly all along generally curved portion  678  and preferably along a downstream part of flat portion  676 . 
         [0128]    Reference is now made to  FIGS. 7A and 7B , which are simplified side view illustrations of a hammer element  700  forming part of the sprinkler of  FIGS. 1A-2B ,  FIGS. 7A &amp; 7B  being mutually rotated by 180 degrees, and to  FIGS. 7C and 7D , which are simplified isometric illustrations of the hammer element of  FIGS. 7A and 7B , taken from two different viewpoints. Reference is also made to  FIGS. 7E ,  7 F and  7 G, which are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 7A , and to  FIGS. 7H ,  7 I,  7 J and  7 K, which are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 7A . 
         [0129]    As seen in  FIGS. 7A-7K , hammer  700  preferably includes a generally central hub portion  702  that defines a cylindrical sleeve portion  704  which is preferably sized to rotatably accommodate vertical hammer mounting shaft  196 . Hub portion  702  also preferably defines a plurality of, typically four, spring mounting protrusions  706 . 
         [0130]    Extending generally forwardly from hub portion  702  is a deflector mounting arm  708  from which extends a deflector  710 . Deflector mounting arm  708  also preferably includes an attachment recess  712  and aperture  714  for optional mounting thereon of spray diffuser  212 . 
         [0131]    Extending generally rearwardly from hub portion  702  is a balancing arm  716 . 
         [0132]    Reference is now particularly made to deflector  710  and to  FIGS. 7E-7K . It is a particular feature of the present invention that deflector  710  includes a first pressurized water stream engagement surface  720 , which receives a water stream from the forward nozzle  190 , and a second pressurized water stream engagement surface  722 , downstream of the first pressurized water stream engagement surface  720 , wherein the first pressurized water stream engagement surface  720  has a pressurized water stream channeling configuration arranged: 
         [0133]    to direct a first portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  720 , which does not exceed a predetermined water stream quantity, onto the second pressurized water stream engagement surface  722 , and 
         [0134]    to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  720 , which second portion exceeds the predetermined water stream quantity, not onto the second pressurized water stream engagement surface  722 . 
         [0135]    Preferably, the second pressurized water stream engagement surface  722  has at least one, and typically two, water stream bypass apertures  724  formed therein and the first pressurized water stream engagement surface  720  is arranged to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  720  through the water stream bypass aperture or apertures  724 . 
         [0136]    It is also a particular feature of the present invention that the first pressurized water stream engagement surface  720  is preferably formed with a central, generally arched water flow channel  726  defined by an elongate arch  728  joining two, mutually spaced generally parallel upstanding vanes  730 , which divide surface  720  into preferably three water engagement sub-surfaces  732 ,  734  and  736 . In the illustrated embodiment, the width of each of water engagement sub-surfaces  732 ,  734  and  736  is generally identical, however, alternatively, the individual sub-surfaces  732 ,  734  and  736  may have different widths. Alternatively, the number of vanes  730  provided may be more or less than two. 
         [0137]    Preferably vanes  730  have increased thickness from a stream incoming edge  740  of first pressurized water stream engagement surface  720  to a stream exiting edge  742  of the first pressurized water stream engagement surface  720 . Preferably vanes  730  each have a tapered stream facing edge  744 . 
         [0138]    First water stream engagement surface  720  is preferably generally flat except for a short tapered portion adjacent incoming edge  740 . 
         [0139]    Both the first and second water stream engagement surfaces  720  and  722  are defined by side walls  750  and  752 , which join first and second water stream engagement surfaces  720  and  722  and define an open space therebetween. 
         [0140]    It is a further particular feature of the present invention that the second pressurized water stream engagement surface  722  is preferably formed with two mutually spaced generally parallel upstanding vanes  760  which divide surface  722  into preferably three water engagement sub-surfaces  762 ,  764  and  766 . 
         [0141]    In the illustrated embodiment, the width of each of water engagement sub-surfaces  762 ,  764  and  766  is generally identical, however, alternatively, the individual sub-surfaces  762 ,  764  and  766  may have different widths. Alternatively, the number of vanes  760  provided may be more or less than two. 
         [0142]    Preferably vanes  760  have a generally uniform thickness from a stream incoming edge  770  of second pressurized water stream engagement surface  722  to a stream exiting edge  772  of the second pressurized water stream engagement surface  722 . Preferably vanes  760  each have a tapered stream facing edge  774 . 
         [0143]    Second water stream engagement surface  722  is preferably generally curved, faces generally oppositely to first water stream engagement surface  720  and includes a generally flat portion  776  adjacent incoming edge  770 , which extends into a generally curved portion  778 , adjacent stream exiting edge  772 . 
         [0144]    It is an additional particular feature of the present invention that preferably water engagement sub-surfaces  762  and  766 , on opposite sides of water engagement sub-surface  764 , are formed with apertures extending nearly all along generally curved portion  778  and preferably along a downstream part of flat portion  776 . 
         [0145]    Reference is now made to  FIGS. 8A and 8B , which are simplified side view illustrations of a hammer element  800  forming part of the sprinkler of  FIGS. 1A-2B ,  FIGS. 8A &amp; 8B  being mutually rotated by 180 degrees, and to  FIGS. 8C and 8D , which are simplified isometric illustrations of the hammer element of  FIGS. 8A and 8B , taken from two different viewpoints. Reference is also made to  FIGS. 8E ,  8 F and  8 G, which are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 8A , and to  FIGS. 8H ,  8 I,  8 J and  8 K, which are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 8A . 
         [0146]    As seen in  FIGS. 8A-8K , hammer  800  preferably includes a generally central hub portion  802  that defines a cylindrical sleeve portion  804  which is preferably sized to rotatably accommodate vertical hammer mounting shaft  196 . Hub portion  802  also preferably defines a plurality of, typically four, spring mounting protrusions  806 . 
         [0147]    Extending generally forwardly from hub portion  802  is a deflector mounting arm  808  from which extends a deflector  810 . Deflector mounting arm  808  also preferably includes an attachment recess  812  and aperture  814  for optional mounting thereon of spray diffuser  212 . 
         [0148]    Extending generally rearwardly from hub portion  802  is a balancing arm  816 . 
         [0149]    Reference is now particularly made to deflector  810  and to  FIGS. 8E-8K . It is a particular feature of the present invention that deflector  810  includes a first pressurized water stream engagement surface  820 , which receives a water stream from the forward nozzle  190 , and a second pressurized water stream engagement surface  822 , downstream of the first pressurized water stream engagement surface  820 , wherein the first pressurized water stream engagement surface  820  has a pressurized water stream channeling configuration arranged: 
         [0150]    to direct a first portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  820 , which does not exceed a predetermined water stream quantity, onto the second pressurized water stream engagement surface  822 , and 
         [0151]    to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  820 , which second portion exceeds the predetermined water stream quantity, not onto the second pressurized water stream engagement surface  822 . 
         [0152]    Preferably, the second pressurized water stream engagement surface  822  has at least one, and typically two, water stream bypass apertures  824  formed therein and the first pressurized water stream engagement surface  820  is arranged to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  820  through the water stream bypass aperture or apertures  824 . 
         [0153]    It is also a particular feature of the present invention that the first pressurized water stream engagement surface  820  is preferably formed with a central water flow channel  826  of generally triangular cross section defined by two mutually inclined generally parallel-extending upstanding vanes  830 , which divide surface  820  into preferably three water engagement sub-surfaces  832 ,  834  and  836 . In the illustrated embodiment, the width of each of water engagement sub-surfaces  832 ,  834  and  836  is generally identical, however, alternatively, the individual sub-surfaces  832 ,  834  and  836  may have different widths. Alternatively, the number of vanes  830  provided may be more or less than two. 
         [0154]    Preferably vanes  830  have increased thickness from a stream incoming edge  840  of first pressurized water stream engagement surface  820  to a stream exiting edge  842  of the first pressurized water stream engagement surface  820 . Preferably vanes  830  each have a tapered stream facing edge  844 . 
         [0155]    First water stream engagement surface  820  is preferably generally flat except for a short tapered portion adjacent incoming edge  840 . 
         [0156]    Both the first and second water stream engagement surfaces  820  and  822  are defined by side walls  850  and  852 , which join first and second water stream engagement surfaces  820  and  822  and define an open space therebetween. 
         [0157]    It is a further particular feature of the present invention that the second pressurized water stream engagement surface  822  is preferably formed with two mutually spaced generally parallel upstanding vanes  860  which divide surface  822  into preferably three water engagement sub-surfaces  862 ,  864  and  866 . 
         [0158]    In the illustrated embodiment, the width of each of water engagement sub-surfaces  862 ,  864  and  866  is generally identical, however, alternatively, the individual sub-surfaces  862 ,  864  and  866  may have different widths. Alternatively, the number of vanes  860  provided may be more or less than two. 
         [0159]    Preferably vanes  860  have a generally uniform thickness from a stream incoming edge  870  of second pressurized water stream engagement surface  822  to a stream exiting edge  872  of the second pressurized water stream engagement surface  822 . Preferably vanes  860  each have a tapered stream facing edge  874 . 
         [0160]    Second water stream engagement surface  822  is preferably generally curved, faces generally oppositely to first water stream engagement surface  820  and includes a generally flat portion  876  adjacent incoming edge  870 , which extend into a generally curved portion  878 , adjacent stream exiting edge  872 . 
         [0161]    It is an additional particular feature of the present invention that preferably water engagement sub-surfaces  862  and  866 , on opposite sides of water engagement sub-surface  864 , are formed with apertures extending nearly all along generally curved portion  878  and preferably along a downstream part of flat portion  876 . 
         [0162]    Reference is now made to  FIGS. 9A and 9B , which are simplified side view illustrations of a hammer element  900  forming part of the sprinkler of  FIGS. 1A-2B ,  FIGS. 9A &amp; 9B  being mutually rotated by 180 degrees, and to  FIGS. 9C and 9D , which are simplified isometric illustrations of the hammer element of  FIGS. 9A and 9B , taken from two different viewpoints. Reference is also made to  FIGS. 9E ,  9 F and  9 G, which are simplified sectional illustrations taken along respective section lines E-E, F-F and G-G in  FIG. 9A , and to  FIGS. 9H ,  9 I,  9 J and  9 K, which are simplified sectional illustrations taken along respective section lines H-H, I-I, J-J and K-K in  FIG. 9A . 
         [0163]    As seen in  FIGS. 9A-9K , hammer  900  preferably includes a generally central hub portion  902  that defines a cylindrical sleeve portion  904  which is preferably sized to rotatably accommodate vertical hammer mounting shaft  196 . Hub portion  902  also preferably defines a plurality of, typically four, spring mounting protrusions  906 . 
         [0164]    Extending generally forwardly from hub portion  902  is a deflector mounting arm  908  from which extends a deflector  910 . Deflector mounting arm  908  also preferably includes an attachment recess  912  and aperture  914  for optional mounting thereon of spray diffuser  212 . 
         [0165]    Extending generally rearwardly from hub portion  902  is a balancing arm  916 . 
         [0166]    Reference is now particularly made to deflector  910  and to  FIGS. 9E-9K . It is a particular feature of the present invention that deflector  910  includes a first pressurized water stream engagement surface  920 , which receives a water stream from the forward nozzle  190 , and a second pressurized water stream engagement surface  922 , downstream of the first pressurized water stream engagement surface  920 , wherein the first pressurized water stream engagement surface  920  has a pressurized water stream channeling configuration arranged: 
         [0167]    to direct a first portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  920 , which does not exceed a predetermined water stream quantity, onto the second pressurized water stream engagement surface  922 , and 
         [0168]    to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  920 , which second portion exceeds the predetermined water stream quantity, not onto the second pressurized water stream engagement surface  922 . 
         [0169]    Preferably, the second pressurized water stream engagement surface  922  has at least one, and typically two, water stream bypass apertures  924  formed therein and the first pressurized water stream engagement surface  920  is arranged to direct at least a second portion of the pressurized water stream impinging on the first pressurized water stream engagement surface  920  through the water stream bypass aperture or apertures  924 . 
         [0170]    It is also a particular feature of the present invention that the first pressurized water stream engagement surface  920  is preferably formed with two, mutually spaced generally parallel upstanding vanes  930 , having parallel mutually facing surfaces and non parallel opposite surfaces, which divide surface  920  into preferably three water engagement sub-surfaces  932 ,  934  and  936 . In the illustrated embodiment, the width of each of water engagement sub-surfaces  932 ,  934  and  936  is generally identical, however, alternatively, the individual sub-surfaces  932 ,  934  and  936  may have different widths. Alternatively, the number of vanes  930  provided may be more or less than two. 
         [0171]    Preferably vanes  930  have a generally truncated triangular cross section and have increased thickness from a stream incoming edge  940  of first pressurized water stream engagement surface  920  to a stream exiting edge  942  of the first pressurized water stream engagement surface  920 . Preferably vanes  930  each have a tapered stream facing edge  944 . 
         [0172]    First water stream engagement surface  920  is preferably generally flat except for a short tapered portion adjacent incoming edge  940 . 
         [0173]    Both the first and second water stream engagement surfaces  920  and  922  are defined by side walls  950  and  952 , which join first and second water stream engagement surfaces  920  and  922  and define an open space therebetween. 
         [0174]    It is a further particular feature of the present invention that the second pressurized water stream engagement surface  922  is preferably formed with two mutually spaced generally parallel upstanding vanes  960  which divide surface  922  into preferably three water engagement sub-surfaces  962 ,  964  and  966 . It is a particular feature of the embodiment of  FIGS. 9A-9K , that vanes  960  are formed as continuations of vanes  930 , such that vanes  930  of the first pressurized water stream engagement surface  920 , vanes  960  of the second pressurized water stream engagement surface  922  and intermediate vanes  968 , each joining a vane  930  with a vane  960 , together define continuous vanes  969 , spanning both first and second pressurized water stream engagement surfaces  920  and  922 . 
         [0175]    In the illustrated embodiment, the width of each of water engagement sub-surfaces  962 ,  964  and  966  is generally identical, however, alternatively, the individual sub-surfaces  962 ,  964  and  966  may have different widths. Alternatively, the number of vanes  960  provided may be more or less than two. 
         [0176]    Preferably vanes  960  have a generally uniform thickness from a stream incoming edge  970  of second pressurized water stream engagement surface  922  to a stream exiting edge  972  of the second pressurized water stream engagement surface  922 . 
         [0177]    Second water stream engagement surface  922  is preferably generally curved, faces generally oppositely to first water stream engagement surface  920  and includes a generally flat portion  976  adjacent incoming edge  970 , which extend into a generally curved portion  978 , adjacent stream exiting edge  972 . 
         [0178]    It is an additional particular feature of the present invention that preferably water engagement sub-surfaces  962  and  966 , on opposite sides of water engagement sub-surface  964 , are formed with apertures extending nearly all along generally curved portion  978  and preferably along a downstream part of flat portion  976 . 
         [0179]    Reference is now made to  FIGS. 10A ,  10 B &amp;  10 C, which are respective simplified front view, top view and back view illustrations of the sprinkler of  FIGS. 1A-3D , showing water flows therethrough when a relatively small nozzle is employed, and to  FIG. 10D , which is a simplified sectional illustration taken along lines D-D in  FIG. 10A . 
         [0180]    As seen in  FIGS. 10A-10D , in the illustrated embodiment, when a relatively small forward nozzle is employed, such as a nozzle  190  having an internal diameter of 2 mm, nearly all of the water stream emanating from nozzle  190 , here designated by reference numeral  1000 , is confined between vanes  330  of first water stream engagement surface  320  in engagement with first water engagement sub-surface  334 , as designated by reference numeral  1002 . Nearly all of the water stream then impinges on second water engagement sub-surface  364 , and is confined between vanes  360  of the second water stream engagement surface  322 , as designated by reference numeral  1004 . Nearly all of the water stream as designated by reference numeral  1006  exits in a direction indicated by an arrow  1008 . Accordingly, nearly all of the water stream applies a rotational force, indicated by an arrow  1010 , to hammer  300 , causing it to rotate about vertical axis  154 . 
         [0181]    Reference is now made to  FIGS. 11A ,  11 B &amp;  11 C, which are respective simplified front view, top view and back view illustrations of the sprinkler of  FIGS. 1A-3D , showing water flows therethrough when a relatively large nozzle is employed, to  FIG. 11D , which is a simplified sectional illustration taken along lines D-D in  FIG. 11A , and to  FIG. 11E , which is a simplified sectional illustration taken along lines E-E in  FIG. 11A . 
         [0182]    As seen in  FIGS. 11A-11E , in the illustrated embodiment, when a relatively large forward nozzle is employed, such as a nozzle  190  having an internal diameter of 5 mm, a water stream  1100  emanates from nozzle  190 . In accordance with a preferred embodiment of the present invention, only part of water stream  1100 , here designated by reference numeral  1102 , is confined between vanes  330  of first water stream engagement surface  320  in engagement with first water engagement sub-surface  334 . 
         [0183]    Two side water streams, respectively designated by reference numerals  1104  and  1106 , flow outside vanes  330  in engagement with respective first water engagement sub-surfaces  332  and  336 . 
         [0184]    Nearly all of the water stream  1102  impinges on second water engagement sub-surface  364 , and is confined between vanes  360  of the second water stream engagement surface  322 , as designated by reference numeral  1110 . Nearly all of the water stream  1110  exits, as designated by reference numeral  1112 , in a direction indicated by an arrow  1114 . Accordingly, nearly all of the water stream  1112  applies a rotational force, indicated by an arrow  1116 , to hammer  300 , causing it to rotate about vertical axis  154 . 
         [0185]    The two side water streams  1104  and  1106  generally do not impinge on the second water engagement surface  364  but rather exit, as respectively designated by reference numerals  1124  and  1126 , through apertures  324  in directions respectively indicated by arrows  1134  and  1136 . The side water streams generally do not apply a rotational force to hammer  300 . 
         [0186]    It is a particular feature of an embodiment of the present invention that, as appreciated from a comparison of  FIGS. 10A-10D  with  FIGS. 11A-11E , it is seen that the proportion of the water stream output from the forward nozzle, which applies a rotational force to hammer  300  varies as a function of the size of the forward nozzle and thus of the discharge volume of the nozzle. 
         [0187]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the invention includes both combinations and subcombinations of the various features described hereinabove as well as modifications and variations thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not in the prior art.