Abstract:
A dripper ( 120 ) comprises a dripper main body ( 121 ) and a movable unit ( 122 ). The moveable unit ( 122 ) forms the ceiling of a pressure reducing flow path ( 125 ) that reduces the pressure of a liquid flowing in the dripper ( 120 ), and the moveable unit advances and retracts in accordance with the pressure of the fluid in a tube ( 110 ). If the pressure is high, the height of the pressure reducing flow path ( 125 ) becomes lower and the flow rate of the liquid in the dripper ( 120 ) is thereby restricted. As a result, the flow rate of liquid discharged from a through hole ( 130 ) in the tube ( 110 ) can be maintained at a substantially constant rate regardless of the aforementioned pressure.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a dripper and a drip irrigation tube including the dripper. 
       BACKGROUND ART 
       [0002]    Drip irrigation methods are known as one of plant cultivating methods. In the drip irrigation methods, a drip irrigation tube is disposed on the soil, and irrigation liquid such as water and liquid fertilizer is slowly supplied from the drip irrigation tube into the soil on which plants are planted, for example. The drip irrigation methods can minimize the liquid consumption, and therefore have increasingly attracted attention in recent years. 
         [0003]    Such a drip irrigation tube typically has a tube and a dripper. Typically, the dripper supplies the irrigation liquid in the tube space to the soil at a set rate at which the irrigation liquid drips into the soil. Known examples of the dripper include a dripper which is disposed in such a manner as to stick into a tube from outside, and a dripper which is bonded on an inner wall of a tube. 
         [0004]    The latter dripper has, for example, a channel including a pressure reduction channel that allows liquid, which has flowed from the tube space to the dripper, to flow toward a through hole of the tube while depressurizing the liquid; and a diaphragm that changes the volume of a part where the depressurized irrigation liquid flows in accordance with the liquid pressure in the tube space. The dripper is composed of three members, i.e., a member bonded to the inner wall of the tube, a member disposed on the member bonded to the inner wall of the tube, and the diaphragm disposed between the two members. The diaphragm is formed of an elastic film such as a silicone rubber film (see, e.g., PTL 1). 
         [0005]    The drippers can suppress variations in the ejection amount of the irrigation liquid regardless of changes in liquid pressure in the tube space. Therefore, the dripper is advantageous from the perspective of growing multiple plants uniformly. 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL 1 
         [0007]    Japanese Patent Application Laid-Open No. 2010-46094 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    The drippers are formed by assembling the three members, and thus an assembly error may occur in the drippers. In particular, the assembly error in the diaphragms may cause variations in operation of the diaphragms, and variations in the ejection amount of irrigation liquid. 
         [0009]    Further, while the dripper is typically formed of an inexpensive resin such as polyethylene and polypropylene, the diaphragm is made of a more expensive elastic material member such as a silicone rubber film. Use of such different materials has a room for improvement in terms of reduction of a material cost. 
         [0010]    In some situation, several hundreds of drippers are disposed in one drip irrigation tube, and in that case pressure drop of the irrigation liquid is large when the drippers bonded on the inner wall of the tube are large. For this reason, in the case where a long drip irrigation tube is used, the pressure for supplying liquid to the tube is required to be high, and as a result the liquid ejection amount of the drippers may be unstabilized. Therefore, it is desired to reduce the size of the drippers from the perspective of suppressing the pressure drop of the liquid in the tube. 
         [0011]    Further, a dripper which can be produced with a single inexpensive material and a smaller number of components is desired from the perspective of suppressing the material cost and the production cost of the dripper. 
         [0012]    An object of the present invention is to provide a dripper capable of stabilizing the ejection amount of irrigation liquid and reducing production cost, and a drip irrigation tube having the dripper. 
       Solution to Problem 
       [0013]    A dripper according to the present invention is configured to form a channel by bonding to an inner wall of a tube at a position where the dripper covers a through hole formed on a wall of the tube, the channel allowing a space in the tube and the through hole to communicate with each other and including a pressure reduction channel that allows liquid flowing into the dripper from the space to flow toward the through hole while depressurizing the liquid, the dripper including: a dripper body configured to form the channel by bonding to the inner wall of the tube, the channel including an open part which opens to the space; and a movable part for changing a cross-sectional area of the channel at the opening in accordance with a pressure of the liquid in the space, the movable part disposed to cover the open part from a space side such that the movable part is movable forward or backward in the open part in accordance with the pressure of the liquid in the space. 
         [0014]    A drip irrigation tube according to the present invention has a tube and the dripper. 
       Advantageous Effects of Invention 
       [0015]    A dripper according to the present invention can be formed with only two members, i.e., a dripper body, and a movable part configured to move when receiving liquid pressure in the tube. The dripper according to the present invention can also, by virtue of the movable part, suppress changes in the ejection amount of the liquid caused by changes in the liquid pressure in the tube. The dripper according to the present invention does not need a diaphragm disposed between two members to suppress the changes in the ejection amount of the liquid, so that the dripper can be smaller (thinner) than a dripper with a diaphragm. Therefore, the dripper according to the present invention is advantageous for suppressing increase in pressure drop of liquid in the tube, and ejecting irrigation liquid at a stable ejection amount. Further, the dripper according to the present invention can reduce production cost in comparison with a dripper composed of three members. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1A  is a schematic plan view of a drip irrigation tube according to Embodiment 1 of the present invention, and  FIG. 1B  is a cross-sectional view of the drip irrigation tube cut along line A-A in  FIG. 1A ; 
           [0017]      FIG. 2  illustrates an enlarged cross-section of a dripper in the drip irrigation tube according to Embodiment 1; 
           [0018]      FIG. 3A  illustrates an upper surface, a front surface, and a side surface of the dripper according to Embodiment 1, and  FIG. 3B  illustrates a bottom surface, the front surface and the side surface of the dripper; 
           [0019]      FIG. 4A  to  FIG. 4D  are a plan view, a front view, a bottom view and a side view of the dripper according to Embodiment 1, respectively; 
           [0020]      FIG. 5A  to  FIG. 5D  are a plan view, a front view, a bottom view and a side view of a dripper body according to Embodiment 1, respectively; 
           [0021]      FIG. 6A  to  FIG. 6D  are a plan view, a front view, a bottom view and a side view of a movable part according to Embodiment 1, respectively; 
           [0022]      FIG. 7A  is a side view schematically illustrating a state before the movement of the movable part of the dripper according to Embodiment 1, and  FIG. 7B  is a side view schematically illustrating a state after the movement of the movable part of the dripper; 
           [0023]      FIG. 8A  is a cross-sectional view schematically illustrating the dripper according to Embodiment 1 cut along line A-A in  FIG. 4C  before the movement of the movable part, and  FIG. 8B  is a cross-sectional view schematically illustrating the dripper cut along line A-A in  FIG. 4C  after the movement of the movable part; 
           [0024]      FIG. 9A  illustrates an upper surface, a front surface, and a side surface of a dripper according to Embodiment 2, and  FIG. 9B  illustrates a bottom surface, the front surface and the side surface of the dripper; 
           [0025]      FIG. 10A  to  FIG. 10D  are a plan view, a front view, a bottom view and a side view of the dripper according to Embodiment 2, respectively; 
           [0026]      FIG. 11A  is a cross-sectional view schematically illustrating the dripper according to Embodiment 2 cut along line A-A in  FIG. 10C  before the movement of a movable part, and  FIG. 11B  is a cross-sectional view schematically illustrating the dripper cut along line A-A in  FIG. 10C  after the movement of the movable part; 
           [0027]      FIG. 12A  illustrates an upper surface, a front surface, and a side surface of a dripper according to Embodiment 3, and  FIG. 12B  illustrates a bottom surface, the front surface and the side surface of the dripper; 
           [0028]      FIG. 13A  is a bottom view of the dripper according to Embodiment 3, and  FIG. 13B  is a cross-sectional view schematically illustrating the dripper cut along line A-A in  FIG. 13A ; 
           [0029]      FIG. 14A  to  FIG. 14D  are a plan view, a front view, a bottom view and a side view of a dripper body according to Embodiment 3, respectively; 
           [0030]      FIG. 15A  to  FIG. 15D  are a plan view, a front view, a bottom view and a side view of a movable part according to Embodiment 3, respectively; and 
           [0031]      FIG. 16A  is a cross-sectional view schematically illustrating the dripper according to Embodiment 3 cut along line A-A in  FIG. 13A  before the movement of the movable part, and  FIG. 16B  is a cross-sectional view schematically illustrating the dripper cut along line A-A in  FIG. 13A  after the movement of the movable part. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0032]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
       [0033]      FIG. 1A  is a schematic plan view of a drip irrigation tube according to Embodiment 1 of the present invention, and  FIG. 1B  is a cross-sectional view of the drip irrigation tube cut along line A-A in  FIG. 1A . 
         [0034]    Drip irrigation tube  100  is composed of tube  110  and drippers  120 . Tube  110  is made of, e.g., polyethylene, and dripper  120  is made of, e.g., polypropylene. Drippers  120  are disposed at a predetermined interval (e.g., 200 to 500 mm) in the axis direction of tube  110 . Each dripper  120  is fixed on the inner wall of tube  110  by welding. Dripper  120  is disposed at a position where dripper  120  covers through hole  130  of tube  110 . Specifically, dripper  120  is disposed such that an ejection part thereof described below covers through hole  130 . The hole diameter of through hole  130  is, for example, 1.5 mm Through hole  130  is typically formed after dripper  120  is welded. 
         [0035]      FIG. 2  illustrates an enlarged cross-section of the dripper in the drip irrigation tube according to the present embodiment.  FIG. 3A  illustrates an upper surface, a front surface, and a side surface of the dripper according to the present embodiment, and  FIG. 3B  illustrates a bottom surface, the front surface and the side surface of the dripper.  FIG. 4A  to  FIG. 4D  are a plan view, a front view, a bottom view and a side view of the dripper according to the present embodiment, respectively. 
         [0036]    Dripper  120  has dripper body  121  and movable part  122  engaged with dripper body  121 , as shown in  FIG. 2 . Dripper  120  forms a liquid channel which is independent from the inner space of tube  110  and allows the inner space of tube  110  to communicate with through hole  130 . The channel includes inflow part  124 , pressure reduction channel  125  and ejection part  126 . Inflow part  124  communicates with the inner space of tube  110  through inflow ports  123 . Pressure reduction channel  125  is formed by fitting a projection of movable part  122  described below with an open part of dripper body  120  described below. 
         [0037]    A depression (also referred to as “top surface side recess”) is formed on the upper surface (top surface) of dripper  120 , and a plurality of protrusions  1201  are disposed in the top surface side recess, as shown in  FIGS. 3A and 4A . Protrusions  1201  extend in transverse direction Y of dripper  120  and are arranged in parallel in longitudinal direction X of dripper  120 . Both ends of protrusion  1201  are apart from side walls of the top surface side recess in Y direction. The height of protrusion  1201  is, for example,  0 . 5  mm, and the interval between protrusions  1201  (the distance between the axes of protrusions  1201 ) is, for example, 0.5 mm. 
         [0038]    A plurality of inflow ports  123  are disposed on the bottom of the top surface side recess at one end part in X direction, as shown in  FIGS. 3B and 4C . Inflow ports  123  are disposed in lines along protrusions  1201  (in Y direction). Inflow port  123  is a hole extending through the bottom of the top surface side recess and allows the upper side of dripper  120  to communicate with inflow part  124 . The hole diameter of inflow port  123  is, for example, 0.3 mm. 
         [0039]    As shown in  FIGS. 3B and 4C , each of inflow part  124  and ejection part  126  is a rectangular depression (also referred to as “bottom surface side recesses”) which is recessed from the bottom surface of dripper body  121  and is disposed at each end part of dripper body  121 . The height of inflow part  124  (the depth of the bottom surface side recess at one end side in X direction) is, for example, 1.0 mm, and the height of ejection part  126  (the depth of the bottom surface side recess at the other end side) is, for example, 1.0 mm. 
         [0040]    Pressure reduction channel  125  allows inflow part  124  to communicate with ejection part  126 , as shown in  FIG. 4C . The shape of pressure reduction channel  125  in plan view is a zigzag shape. The zigzag shape is formed by alternately disposing protrusions each having a substantially triangular prism shape and protruding from side walls of pressure reduction channel  125  in the longitudinal direction of pressure reduction channel  125 . The protrusion is formed such that the tip end of the protrusion does not go beyond the central axis of pressure reduction channel  125  in plan view. Both end parts of pressure reduction channel  125  are formed only with dripper body  121 , and the other part of pressure reduction channel  125  is formed by fitting a projection of movable part  122  together with an open part formed in dripper body  121  ( FIGS. 4B and 4C ). 
         [0041]      FIG. 5A  to  FIG. 5D  are a plan view, a front view, a bottom view and a side view of the dripper body according to the present embodiment, respectively. 
         [0042]    Dripper body  121  is made of, e.g., polypropylene. Dripper body  121  has first end part  1211 , second end part  1212  and connecting part  1213  as shown in  FIGS. 5A to 5C . First end part  1211  includes the top surface side recess, protrusions  1201 , inflow ports  123  and inflow part  124 . Second end part  1212  includes the top surface side recess, protrusions  1201  and ejection part  126 . 
         [0043]    Further, first end part  1211  and second end part  1212  have elastic supporters  1214  and  1215 , respectively, at both end parts of first end part  1211  and second end part  1212 . Both elastic supporters  1214  and  1215  are disposed at relatively high positions on upper surface (top surface) side relative to the center of dripper body  121  in the height (thickness) direction. Elastic supporter  1214  is a plate-shaped elastic member protruding from an end surface of first end part  1211  on second end part  1212  side. Elastic supporter  1215  is a plate-shaped elastic member protruding from an end surface of second end part  1212  on first end part  1211  side. The upper surface (top surface) of each of elastic supporters  1214  and  1215  is parallel with the top surface of dripper body  121 . An inclining surface inclined from top surface side to the bottom surface side is formed at the tip of the upper surface (top surface) of each of elastic supporters  1214  and  1215 . 
         [0044]    Connecting part  1213  connects first end part  1211  with second end part  1212 . 
         [0045]    The shape of connecting part  1213  in plan view is a substantially cross shape formed by cutting out a rectangle having a shape substantially the same as the shape of elastic supporters  1214  and  1215  in plan view from every corner of a rectangle, as shown in  FIGS. 5A and 5C . Connecting part  1213  has a bottom surface on the same plane as the bottom surfaces of first end part  1211  and second end part  1212 , as shown in  FIG. 5B . The thickness (height) of connecting part  1213  is less than half the height of dripper body  121 , and slightly larger than the height of pressure reduction channel  125 . The height of connecting part  1213  is, for example, about  1 . 3  times as large as the height of pressure reduction channel  125 . 
         [0046]    Connecting part  1213  includes open part  1216  which opens to the inner space of tube  110  except for both end parts of pressure reduction channel  125 . The shape of open part  1216  in plan view is the same as the zigzag shape of pressure reduction channel  125 , as shown in  FIGS. 5A and 5C . Open part  1216  is configured of a cut extending through connecting part  1213  in the thickness direction of connecting part  1213 . 
         [0047]      FIG. 6A  to  FIG. 6D  are a plan view, a front view, a bottom view and a side view of a movable part according to the present embodiment, respectively. 
         [0048]    Movable part  122  is made of, e.g., polypropylene. Movable part  122  has pressure receiving part  1221 , spacer  1222 , engaging part  1223  and projection  1224 , as shown in  FIGS. 6A to 6D . Pressure receiving part  1221  forms the top surface of movable part  122 . Pressure receiving part  1221  includes the depression, and protrusions  1201 . The shape of pressure receiving part  1221  is substantially rectangular, but every corner is slightly cut out by a rectangle. The length of the cutout in X direction is several millimeters, and the length of the cutout in Y direction is substantially the same as the length of elastic supporter  1215  in Y direction. End parts of pressure receiving part  1221  in Y direction have a linear cut formed in X direction from each cutout. 
         [0049]    Spacer  1222  is disposed on the bottom surface side of pressure receiving part  1221 . The shape of spacer  1222  in plan view is rectangular. The length of spacer  1222  in X direction is less than the distance between the tip ends of elastic supporters  1214  and  1215  of dripper body  121 , and the length of spacer  1222  in Y direction is substantially the same as the length of pressure receiving part  1221  in Y direction. The thickness of spacer  1222  is substantially the same as the thickness of elastic supporters  1214  and  1215 . Spacer  1222  is disposed at a center of movable part  122  in X direction where spacer  1222  does not touch the tip end of elastic supporter  1214  or elastic supporter  1215 . 
         [0050]    Engaging part  1223  is connected to the bottom surface side of spacer  1222 . The shape of engaging part  1223  in plan view is rectangular. An inclining surface inclined from bottom surface side to the top surface side is formed at both ends of the bottom surface of engaging part  1223  in X direction. The length of engaging part  1223  in X direction is substantially the same as the length of the remaining part of pressure receiving part  1221  in X direction after the cutout at the both end parts. The length of engaging part  1223  in Y direction is substantially the same as the length of pressure receiving part  1221  in Y direction. 
         [0051]    Projection  1224  is a part connected to the bottom surface side of engaging part  1223  as shown in  FIGS. 6B and 6D . The shape of projection  1224  in plan view is the same as the shape of open part  1216  of dripper body  121  in plan view as shown in  FIG. 6C . The protruding height of projection  1224  is the sum of a movable distance of movable part  122  and an additional distance a. The movable distance is a distance from the bottom surface of spacer  1222  to the top surface of connecting part  1213  of dripper body  121 , and is 0.5 mm for example. The distance a is a distance for slightly fitting the top part of projection  1224  with open part  1216  for the positioning of projection  1224 , and is about 0.25 mm for example. 
         [0052]    Dripper  120  is assembled by disposing movable part  122  on connecting part  1213  and by pushing movable part  122  into connecting part  1213 . In response to the pushing, elastic supporters  1214  and  1215  are bent, and the inclining surfaces of the tips of engaging part  1223  slide on the inclining surfaces of the tips of elastic supporters  1214  and  1215 , and thus, elastic supporters  1214  and  1215  are fit in the gap between pressure receiving part  1221  and engaging part  1223 . As a result, elastic supporters  1214  and  1215  support pressure receiving part  1221 , and engage with engaging part  1223 . Movable part  122  is thus supported in dripper body  121  with the elasticity of elastic supporters  1214  and  1215  in a movable manner Projection  1224  of movable part  122  covers open part  1216  from above and is slightly fit with open part  1216  of dripper body  121 . With this fitting, pressure reduction channel  125  is formed. 
         [0053]      FIG. 7A  is a side view schematically illustrating a state before the movement of the movable part of the dripper according to the present embodiment, and  FIG. 7B  is a side view schematically illustrating a state after the movement of the movable part of the dripper.  FIG. 8A  is a cross-sectional view schematically illustrating the dripper according to the present embodiment cut along line A-A in  FIG. 4C  before the movement of the movable part, and  FIG. 8B  is a cross-sectional view schematically illustrating the dripper cut along line A-A in  FIG. 4C  after the movement of the movable part. 
         [0054]    When a sufficient pressure is not exerted on pressure receiving part  1221 , movable part  122  does not move as shown in  FIGS. 7A and 8A . In this case, height h 0  of pressure reduction channel  125  (the distance from the bottom surface of connecting part  1213  to the head of protrusion  1224 ) is 0.75 mm for example. The cross-sectional area of pressure reduction channel  125  has a maximum value in this case. 
         [0055]    When a sufficient pressure is exerted on pressure receiving part  1221 , movable part  122  is biased to the bottom surface side of dripper  120  and elastic supporters  1214  and  1215  supporting movable part  122  are bent as shown in  FIGS. 7B and 8B . Movable part  122  thus moves toward the bottom surface side to allow projection  1224  to slide further into open part  1216 . Height h 1  of pressure reduction channel  125  in this case is smaller than h 0  and 0.25 mm for example. 
         [0056]    When the pressure on pressure receiving part  1221  is released, movable part  122  slides on open part  1216  upward with the elasticity of elastic supporters  1214  and  1215 , and the height of pressure reduction channel  125  increases. In this case, the height of pressure reduction channel  125  is h 0 . Thus, movable part  122  slides forward or backward on open part  1216  in accordance with the pressure on pressure receiving part  1221 , and the height (cross-sectional area) of pressure reduction channel  125  changes. 
         [0057]    The operation of dripper  120  in drip irrigation tube  100  will be described. 
         [0058]    Liquid is supplied in drip irrigation tube  100  in  FIG. 2 . The liquid flows in X direction. The liquid fills gaps between protrusions  1201 . Protrusions  1201  are arranged in parallel in the longitudinal direction (direction X) on the top surface of dripper  120 , and gaps are formed between the both ends of protrusions  1201  in Y direction and side walls of the top surface side recess. With this configuration, the gaps between protrusions  1201  are not completely blocked even when a floating object such as a fallen leaf in the liquid sticks to the top surface of dripper  120 . Thus, the gaps to which inflow ports  123  open between protrusions  1201  are filled with liquid at all times. In this manner, protrusions  1201  provide a function as a filter. 
         [0059]    Inflow ports  123  are through holes formed in dripper body  121  made of polypropylene; therefore, inflow ports  123  has water repellency specific to polypropylene. When liquid pressure is at a specific value (e.g., 0.005 MPa, which is also referred to as “burst pressure”) or higher, the liquid filling the gaps overcomes the liquid surface tension of the water repellency, and flows into inflow part  124  from inflow ports  123 . In this manner, inflow ports  123  provides a low-pressure stopping function to inhibit the inflow of liquid whose pressure is lower than a specific value. The low-pressure stopping function can be adjusted by the hole diameter, pitch, number, open part shape, length (thickness of the bottom of the top surface side recess) of inflow ports  123 , and the like. 
         [0060]    Liquid having a pressure higher than the burst pressure flows into inflow part  124 , and then flows through pressure reduction channel  125 . The liquid flowing through pressure reduction channel  125  is depressurized by pressure drop which is caused by the shape of pressure reduction channel  125  in plan view (zigzag shape). The depressurized liquid is received in ejection part  126 . The liquid received in ejection part  126  is ejected from through hole  130 . The liquid ejected from through hole  130  drips from drip irrigation tube  100  into the soil, for example. 
         [0061]    When the liquid pressure in drip irrigation tube  100  is in a range from the burst pressure to a specific pressure higher than the burst pressure (e.g., 0.05 MPa, which is also referred to as “movement starting pressure”), movable part  122  does not move. This is because the elasticity of elastic supporters  1214  and  1215  overcome the liquid pressure on pressure receiving part  1221 . During this time, the liquid ejection rate from through hole  130  is substantially constant at a set rate. 
         [0062]    When the liquid pressure in drip irrigation tube  100  is equal to or higher than the movement starting pressure, the pressure on pressure receiving part  1221  overcomes the elasticity of elastic supporters  1214  and  1215 , and movable part  122  moves in accordance with the pressure toward the bottom surface side of dripper  120  in a range of less than 0.5 mm. As a result, the height of pressure reduction channel  125  becomes, e.g., 0.5 mm, and the amount of liquid flowing through pressure reduction channel  125  is limited. In this manner, the increase of a liquid flow rate due to the pressure increase is offset by the decrease of the liquid flow rate caused by reduction of the cross-sectional area of pressure reduction channel  125 , and thus a supply rate of the liquid to ejection part  126  is maintained at a substantially constant rate. Consequently, the ejection rate of the liquid from through hole  130  is substantially maintained at the above-mentioned set rate. 
         [0063]    When the liquid pressure in drip irrigation tube  100  is equal to or higher than a specific pressure which is larger than the movement starting pressure (e.g., 0.1 MPa, which is also referred to as “maximum movement pressure”), movable part  122  is further biased by the liquid pressure. As a result, the height of pressure reduction channel  125  minimized (to the above-described h 1 , e.g., 0.25 mm), and the amount of the liquid flowing through pressure reduction channel  125  is further limited. In this manner, the increase of a liquid flow rate due to the further pressure increase is offset by the decrease of the liquid flow rate caused by the further reduction of the cross-sectional area of pressure reduction channel  125  and thus the supply rate of the liquid to ejection part  126  is still maintained at a substantially constant rate. Consequently, the ejection rate of the liquid from through hole  130  is substantially maintained at the above-mentioned set rate. 
         [0064]    Dripper  120  according to the present embodiment includes, as described above, dripper body  121  forming a channel having a part of pressure reduction channel  125  (open part  1216 ) opened to the inner space of tube  110 , and movable part  122  disposed to cover open part  1216  from the space side and be movable forward or backward in open part  1216  in accordance with the liquid pressure in drip irrigation tube  100 . Thus, dripper  120  can suppress changes in the ejection amount due to the increase of the pressure of liquid flowing into dripper  120 . Therefore, dripper  120  can eject liquid at a constant flow rate regardless of the change in the pressure. 
         [0065]    Further, dripper  120  can be composed with only two members, i.e., dripper body  121  and movable part  122 ; therefore, the size (thickness) of dripper  120  can be further reduced in comparison with conventional drippers composed of three members and having a diaphragm. 
         [0066]    Since the size of drippers  120  can be further reduced, drippers  120  can further suppress an increase of liquid pressure drop in tube  110  in comparison with the conventional drippers. As a result, the liquid in drip irrigation tube  100  can be conveyed farther with a low pressure. Therefore, the present embodiment can provide an effect of ejecting liquid at a stable amount even when longer drip irrigation tube  100  is used. 
         [0067]    Dripper  120  can further reduce material cost and production cost (assembling cost) in comparison with the conventional drippers. 
         [0068]    Dripper body  121  further including inflow ports  123  having a low-pressure stopping function is more effective from the perspective of further suppressing the pressure of the liquid flowing into dripper  120  from the inside of drip irrigation tube  100  for the purpose of efficient use of the liquid. 
         [0069]    Dripper  120  does not have a diaphragm in ejection part  126 ; therefore, no diaphragm would be damaged when forming through hole  130  of drip irrigation tube  100  after welding dripper  120 . This means the pressure regulation function of dripper  120  would not be impaired even when through hole  130  is formed after welding dripper  120 . 
         [0070]    The present embodiment thus can produce drip irrigation tube  100  more easily, and further enhance the reliability of drip irrigation tube  100 . 
         [0071]    Dripper body  121  has inflow part  124  and ejection part  126  connected to each other only with pressure reduction channel  125 . This makes it possible to reduce the length of dripper body  121  in X direction. Dripper  120  is thus advantageous also from the perspective of reduction in the size of dripper  120  in X direction. 
       Embodiment 2 
       [0072]    Embodiment 2 is the same as Embodiment 1 except for the structure of the dripper. A dripper according to the present embodiment is different from the dripper of Embodiment 1 in that the dripper further has a communication channel for connecting a pressure reduction channel with an ejection part, and that a movable part changes the cross-sectional area of the communication channel The configurations same as those of Embodiment 1 are given the same symbols as those of Embodiment 1, and the description thereof is omitted. 
         [0073]      FIG. 9A  illustrates an upper surface, a front surface, and a side surface of the dripper according to the present embodiment, and  FIG. 9B  illustrates a bottom surface, the front surface and the side surface of the dripper.  FIG. 10A  to  FIG. 10D  are a plan view, a front view, a bottom view and a side view of the dripper according to the present embodiment, respectively. 
         [0074]    Dripper  220  according to the present embodiment is composed of dripper body  221  and movable part  222 . Dripper body  221  has first end part  2211 , second end part  2212  and connecting part  2213 . First end part  2211  includes inflow ports  123 , inflow part  124  and pressure reduction channel  225 . Pressure reduction channel  225  is configured with a groove recessed from the bottom surface of dripper body  221 . The shape of pressure reduction channel  225  in plan view is the same as that of pressure reduction channel  125 . 
         [0075]    Connecting part  2213  is formed in the same manner as connecting part  1213  except that connecting part  2213  includes open part  2216 , a part of rectangular shaped communication channel  226  in plan view other than the both ends of communication channel  226 , which opens to the inner space of tube  110 ; and that the shape of bottom surface of connecting part  2213  in plan view is rectangular. Open part  2216  is configured of a cut (slit) extending through connecting part  2213  in the thickness direction of connecting part  2213 . The shape of open part  2216  in plan view is rectangular. The width of communication channel  226  and open part  2216  (length in Y direction) is, e.g., 0.5 mm. 
         [0076]    Movable part  222  is formed in the same manner as movable part  122  except for projection  2224 . The shape of projection  2224  in plan view is the same as the shape of open part  2216  in plan view, as shown in  FIG. 10C . Projection  2224  covers open part  2216  from above and partially fits with open part  2216 , and thus communication channel  226  for connecting pressure reduction channel  225  to ejection part  126  is formed. 
         [0077]      FIG. 11A  is a cross-sectional view schematically illustrating the dripper according to the present embodiment cut along line A-A in  FIG. 10C  before the movement of the movable part, and  FIG. 11B  is a cross-sectional view schematically illustrating the dripper cut along line A-A in  FIG. 10C  after the movement of the movable part. 
         [0078]    In the same manner as movable part  122  in Embodiment 1, movable part  222  slides at open part  2216  forward or backward from the bottom surface side of dripper  220  in a distance in accordance with the pressure on pressure receiving part  1221  to change the height (cross-sectional area) of communication channel  226  in a range of h 0  to h 1 , e.g., from 0.25 to 0.75 mm in accordance with the pressure. 
         [0079]    The present embodiment provides the same effects as that of Embodiment 1. Since dripper  220  according to the present embodiment further has a communication channel, dripper  220  can change a cross-sectional area of a part whose shape is simpler than that of the pressure reduction channel in the channel formed with dripper  220 . The shape of projection  2224  of movable part  222  in plan view thus can be further simplified. Therefore, the present embodiment is more effective from the perspective of simplifying the production of movable part  222  and assemblage of dripper  220 . 
       Embodiment 3 
       [0080]    Embodiment 3 is the same as Embodiment 1 except for a pressure reduction channel. A dripper according to the present embodiment is different from that of Embodiment 1 in that the dripper changes a cross-sectional area of the pressure reduction channel by allowing a movable part to move in the width direction of the pressure reduction channel. The configurations same as those of Embodiment 1 are given the same symbols as those of Embodiment 1, and the description thereof is omitted. 
         [0081]      FIG. 12A  illustrates an upper surface, a front surface, and a side surface of the dripper according to the present embodiment, and  FIG. 12B  illustrates a bottom surface, the front surface and the side surface of the dripper.  FIG. 13A  is a bottom view of the dripper according to Embodiment 3, and  FIG. 13B  is a cross-sectional view schematically illustrating the dripper cut along line A-A in  FIG. 13A . 
         [0082]    Dripper  320  is configured with dripper body  321  and movable part  322 . Dripper  320  includes pressure reduction channel  325 . The shape of pressure reduction channel  325  as seen in Y direction (shape of pressure reduction channel  325  in front view) is a zigzag shape. The zigzag shape is the same as the shape of pressure reduction channel  125  in Embodiment 1 in plan view. 
         [0083]      FIG. 14A  to  FIG. 14D  are a plan view, a front view, a bottom view and a side view of the dripper body according to the present embodiment, respectively. 
         [0084]    Dripper body  321  has first end part  1211 , second end part  1212  and connecting part  3213 . Connecting part  3213  includes open part  3216 . Open part  3216  is a bottomed groove with a rectangular shape in plan view. The bottom shape of open part  3216  is such that a plurality of protrusions each having a substantially triangular prism shape are disposed at regular intervals in X direction. The width of open part  3216  (length in Y direction) is, e.g., 0.5 mm. 
         [0085]      FIG. 15A  to  FIG. 15  are a plan view, a front view, a bottom view and a side view of a movable part according to the present embodiment, respectively. 
         [0086]    Movable part  322  is formed in the same manner as movable part  122  in Embodiment 1 except for projection  3224 . The shape of projection  3224  in plan view is rectangular as with the shape of open part  3216  in plan view, as shown in  FIG. 15C . The thickness of projection  3224  (length in Y direction) is, e.g., 0.49 mm. The edge shape of projection  3224  is such that a plurality of protrusions each having a substantially triangular prism shape are disposed at regular intervals in X direction. Each of the protrusions of projection  3224  is formed so as to be placed between every two protrusions of open part  3216  in X direction when movable part  322  is disposed in dripper body  321 . 
         [0087]    When movable part  322  is disposed in dripper body  321 , projection  3224  covers open part  3216  from above and projection  3224  partially fits with open part  3216 . The protrusions of open part  3216  and the protrusions of projection  3224  are disposed alternately in X direction to form pressure reduction channel  325  in the zigzag shape, and thus dripper  320  is formed ( FIG. 13B ). 
         [0088]      FIG. 16A  is a cross-sectional view schematically illustrating the dripper according to Embodiment 3 cut along line A-A in  FIG. 13C  before the movement of the movable part, and  FIG. 16B  is a cross-sectional view schematically illustrating the dripper cut along line A-A in  FIG. 13C  after the movement of the movable part. 
         [0089]    When a sufficient pressure is not exerted on pressure receiving part  1221 , movable part  322  does not move as shown in  FIG. 16A . In this case, width w 0  of pressure reduction channel  325  is 0.5 mm for example, and the cross-sectional area of pressure reduction channel  325  has a maximum value. The width of pressure reduction channel  325  is the distance between parallel inclining surfaces of the protrusion of connecting part  3213  and the protrusion of movable part  322 . 
         [0090]    When a sufficient pressure is exerted on pressure receiving part  1221 , movable part  322  is biased to the bottom surface side of dripper  320  and moved to the bottom surface side. Projection  3224  slides further into open part  3216 . Width w 1  of pressure reduction channel  325  in this case is smaller than w 0  and 0.3 mm for example. The cross-sectional area of pressure reduction channel  325  has a minimum value in this case. 
         [0091]    The present embodiment provides the same effects as those of Embodiment 1. Since the shape of pressure reduction channel  325  of dripper  320  according to the present embodiment in plan view is rectangular, dripper body  321  and movable part  322  can be easily assembled. 
         [0092]    Further, pressure reduction channel  325  is expected to have an excellent self-cleaning function since the width of zigzag shaped pressure reduction channel  325  changes. This is because liquid flow turbulence in a depression between the protrusions of pressure reduction channel  325  changes according to the movement of movable part  322  (change in the width of pressure reduction channel  325 ) whereby a floating object stayed in the depression can easily flow out of the depression. 
         [0093]    Further, pressure reduction channel  325  is configured with only dripper body  321  and movable part  322 , without bonding dripper  320  to tube  110 . With this configuration, the cross-sectional area of pressure reduction channel  325  is maintained at a constant value regardless of the depth of the bonding of dripper  320  to tube  110  or the ease of deformation of tube  110 . Therefore, dripper  320  is more effective from the perspective of further uniformizing the cross-sectional areas of pressure reduction channels  325  of drippers  320  in drip irrigation tube  100 . 
         [0094]    While the embodiments of the present invention have been described hereinabove, the scope of the present invention is not limited thereto. 
         [0095]    For example, tube  110  may be a seamless tube, or a tube made by joining slender sheets along the longitudinal direction. 
         [0096]    While, a dripper is disposed such that the inflow part is located on the upstream side in the liquid flow direction in the tube in the above-mentioned embodiments, the dripper may be disposed such that the inflow part is located on a downstream side. The orientations of the drippers may be identical to each other or different from each other. 
         [0097]    While the low-pressure stopping function based on dripper body material (polypropylene) is imparted to the dripper in the above-mentioned embodiments, the low-pressure stopping function may be imparted by forming a burr protruding to the inner space of the tube from the open part edge on the top surface side of an inflow port, or by covering the open part edge and internal wall of the inflow port with a hydrophobic film. The low-pressure stopping function can be further enhanced by combining multiple methods of imparting the low-pressure stopping function. 
         [0098]    While the same material (polypropylene) is used for the dripper body and the movable part in the embodiments, different materials may be used. 
         [0099]    Methods other than the method of changing the height of the pressure reduction channel or the communication channel may be employed to change the cross-sectional area of the channel formed in the dripper. For example, the cross-sectional area may be changed using a straightening plate or a baffle plate which is movable forward or backward in the pressure reduction channel or the communication channel 
         [0100]    While the movable part is moved forward or backward in the open part of the dripper body with plate springs formed on the dripper sides in accordance with the liquid pressure in the tube in the above-mentioned embodiments, any other means may be employed to move the movable part in accordance with the pressure. For example, it is also possible to move the movable part forward or backward in the open part by employing a movable part composed of an elastic body and expanding or contracting the elastic body in accordance with the pressure. 
         [0101]    This application claims priority based on Japanese patent Application No. 2013-174417, filed on Aug. 26, 2013, and Japanese patent Application No. 2013-198306, filled on Sep. 25, 2013, the entire contents of which including the specifications, the drawings and the abstracts are incorporated herein by reference. 
       INDUSTRIAL APPLICABILITY 
       [0102]    According to the present invention, it is possible to easily provide drippers capable of dripping liquid at a suitable rate using the pressure of the liquid to be dripped. Therefore, further widespread use of such drippers in the technical field of drip irrigations and endurance tests for drippers where a long term dripping is required can be expected, and further development in the technical field can be expected. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  Drip irrigation tube 
           110  Tube 
           120 ,  220 ,  320  Dripper 
           121 ,  221 ,  321  Dripper body 
           122 ,  222 ,  322  movable part 
           123  Inflow port 
           124  Inflow part 
           125 ,  225 ,  325  Pressure reduction channel 
           126  Ejection part 
           130  Through hole 
           226  Communication channel 
           1201  Linear protrusion 
           1211 ,  2211  First end part 
           1212  Second end part 
           1213 ,  2213 ,  3213  Connecting part 
           1214 ,  1215  Elastic supporter 
           1216 ,  2216 ,  3216  Open part 
           1221  Pressure receiving part 
           1222  Spacer 
           1223  Engaging part 
           1224 ,  2224 ,  3224  Projection