Abstract:
A flow path is provided for a drip emitter to reduce the supply pressure in a manner reducing the potential for the flow path to become obstructed and clogged. The path employs a central path with a predetermined size and a series of baffles with predetermined spacing. The flow path further includes a metering chamber and a diaphragm to compensate for changes in supply pressure and an outlet that facilitates self-flushing in conjunction with the operation of the diaphragm.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/666,955, filed Mar. 31, 2005, which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the design of a drip irrigation emitter and, more particularly, to an improved flow path system for a drip irrigation emitter to reduce pressure and reduce clogging. 
     BACKGROUND OF THE INVENTION 
     Drip irrigation is commonly used to supply irrigation to landscaping and crops. Drip irrigation emitters are generally known in the art for use in delivering irrigation water to a precise point at a predetermined and relatively low flow rate, thereby conserving water. The drip emitter taps a portion of the relatively high pressure irrigation water from a supply tube for flow through a typically long tortuous flow duct path to achieve a desired pressure drop prior to discharge at a target trickle or drip flow rate. 
     In a conventional system, a large number of drip emitters are mounted at selected positions along the length of the irrigation supply tube to deliver the irrigation water to a large number of specific points, such as directly to a plurality of individual plants. More specifically, a number of drip emitters are fitted into a conduit and spaced apart at appropriate distances depending on the desired amount of irrigation. Each emitter includes an inlet to receive water flowing through the conduit, an outlet to emit water from the conduit at a specific rate for irrigation, and a body member intermediate-the inlet and the outlet and that defines the flow duct path. 
     Tortuous flow duct paths generally include a number of alternating, flow baffles defining a flow channel and causing frequent, regular, and repeated directional changes in water flow. Accordingly, the water flow takes on a back and forth zigzag pattern. The water experiences multiple directional changes as it is constantly redirected through the tortuous flow duct path. This repeated redirection significantly reduces the water pressure and water flow by the time the water reaches the end of the flow duct path. 
     Experience, however, has revealed that pressure compensating drip emitters may get clogged during operation when they are exposed to water with contaminants. Organic agents and grit, such as algae, also can clog up an emitter and cause the emitter to be unusable. Algae can accumulate in the emitter path both as a result of entering with the water and from growth inside the emitter. Thus, even if the flow path through the emitter is sufficient to pass grit along, it may not pass the grit if algae is present. Accordingly, there is desired a design that permits enhanced flow through the emitter of organic materials, grit and algae to reduce the amount of obstruction and the tendency of emitter clogging. 
     Further, it has been determined that drip emitters tend to become obstructed in the tortuous flow path when grit tends to become lodged between alternating baffles. Also, even more commonly, drip emitters tend to become obstructed near the emitter outlet. Accordingly, there is desired a design that reduces the obstruction of the emitter at both of these locations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of a drip emitter embodying features of the present invention; 
         FIG. 2  is a bottom perspective view of the drip emitter of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the drip emitter of  FIG. 1  showing the emitter mounted in an irrigation supply tube; 
         FIG. 4  is an exploded top perspective view of the drip emitter of  FIG. 1 ; 
         FIG. 5  is a top plan view of a lower housing of the drip emitter of  FIG. 1  showing a flow duct path; 
         FIG. 6  is a bottom plan view of an upper housing of the drip emitter of  FIG. 1 ; and 
         FIG. 7  is a schematic plan view of the flow duct path of the drip emitter of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIGS. 1 and 2 , there is illustrated a preferred embodiment of an emitter  10 . The emitter  10  includes a housing  12  and a cover  20 . An inlet  16  is disposed at one end of the emitter  10  for tapping a portion of the water flow from the irrigation tube  14  ( FIG. 3 ). The housing  12  includes a series of longitudinally extending fins  21  that define a plurality of grooves  22  at the inlet  16 . The fins  21  act to filter out grit and debris that might otherwise clog the emitter  10 . The inlet  16 , however, may include any design of opening or openings in the emitter housing  12 , such as various numbers and arrangements of fins, grooves and holes, that allow access to the interior of the housing  12  and may be located at various points on the emitter housing  12 . 
     The housing cover  20  defines two slots  23  extending centrally and longitudinally in its top surface and separated by guide rib  24  for mounting each emitter  10  to the inside wall  26  of the supply tube  14 . Other orientations and arrangements of slots  23  and guide ribs  24  may be used. During assembly, each emitter  10  is mounted to the inside wall  26  of tube  14 , as shown in  FIG. 3 . More specifically, an insertion device, such as an emitter insertion guide, carries the emitter  10  into the tube  14  as it is being formed. The tube  14  is formed around the emitter  10  and presses against the housing cover  20  of each emitter  10  such that the housing base  28  of the emitter  10  engages the inside wall  26 . The slots  23  and guide rib  24  cooperate with complementary rails on the emitter insertion guide to provide stability and maintain proper orientation of the emitter  10  as it is inserted and mounted to the inside wall of the tube  14 . 
     The housing base  28  defines an outlet  18  at the opposite end of the emitter  10  as the inlet  16 . The base  28  also preferably includes a raised rim  30  extending about its perimeter. The raised rim  30  is used to mount the emitter  10  to the inside surface  26  of the irrigation tube  14  by acting as an attachment zone. More specifically, during assembly, the raised rim  30  of each is pressed into sealing engagement with the inside surface  26  of the irrigation tube  14 , as shown in  FIG. 3 , as the tube  14  is being formed around the emitter  10  being inserted. The raised rim  30  forms a gap between the surface of the housing base  28  inside the raised rim  30  and the inside surface  26  of the tube  14 . The gap forms an outlet bath  32  for the discharge of water from the outlet  16  of the emitter  10 . 
     As shown in  FIGS. 2 and 3 , the housing base  28  also preferably includes an elongated protrusion, or chimney  34 , having an I-shaped cross-section. The chimney  34  is adapted to push outwardly against the tube wall  26  during assembly, thereby forming an area of the irrigation tube  14  that bulges outward. The tube  14  then passes under a cutting tool that cuts the bulging tube portion and projecting end of the chimney  34  to form an outlet  36  through the wall  26  of the irrigation tube  14  for watering. The remaining uncut chimney portion  38  extends between the housing base  28  and through the tube outlet  36 , allowing water to flow to terrain outside the tube  14 . More specifically, water exiting the emitter  10  through the outlet  18  flows into the outlet bath  32  and trickles out to the terrain to be irrigated through the elongated channels formed by the I-shaped cross-section of the remaining chimney portion  38  and the supply tube outlet  36 . 
     With reference to  FIG. 2 , two T-shaped mounts  40  located at the end portions of the housing base  28  also are preferably used in mounting the housing base  28  to the inner surface  26  of the irrigation tube  14 . The T-shaped mounts  40  assist in securing the emitter  10  to the irrigation tube  14  and provide additional mounting support in addition to the raised rim  30 . The T-shaped mounts  40  also provide structural integrity to the emitter  10  for resisting forces exerted by water flowing in the irrigation tube  14  and forces exerted as a result of use of the chimney  34  in the formation of the outlet  36  in the tube wall  26 . These chimney and mounting features are discussed in more detail in U.S. patent application Ser. No. 11/359,181, assigned to the assignee of the present invention, which is incorporated herein by reference. 
     As shown in  FIG. 4 , the housing cover  20  and the housing base  28  may be plastic molded components. The housing cover  20  and the housing base  28  are adapted for easy assembly and define a substantially enclosed housing interior. A diaphragm  42  is disposed in the housing interior between the housing cover  20  and the housing base  78 . 
     A plurality of arms  44  extend from the perimeter of the longitudinal sides of the housing base  28 . The arms  44  define slots  46  for interlocking engagement with complementarily shaped tabs  48  in recesses  50  disposed along the perimeter of the housing cover  20 . The housing cover  20  and the housing base  28  engage one another, preferably by heat bonding, to cause the diaphragm  42  to sealingly engage the interior of the housing base  28 . As should be evident, numerous other structures and attachment methods may be used to couple the housing cover  20  and the base portion  28  together and to seal the diaphragm  42  therebetween. 
     As shown in  FIG. 5 , the interior surface of the housing base  28  and the diaphragm  42  define an internal flow path through the emitter  10  from the inlet  16  to the outlet  18 . The diaphragm  42  is preferably an elongated strip dimensioned to overlap and seal against the flow path and is preferably a silicone or rubber material. Alternatively, the diaphragm  42  may be arcuate in shape to accommodate alternative embodiments of the drip emitter having curved, circular, and/or three-dimensional flow duct paths. 
     The housing base  28  defines a flow duct path  110  and a water metering chamber  51 . More specifically, water flows from the inlet  16 , through the flow duct path  110 , and into the water metering chamber  51 . It then flows through a groove  62 , defined by a water metering surface  52  on the bottom of the watering meter chamber  51 , to the emitter outlet  18 . Water flowing through this flow path experiences a pressure drop. 
     As shown in  FIG. 6 , the interior surface of the housing cover  20  defines an elongated, central channel  56  forming a pressure chamber  57  between the housing cover  20  and the diaphragm  42 . The interior surface of the housing cover  20  does not have a complete sealing engagement with the diaphragm  42 , so that water therefore enters and accumulates in the pressure chamber  57  through a gap between the housing cover  20  and the diaphragm  42  at the inlet and outlet ends. The water in this channel  56  does not flow through the emitter  10 . Instead, water accumulates in the channel  56  at the same general pressure as water flowing in the conduit  14 . 
     Although the pressure chamber  57  need not necessarily be in the shape of an elongated channel  56 , such a channel is desirable to limit the entry of grit and other debris into the region between the housing cover  20  and the diaphragm  42 . The accumulation of grit could otherwise interfere with the flexing of the diaphragm  42 . Also, the channel  56  preferably includes a stop  59  at or near the center of the channel  56  to limit the flow of grit and other debris therethrough. 
     The interior surface of the housing cover  20  preferably includes a generally central raised region  58  which engages the diaphragm  42  and spaces the diaphragm  42  away from the perimeter region of the interior surface. The raised region  58  defines the channel  56 , which extends centrally through this raised region  58 . 
     Water accumulating in the channel  56  presses down against the diaphragm  42 , thereby flexing and deflecting the diaphragm  42  toward and against the water metering surface  52 . This creates a pressure differential between water in the pressure chamber  57  and water in the metering chamber  51 . The water metering surface  52  includes a raised circular portion, or island  60 , with the groove  62  providing a flow path across the island  60  to the emitter outlet  18 . During normal operation, the diaphragm  42  deflects into the groove  62  in response to fluctuations in supply tube pressure. This deflection into the groove  62  compensates for such pressure fluctuations and maintains a relatively constant drip flow rate. This pressure differential also improves a self-flushing ability of the emitter  10 , as described further below. 
     With reference to  FIGS. 4 ,  5 , and  7 , the flow duct path  110  provides a zigzagging tortuous path for the water flow to reduce the pressure of the water. The path is defined by a first set of baffles  122  and second set of baffles  128  opposing the first set  122 . A small, central, elongated path  112  of preferably substantially rectangular cross-sectional shape extends directly through and between the baffles sets without any directional changes. The central path  112  divides the flow duct path  110  into two sets of laterally extending flow recesses  114  and  116 , defined by the first set of baffles  122  and the second set of baffles  128 , respectively. 
     More specifically, each of the flow recesses of one set  114  is defined between a pair of opposing side walls  118 ,  120  of a pair of successive baffles  122  of the first set of baffles  122 . Each of the other flow recesses from the other set  116  is defined between a pair of opposing side walls  124 ,  126  of a successive pair of baffles  128  of the second set of baffles  128 . The flow duct path  110  has a base wall  130 . The flow duct  110  has an inlet  132  and an outlet  134  at the opposite end. 
     The central path  112  and the recesses  114 ,  116  define the tortuous path for the water to travel through the emitter  10 . The size of the tortuous path is an influential factor in determining the flow rate from the emitter  10  at any given operating pressure. An emitter  10  with an appropriate center path  112  reduces the amount of clogging by letting organic materials and grit, such as algae, to flow through the emitter  10  with decreased amount of obstruction by the baffles  122 ,  128 . 
     Each baffle of the two sets of baffles  122  and  128  has a terminal edge, or truncated tip  136  and  138 , respectively. The baffles  122 ,  128  are arranged so that the tip  136  of one baffle  122  on one side of the center flow path  112  points to the midpoint between the tips  138  of two successive baffles  128  on the opposite side of the center flow path  112 . A baffle pitch “A” is defined as the distance between one side wall  120  of one baffle  122  on one side of the flow path  112  to the closest successive side wall  124  of another baffle  128  on the other side of the flow path  112 . The tips of successive baffles that are on the same side of the central flow path  112  are aligned in a collinear manner along a border of the flow path  112 . 
     The width or gap “R” of the center path  112  is defined as the distance between an imaginary line connecting the tips  136  on one side of the flow path  112  and another imaginary line connecting the tips  138  that are on the other side of the flow path  112 . The preferred dimension of R lies in the range of greater than 0, but less than or equal to 0.19 times the baffle pitch A. As an alternative to the linear flow duct path  110  described above, the flow duct path  110  may be disposed in an arcuate, circular, and/or three-dimensional fashion (such as, for example, the layout of the flow duct path shown in U.S. Pat. No. 5,820,029, assigned to the assignee of the present invention, which is incorporated herein by reference), while retaining the same relationship of A and R. 
     The range where 0&lt;R≦0.19A provides a flow duct path geometry that reduces obstruction of the emitter  10  both in the flow duct path  110  and at or near the emitter outlet  18  and thereby improves self-flushing. Without a central flow path  112 , grit would tend to become lodged in or near the baffles  122 ,  128 , resulting in obstruction of the flow duct path  110 . It should be evident that other forms of the flow duct path  110  are available incorporating the spatial relationships described above, including the relationship between baffle pitch, A, and width of the center gap, R. 
     When the emitter  10  is obstructed due to grit becoming lodged in the groove  62  of the water metering surface  52 , the pressure differential between the pressure chamber  57  and the water metering chamber  51  is eliminated and other forces become significant. The concept of “lift ratio” describes these other forces. The lift ratio is defined as F P /F R , where F P  is the pull force exerted by the emitter outlet  18  on the diaphragm  42 , and F R  is the elastic return force of the diaphragm  42 . More specifically, F P =(Π/4)*(diameter^2)*(supply tube water pressure−atmospheric pressure), where the diameter is the diameter of the emitter outlet  18 , and F R =k*D, where k=the spring constant of the diaphragm  42  and D=the amount of deflection of the diaphragm  42 . During normal operation, the amount of deflection is the distance between the diaphragm  42  in its relaxed state and the top of the water metering surface  52  because the diaphragm  42  is designed to bottom out on the metering surface  52  so that it can interact with the groove  62 . 
     The lift ratio describes the interaction of the two forces that are acting at the water metering surface  52  and the emitter outlet  18  when the emitter  10  is obstructed. F P  is the force that “grabs” the diaphragm  42  and holds it at or near the emitter outlet  18  even when there is no flow along the flow path due to grit obstructing the metering groove  62 . F R  is the force reflecting the tendency of the diaphragm  42  to spring back to its relaxed position away from the metering surface  52  when there is an obstruction. It is most advantageous, in order to improve self-flushing of the emitter  10 , to reduce the lift ratio as much as possible within practical limits of emitter design so that F R  is greater than F P  to enable the diaphragm  42  to move away for flushing of the metering groove  52 . 
     Consideration of the formulas for F P  and F R  reveals that there are two general factors that help return the diaphragm  42  to its relaxed position when the emitter  10  is obstructed and thereby improve the self-flushing ability of the emitter  10 : (1) the amount of deflection, D, by the diaphragm  42 ; and (2) the size of the diameter for the emitter outlet  18 . First, the amount of deflection by the diaphragm  42  is a significant factor. For diaphragms with the same physical properties such as dimension, elongation, and modulus, a higher degree of diaphragm deflection depth will tend to return to the diaphragm  42  back to its relaxed position quicker due to higher elastic force. When the pressure differential between the pressure chamber  57  and water metering chamber  51  is suddenly eliminated, a greater deflection of the diaphragm  42  will result in a greater tendency of the diaphragm  42  to return to its relaxed position. This would allow any debris trapped between the water metering surface  52  and the diaphragm  42  to flow. 
     Second, the size of the diameter of the emitter outlet  18  is another factor. As the water flows in the tortuous flow duct path  110 , the water pressure in the flow path drops, resulting in the pressure differential between water in the pressure chamber  57  and water metering chamber  51 . This pressure differential causes the higher pressure water in the pressure chamber  57  to push the diaphragm  42  towards and against the water metering surface  52 . When the emitter  10  becomes obstructed, the pressure differential is eliminated and the diaphragm  42  will tend to return to its relaxed position. However, if the pressure difference between the tube pressure and the atmospheric pressure (the pressure on the outside of the emitter outlet  18 ) is too great, the diaphragm  42  may not return to its relaxed position until the tube pressure is significantly reduced, such as by eliminating water flow through the supply tube  14  entirely. It is not desirable to adjust the line pressure and is preferred that the emitter  10  address this situation in an automatic manner. To address this situation, it is desirable to reduce the diameter of the emitter outlet  18  and thereby reduce F P , that is, the “grabbing” of the diaphragm  42 . The reduction in diameter of the emitter outlet  18  is limited by practical design considerations, but emitter outlets  18  having a diameter as small as 0.030 inches have been found to satisfactorily self-flush without changing the supply pressure. 
     To decrease the lift ratio, the amount of deflection, D, of the diaphragm  42  (the distance between the diaphragm at rest and the top of the water metering surface  52 ) is increased by increasing the pressure differential between the pressure chamber  57  and the water metering chamber  51 . A relatively small pressure in the water metering chamber  51  will result in a greater deflection of the diaphragm  42 . Thus, it is desirable to increase the pressure drop through the flow duct path  110  within design limits, such as emitter length and cost. 
     To achieve this relatively large pressure drop, the central flow path  112  through the flow duct path  110  must be relatively narrow, R≦0.19A. A narrow central flow path  112  results in a greater pressure drop than a wider central flow path  112 , and therefore, a lower lift ratio and less obstruction in the groove  62  near the emitter outlet  18 . Thus, although a wide central flow path  112  tends to reduce clogging of the flow duct path  110 , it results in an increased tendency for clogging near the emitter outlet  18 . Clogging near the emitter outlet  18  is a more common problem than clogging of the flow duct path  110 . 
     Also, to decrease the lift ratio, the diameter of the emitter outlet  18  is reduced within emitter design limits. To decrease lift ratio, the ratio of the diameter of the emitter outlet  18  to the amount of deflection, D, of the diaphragm  42  to the (diameter/deflection) is minimized. The ratio of the diameter to deflection, D, should preferably be less than one. 
     The foregoing relates to preferred exemplary embodiments of the invention. It is understood that other embodiments and variants are possible which lie within the spirit and scope of the invention as set forth in the following claims.