WO2000001219A1

WO2000001219A1 - Irrigation tube with flexible margin

Info

Publication number: WO2000001219A1
Application number: PCT/US1999/014361
Authority: WO
Inventors: Michael Defrank
Original assignee: Rain Bird Sprinkler Manufacturing Corporation
Priority date: 1998-07-06
Filing date: 1999-06-24
Publication date: 2000-01-13
Also published as: AU4717999A

Abstract

A drip irrigation tube (10) formed by longitudinally folding an elongated web having a thick marginal side wall (26), an intermediate central wall (20), and a thin marginal side wall (24), and overlapping and sealing the marginal side walls (24, 26) to form a tube (10). Discrete emitter elements are disposed at spaced intervals along the web and are formed by embossing or otherwise forming recessed emission grooves in the outer overlapping marginal side wall (26) so as to form a flow path from the inside of the tube (34) to the outside. The emitter elements operate to provide a constant flow rate over a wide range of working pressures by controlled deformation and constriction of size of relatively short regulatory passageways (44) formed by a portion of the emission grooves.

Description

IRRIGATION TUBE WITH FLEXIBLE MARGIN

BACKGROUND OF THE INVENTION

This invention relates generally to irrigation equipment designed for delivering irrigation water to crops and the like, and more particularly, to an irrigation tube forming one or more emitters through which the flow rate of irrigation water is controlled and regulated in response to the pressure of water supplied to the irrigation tube.

A variety of so-called continuous tube emitters are available for irrigating crops and other vegetation. Such continuous tube emitters typically comprise an elongated tube of either rigid or flexible construction, having a plurality of outlets formed along its length. Irrigation water is preferably discharged from the outlets at a relatively slow drip flow rate, such as a flow rate less than about one gallon per hour. Such low drip rates discourage root growth into the outlets. To improve cost efficiency and encourage water conservation, the irrigation water is discharged adjacent to crops, which reduces the amount of water emitted, which in turn results in a reduction of water wasted from evaporation and the soil erosion caused by runoff.

Previously available continuous tube emitters have utilized many d fferent structural techniques intended to leak water slowly through outlet openings at spaced intervals along the length of the tube. For example, continuous tube emitters have been suggested with fibrous or other porous substances occluding the outlets to permit slow water leakage therethrough, such as the devices disclosed in U.S. Patents Nos. 3,777,987 and 2,799,422. Other continuous tube emitter designs have proposed concentric or multiple tube constructions wherein irrigation water is leaked through a series of small pressure- and flow-reducing orifices, such as the emitter designs disclosed in U.S. Patents Nos. Re. 28,095; 3,361,359; 3,672,571; 3,903,929; 4,534,515; and 4,626,130. Still other tube emitter designs have proposed relatively complex and elongated or labyrinth flow path configurations for reducing the flow rate and pressure of water discharged through outlets, such as those devices disclosed in U.S. Patents Nos. 4,002,684; 4,077,570; 4,077,571; and 4,763,842. However, in these exemplary continuous tube emitter designs, the requisite low water flow rates have required outlets or leakage paths of fixed, small cross-sectional area which are highly susceptible to clogging by dirt or other particulate matter commonly present in most agricultural water supply systems. Additionally, such designs have not heretofore been capable of reliably and consistently producing a substantially constant flow rate over the full range of working pressures normally encountered in use.

In U.S. Patent No. 4,807,668, there is disclosed a continuous tube emitter formed by folding a plastic web lengthwise with the edges overlapped and heat-sealed together, and which has a preformed groove along one edge to define an elongated secondary conduit of small cross-section within the seam. Small openings are formed at spaced intervals along the seam of the secondary conduit which function as outlets from the tube. With this construction, the inner wall portion of the overlapped web forms a dividing wall between the main conduit and the secondary conduit, and which is said to be capable of producing a throttling effect by deflecting into the groove in response to increased water pressure within the main conduit so as to reduce the size of the secondary passageway and thus regulate the outlet flow. While several attempts to produce flow control devices have employed this approach, none has been capable of precisely and consistently producing a substantially uniform flow rate over the full range of working pressures normally encountered. This is believed to be due to the inability of the inner wall portion to effectively constrict the size of the secondary passageway in response to pressure increases since that wall is subjected to a tensile force created by the internal water pressure within the main conduit, which prevents the wall from appreciably deforming in a controlled manner into the groove. That is, the internal pressure within the main conduit attempts to inflate the tube, thereby placing the tube wall under a tensile load. As the internal water pressure increases, the tensile force on the tube wall also increases, and this tensile force actually reduces the ability of the wall to controllably deform into the groove. A continuous tube emitter which is intended to overcome many of the foregoing problems is disclosed in U.S. Patent No. 4,726,520. The tube emitter design provides for a flexible plastic tube formed from an elongated thin film web having one or more relatively thicker valve members on one side thereof defining a plurality of valve faces, wherein each valve face includes at least one shallow drip emission groove leading into a valve reservoir of wider cross section and communicating respectively with outlet openings through the web. One longitudinal margin of the web is trimmed to form laterally projecting flaps at longitudinal positions generally corresponding with the valve faces. The web is then rolled upon itself about a longitudinal axis and longitudinally seamed to form the continuous tube emitter with the flaps each internally overlying the valve reservoir and a portion of the drip emission groove of a respective valve face to define one of the flow control units. In use, water pressure within the tube forces the flaps into engagement with the aligned valve faces to restrict and control the rate of water flow through the outlet openings. While the foregoing construction provided an improved and more uniform flow rate over normal working pressure range, it was found that the flap-type construction was difficult to consistently manufacture, and that the level of flow was not always predictable.

Typically, continuous tube drip systems are designed to be operational over a working range of pressures, normally between approximately 6 and 10 pounds per square inch. In the event the continuous tube drip system is employed in hilly terrain, the effective working pressure range may be higher for those portions of the tube lying in valleys, and lower for those portions of the tube overlying the crest of a hill, typically by as much as plus or minus two pounds per square inch. Accordingly, it is highly desirable to be able to compensate for such pressure variations to insure that a substantially uniform flow rate from each emitter along the length of the tube is obtained even though substantial pressure variations are present.

The response of any given emitter in a continuous tube emitter system can be characterized by the formula Q = c P^x where: Q is the emission flow rate at the outlet port of the emitter; P is the pressure inside the emitter tube; c is a constant coefficient which can be empirically determined for each type emitter; and x is an emission rate exponent. From this equation, it can be seen that if the emission exponent equals one, then the emission rate is directly proportional to the pressure inside the emitter tube. That is, if the pressure within the tube doubles, the flow rate from the emitter will double. For an emission rate exponent equal to zero, on the other hand, the emission rate is constant regardless of pressure inside the emitter tube. Thus, for any emission rate exponents value greater than zero but less than one, the emitter will have a pressure compensating characteristic. Since it is always desirable to have a substantially constant flow regardless of the water pressure within the emitter tube, it is therefore desirable to attempt to obtain an emission rate exponent as close to zero as possible.

U.S. Patent No. 5,111,995 to Dumitrascu et al. addresses many of the above issues, disclosing a drip irrigation tube formed by longitudinally folding an elongated web having thick marginal side portions, and overlapping and sealing the thick marginal sides to form a tube. Discrete emitter elements are disposed at spaced intervals along the web and are formed by embossing or otherwise forming recessed emission grooves in one of the thick marginal edges so as to form a flow path from the inside of the tube to the outside when the tube is folded. The emitters operate to provide a constant flow rate over a wide range of working pressures by controlled deformation and constriction of size of relatively short emitter passageways formed by a portion of the emission grooves. While this device provides an economically manufactured irrigation device that discharges water at a drip flow rate, and while this device exhibits a relatively small emission rate exponent, it would be preferable to have a device exhibiting an even smaller emission rate exponent.

Accordingly, there has existed a need for a cost efficient irrigation tube having one or more discrete emitters that are capable of producing a substantially constant outlet flow rate over the entire range of working pressures typically encountered in use, and whose emission rate exponent is extremely close to zero. SUMMARY OF THE INVENTION

The present invention provides an irrigation device in which one or more emitters are formed through which the flow rate of irrigation water is controlled and regulated in response to the pressure of water supplied to the irrigation device. It economically provides for the irrigation of soil with water delivered at a consistent and constant rate to a plurality of irrigation locations that can vary in elevation, and from a source that can vary in pressure over a range of pressures.

The irrigation device includes a structure defining an internal chamber that is adapted to be connected to the water source. The structure, which is preferably a longitudinally extending tube made from a web that is rolled upon itself and folded, includes a wall that is a composite of an inboard wall segment and an overlapping outboard wall segment. A regulating passageway is defined between the inboard and outboard wall segments, the passageway placing the internal chamber in fluid communication with the irrigation locations. The inboard and outboard wall segments are joined together along opposite sides of the regulating passageway.

A feature of the invention is that one of the inboard and outboard wall segments, and preferably the outboard wall segment, has a relatively higher bending stiffness than the other. An additional feature of the invention is that the central wall has a relatively higher bending stiffness than one of the inboard and outboard wall segments, and preferably the inboard wall segment. The composite wall deforms in response to fluid pressure within the internal chamber, which puts the inboard wall segment under compression and the outboard wall segment under tension. The deformation varies the cross-sectional size of the regulating passageway to maintain a substantially constant fluid flow rate from the internal chamber to the irrigation locations, and does so at least as long as the fluid pressure varies between the prescribed minimum and maximum pressures. An advantage of these relative-stiffness features is that the relatively flexible inboard wall segment is particularly responsive to the pressure within the conduit to control the constriction of the regulating passageway. This responsiveness is not significantly reduced by circumferential tension in the conduit because the outboard wall carries a large portion of that tension. Thus, the irrigation tube can be configured to emit water at a substantially constant rate regardless of variation of the water source's pressure. Furthermore, as a simple one piece web rolled upon itself into a heat-sealed conduit, the irrigation tube is inexpensive to manufacture.

Other features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a subterranean installation of a drip irrigation tube embodying features of the invention.

FIG. 2 is a schematic representation of the formation of emission grooves in a web to be used to form a drip irrigation tube embodying features of the invention.

FIG. 3 is a cross-sectional view of the web depicted in FIG. 2, taken along line 3-3 of FIG. 2.

FIG. 4 is a schematic representation the web depicted in FIG. 2 being folded into a tubular shape with two marginal portions overlapping. FIG. 5 A is a plan view of the folded web depicted in FIG. 4, extending from a machine that bonds marginal portions together to form a drip irrigation tube, with portions of the web broken away.

FIG. 5B is a second plan view of the bonded web depicted in FIG. 5A, depicting flow paths through an emitter.

FIG. 6 A is a cut-away plan view of a second embodiment of a drip irrigation tube, similar to the drip irrigation tube depicted in FIG. 5A, having an alternate form of an inlet and an alternate form of an outlet.

FIG. 6B is a plan view of a third embodiment of a drip irrigation tube, similar to the drip irrigation tube depicted in FIG. 5 A, having an alternate form of an inlet an alternate form of a regulatory passageway, and an alternate forms of an outlet.

FIG. 7 is a cross-sectional view of the drip irrigation tube depicted in FIG. 5B, taken along line 7-7 of FIG. 5B, showing the effect of having no significant water pressure in the irrigation tube.

FIG. 8 is a partial cross-sectional view of the drip irrigation tube depicted in FIG.

7, taken within region 8 of FIG. 7.

FIG. 9 is a cross-sectional view of the drip irrigation tube depicted in FIG. 7, showing the effects of water pressure approaching a working pressure range inside the irrigation tube, and including, in broken line representation, the effect of having no significant water pressure in the irrigation tube.

FIG. 10 is a cross-sectional view of the drip irrigation tube depicted in FIG. 9, showing the effects of water pressure within the working pressure range inside the irrigation tube. FIG. 11 is a cross-sectional view of the drip irrigation tube depicted in FIG. 9, showing the effects of water pressure exceeding the working pressure range inside the irrigation tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An irrigation tube 10, according to the present invention, is shown in

FIG. 1. The irrigation tube is provided with a plurality of discrete emitters 12 longitudinally spaced at a preselected distance apart along the irrigation tube for the controlled supply of irrigation water to a plurality of outlet locations for agricultural crops and the like located near those outlet locations. The irrigation tube is particularly suitable for use in subterranean drip irrigation applications, although it can be installed above the ground surface, if so desired. The irrigation tube of the present invention incorporates many features of the irrigation tube disclosed in U.S. Patent No. 5,111,995, which is incorporated herein by reference.

The irrigation tube 10 is formed as an elongated, collapsible thin- walled tube adapted for connection to a water supply pipe 14 including a suitable control valve 16 for controlling the supply of a flow of a fluid such as pressurized water. The irrigation tube includes a remote end that is closed by suitable means, such as clamping or sealing, so that the water within the irrigation tube can escape from within the irrigation tube only through the discrete emitters 12.

With reference to FIGS. 1 - 4, the drip irrigation tube irrigation tube 10 is manufactured from relatively inexpensive materials to provide a simple and highly economical continuous tube drip irrigation system which operates reliably and effectively to deliver a controlled and substantially fixed rate of water flow over a relatively wide range of water supply pressures. More particularly, the drip irrigation tube irrigation tube is formed from a relatively inexpensive thin-walled generally flat strip or web 18 of a flexible plastic material, such as linear low density polyethylene, which can be processed economically and at high production rates to form an elongated collapsible tube.

The web 18 is configured with three laterally spaced portions: a central wall 20; a first marginal wall 24; and a second marginal wall 26. The marginal walls are spaced on laterally opposing sides of the central wall. Each marginal wall extends longitudinally along one of the lateral sides 22 of the web. The second marginal wall 26 is generally thicker than the central wall, and is relatively stiffer than the central wall in lateral and longitudinal bending, as well as in tension, by an amount effective to carry a substantial portion of a load applied to the two in parallel. The first marginal wall 24 is generally thinner than both the second marginal wall and the central wall, and is relatively more flexible than either of them in both lateral and longitudinal bending. The lateral connections between the walls can be made with a gentle transition for ease of manufacture and construction. Typical web thicknesses might fall within the following ranges: first marginal wall at .005 to .007 inches; central wall at approximately .009 inches; and second marginal wall at .012 to .013 inches.

Preferably, the web 18 is formed by a continuous extrusion process, and can be stored for subsequent use on a reel 28, or the like. The width of the web is selected such that the web may be rolled into an irrigation tube having a desired diameter. Following formation, the web 18 is fed through an apparatus 30 that embosses or otherwise forms into the surface of the second marginal wall 26 recessed emission grooves 32 spaced at the preselected locations along the length of the web.

Thereafter, as depicted in FIGS. 4, 5 A and 5B, the embossed web 18 is rolled upon itself and folded into a longitudinally extending tubular configuration with the second marginal wall 26 overlapping the first marginal wall 24, the web thus forming a main supply conduit 34. The conduit serves as a housing, and includes the central wall 20 and a composite wall formed by the overlapped marginal walls 24, 26. The second marginal wall, having the emission groove 32, overlies the first marginal wall, with the first marginal wall separating the most of the emission groove from the irrigation tube's conduit. The second marginal wall thus forms an outboard wall segment of the composite wall and the first marginal wall forms an inboard wall segment of the composite wall.

Once the web 18 has been folded with the first and second marginal walls 24, 26 overlapped, the web 18 is then passed through a suitable bonding apparatus 52, preferably being a heated and contoured pressure roller device of generally conventional design. The pressure roller selectively applies a weld to the overlapped marginal portions to heat seal and thus bond them together into an integral structure. The overlapped marginal walls are bonded in a specific bonding pattern to seal the irrigation tube and form the discrete emitters 12 from the recessed emission grooves 32.

The first and second marginal walls 24, 26, including the emission grooves

32, thus cooperatively define the emitters 12. These drip irrigation tube emitters are formed integrally with the web during fabrication of the drip irrigation tube irrigation tube without requiring the addition of other parts or materials.

As depicted in FIGS. 5 A and 5B, the drip irrigation tube irrigation tube 10 defines the main water supply conduit 34 to have a relatively large diameter. This conduit is configured to be coupled with the water supply pipe 14 (see FIG. 1) for the admission of pressurized water into the drip irrigation tube irrigation tube.

The emitters each include three sequentially interconnected functional sections. The first, or inlet, section 36 defines a plurality of emitter inlet passageways 38 leading in a generally lateral direction from the conduit 34 to a longitudinally extending inlet flow collector or manifold passageway 40. It is important that the entrance end of each of the inlet passageways 38 extend beyond the side edge 22 of the underlying inboard wall segment 24 so that the entrance end will be exposed to the conduit 34 of the irrigation tube 10 to provide a passage for water within the conduit into the emission groove 32. The third or outlet section 46, defines a plurality of emitter outlet reservoir passageways 48 leading to laterally directed exit passageways 50 at an irrigation location. The second, or regulating, section 42 defines a regulatory passageway 44 of relatively short length, extending longitudinally along the center portion of the outboard marginal wall 26. The regulatory passageway puts the conduit 34 in fluid communication with the fluid outlets. The flow of fluid from the conduit to the outlets is regulated by the regulatory passageway in response to the fluid pressure in the conduit.

In the process of bonding, relatively wide weld area lines are formed in a preselected pattern cooperating with the emission grooves 32 to further define the emitters 12 and to increase the structural stiffness of the portions of the composite wall of the irrigation tube 10. In this latter respect, the weld area lines are each formed to have raised marginal ribs 54 which aid in providing structural rigidity to the weld areas.

In particular, the overlapped first and second marginal walls 24, 26 are welded together between emitters 12 with a pair of parallel weld lines 56 and 58 spaced to approximately mate with the locations of the web lateral side edges 22 so as to close and seal the irrigation tube between each emitter. Adjacent to the inlet section 36, a transverse weld line 60 is formed to interconnect the two parallel weld lines 56 and 58, and define one end of the inlet section of the emitter 12. An extension 56', of the parallel weld line 56 adjacent the lateral edge 22 of the embossed second marginal wall 26 extends along one side of the regulatory passageway 44, and terminates at the entrance of the outlet section 46 of the emitter 12. This weld line extension 56' forms the bottom of the inlet section 36 of the emitter 12, and at its terminal end, the beginning of the outlet section 46.

Disposed on the side of the overlapped marginal walls 24, 26 opposite the weld line extension 56' are two discrete weld spots 62 and 64, generally square in shape, which are disposed between the inlet passageways 38 to separate those passageways. Extending along the side of the regulatory passageway 44 on the side opposite the weld line extension 56' and parallel with the regulatory passageway is a further weld line 58', forming the beginning of the parallel weld line 58, and which cooperates with the opposed weld line extension 56' to define the sides of the regulating section 42, as well as the side of the outlet section 46 of the emitter 12. A final lateral weld line 66 interconnects the beginning of the next two parallel weld lines 56 and 58 with the further weld line 58' adjacent the outlet passageways 48 to form the end of the outlet section 46. Notably, no weld is formed to close the exit passageways 50 of the outlet section 46 to the exterior of the irrigation tube 10, nor to restrict the flow of water from the conduit into the inlet passageways 38.

As represented by the arrows of FIG. 5B, it can be seen that the emission groove 32 bounded by the first and second marginal walls 24, 26 and the various weld lines, cooperate to define three discrete inlet openings via inlet passageways 38 leading from the conduit 34 of the irrigation tube 10. Notably, the three inlet passageways 38 provide a water inlet opening which is substantially larger than the size of the regulatory passageway 44 so that if one or even two of the inlet passageways were to become clogged or blocked, a sufficient water flow to feed the regulatory passageway would still be obtained.

From the inlet passageways 38, the water flows into the manifold passageway 40 and through the regulatory passageway 44 where the principal flow regulation takes place, and then to the outlet section 46. At the outlet section 46, the grooves bounded by the overlapped marginal walls 24, 26, and the weld lines 58, and 66 cooperate to form a tortuous path through the reservoir passageways 48 to the exit passageways 50 where the water is discharged from the irrigation tube. It should also be noted that the exit passageways 50 also provide a larger area through which water can flow than the area of the regulatory passageway 44. Therefore, should one of the exit passageways 50 become clogged or blocked, water can still be discharged from the outlet portion 46.

As depicted in FIG. 6A, a second preferred embodiment of the drip irrigation tube irrigation tube is configured identically to the first, with the exception of the first, or inlet, section 36, and the third, or outlet, section 46. A weld extension line 56" extends the full length of the emitter 12, connecting to the weld lines 56 on either end of the emitter. Thus, the inlet section comprises an inlet reservoir 40", and the outlet section comprises an outlet reservoir 48", providing larger areas through which water can flow than the area of the regulatory passageway 44. The portion of the inboard marginal wall forming the inlet reservoir includes an entrance cut or slit 38", and the portion of the outboard marginal wall forming the outlet reservoir includes an exit cut or slit 50". These cuts or slits are preferably in a longitudinal direction to accommodate longer slit lengths. The slits provides for water to be emitted without allowing clogging agents to enter and pass through the emitter.

With reference to FIGS. 7 and 8, in accordance with either described embodiment of the present invention, the principle of operation for achieving flow regulation in response to pressure variations within the conduit 34 of the irrigation tube 10 is through controlled and predictable constriction of the relatively short regulatory passageways 44. Constriction of the regulatory passageways is effected by deformation of the overlapped marginal walls 24, 26 in a controlled manner as pressure within the conduit increases, so that the regulatory passageways will each have the flow characteristics of a variable size, flow restricting orifice.

The regulatory passageway 44 is formed with a specific geometry to insure uniform constriction of the passageway for achieving a substantially constant flow of water at all pressures within the working range of supply pressures, yet which provides a relatively large area passageway for flushing particulate matter from the passageway with each cycle of operation. The basic mechanism employed for controlling constriction of the regulatory passageway is that of the compressive and tensile forces formed in a flexible beam supported at its ends, where the flexible beam is the composite wall formed from the bonded marginal walls.

When such a beam is subjected to uniform loading along one side, the beam will deflect away from the load and assume an arcuate shape between its supports. This deflection creates a compression force in the surface of the beam exposed to the load, and a tensile force in the opposed surface, thus attempting to move the loaded surface toward the non-loaded surface, and vice versa. By forming the regulatory passageway 44 centrally between the first and second marginal walls 24, 26, and bonding those walls together to form an integral composite beam having inboard and outboard wall segments, the inboard and outboard wall segments act like a flexible beam supported at its ends by the junctions with the central wall 20.

The regulatory passageway 44 is bounded on one side by the embossed emission groove 32 in the outboard wall segment 26, and on the opposite side by a surface of the inboard wall segment 24. Extending laterally along the sides of the regulatory passageway 44 are the weld lines, specifically the weld line extension 56' and other weld line 58' bonding the inboard and outboard wall segments together. Since the inboard and outboard wall segments are bonded together to form an integral structure along the sides of the regulatory passageway, the effective stiffness, and hence resistance to deformation, of the bonded portions extending along the regulatory passageway is considerably greater than that of the unbonded portions of the inboard and outboard wall segments defining the boundaries of the regulatory passageway. Moreover, the stiffness of the bonded portions is further increased by the provision of the raised ribs 54, the weld extension 56' and lateral weld line 66 (see FIG. 5B) having a square wave shaped pattern along the sides of the emission passageway to enhance rigidity.

With particular reference to FIG. 8, the embossed regulatory passageway 44 is formed in the outboard wall segment 26 to define a central wall 68 of substantially semi-circular shape, joined with opposed laterally directed inclined side wall portions 70 which, in turn, are interconnected with substantially horizontal wall portions 72 extending parallel with, but spaced from the surface of the adjacent portion of the inboard wall segment 24, by end walls 74. Thereby, the regulatory passageway includes a relatively large central main emitter passage 69 with laterally projecting wedge shaped side passages 71 extending to the junction of the bonded inboard and outboard wall segments. The first and second marginal walls thus define a perimeter of the regulating passageway. The shape of the main emitter passage may be varied in different embodiments. As depicted in FIG. 6B, a third preferred embodiment of the drip irrigation tube irrigation tube is configured similar to the first, having inboard and outboard marginal walls 24'", 26"'. A pair of parallel weld lines 56'" and 58"' are spaced 5 to contain a plurality of emitters. An inlet section 36'" defines a pair of emitter inlet passageways 38'" that extend through a break in one of the weld lines 58'". The inlet section leads in a partially lateral direction from a conduit 34'" to a regulatory passageway 44'" extending longitudinally along the outboard marginal wall 26'". The regulatory passageway puts the conduit in fluid communication with a longitudinally slit fluid outlet 10 50'", similar to the one described with regard to FIG. 6A. Of particular interest, the central main emitter passage 69'" of the regulatory passage is sawblade-shaped, zigzagging between a first plurality of points 80'" centered between the weld lines and a second plurality of points 82'" near one of the weld lines 58'".

Returning to the first embodiment, as depicted in FIG. 9, when pressurized 15 water is initially admitted into the conduit 34 of the irrigation tube 10, the irrigation tube begins to inflate from a no-pressure, flat condition (represented by broken lines) to a more circular cross-sectional configuration (represented by solid lines). Notably, initial inflation is confined to the central wall 20, the considerably thicker composite wall portion remaining in the substantially flat condition since the pressure is insufficient to 0 overcome its higher relative stiffness to effect deformation. Thus, at least initially, the central wall 20 inflates by pivoting about its junctions with the inboard and outboard wall segments 24, 26.

During this initial phase of the operating cycle, since the inboard and outboard wall segments 24, 26 remain substantially flat and undeflected, the 5 cross-sectional size of the regulatory passageway 44 includes both the main emitter passage 69 and all of the areas of the wedge shaped side passages 71. As will become apparent, in this condition the cross-sectional size of the regulatory passageway 44 is considerably greater than when the internal pressure within the conduit 34 of the irrigation tube 10 has reached its working range. Thus, particulate matter that may have become trapped in the regulatory passageway when the pressure was previously in the working range will be flushed into the outlet section 46, and either flushed out through the exit passageways 50 or stored in the outlet reservoir 48" (see FIGS. 5B and 6A).

Turning now to FIG. 10, as the internal water pressure within the conduit 5 34 of the irrigation tube 10 initially approaches the lower level of the working pressure range, the radial pressure of inflation against the central wall 20 and the composite inboard and outboard wall segments 24, 26 cause the composite wall portion to begin to deflect to an arcuate shape. During this initial deflection of the composite wall, the deflection causes the inboard wall segment to be subjected to compression, and the 10 outboard wall segment to be subjected to tension. The pressure within the conduit will also cause a tensile force on the composite wall portion. The outboard wall, being thicker than the inboard wall, carries the majority of this tensile force, thus allowing the inboard wall to be subject to compression.

Since the unbonded portions of the inboard and outboard wall segments 24, 15 26 are relatively less stiff than the bonded portions, the inboard wall segment overlying the regulatory passageway 44 will deflect toward the outboard wall segment, and the outboard wall segment and its embossed groove 32 will deflect toward the inboard wall segment, thereby closing the spaces defined between the horizontal wall portions 72 and the adjacent portion of the inboard wall segments. Because the inboard wall segment is 0 thinner and weaker in bending than the outboard wall segment, the inboard wall segment can be configured to deflect significantly more than the outboard wall segment.

As the internal pressure within the conduit 34 continues to rise, the composite inboard and outboard wall segments 24, 26 continue to bend about a radius extending within a plane through the center of the irrigation tube 10 but whose length is 5 considerably greater than that of the radius of curvature of the central wall 20, the composite wall radius becoming shorter as the internal pressure within the conduit continues to increase. Further deflection of the composite inboard and outboard wall segments increases the compressive load experienced by the inboard wall segment as well as the tensile force in the outboard wall segment, thereby producing a further and progressive closing toward the main emitter passage 69 of the inclined wall portions 70 against the opposed inboard wall segment, and causing the regulatory passageway 44 to be further compressed to a smaller overall cross-sectional size. Compression of the regulatory passageway 44 in turn causes an increase in pressure drop to occur as water flows between the inlet section 36 and the outlet section 46, controlling the rate of water flow through the emitter 12 to maintain that rate at a substantially constant level as pressure builds within the conduit 34.

Ultimately, as shown in FIG. 11, when the internal pressure within the conduit 34 exceeds the working pressure range, the radius of curvature of the composite inboard and outboard wall segments 24, 26 will approximate that of the central wall 20, and the regulatory passageway will be constricted to an area less than the size of the main emitter passage 69 due to the high compressive and tensile forces created in the inboard and outboard wall segments. In this condition, the regulatory passageway 44 will no longer experience controlled constriction, and the flow rate will not remain substantially constant with further increases in the internal water pressure within the conduit 34.

Referring back to FIGS. 5 A, 5B and 6B, it should be noted that as the pressure builds within the conduit 34, the inboard wall segment 24 underlying the inlet passageways 38 will be pressed firmly against the underside of the outboard wall segment 26. Thus, the inlet passageways 38 will restrict the size of the water flow passages into the inlet section 36 to the cross sectional area of each of the embossed inlet passageways. This restriction will have a small secondary effect on reducing the pressure of the water flowing from the conduit into the regulatory passageway 44, and will also function to form "strainers" which will assist in preventing particles carried by the water in the conduit that are large enough to potentially block the regulatory passageway from entering the inlet section 36. As previously noted, since there are multiple inlet passageways 38, should one or two such passageways become clogged and blocked, there will still remain another inlet passageway to insure an adequate water supply to feed the regulatory passageway. All of the described embodiments, the one depicted in FIGS. 5 A and 5B, the one depicted in FIG. 6A, and the one depicted in FIG. 6B, exhibit an advantageous feature regarding their outlet sections 46 and the respective reservoirs 48, 48" and 48'" and exit passageways 50, 50" and 50"'. For the first embodiment, when the irrigation tube 10 is in its uninflated, flat condition (see FIG. 7), the exit passageways 50 terminate under the marginal edge of the outboard wall segment 26 which essentially closes those passageways in the absence of water pressure. Once the irrigation tube 10 is inflated by pressurized water within the conduit 34, the flap 78, which is subjected to a tensile force as the outboard wall segment 26 begins to deform, will lift, thereby producing a slot-like outlet opening through which water can be discharged over the full length of the exit passageways 50.

Likewise, when there is no water pressure in the outlet reservoir 48" of the second and third embodiments, the exit slit 50", 50'" assumes its natural position and closes. Once the irrigation tube 10 is inflated by pressurized water within the conduit 34, the exit reservoir 48", 48'" is pressurized, and the sides of the slit open outward to discharge water.

Thus, the outlet sections 46 of the embodiments operate to restrict the entry of dirt and other foreign particles into the emitters 12 when the irrigation tube 10 is in the uninflated condition, such as might occur after a watering cycle has been completed and the irrigation tube is drained. The outlet sections also function to act as a barrier to the entry of roots into the emitters, since in the uninflated condition, the exits are essentially closed to the outside of the irrigation tube.

The first embodiment provides the further advantage of permitting a large outlet opening through which grit or particles previously flushed from the regulatory passageway 44 can pass, insuring that an ample outlet opening area will remain for water to be discharged from the irrigation tube 10 should any exit passageway 50 become blocked. From the foregoing description, it should be appreciated that the drip irrigation tube irrigation tube of the present invention provides a highly reliable and effective device which can be economically and easily formed using conventional plastic fabrication techniques. It employs the principles of a short path, variable orifice emitter in that pressure reduction is obtained by using a constricted passageway of relatively short length over which the requisite pressure drop occurs, yet provides a large flow area for particle flushing on initiation of an irrigation cycle, while still providing a highly reliable pressure compensation mechanism which insures that a substantially constant flow rate is maintained over the full range of normal working pressures. Moreover, the drip irrigation tube irrigation tube provides large inlet and outlet openings to insure that blocking or clogging of the emitters does not occur, and provides a flushing mechanism by which any particles trapped in the regulatory passageway can be flushed therefrom with each cycle of operation. When not in use, the exits are effectively sealed to prevent the intrusion of roots and the ingestion of grit and foreign particles which might form blockages in the system.

While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. For example, rather than the marginal walls having varied thicknesses, they could have the same thickness as the central wall, but have varied stiffness, such as could occur in a web made as a laminate. Thus, although the invention has been described in detail with reference only to the preferred embodiments, those having ordinary skill in the art will appreciate that various modifications can be made without departing from the invention. Accordingly, the invention is not intended to be limited, and is defined with reference to the following claims.

Claims

I claim:

1. An irrigation tube for supplying fluid from a fluid source to a plurality of irrigation locations at a substantially constant flow rate, the fluid source being pressurized between a prescribed minimum pressure and a prescribed maximum pressure, comprising: a longitudinally extending web having a first marginal wall and a second marginal wall on laterally opposing sides of a central wall, the central wall being generally laterally stiffer than the first marginal wall; wherein the web is rolled upon itself, with the first and second marginal walls substantially overlapping, to form a longitudinally extending conduit for receiving fluid from the fluid source; wherein the web defines one or more fluid outlets at each of the plurality of locations; wherein the overlapped first and second marginal walls define one or more regulatory passageways, each regulatory passageway putting the conduit in fluid communication with the fluid outlets at one or more of the plurality of locations; and wherein the regulatory passageway regulates the flow of fluid from the conduit to the outlets in response to the fluid pressure in the conduit.

2. The irrigation tube of claim 1, wherein the first marginal wall is inboard of the second marginal wall.

3. The irrigation tube irrigation tube of claim 2, wherein the second marginal wall includes recessed emission grooves that provide a cross-sectional shape for the regulatory passageway.

4. The irrigation tube of claim 1, wherein the first marginal wall is inboard of the second marginal wall, the second marginal wall being generally stiffer in lateral bending than the central wall.

5. The irrigation tube of claim 1, wherein the regulating passage is configured to cause a fluid flow rate from the conduit to the plurality of irrigation locations that is appropriate for drip irrigation.

6. The irrigation tube of claim 1, wherein the first marginal wall is bonded to the second marginal wall such that bonded portions of the first and second marginal walls define a perimeter of the regulating passageway.

7. The irrigation tube of claim 6, wherein the unbonded portions of the marginal walls have less resistance to deformation than the bonded portions.

8. The irrigation tube of claim 1, wherein the regulating passageway includes a relatively large central portion and laterally oppositely extending and generally converging smaller side portions.

9. The irrigation tube of claim 1, wherein the overlapped first and second marginal walls deform in response to fluid pressure within the conduit to varying the cross-sectional size of the regulating passageway.

10. The irrigation tube of claim 1, wherein the regulating passageway includes a relatively large central portion and laterally oppositely extending and generally converging smaller side portions, the variation of the regulating passageway's cross- sectional size closing off the side portions progressively toward the central portion as the pressure within the conduit is increased.

11. The irrigation tube of claim 1, wherein the tube has a generally flat cross-sectional shape when no pressure is present in the conduit and is inflated to a generally cylindrical shape when pressurized fluid from the fluid source is admitted into the conduit, the cross-sectional shape of the central wall portion being defined by a radius of curvature shorter than the radius of curvature of the overlapped marginal walls for fluid source pressures below the prescribed maximum pressure.

12. The irrigation tube of claim 1, wherein the regulating passageway includes a main passage that is sawblade-shaped.

13. The irrigation tube of claim 1, wherein: the first marginal wall is inboard of the second marginal wall, the second marginal wall being generally stiffer in lateral bending than the central wall. the second marginal wall includes recessed emission grooves that provide a cross- sectional shape for the regulatory passageway; the first marginal wall is bonded to the second marginal wall such that bonded portions of the first and second marginal walls define a perimeter of the regulating passageway, and such that the unbonded portions of the marginal walls have less resistance to deformation than the bonded portions; the overlapped first and second marginal walls deform in response to fluid pressure within the conduit, varying the cross-sectional size of the regulating passageway to cause a fluid flow rate from the conduit to the plurality of irrigation locations that is appropriate for drip irrigation; the regulating passageway includes a relatively large central portion and laterally oppositely extending and generally converging smaller side portions, the variation of the regulating passageway's cross-sectional size closing off the side portions progressively toward the central portion as the pressure within the conduit is increased; and the tube has a generally flat cross-sectional shape when no pressure is present in the conduit and is inflated to a generally cylindrical shape when pressurized fluid from the fluid source is admitted into the conduit, the cross-sectional shape of the central wall portion being defined by a radius of curvature shorter than the radius of curvature of the overlapped marginal walls for fluid source pressures below the prescribed maximum pressure.

14. An irrigation device for supplying fluid from a fluid source to a plurality of irrigation locations at a substantially constant flow rate, the fluid source being pressurized between a prescribed niinimum pressure and a prescribed maximum pressure, comprising: a structure defining an internal chamber adapted for connection to the fluid source to receive pressurized fluid, the structure including a composite wall having an inboard wall segment and an overlapping outboard wall segment; wherein the inboard and outboard wall segments cooperatively define a regulating passageway therebetween, the inboard and outboard wall segments being joined together along opposite sides of the regulating passageway; wherein one of the inboard and outboard wall segments is relatively stiffer in bending than the other; wherein the regulating passageway is configured to place the internal chamber in fluid communication with one or more of the plurality of irrigation locations; and wherein the composite wall deforms in response to fluid pressure within the internal chamber to put the inboard wall segment under compression and to put the outboard wall segment under tension, thereby varying the cross-sectional size of the regulating passageway to maintain a substantially constant fluid flow rate from the internal chamber to the plurality of irrigation locations in response to fluid pressure variations between the prescribed nrinimum and maximum pressures.

15. The irrigation device of claim 14, wherein at least one of the wall segments includes recessed grooves that provide a cross-sectional shape for the regulatory passageway.

16. The irrigation device of claim 14, wherein: the structure is an elongated flexible tube; the internal chamber is a conduit of the tube; and the tube includes a first circumferential wall portion of relatively small stiffness interconnected with the composite wall, the composite wall being a second circumferential wall portion that has relatively greater stiffness than the first circumferential wall portion; and

17. The irrigation device of claim 16, wherein both the first circumferential wall portion and the outboard wall segment are stiffer in bending than the inboard wall segment.

18. The irrigation device of claim 16, wherein the regulating passage is configured to cause a fluid flow rate from the internal chamber to the plurality of irrigation locations that is appropriate for drip irrigation.

19. The irrigation device of claim 16, wherein the tube is formed of thermoplastic sheet material.

20. The irrigation device of claim 14, wherein: the structure is an irrigation tube comprising a longitudinally extending web having a first marginal wall and a second marginal wall on laterally opposing sides of a central wall, the central wall being generally stiffer in lateral bending than the first marginal wall; the web is rolled upon itself, with the first and second marginal walls substantially overlapping, to form the internal chamber as a longitudinally extending conduit; and wherein the first and second marginal walls respectively form the inboard and outboard wall segments.

21. The irrigation device of claim 20, wherein the second marginal wall is stiffer in bending than the central wall.

22. The irrigation device of claim 20, wherein the regulating passage is configured to cause a fluid flow rate from the internal chamber to the plurality of irrigation locations that is appropriate for drip irrigation.

23. The irrigation device of claim 20, wherein the first marginal wall is bonded to the second marginal wall such that bonded portions of the first and second marginal walls define a perimeter of the regulating passageway.

24. The irrigation device of claim 23, wherein the unbonded portions of the marginal walls have less resistance to deformation than the bonded portions.

25. The irrigation device of claim 20, wherein the regulating passageway includes a relatively large central portion and laterally oppositely extending and generally converging smaller side portions.

26. The irrigation device of claim 25, wherein the variation of the regulating passageway's cross-sectional size closes off the side portions progressively toward the central portion as the pressure within the conduit is increased.

27. The irrigation device of claim 20, wherein the tube has a generally flat cross-sectional shape when no pressure is present in the conduit and is inflated to a generally cylindrical shape when pressurized fluid from the fluid source is admitted into the internal chamber, the cross-sectional shape of the central wall portion being defined by a radius of curvature shorter than the radius of curvature of the overlapped side wall portions for fluid source pressures below the prescribed maximum pressure.

28. A drip irrigation tube adapted to be coupled to a source of pressurized water for supplying irrigating water at a substantially constant flow rate over a range of source pressures between a preselected minimum and maximum to a plurality of discrete locations spaced longitudinally along the irrigation tube, said drip irrigation tube comprising: an elongated web of predetermined width, said web having a central wall portion of relatively intermediate thickness, and a pair of laterally spaced marginal wall portions, extending longitudinally along the side edge portions of said web, one of said marginal wall portions being of relatively greater thickness and the other of said marginal wall portions being of relatively lesser thickness, said web being rolled upon itself with said relatively thick marginal wall portions in substantially overlapped confronting relation with each other to form an elongated tube having an inside and an outside and defining an internal conduit for receiving water under pressure from the source; a plurality of discrete emitter elements formed at spaced longitudinal locations along said tube, each of said emitter elements being formed by a recessed groove in one of said marginal wall portions and disposed to form passageways for communicating water from said internal conduit to said outside of said tube between said overlapped confronting marginal wall portions; means bonding said overlapped marginal wall portions to each other around said groove such that unbonded portions including said groove define an inlet passageway section, a regulating passageway section and an outlet passageway section, the passageways of said inlet and said outlet sections each having a cross-sectional size substantially larger than the cross-sectional size of the passageway of said regulating section; said passageway of said regulating section extending longitudinally along said web and being deformable to reduce its cross-sectional size in response to an increase of water pressure within said internal conduit.

29. A drip irrigation device adapted to be coupled to a source of pressurized water for supplying irrigating water at a substantially constant flow rate over a range of source pressures between a predetermined minimum and maximum pressure, said drip irrigation device comprising: a housing structure defining an internal pressure chamber adapted for connection to the source for receiving water under pressure, said housing structure including first and second interconnected wall portions having substantially different resistance to deformation in response to the pressure of water within said pressure chamber; said second wall portion including inboard and outboard overlapping wall segments cooperatively defining a regulating passageway therebetween, said inboard wall segment being relatively thinner than said outboard wall segment, said inboard and outboard wall segments being joined together along opposite sides of said regulating passageway, said inboard and outboard wall segments further defining inlet and outlet ports on opposite sides of said regulating passageway for communicating said regulating passageway respectively with said pressure chamber and with the exterior of said housing structure; said second wall portion being deformable in response to water pressure within said pressure chamber to place said inboard wall segment under compression and to place said outboard wall segment under tension and thereby vary the cross sectional size of said regulating passageway to maintain a substantially constant water flow rate discharge through said outlet portion response to water pressure variations between the predetermined ╧Çiinimum and maximum pressures.

30. A drip irrigation tube for coupling to a source of pressurized water to supply irrigation water at a substantially constant flow rate over a range of source pressures between a predetermined minimum and maximum pressure to a plurality of discrete locations spaced longitudinally along the tube, said drip irrigation tube comprising: an elongated flexible tube defining an internal pressure conduit adapted for connection to the source for receiving water under pressure, said tube including a first circumferential wall portion of relatively small stiffness interconnected with a second circumferential wall portion of relatively greater stiffness; said second wall portion including inboard and outboard overlapping wall segments cooperatively defming a plurality of longitudinally spaced discrete regulating passageways therebetween, said inboard and outboard wall segments being joined together along opposite sides of each of said regulation passageways, said inboard and outboard wall segments further defining a plurality of inlet and outlet openings on opposite sides of said regulating passageways respectively with said pressure conduit and with the exterior of said tube, said outboard wall segment being of relatively greater stiffness than said inboard wall segment; said second wall portion being deformable in response to water pressure within said pressure conduit to place said inboard wall segment under compression and to place said outboard wall segment under tension and thereby vary the cross sectional size of said regulation passageways to maintain a substantially constant water flow rate discharge through each of said outlet openings in response to water pressure variations between said predetermined minimum and maximum pressures.