Self-cleaning Emitter

Abstract

Formed within an emitter body is an elongated channel extending between a fluid inlet port and a fluid discharge port. The cross-sectional area of the channel is small in order to limit the fluid flow to a low level. To obviate clogging by sand particles, and the like, each channel has located transversely therein at least two spaced-apart resilient diaphragms each provided with a central orifice capable of enlarging as a particle lodges in the orifice and causes a pressure differential between the two opposite surfaces of the diaphragm. As the orifice expands, the particle is impelled through the orifice, thereby unclogging the orifice. This process is repeated as the particle proceeds through the emitter, the particle finally emerging from the emitter's discharge port onto the adjacent ground surface.

Description

This invention relates in general to apparatus intended primarily for dispensing irrigation water and dissolved substances, such as fertilizers, pesticides and soil conditioners, and more particularly to apparatus that is capable of dispensing, at very low flow rates, water or other fluids carrying large amounts of suspended solids without the need for a high degree of filtration and without the need for variations in system pressure to effect the self-cleaning action.

Some irrigation practices call for the application of water, and sometimes dissolved substances beneficial to plants, at very low flow rates over long periods of time or at very frequent intervals. Representative flow rates of the elements of the system that dispense water to the plants are on the order of one gallon per hour. In any field irrigation system, basic hydraulic considerations such as pressure loss and changes in elevation dictate that operating pressures will be at least several pounds per square inch (psi). It follows that the water dispensing units, or emitters, must have very small flow passages in order to limit flow to the desired low levels.

Irrigation water inherently contains large amounts of sand, silt, sediment, debris, and other suspended solids because it is commonly taken from ponds, streams, ditches and wells without the expensive treatment and purification necessary for potable water. Consequently, clogging of small flow passages is a constant problem in low-flow systems. Field experience has shown that even water that has been purified and filtered for residential use often cannot be used in low-flow irrigation systems without further filtration.

The need for such extremely clean irrigation water is an obvious disadvantage, since it increases initial system costs for filtration equipment, increases operational costs due to filter maintenance and repair, and reduces overall system reliability because emitter clogging will occur if filter failure occurs or if suspended solids are introduced into the system downstream of the filters.

In some instances, irrigation dripper units have endeavored to overcome the problem by incorporating a filter element within the emitter itself. Exemplary is the disclosure in I. Blass et al. U.S. Pat. No. 3,420,064 dated Jan. 7, 1969.

In other instances, attempts have been made to obviate the stringent water filtration requirements by using so-called "self-cleaning" emitters. Again, field experience has shown that the desired degree of improvement has not heretofore been achieved. The term "self-cleaning" ordinarily pertains to a temporary enlargement of the flow passage in response to a periodic change in system pressure to permit flushing of accumulated solid particles. The change in system pressure may be either an increase or a decrease from the normal operating level. In any case, flushing of the emitter occurs only at predetermined intervals and is necessarily accompanied by a large discharge flow rate. Two major disadvantages of this technique are readily apparent. First, the emitter can, and often does, become clogged immediately after flushing, seriously restricting water delivery until the next flushing cycle. Second, the high discharge rate necessary for adequate flushing can become an appreciable part of the overall water delivery rate, thus influencing the minimum attainable flow rate for a given emitter design.

It is therefore an object of the invention to provide an emitter which is self-cleaning, yet does not entail periodically increasing or decreasing the normal operating level of the system pressure to effect flushing.

It is another object of the invention to provide a self-cleaning emitter for a "drip" type irrigation system, or the like, which obviates any need for filtration equipment.

It is yet another object of the invention to provide an emitter which is self-contained.

It is a further object of the invention to provide a self-cleaning emitter which is capable of delivering a continuous, uninterrupted flow of fluid at a constant rate and for a very extended period of time without replacement or repair.

It is a still further object of the invention to provide a self-cleaning emitter which is relatively inexpensive and compact, yet is reliable, durable and long-lived, and has no moving parts to get out of order.

It is yet another object of the invention to provide a self-cleaning emitter which is versatile in that it can readily be adjusted to provide a desired flow rate.

It is an additional object of the invention to provide a self-cleaning emitter which is adaptable for use in all presently known controlled moisture irrigation systems.

Another object of the invention is to provide a generally improved automatically self-cleaning emitter.

Other objects, together with the foregoing, are attained in the embodiments described in the following description and illustrated in the accompanying drawings in which:

FIG. 1 is a diagrammatic view of a typical irrigation system showing emitters located on branch lines extending laterally from a main line leading from a pump;

FIG. 2 is a median, longitudinal, sectional view of an idealized form of emitter constructed pursuant to the concept herein and with two diaphragms;

FIG. 3 is a view comparable to FIG. 2, but showing a linear form of emitter with a plurality of diaphragms;

FIG. 4 is a fragmentary isometric view, to an enlarged scale, of a modified form of diaphragm, a portion of the figure being broken away to reveal structural details;

FIG. 5 is a fragmentary median, longitudinal sectional view of the diaphragm structure shown in FIG. 4;

FIG. 6 is a fragmentary sectional view, to an enlarged scale, illustrating a variant form of emitter connected to a main line by a modified type of connector;

FIG. 7 is a fragmentary sectional view, to an enlarged scale, of the variant form of emitter shown in FIG. 6, the section being taken on the three planes indicated by the compound line 7--7 in FIG. 6; and,

FIG. 8 is a fragmentary sectional view of another variant form of emitter of the fixed orifice with reed gate type of flow passage.

While the self-cleaning emitter of the invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodiments have been made, tested and used, and all have performed in an eminently satisfactory manner.

A system of irrigation, characterized by the term "dripper" or "drip," has come into use in recent years both in field, or commercial, crop applications and in domestic, or garden, environments. The dripper system finds its major utilization in connection with high value crops and permanent plantings, such as in vineyards and in orchards of almonds, walnuts, pecans, pistachio nuts, prunes, and the like.

The system uniquely lends itself to hillside installations and to use on rocky terrain since the small amount of water used does not create a run-off and since the small volume of water can readily be delivered by flexible hoses, or tubing, over any kind of terrain and dispensed at the base of a tree planted in any suitable pocket of soil. No ground working, or tillage, is necessary and weed-growth can be kept to a minimum. Not only is less water required, but water containing a higher than usually acceptable mineral content can be used. As a further advantage, liquid fertilizers, together with other liquid additives, can readily be applied by introducing them into the stream at suitable locations in the manifold, along the main line or in the lateral lines.

As appears most clearly in FIG. 1, a supply of irrigation water from a suitable source, such as a well, pond, ditch, canal or other waterway, enters a pump 12 from which the water is discharged under pressure to a manifold 13 including a main line 14 connected by fittings 15 to lateral lines 16, 17, 18, 19, and to additional laterals, not shown, leading from the main line extension 20.

The tubing forming the main line and lateral lines is frequently of polyvinyl chloride (PVC) material, or of polyethylene, or the like; and the hydraulic parameters of the system, including the water requirements of the trees determine the layout of the particular installation.

The lateral lines are ordinarily laid down parallel to and spaced a few inches from the bases of the trees forming a tree row. Adjacent each tree, an emitter 21 is connected to the lateral line and serves to dispense to the tree a small but continuous supply of irrigation water. A typical quantity might be on the order of one gallon of water per hour per tree. Evaporation losses are minimal since the water promptly percolates downwardly to the tree roots by gravity and by capillary action.

As previously noted, clogging of the small flow passages through the emitter has heretofore been a constant problem, owing to the presence of sand and other suspended solids in the usual irrigation water supply.

In order automatically to dislodge such particles and flush them away as soon as clogging occurs, we provide a series arrangement of flow controlling elements within the emitter itself.

Each flow control element is so constructed that the area of the flow passage therethrough is regulated by the pressure differential (dp) existing across the element.

The response of the element to an increase in pressure difference (dp) is such that the cross-sectional area of the flow passage is also increased.

If the flow passage in the flow control element should become partially or totally blocked by solid material entrained in the fluid, an increase in the dp across the element will produce an enlargement of the flow passage and thus allow the obstruction to pass through.

The individual flow control elements can take a wide variety of forms so long as the necessary function of responding to a change in dp across the element with a corresponding change in flow passage area is accomplished.

It is important that the individual flow control elements be arranged in series, and that there be at least two of such elements, in series. The significance of the series arrangement is explained as follows, with particular reference to the stylized form of emitter 23 shown in FIG. 2 wherein the direction of fluid flow is indicated by the arrows 24.

A housing 25, or body, includes an inlet port 26 and a discharge port 27 connected by a channel 28, or passageway, having interposed therein an upstream diaphragm 29, or membrane, or partition, and a downstream diaphragm 30. The membranes are of an elastomeric material, such as natural or synthetic rubber, on the order of 1/64 inch in thickness. The peripheries of the membranes 29 and 30 shown in FIG. 2 are suitably mounted on the walls of the passageway 28, as by an adhesive; and formed in the center of each of the membranes 29 and 30 is an orifice 31 and 32, respectively, having a diameter on the order of 1/32 inch. Being of resilient, or flexible material, the membranes are capable of yielding, within limits, under the force exerted by a pressure differential (dp) acting on the opposite faces of the membranes.

Thus, the walls defining the orifices 31 and 32 can stretch under the influence of a dp and thereby allow the orifices to become larger. The greater the dp, the larger the orifice bcomes, within elastic limits.

The areas of the inlet port 26 and the discharge port 27 are fixed in size and are large enough to offer negligible restriction to fluid flow. Thus, with the application of fluid pressure at the inlet port 26 of a given amount, for example 10 pounds per square inch, the rate of flow through the passageway 28 and out the discharge port 27 to the atmosphere is determined by the pressure difference (dp) across the orifice 31 and across the orifice 32 and by the respective areas of the orifices. Where the areas of the two orifices 31 and 32 are identical, the dp across each orifice and the corresponding flow rates through each orifice are the same, bearing in mind that the same quantity of fluid must pass through both orifices. Thus, in the example given herein, a dp of 5 psi would normally exist across diaphragm 29, and a dp of 5 psi would also normally obtain across diaphragm 30, for a total pressure drop of 10 psi.

If, under steady flow conditions, a solid particle should become lodged in one of the orifices, for example, the upstream orifice 31, the flow area of that orifice will be reduced. The reduction in flow area of the orifice 31 will cause a corresponding reduction in the quantity of flow through the upstream orifice 31 into the central chamber 33 (defined at opposite ends by the two membranes 29 and 30) thence through the downstream orifice 32 and out the discharge port 27 to the atmosphere.

Owing to the resultant reduced volume of flow from the chamber 33 through the unobstructed downstream orifice 32 to the atmosphere, the pressure difference across the downstream membrane 30 is reduced, from 5 psi to 2 psi, for example.

However, since the total pressure difference (10 psi) between the inlet port 26 and the discharge port 27 (at atmospheric pressure) remains the same, the pressure differential across the blocked upstream orifice 31 must necessarily increase (from 5 psi to 8 psi, for example). The increase in pressure difference across the blocked orifice 31 will cause the orifice area to increase in size and allow the obstruction to pass through. When the obstruction has passed, the orifice 31 will return to its original size and steady flow will be resumed.

If the obstruction passing through the upstream orifice 31, in the manner just described, then lodges against the downstream orifice 32, the following sequence of events takes place. Owing to the clogging of the downstream orifice 32, flow through the orifice 32 is reduced, the backing up of the flow causing a corresponding reduction in flow through the unobstructed upstream orifice 31. In this situation, the pressure difference across the upstream membrane 29 is reduced, from 5 psi to 2 psi, for example, which means that the effective pressure in the chamber 33 necessarily rises from the normal 5 psi to 8 psi, in this example. This, in turn, increases the pressure differential across the clogged orifice 32 from 5 psi to 8 psi, thereby causing the orifice area 32 to stretch open and release the obstruction, which thereupon passes through the discharge port 27 and onto the subjacent ground surface. When the obstruction thus passes out of the emitter, the orifice 32 returns to its original size and normal steady flow conditions are resumed.

It will be noted that the automatic, self-cleaning action described above is accomplished with no superimposed change in inlet pressure or outlet pressure. If the fluid is a liquid rather than a gas, clearing of a clogged orifice is substantially instantaneous, with a negligable effect on flow rate.

The use of more than two flow control elements in an assembly does not change the basic nature of the invention. If more flow control elements are used, the total pressure difference between inlet and outlet is divided into more and smaller increments. The procedure by which a given orifice is cleared remains the same: the pressure difference across the blocked orifice rises, while that across each of the other orifices drops accordingly. In practice it is desirable to use several flow control elements all with flow passages the same or nearly the same size. For a given flow rate and total pressure difference, the use of a large number of flow control elements allows a larger flow area in each element and a greater margin between the pressure difference across a clean element under normal conditions and the maximum potential pressure difference available to relieve clogging, with the net result that larger solid particles can be tolerated. By the use of elements with the same flow areas, fabrication of the assemblies is simplified.

Having described the construction and operation of the basic form of emitter shown in FIG. 2, reference is now had to the physical embodiment illustrated in FIG. 3, a form which has operated most satisfactorily under rigorous field conditions. In this embodiment, generally designated by the reference numeral 36, the emitter body 37, or housing, includes a tube 38, of PVC material, for example, provided with upstream threads 39, for attachment to a lateral line, and with downstream threads 40 engaged by an interiorly threaded cap 41. Fluid flow is in the direction indicated by the arrow 42, and in the form of emitter illustrated in FIG. 3, flow is in a linear path through an axially disposed channel 43 extending from an inlet port 44 to a discharge port 45 through which the fluid emerges into the atmosphere.

Arranged transversely to the linear flow channel 43 is a plurality of identical circular diaphragms 46 each formed with a central orifice 47. As before, the material from which the diaphragms are made is of an elastomeric nature so that the orifices 47 can enlarge to effect unclogging in the manner previously described in detail in connection with the FIG. 2 form of device. A plurality of annular washers 48, or spacers, interposed between the diaphragms is firmly clamped by taking up on the closure cap 41 which includes an annular shoulder surface 49 bearing against the adjacent one of the washers 48. The alternate washer and diaphragm arrangement is clamped against the shoulder 50 on the other end of the emitter body.

A variant form of diaphragm construction is shown in FIGS. 4 and 5 wherein a pair of annular washers 51 confines, as before, an elastomeric diaphragm 52 with a central orifice 53. In the FIG. 4 and 5 diaphragm arrangement, however, a circular back-up plate 54 with a central orifice 56 is located in face to face engagement with the downstream face of the elastomeric diaphragm 52.

The back-up plate 54 is also inclusive of a star-shaped array of equally spaced radial slits 57 emanating from the central orifice 56 to define a plurality of triangular sectors 58 having their apices at the central orifice 56. The material from which the back-up plate is fabricated is a suitable "plastic" which is less resilient than the elastomeric diaphragm material but which, nevertheless, is capable of being flexed to some extent, particularly in the apex portions 59, as appears most clearly in FIG. 5.

Under normal, steady-flow conditions, both the diaphragm 52 and the back-up plate 54 are substantially planar. When an obstruction lodges in the central orifice 53, however, the sudden increase in differential pressure, stretches the diaphragm orifice 53 and flexes the apices 59 of the triangular sectors, as shown, thereby allowing the obstruction to pass through. After the obstruction clears the orifices, the diaphragm 52 and the back-up plate 54 return to planar condition, the orifices contract in the manner of an optical iris and normal flow is resumed. The close face to face engagement between the diaphragm 52 and the plate 54 prevents any water flow through the slits 57, and the greater strength of the back-up plate affords a long life to the diaphragm while not detracting from the self-cleaning capabilities thereof.

FIGS. 6 and 7 illustrate a variant form of emitter, generally designated by the reference numeral 61. This type is circular or, more properly, disc-like and includes an upper half 77 and a lower half 78 with a plurality of interior recesses and channels which can be arranged in face to face engagement in any desired angular relation so as to provide a sinuous flow passageway which can be adjusted so as to provide any desired length, and thereby regulate the amount of fluid emitted at each station.

As will be appreciated, a comparable labyrinthine path of adjustable length can also be attained by using a facing pair of linear members with interior passageways arranged in a relationship of mirror symmetry. This linear type, not illustrated, would be analogous in structure to a linear slide rule, whereas the wafer, or biscuit form of emitter 61 shown in FIGS. 6 and 7 resembles a circular slide rule.

As appears most clearly in FIG. 6, the tubing 63 connecting the emitter 61 to the feed line 64 requires no cement, or adhesive of any kind in effecting a secure junction to the feed line 64. As previously indicated, polyvinyl chloride (PVC) is widely used as pipe material and in such installations, tubing 63 can be of vinyl material, for example, which can be joined to the PVC line 64 by drilling a hole in the line 64, inserting the end of the tubing 63 and cementing it in place.

Not all plastic pipe and hose materials are cementable, however, particularly polyethylene.

In such cases the construction shown in FIG. 6 is of especial utility. A metal eyelet 66 of bell-shaped configuration, including a neck 67 and flared mouth 68, is previously inserted into the end 69 of the tubing 63 which is to be joined to the main fluid line 64. Then, the end of the tubing containing the eyelet 66 is inserted inwardly through an opening 71 previously drilled in the wall of the line 64.

In order to expedite the insertion of the enlarged portion of the tube end (the extent of the enlargement being somewhat exaggerated in FIG. 6 to illustrate the point more clearly) an instrument such as a pair of pliers (not shown) with the nose end of the pliers provided with a split hollow cone, each half in facing relation, can be utilized to advantage. The apex end of the split cone is inserted in to the previously drilled hole 71 and the plier handles squeezed together so as to expand the opening 71 far enough so that the bulb-like tube end can be inserted through the hollow cone and into the interior of the feed pipe as shown. Then, the pliers are removed and the inherent resilience or elasticity of the pipe material causes the walls of the opening 71 to close into tight encompassing relation with respect to the tubing 63, thereby preventing leakage; and the presence of the eyelet prevents the tubing from pulling out of position.

The opposite, or outlet, end of the tubing is inserted in an inlet opening 73 in the emitter 61 and is connected thereto in water tight relation, as by a suitable bonding agent.

Thus, as can be seen, the tubing connection illustrated in FIG. 6 affords a secure, quickly installed connection which serves to receive a portion 74 of the stream 76 in the feed line and divert it to the emitter.

The diverted portion 74 of the fluid passes through the tubing 63 and enters the top half 77 of the biscuit-shaped emitter 61 through the inlet port 73 formed in the periphery of the emitter.

The emitter 61 includes a circular in plan upper half 77 and a circular in plan lower half 78 separated by a circular membrane 79, or diaphragm, of elastomeric material.

The top half 77, in turn, comprises a perforate plate 81, including a single axial bore 82 connected to the inlet port 73 and a plurality of pairs of axial angularly and radially displaced openings 83 and 84 of any suitable number. The top half 77 also includes a substantially imperforate cover plate 85 mounted on top of the perforate portion 81.

A plurality of shallow channels 86 connects the tops of the respective pairs of openings 83a to 84a, 83b to 84b etc. Thus, with the cover plate 85 mounted as shown most clearly in FIG. 7, the fluid in opening 83b can flow through channel 86b into opening 84b. In similar fashion, as shown in FIG. 6, fluid in opening 83a can flow through the channel 86a into opening 84a.

The bottom half 78 of the wafer 61 is provided with a perforate plate 87 having mounted thereon a substantially imperforate cover plate 88 supported, in the case shown, by the ground 89. The perforate plate 87 has formed therein a single axial bore 91 connected to an outlet port 92 open to the atmosphere. Similar to the arrangement in the top half, the lower half also has formed in the lower perforate plate 87 a plurality of pairs of radially and angularly displaced openings 93 and 94, in the same number and size as the openings 83 and 84 in the upper perforate plate 81. The lower ends of the paired openings are joined by a shallow channel 96 (see FIG. 7). Thus, fluid can flow, for example, from opening 94b through channel 96b into opening 93b. So also, channel 96a, shown in broken line in FIG. 6, connects an opening 94a (below and in register with the bore 82) to an opening 93a (below and in register with the opening 83a).

A plurality of small central orifices 97 in the elastic membrane 79 permits a small quantity of fluid to flow, in the directions indicated by the flow arrows 98 from one opening to another opening in register therewith.

Thus, as can be seen in FIGS. 6 and 7, the fluid entering the inlet port 73 flows into the bore 82 in the upper plate 81 thence downwardly through the orifice 97a in the diaphragm 79 into the subjacent opening 94a in the bottom pate 87, thence across the lower channel 96a to the lower opening 93a, thence upwardly through the orifice 97b into the upper opening 83a and across the upper channel 86a to the upper opening 84a.

From the upper opening 84a, the flow is downwardly through the orifice 97c into the lower chamber 94b, across channel 96b into lower chamber 93b, thence upwardly through orifice 97d into upper opening 83b, across channel 86b into upper opening 84b, down through orifice 97e into single lower bore 91 from which the fluid emerges through outlet port 92 into the atmosphere.

By arranging the upper and lower portions of the wafer in various angular relationships, the length of the tortuous path described by the water can be lengthened or shortened.

During the early stages of tree growth, for example, only a small quantity of fluid flow is desired. In this situation, the upper and lower halves of the wafer are positioned so that the angular displacement between the inlet port 73 and the outlet port 92 is considerable, so that the path is long and the orifices are many, the resultant hydraulic friction serving to reduce fluid flow.

On the other hand, where it is necessary to increase the amount of moisture made available to the recipient tree, the hydraulic resistance is decreased by arranging the upper and lower halves of the emitter in such a manner that the angular displacement between the entry port 73 and the discharge port 92 is small. This decreases the number of orifices and the length of the hydraulic path traversed by the fluid, with a decrease in friction and corresponding increase in flow.

In the event the single axial bore 82 in the upper plate 81 is brought into register with the single axial bore 91 in the lower plate 87, fluid from the entry port 73 passes into the bore 82 thence through the diaphragm orifice 97a into the bore 91 and directly out through the discharge port 92 onto the ground. This type of arrangement is incompatible, however, with the theory of the present invention, as set forth in connection with FIG. 2, wherein it was explained that at least two diaphragms (and their corresponding flow passages) are required in order to give the desired full unclogging effect.

Thus, the angular displacement between the two twin halves should be such that the hydraulic path between the inlet port 73 and the outlet port 92 provides at least two diaphragms.

Although flow is not ordinarily completely cut off at individual emitters, this capability may sometimes be desired, for example, where a tree dies and replacement is not going to occur for a considerable period of time. In this event, the two halves can be angularly arranged so that the upper inlet bore 82 is blanked off against a portion of the underlying elastomeric diaphragm which is not provided with an orifice and which is underlain by one of the solid web portions of the lower plate.

In the wafer type of emitter 61 illustrated in FIGS. 6 and 7 a plurality of bolt and nut type fasteners 99 disposed in registering apertures 100 in the two plates, serve as adjustable clamping members. Other types of clamping means such as circular, radially slotted and centrally bowed springs (not shown) could be utilized to advantage. With this type of bowed spring, a central bolt extending through the opening 102 in the emitter 61 could be used in conjunction with a butterfly nut, for example, to afford quick clamping and unclamping of the two paired halves of the emitter in order readily to adjust the length of the hydraulic path.

It will be recognized that means other than orificed resilient diaphragms can be utilized to perform the two functions of regulating the extent of fluid flow and of purging the flow passages by automatic or self variance of the cross-sectional area of the flow passages in response to pressure buildup.

Thus, for example, an elastomeric tube having a constricted neck portion caused by an encircling ring of resilient material, such as a rubber band or a toroidal tension spring, could serve both to control the extent of fluid flow and to expand against the radial inward urgency of the encircling ring so as to unclog the throat in the event particles of debris become lodged in the constricted throat area.

Other variations could be in the nature of modified forms of spring-loaded poppet or ball check valves, expansible Venturi-shaped constrictions, and leaf spring or laterally oriented flexible reed members covering the downstream side of a fixed orifice and yielding as differential pressure exceeds a predetermined amount so as to expel the obstruction lodged against the flow passage.

The fixed orifice with flexible reed gate type of variable flow passage is illustrated in FIG. 8 in which a transverse disc 111 of rigid material is interposed in a channel 112 traversing the emitter body 113. Covering the fixed orifice 114 is a flexible transverse reed 115 yieldable, as shown in broken line, to expel a debris particle 116.

It can therefore be seen that we have provided an emitter which is not only economical, efficient and self-cleaning but which is also flexible in that it can be constructed and operated so as to meet a wide variety of fluid flow requirements and environmental conditions.

Claims

What is claimed is:

1. A self-cleaning emitter comprising:

a. a body having an inlet port and an outlet port;

b. a channel in said body connecting said inlet port and said outlet port for the flow of fluid therebetween; and,

c. at least two pressure responsive means interposed in said channel in spaced relation for regulating the extent of fluid flow, each of said pressure responsive means including a flow passage having an area capable of varying in size in dependence upon the pressure differential across said flow passage, said flow passage comprising an orifice defined by resilient walls capable of expanding in response to a pressure differential across said orifice in excess of a predetermined amount to expel particles lodged against the upstream side of said orifice and creating said excess.

2. A self-cleaning emitter as in claim 1 in which said channel is substantially linear between said inlet port and said discharge port.

3. A self-cleaning emitter as in claim 1 in which said channel is sinuous between said inlet port and said discharge port.

4. A self-cleaning emitter comprising:

a. a body having an inlet port and an outlet port;

b. a channel in said body connecting said inlet port and said outlet port for the flow of fluid therebetween; and,

c. at least two pressure responsive means interposed in said channel in spaced relation for regulating the extent of fluid flow, each of said pressure responsive means including a flow passage having an area capable of varying in size in dependence upon the pressure differential across said flow passage,

each of said pressure responsive means being an elastomeric diaphragm with a central orifice, said diaphragm being located transversely in said flow channel and deformed by a predetermined differential fluid pressure to enlarge said orifice to an extent sufficient to expel particles clogging said orifice and thereby causing said pressure.

5. A self-cleaning emitter as in claim 4 further including a flexible backing member in engagement with the downstream face of said diaphragm, said backing member including a central aperture registering with said orifice and being radially slit to define an array of individual sectors flexibly yielding under said differential pressure in conjunction with the deformation of said diaphragm.

6. A self-cleaning emitter comprising:

a. a body having an inlet port and an outlet port;

b. a channel in said body connecting said inlet port and said outlet port for the flow of fluid therebetween; and,

c. at least two pressure responsive means interposed in said channel in spaced relation for regulating the extent of fluid flow, each of said pressure responsive means including a flow passage having an area capable of varying in size in dependence upon the pressure differential across said flow passage,

said body comprising a circular in plan disc including two substantially similar halves on each side of a plane parallel to the planar surfaces of said disc, each of said halves including a plurality of openings and cross-connecting passageways defining said channel and being capable of conducting fluid from said inlet port in one of said halves to said outlet port in one of said halves with said openings in each of said halves being in at least partial register; and wherein said pressure responsive means includes a diaphragm located between said halves on said plane separating said halves, said diaphragm including a plurality of orifices formed therein in registry with said openings in said disc halves.

7. A self-cleaning emitter as in claim 6 wherein said openings and said cross-connecting passageways in each of said halves are so arranged as to vary the total resistance to fluid flow between said inlet port and said discharge port in dependence upon the relative angular position between said halves.

8. A self-cleaning emitter comprising:

a. a body having an inlet port and an outlet port;

b. a channel in said body connecting said inlet port and said outlet port for the flow of fluid therebetween in response to a fixed over all pressure difference between said inlet port and said outlet port;

c. at least two substantially similar pressure responsive means interposed in said channel in spaced relation for regulating the extent of fluid flow, each of said pressure responsive means including a flow passage having an area establishing a predetermined pressure differential across said passage, each of said predetermined pressure differentials being substantially similar to the other during normal flow and the sum of all of said predetermined pressure differentials being equal to said fixed over all pressure difference between said inlet port and said outlet port,

each of said areas being variable in size in dependence upon the pressure drop across the respective flow passage to enable said flow passage temporarily to enlarge in order to pass particulate material on the upstream side thereof creating a temporary pressure drop in excess of said predetermined pressure differential.

9. A self-cleaning emitter as in claim 8 in which each of said pressure responsive means is a resilient diaphram having an orifice therein, said diaphragm being located transversely in said flow channel and deformable by said temporary excessive pressure drop to a size adequate to expel particles clogging said orifice and creating said temporary excessive pressure drop.

10. A self-cleaning emitter as in claim 8 in which said flow passage comprises a fixed opening, and a member biased against and at least partially covering the downstream side of said opening, the urgency of said member being capable of being overcome by a predetermined supervening force resulting from said temporary excessive pressure difference across said flow passage and thereby opening said member to expel a particle temporarily lodged on the upstream side of said opening.