CA1301813C - Irrigation system and method - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An irrigation system and method of positioning an irrigation system is disclosed. The method involves providing a plurality of lengths of porous pipe each having inlet and outlet ends with the porosity of the pipe lengths gradually and controllably increasing from the inlet ends to the outlet ends.
The inlet ends of some of the pipe lengths are connected to a first header manifold, and the inlet ends of the remainder of the pipe lengths are connected to a second header manifold, and the first and second header manifolds are then connected to a source of water. In a preferred arrangement, the first and second header manifolds are positioned a substantial distance apart, with the porous pipe lengths connected to the first header mani-fold extending toward the second header manifold and with the porous pipe lengths connected to the second header manifold extending toward the first header manifold. With this irrigation arrangement, an equal amount of water may be provided throughout the irrigated area without the use of extensive pump and manifold systems which in large fields are prohibitively expensive.

Description

IRRIGATION SYSTEM AND METHOD

This invention relates to an irrigation system and related method which provides an equal amount of water throughout the irrigated area without the use of extensive pump and manifold s~stems which in large fields are prohibitively expensive.

Background Art As population steadily increases, water becomes a more important and increasingly scarcer and more expensive resource. Agriculture is one of the most im-portant uses of surface water. It is necessary to develop more efficient systems for delivering water to plants. Above ground irrigating systems have employed flooding or sprinkler systems. Though these systems are simple, surface watering tends to be wasteful since water that is not absorbed quickly enough runs off or evapor-ates, and the water that is absorbed must wet the soil until it reaches the roots, the water gathering system for most plants. Furthermore, surface watering can con-tribute to erosion and to salt buildup in the soil.
Surface irrigation systems must be removed and replaced each time the field is tilled or plowed for replanting. Irrigation systems interfere with mechanical harvesting and require substantial maintenance. ~bove ground watering should usually be conducted during the day since many plants are subject to decay at night.
Furthermore, above-ground watering interferes with usage of recreational areas such as parks, athletic fields and golf courses. Surface watering is non-specific in that the crop and weeds are both equally watered.
' .~

Because of the limitations in above-ground irrigation, subsurface irrigation systems have been developed in which water is directly fed at an optimum subsurface depth to the roots of the crop being culti-vated. The pipe must be inert to the soil environment,must be capable of withstanding hydrostatic pressure in the presence of hard objects such as rocks without collapse and preferably is flexible, so that it does not suffer brittle failure and can be bent to follow crop-line contours.
There are numerous agricultural applications for an irrigation pipe which leaks water slowly over its entire surface and length. Such pipes can be buried underyround at levels appropriate for the particular crop being grown, and will supply water directly to the root system. With proper controls, the water level in the soil can be maintained at near-optimum levels. With some crops, this has been shown to increase yields substantially.
Leak irrigation requires a pipe that will deliver water at a prescribed rate along its length. The soil soaking action is similar to that produced by drip irrigation but the leak rate is continuous along the length of the pipe rather than at discrete points as in drip irrigat:ion. A canvas hose was an early attempt to produce a soaker hose. Canvas hose allows water to ooze out of the pores between the woven threads. However, cotton hoses tend to quickly degrade from the action of sunlight and microbes in the soil. Hoses of synthetic fibers are more resistant to actinic and microbiological attack but are too expensive to justify their use.
A porous irrigation pipe produced from reclaimed rubber mixed with a binder such as polyethylene has been disclosed by Turner in U.S. Patent Nos. 4,003,408;
4,110,420; and 4,168,799. This mixture is extruded to ~3(~1813 form the pipe, and the water present within the hot extrudate vaporizes, producing the smallpores through which water seeps under pressures of a few psi. While this pipe is useful for some applications, it has several drawbacks for many large-scale agricultural uses. The most important problem with the present product is its highly variable porosity. Some sections have no pores and other sections very large pores. The rate at which water emerges from this product varies by 50 to 75 per-cent or more within a few feet along its length. Ifit were used with closely spaced plantings, such as densely packed sugar cane plants, some areas would be overwatered, while others would be essentially dry.
~nother problem is that the overall porosity of the pipe is poorly controlled from lot to lot. This causes severe engineering problems when one tries to design a water system for a particular location. What is normally done is to use many pressure regulators throughout the system. This is expensive and further limits the potential applications of the porous pipe material.
In copending Canadian Patent Application, Serial No. 477,677, filed March Z7, 1985, and assigned to the presentapplicant, an improved porous irrigation pipe is disclosed having a uniform leak rate along its length. It was discovered that the wide~
variation in porosity in the Turner porous pipe is due to failure to control the moisture content of the raw materials. The dry powder is somewhat hygroscopic and prior manufacturing systems disclosed by Turner relied on absorption of water by the crumb material to pro-vide the blowing or pore forming agent. However, the water content of each batch or portion of a batch varies with humidity, temperature, etc. of the environment.

Since the amount of water present in the extrudate is very important to the porosity of the final pipe, varia-tions in the water content of the feed will produce unacceptable variations of the product. Turner attemp-ted to control excess water by venting the extruder but this did not effectively control variations in porosity.
Another problem with the Turner system is uneven feeding of the mixture of powders to the extruder which produces variations in the density, thickness and poro-lo sity of the extruded pipe. Furthermore, the vented extruder process disclosed by Turner produces a pipe having a fairly rough internal surface producing a high coefficient of friction and resulting in excessive pres-sure loss. This further exacerbates the uneven emitting of water along the rung of a length of a porous pipe.
The improved porous irrigation pipe disclosed in copending Canadian Patent application Serial No. 477,677 filed March 27, 1985 is made possible by accurate con-trol of the water content of the raw material and by providing the raw material in a form in which it feeds consistently and reliably to the extruder. The improved pipe is produced by preprocessing the raw material into a shaped pellet form. This material feeds very consis-tently and reliably into a variety of types of single screw extruders. Additionally, the moisture content of the pellets can be adjusted to predetermined, specific values depending on the desired porosity and leak rate.
The pellets are stored under water-excluding conditions such as in vapor barrier containers. The pellets are much less hygroscopic than the high surface area powder materials utilized by Turner.
Another difference in the production methods is that the use of a non-vented extruder becomes poss-ible since water content is known and there is no need to . .
" . ~

~L30~813 vent excess vapor pressure. Since the parameters of water content and feed rate are controlled and the temperature is controllable, porosity can be controlled by preselection of water content of the pellets. Alter-nately, since all variables are controlled, porosity ofa batch or run can be controlled by changing the temp-eratures in the extruder and die.
The porous pipe that is produced by extrusion of the pellets has extremely uniform porosity along its length and can provide very predictable and accurate watering cycles. This makes possible use of the im-proved porous pipe in a much expanded range of irriga-tion applications.
~lowever, all of the extruded porous pipe devel-oped to date, including the above-described uniform por-osity pipe produced from pellets,have a limitation.They only deliver a uniform leak rate over short lengths at the low pressures utili~ed in the field. Typically, a high pressure 50 psi inlet line is reduced to 15 psi or less by means of a regulator and fed to a header at the edge of the field. A length of porous pipe is con-nected to the low pressure header and is buried in the soil at the root level of the plants. The far end of the pipe is plugged. Since water is being continuously emitted along the length of the pipe as the column of water moves away from the header, the pressure contin-uously drops. Pressure also drops due to friction as the water moves toward the plug end of the pipe. Thus, in any normal system, much more water leaks into the soil near the inlet-header end than is emitted at the far end of the pipe. This leads to a number of prob-lems in the field such as overwatering near the header and underwatering adjacent the far end of the pipe.
These factors combine to limit the practical length of porous pipe which can be connected to an inlet manifold.

130~8~3 The pressure drop, porosity and frictional effects limit practical runs of porous pipe to 500 feet or less. In large fields having runs of 2,000 feet or more, many manifolds must be utilized greatly in-creasing the cost of the system.
One way to overcome this problem would be tomake a porous pipe having a low leak rate near the inlet, where the pressure is high, which gradually increases as the pressure drops along the pipe run.
Done properly, it should be possible to maintain very even leak rates over very long runs of such a pipe.
It has been estimated that in many applications por-ous pipe runs of several thousand feet would be pos-sible, if the leak rate of the pipe could be varied correctly.
In the past, it has not been possible to pro-duce such a pipe because the production methods were poorly controlled, varying 25 to 75 percent over short runs of pipes which are designed to have uni-form porosity. Small changes in processing vari-ables produce substantial changes in the product.

Statement of the Invention The system and method of the present invention utilizes pipe having a porosity which varies gradually and controllably throughout the length of the pipe. The pipe preferably used has a very smooth interior wall surface making possible very long runs of pipe having a substantially equal leak rate at continually lower pressure from the inlet to the stopped end of the pipe. The porous pipe can be produced having a leak rate optimized for a specific application so that the pattern of pipes yields the same amount of water throughout a field without the ~ :~01813 use of extensive and expensive manifold systems.

In accordance with an embodiment of the present invention there is provided an irrigation system comprising in combination: a plurality of lengths of porous pipe each having an inlet end and an outlet end and a wall formed of a major portion of vulcanized elastomer particles dispersed in a minor portion of thermoplastic resin binder, the porosity of the pipe gradually and controllably increasing from the inlet end to the outlet end; a first header connecting all the inlet ends; and a second header connecting all the outlet ends.

In accordance with another embodiment of the present invention there is provided a method of positioning an irrigation system comprising: providing a plurality of lengths of porous pipe each having inlet and outlet ends and a wall formed of a major portion of vulcanized elastomer particles dispersed in a minor portion of thermoplastic resin binder, with the porosity of the pipe lengths gradually and controllably increasing from the inlet ends to the outlet ends; connecting the inlet ends of some of the pipe lengths to a first header manifold, and connecting the inlet ends of the remainder of the pipe lengths to a second header manifold: and connecting the first and second header manifolds to a source of water.

The pipe may be produced using the moisture-controlled, unvented extruder process and system as described in copending Canadian application, Serial No.
477,677. All the production variables except the ~3018~3 - 7a -extruder temperatures or pull-off rate are controlled to produce a porous pipe having an increasing porosity which provides an even leak rate at gradually decreasing pressure.

In a preferred method of producing pipe used in the present irrigation system, all of the production parameters except the extruder die temperature are held constant. The temperature of the die, and thus the temperature of the extrudate, are varied according to a predetermined schedule, producing a predetermined, gradually varying porosity in the final pipe. By using a die system with a long land length and very good temperature control, it is possible to obtain very close control of the leak rate of the pipe over a broad range of pressures.
In the second method of producing pipe used in the present irrigation system, all of the production variables of the extruder, die and cooling system are held constant, while varying the pull-off rate of the tractor system. This essentially varies the density of the tubing wall, since no changes have been found in the overall dimensions of the final graduated leak rate pipes produced by this method versus those of pipes made under the same conditions with constant leak rates at constant pressure. This method suffers from the fact that rather small changes in the pull-off rate produce large changes in the 1 k t f ea ra e o ~301813 the pipe. For example, with all other conditions held constant, a change of 0.5 ft/min in the pull-off rate of 9~16 inch ID porous pipe produced a chan~e of approximately 50 GPH/100 ft. of the pipe.
This corresponds to a difference in leak rate of 1 GPH/100 ft. for each change of 0.01 ft/min in the pull-off rate. It is difficult to build a mechanical puller for pipe which will run at a constant rate within 0.01 ft/min., and almost impossible to control variations of such small magnitude with state-of-the-are pulling mechanisms. It should be noted that these tests were run at very low speed, and the speed was varied about 10 percent. At higher production rates, the speed variable will be changed a much smaller per-centage in order to provide the desired variance inleak rate. The speed variation will be much easier to control under industrial manufacturing conditions.
However, the leak rate variation is still more even along the length of pipes produced by vary-ing the die temperature as compared to those made by varying the pull-off rate. The temperature control provided by electronic controllers is much more sen-sitive, precise and stable than mechanical devices for varying the speed of the puller.
The porous pipe described can achieve a linearlyof flow, Cv=O.l or less, and can have a coefficient of friction at least 20 percent better than prior porous pipes of this nature. Runs of pipe can be up to 2000 to 3000 feet or more and yield of crops such as soybeans and peaches is expected to increase from 10 to 50 percent while water use is up to 50 percent less.
These and many other~features and attendant advantages o~ the invention will become apparent as the invention becomes better understood by reference ~3018~3 to the following detailed description when considered in conjunction with the accompanying drawings.

Brief Description of the Drawings Figure l is a schematic view of a first system for producing controlled variable porosity pipej Figure 2 is a schematic view of a second system for producing controlled variable porosity pipe;
Figure 3 is a more detailed schematic view of a die temperature controlled system;
Figure 4 is a cross-section of the pipe; and Figure 5 is a diagrammatic illustration of an irrigation system.

Detailed Description of the Invention The method proceeds by extrusion of a mix-ture of particulate, prevulcanized rubber and a thermo-plastic resin having a uniform low moisture content, below 3 percent, preferably below 1 percent by weight.
The mixture may be preformed into particles or pellets having a uniform size and profile which reliably feeds into a screw extruder. The extruder is operated with all variables controlled except for temperature of the die or pull-off rate. The extruder may be divided into zones having separate heating jacket~ and sepa-rately supplied heating fluids which may be at dif-ferent temperatures.
However, the die is separately heated and is subjected to a gradually varying temperature over a time period corresponding to a predetermined length of porous pipe. The temperature can be continuously raised or continuously decreased over a predetermined run. Both modes may be run consecutivelv. For ~301 S113 example, the temperature of the die can be raised from a minimum to a maximum over 1000 feet of run and then reversed and the temperature of the die continuously lowered over the next 1000 feet of run.
The pipe is manufactured by extrusion of a mix-ture containing a major portion of prevulcanized elas-tomer particles and a minor amount of a thermoplastic binder having a melting temperature below the decom-position temperature of the elastomer. During extru-sion, the thermoplastic particles flow to form a binder phase surrounding and coating the elastomer particles. Pores form extending from the inner wall to the outer wall during extrusion of the mixture throu~h the outlet die. These pores leak water when the pipe contains water at pressures at 1 psi or higher.
The mixture preferably has a uniform water content below 5 percent, usually at a value 0.1 to 3 percent by weight and not varying more than +10 percent throughout the batch.
The mixture is preferably formed into pellets having diameters from about 3 to 20 mm and having a bulk density about 0.2 to about 0.30 gm/cc. Pelleti-zation and extrusion of pipe is facilitated by in-cluding 1.0 to 6 phr of a slip agent, usually a mineral such as talc and 0.1 to 1.0 phr of a lubricant such as a metal stearate.
The elastomer can be natural rubber which is cis-1,4-polyisoprene or synthetic homopolymers of butadiene or isoprene or their copolymers with minor amounts of 0.1 to 20 percent by weight of vinyl mono-mers such as styrene, isobutylene or acrylonitrite.
It is preferred that the elastomer be vulcanized. A
ready and inexpensive source of prevulcanized crumb rubber is available as rubber reclaimed from auto-mobile tires after removal of the metal tire cords ~301813 and metal reinforcement in the head. Another sourceof rubber particles is flashing from newly manufactured tires. The rubber is ground into crumb particles no larger than those passing through a 10 mesh screen, preferably from 20 mesh to 60 mesh.
The binder resin is a thermoplastic material capable of softening at a temperature below 300F so that pores will form during extrusion. The resin must be stable to longterm exposure to soil environ-ment and to fertilizers, herbicides or pesticidesseeping into the adjacent soil or to fertilizers, growth regulators, herbicides or pesticides dispensed by dissolving in the irrigation water. The resin must be inert to the other components of the pipe such as the crumb rubber under extrusion conditionsO
Polyvinyl acetate is excluded from use since it will react with the crumb rubber. Styrene polymers in-cluding impact polystyrene copolymers are useful as are linear polamides such as various nylons, polyvinylchloride, polypheneylene oxide and polyphen-eylene sulfide polymers.
The most preferred group of polymers are thelinear polymers of alkenes of 2 to 4 carbon atoms such as polyethylene, polypropylene or polybutene. These polymers are unreactive in soil and in the extrusion barrel and have long segments of linearity pxoviding crystalline behavior. Polyethylenes have lower melting temperatures, are tougher and hold shape better.
High density polyethylenes have densities from about 0.94 to about 0.97 gm/cc, and porous pipe prepared with all high density polyethylene binder are somewhat stiff, brittle and difficult to extrude. Low density poly-ethylenes have densities from about 0.90 to 0.93 gm/cc, and porous pipe prepared with all low density poly-ethylene binder are very flexible and can readily be ~0~8~

bent to follow a desired path and are readily extruded.
These pipes are very useful for above-ground irrigation.
However, wall stiffness may not be adequate for sub-surface systems. The pipe develops kinks in the bends and does not hold its shape. The optimum binder which provides a porous pipe which holds its shape without brittleness yet has adequate flexibility is composed of 50 percent to 80 percent by weight of high density poly-ethylene, preferably 60 percent to 70 percent to 20 per-cent to 80 percent by weight of low density polyethylene,preferably 30 to 40 percent. The polyethylene can be used in any commercial form such as powder, flake or pellets. Reclaimed polyethylene materials can also be used. The form and color of such materials have little effect upon the product.
The slip agent aids in extruding the rubber bin-der mixture. Finely divided minerals other than talc can be utilized such as clays, silicas, carbonates, or micas. The metal stearate lubricant can be selected from calcium, magnesium or zinc stearates.
The first embodiment of a system for producing controlled, graduated variable porosity pipe is illus-trated in Figure 1. The system 10 includes an extruder 12, a temperature controlled die assembly 14, a windup stand 16 and feed hopper 18. The die assembly 14 com-prises a die 20 having a cylindrical cavity 22. A
conventional rod mandrell 24 is mounted in the end of the extrusion screw 26 for formi.ng the bore of the porous pipe. The die can be heated by electrical ele-ments or heat exchange fluid. As shown, the die 20 is surrounded by a housing 28 containing a cavity 21 through which a heat exchange fluid, HX4, circulates.
The fluid circulates through a path containing a heat exchanger 30 and a pump 32. The heat exchanger contains ~30~8~3 a closed element such as a shell or a tube bank 33 fox controlling the temperature by heat exchange with a secondary fluid such as water. The water circulates in a secondary loop 35 containing a heater such as a tube bank 37 and a pump 39. The tube bank 37 is disposed within a heater 41 such as a gas fired furnace. The operation of the heater 41 and the pump 39 can be con-trolled by a controller 45. A temperature sensor 36 may be attached to the die 20 and its signal fed to the con-troller 45. The controller may be operated manually to gradually raise or lower the temperature as the pipe is extruded or can be automatically operated to control the die temperature. An electrical or mechanical timer can be connected to the controller to linearly raise or lower the temperature of the water in the secondary loop 35 over a set time period determined by the speed of the windup stand 16 and the starting and final die tempera-tures for a given length of porous pipe. The controller can be operated to run alternating lengths of pipe by gradually increasing the die temperature over a first run by increasing the combustion temperature in the hea-ter 41 by gradually increasing the flow rate of combustion gas and air to the furnace. The furnace is then turned off and the flow rate of ambient water from inlet 4~
through the loop 35 i8 continued to gxadually decrease the temperature of HX4 to the ~tarting temperature. The cycle is then repeated.
The system 10 may also include a chiller 38 po-sitioned between the extruder 12 and the windup stand 16 to cool and set the pipe before entering the windup reel.
The chiller receives a flow of water, usually at 20F
to 40F. The extruder includes a feed hopper 18, a barrel 42, a screw 26 and a motor 46 for rotating the screw 44 within the barrel. The wall of the barrel is preferably temperature controlled by means of cavities 48! 50 and 52 receiving flows of heat exchange fluids, 130~8~

HXl, HX2 and H~3 at temperature Tl, T2 and T3, res-pectively. The temperature of the barrel usually in creases toward the die.
In the embodiment shown in Figure 2, all vari-ables including the die temperature are held constantand the speed of pull-off is varied by means of the controller 58 varying the speed of the drive motor 60 for take up stand 16. In industrial practice, a moto-rized tractor receives the porous pipe from the chiller and carries it to the windup stand~ The speed of the tractor can be gradually increased to vary the porosity of the pipe. The heat exchange fluid, HX4, is maintained at constant temperature as it circulates through a cavity 62 in housing 64 by means of a heater 66. The barrel of the extruder 12 may contain a single cavity 68 through which a heat e~change fluid heated by a heater 67 circulates.
A more detailed system is shown in Figure 3.
The system is illustrated using preformed pellets of the elastomer and binder.
Referring now to Figure 3, the pellets 132 are fed to hopper 160 of a pipe extruder 162. The hopper has a lid 161 to isolate the feed from the environment. The extruder preferably contains a single low pressure screw 164 and has a length to diameter ratio of at least 24/1, preferably at least 35/1. The compression ratio of the feeding section to the metering section can be from 1.5/1 to 2.2/1. The diameter of the barrel 166 is suitable to produce pipes having outside diameters from 2 to 10 inches, usually from 3 to 6 inches. Mixing pins are to be avoided since the crumb rubber can foul these elements.
The process is operated at a temperature high enough to melt the binder resin but below the melting temperature of the elastomer. Good temperature control of the barrel is required usually to within ~5F. A more uniform porous pipe is prepared by providing an increasing 1~018~3 temperature profile over the length of extruder 162.
Separate heating jackets 70, 72, 74 can surround the feeding, transition and metering sections, respectively, of the extruder barrel 166. Each jacket receives a separate flow of heat exchange fluid. The feedlng sec-tion can be heated to 340F - 360F (Tl), the transi-tion section from 360F - 370F (T2), and the metering section from 365F - 375F (T3).
The die 168 is also provided with a separate but variable temperature control. A suitable die is shown in Figure 5 of U.S. Patent No. 4,168,799. The die 168 contains an outlet orifice 73 in front of which is mounted a mandrel 84 for forming the bore 86 of the porous pipe 88. The mandrel may be removable to vary the wall thickness of the pipe. The thickness is se-lected depending on desired flow rate, leak rate and wall strength to avoid collapse. Wall thickness is usually from 0.1 to 2.0 inches.
In accordance with the present invention, the barrel need not be vented and the die is controllably heated to temperatures continuously varying from 240F
to 300F to control and vary porosity of the porous pipe.
An annular jacket 90 receives a flow of preheated heat exchange fluid HX4 at a temperature (T4) through inlet 91. The fluid ~IX4 circulates in a cavity 107 past the die 168 and is recovered through outlet 93 at tempera-ture T5. The fluid then enters the heater 95 and flows past an electrical heating element 97 and is heated to the temperature of the element determined by the con-troller 99. A signal from die temperature sensor 101 may be fed by line 103 to the controller 99. The fluid heated to temperature T4 is returned by means of pump 105 to the inlet 91.
As the screw 164 is rotated by the motor 92, the feed moves forwardly and the binder resin melts. The resin flows around the particles and a network of pores 96 forms extending from the bore 86 to the surface 98 of the porous pipe. The pipe 88 can be extruded through the die 168 into the ambient and enters a chilling bath 100 containing water at a temperature of about 25F to 50F before being pulled onto windup stand 102. The chiller bath 100 usually has a length of at least 40 feet.
The invention will now be illustrated by the following specific examples of practice.
The dry materials were mixed in a ribbon blender and fed into the hopper of a twin-screw extruder heated to 360F - 390F with a 5 mm die heated to 300F. The water bath was maintained at 35F - 40F and the 5 mm strand was chopped into approximately ground pellets about 8 - 9 mm in diameter by an air knife. After drying, the pellets had a density of 0. 275 gm/m.
Example 1 The following mixture was pelletized and dried 20 to 0.75 percent moisture content.
Crumbed Tire Rubber (48 Mesh) 100 lb.
Low Density Polyethylene35 lb.
Finely Powdered Talc 3 lb.
Zinc Stearate . 25 lb.
These pellets were extruded in an unvented single screw extruder into porous pipe with an ID of 0. 55 inch and a wall thickness of 0.2 inch. The extruder tempera-tures were:
Extruder (all zones) 350F
Gate 340F
Spider 335 F
Die 335F
This porous pipe has the following properties at 10 psi:

~ 3~813 0.27+0.2 GPM/100 Linear Feet 0.11+.003 GPM/100 Square Feet Example 2 This same pelletized raw material of Example 1 was extruded under the same conditions, except that the die temperature was 290F. This pipe had the following properties at 10 psi:
0.19~0.17 GPM/100 Linear Feet 0.076+0.007 GPM/100 Square Feet Example 3 Example 1 was repeated except that 35 lb. of high density polyethylene was substituted for the low density polyethylene binder. The pellets were more difficult to extrude and the pipe was more brittle and less flexible.
Example 4 Crumbed Tire Rubber (40 Mesh)100 lb.
High Density Polyethylene25 lb.
Low Density Polyethylene10 lb.
Slip Agent-Talc 3 lb.
Lubricant-Calcium Stearate.25 lb.
The formulation was processed into pellets and dried to contain 1.0 percent moisture. The pellets were extruded in a 2.5 inch diameter, 24/1 L/D, *prodex single-screw extruder. The extruder was equipped with a PVC type ~crew, which had a compression ratio of 1.9/1, and a circular pipe die with a land-length of 16/1.
Temperatures in the extruder were maintained at 340F -360F. The gate, spider and die temperatures were ad-justed to yield an extrudate having the temperatures i 30 shown below. Porous pipes having a wall thickness of 0.165 inch were produced having the following properties:

* Trade Mark .

13(~18~3 ~PPROXIMATE LEAK R~TE

Extrudate GPM/100 Linear Feet Temperature 0.5" 1.0"
(F) GPM/100 sq ft ID Pipe ID Pipe 250-260 0.10~0.02 0.25+0.04 0.50+0.08 275-285 0.20+~.03 0.50+0.08 1.00+0.16 300-320 0.40+0.06 1.00+0.16 2.00+0.32 340-360 0.80+0.12 2.00+0.32 4.00+0.64 The pellet material fed smoothly and the porous pipe had good compression strength, yet was flexible.
The pipe had uniform porosity along its length. ThP
consistency of leak rate is measured by determining the amountof flow of one foot increments over 50 feet of pipe to determine the consistency factor, Cv--the standard deviation/flow rate.
A one-half inch I.D. porous pipe having a flow rate of 1 gpm/100 linear feet at 10 psi pressure has a Cv of 0.1 to 0.15 and a porous pipe having a flow rate of 0.25 gpm/100 linear feet has a measured Cv of 0.05 to 0.1.
The data in Table 1 demonstrates that the leak rate at constant pressure can be varied by control of the die temperature. Therefore, a pipe can be manufactured having a constant leak rate at gradually increasing pres-sure. Though the relationship of flow to pressure follows a parabolic curve, a pipe having porosity that varies linearly over length provides a close approximation of a constant leak rate over the pressure drops experienced in practice.
A run was conducted in which 9/16 inch I.D. was produced. The die temperature was maintained constant at 350F and all other parameters were held constant except that the pull-off rate was varied from about 5 feet per .~

~3~1~313 minute to 4.5 feet per minute, a change of 0.5 feet per minute. This produced a change of about 50 GPH/100 feet of the pipe. This corresponds to a leak rate of 1 GPH/100 feet for each change of 0.01 feet per minute in the pull-off rate.
Several more examples of porous pipe produced by varying the die temperature at a constant pull-off rate follow:

._______________________________.,_______________________________________ LEI~TH DIE LE~K EXTRUDER
~LoN~ THE TEMP. RATE SET-UP
PIPE ~DE8.F) 8PH~100' ~T CT~RT?
._______________________________________________________________________ 0 349 52 ZONE TEMP IF) 34~ 58 1 360 343 ~3 3 34 . DIE 34 SCREW 40 R~M
336 7~
R~TE - ~ FT,'~IN
~0 33~ 76 ~ 333 7 33~ 83 10~ 329 8 .______________..______________________ ________________________________.~

" 1~0~313 TAE~LE 3 .____,___________________________~______________________________________ EEN~TH DIE LE~K EXTRU~ER
~EON13 THE tEMP. R~TE 8ET-UP
PtPE ~DEn.F) t8PH~100') (~T ST~RT) ._____~_________________________________________________________________ 8 3702e ZONE TEMP ~F) __________________ 36~2S I 370 2 37~
36S27 3 35g ' SCREW 6~ RPM
le0 35~ 37 R~TE ~7.5Ft~MlN

160 35~ 47 la0 3S3 51 200 3~
._______________________________________________________________________ TAI~LE 4 ._______________________________________________________________________ LEN8TH DIE LE~K EXTRUDER
ALON~ THE TEMP. R~TE 8ET-UP
PIPE ~DE~.F~ OPHX100' I~T ST~PT~
.__________________.____________________________________________________ 0 37712 ZONE TEMP ~F) __________________ S~ 37S1~ 1 375 100 36~22 3 390 1~0 36228 200 ~ ' 3S83S

25~ 35539 R~TE -7.5FT~IN

950 34~44 400 344~2 S~0 33~61 ._______________________________________________________________________ 13018~3 The gradual variation in leak rate of constant pressure is much more even along the length of pipes produced by varying the temperature of the die as com-pared to those produced by varying the pull off rate.
It is expected that this will be true when scaled up to industrial operation since electronic temperature con-trollers are more reliable and precise than speed con-trollers especially since a yielding thermoplastic-rubber is being pulled. Preferred industrial practice would be to control all constant variables with a com-puter and also control the variable parameter by means of a microprocessor specially programmed for control of pull-off speed or die temperature variation.
The porous pipe is found to have a very smooth wall having a Cv from 0.05 to 0.1 and a porosity varying up to 5 magnitudes over 500 feet. This makes possible the deployment of irrigation systems with very few headers, pumps and manifolds as illustrated in Figure 5.
Referring now to Figure 5, the system 200 is deployed in a field 202. Parallel runs 204, 206 of porous pipe at least S00 feet in length and suitably from 1000 feet to 3000 feet in length extend from header manifolds 208, 209. These pipes contain plugs 210 at their outer ends 212 and typically have an inner diameterof about 0.5 inch and a wall thickness of about 0.15 inch. The field is fed pressurized water from a municipal or well source such as a 4 inch diameter line 112 at 50 psi.
The inlet pressure is reduced by means of pressure re-ducer 114 to about 15 psi and is fed by lines l16,~
to the headers 208, 209. Water flowing at 20 gpm and 15 psi is found to give a constant leak rate throughout the field.
It is to be realized that only preferred embodi-ments of the invention have been described and that ~:~01813 numerous substitutions, modifications and alterations are permissible without departing from the spirit and scope of the invention as defined in the following claims.

Claims (21)

1. An irrigation system comprising in combination:
a plurality of lengths of porous pipe each having an inlet end and an outlet end and a wall formed of a major portion of vulcanized elastomer particles dispersed in a minor portion of thermoplastic resin binder, the porosity of the pipe gradually and controllably increasing from the inlet end to the outlet end;
a first header connecting all the inlet ends; and a second header connecting all the outlet ends.

2. A system according to claim 1 further including a source of pressurized water connected to the first header.

3. A system according to claim 1 or 2, in which the walls of the porous pipe contain a pattern of pores extending from the inside surface to the outside surface of the wall.

4. A system according to claim 1, in which the leak rate of the lengths of porous pipe increases linearly from end to end.

5. A system according to claim 4, in which the water leak rate of each length of porous pipe is substantially constant throughout the length of pipe as the pressure drops from inlet to outlet end.

6. A system according to claim 5, in which the porosity changes at least 100 percent over a length of 500 feet.

7. A system according to claim 6, in which each pipe has a length up to 3,000 feet, a diameter from 1/2 to 12 inches and a wall thickness from 0.1 to 2.0 inches.

8. A system according to claim 1, in which the binder resin is a linear polyethylene having a melting point below 300°F.

9. A system according to claim 1 or 8 in which the binder resin is a mixture of 50 to 80 percent high density polyethylene and 20 to 50 percent by weight of low density polyethylene.

10. A system according to claim 1, in which the second header includes a drain aperture and a removable plug received in the aperture.

11. A method of positioning an irrigation system comprising:
providing a plurality of lengths of porous pipe each having inlet and outlet ends and a wall formed of a major portion of vulcanized elastomer particles dispersed in a minor portion of thermoplastic resin binder, with the porosity of the pipe lengths gradually and controllably increasing from the inlet ends to the outlet ends, connecting the inlet ends of some of the pipe lengths to a first header manifold, and connecting the inlet ends of the remainder of the pipe lengths to a second header manifold, and connecting the first and second header manifolds to a source of water.

12. A method according to claim 11, wherein the first and second header manifolds are positioned a substantial distance apart, with the porous pipe lengths connected to the first header manifold extending toward the second header manifold and with the porous pipe lengths connected to the second header manifold extending toward the first header manifold.

13. A method according to claim 11 or 12, further comprising providing the outlet ends of the porous pipe lengths with plugs.

14. A method according to claim 11 or 12, including providing a water pressure reducer in the connection between the said header manifolds and the source of water.

15. A method according to claim 11, in which the walls contain a pattern of pores extending from the inside surface to the outside surface of the wall.

16. A method according to claim 11, in which the water leak rate of the lengths of porous pipe increases linearly from end to end.

17. A method according to claim 16, in which the water leak rate of each length of porous pipe is substantially constant throughout the length of pipe as the pressure drops from inlet to outlet end.

18. A method according to claim 17 in which the porosity of the porous pipe changes at least 100 percent over a length of 500 feet.

19. A method according to claim 18 in which each pipe has a length up to 3,000 feet, a diameter from 1/2 to 12 inches and a wall thickness from 0.1 to 2.0 inches.

20. A method according to claim 11, in which the binder resin is a linear polyethylene having a melting point below 300°F.

21. A method according to claim 11 or 20 in which the binder resin is a mixture of 50 to 80 percent high density polyethylene and 20 to 50 percent by weight of low density polyethylene.