U.S. patent number 3,874,598 [Application Number 05/425,576] was granted by the patent office on 1975-04-01 for irrigation tube.
This patent grant is currently assigned to The Dow Chemical Company. Invention is credited to Carl B. Havens.
United States Patent |
3,874,598 |
Havens |
April 1, 1975 |
IRRIGATION TUBE
Abstract
Plastic low pressure irrigation tube is prepared by forming a
two-passageway tube having a supply and discharge passage. The wall
separating the two passages is perforated to permit liquid to flow
from the supply to the discharge passage. The external wall forming
the discharge passage is perforated at locations remote from
perforations connecting the supply and discharge passages to
provide relatively even distribution of water therefrom with
variations in the pressure head on the inner tube.
Inventors: |
Havens; Carl B. (Fresno,
CA) |
Assignee: |
The Dow Chemical Company
(Midland, MI)
|
Family
ID: |
26968164 |
Appl.
No.: |
05/425,576 |
Filed: |
December 17, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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293822 |
Oct 2, 1972 |
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Current U.S.
Class: |
239/542; 138/42;
239/566; 239/450 |
Current CPC
Class: |
A01G
25/06 (20130101) |
Current International
Class: |
A01G
25/00 (20060101); A01G 25/06 (20060101); B05b
015/00 () |
Field of
Search: |
;239/145,450,542,547,566,558 ;61/12 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wood, Jr.; M. Henson
Assistant Examiner: Mar; Michael
Attorney, Agent or Firm: Ingraham; Robert B.
Parent Case Text
This application is a continuation-in-part of my co-pending
application Ser. No. 293,822, filed Oct. 2, 1972, now abandoned.
Claims
What is claimed is:
1. An irrigation tubing comprising
a first or inner conduit, the inner conduit having generally
constant wall thickness,
a plurality of perforations disposed in the wall of the inner
conduit providing a plurality of passages through the wall
thereof,
an outer adjacent conduit enclosing the inner conduit, the adjacent
conduit having
a plurality of openings passing through the wall thereof, the total
cross-sectional area of the openings per unit length of the
conduits being greater in the outer conduit than in the inner
conduits, the inner and adjacent conduits being of flexible plastic
material readily deformable to a flat ribbon-like shape, with the
further limitation that
the outer adjacent tube has spaced apart annular regions of reduced
diameter and the inner tube and the outer tube define a plurality
of generally annular elongated compartments therebetween.
2. The tubing of claim 1 wherein the plastic tubing has a wall
thickness of from about 2 to 20 mils.
3. The tubing of claim 2 wherein the inner and adjacent tubes have
a wall thickness of from about 3 to 12 mils.
4. The tubing of claim 1 wherein the ratio of the area of the
openings in the adjacent tube to the area of the openings in the
inner tube is from about 1.1 to 50.
5. The tubing of claim 1 wherein the inner tube is an extruded
seamless tube.
6. The tubing of claim 1 wherein the inner and outer adjacent tubes
each have a longitudinal axial lap seal.
7. The tubing of claim 1 wherein the inside diameter of the outer
adjacent tube and the outside diameter of the inner tube differ by
about 0.1 to about 10 percent of the diameter of the inner
tube.
8. The tubing of claim 7 wherein the inside diameter of the outer
adjacent tube and the outside diameter of the inner tube differ by
about 0.2 to about 4 percent of the diameter of the inner tube.
Description
Plastic irrigation tube is known which consists of multiple passage
tubing such as a double wall tube having perforations in both the
inner or supply and outer or discharge tubes, the area of the
perforations in the outer tube being substantially greater than
perforations on the inner tube. Thus, pressure of a liquid in the
inner tube may vary but the volume of water discharged from the
outer tube will vary to a degree significantly less than if a
single perforated tube is employed. Such commercially available
tubes are prepared from thin plastic film wherein two flat strips
previously perforated are placed in face to face relationship,
folded and heat sealed to form a fin seal. For example, if a
plastic film is wrapped about a mandrel and end portions brought
into abutting relationship wherein the end portion of the surface
contacting the mandrel is brought into contact with itself and
sealed, the result is a fin seal. Such a seal usually is weak when
internal pressure is applied. Such plastic irrigation tubing is of
substantial benefit particularly in arid climates. The light nature
of the tubing permits it to be readily buried by hand or
beneficially by the use of a mole plow, wire laying plow or like
apparatus to convenient depth in the soil. By maintaining water
pressure, usually on the order of a few pounds per square inch, a
continuous supply of moisture is fed into the soil generally in the
region of the plant roots. Such an irrigation system is relatively
low in cost to install and presents substantial economies in the
utilization of water wherein surface evaporation is significantly
reduced over irrigation techniques such as spraying and the like.
Generally when employing such a low pressure irrigation system it
is necessary that the plastic tubing be installed in such a manner
that its elevation is maintained reasonably constant, otherwise
flow in lower portions will be much greater than in higher
portions.
It would be desirable if there were available an improved surface
or subsurface irrigation tubing.
It would also be desirable if there were available an improved
irrigation tubing which is more tolerant of elevation.
These benefits and other advantages in accordance with the present
invention are achieved in an irrigation tubing comprising a first
conduit, the first or supply conduit having generally constant wall
thickness, a plurality of perforations disposed in the wall of the
first conduit providing a plurality of passages through the wall
thereof, a second or discharge conduit having at least a portion of
the wall of the first conduit common thereto, the common portion of
the wall having the perforations, the second conduit having a
plurality of openings passing through the wall thereof not common
to the first conduit, the total cross-sectional area of the
openings per unit length of the conduits being greater in the
second conduit than in the first conduit, the first and second
conduits being of flexible plastic material readily deformable to a
flat ribbon-like shape, with the further limitation that the second
tube defines a plurality of generally elongated compartments.
Further features and advantages of the present invention will
become more apparent from the following specification taken in
connection with the drawing wherein:
FIG. 1 schematically depicts the application of conduit in
accordance with the present invention.
FIG. 2 is a schematic longitudinal sectional view of a conduit in
accordance with the present invention.
FIG. 3 is a schematic cross-sectional view of a conduit such as the
conduit of FIG. 2.
FIGS. 4 and 5 depict an alternate conduit in accordance with the
present invention.
FIG. 6 is a cross-sectional view of another embodiment of the
invention.
FIG. 7 is a longitudinal sectional view of a portion of the
embodiment of FIG. 6.
In FIG. 1 there is depicted an installation of tubing in accordance
with the present invention generally designated by the reference
numeral 10. The installation 10 comprises earth 11 having disposed
therein perforate irrigation tube 12. The tube 12 has a closed
terminal end 13 having an inlet end 14 in operative communication
with a water source 15. Water from the source 15 flows into the
open end 14 and is gradually discharged into the earth 11 in
proximity to the roots of plants 16 disposed within the earth
11.
In FIG. 2 there is schematically depicted an axial cross-sectional
view of a tube in accordance with the present invention designated
by the reference numeral 20. The tube 20 comprises an inner or
supply tube 21 having a first end 22 and a second end 23. The tube
21 has an annular wall 24 of generally constant thickness and is of
seamless extruded construction. The wall 24 defines a plurality of
openings 25. The openings 25 provide communication between the
interior and the exterior of the tube. About the inner tube 21 is
disposed an exterior outer adjacent tube 27. The exterior tube 27
encloses the interior tube 21. The tube 27 has a first end 28 and a
second end 29 and a wall portion 31. The wall portion 31 defines a
plurality of openings 32. The openings 32 have a substantially
greater cross-sectional dimension per unit of length of the tube 20
than do the openings 25 in the wall 24 of the tube 21. A plurality
of regions of reduced diameter 34 are defined by the tube 27. The
regions of reduced diameter are generally circumferentially
extending and axially spaced. Between adjacent regions of reduced
diameter 34 are defined a plurality of generally annular,
longitudinally spaced compartments 35.
In operation of the tube such as the tube 20 of FIG. 2, one end
such as the end 23 is closed by heat sealing or suitable plug and a
liquid under pressure applied to the remaining end such as the end
22. Liquid under pressure flows within the tube 21, passes within
the openings 25 into the various compartments 35. From the
compartments 35 the fluid is discharged through the openings 32. By
appropriate selection of the relative cross-sectional areas of the
openings 25 and 32 and the cross-sectional area of the compartments
35, a relatively large pressure drop is caused to occur in the
liquid as it passes from the inner tube 21 into the annular space
or compartment 35. As the area of the openings 32 is substantially
greater than the area of the openings 25, a relatively small
pressure drop occurs in the liquid as it is passed from the
compartment 35 to the space external to the tube. The compartments
35 are separated from each other at least to a substantial degree
by the regions of reduced diameter 34. The regions 34 beneficially
may form liquid-tight seals. Thus, if the tube 20 of FIG. 2 is
disposed with the end 22 higher or lower than the end 23, the
influence of gravity on the volume of liquid being discharged from
any given region between the area of reduced diameter will be
significantly and substantially less than the differences in volume
discharged if the regions of reduced diameter were omitted. Thus,
irrigation tubing such as the tubing of FIG. 2 can readily be
installed in a field or plot of earth with substantially less
concern for difference in elevation than in conventional irrigation
tubes wherein an annular space such as the space 35 is generally
continuous along substantial lengths of the tubing. Employing
conventional irrigation tubing in order to maintain uniform
irrigation, it is generally desirable that the level be maintained
within about one foot, whereas tubing in accordance with the
present invention provides very desirable irrigation where levels
may vary as much as 6 feet or more.
FIG. 3 schematically depicts a cross-sectional view of the tube 20
of FIG. 2 showing the outer tube 27 having openings 32 disposed
about the inner tube 21 having openings 25. The outer tube 27 as
depicted in FIG. 3 has been formed by folding a ribbon about the
inner tube 21 and forming a lap seal in the region designated by
the reference numeral 39. Optionally, if desired, an additional
longitudinal seal is readily made at a location indicated by the
reference numeral 40 which effectively seals the inner and outer
tubes into a single unit.
FIG. 4 schematically depicts an alternate tube of the present
invention wherein there is shown a coaxial tube assembly 45. The
assembly 45 comprises a first or inner tube 46 and a second or
outer tube 47 generally coaxially disposed. Beneficially, tubes
such as the tube 45 are readily extruded from coaxial annular
tubing dies in communication with a single or double source of
plastified synthetic resinous material. A first laser or source of
coherent electromagnetic radiation 48 is disposed adjacent the tube
45 and is focused on a wall of the outer tube 47. A second laser or
source of coherent electromagnetic radiation 49 is disposed within
and focused on a wall of the inner tube 46. The source 49 is
conveniently supported on the extrusion die and energy brought
through the die and focused on the tube by a mirror. By pulsing and
laser energy a desired pattern of openings is readily prepared in
both the inner and outer tubes. At the location where the
electromagnetic energy from the laser source 49 passes the wall of
the tube 47, insufficient energy is localized in the wall 47 to
cause perforation thereof. A generally similar situation exists
with regard to the tube 46 and the electromagnetic energy from the
laser 48. Thus, the tubes 46 and 47 are independently perforated
although they are simultaneously prepared one inside the other. The
tubes 46 and 47 may be joined to each other to form compartments as
in FIG. 2 when they are extruded by pinching the tube 47 onto the
tube 46, or the outer tube 47 may be reheated and pinched to heat
seal to the tube 46.
In FIG. 5 there is schematically depicted a cross-sectional
configuration of an alternate irrigation tube in accordance with
the present invention generally designated by the reference numeral
50. The tube 50 comprises an inner tube 51 having a lap seal 52 and
perforations 53 in the walls of the tube 51. An outer tube 55
surrounds the tube 51 and defines a generally annular space 56
therebetween. The tube 55 has a lap seal 57 which is integrally
bonded or sealed to the seal 52 of the tube 51. The tube 55 has a
plurality of perforations 58 in the walls thereof, beneficially in
axial spaced relationship to perforations 53 in the tube 51. The
embodiment of FIG. 5 is readily prepared without the use of a
tubing extruder.
In FIG. 6 there is depicted an end view of a tube in accordance
with the present invention generally designated by the reference
numeral 60. The tube 60 comprises a first or supply conduit 61
formed of a single piece of film having a lap seal 62. A second
conduit 63 is defined by a second conduit wall 64 and an adjacent
portion of the conduit 61. The second conduit wall 64 has a
generally arcuate configuration and is affixed to the conduit 61 at
locations 65 and 66 which are radially separated by about
120.degree..
FIG. 7 depicts a longitudinal sectional view of the conduit 60 of
FIG. 6. The second conduit wall 64 is sealed or joined to the
conduit 61 at a plurality of locations 67 to form a plurality of
compartments 68 along the length of the tube 60.
The embodiment of FIGS. 6 and 7 is particularly convenient in that
a distribution conduit is obtained employing a minimal quantity of
raw material and formation of the tube is accomplished readily.
Tubes in accordance with the present invention are readily prepared
from a wide variety of plastic materials, the selection of the
particular plastic materials depending primarily upon service
conditions and economic conditions. Any extrudable water resistant
synthetic resinous plastic which is sufficiently flexible to be
wound upon a roll as a flattened tube can be used. Particularly
desirable plastic materials include nylon 66, polyvinylchloride,
polyethylene, polypropylene and the like. Generally for most
applications the outer tube, such as the tubes 27 and 47, are of an
ultraviolet and water resistant material such as polyethylene
containing 2 percent by weight carbon black. For most applications
it is desirable that the thickness of the individual tubes be
between about 2 and 20 mils, depending upon the size, the manner of
installation and the like. Generally satisfactory service is
obtained wherein the individual tubes have a wall thickness of from
about 3 to 12 mils. It is very desirable that the tubing in
accordance with the present invention be prepared from materials
which are flexible under ambient conditions. By "flexible" is meant
that the tubes have sufficient flexibility that they may be
flattened into the form of a ribbon, wound onto a reel, unwound
from the reel and re-inflated with an irrigating liquid such as
water. Polyethylene terephthalate; nylon; plasticized
polyvinylchloride; olefin polymers including polyethylene,
polypropylene and ethylene; copolymers of ethylene and propylene
are all eminently satisfactory.
It is essential in the practice of the present invention that at
least the inner tube and beneficially the outer tube also, have not
more than one edge portion exposed on the outer surface of the
particular tube. Tubes which meet these requirements include
seamless extruded tubes and tubes having a longitudinal lap seal
(as depicted in FIGS. 3 and 5). More stringently stated, a tube
suitable for use as an inner tube, when expanded to generally
cylindrical form by internal pressure within the tube, may have a
tangent to the cross-sectional configuration placed on the outer
surface thereof and the tangent shall pass through not more than
one layer of tube-forming material. A tube having a fin seal is
unsuitable for the inner tube of irrigation tubing in accordance
with the present invention.
It is advantageous in the practice of the present invention to
maintain the area of the openings in the outer tube greater than
the inner tube; that is, for a unit length of irrigation tubing in
accordance with the invention the sum of the cross-sectional areas
in the outer tube should exceed the sum of the area of the opening
in the inner tube. Beneficially, the area ratios per unit length
are within the range of from about 1.1 to about 50, and more
beneficially in the range of from about 2 to 10.
In the preparation of tubing such as that depicted in FIGS. 2 and
3, the inner tubes such as the tube 21 are extruded from the tubing
die and flattened, perforated by any convenient means including hot
metal punch to provide openings on the opposite sides of the tube.
In general it is usually undesirable to form the openings such as
the openings 25 by means of slitting with a sharp blade or similar
device. Such openings have a tendency to tear when higher pressures
are applied to the interior. Usually it is desirable to employ a
means that raises the temperature of the plastic in the region of
the opening to a sufficient degree that at least some plastic flow
occurs and a relatively smooth opening is obtained generally having
a somewhat eyelet-like configuration. Such techniques of
perforating plastic film are well known in the art and are typified
by perforation with a hot needle. Electromagnetic radiation such as
is obtainable from a coherent light beam or laser is very
satisfactory for perforating tube. Such laser beams will radiate
small openings without stress concentrating leaks or fissures.
A particularly desirable embodiment of the present invention
employs inner and outer tubes of about equal diameter; i.e., tube
which on inflation exhibits a minimal difference in diameter while
still providing an annular space for the flow of irrigating fluid
therebetween. By providing such a narrow annular space, a further
pressure drop is obtained in the annular space as well as through
the openings in the walls of the inner and outer tubes.
Beneficially the diameter difference between the outer tube and the
inner tube is from about 0.1 percent to about 10 percent of the
diameter of the inner tube, and advantageously up to about 4
percent. In a preferred embodiment, the diameter difference is from
0.2 percent to about 2 percent. By the term "diameter difference"
is meant the percentage difference between the outside diameter of
the inner tube and the inside diameter of the outer tube. In
installing irrigation tubing of the present invention it is
oftentimes desirable to orient the openings in the outer tubing in
a downward direction, particularly if the inner tube is unattached
to the outer tube and the resin from which the inner tube is
prepared is lighter than water. Occasionally such tubing exhibits a
tendency for the inner tube to float due to the presence of water
and restrict the flow from some of the openings in the outer tube.
Tubes in accordance with the present invention are readily prepared
employing one or more perforate tubes between the inner and outer
tubes to provide increased pressure drop if desired.
By way of further illustration, an inner tube is prepared having a
wall thickness of 10 mils and a width of 1.3 inches when flat. One
opening about 0.015 inch in diameter is formed with a laser beam at
6 foot intervals. An outer tube is formed about the inner tube from
a strip of 6 mil thick polyethylene containing an ultraviolet light
stabilizer. The strip has perforations of about 0.015 inch spaced
every 2 feet along its length. The strip for the outer wall is
about 3.25 inches in width and is folded about the inner tube and
is heat sealed to form a lap joint. The composite tube is heat
sealed transversely at one end. The remaining end is connected to a
water source after the tube has been buried about 8 inches below
the surface of the ground. A generally uniform supply of moisture
to the ground is obtained.
An irrigation tube is provided by employing an inner tube of like
dimensions to that applied to the previous illustration with the
exception that openings of about 0.015 inch diameter are formed
through both walls of the flattened tube by means of the laser
beam. The outer wall is formed from the strip as employed in the
previous illustration with the additional step that locations
spaced about 18 feet apart are heated with a blast from an electric
hot air gun to cause shrinkage of the exterior tube about the
interior tube when the composite tube is installed. In a manner
similar to the foregoing illustration and a difference in level of
5 feet between one end and the other, satisfactory distribution of
moisture into the soil is obtained.
An irrigation tube is prepared employing a continuous seamless
polyethylene tube having a diameter of 0.80 inch, overall wall
thickness of 0.010 inch having an opening through the wall of about
0.022 inch spaced on about 5 foot centers. The outer tube has
perforations of 0.012 inch on about 2 foot centers. The diameter of
the outer tube, which is polyethylene, is about 0.82 inch and has a
wall thickness of about 0.006 inch. The tubing is closed at one end
and water under a pressure of about 7 pounds per square inch
applied to the remaining end. Flow rate from various openings is
determined as the height of various portions of the tube is varied.
The flow is maintained within 14 percent of the average for all
holes with height variations of 6 feet. The slowest flow rate
observed for a hole is 79 percent of the average for all holes.
As is apparent from the foregoing specification, the present
invention is susceptible of being embodied with various alterations
and modifications which may differ particularly from those that
have been described in the preceding specification and description.
For this reason, it is to be fully understood that all of the
foregoing is intended to be merely illustrative and is not to be
construed or interpreted as being restrictive or otherwise limiting
of the present invention, excepting as it is set forth and defined
in the hereto-appended claims.
* * * * *