Drip irrigation hose and method for its manufacture

A drip irrigation hose of the continuous emitter type in which the outlets from the regulating passage each comprise a single longitudinal slit. By controlling the length of the slits and the flexibility of the film, water drips from the outlets when the hose is pressurized without clogging when the hose is depressurized. The slits are sufficiently long and the film is sufficiently flexible so the water drips from the outlets when the hose is pressurized. The slits are sufficiently short and the film is sufficiently rigid so the outlets close completely when the hose is depressurized. An outlet forming wheel has a knife blade on its periphery. A backing wheel engages the outlet forming wheel to establish a first nip therebetween. The backing wheel has on its periphery a circumferential slot into which the knife blade fits at the first nip. A rib forming wheel has around its periphery impressions that define a desired track pattern for the ribs. The outlet forming wheel and the rib forming wheel are mounted on a common shaft to operate in synchronism. A continuous strip of plastic film is directed in a path that reverses direction four times to accommodate these wheels.

BACKGROUND OF THE INVENTION 
This invention relates to drip irrigation and, more particularly, to a drip 
irrigation hose with an improved outlet construction and a method for its 
manufacture. 
Drip irrigation hose can be classified into two types--those having 
discrete emitters and those having continuous, integral emitters. An 
example of a drip irrigation hose having discrete emitters is shown in 
U.S. Pat. No. 4,850,531. An example of a drip irrigation hose having 
continuous, integral emitters is shown in U.S. Pat. No. 4,247,051. A drip 
irrigation hose having continuous integral emitters offers the possibility 
of lower cost and ease of manufacture and installation. 
The design of the inlets to and outlets from the emitters is critical. If 
the effective outlet area of the emitters is too large, dirt and debris 
can collect externally in the outlets, thereby causing external clogging. 
If the effective inlet and outlet areas of the emitters are too small, 
they become clogged internally and cease to serve their purpose. Further, 
if the effective outlet areas of the emitters are too small, water squirts 
out of the hose instead of dripping, and soil erosion results. 
U.S. Pat. No. 4,247,051 discloses a drip irrigation hose formed by bending 
a strip plastic film along its length to form an overlapping longitudinal 
seam between opposing longitudinal margins of the film. First and second 
longitudinally extending, laterally spaced, transverse ribs interconnect 
the opposing margins along their length to seal the overlapping 
longitudinal seam. The ribs are formed by one or more molten plastic beads 
extruded onto the film. As a result, a flow regulating passage is defined 
by the ribs and the opposing margins and a supply passage is defined by 
the remainder of the film. Water flows from the supply passage to the flow 
regulating passage through a plurality of longitudinally spaced inlets. 
Water flows from the flow regulating passage to the exterior of the hose 
through a plurality of longitudinally spaced outlets longitudinally spaced 
from the respective inlets to provide a substantial path length from each 
inlet to a respective outlet. In one embodiment, the outlets each comprise 
two parallel slits that form between them a flexible flap. The flap serves 
as an outlet valve, opening and closing as the hose is pressurized and 
depressurized. However, unless the plastic film is very thick and rigid, 
the flaps do not close consistently when the hose is depressurized and 
therefore, the outlets can become clogged by soil drawn into the slits. 
A problem encountered in the manufacture of continuous emitter drip 
irrigation hose is coordinating the position of the outlets and the track 
pattern of the ribs. If care is not taken, the track pattern of the ribs 
may overlap the outlets, and thereby cause the outlets to be on the high 
pressure side of the flow regulating passages. 
SUMMARY OF THE INVENTION 
One aspect of the invention is a drip irrigation hose of the continuous 
emitter type in which the outlets from the regulating passage each 
comprise a single longitudinal slit. By controlling the length of the 
slits and the flexibility of the film, water drips from the outlets when 
the hose is pressurized without clogging when the hose is depressurized. 
The slits are sufficiently long and the film is sufficiently flexible so 
the water drips from the outlets when the hose is pressurized. The slits 
are sufficiently short and the film is sufficiently rigid so the outlets 
close completely when the hose is depressurized. 
Another aspect of the invention is a method for making a drip irrigation 
hose having longitudinal single slit outlets and/or inlets. A first outlet 
and/or inlet forming wheel has one or more knife blades on its periphery. 
A second backing wheel engages the first wheel to establish a first nip 
therebetween. The backing wheel has on its periphery a circumferential 
slot into which the knife blade fits at the first nip. A third rib forming 
wheel has around its periphery impressions that define a desired track 
pattern for the ribs. A second nip is established with a third wheel in 
which the desired track pattern is formed. The first and second wheels are 
mounted on a common shaft to operate in synchronism. A continuous strip of 
plastic film is directed in the following path in the order recited. The 
film is wrapped around the second wheel to reverse direction and pass into 
the first nip, thereby forming the outlet slits. The direction of the film 
is reversed leaving the first nip to transport the film toward the first 
wheel. The film is wrapped around a portion of the periphery of the first 
wheel spaced laterally from the knife blade to reverse direction. The 
direction of the film is reversed to transport the film toward the third 
wheel. The film is transported under an extruder to deposit a bead of 
molten plastic on the film before the third wheel. The film is transported 
into the second nip to form the desired track in the molten plastic. After 
the film leaves the third wheel, the hose is finished. The described 
method forms the inlet slits and the track pattern in a coordinated 
fashion. As a result, the outlets are not restricted or plugged by the 
ribs.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENT 
The disclosures of U.S. Pat. Nos. 4,247,051, 4,984,739 and 5,123,984 are 
incorporated fully herein by reference. 
The drip irrigation hose of the invention is made from a continuous strip 
of flexible, water impervious plastic film, generally ranging in thickness 
between 4 and 15 mil. As depicted by block 10 in FIG. 1, outlets and/or 
inlets are formed in the strip of film along one margin. As described in 
more detail below, each outlet and/or inlet comprises a single 
longitudinal slit in the film. Next, as depicted by block 12, two molten 
plastic beads made of material compatible with the film are deposited by 
an extruder on the margin of the film on either side of the outlet slits. 
Next, as depicted by block 14, the track pattern of the ribs is formed in 
the molten beads by a rib forming wheel. The track pattern is repeated 
each time the rib forming wheel completes a revolution. As depicted by 
block 16, after the ribs are formed, the margins of the film are 
overlapped to position between them the track pattern. Finally, as 
depicted by block 18, the overlapping margins are sealed by the still 
molten ribs to form the finished hose. The described steps, except for 
formation of the outlets and/or inlets, are shown in more detail in the 
referenced '984 patent. Alternatively, either the inlets or the outlets 
could be formed as interruptions in one of the ribs. 
FIG. 2 illustrates the path of a continuous strip of film 38 from which the 
drip irrigation hose is made between the formation of the outlets and/or 
inlets (block 10) and the formation of the track pattern (block 14). An 
outlet forming wheel 20 and a rib forming wheel 22 are mounted on a common 
shaft 24 to synchronize their operation. Wheels 20 and 22 have the same 
diameter. A backing wheel 26 engages outlet forming wheel 20 to establish 
a nip 28 therebetween. A knife blade 30 is mounted on the periphery of 
wheel 20. Wheel 26 has a circumferential slot 32 into which knife blade 30 
fits at nip 28. Direction changing wheels 34 and 36 also define part of 
the film path. Wheels 20, 22, 26, 34, and 36 have flanges to guide film 38 
laterally during the manufacturing operation. 
Wheel 22 has, around its periphery, impressions 66 (FIG. 5) that define the 
desired track pattern, for example, one of the track patterns is shown in 
the '051 patent or in the '739 patent. The direction of movement of film 
38 is depicted by the arrows in FIG. 2. Film 38 is wrapped around wheel 26 
to reverse direction and pass into nip 28. As a result, a slit is formed 
in film 38 each time blade 30 passes into nip 28. A slit is formed each 
time wheel 20 completes one revolution. After leaving wheel 26, film 38 is 
wrapped around wheel 34 to reverse direction and return toward wheel 20. 
Film 38 is wrapped around a portion of the periphery of wheel 20, spaced 
laterally from knife blade 30, to reverse direction. After leaving wheel 
20, film 38 is wrapped around wheel 36 to reverse direction and move 
toward wheel 22. Wheel 36 could be canted slightly to provide a smooth 
transition in the film path between wheels 20 and 22, and the film could 
twist slightly between wheels 36 and 22. As shown in FIG. 5, between 
wheels 36 and 22, film 38 passes under extruders 61 which deposit one or 
more molten plastic beads on one margin of film 38. A backing wheel 64 
underlies wheel 22 to form a nip through which film 38 passes to form the 
molten beads. Since wheels 20 and 22 are mounted on a common shaft, the 
formation of the outlets and the track pattern is coordinated and their 
relative positioning is closely controlled. After leaving wheel 22, film 
38 is finished in the manner illustrated in FIG. 5 Specifically, the 
external overlapping margin of film 38 is folded by a guide 68 to overlap 
the internal overlapping margin of film 38. As a final step, the 
overlapped film 38 passes through the nip of a form wheel 71 and a backing 
wheel 72. Form wheel 70 has a groove 71 that depresses the beads formed by 
extruders 61 to set the bead height at a specified value that determines 
the flow rate of the hose. In a typical embodiment, the diameter of wheels 
20 and 22 would be about from 3 to 6 inches, the diameter of wheel 26 
would be about 4 inches, the diameters of wheels 34 and 36 would be about 
4 inches, and the distance between wheels 22 and 36 would be about 24 
inches. 
If the inlets also comprise slits another knife blade is mounted on the 
periphery of wheel 20 laterally spaced from knife blade 30 and wheel 26 
has another circumferential slot laterally spaced from slot 32 into which 
the other knife blade fits. The inlets as well as the outlets are formed 
as the respective knife blades pass into nip 28. 
FIG. 3 illustrates an alternative film path arrangement that permits wheels 
20 and 22 to have different diameters so that the outlet spacing can be 
greater than the track pattern length, which produces a skip in the outlet 
configuration. Wheel 20 and a toothed wheel 50 are mounted on a shaft 52. 
Wheel 22 and a toothed wheel 54 are mounted on a shaft 56. A toothed belt 
58 couples wheels 50 and 54 to synchronize the rotation of wheels 20 and 
22 in a ratio to cause the desired skip in the outlet spacing relative to 
the track pattern length. In short toothed wheels 50 and 54 and toothed 
belt 58 replace shaft 24 in the embodiment of FIG. 2. The diameters of 
wheels 20, 22, 50, and 54 are selected so the angular velocity of wheel 22 
is a multiple of the angular velocity of wheel 20, depending upon the 
desired outlet skip. As a result, the same rib forming wheel 22 can be 
used to produce a variety of outlet spacings, i.e., skipped outlet 
configurations. 
In FIG. 4, the completed drip irrigation hose is shown. Strip 38 is bent 
along its length to form an overlapping longitudinal seam between an 
interior margin and an exterior margin of the strip. Spaced apart, 
transverse ribs 42 and 43 extend longitudinally through the seam to 
connect the margins of strip 38, forming a seal and a flow regulating 
passage 44 therebetween. A water supply passage 45, having a much larger 
cross-section area then flow regulating passage 44 is defined by the 
remainder of strip 38. Longitudinally spaced apart slits 46 in the portion 
of strip 38 between supply passage 45 and flow regulating passage 44 serve 
as inlets to flow regulating passage 44. Longitudinally spaced apart slits 
47, formed in the exterior margin of strip 38, serve as outlets from the 
hose. Slits 47 are displaced from the respective slits 46 to provide a 
substantial path length from each inlet to a respective outlet. 
Preferably, cross ribs 48 are employed to divide the flow regulating 
passage into segments, such that slit 46 is at one end of the segment and 
a slit 47 is at the other end of a segment. Alternatively, the inlets 
could be formed by interruptions in rib 42 as illustrated in FIGS. 5 and 6 
of the '051 patent and as illustrated in the '739 patent. The shape of 
ribs 42, 43 and 48 are determined by the track pattern on wheel 22 (FIG. 
2). Preferably, chevrons are formed on the adjacent interior surfaces of 
ribs 42 and 43 to create turbulent flow in the flow regulating passage as 
illustrated in the '739 patent. 
By controlling the length of the slits and the flexibility of the film, 
water drips from the outlets when the hose is pressurized without clogging 
when the hose is depressurized. Typically, the line pressure of the water 
used for crop irrigation ranges from about 4 psig to 14 psig. Slits 47 are 
sufficiently long and strip 38 is sufficiently flexible so the water drips 
from the outlets when the hose is pressurized, rather than squirting. The 
effective area of the outlets remains small because the material on both 
sides of the slits remain in the same plane, rather than buckling. If the 
slits are too short or the strip is too rigid, the material on either side 
of the slits does not move sufficiently to make a large hole when the hose 
is pressurized and water squirts out the hose and erodes the soil. Slits 
47 are sufficiently short and strip 38 is sufficiently rigid so the 
outlets close completely when the hose is depressurized. If the slits are 
too long or the strip is too flexible, the slits do not close when the 
hose is depressurized. Typically, the slits are about 1/4 inch for a 4 mil 
film thickness and the slits are about 3/8 inch for a 15 mil film 
thickness. Thus, if the slits are much shorter than about 1/4 inch for a 4 
mil film thickness or if the film is much thicker than about 4 mil for a 
slit length of about 1/4 inch, the water may squirt from the outlets. 
Similarly, if the slits are much longer than about 3/8 inch for a 15 mil 
film thickness or if the film is much thinner than about 15 mil for a slit 
length of about 3/8 inch, the outlets may not close after the hose is 
depressurized. 
The described embodiment of the invention is only considered to be 
preferred and illustrative of the inventive concept; the scope of the 
invention is not to be restricted to such embodiments. Various and 
numerous other arrangements may be devised by one skilled in the art 
without departing from the spirit and scope of this invention.