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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the maintenance of air core cables such as air
core plastic insulated telephone cables and more particularly, to a method
and apparatus for treating air core cables. The apparatus of this
invention includes a treatment tank for containing a treatment liquid,
with an air space provided between the surface of the liquid and the top
of the tank, a cable block applied to a segment of the cable, in order to
isolate a length of the cable to be treated and an air application fitting
and at least one liquid application fitting applied to the cable in spaced
relationship over windows cut in the cable, for introducing air and liquid
into the cable and treating the cable pairs inside the cable. The method
of this invention includes the steps of isolating a segment of cable to be
treated by blocking one end of the segment to be treated, cutting a pair
of spaced windows in the cable and applying an air application fitting to
one of the windows and a liquid application fitting to the other window,
and pumping air and liquid in sequence from the treatment tank through the
air application fitting and the liquid application fitting, respectively,
to treat the cable pairs in the air core of the cable.
2. Description of the Prior Art
One of the problems realized in maintaining the many miles of air core
cables such as air core plastic insulated telephone cables which have been
laid over the years, is that of water intrusion, corrosion and galvanic
action which takes place due to the presence of dissimilar metals in the
cables. These actions produce undesirable electrical shorting of the cable
pairs in the cable core and cause noise, interference and cross-telephone
conversations in telephone lines which are served by the cable. Various
techniques have been used to alleviate this problem, including the pumping
of liquids and gases such as air and nitrogen through the cable to clear
the cable of water and dry the telephone cable pairs. Various types of
compounds such as copper sulfate and sulfuric acid are also formed in the
cables and water intrusion changes the capacitance of the cable, which
increases the noise level in telephone conversations. This problem is
further complicated by the fact that many air core cables include a
plastic outer sheath, an intermediate liner constructed of a metal such as
copper, aluminum or steel metal and an optional plastic inner sheath,
which contains the cable pairs. Under circumstances where the inner
plastic sheath is worn, pitted or otherwise damaged to facilitate water
intrusion to the metal jacket, or where no plastic inner sheath is placed
in the cable, the copper, aluminum or steel oxidizes and forms compounds
which are detrimental to the life and service of the cable pairs located
in the air core cable.
Accordingly, it is an object of this invention to provide a new and
improved method and apparatus for cleaning and treating air core cables
and air core plastic insulated telephone cables in particular, to
eliminate or minimize shorts, crosses and grounds in the cable pairs and
to shield against galvanic action.
Another object of this invention is to provide a new and improved method
and apparatus for treating air core plastic insulated telephone cables by
removing water and moisture from the cables and cleaning the cables and
sheaths of conductive corrosion which interferes with the transmission of
electric current through the cable pairs.
Yet another object of this invention is to provide a method and apparatus
for treating air core plastic insulated telephone cables to seal pin holes
in the cable sheaths, prevent further intrusion of water into the cables
and renew the flexibility of the insulation, as well as to reinsulate bare
spots in the cable pairs which are caused by corrosion.
Still another object of the invention is to provide a new and improved
method and apparatus for treating and internally repairing air core
telephone cables of substantially any size along a cable path of up to
about 1200 feet, including air core telephone cables characterized by
non-filled splices.
Yet another object of the invention is to provide a method and apparatus
for treating air core cables such as air core plastic insulated telephone
cables with air or nitrogen in a first step and a low viscosity, light
demoisturizing insulating and cleaning oil as a treating agent, in a
second step.
Still another object of the invention is to provide a new and improved
method and apparatus for treating air core telephone cables, which method
and apparatus is cost-effective and can be accomplished for about
one-fifth of the replacement cost of the cable.
SUMMARY OF THE INVENTION
These and other objects of the invention are provided in a new and improved
method and apparatus for cleaning and treating air core cables such as air
core plastic insulated telephone cables, including toll and trunk cables,
to reduce hearing loss and noise levels in the telephone system, which
apparatus includes a specially designed treatment tank for containing a
treatment liquid and air or an inert gas, an air application fitting and
liquid application fitting provided on a blocked segment of the cable to
be treated and a pump for pumping air and liquid through the air
application fitting and the liquid application fitting, respectively, to
clear the cable of water and moisture, and treat the cable pairs in the
cable.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be better understood by reference to the accompanying
drawing, wherein:
FIG. 1 is a perspective view of a segment of air core cable to be treated,
further illustrating a cable block and an air application fitting and
liquid application fitting located in functional position for treating the
cable;
FIG. 2 is a sectional view of an alternative preferred embodiment, wherein
a pair of liquid application valves are provided for treating an air core
cable having at least 400 cable pairs;
FIG. 3 is a side view of a preferred treatment tank for containing
treatment liquid;
FIG. 4 is a sectional view of alternative air application pipe and liquid
application pipe fittings for the treatment tank illustrated in FIG. 3;
FIG. 5 is a sectional view of second alternative air application pipe and
liquid application pipe configurations;
FIG. 6 is a side elevation of a typical air and liquid flexible hose used
to connect the saddle air nipple from the air application fitting to the
air application pipe on the treatment tank;
FIG. 7 is a section of the air core cable illustrated in FIG. 1, with a
pair of windows cut in the outer sheath and cable wall and communicating
with the cable pairs for application of the air application fitting and
liquid application fitting illustrated in FIG. 1; and
FIG. 8 is a section of the air core cable illustrated in FIG. 1, more
particularly illustrating a preferred sequence of taping the air
application fitting to the cable.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring initially to FIGS. 1 and 7 of the drawing a section of air core
plastic insulated telephone cable, herein designated as air core cable, is
generally illustrated by reference numeral 1. The air core cable 1 is
blocked at a designated point by a cable block 6 in conventional fashion,
to define a treatment segment which is open at the open end 5. The cable
block 6 is applied to the appropriate point on the air core cable 1 by
injecting a suitable blocking compound such as "Scotchcast 4407
Encapsulating and Blocking Compound", a product manufactured by the 3M
Company, through openings cut in the outer sheath 2 and the inner sheath
3, to block the air core between the cable pairs 4 which extend throughout
the length of the air core cable 1, as illustrated in FIG. 1. Other types
of "blocks" which may be used for isolating a specific segment of the air
core cable 1 to be cleaned and treated, are the "moisture block", "wrapped
block" and "in-sheath pressure block", in addition to the injected block
noted above. The cable block 6 is first effected at the desired location
in the air core cable 1 by well known techniques, according to the
knowledge of those skilled in the art. After the cable block 6 is securely
in place, the air core cable 1 is prepared for installation of an air
application fitting 7 and at least one liquid application fitting 16, as
illustrated in FIG. 1, by cutting a pair of windows 25 in spaced
relationship through the outer sheath 2 and the inner sheath 3 of the air
core cable 1, as illustrated in FIG. 7. The windows 25 communicate with
the air core inside the air core cable 1 and with the cable pairs 4, in
order to facilitate the injection of air or an inert gas such as nitrogen,
as well as a liquid treating solution through the windows 25 and into the
air core cable 1, as hereinafter further described. When the cable block 6
has sufficiently cured and the windows 25 are cut in the air core cable 1
in spaced relationship, the area on the outer sheath 2 surrounding the
windows 25 is then cleaned with a solvent and is scoffed to abrade the
surface of the outer sheath 2. A cement such as a black rubber cement is
then painted around the windows 25 and allowed to dry until "tacky" to the
touch. This technique prepares the air core cable 1 for a "pressure wrap"
installation, as follows. An air application fitting 7, such as the
injection pressure fitting identified as the "Scotchcast 4475" fitting is
then applied to the first of the windows 25 which is closest to the cable
block 6, by placing the air saddle 9 on top of the black rubber cement
coated area adjacent the windows 25, with the saddle air nipple 8
projecting upwardly and communicating with the window 25, as illustrated
in FIG. 1. A strip of 3/4 inch D.R. waterproof splicing tape 38 is then
wrapped around both edges of the air saddle 9 and around the outer sheath
2 of the air core cable 1, to secure the air saddle 9 tightly against that
portion of the outer sheath 2 which surrounds the first of the windows 25.
A D.R. waterproof splicing tape which is suitable for this application is
the "TL-192 Rubber Splicing" tape manufactured by Plymouth Rubber Company,
Inc., of Canton, Mass. A double half-lapped wrap of the D.R. tape 38 is
then completed around and over the air saddle 9 and the outer sheath 2 of
the air core cable 1, to further secure the air application valve 7 to the
first of the two windows 25. In like manner, the liquid saddle 18 of the
liquid application fitting 16 is seated over the remaining area of the
outer sheath 2 which is coated with black rubber cement around the second
of the two windows 25, with the saddle liquid nipple 17 upward-standing
from the liquid saddle 18 and communicating with the underlying window 25.
The liquid application fitting 16 may also be characterized by a
"Scotchcast 4475" fitting, or an equivalent fitting, as desired. Two
strips of D.R. tape 38 are then wound around the liquid saddle 18 near the
edges thereof, in order to secure the liquid saddle 18 tightly over the
second of the two windows 25, as further illustrated in FIG. 1. A double
half-wrap of 3/4 inch D.R. tape 38 is then applied to the entire liquid
saddle 18 to further secure the liquid application fitting 16 in position
over the second of the two windows 25.
Referring now to FIGS. 1 and 8 of the drawing, a double half-lapped wrap of
aluminum tape 39 is then wrapped over the D.R. tape 38, with the
half-lapped wrap extending at least one-half an inch beyond the D.R. tape
38 on either end of the wrap. The aluminum tape 39 is then smoothed with a
smooth object such as a hammer handle, to conform it to the D.R. tape 38
wrap. The aluminum tape 39 is typically characterized by "Aluminum Foil
Pressure-Sensitive Tape 49" manufactured by the 3M Company and serves to
provide an effective moisture barrier over the air saddle 9 and the liquid
saddle 18. A single layer of polyglass tape 40 is then half-lapped over
the aluminum tape 39, to extend at least one-half inch beyond the aluminum
tape 39. The polyglass tape 40 is characterized by the "Scotch Brand 27
Glass Cloth-Backed Electrical Tape" and incorporates great strength at
variable temperature in sealing the air saddle 9 and liquid saddle 18 to
the air core cable 1. A pair of hose clamps 41 are then applied on each
side of the saddle air nipple 8 and the saddle liquid nipple 17 of the air
application fitting 7 and the liquid application fitting 16, respectively,
as illustrated in FIG. 8, to further secure the air saddle 9 and the
liquid saddle 18 tightly over the respective windows 25. Nipple caps (not
illustrated) are then threadibly secured to the projecting, threaded
saddle air nipple 8 and the saddle liquid nipple 17 to protect the threads
(not illustrated) thereon. A final half-lapped layer of vinyl plastic tape
42 is then wrapped over the previously applied polyglass tape 40 and the
hose clamps 41, to cover all areas of the air application fitting 7 and
liquid application fitting 16 installations except the saddle air nipple 8
and the saddle liquid nipple 17. The vinyl plastic tape 42 is typically
the "No. 88T All Weather Telephone Vinyl Plastic Tape" manufactured by the
3M Company.
Referring now to FIGS. 1, 3, 5 and 6 of the drawing, a desired quantity of
treatment liquid is poured into the treatment tank 26 through the filler
neck 27, leaving an air space 15 between the surface 15a of the treatment
liquid and the tank top 29 of the treatment tank 26. In a most preferred
embodiment of the invention the filler neck 27 is located on one end of
the treatment tank 26 at a level which determines the liquid level, or
surface 15a, and hence the size of the air space 15, in the treatment tank
26. An air application pipe 14 extends through the tank top 29 and
terminates in the air space 15 between the surface 15a of the treatment
liquid and the tank top 29. The suction end 24 of a companion liquid
application pipe 23 extends in close proximity to the tank bottom 28 of
the treatment tank 26, leaving an intake space 37 between the suction end
24 and the tank bottom 28, as illustrated in FIGS. 3-5. The discharge end
24a of the liquid application pipe 23 projects through the top of the tank
top 29 in parallel, spaced relationship with respect to the air
application pipe 14, as illustrated. An air fitting 31 is welded or
otherwise attached to the treatment tank 26 near the filler neck 27 and
includes a tee leg 34 and a pressure gauge 32, for monitoring the pressure
of an incoming gas, such as air, which is injected into the treatment tank
26 by a suitable compressor (not illustrated), or nitrogen, from a storage
bottle, as hereinafter described. A handle 30 is provided intermediate the
air application port 14 and the air fitting 31, for carrying the treatment
tank 26 and a leg 36 is provided on one end of the treatment tank 26
beneath the filler neck 27, in order to facilitate tilting the treatment
tank 26 such that small remaining volumes of treatment liquid will flow
through the suction end 24 of the liquid application pipe 23 during the
treatment phase of the process.
In operation, when it is desired to clear that segment of the air core
cable 1 which extends between the cable block 6 and the open end 5 of
water and other accumulation and treat the cable pairs 4, an air hose 11
is first extended between the treatment tank 26 and the air application
fitting 7. The air nipple connectors 10, located on each end of the air
hose 11, are then attached to the saddle air nipple 8 of the air saddle 9
and the air application pipe 14, extending from the treatment tank 26 at
the air nipple end 12 and the air feed end 13, respectively. It will be
appreciated that the air nipple connectors 10 may be each characterized by
quick-disconnect fittings which are compatible with the hydraulic fitting
35 provided on the discharge end 24a of the liquid application pipe 23 and
on the air application pipe 14, as illustrated in FIG. 5, or on such other
fitting as may be compatible with the liquid application pipe 23,
according to the knowledge of those skilled in the art. Furthermore, a
liquid hose 20 is prepared for extension between the treatment tank 26 and
the liquid application fitting 16, with the liquid nipple connector 19
located on the end of the liquid hose 20 which connects to the liquid
application pipe 23, and the air nipple connector 10 adapted for securing
to the saddle liquid nipple 17 in the liquid saddle 18. As in the case of
the air nipple connectors 10, the liquid nipple connector 19 can be
characterized by a quick-disconnect coupling or other coupling designed to
engage the hydraulic fitting 35 located on the discharge end 24a of the
liquid application pipe 23. When the air hose 11 is secured in position as
illustrated in FIG. 1, and in a first embodiment, a cap (not illustrated)
is threaded on the discharge end 24a of the liquid application pipe 23,
the treatment tank is filled to the filler neck 27 with treatment liquid,
the filler cap 27a is threaded on the filler neck 27 and nitrogen or air
is supplied under pressure to the air fitting 31 by means of a pressurized
bottle or a compressor (not illustrated). Alternatively, the self-sealing
hydraulic fittings 35 illustrated in FIG. 5 may be used on the discharge
end 24a of the liquid application pipe 23 and the air application pipe 14
and pressure in the treatment tank 26 need not be reduced. Air pressure
normally not exceeding about 60 psig is then applied to the air space 15
between the surface 15a of the liquid and the tank top 29, with the air
pressure monitored on the pressure gauge 32, located in the air fitting
31. Air is pumped into the air core cable 1 through the air hose 11 and
operates to force water and other accumulated liquid from the air core
cable 1. When the accumulated water and moisture have been substantially
removed from the air core cable 1, the first stage of the method of this
invention has been accomplished and the second stage is undertaken. The
second or liquid treatment stage is then initiated by reducing the air
pressure in the treatment tank 26, removing the cap from the discharge end
24a of the liquid application pipe 23 and connecting the liquid nipple end
22 of the liquid hose 20 to the saddle liquid nipple 17 by means of one of
the liquid nipple connectors 19. The liquid feed end 21 of the liquid hose
20 is then connected to the liquid application pipe 23 by operation of the
air nipple connector 10. The air hose 11 is then removed from connection
to the saddle air nipple 8 and the air application pipe 14 and the air
application pipe 14 is closed with the threaded cap (not illustrated). Air
is again introduced into the treatment tank 26 at least 30 psig and air
pressure forces the treatment liquid from the treatment tank 26 through
the suction end 24 of the liquid application pipe 23 and the liquid hose
20 and through the air core cable 1 in a solid mass, and exits the air
core cable 1 at the open end 5. As noted above, under circumstances where
the self-sealing hydraulic fittings 35 are used on the liquid application
pipe 23 and the air application pipe 14, the air pressure need not be
reduced in the treatment tank 26 and the liquid hose 20 is connected to
the saddle liquid nipple 17 and to the liquid application pipe 23 without
using the cap. When the treatment liquid has completely drained from the
treatment tank 26, air begins to flow through both the air application
port 14 and the liquid application pipe 23 and the air causes a drying
effect in the air core cable 1 and on the cable pairs 4 and serves to aid
in coating the treatment liquid on the cable pairs 4. Since the treatment
liquid coats the cable pairs 4 and the inside surface of the inner sheath
3 of the air core cable 1, the volume of liquid which exits the open end 5
of the air core cable 1 is less than that which was introduced into the
treatment tank 26 and the air core cable 1. After the flow of liquid from
the open end 5 of the air core cable 1 has ceased, the air pressure is
maintained in a range of from about 30 to about 60 psig in the treatment
tank 26 for a sufficient length of time necessary to observe that there is
no liquid bubbling at the open end 5 of the air core cable 1. The air
pressure should be maintained at at least 30 psig, since if the pressure
drops below about 10 psig, the liquid treatment material will "pool" in
the air core cable 1 and the treatment process must be repeated. It has
been found that the liquid treatment material must flow through the air
core cable 1 in a substantially solid wall or slug at least 100-150 ft. in
length, in order to effectively coat the cable pairs 4 and treat the air
core cable 1. When the bubbling of liquid treatment material is minimal at
the open end 5 of the air core cable 1, the cable block 6, air application
fitting 7 and the liquid application fitting 16 are removed from the air
core cable 1 and the air core cable 1 is restored to its original
condition.
As illustrated in FIG. 2 of the drawing, when the process and apparatus of
this invention are used to treat an air core cable 1 having 400 or more
cable pairs 4, an additional window (not illustrated) is cut into the air
core cable 1 and an additional liquid application fitting 16 is taped to
the air core cable beneath the first liquid application fitting 16 in the
same manner as is illustrated in FIGS. 1 and 8. A pair of liquid hoses 20
are then connected to the tee leg 34 of the liquid application pipe 23,
illustrated in FIG. 4, and to the respective saddle liquid nipples 17,
when it is desired to pump treatment liquid into the air core cable 1.
Otherwise, the treatment process is identical to the procedure outlined
above.
It will be appreciated by those skilled in the art that the method and
apparatus for treating air core cables of this invention provides a quick,
efficient and cost-effective means for treating air core cables and air
core plastic insulated telephone cables in particular. The method and
apparatus disclosed herein is inexpensive, in that it requires
approximately one-fifth the cost of replacing the cable and can be
utilized to drastically reduce noise in the cable pairs existing in the
air core cable.
While the preferred embodiments of the invention have been described above,
it will be recognized and understood that various modifications may be
made therein and the appended claims are intended to cover all such
modifications which may fall within the spirit and scope of the invention.
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