Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a fluid supply
system and in particular although not exclusively to such
a system for use in inclement environments.
It is of course well known that fluids such as
water may be delivered between spaced locations by using
an enclosed duct such as a plastics pipe with the fluid
being pumped along the pipe. In certain installations,
the pipe may be exposed to sufficiently low temperatures
that the fluid in the pipe may freeze and cause extensive
damage to the fluid supply system. One solution to this
problem is to ensure that the pipe is buried at a depth
where the freezing temperatures are not encountered.
This of course is the normal manner in which water is
supplied to a house.
In certain environments, however, it is not
possible to bury the pipe due to the nature of the
ground, and so alternative solutions have to be found.
Attempts to insulate the pipe are unsuccessful because
the supply may be used intermittently and there is no
residual heat to maintain the fluid above freezing
temperature.
One system that has been utilized is a heating
cable installed within the pipe. However, these have not
been particularly successful as the heating cables do not
permit insulation of the pipe. The heating effect is
constant and may therefore cause boiling of the fluid
within the pipe. To ensure a constant heat loss, the
pipe must remain uninsulated which also means that the
previous systems are very expensive to run. Moreover,
pervious systems require the heater to be activated if
there is any possibility of the temperature falling below
the freezing point which means that the time over which
they must be used is extensive.
It is an object of the present invention to
provide a fluid supply system in which the above
disadvantages are obviated or mitigated.
According to the present invention, there is
provided a fluid supply system comprising an enclosed
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duct having a peripheral wall for conveying fluid between
a pair of spaced locations, thermal insulating means
encompassing the outer surface of said duct, heating
means extending along said duct and coupling means to
permit passage of said heating means across the wall of
said duct, said heating means comprising a self-limiting
heater cable for connection at one end to a power source
external of said duct and sealed at its opposite end to
prevent ingress of said fluid.
By utilizing a self-regulating heating cable
which reduces the heating effect as the temperature
increases, the power consumption is reduced and the pipe
may be insulated to improve the efficiency of the system
further.
In a preferred embodiment, the heater cable
enters the duct along an axis normal to the longitudinal
axis of the duct which then ensures that fluid flow
through the duct is not unduly disturbed.
As a further preference, the coupling through
which the cable may enter the duct includes a pair of
opposed conical surfaces with a complimentary sealing
member disposed between them. The cable passes through
the sealing member.
It is also preferred that the sealing member
has a planar shoulder abutting a planar surface in the
coupling to ensure an effective seal about the cable.
An embodiment of the invention will now be
described by way of example only with reference to the
accompanying drawings in which
figure 1 is a sectional view through a portion
of a water supply system; and
figure 2 is an exploded view similar to figure
1 showing the components of the fluid supply system.
Referring the drawings, a water supply system
10 includes an enclosed duct 12, preferably a plastics
pipe, to convey water from a source not shown to a pump
not shown. Duct 12 includes a continuous peripheral wall
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14 and has a coupling 16 located between two runs of the
duct 12.
The coupling 16 includes a T-fitting 18 having
a pair of aligned threaded bosses 20,22 and a third boss
24 disposed at 90o to the longitudinal axis of the duct
12. Bosses 20,22 receive sleeves 26 each of which has a
nipple 28 at one end for insertion into the duct 12 and
an annular boss 30 at the opposite end for insertion
within the T-fitting 18. A flange 32 extends radially
beyond the boss 30 and is secured to the T-fitting by
means of a compression ring 33 and a threaded collar 34
which co-operates with the respective one of the threaded
bosses 22,24. An O-ring 36 is used to seal between the
boss 30 and the interior of the T-fitting 18 to ensure
watertight connection.
The boss 24 disposed at right angles to the
bosses 22 and 24 is provided to permit entry of a heater
cable 38 into the interior of the duct 12 without causing
a change in teh direction of the flow of water along duct
12. Heater cable 38 is a self-limiting cable such as
that available from the Raychem Corporation under serial
number 3BTV1-CT. Cable 38 is arranged with a pair of
parallel conductors interconnected by heating elements
and operates to reduce the heating effect as the ambient
temperature increases. The distil end of cable 38 is
sealed as indicated at 40 to prevent ingress of fluid
into the cable. The cable comprises a pair of space
conductors with a semi-conductive core extending between
them.
Cable 38 is sealed within the T-fitting 18 by a
sealing member 42 having a pair of oppositely directed
conical surfaces 44,46 that are interconnected by means
of a planar shoulder 48. Seal member 42 has a bore 50
extending through it to accomodate the cable 38 and the
lower conical surface 46 terminates in a cylindrical plug
52.
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The sealing member 42 is received within a
collar 54 that has a conical surface 56. The collar 54
has a circumferential flange 58 that abuts against the
upper surface of the boss 24 with an 0-ring 60 to seal
between the collar and the boss.
The opposite conical surface 44 of seal member
42 is received within the innermost of a pair of nested
rings 62,64. The rings are retained within one another
by means of a detente indicated at 66 and may rotate
relative to one another and thereby avoid transmitting
torque between the two rings.
The rings 62,64 are retained on the boss 24 by
means of the threaded collar 68 engaging with the threads
of the boss 24.
The duct 12 to either side of fitting 16 is
encompassed by an insulating layer 70 of appropriate
thickness to minimize heat transfer. It will also be
appreciated that the heater cable 38 may be connected to
a suitable source of electrical power by means of a
conventional electrical outlet or the like which has not
been shown.
In operation, the fitting 16 is assembled in
the duct 12 and the cable inserted through the seal
member 42 and collar 54. The nested rings 62,64 are then
slid over the cable and onto the outer surface of the
seal member 42. The collar 68 is then threaded onto the
boss and tightened to compress the seal member 42. The
disposition of the rings 62,64 ensures that the torque
induced by the threaded collar 68 is not transmitted into
the seal member 42 and so does not twist the seal member
within the fitting. Moreover, the shoulder 48 provided
between the opposed conical surfaces 44,46 provides a
positive abutment against the upper surface of collar 54
that ensures correct compression of the conical portion
44 by the rings 60,62 and ensures a proper seal against
the cable 38.
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Once the cable is inserted, it is connected to
a suitable power source and then operates to generate
heat within the duct 12. This heat is of course
transferred to fluid in the duct 12 and prevents freezing
of that fluid. Because the cable 38 is self-limiting,
its heating effect diminishes as the temperature about it
increases. Thus, there is no danger of fluid in the duct
12 boiling or any danger of the cable being damaged in
the event that there is no fluid in the duct due to it
having drained.
Because of the self-limiting nature of the
cable 38, it is possible to insulate the duct as shown by
the insulation 70 and thus lower operating costs and also
provide protection against marginal conditions in which
the heating cable is not activated.
It will b e noted that the cable is inserted
through the T-fitting and so does not cause a diversion
of the flow of fluid through the duct 12 at the fitting.
This is of significant importance in the installation as
any undue changes in direction can impede the performance
of the pump connected to the fitting.
