Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for
providing a continuous indication of the interior condition of an
enclosed fluid container such as a water heater tank having a
cathodic corrosion protection means therein.
- Containers for fluid such as water heater tanks com-
monly have a steel housing to provide an enclosed chamber for
holding the fluido The interior surface of such steel housing
is subject to corrosion due to contact with the fluid. In order -;
to prevent the corrosion usually the interior surface is lined
with a corrosion resistant material such as glass. However, even
in such glass lined housing, there ls still some bare iron sur-
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face which is exposed to the fluid in the container. ~ ;
The bare iron interior surface in a glass lined orunlined water heater tank is subject to a corrosive action mani-
fested by the existence of a galvanic electromotive force generated
~, between different points on the iron surface and the free ions in
the water. The iron surface is anodic with respect to the water;
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-1 this causes the iron to dissolve gradually. Such corrosion of the
iron interior surface of the water heater tank can be prevented by
mounting in the tank a metal element which is strongly anodic with
respect to all the bare iron surface. The anodic metal element is
electrically connected to the iron interior surface so that it forms
a cell with the iron surface and the water serves as the electro-
lyte of such cell. The iron interior surface becomes cathodic with .
respect to the metal element and the anodic metal element will dis-
-~olve in the process instead of the iron interior surface. Such
anodic metal element is referred to as a sacrificial anode because -
~it is sacrificed in the process such that there is no corrosion of
~he iron interior surface. Magnesium may be used as a sacrificial
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anode in water heater tanKs ~ecause lt does not release any ~oxic
material into the water in the process.
Since the sacrificial anode is depleted in the cathodic
protection process, it is essential to inspect it from time to
time to see if it has been depleted to an ~nsatisfactory state or
if it has depleted completely or there is such an excess amount of . :
liming in the tank that the cathodic protection process is no
longer in operation. Liming is the deposition or accumulation of
.
a layer of hard calcareous material in the tank. However, as ~
10 water heater tanks all have a fully enclosed structure, visual .. -
. inspection of the sacrificial anode and the interior of the tank
: is not possible. Removal of the sacrificial anode for inspection
may not be safely or conveniently made by the user since the
anode must be mounted carefully and the temperature and pressure
in the tank are hazardous if proper preca~ltions are not adopted
in removing the anode. Furthermore, the requency of the removal
of the anode for inspection ma~ not be easily established as it
; varies according to variable conditions such as the mlneral content
in the water supply in a particular district and the rate of water
20 flow according to the amount of water used by the user. ; ~
PURPOSE OF T~IE INVENTION
: It is the principal object of the present invention
to provide a method and apparatus which provides a continuous
indication of the corrosion conditions within an enclosed fluid
. - container having a sacrificial anode therein for preventing
corrosion of said container.
It is an object of the present invention to provide a
,
reference probe means which may be removably mounted on a water - .
heater tank for providing en electrical measurement which is :
indicative of the coxrosion conditions within an enclosed water
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~ heater tank having a sacrificial anode tberein. :
- It is another object of the present lnvention to pro-
vide a means for indicating the liming condition of an enclosed
water heater tank. ,
It is a further object of the present invention to pro-
vide a means for measuring the frequency of water withdrawals from
an enclosed water heater tank.
.; BRIE~ DESCRIPTION OF DR~:WINGS
These and other objects of this invention together with
itsi advantages will be more apparent from the following description
and drawings which illustrate a specific embodiment by way of
example and in which:
Figure 1 is a schematic side elevation view of a water
heater tank having a reference probe means
, according to the present invention;
; Figure 2 is a sectional side view of water heater tank
il drain cock incorporating the reference probe -
means according to the present invention; and
Figure 3 is an exploded perspective view showing the
component parts of the drain cock reference
.;
probe arrangement of Figure 2.
DESCRIPTION OF SPECIFIC EMBODIMENT
,, .
Referring to the drawings, a gas fired hot water tank ~
10 is shown. A gas fired hot water tank is shown as an example of ~ -
the present invention. It will be apparent to one skilled in the
art that similar structures may be incorporated in electrically or
oil operated hot water tanks. The tank has an enclosed steel hous- .
ing 11, the interior surface 12 of which may be lined with a
~ corrosion resistant material such as glass. Usually, in such glass
-, 30 lined water heater tank, many bare iron surfaces still exist such
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as the iron surface of inlet and outlet water pipe couplings,
defects in the glass lining, and, for simplicity of illustration,
the interior surface 12 herein is an unlined bare iron surface.
Water is supplied to the tank through inlet pipe 13
and the volume of water 14 in the tank is heated by a heat transfer
surface 15 provided in the tank~ The heat transfer surface 15 as
shown in this specific embodiment is heated by a gas burner 16.
Gas is supplied to the burner 16 through gas supply condui~ 17 and
a thermostatic controller 18. The gas is also supplied to a pilot
burner 19, The burnt gas is exhausted through a flue 20 having a
flue haffle 21. The hot water is withdrawn from the tank through
outlet pipe 22.
The temperature of the water 14 in the tank is detected
by temperature sensing means 23 and the signal from the temperature
sensing means 23 is fed to the thermostatic control 18 which
controls the supply of the gas to the heating device 15 or the
actuation of the electric heating elements in an electric hot water
tank.
. ~J, The water heater tank 10 is commonly provided with a
.,
drain pipe 24 located at the side and close to the bottom of the
- tank so that the water in the tank may be complately drained if
' re~uired.
A sacrificial anode element 25 is mounted in the tank
in order to provide cathodic protection to the iron interior
surface 12. The sacrificial anode element may be in the form of
an iron or copper core coated with a layer of highly anodic metal
such as zinc, magnesium, aluminium or an alloy of such highly
anodic metals. The sacrificial anode element 25 must be mounted
in direct electrical contact with the iron interior sur~ace 12.
, 30 ~s shown in Figure 1, the top end of the sacrificial anode element
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is in direct electrical contact with the iron interior surface 12. ;
Due to the electrical contact between the sacrificial anode
element and the interior surface and the presence of water 14
which serves as an electrolyte, a current will flow from the higher
potential anode element through the water to the iron interior
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;; surface. This natural electrochemical process will provide a
cathodic protection to the iron interior surface 12. The magnesium
layer on the anode element will be depleted in the process to form
a magnesium salt which is dissolved in the water. No corrosion
will occur in the iron interior surface since it is cathodic with
respect to the water 14 as well as the sacrificial anode element
25.
The effectiveness of the cathodic protection is pro-
portional to the amount of current flowing from the sacrificial ;
anode to the iron interior surface through the water. The current
decreases as the amount of anodic metal of the sacrificial anode
is gradually depleted in the process. It also decreases due to
the accumulating liming deposit which physicall~ insulates the '
anodic metal from the water. Thus, by measuring this current a
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' 20 continuous indication of the condition of the sacrificial anode
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may be obtained. According to the present invention, this current
is indirectly measured by measuring the voltage between the water
and the iron interior surface. The voltage measurement is made by
connecting the negative terminal of a voltmeter to the iron interior
surface and con~ecting its positive terminal to the water. The ~;
connection to the iron interior surface may be made at any con-
venient location such as through the thermostatic controller 18.
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The connection to the water is made through a reference probe means
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26 incorporated in the drain cock 27 which is mounted at the drain
-~ 30 pipe 24. The reference probe means 26 is electrically insulated
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such that it has no direct electrical contact with the iron
interior surface. In this manner, there is no electrochemical
action between the reference probe means and the iron interior
surface, and the reference probe means merely provides an electrical
connection from the water to the positive t~erminal of -the voltmeter.
It is found that typically a voltage potential measurement of more
negative than about ~0.3 volt obtained between the reference probe
and the iron interior surface indicates that adequate cathodic -~
protec~ion is provided by the sacrificial anode element to the iron
interior surface. When the anode element has deteriorated to an
unsatisfactory state, the potential measurement will become more
positive than about -~0.3 volt.
The potential may be measured by a high resistance
'~ voltmeter 28 or other sensitive potential measuring devices which
can provide voltage readings in the millivolt range such as a
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potentiometer so as to avoid polarization errors causPd by current
flowing through the measurement circuit. Thus, the voltmeter ;
provides a continuous visual indication of the efficiency of the
; cathodic protection provided by the sacrificial anode element
. . .
without having to remove the anode element fxom the tank or to
cut open the tank for inspection. Other suitable devices may be
incorporated to provide a visual light signal or sound signal when
, the potential is more positive than positive 0.3 volt.
;' Furthexmore, since the liming deposit on the reference
~ probe means is similar to the liming deposit on the interior
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surface on the tank as well as the surface of the sacrificial anode
element, the reference probe means may be conveniently removed to
,~ provide an indication o~ the degree of liming accumulation in the
~ tank.
-~ 30 The re~erence probe means is preferably made of a ;
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metal which does not release any harmful or toxic material into
the water and does not form corrosion products of variable composi-
tion which could interfere with the potential to be measured. The
corrosion products will make the measured potential erra~ic. Zinc
or stainless steel may be used for such purpose~
Figures 2 and 3 show a specific embodiment of the refer-
ence probe means incorporated in a drain cock of known design. The
reference probe means 26 is a zinc rod. One end of the rod is
mounted over a copper rod or core 30 which :is threadingly mounted
to a substantially cylindrical drain cock body 31 made of an electri-
cally insulating material such as polyvinyl chloride plastics or
hard rubber. The cylindrical cock body 31 has a threaded cylindrical ;
portion 32, a narrow neck portion 33 and a cylindrical tubular
portion 34. The threaded surface of the threaded cylindrical por-
tion 32 is engageable with a threaded collar 35 provided in a plastic
electrically insulated lining 36 formed on the interior surface of
the drain pipe 24. A plurality of longitudinal channels 37 are `
formed on the threaded cylindrical portion 32. The cylïndrical
tubular portion 34 has a circular groove 38 formed at its junction ~'~
with the neck portion for receiving an O-ring 39 to be mounted the~cn. ,~
At least two ports 40 are formed on the tubular portion -
34. The ports 40 communicate with the center longitudinal cavity
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41 of the tubular portion. A second O-ring 42 is mounted on the
tubular portion and positioned against a collar 43 immediately
j adjacent to the ports 40. Four longitudinal ridges 44 are formed
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~l on the tubular portion 34 and an expanded end portion 45 is formed
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'`1 at its free end. The end portion 45 has a bevelled surface
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slanting outwards toward the longitudinal axis o the cylindrical
, ~ body 31. A pluraIity of slits 46 are formed in the end portion
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-~ 30 45 such that it is resiliently flexible radially with respect to
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the longitudinal axis of the cylindrical body.
The cylindrical body 31 is mounted on a cap-like cover
member 47 which has a central sleeve portion 48. The tubular
portion 34 of the cylindrical body 31 may be snugly mounted in
this central sleeve portion as best shown in Figure 2. The radial
resiliency of the end portion of the cylindrical body 31 and the
bevelled surface of the end portion 45 facilitate the insertion
of the tubular portion 34 into the central sleeve portion 48. The
O-ring 42 will be held in a groove 49 formed between the collar 44
of the tubular portion 34 and the sleeve portion 48. The inside
wall of the sleeve portion has a plurality of longitudinal grooves
which engaye with the ridges 44 to prevent any relative rotational
movements between the cylindrical body 31 and the cover body 47.
The central sleeve 48 is surrounded by a spaced con-
centric threaded sleeve 50. The threads 51 of the threaded sleeve ;~
are engageable with the threads 52 of the drain pipe 24 of the
tank for mounting the drain cock thereon. A threaded coupling ~
tube 53 is provided on the drain cock for connection to a con- ~;
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ventional hose for conducting the water to a drain during the
draining operation.
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As best shown in Figure 2, the copper rod 30 extends
throughout the entire length of the cylindrical body 31. A short
end portion o~ the copper rod 30 extends beyond the end of thethrea-
ded cylindrical portion 32 for mounting the zinc rod 54 thereon.
The short end portion of the copper end will be completely covered
by the zinc rod such that the copper rod is not exposed to the ~ -
water in the tank. The other end portion of the copper rod 30
extends through the center o~ the tubular portion 34 of the
`' cylindrical body and the coupling tube 53 for electrical connection
, 30 to the voltmeter 28.
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The threads on the threaded cylindrical portion 32 of
the cylindrical body 31 and the threads on the threaded collar 35
of the drain pipe 14 are left-handed, while the threads 51 and 52
on the threaded sleeve 48 and the drain pipe 24 are right-handed.
The drain cock is mounted on the drain pipe by ro~ating the cover
body 47 counterclockwise such that the threaded cylindrical portion
32 engages with the collar 35. As soon as the threaded cylindrical
portion 32 is drawn past the collar 35, the threaded sleeve 50 may
be engaged with the drain pipe 24 by rotating the cover body
clockwise. The O-ring 42 will snugly engage with the inside wall
of the drain pipe to prevent water from passing between the
cylindrical body 31 and the drain pipe 24. The drain cock may be
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tightened by continuing rotating the cover body clockwise so that
the O-ring 39 will press tightly against the collar 35 to close the
drain pipe.
In the draining operation, the drain cock is loosened - `
by rotating the cover body 47 counterclockwise until the O-ring 39
is spaced from the collar 35 such that the drain pipe is opened, as
shown in Figure 2. The water as shown by the arrows will flow out .
of the tank through the space between the neck portion 33 and the
drain pipe 24 then through the ports 40 and the cavity 41 to the
coupling tube 53. The channels 37 on the threaded cylindrical por-
tion 32 of the cylindrical body 31 acilitate the water to flow more
freely to the space between the cylindrical body and the drain pipe.
The potential measurements provided between the refer-
ence probe means and the iron interior surface of the tank is also
affected by the rate of water flow through the water heater tankO
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Thus, the potential measurements may also be utilized to monitor
the water withdrawal from the tank.
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~l 30 While the invention has been particularly shown and ~
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described with reference to a preferred embodiment thereof, it will
be understood by those skilled in the art that various changes in
form and detail may be made therein without departing from the
spirit and scope of the inventio.n.
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