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The present invention is an improvement over the invention described in the
U.S. Pat. No. 4,232,698, entitled "Pressure Relief Valve with Pressure
Indicating Means".
The present invention relates to pressure relief valves for pressure
cylinders and, more particularly, to pressure relief valves which provide
an indication of the pressure within the cylinder irrespective of the
number of fill and evacuation cycles of the cylinder.
Conventional cylinders which house a fluid under pressure, whether the
fluid be a liquid or a gas, include a conventional valve for controlling
the outflow for the fluid and an upstream located pressure relief valve.
These cylinders, generally referred to as bottles, are usually filled at a
depot to a predetermined pressure, which pressure equates with the
quantity of fluid contained therein. During use of these bottles, pressure
gauges are sometimes not employed and the quantity of the contents within
the bottles is not always accurately known when the bottles are returned
to the depot for refilling. Prior to refilling of the bottles, they are
generally evacuated (pursuant to federal regulations); thus, a user who
returns for refilling partly filled bottles will lose the benefit of the
unused contents. This "lost cost factor" can be substantial over a period
of time. Unnecessarily, the users of the bottles often waste time and
effort in returning nearly filled bottles. Moreover, the users sometimes
misjudge the quantity of contents remaining and run out of fluid at
inopportune moments.
It is, of course, possible to attach conventional gauges to the bottle and
thereby obtain an accurate indication of the quantity of fluid remaining.
However, the attachment of such gauges is time consuming. Another method
of determing the contents of each bottle is that of weighing the bottle.
However, such weighing requires accurate scales and detachment of the
bottle from any equipment to which it might be attached.
There are prior art devices relating to the present invention, including
the safety relief valve described in U.S. Pat. No. 2,526,794. Various
pressure responsive impedance variable devices are illustrated and
described in U.S. Pat. Nos. 2,367,866 and 3,222,581. Circuitry for
providing an indication of pressure extant within a chamber is described
in U.S. Pat. No. 2,355,088.
In the present invention, a conventional rupturable curved disc is
electrically mated with an adjacently located segmented disc to provide a
source of impedance variable in proportion to the pressure within an
accompanying bottle. Due to the nature of the material of the conventional
rupturable curved disc, deformation by increased curvature thereof
(displacement at center) occurs to a more or less perceptable degree
during each evacuation and fill cycle. Therefore, the curvature of the
rupturable disc is repetitively altered. Such alteration is accommodated
by the segmented disc without incurring an accompanying change in the
capacitive range of the capacitor formed by the curved and segmented discs
during each evacuation of the bottle. Such constancy in capacitive range
is achieved by deformation of the segmented disc in correspondence with
equivalent deformation of the rupturable disc during each fill cycle. A
translatable plunger element is physically and electrically in contact
with the segmented disc and serves as an electrical conductor to maintain
electrical continuity. Impedance sensing circuitry is electrically
connected across the plunger element and the rupturable disc, which
circuitry generates a signal responsive to the impedance of and generated
by the capacitor and reflective of the state of pressure and hence state
of fill of the bottle.
It is, therefore, a primary object of the present invention to provide a
means for obtaining an indication of the pressure of a fluid within a high
pressure cylinder during any of many fill and evacuation cycles.
Another object of the present invention is to provide an indication of the
pressure of a fluid within a high pressure cylinder despite cumulative
deformation during each fill cycle of a pressure responsive element.
Yet another object of the present invention is to provide apparatus for
maintaining constant the range of variation of a pressure sensing element
in a high pressure cylinder despite repeated deformations of such element
due to repeated fills of the cylinder.
Yet another object of the present invention is to provide apparatus for
maintaining constant the capacitive range of adjacent capacitor plates of
a pressure sensing element mounted within a pressure relief valve despite
deformation of one of the plates.
A further object of this invention is to provide a deformable capacitor
within a pressure relief valve which capacitor maintains a predetermined
capacitive range subsequent to such deformations.
A yet further object of the present invention is to provide an inexpensive
pressure relief valve which provides an indication of the pressure acting
upon the valve despite deformation of the valve resulting from multiple
fill and evacuation cycles of an attached high pressure cylinder.
These and other objects of present invention will become apparent to those
skilled in the art as the description there proceeds.
The present invention may be described with greater specificity and clarity
with reference to the following drawings, in which:
FIG. 1 illustrates a pressure relief valve embodying the present invention
in the stem of a valve connected to a high pressure cylinder;
FIG. 2 is a cross-sectional view taken along lines 2--2, as shown in FIG. 1
and FIG. 2a is a detail view of structure shown in FIG. 2;
FIG. 3 is a plan view of a segmented disc located within the pressure
relief valve;
FIG. 4 illustrates a first state, reflective of a filled cylinder, of the
pressure responsive elements within the pressure relief valve;
FIG. 5 illustrates a second state, reflective of an evacuated cylinder, of
the pressure responsive elements within the pressure relief valve; and
FIG. 6 illustrates a third state, reflective of an again filled cylinder,
of the pressure responsive elements within the pressure relief valve.
Referring to FIG. 1, there is shown a conventional high pressure cylinder
or bottle 10 which bottle might contain a fluid, such as oxygen or other
gas. A conventonal valve assembly 12, including an outlet pipe 14, is
generally permanently attached to the bottle. It is to be understood that
many configurations serving the function of valve assembly 12 are in
commercial use. For most fluids, federal regulations require that the
relief valve be attached to bottle 10 to prevent explosion in the event
the pressure of the fluid within the bottle exceeds the pressure retaining
capacity of the bottle. Therefore, most permanently attached valve
assemblies also include a pressure relief valve, which valve is identified
by numeral 16.
In order to determine the degree of fill of bottle 10, a pressure gauge is
generally used and the indication of pressure provided thereby can be used
to calculate the degree of fill. The attachment of the pressure valve,
such as to outlet pipe 14, is time consuming and necessitates a loss of
fluid upon removal of the pressure gauge. For some fluids, such loss is
inconsequential, but where toxic or poisonous fluids are released, severe
health hazards may be present. Additionally, some financial detriment
results from the loss of fluids. Aside from these losses, the necessary
time for an operator to attach a pressure gauge, obtain a reading
therefrom and then detach the pressure gauge, represents a substantial
labor expense, which expense should be avoided if possible.
As pressure relief valve 16 is necessarily always in fluid communication
with the interior of bottle 10, the conventional rupturable element or
curved disc contained therein is responsive by flexing to the ambient
pressure. Should the pressure within bottle 10 increase beyond the
specified upper limits, the flexing capability of the disc will have been
exceeded and it will rupture. Upon rupture, the fluid will flow through
the rupture and be dissipated through relief ports 18 disposed as part of
the pressure relief valve. As the rupturable disc flexes in response to
pressure variations, such flexing, if the disc constitutes one plate of a
capacitor, produces a change in capacitance or impedance of the capacitor.
By maintaining a second plate of the capacitor in a fixed position
relative to the maximum (full) pressure position of the first plate, the
variation in impedance of the capacitor resulting from the flexing disc in
response to pressure variations can be sensed by impedance responsive
circuitry.
Still referring to FIG. 1, there is shown an electrical conductor 20
electrically attached to the housing of pressure relief valve 16, which
housing is electrically connected to the flexing disc. An electrical
conductor 22 is electrically attached to lead 24, which lead is an
electrical communication with the second plate of the capacitor. A sensing
circuit 26 is responsive to a variation in the electrical signal across
electrical conductors 20 and 22 which signal results from a change in
impedance of the capacitor. The response sensed may be displayed upon a
meter 28 to reflect either the degree of pressure or the amount of fluid
within bottle 10.
Referring to FIG. 2, the constructional details of pressure relief valve 16
will be described. A collar 30 threadedly engages a hollow stem 32
extending from outlet pipe 34 (see FIG. 1) of valve assembly 12. Collar
30, by means of annular shoulder 36 and a malleable annular seat 38
sealingly secures a rupturable flexible curved disc 40 across outlet 42 of
stem 32. Thereby, leakage through stem 32 will not occur unless curved
disc 40 ruptures. In the event curved disc 40 ruptures, a fluid flow
through the curved disc will be dissipated through relief ports 18
extending through shank 44 of collar 30.
Generally, curved disc 40 may be of beryllium copper or nickel-based alloys
which have electrical properties suitable for employing the curved disc as
one plate of a capacitor and are of sufficient elasticity and tensile
strength to flex predictably in response to pressure variations within the
cylinder. An electrically insulating centrally apertured plug 46 is in
threaded engagement with the interior surface of shank 44. Central
passageway 48 within plug 46 supports a pedestal 50, one end of which
includes a cylindrical cavity 52. A dished contact 54 is attached to a
translatable shank 56, which shank is slidably located within cylindrical
cavity 52. The tolerance of fit between shank 56 and cylindrical cavity 52
is such that the shank will slide under pressure (in response to a force)
but it will not return to its former position and it will maintain the new
position. Both the dished contact and its shank are electrically
transmissive and in electrical communication with pedestal 50 via the
surface of cavity 52.
Referring jointly to FIGS. 2 and 3, the elements forming the capacitor
within the pressure relief valve will be described. A curved centrally
segmented disc 58 includes a pluarlity of inwardly extending segments 60.
Each segment may be triangular shaped as illustrated and may have an apex
62 located in proximity to the center of the disc. The segments should be
manufactured to have a permanent bias against curvature to a smaller
radius of curvature. During original installation, apices 62 of the
segmented disc will be compressed against dished contact 54 to a smaller
radius of curvature. Because of the bias, the segments will continuously
bear against the dished contact despite translation of the dished contact.
Electrical separation between curved disc 40 and segmented disc 58 may be
established by a layer of insulation 66 developed upon the surface of the
segmented disc facing the curved disc. An insulating ring 66 is located
circumferentially within bore 70 of collar 30 to prevent segmented disc 58
from shifting laterally and from preventing electrical contact with the
collar.
As illustrated in FIG. 2, the free ends terminating at apices 62 of
segments 60 acting through dished contact 54 will force shank 56 to
translate axially further into cylindrical cavity 52. Thereby, further
bending for an increase in curvature of segmented disc 58 is not inhibited
and yet electrical contact between the segmented disc and dished contact
54 is maintained inviolate.
It is well known that each fill cycle of bottle 10 will cause a degree of
displacement or deformation of the curved disc which results in a
permanent increased curvature. Despite each such deformation, the curved
disc will respond to a reduction in pressure within the bottle during
evacuation by a physical change to a less curved (displaced)
configuration. For reasons not presently precisely known, the amount of
reduced curvature (or displacement) of the curved disc resulting during a
reduction in pressure within the bottle will be essentially constant
despite previous substantial increases in curvature in the curved disc due
to deformation thereof resulting from past repeated fill cycles.
Because curved disc 40 is deformed in curvature during each fill cycle,
even though the change in displacement it exhibits during each evacuation
cycle is essentially constant, a second element associated therewith to
render the combination functional as a capacitor must be deformed in a
similar manner and to the same extent. Otherwise, the impedance
represented by curved disc 40 and segmented disc 58 acting as the plates
of a capacitor would progressively alter as deformation occurred. An
indication responsive to such impedance would not be indicative of the
state of fill of the bottle. It is therefore the function of segmented
disc 58, in cooperation with curved disc 40, to serve as a reference point
to permit the two discs to act as a capacitor capable of providing useful
information.
It is known that conventionally sized rupturable discs, like curved disc
40, may be deformed and displaced at the center on the order of
0.020-0.030 inches during the life of the pressure relief valve. It is
also known that the change in displacement at the center of the curved
disc during each evacuation cycle is on the order of 0.001 inch. This
latter displacement remains essentially constant even though the center of
the disc may have been deformed 0.030 inch during past fill cycles.
During each evacuation and fill of bottle 10, curved disc 40 will respond
by a change in displacement or curvature, in the order of 0.001 inch as
noted above, in response to the attendant pressure variations acting
thereon. As such pressure variations do not act upon segmented disc 58,
the latter is maintained in a stable physical configuration. Accordingly,
the capacitance between curved disc 40 and segmented disc 58 will be a
function of the change in curvature of curved disc 40. Such change in
capacitance may be sensed by circuitry 26 and indicated by meter 28 as the
degree of fill of bottle 10.
Each new fill of bottle 10 will cause further deformation of curved disc 40
resulting in increased curvature of the disc, which increased curvature
will impose an increased pressure upon each of segments 60, causing
angular displacement of each segment. Such displacement of the segments
results in translation or displacement of apices 62 away from one another
and in the direction of dished contact 54. The resulting force exerted by
apices 62 upon the dished contact will produce commensurate translation of
shank 56 within cavity 52 as a function of both the force exerted and the
surface configuration of the dished contact against which the apices bear.
It may be emphasized that physical and electrical contact between the
apices and the dished contact is maintained during such change in
displacement or curvature of segments 60. Moreover, as the surface area of
segmented disc 58 coincident with curved disc 40 remains essentially
unchanged, the basic parameters of the capacitor formed remain essentially
constant.
As curved disc 40 reduces in displacement or curvature upon evacuation of
bottle 10, no corresponding force will act upon segmented disc 58 and the
latter will remain in a stable position. Accordingly, the degree of
capacitance between the two discs will change during evacuation and the
change can be indicated by meter 28. During the next fill of bottle 10,
further deformation of curved disc 40 will occur and commensurate
repositioning of segments 60 and displacement of apices 62 will result and
the segmented disc is repositioned to a new reference location.
The above described relationships are graphically illustrated in FIGS. 4,
5, and 6. For demonstrative purposes it will be assumed that the
configuration of curved disc 40, segmented disc 58 and dished contact 54
shown in FIG. 4 represents a filled state of an associated bottle 10. In
this state, the displacement of curved disc 40 from a reference line, "R",
is equivalent to the distance represented by "a.sub.1 ". Likewise, the
displacement of the apex of segmented disc 58 is equivalent to the
distance represented by "b.sub.1 ".
FIG. 5 is representative of a second state of fill of bottle 10, in this
case empty. The displacement of the apex of curved disc 40 is now
represented by "a.sub.2 " and the displacement of the apex of segmented
disc 58 is still represented by "b.sub.1 ", as no force has acted upon the
segmented disc to induce a change in displacement. For reasons stated
above, the difference between dimensions a.sub.1 and a.sub.2 is
approximately 0.001 inches.
FIG. 6 illustrates a second state of fill of bottle 10 which fill cycle has
caused a deformation of curved disc 40. Dimension a.sub.1 represents the
maximum displacement of curved disc 40 during the previous cycle. During
the subsequent fill, curved disc 40 has been deformed to locate the apex
at a displacement represented by "a.sub.3 ", where a.sub.3 is greater than
a.sub.1 ; the displacement or curvature of the curved disc has therefore
been increased. The increased curvature of curved disc 40 acting upon
segmented disc 58 will cause a change in displacement or curvature of the
segmented disc. Such change in curvature results in relocating apices 62
further from each other and from reference line R at a dimension
equivalent to b.sub.2 where b.sub.2 is greater than b.sub.1. The
difference between b.sub.2 and b.sub.1 is the same as the difference
between a.sub.3 and a.sub.1. During the next evacuation cycle, the changes
described with reference to FIG. 5 would be repeated.
It may be noted that the material of which the segmented disc is formed
must be of such stability and elasticity to permit displacement or
deformation in response to the deformed expansion of curved disc 40 but,
due to the originally imposed bias the segmented disc is not permitted to
resume its previus state of curvature.
While the principles of the invention have now been made clear in an
illustrative embodiment, there will be immediately obvious to those
skilled in the art many modifications of structure, arrangement,
proportions, elements, materials, and components, used in the practice of
the invention which are particularly adapted for specific environments and
operating requirements without departing from those principles.
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