U.S. patent application number 11/101904 was filed with the patent office on 2005-11-24 for trapped gas removal in liquid gas accumulator.
Invention is credited to Draper, Don R..
Application Number | 20050257844 11/101904 |
Document ID | / |
Family ID | 34592559 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050257844 |
Kind Code |
A1 |
Draper, Don R. |
November 24, 2005 |
TRAPPED GAS REMOVAL IN LIQUID GAS ACCUMULATOR
Abstract
A hydraulic accumulator of the liquid-gas type, comprising a
housing (11) defining a chamber (11C), a gas port (30) and a liquid
port (19). A gas charging valve (31) is disposed in the gas port
(30) to control admission of high pressure gas. A semi-permeable
separator (35) is disposed within the housing (11) to separate the
internal chamber (11C) into a gas chamber (33) in communication
with the gas port (30), and a liquid chamber (21) in communication
with the liquid port. A means (41) is within the liquid chamber for
collecting gas which passes from the gas chamber (33), through the
semi-permeable separator, and into the liquid chamber. Included is
a conduit (45) having one end (45a) in communication with the gas
collecting means (41), and another end (45b) operably associated
with the housing (11, 27) to communicate gas from the collecting
means (41) out of the liquid chamber.
Inventors: |
Draper, Don R.; (Chanhassen,
MN) |
Correspondence
Address: |
EATON CORPORATION
EATON CENTER
1111 SUPERIOR AVENUE
CLEVELAND
OH
44114
|
Family ID: |
34592559 |
Appl. No.: |
11/101904 |
Filed: |
April 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11101904 |
Apr 8, 2005 |
|
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10752209 |
Jan 6, 2004 |
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Current U.S.
Class: |
138/30 ; 138/26;
220/530; 220/721 |
Current CPC
Class: |
F15B 2201/205 20130101;
F15B 2201/43 20130101; F15B 21/044 20130101; F15B 1/165 20130101;
F15B 2201/3155 20130101; F15B 2201/4155 20130101; F15B 1/10
20130101; F15B 1/106 20130101; F15B 2201/3152 20130101; F15B
2201/411 20130101 |
Class at
Publication: |
138/030 ;
138/026; 220/721; 220/530 |
International
Class: |
F16L 055/04 |
Claims
What is claimed is:
1. A hydraulic accumulator of the liquid-gas type, comprising a
rigid housing defining an internal chamber and a gas port and a
liquid port; a gas charging valve disposed in said gas port to
control the admission of high pressure gas; a deformable,
semi-permeable separator disposed within said housing to separate
said internal chamber into a gas chamber in communication with said
gas port, and a liquid chamber in communication with said liquid
port; characterized by: (a) means disposed within said liquid
chamber for receiving and collecting gas which passes from said gas
chamber, through said semi-permeable separator, into said liquid
chamber; and (b) conduit means having one end in fluid
communication with said gas collecting means, and another end
operably associated with said housing to communicate gas from said
gas collecting means out of said liquid chamber.
2. A hydraulic accumulator as claimed in claim 1, characterized by
said rigid housing is generally cylindrical and horizontally
elongated, said gas port being disposed at one axial end of said
housing, and said liquid port being disposed at the other axial end
of said housing.
3. A hydraulic accumulator as claimed in claim 2, characterized by
said semi-permeable separator comprising an elongated, generally
cylindrical, elastically-deformable bladder defining therein said
gas chamber, and having one end thereof fixed relative to said
rigid housing adjacent said gas charging valve.
4. A hydraulic accumulator as claimed in claim 3, characterized by
said generally cylindrical bladder being generally centrally
disposed within said internal chamber defined by said rigid
housing; said bladder being surrounded by said liquid chamber under
most operating conditions of said accumulator.
5. A hydraulic accumulator as claimed in claim 4, characterized by
said gas collecting means being elongated, and extending axially
over at least a major portion of the axial length of said internal
chamber, and being disposed above said bladder when said
accumulator is in its operational position.
6. A hydraulic accumulator as claimed in claim 1, characterized by
said means for receiving and collecting gas comprises a transfer
membrane including a gas storage portion through which gas can
travel when said transfer membrane is subjected to normal operating
pressures in said liquid chamber.
7. A hydraulic accumulator as claimed in claim 6, characterized by
said transfer membrane includes a layer of material which is
generally permeable to said gas in said gas chamber, while being
generally impermeable to liquid, said layer of material being
disposed between said gas chamber and said gas storage portion of
said transfer membrane.
8. A hydraulic accumulator as claimed in claim 1, characterized by
said conduit means comprises a tube member having one end in
communication with said gas collecting means and another end in
communication with said housing, said tube member extending
generally axially from said one end to said another end.
9. A hydraulic accumulator as claimed in claim 1, characterized by
said conduit means comprises at least one radially-extending
fitting, said fitting being disposed within a wall of said housing,
and having its radially inner end in communication with said gas
collecting means, and a radially outer end in open communication
with the exterior of said accumulator.
10. A hydraulic accumulator of the liquid-gas type, comprising a
rigid housing defining an internal chamber and a gas port and a
liquid port; a gas charging valve disposed in said gas port to
control the admission of high pressure gas; a deformable,
semi-permeable separator disposed within said housing to separate
said internal chamber into a gas chamber in communication with said
gas port, and a liquid chamber in communication with said liquid
port; characterized by: (a) means disposed within said liquid
chamber for receiving and collecting gas which passes from said gas
chamber, through said semi-permeable separator, into said liquid
chamber, said means comprising said rigid housing having disposed
therein a liner, including at least a portion of which is
semi-permeable with respect to said gas; and (b) conduit means
having one end in fluid communication with said gas collecting
means, and another portion operably associated with said housing to
communicate gas from said gas collecting means, said conduit means
comprising said rigid housing being formed from a porous filament
material which is semi-permeable with respect to said gas.
11. A hydraulic accumulator as claimed in claim 10, characterized
by said liner comprising a material which is substantially
impermeable with respect to said liquid, but generally permeable
with respect to said gas.
12. A hydraulic accumulator as claimed in claim 10, characterized
by said porous filament material being selected such that the ratio
of the dissolved gas within the liquid chamber to the solubility
limit of said gas within said liquid remains below 1.0 during the
normal operating life of the accumulator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part (CIP) of
co-pending application U.S. Ser. No. 10/752,209, filed Jan. 6,
2004, in the name of Don R. Draper for a "Trapped Gas Removal In
Liquid Gas Accumulator".
BACKGROUND OF THE DISCLOSURE
[0002] The present invention relates to hydraulic accumulators of
the liquid-gas type, and more particularly, to such accumulators of
the type having a separator between the gas chamber and the liquid
chamber, wherein the separator is at least somewhat permeable with
respect to the gas.
[0003] Liquid-gas accumulators, of the type to which the present
invention relates, are now generally well known to those skilled in
the art, an example of such an accumulator being shown in U.S. Pat.
No. 5,520,208, incorporated herein by reference.
[0004] A typical liquid-gas hydraulic accumulator is used as a
hydraulic energy storage device, wherein the accumulator may be
"pumped up" with hydraulic fluid (the "liquid") by displacing the
gas volume with hydraulic fluid. The gas pressure within the
accumulator rises, in accordance with the physical properties of
the gas being used, and is approximately equal to the pressure of
the liquid within the accumulator. Subsequently, when hydraulic
pressure is required somewhere in the hydraulic circuit with which
the accumulator is associated, a control device (such as a valve)
will open, thus releasing the stored hydraulic energy, to provide
pressurized flow within the circuit.
[0005] In the typical hydraulic accumulator of the type to which
the present invention relates, there is a rigid outer shell (or
"housing") defining an internal chamber, and some sort of separator
is disposed within the chamber, dividing it into a liquid chamber
and a gas chamber. As is also typical, the liquid chamber is in
communication with the external hydraulic circuit by means of a
hydraulic port and conduit, which may or may not contain a valve
assembly, while the gas chamber is able to receive high pressure
gas from a source of pressurized gas, through a gas charging valve.
Typically, the gas is some form of a relatively inert gas, such as
a nitrogen gas, although it should be understood that the present
invention is not limited to the use of any particular type of gas,
or to any particular type of hydraulic valve or gas valve, or even
to the presence of either of such valves.
[0006] In the conventional hydraulic accumulator of the liquid-gas
type, the separator between the liquid chamber and the gas chamber
may comprise a piston (sealed by an elastomeric sealing ring), or
may comprise some sort of bellows arrangement, or any one of a
number of other separator configurations, which are well known in
the accumulator art. However, most frequently, the separator
comprises an elastomeric bladder comprising any one of a number of
suitable bladder materials known in the art, such as nitrile
rubber. Typically, the materials used for such bladders are
permeable, or at least "semi-permeable", i.e., the material does,
over a period of time, permit some of the nitrogen gas to pass
through the bladder material, into the adjacent liquid chamber.
[0007] The above-described problem of gas permeation through the
bladder is more likely to occur in a relatively high pressure
accumulator, i.e., one in which the maximum pressure of the liquid
is in excess of 3000 or 4000 psi. or more, but such gas permeation
also occurs, to a lesser extent, in low pressure accumulators. As
is well known in the accumulator art, the gas permeation rate is a
function of, among other factors, the gas pressure. In such
liquid-gas accumulators, any gas which permeates through the
bladder will typically remain in solution within the pressurized
liquid. However, at some point, the high pressure liquid containing
the nitrogen gas will flow to a relatively low pressure portion of
the hydraulic circuit, at which point the nitrogen gas will be able
(because of the lower pressure on the liquid) to form gas bubbles
within the circuit. As is well known to those skilled in the
hydraulic art, the presence of air or gas bubbles within a
hydraulic circuit can result in noisy operation of various
hydraulic components, and can cause damage to exposed surfaces of
various hydraulic components (through a process known as
"cavitation"), and eventually, can result in reduced performance
of, or failure of such components.
BRIEF SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the present invention to
provide an improved hydraulic accumulator of the liquid-gas type
which is able to minimize the damage caused within its associated
hydraulic circuit by gas bubbles, resulting from permeation of the
pressurized gas through the permeable separator.
[0009] It is a more specific object of the present invention to
provide an improved hydraulic accumulator which is able to achieve
the above-stated object by receiving the gas which permeates
through the separator, and communicating it to a location external
to the accumulator.
[0010] The above and other objects of the invention are
accomplished by the provision of an improved hydraulic accumulator
of the liquid-gas type, comprising a rigid housing defining an
internal chamber and a gas port and a liquid port. A gas charging
valve is disposed in the gas port to control the admission of high
pressure gas. A deformable, semi-permeable separator is disposed
within the housing to separate the internal chamber into a gas
chamber in communication with the gas port, and a liquid chamber in
communication with the liquid port.
[0011] The improved hydraulic accumulator is characterized by means
disposed within the liquid chamber for receiving and collecting gas
which passes from the gas chamber through the semi-permeable
separator into the liquid chamber. A conduit means has one end in
fluid communication with the gas collecting means, and another end
operably associated with the housing to communicate gas from the
gas collecting means out of the liquid chamber.
[0012] In accordance with a more limited aspect of the invention,
the conduit means may comprise the rigid housing being formed from
a porous filament material which is semi-permeable with respect to
the gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a fragmentary, broken-away axial cross-section of
a hydraulic accumulator utilizing the present invention.
[0014] FIG. 2 is an enlarged, fragmentary axial cross-section,
similar to FIG. 1, illustrating the gas collecting means of the
present invention within the accumulator housing.
[0015] FIG. 3 is an enlarged, fragmentary view, taken in an upward
direction in FIG. 2, but on a somewhat smaller scale than FIG. 2,
illustrating the gas collection means of the present invention.
[0016] FIG. 4 is a fragmentary view, similar to FIG. 2, and on
approximately the same scale, but without showing the accumulator
housing, showing in greater detail certain portions of the gas
collecting means of the present invention.
[0017] FIG. 5 is a transverse cross-section through the gas
collecting means of the present invention, taken on line 5-5 of
FIG. 2.
[0018] FIG. 6 is a fragmentary, transverse cross-section, similar
to FIG. 5, illustrating an alternative embodiment of the present
invention.
[0019] FIG. 7 is a further enlarged, fragmentary, transverse
cross-section, similar to FIG. 5, illustrating another alternative
embodiment of the present invention.
[0020] FIG. 8 is an enlarged, fragmentary, axial cross-section,
similar to FIG. 2, illustrating a further embodiment of that aspect
of the present invention.
[0021] FIG. 9 is a graph of the Ratio (of dissolved gas to the
solubility limit) as a function of Time in days, comparing the
present invention to an accumulator not having the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Referring now to the drawings, which are not intended to
limit the invention, FIG. 1 is a fragmentary, broken-away, axial
cross-section of a typical hydraulic accumulator, modified to
include the present invention. The accumulator includes a housing
11, defining an internal chamber 11C. The housing 11 may be of any
suitable configuration, such as spherical, but is shown herein as
being cylindrical and horizontally elongated. By way of example
only, an embodiment of an accumulator being developed by the
assignee of the present invention includes a housing which is
approximately ten inches in diameter, and approximately forty
inches long. In one hydraulic system being developed by the
assignee of the present invention, both a high pressure accumulator
and a low pressure accumulator are included in the system. In that
particular system, and by way of example only, the present
invention is included as part of the low pressure accumulator.
[0023] Disposed within an opening formed at the left end of the
housing 11 is an oil port ring 13, and bolted to the ring 13 is a
mounting flange member 15, by means of which the accumulator may,
by way of example only, be bolted to a manifold block, or to some
other type of support structure. Disposed within the ring 13 and
flange member 15 is a sleeve 17 which defines a fluid passage 19
(also referred to hereinafter as a "liquid port"), providing fluid
communication between the external hydraulic circuit (not shown)
and a fluid (liquid) chamber 21 disposed within the housing 11.
[0024] The sleeve 17 supports, for reciprocable movement therein, a
valve element 23 which, as is well known to those skilled in the
accumulator art, is biased by a spring 25 toward the open position
of the valve element 23, as shown in FIG. 1. The operation of the
valve element 23, and its interaction with the bladder (which will
be introduced and described subsequently), is well known to those
skilled in the art, is beyond the scope of the present invention,
and therefore, will not be described further herein. It should be
understood by those skilled in the art that the present invention
is not limited to any particular type or configuration of fluid
port and valve arrangement. All that is essential to the present
invention is that the accumulator include some suitable arrangement
for communicating pressurized fluid between the external hydraulic
circuit and the fluid chamber 21.
[0025] Referring still primarily to FIG. 1, disposed within a
right-hand, open end of the housing 11 is a gas port ring 27 (which
is at times hereinafter considered, and referred to, as part of the
"housing"), and bolted to the gas port ring 27 is a cap member 29.
The cap member 29 defines a gas port 30, and disposed within the
gas port 30 is a gas charging valve assembly 31, by means of which
pressurized gas may be communicated from an external source of
pressurized gas into a gas chamber 33 disposed within a bladder 35,
in a manner generally well known to those skilled in the art.
Typically, and by way of example only, the bladder 35 is molded, or
formed by some other suitable means, such that, in the presence of
pressurized gas within the gas chamber 33 (and in the absence of
substantial hydraulic pressure in the fluid chamber 21), the
overall configuration of the bladder 35 will conform generally to
that of the housing 11, as it is represented in FIG. 1. As is shown
only in FIG. 1, the bladder 35 includes, at its rightward end, an
enlarged bead 37 which is retained between the gas port ring 27 and
the cap member 29.
[0026] The accumulator is illustrated in FIG. 1 as being
horizontally oriented, with the fluid valve element 23 being
disposed at one axial end thereof, and the gas charging valve
assembly 31 being disposed at the other axial end thereof. However,
those skilled in the art will understand that, if the accumulator
were to be oriented vertically, rather than as shown in FIG. 1,
there could be provided an annular (rather than elongated) version
of the gas receiver and collector of the present invention, and it
could be disposed under the gas port ring 27. Therefore, although
the present invention would probably be most effective with the
accumulator in the horizontal position shown in FIG. 1, it should
be clear that neither configuration nor orientation comprise
essential features of the invention.
[0027] Referring now to FIG. 2, in conjunction with FIG. 1, it may
be seen that there is preferably a liner 39 (shown also in FIG. 5)
disposed against the interior surface of the housing 11, for
reasons which are now generally well understood in the accumulator
art, and which bear no relationship to the present invention. By
way of example only, the preferred embodiment of the present
invention includes the liner 39 because the housing 11 comprises a
filament wound (or fiber-reinforced) polymeric housing which, in
the absence of the liner 39, could be sufficiently porous to permit
the flow therethrough of a small amount of the hydraulic fluid
contained in the fluid chamber 21.
[0028] Referring still primarily to FIG. 2, the present invention
provides a gas receiving and/or collecting assembly, generally
designated 41, a portion of which may also be referred to
hereinafter as a "transfer membrane", for reasons which will become
apparent to those skilled in the art from a reading and
understanding of the rest of the specification. Preferably, with
the accumulator having its axis of elongation oriented
horizontally, the gas collecting assembly 41 of the primary
embodiment would be disposed at or near the "top" of the internal
chamber (fluid chamber 21) defined by the housing 11, as is shown
in FIGS. 1, 2 and 5. It is preferable, for reasons which will
become apparent subsequently, for the gas collecting assembly 41 to
extend over a major portion of the entire axial extent of the
accumulator, although it should be understood that such is not
essential to the invention, except as is specifically otherwise
noted in the claims. For example, in the subject embodiment, with
the overall accumulator length being about forty inches, as was
mentioned previously, the axial length of the gas collecting
assembly 41 is about thirty inches.
[0029] Referring now primarily to FIGS. 2 through 5, the gas
collecting assembly 41 will be described in greater detail. The gas
collecting assembly 41 includes an internal layer of transfer
fabric 43 which would preferably comprise an open-weave fabric, or
felt, or open-cell foam, or any other suitable fabric or foam-type
material which would not be readily degraded by the particular type
of gas being used as the charging gas in the gas chamber 33 of the
accumulator. However, the transfer fabric 43 must still allow the
passage of the gas (nitrogen or other type of gas) through the body
of the fabric. The primary function of the transfer fabric 43 is to
allow movement of the nitrogen gas which has penetrated to the
inside of the gas collecting assembly 41. The gas collected within
the assembly 41 is the gas which has permeated through the bladder
35, and has risen through the fluid contained within the fluid
chamber 21. By way of example only, the layer of transfer fabric 43
comprises, over most of the axial length of the assembly 41, a true
"layer", approximately as shown in the left-hand portion of FIG. 4
and in FIG. 5.
[0030] The gas collecting assembly 41 further includes an external
barrier layer of semi-permeable material 41 a (not visible in FIG.
4; see FIG. 5), which would preferably comprise a polymeric
material (such as a silicone rubber), and which will allow the
passage (permeation) of gas molecules, but will prevent, or at
least inhibit the passage of the larger hydraulic fluid molecules.
Therefore, as gas rises within the fluid chamber 21, the gas will
readily pass through the barrier layer 41a, and into the transfer
fabric 43.
[0031] At the right end, in FIGS. 2 through 4, of the transfer
fabric 43 is a tube member 45, which has one end 45a (its left in
FIGS. 2 and 4) attached, by any suitable means, such as an adhesive
connection 47, to the gas collecting assembly 41. As may best be
seen in FIG. 2, while the left end 45a of the tube 45 is connected
to the transfer fabric 43 of the assembly 41, there is a right end
45b of the tube member 45, and the right end 45b is received within
an angled bore formed in the gas port ring 27, such that the right
end 45b of the tube member 45 is in open communication with a gas
vent passage 49. The gas molecules, which are collected within the
transfer fabric 43, are free to migrate through the fabric, and
eventually work their way to and through the tube member 45, and
out through the vent passage 49. The migration of the gas molecules
through the transfer fabric 43, and out the tube member 45 is only
slightly assisted by periodic increases in pressure in the fluid
chamber 21, squeezing the layer of the transfer fabric 43.
[0032] Thus, the transfer fabric 43 and the barrier layer 41 a
together comprise the gas collecting assembly 41, which is also
referred to hereinafter in the appended claims as a "means for
receiving and collecting gas", and similar terms. The tubular
member 45 is also referred to hereinafter in the appended claims as
a "conduit means to communicate gas", and similar terms. It may be
seen by comparing FIGS. 4 and 5 that the layer of transfer fabric
43 is not necessarily uniform over its entire axial length. As
noted previously, the left-hand portion (in FIG. 4) of the transfer
fabric 43 is a true layer, but in the region of the left end 45a of
the tube member 45, the transfer fabric 43 includes an enlarged
"transition" region which, in the subject embodiment, appears
generally wedge-shaped surrounding the left end 45a.
[0033] Preferably, and as may best be seen in FIGS. 3 and 5, on the
underside of the gas collecting assembly 41 is a structural layer
51. In the subject embodiment, but by way of example only, the
structural layer 51 acts as a shield to protect the relatively
fragile surface of the gas collecting assembly 41. More
specifically, the purpose of the structural layer 51 is to protect
the assembly 41 from engagement with the bladder 35, as the bladder
moves, while it is expanding or contracting. In the subject
embodiment, and by way of example only, the structural layer 51
comprises a relatively stiff plastic member defining a series of
holes 53, by means of which hydraulic fluid and gas can pass
through the layer 51, and the gas can permeate the assembly 41, as
described previously. Alternatively, the structural layer 51 could
comprise a fabric member, or a perforated metal member, and it
should be understood that the particular details of the layer 51
are not essential features of the invention. As may best be seen in
FIG. 5, the opposite edges of the layer 51 are preferably attached
(such as by a suitable adhesive) to the surface of the liner 39,
thus "enclosing" the gas collecting assembly 41.
[0034] Those skilled in the art will understand that the gas vent
passage 49 may be connected either to the atmosphere, in situations
where it is acceptable for the particular charging gas to be vented
to the atmosphere, or to some sort of gas collection arrangement,
which would typically be disposed external to the accumulator, and
which is beyond the scope of the present invention. What is
important to note is that the tube member 45 is shown by way of
example only, and all that is essential to the present invention is
that there be provided some sort of "conduit means", which simply
means some arrangement or structure or whatever by means of which
the trapped gas can pass from the transfer fabric 43 to another
location.
[0035] For example, and now by reference to FIG. 6, the "conduit
means" could comprise the housing 11 being formed from a porous
filament material, as previously described, in which the polymeric
material is selected to have a porosity such that the wall of the
housing 11 is semi-permeable with respect to the particular gas
being used to charge the accumulator. By "semi-permeable", as used
herein, what is meant is that the material permits enough gas to
pass through (see arrows in FIG. 6), such that gas does not build
up, undesirably, within the fluid chamber 21. At the same time, the
housing would not permit (would be impermeable with respect to) the
passage of fluid from the fluid chamber 21. It is believed to be
within the ability of those skilled in the art of polymers to
select the filament wound polymeric material having the desired
"semi-permeability" as described above.
[0036] Preferably, in the embodiment of FIG. 6, although the
assembly 41 of the main embodiment would be eliminated, as would
the tube member 45, the liner 39 would still be included to further
hinder the passage of fluid through the housing 11. It should be
understood that terms such as "means for receiving and collecting
gas" apply to any of the embodiments shown herein, even though the
end result may be that the gas merely escapes from the accumulator,
and is not literally "collected", in the sense of being capable of
thereafter being communicated to a particular location.
[0037] Alternatively with respect to the embodiment of FIG. 6, the
gas collecting assembly 41 may comprise a single layer of a
semi-permeable material bonded to the liner 39, and bridging a gap,
or a series of gaps, in the liner 39. Therefore, in this
embodiment, gas which has passed from the liquid in the fluid
chamber 21 through the semi-permeable material may then continue
through the gaps in the liner 39, and then penetrate (permeate) the
porous molecular structure of the composite windings of the housing
11. Eventually, this gas will emerge from the housing 11 as free
molecular gas, and pass into the environment. It is believed to be
within the ability of those skilled in the art to select the number
and size of the openings or gaps in the liner 39 so as not to
create significant resistance to the movement of gas molecules
through the liner 39. In accordance with this alternative
embodiment, the tube member 45 and the gas vent passage 49 are not
required elements of the invention, and instead, the porous
passages through the housing 11 comprise the "conduit means" of the
appended claims.
[0038] As a further alternative embodiment, the gas collecting
assembly may comprise a single component, in the form of a
semi-permeable material being used as the material for the liner
39, at least over some portion of the "top" inside surface of the
housing 11, i.e., the portion wherein the assembly 41 of the main
embodiment resides. For example, in this embodiment, the liner 39
(or a local portion thereof) could comprise the same material as
would be used for the semi-permeable material 41a in the primary
embodiment. In accordance with this alternative embodiment, the
tube member 45 and the gas vent passage 49 are again not required
elements of the invention, and instead, that portion of the liner
comprises the "means for receiving and collecting gas" for purposes
of the appended claims, and the porous passages through the liner
39 and through the housing 11 comprise the "conduit means" of the
appended claims.
[0039] As a example of a slightly different embodiment, and with
reference now to FIG. 7, the tube member 45 could be replaced by a
radially oriented tubular fitting 61 defining a radial passage 63
through which trapped gas would escape radially from the transfer
fabric 43. The fitting 61 could be formed of plastic or metal or
any other suitable material, and would preferably be configured
such that it would be retained, as shown, against an inner surface
of the semi-permeable material 41a. In the embodiment of FIG. 7,
but by way of example only, the primary difference from the main
embodiment is the replacement of the tube member 45 with the
fitting 61, thus overcoming any potential problems associated with
flexing and wear of the tube member 45, and the extra expense of
providing and assembling the tube member 45. Also, it should be
apparent that, if desired, several of the fittings 61 could be
provided at various locations around or along the housing 11, and
it is believed to be within the ability of those skilled in the
art, based upon a reading and understanding of this specification,
to select the number and locations of the fittings 61.
[0040] Although the present invention has been illustrated and
described in connection with an embodiment in which the gas chamber
33 is surrounded by the liquid chamber 21, it should be understood
that the present invention is not so limited. Instead, the bladder
35 could contain the liquid, and be surrounded by the gas chamber,
in which case, the gas collecting assembly 41 would be disposed
within the bladder 35 (and probably disposed toward the "top"
thereof), and surrounded by the hydraulic fluid. In this
embodiment, which is within the scope of the appended claims,
unless otherwise specifically noted, the gas which permeates the
bladder 35 would pass through the hydraulic fluid and be received
by and collected within the assembly 41, and then communicated to
the exterior of the accumulator, as described previously.
[0041] Referring now briefly to FIG. 8, there is shown an
alternative version of the main embodiment, simply to illustrate
one possible aspect of the invention which may need to be
addressed. In FIG. 8, the gas vent passage 49, rather than being
fairly small in cross-section over its entire length as in FIG. 2,
includes an enlarged passage portion 71. Disposed within the
passage portion 71 is a check valve assembly 73, the details of
which form no part of the invention. The check valve assembly 73 is
included merely to illustrate and explain that it may be necessary,
in implementing the present invention, to provide suitable
structure so that trapped gas can escape, but air from outside the
accumulator cannot freely enter and mix with the charging gas or
with the fluid in the fluid chamber 21.
[0042] Referring now to the graph of FIG. 9, there is presented a
comparison of the present invention (graph comprising XXX's) versus
an accumulator without the invention (graph comprising OOO's). In
each case, the ordinate is the Ratio of dissolved gas to the
solubility limit (i.e., for that particular gas within the fluid
being used). In the graph of FIG. 9, the numbers relate to reaching
the saturation limit of nitrogen in oil at 60 psig., and at room
temperature. As will be understood by those skilled in the art, it
is desirable for the ratio to always remain below "1.0" to avoid a
build-up of gas within the fluid. By way of example, in a
mathematical analysis of an accumulator of a particular size, with
and without the invention, it has been determined that, without the
invention, the Ratio would rise above "1.0" within what may be
considered a fairly short time (a little over 1000 days) in certain
applications, whereas, with the invention, the Ratio would level
off as shown, and remain well below "1.0" for what apparently would
be an indefinite time.
[0043] The invention has been described in great detail in the
foregoing specification, and it is believed that various
alterations and modifications of the invention will become apparent
to those skilled in the art from a reading and understanding of the
specification. It is intended that all such alterations and
modifications are included in the invention, insofar as they come
within the scope of the appended claims.
* * * * *