Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR A DOUBLE ACTING
RECIPROCATING PISTON ASSEMBLY
Field of the Inveatioa
The present invention relates to a method and
apparatus for improving a double acting
reciprocating piston assembly. NYore particularly,
the reciprocating piston is a free-floating piston
assembly and the method and apparatus may be
employed to recover fluid that leaks by the piston
ring seals.
8ackgrouad of the Iaveation
A reciprocating piston assembly that is a
free-floating piston divides a cylinder into a
drive chamber and a compression chamber. Fluid
pressure in the drive chamber is controlled to
provide a differential pressure between the drive
chamber and the compression chamber to cause
reciprocating movement of the piston assembly.
That is, to cause a compression stroke, fluid
pressure within the drive chamber is higher than
the fluid pressure in the compression chamber. To
reverse the direction of piston movement, fluid
pressure within the drive chamber is reduced so
that fluid pressure within the compression chamber
is higher than fluid pressure within the drive
chamber.
An apparatus comprising a double acting free-
floating piston assembly may be employed to
compress a gas or to pump a liquid. The drive
fluid may be a gas or a liquid. By way of example,
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an apparatus that employs an oil as the drive
fluid is commonly referred to as being
hydraulically driven, whereas an assembly that
employs pressurized air as the drive fluid is
commonly refexred to as being pneumatically
driven.
In an apparatus comprising a double-acting
reciprocating piston assembly, there are at least
two compression chambers and fluid is compressed
when the piston moves in both directions. When a
free-floating piston is employed, there are two
drive chambers with one drive chamber powering the
compression stroke in one compression chamber and
the other drive chamber powering the compression
stroke in the other compression chamber. The
apparatus operates by alternating between
compression and intake strokes fox each
compression chamber with the operation of one
compression chamber offset from tlhe other
Compression chamber by 180 degrees.
In FIG. 1 conventional apparatus 100 employs
a double acting free-floating piston assembly.
Cylinders 101 and 102 are welded to central flange
105 to define a hollow cylindrical body. Fnd
plates '107 and 108 are screwed into and seal
respective ends of cylinders 101 and 102. A free-
floating piston assembly comprises two pistons 110
and 112, which are connected to each other by
solid rod 114. Defined within cylinder 101 are
first compression chamber 120 between piston 110
and end plate 107, and first drive chamber 122
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between piston 1l0 and central flange 105.
Defined within cylinder 102 are second compression
chamber 124 between piston 112 and end plate 108
and second drive chamber 126 between piston 112
and central flange 105.
Fluid flows into first and second compression
chambers 120 and 124 through respective one-way
valves 132 and 136 end out of the same compression
chambers 120 and 124 through respective one-way
valves 134 and 138. Drive fluid flows into and
out of first and second drive chambers 122 and 126
through respective fluid passages 140 and 142.
Double acting reciprocating piston apparatus
100 operates as described in the following
paragraphs.
When the free-floating piston assembly moves
to the left in FIG. l, piston 110 is in the midst
of a compression stroke. Fluid within first
compression chamber 120 is compressed and expelled
therefrom through one-way valve 134 when pressure
within first compression chamber 120 is greater
than'the pressure within the pipe connected to
one-way valve 134. Drive fluid is directed to
first drive chamber 122 through fluid passage 140
to propel first piston 110 towards end plate 107.
Simultaneously, piston 112 is in the midst of an
intake stroke, as drive fluid flows out from
second drive chamber 126 through .fluid passage
142, and new fluid fills expanding second
compression chamber 124 through one-way valve 136.
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When piston 110 completes its compression
stroke, the free-floating piston assembly reverses
direction, and piston 110 begins an intake stroke
and piston 112 begins a compression stroke. That
is, with reference to FIG. 1, the free-floating
piston assembly begins to move to the right, when
drive fluid is directed to second. drive chamber
126 and flows out from first drive chamber 122.
Fluid within second compression chamber 124 is
compressed and eventually expelled therefrom
through one-way valve 138 when pressure within
second compression chamber 124 is higher than
pressure within the pipe connected to one-way
valve 138. Meanwhile, fluid flowing through one-
way valve 132 fills expanding first compression
chamber 120.
Dynamic seals are employed to guard against
fluid leakage between the compression and drive
chambers around the moving components of the free-
floating piston assembly. For example, pistons
110 and 112 have respective ring seals 150 and 160
and seals 170 are provided within central flange
105 around rod 114 to guard against leakage
between the drive chambers.
A problem with a conventional apparatus such
as the one shown in FIG. 1 is that a dynamic seal
has not yet been developed that can guarantee
completely effective sealing. Over the course of
time, a ring seal may wear out and allow some
fluid to leak by it. A ring seal may also have
manufacturing or material defects that can also
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result in leakage. Accordingly, there is a need
for a method and apparatus for recovering fluid
that leaks by dynamic seals between compression
and drive chambers, and guarding against
contamination of one fluid with the other fluid.
Summary of the Invention
A double-acting free-floating piston
apparatus comprises:
(a) a first chamber wherein a first fluid is
introducable and removable;
(b) a second chamber wherein the first fluid
is introducable and removable;
(c) a free floating piston assembly
comprising:
a first piston defining a dynamic
boundary to the first chamber;
a second piston defining a dynamic
boundary to the second chamber; and
an elongated body disposed between
and attached to each one of the first
and second pistons; and
(d) a fluid recovery system comprising:
a first pair of ring seals spaced
apart from each other and disposed
around the circumference of the first
piston;
a first one-way fluid conduit
through which fluid is flowable from a
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space between the first pair of ring
seals to the second chamber;
a second pair of ring seals spaced
apart from each other and disposed
around the circumference of the second
piston; and
a second one-way fluid conduit
through which fluid is flowable from a
space between the second pair of ring
to seals to the first chamber.
In a preferred embodiment, the double-acting
free-floating piston apparatus comprises:
(a) a free-floating piston assembly that
comprises:
a first piston having a first
diameter;
a second piston hawing a second
diameter;
an elongated body disposed between
and attached to each one of the first
and second pistons, the body having a
longitunal portion with a length that is
at least as long as a full piston
stroke, the longitudinal portion having
a third diameter that is less than the
first and second diameters;
(b) a cylinder comprising a bore within
which the free-floating piston assembly
is reciprocable, wherein the bore
comprises:
CA 02379447 2002-03-28
a first section with a diameter
that is a matched fit with the first
diameter;
a second section that is a matched
fit with the second diameter; and
a divider section that is disposed
between the first and second sections
that is a matched fit with the third
diameter; and
(c) a fluid recovery system that comprises:
a first pair of ring seals spaced
apart from each other and disposed
around the circumference of the first
piston;
a second pair of ring seals spaced
apart from each other and disposed
around the circumference of the second
piston;
a first one-way fluid conduit
disposed within the free-floating piston
through which a fluid may flow from a
space between the first pair of ring
seals to a second chamber defined by a
space between the divider section and
the second piston; and
a second one-way f:Luid conduit
disposed within the frees-floating piston
through which the fluid may flow from a
space between the second pair of ring
seals to a first chamber defined by a
CA 02379447 2002-03-28
space between the divider section and
the first piston.
In another preferred embodiment of the
apparatus comprises a free-floating double acting
piston that is reciprocable within a cylinder and
a fluid recovery system that comprises:
(a) a first pair of ring seals spaced apart
from each other and disposed around the
circumference of a first piston;
(b) a second pair of ring seals spaced apart
from each other and disposed around the
circumference of a second piston;
(c) a first one-way fluid conduit disposed
within the free-floating piston assembly
through which the fluid may flow from a
space between the first pair of ring
seals to a chamber defined by a space
between the second piston and an end
that seals the portion of the cylinder
within which the second piston
reciprocates; and
(d) a second one-war fluid conduit disposed
within the free-floating piston assembly
through which the fluid may flow from a
space between the second pair of ring
seals to a chamber defined by a space
between the first piston and an end
plate that seals the portion of the
cylinder within which the first piston
reciprocates.
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The first and second one-way fluid conduits
may be formed by boring into the solid body of the
free-floating piston assembly. However, in
preferred embodiments, the elongated body is
hollow, and the fluid conduits are formed, at
least in part, by pipes disposed within the hollow
interior of the elongated body. Such pipes
preferably each comprise an inlet end that is
connected to a fluid passage that passes through
one of the first and second cylinder heads. The
fluid passage communicates with a space between a
respective one of the spaced ring seals. The pipe
further comprises an outlet end that is connected
to a port opening into a respective one of the
first and second chambers, as described above.
The first and second one-way fluid conduits
extend substantially from one end of the elongated
body associated with the first piston to an
opposite end of the elongated body associated with
the second piston. In preferred embodiments,
during operation of the apparatus, the outlet end
of the pipe is always in communication with the
chamber with which it is associated, regardless of
the position of the free-floating piston assembly.
Each one of the one-way fluid conduits
preferably comprises a check valve for controlling
the direction of flow to allow flow only in the
desired direction. The check valves are located
proximate to respective outlet ends of the fluid
conduits to prevent a significant amount of fluid
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from filling the conduit between the outlet and
the check valve when the associated chamber is
undergoing a compression stroke.
The apparatus is suitable for recovering a
gas or a liquid, although, as described herein,
when the fluid is a gas, piping may not be
required, and the hollow interior of the elongated
body may be employed to convey the recovered gas.
Typically the first and second pistons have
equal diameters, but the apparatus may also be
employed with two pistons that have different
diameters.
A method is provided for recovering a fluid
that leaks within an apparatus comprising a
reciprocable double-acting free-floating piston
assembly. The method comprises:
defining a dynamic boundary to a first
chamber with a first piston of the piston
assembly;
defining a dynamic boundary to a second
chamber with a second piston of the piston
assembly;
capturing the fluid in a first recovery space
between a first pair of spaced ring seals that are
disposed around the circumference of the first
piston, when the fluid leaks from the first
chamber;
directing the fluid from the first recovery
space through a first fluid conduit disposed
within the free-floating piston assembly to the
second chamber;
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capturing the fluid in a second recovery
space between a second pair of spaced ring seals
that'are disposed around the circumference of the
second piston, when the fluid leaks from the
second chamber; and
directing the drive fluid from the second
recovery space through a fluid conduit disposed
within the free-floating piston assembly to the
first drive chamber.
The method may further comprise:
defining a dynamic boundary to a third
chamber with the first piston;
defining a dynamic boundary to a fourth
chamber with the second piston;
capturing a second fluid, which leaks from
the third chamber, in a third recovery space
between a third pair of spaced ring seals that are
disposed around the circumference of the first
piston;
directing the second fluid from the third
recovery space through a fluid conduit disposed
within the free-floating piston to the fourth
chamber;
capturing the second fluid, which leaks from
a fourth chamber, in a fourth recovery space
between a fourth pair of spaced ring seals that
are disposed around the circumference of the
second piston; and
directing the second fluid from the fourth
recovery space through a fluid conduit disposed
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within the free-floating piston assembly to the
third chamber.
In preferred methods, the first fluid is a
liquid and the second fluid is a gas.
Brief Description of the Drawings
FIG. 1 is a section view of a prior art
double acting reciprocating piston apparatus with
a free-floating piston;
FIG. 2 is a section view of an embodiment of
an improved double acting reciprocating piston
apparatus with a free-floating piston assembly.
In this embodiment, the apparatus comprises
features for recovering fluid that leaks by the
piston ring seals . More specifically, the
apparatus comprises fluid passages provided within
the body of the piston assembly for recovering
fluid that leaks from two of the fluid chambers
within the apparatus;
FIG. 3 is an enlarged partial section view of
the embodiment of FIG. 2 showing details of the
fluid recovery features; and
FIG. 4 is a partial section view of another
embodiment of a double-acting free-floating piston
assembly that comprises fluid passages provided
within the body of the piston assembly for
recovering fluid that leaks from the outer fluid
chambers that are between the pistons and
respective end flanges.
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While FIGS. 2 through 4 illustrates specific
embodiments of the invention, it should not be
considered as restricting the spirit or scope of
the invention in any way.
Detailed Description of Preferred ~nbodimeat(s)
With reference to FIG. 2 (and FIG.3 which is
an enlarged view of portions of the apparatus of
FIG. 2); apparatus 200 comprises a double-acting.
free-floating piston assembly that is reciprocable
within a hollow cylindrical body. The hollow
cylindrical body is defined by coaxial cylinders
201 and 202 which each have respective open
flanged ends 203 and 204, and closed ends covered
by respective endplates 207 and 208. Flanges 203
and 204 are employed to join and align the open
ends of cylinders 201 and 202.
The free-floating piston assembly comprises
pistons 210 and 212 and elongated body 214.
Elongated body 214 is disposed between and
attached' to each one of pistons 210 and 212.
Elongated body 214 has a diameter that is less
than the diameters of pistons 210 and 212. The
length of elongated body 214 is at least as long
as a full stroke of the piston assembly.
Piston 210 is reciprocable within a bore of
cylinder 201 and piston 212 is reciprocable within
a bore of cylinder 202. The longitudinal axis of
cylinders 201 and 202 and their respective bores
are aligned with each other in addition to being
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aligned with the longitudinal axis of the free-
floating piston assembly.
Apparatus 200 comprises a pair of drive
chambers and a pair of compression chambers. One
pair of chambers is outer chambers 220 and 224
defined by spaces within respective cylinders 201
and 202 between respective pistons 210 and 212 and
respective end plates 207 and 208. The other pair
of chambers is inner chambers 222 and 226 defined
by the respective annular spaces between elongated
body 214 and respective cylinders 201 and 202,
between divider 205 and the back sides of
respective pistons 210 and 212. 'The pair of
chambers that act as drive chambers depends upon
the function of the apparatus.
In the example illustrated by FIGS. 2 and 3,
inner chambers 222 and 226 are preferably filled
with liquid and outer chambers 220 and 224 are
filled'with a gas. If this apparatus is employed
to pump a liquid using gas pressure directed to
outer chambers 220 and 224, then i~hese outer
chambers act as the drive chambers. For other
applications, the apparatus may be configured to
compress a gas in outer chambers 220 and 224, in
which case inner chambers 222 and 226 would act as
the drive chambers. Apparatus 200 is operable as
a pump or compressor in a manner similar to known
apparatuses with double-acting free-floating
piston assemblies.
A sealing arrangement within apparatus 200
provides a method and apparatus for recovering
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fluid that leaks by a piston rings seal, and
returning the. recovered fluid to an appropriate
chamber within the apparatus. That is, the fluids
from the drive and compression chambers are kept
apart and recovered liquid is returned to a
liquid-filled chamber while recovered gas is
returned to a gas-filled chamber.
A pair of ring seals disposed around the
circumference of piston 210 provides a dynamic
seal for containing fluid within inner chamber
222. Ring seal 25O is spaced apart from ring seal
251. During operation, fluid that leaks by ring
seal 250 is captured in the space between ring
seals 250 and 251. Fluid conduit 252 fluidly
connects the space between rings seals 250 and 251
with inner chamber 226. A one-way flow
controller, such as check valve 253 allows fluid
to flow through conduit 252 only in the direction
of inner chamber 226. Fluid conduit 252 and check
valve 253 are disposed within the body of the
free-floating piston assembly.
A similar arrangement is provided for
recovering fluid that leaks from inner chamber
226. A pair of ring seals disposed around the
circumference of piston 212 provides a dynamic
seal for containing fluid within inner chamber
226. Ring seal 260 is spaced apart from ring seal
261. During operation, fluid that leaks by ring
seal 260 is captured in the space between ring
seals 260 and 261. Fluid conduit 262 fluidly
connects the space between rings seals 260 and 261
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with inner chamber 22:2. A one-way flow
controller, such as check valve 263 allows fluid
to flow through conduit 262 only in the direction
of inner chamber 222.
Pressure alternates between inner chambers
222 and 226: When the pressure within inner
chamber 222 is higher than the pressure within
inner chamber 226, the pressure of the fluid
within conduit 252 is higher than the pressure of
the fluid within inner chamber 226, and the fluid
that leaked from inner chamber 222 is recovered
within inner chamber 226. Similarly, when the
pressure within inner chamber 226 is higher than
the pressure within inner chamber 222; the
pressure of the fluid within conduit 262 is higher
than'the pressure of the fluid within inner
chamber 222, and the fluid that leaked from inner
chamber 226 is recovered within inner chamber 222.
In the illustrated embodiments, elongated
body 21:4 is hollow, reducing weight and material
costs, while also providing a convenient space for
conduits 252 and 262.
An additional feature shown .in the embodiment
of FIGS. 2 and 3 is a sealing arrangement for
recovering gas that leaks from outer chambers 220
and 224. A pair of ring seals disposed around the
circumference of piston 210 provides a dynamic
seal far containing the gas within outer chamber
220. Ring seal 255 is spaced apart from ring seal
256. During operation, fluid than leaks by ring
seal 255 is caught in the space between ring seals
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255 and 256. Fluid conduit'257 fluidly connects
the space between rings seals 255 and 256 with the
hollow interior of elongated body 214. Another
pair of ring seals disposed around the
circumference of piston 212 provides a dynamic
seal for containing the gas within outer chamber
224. Ring seal 265 is spaced apart from ring seal
266. During operation, fluid that leaks by ring
seal 265 is caught in the space between ring seals
265 and 266. Fluid conduit 267 fluidly connects
the space between rings seals 265 and 266 with the
hollow interior of elongated body 214.
One-way fluid passage 258 allows gas to flow
from the interior of elongated body 214 into outer
chamber 220. One-way fluid passage 258 preferably
comprises check valve 259 disposed within the
piston head of piston 210. One-way fluid passage
268 allows gas to flow from the interior of
elongated body 214 into outer chamber 224. One-
way fluid passage 268 preferably comprises check
valve 269 disposed within the piston head of
piston 212. Accordingly; gas that leaks from
outer chambers 220 and 224 collects within the
interior of elongated body 214 until the gas
pressure therein is higher than the gas pressure
within one of outer chambers 220 and 224, at which
point the gas is recovered within the outer
chamber with the lower pressure. This normally
occurs when one of outer chambers 220 and 224 is
undergoing a suction stroke, or when the apparatus
is shut down.
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With reference to FIG. 4, many of the
component parts of apparatus 400 are substantially
the same as the components of apF>aratus 200 and
like components with like functions will not be
described again.
The embodiment of FIG. 4 is suitable for an
apparatus that fills outer chambers 420 a.nd 424
with a liquid, and inner chamber 422 and 426 with
a gas. An example of an apparatus that employs
this configuration would be a gas. intensifier. A
gas intensifier is employed to raise the pressure
of a gas to a very high pressure, and so apparatus
400 utilizes the piston surface area differential
in favor of the drive fluid. That is, by applying
hydraulic fluid pressure to the side of the piston
with the larger surface area, the gas can be
compressed to higher pressures without raising the
pressure of the hydraulic fluid to the same high
pressure.
Apparatus 400 operates on the same principal
as apparatus 200, except that instead of
connecting inner chambers 422 and 426, the fluid
recovery systems connect outer chambers 420 and
424. Ring seals 455 and 456 are spaced apart from
each other and provide dynamic seal between piston
410 and cylinder 401 to contain a fluid within
outer chamber 420. During operation, fluid that
leaks from outer chamber 420 by ring seal 455 is
caught in the space between ring seals 455 and
456. Fluid conduit 457 fluidly connects the space
between rings seals 455 and 456 with outer chamber
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424. A one-way flow controller, such as check
valve 458 allows fluid to flow through conduit 457
only in, the direction of outer chamber 424. Fluid
conduit 457 and check valve 458 are disposed
within the body of the free-floating piston
assembly. Ring seals 465 and 466, fluid conduit
467, and check valve 468 function.-in the same
manner, but to capture fluid that leaks from outer
chamber 424 and direct it to outer chamber 420.
Check valves 458 and 468 are preferably disposed
within the piston heads of respective pistons 412
and 410.
Illustrated apparatus 400 is suitable for
filling inner chambers 422 and 426 with a gas.
Gas that leaks from inner chamber 422 by ring seal
450 is captured between ring seal 450 and 451 and
then'directed to the interior of the free-floating
piston assembly. Similarly, gas that leaks from
inner chamber 426 by ring seal 460 is captured
between ring seal 460 and 461 and then directed to
the interior of the free-floating piston assembly.
When gas pressure within the interior of the
free=floating piston assembly is greater than the
gas pressure within one of inner chambers 422 and
426, gas is returned to the inner chambers through
respective one-way fluid passages 463 or 453.
In another embodiment (not shown), an
apparatus may incorporate both fluid passages 252
and 262 of FIGS. 2 and 3, and fluid passages 257
and 267 of FIG. 4. Such an arrangement may be
employed, for example, when the apparatus is a
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hydraulically driven liquid pump, and such an
arrangement would allow recovery of drive fluid
and the pumped liquid, without filling the hollow
piston-assembly with liquid.
An advantage of the disclosed fluid recovery
arrangement is that leaked fluid is continuously
and immediately recoverable within the apparatus
because of the gressure differential between the
source chamber and the recovery chamber.
As will be apparent to those skilled in the
art in the light of the foregoing disclosure, many
alterations and modifications are possible in the
practice of this invention withowt departing from
the spirit or scope thereof. Accordingly, the
scope of the invention is to be construed in
accordance with the substance defined by the
following claims.
