Note: Descriptions are shown in the official language in which they were submitted.
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"Reciprocating Pump"
Field of the Invention
This invention relates to a reciprocating pump.
The invention has been devised particularly for pumping seawater at high
pressure. It should, however, be understood that the invention may also find
application for pumping of various fluids other than seawater.'
Background Art
In International Application PCT/AU03/00813, there is a proposal for
harnessing
wave energy and converting the wave energy to pressurised fluid for use in any
appropriate way. In a typical application, the fluid comprises seawater drawn
from
the ocean environment in which the apparatus operates. The seawater is pumped
under high pressure to shore for utilisation there.
Pumping of seawater at high pressure, possibly in excess of 70 Bar, utilising
a
reciprocating pump powered by wave energy (and thus likely to have a
relatively
slow moving, variable stroke) can present technical difficulties.
A pump exposed to difficult operational conditions, such as pumping of
seawater
at high pressure, may require the various attributes. The pump may, for
example, require the ability to handle corrosive or other aggressive fluids
(such as
seawater) over an extended service life. Further, the pump may require the
ability
to operate with irregular and non-sinusoidal strokes (as may be produced from
a
drive train powered directly by a renewable energy source such as wave
motion).
There may also be a need to tolerate a degree of misalignment (i.e. tilting of
the
piston axis). It may also be desirable that the pump be relatively easy to
maintain
(for example, easy to lubricate). Further, relatively low mechanical
dissipation (i.e.
relatively high efficiency) would be particularly advantageous.
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The present invention seeks to provide a pump capable of meeting at least one
of
the attributes specified above.
Disclosure of the Invention
According to one aspect of the invention there is provided a reciprocating
pump
comprising a body defining an internal space and an opening onto the internal
space, an operating element extending through the opening and into the
internal
space, a sheath closing the opening and embracing an inner portion of the
operating element, a pumping chamber defined between the body and the sheath,
the sheath being deformable in response to reciprocatory movement of the
operating element to effect volume change within the pumping chamber, and a
cavity about the operating element adjacent the open end of the sheath.
The cavity may serve one or more purposes. The cavity may, for exarriple,
provide a reservoir for lubricant. In addition, or alternatively, the cavity
may assist
in accommodating angular misalignment of the operating element.
Typically, the cavity comprises an annular cavity.
Preferably, the cavity is defined between the periphery of the operating
element
and a surrounding surface.
In one arrangement, the surrounding surface may be defined by a reinforcement
sleeve formed separately of the sheath and located in a recess within the
sheath.
In another arrangement, the surrounding surface may be defined by the open end
portion of the sheath. In such an arrangement, the open end portion of the
sheath
may incorporate reinforcement for maintaining the end in an open condition
spaced from the operating element, whereby the cavity comprises the space
between the open end portion of the sheath and the operating element. The
reinforcement may comprise a reinforcement ring incorporated into the sheath.
The cavity may be closed at the outer end thereof by a seal such as a wiper
seal.
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The operating element may be configured as a plunger.
The open end of the sheath may be configured to provide a mounting flange.
The sheath may comprise a first portion which is generally stable and which
preferably provides the mounting flange, and a second portion which embraces
the plunger and which deforms through expansion and contraction upon
reciprocatory movement of the plunger
Preferably, the cavity is accommodated within the confines of the first
portion.
The second portion may comprise a surface which confronts the plunger. The
surface of the shroud second portion confronting the plunger may be configured
to
accommodate lubricant.
The configuration of the surface for accommodating lubricant may comprise
formations on the surface. The formations may create interstices in which
lubricant can be trapped. The formations may be of any appropriate form, such
as knobs, ridges or other protrusions, or alternatively dimples.
The lubricant may be any substance that reduces the sliding friction between
the
outer surface of the plunger and the inner surface of the sheath .so that
there is
uniform sliding between the two surfaces without striction.
The lubricant may, for example, comprise seawater itself, silicon grease,
castor
oil, brake fluid and polypropylene glycol.
The outer surface of the plunger may be coated with an appropriate low-
friction
material, such as polytetrafluoroethylene.
There may be provision for lubricant to be fed within the sheath. Such
provision
may include formations on the inner surface of the sheath. The lubricant may
be
so fed either under gravity or under pressure.
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In one arrangement, lubricant can be fed to the region adjacent the inner end
of
the sheath. This can be done by way of a lubricant delivery path in the
operating
element.
According to a second aspect of the invention there is .provided a
reciprocating
pump comprising a body defining an internal space and an opening onto the
internal space, an operating element extending through the opening and into
the
internal space,, a sheath closing the opening and embracing an inner portion
of
the operating element; a pumping chamber, defined between the body and the
sheath, the sheath being deformable in response to reciprocatory movement of
the operating element to effect volume change within the pumping chamber, a
recess in the sheath adjacent the open end thereof, a reinforcement sleeve
located in the recess, whereby a cavity is defined between the reinforcement
sleeve and the operating element.
According to a third aspect of the invention there is provided a reciprocating
pump
comprising a body defining an internal space and an opening onto the internal
space, a plunger extending through the opening and into the internal space, a
sheath closing the opening and embracing an inner portion of the plunger, a
pumping chamber defined between the body and the sheath, the sheath being
deformable in response to reciprocatory movement of the plunger to effect
volume
change within the pumping chamber, the sheath comprising a first portion which
is
generally stable and a second portion which embraces the plunger and which
deforms through expansion and contraction upon reciprocatory movement of the .
plunger, the first portion defining a mounting flange clampingly engaged with
the
body.
According to a fourth aspect of the invention there is provided a
reciprocating
pump comprising a body defining an internal space and an opening onto the
internal space, a plunger extending through the opening and into, the internal
space, a sheath closing the opening and embracing an inner portion of the
plunger, , a pumping chamber defined between the body and the sheath, the
sheath being deformable in response to reciprocatory movement of the plunger
to
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effect volume change within the pumping chamber, and feed means for feeding
lubricant into the region between the plunger and the sheath.
According to a fifth aspect of the invention there is provided a sheath
comprising a
first portion defining a mounting flange and a second portion adapted to
embrace
a plunger received within the sheath, the second portion being adapted to
expand
and contract upon reciprocatory movement of the plunger.
Brief Description of the Drawings
The invention will be better understood by reference to the following
description of
several specific embodiments thereof as shown in the accompanying drawings in
which:
Figure 1 is a schematic perspective view of a reciprocating pump according
to a first embodiment;
Figure 2 is a sectional elevational view of the pump of Figure 1;
Figure 3 is a sectional side elevational view of the pump of Figure 1;
Figure 4 is a fragmentary view, on an enlarged scale, illustrating an
arrangement of parts between the pump plunger and the pump body;
Figure 5 is a sectional elevational view of the pump body;
Figure 6 is a schematic perspective view of a sheath forming part of the
pump;
Figure 7 is a side view of the sheath;
Figure 8 is a fragmentary view illustrating part of the sheath on an enlarged
scale;
Figure 9 is a side elevational view of an upper part of the pump plunger;
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Figure 10 is a.perspective view of a lower part of pump plunger;
Figure 11 is a sectional elevational view of the lower plunger part;
Figure 12 is a fragmentary view, on an enlarged scale, of one end of the
plunger, illustrating a diffuser accommodated therein;
Figure 13 is a sectional elevational view of the diffuser;
Figure 14 is a schematic perspective view of diffuser;
Figure 15 is a schematic elevational view of a sheath for a pump according
to a second embodiment; and
Figure 16 is a fragmentary view illustrating part of the sheath of Figure 15.
Best Models) for Carrying Out the Invention
Referring to Figures 1 to 14 of the drawings, there is shown a reciprocating
pump
10 according to a first embodiment which is particularly suitable for pumping
seawater under high pressure. The seawater is drawn from the ocean itself and
so is at an initial pressure corresponding to the hydrostatic pressure at the
ocean
depth from which the seawater is drawn.
Where the pump 10 is powered by wave energy, it typically operates with a slow-
moving, variable stroke. The pump is of a construction particularly suited to
such
an application.
The pump 10 comprises a body 11 configured as a cylindrical pressure vessel
defining an internal space 13. The body 11 comprises a cylindrical side wall
15
and an end wall 17 at one end of the cylindrical side wall 15. The end wall 17
has
an opening 18 therein. The other end of the cylindrical side wall 15 is closed
by a
base 19.
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The end wall 17 is defined by an end plate 20 detachably connected to the
cylindrical side wall 15, the detachable connection in this embodiment being
provided by machine screw fasteners
The pump 10 further comprises an operating element 23 comprising a plunger 25
having a cylindrical side face 26 and an end face 27. The plunger 25 is
attached
to a connector 28 adapted to undergo reciprocatory.motion under the influence
of
a drive train powered, for example, by wave motion. .In this embodiment, the
connector 28 is configured as a hinge bush which . receives a hinge pin 29
connected . to a lever (not shown), whereby reciprocation of the lever imparts
reciprocation motion to the plunger 25.
The plunger 25 extends into the internal space 13 through the opening 18
within
the end wall 17.
A sheath 30 is mounted on the body 11 about the opening 18 for embracing that
portion of the plunger 25 extending into the internal space 13. The sheath 30
is
made of an, elastomeric material, preferably rubber.
The sheath 30 is attached to the body 11 to close the opening 18, whereby a
pumping chamber 33 is defined between the sheath 30 and the body 11. The
sheath 30 provides a deformable boundary surface for the pumping chamber 33,
whereby deformation of the boundary surface effects a change of volume of the
pumping chamber 33.
The body 11 incorporates an inlet 12 and an outlet 14, both of which
communicate
with the pumping chamber 33.
The sheath 30 comprises a first portion 31 and a second portion 32, with the
two
portions being formed integrally. The first portion 31 is substantially rigid
in the
sense that it does not undergo significant deformation during operation of the
pump. The second portion 32 embraces the plunger 25 and is adapted to
undergo extension and contraction during operation of the pump.
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The first portion 31 is configured to provide a mounting flange 35. The second
portion 32 is of generally tubular construction; involving a tubular wall
section 36
and a~ end section 37, with the flange 35 provided by the first portion 31
being at
one end of the tubular wall section 36 and the other end of the tubular wall
section
being closed by the end section 37.
The mounting flange 35 defined by the first portion 31 is secured to the body
11
through clamping engagement between the end wall. 17 and an annular seat 38.
The seat 38 is defined by a seat element 39 mounted on an annular shoulder 40
provided internally on the cylindrical side wall 15 inwardly of the end wall
17.
The mounting flange 35 has an outer end face 41 for bearing against end wall
17
and an inner end face 43 for bearing against seat 38 in sealing engagement
therewith.
The first portion 31 further includes an annular recess 45 which opens onto
outer
end face 41. ~ The recess 45 is adapted to receive a reinforcement sleeve 47.
The
reinforcement sleeve 47 is of annular construction, having an inner face 49
which
defines a central opening of diameter larger than the diameter of the plunger
25.
In this way, a gap 51 is defined between the sleeve 47 and the plunger 25.
The reinforcement sleeve 47 is of rigid construction, being made of steel in
this
embodiment. The reinforcement sleeve 47 serves to provide reinforcement for
the flange and more particularly maintain the presence of the gap 51.
The purpose of the gap 51 is to provide a cavity for accommodating a
lubricant.
The lubricant may be any liquid that reduces the sliding friction between the
outer
surface of the plunger 25 and the inner surface of the sheath.
Additionally, the gap 51 provides some clearance space for accommodating any
slight misalignment of the plunger 25 with respect to the body 11.
Further, the reinforcement sleeve 47 serves to exert an outward radial force
on
the flange 35 when the latter is compressed by the clamping engagement
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between the mounting flange 35 and the seat 38, thereby ensuring that a high
pressure seal is formed between the sheath 30 and the body 11. More
particularly, the radial force exerted by the sleeve 47 serves to ensure that
there is
a high pressure seal established between the inner face 43 of the flange and
the
annular supporting seat 38.
The reinforcement sleeve 47 has a recess 52 on the inner face thereof which
receives a wear band 53 for sliding contact with the outer surface of the
plunger .
25. The wear band 53 thus projects beyond the inner face of the reinforcement
sleeve 47, as shown in the drawings. The wear band 53 does not fully occupy
the
gap 51 so that the latter can perform its intended purpose. .
A wiper seal 55 is accommodated between the. reinforcement sleeve 47 and the
end plate 20. The wiper seal 55 is in sliding engagement with the plunger
25.and
is provided for the purposes of inhibiting loss of lubricant as the plunger
executes
its reciprocatory motion.
The outer surface of the plunger 25 may be coated with an appropriate non-sick
material.
While not shown in the drawings, the pump 10 also comprises a suitable
arrangement of valves for controlling the direction of fluid flow through
inlet 12 into
the pumping chamber 33 and out of the pumping chamber 33 through outlet 14.
The second portion 32 of the sheath 30 is shaped to follow the contour of the
plunger 25 so that the extension of the sheath occurs primarily in the tubular
wall
portion 36 thereof. This results in a thinning down of the tubular wall
portion 36 as
the plunger 25 moves inwardly during a pumping stroke, stretching the
elastomer
material. The pressure generated by the seawater during a pumping cycle will
generally be isostatic if the fluid velocities around the sheath are low
(which they
will be) so the fluid force acts to keep the sheath in contact with the
plunger 25.
This assists in maintaining the durability and service life of the sheath by
preventing the formation of folds or local areas of enhanced fibre stress. The
plunger 25 provides a surface which affords lateral support to the tubular
wall
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section 36, as well as the end section 37, as they are subjected to high fluid
pressure.
Where the elastomeric material forming the sheath is natural rubber, and where
the pump is employed for pumping of seawater as alluded to above, it is
estimated that up to 2mm of surface of the rubber in contact with the water
will
abrade over a period of say 20 years. In such an instance, it is important
that the
sheet thickness be made large enough to accommodate this reduction over the
usable lifetime of the pump.
The sheath 30 incorporates ribbing 61 on its internal surface in the region
below
recess 45 to allow lubricant to feed under the influence of gravity from the
lubricant reservoir provided by gap 51 downwardly to other parts of the
sheath.
The downward flow of lubricant may also be assisted by making the internal
diameter of the second portion 32 of the sheath 30 slightly greater than the
outside diameter of the plunger so that there is some clearance at least
during the
initial part of the intake stroke of the pumping cycle when the pressure of
fluid
being pumped is not yet high enough to force this clearance to zero.
The plunger 25 incorporates an axial passage 71 extending to the end face 27
thereof for delivery of lubricant thereto. The passage 71 receives lubricant
from
an external source. With this arrangement, lubricant can be delivered to the
region adjacent the inner end of the sheath 30; that is, to the interface
between
the plunger end face 27 and sheath end section 37.
The lubricant may comprise a continuous flow of lubricant material (such as
seawater) flowing downwardly along the passage 71, and then upwardly between
the cylindrical face 26 of the plunger 25 and the tubular wall portion 36 of
the
sheath. With this arrangement, any surplus lubricant can simply flow from the
sheath 30 through the open end thereof.
In this embodiment, the lubricant comprises seawater which is sourced from the
high-pressure seawater delivered by the pump. This is accomplished by way of a
bypass line 75 extending from the pump outlet 14 to the axial passage 71, as
best
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seen in Figures 1 and 2 of the drawings. The bypass line 75 of course needs to
be flexible or otherwise constructed in order to accommodate movement of the
plunger 25 relative to the pump body 11 with which the outlet 14 is formed. A
valve 77, which in this embodiment comprises a needle valve, is associated
with
the bypass line 75 for regulating the supply of high-pressure seawater from
the
pump outlet 14 to the axial passage 71.
The plunger 25 comprises a first part 81 which includes : a head section 83
attached to the connector 28 and a tube 85 extending downwardly from the head
section 83. The plunger 25 further comprises a second part 87 adapted to fit
onto
the first part 81 in order to provide the cylindrical side face 26 and the end
face 27
of the plunger. The second part 87 is of a generally cylindrical form, having
a
cylindrical sidewall portion 91 and an end wall portion 93. The end wall
portion 93
incorporates an opening 95 into which the tube 85 locates when the second
;part
87 is fitted on to the first part 81. The opening 95 is configured to receive
a
diffuser 97. The diffuser 97 threadingly engages with the tube 85. The
diffuser 97
has a diffuser passage 99 which communicates with the tube 85 to receive
seawater delivered along the tube and diffuse it from the plunger.
A deflector plate 101 is incorporated into the sheath 30 to confront the
diffuser 97.
In this way; seawater delivered through the diffuser 95 impacts upon the
deflector
plate 101 which then distributes the seawater within the interface between the
plunger 25 and the sheath 30.
Referring now to Figures 15 and 16 of the drawings, there is shown a sheath 30
for a pump according to a second embodiment. The pump according to the
second embodiment is similar in many respects to the first embodiment and so
corresponding reference numerals are used to identify like parts. In this
embodiment, the sheath 30 is constructed in a similar fashion to the sheath
for the
first embodiment, with the exception that formations 105 are provided on the
inner
face 107 of the second portion 32 of the sheath, confronting the adjacent face
26
of the plunger 25. The formations 105 are configured to define interstices 111
for
accommodating lubricant. In this embodiment, the formations 105 comprise an
array of protrusions 109 between which there are defined spaces 113 which
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provide the interstices 111 for accommodating lubricant. The spaces 113 may
allow the lubricant to migrate about the interface between the plunger 25 and
the
sheath 30, particularly at the stages during the pumping cycle where the
sheath
30 is not pressed firmly into engagement with the confronting surface 26 of
the
plunger. At the; stage where the fluid pressure within the pumping chamber 33
is
at a level that the second portion 32 'of the sheath 30 is pressed firmly into
engagement with the confronting surface.26 of the plunger 25, the formations
105
cooperate to create pockets or zones which trap the lubricant in position,
thereby
ensuring that there is some lubricant at the interface between the second
portion
32 of the sheath 30 and the plunger 25.
In certain pump applications, it may be possible to rely upon lubrication by
way of
gravity feed from the gap 51 and also by way of the formations 105; without
the
need for lubricant delivery through, the plunger.
In another embodiment, which is not shown, the end section 37 of the second
portion 32 of the sheath 30 may be attached to the end face of the plunger 25.
The attachment may be provided by way of a fastener, with the sheath end
section 37 being clamped between the end face 27 of the plunger 25 and a
clamping plate through which the fastener extends for attachment to the
plunger.
Such attachment would ensure that the sheath 30 is always withdrawn along with
the return (outward) stroke of the plunger 25. It would, of course, be
necessary to
ensure that adequate fluid sealing is established around the fastener, whereby
the
integrity of the sheath is not compromised.
From the foregoing, it is evident that the present embodiments provide a
simple
yet highly effective pump which can perform in harsh environments. This is
because working surfaces of the pump to which the seawater is exposed during
pumping cycles are surfaces of the pump body 11 and the sheath 30
accommodated therein. Because of its construction, the pump is able to operate
with the irregular and non-sinusoidal strokes arising from a drive system
powered
by wave energy. Further, because of the manner in which the plunger 25 is
supported within the pump body 11, a degree of. misalignment between the
plunger 25 and the pump body 11 can be tolerated. The flexible nature of the
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sheath 30, at both the first and second portions 31, 32 thereof, assists in
providing
this tolerance.
It should be appreciated that the scope of the invention is not limited to the
scope
of the embodiments described. For example, while the pumps according to the
embodiments have been described in relation to pumping of seawater, a pump
according to the invention may find application in the pumping of various
other
fluid materials, including liquids, gases and slurries.
Modifications and changes can be made without departing from the scope of the
invention:
Throughout the specification, unless the context requires otherwise, the word
"comprise" or variations such as "comprises" or "comprising", will be
understood to
imply the inclusion of a stated integer or group of integers but not the
exclusion of
any other integer or group of integers.
