Note: Descriptions are shown in the official language in which they were submitted.
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~ FLUID PUMP APPARATUS AND VALVE DEVICE
BACKGROUND OF THE INVENTION
Field of the Invention
This is a divisional application of copending
Canadian application serial no. 594,378 filed on March 21,
1989.
This invention relates to a fluid pump apparatus for
ultrahigh pressure pumping of fluids and a valve device that
prevents valve-piece vibration to thereby provide reliable
valve operation.
Description of the Prior Art
Pumps include reciprocating pumps in which the
reciprocating action of a piston is used to open and close
valves to pump a fluid such as water, for example. In
accordance with the configuration of the piston, reciprocating
pumps are divided into the bucket type, the plunger type and
the piston type.
Each type of reciprocating pump has its own uses,
but in all such pumps the sliding parts are prone to wear. In
the prior art there is known a technique whereby the fluid is
prevented from coming into direct contact with the sliding
parts of the reciprocating pump, consisting of providing a
diaphragm in front of the piston and filling the space on the
inner side of the diaphragm with fluid in order to transmit
the force of the piston (Japanese Patent Publication No. 48-
35405).
However, in the said conventional configuration the
diaphragm is exposed to the fluid, and as a result the
diaphragm wears quickly and has to be replaced each time.
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The diaphragm has to be replaced especially frequently when
the pump is being used in cement mills, for example.
When plunger pumps, too, are used in cement
mills, for example, the rapid wear of packings caused by
cement particles has limited pumping pressures to 200
kgf/cm2.
The flow of fluid is limited and controlled
by various types of valves. A valve device used on plunger
pumps, (a type of pump which is often used for high-
pressure applications), may be constituted of a tubular
seat, a valve-piece provided with a surrounding flange, and
a valve spring which urges the valve-piece against the
seat.
Because plunger pumps are used to pump materials
such as cement clinker, in the conventional valve device
solid particles entrained in the fluid may be caught
between the valve-piece and the seat.
The tubular shape of the seat used in the
conventional valve device makes it easy for solid particles
to pass through; in addition, because the seat and the
valve-piece are made of metal the operation of the valve
may be adversely affected by solid particles that are
caught therebetween. The result is that it has sometimes
been impossible to pump a constant amount of fluid at a
constant rate, so that operation of the pump was
accompanied by a decline in efficiency. Furthermore, solid
particles caught between the seat and the valve-piece can
damage the seat and valve-piece, leading to leakage of
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fluid. Conventionally, therefore, the valve device has to
be replaced at this point, which interrupts operations.
This led to the invention of Japanese Patent
Application 62-237996, a valve device that prevented the
inflow of solid particles present in the fluid and
increased the durability of the device. The valve device
of the said invention comprises a seat having a valve seat
formed as a concave surface corresponding to a part of a
spherical surface, and a prescribed number of fluid
passages which are formed in the seat and open into the
concave surface. There are also a valve-piece that has a
surface corresponding to the shape of the concave surface
in the seat, and a valve cover and spring retainer that
maintain the valve-piece on the concave surface of the seat
via a valve spring. In the valve device thus configured at
least one of the seat and the valve-piece is either formed
of, or covered with, a hard resilient material, or one is
formed of a hard resilient material and the other is
covered with a hard resilient material. In addition, wood
may be used instead of the hard resilient material.
With the valve device thus configured, the
fluid passages formed in the seat have a small diameter
which makes it difficult for solid particles to pass
therethrough. Even if solid particles should pass through
the fluid passages and get caught between the seat and the
valve-piece, the resilience of the valve seat and/or the
valve-piece ensures that the functioning of the valves will
be not obstructed.
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However, the conventional device thus
configured has been inadequate for pumping at higher
pressures because increasing the amount being pumped causes
the valve-piece 108 to vibrate during the inflow of fluid.
Summary of the Invention
An object of the present invention is to
provide a valve device that prevents valve-piece vibration
to thereby provide reliable valve operation; the present
invention also relates to a fluid pump apparatus for
ultrahigh pressure pumping of fluids which incorporates the
valve device.
Thus the present invention provides a valve
device comprising: a seat in the face of which are formed
valve seats spaced at regular intervals around the edge,
each shaped into a concave form that corresponds to part of
a spherical surface; a multiplicity of fluid passages
formed in the said valve seats as seat through passages;
valve-pieces arranged in the valve seats, each valve-piece
having a spherical surface that corresponds to the surface
of the valve seats; and a valve housing provided with
resilient means that resiliently presses the valve-pieces
onto the valve seat surfaces.
The present invention also relates to a
fluid pump apparatus in which the reciprocating action of
a piston provided in a cylinder draws fluid into a valve
chamber and pumps fluid from the valve chamber wherein: a
partioning pressure action member is provided between the
cylinder and the valve chamber and the cylinder side of the
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.
partioning pressure action member contains an operating
medium that transmits the actuation of the piston; and a
screening member is provided in a passage between the
pressure action member and the valve chamber whereby only
particles in the fluid that do not exceed a prescribed size
are passed. The present invention also relates to a fluid
pump apparatus in which the reciprocating action of a
piston provided in a cylinder draws fluid into a valve
chamber and pumps fluid from the valve chamber wherein: a
pressure-action chamber is provided between the cylinder
and the valve chamber, the said pressure-action chamber
being filled with a liquid that has a different specific
gravity than that of the said fluid; and a passage that
connects the pressure-action chamber and the valve chamber
is provided at a position at which the height relative to
the pressure-action chamber and the valve chamber is such
that the liquid does not flow owing to the difference in
specific gravity between the liquid and the fluid.
The suction action of the piston causes the
pressure action member to contract and an amount of fluid
equal to the amount of change in the volume of the pressure
action member is drawn into the valve chamber. Particles
in the fluid that exceed a prescribed size are eliminated
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by the screening member and therefore do not come into
contact with the pressure action member. Next, the
expulsion action of the piston causes the pressure action
member to expand, thereby expelling the fluid in the valve
chamber. The suction action of the piston then causes
fluid to flow into the valve chamber. The liquid contained
in the pressure-action chamber is moved in the passage by
an amount that corresponds to the change in the volume of
the pressure action member, and there is a corresponding
inflow of fluid. Then, the expulsion action of the piston
produces a movement of liquid in the passage, in accordance
with which fluid is expelled from the valve chamber. Thus,
because the liquid in the pressure-action chamber has a
specific gravity that is different to that of the fluid,
lS the liquid moves between the pressure-action chamber and
the passage but does not flow out at the valve chamber
side. Also, fluid that enters the valve chamber is
expelled from the valve chamber without coming into contact
with the piston.
Furthermore, the valve operation takes the form
of numerous actions that have a small amplitude of
movement, which enables vibration accompanying the opening
and closing action of the valve to be prevented.
The above and other features of the invention
will become apparent from the description made below with
reference to the following drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure l is a general cross-sectional view of a
first embodiment of the fluid pump apparatus according to
the present invention;
Figure 2 is an enlarged cross-sectional view of
part of the device shown in Figure 1;
Figure 3 is a general cross-sectional view of a
second embodiment of the fluid pump apparatus;
Figure 4 is a general cross-sectional view of a
third embodiment of the fluid pump apparatus;
is a perspective view of the valve device;
Figures 5 and 6 are general cross-sectional views
of a fourth embodiment of the invention;
Figure 7 is cross-sectional view of a fifth
embodiment of the invention applied to an ultrahigh
pressure pump;
Figure 8 is a cross-sectional view of a valve
device for the fifth embodiment;
Figure 9 is a perspective view of the valve
device of Figure 8, shown disassembled;
Figure 10 is a plan view of the valve housing
shown in Figure 9;
Figure 11 is a cross-sectional view taken along
line A--A of Figure 10;
Figure 12 is a plan view of the seat shown in
Figure 8;
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Figure 13 is a cross-sectional view taken
along line A--A of Figure 12;
Figures 14 and 16 are cross-sectional views
of conventional valve devices; and
5Figures 15 and 17 are perspective views of
conventional valve devices.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As mentioned above, the flow of fluid is
limited and controlled by various types of valves. Figures
1014 and 15 show a valve device used on plunger pumps, a type
of pump which is often used for high-pressure applications.
This valve device is constituted of a
tubular seat 100, a valve-piece 102 provided with a
surrounding flange 101, and a valve spring 103 which urges
15the valve-piece 102 against the seat 100.
Because plunger pumps are used to pump
materials such as cement clinker, in the conventional valve
device solid particles entrained in the fluid may be caught
between the valve-piece 10-2 and the seat 100.
20The tubular shape of the seat 100 used in
the conventional valve device makes it easy for solid
particles to pass through; in addition, because the seat
100 and the valve-piece 102 are made of metal the operation
of the valve may be adversely affected by solid particles
25that are caught therebetween. The result is that it has
sometimes been impossible to pump a constant amount of
fluid at a constant rate, so that operation of the pump was
accompanied by a decline in efficiency. Furthermore, solid
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-
particles caught between the seat 100 and the valve-piece
102 can damage the seat and valve-piece, leading to leakage
of fluid. Conventionally, therefore, the valve device has
to be replaced at this point, which interrupts operations.
This led to the invention of Japanese Patent
Application 62-237996, a valve device that prevented the
inflow of solid particles present in the fluid and
increased the durability of the device.
The valve device of the said invention
comprises a seat 107 having a valve seat 104 formed as a
concave surface 105 corresponding to a part of a spherical
surface, and a prescribed number of fluid passages 106
which are formed in the seat 107 and open into the concave
surface 105. There are also a valve-piece 108 that has a
surface corresponding to the shape of the concave surface
105 in the seat 107, and a valve cover 110 and spring
retainer 111 that maintain the valve-piece 108 on the
concave surface 105 of the seat 107 via a valve spring 109.
In the valve device thus configured at least one of the
seat 107 and the valve-piece 108 is either formed of, or
covered with, a hard resilient material, or one is formed
of a hard resilient material and the other is covered with
a hard resilient material. In addition, wood may be used
instead of the hard resilient material.
With the valve device thus configured, the
fluid passages 106 formed in the seat 107 have a small
diameter which makes it difficult for solid particles to
pass therethrough. Even if solid particles should pass
8a
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through the fluid passages 106 and get caught between the
seat 107 and the valve-piece 108, the resilience of the
valve seat and/or the valve-piece ensures that the
functioning of the valves will be not obstructed.
However, the conventional device thus
configured has been inadequate for pumping at higher
pressures because increasing the amount being pumped causes
the valve-piece 108 to vibrate during the inflow of fluid.
A first embodiment of the present invention
will now be described with reference to Figure 1, which is
a general cross-sectional view of the invention applied to
a plunger pump used for pumping fluid containing a high
level of particles, such as cement particles, for example.
In Figure 1 a fluid pump apparatus is
comprised of a valve box 2 provided with a valve chamber 1,
a plunger box 4 provided with a plunger 3, and a box 5
forming a pressure action chamber 5a disposed between the
valve box 2 and the plunger box 4.
The valve box 2 has an inlet passage 6 and
an outlet passage 7 that communicate with the valve chamber
1 and which are provided with an inlet valve 8 and an
outlet valve 9, respectively. The inlet valve 8 and the
outlet valve 9 each have a valve seat which is formed into
a concave, semi-spherical shape; a seat 11 in which there
are a multiplicity of small holes 10 that extend axially
from the concave valve seats; a valve-piece 12 that has a
spherical shape corresponding to the said concave valve
seats; and a valve spring 13 that urges the valve-piece 12
8b
1 3383~
against the seat 11. The holes 10 are for limiting the
entry into the valve chamber 1 of particles in the fluid 14
that exceed a given size.
The valve-piece 12 of the inlet valve 8 can open
in the direction of the valve chamber 1 and is therefore
urged toward the seat 11 by the valve spring 13 via a valve
retainer 15, one end of the valve spring 13 being engaged
with the inner wall of the valve chamber 1. The valve-
piece 12 of the outlet valve 9 opens away from the valve
chamber 1 and is therefore urged against the seat 11 by a
valve spring 13 provided between the valve box 2 and a
valve cover 16.
Provided in the side wall 2a of the valve box 2
is a passage 17 that connects the pressure-action chamber
5a with the interior of the valve chamber 1, the said
passage 17 opening into the lower part of a recess 18
formed in the side wall 2a of the valve box 2.
The valve box S that constitutes the pressure-
action chamber 5a is provided with a screening member 19
2~ disposed between the recess 18 and the pressure-action
chamber 5a, as shown in the enlarged view of Figure 2. A
mesh screen, for example, is used for the screening member
19, and formed therein are passages 20 to prevent the entry
into the pressure-action chamber 5a of particles that
exceed a given size. The passages 20 may be formed
integrally in the side of the valve box 5, and are set at
a prescribed inclination toward the passage 17 side.
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.
The end of a plunger 3 maintained within a
cylinder 21 in the plunger box 4 via a V-packing 22
projects into the pressure action chamber 5a and is
reciprocated at high speed by a drive means (not
illustrated).
A resilient membrane 23 is provided in the
pressure-action chamber 5a to divide the pressure-action
chamber 5a into a cylinder 21 side A and a valve chamber 1
side B. The cylinder 21 side A of the resilient membrane
23 is filled with an operating medium 25, such as oil, via
an oil passage 24 of the plunger box 4.
With the above configuration, when suction
operation of the plunger 3 causes the resilient mem~rane 23
to contract, reducing the volume on the cylinder 21 side A
of the pressure-action chamber 5a, and a corresponding
amount of fluid 14 flows into the valve chamber 1. At this
time, particles in the fluid 14 that exceed a given size
are eliminated by the seat 11 and are thus prevented from
flowing into the valve chamber 1. Also, as particles in
the fluid 14 that exceed a given size cannot pass the
screening member 19, any such particles in fluid 14 that
flows into the valve chamber 1 cannot enter the valve
chamber 1 side B of the pressure-action chamber 5a.
The expulsion operation of the plunger 3 expands
the resilient membrane 23, causing fluid 14 that has
entered the valve chamber 1 to be expelled from the valve
chamber 1.
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Figure 3 shows a second embodiment of the present
invention. In Figure 3, parts that are the same as parts
shown in Figure 1 have been given the same reference
numerals. In the second embodiment, a resilient membrane
26 directly covers the plunger 3 and the reciprocating
action of the plunger 3 directly expands the resilient
membrane 26. In this embodiment the passages 20 provided
in a screening member 27 are not disposed facing the
passages 17 but are instead located higher, which fully
prevents the entry of any particles in the fluid 14. When
pumping operations are being carried out where there are
high levels of particles, such as in a cement mill, large
particles contained in the fluid 14 can be fully prevented
from entering the valve chamber 1 side B by filling the
valve chamber 1 side B of the pressure-action chamber 5a
with a liquid such as water that contains no particles,
prior to the start of the pumping.
Figure 4 shows a third embodiment of the present
invention. In Figure 4, parts that are the same as parts
shown in Figure 1 have been given the same reference
numerals. In this third embodiment the side wall 2a of the
valve box 2 is provided with a passage 17 that connects the
pressure-action chamber 5a with the valve chamber 1. As
explained ~elow, the position of the passage 17 is
determined according to the difference in specific gravity
between a liquid and the fluid 14. When the liquid has a
higher specific gravity than the fluid the passage 17 is
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,
located at a higher position in the pressure-action chamber
Sa, and when the liquid has a lower specific gravity the
passage 17 is positioned lower. In the illustrated example
the position where the passage 17 opens into the pressure-
action chamber Sa is higher than the inlet of the of the
valve chamber 1. Thus, in this embodiment the position of
the passage 17 is determined according to the relationship
between the heights of the pressure-action chamber Sa and
the valve chamber 1 and a consideration of the specific
gravities of the liquid and the fluid 14.
The end of the plunger 3 maintained within the
cylinder 21 in the plunger box 4 via V-packing 22 projects
into the pressure action chamber Sa and is reciprocated at
high speed by a drive means (not illustrated).
lS A resilient membrane 23 is provided in the
pressure-action chamber 5a to divide the pressure-action
chamber 5a into a cylinder 21 side A and a valve chamber l
side B. The cylinder 21 side A of the resilient membrane
23 is filled with an operating medium 25, such as oil, via
an oil passage 24 of the plunger box 4. In addition, the
valve chamber 1 side of the pressure-action chamber Sa and
part of the passage 17 are filled with a liquid 28, such as
oil, which has a lower specific gravity than the fluid 14
used in a cement mill, for example, and does not mix with
the fluid 14. The liquid 28 comes into contact with the
fluid 14 part-way along the passage 17.
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Provided between the pressure-action chamber 5a
and the passage 17 is a screening member 29 that uses a
mesh screen, for example, to prevent particles that exceed
a given size from entering the pressure-action chamber 5a.
The screening member 29 may be formed as an integral part
of the valve box 5 which forms the pressure-action chamber
5a, and the passages 20 therein are set at a downward
inclination toward the passage 17 side.
With the above configuration, suction operation
of the plunger 3 causes the resilient membrane 23 to
contract, reducing the volume on the cylinder 21 side A of
the pressure-action chamber 5a and increasing the volume on
the valve chamber 1 side B. The change in volume results
in a rise in the level of the liquid 28 in the passage 17.
Also, an amount of fluid 14 corresponding to the change in
volume flows into the valve chamber 1 as the inlet valve 8
opens. The expulsion operation of the plunger 3 causes the
resilient membrane 23 to expand via the operating medium
25, and with the reduction in the volume of the valve
chamber 1 side B the liquid 28 in the valve chamber 1 side
B of the pressure-action chamber 5a is expelled. Also, the
level of the liquid 28 in the passage 18 decreases and a
corresponding amount of fluid 14 is forced out as the
outlet valve 9 opens. The liquid 28 is only forced part-
way along the passage 17 and does not flow over to the
valve chamber 1 side.
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Figure 5 shows a fourth embodiment of the present
invention. In ~igure 5, parts that are the same as parts
shown in Figure 1 have been given the same reference
numerals. In this embodiment, a pre-chamber 30 filled with
liquid 28 is also provided on the outside of the valve box
5. The pre-chamber 30 is communicated with the liquid 28
in the passage 17 by means of a branch pipe 31. With this
embodiment the point of confluence of the liquid 28 and the
fluid 14 does not move above the pre-chamber 30, and
therefore the liquid 28 in the pressure-action chamber 5a
can be kept fresh by changing the liquid 28 in the pre-
chamber 30.
Figure 6 illustrates the insertion of a liquid 32
having a specific gravity that is midway between the
specific gravities of the liquid 28 and the fluid 14 and
which, in addition, does not mix with the fluid 14. With
this arrangement, there is no direct contact between the
liquid 28 and the fluid 14. A partitioning medium disposed
between the liquid 28 and the fluid 14 may be used in place
of the liquid 32.
In the above embodiments a liquid 28 is used
having a lower specific gravity than the fluid 14, but a
liquid having a higher specific gravity than the fluid 14
may also be used. In such a case the passage connecting
the pressure-action chamber 5a with the valve chamber 1
should be provided toward the upPer Part of the pressure-
action chamber 5a. A premise for such an arrangement is
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that the positional relationship between the height of the
pressure-action chamber 5a and the valve chamber 1 will be
adjusted.
Also, the above embodiments have been described
with reference to the provision of a resilient membrane 23
in the pressure-action chamber 5a. However, the resilient
membrane 23 may be dispensed with if the liquid 28 is one
like oil that has lubricative properties and will not mix
with the 14.
Figure 7 shows a fifth embodiment of the present
invention applied to an ultrahigh pressure pump for use in
cement mills, for example. In Figure 7, parts that are the
same as parts shown in Figure 1 have been given the same
reference numerals. In this embodiment the ultrahigh
pressure pump consists of a valve box 2 that has a valve
chamber l; a plunger box 4 containing a plunger; and a
valve box 5 forming a pressure-action chamber 5a that is
disposed between the valve box 2 and the plunger box 4.
The valve box 2 has an inlet passage 6 and an
outlet passage 7 that communicate with the valve chamber 1
and which are provided with an inlet valve 80 and an outlet
valve 81, respectively. As shown in Figures 8 to 13, the
inlet valve 80 and the outlet valve 81 have a seat 84 in
the face 82 which are formed a multiplicity of valve seats
83 (eight, in the illustrated example) spaced at regular
intervals around the edge, each shaped into a concave form
that corresponds to part of a spherical surface; spherical
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valve-pieces 85 arranged on the valve seats 83; and a valve
housing 87 that presses the valve-pieces 85 onto the valve
seats 83 by means of springs 86.
In each of the valve seats 83 in the seat 84
5there are formed multiple fluid passages 88 (three in each
case, in the illustrated example) that extend axially
through the seat 84. Disposed around the edge of the valve
housing 87 are fluid passages 89 corresponding to the valve
seats 83 and into which the valve-pieces 85 fit. The exit
10end of each of the fluid passages 89 is formed into a
smaller diameter portion by a lip 90. One end of each of
the valve springs 86 are held in place at the said lip 90.
The valve housing 87 and seat 84 are each
provided with respective central bolt through-holes 91 and
1592 whereby they are bolted together by a bolt 93 and a nut
94.
In addition to metal, the valve-pieces 85 and/or
the seat 84 may be made of, or covered with, a hard
resilient material such as synthetic resin, for example.
20In the side wall 2a of the valve box 2 is a
passage 17 that connects the pressure-action chamber 5a
with the interior of the valve chamber 1, and provided at
the opening of the passage at the pressure-action chamber
5a end is a screening member 29 constituted of a mesh
25screen or the like that limits the entry of particles that
exceed a given size.
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The end of a plunger 3 maintained within a
cylinder 21 in the plunger box 4 via a V-packing 22
projects into the pressure action chamber 5a and is
reciprocated at high speed by a drive means (not
illustrated).
A resilient membrane 23 is provided in the
pressure-action chamber 5a to divide the pressure-action
chamber 5a into a cylinder 21 side A and a valve chamber 1
side B. The cylinder 21 side A of the resilient membrane
23 is filled with an operating medium 25, such as oil.
Also, the valve chamber 1 side B of the pressure-action
chamber 5a is filled with a liquid such as oil having a
specific gravity that differs from that of the fluid, so
that the pumped fluid does not enter the pressure-action
chamber 5a.
With the above configuration, when suction
operation of the plunger 3 causes the resilient membrane 23
to contract, reducing the volume on the cylinder 21 side A
of the pressure-action chamber 5a, the result is that the
valve-pieces 85 on the inlet valve 80 side open against the
resistance of the springs 86, and cement mill fluid 14
flows into the valve chamber 1. At this time, the valve-
pieces 85 of the outlet valve 81 are drawn in the direction
of their closed positions, and therefore remain closed.
Before the fluid can flow into the valve chamber 1,
entrained particles that exceed a given size are removed ~y
the fluid passages 88 and then by the screening member 29.
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The expulsion operation of the plunger 3
expands the resilient membrane 23, causing fluid 14 that
has entered the valve chamber 1 to open the outlet valve 81
and be pumped out.
Because the operation of the valves 80 and
81 takes the form of small amplitude movements of the
numerous valve-pieces 85, vibration accompanying the
opening and closing action of the valves can be prevented.
As has been described in the foregoing, a
fluid pump apparatus according to the present invention
offers numerous features, advantages and effects, which
will now be summarized with reference to the claims.
The provision of a screen member as
described herein may stop the entry of particles in the
fluid that exceed a given size. Thus preventing large
particles from coming into direct contact with the pressure
action member eliminates a source of wear and damage to the
pressure action member, and as such increases the
durability. When applied to a pump, it allows pressures of
around 500kgf/cm2 to be achieved, and therefore can provide
major improvements in efficiency if employed for pumping
operations in civil engineering projects.
The provision of a resilient membrane as
described herein can ensure reliable transmission of the
piston action. In accordance with the present invention it
is possible to use a resilient membrane to cover a plunger.
18
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-
As described herein, it is possible to
exploit a specific gravity differential between the fluid
and the stated liquid to prevent the liquid flowing from
the pressure-action chamber into the valve chamber.
Consequently there is no inflow of the fluid into the
pressure-action chamber, and hence no wear and tear to the
frictional parts of the piston. This results in a major
boost in pump output levels, compared to the conventional
apparatuses.
As described herein, the freshness of liquid
in the pressure-action chamber can be maintained by
changing the liquid in the pre-chamber. A partitioning
medium arrangement as described may be a reliable way to
prevent mingling between liquid and fluid. As described
herein, a screening member may be provided which enables
all particles, dirt, etc., in the fluid that exceed a given
size to be prevented from entering the pressure-action
chamber.
In accordance with the present invention, a
screen member can be dispensed with. In accordance with
the present invention, piston lubricant of the like may be
provided on the cylinder side of the pressure-action
chamber, which increases the durability of the piston
frictional parts. In accordance with the present invention
it is possible to provide an arrangement which may provide
sure response to the piston operation and is easy to
implement. In accordance with the present invention
particles in the fluid that exceed a given size can be
19
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removed before reaching the valve chamber. An arrangement
in accordance with the present invention enable valve-piece
vibration to be prevented, and when applied to pumps can
provide reliable valve function and increased durability,
compared with conventional arrangements.
B
