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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates generally to positive displacement pumps, and
more particularly, to an improved "valveless" positive displacement pump
of the type wherein the pumping action results from a combination of
rotating and reciprocating action of a relieved piston within a ported
cylinder. Because of the positive displacement action available with such
kinds of pumps, they are capable of extremely high precision and are used
in a wide variety of applications. Certain of these applications range
from supplying ink to enormous printing presses of the type used to print
daily newspapers to other applications, which include dispensing products
that must be mixed with precision, including pharmaceuticals, chemical
products of all kinds, and other liquids.
In general, pumps embodying the concept of a rod-type, relieved piston that
reciprocates and rotates within a cylinder are well known. In the basic
form, such an arrangement includes two basic parts, including a cylinder
having inlet and outlet ports or passages, a rod-like piston that both
rotates and reciprocates within the cylinder, and a relief extending
chordwise across one end part of the piston so as to form a flat providing
a part of a flow passage for liquid to be drawn into and expelled from a
closed end pumping chamber.
In operation, the other or remote end of the rod on which the piston is
formed includes a connecting rod or pin, one end of which extends radially
outwardly from the piston remote end and the other end of which is
journaled for universal movement, typically by a rod end or spherical
bearing, within an offset leg on a portion of a rotary mechanism. In a
typical construction, the rotary or driving mechanism is a crankshaft
extending from the armature of an electric motor or the equivalent. This
crank mechanism includes a shaft section concentric with the motor, an
offsetting cheek or flange and a drive leg extending parallel to the shaft
section and typically containing a spherical bearing. In such mechanisms,
when the rotational axis of the piston and cylinder are inclined with
respect to the rotational axis of the driving element, then the spherical
bearing portion of the crank just referred to, upon rotation, will trace a
circle in respect to the axis of its own shaft, but will trace an ellipse
with respect to the axis of the driven element.
Consequently, the outer diameter end of the connecting rod or pin
journalled in the spherical bearing will move through a path which
oscillates axially with respect to the axis of the piston or driven
element. The total axial excursion is the piston stroke. Pumps of this
sort are shown, for example, in U.S. Pat. Nos. 3,168,872, 4,008,003, and
5,020,980.
While pumps of the type illustrated in this application have a number of
advantages, including the ability to be tightly sealed, to create
substantial static pressures and consequently to deliver very accurately
metered quantities of liquid, one significant drawback to such pumps is
that, with respect to any one particular pump, the instantaneous output of
the pump varies throughout the operating cycle. In one-half of the
operating cycle, there is no output, and in other portions, it varies
depending on the crank angle. Thus, representing the operation of a
typical pump as a sine wave laid out on a horizontal axis, the first
180.degree. or positive half wave form of a trace would represent pump
output with respect to crank angle, while the second or negative
180.degree. portion of the sine wave would represent liquid taken in.
Thus, it is clear that during one half of its operating cycle, the pump is
delivering liquid and on an alternate part of the cycle, the pump is
drawing liquid in. Consequently, driven at a constant speed, such a liquid
pump not only has an oscillating or pulsating output, but also has no
output half the time.
In the past, it has been suggested to overcome this drawback in two ways,
neither of which has proven entirely satisfactory. One suggested method
has been simply to arrange two pumps in substantially back-to-back
relation, one on either side of a motor, placing their crankshafts in a
180.degree., out-of-phase relationship. Thus, while one piston and
cylinder delivers liquid in one portion of its operating cycle, the other
pump is drawing liquid in and when the first pump begins to draw in
liquid, the second pump would displace or pump liquid out. This
arrangement has disadvantages of higher costs and taking up more space. It
requires that the liquid handling arrangements, such as porting and
manifolding, for example, be doubled. In effect, it is no better than
simply having two pump and motor arrangements operated together.
Another approach that has been taken is to have a single, double ended
piston, provided with two reliefs, one on each end of the piston, and
providing intake and exhaust ports for each one. According to this
arrangement, a movement in one direction of the piston would displace
liquid and at the same time draw liquid into the other end of the
arrangement, in a manner partly analogous to the operation of a two-stroke
cycle internal combustion engine.
However, there are significant drawbacks associated with this concept, the
main difficulties being the need to provide the second piston with an
extension or rod to equalize volume changes per degree of stroke on each
end of the piston. This creates space problems and also creates very
significant difficulties with sealing the components. One advantage of
liquid pumps of this type in the first place is that they run in the
presence of a liquid which is usually non-abrasive, and accordingly can
use very tight but low friction seals. With the double ended arrangement
discussed above, auxiliary seals such as rod wiper seals, O-rings, or the
like are needed. This need to introduce auxiliary seals is a serious
drawback in the prior art approach just discussed.
Consequently, there has been a need for an improved positive displacement
pump of the above type wherein the advantages of a full wave operating
cycle could be achieved in a manner which would not require excessive
space or unduly large components, which would not require duplication of
most of the elements of the drive mechanism and which, furthermore, would
not require complex, unwieldy seal mechanisms.
In view of the failure of the prior art to provide a pump having certain of
the foregoing advantages and characteristics, it is an object of the
present invention to provide an improved positive displacement fluid pump.
Another object of the present invention is to provide a positive
displacement fluid pump that will provide a substantially uninterrupted
flow of liquid and requires operation only by a single crank mechanism.
A further object of the invention is to provide an improved positive
displacement liquid pump able to be driven by a single driving element and
yet providing liquid flow during all portions of its operating cycle.
A still further object of the invention is to provide an improved liquid
pump that is simple in operation and very compact relative to prior known
pumps.
Yet another object of the invention is to provide a positive displacement
liquid pump with two pistons, and wherein a portion of one of the pump
pistons also serves as a cylinder, and locates a second piston, with both
pistons and cylinders being concentrically arranged.
Another object of the invention is to provide a positive displacement fluid
pump or motor wherein each of a pair of pistons includes a connecting rod
fixed to a piston end and wherein the drive mechanism includes a yoke
arrangement with a bearing carded by each opposed leg of a single crank
mechanism.
A further object of the invention is to provide a pump and pump drive
arrangement which includes a pair of concentrically arranged pistons, one
being solid and the other one being hollow, with the solid piston moving
within the cylinder formed as a part of the hollow piston.
A still further object of the invention is to provide a positive
displacement motor and drive arrangement wherein the pump includes
concentrically arranged pistons and cylinders and the drive mechanism
includes a rotary shaft portion and a yoke including parallel, spaced
apart legs each carrying a bearing journalling an end of a connecting rod
extending radially from an associated piston.
Yet another object of the invention is to provide a pump assembly having
operating characteristics of two pumps but being formed in a single
mechanism and able to be driven by a improved control system which
includes a stepping motor arrangement.
Another object of the invention is to provide a pumping arrangement for
supplying ink to large printing presses, said arrangement comprising a
page pack including a housing receiving the improved ink, plural drive
motors mounted on the housing, and appropriate manifolding arranged to
permit continuous ink flow from the pumps during their operating cycles.
The foregoing and other objects and advantages of the invention are
achieved in practice by providing a compact pump mechanism that includes
an outer cylinder sleeve with two inlet and two outlet ports or passages,
a combination piston and cylinder received within the outer sleeve and a
piston received within the inner cylinder, with the piston and cylinder
unit including a pair of chordwise reliefs and the inner cylinder a
passage connecting one relief to its interior, and with each of the
pistons including a remote end adapted to be journaled for rotation by a
drive mechanism normally operated at an axis inclined to the rotational
axis of the pistons in the pump unit.
The exact manner in which the foregoing and other objects and advantages of
the invention are achieved in practice will become more clearly apparent
when reference is made to the following detailed description of the
preferred embodiment of the invention set forth by way of example and
shown in the accompanying drawings, in which like reference numbers
indicate corresponding parts throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an ink delivery assembly incorporating
positive displacement pumps made according to the invention, and showing a
housing for a plurality of individual motors and pumps, and various
fittings used in supplying ink and electric current to the pumps and
motors, respectively;
FIG. 2 is a vertical sectional view, taken along lines 2--2 of FIG. 1, and
showing certain elements of the novel positive displacement pump unit of
the invention;
FIG. 3 is an exploded view of three principal components of the positive
displacement pump of the invention, a cylinder sleeve, a combination outer
piston and cylinder and an inner piston;
FIG. 3A is a view of one of the components of FIG. 3, showing the same in a
different position;
FIG. 3B is a sectional view, taken along lines 3B--3B of FIG. 3 and showing
the relief and the flow passage in the inner cylinder in greater detail;
FIG. 4 is a perspective view showing a portion of the pump housing, a motor
mounted on the housing, and certain portions of the drive mechanism for
the novel pump assembly, with certain portions of the housing shown broken
away for clarity;
FIG. 5 is an enlarged fragmentary vertical sectional view of the working
portions of the novel pump assembly of the invention, showing the pump
components in a first position;
FIG. 6 is a vertical sectional view similar to that of FIG. 5, but showing
the pump components in another position of their operating cycle;
FIG. 7 is a diagram showing the relation of ink flow and crank angle in a
pump made according to the invention; and,
FIG. 8 is a counterpart diagram of ink flow in a prior art pump.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
While the positive displacement valveless fluid pump of the invention has a
very wide variety of applications, one preferred use of the product is in
the ink delivery system of large scale printing presses, such as daily
newspaper printing presses. In such an application, a plurality of
individual pumps are arrayed together within a single housing, and a drive
motor is provided for each of the pumps. In a further preferred form, the
motors for the pumps are so-called stepping motors. In the preferred
arrangement, a digital control circuit provides precisely timed output
pulses, and each output pulse results in a very small step of the motor,
which typically requires 300 to 400 steps per revolution. Control of each
stepping motor is achieved by a keyboard which the operator uses to
instruct a dedicated microcomputer in an arrangement whereby individual
pump microcomputers communicate with a master computer via serial
communications. Typically, a seven-wire bus is provided wherein pulse
trains travel throughout the control system and are individually addressed
to the appropriate microcomputer. The digital pulse train controls the
power supplied to the motors, provides communications or instructions, and
advises the microcomputers of the press speed, which regulates the overall
output rate of all the pumps. The combination of a set of pumps, motors,
their housing and the associated controls are sometimes referred to as a
"page pack," i.e., the unit delivers ink to a press that prints in widths
that are a multiple of one page. A full-width press may print in widths of
four pages. However, while the pumps of the invention are not by any means
limited to this kind of application, they possess many advantages when so
used. Other applications for the improved liquid pumps are referred to
herein.
Referring now to FIG. 1, a typical page pack generally designated 2 is
shown. This page pack includes a cast or other monolithic housing
generally designated 4 having fittings 6, 8 for connection to electrical
sources, a liquid inlet fitting 10 which supplies ink to interior passages
comprising manifolding within the housing 4. A plurality of individual
outlet fittings 12 are provided to supply the ink from the pumps inside
the housing to what is termed an orifice plate (not shown), i.e., an area
adjacent the inking roller of a press wherein a film or bath or ink is
formed for pickup by the inking roller.
Referring again to FIGS. 1 and 2, it will be noted that a plurality of
individual motors generally designated 14 are fixed in relation to the
housing 4 and that a printed circuit-type control board generally
designated 16 is secured to another area of the pump housing. A protective
sheet metal cover 18 for the circuitboard is secured to the housing, which
preferably includes open pockets 19 wherein the connections between the
motors 14 and the pumps are made.
Referring again to the drawings in greater detail, and especially to FIGS.
1-6, the principal working portions of the improved positive displacement
liquid pump of the invention are shown. Here, a pump assembly generally
designated 20 is situated within the housing generally designated 4.
Inside the housing 22 are a liquid inlet manifold passage 28 and a liquid
outlet passage 30, with the passages 28, 30 being respectively associated
with the fittings 10, 12.
According to the invention, the improved pump operates on the principle of
providing a first pump chamber 32 best shown in FIGS. 5 and 6, and a
second, concentrically arranged but axially offset pump chamber generally
designated 34. The first pump chamber 32 lies within an outer cylinder
sleeve 36, with such cylinder including an inwardly directed cylindrical
wall 38, an inner end face 40 formed on a plug 41 and an open end portion
generally designated 42. As used herein, the end adjacent the inner end
face 40 may be referred to as the axially inner or proximate end of the
cylinder sleeve 36 and the opposite end as the outer, remote or open end
42 of the cylinder.
According to the invention, there are a pair of generally oppositely
disposed ports or passages in the outer cylinder sleeve 36 to permit
liquid to flow into and out of the first pump chamber 32, namely, a first
or axially inner inlet port 44 and a first or axially inner outlet port
46. Preferably the center lines of these ports 44, 46 are disposed
opposite each other, i.e., across the bore of the outer cylinder 36. In
FIG. 5, they are at the bottom and top, respectively. Thus, the ports
extend radially inwardly perpendicular to the center line axis of the
cylinder sleeve 36.
In the preferred form of apparatus, the outer cylinder 36 also includes a
second or axially outer pair of ports, i.e. a second inlet port 48 and a
second outlet port 50. The ports 44, 48 are respectively connected to each
other by a common inlet passage 52 and the first and second outlet ports
46, 50 are connected by a common outlet passage 54. In FIG. 3, a slot 56
is shown provided for locking the outer cylinder 36 in position within the
housing 22. This is preferably done by a locking plate 58 (FIG. 1) held in
place by a fastener 59, thus insuring that the cylinder will not rotate or
move axially relative to the housing.
According to the invention, another major part of the pump 20 is an
intermediate unit generally designated 60 (FIG. 3) and shown to comprise a
combination outer piston and inner cylinder body 62. This unit includes a
radially outwardly facing cylindrical sidewall 64, and an inner or
proximate end face surface 66 (FIGS. 5, 6). The inner end of the piston
and cylinder body 62 also includes a chordwise relief 63 combining with
the interior of the cylinder wall 38 to define a passage space 64. Thus,
because the piston end face 66 never moves rearward enough to uncover the
ports 44, 46, liquid flowing through either port 44, 46 into or out of the
first pump chamber 32 must flow through the passage space 64 between the
relief 63 in the piston body 62 and the outer cylinder sidewall 38.
The outer portion of the piston and cylinder body 62 includes a connecting
rod carrier generally designated 70 in the form of an enlarged diameter
body 72 having a slot generally designated 74 in one of its cylindrical
sidewall surfaces and an opening 76 (FIG. 5)in the other; a first
connecting rod 78 extends through this opening 76 and is held in place by
a connecting rod set screw 80. Referring again to the piston and cylinder
body 62, this element also includes an inner bore generally designated 82
and is shown to include a cylindrical inner sidewall 84 having a closed or
inner end portion 86 as well as a rear or open end portion generally
designated 88.
The body 62 further includes a chordwise second relief 90 providing a
passage space 92 between its surface and the inner surface of the outer
cylinder sidewall 38. Moreover, the second chordwise relief 90 is arranged
so as to lie axially outwardly of the inner end face portion 86 of the
inner bore 82. A radial flow passage generally designated 94 extends from
the face of the relief 90 into the closed end portion 86 of the inner bore
82.
A still further essential component of the pump positive displacement pump
of the invention is a second or radially inner piston unit generally
designated 96. This inner piston unit is in the form of a piston body 98
having a cylindrical sidewall 100 and an inner end face 102. The space
between the inner end face 102 and the closed end portion 86 of the inner
bore 82 forms the second pump chamber 34 referred to above. The remote or
outer end portion of the piston body 98 receives and fixedly positions a
radially extending connecting rod 106.
Referring now to the other or driving part of the pump assembly, which
drive elements include the motor generally designated 14, the motor has an
output shaft 110 forming a part thereof. It will be understood that the
shaft 110 conventionally forms an extension of the armature, but that any
other suitable connective arrangement between the motor or other prime
mover and the shaft is acceptable. At the end of the shaft is a yoke
assembly generally designated 112 and shown to include a transverse or
radially outwardly extending flange 114, at the respective ends of which
are first and second offset legs generally designated 116, 118. In each of
the legs is substantially identical, and therefore a detailed description
of only one is believed necessary to an understanding of the invention.
Thus, leg 116 includes an opening generally designated 120 which receives a
bearing socket 122 which in turn journals a spherical bearing 124. The
spherical bearing element 124 includes a center cylindrical bore 126 to
receive an end portion of the connecting rod 78. According to the
invention, the connecting rod 78 is free to slide radially within the
opening 126 and the spherical or rod-end type bearing 124 is free to
undergo universal movement within its socket 122, such motions being
necessary to achieve the rotary and reciprocating motions that
characterize the operation of the inventive pump.
Referring now to the operation of the novel valveless positive displacement
pump of the invention, the basic motions undergone by the elements during
a working cycle are as follows. For the intake stroke, the piston
withdraws from the chamber while the relief is indexed with an inlet
passage, with the resulting suction filling the working chamber. By the
time the piston begins stroking backwardly towards the closed end of the
cylinder, its rotary motion has indexed the relief with the outlet port in
the opposite side of the cylinder. This expels the ink or other liquid
which was in the chamber and this action continues until the bottom of the
stroke is reached, at which point the rotary motion has indexed the relief
back into a position where at it is beginning to register with the inlet
port again.
In particular, and referring to FIGS. 5 and 6, the connecting rod 78 is
rotated and reciprocated, withdrawing the endface 66 of the piston 60 from
the end face 40 of the plug, while the chordwise relief 63 is registered
with the inlet passage 44 (FIG. 6). Continued motion permits ink to flow
from the manifold 28 through the passage 44 and into the working chamber
32 during this time. When the piston has been fully withdrawn and begins
stroking forward, the relief 63 comes into registry with the outlet port
46 as the end face 66 of the piston begins to reduce the volume of the
chamber 32, thus expelling liquid out the port 44 and through the passage
54, ultimately passing outward through the fitting 12.
According to the invention, at the same time that this action is occurring
with the end face 66 and the relief 63 in the near or forward end of the
piston and cylinder assembly 60, a similar but exactly opposite phase
action is occurring with regard to the second working chamber 34. Here,
with the connecting rod 106 being in an appropriate phase relation to the
connecting rod 78, as shown in FIG. 6, and further assuming the chamber 34
to have fluid therein, the end face 102 of the piston 98 has moved forward
while the relief 90 is in registry with the outlet port 50. This expels
ink from the cylinder with the ink also passing through the relief passage
94.
Upon continued rotation, the piston 98 begins withdrawing from the chamber
34, while the relief 92 is registered with the second or axially outer
inlet port 48. This draws ink or other liquid from the manifold 28 through
the passages 52 and 48 into the working chamber 34. As the rotation of the
piston 98 continues, the piston stroke reaches the end of its travel and
begins stroking toward the end face 86 of the chamber 34 just as the
relief 90 indexes with the outlet port 50 (FIG. 6).
Inasmuch as the reliefs 63, 90 are formed on the same piston and cylinder,
there is no chance for the reliefs to register improperly.
As is believed known to those skilled in the art, the angular relation
between the driving axis of the yoke 112 and that of the cylinder bore 38
accounts for the reciprocation of the piston. In this connection, it will
be noted that when a member such as the yoke 112 is rotated, a given point
on one of the yoke legs will trace a circle in relation to the rotational
axis of the yoke. However, with relation to an angularly offset axis, an
ellipse will be traced, such as on an imaginary cylinder whose axis is
inclined with respect to that of the first axis. Consequently, a trace of
this movement will be seen as axial motion in respect to the pump. FIGS. 5
and 6 show this action, wherein it is shown that the two pistons, move
axially with respect to each another while they are rotating about a
common center line axis.
Referring now to FIGS. 7 and 8, there is shown a schematic view of the ink
delivery versus crank angle when utilizing the pump of the present
invention. Assuming that the horizontal axis of the graph represents
degrees of crankshaft rotation and the vertical axis the output of the
pump, inasmuch as the reciprocating motion is in effect a sinusoidal
movement, a trace of volume delivery will represent a series of half sine
waves. Referring again to FIG. 7, it will be noted that there are three
lobes, each representing a positive amount of liquid flow, albeit one with
a somewhat pulsating character.
Referring to FIG. 8, this shows a flow delivery versus crank angle relation
of a prior art pump. In the center of FIG. 8, where the expression "dwell"
is shown, reference is made to the position of registry between the relief
or fiat on the piston and the exhaust port. When there is no registry of
these parts, there is no ink flow and accordingly, prior art pumps develop
flow only during one-half of their operating cycle.
In view of the critical nature of the flow which fluid pumps are sometimes
required to produce, the ability to be free from lapse or deadspace times
is a significant advantage of the present invention.
Whereas, if necessary, it is possible to even out the flow of the operating
cycle of the individual pumps by the fine control of motor speed, this is
not normally necessary. However, if it is desired to do so, a rapid pulse
train may be sent to the stepping motor from the output driver during a
portion of the cycle wherein the rate of axial piston movement is low,
i.e., near both ends of the stroke, while a reduced pulse rate may be
utilized during the center portion of the stroke, i.e. portion of the
operating cycle wherein the piston moves most rapidly relative to its
rotation.
Referring now to the other aspects of the invention, many liquids may be
pumped using the improved pump of the invention. Provided that the
substance being pumped is not antagonistic to the materials from which the
pump is made, and is not unduly abrasive, virtually any liquid may be
advantageously pumped in a precise manner using the concept of the present
invention. Engineering plastics as well as high quality steels or other
metals may be used to form the components. Pumps of the kind in question
do not normally require lubrication, and since they run in the presence of
liquids, are able to operate for long periods without undue wear. While
the pumps of the invention are advantageous in that they are positive
displacement pumps, the concept of the two pistons operating in an axially
offset manner along a common rotational and stroking axis is applicable to
compressible fluids as well as liquids.
In applications such as a printing press ink flow control referred to
herein, the novel pump has proved exceptionally advantageous and
satisfactory in use.
In those applications wherein the fluid to be pumped is substantially
incompressible, it is important that the relief be constructed and
arranged relative to the inlet and outlet ports such that at least a
portion of the relief begins to register with such port just as the piston
begins to stroke. If the fluid is compressible, this is not a requirement.
The specification and drawings have illustrated a chordwise relief that is
of an extremely simple form, namely, a single fiat chordwise cut across
the end of the rodlike outer piston. However, the exact configuration of
the relief may also be a matter of choice provided that it provides for
proper registration with the inlet and exhaust ports. As noted, the inner
piston does not require a relief per se; however, the relief is provided
on another portion of the structure, i.e., the body forming the outer
piston and cylinder. The relief thus serves the function of being
respectively in and out of registry with the various ports at desirable
portions of the stroke.
In the case of the inner piston and its cylinder, the passage for liquid
into and out of the pumping chamber comprises not only the chordwise
relief and a portion of the cylinder, but also the radial passage between
the two. Accordingly, it will be appreciated that as long as a
reciprocable piston can create suction and expulsion for intake and
outflow of liquid, the exact porting arrangement is not critical. The
preferred embodiment provides an ideal arrangement in that the slot 74 for
the inner piston connecting rod lies opposite the position of the outer
connecting rod and the slot 74 further insures that the two piston
elements will rotate together remain in their 180.degree. out-of-phase
relation, while the formation of the reliefs on the same element, i.e.,
the piston and cylinder, insure the continued alignment of these parts.
This arrangement is ideal for a compact, fool-proof mechanism.
The provision of spherical bearings is the preferred manner of permitting
the range of movements required of the components in question, i.e.,
change of angle relative to the yoke and a slight radial movement of the
rod relative to the spherical bearing. Clearly, a spline or other
telescoping arrangement of rod could be provided if the axial rod movement
within the bearing were not desired or permitted for some reason.
In the arrangement shown, the same fluid is taken from a manifold or other
single inlet and discharged in a single outlet. However, the common
passage connecting the respective pairs of inlet and outlet ports could be
eliminated and individual supply and outlet connections to the ports could
be made if it were desired to pump two different fluids. In this
arrangement, while each of the pumps would have a dead space or zero
output dwell time, the advantages of the compact arrangement could still
be preserved, however.
While the preferred drive arrangement has been that of an electrically
controlled, digital pulse-actuated stepping motor, any form of fixed speed
or other kind of variable speed drive could be utilized advantageously
with the compact positive displacement pump of the invention. Other
variations in certain aspects of the design will also be apparent to those
skilled in the art.
In the description given, the yoke serving to drive the opposed connecting
rods is in the form of a pair of spaced apart legs affixed to a radial
flange. It is to be understood that any suitable means for positioning
such connections to the connecting rod ends is appropriate. Thus, the yoke
may be in the form of a hollow cylinder or other arrangement adapted to
space the connectors to the rod ends at a distance from the center line
axis of the drive element.
It will thus be seen that the present invention provides a new and improved
positive displacement pump for liquids having a number of advantages and
characteristics including those pointed out herein and others which are
inherent in the invention. A description of one form of the positive
displacement pump of the invention having been illustrated by way of
example, it is anticipated that variations and modifications of the
described form of apparatus will occur to those skilled in the art and it
is anticipated that such variations and changes may be made without
departing from the spirit of the invention or the scope of the appended
claims.
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