U.S. patent number 3,809,506 [Application Number 05/313,756] was granted by the patent office on 1974-05-07 for hermetically sealed pump.
This patent grant is currently assigned to Columbia Gas System Service Corporation. Invention is credited to Norman D. Malcosky.
United States Patent |
3,809,506 |
Malcosky |
May 7, 1974 |
HERMETICALLY SEALED PUMP
Abstract
A hermetically sealed pump includes a cylinder that defines a
piston chamber for a reciprocating piston driven through an
eccentric cam member and a cam follower operatively connected
between the piston and the cam. A fluid manifold is associated with
the piston cylinder and has suction and discharge ports located in
communication with the piston chamber for supplying fluid to and
discharging fluid from that chamber, and a pair of valves are
operatively associated with these ports for simultaneously opening
one of the ports and closing the other of the ports, in response to
pressure in the piston chamber. A toroidally shaped rolling
diaphragm hermetically seals the piston chamber on the side of the
piston opposite the ports, thereby to prevent loss of fluid in the
pump through the piston chamber.
Inventors: |
Malcosky; Norman D. (Columbus,
OH) |
Assignee: |
Columbia Gas System Service
Corporation (Wilmington, DE)
|
Family
ID: |
23217013 |
Appl.
No.: |
05/313,756 |
Filed: |
December 11, 1972 |
Current U.S.
Class: |
417/439; 92/98R;
417/571; 417/902 |
Current CPC
Class: |
F04B
53/102 (20130101); F04B 39/048 (20130101); F16J
15/52 (20130101); F04B 53/105 (20130101); Y10S
417/902 (20130101) |
Current International
Class: |
F16J
15/50 (20060101); F16J 15/52 (20060101); F04B
53/10 (20060101); F04B 39/04 (20060101); F04b
021/02 (); F04b 039/00 () |
Field of
Search: |
;417/571,439,902,413
;92/98D,98R,165 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Croyle; Carlton R.
Assistant Examiner: Gluck; Richard E.
Attorney, Agent or Firm: Curtis, Morris & Safford
Claims
1. A pump comprising, a cylinder defining a piston chamber, a
piston located in said cylinder for reciprocation therein, a fluid
manifold associated with said piston cylinder and having suction
and discharge ports located in communication with said piston
chamber, valve means operatively associated with said ports for
simultaneously opening one of said ports and closing the other of
said ports in response to the pressure in said piston chamber,
means for hermetically sealing said piston chamber on the side of
said piston opposite said ports, thereby to prevent loss of fluid
in said pump through said piston chamber, and means for
reciprocating said piston including a driven eccentric cam and a
cam follower operatively connected between said piston and said
cam, and means biasing said cam follower into engagement with said
cam whereby rotation of said eccentric cam causes reciprocation of
said piston in said chamber to alternately produce relatively low
and high pressures in said chamber, thereby to draw fluid from said
manifold through said suction port into said piston chamber and
thence discharge said fluid through said discharge port; said means
for hermetically sealing said piston chamber comprising a diaphragm
formed of an elastomeric material operatively connected between
said cylinder and said piston and having a first side facing said
piston chamber and a second side opposite said first side and
remote from said piston chamber; said diaphragm having inner and
outer edge portions respectively connected to said piston and said
cylinder and having a thickness between said inner and outer edge
portions which is greater than the thickness of said edge portions
thereby to form a bulge in said diaphragm between said edge
portions to define a pair of curved rolling surfaces thereon; and
means forming a pair of opposed continuously curved surfaces
adjacent said second side of said diaphragm in predetermined
relation to each other whereby said curved rolling surfaces of the
diaphragm roll along said opposed continuously curved surfaces in
opposite
2. A pump as defined in claim 1 wherein said piston includes a
piston rod connected to said follower, and said means forming said
opposed continuously curved surfaces includes a guide flange having
a central bore opening towards said piston and piston chamber, said
flange having a peripheral edge portion surrounding said bore, said
edge portion being rounded to form one of said continuously curved
surfaces, and a generally disk shaped guide member on said piston
rod having a peripheral rounded
3. A pump as defined in claim 2 wherein said diaphragm has a
generally toroidal configuration when viewed in plan, said outer
edge portion being clamped between said guide flange and said
cylinder and said inner edge portion being clamped between said
piston and said guide member thereby to form said bulge in said
diaphragm between said inner and outer edge portions and form said
curved rolling surfaces engaging the continuously
4. A pump as defined in claim 3 wherein said guide member is
positioned to have its curved surface located at a level above the
curved surface of said flange when said piston is in its top dead
center position and at a level below the curved surface of said
flange when said piston is in its
5. A pump as defined in claim 2 wherein said means for biasing said
cam follower into engagement with said cam comprises a compression
spring
6. A pump as defined in claim 2 wherein said valve means includes a
flap
7. A pump as defined in claim 6 wherein said valve means further
includes a check valve operatively associated with said discharge
port for opening
8. A pump as defined in claim 7 including an electric motor having
an output shaft, and said eccentric cam comprises an eccentric cam
bushing secured to said shaft and a rotary bearing mounted on said
cam bushing in
9. A pump as defined in claim 1 wherein said diaphragm cooperates
with said piston to form a fluid chamber therebetween in said
cylinder, and said cylinder has a fluid passage formed therein
providing fluid communication
10. The pump as defined in claim 3 wherein said continuously curved
surfaces are spaced from each other and the bulge in said diaphragm
enters the space between said continuously curved spaces thereby
allowing said
11. A pump comprising, an electric motor having a rotary power
output shaft, means forming an eccentric rotary cam surface mounted
on said shaft, and a piston assembly operatively associated with
said eccentric cam surface including a piston cylinder having a
piston chamber formed therein, a piston located in said cylinder,
having a piston rod and an operatively associated cam follower, a
guide flange operatively connected to said cylinder between said
cylinder and said cam and having a central bore opening towards
said piston and piston chamber, said piston rod extending through
said bore and being guided thereby during reciprocation of said
piston, a compression spring operatively connected between said
flange and said cam follower for biasing said cam follower into
engagement with said cam surface whereby said piston is
reciprocated during rotation of said cam surface to alternately
produce relative low and high pressures in said cylinder, a fluid
manifold operatively associated with said cylinder and having
independent fluid inlet and outlet ports formed therein, anc
communicating with said piston chamber, first valve means
operatively associated with said inlet port for opening said inlet
port and permitting fluid to flow into said piston chamber during
the downward suction stroke of said piston and closing said inlet
port on the upward-discharge stroke of said piston, and second
valve means operatively associated with said outlet port for
closing said outlet port on the downward-suction stroke of said
piston, and opening said outlet port on the upward-discharge stroke
of said piston, and a generally toroidally-shaped diaphragm formed
of an elastomeric material operatively connected between said
cylinder and said piston for hermetically sealing said piston
chamber to prevent loss of fluid therefrom during operation of said
pump; said diaphragm having a first side facing said piston
chamber, a second side opposite said first side and remote from
said piston chamber, inner and outer edge portions respectively
connected to said piston and said cylinder, and a thickness between
said inner and outer edge portions which is greater than the
thickness of said edge portions, thereby to form a bulge in said
diaphragm between said edge portions to define a pair of curved
rolling surfaces thereon: said flange bore having a rounded upper
peripheral edge portion adjacent said cylinder defining a first
continuously curved diaphragm rolling and support surface and said
piston rod having a generally disc-shaped guide member adjacent
said piston and a rounded peripheral surface defining a second
continuously curved diaphragm rolling and support surface; said
continuously curved diaphragm rolling and support surfaces
respectively engaging said pair of diaphragm curved rolling
surfaces to support said diaphragm during reciprocation of said
piston, whereby said diaphragm curved rolling surfaces roll along
said continuously curved diaphragm rolling and support surfaces of
the flange and guide member in opposite directions during
12. A pump as defined in claim 11 wherein said disk shaped guide
member is located in predetermined relation with respect to said
flange thereby to position said second diaphragm rolling and
support surface at a level above said first rolling and support
surface when said piston is in its top dead center position and at
a level below said first diaphragm rolling and support surface when
said piston is in its bottom dead center position, whereby said
diaphragm rolls along said diaphragm rolling and support surfaces
in opposite directions during reciprocation of said
13. A pump as defined in claim 11 wherein said first valve means
comprises a flap valve and said second valve means comprises a
spring biased check
14. A pump as defined in claim 11 wherein said means forming an
eccentric rotary cam surface comprises an eccentric cam bushing
mounted axially on said output shaft and a rotary bearing mounted
on said cam bushing and
15. A pump as defined in claim 11 wherein said diaphragm cooperates
with said piston to form a fluid chamber therebetween in said
cylinder, and said cylinder has a fluid passage formed therein
providing fluid communication between said fluid chamber and said
suction port.
Description
The present invention relates to a fluid pump and in particular to
a pump for liquids which must be pumped at high pressure
differentials and low flow rates.
There presently is a demand for high quality precision liquid pumps
which are adapted to be utilized in airconditioning systems wherein
high pressure differentials and low flow rates are required. Such
pumps are extremely important in airconditioning systems of the
absorption type and preferably must be hermetically sealed to
eliminate the possibility of loss of the refrigerant fluids during
the pumping cycle.
Accordingly, it is an object of the present invention to pump
liquids at high pressure differentials and low flow rates by an
efficient hermetically sealed pump.
Yet another object of the present invention is to provide a fluid
or liquid pump which is hermetically sealed and adapted to pump
liquids at high pressure differentials and low flow rates.
Yet another object of the present invention is to provide a pump of
the character described which is relatively inexpensive to
manufacture, simple and durable in operation.
In accordance with an aspect of the present invention a
hermetically sealed pump is provided for use in absorption type
refrigeration systems wherein it is desired to pump liquids, such
as the refrigerant solution, at high pressure differentials and at
low flow rates. The pump preferably is provided with an electric
motor having a rotary power output shaft on which an eccentric
rotary cam surface is provided for driving a piston assembly
operatively associated with the motor.
The piston assembly includes a piston cylinder having a piston
chamber formed therein, in which a piston is located for
reciprocation through a piston rod and cam follower from the rotary
cam element. The piston rod is guided in a guide flange which is
operatively connected to the piston cylinder, between the cylinder
and the cam, and has a central bore opening towards the piston and
piston chamber, through which the piston rod extends. A compression
spring operatively connected between the flange and the cam
follower biases the cam follower into engagement with the cam so
that the piston is reciprocated during rotation of the cam by the
electric motor, thereby to alternately produce relatively low and
high pressures in th cylinder.
A fluid manifold is located on the opposite side of the piston
cylinder from the guide flange. This manifold has independent fluid
inlet and outlet ports formed therein for separate communication
with the piston chamber. A flap valve is operatively associated
with the inlet port for opening that port and permitting fluid to
flow into the piston during the downward - or suction - stroke of
the piston, i.e., when there is low pressure in the chamber, while
closing the inlet port on the upward - or discharge - stroke of the
piston, i.e., when there is high pressure in the chamber. On the
other hand, a check valve is operatively associated with the outlet
port for closing the outlet port on the downward suction stroke of
the piston and opening the outlet port on the upward discharge
stroke of the piston, thereby assuring efficient pumping
operation.
Finally, the pump is hermetically sealed by a generally toroidally
shaped diaphragm formed of an elastomeric material and operatively
connected between the cylinder and the piston on the side of the
piston opposite the manifold. The diaphragm is of the rolling type
and prevents loss of fluid from the piston cylinder during the
pumping operation.
The above, and other objects, features and advantages of this
invention, will be apparent in the following detailed description
of an illustrative embodiment thereof which is to be read in
connection with the accompanying drawings, wherein:
FIG. 1 is a side view, with parts broken away and parts in section,
of a hermetically sealed liquid pump constructed in accordance with
one embodiment of the present invention;
FIG. 2 is a top view of the pump illustrated in FIG. 1;
FIG. 3 is an enlarged schematic sectional view of the piston
assembly during its downward suction stroke;
FIG. 4 is a sectional view similar to FIG. 3 showing the piston
assembly during its upward discharge stroke;
FIG. 5 is a view taken along line 5--5 of FIG. 3 showing the
relationship of the valves of the piston assembly; and
FIG. 6 is a schematic illustration of another embodiment of the
present invention.
Referring now to the drawing in detail and initially to FIG. 1
thereof, it will be seen that a pump 10, constructed in accordance
with the present invention, includes an electric motor 12 having a
shell 14 in which a cylindrical core 16 and central shaft 18 are
rotatably mounted. Motor 12 also includes a coil 20 which, in the
conventional manner, causes rotation of core 16 and shaft 18. The
latter has a motor cooling fan blade 19 rigidly mounted thereon and
is utilized to drive a piston assembly 22 which includes a manifold
24 having a threaded inlet port 26 and a threaded outlet port 28.
Upon operation of motor 12, shaft 18 operates the piston assembly
22, as more fully described hereinafter, in order to draw liquid
through the inlet 26, into the piston assembly, and thence
discharge the liquid through the outlet 28.
In the illustrative embodiment of the present invention, motor
shaft 18 includes a threaded end portion 30 on which a cam bushing
32 is threadedly secured. Cam bushing 32 includes a central cam
portion 34 whose axis of rotation is slightly offset from the
central axis of rotation 36 of shaft 18 and the remainder of
bushing 32 so that the outer peripheral surface 38 of the cam
bushing moves in an eccentric path about the axis of rotation of
shaft 18. Surface 38 thereby defines a cam surface for operating
piston assembly 22.
Cam bushing 32 also includes an inner portion 40 whose peripheral
surface is substantially coaxial with that of shaft 18, so that the
shaft and the cam bushing can be rotatably mounted in bearing 41
seated in the front cover plate 42 of housing 12. It is only that
portion 34 of cam bushing 32, located exteriorly of cover 42, which
has the eccentricity described above.
A bearing 44 is secured on eccentric surface 38 in order to drive
piston assembly 22, as described hereinafter. This bearing is
retained on member 32 between a snap ring 46 and a shoulder 48
milled in the cam bushing. Beyond snap ring 46, cam bushing 32
includes an elongated shaft portion 50 which may be used to
transmit power to other devices, as for example, pumps, fans, or
the like, through a conventional gear or pulley arrangement. Of
course, extension 50 is formed to be coaxial with shaft 18 so that
no eccentricities result during the use thereof in driving any
other equipment.
Piston assembly 22 (FIGS. 3 and 4) includes a piston cylinder 52
secured to cover plate 42 of housing 14 in any convenient manner.
Cylinder 52 includes an interior chamber 54 defined by an axial
piston bore 56 formed therein. Thus, chamber 54 defines a piston
chamber in which a piston 58 is positioned for reciprocation by the
eccentrically rotated bearing 44.
Manifold 24 is operatively secured to cylinder 52 with a valve
plate 60 secured therebetween. The manifold, as mentioned above,
includes an inlet port 26, through which fluid passes to the piston
assembly 22, and an outlet port 28, through which fluid is
discharged from the piston assembly during operation of the device.
Inlet port 26 is in communication with a suction port 61 formed in
the valve plate 60, whereby communication is provided between the
inlet port and chamber 54. Similarly, valve plate 60 includes an
outlet port 62 which provides communication between piston chamber
54 and outlet 28, for discharge of fluid drawn into the piston
chamber.
During operation of the piston assembly, piston 58 reciprocates
between a top dead center position and a bottom dead center
position, illustrated respectively in FIGS. 4 and 3. As the piston
moves downwardly towards its bottom dead center position, it
increases the volume within piston chamber 54, thereby decreasing
the pressure therein. As a result of this decrease in pressure, the
pressure of liquid in the inlet port forces open a valve mechanism
63 to permit fluid to enter the piston chamber. Valve mechanism 63
comprises a flap valve 64 located between valve plate 60 and
cylinder 52. Flap valve 54 includes a main body portion 65,
illustrated most clearly in FIG. 5, having an aperture 66 therein
which is generally complementary to the area of piston chamber 54.
The main body of flap valve 64 includes an elongated extension 68
which extends across opening 66, and has an enlarged head portion
70 positioned to cover inlet port 61 in valve plate 60. Flap valve
64 is formed of a flexible plastic, or metal, material so that the
extension 68 can flex under variations in pressure between the
piston chamber and the inlet port. Thus, as piston 58 moves in its
downward - or suction - stroke, the pressure in chamber 54
decreases and the pressure in inlet port 26 causes extension 68 to
move downwardly, away from port 61, thereby permitting liquid to
enter piston chamber 54. On the other hand, in the upward -
pressure - stroke of piston 58, i.e., towards its top dead center
position, the pressure within chamber 54 increases above that in
the inlet line 26 so that the enlarged portion 70 of extension 68
is moved back into engagement against the lower surface of valve
plate 60, thereby to close port 63 and prevent liquid flow from
chamber 54.
During the upward stroke of piston 58, fluid pressure within piston
chamber 54 is increased and thus fluid is discharged through outlet
port 62 in valve plate 60. However, a check valve 72 is located in
complementary bores 74, 76 formed respectively in discharge port 62
and outlet port 28. This check valve includes an outer cylindrical
body 78 which includes a valve seat 80 therein. A valve disk 82 of
conventional construction is located within valve body 78 and is
biased towards a closed position, illustrated in FIG. 3, by a
spring 84. Thus, upon the downward stroke of piston 58, spring 84
holds valve disk 82 against seat 80 to prevent liquid in port 28
from flowing backwardly into chamber 54. On the other hand, during
the upward pressure stroke of piston 58, the increasing pressure of
the fluid within chamber 54 ultimately overcomes the bias of spring
84, thereby to move disk 82 against spring 84 and permit the
pressurized fluid within chamber 54 to discharge through discharge
port 62 and outlet port 28. Accordingly, it is seen that during the
operation of the device, one or the other of the valves 64, 72 is
open and that these valve assemblies are responsive to pressure
within piston chamber 54, so as to automatically meter fluid into
and out of the piston cylinder.
Piston 58 is mounted on a piston rod 90 having a free end 92 which
is connected through a dowel rod (or in any convenient manner) to a
cam follower or shoe 96. The latter is engaged against the surface
98 of bearing 44 so as to be reciprocated by the bearing during its
eccentric rotation with cam bushing section 38. Piston rod 92 is
guided during this reciprocation in an annular guide flange 100
which is secured in any convenient manner to piston cylinder 52.
Flange 100 includes an inner bore 102 which opens towards piston 58
and piston chamber 54 and which is in axial alignment with an
auxiliary guide bore 104. A guide bushing 106 is located in bore
104 and engages piston rod 90 to assure low friction sliding of the
piston rod in the guide flange.
Guide flange 100 also provides a mounting for a compression spring
108 which surrounds the portion of flange 100 forming guide bore
104. One end of spring 108 is engaged against flange 100 and the
opposite end thereof is engaged against a spring retainer 106
secured to the free end of piston rod 92. In this manner, spring
108 biases cam follower 96 against the surface of bearing 44 to
assure positive contact therebetween at all times so that cam shoe
94 always follows the eccentrically rotating bearing. In this
manner piston 58 is automatically and positively returned to its
bottom dead center position.
Piston assembly 22 is hermetically sealed to prevent loss of liquid
or gas from the piston chamber through the lower side thereof by a
rolling diaphragm assembly 110. This assembly includes a generally
toroidally shaped diaphragm 112 formed of an elastomeric material.
Diaphragm 112 has an outer edge 114 which is clamped between flange
100 and cylinder 52, as most clearly seen in FIGS. 3 and 4, and an
inner edge 116 which is similarly clamped between piston 58 and an
enlarged, generally circular guide disk 118 formed integrally with
piston rod 90.
Diaphragm 112 can be squeezed between the various parts, in the
manner illustrated in FIGS. 3 and 4, and held therebetween by
frictional engagement with the parts, or it may be otherwise
secured in position in any convenient manner. In any case, the
diaphragm is held tightly in the position illustrated so that the
edges thereof are slightly compressed, causing the central portion
of the diaphragm to bulge, and thereby form a curved surface 120
along its lower side.
Preferably, flange 100 and guide 118 are provided with curved edge
portions 112, 124, respectively, located adjacent the curved
surface 120 of diaphragm 112, thereby to support the diaphragm
during rolling movement. As seen in the drawing, curved surface 122
of flange 100 is formed along the top edge of bore 102 and curved
surface 124 of guide disk 118 is formed along the top edge of its
peripheral annular wall. It is noted that diaphragm 112 is formed
of a relatively thick layer of material, so that the diaphragm will
have the capacity for a wide range of movement and can enter the
space between surfaces 122, 124. The large range of movement
permits the pump to withstand higher pressures as the diaphragm
moves further down into the space between the surfaces 122, 124
under increasing pressures but is continuously supported by these
surfaces to resist such pressures.
Piston 58, and piston rod 90, are dimensioned so that at the top
dead center of the piston's stroke, curved surface 124 of guide
disk 118 is located at a slightly higher level than guide surface
122, as seen in FIG. 4, while at its bottom dead center position,
guide surface 124 is located at a slightly lower level than surface
122 (FIG. 3). As a result, during movement between top dead center
and bottom dead center, the rolling diaphragm rolls along surfaces
122, 124 in opposite directions. That is, for example, as
illustrated in FIG. 4, diaphragm 112, at the top dead center of
piston 58, contacts rolling surface 122 at point A, while
contacting the curved surface 124 at a point B (FIG. 4). As piston
58 moves downwardly the point of contact between diaphragm 112 and
surface 122 moves downwardly to the point A' (FIG. 3) whereas the
point of contact between the diaphragm and the guide surface 124
moves upwardly to the point B' (FIG. 3). Thus, these points of
contact move in the opposite direction, thereby defining contact
zones (A" and B" respectively) on surfaces 122, 124 at which the
rolling diaphragm is continuously supported during operation of the
device. (It is noted that for clarity, zones A" and B" have been
stipled in the drawing.) This rolling support improves the sealing
characteristics of the diaphragm and its useful life.
Any pressure increase in chamber 127 above diaphragm 112, i.e.,
between piston 58 and the diaphragm, will cause the zones of
contact with the surfaces 122 and 124 to move downwardly. On the
other hand, any decrease in pressure in the area above the
diaphragm will cause those zones of contact to move upwardly. The
diaphragm is constructed of sufficient thickness to allow this
movement without effecting the generally toroidal shape of the
elastomeric material. In any case, because of the construction of
the invention, the diaphragm will always be in contact with and
supported by the curved surfaces 122, 124 during operation of the
device, irrespective of the pressure above the diaphragm. In this
regard, it is noted that the diaphragm is important in hermetically
sealing the piston in that it is possible that during operation of
the device, some liquid or gas can escape past the piston rings 126
of piston 58 into chamber 127 above the diaphragm. In previously
proposed devices, these gases or liquids would simply leak out,
causing damage and also decreasing the supply of refrigerant fluid
in the airconditioning system in which the pump is utilized. With
the present invention, on the other hand, the fluid remains in the
system, flowing through conduit 128 to the pump inlet 26, and thus
is contained in the system. Conduit 128 provides communication
between chamber 127 and inlet port 26, thereby assuring that the
diaphragm 112 is not subjected to varying and excessive pressures,
but rather only to the inlet fluid pressure. This extends the
useful life of the diaphragm. It is noted that the diaphragm
construction and mounting is such that the volume of chamber 127
remains substantially constant through the operation of the pump.
Thus, the fluid pressure in chamber 127 is always substantially
equal to the pressure in the suction inlet port.
In the operation of pump 10, rotation of shaft 18 by electric motor
12 causes rotation of eccentric cam bushing 32. As a result, the
eccentric section 38 thereof causes eccentric rotation of the
bearing 44. By engagement of cam follower 96 against the surface of
bearing 44, piston 58 is reciprocated within piston chamber 54. As
a result, on the downward-suction stroke of the piston, liquid or
fluid to be pumped is drawn in through inlet port 26 and passes
through suction port 63 and the now open flap valve 64 to piston
chamber 54. On the upward stroke of piston 58, the flap valve 64
automatically closes and the bias of spring 84 in check valve 74 is
overcome, so as to permit the pressurized liquid to be discharged
through the outlet 28. Loss of fluid of course is prevented by the
hermetic seal arrangement provided by rolling diaphragm 112,
clamped between the flange 100, cylinder 52, piston 58 and guide
disk 118.
In another embodiment of the present invention, illustrated in FIG.
6 of the drawings, more than one piston assembly 22 can be utilized
with the motor 12. As shown therein, two piston assemblies 22 are
operatively connected on opposite sides of eccentric bearing 44. In
this case springs 108 operate in the same manner as described above
to hold shoes 96 of the piston rods against the cam bearing. As a
result, piston assemblies 22 are operating in opposite phases to
draw fluid from inlet supply 125 to theri respective inlet ports.
In this manner, the capacity of th pump is substantially double
that of the embodiment of FIGS. 1 to 5. Of course, other piston
assemblies may also be mounted on pump 10, in a similar manner, as
would be understood by those skilled in the art, to further
increase the capacity of the entire pump arrangement.
Accordingly, it is seen that a relatively simple and inexpensive
pumping mechanism is disclosed which provides accurate pumping at
high pressure differentials and low flow rates. The pumping
assembly is hermetically sealed, because of the elastomeric rolling
diaphragm sealing arrangement described above. This seal has a
relatively long life and prevents leakage from the piston assembly.
In addition, the spring biased piston arrangement utilized in the
present invention guarantees that the cam follower on the piston
rod remains in contact with the cam drive mechanism in order to
retract the piston to its bottom dead center position, thereby to
produce suction in the piston chamber 54 and draw liquid into the
chamber for pressurization and discharge through outlet port
28.
Although illustrative embodiments of the present invention have
been described herein with reference to the accompanying drawings,
it is to be understood that the invention is not limited to those
precise embodiments and that various changes and modifications may
be effected therein by one skilled in the art without departing
from the scope or spirit of this invention.
* * * * *