U.S. patent number 3,874,826 [Application Number 05/431,753] was granted by the patent office on 1975-04-01 for intravenous delivery pump.
Invention is credited to Ingemar H. Lundquist.
United States Patent |
3,874,826 |
Lundquist |
April 1, 1975 |
INTRAVENOUS DELIVERY PUMP
Abstract
The present invention comprises a small, precise measuring pump
provided with a germ barrier that is specifically designed for
intravenous feeding devices and comprises: inlet and outlet
chambers which are preferably integral one with the other, an inlet
adapted to receive a tube from a storage device and the outlet
chamber provided with an outlet adapted to receive a tube for
delivery of material pumped to a patient; a passageway between the
two chambers, which serves as an outlet from the inlet chamber and
an inlet into the outlet chamber; a valve (preferably a float
valve) associated with each inlet; and an actuating device which
includes a piston and a tightly fitting resilient sheath enclosing
the piston, the combination of piston and sheath projecting into
the inlet chamber. The movement of the piston inwardly and
outwardly within the inlet chamber provides the pumping force for
the operation of the pump, and the sheath provides a sterile seal
between the piston and the body of the pump and also, if made of
resilient material, such as rubber, provides a force for returning
the piston to an inoperative position. A pumping force may be
applied to the external end of the piston by any suitable
means.
Inventors: |
Lundquist; Ingemar H. (Oakland,
CA) |
Family
ID: |
26986782 |
Appl.
No.: |
05/431,753 |
Filed: |
January 8, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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329425 |
Feb 5, 1973 |
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Current U.S.
Class: |
417/565;
128/DIG.12; 604/123; 604/152; 74/18.2; 222/373; 222/380;
604/127 |
Current CPC
Class: |
F04B
53/10 (20130101); F04B 53/00 (20130101); A61M
5/14224 (20130101); F04B 53/143 (20130101); F16K
31/22 (20130101); Y10S 128/12 (20130101) |
Current International
Class: |
A61M
5/142 (20060101); F16K 31/22 (20060101); F16K
31/18 (20060101); F04B 53/10 (20060101); F04B
53/14 (20060101); F04B 53/00 (20060101); F04b
039/10 () |
Field of
Search: |
;74/18,18.1,18.2 ;184/24
;417/221.5,507,536,568,565,559,127 ;128/214F,273,214C,235 ;132/527
;222/319,377,380,373 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Freeh; William L.
Attorney, Agent or Firm: Wilcox; Robyn
Parent Case Text
This application is a continuation-in-part of my application Ser.
No. 329,425, filed Feb. 5, 1973, now abandoned.
Claims
What is claimed is:
1. A small, precise measuring pump having a germ barrier
comprising:
a. a non-deformable inlet chamber and an outlet chamber attached
thereto;
b. an inlet into said inlet chamber and a communication duct from
said inlet chamber into said outlet chamber;
c. a valve in said inlet chamber cooperating with said inlet and a
valve in said outlet chamber cooperating with said communication
duct;
d. an outlet from said outlet chamber;
e. a piston having an inner end section projecting through the wall
of said inlet chamber and adapted to be moved inwardly and
outwardly therein, said piston having an exposed outer end portion
which remains outside said chamber and is adapted for engagement by
a piston actuating means;
f. a resilient sheath entirely enclosing the portion of said piston
which is inside said inlet chamber and having means external to the
inlet chamber for sealing engagement with the outer wall of the
inlet chamber and further means external of the inlet chamber for
sealing engagement with the outer surface of said piston.
2. A disposable intravenous liquid pump adapted for delivering a
sterile liquid at a variable controlled rate comprising:
a. a pump chamber having an inlet duct and an outlet duct;
b. a valve cooperating with each said inlet and outlet ducts;
c. a displacement piston having an inner end portion projecting
inwardly through a wall of said pump chamber adapted to be moved
from an inoperative position inwardly and outwardly therein within
variable controlled limits, said piston having an exposed outer end
portion which remains outside said chamber with the said outer end
thereof adapted for engagement by a piston actuating means;
d. a flexible sheath having the interior surface throughout the
length thereof disposed in contact with the outer surface of said
inner end portion of said piston, and said sheath having the outer
end thereof in sealing engagement with said wall of said pump
chamber; and
e. sealing means preventing the admission of air between said
piston and said sheath comprising an inwardly extending lip on said
sheath tightly engaging the outer surface of the piston and
normally having an internal diameter which is less than that of
said outer surface.
3. An apparatus as in claim 2 wherein said flexible sheath exerts a
force on said piston in an axially outwardly direction when said
piston is moved by a said piston actuating means from an
inoperative position axially inwardly within the interior of said
chamber, and said force being sufficient to effect movement of said
piston outwardly to said inoperative position when said piston
actuating means ceases to apply an axially inwardly force to said
piston.
4. The apparatus of claim 2 wherein the sheath is thicker at the
end of said piston than along the side wall thereof.
5. An intravenous delivery pump comprising:
a. a spherical inlet chamber and an outlet chamber attached
thereto;
b. an inlet projecting inwardly into said inlet chamber and a
communication duct from said inlet chamber projecting into said
outlet chamber;
c. a float valve in said inlet chamber cooperating with said inlet
and a float valve in said outlet chamber cooperating with said
communication duct;
d. an outlet from said outlet chamber;
e. a piston projecting through the wall of said spherical inlet
chamber and adapted to be moved inwardly and outwardly therein;
f. a resilient sheath tightly enclosing said piston, the outer end
of said sheath being in sealing engagement with the wall of said
spherical inlet chamber and the inner end thereof entirely
enclosing the piston.
6. The apparatus of claim 5 wherein the sheath is provided with an
inner lip at the open outer end thereof adapted to tightly engage
the piston, and the end wall of said sheath is thicker than the
side wall thereof.
7. The apparatus of claim 5 wherein the valve for said inlet and
said intermediate duct comprises a float, an arm attached to said
float, said arm being pivotally mounted in a wall of the respective
chamber and said arm carrying a sealing gasket adapted to engage
the end of said inlet or the said intermediate duct,
respectively.
8. The apparatus of claim 5 wherein the inlet into said inlet
chamber projects inwardly in said chamber and terminates at a
central elevation.
9. The apparatus of claim 5 comprising also a lubricant between the
sheath and the piston.
Description
BACKGROUND OF THE INVENTION
In recent years there has been considerable interest in intravenous
delivery pumps, particularly for the feeding of saline solutions,
and the like, to a patient. For many years such materials were fed
to a patient only by the force of gravity, which necessitated
placing the container containing the liquid for delivery to the
patient at a considerable elevation above the patient. These
devices were not entirely satisfactory in view of the height
requirement and the difficulty in accurately regulating their flow.
Regulation of flow could only be secured by counting drops of fluid
in a predetermined period of time and then requiring periodical
checking by a nurse. Furthermore, it was difficult to maintain a
regulated flow over a prolonged period of time. Therefore, in
recent years there has been a trend toward developing a positive
acting pump which could be accurate in its delivery of intravenous
feeding material to the patient, could be readily adjusted and
would be positive in its operation, without requiring the placing
of the bottle containing the liquid at some distance above the
patient. The difficulty with these pumps has been, for the most
part, that they were subject to slight variations in the quantity
of material delivered, so that absolute accuracy was still
impossible. They also have the disadvantage that they were rather
expensive and could not be used once and then thrown away, and they
were difficult to disassemble, sterilize, and re-assemble, so that
sterilization and the maintenance of sterile conditions was
difficult. One of the causes of inaccuracy in pumping was the shape
of the chamber in which the pumping operation took place. If this
is square or cylindrical in shape and is made of light plastic
material, the exertion of a pumping force to the material within
the chamber causes flexing of the chamber walls and therefore
introduces inaccuracies. Many of these pumps used float valves,
most of which were cylindrical in shape, and again the force
applied to the liquid within the pumping chamber caused flexing of
the top and bottom of the cylindrical float. Some of the pumps
heretofore suggested have utilized a piston moving into and out of
the pumping chamber to apply the pumping force to the liquid within
the chamber and this introduced the possibility of leakage and,
more important, the possibility of septic materials coming from
outside the pump through the wall in which the piston operates and
into the material in the chamber. Such a construction involved a
rubbing contact between the piston and the wall of the pumping
chamber, which produces wear and eventual leakage, and prevented
their use for pumping blood.
These disadvantages have been removed in the present invention in
which the pump is preferably made of light plastic material, so
that it can be made in a few simple moldings and therefore is so
inexpensive that it can be thrown away with each use. The pumping
chamber is preferably spherical in shape so that the application of
pressure to the liquid therein is equal in all directions and
cannot deform spherical walls. I use, preferably, a particular form
of float valve in which a spherical float is mounted on one end of
a lever arm, the other end of which is pivoted to the walls of the
respective chambers, which arm carries at an intermediate point a
gasket aligned with the inlet into the respective chambers. The
gasket preferably is located substantially closer to the pivot
point than to the center of the spherical float, thereby giving the
float increased force against the inlet due to the multiplication
of force through the lever action. The pumping member is a piston
enclosed in a tight fitting sheath which is preferably shaped to
prevent the entrance of air between the sheath and the piston and
is shaped so that the stretching of the sheath occurs in the
cylindrical walls thereof rather than at the end, so that there is
considerable force applied to the sheath against the piston to
return it to its normal, inoperative position. Movement of the
piston can be from any suitable prime mover, such as a small motor
rocking a lever against the outer end of the piston. Further, the
preferred form of pump shown and described permits it to be used as
a positive acting and highly accurate pump when it is placed in one
position, and can also be used in gravity feed by merely turning
the pump upside-down. Thus, the device of the present invention can
be used as a pump or in connection with gravity feed without
removing it from the feed line, as conditions may warrant.
OBJECTS
It is a primary object of the present invention to provide a small
pump particularly adapted for intravenous feeding, which is small
in size, can be readily made of moldable materials, such as
styrene, or other plastic, is inexpensive to fabricate, and which
is extremely accurate in its rate of delivery.
It is another object of the present invention to provide an
improved intravenous delivery pump in which there is no rubbing
contact between the forcing element and any part of the pump
casing, so that it can safely be used for pumping whole blood.
It is a further object of the invention to provide a very small,
very light weight, and very precise measuring pump which has a germ
barrier, that prevents the possibility of contamination of the
material being pumped.
It is still another object of the present invention to provide a
pump small in size and light in weight in which the rate of
delivery can be readily adjusted by controlling the depth of
movement of a piston into the pumping chamber and by the timing of
the separate strokes.
It is another object of the present invention to provide an
intravenous feeding device which cannot pump air into the patient's
blood stream which will become inoperative in the event a quantity
of air becomes entrapped therein.
It is still another object of the present invention to provide a
pump which can either be positively operated or used as a
"flow-through" device by merely changing its position, so that it
does not have to be removed from the supply system (with its
consequent problems of maintaining sterile conditions) when it is
desired to shift from positive operation to gravity feed.
These and other objects of the present invention will become
apparent from a review of the accompanying drawings when taken in
connection with the description which follows.
DRAWINGS
FIG. 1 is an enlarged cross-sectional side view of the pump of the
present invention.
FIG. 2 is a cross-sectional plan view of the pump shown in FIG. 1
taken along the planes indicated by the lines 2--2 of FIG. 1.
FIG. 3 is a detail of the construction of the sealing gasket
preferred for use in connection with the valve of the present
invention.
FIG. 4 is an exploded view of the pump piston and its sheath.
In its preferred form the pump of the present invention comprises
an inlet chamber 10 and an integral outlet chamber 11 preferably
formed of three molded plastic sections: an upper generally
hemispherical hollow section 12, a middle section 13, the upper
portion of which is a hollow hemisphere adapted to fit in tight
engagement with the upper hemisphere 12 and a lower section which
is the upper part of a cylindrical outlet chamber; and a lower
section 14 which completes the outlet chamber 11. The upper section
12 is formed with an integral inlet duct 15 which preferably
extends downwardly to the end of the section or slightly beyond.
The middle section has a hemispherical wall which, when affixed to
the wall 12 of the upper section, forms the spherical inlet chamber
10 and is provided with an outlet port 16 which preferably extends
downwardly to the level of the integral circular wall 37 which
forms the upper portion of the outlet chamber 11. A discharge port
17 is formed in the lower end of the lower section 14. The inlet
port 15 is of a size adapted to receive a supply tube 42 leading
from a supply of material to be delivered to the patient, such as a
bottle of saline solution, or the like, and the outlet 17 is
likewise of a size adapted to engage a tube 43 for delivery of the
pumped material to the patient.
The respective sections are connected together by means of a pair
of interlocking lips, such as 32, on the interior wall of upper
section 12 and the cooperating outer lip 33 on the outer wall of
the hemispherical portion of section 13; and an inner lip 34 on the
inner wall of the cylindrical portion 37 of the middle section 13,
and lip 35 on the outer wall of section 14. The connections between
the respective sections must be water and air-tight, and they must
be strong enough to resist the pumping force applied to liquid
within chamber 10 or to the weight of the liquid in the outlet
chamber 11. This can readily be secured by cementing the respective
lips 32, 33 and 34, 35 together, although the parts could be made
to such accuracy that friction force alone would be sufficient to
hold the parts together.
The interiors of the two chambers 10 and 11 are provided with a
pair of parallel ribs, or bosses, such as 18 shown in FIG. 1 in the
upper section 12; 19 and 20 in the hemispherical section of section
13 (shown in FIG. 2); and 22 (shown in FIG. 1) in the cylindrical
portion of section 13, and 24 shown in the lower section 14. These
bosses serve two purposes: (1) to properly align the various
sections together, the device being properly assembled when boss 18
is aligned with boss 20 and the boss, or rib, 22 is aligned with
the boss, or rib, 24; and (2) they form the bearings for the float
valves to be described hereafter. The bearings are formed by
providing bearing slots, such as 26 shown in dotted lines in FIG.
1, in the lower pair of each set of ribs. Again, when the parallel
ribs are properly aligned, the upper pair cooperates with the lower
pair to form a cover for the bearing slots, so that the float
valves cannot be displaced.
Each of the chambers 10 and 11 is provided with a float valve 50
cooperating respectively with the inlet 15 and the intermediate
conduit, or duct, 16. Since these two float valves preferably are
identical in construction, a description of one will be sufficient
for both, and since they are identical in construction, the same
reference characters can be applied to both float valves.
Preferably, the two float valves are held against extreme opening
action by stops 38 and 39 which are formed in the bottom of the two
chambers 10 and 11, as shown in FIG. 1. Such a limiting of movement
of the float is desired to prevent any possibility of the float
blocking the outlet from its chamber.
The valve of the present invention comprises a spherical float 50
preferably formed of two hollow hemispheres 51 and 52 tightly
fitted together. A suitable connection between the two sections 51
and 52 can be formed by providing one section, such as 51, with an
interior lip, not shown, and the other section, such as 52, with an
outer lip, likewise not shown, which are slightly oversize and
therefore must be forcibly inserted one within the other to form a
water-tight seal. In this instance, any pressure exerted by fluid
in the chamber 10 will be forcing toward the center of the float
and therefore there is no danger of the two sections being forced
apart from pressure of the fluid being pumped. It does, however,
require a water-tight seal so that fluid will not leak into the
interior of the float 50.
The float 50 is mounted on a lever arm 60, preferably formed
integrally with the lower hemispherical section 52 as shown
particularly in FIG. 1. The arm 60 is pivotally mounted within the
chamber by means of a pivot shaft 61, the ends of which are reduced
to provide suitable journals 62 and 63 (FIG. 2) adapted to be
inserted in the bearing slots, such as 26 described above. In order
to provide strength for the bearing shaft 61, it is preferred that
a longitudinally extending rib 64 (FIG. 1) be formed integrally
with the pivot shaft 61 and that the arm 60 be integral therewith.
Even though the pump casing comprising chambers 10 and 11, and the
valve element comprising the pivot shaft 61, lever arm 60 and lower
hemisphere 52 of the float 50 are made of styrene, which has no
self-lubricating properties, the assembly of the bearing notches 26
and the journals 62, 63 provide for easy movement of the valve
within its pivot bearing as the liquid in the chambers provides
very excellent lubrication. Hence, the float will be responsive to
exceedingly small differences in the pressure within the chamber
10. It can be mentioned at this point that when the pump is in
operation, both chambers are filled with the liquid being pumped.
Both valves have a buoyancy which causes them to rise as far as
possible toward the top of their respective chambers. When the
piston 100 and its sheath 102 (to be described hereafter) are
projected inwardly, the increase in pressure in chamber 10 forces
the valve in chamber 11 open, and liquid will flow from chamber 10
into chamber 11. When movement of the piston stops, the valve in
chamber 11 closes immediately. Then as the piston is withdrawn, it
causes a negative pressure, or suction, in chamber 10, thereby
causing the valve in that chamber to open and permitting the inflow
of further liquid from the source of supply. Obviously, the size of
the float 50 must be carefully calculated so that it will close
inlet 15 with more force than will come from the height of liquid
above it and small enough to be responsive to the suction caused by
the withdrawal of the piston.
The lever arm 60 is provided at an intermediate point with a
doughnut-shaped section 65 (FIG. 1) adapted to receive a sealing
gasket 70 to be described in the next paragraph. Preferably, this
doughnut-shaped section 65 will be located about one-third of the
distance from the axis of the pivot shaft 61 to the center of the
spherical float 50, whereby any lifting force on the float 50 will
be multiplied by the ratio 3:1 to apply force from the gasket 70
against the lower end of the inlet 15 or 16, as the case may be.
Obviously, this doughnut-shaped section 65 must be in alignment
with the inlet valve 15.
The sealing gasket 70 is shown particularly in detail in FIG. 3.
Preferably it is made of a very light and very flexible silicone
rubber of medically approved quality. It comprises a plate section
71 adapted to be at about the plane of the upper edge of the arm
60; a stem 72 adapted to fit tightly within the interior 66 of the
doughnut-shaped section 65; and a conical section 74, connecting
the plate 71 and stem 72. Preferably it has a smaller section 73 at
the lower end of the stem 72. The smaller section 73 is desirable
in that it makes it easy to start the gasket 70 into the hole 66 of
the doughnut-shaped section 65, and then it can be used to pull the
tightly fitting stem into the hole 66. The conical section 74
between the plate 71 and the stem 72 enables the plate to be
removed slightly from arm 60, so that it can tilt easily in order
to conform to the open end of its inlet port. Preferably, the
gasket is formed of very resilient material so that it may readily
be inserted in the lever arm 60 and so that the plate section 71 of
the gasket will deform to fit tightly against any irregularities
occurring in the lower end of the inlet 15 or 16 and be tilted, if
necessary, to form a tight-fitting seal with the inlet 15 or
16.
The pumping displacement, or force, of the present invention is
secured by the inward and outward movement of a piston 100 shown in
place in FIG. 1 and in an exploded view in FIG. 4. Associated with,
and cooperating with, the piston 100 is a tightly fitting sheath
102. The piston and sheath extend into the inlet chamber 10 through
an opening 108 in the upper portion of the upper section 12, so
that movement of the piston 100 and sheath 102 inwardly toward the
center of the inlet section applies a pumping force to liquid
within that chamber, assuming that the chamber is full of liquid,
as it should be to secure a pumping operation.
The open end of the sheath 102 is provided with an inwardly
extending lip 103 which must be forced and deformed to receive the
piston 100 as the piston 100 fits tightly within the body of the
sheath 102. It is desired that there be no possibility for the
entrapment of air between sheath 102 and piston 100, and the
inwardly extending lip 103 provides a sealing ring for that
purpose, which sealing ring is applied with some force to the
piston as the sheath is extended. It will be noted in FIG. 4 that
the cylindrical wall 104 of the sheath 102 is thinner than the end
wall 105. This is done to prevent stretching of the sheath from
occurring at the end of the piston, as that would tend to form a
break in the sheath at the end of the piston. Thus, the sheath is
stronger at the end where tension would normally be greater and the
tension caused by stretching the sheath is transferred to the
cylindrical wall 102. This has the advantage of not only preventing
rupture of the sheath, but also provides greater force for the
return of the piston to its outward and inactive position.
It is assumed in this application that the operating force will be
applied by some drive member (not shown), such as a lever or rocker
arm operated by a small electric motor. One such device is
described in my copending application, filed April 25, 1973, Serial
No. 354,242. The necessary action can be secured by pushing the
piston inwardly and then releasing it, leaving the return force to
the tension within the sheath 102, which preferably is formed of a
resilient rubber-like material.
The sheath is also provided with an outwardly extending annular
sealing ring section 106 adapted to fit into a depression 109
formed as an annular groove around the entrance 108 for the piston
and sheath. When a cap member 107 is forced down upon the sealing
section 106, as by cementing, the use of the threaded parts, or the
like, the pressure deforms the sealing section 106 to form a
completely air-tight seal between the sheath and the casing of the
pump. As shown in FIGS. 1 and 4, it is preferred that the outer end
101 of the piston 100 be of reduced diameter so that the cap
section 107 not only locks the sheath in place, but also holds the
piston 100 from moving out of its proper position in the pump, the
enlarged section of the piston 100 abutting the smaller aperture
110 at the outer end of the cap 107.
It perhaps should be mentioned that in its preferred form the
sheath 102 should fit snugly on the piston 100 so that no air will
be trapped between the two. Preferably, the sheath 102 is so
proportioned that when the piston 100 and sheath 102 are inserted
in the chamber 10, the shoulder between the piston 100 and its neck
101 will abut the inside of the outer end of the cap 107 and the
sheath will be relaxed, i.e., not under tension, but still tightly
fitting to the piston at all points. However, when the pump is
placed in its operating position with respect to the pump driver,
it is preferred that the piston be moved inwardly slightly so that
at that time, but not before, there will be a little tension in the
side wall of the sheath. What must be emphasized is that when a
vacuum is created in the chamber 10 by the withdrawal of the
piston, there must be no air between the piston and the sheath or
the vacuum in the chamber might cause the sheath to bulge and thus
make the pump inaccurate.
It should also be mentioned that in the assembly of the pump it is
necessary to place a lubricant on the piston whereby the piston and
the sheath can have a sliding contact with each other. It is well
known that rubber has a relatively high coefficient of friction,
and it is necessary to have as little friction as possible between
the piston and the sheath so that the force from the tensioning of
the cylindrical wall of the sheath will be sufficient to quickly
force the piston to its most retracted position. I have found that
a good grade of silicone lubricant is sufficient for this
purpose.
It is believed that operation of the pump will be readily
understood. At the start, the two chambers 10 and 11 are completely
filled with liquid to be pumped. This is readily secured by turning
the pump from the upright position shown in FIG. 1 to a horizontal
position at 90.degree. thereof. When this is done, the float valves
50 become inoperative and both chambers fill completely with liquid
from the source of supply, not shown, entering through tube 42.
Then, when the pump is turned to the upright position, both
chambers are full of liquid, and the valves are operative to close
both inlets 15 and 16. The pump is now ready for operation. The
periodic application of force inwardly against the outer end of
piston 100 causes the piston and sheath to penetrate into the
liquid in chamber 10, thereby forcing the liquid through the
intermediate duct 16 into the lower chamber 11. Normally, this
chamber is closed by the buoyancy of the float 50 in that chamber.
However, when the piston and its sheath are projected into chamber
10, the liquid in that chamber (being incompressible) must overcome
the closing force of the float valve 50, 60, 70 in the lower
chamber 11. When the piston 100 is withdrawn, the float valve in
chamber 11 closes, as the force secured from the float 50 in the
chamber is greater than the weight of fluid in chamber 10. Then, as
the piston and its sheath moves outwardly, it creates a suction, or
negative liquid pressure, in chamber 10, and the float valve 50
into that chamber opens and lets further material come from the
supply source through tube 42. By this means an adequate and very
accurate flow of intravenous feeding liquid is secured. The amount
of liquid delivered with any stroke of the piston is readily
controlled by adjusting the length of the stroke, and the frequency
of such delivery is secured by controlling the frequency of piston
operation. Thus, the pump of the present invention is easily
adjustable as to amount of material supplied with any pump stroke
and the frequency of strokes is also readily controlled, as is
clearly described in my copending application above mentioned.
In the event it is desired to disconnect the pump from its actuator
(as when moving a patient from one room to another) and to use it
as a "through-flow" device to avoid disconnecting the pump from its
inlet and outlet tubes 42 and 43, it can readily be done by turning
the pump upside down. In that position, both of the float valves
are disabled as the floats lift the valve seals 70 away from the
respective inlets. So long as the source of material is higher than
the patient, the liquid will flow upwardly through the inlet 15 and
thence through inlet 16, and thence to outlet 17 and tube 43. Thus
the pump of the present invention, when once filled and connected
to a patient through tube 43 to the patient, can be used as a pump
or not used, without disconnecting the pump from either tube 42 or
43, or removing the needle from the patient.
It is believed obvious that since there is no rubbing contact
between the piston or its sheath, and any part of the pump body,
there is no danger of leakage or the material within the pump
becoming polluted or unsterile. Also, the pump can be used for
pumping blood as there is no rubbing contact which is destructive
of blood cells. One further point that can be mentioned is that
should air enter the pump through the tube 42, it can only form a
bubble in the top of chamber 10 and cannot be pumped to the blood
stream of the patient. Such a bubble can cause slight inaccuracies
in the amount of liquid being pumped as air is readily compressed.
In the event the air bubble were large, the pump would become
inoperative as the air would compress sufficiently to completely
balance the pumping force from the piston, but still no air would
be pumped to the patient. Thus, the pump of the present invention
is inherently a bubble trap as well.
It is obvious that many slight modifications can be made in the
preferred form of the present invention, such as changing the shape
of the chambers, although the spherical shape of the inlet and
pumping chamber is highly preferable, the float valve can be of
other construction, and the like. Accordingly, the claims should be
given an interpretation commensurate with their wording.
* * * * *