Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
117(3532
DESCRIPTION
Syringe Pump
Technical Field
This invention relates to a continuous pump and a
system employing such a pump for the delivery of liquids to
human patients and for veterinary purposes, for example, for
blood and plasma transfusions, for the delivery of medication,
for the supply of nutrients, etc.
Background Art
At present there are a variety of delivery systems
for such purposes. One such apparatus or system which is one
of the oldest, if not the oldest, is the familiar syringe having
a fitting at its delivery end for a needle or for a tube leading
to a catheter or needle. The syringe may be mounted on a motor
device designed to move the syringe barrel. In its simplest
and most familiar form, assuming that a needle is attached, the
plston belng in its bottommost position and the rod and piston
are then pulled out to draw in the deslred quantity of the fluid
to be dispensed. Then the needle is inserted, for example,
intravenously, or a catheter is inserted after having been fitted
to a fitting at the delivery end of the barrel of the syringe.
The rod is then pushed inwardly by the mechanized action of the
motor carrying with it the piston and dispensing the fluid in
the syringe.
Certain disadvantages of such an apparatus are quite
apparent. For one thing, if a protracted delivery is required
such that the barrel of the syringe must be replenished from
time to time, it must be detached from the system connecting it
to the patient and refilled or a large syringe must be used.
This repeated refilling of the syringe multiplies the chance of
infection and of entrapment of air which might cause an embolism.
Even where such a syringe is mechanised so that its piston
li7~53Z
travels automatically and at a controlled rate without
the in~ervention of human hands,-these flaws persist.
Also withdrawal from the barrel of the rod which operates
the piston exposes the rod to the atmosphere and there-
fore to microbial contamination, which has a certain
likelihood of being communicated to the working part of
the barrel and the contents thereof.
A further disadvantage of such an apparatus derives
from the need to make syringes with a long stroke. This
leads to the need to assemble a rigid mechanical drive
system that contains a high precision threaded shaft in
order to move the rod at a constant rate over its full
length of travel. In order to achieve the desired
accuracy these electromechanlcal devices must be fairly
heavy and expensive.
There ls a need for a slmpler type of fluid delivery
system employlng the syrlnge and employing linear motion,
lncludlng forward and backward movement of the piston of
the syrlnge, whlch ls capable of delivering a fluid
contlnuously during both the forward stroke and the return
stroke and thus automatically transferring fluid from a
reservoir to the patient. Such a device would have the
advantage of simplicity and it would obviate some of the
more significant drawbacks of the syringe type of delivery
apparatus. It is also desirable to provide such a pump
which precludes microbial contamination.
A pump of rather ancient vintage operating on a
principle similar to the operation of the syringe des-
cribed hereinbelow is known, such being described in a
j 30 book published in 1890 by P.A. Bjorling, entltled Pumps:
¦ Historically, Theoretically, ar,d Practically Considered.
At page 27, Figure 8 shows such a pump which is intended
to pump water from a well. The description appears at
pages 187 and 188. Water is drawn, evidently through a
check valve, into the barrel of the pump by a plunger
having in it a second check valve. The plunger
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has a rod which is reciprocated manually or which may be
operated by machinery. AS the plunger is lifted water
is drawn by suction into the space in the barrel between
the first check valve and the plunger, return of such
water being prevented by the first check valve. During
this upstroke water in the barrel occupying the annular
space between the inner wall of the barrel and the rod
is displaced and constitutes the portion of water delivered
on the upstroke of the plunger. When the rod and the
plunger are caused to descend, the space between the rod and
the aforesaid first check valve is diminished and the water
displaced thereby flows upwardly through the valve in the
plunger and into the annular space. Inasmuch as this dis- -
placement is greater than the annular space into which this
water i9 pumped, the excess constitutes that portion of the
water which is delivered on the downstroke. By appropriate
proportioning of the diameter of the rod and the inside
diameter of the barrel, the two portions of the flow cycle
can be made the same.
However, to our knowledge no one has adapted this
princlple of a water pump to the operation of a syringe
for biological purposes such as those mentioned above.
Further, the water pump requires exposure to the atmosphere
because it is atmospheric pressure which causes water to
rise. Also, the water pump is used to raise water only,
while the purpose of a syringe pump is to transfer fluid
from a reservoir to a patient, irrespective of their
relative positions.
Disclosure of Invention
The invention presented herein is a pumping system for
continuous delivery of fluid from a renewable source to a
- point of delivery, more particularly for delivery of
medicaments and biological fluids to human patients and
animals.
The pumping system consists primarily of a syringe-
type apparatus with an inlet end connected to a
;117()532
renewable reservoir of the fluid to be delivered, an
outlet for egress of liquid from the barrel of the syringe
to the patient or other point of delivery and a power
source and mechanism which drives a reciprocating piston
within the barrel. The pump is also fitted with a fluid
by-pass means connecting the inlet chamber in front of
the piston to the annular chamber behind the piston, and
appropriate valving such that fluid is delivered to the
outlet continuously and at a substantially constant rate
throughout the reciprocating forward and return strokes
of the piston.
The reciprocating action of the pump provides
several advantages over the prior art. First, automatic
and continuous transfer of fluid from a reservoir to the
patient is provided, thereby permitting protracted de-
llvery wlthout interruption of fluid flow and disconnec-
tion of the delivery portal from the patient. This
feature is a distinct improvement over certain devices
in the prior art which deliver fluid only during the
forward stroke of the piston, and thus require frequent
refilling of the syringe, which can lead to contamination
and entrapment of air. Second, the reciprocating action
of the pump permits a relatively short piston stroke.
This is advantageous over prior syringe pumps which
delivered fluid by a single low, slow stroke, in that
the pump can be driven by a simple cam mechanism, rather
than requiring a rigid, high precision threaded shaft,
and heavy electromechanical drive system.
In addition, this improved pump and pumping
system possesses a sealing means for sealing off that
portion of the rod which projects from the barrel, such
that contamination of the fluid via exposure of the rod
to external contaminants is prevented. Such sealing
means allows reciprocating movement of the rod, and may
be in the form of an external flexible bellows, or an
elastomeric sheath enclosing the rod within the barrel
and attached to the end of the barrel. This improvement
1170.53~
is an advantage over prior art in that it prevents com-
munication of contaminants to the contents of the syringe
barrel during the working of the pump.
These seals further permit supplying the syringe
in sterile form, completely enclosed and hermetically
sealed so that when delivered it is completely sterile
and can be connected with a drive means or piston and
drive means without breaking the seal or exposing the
working elements of the pump to contamination. An
additional advantage of the elastomeric sheath-type seal
is the elimination of one sliding seal, and the consequent
diminution of a shearing effect which may have a damaging
effect on blood cells.
A further improvement consists in a fail-safe
external valving system that ensures that liquid is not
supplied to the patlent by gravity ln the event of any
failure of the syringe pump described herein.
Brief Description of Drawings
Certain embodiments of the invention are shown by
way of example in the accompanying drawings, in which:
Figure 1 is a diagrammatic view of a system employing
i a continuous syringe pump;
Figure 2 is a longitudinal section taken through the
syringe pump;
Figure 3 is a view similar to that of Figure 2
but showing a different valving system;
Figure 4 is a longitudinal section through a syringe
pump having yet a different design.
Figure 5 is a fragmentary view of a modiflcation of
Figure 4.
Figure 6 is a fragmentary view of a different type of
seal for the rod which operates the piston.
Figure 7 is a diagrammatic view of a valving system
which is failsafe in that it ensures that one of two valves
between the source of liquid and the patient is always
closed.
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Figure 8 illustrates another embodiment of the
failsafe feature.
Best Mode for Carrying Out the Invention
Referring now to Figure 1, the system as a
whole is designated by the reference numeral 10 and it
comprises a syringe pump 11 connected by a tube 12 containing
a check valve 13 to a supply of the fluid to be delivered,
which is in a vessel, tank or other suitable container
14. An outlet is shown at 15 which is connected
to a hypodermic needle, to a catheter or other
delivery instrument of well-known construction requiring
no further description herein. The rod of the syringe 11
(not shown in Figure 1) is connected by connecting means
16 to driving means 17 which is capable of imparting a
reciprocating motion to the connector member 16 and
therefore to the working parts of the syringe 11.
Referring now to Figure 2, the syringe 11 is
shown as having a barrel 25 within which is a piston 26
having sealing lips 27 which seal against the interior
8urface of the barrel in sliding contact, and to which is
attached a rod 28. The rear end of the rod passes
through and is in sliding contact with a stationary seal
29 having sealing lips 30 which seal against the rod.
Affixed to the barrel and to the rod is a bellows type
of seal 31 made of suitable material such as rubber
which is sealed circumferentially about the rear end of
the barrel at 32 and is sealed at 32a to the rear surface
of the rod 28. The purpose of this seal is to keep
the rod sterile at all times and out of contact with the
atmosphere as it moves in and out of the barrel. The
driving means 17 is shown as an electric motor 33 having
a shaft 34 to which is affixed a cam 35. The connector
means 16 is shown as being connected at one end of the
end of the rod 28 with the bellows intervening between
the end of the connector member 16 and the rod. At the
other end of the connector 16 is a cam follower 36 which
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is held against the cam 35, as for example, by a spring
or by a spring or by being received in a groove formed in
a grooved cam. The driving means 17, although shown in the
form of a motor 33 and a cam 35, may be any other type of
driving means such as, for example, a crank or a motor
which is reversible and, by suitable control means is caused
to operate first in one direction and then in the other
direction and having suitable means for converting rotary
motion of the motor shaft into linear motion of the connecting
member 16. It will be understood, of course, that
suitable gear reduction means (not shown) may be employed
or that the motor may be a variable speed motor, all
to the end of operating the rod 28, the piston 26 and
thereby the syringe 11 at a suitable speed and doing so
continuously. If a variable delivery is desired, e.g.,
where a patient requires administration of a drug
according to a diurnal pattern, suitable timing means may be
employed to vary the motor speed according to a program.
In the embodiment shown in Figure 2, an inlet
passage 41 is provided at the front end ~or lefthand end
as viewed in Figure 2) of the rod 28, which is connected
by a check valve 42 to an outlet passage 43, thus providing
a one-way path (from left to right as viewed in Figure 2)
from the interior of the barrel on the left of the piston
(space A) to the annular space (space B) on the right of
the piston. It will be apparent that as the rod 28 and
piston 26 are moved to the right (hereinafter referred
to a,s the return stroke), liquid will pass by suction
and/or gravity from the reservoir 14 through line 12 and
check valve 13 to the space A in the barrel of the pump.
During each such stroke an amount of liquid will be
dispensed through outlet 15 proportional to the product of
the area of the annular space B and the length of stroke
of the piston. At the same time the space A will be filled
as it expands by fluid coming from the reservoir 14
through the line 12 and check valve 13, so as to maintain
the space A full of liquid at all times. On the stroke
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from right to left (hereinafter referred to as the forward
stroke), the check valve 13 will prevent back flow of
liquid from space A into line 12. The fluid displaced
in space A by such forward stroke is equal to the product
of the cross-sectional area of space A (that is to say,
the cross-sectional area of the interior of the syringe
barrel) and the length of the forward stroke of the piston.
This displaced liquid can pass only through one-way
passages 41 and 43 and check valve 42 into space s.
Inasmuch as this volume of liquid exceeds the expansion
of space B due to the difference in cross-sectional areas
of A and B, the surplus will be delivered through the
outlet 15 to the patient.
By this means it will be apparent that a continuous
delivery of fluid is provided through the outlet line
15 on both the forward and return stroke, except for
a very small dwell at the end of each stroke. The syringe
pump is a true, double acting piston pump which can be
made to operate very slowly or fast and, if an adequate
supply of liquid is maintained in vessel 14, delivery
can be maintained for a long period of time. The fluid
in vessel 14 can be replenished without interrupting
the delivery of liquid to a patient, e.g., by refilling
it when the liquid level is low. Such refilling can be
carried out under controlled, sterile conditions, and
the infrequency of refilling diminishes the chance of
contamination. The bellows 31 isolates the only part of
the pump which alternately contacts the liquid being
delivered and the exterior air space around the syringe.
One can achieve uniformity of flow during each
stroke, if that is desired, by a proper proportioning of
the inside diameter D of the barrel 25 and the diameter d
of the rod 28, as shown by the following analysis, in
which the following symbols have the following meanings.
A signifies the space in barrel 25 to the left
of the piston 26. This is a variable quantity depending
upon the position of the piston.
3Z
B signifies the annular space within the barrel
to the right of the piston and surrounding the rod 28 and
to the left of the seal 29. This is also a variable space
depending upon the position of the piston.
D is the inside diameter of the barrel 25.
d is the outside diameter of the rod 28.
L in the length of stroke of piston 26.
Vl is the volume of liquid delivered to the
outlet 15 by the stroke of piston 28 from left to right,
herein called the "return" stroke.
V2 is the volume of liquid delivered to the
outlet 15 by the stroke from right to left, herein called
the "forward" stroke.
The applicable equations are as follows:
(1) Vl 4 D2L - 4 d2L = -4L (D2_d2)
(2) V2 ~ D2L ~ [ ~4 D2L _ 4 d L~ 4
In order for Vl ~ V2 (i.e., to achieve equal delivery
during both strokes)
(3) 4 L(D2-d2) = d2L
or
(3a) D2 = 2d2
or
(3b) D - ~ x d
Figure 3 depicts an alternative design. The
syringe is very similar to the syringe 11 of Figure 2.
Similar or identical parts bear the same reference numerals.
The inlet conduit 12 is connected by check valve 13
to a conduit segment 50 which is fitted at one end to the
check valve 13 and at its other end to the inlet of the
barrel 25. This conduit segment has a branch conduit 51.
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-- 10 --
In operation, this syringe functions as follows:
on the forward stroke liquid in space A is forced to the
left into the conduit segment 50 and through conduit 51
to the junction with outlet conduit 15. A portion of
this liquid passes into chamber B sufficient to keep it
full; this is accomplished by the suction created in B by
the forward movement of the plunger. Such flow is indicated
by the upwardly pointing arrow. Another portion passes,
as indicated by the downwardly pointing arrow, to the
needle, catheter or other equipment employed in the
delivery. On the return stroke the check valve 52
prevents back flow of liquid through the conduit 51. The
only liquid delivered to outlet 15 is that which is
displaced in chamber B by movement of the piston 26.
It will be apparent that, although the valving
is external to the syringe barrel 25, the mode of operation
is the same as in Figure 2 and the same considerations
apply. Uniformity of flow is achieved by proportioning
the outside diameter (d) of rod 28 in relation to the
insided ~ eter (D) of the barrel 25 such that the
equation 3(b) applies, i.e.,
D = ~ x d
Regarding materials of construction of the
syringe 11, the barrel 25 may be of glass or suitable
plastic such as polyethylene, polystyrene, polystyrene
acrylonitrile, or polypropylene. It is generally considered
important to use a material with adequate transparency
to permit visual inspection. The rod 28 may be
constructed of metal, for example, stainless steel
or an aluminum alloy or plastic material such as
polystyrene or polyethylene. The piston 26 and the seal
29 may be constructed of rubber, either synthetic or
natural, having a suitable balance between hardness and
flexibility to permit their proper operation. Syringes
available commercially, of which there are a variety,
may be adapted for use in the present invention. The
bellows, as stated, may be constructed of rubber and
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-- 11 --
it may also be constructed of a plastic material such as
polyethylene, poly(ethylene-vinyl acetate), polyvinyl-
chloride, polypropylene, etc., such being constructed to
act as a bellows. The various valves may be constructed
of materials suitable for values brought into contact
with biological and other fluids intended to be injected
into a human patient.
The syringe 11, with or without the motive means
17, may be supplied in sterile form and completely enclosed
and hermetically sealed so that when delivered, it is
completely sterile. It may be rigidly attached to reservoir
14 or it may be equipped with a means to connect to a
separate reservoir.
At the time of use, the package is broken open,
using ordinary precautions to prevent contamination. The
~yringe may be provided with the inlet and outlet tubes
12 (fitted with a check valve) and 15 which in turn may
have fittings to connect to a vessel 14 (in the case of
conduit 12) or to a needle or catheter (in the case of
conduit 15). The embodiment shown in Figure 3 may be
similarly provided such that only two connections need
be made, i.e., to a supply of liquid to be delivered and
to a needle or catheter.
The syringe may also be packaged with the
drive ready to plug into a power source.
The cyringe and all of the spaces through
which liquid flows are primed. This i8 easily accomplished
with the fluid from the reservoir by moving the plunger
to and fro. Once primed the tubing is attached to the
patient and infusion therapy begun.
Referring now to Figure 4, an alternative form
of syringe is there shown and is generally designated
by the reference numeral 60. It comprises a barrel 61
having an inside diameter D. Within the barrel is a
piston 62 comprising a disc 63 which may be integral
with the rod 64. Affixed to the piston is a combined
seal and valve 65 whose inner lips 66 are fixed to the
()S32
rod 64 and whose outer lips 67 are in sliding contact
with the inner surface of the barrel 61 such that upon
the down or forward stroke fluid displaced from chamber
A passes into chamber B. On the up or return stroke the
S outer lips 67 seal against the barrel. Also shown is a
stationary seal 68 affixed to the barrel and in sliding,
sealing contact with the rod 64. An inlet conduit 69
is shown which may contain a check valve as in Figure 2
or as shown in Figure 3. Alternatively, the check valve
may be in the form of a simple disc 70 whose buoyancy is
such that it will easily float and be forced upwardly
on the upward stroke of the piston 63 to allow entry of
the fluid to be dispensed, and such that upon the down
or forward stroke of the piston it will seal the conduit
69 and prevent flow of liquid through that conduit. Where
it is desired to use the syringe in a horizontal position,
a check valve such as shown in Figure 2 may be incorporated
in the conduit 69 or the valve disc 70 may be provided
with a stem to extend into the conduit 69. An outlet
71 i5 shown. The operation of the valve will be
apparent from the description above and the description
of Figure 2.
Referring to Figure 5, an alternative type of
seal and valve is shown, generally designated by the
reference symbol 75 which is received in a groove 76 at
the junction of the rod 64 and the disc 63, and which has
an outer cylindrical lip 77 which functions as a
combined seal and valve as in Figure 4.
It will be apparent that, although cylindrical
barrels, pistons and such are preferred, other shapes,
e.g., elliptical and polygonal, may be used, so long as
a reliable sliding seal may be achieved.
Referring now to Figure 6, a syringe pump is
shown and is generally designated by the reference number
80. It comprises a barrel 81 and a piston 82 reciprocable
in the barrel, and to which a rod 83 is attached as
described hereinafter. An end fitting 84 is provided having
1~7(~532
- 13 -
an axial opening 85 within which the rod 83 may freely
slide. This fitting need not be a tight fitting and
need serve only as a guide for the rod 83. A combined
seal and end closure is provided by an elastomeric sheath
86 which is anchored at 87 in an annular groove 88 formed
in the fitting 84. The sheath 86 extends around the
inner end of the rod 83. The inner end of the rod is
connected to the piston 82 by, for example, a ball and
socket joint consisting of a ball 89 formed at the inner
extremity of the rod and a socket 90 formed in the piston.
Valving such as shown in Figure 2 or in Figure 3 is
provided, such valving not being shown in Figure 6.
An advantage of this construction is that it
eliminates one sliding seal, namely, the seal 29 in
Figures 2 and 3. Such seals may have a shearing effect
on liquid which may have a damaging effect on blood cells.
The seal provided by the sheath 86 does not have a shearing
effect. This construction is especially suited to a
low volume rate of pumping which does not require an
excessive rate of stretching of the sheath. The sheath
may be made of rubber or any other suitable elastomeric
material which is capable of repeated stretching to a
sufficient degree to provide the necessary pumping action
without imposing excessive strain on the material of the
seal. Thus the ball and socket connection between rod 83
and piston &2 may be a snap fit permitting attachment
and detachment of the rod. Further, the rod 83 may be an
integral part of the drive, e.g., it may be connected to
a motor such as 33, and a cam such as 34 (see Figure 2).
In such a case the barrel 81, piston 82, sheath 86 and
necessary inlet and outlet ducts and valving, may be a
disposable unit to which the rod 83 is fitted at the time
of use and disconnected after use.
Referring now to Figure 7, a system is shown
which is generally designated by the reference numeral 100
and which comprises an external valving system 101. A
syringe 102 having a barrel 102a, a piston 103 and a
'
,~
1 1 7(Js3z
- 14 -
rod 104 is provided. The barrel is connected at one end
to a duct 105 which communicates with chamber A and at
its other end it is connected to a duct 106 which communicates
with chamber B. These ducts in turn connect with a
tube 107 having an inlet 108 and an outlet 109. The
external, fail-safe valving system 101 includes the
tube 107 and a pair of valves 110 and 111. Valve 110 is
upstream from duct 105 and the valve 111 is downstream
from duct 105 but upstream from duct 106. Each valve
includes a valve seat 112 and a valve member 113. The
valve members 113 are connected by a rigid rod 114 such
that the two valves operate in unison. The arrangement
is such that when one valve is closed, the other valve
is open. A spring 115 anchored at one end to valve member
113 of valve 110 and at its other end to the tube 101
acts normally to open valve 110 and to close valve 111.
When piston 103 makes its forward stroke to the
left, it forces liquid through duct lOS into duct 107 and
acts against the force of spring 115 to open valve 111 and
to close valve 110. This supplies liquid to outlet 109
~ and thence to the patient. When piston 103 makes its
- return stro~e to the right, it forces liquid through
duct 106. The suction in chamber A together with the
' force of spring 115 act to close valve 111 and to open
valve 110. Liquid is delivered to the patient through
line 109 and liquid in chamber A is replenished.
This coupled valve arrangement ensures that
liquid is not supplied to the patient by gravity in the
event of failure of the syringe pump 102a. Thus if the
pump 102a fails and if the supply of liquid in vessel
14 (see Figure 1) is suspended rather high above the
patient such that there is a substantial hydrostatic
pres~ure acting on tube 107, such pressure will overcome
the force of spring 115 and will close valve 110.
Referring now to Figure 8, another valving
system is shown, generally designated by the reference
numeral 130. Its purpose is the same as that in Figure 7,
~/
117()532
but the method of construction is intrinsically cheaper.
The syringe pump comprises a barrel 131, a piston 132
and a rod 133. An inlet tube is shown at 134 and an
outlet tube at 135, these being connected by a segment
of tube 136 which is located between inlet duct 137 to
the syringe barrel and outlet duct 138 from the syringe
barrel. These two ducts are connected to the tubing
134, 136, 135. Tubing 134 and 136 are made of thin-
walled collapsible material. An automatic valving system
is provided by a solenoid operated device generally
designated by the reference number 140. This comprises
pads 141 and 142 connected by a rigid rod 143 and rocking
on a fulcrum 144. These pads are of magnetic material
and are acted upon by coils 145 and 146 respectively
having cores 145a and 146a. The apparatus 140 may
be of any known commercially available type in which
direct electric current is supplied alternately to the
coils 145 and 146 at a frequency which is adjustable
and is compatible with the desired pumping rate. In the
mode shown in Figure 8 with the pad 141 depressed and
squeezing of the tube 134, the piston 132 will be under-
going its forward stroke or to the left and fluid is
pumped from chamber A through duct 137 to duct 136 and
outlet 135. On the return stroke while pad 142 is in
contact with the tube segment 136, fluid is pumped from
chamber B through connecting duct 138 to the outlet 135.
By suitable switching means (not shown) the operation
of coils 145 and 146 is synchronized with operation of
piston 132. In the event that the pump 130 fails, the
current to coils 145 and 146 will be terminated.
Residual magnetism in the cores 145a and 145b will be
terminated. Residual magnetism in the cores 145a and
' 145b will be such that the pad 141 or 142 closer to a
core will be attracted to and held by it whereby the
other pad will pinch tube 134 or 136. To avoid the
possibility of failure of the pump 130 when the pads
are at dead center, one may be weighted more than the
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~ 16 -
other. Electric energy may be supplied to the coils
in pulses to conserve energy.
It will be recognized that the systems of
Figures 7 and 8 are similar to that of Figure 3 but that
by reason of their fail-safe valving one valve is always
closed. Therefore if, by chance, the vessel 14 is
suspended at an excessive height above the connection to
the patient, the danger of bypassing the syringe pump
should it fail is prevented.
It should be understood that the coupled
valving exemplified by Figures 7 and 8 could be used
- with syringes of alternative design such as in Figures 3
and 6. It will also be understood that in the embodiment
of Figures 4, 5, 7 and 8 seals such as shown in Figures
2, 3 and 6 may be used to prevent contamination of that
part of the rod which projects from the syringe barrel.
It will, therefore, be apparent that novel
and advantageous syringe pumps have been provided.
