WO1981001445A1

WO1981001445A1 - Double acting continuous flow system type pump

Info

Publication number: WO1981001445A1
Application number: PCT/US1980/001538
Authority: WO
Inventors: R Buckles
Original assignee: Bionostics Sa; R Buckles
Priority date: 1979-11-19
Filing date: 1980-11-18
Publication date: 1981-05-28
Also published as: EP0040250A4; EP0040250A1; GB2074665B; NL8020473A; CA1170532A; GB2074665A

Abstract

It is an object of the present invention to provide an improved fluid delivery system (10) for continuous and substantially constant delivery of liquids such as medications, nutrients, blood, plasma, etc. from a reservoir (14) to animals and human patients which employs a syringe type mechanism (11) with a reciprocating piston (26). A passage (43) and appropriate valving (13 and 42) permit constant and equal fluid delivery throughout the reciprocating motion of the piston. An additional object is to provide a sealing means which prevents contamination of the fluid and internal working elements of the pump during all stages of pump use and operation via exposure of the driving rod to external contaminants. A further object of the invention is to provide a fail-safe external valving system (101) that ensures that fluid is not supplied to the patient by gravity from the reservoir in the event of any failure of the pump.

Description

DOUBLE ACTING CONTIGUOUS FLOW SYSTEM TYPE PUMP

DESCRIPTION

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 fa ilar syringe having a fitting at its delivery and 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 familar form, assuming that a needle is attached, the piston being in its bottom¬ most position and the rod and piston are then pulled out to draw in the desired quantity of the fluid to be dis¬ pensed. Then the needle is inserted, for example,

OMPI 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 mech¬ anized 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, it a protracted delivery is re¬ quired such that the barrel of the syringe must be re¬ plenished 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 multiples the chance of infection and of en¬ trapment of air which might cause an embolism. Even where such a syringe is mechanized so that its piston travels automatically and at a controlled rate without the inter¬ vention of human hands, these flaws persist. Also with¬ drawal from the barrel of the rod which operates the pis¬ ton exposes the rod to the atmosphere and therefore to icrobial 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 accu¬ racy these electromechanical devices must be fairly heavy and expensive. There is a need for a simpler type of fluid delivery system employing the syringe and employing linear motion, including forward and backward movement of the piston of the syringe, which is capable of delivering a fluid con¬ tinuously 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 described hereinbelow is known, such being described in a book pub- lished ub 1890 by P. A. Bjorling, entitled "Pumps: His¬ torically, Theoretically, and 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 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 por¬ tion of water delivered on the upstroke of the plunger. When the rod and 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 displacement is greater than the annular space into which this water is pumped, the excess consitutes 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 bar¬ rel, the two portions of the flow cycle can be made the same.

O.V-PI - However, to our knowledge no one has adapted this principle 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, inresspective of their rela¬ tive 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 medi¬ caments 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 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 pum 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 recipro¬ cating forward and return strokes of the piston.

The reciprocating action of the pump provides several advantages over the prior art. First, automatic and con¬ tinuous transfer of fluid from a reservoir to the patient is provided, thereby permitting protracted delivery with¬ out interruption of fluid flow and disconnection 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 rela- tively 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 contamina¬ tion of the fluid via exposure of the rod to external con¬ taminants is prevented. Such sealing means allows recipro- eating movement of the rod, and may be in the form of ex¬ ternal flexible bellows, or an elastomeric sheath enclosing the rod within the barrel and attached to the end of the barrel. This improvement is an advantage over prior art in that it prevents communication of contaminants to the con- tents 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 exter¬ nal valving system that ensures that liquid is not sup¬ plied to the patient by gravity in the event of any failure of the syringe pump described herein.

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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 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 modification 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. 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 designted by the reference numeral 10 and is 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

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O- Pl 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 surface 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 suit¬ able material such as rubber which is sealed circumfer- entially about the rear end of the barrel at 32 and is sealed at 32a to the rear surface of the rod 28. The pur¬ pose 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 con¬ nected at one end to 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 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 con¬ trol 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

O-VIPI 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 pass¬ age 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 as the return stroke) , liquid will pass by suction and/or gravity from the reservoir 14 through line 12 and check calve 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 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 pis¬ ton. This displaced liquid can pass only through one-way passages 41 and 43 and check valve 42 into space B.. In¬ asmuch as this volume of liquid exceeds the expansion of space B due to the difference is 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 vessel¹14, delivery can be main¬ tained for a long period of time. The fluid is 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 frequency of re¬ filling diminishes the chance of contamination. The bellows 31 isolates the only part of the pump which alter¬ nately 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 in¬ side 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.

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 is the length of stroke of piston 26. V-, 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.

V,-, 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) V, = π D²L - d²L -= TΓ L (D²-d²) ¹ 4 4 5

(2) V. = TT D L IT D² - IT d² IT

4 A

In order for V, = V« (i.e., to achieve equal delivery during both strokes)

(3) 1 L(D²-d²) IT d²

or

(3a) D² = 2d² or

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 con¬ duit 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.

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

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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 pre¬ vents back flow of liquid through the conduit 51. The only liquid delivered to outlet 15 is that which is dis- placed 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 in¬ side diameter (D) of the barrel 25 such that the equation 3(b) applies, i.e.,

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 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 valves 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 com¬ pletely 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 syringe 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 syringe and all of the spaces through which liquid flows are primed. This is 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 denerally designated by the reference numeral 60. It comprises a barrel 61 having an inside diameter D. Within the barrel is a piston 62 com¬ prising a disc 63 which may be integral with the rod 64.

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O.V. Affixed to the piston is a combined seal and valve 65 whose inner lips 66 are fixed to the rod 64 and whose outer lips 67 are in sliding contact with the inner sur¬ face 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 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 54. An inlet conduit 69 is shown which may con- tain a check valve as in FIGURE 2 or as shown in FIGURE 3. Alternately, 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 is 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., ellip¬ tical and polygonal, may be used, so long as a reliable sliding seal may be achieved.

Oi PI 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 des- cribed hereinafter. An end fitting 84 is provided having 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 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 elim¬ inates 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 shear¬ ing effect. This construction is especially suited to a low volume rate of pumping which does not require an ex- cessive 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 82 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 disconected after use. Referring now to FIGURE 7, a system is shown which is designated by the reference numbe a1 100 and which com¬ prises an external valving system 101. A syringe 102 having a barrel 102a, a piston 103 and a rod 104 is pro¬ vided. 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 tc open valve 110 and to close valve 111. When piston 103 makes its forward stroke to the left, it forces liquid through duct 105 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 stroke 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 pressure act¬ ing 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 ^~i\ , 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 avail¬ able 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 de¬ pressed and squeezing of the tube 134, the piston 132 will be undergoing 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

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O PI 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 magne¬ tism in the cores 145a and 145b will be terminated. Re¬ sidual 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 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 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 pro¬ jects from the syringe barrel.

It will, therefore, be apparent that novel and ad- vantageous syringe pumps have been provided.

.. O PI_

Claims

CLAIMS :

1. A pumping system comprising:

(1) a reciprocating pump comprising:

(a) a barrel having a first, closed end and a second, inlet end spaced from the closed end, the inlet end being provided with an inlet for Ingress of liquid into the barrel at its inlet end from an exterior source,

(b) an outlet for egress of liquid from the barrel to the exterior, such outlet being located between the barrel inlet and the closed end of the barrel,

(c) a piston reciprocable within, longi¬ tudinally of, and in sliding, sealing contact with the interior surface of the barrel and positioned between inlet end and the outlet,

(d) a rod affixed to the piston, ex¬ tending between the piston and the closed end of the barrel and projecting from such closed end,

(e) the inlet end of the barrel and the neighboring face of the piston, together with the interior surface of the barrel, defining and forming a chamber, A, of variable volume depending upon the position of the piston,

(f) the closed end of the barrel and the other face of the piston, together with the interior surface of the barrel, forming a second, annular chamber, B, of variable volume depending upon the position of the piston,

(2) a portable vessel for holding a supply of liquid to be dispended, (3) inlet means connecting said vessel with said barrel inlet including means acting to permit flow of liquid from such vessel through said inlet means and into chamber A, but acting to prevent reserve flow of liquid from chamber A into said vessel, and -

(4) by-pass means acting to pass liquid from chamber A to chamber B and said outlet during movement of said piston from the closed end to the inlet end of the barrel.

2. The pumping system of Claim 1 wherein said by¬ pass means (4) includes a check valve allowing flow of liquid from chamber A through the piston to chamber B when the piston is moving toward the inlet end of the barrel and which prevents back flow when the piston is moving in the opposite direction.

3. The pumping system of Claim 1 wherein said by¬ pass means is in the form of a bypass conduit external to the barrel, connected at one end to the inlet of chamber A and at its other end to said outlet, such by- pass conduit including a check valve permitting flow of liquid from chamber A to the barrel outlet and to chamber B but preventing reverse flow.

4. The pumping system of Claim 1, including rod sealing means for sealing that portion of the rod which projects from the closed end of the barrel such that contamination of the projecting portion of the rod is prevented, said sealing means allowing reciprocating movement of the rod.

5. The pumping system of Claim 4 wherein said rod sealing means includes a flexible seal surrounding and sealed to the end of the barrel and to the end of the rod projecting from the closed end of the barrel.

6. The pumping system of Claim 1 wherein the closed end of the barrel includes a seal surrounding and in sliding contact with the rod.

7. The pumping system of Claim 4 wherein the closed end of the barrel includes an elastomeric sheath enclosing the rod within the barrel, and attached to the end of the barrel to provide the end closure of the barrel and to enclose that portion of the rod which penetrates, the barrel,

8. The pumping system of Claim 1 wherein the inside diameter of the barrel and the outside diameter of the rod are such that the volumes of liquid delivered through outlet (b) during forward and return strokes of the piston are equal.

9. The pumping system of Claim 8 including rod sealing means for sealing that portion of the rod which projects from the closed end of the barrel such that con¬ tamination of the projecting portion of the rod is pre¬ vented, said sealing means allowing reciprocating movement of the rod.

O.V.PI , - _ WiPO

10. The pumping system of Claim 9 wherein said rod sealing means includes a flexible seal surrounding and sealed to the end of the barrel and to the end of the rod projecting from the closed end of the barrel.

11. The pumping system of Claim 8 wherein the closed end of the barrel includes a seal surrounding and in sliding contact with the rod.

12. The pumping system of Claim 9 wherein the closed end of the barrel includes an elastomeric sheath enclosing the rod within the barrel, and attached to the end of the barrel to provide the end closure of the barrel and to enclose that portion of the rod which penetrates the barrel.

13. A syringe pump comprising a barrel having an inlet end formed with an inlet, a closed end, a piston reciprocable within the barrel and defining, with the inlet end of the barrel and the walls of the barrel a first chamber A between the piston and the inlet end and defining with the closed end of the barrel and the walls of the barrel a second chamber B between the piston and the closed end, said chambers having variable volumes depending upon the position of the piston, said pump also comprising:

(a) a rod connected to the piston and passing through the closed end of the barrel, said barrel having an outlet between the piston and the closed end of the barrel, and

-BU R EA U (b) means for passing liquid from chamber A to chamber B upon movement of the piston toward the inlet end of the barrel, such means acting to prevent reverse flow of liquid with movement of the piston in

_5 the opposite direction, and

(c) a seal attached to the closed end of the barrel and to the rod, such seal allowing recipro¬ cating movement of the rod but isolating that portion of the rod which moves through the closed end of the barrel 0 from liquid in the barrel.

14. The syringe pump of Claim 13 including an annular seal fixed to the closed end of the barrel end and in sliding contact with the rod.

15. The syringe pump of Claim 13 including an 5 elastomeric sheath fixed to the closed end of the barrel, surrounding that portion of the rod which penetrates the barrel and serving to close the end of the barrel and to isolate the rod from the liquid content of the barrel.

16. The syringe pump of Claim 13 wherein the inside 0 diameter of the barrel and the outside diameter of the rod are such that the volumes of liquid delivered through the barrel outlet during forward and return strokes of the piston are equal.

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17. In a syringe pump including a barrel having an inlet end provided with an inlet and having a closed end, a piston reciprocable within the barrel and a rod fixed at one end to the piston and extending through the closed end of the barrel, said barrel having an outlet between the piston and the closed end of the barrel, said piston together with the walls of the barrel defining a chamber A on the inlet side of the piston and an annular chamber B on the opposite side of the piston, said pump also comprising valving means for transferring liquid from chamber A to chamber B during the forward stroke of the piston toward the inlet end of the barrel and serving to deliver a volume of liquid through the,outlet during both strokes of the piston, the improvement which com- prise^*s:

(a) a conduit having a first connection to the barrel inlet and a second connection to the barrel outlet, said conduit having an inlet upstream from said first connection to receive liquid to be pumped from a source thereof and having an outlet downstream from the second connection for delivering pumped liquid to the intended point of delivery,

(b) a first valve means upstream from said first connection, (c) a second valve means downstream from said first connection but upstream from second con¬ nection,

(d) and automatic valve operating means whereby during the forward stroke of the piston said first valve is kept closed and said second valve is kept open and during the return stroke of the piston the first valve Is kept open and the second valve is kept closed.

18. The syringe pump of Claim 17 wherein said valve operating means (d) comprises a rigic connection between the first and second valve means whereby movement of one valve means causes movement of the other valve means.

19. The syringe pump of Claim 18 Including spring biasing means acting normally to open said first valve means and to close said second valve means but yielding under the influence of fluid pressure when said piston makes its forward stroke to close the first valve means and open the second valve means.

20. The syringe pump of Claim -17 wherein said valve operating means (d) includes a flexible tube having an inlet upstream from said inlet and an outlet downstream from said outlet, and tube pinching means operable to pinch off and close the inlet piston of said tube during the forward stroke of the piston and to pinch off and close said tube^" downstream from the said inlet and up¬ stream from said outlet.

21. The syringe pump of Claim 20 wherein said tube pinching means is in the form of electromechanical means.

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