EP0044217A1

EP0044217A1 - Volumetric pump

Info

Publication number: EP0044217A1
Application number: EP81303189A
Authority: EP
Inventors: Mats Lindroth
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-07-15
Filing date: 1981-07-13
Publication date: 1982-01-20

Abstract

A volumetric pump comprises a housing (1) defining a substantially spherical cavity (2) in which is mounted or mountable a hollow resilient substantially spherical member (3) and plunger means (8) for continuously successively deforming the resilient member (3) to effect a predetermined change in the volume thereof. Valve means (4a, 5a) are provided for controlling the flow of liquid to and from the interior of the resilient member (3). The resilient member (3) is preferably part of an infusion set for the parenteral infusion of a liquid into a patient and the invention includes such an infusion set and a volumetric pump and infusion set combination.

Description

This invention relates to volumetric pumps for pumping measured quantities of fluids.
In medical establishments, such as hospitals, liquids are frequently administered to patients by parenteral infusion. The infusion apparatus used includes what is usually referred to as an infusion set comprising means for connecting the infusion set to a container containing a liquid to be infused, a drip chamber, means for controlling the rate of drip in the drip chamber and hence the rate of feed of the liquid to be infused, a needle for introducing the liquid to be infused into the body of a patient, and flexible tubing connecting the various components together. In the majority of cases the liquid to be infused is gravity fed to the patient. However, where drugs are being administered to a patient by parenteral infusion and the dosage thereof administered needs to be very carefully controlled then the liquid is frequently infused under pressure using suitable pump means. Among the pump means used are peristaltic pumps and diaphragm pumps. Neither of these types of pump is sufficiently accurate to ensure that the liquid to be infused will be delivered at a precisely controlled rate and accordingly where such pumps are used it is necessary to provide expensive control means, e.g., comprising a sensor for determining the rate of drip in the drip chamber and means for controlling the operation of the pump to maintain the rate of drip in the drip chamber at a predetermined level. Another type of pump used is a piston pump the piston and cylinder of which resemble a conventional syringe and which are produced in a disposable cassette form with the piston and cylinder encapsulated to prevent contamination of the liquid being pumped during reciprocation of the piston. Such piston pumps are capable of delivering a precisely measured volume of liquid. They are, however, difficult to prime and the disposable cassettes incorporating the piston and cylinder are expensive to produce. Moreover, the reciprocation of the piston can result in vaporization of liquid being pumped and the consequent formation of gas bubbles in the liquid and great care has to be taken to ensure that such gas bubbles do not enter a patient being infused.
The present invention has for its object to provide a volumetric pump which is capable of pumping liquids in measured quantities under sterile conditions or under conditions where the liquid e.g., because of its toxicity or corrosive properties, should not come into direct contact with the pumping mechanism and which when used for the parenteral infusion of liquids can be used with an infusion set which, although specially adapted, need be little more expensive than the infusion sets used in parenteral infusion by gravity. The invention also has as its object to . provide an infusion set for use with the volumetric pump. of the present invention.
The present invention provides a volumetric pump comprising a housing defining a substantially spherical cavity, a hollow resilient substantially spherical member mounted or mountable within said cavity so as to closely follow the internal contour of said cavity, means providing an inlet for liquid to and means providing an outlet for liquid from the interior of said resilient member, and means for continuously successively deforming said resilient member to effect a predetermined change in volume thereof and for allowing said resilient member to return to its original volume.
Said housing is preferably formed in two parts which meet in a plane extending diametrically of said cavity and which are separable to allow access to said cavity for the mounting of a said resilient member therein.
Said resilient member may have inlet and outlet passages communicating with the interior thereof and said housing may have bores or channels therein for receiving said passages. Preferably said bores or channels are formed in two mating halves in said two parts of the housing.
The said inlet and outlet passages may have suitable valve means associated therewith for controlling the flow of liquid to and from the interior of said resilient member, e.g., suitable non-return valves for preventing liquid in said resilient member from returning along said inlet passage and for preventing liquid in said outlet passage from returning to the interior of the resilient member.
The means for continuously successively deforming the resilient member to effect a predetermined change in volume thereof and for allowing the resilient member to return to its original volume may comprise suitable reciprocatable plunger means mounted in said housing. Preferably that end of said plunger means which engages said resilient member to effect deformation thereof is part-spherical and has a radius substantially equal to the radius of said resilient member.
Where the volumetric pump of the present invention is intended for use in the parenteral infusion of liquids under pressure into patients the said hollow resilient member may comprise part of an infusion set for use with the pump. Thus the invention also provides an infusion set for use with a pump according to the present invention and comprising a said hollow resilient member.
The invention will be more particularly described with reference to the accompanying diagrammatic drawings, in which:-

Fig. 1 is a side elevation of a volumetric pump according to the present invention,
Fig. 2 is a cross-sectional elevation of the volumetric pump shown in Fig. 1, and
Fig. 3 is a fragmentary sectional elevation of a hollow resilient member used in the pump of Figs. 1 and 2.

Referring to the drawings it will be seen that the volumetric pump illustrated therein comprises a housing 1 formed in two parts la, lb and defining a substantially spherical cavity 2. The two housing parts 1a, 1b meet in a plane extending diametrically of the cavity 2. Mounted within the cavity 2 is a hollow resilient substantially spherical member 3 which closely follows the internal contour of the cavity 2 and which has an inlet passage 4 and an outlet passage 5 communicating with the interior thereof. The inlet passage 4 and the outlet passage 5 are received in bores 6, 7 respectively defined by the mating housing parts la, lb. Suitable valve means 4a, 5a are associated with the inlet passage 4 and'outlet passage 5 respectively for controlling the flow of liquid through said passages. Said valve means may comprise suitable non-return valves or, where the walls of said passages 4 and 5 are formed from resilient material, may comprise means for compressing and releasing the walls of said passages so as to selectively close or open said passages.
Mounted for reciprocating movement within the housing part la is a plunger 8 one end 9 of which is part-spherical with a radius substantially the same as that of the resilient member 3 and which is adapted to engage the resilient member 3 and the other end 10 of which is enlarged and is engaged by an eccentric 11. A helical spring 12 mounted on the plunger 8 between the enlarged end 10 thereof and the housing part la serves to urge the plunger 8 in a direction away from the resilient member 3 and into engagement with the eccentric 11. Means (not shown) is provided for rotating the eccentric 11 about an axis indicated at 13 for imparting reciprocatory movement to the plunger 8. As will be seen from Fig. 2 of the drawings, when in its retracted position the plunger 8 deforms the resilient member 3 by a small amount as shown at 14. The advance movement of the plunger 8 is preferably from 10 to 25% of the diameter of the resilient member 3 so that when fully advanced the resilient member 3 where engaged by the plunger 8 will be deformed inwards as indicated by the broken line 15 to effect a predetermined change in the volume of the resilient member 3.
The resilient member 3 may be formed from any suitable resilient material, e.g., a suitable plastics material such as polyurethane.
The speed of reciprocation of the plunger 8 will be not greater than the speed of recovery of the material from which the resilient member 3 is formed so that the resilient member 3 will closely follow the movements of the plunger 8.
It will readily be appreciated that the volumetric pump of the present invention is extremely simple in design and is capable of delivering liquid at a precisely measured rate. Also the resilient member 3 acts as a pumping chamber which is readily replaceable at little cost, e.g., each time an infusion set is changed, thus making the pump particularly suitable for the pumping of liquids under sterile conditions or under conditions where it is necessary to prevent the liquid being pumped from coming into direct contact with the pumping mechanism. Another advantage is that manual pumping is possible simply by manually squeezing the resilient member 3 and this can be useful, e.g., when first setting up an infusion set. Further, when the resilient member 3 is mounted so that the inlet passage 4 and outlet passage 5 extend substantially horizontally, any gas bubbles which may form or be present in the liquid being pumped will tend to collect in the top of the resilient member 3. Thus the resilient member 3 will act as a gas trap and there will be little likelihood of any gas passing from the resilient member 3 through the outlet passage 5. Moreover, with the resilient member 3 acting as a gas trap it becomes easy to incorporate suitable means, e.g., suitable optical or ultrasonic means or means relying upon a change in electrical capacitance, for detecting any build-up of gas in a liquid system incorporating a pump according to the present invention.
When used for the parenteral infusion of liquids under pressure, the resilient member 3 may comprise part of an infusion set. Since infusion sets are normally at least partly made from transparent resilient plastics materials such as polyurethane it will readily be appreciated that the resilient member 3 may readily be incorporated therein, e.g., in a resilient flexible tube thereof, at very little additional cost. This makes it possible to incorporate a resilient member 3 in all infusion sets whether these are to be used for parenteral infusion of liquids under gravity feed or under pressure and to simply insert the resilient member 3 into the cavity 2 of the pump apparatus and to actuate the plunger 8 when infusion under pressure is required.
Whilst the resilient member 3 is preferably in the shape of a true sphere because it is this shape which has the best recovery when deformed, it will be understood that the resilient member 3 could be of other hollow substantially spherical shapes, such as ovoid, if desired and the term "substantially spherical" as used herein is intended to include such variations in shape from a true sphere.

Claims

1. 'A volumetric pump comprising a housing defining a substantially spherical cavity, a hollow resilient substantially spherical member mounted or mountable within said cavity so as to closely follow the internal contour of said cavity, means providing an inlet for liquid to and means providing an outlet for liquid from the interior of said resilient member, and means for continuously successively deforming said resilient member to effect a predetermined change in volume thereof and for allowing said resilient member to return to its original volume.

2. A volumetric pump according to claim 1, wherein said housing is formed in two parts which meet in a plane extending diametrically of said cavity and which are separable to allow access to said cavity for the mounting of a said resilient member therein.

3. A volumetric pump according to claim 1 or 2, wherein said resilient member has inlet and outlet passages communicating with the interior thereof and said housing has channels therein for receiving said passages,

4. A volumetric pump according to claim 3, wherein said channels are formed in two mating halves in said two parts of the housing.

5. A volumetric pump according to any one of the preceding claims, wherein said resilient member has inlet and outlet passages communicating with the interior thereof and wherein valve means is provided for controlling the flow of liquid to and from the interior of said resilient member.

6. A volumetric pump according to claims 5, wherein said valve means comprises a non-return valve associated with said inlet passage.

7. A volumetric pump according to claim 5 or 6, wherein said valve means comprises a non-return valve associated with said outlet passage.

8. A volumetric pump according to any one of the preceding claims, wherein said means for continuously successively deforming the resilient member comprises reciprocatable plunger means mounted in said housing.

9. A volumetric pump according to claim 8, wherein that end of said plunger means which engages said resilient member to effect deformation thereof is part-spherical and has a radius substantially equal to the radius of said resilient member.

10. A volumetric pump according to claim 8 or 9, wherein said plunger means is adapted to be reciprocated such that the advance movement thereof is from 10 to 25% of the diameter of the resilient member.

11. A volumetric pump according to any one of claims 8 to 11, wherein said plunger means is biassed towards a retracted position and wherein cam means is provided for advancing the plunger means against said bias.

12. A volumetric pump according to any one of the preceding claims, wherein said hollow resilient member is formed from synthetic plastics material.

13. A volumetric pump according to any one of the preceding claims, wherein said hollow resilient member comprises part of an infusion set for use in the parenteral infusion of a liquid under pressure into a patient.

14. A volumetric pump and infusion set combination comprising a housing defining a substantially spherical cavity, an infusion set for use in the parenteral infusion of a liquid under pressure into a patient, said infusion set comprising a hollow resilient substantially spherical member mountable within said cavity so as to closely follow the internal contour of said cavity and means communicating the interior of the hollow resilient member with both a source of liquid to be infused and an outlet end of the infusion set, means for continuously successively deforming said resilient member. to effect a predetermined change in volume thereof and for allowing said resilient member to return to its original volume, and valve means for controlling the flow of liquid to and from the interior of said resilient member.

15. An infusion set for use in the parenteral infusion of a liquid under pressure into a patient and adapted for use with a volumetric pump comprising a housing defining a substantially spherical cavity and means for continuously successively deforming a hollow resilient body contained within said cavity, said infusion set comprising a hollow resilient substantially spherical member adapted to be mounted within said cavity and to form said hollow resilient body.