GB2233070A

GB2233070A - Flow regulator

Info

Publication number: GB2233070A
Application number: GB9012422A
Authority: GB
Inventors: Raymond Jeffrey Summers
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1989-06-07
Filing date: 1990-06-04
Publication date: 1991-01-02
Anticipated expiration: 2010-06-04
Also published as: GB9012422D0; GB8913083D0; GB2233070B

Abstract

A parenteral administration set has a flow regulator 3 formed by an elastomeric check valve 31 having a duck bill 32 within a deformable sleeve 30 and oriented towards a liquid reservoir. A calibrated screw clamp 8 is used to apply a lateral force that deforms the duck bill from its closed position. The degree of deformation determines the rate of flow to an infusion catheter, the valve 31 maintaining a substantially constant flow rate. The duck bill 32 also prevents flow of liquid when pressure downstream falls below a certain level. <IMAGE>

Description

FLOW REGULATING DEVICES AND PARENTERAL ADMINISTRATION BETS The invention relates to flow regulating devices and to parenteral administration sets including such devices.

Accurate and reproducible flow of liquid through flexible tubular passages is required in several industries, such as the chemical industry, oil industry and in medicine. Conventionally, the flow rate may be controlled by restricting the cross sectional area of the passage available for the liquid to flow through. This is usually achieved by compressing the tubing such as by means of a roller clamp. Unfortunately, this often causes the polymer forming the tubing to creep under compression, thus altering the flow rate and requiring the system to be reset. Changes in the pressure head, such as caused by a fall in the level of liquid in ths reservoir, will also affect the flow rate.Changes in pressure at the liquid outlet, such as caused by bending of the outlet tubing or change in the venous back pressure in the patient, can also affect the flow rate if no compensation is made.

Attempts have been made to reduce these difficulties, such as described in GB 1519558, GB 2012393At GB 1551170 and GB 1416856, but these have not been entirely satisfactory.

It is an object of the present invention to provide a flow regulating device that can be used to avoid these disadvantages.

According to one aspect of the present invention there is provided a flow regulating device for controlling the rate of flow of liquid through a passageway comprising a tubular passage adapted for connection at one end to a source of liquid and at the other end for connection to an outlet for the liquid, flow control means comprising a check valve inside the tubular passage, and means external to the passage for variably deforming the check valve from its closed position whereby the degree of deformation of the check valve determines the rate of flow of liquid through the passage and the check valve operates to maintain a substantially constant flow rate through the passage.

The check valve preferably includes a duck bill valve having a duck bill portion that is oriented towards the source of liquid. A portion at least of the tubular passage may be deformable, the duck bill valve being located within the deformable portion. The check valve may be of a flexible elastomeric material and may be arranged to close and prevent flow of liguid through the device when pressure downstream of the check valve falls below a predetermined value. The means for variably deforming the check valve may include a screw clamp or a non-circular orifice in a rotatable sleeve which embraces the passage such that rotation of the sleeve varies the deformation of the check valve. The means for variably deforming the check valve is preferably calibrated.

According to another aspect of the present invention there is provided a parenteral administration set comprising a liquid reservoir, a drip chamber, tubing, infusion means and means for controlling the flow of liquid through the tubing, the control means including a tubular passage containing a check valve inside the tubular passage and means external to the tubular passage for deforming the check valve from its closed position whereby the degree of deformation determines the rate of flow of liquid through the passage and the check valve operates to maintain a substantially constant flow rate to the infusion means.

The set may include means for sensing the drip chamber and for controlling the degree of deformation of the check valve in accordance therewith such as to maintain a substantially constant drip rate.

A parenteral administration set including a flow regulator, in accordance with present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation view of the set; Figure 2 is a cross-sectional side elevation view of the flow regulator to a larger scale; Figure 3 is a transverse section along the line III - III of Figure 2; and Figure 4 is a transverse section along the line IV - IV of Figure 2.

With reference to Figure 1, the parenteral administration set includes a liquid reservoir 1, the outlet of which is connected to an infusion catheter 2 via a passageway including a flow regulating device 3 and a drip chamber 4 upstream of the flow regulating device.

The reservoir 1, catheter 2 and drip chamber 4 are all of conventional construction, the reservoir containing an infusion liquid and being suspended at a level above the tip of the catheter.

With reference now also to Figures 2 to 4, the flow regulating device 3 has an outer sleeve 30 of cylindrical shape and circular section which is made of a deformable, resilient material, such as a plastics material. The upper end of the sleeve 30 is joined to tubing 5 coupled to the outlet of the drip chamber 4; the lower end of the sleeve is joined to tubing 6 which extends to the catheter 2 so that the sleeve 30 provides a passage for flow of liquid to the catheter. Mounted within the sleeve 30 is a duck-bill check valve 31 such as of the kind sold by Vernay Laboratories Inc, Yellow Springs, Ohio, USA. The valve 31 is an integral moulding of a soft elastomeric material such as rubber, silicone rubber or neoprene. It will be appreciated that the material of the check valve 31 and the sleeve must be compatible with the liquid being infused.At its upper end, the valve 31 has a vertically-extending duck-bill shape portion 32 comprising two parallel rectangular walls 33 and 34 joined face-to-face along their vertical edges 35 and 36. In their natural state, as moulded, the two walls 33 and 34 lie flat against one another so that passage of fluid between the walls is prevented. The width of the duck-bill portion 32 is equal to the internal diameter of the sleeve 30 whereas its thickness is less than the diameter of the sleeve, so that there is a space between the sleeve on both sides of the duck-bill portion.

At its lower end, the duck-bill portion 32 joins with a base 37 of cylindrical shape and circular section, via a tapering portion 38. The diameter of the base 37 is equal to the internal diameter of the sleeve 30 and the base is joined into the sleeve around its outer edge, such as by means of an adhesive, to produce a fluid-tight seal between the sleeve and the exterior of the valve 31. A bore 39 of circular section extends through the base 37 and communicates with the interior of the duck-bill portion 32.

The flow regulator 3 also includes a clamp 8 which embraces the sleeve 3-0 in the region of the duck-bill portion 32 of the valve. The clamp 8 may take many different forms, the one illustrated being a screw clamp with a fixed pad 80 on the left hand of the valve and an adjustable pad 81 diametrically opposite the fixed pad, on the right hand of the valve. The adjustable pad 81 is rotatably mounted on one end of a screw-threaded post 82 which extends through a screw-threaded aperture 83, the other end of the post carrying a knob 84 which, when manually rotated, causes the pad 81 to be moved towards or away from the fixed pad 80. The post 82 or knob 84 may be calibrated so that the flow rates are reproducible and presettable. In this way, the clamp 8 applies an adjustable pressure across the duck-bill portion 32 which is aligned with its plane.The deformable nature of the outer sleeve 30 ensures that it can flex without damage to the seal with the valve. It will be appreciated that, when the clamp 8 is relaxed, the duck bill portion 32 will be closed preventing fluid flow through the valve. When, however, a force is applied laterally across of the valve, such as by the clamp 8, the two walls 33 and 34 of the duck-bill portion will bow outwardly to a convex shape, as shown in Figures 3 and 4. This forms a passage between the two walls 33 and 34 so that fluid can flow along the valve. It has been found that the valve will exhibit a self-regulating effect that controls fluid flow through it. This arises because fluid in the upper part of the sleeve 30 will exert an inward force on both walls 33 and 34 of the duck-bill portion 32, tending to close it.It can be seen, therefore, if the fluid pressure at the inlet to the valve should fall (such as, for example, caused by a fall in the level of infusion fluid in the reservoir 1) that this would reduce the pressure in the sleeve tending to close the duck-bill portion 32, thereby allowing it to open more. The increase in cross-sectional area of the flow path through the duck-bill portion 32 reduces the resistance to flow, compensating for the reduced input pressure in such a way that that flow through the regulator 3 is maintained constant. The valve 31 being flexible and elastomeric, it can respond to small pressure changes.

The inwardly-directed force on the duck-bill 32 produced by fluid pressure outside the duck-bill is counteracted to a certain extent by fluid pressure within the duck-bill portion which exerts an outwardly-directed force on the walls 33 and 34. This internal fluid pressure is related to the pressure at the outlet of the regulator 3, so a fall in pressure in the tubing 6 would reduce this counteracting effect. More particularly, the regulator 3 can be arranged, by suitably setting the clamp 8, to provide a safety feature whereby, if the tubing 6 becomes disconnected, the duck-bill 32 will be closed by the increase in differential pressure across its walls, thereby preventing escape of liquid. The regulator 3 can be reopened after reconnection, by tightening the clamp 8 further until flow recommences and fluid pressure at the regulator outlet builds up again.Once this happens, the clamp 8 can be relaxed until the desired flow is achieved.

The valve 31 responds in the opposite way to an increase in pressure in tubing 6 such as caused, for example, by a kink in the tubing. Because this would produce an increase in pressure within the duck-bill portion 32, this would cause it to open, thereby increasing pressure in the tubing so that flow downstream of the kink is stabilized.

Similarly, variations in venous back pressure will be compensated for, so that the flow rate of infusion liquid remains constant.

The extent to which the valve opens is a combination of several factors, namely the applied lateral force, the elastic properties of the valve, the fluid pressure head upstream of the valve and the pressure downstream of the valve.

It is of considerable importance in the treatment of patients by the administration of liquids that the liquids are administered at a constant and controllable flow rate.

In one test, the drip rate was set to 28 drops per minute (dpm) and the rate observed over a period of time.

There was a slight decrease in the drop rate over 35 minutes but not as large as that produced with a conventional roller clamp. The reservoir 1 was then raised and lowered and then returned to its original level. The rate initial rose to 30dpm but settled to 28dpm for the next 2.5 hours. Despite handling, moving the administration set and decreasing the fluid head, the rate remained the same as that originally set.

Duck bill valves of the kind described have been used previously as one-way valves. In such applications, flow of liquid is in the opposite direction to that of the present invention, with the duck bill directed downstream and with fluid emerging out of the tip of the duck bill.

The arrangement of the present invention is, therefore, in direct contrast to conventional use of such valves.

The level of applied force governs the cross-sectional area of the passage through the duck bill.

In precise flow control operations this force will be minimal to give very low flow rates. This is in contrast with previous arrangements such as roller clamps where the minimum flow rate requires the use of the maximum force which, in turn, creates stress and related problems with the plastics tubing.

Various different means could be used to provide the lateral force across the valve. For example, an electronically-controlled clamp could be used which receives an input from a drip rate sensor 9 so that the force applied to the clamp is altered in response to variations in the drip rate. Alternatively, the force could be provided by an aperture of elliptical or other non-circular shape in a rotatable collar around the regulator. Rotation of the collar would alter the orientation of the orifice relative to the plane of the duck-bill portion and hence cause the valve to open or close.

Instead of locating the valve 31 within a deformable sleeve 30, the sleeve could be rigid and a part of the valve exposed on its outer surface so that it is acted on directly by the lateral force. The check valve need not necessarily have a natural closed state, it could be slightly open, because the pressure upstream would still tend to close the valve in the absence of the lateral deforming force.

The flow regulator is not confined to use in medical fluid systems but could be used other applications where a steady flow rate is required or where it is desired to shut off flow automatically on a fall in outlet pressure.

It is not essential for the check valve to be a duck bill valve. Other forms of check valve, that is, valves which open to allow flow of fluid in one direction but prevent flow in the opposite direction, could be used.

One other form of check valve could be a membrane valve in which a flexible membrane moves with respect to a liquid outlet.

Claims

1. A flow regulating device for controlling the rate of flow of liguid through a passageway comprising a tubular passage adapted for connection at one end to a source of liquid and at the other end for connection to an outlet for the liquid, flow control means comprising a check valve inside the tubular passage, and means external to the passage for variably deforming the check valve from its closed position whereby the degree of deformation of the check valve determines the rate of flow of liquid through the passage and the check valve operates to maintain a substantially constant flow rate through the passage.

2. A flow regulating device according to Claim 1, wherein the check valve includes a duck bill valve having a duck bill portion that is oriented towards the source of liquid.

3. A flow regulating device according to Claim 2, wherein a portion at least of the tubular passage is deformable, and wherein the duck bill valve is located within said deformable portion.

4. A flow regulating device according to any one of the preceding claims, wherein the check valve is of a flexible elastomeric material.

5. A flow regulating device according to any one of the preceding claims, wherein the check valve is arranged to close and prevent flow of liquid through the device when pressure downstream of the check valve falls below a predetermined value.

6. A flow regulating device according to any one of the preceding claims, wherein the means for variably deforming the check valve includes a screw clamp.

7. A flow regulating device according to any one of Claims 1 to 5, wherein the means for variably deforming the check valve includes a non-circular orifice in a rotatable sleeve which embraces the passage such that rotation of the sleeve varies the deformation of the check valve.

8. A flow regulating device according to any one of the preceding claims, wherein the means for variably deforming the check valve is calibrated.

9. A flow regulating device substantially as hereinbefore described with reference to the accompanying drawings.

10. A parenteral administration set including a flow regulating device according to any one of the preceding claims.

11. A parenteral administration set comprising a liquid reservoir, a drip chamber, tubing, infusion means and means for controlling the flow of liquid through the tubing, wherein the control means includes a tubular passage and a check valve inside the tubular passage and means external to the tubular passage for deforming the check valve from its closed position whereby the degree of deformation determines the rate of flow of liquid through the passage and the check valve operates to maintain a substantially constant flow rate to the infusion means.

12. A parenteral administration set according to Claim 11, wherein the set includes means for sensing the drip chamber and for controlling the degree of deformation of the check valve in accordance therewith such as to maintain a substantially constant drip rate.

13. A parenteral administration set substantially as hereinbefore described with reference to the accompanying drawings.

14. Any novel feature or combination of features as hereinbefore described.