GB2276223A

GB2276223A - Liquid-dispensing device

Info

Publication number: GB2276223A
Application number: GB9305789A
Authority: GB
Inventors: David E Armstrong
Original assignee: Haemocell PLC
Current assignee: Surgical Innovations Group PLC
Priority date: 1993-03-19
Filing date: 1993-03-19
Publication date: 1994-09-21
Also published as: GB9305789D0

Abstract

A dispensing system, particularly for blood, is provided and comprises a container (4) having at its bottom a valve assembly (V) controlling outflow of a liquid (5) from the container into an outlet duct (C, 10, 11), the valve assembly comprising a float (F) which cooperates with a seating at an entrance (19) to the outlet duct so as to fall and close the entrance (19) when the liquid in the container falls to a lower level, characterised in that the valve assembly (V) further comprises a bleed duct (22) leading from within the container at a level above said lower level to the outlet duct at a location downstream of the seating. <IMAGE>

Description

LIOUID DISPENSING SYSTEM The invention relates to a system in which a liquid is drawn from the bottom of a container, within which there is a reservoir of the liquid, either under gravity or suction.

In the event of the reservoir of liquid containing a contaminant which has a lower specific gravity than the liquid, and which therefore tends to float on the surface of the reservoir of liquid, there is a danger that a concentrated quantity of the contaminant will be dispensed from the container as the last of the liquid is withdrawn from the container. This may have serious consequences, for example if the liquid is whole blood or blood plasma, and the contaminant is fatty lipids, an application of the invention in which we are particularly interested.

However, there will be other applications where similar considerations apply.

In accordance with the present invention, a liquid dispensing system comprises a container having at its bottom a valve assembly controlling outflow from the container into an outlet duct, the valve assembly comprising a float which cooperates with the seating at an entrance to the outlet duct so as to fall and close the entrance when the liquid in the container falls to a lower level, and a bleed duct leading from within the container at a level above said lower level to the outlet duct at a location downstream of the seating.

With this arrangement, when most of the liquid has been withdrawn from the container through the entrance to the outlet duct, the float closes the entrance thereby trapping an upper layer of the liquid, including any floating contaminant, within the container. However the bleed duct, which leads at that time from within the container above the upper level of the liquid and floating contaminant, allows air to bleed into the outlet duct downstream of the seating, so that the liquid which would otherwise be trapped in the outlet duct is able to flow away through the outlet duct. As a result there is no danger of liquid being held in and stagnating in the outlet duct, or of cavitating if suction continues to be applied to draw the liquid from the container, both being potentially serious problems when the liquid is blood. In fact, in a blood dispensing system, the blood will normally be withdrawn from the container at a standard flow rate by means of, for example, a roller pump and it is conventional for the pump to be switched off by sensing automatically or manually the blood/air interface as the last of the blood passes down through a transparent portion of the outlet duct towards the pump.

In a particularly neat arrangement, the float is constrained to move upwards and downwards in a vertical guide tube having one or more apertures through its wall at its lower end adjacent to, but upstream of, the seating.

In normal withdrawal of liquid from the container, it is able to pass into the guide tube below the float and down through the seating without having to pass through a narrow annular gap between the periphery of the float and the inner surface of the guide tube.

In order to avoid the danger of floating contaminant which sediments on the top of the bleed duct as the upper liquid level moves down past the top of the bleed duct, the entrance to the bleed duct preferably faces at or below horizontal. There is then little danger of sedimented contaminant being drawn into the bleed duct when air is drawn through the bleed duct after the valve has closed the seating.

The guide for the float and the bleed duct may be formed in a unitary plastic moulding, a lower end of the moulding being arranged to be fitted into a recess in the bottom of the container, the seating and a downstream end of the bleed duct opening through a bottom wall of the moulding into a common chamber formed between the bottom wall and the base of the recess, the outlet duct then comprising the chamber and a passageway opening in the base of the recess and leading down from the bottom of the container.

A blood dispensing system constructed in accordance with the present invention is illustrated in the accompanying drawings in which: Figs. 1 and 2 are vertical sectional views showing a valve assembly mounted at the bottom of a container at different stages in the liquid dispensing cycle; and, Fig. 3 is a exploded view of the valve assembly; and, Fig. 4 is a vertical section through the valve assembly.

As shown in figure 1, an open topped plastics container 4 is shown containing a reservoir 5 of a liquid, such as blood. At the centre of the bottom wall of the container 4, there is an oval opening surrounded by a flange 6. A valve assembly V, which is shown in more detail in figure 3, is mounted at the opening to control the dispensing of liquid from the container down through a discharge hose 7.

A mounting for the valve assembly V is provided by a unitary plastics moulding M1, having an upstanding oval side wall 8, which is arranged to be a push fit up within the flange 6, and to be retained there by a suitable assembly method. The wall 8 upstands from a base 9 formed with a central hole 10, leading to a downwardly projecting tubular spigot 11, in which the upper end of the hose 7, leading to, e.g., a roller pump, is arranged to be secured by a suitable assembly method.

If uncontrolled dispensing of the liquid from the container 4 is acceptable, the container may be used merely with the mounting M1 fitted in position. However, if controlled dispensing is required, then the valve assembly V is fitted into the recess defined by the base 9 and wall 8 of the mounting M1 either before or after the mounting has been fitted to the container.

The valve assembly comprises a second unitary plastics moulding M2 comprising a bottom wall 12 with a downwardly projecting oval side wall 13 which is arranged to be received as a push fit within the wall 8 of the mounting, and to be secured there by the automatic snap fit engagement of projections 14 on opposite sides of the wall 13 with complementary detents 15 in the wall 8. Projecting upwardly from bottom wall 12 is a guide tube 16 for a float F formed by a hollow body 17 the upper end of which is closed by a stopper 18. The body 17 is provided with longitudinal ribs 17A which ensure vertical guidance of the float in the tube but adequate clearance to prevent the float sticking in the tube by capillary stiction. The undersurface of the body 17 is conical with a shallow obtuse included angle. Coaxially with the guide tube 16, the bottom wall 12 is formed with a hole 19 leading, when the valve assembly is fitted to the mounting, into a chamber C formed between the bottom wall 12 and the base 9.

Immediately above the bottom wall 12 the guide tube 16 is formed with two apertures 20 in its side wall.

Fixed to one side of the guide tube 16 is a cylindrical bleed tube 21 of smaller diameter than the guide tube 16. The bottom wall 12 is formed, in alignment with a bleed duct 22, defined by the inner wall of the bleed tube 21, with a second hole 23 also leading into the chamber C. At its upper end, the tube 21 is formed with a vertical slit 24, the lower edge 25 of which is inclined radially outwardly and downwardly. A closure element E has a cylindrical portion 26 which is arranged to be a push fit down into the top of the tube 21 until a flat tab 27 of the element comes to rest in a notch 28 in the adjacent side wall of the tube 16. The tab 27 captures the float F within the tube 16. The element E also has a projecting nib 29 with a downwardly and outwardly inclined lower edge 30 which, when the element E is fully fitted into the tube 21 is spaced slightly above the edge 25, to provide a narrow inlet 31 to the bleed duct 22 in the tube 21, the inlet facing at about 450 below the horizontal.

In use when the container is full of liquid, the float F remains within the top of the tube 16 and liquid is free to be dispensed out of the container through the apertures 20, the hole 19, the chamber C, the hole 10, the spigot 11 and hose 7. However, when, as shown in figure 2, the level L of the liquid 5 in the container 4 drops sufficiently for the float F to come to rest on the seating around the hole 19 in the bottom wall 12, the conical undersurface of the float enters and closes the hole 19. At this time the inlet 31 is well above the liquid level and air can bleed through the inlet 30, bleed duct 22 and the hole 23 into the outlet duct consisting of the chamber C, spigot 11 and tube 7. The bleed duct sufficiently restricts the air flow for the roller pump to maintain a partial vacuum in the chamber C, hence puling the float down onto its seating to keep the hole 19 closed. Because the inlet 31 faces downwardly, there is little or no chance of any contaminant sedimenting on top of the valve assembly as the liquid level is lowered past the top of the assembly, coming to rest in any position adjacent to the inlet from which it may be sucked into the bleed duct.

Claims

1. A liquid dispensing system comprises a container (4) having at its bottom a valve assembly (V) controlling outflow of a liquid (5) from the container into an outlet duct (C,10,11), the valve assembly comprising a float (F) which cooperates with a seating at an entrance (19) to the outlet duct so as to fall and close the entrance (19) when the liquid in the container falls to a lower level, characterised in that the valve assembly (V) further comprises a bleed duct (22) leading from within the container at a level above said lower level to the outlet duct at a location downstream of the seating.

2. A system according to claim 1 wherein the float (F) is constrained to move upwards and downwards in a vertical guide tube (16) having one or more apertures (20) through its wall at its lower end adjacent to, but upstream of, the seating.

3. A system according to any one of the preceding claims, wherein the entrance (24) to the bleed duct (22) faces at the, or below, horizontal.

4. A system according to any one of the preceding claims, wherein the guide tube (16) and the bleed duct (21) are formed as a unitary plastic moulding (M2), a lower end (13) of the moulding being arranged to be fitted into a recess (8,9) in the bottom of the container (4), the entrance (19) and a downstream end (23) of the bleed duct opening through a bottom wall (12) of the moulding into a common chamber (C) formed between the bottom wall (12) and the base (9) of the recess, the outlet duct then comprising the chamber (C) and a passageway (10,11) opening in the base (9) of the recess and leading down from the bottom of the container.

5. A system according to claim 4, wherein the recess is formed by the walls (8) and base (9) of a unitary plastic moulding which is arranged to be a push-fit within an opening (6) in the bottom wall of the container (4).