GB1597955A

GB1597955A - Dispensing of viscous fluids

Info

Publication number: GB1597955A
Application number: GB757978A
Authority: GB
Original assignee: Shandon Southern Products Ltd
Current assignee: Shandon Diagnostics Ltd
Priority date: 1978-02-24
Filing date: 1978-02-24
Publication date: 1981-09-16

Description

(54) IMPROVEMENTS RELATING TO THE DISPENSING OF VISCOUS FLUIDS (71) We, SHANDON SOUTHERN PRODUCTS LIMITED, a British Company of 93-96 Chadwick Road, Astmoor Industrial Estate, Runcom, Cheshire WA7 iPR, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns the dispensing of viscous fluids, a term used herein to define liquids, slurries, pastes and semi-liquids that have a relatively high viscosity but that nevertheless are capable of being pumped or otherwise caused to flow through a conduit.

In many technical and industrial applications it is required to dispense, for instance, an adhesive or like viscous fluid in a controlled manner so that a required quantity of the fluid is dispensed, e.g. discharged from a nozzle, within a predetermined period of time.

In some cases the amount of fluid to be dispensed is rather small, for instance one or a few drops, and the accurate dispensing of such small quantities is difficult to accomplish. One of the reasons for such difficulty is that the force needed to cause flow of the fluid and its discharge from, say, a nozzle, involves significant pressures being developed in the fluid upstream of the discharge point or nozzle so that if a flow-control valve is disposed a significant distance upstream of the discharge point, fluid flow tends to continue at the discharge point after the control valve has been closed, as a result of expansion of the fluid in the conduit between the valve and the discharge point, and, possibly, as a result of relaxation by contraction of the conduit when this is resilient.In the case of some fluids this additional flow of exudation at the discharge point may give rise to problems such as a change in the character of the fluid while exposed to the external atmosphere at the discharge point-for instance an adhesive may com mence setting or curing-and this may in some cases affect the subsequent discharge of fluid, or degrade the fluid subsequently discharged.

For these reasons it has been usual to arrange the control valve as close as practicable to the discharge point, thereby to minimise the amount of fluid that is disposed between the control valve and the discharge point when the control valve closes. However this is not always a convenient arrangement in practice.

An object of the invention is therefore to provide a method of effecting controlled intermittent discharge of viscous fluid that at least substantially avoids these problems.

A further object of the invention is to pro vide a dispensing apparatus suitable for dis pensing viscous fluid, especially in small quantities, at a discharge point disposed at a significant distance from a valve con trolling the flow of fluid to the discharge point.

In one aspect, therefore, the invention provides a method of dispensing a viscous fluid from a discharge orifice via a fluid flow path constituted at least in part by a resilient conduit, comprising feeding such fluid under maintained pressure to a pinch valve comprising means for squeezing or pinching the conduit to occlude its bore; inducing flow of fluid to said orifice by opening said pinch valve while concurrently compressing a part of said conduit downstream of the valve so as partly to occlude its bore and effect a reduction in the bore volume of that part of the conduit; and thereafter closing said pinch valve by squeezing or pinching said conduit while concurrently releasing compression of said conduit downstream of said valve to increase the volume of said part of the conduit by an amount at least sufficient to accommodate relative expansion of the fluid in said flow path downstream of said pinch valve.

The expression "relative expansion of the fluid in the flow path downstream of the pinch valve" is to be understood to mean the apparent increase in volume of the fluid relative to the volume of the flow path in which the fluid is contained. As the flow path is defined at least in part by a resilient conduit that is liable to expand in response to the pressure of the fluid therein when the pinch valve is open, and contract in response to to falling fluid pressure when the pinch valve is subsequently closed, the apparent expansion of the fluid upon closing of the pinch valve will in practice exceed the actual volumetric expansion of the fluid due to the decrease in pressure therein, by an amount corresponding to the accompanying contraction of the flow path.Accordingly to prevent exudation of fluid from the orifice upon closure of the pinch valve, the increase in flow path volume by release of compression upon the conduit downstream of the pinch valve must at least compensate for the resultant contraction of the conduit in response to falling pressure in the fluid, as well as for the actual expansion of the fluid.

Preferably the said increase in volume of the flow path, upon closing the pinch valve, by releasing the compression of the conduit exceeds the relative expansion of the fluid in the flow path so that the fluid tends to be drawn back into the flow path from the vicinity of the orifice, thereby minimising risk of exudation of fluid or the formation of external drops at the orofice.

The invention further includes apparatus for the aforesaid purposes and thus in a further aspect the invention provides apparatus for controlling the flow of a viscous fluid, comprising pressurising means for maintaining a body of such a fluid under pressure sufficient to cause flow thereof to a discharge point through a flow path constituted at least in part by a length of resilient conduit; a pinch valve comprising means for squeezing or pinching the resilient conduit to occlude its bore; and means for compressing a part of said resilient conduit downstream of said pinch valve so as partly to occlude its bore to effect a reduction in the bore volume of that part of the conduit in coordination with operation of said pinch valve so that said bore volume is reduced concurrently with opening of the pinch valve and is increased concurrently with closing of said pinch valve.

The pressurising means for maintaining the body of viscous fluid under pressure may take any convenient form, depending upon the nature of the fluid and any procedures that have to be applied thereto. For instance it may in some instances be necessary to heat or otherwise control the temperature of the fluid and in such cases the means for maintaining the fluid under pressure may be incorporated in suitable means for heating or controlling the temperature of the fluid.

The pressurising means may be mechanical in nature and comprise, for instance, a pump or a container having a deflectable wall subject to external force to decrease the container volume. Alternatively the pressurising means may involve the application of fluid--e.g. inert gas-pressure directly or indirectly to the body of viscousfluid to be dispensed.

In a preferred embodiment of the invention, the pressurising means comprise a flexible tubular container sealed at one end and having an outlet at its other end, and a pair of pressure plates between which the said container is located, spring or like resilient means being arranged to tend to close the pressure plates upon the container so as thereby to tend to squeeze a viscous fluid contained therein from the container outlet.

Conveniently said pressure plates are hingedly connected and the container is arranged with its sealed end nearer to the hinge connection.

The container may at least in part be constituted by the normal packaging of the viscous fluid to be dispensed.

In one convenient form of this preferred arrangement, the pressure plates are connected by a toggle linkage including a pair of spring links that in one over-centre condition of the linkage act to urge the pressure plates together.

The pinch valve is conveniently solenoid operated. The means for compressing a part of said resilient conduit preferably comprise a further pinch valve that is conveniently also solenoid operated. In this case, both pinch valves are preferably actuated by a common solenoid, but in opposite senses.

Thus in a preferred embodiment, the resilient conduit extends between rigid supports and a pair of fingers carried by a plunger that is spring biased in one direction and coupled to a solenoid for movement thereby in the other direction, said fingers engaging longitudinally spaced parts of the conduit and being so arranged that in one condition of the solenoid the upstream finger pinches the conduit against one support completely to occlude the conduit bore whereas in the other condition of the solenoid the downstream finger pinches the conduit against the other support partly to occlude the conduit bore.

Although the method and apparatus of the invention have many potential applications, a particularly application is in connection with dispensing small quantities of mountant fluid onto microscope slides or cover slips therefor in an automatic microscope slide coverslipping machine, for instance a machine such as that disclosed in our copending Application Number 9342/77 (Serial No. 1,597,954) and an embodiment of the invention suitable for such application is illustrated by way of example in the accompanying drawings in which: FIGURE 1 is an exploded perspective view of a mountant fluid dispenser embodying the invention; and FIGURES 2 and 3 are diagrammatic illustrations of the pinch valve and volumeadjusting means of the dispenser in Figure 1, showing the pinch valve in its closed and open conditions respectively.

The dispenser shown in Figure 1 is intended to dispense cover slip mountant or fixative fluid that is obtainable packed in tubular containers that are sealed at one end and have a capped opening at their other end and through which the mountant may be discharged by squeezing the container.

Accordingly the illustrated apparatus is intended to utilise the original packing of the mountant as part of the means for pressurising a body of the fluid.

The apparatus shown in Figure 1 comprises a pair of pressure plates 1, 2 connected by a hinge 3 and between which the aforesaid packing container 4 of a body of mountant fluid may be positioned with its sealed end 5 adjacent to the hinge 3 and its outlet-provided end 6 extending from between the pressure plates 1 and 2.

The pressure plate 2 has an upstanding transverse rib 7 on its outer surface near the free end thereof and this rib has trunnions constituted by the ends of a rod 8 that provides a pivotal connection to each of a pair of triangular toggle links 9 that are fixed to a toogle lever 10 whereby the links 9 may be rocked about the rod ends 8. The links 9 are each pivotally connected to an individual telescopic spring link 11 that consists of a plunger 12 reciprocable in a housing 13 that is pivoted to the pressure plate 1 near the free end thereof and that contains a spring acting on the plunger 12 so as to tend to contract the length of the link 11.In the condition of the parts shown in Figure 1, the spring links 11 act through the links 9 and rib 7 to urge the free end of the pressure plate 2 towards the pressure plate 1 and thereby tend to squeeze the container 4 and so maintain a pressure upon the fluid contents of the container 4.

It will be apparent that by pulling the lever 10 forwardly and downwardly to rock the links 9 about the rod ends 8, the spring links 11 will move over-centre and permit the pressure plate 2 to pivot about the hinge 3 away from the pressure plate 1 for the purpose of relieving the pressure applied to the container 4 and to facilitate the removal of the latter and its substitution by another such container.

The illustrated dispenser further includes twin combined pinch valve and volumeadjusting assemblies for controlling the flow of fluid from the container 4 to a pair of discharge points. The flow path to each discharge point consists in part of an individual resilient tube 14 that extends from a cap 15 fitted to the open end of the container 4, to. and through an individual channel 16 formed in a mounting plate 17 that although shown separated from the pressure plate 1 in Figure 1 is in fact fitted to the rear (hidden) face of the pressure plate 1 so that channels 16 are closed by the rear surface of the plate 1. The mounting plate 17 is provided with counterbore holes 18 through which fixing bolts or the like may extend to secure the plate 17 to a supporting structure.The mounting plate 17 is further provided with a pair of keyhole slots 19 for cooperation with fixing bolts (not shown) on the rear face of the pressure plate 1 to secure the mounting plate 17 thereto.

The channels 16 in the mounting plate 17 are of horseshoe shape as shown and each terminates in an individual enlarged recess 20 that receives the end of a flexible discharge conduit 21 that is connected to the relevant tube 14 in the associated channel 16.

The tubes 14 extend through the recess 22, passing over a rib 23 and an angled channel 24.

Laterally outboard of each tube 14 as it passes through the recess 22 is a hole 25 through which extends, reciprocably, an individual plunger 26 coupled by a rod 27 to an operating solenoid and spring-loading assembly (not shown).

Each plunger 26 is fitted with a pair of fingers 28, 29 respectively that project radially from the plunger 26 at positions spaced longitudinally thereof by a distance approx mating to the diameter of the associated tube 14.

The finger 29 lies in the associated angled channel 24 and thus underneath the tube 14 whereas the finger 28 lies over the tube 14 and parallel with the rib 23.

The operation of each flow control pinch valve and volume-adjusting assembly constituted by one of the solenoid-operated plungers 26 and its fingers 28 and 29 in cooperation with the associated tube 14 is best understood from a consideration of Figures 2 and 3. In these figures the actuating solenoid and spring-loading unit for a plunger 26 is shown diagrammatically at 30 and the rib 23 has been omitted for ease of illustration, as has also the pressure plate 1, the hidden face of which is recessed in the region of the plunger 26 and finger 28 to permit movement to the condition shown in Figure 3, but which lies against the tube 14 in the region opposite to the angled channel 24 and finger 29 so as to provide a support against which the tube 14 may be compressed by the finger 29 in the manner shown in Figure 3.

Figure 2 shows the condition of the parts when the plunger 26 has been moved fully rearwardly of the mounting plate 17, i.e. in the direction indicated by the arrow in Figure 2. Typically this will be the position resulting for deenergisadon of the solenoid of the unit 30. movement of the plunger 26 to this poseidon being caused by the spring of the unit 30. This position represents the closed condition of the flow control pinch valve comprising the finger 28 that, as shown, pinches the tube 14 (in practice against the rib 23) so as totally to occlude the tube bore and thus prevent fluid flow therethrough.

On the other hand in this position of the plunger 26, the finger 29 is fully housed in the angled channel 24 and thus imposes no constraint upon the tube 14.

Figure 3 shows the position of the parts when the plunger 26 has moved fully forward-i.e. in the direction indicated by the arrow in Figure 3. This condition of the parts particularly results from energisation of the solenoid of the unit 30 so that it overcomes the spring-loading tending to move the parts to the Figure 2 condition.

In the condtiion illustrated in Figure 3, the finger 28 no longer pinches the tube 14 to occlude its bore and prevent flow of fluid through the tube (in the direction of the arrow 31); however the finger 29, as shown, compresses a portion of the tube 14 downstream of the pinch valve (finger 28) and partly occludes the tube bore at this region (thereby to reduce the effective total volume of the flow path constituted by the tube 14 and associated conduit 21 downstream of the control valve.

It will be apparent that in moving from the valve-open position of Figure 3 to the valveclosed position of Figure 2, the finger 29 will release its compressive load on the tube 14 and so permit this re-expand to its natural bore cross section and therefore increase its volume downstream of the pinch valve so as to accommodate expansion of the fluid in the tube 14 and conduit 21 so as to prevent exudation of the fluid at the discharge point fed by the conduit 21.

Preferably the volume adjustment effected by the movement of the finger 29 exceeds the likely change in contained fluid volume and also any change in the flow path volume resulting from changes in internal pressure, so that upon closing of the pinch valve there is a tendency for fluid within the flow path near the discharge point to be pulled back into the flow path and thereby partly shrouded from the ambient atmosphere in the region of the discharge point.

WHAT WE CLAIM IS:- 1. A method of dispensing a viscous fluid from a discharge orifice via a fluid flow path constituted at least in part by a resilient conduit, comprising feeding such fluid under maintained pressure to a pinch valve comprising means for squeezing or pinching the conduit to occlude its bore; inducing flow of fluid to said orifice by opening said pinch valve while concurrently compressing a part of said conduit downstream of the valve so as partly to occlude its bore and effect a reduction in the bore volume of that part of the conduit; and thereafter closing said pinch valve by squeezing or pinching said conduit while concurrently releasing compression of said conduit downstream of said valve to increase the volume of said part of the conduit by an amount at least sufficient to accommodate relative expansion of the fluid in said flow path downstream of said pinch valve.

2. Apparatus for controlling the flow of a viscous fluid, comprising pressurising means for maintaining a body of such a fluid under pressure sufficient to cause flow thereof to a discharge point through a flow path constituted at least in part by a length of resilient conduit; a pinch valve comprising means for squeezing or pinching the resilient conduit to occlude its bore; and means for compressing a part of said resilient conduit downstream of said pinch valve so as partly to occlude its bore to effect a reduction in the bore volume of that part of the conduit in coordination with operation of said pinch valve so that said bore volume is reduced concurrently with opening of the pinch valve and is increased concurrently with closing of said pinch valve.

3. Apparatus according to claim 2, wherein said pressurising means comprise a flexible tubular container sealed at one end and having an outlet at its other end, and a pair of pressure plates between which the said container is located, spring or like resilient means being arranged to tend to close the pressure plates upon the container.

4. Apparatus according to claim 3, wherein said pressure plates are hingedly connected and the container is arranged with its sealed end nearer to the hinge connection.

5. Apparatus according to claim 4, wherein the pressure plates are connected by a toggle linkage including a pair of spring links that in one over-centre condition of the linkage act to urge the pressure plates together.

6. Apparatus according to claim 2, wherein said pressurising means includes means for applying a fluid pressure directly or indirectly to the body of viscous fluid to be dispensed.

7. Apparatus according to any one of claims 2 to 6, wherein said pinch valve is solenoid operated.

8. Apparatus according to any one of claims 2 to 7, wherein said means for compressing a part of said resilient conduit comprise a further pinch valve.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. when the plunger 26 has been moved fully rearwardly of the mounting plate 17, i.e. in the direction indicated by the arrow in Figure 2. Typically this will be the position resulting for deenergisadon of the solenoid of the unit 30. movement of the plunger 26 to this poseidon being caused by the spring of the unit 30. This position represents the closed condition of the flow control pinch valve comprising the finger 28 that, as shown, pinches the tube 14 (in practice against the rib 23) so as totally to occlude the tube bore and thus prevent fluid flow therethrough. On the other hand in this position of the plunger 26, the finger 29 is fully housed in the angled channel 24 and thus imposes no constraint upon the tube 14. Figure 3 shows the position of the parts when the plunger 26 has moved fully forward-i.e. in the direction indicated by the arrow in Figure 3. This condition of the parts particularly results from energisation of the solenoid of the unit 30 so that it overcomes the spring-loading tending to move the parts to the Figure 2 condition. In the condtiion illustrated in Figure 3, the finger 28 no longer pinches the tube 14 to occlude its bore and prevent flow of fluid through the tube (in the direction of the arrow 31); however the finger 29, as shown, compresses a portion of the tube 14 downstream of the pinch valve (finger 28) and partly occludes the tube bore at this region (thereby to reduce the effective total volume of the flow path constituted by the tube 14 and associated conduit 21 downstream of the control valve. It will be apparent that in moving from the valve-open position of Figure 3 to the valveclosed position of Figure 2, the finger 29 will release its compressive load on the tube 14 and so permit this re-expand to its natural bore cross section and therefore increase its volume downstream of the pinch valve so as to accommodate expansion of the fluid in the tube 14 and conduit 21 so as to prevent exudation of the fluid at the discharge point fed by the conduit 21. Preferably the volume adjustment effected by the movement of the finger 29 exceeds the likely change in contained fluid volume and also any change in the flow path volume resulting from changes in internal pressure, so that upon closing of the pinch valve there is a tendency for fluid within the flow path near the discharge point to be pulled back into the flow path and thereby partly shrouded from the ambient atmosphere in the region of the discharge point. WHAT WE CLAIM IS:-

1. A method of dispensing a viscous fluid from a discharge orifice via a fluid flow path constituted at least in part by a resilient conduit, comprising feeding such fluid under maintained pressure to a pinch valve comprising means for squeezing or pinching the conduit to occlude its bore; inducing flow of fluid to said orifice by opening said pinch valve while concurrently compressing a part of said conduit downstream of the valve so as partly to occlude its bore and effect a reduction in the bore volume of that part of the conduit; and thereafter closing said pinch valve by squeezing or pinching said conduit while concurrently releasing compression of said conduit downstream of said valve to increase the volume of said part of the conduit by an amount at least sufficient to accommodate relative expansion of the fluid in said flow path downstream of said pinch valve.

9. Apparatus according to claim 8, where

in said further pinch valve is solenoid operated.

10. Apparatus according to claims 7, 8 and 9, wherein both pinch valves are actuated by a common solenoid.

11. Apparatus according to claim 10, wherein said resilient conduit extends between rigid supports and a pair of fingers carried by a plunger that is spring biased in one direction and coupled to a solenoid for movement thereby in the other direction, said fingers engaging longitudinally spaced parts of the conduit and being so arranged that in one condition of the solenoid the upstream finger pinches the conduit against one support completely to occlude the conduit bore whereas in the other condition of the solenoid the downstream finger pinches the conduit against the other support partly to occlude the conduit bore.

12. A method of dispensing a viscous fluid, substantially as described with reference to the accompanying drawings.

13. Apparatus for dispensing viscous fluids substantially as described with reference to and as shown in the accompanying drawings.