GB2274326A - Pinch valve with adjustable reaction member - Google Patents

Abstract

A pinch valve has a length of flexible tubing (42), preferably comprising two concentric tubes. The tubing is supported on an adjustable reaction member (43) below a cam follower (39) which cooperates with a cam (38). The cam (38) is driven by the prime mover (24) and the adjustable member (43) allows use of different sizes of flexible tubing. The prime mover is preferably an electric motor which drives the cam via a gear train. The valve may comprise more than one length of tubing which are pinched simultaneously or sequentially. <IMAGE>

Description

PRINT VALVES AND A CHEMICAL REPLENISHMENT SYSTEM INCORPORATING SUCH PINCH VALVES DESCRIPTION This invention relates to pinch valves and to a chemical replenishment system incorporating such pinch valves.

Pinch valves generally comprise an electrical solenoid operating against a spring whereby the plunger compresses a section of flexible tubing in order to arrest the flow of solution in the tube.

Normally open and normally closed versions are available. US-A-4993456, US-A-4921206, US-A-4570822, US-A-4524802, US-A-4508148, US-A-4491156, US-A-4645094, US-A-354116, US-A-4259985, US-A-5078361, US-A-4496133, CA-A-1225972 and DE-A-2741749 together with Japanese published applications nos. 63-120966, 57-24622 and 54-96545 describe various forms of solenoid operated pinch valves.

This type of valve has several disadvantages: 1. During the active phase of the solenoid, whether it be normally open or normally closed, power is consumed throughout its operation.

2. Solenoid operated pinch valves have a limited range of tubing sizes. Generally a particular tube size is specified by the manufacturers. Any attempt to increase the range of movement of the actuating element would be accompanied by a reduction in the necessary power which is liable to result in the pinch action being inadequate.

3. In some models the spring tension needs to be set up to ensure reliable operation. Adjustment may be necessary if the tubing is changed.

US-A-4682755 discloses a closure mechanism for a pinch valve which comprises two cams rotatably supported in the housing on the opposite sides of the tubing and connected to a hub via drive links. The hub is rotated manually by a handle or automatically by an actuator to pinch the tubing between the two cams which are moved towards one another. This mechanism is complex being designed to allow axial replacement of the piping and also for alternative pinch operation by fluid pressure.

US-A-4457339 discloses a multi-way pinch valve module comprising a rotor within a cylindrical cavity.

Lengths of flexible tubing are led around respective arcuate portions of the inner wall of the cavity between that wall and the rotor. The latter has angularly-spaced lobes and is driven by a stepper motor to act as a cam. The lobes urge circumferentially-spaced followers to pinch the flexible tubing. The followers are located for the required sequence of operation whereby the lengths of flexible tubing may be closed or opened in any sequence and whereby more than one of them may be closed at once. As is the case with solenoid operated pinch valves, this pinch valve mechanism is only suitable for use with a limited range of sizes of flexible tubing. It would be necessary to replace the rotor to enable the module to be used with smaller sizes of tubing. Also all the lengths of tubing led through the module need to be of substantially the same size.

An object of this invention is to avoid the foregoing difficulties, and in particular to enable the optimum pinch operation to be achieved simply with different sizes of tubing.

According to one aspect of this invention there is provided a pinch valve including a prime mover with a power output, one static reaction member, means operable to support one length of flexible piping so that it extends across said static reaction member, and means driven by said power output and operable to pinch said one length of flexible piping against said static reaction member, wherein said static reaction member is mounted adjustably so that its position relative to said prime mover is adjustable to suit different sizes of flexible piping. Preferably said prime mover has a rotary power output.

Use of a rotary power output has the potential for selection of a suitable range of actuating movement without any significant reduction in power and with considerable mechanical advantage. Adjustable mounting of the static reaction member enables the range of actuating movement to be limited which is convenient in practice.

In the preferred embodiments, said means driven by said rotary power output comprise an eccentrically mounted cam. Preferably said cam and said static reaction member are arranged so that the flexible piping is pinched therebetween when said cam is at its bottom dead centre position. This has the advantage that power need only be consumed during the transition to and from the pinch condition. The power consumption may be zero whilst the cam is at its bottom dead centre position when the tubing is pinched so that the valve is closed.

Conveniently said means driven by said rotary power output include a cam follower which is operatively associated with said cam and guiding means whereby said cam follower is constrained for rectilinear movement to and fro relative to said static reaction member.

One form of pinch valve in which is embodied includes further means operable to support another length of flexible piping alongside said one length of flexible piping so that the other length of flexible piping extends across a respective static reaction member and said means driven by said rotary power output are operable simultaneously to pinch both lengths of flexible piping against their respective static reaction member.

Another form of pinch valve in which this invention is embodied includes additional means operable to support another length of flexible piping between said cam and another static reaction member, said cam being between said static reaction member and the other static reaction member.

In such another form of pinch valve said cam may be operable to pinch either said one length of flexible piping or the other at any one time, alternatively said cam may be operable to pinch both said one and the other lengths of flexible piping at the same time.

It has been found that if a piece of silicon rubber tubing is left in a closed or pinched condition for a length of time, then sometimes it sticks in that closed condition and will not open. By mounting the tubing inside a series of concentric tubes, the wall elasticity is increased and there is a greater restoring force to open the tube after a long period of closure. Accordingly it is convenient that the or each length of flexible piping comprises concentrically mounted tubes of elastomeric material.

The preferred form of prime mover is a DC motor. In the preferred embodiment, the cam is driven by the motor via a gear train. The latter facilitates provision of the desired range and power.

Conveniently the rotary power output is the shaft of a position indicating potentiometer which is coupled to the DC motor by the gear train.

WO91/18326 and W091/18327 disclose a chemical replenishment system for a chemical process comprising one or more storage containers mounted on weigh scale means, each container having an outlet with a respective valve operable to control discharge from the respective container through the respective outlet, and control means responsive to the weigh scale means and operable to control operation of each valve which has one condition in which it is open to allow discharge and another condition in which it is closed to prevent discharge, the control means being arranged to be responsive to weight measurement by the weigh scale means so that the or each valve is opened to allow a predetermined amount by weight to be discharged from the respective container, and is then reclosed. It has been proposed that a pinch valve be used to control discharge from the or each storage container.However the conventional commercially available pinch valves were found to be unsuitable for that purpose. Either they were too large and required too much power or the tubing size was too small.

According to another aspect of this invention, in such a chemical replenishment system, the or each valve is a pinch valve according to said one aspect of this invention.

A feature of the chemical replenishment system disclosed in W091/18326 is the provision of a plurality of bulk chemical storage containers, each having an outlet connected to a respective one of the storage containers mounted on the weigh scale means via a respective piece of tubing of a multi-way valve. However no suitable multi-way pinch valve was available. Hence a feature of the other aspect of this invention is the use of a multi-way pinch valve in which the one aspect of this invention is embodied as the multi-way valve in which this invention is embodied.

The invention will now be described, by way of example, with reference to the accompanying drawings, of which: Figure 1 is a schematic diagram of a chemical replenishment system in which this invention is embodied; Figure 2 is a side view of a single way pinch valve of the system shown in Figure 1, the casing of the pinch valve being sectioned to reveal the operating elements of that pinch valve and the valve being shown in its open condition; Figure 3 is a view on arrow A of the pinch valve shown in Figure 2 with the outer casing removed; Figure 4 is a diagrammatic side view of the servo motor mechanism of the pinch valve shown in Figure 2; Figure 5 is a circuit diagram of the electronic control circuit of the servo motor mechanism shown in Figure 4; Figure 6 is a view similar to Figure 2 showing the valve in its closed position;; Figure 7 is a diagram illustrating the state of the elements of the valve in the condition shown in Figure 6 and as seen in the direction of arrow A; Figure 8 is a side view of a multi-way pinch valve of the system shown in Figure 1, the casing of the pinch valve being sectioned to reveal the operating elements of the valve which is shown in its open condition; Figures 9 and 10 show alternative forms of multi-way pinch valves in which this invention is embodied for other applications; Figure 11 is a diagram similar to Figure 7 illustrating the state of the elements of the valve shown in Figure 10 when closed; and Figure 12 shows a further alternative form of multiway pinch valve in which this invention is embodied for other applications.

Figure 1 shows bulk storage containers 10-12 of replenisher chemical solutions mounted on a platform 13 above a weigh scale 14 on which are mounted 3 small, intermediate containers 15-17, each having a volume just larger than the required shot of replenishment chemical solution. Each intermediate container 15-17 has an outlet with its own one-way pinch valve 18-20. Each bulk storage container 10-12 is connected to a respective one of the intermediate containers 15-17 through a respective piece of flexible tubing of a multi-way pinch valve which is shown diagrammatically at 22. Control means 23 sense the weight on the weigh scale 14 and control operation of the pinch valves 18-20 and 22.

The number of bulk storage containers, intermediate containers and interconnecting pinch valve flexible tubes shown are exemplary. As many as are required for a particular application would be provided.

The apparatus is prepared for use by having each of its intermediate containers 15-17 filled with the respective chemical solution by gravity feed from the respective bulk storage container 10-12 through the multi-way pinch valve 22 which would be open, the single way pinch valves 18-20 being closed. The multi-way pinch valve 22 is then closed.

Replenishment of small amounts of chemical by gravity feed from each intermediate container 15-17 is then begun by automatically opening the respective pinch valve 18-20, the consequent reduction of weight on the weigh scale 14 being monitored by computing means which are incorporated in the control means 23 and which are programmed to actuate closure of the respective single way pinch valve 18-20 when a certain weight of replenishment chemical has been dispensed.

The multi-way pinch valve 22 is opened automatically when the replenishment chemicals have been dispensed and the one-way pinch valves 18-20 closed. All the intermediate containers 15-17 are allowed to be refilled to capacity whereafter the multi-way pinch valve 22 is reclosed for the next replenishment cycle. This speeds up the refill process, ensures that no intermediate container 15-17 can empty, and that there are no cumulative errors.

In one particular embodiment which is designed for a photographic processor, there are 8 chemical solutions to be replenished. Hence, in that embodiment there are 8 bulk storage containers mounted at a convenient location. Also it has been found to be more practical to locate the 8 bulk storage containers below the weigh scale 14 and to provide pumping means for pumping the respective solution to the respective intermediate container on the weigh scale 14 via the respective way of the respective multi-way pinch valve.

Figures 2 and 3 show a one-way pinch valve in which this invention is embodied and which is suitable for use as a one-way pinch valve 18-20 of the apparatus illustrated in Figure 1.

The pinch valve shown in Figures 2 and 3 has a prime mover 24 with a rotary power output shaft 25 which comprises a consumer quality model control servo mechanism. Figure 4 shows the servo mechanism comprises a low voltage permanent magnet DC motor 26 coupled via a train 27 of plastic reduction gears to a position indicating potentiometer which carries the output shaft 25. The latter is splined and is drivingly engaged with a disc 28. End stops (not shown) limit the range of angular movement of the output shaft 25 to 2700.

Operation of the servo mechanism is controlled by an electronic amplifier circuit of which Figure 5 is a diagram. The circuit comprises a dual power operational amplifier 29 which is in the form of a single integrated circuit chip and which has two output terminals which are connected each to a respective terminal of the DC motor 26.

The positive input of one, 31 of the two amplifiers 31 and 32 of the dual power operational amplifier 29 is connected to the movable pick-off terminal 32 of the position indicating potentiometer. The positive input of the other amplifier 32 is connected to the output of a bistate analogue switch 34 which its also connected through a resistor 35 to the negative input of the amplifier 31. The bistate analogue switch 34 has two inputs and a control port, as well as its output. A logic input signal to the control port determines the setting of the bistate analogue switch 34. Each of the inputs of that switch 34 is connected to the movable pick-off terminal of a respective one of two potentiometers 36 and 37 which are set to different output potentials.Whichever one of those pick-off terminals, and thus the potential that is applied by the bistate analogue switch 34 to the dual power operational amplifier 29, is determined by the setting of that switch 34. The motor 26 is driven in one direction until the dual power operational amplifier 29 is in balance. The motor 26 rests in that condition until the state of the bistate analogue switch 34 is changed by a change in the logic input signal. The resultant change in the potential applied to the dual power operational amplifier 29 puts it out of balance so that the motor 26 is driven in the other direction until the balance is restored and the motor 26 rests again.

Figures 2 and 3 show a cam 38 is fitted eccentrically to the disc 28. The cam 38 cooperates with a cam follower 39 which is constrained in a grooved track 41 for movement up and down. The length 42 of flexible piping, which comprises at least two concentric tubes of elastomeric material, extends between the cam follower 29 and an adjustable abutment 43.

Mounting the tube through which replenishment chemical solution is discharged from the respective intermediate container 15-17, inside a series of several concentric tubes increases the wall elasticity and the restoring force tending to open the tube after a long period of closure by pinching.

The adjustable abutment 43 is positioned so that the optimum pinch of the tubing 42 between it and the cam follower 39 is achieved when the cam 38 is at bottom dead centre (as shown in Figures 6 and 7) for whatever diameter of tubing is used. Since the optimum pinch is achieved at bottom dead centre of the cam 38, the power supply to the motor 26 can be switched off, the pinch being maintained by the cam 38 which remains at its bottom dead centre position.

The pick-off terminal of one of the potentiometers 36 and 37 is positioned so that the operational amplifier 29 is in balance when the cam 38 is at bottom dead centre. The position of the pick-off terminal of the other of the potentiometers 36 and 37 governs the other rest position of the cam 38 at which the motor 26 stops and the power can be switched off.

It will be understood the cam 38, which is driven by the motor 26 through the gear train 27, drives the cam follower 39 down to pinch the tube 42 between it and the abutment 43 (see Figures 6 and 7). That pinch is maintained whilst the motor 26 is switched off.

The pinch is relieved by a change of the logic input signal which restarts the motor 26 to rotate the cam 38 away from the bottom dead centre to its other rest position at which the motor 26 is switched off again.

Movement of the cam 38 away from bottom dead centre unloads the cam follower 39, the tubing 42 being free to be reopened by the restoring force due to its wall elasticity so that the cam follower is raised by restoration of the tubing 42 to its open state.

Figure 8 shows a four way pinch valve in which this invention is embodied and which is suitable for use as a multi-way pinch valve 22 of the apparatus illustrated in Figure 1. This pinch valve differs from the one way pinch valve described above with reference to Figures 2 to 7 in the following respects. Firstly the cam 48 is oval shaped and cooperates with two diametrically opposed cam followers 49 and 50, one, 50 above and one, 49 below the cam 48. The cam followers 49 and 50 are constrained each in a respective grooved track for movement up and down. There are two juxtaposed lengths 42A and 42B, 42C and 42D between each cam follower 49,50 and a respective adjustable abutment 52 and 53.Thus when the major axis of the oval cam 48 is generally horizontal as is the case in Figure 8, all the four lengths 42A-42D of flexible tubing are free to adopt their open condition whereas they are all pinched between the cam 48 and the adjacent abutment 52,53 when the major axis of the cam 48 is upright. The latter is equivalent to the bottom dead centre position of the cam 38 in Figures 2 to 7 so that the power supply to the motor can be switched off as it can be when the pinch valve is in the condition shown in Figure 8. Thus the 4-way pinch valve shown in Figure 8 provides simultaneous normally-open or normally closed operation for its four lengths 42A-42D of flexible tubing. The arrangement of cam followers 49 and 50 on opposite sides of the cam 48 relieves radial stress on the cam 48 and its support structure.

A PTC thermistor would be fitted in series with the motor 26 of the 4-way pinch valve described above with reference to Figure 8 as an excess current protection device for the motor 26 to save the motor 26 from burn out.

The setting of the potentiometers 36 and 37, particularly of the one that determines -the location of the cam 38,48 when the tubing 42,42A-42D is pinched, can be varied by external adjustment to effect a controlled variation of flow through the pinch valve rather than full closure should that be required for any application of the pinch valve other than its use in a chemical replenishment system as described above. Such a variable flow control may be achieved more simply by replacing the two potentiometers 36 and 37 and the bistate switch 34 by a suitable variably controllable source of DC power.

The facility of switching off the power when the motor 26 is at either end of its range of movement may have to be dispensed with, but the mechanism by which the rotary power output of the DC motor 26 is transmitted to the cam 38 may have sufficient mechanical advantage for the cam 38 to remain in the position it is when the motor 26 is switched off regardless of where that might be.

As mentioned above, all the one-way pinch valves 18-20 may be operated one at a time, or together.

Indeed they may be grouped together, perhaps in pairs, or in pairs of pairs as in the 4-way valve of Figure 8, for either simultaneous normally open or normally closed operation or alternatively for alternate normally open and normally closed operation as required for a particular application. In each of the following examples of such other forms of multi-way pinch valves in which this invention is embodied, the prime mover 24 with a rotary power output shaft 25 is the same as has been described above with reference to Figures 2 to 7.

Figure 9 shows the pinch valve described above with reference to Figures 2 to 7, modified to provide alternate normally open and normally closed operation of a pinch valve having two lengths of flexible tubing. The second length 44 of flexible tubing is located above the cam 38 and between a second cam follower 45 and adjustable abutment 46, the second cam follower 45 again being guided for movement up and down by guide means (not shown). Thus when the cam 38 is in its bottom dead centre position, the lower length 42 of flexible tubing is pinched whilst the second length 44 is open, and vice versa. There is a better balance of the loads on the cam 38 with this version than with the version of Figure 2.

Figure 10 shows a two way pinch valve, similar to that shown in Figure 9 but adapted for simultaneous normally open or normally closed operation, the cam being oval shaped like that shown in Figure 8 as can be seen from Figure 11.

Figure 12 shows a four way pinch valve similar to that shown in Figure 8 but adapted for alternate normally open or normally closed operation of each juxtaposed pair of lengths 42a and 42B or 42C and 42D of flexible tubing, the cam 54 being eccentrically mounted on the disc 28 as is the cam 38 of the pinch valve shown in Figures 2 to 7 and in Figure 9, but being sufficiently long to pinch each juxtaposed pair of lengths 42A and 42B or 42C and 42D at the same time as is the case with the four way pinch valve shown in Figure 8.

Each cam may be designed so that the torque reaction is constant throughout the range of its angular movement.

Claims (17)

1. A pinch valve including a prime mover with a power output, one static reaction member, means operable to support one length of flexible piping so that it extends across said static reaction member, and means driven by said power output and operable to pinch said one length of flexible piping against said static reaction member wherein said static reaction member is mounted adjustably so that its position relative to said prime mover is adjustable to suit different sizes of flexible piping.

2. A pinch valve according to claim 1, wherein said prime mover has a rotary power output.

3. A pinch valve according to claim 2, wherein said means driven by said rotary power output comprise an eccentrically mounted cam.

4. A pinch valve according to claim 3, wherein said cam and said static reaction member are arranged so that the flexible piping is pinched therebetween when said cam is at its bottom dead centre position.

5. A pinch valve according to claim 3 or claim 4, wherein said means driven by said rotary power output include a cam follower which is operatively associated with said cam and guiding means whereby said cam follower is constrained for rectilinear movement to and fro relative to said static reaction member.

6. A pinch valve according to any one of claims 2 to 5, including further means operable to support another length of flexible piping alongside said one length of flexible piping so that that other length of flexible piping extends across a respective static reaction member and said means driven by said rotary power output are operable simultaneously to pinch both lengths of flexible piping against their respective static reaction member.

7. A pinch valve according to any one of claims 3 to 5, or to claim 6 when appended to claim 3, including additional means operable to support another length of flexible piping between said one cam and another static reaction member, said cam being between said static reaction member and the other static reaction member.

8. A pinch valve according to claim 7, wherein said cam is operable to pinch either said one length of flexible piping or the other at any one time.

9. A pinch valve according to claim 7, wherein said cam is operable to pinch both said one and the other lengths of flexible piping at the same time.

10. A pinch valve according to claims 1 to 9, wherein the or each length of flexible piping comprises concentrically mounted tubes of elastomeric material.

11. A pinch valve according to any one of claims 2 to 10, wherein said prime mover is a DC motor.

12. A pinch valve according to claim 10 when appended to claim 3, wherein the cam is driven by the motor via a gear train.

13. A pinch valve according to claim 12, wherein the rotary power output is the shaft of a position indicating potentiometer which is coupled to the DC motor by the gear train.

14. A chemical replenishment system for a chemical process comprising a plurality of storage containers mounted on weigh scale means, each container having an outlet with a respective pinch valve operable to control discharge from the respective container through the respective outlet, and control means responsive to said weigh scale means and operable to control operation of each pinch valve which has one condition in which it is open to allow discharge, the control means being arranged to be responsive to weight measurement by said weigh scale means so that the pinch valves are opened to allow a predetermined amount by weight to be discharged from each of the containers, and are then reclosed, wherein each pinch valve is a pinch valve according to any one of claims 1 to 5, or any one of claims 10 to 13 when appended to any one of claims 1 to 5.

15. A chemical replenishment system according to claim 14, comprising a plurality of bulk chemical storage containers, each having an outlet connected to a respective one of the lengths of flexible piping of a pinch valve according to any one of claims 6 to 9, or any one of claims 10 to 13 when appended to either claim 6 or claim 7.

16. A pinch valve substantially as described hereinbefore with reference to the accompanying drawings and as illustrated in Figures 2 to 7, or Figure 8, or Figure 9, or Figures 10 and 11, or Figure 12 of those drawings.

17. A chemical replenishment system substantially as described hereinbefore with reference to the accompanying drawings and as illustrated in Figures 1 to 8 of those drawings, or modified substantially as described hereinbefore with reference to and as illustrated in Figure 9, or Figures 10 and 11, or Figure 12 of those drawings.