Proportional pinch valve

Abstract

A proportional pinch valve for controlling the pressure of a fluid in a continuous flow system comprises an anvil for pinching a length of a tubing in the continuous flow system, and a drive mechanism including a displacement element for moving the anvil towards the tubing. The anvil is indirectly coupled to the displacement element via an elastic spring element. The elastic spring element provides a defined play (i.e. elasticity) for the anvil at least as long as the tubing is not fully pinched so that displacement of the anvil is force-controlled by the elastic spring element. A method of controlling the pressure of a fluid in a continuous flow system makes use of such a proportional pinch valve.

Claims

1. A method of controlling pressure of a fluid in a continuous flow system, comprising steps of: providing a proportional pinch valve comprising: an anvil for pinching a length of a tubing in the continuous flow system, and a drive mechanism including a displacement element for moving the anvil towards the tubing, the anvil being indirectly coupled to the displacement element via an elastic spring element; the displacement element moving the anvil towards the tubing and pressing the anvil into the tubing to an extent that an effective flow cross section of the tubing is reduced, but a flow through the tubing is not completely blocked; and the elastic spring element providing a defined play for the anvil at least as long as the tubing is not fully pinched so that displacement of the anvil is force-controlled by the elastic spring element in that the force applied to the anvil by the spring element is balanced by an average pressure inside the tubing plus a force to deform the tubing; wherein the displacement element can be displaced into an end position in which the tubing is fully pinched, the displacement element being in contact with the anvil in the end position.

2. The method of claim 1, characterised in that, in response to a back-pressure acting on the fluid flowing through the tubing, pinched surfaces of the tubing are forced apart against a bias of the elastic spring element.

3. The method of claim 1, characterised in that the continuous flow system is a cross-flow filtration system.

4. A proportional pinch valve for controlling pressure in a continuous flow system, the proportional pinch valve comprising: an anvil for pinching a length of a tubing in the continuous flow system, and a drive mechanism including a displacement element for moving the anvil towards the tubing and pressing the anvil into the tubing to an extent that an effective flow cross section of the tubing is reduced, but a flow through the tubing is not completely blocked, the anvil being indirectly coupled to the displacement element via an elastic spring element, the elastic spring element providing a defined play for the anvil at least as long as the tubing is not fully pinched so that displacement of the anvil is force-controlled by the elastic spring element in that the force applied to the anvil by the spring element is balanced by an average pressure inside the tubing plus a force to deform the tubing, further comprising a switch mechanism for switching the driving mechanism between a first mode, in which the anvil is directly coupled to the displacement element, and a second mode, in which the anvil is indirectly coupled to the displacement element via the spring element.

5. The proportional pinch valve according to claim 4, characterised in that the spring element is a coil spring.

6. The proportional pinch valve according to claim 5, characterised in that the displacement element is a leadscrew nut arranged on a leadscrew.

7. The proportional pinch valve according to claim 6, characterised in that one end of the coil spring is supported on the leadscrew nut and the other end of the coil spring is supported on the anvil.

8. The proportional pinch valve according to claim 4, characterised in that the drive mechanism includes an automated drive for displacing the displacement element.

9. The proportional pinch valve according to claim 8, characterised in that the automated drive comprises a stepper motor for displacing the displacement element.

10. The proportional pinch valve according to claim 4, characterised by a support member having one or more receptacles and a cover plate cooperating with the support member for holding the tubing.

11. The proportional pinch valve according to claim 4, characterised in that a length of a front surface of the anvil contacting the tubing to a diameter of the non-pinched tubing is greater than 5 mm.

12. The proportional pinch valve according to claim 4, characterised by a ridge projecting from a front face of the anvil facing the tubing.

13. The proportional pinch valve according to claim 12, characterised in that the ridge extends perpendicular to a longitudinal direction of the tubing.

14. The proportional pinch valve according to claim 4, characterised by a seal, for sealing a free space around the pinched tubing from the drive mechanism.

15. The proportional pinch valve according to claim 14, wherein the seal for sealing the free space around the pinched tubing from the drive mechanism comprises a rubber diaphragm.

16. The proportional pinch valve according to claim 4, characterised by a pin coupled to the displacement element, the pin cooperating with a slot decoupled from the displacement element in order to prevent the displacement element from unintentional rotation.

17. The proportional pinch valve according to claim 4, characterised by a position sensor for detecting at least a home position of the displacement element.

18. The proportional pinch valve according to claim 4, characterised in that the displacement element can be displaced into an end position in which the tubing is fully pinched, the displacement element not being in contact with the anvil in the end position.

19. A proportional pinch valve for controlling pressure in a continuous flow system, the proportional pinch valve comprising: an anvil for pinching a length of a tubing in the continuous flow system, and a drive mechanism including a displacement element for moving the anvil towards the tubing, the anvil being indirectly coupled to the displacement element via an elastic spring element, the elastic spring element providing a defined play for the anvil at least as long as the tubing is not fully pinched so that displacement of the anvil is force-controlled by the elastic spring element, wherein the displacement element can be displaced into an end position in which the tubing is fully pinched, the displacement element being in contact with the anvil in the end position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will become apparent from the following description and from the accompanying drawings to which reference is made. In the drawings:

(2) FIG. 1 shows a proportional pinch valve according to the invention with a loaded tubing but without the front cover plate;

(3) FIG. 2 shows the proportional pinch valve with the loaded tubing and the front cover plate;

(4) FIG. 3 shows the proportional pinch valve with tubing in longitudinal section in a first state;

(5) FIG. 4 shows the proportional pinch valve in longitudinal section with tubing in a second state;

(6) FIG. 5 shows the proportional pinch valve in longitudinal section with tubing in a third state; and

(7) FIG. 6 shows a detail of a variant of the proportional pinch valve in which the anvil has a ridge with a loaded tubing in the second state in longitudinal section.

DETAILED DESCRIPTION OF THE INVENTION

(8) Referring to FIGS. 1 and 2, a proportional pinch valve 10 is shown for controlling pressure of a medium flowing through a flexible tubing 12 made from a soft elastomer material, for example. In the preferred applications, the tubing 12 is a disposable pipe of a single-use component or system, such as a UF/DF cross-flow filtration system.

(9) The tubing 12 is received in opposite receptacles 14 formed on a front side of an annular support member 16. After loading the tubing 12, a front cover plate 18 is fixed to the front side of the support member 16 by screws 20 or other suitable attachment means as shown in FIG. 2. The receptacles 14 are covered by the front cover plate 18, and the tubing 12 is thus fixed in axial and radial directions.

(10) The section of the tubing 12 between the opposite receptacles 14 is exposed to an anvil 22. In particular, the anvil 22 faces the side of the tubing 12 opposite to the side of the tubing 12 which rests against the front cover plate 18. The anvil 22 can be seen in FIGS. 3 to 5, which show the proportional pinch valve 10 in longitudinal section.

(11) The anvil 22 is radially supported in a housing member 24 so as to be axially movable towards and away from the exposed section of the tubing 12. The front surface of the anvil 22 facing the tubing 12 is of such dimensions that the length of the tubing 12 that can be contacted by the anvil 22 is application specific but preferably in the range of 5 to 10 mm. For low pressure applications (less than 1 bar) a longer contact length may be desirable.

(12) A disk-shaped rubber diaphragm 26 is provided to seal the free space 28 of the support member 16 where the tubing 12 is exposed from the internal sliding surfaces of the proportional pinch valve 10, in particular the peripheral surface portion of the anvil 22 engaging the surrounding inner surface of the housing member 24. The outer periphery of the diaphragm 26 is clamped between the front end of the housing member 24 and the opposing surface of the support member 16. The inner periphery of the diaphragm 26 is received in a circumferential groove 30 of the anvil 22.

(13) The anvil 22 is indirectly coupled to a displacement element. In the preferred embodiment shown in the drawings, the displacement element is a leadscrew nut 32 which is arranged on a leadscrew 34. More specifically, the anvil 22 is indirectly coupled to the leadscrew nut 32 via an interposed elastic spring element 36.

(14) The spring element 36 here is a coil spring. One end of the coil spring is placed on a projection 38 at the end of the leadscrew nut 32 facing the back side of the anvil 22 and supported by an adjacent shoulder. The other end of the coil spring is supported by a flange of the anvil 22.

(15) However, instead of a coil spring, it is also possible to employ a gas cylinder or an elastomer member as the spring element 36, for example.

(16) The leadscrew 34 is driven by a stepper motor 40 coupled to an electronic controller (not shown). In principle, the leadscrew 34 could also be driven manually by a handwheel or the like.

(17) The leadscrew 34 and the leadscrew nut 32 are accommodated in the housing member 24 of the proportional pinch valve 10. A thrust bearing 42 resting on the stepper motor casing and surrounding the leadscrew 34 is able to support the axial load of the leadscrew nut 32.

(18) A radially extending pin 44 is fixed to the leadscrew nut 32. The pin 44 cooperates with a slot 46 formed in the housing member 24 and extending in axial direction. The pin 44 extends through the slot 46 and prevents the leadscrew nut 32 from unintentional rotation.

(19) Moreover, the pin 44 has another function. A position sensor 48 arranged on the housing member 24 is able to detect a home position of the pin 44.

(20) The home position of the pin 44 corresponds to the first state of the proportional pinch valve 10, shown in FIG. 3, in which the anvil 22 is in a position not interfering with the tubing 12. In the home position, the spring element 36 is basically relaxed, which means that the anvil 22 exerts no significant pressure, or no pressure at all, on the tubing 12. Accordingly, the tubing 12 is not pinched, and the flow of the medium through the tubing 12 is not restricted.

(21) FIG. 4 shows the proportional pinch valve 10 in a second state in which the tubing 12 is pinched. The stepper motor 40 has driven the leadscrew 34 so that the leadscrew nut 32 has axially moved a distance towards the tubing 12. The anvil 22 is thus pressed into the tubing 12 to an extent that the effective flow cross section of the tubing 12 is reduced. However, the flow is not completely blocked.

(22) It is to be recalled here that the anvil 22 is not directly coupled to the leadscrew nut 32, but to the spring element 36. Accordingly, the pinching of the tubing 12 is not simply proportional to the displacement of the leadscrew nut 32, but controlled by the force indirectly transferred from the leadscrew nut 32 to the anvil 22 via the spring element 36. Since the spring element 36 is resilient, the counterforce of the tubing 12 acting on the anvil 22 can cause a compression of the spring element 36 to a certain extent. As a result, the force that the spring element 36 applies to the anvil 22 is balanced by the average pressure inside the tubing 12 (plus the force to deform the tubing 12).

(23) The spring element 36 is chosen such that significant movement of the leadscrew 34 is required to create the change in force necessary to pinch the tubing 12. As an example, the spring element 36 chosen might be such that the ratio of leadscrew movement to pressure change is at least 10 times higher than in a pinch valve design without a spring element (e.g. if a leadscrew nut would directly displace an anvil). Therefore, using the spring element 36 allows fine tuning of the resulting force acting on the tubing 12 so that the pinching of the tubing 12 can be precisely adjusted.

(24) Using the spring element 36 in the proportional pinch valve design can also make the pressure setpoint more stable. For example, if the upstream pressure is being controlled (as in the case of UF/DF), then an increase in the upstream pressure results in an increasing counterforce on the anvil 22. This in turn compresses the spring element 36 a little further, which allows the anvil 22 to decompress the tubing 12 a little. This decompression of the tubing 12 brings the pressure back to the target setpoint.

(25) Furthermore, due to the increased length of the tubing 12 being pinched by the anvil 22 (as compared to conventional pinch valves), the proportional pinch valve 10 is made more sensitive to the pressure inside the tubing 12, which improves the sensitivity and increases the resolution of the pressure control.

(26) In FIG. 5 the proportional pinch valve 10 is shown in a third state in which the anvil 22 is displaced to a maximum. The tubing 12 is fully pinched, and the flow of medium is interrupted.

(27) According to a first design principle, as shown in FIG. 5, this third state of the proportional pinch valve 10 is characterised in that the projection 38 of the leadscrew nut 32 contacts the back side of the anvil 22 such that the spring element 36 no longer has any influence on the displacement of the anvil 22. This design provides a high security of the flow being pinched off, regardless of the pressure in the tubing 12 or the stiffness of the tubing 12.

(28) According to a second design principle, not shown in the Figures, the third state of the proportional pinch valve 10 where the tubing 12 is fully pinched is achieved just by the force of the spring element 36, i.e. without the projection 38 of the leadscrew nut 32 contacting the back side of the anvil 22. Since according to this design the spring element 36 still allows a defined “play” (i.e. elasticity) of the anvil 22 in the direction away from the tubing 12, the proportional pinch valve 10 can be used as a pressure relief valve. For example, if the maximum working pressure of the filtration system using the tubing 12 is 3 bar, then, by design, when the leadscrew nut 32 is fully displaced (but not contacting the anvil 22), the force exerted on the tubing 12 by the anvil 22 via the spring element 36 is such that medium will be allowed to pass when the pressure in the tubing 12 is above 6 bar. This provides an added level of safety without the addition of a separate pressure relief valve.

(29) According to a third design principle, not shown in the Figures, the proportional pinch valve 10 can make use of both the first and the second design principles. A switch mechanism is provided for switching between a pure displacement-controlled mode, in which the anvil 22 is directly coupled to the leadscrew nut 32, and a force-controlled mode, in which the anvil 22 is indirectly coupled to the leadscrew nut 32 via the spring element 36. The switch mechanism may employ, for example, a power actuated latch/coupling that can directly couple the leadscrew nut 32 and the anvil 22 together, or alternatively, a passive “click-click” mechanism that can be used to directly transmit force between the leadscrew nut 32 and the anvil 22.

(30) FIG. 6 shows a variant of the proportional pinch valve 10 with a differently shaped front face of the anvil 22. In particular, a ridge 50 of small height is provided which extends perpendicular to the loaded tubing 12. The purpose of the ridge 50 is to more effectively use the pressure in the tubing 12 to act on the anvil 22 and hence the spring element 36.

(31) The ridge 50 is useful in cases where a high differential pressure is needed across the proportional pinch valve 10. The problem in these cases is that in the pinched condition of the tubing 12 a significant proportion of the internal surfaces of the tubing 12 are in contact with each other. Accordingly, medium flow is possible only at either edge of the pinched tubing 12. Under these circumstances, sensitivity to the pressure in the tubing 12 is significantly reduced. This problem is overcome by the ridge 50 as it further enhances the already elongated length of pinched tubing 12. Due to the ridge 50 most of the pressure drop is created across the short length of the ridge 50. Therefore, the internal tubing surfaces elsewhere in the pinched section are allowed to not be in contact with each other. In this way, the non-contacting tubing surfaces are subject to the pressure within the tubing 12 and therefore can act on the anvil 22.

(32) The ridge 50 can be either upstream, downstream, in the middle or any other position along the length of the tubing section to be pinched. The position of the ridge 50 can be chosen depending on whether it is important to control pressure upstream or downstream. For example, if upstream pressure is to be controlled, then a ridge on the downstream side of the pinched tube would be used. A universal valve would have the ridge in the middle of the pinched tube.

(33) In case of leaking of the tubing 12, the diaphragm 26 prevents process fluids from contaminating the valve components inside the housing member 24 as it isolates the area where the tubing 12 is pinched from the internal sliding surfaces of the proportional pinch valve 10.

LIST OF REFERENCE SIGNS

(34) 10 proportional pinch valve 12 tubing 14 receptacles 16 support member 18 front cover plate 20 screws 22 anvil 24 housing member 26 diaphragm 28 free space 30 groove 32 leadscrew nut 34 leadscrew 36 spring element 38 projection 40 stepper motor 42 thrust bearing 44 pin 46 slot 48 position sensor 50 ridge