Device for controlling a fluid flow

The invention relates to a device according to the preamble of Claim 1. Such devices are known, for example as a reducing valve by means of which a fluid flow at a certain pressure is converted into a fluid flow at a lower pressure. Similar valves are known to switch a fluid flow on or off. The disadvantage of the known devices is that the adjustment of the pressure to be supplied is very time-consuming or that the additional components required for switching the valve body into an open or a closed position are very complicated.

In order to avoid these disadvantages, the device is designed according to the characterizing part of Claim 1. Adapting one of the sealing surfaces, so that the diference in the distance to the other sealing surface at the inner diameter and the outer diameter changes, makes it possible to change the forces on the valve body and therewith to change the flow through the annular gap. Through this change, the annular gap becomes convergent, parallel or divergent. This causes the pressure pattern in the gap, and consequently the average pressure in said gap, to change. Changing the average pressure in the gap causes the forces upon the valve body to change, and the valve body will move until there is a new state of equilibrium in the forces upon the valve body. This new state of equilibrium means a different position of the valve body, and therefore a different gap width between housing and valve body, so that the fluid flow from the first pipe connection to the second pipe connection changes. This repositioning of the valve body makes it possible to switch the valve from closed to open or vice versa or to adjust the setting of the valve body.

In accordance with one embodiment, the device is designed according to Claim 2. As a result of this, it is easy to change the difference in the distance towards the other annular sealing surface.

In accordance with one embodiment, the device is designed according to Claim 3. As a result of this, it the diaphragm is bent in an easy way.

In accordance with one embodiment, the device is designed according to Claim 4. As a result of this, it easy to control the change in the diaphragm, as only very little volume change at one side of the diaphragm is required to change its shape sufficiently. The pump can be very small and is easy to control and might be only an plunjer inserted at various depths in the chamber at one side of the diaphragm.

In accordance with one embodiment, the device is designed according to Claim 5. As a result of this, when there is a pressure pulsation at one side of the diaphragm, there is a pressure difference between the the ones side and the other side for a short time. As a result of this, the diaphragm is deformed and the valve body moves away from the diaphragm for a short time, and fluid flows away from the one side through the annular gap. After the pressure difference disappears, the valve body moves to the diaphragm, and the annualar gap closes. As a result of this, the pressure pulsations at the one side of the diaphragm are damped.

In accordance with one embodiment, the device is designed according to Claim 6. As a result of this, it is easy to control the device.

In accordance with one embodiment, the device is designed according to Claim 7. As a result of this, the force required to deform diaphragm is independent of the pressure in the valve, so that the device is easier to control.

In accordance with one embodiment, the device is designed according to Claim 8. As a result of this, it is easy to measure the deformation of the diaphragm and through that the setting of the valve.

In accordance with one embodiment, the device is designed according to Claim 9. As a result of this, there is less deformation in the diaphragm as it will bend only very little. This makes the shape of the

annular gap more predictable and the setting of the valve is more accurate.

In accordance with one embodiment, the device is designed according to Claim 10. As a result of this, fixing an actuator to the diaphragm is easy.

In accordance with one embodiment, the device is designed according to Claim 11. As a result of this, it is easy to make a simple hinge between the diaphragm and for instance the housing. In accordance with one embodiment, the device is designed according to Claim 12. As a result of this, it easier to make the pressure in the annular gap more stable .

In accordance with one embodiment, the device is designed according to Claim 13. As a result of this, a stable valve is obtained that is suitable for high viscosity and small flows.

In accordance with one embodiment, the device is designed according to Claim 14. As a result of this, a stable valve is obtained that is suitable for low viscosity and high flows.

In accordance with one embodiment, the device is designed according to Claim 15. As a result of this, it is easier to obtain stable flow conditions. In accordance with one embodiment, the device is designed according to Claim 16, 17 or 18. As a result of this, a fast switching and/or in high volumes easy to produce valve is available.

In accordance with one embodiment, the device is designed according to Claim 19 or 20. As a result of this, a stable and easy to control valve is available.

In accordance with one embodiment, the device is designed according to Claim 21. As a result of this, through the slight deformation of the diaphragm, a larger gap is produced locally between the valve body and the diaphragm. In the situation in which the fluid pressure at the outer periphery of the valve body is greater than that at the other side of the annular gap, because of the locally larger gap the valve body will

move away from the diaphragm, and will remain away from it. In this way a permanent pressure relief is achieved with a slight movement.

The invention is explained below on the basis of a number of exemplary embodiments with reference to a drawing. In the drawing:

Figure 1 shows a diagrammatic section of a valve designed for influencing or switching a fluid flow, in which the valve is shown in a neutral position; Figure 2 shows a diagrammatic section of the valve of Figure 1, in which the valve is closed and set in such a way that said valve remains closed;

Figure 3 shows a diagrammatic section of the valve of Figure 1, in which the valve is closed and is set in such a way that said valve will open;

Figure 4 shows a diagrammatic section of the valve of Figure 1, in which the valve is opened and is set in such a way that said valve will remain opened;

Figure 5 shows a diagrammatic section of the valve of Figure 1, in which the valve is opened and is set in such a way that said valve will close;

Figure 6 shows a diagrammatic section of the valve of Figure 1, in which said valve has been adapted to a second embodiment so that it can be used as a pulsation damper;

Figure 7 shows a diagrammatic section of a diaphragm of a third embodiment of the valve according figure 1;

Figure 8 shows a detail A of the diaphragm of a further adaptation of the valve according to figure 7;

Figure 9 shows a diagrammatic section of a diaphragm of a fourth embodiment of the valve according to figure 1;

Figure 10 shows a detail B of the diaphragm of a further adaptation of the valve according to figure 9;

Figure 11 shows a diagrammatic section of a fifth embodiment of the valve according to figure 1;,

Figure 12 shows a diagrammatic section of a sixth embodiment of the valve according to figure 1; and

Figure 13 shows a seventh embodiment of a valve designed for switching or controlling a fluid flow.

Figure 1 shows a housing 24 having a cylindrical bore 1 with an axis 4. A valve body 6 can move in the bore 1 in the direction of the axis 4 in the housing 24, in the course of which the internal wall of the cylindrical bore 1 and the external wall of the valve body 6 can move relative to each other without leakage occurring. On the one side the cylindrical bore 1 is connected to a first pipe connection 3, and on the other side the bore 1 ends in a chamber 8 which is connected to a second pipe connection 23. Running through the valve body 6 is a channel 17 which connects the first pipe connection 3 and the chamber 8 to each other. On the side opposite the cylindrical bore 1, the chamber 8 has a diaphragm 18 having at the position of the valve body a flexible wall 19 against which a sealing surface 21 of the valve body 6 can be pressed. As a result of this, a gap 20 between the valve body 6 and the flexible wall 19 can become so small that the valve body 6 forms a seal on the flexible wall 19. When the valve body 6 with the sealing surface 21 forms a seal on the flexible wall 19 the connection between the first pipe connection 3 and the second pipe connection 23 is blocked or closed, and when the valve body 6 is at some distance from the flexible wall 19 and the gap 20 is of some size the connection between the first pipe connection 3 and the second pipe connection 23 is open . The valve body 6 is forced by a spring 2 in the direction of the axis 4 towards the diaphragm 18. In order to support the spring 2 on the valve body 6, the valve body 6 has a supporting ring 7. On the side facing the flexible wall 19 or the diaphragm 18, the valve body 6 has a broad edge 22, with the result that the sealing surface 21 has a width B. In the situation shown the flexible wall 19 is parallel to the sealing surface 21. When the fluid pressure in the channel 17 is equal to P and the fluid pressure in the second pipe

connection 23 is zero, a pressure profile 9 shows the curve of the fluid pressure in the gap 20: the fluid pressure in the gap 20 has a logarithmically decreasing curve and at a small width B relative to the diameter of the sealing surface 21 decreases more or less linearly over the width B of the gap 20, and in doing so exerts a force upon the valve body 6 in the direction of the axis 4. The average fluid pressure in the gap 20 in this case is approximately half the difference between the pressure at the beginning and end of the gap 20.

The valve body 6 is also subject to other forces in the direction of the axis 4 through fluid pressure on surfaces of the valve body 6. If the fluid pressure in the second pipe connection 23 is equal to zero, the valve body 6 is subject only to a force exerted by the fluid pressure of the first pipe connection 3 inside the cylindrical bore 1 upon the surface of the valve body 6, viewed in the direction of the axis 4 towards the flexible wall, possibly minus the surface that is visible in the opposite direction. In the example shown the fluid pressure is effective only upon an annular surface of the valve body 6 on the side of the first pipe connection 3. A constant fluid pressure P with a flat pressure profile 5 prevails upon this surface.

So long as the closing forces upon the valve body 6, as a result of the pressure profile 5 and the force of the spring 2, are greater than the oppositely directed forces of the pressure profile 9, the valve body 6 will remain resting against the flexible surface 19. If the oppositely directed forces become greater than the closing forces through the rise in the fluid pressure P in the first pipe connection 3, the valve body 6 will move away from the flexible surface 19, and the gap 20 will become greater. It will be clear to the person skilled in the art that for this to occur the surface of the gap 20 against which the oppositely directed force occurs, and where the average fluid pressure is about half the fluid pressure P in the

channel 17, must be at least twice as large as the surface upon which the fluid pressure P prevailing in the channel 17 causes a part of the closing force. Through the increase in the size of the gap 20, the spring force of the spring 2 will increase, with the result that the closing force becomes greater until the closing force and the oppositely directed force are in equilibrium with each other. Through the enlarged gap 20, fluid will now flow from the first pipe connection 3 to the second pipe connection 23, the fluid pressure P in the channel 17 being dependent upon the spring 2 and the width B of the broad edge 22. The functioning of the valve described above is the same as the functioning of a valve that is known as a reducing valve, in which case changing the force of the spring 2 makes it possible to set the maximum fluid pressure in a fluid system connected to the first pipe connection 3.

The valve of Figure 1 differs from the known reducing valve in that the diaphragm 18 can be deformed to a sloping surface by an actuator 14. On the outside diameter of the diaphragm 18 said sloping surface is generally more or less perpendicular to the axis 4 and acquires an increasing slope as it approaches the axis 4. On the side of the diaphragm 18 facing away from the valve body 6 a chamber 11 is provided for this purpose in the housing 24. The chamber 11 has a diameter that more or less corresponds to or is slightly larger than the greatest diameter of the gap 20. The chamber 11 preferably has a diameter that corresponds to 0.5 to 1.5 times the largest diameter of gap 20. The chamber 11 is connected by a bore 10 to the channel 17, with the result that the fluid pressure in the channel 17 and the chamber 11 is the same. As a result of this and as a result of the limited maximum dimension of the chamber 11, the fluid pressure in the channel 17 has no influence on the shape and/or deformation of the diaphragm 18. An adjusting pin 15 with a shoulder 25 projects through a hole 16 in the diaphragm 18. The

adjusting pin 15 also projects through a hole 13 in the external wall of the housing 24 and can be moved in the direction of the axis 4 by an actuator 14. There are means (not shown) that prevent leakage from occurring through the hole 13 along the adjusting pin 15. Between the wall of the housing 24 and the diaphragm 18 a spring 12 is fitted around the adjusting pin 15, which spring is forced against the diaphragm 18.

The actuator 14 can move the adjusting pin 15 in the direction of the axis 4, and in doing so together with the spring 12 causes an elastic deformation of the diaphragm 18 in such a way that the gap 20, viewed from the channel 17, can become divergent (see Figures 2 and 5) or convergent (see Figures 3 and 4) . A usual diameter of the valve body 6 is between 10 and 50 mm, and the thickness of the diaphragm 18 is approximately 0.5 to 1.5 mm. Owing to the fact that the diaphragm 18 is subject to the same pressure on both sides, it may also be thinner, if desired. The movement of the adjusting pin 15 from the centre position, in which the gap 20 has parallel walls, is at most approximately 250 μm. A movement of approximately 5 - 50 μm in the case of smaller diameters of the valve body 6 is generally sufficient to achieve the effect of changing the shape of the gap 20 described below. The deformation of the diaphragm 18 has an influence on the shape of the gap 20 by changing the slope of the flexible wall 19. Through the change in the shape of the gap 20, the pressure profile 9 changes, and consequently so does the oppositely directed force upon the valve body 6. It is therefore possible, by changing the slope of the flexible wall 19 and the diaphragm 18, to change the forces upon the valve body 6, and consequently also the position of the valve body 6, and therefore also to change the size of the gap 20.

The actuator 14 for the elastic deformation of the diaphragm 18 can be provided in different forms. The actuator 14 can be in the form of a mechanical adjusting device of the adjusting pin 15, for example

with a screw thread or with a lever, it being possible for the adjustment to be made manually or by an electrically controlled drive. Adjustment is also possible by hydraulic means or by electrical means. The construction shown comprises the adjusting pin 15, which is inserted through the hole 16 in the diaphragm 18. The elastic deformation of the diaphragm 18 can also be achieved without the intervention of an adjusting pin 15, by making an actuator 14 exert a force directly upon the diaphragm 18. This can be achieved by exerting purely pressure forces upon the diaphragm 18, or also by fixing on the diaphragm 18 a pin that can be pulled. In order to make it possible for the valve to be adjusted quickly, the actuator 14 can be designed with piezoelectric elements for moving the diaphragm 18 and/or the adjusting pin 15.

In the disclosed embodiment, the diaphragm 18 is shown with a flat surface. It will be clear to the skilled man that the described small deformation of the diaphragm 18 will occur in a similar way if the gap 20 has a conical shape.

Figure 2 shows the valve of Figure 1, in which by movement of the actuator 14 the spring 12 has pushed the diaphragm 18 towards the valve body 6, with the result that the sealing surface 21 is resting upon the internal diameter of the gap 20 against the flexible sealing surface 19. As a result of this, the gap 20, viewed from the channel 17, is divergent and if there is a higher fluid pressure at the first pipe connection 3 than is the case at the second pipe connection 23, no build-up of pressure will occur in the gap 20. Through the force of the spring 2 and the pressure profile 5 upon the valve body, the valve body 6 remains sealing upon the housing 24, and the valve remains closed, irrespective of the pressure in the first pipe connection 3. The pressure in the first pipe connection 3 has no influence because the fluid pressure in the chamber 11 is the same as that in the channel 17 and the fluid pressure in the chamber 11 acts upon the

diaphragm 18 in the opposite direction to that of the fluid pressure upon the valve body 6 when the latter is resting upon the diaphragm 18. The shape of the diaphragm 18 does not change as a result of this when there is an increase or a decrease in the pressure in the channel 17, and the valve remains closed.

Figure 3 shows the valve of Figure 1 when the actuator 14 has just pulled the diaphragm 18 away from the valve body 6. As a result of this, the sealing surface 21 is resting upon the outside diameter of the gap 20 against the flexible sealing surface 19. As a result of this, the gap 20, viewed from the channel 17, is convergent and from the channel 17 build-up of pressure will occur in the gap 20, as shown by a pressure profile 26. Depending on the distance over which the actuator 14 has moved the diaphragm 18 and the convergence in the gap 20, the fluid pressure in the gap 20 will more or less correspond to the pressure in the channel 17. If the counterforce generated by the fluid pressure in the gap 20 is greater than the closing force, the valve body 6 will move away from the diaphragm 18, with the result that the valve opens and the first pipe connection 3 goes into communication with the second pipe connection 23. This situation is shown in Figure 4.

In Figure 4 the valve is open and fluid is flowing through the convergent gap 20 of the first pipe connection 3 to the second pipe connection 23. Through the slight convergence in the gap 20, the flow in the gap 20 causes a pressure profile 27 upon the valve body 6 that differs from the pressure profile arising if the gap 20 has parallel walls 19, 21. Through the slight convergence in the gap 20, the average fluid pressure over the width B is greater than that in the situation where the gap 20 has parallel walls 19, 21. As a result of this, the counterforce upon the valve body 6 is greater than that in the situation where the walls 19, 21 are parallel, so that the gap 20 will remain open through the greater counterforce. The valve being open

is therefore primarily dependent upon the shape of the gap 20. The counterforce can be influenced by changing the shape of the gap 20, and in particular by changing the slope of the flexible wall 19. With changing counterforce the position of the valve body 6 in the housing 24 will also change, because the force exerted by the spring 2 upon the valve body 6 also has to change as a result of the changes in the counterforce. By changing the shape of the gap 20 it is therefore possible to change the position of the valve body 6, and therefore to change the size of the gap 20. Changing the size of the gap 20 changes the throughflow of the fluid through the valve, and it therefore appears to be possible when the valve has been opened to regulate the throughflow through the valve by means of the actuator 14. An adjustable throughflow can be achieved with the valve described here by measuring the result of the changed throughflow through the valve by means of a sensor (not shown) and feeding this value back to the control (not shown) of the actuator 14. An adjustable pressure can be achieved in a comparable way with the valve.

It will be clear that the housing 24, the valve body 6 and the other parts of the valve are shaped in such a way that the flow through the valve and/or the gap 20 in the positions of the valve body 6 occurring takes place without the flow diverging from the walls. This means that edges and corners are rounded and/or bevelled where necessary. Furthermore, the various parts shown diagrammatically here can be composed of or assembled from various parts, and connections, seals and the like provided where necessary.

Figure 5 shows the situation in which the actuator 14 has just changed the shape of the gap 20 to a divergent shape. Through the divergent shape, the flow through the gap 20 acquires a pressure profile 28 which makes the average pressure of the fluid in the gap 20 lower than that in the situation in which the walls 19, 21 of the gap 20 are parallel. The counterforce upon

the valve body 6 has consequently been reduced, and the valve body 6 will move towards the flexible wall 19 and close the valve, with the result that the situation shown in Figure 2 is produced. It will be clear to the person skilled in the art that the closing of the valve is not influenced by the fluid pressure in the first pipe connection 3 and the channel 17 connected to it. This has already been explained above. Furthermore, changes in the fluid pressure in the second pipe connection 23 and the chamber 8 connected to it do not have any influence on the opening or closing of the valve. Although the average pressure in the gap 20 depends partly on the fluid pressure in the chamber 8, the closing force is also increased with increasing pressure in the chamber 8 through the fact that said fluid pressure in the chamber also exerts an influence upon the surface of the broad edge 22 facing the flexible edge. On balance, the resulting force as a consequence of fluid pressures on the valve body 6 is therefore dependent only on the shape of the gap 20.

The exemplary embodiment discussed above illustrates a valve with two pipe connections, in which the first pipe connection 3 is connected to the higher fluid pressure. Embodiments of valves in which the higher pressure is applied to the second pipe connection 23 are also possible. An example of an application for this is the opening of the valve through deformation of the diaphragm 18, after which the valve cannot be closed again until the pressure in the first pipe connection 3 has acquired a comparable value to that of the fluid pressure in the second pipe connection 23. In this application the diaphragm 18 can be deformed by the actuator 14. Instead of moving the inner periphery of the annular diaphragm 18, it is also possible to design the diaphragm as a closed flat disc on which a stub is fixed. Said stub can be moved in the direction of movement of the valve body 6, and also in the plane of

the diaphragm 18. Moving the stub in the plane of the diaphragm 18 causes the flexible wall 19 to acquire an undulating surface, so that openings occur between the sealing surface 21, and the fluid can flow through the gap 20, and the valve body 6 comes away from the diaphragm 18.

In another embodiment of the invention the gap can be made convergent and divergent by designing the valve body with a flexible wall that forms a gap with a fixed wall of the housing. The actuator then forms part of the valve body and is designed, for example, with piezoelectric elements that are connected by means of a cord to a control mechanism.

In another exemplary embodiment of the invention a valve has three pipe connections, it being possible by moving a valve body to connect the first pipe connection to the other two pipe connections or to one of the two pipe connections. In this embodiment the first pipe connection is connected to a channel in the valve body which can move in a housing, the valve body being either able on the one side to form a seal with a first flexible wall of the housing or on the other side to form a seal with a second flexible wall of the housing. The valve body can also come to rest between the two flexible walls with gaps on both sides of the valve body, which gaps can have parallel, divergent or convergent walls through elastic deformation of the flexible walls by means of actuators. By deforming the first flexible wall and the second flexible wall, the valve can be operated in such a way that the valve body seals against either the first flexible wall or the second flexible wall, or neither of the two.

A second embodiment of the invention is shown in Figure 6. This embodiment is comparable to the embodiment shown in the previous figures, though in this embodiment the diaphragm 18 being deformed by the pressure difference between the channel 17 and the chamber 11. This pressure difference arises because the channel 17 and the chamber 11 are in communication with

each other only through a restriction 29, a small opening. As a result of this, changes in the fluid pressure in the channel 17 will not lead to corresponding changes in the fluid pressure in the chamber 11 until after some time. During this time a pressure difference prevails between the two sides of the diaphragm 18, and the diaphragm 18 will deform through this pressure difference.

If a rapid increase in pressure occurs in the channel 17, the diaphragm 18 will deform in such a way that the flexible wall 19 moves away from the gap 20 on the inner diameter of the valve body 6, and gap 20 is divergent, with the result that the valve body 6 moves away from the diaphragm 18 and the valve opens. As a result of this, fluid flows out of the channel 17 and the fluid pressure will decrease, with the result that the diaphragm 18 moves to the valve body again, the flexible wall 19 goes parallel to the sealing surface 21 again so that the gap 20 has parallel walls again, and the valve body 6 seals again against the diaphragm 18. By removing fluid from the channel 17 with a pressure pulse in the channel 17, these pressure pulsations are damped and the valve can be used as a pulsation damper.

Figure 7 shows an embodiment of a valve whereby the flexible wall 19 is formed by a control ring 32 which is connected by a bridge 37 to an outer ring 30. The bridge 37 is created by having a first groove 38 between the outer ring 30 and the control ring 32. The outer ring 30 is fastened to the housing 24 by fasteners 31 such as bolts. The control ring 32 has a thickness 36 which is considerably more than the thickness of the bridge 37 so that the control ring 32 can hinge around the bridge 37 in respect to the outer ring 30. At the inner diameter of the control ring 32 an upper ring 34 and a lower ring 35 form a clamp connection 33 for coupling the control ring 32 to the actuator 14. The upper ring 34 and the lower ring 35 are considerably stiffer than the control ring 35 and hardly deform as a result of the deformation of the bridge 37 or the control ring 32. This means that

the movement of the actuator 14 directly changes the inclination of the control ring 32 and the flexible wall 19 and its required movement is small. Due to the thickness 36 of the control ring 32, which is preferably at least three times the thickness of the bridge 37 the flexible surface 19 forms in radial direction a more or less straight line, which increases the desired effect of the inclination of the control ring 32.

Figure 8 shows in a detail A of the valve of figure 7 an adaptation of the connection between the control ring 32 and the outer ring 30 as shown in figure 7 by providing a second groove 39 opposite to the first groove 38 so creating a more or less cylindrical rim 40, which rim 40 has a thickness that is comparable to the thickness of the bridge 37. In this way a flexible connection between the control ring 32 and the outer ring 30 and the housing 24 is created, which makes considerable inclinations of the control ring 32 possible whereby high stresses in the material of the control ring 32 are avoided.

Figure 9 shows an embodiment of the valve of figure 1 whereby the flexible wall 19 is moved to an inclination by the hydraulic fluid in the chamber 11. A control ring 41 forms the flexible wall 19; the control ring 41 is attached to the outer ring 30, in a similar way as described in figure 7, and at its inner diameter to a disc 43. The control ring 41 and the disc 43 form a separation between the chamber 11 and the channel 17. The chamber 11 is more or less closed and in the chamber 11 a pin 44 can extend at a controlled distance into the chamber 11. The pin 11 can be move by an actuator (not shown) such as a magnet, piezoelectric elements or mechanical or hydraulic actuators. The pin 44 can move in a bore 45 in the housing 24 and between the pin 44 and the housing 24 there is a seal 46. When the actuator moves the pin 44 a stroke S into the chamber 11 the fluid in the chamber 11 presses against the disc 43 and the control ring 41 and so changes the inclination of the control ring 41.

The pin 44 can have a small diameter as the required displacement of the disc 43 and/or the control ring 41 for obtaining the desired inclination of the flexible wall 19 can be very small. For valves with a diameter of the valve body 6 of 15 - 50 mm the diameter of the pin 44 can be 2 - 4 mm and the stroke can be less than 8 mm. Due to the small diameter of the pin 44 the forces required for displacing the pin 44 can be small too so making rapid adjustments possible, whereby the movement of the pin 44 can be controlled by a simple coil .

For reducing the deformation of the control ring 41 there can be a bridge 37 between the control ring 41 and the disc 43 and/or the control ring 41 and the outer ring 30 by applying a first groove 38. For further reducing deformations and/or stresses in the material second groove 39 can be applied similar as shown in figure 8 or as shown in figures 10.

In order to prevent that slow pressure changes lead to pressure differences between the chamber 11 and the channel 17 there can be a pressure equalizing opening 42 in the disc 43.

Figure 11 shows an adaption of the valve of figure 1 which adaption is specifically suitable for fluids of high viscosity or situations whereby the valve has a large diameter. Under these conditions, the fluid flow through gap 20 is laminair and special measures are required to prevent that the pressure in the gap 20 fluctuates due to irregular transition to a turbulent flow. For this reason all ridges and corners of a valve body 49, which is similar to the earlier described valve body 6, are rounded off.

The inside and the outside of the valve body 49 have in the area near the gap 20 a rounding 50. The sealing surface 21 of the valve body 49 along the gap 20 has two concentric ridges, an outer gradual ridge 47 and an inner gradual ridge 51. These ridges 47, 51 are designed such that the flow through the gap 20 follows the contour of the sealing surface 21, also in a recess

48 between the two ridges 47, 51 and does not diverge from the walls. This ensures that the flow remains laminair also in situations when the gap 20 is convergent or divergent and one of the ridges 47, 51 is at a smaller distance from the diaphragm 18 than the other ridge. In this embodiment two ridges 47, 51 are shown at one side of the gap 20. A similar effect will be reached with more ridges, and with ridges on either side of the gap 20. In this situation whereby the flow remains laminair the pressuredrop in the gap gradually over the width of the gap 20. It will be clear that measures must be taken that prevent the flow speed to increase to too high values or that the viscosity changes to too low values as then the flow might be getting turbulent. In this situation, the pressure in the gap might change locally so that the forces on the valve body 49 will change thereby changing its position and the width of the gap 20. This inconstant situation is undesirable. Figure 12 shows an adaption of the valve of figure 1 which adaption is specifically suitable for fluids of lower viscosity or situations whereby the valve has a smaller diameter. The adaptions result in a turbulent flow through the gap 20 over the full area of use of the valve. A valve body 56, which is similar to the valve body 6 of figure 1, is provided at its sealing surface 21 along the gap 20 with two concentric sharp ridges, an inner sharp ridge 55 and an outer sharp ridge 53. Each ridge 53, 55 has a sharp edge 52, which is suitable to seal on the diaphragm 18. Due to the sharp edges 52, the high flow speed and the low viscosity the flow through the gap 20 is turbulent, also when the gap 20 is wider. If necessary, more sharp ridges are provided and/or the sharp ridges are on both sides of the gap 20. Due to the sharp ridges, the flow is also turbulent in a recess 54 between the ridges 53, 55. The result of this turbulence is that the pressure in the recess 54 is more or less constant and independent of flow conditions such as flow speed and viscosity. The pressure of the

fluid in the recess 54 is therefore dependent of the pressuredrop between the inner sharp ridge 55 and the diaphragm 18 and the pressuredrop between the outer sharp ridge 53 and the diaphragm 18. These depend on the inclination, divergence or convergence, of the diaphragm 18 and can be controlled accurately as described earlier. The pressure in the recess 54 controls one of the forces on the valve body 56 and so controls the position of the valve body 56 and the flow through the valve.

In order to predict the flow through the valve accurately it is sufficient to determine the inclination of the diaphragm 18. For this strain gages (not shown) can be glued on the diaphragm. The deformation of the diaphragm 18 can be determined using these strain gages and so the position of the valve body 56.

Figure 13 schematically shows a further embodiment of a valve according to the invention. A cup shaped valve body or poppet 58 can slide over a guide 66 in a chamber 8 that is inside a housing 57. A first pipe connection 3 connects to a channel 17 at the inside of the valve body 58. A second pipe connection 23 connects to the chamber 8. A spring 2 pushes the valve body or poppet 58 to a closed position whereby it can seal against the housing 57 or against a control piston 60. Around the piston 60 the housing 57 has a recess 59 with a recess inner diameter 64. The control piston 60 can move in movement direction M in a seal 67 and has an outer diameter 63. The channel 17 of the valve body or poppet 58 has an inner poppet diameter, which is slightly smaller than the piston outer diameter 63 and the valve body or poppet 58 has a poppet outer diameter 61, which is slightly larger than the recess inner diameter 64. Due to these differences in diameter, there is an overlap on two circular locations between the movable poppet 58 and the housing 57 with the control piston 60.

The overlap of the poppet 58 with the control piston 60 generates an inner flow resistance R ₁ in the

fluid flow from channel 17 to chamber 18 through a gap 65. The overlap of the poppet 58 and the housing 57 generates an outer flow resistance R ₀ in the fluid flow through the gap 65. The inner flow resistance R ₁ is determined by an inner flowopening a and the outer flow resistance R ₀ is determined by an outer flow opening b. If the channel 17 has an inside pressure P ₁ the inner flow resistance R ₁ reduces this pressure to a gap pressure P _g , and the the outer flow resistance R ₀ reduces the gap pressure P _g to an outer pressure P ₀ . The gap pressure P _g determines the position of the poppet 58 and therewith the flow through the valve and this pressure depends directly on the inner flow resistance R ₁ and the outer flow resistance R ₀ and so on the flow openings a and b. These flow openings are determined by the position of the control position 60 and the position of the poppet 58 so that movement M directly controls the flow through the valve.

The control piston 60 needs to have only a very limited stroke. In figure 13 the difference between the inner flow opening a and the outer flow opening b can be limited to 50 - 100 μm, so that the stroke of the control piston 60 can be limited to 0,2 mm. This stroke can be obtained in various ways similar to the means used to deform the diaphragm 18 in the earlier described embodiments. In one embodiment the control piston 60 can be moved by bringing a liquid volume in a chamber (not shown) between the control piston 60 and the housing 57. A control rod is positioned at a certain distance in the chamber and the control piston 60 will move when this distance is changed, more or less similar to the design in figure 9. In a further embodiment he control piston 60 can be moved by using piezoelectric elements. Also in a further embodiment the control piston 60 can have a sloped surface (not shown) at the side away from the annular gap 20. A wedge supports this sloped surface and this wedge can move in a direction perpendicular to the piston movement M and so positions the control piston 60 in the direction M. The wedge can be moved with a screw

that is rotated by hand or by a controlled motor such as a stepper motor. In this way the position of the control piston 60 is accurately known, so that the position of the valve body 58 is accurately known and there with the setting of the valve.

The disclosed embodiments all show how the shape of the gap between a valve body and a housing can be changed to alter the pressure and flow conditions in the gap. The use of deformable materials can also change the shape of the gap, for instance if one side of the gap is made from massive or layered material that under for instance electrical tension expands at its inner diameter more than at its outer diameter. Also two concentric ridges can be used of which the one or the other is forced to expand by applying tension or creating a higher temperature.

The described valves are used for controlling the flow of a fluid and are specifically suitable for switching and controlling the flow of a liquid such as oil.