SLIDE VALVE

Abstract: A slide valve has a cylindrical valve housing (1) with at least one opening (2) and a turnable slide (3, 5) for closing and uncovering the opening (2). The valve slide, whose sealing surface is congruent with the valve housing, comprises a body (3) and a sleeve (5) made of a yieldable material and movably arranged on the outside of the body. The outside of the sleeve is made of a material with good sealing properties. The friction between the sleeve (5) and the valve housing (1) is normally higher than the friction between the body (3) and the sleeve (5), such that, as the slide (3) is turned, the body slides inside the sleeve (5) and the sleeve (5) rolls on the inside of the valve housing (1). In this valve, a good sealing is obtained without necessitating great force for operating the slide (3) and without the outside of the sleeve being improperly worn. The principle may also be applied to other valve configurations than a cylindrical valve housing and a turnable slide.

Description: SLIDE VALVE Technical Field The present invention relates to a slide valve for controlling the volume of a flow, comprising a flow duct having a wall with at least one opening, and a slide hav- ing a sealing surface, which is congruent with the wall of the flow duct and which is movable in the flow duct for closing and uncovering said opening. Background Art In petrol pumps there is a need of controlling the volume of the petrol flow. This can be carried out by means of a control valve with a slide which can be set in various positions so as to close the inlet or outlet of the valve to a varying degree. In order to accomplish an accurate control of the volume of the petrol flow, the difference between a com¬ pletely closed opening and a completely uncovered open¬ ing in the valve should correspond to as large a move¬ ment of the slide as possible. Moreover, the valve should be designed such that the flow through the valve may be varied in a desired manner as a function of the movement of the slide. Fig. 1 is a schematic cross-sectional view of a prior-art slide valve which is used to control flows in petrol pumps. The valve has a cylindrical valve housing 1, which is the inlet of the valve. In the wall of the valve housing there is an opening 2. In the valve housing 1 there is also mounted a semicylindrical slide 3 having an arcuate sealing surface 3a, which is congruent with the wall of the valve housing, and a flat boundary sur- face 3b, which defines the opening 2 during closing and uncovering thereof. The slide 3 can be turned by a shaft 4 by means of a motor (not shown) for setting the slide in various positions in relation to the opening 2, there¬ by making it possible to control the flow therethrough. In this prior-art valve, the slide 3 is turned through an equally large angle as is occupied by the opening 2 when the valve is operated from a completely closed position to a completely open position. This means that a high resolution when controlling the volume of the flow can be accomplished. By the sealing surface 3a of the slide being congruent with the wall of the valve housing, a desired flow as a function of the turn¬ ing of the slide can basically be accomplished by design- ing the slide opening in some suitable fashion. A problem in this context, however, is the sealing. A satisfactory sealing between the slide 3 and the opening 2 requires that the sealing surface 3a of the slide 3 adapt very well to the shape of the valve housing 1, which requires very fine work tolerances, which in turn makes the valve expensive. Besides, a good sealing causes a high friction between the slide 3 and the valve housing 1, which means that a great moment is required to turn the slide, which also makes the construction expensive when the valve is powered. Moreover, if the slide is covered on its sealing surface with rubber or some similar material so as to improve the sealing properties, this is worn far too fast owing to the friction against the valve housing and may even be torn apart if there are burrs or the like adja- cent to the opening. Summary of the Invention An object of the invention therefore is to provide a slide valve, which is suited for controlling the volume of a flow, which seals efficiently, which can be operated by applying little force and which besides has a long service life. This object is achieved by a slide valve according to claim 1. Preferred embodiments of the slide valve are defined in the subclaims. According to the invention, the slide valve com¬ prises a flow duct, which has a wall with at least one opening and a slide which is movable in the flow duct for closing and uncovering said opening. The flow duct can form an inlet of the valve and the opening in the wall an outlet of the valve or vice versa. The wall may be flat or bent or be of any other suitable shape. The slide can be moved in a translational motion or in a turning motion. The slide has a sealing surface, which is congruent with the wall of the flow duct. When the slide is moved in the flow duct, it thus connects with the wall and the imaginary extension of the wall through the opening. The slide further comprises a body and a sleeve made of a yieldable material, which is movably arranged on the outside of the body, i.e. on the side which is directed outwards to the wall in the flow duct and which is to close and uncover the opening. When the difference in friction between on the one' hand the sleeve and the wall of the flow duct and, on the other hand, the sleeve and the body is sufficient, the body will begin to slide against the sleeve and the sleeve will begin to roll on the wall of the flow duct. Then there will be no relative motion between those points on the sleeve and on the wall of the flow duct which are in contact with each other. Since the sleeve is arranged on the outside of the body and besides is yieldable, its centre of gravity will follow as the body moves, thereby changing the shape of the sleeve. This function of the valve may also be described as the mov- ability of the slide being made up of a primary movabi- lity of the body and a secondary movability of the sleeve in the same direction of movement, where the secondary movability of the sleeve is conditioned by the primary movability of the body. By the valve having this function, the outside of the slide can be coated with a material having good seal¬ ing properties, without any risk of this material being torn apart. When the sleeve rolls on the wall of the flow duct, the wear on the outside of the slide will also be less significant than in the case where the slide slides against the wall of the flow duct. Moreover, the required operating force will be smaller than the one required in the prior-art valve to provide a good sealing, since the body slides against the inside of the sleeve with low friction. Because the actual body is not subjected to wear exerted by the wall of the flow duct, the demands placed on the durability of the body will be lower and therefore it may be made of other materials than tradi¬ tional ones, for instance it may be moulded of plastic. The above-mentioned difference in friction which results in the sleeve rolling on the wall of the flow duct can, but need not, be present all the time. For instance, it may arise under certain operating condi¬ tions only, such as if the outside of the sleeve catches some irregularity in the wall of the flow duct, thereby increasing the friction between the sleeve and the wall of the flow duct. However, the body, the sleeve and the wall of the flow duct are preferably so designed that the friction between the sleeve and the wall of the flow duct is higher than the friction between the sleeve and the body. For example, the wall of the flow duct and the body can be made of different materials or with different sur- face properties, which makes them obtain different fric- tional coefficients. However, the sleeve may suitably have different friction properties on the outside and on the inside, the frictional coefficient on the outside being higher than that on the inside. It goes without saying that different friction properties of the body and the wall of the flow duct may also be combined with dif¬ ferent friction properties of the inside and outside of the sleeve. The different friction properties of the inside and outside of the sleeve can be achieved by the sleeve being made of different materials on the outside and the inside. For example, the sleeve may on the outside be made of metal or plastic or some other material having a low frictional coefficient, and on the outside be made of rubber or thermoplastic or some other material hav¬ ing good sealing properties and a high frictional coef- ficient. A design of the sleeve that has been tested with satisfactory results is an inner part of Stanyl ® , on which rubber has been vulcanised. A different technique of achieving higher friction between the sleeve and the wall of the flow duct than between the sleeve and body is to arrange the body and the sleeve in such manner, that the flow, preferably a flow of liquid, can enter between the body and the sleeve and reduce the friction between these parts. The body can be formed with, for instance, grooves such that the sleeve does not abut against the entire body. Alterna¬ tively, the body can be made hollow and its circumferen¬ tial surface may be perforated so that flow can enter the body and then escape into the space between the body and the sleeve. This technique of changing the friction also results in an improved sealing since the sleeve is press¬ ed harder by the flow against the wall of the flow duct. A special advantage of making it possible for liquid to enter between the body and the sleeve is that the dif¬ ference in friction which leads to the sleeve rolling on the first element may exist merely when the liquid is pressurised because a pump is operating. When the pump is switched off and the pressure on the liquid disappears, the frictional relationship between on the one hand the sleeve and the first element and, on the other hand, the sleeve and the body can be changed such that, as the body is moved in relation to the first element, there is no relative motion between the body and the sleeve, but the sleeve slides against the first element. The fact that this occurs sometimes is an advantage since a different part of the sleeve will then abut against the opening in the valve housing where burrs and the like that may affect the sleeve can be found. Of course, this way of accomplishing the difference in friction can be combined with other techniques as described above. To permit the movement of the body within the sleeve, the inner perimeter of the sleeve is preferably greater than the outer perimeter of the body. Alterna¬ tively, the sleeve could, however, be elastic, in which case its inner perimeter could be equal to the outer perimeter of the body. With a view to achieving good sealing properties but still not risking that the sleeve becomes flabby on the body or gets out through the opening, the sleeve may have an inner part which is more rigid than the outer part. In a preferred embodiment, the flow duct is a cylin- drical valve housing, in the circumferential surface of which the opening is formed. Furthermore, the slide is turnably mounted in the valve housing on a shaft arranged in the centre of the valve housing. The body preferably is so designed that the centre of the valve housing is located inside the outer perimeter of the body when the slide is mounted in the valve housing. The shaft is preferably attached to the body because this makes the slide easier to construct. It is often desirable to have a large opening in the valve housing and therefore the sealing surface of the slide preferably extends through a large angle, up to 180°, in the valve housing. It may have the approximate cross-sectional shape of a sector of a circle, preferably a semicircle. However, the flow duct and the slide may have other shapes. The wall of the flow duct may, for instance, be in the form of a plane and the slide may have the shape of a rectangular parallelepiped which moves in a transla- tional motion across the plane for closing or uncovering of the opening. The valve may be used for gas as well as liquid. It is suited for all flow control valves, in which a good sealing in combination with a small amount of operating force is important. A specific intended application is in petrol pumps, where two valves according to the inven¬ tion can be used to mix 95-octane and 98-octane fuel to 97-octane fuel. Brief Description of the Drawings The present invention will now be described by means of an embodiment and with reference to the accompanying drawings, in which Fig. 1, as discussed above, is a schematic cross- sectional view of a prior-art valve; Fig. 2 is a cross-sectional view and illustrates schematically an embodiment of the present invention in a first position of the valve slide; Fig. 3 is a side view and illustrates schematically the same embodiment of the invention as in Fig. 2; Fig. 4 is a cross-sectional view and illustrates schematically the same embodiment of the invention as in Fig. 2, but in a different position of the valve slide; Fig. 5 is a cross-sectional view and illustrates schematically the same embodiment of the invention as in Fig. 2 and the same position of the valve slide as in Fig. 4, but under different operating conditions; and Fig. 6 is an exploded view of an example of how the invention has been accomplished in practice, the valve housing being shown with a cut-away portion. Description of a Preferred Embodiment of the Invention Fig. 2 shows a valve, which has a cylindrical valve housing 1, which constitutes the inlet of the valve, and an opening 2 in the wall of the valve housing, which con- stitutes the outlet of the valve. In the valve housing there is a slide 3, which can be turned, by means of a motor (not shown), about a shaft 4 arranged in the centre of the valve housing. The slide has essentially the shape of a semicylinder. It has a sealing surface 3a which is congruent with the wall of the valve housing and a bound¬ ary surface 3b, which connects the terminal points on the sealing surface. By turning the slide, the outlet 2 can be closed or uncovered to a varying extent. The valve is adapted to be arranged in a petrol pump for controlling the flow of dispensed petrol. The slide comprises a body 10, which is hollow and open at its ends. The shaft 4 is attached to the body 10. The body 10 further has perforations 8 in the rounded part of the circumferential surface. It is surrounded by a sleeve 5. The sleeve 5 is congruent with the body 10 and its inner perimeter is somewhat longer than the outer perimeter of the body 10, which results in some slack in the sleeve. The sleeve consists of a yieldable, but still relatively rigid inner ring 6 made of plastic which yields low friction as the body moves in relation to the sleeve 5. On the outside of the ring there is an outer layer 7 of rubber, which yields high friction against the wall of the valve housing and good sealing properties of the slide. Further the body may suitably have retaining means, for instance flanges, which retain the sleeve in the longitudinal direction on the body 3. Fig. 3 is a side view of the cylindrical valve hous¬ ing 1 and the opening 2. The opening 2 has a first por¬ tion 2a, in which the width of the opening increases linearly in the circumferential direction of the valve housing, and a second portion 2b having a constant width in the circumferential direction. This design of the opening renders it possible to control even small flows accurately, which is advantageous when a predetermined volume is to be dispensed, for instance in a cash-operat¬ ed petrol pump. The function of the valve, and especially the sleeve, under normal operating conditions, i.e. when the pump is operating in this embodiment, is apparent from Figs 2 and 4, in which reference points A1-A3, B1-B3 and C1-C3 have been marked on the slide, the sleeve and the valve housing, thereby making the function more obvious. Fig. 2 shows the valve slide in a first position, in which it closes the outlet 2. In Fig. 2, the reference points A1-A3, B1-B3 and C1-C3, respectively, are posi¬ tioned in front of each other. When the slide is turned to the position shown in Fig. 3, in which the outlet 2 is partly open, the body 10 turns inside the sleeve 5, such that the points Al-Cl are moved in relation to the points A2-C2 in the sleeve 5 and A3-C3 in the valve housing 1. Since the sleeve 5 is just slightly larger than the body 10, its centre of gravity will follow the body 10 in the turning motion. Owing to the high friction between the outside of the sleeve and the inside of the valve housing 1, the sleeve will however roll, without slipping, on the inside of the valve housing, the point B2 on the sleeve 5 and the point B3 on the valve housing 1 having the same relative position before and after turning of the slide. This also applies to the points C2 and C3. After the turning, the points A2 and A3 are no longer in contact with each other, but the point A2 has been moved inwards in the valve housing 1. During turning of the slide, the outside of the sleeve 5 is thus not rubbed against the inside of the valve housing, but the outside of the sleeve 5 just moves into or out of contact with the inside of the valve housing. The outside of the body slides against the inside of the sleeve, but with low friction. With this sleeve, a reliable sealing of the outlet of the valve is thus effected, without necessi¬ tating a great moment for turning the slide. Fig. 5 illustrates what happens during turning of the slide from the position shown in Fig. 2 to the posi¬ tion shown in Fig. 4, when the pump is not in operation and thus no pressure is exerted on the petrol in the valve. In this case, the sleeve 5 is pressed against the valve housing 1 with less force, the friction between the sleeve 5 and the body 10 being greater than the friction between the sleeve 5 and the valve housing 1. When the body turns, it therefore entrains the sleeve by means of friction coupling. After the turning, the points Al and A2, Bl and B2 and Cl and C2, respectively, are still in contact with each other. However during turning, the sleeve 5 slides against the valve housing 1, such that the points A2 and A3, B2 and B3 and C2 and C3, respec¬ tively, are offset relative to each other. When normal operating conditions are restored, another part of the sleeve 5 will thus be in contact with the valve housing 1. Fig. 6 shows an example of how the valve has been accomplished in practice. A cylindrical valve housing 1 with an opening 2 is part of a valve assembly 11. From the valve housing 1 extends a bore 12 in the axial direc¬ tion through the valve assembly 11 to a circular space 13, which is adapted to receive a stepping motor (not shown) . The valve slide 3 comprises a body 10 and a sleeve 5. The body 10 is essentially semicircular in cross-sec¬ tion. In the rounded part corresponding to the sealing surface of the slide, perforations 8 are formed, which make it possible for petrol in the body 10 to escape between the body and the sleeve 5. The body further has two flanges 14 for retaining the sleeve 5 and a shaft- retaining portion 15, in which a shaft 4 is attached by means of a pin 16 which is arranged to extend through the shaft-retaining portion 15 and through a transverse hole 17 in the shaft 4. The shaft 4 is here shown as a shaft which can be rotated manually. It may be replaced by an output shaft from a stepping motor which is arranged in the space 13. Finally the sleeve comprises a cover 18 which is snapped into the body 10 by means of two resi- lient legs 19 provided with hooks. The cover 18 has two lugs 20 which serve as retaining means for the sleeve. The cover is perforated such that liquid can penetrate into the body and further out through the perforations 8. The valve in Fig. 6 functions in the manner described above with reference to Figs 2-5.

Claims: CLAIMS 1. A slide valve for controlling the volume of a flow, comprising a flow duct having a wall (1) with at least one opening (2), and a slide (3, 5, 10) having a sealing surface (3a), which is congruent with the wall of the flow duct and which is movable in the flow duct for closing and uncovering said opening, c h a r a c - t e r i s e d in that the slide comprises a body (10) and a sleeve (5) made of a yieldable material, which is movably arranged on the outside of said body. 2. A slide valve as claimed in claim 1, wherein, at least under certain operating conditions, the sleeve rolls on the wall of the flow duct (1) and the body (10) slides in relation to the sleeve ( 5 ) while the slide moves in the flow duct. 3. A slide valve as claimed in claim 1 or 2, where¬ in the body ( 10), the sleeve ( 5) and the wall of the flow duct ( 1 ) are so designed that the friction between the sleeve (5) and the wall of the flow duct (1) is higher than the friction between the body ( 10) and the sleeve (5). 4. A slide valve as claimed in claim 1, 2 or 3, wherein the outside of the sleeve (5) has a higher fric¬ tional coefficient than the inside thereof. 5. A slide valve as claimed in any one of the pre¬ ceding claims, wherein the sleeve (5) has an inner part and an outer part, and the inner part is more rigid than the outer. 6. A slide valve as claimed in any one of the pre¬ ceding claims, wherein the inside of the sleeve (5) is made of metal or plastic. 7. A slide valve as claimed in any one of the pre- ceding claims, wherein the outside of the sleeve (5) is made of rubber or thermoplastic. 8. A slide valve as claimed in any one of the pre¬ ceding claims, wherein the inner perimeter of the sleeve (5) is longer than the outer perimeter of the body (10). 9. A slide valve as claimed in any one of the pre- ceding claims, wherein the cross-sectional shape of the slide (3) is essentially a sector of a circle. 10. A slide valve as claimed in claim 9, wherein the cross-sectional shape of the slide (3) is essentially a semicircle. 11. A slide valve as claimed in any one of the pre¬ ceding claims, wherein the sleeve (5) and the body (10) are so designed that the flow can enter between the sleeve and the body. 12. A slide valve as claimed in claim 11, wherein the body is hollow and has perforations (8) in its cir¬ cumferential surface. 13. A slide valve as claimed in any one of the pre¬ ceding claims, wherein the flow duct is a cylindrical valve housing, in whose circumferential surface said opening is formed, and wherein the slide is turnably mounted on a shaft in the centre of the valve housing. 14. A slide valve as claimed in claim 13, wherein the shaft (4) is attached to the body (10).

Inventors: LARSSON BENGT, SVENSSON VIVEKA, LARSSON, BENGT, SVENSSON, VIVEKA
Applicants: DRESSER WAYNE AB, LARSSON BENGT, SVENSSON VIVEKA, LARSSON, BENGT, SVENSSON, VIVEKA
Application year: 1997
Main classification: F16K7
IPC codes: B67D5, F16K5