Not Applicable.
Not Applicable.
The present invention relates in general to valve seals, and, more specifically, to face-to-face sealing in a fluid valve, such as a pneumatic valve.
Face seals are formed in valves when two substantially flat surfaces are selectably brought together to block a fluid flow path. The surfaces may comprise metal or molded plastic, for example. One surface typically includes an orifice which is closed off when the surfaces are brought together. To augment the sealing, an elastomeric seal is typically retained on one surface to contact a valve seat area on the other surface concentrically around the orifice. The seal extends from the one surface and is compressed between the two surfaces during sealing.
An o-ring is a common type of seal used in various types of valves. Most commonly, o-rings are made of rubber or other elastomeric material in an toroidal shape. They are often inserted into an annular groove in a cylindrical surface to form a seal between a moving cylinder and a bore. O-rings are commercially available in many sizes and formed of many different compositions with a wide range of properties (e.g., temperature range, stability in different chemical environments, and elasticity). Due to the extensive use of o-rings, they are manufactured in high volumes. Consequently, the cost of an o-ring seal is low compared to other seals that are produced for more specialized sealing applications.
The use of o-rings in face seals has been fraught with difficulties in finding a method to retain the o-ring reliably and without relatively expensive machining or other manufacturing processes. Lacking an acceptable way of deploying an o-ring, many valve applications have used other seal shapes such as molded rubber discs with enlarged peripheral edges (i.e., an o-ring combined with a flat internal washer). However, such specially molded parts may be five to ten times as expensive as an o-ring.
In order to use a standard o-ring in a face seal, a groove has been formed in a sealing face with undercut sides such that the top of the groove has a narrower transverse width than the bottom of the groove and the o-ring can be trapped within the groove. Inserting the o-ring into the groove can be accomplished by adjusting one or both sides of the groove after inserting the o-ring (e.g., by rolling the edge of a metal valve body in which the groove is formed to close off the top of the groove) or by deforming the o-ring during insertion. However, rolling adds expense to the manufacturing process and can only be performed for metal components. Therefore, cheaper and lighter plastic molded parts cannot be assembled with an o-ring in this way. Also, when rolling an edge of a valve element to trap the o-ring, the groove for the o-ring must be fairly close to the edge of the element. Therefore, the strength of the groove sidewall is limited.
In the case of deforming (e.g., stretching) the o-ring during insertion, the top opening of the groove has to remain a large fraction of the o-ring thickness because the amount of deformation obtainable during insertion is limited. Thus, the retention of the o-ring may be less reliable than desired. Furthermore, the groove dimensions have not been easily matched to the shape of the o-ring, resulting in unoccupied space within the groove. When the valve is pressurized, a high pressure fluid in the valve may enter the unoccupied space. When the valve is later depressurized, the high pressure fluid in the unoccupied space behind the o-ring may dislodge the o-ring from the groove thereby causing the seal to fail.
The present invention has the advantages of providing a low cost, high reliability face seal using an o-ring that avoids the foregoing problems of the prior art. Either machinable metal valve components or moldable plastic valve components can be used, although molded components are preferred.
In one aspect of the invention, a valve assembly comprises a movable valve element having a first face surface. A valve seat is provided having a second face surface for forming a face seal with the first face surface, wherein one of the first face surface and the second face surface includes a cavity sunk into the one face surface. The cavity has a peripheral bearing surface. An o-ring is inserted into the cavity and has an outer edge contacting the peripheral bearing surface. A retainer is secured into the cavity internally of the o-ring, the retainer having a sloped peripheral edge squeezing the o-ring against the peripheral bearing surface such that the o-ring is deformed to substantially fill the cavity between the peripheral bearing surface and the sloped peripheral edge. A portion of the o-ring extends out of the cavity above the one face surface for forming a seal between the first and second face surfaces.
Referring to
The structure for retaining o-ring 16 includes a bowl-shaped cavity 17 with a peripheral bearing surface 18. During assembly, o-ring 16 is inserted into cavity 17 such that its outer edge contacts the peripheral bearing surface. An o-ring retainer 19 is substantially disc-shaped to fit into cavity 17 internally of o-ring 16. Retainer 19 has a sloped peripheral edge 20 for squeezing o-ring 16 against the peripheral bearing surface of cavity 17. The diameter of o-ring 16 is preferably greater than the depth of cavity 17. The average distance between sloped peripheral edge 20 of retainer 19 and the peripheral bearing surface of cavity 17 is likewise smaller than the diameter of o-ring 16. Retainer 19 applies sufficient force to deform o-ring 16 so that it substantially fills the portion of cavity 17 between the peripheral bearing surface and peripheral edge 20. The deformation may additionally increase the extension of o-ring 16 outside of cavity 17 toward valve seat 12. Since the bottom side of o-ring 16 deforms to substantially fill the otherwise open area of cavity 17, it is not expected that any significant amount of high pressure fluid can enter that would tend to dislodge o-ring 16.
Retainer 19 can be attached to movable valve element 11 in any suitable manner. As shown in
In order to avoid potential damage from o-ring 16 contacting any sharp edges, sloped edge 20 of retainer 19 ends in an unsloped (i.e., straight cylindrically-shaped) portion 24. In addition, a chamfer 25 is formed along the top, outside edge of cavity 17. Besides softening the contact edge of cavity 17, chamfer 25 provides a space into which some of o-ring 16 can be deflected when the face surfaces are brought together for sealing.
Sloped peripheral edge 20 preferably forms an angle with respect to the cavity peripheral bearing surface of between about 15° and 45°, and most preferably around 30° to provide optimal retention of o-ring 16. The peripheral bearing surface may be perpendicular to the sealing face, as shown, which allows the valve element to be molded from plastic and used without further modification. Alternatively, a molded plastic element can also be machined to provide a tapered wall or undercut. The sloped edge 20 would preferably be adjusted so that the angle made with the bearing surface remains about 30°.
As shown in
Movable valve elements 38 and 40 include cavities 44 and 45 for receiving o-rings 35 and 36, respectively. Double-ended retainer 39 includes first disc 46 and second disc 47 deformably retaining o-rings 35 and 36 when assembly 32 is clamped together by nuts 42 and 43. Thus, low cost, high reliability sealing is obtained in a control valve with face sealing poppets.