CA1100119A - Disc valve - Google Patents

Abstract

Abstract of the Disclosure A disc valve having a valve housing with a conduit therethrough and a seal ring mounted to the housing. A disc can be pivoted about a pivot axis that is offset from the main valve axis and perpendicular thereto between an open position and a closed position in which a seating surface of the disc contacts a sealing surface of the seal ring In a sealing plane that is perpendicular to the valve axis. The seating surface of the disc is a conically shaped surface that is concentric with the valve axis when the disc is in the closed position. At least a portion of the sealing surface of the seal ring at the intersection between the sealing surface and the sealing plane has the same conical shape. The seal ring can be deflected by moving the disc beyond the closed position to thereby increase the sealing pressure between them. The seal ring can be aligned with the seating surface of the disc by initially floatingly mounting the ring to the housing, then closing the disc to center the seal ring, and thereafter locking the seal ring to the housing in the centered position.
Opposing faces of the disc are slanted relative to the axis of the conically shaped seating surface.

Description

3~

IMPROVED DISC ~IALVE

The present invention relates to disc or butterfly type valves in which a disc is pivotally disposed within a conduit of the valve defined by a generally cylindrical housing for pivotal movement of the disc between an open position, in which it is generally parallel to an axis of the valve, and a closed position in which the disc is generally perpendicular to the valve axis.
Disc valves as such are presently in wide use. The specific construction of such valves differs widely. One advantageous construction is disclosed and claimed in U.S.
Patent No. 3,442,488, issued May 6! 1969 to Adams. The valve disclosed in that patent includes a disc fitted with a peripheral seal ring and rotatable about an eccentric axis for moving the seal ring into and away from sealing en-gagement with an internal sealing surface of an annular valve seat defined by the housing of the valve. The sealing surface is a conical surface whose axis forms an acute angle with the axis of the valve housing. An improvement to such 2Q a valve and in particular to the construction, alignment and operation of the sealing ring carried by its disc is dis-closed in U.S. Patent No. 4,003,394, issued January 18, 1977 to Adams.
The valves disclosed in the above-referenced U.S.
patents have yielded excellent operating results, that is they assure air tight seals under the most adverse operating conditions such as high fluid pressures and/or temperature, high flow rates, the handling of chem-ically or mechanically abrasive fluids, etc., and they have enjoyed a corresponding commercial success. It is believed that the technological efficiency of such valves is at least in part the result of the particular sealing arrangement employed by them, especially the provision of an angularly offset (with respect to the valve axis) but otherwise conical seating surface in the valve housing and a corres-pondingly arranged seal ring in the disc which assured that 1~ the latter is wedged into sealing engagement with the former when the disc is tilted into its closed position. The wear of the seating surface and/or of the seal ring from pre~
dominantly sliding engagement is thereby reduced or elimi-nated.
This advantageous operating characteris*ic of the valve, however, complicated its manufacture and re~uired, for e~ample, special jigs, tools, and machinery to accura-tely machine the angularly offset, conically shaped seating surface in the housing. This is particularly true for valves of relatively large diameter, say in the in the order of 2~ inches or more where the cost of such jigs, tools, etc, can be a signlficant factor in the overall cost of the finished valve. Similar care had to be exercised in manu-facturing the disc and the seal ring mounted therein. Thus such vaLves are not alwa~s as economical to manuaature as may be desired.
On the other hand, attempts to build disc valves with conical seal rings and seats that are coaxial with the valve axis have met only limited success. Although such .. . .

constructions can sometimes be effective ~or low pressure, particularly in instances in which a perfect seal is not required, they have generally been ineffective for establish-ing air tight seals under adverse operating conditions since even the slightest degree of eccentricity can cause the loss of the seal. Further, such arrangements are effectively limited to disc valves in which the disc acts as a ~lap e.g., in which the disc is pivoted about a pivot axis that is located outside the seal ring diameter. Since such arrangements require a high operating torque for opening the disc against fluid pressure, they are only feasible for low pressure applications.
Generally spea]cing, the present invention provides a disc valve of the type described above, that is one which comprises a valve housing including a conduit through the valve and an eccentrically mounted, pivotal disc that is movable between an open and a closed position. Mounted to the housing is a seal ring which defines a sealing sur~ace at least a portion of which lies in a plane (hereinafter sometimes referred to as the "sealing plane") that is perpendicular to the valve axis. Further, at least that portion has a conical shape whlch is coaxial with the valve axis (as defined by the properly centered seal ring).
A co-operating seating surface on the disc has a portion which has the same conical shape as the portion of the sealing surface at the sealing plane. The disc is sufficiently wide so that it can be moved beyond its closed -~ position (in which the seating surface contacts the sealing surface at the intersection between the latter and the sealing plane), and in which the two portions of the sealing ~3--surface and the seating surface are in mutual alignment, to thereby increase the sealing pressure generated between the two surfaces and ~hus enhance the seal formed by the valve.
To avoid a premature contact between the sealing surface of the seal ring in the housing and the seating surface of the disc, faces of the disc are slanted relative to the axis of the conically shaped portion of the seating surface.
A valve constructed as broadly outlined in the preceding paragraphs has the advantage that the housing ls of an entirely concentric construction. Thus, the valve housing can be more readily manufactured with relatively simple machinery without requiring special jigs and tooling which take into aFcount angular offsets as was the case with some of the earlier discussed prior art valves. The manu-facture of the valve disc and seal ring is similarly sim-plified. Preferably, a simple jig is provided for machining the disc while taking into account the slight slanting of the disc face. The seal ri~g is entirely perpendicular to its axis and therefore requires no jigs for its manufacture.
As a conse~uence a valve constructed in accordance with the present invention can be made at a relatively lesser ccst.
While the present invention provides significant economies in the manufacture of the valve, the operating characteristics of such a valve are excellent and they are further enhanced by constructing the seal ring so that a member thereof which defines the sealing surface can be resiliently de1ected when the disc is moved beyond its closed position to increase sealing pressures and assure an air tight seal even under the adverse operating conditions such as high pressures, temperatures and difficult to handle fluid media.
In accordance with another aspect of the present invention, this is accomplished ~y constructing the seal ring so that it comprises an annular base, the above men-tioned seal ring member and a web interconnecting the two.The base has a given width (in a radial direction) and thickness (in an axial direction) while the sealing member is spaced radially inward of the base and defines the radially inwardly facing sealing surface for engaging the seating surface of the disc. The web is constructed of a resilient material and interconnects the base with the sealing member. It extends in a generally radially inward direction from the base to the sealing member, but is slanted relative to the housing axis so that it is generally perpendicular to the conical surface defined by the above-mentioned portion of the sealing surface at the sealing plane. The web further has a thickness (in an axial direc-tion) which is subs-tantially less than the thickness of the base so that it can be resiliently deflected when an axially acting force is ap~lied to it to thereby effect the above-mentioned deflection of the sealing surface.
Preferably, the cross-section of the sealing surface of the seal ring is curved, preferably arcuately curved (meaning circularly arcuate) having a radius of curvature which is greater, for example by a factor of 1.5:1, than the distance between the intersection of the sealing surface and the sealing plane and the intersection of the center of the web and the base of the seal rlng.
When so constructed, movement of the disc beyond the closed position causes the deflection of the seal ring along a ~ ~r~
~'.~ ~ ~J

circular path having its center at the intersection between the seal ring base and the web. Since the radius of curva-ture of the sealing surface exceeds the radius about which the sealing surface is deflected, the closure of the disc beyond the closed position result in an increased contact pressure between the sealing surface of the seal ring and the seating surface of the disc.
The effectiveness of the seal provided by a valve constructed in accordance with the present invention is further enhanced by an increase in the contact pressure between the seating surface and the sealing surface when the disc is in its closed position and the fluid pressure on either side of the disc is increased. The resulting pressu-re differential slightly deflects the sealing member of the seal ring, together with the web, in one or the other direction, again about the intersection between the web and - the base (which is rigidly clamped to the housing). Such deflection of the sealing member, however, increases tha surface contact and the contact pressure between the sealing surface and the seating surface of the disc thereby en-hancing the seal and thus rendering the valve of the present invention effective for establishing an air tight seal even when it is sub~ected to high pressure differentials.
The contact pressure obtained with the valve of the present invention is thus not only a unction o~ the force with which the disc is closed, that is with which the seating surface presses against the sealing surface due to their relative positions and dimensions, but is further a function of the pressure differential between the two sides .

of the closed discs. In other words, if the pressure , . . .

differential increases the sealing force between the seal ring and the disc also increases, thereby assuring an air tight seal even at very high pressures without requiring the application of correspondingly larger forces to the disc when it is closed to mechanically generate the required contact pressure.
Thus, since it is not necessary to generate such high contact pressure with the closed disc and the assoc-iated actuating mechanism therefor, the pivot axis for the disc can be brought closer to the valve axis, thereby reducing the torque that is required for opening the disc against fluid pressure applied to one side thereof. In the past, it was frequently necessary to provide relatively large eccentricities or tha disc pivot axis to facilitate the generation of the required, relatively high contact pressure between the disc and the seal ring. This had the adverse consequence, however, of corrsspondingly increasing the torque for operating the disc under pressure conditions.
Since the present invention eliminates such requirements, it is now possible to operate the disc with pivot axis eccen-tricities of as little as 1 to 5 mm and normally no more than about 10 mm. This, in turn, enables one to provide smaller valve actuators which correspondin~ly reduces the overall costs of the valve.

To further reduce manufacturing costs, the require-ment to maintain alose tolerances, etc. the presen~ in-vention contemplates to mount khe seal ring in an inwardly -~ opening groove defined by the housing which is dimensioned so that the seal ring can be adjusted~ e.g. moved in a radial direction and by providing means such as a clamping ring for locking the seal ring in any desired relative position in the groove. The seal ring can be centered relative to the seating surface of the disc by loosening the clamping ring, closing the disc so that the seating surface engages the seal ring surface, whereb~ the seal ring is centered relative to the disc, and, thereafter, while the disc is in its closed position, tightening the clamping ring so as to lock the seal ring in its centered position. In this manner, the valve housing as well as the seal ring can be manufactured with relatively loose tolerances and manu-facturing costs can be reduced while a perfect alignment between the seal ring and the co-operating seating surface of the disc is assured.
It is apparent that the present invention provides a disc valve which has operating characteristics and capa-bilities at least as good if not better than those e~hibited by the highest quality prior art valves. In addltion, the disc valve of the present invention exhibit the same sealing characteristics irrespective of whether the upstream or the downstream side of the valve disc only is pressurized. Yet, by virtue oE the present invention, such a valve can be manufactured at a relatively low cost.
The invention is illustrated by way of example, in the drawings, in which:
Figure 1 is a side elevational view, in section, of a valve constructed in accor~ance with the present invention and shows, in dotted lines, the disc of the valve in its open position;
Figure 2 is a fragmentary, simplified side eleva~
tional view, in section, and illustrates the geometric relationships of the valve housing, the seal ring and the valve disci Figure 3 is an enlarged, fragmentary, side eleva tional view which illustrates the sealing arrangement of the present invention in greater detail; and Figure 4 is an enlarged, side elevational view, in section, illustrating in detail the seal ring cross-section and the deflection of the seal ring under axially acting forces.
Referring first to Figure l, a valve 2 constructed in accordance with the present invention generally comprises a valve housing 4 which includes a conduit 6 that extends through the housing. A valve disc ~ is disposed within the conduit and pivotally mounted thereto with a shaft lO that is suitably journalled in the valve housing and that defines a pivot axis 12 for the disc for pivotally moving the disc between its open position, shown in dotted lines, in which ...
the disc is generally parallel to a valve axis 14 and a closed position in which the disc is generally perpendicular -to the valve a~is as is more ~ully described hereina~ter.
The conduit 6 includes a cylindrical section 16 which extends from a ~irst end 18 of the housing towards a second end 20,~an inwardly protruding, tapered section 22 which is disposed intermediate the housing ends, and a second cylindrical conduit section 24 of an enlarged outer dlameter that terminates at the second housing end.
~ An annular recess i5 formed in the inwardly protruding section 22 of the housing, its radially outermost extent is defined by a cylindrical wall 28. A clamping ring 30 is positioned within the second cylindrical conduit _g_ g section 24 and it is secured to the housing with a plurality of axially oriented bolts 32. Preferably, the clamping ring has a slanted inner wall 3~ which slopes from the second housing end towards the annular recess 26 and which has an innermost diameter approximately equal to the innermost diameter of the protrud ng housing section 22. Thus, annular recess together with the portion of clamping ring 30 that extends beyond the cylindrical wall 28 define a radially inwardly open, annular groove 36 in the housing.
Disposed within groove 36 is a seal ring 38 which is constructed as is further described below. It has a base 40 that terminates in a radially outermost, cylindrical wall 42 of a diameter less than the diameter of groove wall 28 so that the seal ring can be adjusted in radial directions within the confines of the groove. For instances in which the seal ring is constructed of a metal or similar material, a gasket ring 44 may be placed between the seal ring base and the inwardly protruding section 22 of the housing so as to prevent the leakage of fluid therebetween when the disc is in its closed position and one or the other side of the disc is pressurized.
The operation of valve 2 illustrated in Figure 1 can now be briefly su~marized. When the valve is to be closed, a valve actuator (not separately shown) coupled to shaft 10 is energized to pivotally move disc 8 about pivot axis 12 in a counterclockwise direction, as indicated by corresponding arrows in Figure 1, from the open position (shown in dotted lines) into the closed position in which the disc is oriented transverse to valve axis 14. In the closed position a sealing plane 46 defined by the theore-~ical line of contact between a seating surface 48 of thedisc and a sealing surface 50 of the seal ring is perpen~
dicular to the valve axis. To open the valve, the actuator is energized to pivot the disc in Figure 1, in the opposite direction until it is again substantially parallel to the valve axis.
Referring now to Figure 2, the detailed cons-truction, position and co-operation of seating surface 48 of disc 8 and sealing surface 50 of seal ring 38 are described.
The seating surface 48 of disc 8 has a conical shape and it is selected so that when the disc is in the closed position, the apex "A" of the (seating surface) cone 52 (shown in dotted lines) is on valve axis 14 and the axis 'IX" of the cone is coaxial, that is coincides with valve axis 14.
Further, the disc is given an excess thickness "T" (measured parallel to cone axis "X") and disc end faces 54, 56 are slanted by an angle~"a" of between 1 to 10 and preferably of no more than about 5 relative to a plane which is perpe~dicular to the housing axis "X".
The end faces 54, 56 of the disc are normally substantially parallel with respect to each other and they are slanted so that slant angle "a" lies in a plane that ;-includes~cone axis "X" and is perpendicular to pivot axis 12. Further, the slant angle is chosen so that the end faces slope away from the (counterclockwise) pivotal closing ~movement of the disc as is clearly illustrated in Figure 2 to avoid a premature contact between the disc and the seal .
rlng. Such premature contact would take place if the end faces were perpendicular to cone axis "X" as is indicated in Figure 2 in dotted lines and identiied with reference ~- ~

numerals 54' and 56', respectively.

If the end faces were not so slanted, the end faces and the seating surface 48 would meet at (imaginary) leading edges 58 and 60 (during movement of the disc from the open to the closed position in a counterclockwise direction). Since the distance from the disc pivot axis 12 to imaginary leading edges 58, 60 is greater than the distance from the pivot axis to the intersection points 62 between sealing plane 46 and seating surface 48 (or sealing surface 50), the leading edges would contact the sealing surace before the disc is in its closed position. To avoid such contact and potential damage to the seal ring, the disc faces 54, 56 are slanted as above described to thereby in effect form recesses in perpendicular disc faces 54', 56' which avoid such premature contact. Moreover, the transition between the end faces and the seating surface is curved as is illustrated as a further precaution against such premature contact.
To facilitate and simplify the further discussion of the application herein, and to simplify claim termi-nology, the orientation of the slant angle "a" as abovedescribed will hereinafter be sometimes referred as a slant "angle trailing the closing motion of the disc" or as a "trailing slant angle".
The detailed construction of seal ring 38 is set forth later on. In its broadest ~orm, however, it may have any cross-sectional profile so long as at least a portion of i~s sealing surface ~0 at the intersection 62 between the sealing surface and the sealing plane 46 has the same conical shape as the conical shape of seating surface 48 of disc 8 at these points. In a preferred embodiment of the invention, such conically shaped portion is defined by a . . . - .
-curved sealing surface which, at point 62, has a tangentthat defines over the full circular extent o~ the seal ring a tangent cone. The tangent cone is the same cone as the cone of which seating surface 48 is a part. Further, the tangent cone has the same orientation as the cone of the seating surface when the disc is in its closed position.
Thus, the tangent cone, like the cone defined by the seating surface has an apex "A" on valve axis 14 and a cone axis "X"
which is coaxial with the valve axis.
It should also be noted that the seating surface 48 of disc 8 and the sealing surface 50 of seal ring 38 are constructed and arranged so when the disc is in its closed position sealing plane 46 intersects the conical seating surface but is otherwise immediately adjacent the (pro-ximate) end face 5~ (upper half of disc in Figure 2) and 56 (lower disc half) and the curved transition between the respective end faces and the seating surface. Thus, there is an additional width of seating surface, identified with reference numeral 64, which is available for contacting the sealing surface of the seal ring. In other words, the seating surface is given an additional width thickness over what is theoretically necessary to establish a seal. By slanting the end faces in the above-discussed Inanner the additional width is provided withou~ correspondingly in-creasing the thickness of the disc (to "T"). The additionalsaating surface width Z4 allows one to increase the contact pressure between the disc and the seal ring as is more fully described below.
Referring now to Figures 3 and 4, the construction of seal ring 38 and its co-operation with valve disc 8 are described in detail. Generally speaking, the seal ring may have a variety of cross-sections, for example, it may have the cross-section shown in Figure 2, and its seal rings surface 50 may have varying configurations so long as it defines the above-described conically shaped sealing surface at least at the intersection between the sealing surface and sealing plane 46. Therefore, the sealing surface may, for example, have a conical shape complementary to that of seating surface 48. One aspect of the present invention, however, contemplates to give the sealiny surface in cross-section, a convex, arcuately curved shape. Furthermore, the sealing surface is defined by a sealing member 66 of the seal ring which is deflectable under axially acting pre-ssure.
Structurally, the cross-section of the seal ring comprises the above mentioned generally rectangular seal ring base 4~ whlch has a width and a thickness so that the base is compressed in seal ring yroove 36 when clamping riny 30 is tightened to prevent the leakage of fluid between the seal ring base and the valve housing 4. If a gasket 44 is used thè thickness of the base i5 such that it slightly exceeds the distance between the opposing~faces of the gasket~and the ¢lamping ring.
Joined to the base is a generally radially in-wardly extending web 70'which has a thickness (in the axial direction~ substantially less than the thickness of the base so as to~render the web relatively flexible. Further, the web is slanted so that it is generally perpendicular to that tangent at the intersection between seal ring surface 50 and the sealing plane 46. Expressed in other words, the web is .

.

, . :. . .

perpendicular to seating surface 48 of the disc when the disc is in its closed position. Lastly, in cross-section the sealing member 66 extends generally perpendicular to the web to either side thereof, somewhat akin to the flange of an I-beam, for example.
Particularly for high temperature applications the seal ring is constructed of a resiliently deformable metal such as steel, stainless steel, berylium, copper or the like. For such applications it is necessary to provide gasket 44 to prevent fluid leakage past the base. For low temperature applications, say for applications in which the maximum temperature does not exceed 150C the seal ring may also be constructed of an elastomeric material such as plastic, rubber or the like of the desired hardness. In such instances, it is normally not necessary to provide a separate gasket 44 since the tightened clamping ring 30 provides sufficient pressure between the seal ring base and the housing to prevent fluid leakage past them. In both in-stances the base, the web and the sealing member are prefer-ably integrally constructed.
The radial width of base 40 is selected so thatthe intersection between the (imaglnary) extension of its radially inwardly facing, cylindrical surface 72 with a center 1ine 74 of the web (which lS perpendicular to the conical seating surface at point 62) defines a center of deflecticn 76 for sealing member 66 and web 70 that is spaced from sealing point 62 a distance "r". Further, sealing surface 50 is convexly arcuately shaped about a center point 78 which lies on a straight line extension of ~web center line 74 and which is spaced from sealing point 62 a distance "R" which is greater than "r", preferably by a ' factor of at leas-t about 1.5:1.
The seat ring 38 constructed as above described assures that the contact pressure generated at sealing point 62 between disc seating surface 48 and ring sealing surface 50 can be increased by moving the disc beyond its closed position. The contact pressure further increases as a function of the pressure differential that may act on the seal ring when the disc is closed whether the pressure differential acts from one side or the other of the seal ring. This results from the fact that the relatively thin and, there~ore, flexible web is connected to the rigidly clamped seal ring base 40 so that an axial force component will swing the web and, therewith the sealing member 66 approximately above a circular pa-th which is centered at point 76.
~` Thus, if pressure Pl acts ~rom the left, as illus-trated in Figure 4, disc 8 is closed and the opposite side is at a lower pressure, say at atmospheric pressure, the forces applied against the lefthand side of sealing member 66~ and web 70 force the two to the right along a generally circular path having its center at point 76 and into the position shown in Figure 4 in dotted lines and identified with the referencé numeral 80. Since the radius of curva-ture "R" of sealing surface 50 is greater than the swing radius "r" of the sealing member, a lefthand ~o~tion 82 (as seen in Figure 4) of sealing surface 50 moves radially inward as is indicated by the dotted lines in Figure 4. In actuality such a radial movement of the sealin~ member is prevent~ed by the closed disc 8; instead, the sealing member 30 ~ and the web are moved slightly to the right and resiliently compressed, thereby correspondingly increasing the contact , , ' : , ' '. ' ' ' : ' ' .

pressure between seating surface 48 and sealing surface 50 as a function of the magnitude of the pressure diferential sides yenerated by Pl.
Accordingly, the greater the pressure differen-tial, which normally increases the danger of a resultingleak between the seal ring and the valve disc, the greater is the contact pressure between the two, thereby preventing such leaks and assuring that the ~alve of the present invention maintains a complete seal irrespective of the pressure which it must seal off.
If the pressure differential acts from the right of the seal ring as seen in Figure 4 by virtue of a fluid pressure P2 which exceeds the pressure on the lefthand side of the ring, the same result is obtained. The pressure differential causes sealiny member 66 and wéb 70 to swing to the left about point 76 into the position indicated by reference numeral 84. By virtue of the above described relationship between "R" and "r" the righthand portion of sealing surface 50 is theoretically moved radially inward as is indicated at 86. Since the disc blocks a radially inward motion, the contact pressure between the seal ring and the disc is again increased in the above described manner.
Lastly, the contact pressure between the ~isc and the seal ring can be increased by pivotally moving disc 8 about pivot axis 12 beyond ltS closed position, that is beyond the position in which cone axis "X" of the conically shaped sealing surface 48 is coaxial with valve axis 14, so that the apex "A" of the cone would fall below the valve axis and below point "~" as viewed in ~igure 2. This is accomplished by selecting the conical shape of seatiny surface 48 relative to the position of pivot axis 12 so that .

.
- : . .

- the dlstance from ~he pivot axis to the sealing point 62 (when the valve is in its normal, theoretically closed position) is less than the distance from the pivot axis to any of the points on the remaining width 64 of the seating surface, such as points 88 (Figures 2-4) and 90 (Figure 2).
If this condition is met, movement of the disc beyond its closed position will resiliently compress sealing member 66 and web 70, thereby increasing the contact pressure. Such movement of the disc beyond its closed position may be accompanied by a slight resilient deflection of the sealing member and the web in the direction in which the disc moves thereby swinging the two about point 76 to the ~ight (as seen in Figure 4) which causes an additional increase in the contact pressure.
In presently preferred embodiments of the in-vention with an offset between pivot axis 12 and valve axis 14 of between 1 to 5 mm, a cone angle "b" (Figure 2) in the range of between about 20 to 70 has yielded good results although under given circums~tances the angle may exceed the stated range so long as the above condition is satisfied.
For many applications the optimal angle is in the vicinity of about 40 and generally it can be ohserved that smaller diameter valves will have larger cone angles and vice versa because of the relative position of shaft axis 12 and, in the case of larger diameter valves, the need for limiting the thickness of the valve disc. Thus, in one example, a valve of a nominal valve diameter of 300 mm may have a cone angle "b" of appro~imately 34 while a valve of a nominal valve diameter of 600 mm may have a cone angle "b" of approximately 25, the valves having an eccentricity between ~. ~

the valve axis and the pivot axis of 2 and 3 mm, respec-tively.

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Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a disc valve of the type having a housing including a valve conduit defining a main axis of the valve, a seal ring carried by the housing and having a sealing surface, a valve disc defined by opposing, spaced apart end faces and a seating surface interconnecting the end faces and arranged for sealingly engaging the sealing surface of the seal ring when the disc is in its closed position, and means for pivotally moving the disc about a pivot axis which is offset from and perpendicular to the main valve axis of the valve between a closed position in which the seating surface engages the sealing surface and an open position in which the disc is generally parallel to the main valve axis, the improvement to the sealing surface and the disc comprising in combination: a sealing surface at least a portion of which defines a conical surface which is coaxial with respect to the main valve axis; the seating surface of the disc having a conical shape which includes the conical shape of said portion of the sealing surface and which is arranged so as to be coaxial with the main valve axis when the disc is in the closed position in which the sealing surface and the seating surface are in mutual contact in a plane perpendicular to the main valve axis; the disc including generally parallel faces which are slanted relative to the axis of the conically shaped seating surface by an angle which lies in a plane that is substantially perpendicular to the pivot axis and includes the main valve axis, the angle being further arranged so that it trails the closing motion of the disc to prevent a premature contact between the disc and the ring as the disc moves from its open into its closed position.

2. A valve according to claim 1 wherein the recesses in the disc faces are defined by generally parallel faces which are slanted relative to the axis of the conically shaped seating surface by an angle which lies in a plane that is substantially perpendicular to the pivot axis and includes the main valve axis, the angle being further arranged so that it trails the closing motion of the disc.

3. A valve according to claim 1 wherein the disc faces are slanted relative to the axis of the conically shaped seating surface by an angle of no more than about 5°.

4. A valve according to claim 1 wherein the housing inludes a groove for receiving the seal ring, the groove having a generally cylindrical, outermost diameter; wherein the seal ring has an outer diameter which is less than the outermost diameter of the groove; and including means for releasably locking the seal ring to the groove; whereby the seal ring can be centered relative to the seating ring by releasing the locking means, closing the disc so as to engage the sealing surface with the seating surface to thereby center the ring relative to the disc, and thereafter tighten-ing the locking means to secure the sealing ring in the desired position.

5. A valve according to claim 1 wherein the sealing surface is convexly curved in the direction of the valve axis, and wherein said portion of the sealing surface defining a conical surface is defined by the tangent to the sealing surface at the intersection between the sealing surface and the perpendicular plane.

6. A valve according to claim 5 wherein the seal ring includes means for resiliently deflecting the sealing surface in response to a pivotal motion of the disc beyond the closed position.

7, A valve according to claim 6 wherein the sealing surface is arcuately curved and has a given radius of curvature "R", and wherein the means for resiliently deform-ing the sealing surface includes means permitting resilient movement of the sealing surface along a generally circularly shaped path having a radius "r" which is smaller than "R".

8. A valve according to claim 7 wherein the ratio between the "R" and "r" is at least about 1.5:10

9. A valve according to claim 1 wherein the pivot axis is offset relative to the main valve axis by no more than about 10 mm.

10. A valve according to claim 9 wherein the pivot axis is offset relative to the main valve axis by between about 1 to about 5 mm.

11. A valve according to claim 1 wherein the seal ring is constructed of a resiliently deformable metal, and including gasket means between the seal ring and the valve housing for preventing the leakage of fluid media therebetween.

12. A valve according to claim 1 whereint he conical surface has an included angle of between about 20° to about 70°.