WO2002033299A1

WO2002033299A1 - Optimized sealing surface for a valve

Info

Publication number: WO2002033299A1
Application number: PCT/FI2001/000877
Authority: WO
Inventors: Kai Laitinen; Hannu Itkonen
Original assignee: Metso Field Systems Oy
Priority date: 2000-10-16
Filing date: 2001-10-10
Publication date: 2002-04-25
Also published as: FI20002279A; AU2001295639A1; FI113396B; FI20002279A0

Abstract

The present invention relates to a structure of valve sealing surfaces. The invention is characterized in that lineal contact length of the sealing surface (2) of a valve sear ring (1) and a valve plug member in direction of their mutual sliding and/or continuous sliding distance of the sealing surfaces are optimally reduced in order to avoid wear, especially galling of the sealing surfaces (2). This can be achieved for instance by means of a structure wherein the continuous sealing surface (2) of the seat ring (1) or the valve plug member is interrupted by means of recesses, grooves or concavities in such a way that no leakage passageways are formed when the valve is in its closed position.

Description

OPTIMIZED SEALING SURFACE FOR A VALVE

The present invention relates to the structure of valve sealing surfaces. The valve may be a ball valve or any other type of valve, the sealing surfaces of which being in a sliding contact with each other.

A lot of different solutions have been developed in order to improve sealing properties of a valve, which solutions have been directed mainly to material composition of the sealing surface, e.g. to the use of low-friction materials, as is taught in FI patent publication No. 68,715 and US patent publication. No. 5,108,813.

Galling, also named scuffing or severe wear refers to a wear phenomenon wherein surfaces being in a sliding contact with each other are damaged quite rapidly. Typi- cally, galling becomes evident as a loss of material from the surfaces in the form of relatively large chips leaving pits and grooves on the damaged surfaces. Previously no attempts have been made to prevent severe wear, particularly galling of sealing surfaces by modifying the structure of a valve sealing surface.

Tests have shown that galling in a sliding contact is caused by frictional heat. Previous experiments have indicated that galling depends only on surface pressure and sliding velocity, but in fact it is also affected by the overall sliding distance and a new parameter, below named lineal contact length. This new parameter has a significant impact on the distribution of the frictional heat on the sliding surfaces. Thus, in addition to information of surface pressure and velocity, determination of the galling tendency of a given contact geometry also requires information of lineal contact length and overall sliding distance, when the latter considerably exceeds the lineal contact length.

The effect of the overall sliding distance and the lineal contact length can be explained e.g. by assuming that a smaller object is sliding on a larger stationary surface. Herein, sliding generates frictional heat and the overall sliding distance affects the total amount of heat being generated. In other words, the longer the distance said surfaces are sliding against each other the higher the temperature of the smaller moving object will increase, until the amont of heat transfered to the environment reaches a balance with generated frictional heat. On the other hand, temperature increase at a given stationary point will start, when a leading edge of the sliding object passes said point and ends when trailing edge of the sliding object leaves said point. This will result in the fact that the longer the lineal contact length of the sliding object, i.e. the dimension of said object in the direction of sliding is, the more it will heat up said stationary point.

Galling of surfaces is on one hand caused by the temperature increase of the smaller surface caused by long sliding distances and, on the other hand, by local heating of the stationary surface and of thermal expansion and concentration of load resulting thereof. Assuming static conditions and normal materials, the effect of the lineal contact length on the galling conditions can be determined from equation:

PVL" = galling factor

In this equation P is the surface pressure, Vis the sliding velocity, L is the lineal contact length and n is an exponent having a value greater than 1. As galling is crucially dependent on the lineal contact length, it is advantageous to minimize the value of the equation PVL" in order to avoid galling.

For instance in ball valves, the lineal contact length varies along the periphery of the seat ring so that this parameter has its largest value at two opposed parts of the seat ring, namely, at those lines that intersect the center axis line orthogonally and are drawn tangentially past the inner edge of the sealing surface, and decreases gradually in either direction from these lines so that the lineal contact length is zero at the intersection of the valve member center axis and the outer edge of the sealing surface, while a second minimum value is reached at a line passing through the center point of the seat ring and intersecting the central axis at right angles. It is an object of the present invention to avoid wear, particularly galling, of sealing surfaces in valves by virtue of a structure of the sealing surfaces achieved by way of optimally reducing the lineal contact length between the sealing surfaces of the seat ring and the valve plug member in the direction of their mutual sliding and/or the continuous sliding distance of the sealing surfaces in order to avoid wear of the sealing surfaces, particularly in regard to galling.

In ball valves, a portion of the valve seal is in a continuous contact with the valve plug member, i.e. the valve ball, thus constituting a long sliding distance of the seal during the opening and closing of the valve, whereby the frictional heating becomes substantial. This continuous contact can be interrupted by arranging recesses on the surface of the valve plug member in the form of, e.g., dents, grooves or concavities, however, without causing leakage passageways when the valve is in its closed position. These recesses assure cooling of the seat ring surface when said surface slides over them, whereby the galling tendency of the seat ring surface is reduced.

In ball valves, the lineal contact length is the length across the sealing surface of the seat ring. This length can be interrupted by arranging recesses, grooves or concavities into the sealing surface of the seat ring, however, without causing leakage pas- sageways when the valve is in its closed position. The shape of the recesses, grooves or concavities can be freely selected with the provision that they do not act as such leakage passageways. The closer such recesses, grooves or concavities are located to each other in the direction of motion, the higher their effect will be. At the same time, however, the load bearing surface area must be kept sufficiently large.

The lineal contact length across the seat ring may also be reduced by reducing the width of the seat ring. However, no significant benefit is attained if the width of the seat ring is reduced over the entire periphery of the seat ring. This is because reduction of the seat ring width also reduces the area of the sealing surface, whereby the surface pressure, i.e. the value of term P in the equation PVL" increases. Hereby the value of the equation would not decrease significantly. However, a significant benefit is attainable if the surface area of the seal is minimized only at portions most suscep- tible to galling while keeping the width of the sealing surface unchanged at the rest of the seal. This finding forms the basis of a second preferred embodiment of the invention.

According to a further embodiment of the invention reduction of the lineal contact length of the sealing surface of a ball valve is implemented by dividing the sealing surface of the seat ring into a plurality of concentric rings.

Other features of the invention will be evident from the appended dependent claims.

Next, the invention will be described in greater detail with reference to attached drawings, wherein

FIG. 1 shows a planar view of a seat ring of a ball valve;

FIG. la shows a cross section of the seat ring taken along line I-I;

FIG. 2 shows an exemplary embodiment of a sealing surface structure according to the invention;

FIG. 3 shows a second exemplary embodiment of a sealing surface structure according to the invention;

FIG. 4 shows a third exemplary embodiment of a sealing surface according to the invention;

FIG. 4a shows a cross section of the seat ring of FIG. 4 taken along line II-II;

FIG. 5 shows diagrammatically in a side view an exemple of portions of the sealing surface of a valve plug member, into which a structure according to the invention can be arranged; and FIG. 5a shows a right-hand view of the valve plug member of FIG. 5.

The drawings refer to a seat ring 1 and a valve plug member 8 of a ball valve, and to a wear, especially a galling preventing structure according to the invention formed at their sealing surfaces 2 and 9, respectively. FIG. 1 shows by horizontal lines, how lineal contact length of a sealing surface of a seat ring varies at different points along periphery of the seat ring. The lineal contact length is longest at those two horizontal lines 3 being in contact with the inner edge 2a of the sealing surface 2, and dicreases on moving to either side from these horizontal lines 3 so that the lineal contact length bis zero at those two points where the center axis line 4 intersects the outer edge 2b of the sealing surface 2 and reaches another minimum value at the horizontal dashed line 5 passing through the center point of the seat ring 1. The valve plug member, i.e. the valve ball rotates around the center axis line 4 in a direction indicated by arrow 6.

In FIG. 2 is shown an exemplary embodiment of a structure, wherein the lineal contact length of the sealing surface 2 in its sliding direction is minimized. In the shown structure, the continuous sealing surface 2 is interrupted by means of dents, grooves or concavities 7 shaped and located so as not to cause leakage passageways on the sealing surface 2 when the valve is in its closed position. In the embodiment shown in FIG. 2, the grooves or concavities 7 are formed by a plurality of elongated recesses disposed in a dense pattern but spaced apart from each other. They may be aligned, e.g., in a plurality of rows spaced apart from each other and generally oriented parallel to the center axis line 4. In the embodiment shown in FIG 3, the recesses 7 have a round shape and they are arranged in such a mutual pattern that the sliding direction of between the sealing surface 2 and the valve plug member can be chosen freely. Thence, the axis 4 of rotation of the valve plug member can be oriented in any direction, i.e. turned 0° to 180° from the shown position around the center point of the sealing surface. Preferably, the grooves or concavities 7 are located slightly staggered relative to each other in the direction of movement, e.g., as shown in the enlarged partial view of FIG. 2 or 3. Of course the grooves or concavities 7 may have another shape and arranged in a different way provided that no leakage passageways are created. According to a second embodiment, the lineal contact length is minimized by modifying the shape of the sealing surface 2 itself so that the width of the sealing surface is smaller at those areas where risk of galling generally is greatest.

According to a third embodiment, the sealing surface 2 of the seat ring 1 is divided into a number of concentric rings 2c, e.g., as shown in FIGS. 4 and 4a, wherein the sealing surface 2 is divided into three concentric rings 2c by means of two concentric annular grooves 7a.

Also the sealing surface 9 of the valve plug member 8 can be provided with similar dents, grooves or concavities 7 as those at the sealing surface 2 of the seat ring 1, either together with the grooves or concavities 7 of the seat ring or simply alone. The grooves or concavities 7 of the valve plug member 8 are primarily located at areas which will be in contact with the sealing surface 2 of the seat ring 1 during operation of the valve.

To those skilled in the art it is obvious that a lot of modifications can be made to the above-disclosed structure without departing from the scope and spirit of the inven- tion. The appended drawings serve only to elucidate and not to limit the invention. The scope of the invention is defined in the appended claims.

Claims

Claims:

1. A structure of sealing surfaces (2, 9) of a valve, characterized in that lineal contact length between sealing surfaces (2, 9) of a valve seat ring (1) and a valve plug member (8) in direction of their mutual sliding and/or continuous sliding distance of the sealing surfaces (2, 9) are optimally reduced in order to avoid wear, especially galling of the sealing surfaces (2, 9).

2. Structure of the sealing surfaces according to claim 1, characterized in that the continuous sealing surface (2, 9) of the seat ring (1) and/or the valve plug member

(8) is interrupted by means of recesses, grooves or concavities without causing any leakage passageways when the valve is in its closed position.

3. Structure of the sealing surface according to claim 2, characterized in that the recesses, grooves or concavities (7) are arranged in a dense pattern but spaced apart from each other.

4. Structure of the sealing surface according to claim 3, characterized in that the recesses, grooves or concavities (7) are aligned in a plurality of rows spaced apart from each other and substantially oriented parallel to an axis (4) of rotation of the valve plug member.

5. Structure of the sealing surface according to claim 3 or 4, characterized in that the recesses, grooves or concavities (7) are located slightly staggered relative to each other in the direction of motion.

6. Structure of the sealing surfaces according to claim 1, characterized in that the width of the sealing surface (2) of the seat ring is smaller at areas where risk of wear is greatest.

7. Sealing surface of claim 1, characterized in that the sealing surface (2) of the seat ring is divided into a plurality of concentric rings (2c).