The invention relates generally to fluid seals and more particularly to seals for the connection of two fluid-containing members that is subjected to thermal cycling.
All the fluid-containing members need to be connected or enclosed to withstand a pressure. The connections shall complete the two kinds of sealing and fastening tasks, and are often realized by welding, threading, flanging, flaring, swaging etc. The sealing arrangement is different as the connecting or fastening method differs. The weld connection completes sealing and fastening at the same time by weld metal. The connection by jointing threads where pressure tight joints are made on the threads completes its sealing and fastening by the same threads. The connection by fastening threads where pressure tight joints are not made on the threads completes its fastening by threads or bolts disposed around the flow path, and its sealing by annular sealing gaskets or packing disposed between the end faces to be joined. The annular sealing gasket is often made of non-metal, and sometimes compressed into a metal cavity which is enclosed by the connecting components in order to meet a higher requirement. The non-metal and metal often have a thermal expansion coefficient very different from each other, and create problems with the seal integrity when subjected to thermal cycling. U.S. Pat. No. 6,837,482 disclosed a diamond-shaped cross-sectional thermally-assisted sealing arrangement to try to make use of material thermal expansion to enhance sealing connection. However, the patent could not disclose a complete principle of thermally-assisted sealing cavities, and misunderstood that any annular non-metal packing would simply move radially relative to its containing metal cavity into one of the converging end portions of the diamond-shaped cavity to enhance the sealing connection in response to temperature changes. As it is, it is not so simple. As well known, any differences in thermal expansion or contraction coefficients will cause the sectional area and gyro-radius of the said annular gasket to either increase or decrease in response to temperature changes at the same time relative to the cavity enclosing the annular gasket, regardless of whether the coefficient of the annular gasket material is greater or less than the gasket-containing cavity material. That the annular packing increases in sectional areas and gyro-radii relative to its containing cavity means that more packing material is to be compressed into a smaller cavity, and so any shape of cavities does not create sealing problems provided the tensile strength of packing material is lower than the strength of cavity material. However, when the annular packing decreases in sectional areas and gyro-radii relative to its containing cavity, the annular packing whose gyro-radius is decreasing shall be strong enough for contracting into a radially inward converging portion of the cavity to compensate the decreasing sectional area of the annular packing, that is to say, the annular packing shall have enough tensile strength for carrying out such a compensation.
As for the diamond-shaped design of U.S. Pat. No. 6,837,482, the first, the annular packing has to move diagonally or not radially relative to its containing cavity to provide a thermally-assisted compensating seal in response to temperature changes, whereas the packing-expanding or contracting force is radial; that is to say, the force diagonally moving the annular packing is only a component of the radial packing-expanding or contracting power. In another words, the diamond-shaped design of U.S. Pat. No. 6,837,482 cannot fully utilize the thermal expansion or contraction force of the annular packing relative to its cavity to perform the thermally-assisted compensating seal and is not yet an ideal design.
The second, the diamond-shaped cavity shall be made of two halves separately in two end face to be joined; if not, for example, if the diamond-shaped cavity is designed to completely sink into one face of the two butt end faces and the other end face is fully plain, the annular packing in its containing cavity will be diagonally away from and cause leakage along the plain face when the annular packing moves inward to its diagonal corner in response to temperature changes. It is well known that it is the most simple for user's connection designs and the most convenient for user's application for the packing-containing cavity to be designed completely at the manufacturer's product end. However, it is very difficult for the design to be machined with a complete diamond-shaped cavity at one end even if there would be no leakage problem with the diamond-shaped design. Therefore it may be said that the diamond-shaped design of U.S. Pat. No. 6,837,482 is neither ideal nor practical.
The last, U.S. Pat. No. 6,837,482 incorrectly taught that any forms of air and jell in the diamond-shaped cavity could move along its sectional diagonal and provide a thermally-assisted compensating seal in response to temperature changes. Actually it is impossible because any gas or jell free in a container can not expand or contract or move along a certain direction excluding gravity direction in response to temperature changes; that is to say, U.S. Pat. No. 6,837,482 may cause an incorrect application without reliability.
Valves, as the controlling unit for fluid conveying, have a valving member, such as the ball in ball valves, the gate in gate valves, etc. The valving member is installed in a flow path, and has an open position, which allows media to flow through the valve, and a closed position, which prevents media from flowing through the valve. The shifting of the two positions of the valving member in its seat is realized by a stem extending out of the valve. The installing or fixing of the valving member and its seats in the valve flow path relates to the sealing connection realized by annular sealing gaskets or packing disposed around the flow path and between the end faces to be joined, and relates to one of the three basic fastening connections realized by fastening threads or bolts, one is by bolted flanges, another, by threaded flanges or threaded upset ends, and the other, by threaded unupset ends.
The object of the invention is to provide an improved thermally-assisted sealing arrangement for the connection of two fluid-containing members connected by fastening threads or bolts.
The thermally assisted sealing arrangement of the invention is a trapezoid-sectional annular sealing arrangement, including a trapezoid-sectional annular cavity and gasket or packing used to realize the sealing connection of two fluid-containing members connected by fastening threads or bolts. The said trapezoid-sectional annular gasket or packing, generally with a sectional area slightly bigger than the sectional area of the said cavity, is enclosed in the said cavity formed by the said two fluid-containing members as joined together by fastening threads or bolts, and the said trapezoid is disposed to converge radially and inward. The said trapezoid-sectional annular cavity is preferably designed to completely sink into one face of the two end faces to be joined. When the thermal expansion coefficients of materials used for the annular cavity and the annular gasket are different from each other, the sectional area and gyro-radius of the annular gasket will either increase or decrease in response to temperature changes at the same time relative to the cavity containing the annular gasket, regardless of whether the coefficient of the annular gasket material is greater or less than the gasket-containing cavity material. That the annular packing increases in sectional areas and gyro-radii relative to its containing cavity means that more packing material is to be compressed into a smaller cavity, and so any shape of cavities does not create sealing problems provided the tensile strength of packing material is lower than the strength of cavity material. However, when the annular packing decreases in sectional areas and gyro-radii relative to its containing cavity, the annular packing whose gyro-radius is decreasing shall be strong enough for contracting into a radially inward converging portion of the cavity to compensate the decreasing sectional area of the annular packing, that is to say, the annular packing shall have enough tensile strength for carrying out such a compensation.
One embodiment of the thermally assisted sealing arrangement is that the said trapezoid-sectional annular cavity is made of metal, and the said annular packing or gasket is made of non-metal, such as PTFE (Polytetrafluoroethylene) and the like. Another embodiment of the thermally assisted sealing arrangement is that it is disposed between two flange end faces to be connected, where the flanges are connected by either bolts or threads. Another embodiment of the thermally assisted sealing arrangement is that it is disposed on the end face of either externally threaded parts or internally threaded parts, where the male and female threads fasten the two fluid-containing parts together by engagement. Another embodiment of the thermally assisted sealing arrangement is that it is used to realize the sealing connection of valve bodies or valve flow paths, where the fastening connection is realized by threads or flanges.
a is a partially enlarged view of the trapezoid-sectional annular sealing arrangement of
One embodied application and disposition of the trapezoid-sectional annular sealing arrangement in the connection of two fluid-containing members can be found in the flow controlling path of the two-body type ball valve shown in
What is shown in
The trapezoid-sectional annular gasket shown in
As a matter of fact, the trapezoid-sectional annular sealing arrangement can be used as the thermally assisted seal in any connections of two fluid-containing members connected by bolted flanges (
Number | Date | Country | Kind |
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200510097905.6 | Aug 2005 | CN | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CN2006/002157 | 8/23/2006 | WO | 00 | 2/22/2008 |