阅读说明：本技术 阀体与阀座的密封结构及闸阀 (Sealing structure of valve body and valve seat and gate valve ) 是由 王良 王健 于 2020-04-28 设计创作，主要内容包括：本发明的实施方式涉及一种闸阀,特别涉及了一种阀体与阀座的密封结构及闸阀,阀体内开设用于安装阀座的环形区,环形区包括：被阀座部分插入的第一环槽、与第一环槽同轴且相连的第二环槽,阀座与第一环槽的槽壁之间形成密封,第二环槽的内径大于所述第一环槽的内径,第二环槽的槽壁与阀座之间相互隔开,形成一环形空间,密封结构包括：套接于阀座上的环形碳素密封件和环形抵压件,还包括：设置于所述环形空间内的加力组件,加力组件用于朝第二环槽的槽底的方向推动并锁止环形抵压件。同现有技术相比,保证了阀座与阀体之间可实现无缝隙密封,同时借助于环形碳素密封件的耐高温和耐腐蚀特性,使得整个闸阀可满足于化工生产时的使用需求。(The embodiment of the invention relates to a gate valve, in particular to a sealing structure of a valve body and a valve seat and a gate valve, wherein an annular area for installing the valve seat is arranged in the valve body, and the annular area comprises: by first annular of valve seat part male, with the coaxial and continuous second annular of first annular, form between the cell wall of valve seat and first annular sealedly, the internal diameter of second annular is greater than the internal diameter of first annular, separate each other between the cell wall of second annular and the valve seat, form an annular space, seal structure includes: the annular carbon element sealing member and the annular pressing member which are sleeved on the valve seat further comprise: and the force applying component is arranged in the annular space and used for pushing towards the direction of the groove bottom of the second annular groove and locking the annular pressing piece. Compared with the prior art, seamless sealing between the valve seat and the valve body is guaranteed, and meanwhile, the use requirement of the whole gate valve during chemical production can be met by means of the high-temperature resistance and corrosion resistance of the annular carbon sealing element.)

1. The utility model provides a seal structure of valve body and disk seat, sets up the annular district that is used for installing the disk seat in the valve body, its characterized in that, the annular district includes: by valve seat part male first annular, with the coaxial and continuous second annular of first annular, the valve seat with form sealedly between the cell wall of first annular, the internal diameter of second annular is greater than the internal diameter of first annular, the cell wall of second annular with separate each other between the valve seat, form an annular space, seal structure includes:

the annular carbon sealing element is sleeved on the valve seat and embedded into the annular space; the outer ring of the annular carbon sealing element abuts against the groove wall of the second annular groove to form sealing, and the inner ring of the annular carbon sealing element abuts against the valve seat to form sealing;

the annular abutting part is sleeved on the valve seat and is embedded into the annular space to abut against the annular carbon sealing element;

and the force application assembly is arranged in the annular space and used for pushing towards the direction of the groove bottom of the second annular groove and locking the annular pressing piece.

2. A valve body to valve seat seal according to claim 1, wherein the force assembly comprises: the annular supporting seat is arranged in the second annular groove;

the annular supporting seat is provided with a plurality of threaded holes around the axis direction of the annular supporting seat, and the number of the threaded holes is the same as that of the screws and is only corresponding to that of the screws; each screw is in threaded connection with the annular supporting seat through the only corresponding threaded hole, and each screw is used for penetrating through the only corresponding threaded hole and abutting against the annular abutting part;

any screw is used for performing linear motion along the axial direction of the threaded hole when the screw rotates in the only corresponding threaded hole.

3. A valve body to valve seat sealing structure according to claim 2, wherein each of said threaded holes is provided equidistantly on said annular support seat.

4. A valve body to valve seat sealing structure according to claim 2, wherein said annular support seat comprises: an outer edge surface, an inner edge surface opposite the outer edge surface;

the outer edge surface is partially protruded towards the direction far away from the inner edge surface to form an annular protrusion, the outer edge surface is separated from the groove wall of the second ring groove, and the inner edge surface is tightly attached to the valve seat;

the seal structure further includes: and the positioning component is arranged on the groove wall of the second annular groove, and the positioning component is abutted and buckled with the annular bulge along the axis direction of the second annular groove.

5. The valve body to valve seat sealing structure of claim 4, wherein the positioning member is a positioning ring disposed coaxially with the second annular groove;

alternatively, the positioning member includes: and the positioning blocks are arranged around the axis direction of the second ring groove.

6. A valve body to valve seat sealing structure according to claim 5, wherein the positioning member comprises: a plurality of positioning blocks arranged around the axis direction of the second ring groove;

and the groove wall of the second ring groove is also provided with mounting grooves embedded by the positioning blocks, and part of each positioning block is exposed out of the mounting groove and is abutted and buckled with the annular bulge of the positioning ring.

7. A valve body to valve seat sealing structure according to claim 1, wherein a seal is formed between the outer ring of the annular pressing member and the valve body, and a seal is formed between the inner ring of the annular pressing member and the valve seat.

8. The sealing structure of valve body and valve seat according to claim 1, wherein the groove bottom of the second ring groove is an annular inclined surface;

the vertical distance from the inner ring of the annular inclined plane to the groove bottom of the first annular groove is smaller than the vertical distance from the outer ring of the annular inclined plane to the groove bottom of the first annular groove, and the annular carbon sealing element abuts against one side of the annular inclined plane and is matched with the annular inclined plane.

9. The sealing structure of the valve body and the valve seat according to any one of claims 1 to 8, wherein the annular carbon sealing member is a flexible graphite sealing ring, and the flexible graphite sealing ring is configured to deform in a direction perpendicular to the axis of the second annular groove under the thrust of the thrust assembly.

10. A gate valve, comprising: the valve comprises a valve body, two valve seats arranged in the valve body and a valve plate arranged in the valve body, wherein one valve seat is communicated with the water inlet side of the valve body, the other valve seat is communicated with the water outlet side of the valve body, the two valve seats are mutually separated to form a cut-off area which can be inserted or withdrawn by the valve plate,

a sealing structure between the valve body and the valve seat according to any one of claims 1 to 9 is arranged between any one of the valve seat and the valve body.

Technical Field

The embodiment of the invention relates to a gate valve, in particular to a sealing structure of a valve body and a valve seat and a gate valve with the sealing structure.

Background

In material systems such as petrochemical industry, coal chemical industry, polycrystalline silicon, power plant ash removal, slurry, boiler slag removal and the like, gate valves are often adopted as switching elements for cutting off pipelines of the material systems, and because the conveying temperature of the media in the material systems is generally high (generally greater than or equal to 500 ℃), the sealing performance of the gate valves is particularly important, namely the sealing performance between the valve seats and the valve bodies. The conventional gate valve generally adopts O-shaped rings to realize sealing between the valve seat and the valve, and the sealing rings are generally made of rubber materials which are difficult to bear high temperature and corrosion resistance, so that the sealing requirement of chemical production is difficult to meet.

Disclosure of Invention

The embodiment of the invention aims to design a sealing structure of a valve body and a valve seat and a gate valve, which can improve the sealing and corrosion resistance between the valve seat and the valve body so as to meet the use requirement of the gate valve in chemical production.

In order to solve the above technical problem, an embodiment of the present invention provides a sealing structure between a valve body and a valve seat, wherein an annular region for installing the valve seat is formed in the valve body, and the annular region includes: by valve seat part male first annular, with the coaxial and continuous second annular of first annular, the valve seat with form sealedly between the cell wall of first annular, the internal diameter of second annular is greater than the internal diameter of first annular, the cell wall of second annular with separate each other between the valve seat, form an annular space, seal structure includes:

the annular carbon sealing element is sleeved on the valve seat and embedded into the annular space; the outer ring of the annular carbon sealing element abuts against the groove wall of the second annular groove to form sealing, and the inner ring of the annular carbon sealing element abuts against the valve seat to form sealing;

the annular abutting part is sleeved on the valve seat and is embedded into the annular space to abut against the annular carbon sealing element;

and the force application assembly is arranged in the annular space and used for pushing towards the direction of the groove bottom of the second annular groove and locking the annular pressing piece.

In addition, an embodiment of the present invention also provides a gate valve including: the valve body, set up in two disk seats in the valve body, set up in valve plate in the valve body, one of them the disk seat with the side intercommunication of intaking of valve body, another the disk seat with the play water side intercommunication of valve body, two separate each other between the disk seat, form can by the cutting area that the valve plate inserted or exited, arbitrary one the disk seat with be equipped with between the valve body as above the seal structure of valve body and disk seat.

Compared with the prior art, the embodiment of the invention has the advantages that the annular area formed on the valve seat consists of the first annular groove and the second annular groove, the first annular groove can be inserted into the valve seat, the inner diameter of the second annular groove is larger than that of the first annular groove, so that the groove wall of the first annular groove can be mutually separated from the valve seat to form an annular space, meanwhile, the whole sealing structure comprises the annular carbon sealing element and the annular pressing element which are sleeved on the valve seat, the annular carbon sealing element and the annular pressing element are directly embedded into the annular space, the outer ring and the inner ring of the annular carbon sealing element are respectively pressed against the groove wall of the second annular groove and the valve seat to form sealing, the annular pressing element is directly pressed against the annular carbon sealing element, and the sealing structure also comprises the force applying assembly arranged in the annular space, when in actual application, the force applying assembly is used for pushing and locking the annular pressing element towards the groove bottom of the second annular, the annular pressing piece can firmly press the annular carbon sealing piece at the groove bottom of the second annular groove so as to ensure seamless sealing between the valve seat and the valve body, and meanwhile, the use requirement of the whole gate valve during chemical production can be met by means of the high-temperature resistance and corrosion resistance of the annular carbon sealing piece.

Further, the force application assembly comprises: the annular supporting seat is arranged in the second annular groove;

the annular supporting seat is provided with a plurality of threaded holes around the axis direction of the annular supporting seat, and the number of the threaded holes is the same as that of the screws and is only corresponding to that of the screws; each screw is in threaded connection with the annular supporting seat through the only corresponding threaded hole, and each screw is used for penetrating through the only corresponding threaded hole and abutting against the annular abutting part;

any screw is used for performing linear motion along the axial direction of the threaded hole when the screw rotates in the only corresponding threaded hole.

Further, each threaded hole is arranged on the annular supporting seat at equal intervals.

Further, the annular supporting seat comprises: an outer edge surface, an inner edge surface opposite the outer edge surface;

the outer edge surface is partially protruded towards the direction far away from the inner edge surface to form an annular protrusion, the outer edge surface is separated from the groove wall of the second ring groove, and the inner edge surface is tightly attached to the valve seat;

the seal structure further includes: and the positioning component is arranged on the groove wall of the second annular groove, and the positioning component is abutted and buckled with the annular bulge along the axis direction of the second annular groove.

Further, the positioning component is a positioning ring which is coaxial with the second annular groove;

alternatively, the positioning member includes: and the positioning blocks are arranged around the axis direction of the second ring groove.

Further, the positioning member includes: a plurality of positioning blocks arranged around the axis direction of the second ring groove;

and the groove wall of the second ring groove is also provided with mounting grooves embedded by the positioning blocks, and part of each positioning block is exposed out of the mounting groove and is abutted and buckled with the annular bulge of the positioning ring.

Further, a seal is formed between the outer ring of the annular pressing piece and the valve body, and a seal is formed between the inner ring of the annular pressing piece and the valve seat.

Further, the groove bottom of the second ring groove is an annular inclined plane;

the vertical distance from the inner ring of the annular inclined plane to the groove bottom of the first annular groove is smaller than the vertical distance from the outer ring of the annular inclined plane to the groove bottom of the first annular groove, and the annular carbon sealing element abuts against one side of the annular inclined plane and is matched with the annular inclined plane.

Furthermore, the annular carbon sealing element is a flexible graphite sealing ring, and the flexible graphite sealing ring is used for generating deformation along the direction perpendicular to the axis of the second annular groove under the thrust action of the stress application assembly.

Drawings

One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.

Fig. 1 is a schematic view of the internal structure of a valve body in a first embodiment of the present invention;

FIG. 2 is a schematic view of the assembly of the valve body and the valve seat according to the first embodiment of the present invention;

FIG. 3 is an enlarged view of a portion A of FIG. 2;

FIG. 4 is a schematic diagram illustrating the distribution of the positioning blocks on the valve body according to the first embodiment of the present invention;

FIG. 5 is a schematic view of the configuration of the annular region on the valve body in the first embodiment of the present invention;

FIG. 6 is a schematic view of a ring support according to a first embodiment of the present invention;

FIG. 7 is a schematic structural view of a gate valve according to a second embodiment of the present invention;

fig. 8 is a partially enlarged view of a portion B in fig. 7.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be appreciated by those of ordinary skill in the art that numerous technical details are set forth in order to provide a better understanding of the present application in various embodiments of the present invention. However, the technical solution claimed in the present application can be implemented without these technical details and various changes and modifications based on the following embodiments.

A first embodiment of the present invention relates to a valve body and valve seat sealing structure, as shown in fig. 1 and 5, in the present embodiment, an annular region 11 for mounting a valve seat 2 is provided in a valve body 1, and the annular region 11 includes: a first ring groove 111 into which the valve seat 2 is partially inserted, and a second ring groove 112 which is coaxial with and connected to the first ring groove 111. Meanwhile, as shown in fig. 1, a seal is formed between the valve seat 1 and the groove wall of the first ring groove 111. Specifically, as shown in fig. 2 and fig. 3, an annular receiving groove (not labeled) may be formed on a groove wall of the first ring groove 111 around an axis direction thereof, and a sealing ring 3 is disposed in the annular receiving groove, the sealing ring 3 further abuts against the valve seat 2, so that a sealing surface may be formed between the valve seat 2 and the groove wall 1111 of the first ring groove 111 by means of the sealing ring 3.

In addition, in the present embodiment, as shown in fig. 3 and 5, the inner diameter of the second ring groove 112 is larger than the inner diameter of the first ring groove 111, so that the groove wall 1121 of the second ring groove 112 and the valve seat 2 can be spaced apart from each other to form an annular space (not shown). As shown in fig. 2 and 3, the seal structure according to the present embodiment includes: the annular carbon sealing element 4 and the annular pressing element 5 are sleeved on the valve seat 2, wherein the annular carbon sealing element 4 and the annular pressing element 5 are embedded into the annular space, the annular carbon sealing element 4 and the annular pressing element 5 are arranged along the direction from the water inlet side 12 to the water outlet side 13 of the valve body 1 and are mutually abutted, meanwhile, the outer ring of the annular carbon sealing element 4 is abutted against the groove wall 1121 of the second annular groove 112 to form sealing, and the inner ring of the annular carbon sealing element 4 is abutted against the valve seat 2 to form sealing.

As shown in fig. 2 and 3, the seal structure of the present embodiment further includes: and the force applying component 6 is arranged in the annular space, and the force applying component 6 is used for pushing and locking the annular pressing piece 5 towards the direction of the groove bottom of the second annular groove 112.

It can be seen from the above that, in practical application, the force application assembly 6 can be used to push and lock the annular pressing member 5 in the direction of the groove bottom of the second annular groove 112, so that the annular pressing member 5 can firmly press the annular carbon sealing member 4 against the groove bottom of the second annular groove 112 to ensure seamless sealing between the valve seat 2 and the valve body 1, and meanwhile, by means of the high temperature and corrosion resistant characteristics of the annular carbon sealing member 4, the whole gate valve can meet the use requirements in chemical production.

Specifically, in the present embodiment, as shown in fig. 3, the force application unit 6 includes: a plurality of screws 61, an annular supporting seat 62 arranged in the second annular groove 112. As shown in fig. 6, the annular support seat 62 is provided with a plurality of threaded holes 621 around its own axis, and the number of the threaded holes 621 is the same as that of the screws 61 and corresponds uniquely. In practical application, as shown in fig. 3, each screw 61 can be in threaded connection with the annular support seat 62 through each uniquely corresponding threaded hole 621, each screw 61 is used for penetrating through the uniquely corresponding threaded hole 621 and abutting against the annular abutting member 5, and any screw 61 can rotate in the threaded hole 621 by means of the uniquely corresponding threaded hole 621, and when any screw 61 rotates, the screw can linearly move along the axial direction of the threaded hole 621, so that the annular abutting member 5 is pushed, and meanwhile, under the rotating action of each screw 61, the acting force applied to the annular carbon seal 4 by the annular abutting member 5 can be adjusted, so that the annular carbon seal 4 has better sealing performance with the valve body 1 and the valve seat 2. And, as a preferable scheme, the threaded holes 621 are equidistantly arranged on the annular supporting seat 62, so that when the screws 61 push the annular pressing member 5, the acting force exerted by the annular pressing member 5 on the annular carbon sealing member 4 can be uniformly distributed, and the phenomenon of excessive local acting force is avoided.

It should be noted that, in this embodiment, the annular carbon sealing element 4 may be a flexible graphite sealing ring, so that after the sealing ring receives the acting force of the annular pressing element 5, the sealing ring may deform to a certain extent in the direction perpendicular to the axis of the second annular groove 112, so that the valve seat 2 and the valve body 1 may be respectively attached to the annular carbon sealing element 4 more tightly, and the sealing performance between the valve seat 2 and the valve body 1 is further improved. Preferably, as shown in fig. 3 and 5, the groove bottom 1122 of the second ring groove 112 disclosed in this embodiment is an annular inclined surface, and the vertical distance from the inner ring of the annular inclined surface to the groove bottom of the first ring groove 111 is smaller than the vertical distance from the outer ring of the annular inclined surface to the groove bottom of the first ring groove 111, and one side of the corresponding annular carbon sealing element 4 abutting against the annular inclined surface is engaged with the annular inclined surface, so that the annular carbon sealing element 4 can be automatically displaced and pressed in the direction of the valve seat 2 by the cooperation with the annular inclined surface of the second ring groove 112 after receiving the acting force of the annular pressing element 5, thereby further improving the tightness of the fit between the annular carbon sealing element 4 and the valve seat 2, and further improving the sealing performance between the valve seat 2 and the valve body 1.

In addition, it should be noted that, in order to fix the annular support seat 62 in the second annular groove 112, in the present embodiment, as shown in fig. 3, the annular support seat 62 includes: the outer edge surface 622, the inner edge surface 623 opposite to the outer edge surface 622, and the outer edge surface 622 of the annular support seat 62 has an annular protrusion 624 partially protruding away from the inner edge surface of the annular support seat 62, and meanwhile, the outer edge surface 622 of the annular support seat 62 is spaced apart from the groove wall 1121 of the second annular groove 112, and the inner edge surface 623 of the annular support seat 62 is tightly attached to the valve seat 2. Further, the seal structure of the present embodiment further includes: the positioning members 7 are disposed on the groove walls 1121 of the second ring groove 112, and the positioning members 7 and the annular protrusion 624 are abutted against each other along the axial direction of the second ring groove 112, so that the annular supporting seat 62 can be retained in the second ring groove 112 by the abutting engagement of the positioning members 7 and the annular protrusion 624, and the annular supporting seat 62 is prevented from being withdrawn from the second ring groove 112 due to the reverse acting force of the screws 61.

Meanwhile, in order to facilitate the assembly and fixation of the positioning member 7 and the annular supporting seat 62 in the second annular groove 112, as shown in fig. 4, in the present embodiment, the positioning member 7 is composed of a plurality of positioning blocks 71 disposed around the axial direction of the second annular groove 112, and as shown in fig. 5, an installation groove 1123 capable of being embedded by each positioning block is further formed on a groove wall 1121 of the second annular groove 112, and each positioning block is disposed in the installation groove 1123. For example, in the present embodiment, two positioning blocks 71 are provided, each positioning block 71 may be similar to a semicircular structure, and the corresponding mounting groove 1123 is an annular structure, when mounting, the two semicircular positioning blocks 71 may be spliced together in the mounting groove 1123 to form an annular positioning member 7, and each positioning block 71 is partially exposed outside the mounting groove 1123 to be abutted against the annular protrusion 624 of the annular supporting seat 62, and by this assembly, the assembly of the positioning member 7 and the annular supporting seat 62 in the second annular groove 112 may be completed without using any locking member, so that the whole assembly process is very simple.

It should be noted that, in the practical application process, the number of the mounting grooves may also be correspondingly matched according to the number of the positioning blocks 71, for example, the number of the positioning blocks 71 and the number of the mounting grooves may be set to be the same, each mounting groove is also annularly arranged around the axial direction of the second annular groove 112 and is uniquely arranged corresponding to each positioning block 71, and in the operation process, each positioning block 71 may be embedded in each uniquely corresponding mounting groove 1123, and in this way, the abutting of each positioning block 71 on the annular protrusion 624 of the annular supporting seat 62 may also be achieved. Of course, as an alternative, the positioning member 7 may also be a fixing ring in the present embodiment, that is, the positioning member 7 is an annular member disposed around the axial direction of the second annular groove 112, and the annular member 7 can also be used to engage with the annular protrusion 624 of the annular supporting seat 62.

In addition, as a preferable mode, in order to further improve the sealing performance between the valve seat 2 and the valve body 1, in the present embodiment, as shown in fig. 3, the annular pressing member 5 forms a seal with the valve seat 2 and the groove wall 1121 of the second annular groove 112, specifically, a groove may be formed in each of the annular pressing member 5 and the valve seat 1, a sealing member 20 may be disposed in the groove, and a sealing surface may be formed between each of the annular pressing member 5 and the groove wall 1121 of the valve seat 2 and the second annular groove 112 by the sealing member 20, so that the sealing performance between the valve seat 2 and the valve body 1 may be further improved.

A second embodiment of the present invention relates to a gate valve, as shown in fig. 7, including: the valve comprises a valve body 1, two valve seats 2 arranged in the valve body 1 and a valve plate 8 arranged in the valve body 1. The valve body 1 comprises a water inlet side 12, a water outlet side 13 opposite to the water inlet side 12, and a flow passage 14 communicating the water inlet side 12 and the water outlet side 13. Meanwhile, one of the two valve seats 2 is opposite to and communicated with the water inlet side 12 of the valve body 1, the other valve seat 2 is opposite to and communicated with the water outlet side 13 of the valve body 1, and the two valve seats 2 are separated from each other to form a cut-off area (not marked in the figure) which can be inserted or withdrawn by the valve plate 8.

In the present embodiment, as shown in fig. 8, the seal structure according to the first embodiment is provided between any one of the valve seats 2 and the valve body 1. Therefore, as the sealing structures in the first practical mode are adopted between the two valve seats and the valve body, seamless sealing can be realized between the valve seat 2 and the valve body 1, and meanwhile, the use requirement of the whole gate valve during chemical production can be met by means of the high-temperature resistance and corrosion resistance of the annular carbon sealing element 4 in the sealing structures.

Further, as shown in fig. 8, the gate valve according to the present embodiment further includes: set up in a plurality of resilience part 10 of the tank bottom of each first annular 111, and each resilience part 10 in every first annular 111 all sets up around the axis direction of this first annular 111, and each resilience part 10 in every first annular 111 all exerts resilience force to valve seat 2 along the axis direction of this first annular 111, thereby after valve plate 8 is cutting off the runner 14 of valve body 1, promptly valve plate 8 inserts in the truncation district that forms between two valve seats 2, but valve seat 2 can rely on the laminating that resilience force of each resilience part 10 can be inseparable on valve plate 8, thereby guaranteed the sealing performance between 14 backs of runner and valve seat 2 of valve plate 8 truncation, avoid appearing the leakage phenomenon.

In addition, in the present embodiment, since the annular supporting seat 62 and the positioning blocks 71 of the positioning component 7 are abutted against each other, when the valve seat 2 moves towards the valve plate 8 by means of the resilient components 10, the annular supporting seat 62 can be prevented from exiting the second annular groove 112 due to the acting force of the valve seat 2 by virtue of the abutting relationship of the positioning blocks 71, so that the annular carbon sealing element 4 can still be tightly attached to the bottom of the second annular groove 112, and form a seal with the groove wall 1121 of the second annular groove 112 and the valve seat 2, thereby effectively ensuring the sealing performance between the valve body 1 and the valve seat 2.

In the present embodiment, as shown in fig. 8, springs are used for the respective resilient members 10, and in order to prevent the respective springs from being bent during the resilient process, a groove 21 into which the spring 10 is partially fitted is formed on the valve seat 2 on the side of the groove bottom of the first ring groove 111, and the spring 10 is partially accommodated in the groove 21, so that the resilient force applied to the valve seat 2 by the respective springs 10 can be concentrated on the groove bottom of the respective grooves 111, and the valve seat 2 can be prevented from being deflected due to the uneven resilient force applied by the respective springs 10.

It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific embodiments for practicing the invention, and that various changes in form and details may be made therein without departing from the spirit and scope of the invention in practice.