阅读说明：本技术 一种天然气用具有防泄漏结构的低温切断阀 (Natural gas is with low temperature trip valve that has anti-leakage structure ) 是由 李红 于 2021-01-04 设计创作，主要内容包括：本发明涉及低温切断阀技术领域,具体为一种天然气用具有防泄漏结构的低温切断阀,所述阀门主体包括阀体,所述阀体的上方设置有阀盖,所述阀盖的内部贯穿有阀杆,所述阀体的两端皆固定连接有法兰,所述阀体的内部固定连接有阀座组件,所述阀门主体的上方固定连接有填料螺母,所述阀门主体的顶部固定连接有气缸,所述气缸的上方设置有旋转把手,所述阀杆的外部设置有柱塞组件。本发明通过设置双重密封柱塞进行密封连接,能够实现对阀门的紧密密封,从而提高其防泄漏作用,且双重密封其密封效率更好,起到双重保险,且采用组装式结构,放便后期对磨损柱塞进行更换。(The invention relates to the technical field of low-temperature cut-off valves, in particular to a low-temperature cut-off valve with a leakage-proof structure for natural gas. The double-seal type valve has the advantages that the double-seal plunger pistons are arranged for sealing connection, the tight seal of the valve can be realized, the anti-leakage effect of the valve is improved, the double-seal type valve has better sealing efficiency and double safety, and the wear plunger pistons are replaced at the later stage of defecation by adopting an assembled structure.)

1. The utility model provides a natural gas is with low temperature trip valve that has anti-leakage structure, includes valve main part (1) and cylinder (3), its characterized in that: the valve body (1) comprises a valve body (11), a valve cover (12) is arranged above the valve body (11), a valve rod (13) penetrates through the valve cover (12), both ends of the valve body (11) are fixedly connected with flanges (15), the valve body (11) is fixedly connected with a valve seat assembly (14), the valve seat assembly (14) comprises a valve seat body (141), the left side of the valve seat body (141) is fixedly connected with a fixing plate (142), the upper surface of the fixing plate (142) is provided with a first fixing groove (143), the inside of the first fixing groove (143) is connected with an elastic element (144), the other end of the elastic element (144) is connected with a movable top plate (146), the right side of the movable top plate (146) is fixedly connected with a sliding block (147), and the left side of the valve seat body (141) is provided with a sliding groove (148), the left side of fixed plate (142) is provided with first sealing end face (145), the left side of valve seat main part (141) is provided with second sealing end face (149), the top fixedly connected with packing nut (2) of valve main part (1), top fixedly connected with cylinder (3) of valve main part (1), the top of cylinder (3) is provided with rotatory handle (4), the outside of valve rod (13) is provided with plunger subassembly (5), plunger subassembly (5) include first plunger (51), the below of first plunger (51) is provided with second plunger (52), first plunger (51) and the outside of second plunger (52) all fixed connection at valve rod (13).

2. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 1, characterized in that: the upper surface of the valve body (11) is provided with a groove, a sealing ring is arranged inside the valve body, a convex strip is arranged on the lower surface of the valve cover (12), the valve body (11) is in plug-in connection with the valve cover (12), and the valve cover (12) is fixedly connected to the upper surface of the valve body (11) through bolts.

3. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 1, characterized in that: the valve rod (13) comprises a main rod (131), a first connecting rod (132) is fixedly connected to the lower portion of the main rod (131), a second connecting rod (133) is fixedly connected to the lower portion of the first connecting rod (132), the diameter of the first connecting rod (132) is half of the diameter of the main rod (131), and the diameter of the second connecting rod (133) is half of the diameter of the first connecting rod (132).

4. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 1, characterized in that: spout (148) are the slope form, and inclination is the same with the inclination of first sealing end face (145), activity roof (146) are sliding connection through slider (147) and valve seat main part (141), first sealing end face (145) are the ring structure, activity roof (146) are the circular arc structure, and activity roof (146) are provided with four groups altogether.

5. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 1, characterized in that: the valve seat main part (141) is L shape structure, and the below is the ring structure, the connected mode of valve seat main part (141) and second plunger (52) is plug-in connection, fixed plate (142) and activity roof (146) are plug-in connection with the connected mode of first plunger (51), the inclination of first sealed terminal surface (145) equals the inclination of first extrusion terminal surface (515), the inclination of second sealed terminal surface (149) equals the inclination of second extrusion terminal surface (522).

6. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 1, characterized in that: the first plunger (51) comprises a sealing plug (511), a cover plate (512) is fixedly connected to the upper portion of the sealing plug (511), a threaded cylinder (514) is fixedly connected to the inner portion of the cover plate (512), a sealing pressing plate (513) is fixedly connected to the outer portion of the cover plate (512), and a first extrusion end face (515) is arranged on the outer portion of the sealing plug (511).

7. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 6, characterized in that: threaded cylinder (514) is threaded connection with the connected mode of head rod (132), sealing plug (511) are flexible structure, the below of sealing clamp plate (513) is provided with seal gasket, sealing plug (511) are the frustum structure, and the bottom of sealing plug (511) is vertical form.

8. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 6, characterized in that: the diameter of the sealing pressure plate (513) is larger than the inner diameter of the movable top plate (146), and the minimum diameter of the sealing plug (511) is equal to the maximum diameter of the fixing plate (142).

9. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 1, characterized in that: second plunger (52) include rubber buffer (521), the outside of rubber buffer (521) is provided with second extrusion terminal surface (522), the last fixed surface of rubber buffer (521) is connected with thread bush (523).

10. The cryogenic cutoff valve with leakage prevention structure for natural gas according to claim 9, characterized in that: thread bush (523) fixed connection is in the outside of second connecting rod (133), the connected mode of second connecting rod (133) of thread bush (523) is threaded connection, rubber buffer (521) are the frustum structure, and the bottom is cylindricly, the minimum diameter of rubber buffer (521) equals the maximum diameter of second seal terminal surface (149), the maximum diameter of rubber buffer (521) is greater than the maximum diameter of second seal terminal surface (149).

Technical Field

The invention relates to the technical field of low-temperature cut-off valves, in particular to a low-temperature cut-off valve with a leakage-proof structure for natural gas.

Background

The cut-off valve is one of actuating mechanisms in an automatic system, consists of a multi-spring pneumatic membrane actuating mechanism or a floating piston actuating mechanism and a regulating valve, receives signals of a regulating instrument, controls the cut-off, the connection or the switching of fluid in a process pipeline, has the characteristics of simple structure, sensitive response, reliable action and the like, can be widely applied to industrial production departments such as natural gas transportation, petroleum, chemical engineering, metallurgy and the like, and particularly has great significance on the anti-leakage effect of the adopted low-temperature cut-off valve in the field of natural gas transportation when in use.

To this end, the chinese application patent No. CN105782474B discloses a low temperature cut-off valve, which belongs to the technical field of low temperature cut-off valves, and particularly relates to a low temperature cut-off valve, comprising a valve seat with a water through hole in the middle and a valve flap above the water through hole, wherein a sealing assembly is arranged between one end of the valve seat close to the valve flap and the valve flap, the sealing assembly comprises a sealing member, the sealing member comprises a first sealing portion and a second sealing portion, the sealing assembly further comprises an extrusion member for extruding the first sealing portion, the second sealing portion is used for jacking the extrusion member, the low temperature cut-off valve provided by the present invention, the first sealing portion contacts with the extrusion member by driving the valve flap to move towards the water through hole, and the extrusion member contacts with the first sealing portion more and more tightly along with the movement of the valve flap, i.e. the sealing performance between the two is more and more good, and more, and at the, the second sealing part can be pressed on the extrusion part to achieve the effect of double composite sealing, when the valve is sealed, the upper part and the lower part are sealed to perform extrusion sealing, but only one sealing stopping point is arranged, when the valve is used, the sealing effect is reduced due to the abrasion of one of the upper part and the lower part, so that the natural gas is leaked, the valve does not have an effective sealing effect to realize the sealing connection of the valve, and the natural gas is leaked in the use process of the valve.

It is therefore desirable to design a cryogenic shut-off valve for natural gas having a leak-proof structure to solve the above problems.

Disclosure of Invention

The invention aims to provide a low-temperature cut-off valve with a leakage-proof structure for natural gas, which aims to solve the problems of poor leakage-proof effect and incapability of replacing a plunger in the background technology.

In order to achieve the purpose, the invention provides the following technical scheme: a low-temperature cut-off valve with an anti-leakage structure for natural gas comprises a valve body, a valve cover is arranged above the valve body, a valve rod penetrates through the valve cover, flanges are fixedly connected to two ends of the valve body, a valve seat assembly is fixedly connected to the interior of the valve body and comprises a valve seat main body, a fixed plate is fixedly connected to the left side of the valve seat main body, a first fixed groove is formed in the upper surface of the fixed plate, an elastic element is connected to the interior of the first fixed groove, the other end of the elastic element is connected with a movable top plate, a sliding block is fixedly connected to the right side of the movable top plate, a sliding groove is formed in the left side of the valve seat main body, a first sealing end face is arranged on the left side of the fixed plate, a second sealing end face is arranged on the left side of the valve, the top fixedly connected with cylinder of valve main part, the top of cylinder is provided with rotatory handle, the outside of valve rod is provided with the plunger subassembly, the plunger subassembly includes first plunger, the below of first plunger is provided with the second plunger, first plunger and the outside of the equal fixed connection of second plunger at the valve rod.

Preferably, the upper surface of the valve body is provided with a groove, a sealing ring is arranged in the groove, the lower surface of the valve cover is provided with a convex strip, the valve body is connected with the valve cover in an inserting manner, and the valve cover is fixedly connected to the upper surface of the valve body through bolts.

Preferably, the valve rod includes the mobile jib, the below fixedly connected with head rod of mobile jib, the below fixedly connected with second connecting rod of head rod, the diameter of head rod is half of mobile jib diameter, the diameter of second connecting rod is half of head rod diameter.

Preferably, the spout is the slope form, and inclination is the same with the inclination of first sealing end face, the activity roof is sliding connection through slider and disk seat main part, first sealing end face is the ring structure, the activity roof is the circular arc structure, and the activity roof is provided with four groups altogether.

Preferably, the disk seat main part is L shape structure, and the below is the ring structure, the disk seat main part is plug-in connection with the connected mode of second plunger, the connected mode of fixed plate and activity roof and first plunger is plug-in connection, the inclination of first seal face equals the inclination of first extrusion terminal surface, the inclination of second seal face equals the inclination of second extrusion terminal surface.

Preferably, the first plunger comprises a sealing plug, a cover plate is fixedly connected above the sealing plug, a threaded cylinder is fixedly connected inside the cover plate, a sealing pressing plate is fixedly connected outside the cover plate, and a first extrusion end face is arranged outside the sealing plug.

Preferably, the connection mode of a screw thread section of thick bamboo and first connecting rod is threaded connection, the sealing plug is flexible structure, sealing gasket is provided with in the below of sealing pressure plate, the sealing plug is the frustum structure, and the bottom of sealing plug is vertical form.

Preferably, the diameter of the sealing pressure plate is larger than the inner diameter of the movable top plate, and the minimum diameter of the sealing plug is equal to the maximum diameter of the fixing plate.

Preferably, the second plunger includes the rubber buffer, the outside of rubber buffer is provided with the second and extrudes the terminal surface, the last fixed surface of rubber buffer is connected with the thread bush.

Preferably, thread bush fixed connection is in the outside of second connecting rod, the connected mode of the second connecting rod of thread bush is threaded connection, the rubber buffer is the frustum structure, and the bottom is cylindricly, the minimum diameter of rubber buffer equals the maximum diameter of the sealed terminal surface of second, the maximum diameter of rubber buffer is greater than the maximum diameter of the sealed terminal surface of second.

Compared with the prior art, the invention has the beneficial effects that:

1. this low temperature trip valve for natural gas realizes the sealing connection to the trip valve through the mode that adopts the dual seal plunger, adopt elastic element to realize the further elastic extrusion of below roof to the top plunger simultaneously, thereby the effectual zonulae occludens of sealed plunger with the disk seat that has improved, thereby play and prevent leaking the effect, and can effectually improve it through the mode of dual seal and prevent leaking the effect, avoid the damage leakage that the nevertheless plunger type structure of tradition leads to, thereby make it prevent leaking the effect and play the dual fail-safe through the dual seal setting, improve its and prevent leaking the effect.

2. This low temperature trip valve for natural gas connects sealed plunger through the mode that adopts threaded connection and uses, and then can realize the change to the plunger when wearing and tearing appear in the plunger to improve its sealed effect, guarantee that it prevents leaking the effect, compare traditional monolithic structure, and removable dismantlement structure can save the waste of resource, and the maintenance change in the later stage of being convenient for.

Drawings

FIG. 1 is a schematic front view of the present invention;

FIG. 2 is a schematic view of a partial cross-sectional structure of the present invention;

FIG. 3 is an enlarged view of the structure A in FIG. 2 according to the present invention;

FIG. 4 is a structural diagram illustrating a first operating state of the present invention;

FIG. 5 is a structural diagram illustrating a second operating state of the present invention;

FIG. 6 is an enlarged view of B of FIG. 5 according to the present invention;

fig. 7 is a schematic front sectional view of the elastic element of the present invention.

In the figure: 1. a valve body; 11. a valve body; 12. a valve cover; 13. a valve stem; 131. a main rod; 132. a first connecting rod; 133. a second connecting rod; 14. a valve seat assembly; 141. a valve seat body; 142. a fixing plate; 143. a first fixing groove; 144. an elastic element; 145. a first sealing end face; 146. a movable top plate; 147. a slider; 148. a chute; 149. a second sealing end face; 15. a flange; 2. a packing nut; 3. a cylinder; 4. rotating the handle; 5. a plunger assembly; 51. a first plunger; 511. a sealing plug; 512. a cover plate; 513. sealing the pressure plate; 514. a threaded barrel; 515. a first extrusion end face; 52. a second plunger; 521. a rubber plug; 522. a second extrusion end face; 523. and (4) a threaded sleeve.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1-7, an embodiment of the present invention is shown:

the utility model provides a natural gas is with low temperature trip valve that has anti-leakage structure, including valve main part 1 and cylinder 3, cylinder 3 is one kind and twists at the epaxial nut of pipeline, its effect is fixed with packing and targets in place, thereby form inseparable sealed in the pipeline, thereby realize using the sealing connection of valve rod 13, valve main part 1 includes valve body 11, the top of valve body 11 is provided with valve gap 12, valve rod 13 has been run through to the inside of valve gap 12, the both ends of valve body 11 are fixedly connected with flange 15 all, the inside fixed connection of valve body 11 has valve seat subassembly 14.

The valve seat assembly 14 includes a valve seat main body 141, a fixing plate 142 is fixedly connected to the left side of the valve seat main body 141, a first fixing groove 143 is formed in the upper surface of the fixing plate 142, an elastic element 144 is connected to the inside of the first fixing groove 143, the elastic element 144 is made of polyurethane and is a substance formed by polymerization of ethane organic unit chains, the substance is soft, elastic and has good flexibility, a movable top plate 146 is connected to the other end of the elastic element 144, a slider 147 is fixedly connected to the right side of the movable top plate 146, a sliding groove 148 is formed in the left side of the valve seat main body 141, a first sealing end surface 145 is formed in the left side of the fixing plate 142, a second sealing end surface 149 is formed in the left side of the valve seat main body 141, the movable top plate 146 and the fixing plate 142 are connected, when sealing is performed, the movable top plate 146 can be pressed by the first plunger 51, and the first sealing end, meanwhile, the tight connection between the second sealing end face 149 and the second extrusion end face 522 can be realized, so that a dual protection effect is realized, when the sealing pressing plate 513 extrudes the first sealing end face 145, the rising resilience of the movable top plate 146 can be realized through the elastic effect of the elastic element 144, so that the tight contact between the movable top plate 146 and the sealing pressing plate 513 is improved, and the sealing effect of the sealing pressing plate is improved.

Top fixedly connected with packing nut 2 of valve main part 1, the top fixedly connected with cylinder 3 of valve main part 1, the inside of cylinder 3 includes spring and piston, and the bottom of piston is connected with valve rod 13, the top of cylinder 3 is provided with rotatory handle 4, the outside of valve rod 13 is provided with plunger subassembly 5, plunger subassembly 5 includes first plunger 51, the below of first plunger 51 is provided with second plunger 52, first plunger 51 and the outside of the equal fixed connection of second plunger 52 at valve rod 13, drive the lift of first plunger 51 and second plunger 52 through valve rod 13, realize the sealed to valve main part 1, and through the double sealing effect, can improve its sealing effect, and then realize the promotion of preventing leaking the effect.

The upper surface of valve body 11 is seted up flutedly, and inside is provided with the sealing washer, and the lower surface of valve gap 12 is provided with the sand grip, and valve body 11 is plug-in connection with valve gap 12's connected mode, and valve gap 12 passes through bolt fixed connection at the upper surface of valve body 11, through the connection of this structure, can realize the zonulae occludens of valve body 11 and valve gap 12, further plays sealed effect, the further installation and use of the part above the valve gap 12 of being convenient for.

The valve rod 13 includes the mobile jib 131, the below fixedly connected with head rod 132 of mobile jib 131, the below fixedly connected with second connecting rod 133 of head rod 132, the diameter of head rod 132 is half of mobile jib 131 diameter, the diameter of second connecting rod 133 is half of head rod 132 diameter, setting through this structure, can realize the installation of first plunger 51 and second plunger 52, and the bottom of second connecting rod 133 is provided with the external screw thread, be convenient for realize fixed to the installation of second plunger 52.

The sliding groove 148 is inclined, the inclination angle is the same as that of the first sealing end surface 145, the movable top plate 146 is in sliding connection with the valve seat main body 141 through the sliding block 147, the first sealing end surface 145 is in a circular ring structure, the movable top plate 146 is in a circular arc structure, four groups of movable top plates 146 are arranged, descending extrusion of the movable top plate 146 through the sealing pressing plate 513 is achieved, connection sealing of the first plunger 51 and the second plunger 52 with the valve seat main body 141 is achieved, springback of the movable top plate 146 can be achieved through the elastic characteristics of the elastic element 144, and then tight connection of the movable top plate 146 and the sealing pressing plate 513 is increased, and therefore sealing effects of the first plunger 51 and the second plunger are improved.

The valve seat main part 141 is L-shaped structure, and the below is the ring structure, the connection mode of valve seat main part 141 and second plunger 52 is plug-in connection, the connection mode of fixed plate 142 and activity roof 146 and first plunger 51 is plug-in connection, the inclination of first seal terminal surface 145 equals the inclination of first extrusion terminal surface 515, the inclination of second seal terminal surface 149 equals the inclination of second extrusion terminal surface 522, through the setting of its inclination, can realize that connection between them is sealed, can pass through the setting of its toper structure simultaneously, avoid its sealed effect that wearing and tearing lead to appear to reduce, thereby improve its life, and then play lasting leak-proof effect.

The first plunger piston 51 comprises a sealing plug 511, a cover plate 512 is fixedly connected above the sealing plug 511, a threaded cylinder 514 is fixedly connected inside the cover plate 512, a sealing pressing plate 513 is fixedly connected outside the cover plate 512, a first extrusion end face 515 is arranged outside the sealing plug 511, the cover plate 512, the sealing pressing plate 513 and the threaded cylinder 514 are all made of metal materials, the first plunger piston 51 is driven to descend by the descending of the valve rod 13 conveniently, the first plunger piston 51 can be installed and used conveniently, carbon steel is adopted, the mass fraction of carbon is low, the plasticity is good, the strength is low, compared with a traditional cast iron type valve, the service effect of the cast iron type valve in an ultrahigh temperature state and a low temperature state can be improved, the service life of the cast iron type valve is prolonged, the sealing plug 511 is made of polytetrafluoroethylene, and the cast iron type valve has excellent chemical stability, corrosion resistance, sealing performance, high lubrication, the high-temperature-resistant rubber plug is high-temperature-resistant, the working temperature reaches 250 ℃, the low-temperature-resistant rubber plug is low-temperature-resistant, the mechanical toughness is good at low temperature, the 5% elongation can be kept even if the temperature is reduced to-196 ℃, the corrosion resistance is realized, the inertia is shown to most of chemicals and solvents, the strong acid, strong alkali, water and various organic solvents can be resisted, the weather resistance is good, the best aging life in plastics is achieved, and the material of the sealing plug 511 is the same as that of the rubber plug 521.

Threaded cylinder 514 is threaded connection with the connected mode of head rod 132, sealing plug 511 is flexible structure, the below of sealing pressure plate 513 is provided with seal gasket, sealing plug 511 is the frustum structure, and the bottom of sealing plug 511 is vertical form, the diameter of sealing pressure plate 513 is greater than the internal diameter of activity roof 146, the minimum diameter of sealing plug 511 equals the maximum diameter of fixed plate 142, through its frustum formula structure, can guarantee at the sealing plug 511 to the extrusion sealing of fixed plate 142 and activity roof 146, simultaneously through the seal gasket that sets up below sealing pressure plate 513, further improve the connection seal between them, and the surface of surface seal gasket adopts concavo-convex structure, sealing effect when can improving the extrusion.

The second plunger 52 comprises a rubber plug 521, a second extrusion end surface 522 is arranged outside the rubber plug 521, a threaded sleeve 523 is fixedly connected to the upper surface of the rubber plug 521, the threaded sleeve 523 is fixedly connected to the outside of the second connecting rod 133, the second connecting rod 133 of the threaded sleeve 523 is in threaded connection, the rubber plug 521 is in a frustum structure, the bottom of the frustum structure is cylindrical, the minimum diameter of the rubber plug 521 is equal to the maximum diameter of the second sealing end surface 149, the maximum diameter of the rubber plug 521 is larger than the maximum diameter of the second sealing end surface 149, the structure further plays a role in sealing connection, the plunger assembly 5 can be pressed downwards when the plunger assembly is used, the first plunger 51 and the second plunger 52 are respectively connected and sealed, the sealing efficiency can be improved, a double-layer safety effect is achieved, and a good anti-leakage effect is achieved.

The working principle is as follows: when the invention is used, the flange 15 is firstly arranged on a natural gas conveying pipeline to ensure the connection tightness, when the cylinder 3 is charged with specified pressure, the piston rises to drive the valve rod 13 to open the valve main body 1, when the valve rod 13 is closed, gas in the rotating handle 4 is released, the piston drives the valve rod 13 and the plunger assembly 5 to move downwards under the action of the spring, the plunger assembly 5 presses the valve seat main body 141, the valve main body 1 is closed, and when the valve rod 13 drives the plunger assembly 5 to descend, the tight connection with the movable top plate 146 can be realized through the second extrusion end surface 522, the tight connection with the first sealing end surface 145 is realized through the first extrusion end surface 515, further the extrusion sealing of the valve seat main body 141 is realized through the first plunger 51 and the plunger 52, the sealing effect is improved, the double-seal connection plays a role in multiple protection and improves the leakage-proof efficiency, and when first plunger 51 pushes down, can realize the extrusion to activity roof 146 through sealed clamp plate 513, and can push down activity roof 146 to being close to fixed plate 142, realize tightening up through first fixed slot 143 simultaneously, and realize the jacking to activity roof 146, can realize simultaneously that activity roof 146 is inseparable to the extrusion of sealed clamp plate 513, improves sealed effect between them.

During pneumatic operation, be used for low temperature tank wagon when the ambient temperature of valve main part 1 reaches fusible metal melting temperature, the quick-witted fusible plug of quick-witted instant stop of low temperature tank container should melt at 75 ℃ +/-5 ℃, the inside fusible metal of fusible plug will melt, operating pressure in the cylinder 3 can automatic discharge, the piston drives valve rod 13 and 5 downstream of plunger subassembly under the effect of spring, plunger subassembly 5 presses valve seat main part 141, valve main part 1 closes, rotatory handle 4 at rotatory top drives valve rod 13 and 5 upstream of plunger subassembly, can manually open valve main part 1.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.