BACKGROUND ART As shown in Figures 1 through 3, the conventional ball valve includes a valve body having a ball operating space formed therewithin and an inlet and outlet formed at both sides of the ball operating space, with a valve ball being rotatable within the ball operating space and having a valve hole communicating with the inlet and outlet, respectively. In the thusly constituted ball valve, as the valve ball is rotated, the valve hole is opened to communicate with the inlet and outlet. When the center axis of the valve hole is perpendicular with respect to the center axis of the inlet and outlet, the inlet and outlet are blocked.

The above-described ball valve is classified into a side entry type ball valve and a top entry type ball valve.

Here, in the side entry type valve ball, the valve ball is inserted from one side of the valve body for thereby assembling the ball valve. In the top entry type, the valve ball is inserted from the top portion of the valve body.

Figures 1 through 3 illustrate the conventional side entry type ball valve.

As shown therein, a valve body 10 includes a cylindrical body 11 and flange tubes 12 and 13. A ball operating space is defined between the body 11 and the flange tubes 12 and 13, and an inlet P1 and an outlet P2 are formed respectively in the flange tubes 12 and 13. When assembling the valve ball 20, in a state that the flange tube 12 is assembled to the body 11, the valve ball 20 is inserted into the ball operating space in the direction that the flange tube 13 is assembled. A ball rotation member is assembled from the top of the body 11.

Big diameter portions 12a and 13a and small diameter portions 12b and 13b are formed in the respective inner circumferential surfaces of the flange tubes 12 and 13, and respective spring engaging surfaces 12c and 13c are

formed therebetween.

Inner flange portions 12d and 13d fixedly engaged with the respective ends of the body 11 by fixing screws 14a and 15a are formed in the inner end portions of the flange tubes 12 and 13. In addition, outer flange portions 12e and 13e having screw holes 14b and 15b are formed in the respective outer end portions of the same for connecting a pipe line (not shown).

The valve ball 20 includes an outer circumferential surface portion 21 for blocking the inlet P1 and the outlet P2, and a valve hole 22 for communicating the inlet P1 with the outlet P2.

On each of the upper and lower portions of the valve ball 20, a ball shaft 23 protrudes, by which the valve ball 20 is rotatably supported by a bearing plate 25 having a circular support hole 25a and a bushing 26 inserted between the inner circumferential surface of the circular support hole 25a of the bearing plate 25 and the outer circumferential surface of the ball shaft 23. Each bearing plate 25 is in turn fixing protrusions 24 formed in an inner circumferential surface in the ball operating space by fixing pins 24a.

The bearing plates 25 are constructed such that the circular support hole 25a is formed in the center portion of a square plate member. The diameter of the circular support hole 25a is larger than the diameter of the ball shaft 23 by the thickness of the bushing 26. The bushing 26 is made of a material such as copper and is disposed at a friction point.

The ball rotation unit includes a decelerating member 28 for decelerating the rotation of an operating handle 27 and a stem 29 connecting the output shaft of the decelerating member 28 and the ball shaft 23.

Seat assemblies 30 and 40 are respectively inserted into the flange tubes 12 and 13 which define the inlet P1 and the outlet P2.

The seat assemblies 30 and 40 respectively include seat rings 31 and 41 inserted into the flange tubes 12 and 13 and seats 32 and 42 engaged with the seat rings 31 and 41 and being closely contacted with the outer circumferential surface portion 21 of the valve ball 20.

Big diameter portions 31 a and 41 a and small diameter portions 31 b and 41 b respectively corresponding with the big diameter portions 12a and 13a and the small diameter portions 12b and 13b formed in the inner circumferential

surfaces of the flange tubes 12 and 13 are formed in the outer circumferential surfaces of the seat rings 31 and 41. Spring engaging surfaces 31 c and 41 c to which respective pressurizing springs 34 and 44 are engaged are respectively formed between the big diameter portions 31 a and 41 a and the small diameter portions 31 b and 41 b. Pressurizing surfaces 31 d and 41 d against which the fluid pressure from the inlet P1 and outlet P2 is applied are formed in the respective outer end portions of the seat rings 31,41. Slanted surfaces 31 e and 41 e to which a predetermined fluid pressure of a fluid flowing in the interior of the valve hole 22 is applied are formed in the respective inner end portions of the seat rings 31,41.

0-rings 33 and 43 are respectively inserted into respective grooves formed in the outer circumferential surface of the small diameter portions 31 b and 41 b of the seat rings 31 and 41 and respectively closely contact with the small diameter portions 12b and 13b of the flange tubes 12 and 13 for thereby implementing a sealing effect.

Pressurizing springs 34 and 44 are respectively disposed between the spring engaging surfaces 31 c and 41 c of the seat rings 31 and 41 and the spring engaging surfaces 12c and 13c of the flange tubes 12 and 13.

Among the thickness A of the pressurizing surfaces 31d and 41d, the vertical length B of the slanted surfaces 31 e and 41 e, the thickness D which is obtained by subtracting the vertical height B from the thickness of the inner end portion of the seat rings 31 and 41, and the thickness C which is obtained by subtracting the thickness A of the pressurizing surfaces 31 d and 41 d from the thickness of the inner end portion of the seat rings 31 and 41, the following relation is obtained: A+C = B+D, A>B, D>C>A. In addition, if the fluid pressures on the inlet P1, the outlet P2 and the valve hole 22 are identical, among the pressure Pa applied to the pressurizing surfaces 31 d and 41 d, the elastic force Ps of the pressurizing springs 34 and 44, and the pressure Pb applied to the slanted surfaces 31 e and 41 e based on the fluid pressure of the inlet P1 and the outlet P2, the following relation is obtained: Pa + Ps > Pb.

In a state that the valve as shown in Figures 1 through 3 is opened, the pressure Po of the fluid flowing along the path from the inlet P1 to the outlet P2 through the valve hole 22 of the valve ball 20 becomes constant.

Therefore, the pressure Poau (= Po x A) applied to the pressurizing surface 31 d of the seat ring 31 in the side of the inlet P1 which is at the up- stream side and the pressure Poad (= Po x A) applied to the pressurizing surface 41 d of the seat ring 41 in the side of the outlet P2 which is at the down- stream side are identical. In addition, the pressure Pobu (=Po x B) applied to the slanted surface 31 e of the seat ring 31 in the side of the inlet P1 and the pressure Pobd (= Po x B) applied to the slanted surface 41 e of the seat ring 41 in the side of the outlet P2 are identical.

At this time, because the thickness A (and hence the area) of the pressurizing surfaces 31 a and 41 a is greater than the thickness B (and hence the area) of the slanted surfaces 31 b and 41 b, Poau>Pobu, Poad>Pobd. The contacting force between the seat 32 engaged to the seat ring 31 in the side of the inlet P1 and the outer circumferential surface portion 21 of the valve ball 20 is (Poau + Posu)-Pobu, and the contacting force between the seat 42 engaged to the seat ring 41 in the side of the outlet P2 and the outer circumferential surface portion 21 of the valve ball 20 is (Poad + Posd)-Pobd.

Namely, in the state that the valve is opened, the contacting forces between the valve ball 20 and the seats 32 and 42 are the same as the pressures at the inlet P1 and the outlet P2.

In addition, in the state that the valve is closed, since the flowing path in the inlet P1 and the flowing path in the outlet P2 are blocked by the valve ball 20, the pressure Pcu of the fluid in the flowing path in the inlet P1 which is in the up-stream is larger than the pressure Pcd of the fluid in the flowing path in the outlet P2.

The pressure Pcau (= Pcu x A) applied to the pressurizing surface 31 d of the seat ring 31 at the inlet P1 side is larger than the pressure Pcad (= Pcd x A) applied to the pressurizing surface 41 d of the seat ring 41 at the outlet P2 side, and the pressure Pcbu (= Pcux B) applied to the pressurizing surface 31 e of the seat ring 31 at the inlet P1 side is smaller than the pressure Pcau applied to the pressurizing surface 31 e of the seat ring 31 at the inlet P1 side, and the pressure Pcbd (Pcd x B) applied to the pressurizing surface 41 e of the seat ring 41 at the outlet P2 side is smaller than the pressure Pcad applied to the pressurizing surface 41 d of the seat ring 41 at the outlet P2 side, so that the

contacting force (Pcau + Pcsu)-Pcbu between the seat 32 at the inlet P1 side and the outer circumferential surface portion 21 of the valve ball 20 is larger than the contacting force (Pcad + Pcsd)-Pcbd between the seat 42 at the outlet P2 side and the outer circumferential surface portion 21 of the valve ball 20. in the state that the ball valve is closed, since the pressure Pcu in the up-stream inlet p1 side is larger than the pressure Pcd in the down stream outlet P2 side, the contacting force between the seat 32 in the up stream inlet P1 side and the outer circumferential surface portion 21 of the valve ball 20 is increased for thereby preventing an internal leakage.

Here, the internal leakage is a leakage between the up stream inlet P1 and the down stream outlet P2 in a state that the ball valve is closed. Namely, even in the state that the ball valve is closed, the fluid should be prevented from flowing to the outlet P2 side through the ball operating space.

However, in the conventional art, if the seats 32 and 42 are damaged, a sufficient contacting state between the seats 32 and 42 and the valve ball 20 may not be implemented due to the pressure applied to the pressurizing surfaces 31 d and 41 d and the elastic forces of the pressurizing springs 34 and 44, so that an internal leakage occurs.

In addition, in the conventional art, if the above-described internal leakage occurs, there is no method for effectively preventing the internal leakage except that a sealant such as grease is packed between the seats 32 and 42 and the valve ball 20.

Namely, as shown in Figures 1 through 11, sealant injection portions 16a and 17a are respectively formed in the outer circumferential walls of the flange tubes 1 and 13, and one end portion of each of the seat rings 31 and 41 is respectively connected with the corresponding sealant inlets 16a and 17a, and in the other end portions of the same, sealant injection paths 16b and 17b are formed, which are opened at the slanted surfaces 31e and 41e, so that the sealant is provided between the slanted surfaces 31e and 41e and the seats 32 and 42 and the valve ball 20.

In addition, check valves 16c and 17c are installed for preventing the sealant provided through the sealant injection portions 16a and 17a from flowing

reversely.

In the technique that the sealant is provided between the seat rings 31 and 41 and the valve ball 20, if a fluid which is provided into the pipe in which the ball valve is installed is a fluid which chemically or physically reacts with the sealant, for example, if a reactive medium such as a chlorine gas is provided in the pipe, it is impossible to obtain a sealing effect due to the reaction between the sealant and the fluid, so that an internal leakage is not effectively blocked.

Also, in the top entry arrangement, the ball valve includes a ball operating space formed in the interior when the inlet and outlet are engaged, a pair of flange type bodies having an opening portion through which the ball is provided on the upper portion of the ball operating space and a cover for covering the opening. In this case, in order to disassemble the valve ball rotatably installed in the ball operating space, the flange body must be disengaged from the pipe and then the flange body must be disengaged for thereby disassembling the valve ball and the seat, so that the assembling and disassembling operation of the valve is complicated.

DISCLOSURE OF THE INVENTION Accordingly, it is an object of the present invention to provide a ball valve which overcomes the aforementioned problems encountered in the conventional art.

It is another object of the present invention to provide a ball valve which is capable of effectively preventing an internal leakage without using a sealant.

It is another object of the present invention to provide a ball valve which is capable of easily rotating a valve ball in case that there is a big pressure difference between the pressure at an inlet side and the pressure at an outlet side.

It is another object of the present invention to provide a ball valve which allows a predetermined amount of fluid to flow from an inlet side to an outlet side by without rotating a valve ball to open the valve.

It is another object of the present invention to provide a top entry type ball valve which is capable of easily disassembling a valve ball and seat without

taking out the valve from a pipeline.

To achieve the above objects, there is provided a ball valve according to a first embodiment of the present invention which includes a valve body including a cylindrical body portion and a pair of flange tubes engaged at both sides of the body, said flange tubes respectively forming an inlet and an outlet and each having a big diameter portion and a small diameter portion formed in an inner circumferential surface of the same and a spring engaging surface formed between the big diameter portion and the small diameter portion; a valve ball rotatably installed within a ball operating space defined within the valve body and having a valve hole for communicating the inlet and outlet and an outer circumferential surface for blocking the inlet and the outlet; a pair of seat assemblies including a big diameter portion and a small diameter portion corresponding with the big and small diameter portions of a corresponding flange tube; a spring engaging surface formed between the big diameter portion and the small diameter portion; a pressurizing surface formed in an outer end portion; a seat ring having a slanted surface formed at an inner end portion for contacting with the valve ball and a depressurizing surface formed at an inner end portion and contacting with a space formed between an inner circumferential surface of the flange tube and an outer circumferential surface of the valve ball; and a seat engaged in the slanted surface of the seat ring for contacting with an outer circumferential surface portion of the valve ball; a pressurizing spring for elastically urging the seat assembly toward the valve ball; 0-rings inserted into the big diameter portion and small diameter portion of the seat ring, respectively, and closely contacting with the big diameter portion and the small diameter portion of the flange tube; and a seat pressure control means including a pressurizing fluid supply source; a main supply tube having a main valve and connected with the pressurizing supply source; inlet- side and outlet-side pressurizing supply tubes one end of each of which is connected with the main supply tube and the other end of each of which is communicated with a respective space formed between a spring engaging surface of a corresponding seat assembly and flange tube, each of the inlet- side and outlet-side pressurizing supply tubes having a pressurizing valve therein; and a depressurizing connection tube, one end of which is connected

with the main supply tube and the other end of which is connected with a space (S1) formed between an inner circumferential surface of the valve body and an end portion of a shaft of the valve ball, said depressurizing connection tube including a depressurizing valve therein.

To achieve the above objects, there is provided a ball valve according to a second embodiment of the present invention which includes a valve body including a ball operating space formed interiorly therein; an opening portion formed in an upper portion of the valve body; a pair of flange-shaped body portions extending laterally therefrom and respectively defining an inlet and an outlet; and a cover for covering the opening in the body; a valve ball rotatably installed within the ball operating space and having a valve hole for communicating the inlet and outlet and an outer circumferential surface for blocking the inlet and the outlet; a seat assembly including a big diameter portion and a small diameter portion corresponding with a big diameter portion and a small diameter portion of a corresponding flange tube; a spring engaging surface formed between the big diameter portion and the small diameter portion; a pressurizing surface formed in an outer end portion; a seat ring having a slanted surface formed in an inner end portion for contacting with the valve ball and a depressurizing surface formed in an inner end portion and contacting with a space formed between an inner circumferential surface of the corresponding flange-shaped body and the valve ball; and a seat engaged with the slanted surface of the seat ring for contacting with an outer circumferential surface portion of the valve ball; a pressurizing spring for elastically urging the seat of the seat assembly to be closely contacted with an outer circumferential surface of the valve ball; 0-rings each inserted into the big diameter portion and small diameter portion of the seat ring, respectively, and closely contacting with the big diameter portion and the small diameter portion of the flange tube; and a seat pressure control means including a pressurizing fluid supply source; a main supply tube having a main valve and connected with the pressurizing supply source; inlet-side and outlet-side pressurizing supply tubes one end of each of which is connected with the main supply tube and the other end of each of which is communicated with a respective space formed between a spring engaging surface of a corresponding seat assembly and flange tube, each of

the inlet-side and outlet-side pressurizing supply tubes having a pressurizing valve therein; and a depressurizing connection tube, one end of which is connected with the main supply tube and the other end of which is connected with a space formed between an inner circumferential surface of the valve body and an end portion of a shaft of the valve ball, said depressurizing connection tube including a depressurizing valve therein.

To achieve the above objects, there is provided a ball valve according to a third embodiment of the present invention which includes a valve body including a cylindrical body portion and a pair of flange tubes engaged at respective sides of the body, said flange tubes respectively forming an inlet and an outlet and each having a big diameter portion and a small diameter portion formed in an inner circumferential surface of the same with a spring engaging surface formed between the big diameter portion and the small diameter portion; a valve ball rotatably installed within a ball operating space defined within the valve body and having a valve hole for communicating with an outer circumferential surface partitioning the inlet and the outlet and the inlet and the outlet, respectively; a seat assembly including a big diameter portion and a small diameter portion corresponding with the big and small diameter portions of the flange tube; a spring engaging surface formed between the big diameter portion and the small diameter portion; a pressurizing surface formed in an outer end portion; a seat ring having a slanted surface formed at an inner end portion for contacting with the valve ball and a depressurizing surface formed at an inner end portion and contacting with a space formed between an inner circumferential surface of the flange tube and an outer circumferential surface of the valve ball; and a seat engaged with the slanted surface of the seat ring and contacting with an outer circumferential surface portion of the valve ball; a pressurizing spring for elastically urging the seat of the seat assembly to an outer circumferential surface of the valve ball; 0-rings each inserted into the big diameter portion and small diameter portion of the seat ring, respectively, and closely contacting with the big diameter portion and the small diameter portion of the flange tube; and a seat pressure control means including a pressurizing fluid supply source; a main supply tube having a main valve and connected with the pressurizing supply source; inlet-side and outlet-

side pressurizing supply tubes one end of each of which is connected with the main supply tube and the other end of each of which is communicated with a respective space formed between a spring engaging surface of a corresponding seat assembly and flange tube, each of the inlet-side and outlet-side pressurizing supply tubes having a pressurizing valve therein; a depressurizing connection tube, one end of which is connected with the main supply tube and the other end of which is connected with a space formed between an inner circumferential surface of the body and an end portion of a shaft of the valve ball, said depressurizing connection tube including a depressurizing valve therein; and a plurality of bypass tubes each formed by extending the inlet-side pressurizing supply tube and the outlet-side pressurizing supply tube and contacting with the pressurizing surface and each having a bypass valve installed at a predetermined portion of the same.

Additional advantages, objects and features of the invention will become more apparent from the description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: Figure 1 is a cross-sectional view illustrating a conventional ball valve; Figure 2 is an enlarged cross-sectional view illustrating the portion"A" of Figure 1; Figure 3 is an enlarged cross-sectional view illustrating the portion"B" of Figure 2; Figures 4 through 8 are views illustrating a ball valve according to a first embodiment of the present invention, of which: Figure 4 is a cross-sectional view illustrating an open state of a ball valve according to the present invention; Figure 5 is a cross-sectional view illustrating a closed state of a ball valve according to the present invention; Figure 6 is an enlarged cross-sectional view illustrating the portion

"C"of Figure 4; Figure 7 is an enlarged cross-sectional view illustrating the portion "D"of Figure 6; Figure 8 is an enlarged cross-sectional view taken along line VIII- VIII of Figure 5; and Figures 9 through 11 are views illustrating a ball valve according to a second embodiment of the present invention, of which: Figure 9 is a cross-sectional view illustrating an open state of a ball valve according to the present invention; Figure 10 is an enlarged cross-sectional view illustrating the portion"E"of Figure 9; and Figure 11 is an enlarged cross-sectional view illustrating the portion"F"of Figure 10; Figures 12 through 15 are views illustrating a ball valve according to a third embodiment of the present invention, of which: Figure 12 is a cross-sectional view illustrating an open state of a ball valve according to the present invention; and Figures 13 through 15 are partial enlarged cross-sectional views illustrating a disassembling procedure of a ball valve according to the present invention.

MODES FOR CARRYING OUT THE INVENTION A first embodiment of the side entry type ball valve according to the present invention will now be explained with reference to Figures 4 through 8.

The ball valve according to the first embodiment of the present invention includes a valve body 110 having a ball operating space and an inlet P1 with outlet P2, a valve ball 120 rotatably installed in the ball operating space and having a valve hole 122 communicating the inlet P1 and the outlet P2 and an outer circumferential surface portion 121 blocking the inlet P1 and the outlet P2, seat assemblies 130 and 140 respectively installed in the inner circumferential surface portions of the inlet P1 and outlet P2 of the valve body 110, and a seat pressure control unit for pressing the seat assemblies 130 and 140 against the outer circumferential surface portion 121 of the valve ball 120.

In the present invention, the valve body 110 includes flange tubes 112 and 113 engaged to both sides of a cylindrical body 111. The ball operating space is formed by the cylindrical body 111 and the inner end portions of the flange tubes 112 and 113, and the inlet P1 and the outlet P2 are formed in the flange tubes 112 and 113, respectively.

Big diameter portions 112a and 113a and small diameter portions 112b and 113b are formed in the respective inner circumferential surfaces of the flange tubes 112 and 113 with a step (shouldered) therebetween. Spring engaging surfaces 112c and 113c against which pressurizing springs 134 and 144 of a seat pressurizing control unit are engaged are respectively formed by the steps (shoulders) between the big diameter portions 112a and 113a and the small diameter portions 112b and 113b.

Inner flange portions 112d and 113d fixedly engaged with both sides of the body 111 by fixing screws 114a and 115a or bolts are respectively formed in the inner end portions of the flange tubes 112 and 113, and outer flange portions 112e and 113e having screw holes 114b and 115b are respectively formed in the outer end portions of the same for connecting a pipe line (not shown).

The valve ball 120 includes an outer circumferential surface portion 121 blocking the inlet P1 and the outlet P2 valve ball 120 is rotated to its closed position and a valve hole 122 communicating the inlet P1 with the outlet P2 when the valve ball 120 is in its open position.

The valve ball 120 has at each of its top and bottom portions a protruded ball axis 123 by which the valve ball 120 is rotatably supported in a circular support hole 125a of a bearing plate 125 and a bushing 126 formed between the inner circumferential surface of the circular support hole 125a of the bearing plate 125 and the outer circumferential surface of the ball shaft 123.

The plate 125 is fixed to fixing protrusions 124 formed in an inner circumferential surface of the ball operating space by fixing pins 124a.

As shown in Figure 8, each bearing plate is configured with the circular support hole 125a formed at a center portion of a square plate, and the inner diameter of the circular support hole 125a is smaller than the outer diameter of the ball shaft 123 by the thickness of the bushing 126. The bushing 126 is

made of a material such as copper and is friction fitted.

As shown in Figures 4 and 5, a space S1 is formed between an end portion of the ball shaft 123 and an inner surface of the body 111, and spaces S2 and S3 formed by the outer circumferential surface 121 of the valve ball 120 are blocked by the bearing plate 125. As shown in Figure 8, since the bearing plate 125 is square-shaped, the space S1 and the spaces S2 and S3 communicate with each other through paths"a".

The ball rotation unit includes an operating control handle 127, a decelerating unit 128 decelerating the rotation of the operating control handle 127 and a stem 129 connecting an output shaft of the decelerating unit 128 with the upper ball shaft 123a.

The seat assemblies 130 and 140 include seat rings 131 and 141 respectively inserted into the inner circumferential surfaces of the flange tubes 112 and 113, and seats 132 and 142 respectively engaged with the seat rings 131 and 141 and closely contacting with an outer circumferential surface portion 121 of the valve ball 120.

As shown in Figures 6 and 7, the seat rings 131 and 141 include respective big diameter portions 131 a and 141 a and respective small diameter portions 131 b and 141 b respectively formed on an outer circumferential surface thereof and corresponding respectively with the big diameter portions 112a and 113a and the small diameter portions 112b and 113b formed on the inner circumferential surface of the flange tubes 112 and 113. Spring engaging surfaces 131 c and 141 c against which the other end portions of the pressurizing springs 134 and 144 of the seat pressure control unit to be described later are engaged are formed between the big diameters 131 a and 141 a and the small diameter portions 131b and 141b. Pressurizing surfaces 131d and 141d respectively opposite the inlet P1 and the outlet P2 are formed at respective outer end portions of the seat rings 131,141. Slanted surfaces 131e and 141e into which the seats 132 and 142 are respectively inserted are formed in respective inner end portions of the seat rings 131,141. Depressurizing surfaces 131f and 141f respectively contacting with the spaces S2 and S3 between the inner circumferential surface of the body 111 and the outer circumferential surface of the valve ball 120 are formed at respective inner end

portions of the seat rings 131,141.

The slanted surfaces 131e and 141e are formed to face with the inlet P1 and the outlet P2.

0-rings 133a, 143a and 133b, 143b are installed in ring grooves formed respectively in the outer circumferential surfaces of the big diameter portions 131 a and 141 a and the small diameter portions 131 b and 141 b of the seat rings and closely contact with the respective corresponding inner circumferential surfaces of the big diameter portions 112a and 113a and the small diameter portions 112b and 113b of the flange tubes 112 and 113.

Pressurizing springs 134 and 144 are installed between the spring engaging surfaces 112c and 113c of the flange tubes 112 and 113 and the spring engaging surfaces 131c and 141c of the seat rings 131 and 141 for elastically urging the seat rings 131 and 141 toward the valve ball 120.

The seat pressure control unit includes a pressurizing fluid supply source 151, a main supply tube 152 connected with the pressurizing fluid supply source 151 and having a main valve 152a installed at an intermediate portion thereof, pressurizing supply tubes 153 and 154 having respective pressurizing valves 153a and 154a, one end of each of which tubes 153,154 is connected with the main supply tube 152 and the other end of each of which is communicated with a respective space formed between the spring engaging surfaces 112c and 113c and 131c and 141c, and a depressurizing connection tube 155 having a depressurizing valve 155a, one end of which tube 155 is connected with the main supply tube 152 and the other end of which tube 155 is connected with the space S1 formed between the inner circumferential surface of the body 111 and the outer circumferential surface of the valve ball 120.

The pressurizing fluid supply source 151 pressurizes a fluid which does not react with the fluid flowing in the pipe in which the ball valve is connected.

For example, if the fluid flowing within the pipe is chlorine gas, N2 gas or an inert gas such as Ar may be used as the pressurizing fluid.

The depressurizing connection tube 155 passes through the wall of the body 111 and communicates with the space S1.

The valves 152a, 153a, 154a and 155a may be selected from a manual operating valve or a solenoid valve.

The operation of the ball valve according to the first embodiment of the present invention will now be explained with reference to the accompanying drawings.

In a state that an internal leakage due to the friction of the seats 132 and 142 does not occur, only the main valve 152a installed in the main supply tube 152 is closed, and the pressurizing valves 153a and 154a installed in the pressurizing supply tubes 153 and 154 and the pressurizing valves 155a installed in the depressurizing connection tube 155 are opened.

In this state, the seats 132 and 142 engaged to the seat rings 131 and 141 closely contact with the outer circumferential surface portion 121 of the valve ball 120 by the pressure applied to the pressurizing surfaces 131d and 141d of the seat rings 131 and 141 and the elastic force of the pressurizing springs 134 and 144, so that an internal leakage does not occur.

If there is a possibility that an internal leakage occurs due to the friction of the seats 132 and 142, the seat rings 131 and 141 in which the seats 132 and 142 are engaged are pressurized by the seat pressure control unit, so that the contacting force between the seats 132 and 142 and the valve ball 120 is increased for thereby preventing an internal leakage.

Namely, when a pressurizing fluid is supplied from the pressurizing fluid supply source 151 by closing the depressurizing valve 155a and opening the main valve 152a and the pressurizing valves 153a and 154a, the pressurizing fluid is supplied to the portions between the spring engaging surfaces 112c and 113c of the flange tubes 112 and 113 and the spring engaging surfaces 131 c and 141c of the seat rings 131 and 141 through the main supply tube 152 and the pressurizing supply tubes 153 and 154, so that the seat rings 131 and 141 are pressurized toward the valve ball 120, and the seats 132 and 142 engaged in the seat rings 131 and 141 strongly contact with the outer circumferential surface portion 121 of the valve ball 120 for thereby preventing an internal leakage.

At this time, assuming that the pressure of a pressurizing fluid is Pf, if the area of the pressurizing surfaces 131c and 141c of the seat rings 131 and 141 are"C", the pressures Pfu and Pfd applied to the spring engaging surfaces 131c and 141c are Pf x C.

Therefore, in a state that the valve is closed, the entire pressure Ptu applied to the seat ring 131 at the inlet P1 side is obtained by summing the pressure Pcau applied to the pressurizing surface 131d by the pressure Pcu of the fluid and the pressure Pfu applied to the spring engaging surface 131c by the pressurizing fluid, namely,"Pcau + Pfu". The entire pressure applied to the seat ring 141 at the outlet P2 side is obtained by summing the pressure Pcad applied to the pressurizing surface 141d by the pressure Pcd of the fluid at the outlet P2 side and the pressure Pfd applied to the spring engaging surface 141 c by the pressurizing fluid, namely,"Pcad + Pfd".

Here, even if the pressures Pfu and Pfd based on the entire pressure Ptu applied to the seat ring 131 at the inlet P1 side and the entire pressure Ptd applied to the seat ring 141 at the outlet P2 side are identical, in a state that the ball valve is closed, since the fluid pressure Pcu at the upstream inlet P1 side is relatively larger than the fluid pressure Pcd at the downstream outlet P2 side, the entire pressure Ptu is larger than the entire pressure Ptd.

Therefore, an internal leakage at the upstream inlet P1 side in which the fluid pressure Pcu is high is effectively prevented.

In addition, in a state that the ball valve is closed, if it is impossible to rotate the valve ball 120 because the pressure at the upstream inlet P1 side is too strong or the valve is damaged, the pressure applied to the depressurizing surfaces 131f and 141f of the seat rings 131 and 141 is increased more than the pressure which is obtained by summing the pressure applied to the pressurizing surfaces 131d and 141d and the elastic force of the spring rings 134 and 144, so that the valve ball 120 is able to be easily rotated by backwardly moving the seat rings 131 and 141.

As shown in Figure 5, in a state that the ball valve is closed, the pressurizing valve 153a and the depressurizing valve 155a at the inlet side are closed, and the main valve 152a and the pressurizing valve 154a at the outlet side are opened, namely, in a state that more than the difference pressure APt (=Ptu-Ptd) between the entire pressure Ptu applied to the seat ring 131 at the inlet side and the entire pressure Ptd applied to the seat ring 141 at the outlet side is applied, the pressurizing valve 154a at the outlet side is closed.

Thereafter, the depressurizing valve 155a is opened, and the

pressurizing fluid of the pressurizing fluid supply source 151 is supplied to the depressurizing surfaces 131f and 141f through the main supply tube 152, the depressurizing connection tube 155, the space S1 and the spaces S2 and S3, so that the pressure applied to the depressurizing surfaces 131f and 141f becomes a difference pressure At, and the depressurizing valve 155a is then closed.

In a state that the main supply tube 152 is exposed to the outside, when the main valve 152a and the pressurizing valve 153a at the outlet side are opened, the spaces S2 and S3 are exposed to the outside through the main supply tube 152, the depressurizing connection tube 155 and the space S1, and only an elastic force is applied to the spring engaging surfaces 131c and 141 c by the pressurizing springs 134 and 144.

At this time, a pressure more than APt is applied to the depressurizing surface 131f of the seat ring 131 at the inlet side. In addition, among the area A of the pressurizing surface 131d, the area B of the slanted surface 131e, the area C of the spring engaging surface 131c, and the area D of the pressurizing surface 131f, the following condition is satisfied: B+D>C+A. Since the pressure applied to the area C of the spring engaging surface 131c is"0" (atmospheric pressure), and the pressure applied to the slanted surface 131e and the pressurizing surface 131d is the same as the pressure Pcu of the fluid at the inlet side, the depressurizing force (Pb+Pd) applied to the seat ring 131 is larger than the pressurizing force (Pc+Pa+Ps), so that the seat ring 131 moves backwardly, and the seat 132 is separated from the outer circumferential surface portion 121 of the valve ball 120, so that the inlet P1 and the spaces S2 and S3 communicate with each other.

In this state, when the pressurizing valve 154a at the outlet side is opened, the depressurizing valve 155a is closed, and the main valve 152a and the pressurizing valve 153a are opened. The depressurizing force (Pb+Pd) applied to the seat ring 141 is greater than the pressurizing force (Pc+Pa+Ps) applied to the seat ring 131 at the inlet side, so that the seat ring 131 at the inlet side moves backwardly. Therefore, the seat 142 is separated from the outer circumferential surface portion 122 of the valve ball 120, and the outlet P2 communicates with the space S1 through the space S2.

At this time, since the inlet P1 communicates with the space S1 through the space S2 at the inlet side, and the outlet P2 communicates with the space S1 through the space S3 at the outlet side, the inlet P1 and the outlet P2 communicate with each other through the spaces S2, S1 and S3, and the fluid at the inlet P1 side flows toward the outlet P2 through the spaces S2, S1 and S3.

Therefore, the difference pressure APt between the entire pressure Ptu applied to the seat ring 131 at the inlet side and the entire pressure Ptd applied to the seat ring 141 at the outlet side is decreased, so that it is possible to rotate the valve ball 120 using a small amount of force, whereby it is possible to prevent friction and damage of the seats 132 and 142 and the ball 120 which are the disadvantages of the conventional ball valve.

In a state that the valve is opened, if the main valve 152a is closed, and the depressurizing valve 155a is opened, the pressure in the spaces S1, S2 and S3 and the pressure applied to the spring engaging surfaces 131c and 141 c become equalized. Therefore, the seat rings 131 and 141 moves forwardly by the elastic force of the pressurizing springs 134 and 144, and the seats 132 and 142 contact with the outer circumferential surface portion 121 of the valve ball 120.

In the case that the valve ball 120 is rotated and closed, when the main valve 152a is closed and the depressurizing valve 155a is opened, the pressure in the spaces S1, S2 and S3 and the pressure applied to the spring engaging surfaces 131c and 141c become equalized, so that the seat rings 131 and 141 move forwardly by the elastic force of the pressurizing springs 134 and 144, and the seats 132 and 142 contact with the outer circumferential surface portion 121 of the valve ball 120, whereby the inlet P1 and outlet P2 are blocked.

Figures 9 through 11 illustrate a ball valve according to another embodiment of the present invention.

As shown therein, the thickness (and hence the area) of the slanted surfaces 231 e and 241 e is greater than the thickness A (and hence the area) of the pressurizing surfaces 231 d and 241 d of the seat rings 231 and 241, and the pressurizing supply tube 253 at the inlet side and the pressurizing supply tube 254 at the outlet side are extended, and bypass tubes 256 and 257

communicate respectively with the pressurizing surfaces 231 d and 241 d, and bypass valves 256a and 257a are respectively installed in the bypass tubes 256 and 257. Parts and assemblies which are similar to those in the earlier embodiment of the present invention are assigned identical reference numerals and their repeated detailed description will be omitted.

In a state that the ball valve is closed, the main valve 252a, the depressurizing valve 255a, and the bypass valve 257a at the outlet side are opened, and the pressurizing valves 253a and 254a and the bypass valve 256a at the inlet side are closed.

In this state, the pressure at the inlet side is applied to the spring engaging surface 241c of the seat ring 241 at the outlet side through the bypass tube 256 at the inlet side, the pressurizing supply tube 253 at the inlet side and the pressurizing supply tube 254 at the outlet side. In addition, at the outlet side, the seat 242 closely contacts with the outer circumferential surface of the valve ball 220, so that it is possible to prevent an internal leakage between the inlet and outlet.

In the state that the ball valve is closed, when the bypass valve 256a is closed and the bypass valve 257a is opened, the pressure applied to the spring engaging surface 231 c of the seat ring 231 at the inlet side is removed through the pressurizing supply tube 253 at the inlet side, the pressurizing supply tube 254 at the outlet side, and the bypass tube 257 at the outlet side, and the seat ring 231 at the inlet side moves backwardly. At the same time, the pressure applied to the spring engaging surface 241 c of the seat ring 241 at the outlet side is removed through the pressurizing supply tube 254 at the outlet side and the bypass tube 257. In the seat ring 241 at the outlet side, the pressure Pcd at the outlet P2 is applied only to the pressurizing surface 241 d and the slanted surface 241 e. At this time, since the thickness B (and hence the area) of the slanted surface 241 e is larger than the thickness A (and hence the area) of the pressurizing surface 241d, the pressure Pcbd applied to the slanted surface 241 e is larger than the pressure Pcad applied to the pressurizing surface 241 d, so that the seat ring 241 moves backwardly. Therefore, the seats 232 and 242 are separated from the outer circumferential surface portion 221 of the valve ball 220, and the inlet P1 and the outlet P2 communicate with each other

through the spaces S2 and S3. Therefore, the fluid in the side of the inlet P1 flows toward the outlet P2, and the difference pressure AP between the inlet and the outlet is decreased.

In the present invention, because the inlet P1 and the outlet P2 can be communicated via the bypass tubes 256 and 257 and the pressurizing supply tubes 253 and 254, in a state that the ball valve is closed, it is possible to control the bypass valves 256a and 257a without rotating the valve ball 220, whereby a predetermined amount of fluid can be made to flow from the inlet P1 to the outlet P2.

Therefore, a large amount of fluid is able to flow by the rotation of the valve ball 220, and a small amount of fluid is able to flow by operating the bypass valves 256a and 257a, so that the ball valve is applicable as a control valve.

In a state that the bypass valves 256a and 257a of the bypass tubes 256 and 257 are closed, the above-described operation is also implemented.

Figures 12 through 15 illustrate a ball valve according to another embodiment of the present invention which is adapted to a top entry type ball valve.

In this embodiment of the present invention, a valve body 310 is configured to have an inlet P1 and an outlet P2, and a ball operating space is formed therein. In this embodiment, the ball valve includes a valve body 310 formed as a single unit with a pair of flange-shaped bodies 312,313 extending outwardly at the respective sides thereof. An opening 311 is formed in the top of the valve body 310 for permitting the insertion of a valve ball 320 and seat rings 331,341 into the valve body 310. The opening 311 is closed by a cover 319 which carries a ball operating shaft and seat ring fixing screws as will be descried in more detail below. Here, parts and assemblies which are similar to those in the eariier-described embodiments of the present invention are assigned identical reference numerals and their repeated detailed description will be omitted.

The cover 319 is engaged to the valve body 310 by fixing screws or bolts.

Seat ring fixing screws 361 and 362 are threadedly engaged in the

bodies 312 and 313 for fixing the seat rings 331 and 341 in respective rearwardly moved positions. Fixing portions 361 a and 362a are formed in the respective lower end portions of the seat ring fixing screws 361 and 362, and fixing grooves 335 and 345 corresponding with the fixing portions 361 a and 362a are respectively formed in the seat rings 331 and 341.

The seat ring fixing screws 361 and 362 have respective square head portions 361 b and 362b, and corresponding wrench shafts 363 and 364 are rotatably engaged in the cover 319 for respectively rotating the seat ring fixing screws 361 and 362.

Preferably, the fixing portions 361 a and 362a and the fixing grooves 335 and 345 are conically shaped. Square groove portions 363a and 364a are respectively formed in the lower end portions of the wrench shafts 363 and 364 to be engaged with the square head portions 361 b and 362b of the seat ring fixing screws 361 and 362, and corresponding square head portions 363b and 364b are respectively formed on the upper end portions of the same for implementing an easier rotation of the screws 361,362.

In the drawings, reference numerals 365 and 366 represent 0-rings for sealing the portion between the cover 319 and the wrench shafts 363 and 364.

The seat ring fixing screws 361 and 362 and the wrench shafts 363 and 364 are shown in Figure 13.

As shown in Figure 13, the fixing portions 361 a and 362a of the seat ring fixing screws 361 and 362 are not inserted into the fixing grooves 335 and 345 of the seat rings 331 and 341. Namely, the fixing portions 361 a and 362a are separated from the big diameter portions 331 a and 341 a of the seat rings 331 and 341, so that the seat rings 331 and 341 move forwardly and rearwardly by the pressurizing and depressurizing operation. Since the opening/closing operation and the pressurizing and depressurizing operations are the same as the embodiments of Figures 4 through 8, the detailed description thereof will be omitted.

In this embodiment of the present invention, the valve ball and the seats may be disassembled without disengaging the valve body 310 from the pipe line.

Namely, the seat rings 331 and 341 are rearwardly moved in the manner

of the embodiments of Figures 4 through 8 from the state shown in Figure 13 to the state shown in Figure 14. Therefore, the fixing portions 335 and 345 of the seat rings 331 and 341 are positioned below the corresponding fixing portions 361 a and 362a of the seat ring fixing screws 361 and 362. In this state, the square head portions 363d and 364d of the wrench shafts 363 and 364 which are rotatably engaged in the cover 319 are rotated using a tool such as a wrench, etc. in the screw engaging direction, whereby the seat ring fixing screws 361 and 362 having the square head portions 361 b and 362b inserted into the square groove portions 363a and 364a of the wrench shafts 363 and 364 are rotated in the engaging direction. The fixing portions 361 a and 362a are respectively engaged into the fixing grooves 335 and 345 of the seat rings 331 and 341. In this state, even when the depressurizing force by which the seat rings 331 and 341 are backwardly moved is removed, the seat rings 331 and 341 are kept in a rearwardly moved state.

Thereafter, even when the cover fixing screws 319a are disengaged, and the cover 319 is removed, as shown in Figure 15, the seat rings 331 and 341 remain in a rearwardly moved or retracted state by virtue of the seat ring fixing screws 361 and 362. In this state, the valve ball 320 is able to be removed to the outside through the opening 311 for thereby effectively taking out the valve ball 320.

I n the state that the valve ball 320 is removed, the seat ring fixing screws 361 and 362 are rotated in the screw disengaging direction using a tool such as a wrench for thereby separating the fixing portions 361 a and 362a from the fixing grooves 335 and 345 of the seat rings 331 and 341. Thereafter, the seat rings 331 and 341 are moved to the ball operating space and then are removed through the opening 311 for thereby disassembling the seat rings 331 and 341.

When assembling the valve ball 320 and the seat rings 331 and 341, the assembling procedure of the same is performed in the reverse sequence of the disassembling operation.

In the present invention, it is possible to disassemble the valve ball 320 and the seat rings 331 and 341 without removing the valve body 310 from the pipe line. Therefore, it is possible to easily implement an exchange operation of the valve ball 320 and the seat rings 331 and 341.

In the present invention, the embodiment of Figures 4 through 8 is adapted to the top entry type ball valve. More preferably, the embodiment of Figures 9 through 11 may be adapted to the top entry type ball valve.

As described above, according to the present invention, although the seats and valve ball become worn, it is possible to prevent an internal leakage without inserting a sealant. In addition, in a state that the ball valve is closed, if there is a big pressure difference between the inlet and the outlet, the valve ball is still able to be easily rotated for thereby opening the same, so that the seats and valve ball are not easily worn.

In addition, in a state that the ball valve is closed, it is possible for a small amount of fluid to flow from the inlet to the outlet, and a large amount of fluid to flow by rotating the valve ball. Furthermore, it is possible for a small amount of fluid to flow by controlling the bypass valve. Therefore, the ball valve according to the present invention may be used as a control valve.

If the ball valve according to the present invention is adapted to a top entry type ball valve, it is possible externally to fix the seat rings in a state that the seat rings are rearwardly moved. Therefore, the valve ball and seats are easily removed without disassembling the valve body from the pipe line.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as recited in the accompanying claims.