Ball valve

1. A ball valve comprising:

an inlet and an outlet with a flow path for fluid therebetween;

a rotatable ball positioned in the flowpath, wherein the flow of fluid along the flowpath is dependent on the rotation of the ball;

a first bellow arranged between the inlet and the ball, wherein the first bellow is fixed in a housing under compression so that a mechanical seal is maintained between a seat of the first bellow and the ball; and

a second bellow arranged between the outlet and the ball, wherein the second bellow is fixed in the housing under compression so that a mechanical seal is maintained between a seat of the second bellow and the ball;

a stem that extends from first and second sides of the ball;

a third bellow arranged around the stem extending from the first side of the ball, wherein the third bellow has an integral seat in contact with the ball; and

a fourth bellow arranged around the stem extending from the second side of the ball, wherein the fourth bellow has an integral seat in contact with the ball;

wherein the third and fourth bellows have longitudinally elastic properties and are fixed in the housing under compression such that the compression in the third and fourth bellows ensures a mechanical seal between the seats of the third and fourth bellows and the ball;

wherein at least the third bellow comprises a polymeric material seal between the stem and a plug of the third bellow and the stem extends through the polymeric material seal out of the housing;

wherein the polymeric material seal is arranged in the housing so that fluid from the main flow path can only reach the polymeric material seal if the fluid leaks across at least the mechanical seal between the seat of the third bellow and the ball;

wherein each of the first and second bellows comprises: a seat, which is metallic, at an end of the bellow for providing a contact surface with the ball of the ball valve; and

a metallic body integral with the seat;

wherein the metallic body has a longitudinally elastic property such that substantially only the compression in the bellow causes the seat to apply a sealing force against the ball of the ball valve that maintains a mechanical seal between the seat and the ball of the ball valve; and

wherein the bellow further comprises an integral plug, at an opposite end of the bellow to the seal, the plug being Electron Beam or laser welded to the exterior of the housing of the ball valve.

2. The ball valve according to claim 1 , wherein the only manufactured components in the housing of the ball valve that are configured to force the seats of the first and second bellows against the ball are the first and second bellows.

3. The ball valve according to claim 1 , wherein for each of the first and second bellows, a cross-section of the bellow comprises a series of linear sections connected to each other by 90 degree turns, wherein a first thickness of a linear section aligned along a longitudinal axis of the bellow is 1.5 mm, a second thickness of a linear section aligned perpendicular to the longitudinal axis of the bellow is 1.2 mm, the spacing between linear sections aligned perpendicular to the longitudinal axis of the bellow is 2 mm and the spacing between linear sections aligned along the longitudinal axis of the bellow is 4 mm.

4. The ball valve according to claim 1 ,

wherein the housing, first, second, third and fourth bellows and ball are made from an austenite nickel-chromium-based superalloy; and

wherein the first, second, third and fourth bellows are fixed to the housing by Electron Beam or laser welding.

5. The ball valve according to claim 1 , wherein the torque required to rotate ball is 400 Nm or less under all operating conditions of the ball valve.

6. A method of manufacturing a ball valve, the method comprising:

positioning a ball of a ball valve in a housing of the ball valve;

positioning a first bellow, which is metallic, in the housing such that a seat, which is metallic, at a first end of the first bellow is in contact with a first side of the ball, wherein the first bellow has a longitudinally elastic property and the seat of the first bellow is integral with the body of first bellow;

positioning a second bellow, which is metallic, in the housing such that a seat, which is metallic, at a first end of the second bellow is in contact with a second side of the ball, wherein the second bellow has a longitudinally elastic property and the seat of the second bellow is integral with the body of second bellow;

applying a force that compresses the first and second bellows; and

welding the second ends of the first and second bellows to the housing when the first and second bellows are under compression, such that, when welded, substantially only the compression of the first and second bellows causes the seats of the first and second bellows to apply a sealing force against the ball; and

said sealing force maintains a mechanical seal between each seat and the ball;

wherein said second ends of the first and second bellows each comprise an integral plug, at the opposite end of the bellow to the seat; and

said welding the second ends of the first and second bellows to the housing comprises Electron Beam or laser welding each plug of the first and second bellows to the exterior of the housing;

the method further comprising:

positioning a third bellow, which is metallic, in the housing such that a seat, which is metallic, at a first end of the third bellow is in contact with a third side of the ball, wherein the third bellow has a longitudinally elastic property and the seat of the third bellow is integral with a body of the third bellow;

positioning a fourth bellow, which is metallic, in the housing such that a metallic seat at a first end of the fourth bellow is in contact with a fourth side of the ball, wherein the fourth bellow has a longitudinally elastic property and the seat of the fourth bellow is integral with a body of the fourth bellow;

applying a force that compresses the third and fourth bellows; and

welding the second ends of the third and fourth bellows to the housing when the third and fourth bellows are under compression, such that, when welded, substantially only the compression of the third and fourth bellows causes the seats of the third and fourth bellows to apply a second sealing force against the ball; and

said second sealing force maintains a mechanical seal between each seat of the third and fourth bellows and the ball;

wherein the first and second bellows are arranged co-linearly with each other;

the third and fourth bellows are arranged co-linearly with each other; and

the longitudinal axes of the third and fourth bellows are perpendicular to the longitudinal axes of the first and second bellows; and

wherein the third bellow is arranged around a stem that extends from the ball and a polymeric material seal is provided such that fluid from the main flow path through the ball valve can only reach the polymeric material seal if the fluid leaks across the mechanical seal between the seat of the third bellow and the ball.

7. The method according to claim 6 , further comprising:

turning the ball of the ball valve when the first and second bellows are under compression; and

determining to weld the first and second bellows to the housing in dependence on a torque required to turn the ball valve being within a desired range of torque values.

8. The method according to claim 6 , further comprising:

repeatedly changing the applied force to compress the first and second bellows and measuring the torque required to turn the ball of the ball valve until a measured torque has a predetermined value.

9. The method according to claim 6 , wherein the third and fourth bellows are positioned in the housing and compressed prior to the first and second bellows being positioned in the housing and compressed.

10. The method according to claim 6 , wherein, other than the first and second bellows, the method does not comprise providing any other components in the housing for contributing to the applied sealing force between the seats of the first and second bellows and the ball.

11. A ball valve manufactured according to the method of claim 6 .

12. The method according to claim 6 , further comprising:

turning the ball of the ball valve when the third and fourth bellows are under compression; and

determining to weld the third and fourth bellows to the housing in dependence on a torque required to turn the ball valve being within a desired range of torque values.

13. The method according to claim 12 , further comprising:

repeatedly changing the applied force to compress the third and fourth bellows and measuring the torque required to turn the ball of the ball valve until the measured torque has a predetermined value.