Valves and valve actuation – Fluid actuated or retarded – With mechanical movement between actuator and valve
Reexamination Certificate
2001-06-07
2004-03-23
Bastianelli, John (Department: 3754)
Valves and valve actuation
Fluid actuated or retarded
With mechanical movement between actuator and valve
C251S192000
Reexamination Certificate
active
06708946
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a valve for controlling the flow of the fluid through a bore and particularly, but not exclusively, the invention relates to a ball valve for use in the oil and chemical process industry.
BACKGROUND OF THE INVENTION
Ball valves are commonly used in both industries. The type of ball valve of interest in relation to controlling flow of a fluid is an apertured ball valve such as is disclosed in applicant's co-pending published Patent Application No. WO 93/03255 which was published on Feb. 18, 1993. In an apertured ball valve the valve operation or function may be broken down into two separate stages. Firstly, the ball moves between an open and a closed position by rotating through 90° such that the ball aperture from an orientation coaxial with the flow direction, i.e. when the valve is open, to a position whereby the ball aperture is normal or perpendicular to the flow direction. Secondly, the valve seals in the closed position to prevent flow through the bore across the ball valve. Therefore, the on-off control of flow through the valve is achieved by rotating the ball through 90° within the valve housing.
There are two basic types of ball valve mechanism which currently exist which fulfil the above functions. Firstly, there is the trunnion mounted ball system in which the ball element is positionally constrained inside the valve, usually by radial bearings. The ball is rotated by the application of torque to the trunnion. Sealing occurs as a result of the valve seat “floating” onto the ball element. The advantage of this system is that it provides highly reliable rotation between the valve open and the closed positions. The principal disadvantage of this system is that seal reliability is reduced because the sealing force only develops in proportion to the annular area of the valve seat. Thus, when trunnion mounted ball systems are used in high pressure wells and especially those in which the well fluid has a high proportion of particulate matter, being generally known as “aggressive” wells, the pressure is such that the particulate matter can leak past seals between the ball and the valve seats and become jammed in all surfaces of the valve. This often results in the valve not achieving integrity of sealing. In such cases this type of ball valve is unable to operate properly in such conditions.
The second type of ball valve mechanism which effects the abovementioned function is known as the “floating ball system”. In this system the ball is not positionally constrained relative to the valve body. Rotation is caused by the application of force to a point which is offset from the ball centre which, in conjunction with the mating curvatures of the ball and seat, cause the ball to rotate. Sealing occurs as a result of the ball “floating” onto the valve seat. The advantage of this mechanism is that the reliability of the seal is increased because the sealing force develops in proportion to the circular area of the ball to seat contact. The disadvantage of this type of mechanism is that the rotational reliability is reduced as the friction factor between the ball and seat are considerably larger than that of trunnion mounted devices. With aggressive types of wells and particulate flows of the type described above, the reliability of this valve creates a problem in that the valve seizes between the open and the closed position giving rise to serious problems in both operational and safety terms.
An object of the present invention is to provide improved ball valve which obviates or mitigates at least one of the aforementioned disadvantages.
SUMMARY OF THE INVENTION
This is achieved by allowing a very slight movement of a ball valve retaining mechanism to allow that the ball element to be unloaded off the valve seat during rotation, but remain in contact with the valve seat so as to prevent debris ingress between the ball and the valve seat, and to instantaneously reload onto the valve seat upon the event of closure. This instantaneous and automatic redirection of the reaction load path at the occurrence of closure provides an effective seal against high pressure aggressive fluids to prevent fluid escaping beyond the valve components whilst, at the same time, allowing effective rotational movement of the valve to occur without providing rotational reliability.
This solution allows conflicting load paths through the valve to be resolved, namely through the trunnion during rotation and through the valve seat during sealing.
The slight movement of the ball retaining mechanism which is required may be variable depending on a number of factors but requires to be only very slight and in the preferred arrangement hereinafter described is of the order of 0.025″ (0.60 mm).
According to one aspect of the present invention, there is provided a ball valve structure comprising:
a valve housing having a wall defining a housing bore having a longitudinal bore axis,
an apertured ball element disposed within a ball cage, said ball element and said ball cage being disposed within said bore for rotation between a first position in which said ball element is oriented such that the aperture of the ball element is aligned with the bore, this position defining a valve open position, and a second position in which said ball element is rotated through approximately 90° such that said ball element fully obstructs said bore, this position being defined as the closed position,
piston means disposed within said housing and coupled to said ball element such that movement of said piston means in the direction of the longitudinal axis of said bore causes said ball element to rotate between said open and said closed position,
valve seat means disposed downstream of said ball element between said ball element and a valve housing cap, said valve seat means being coupled to first resilient means for applying a first spring force for biasing said valve seat into contact with said ball element as it moves between said open and said closed positions,
compression spring means coupled to said piston means and responsive to movement of said piston means to move between a first position defining a first compressive spring force sufficient to maintain said ball element in said closed position and a second compressed position in which said piston is actuated to move that said ball element to said open position, said first compression spring means being retained in a direction substantially parallel to said longitudinal bore axis within said housing by a top plate means and by said lower plate means,
a generally tubular mandrel coupled to said ball cage and to said bottom plate means, such that said mandrel, said ball cage and ball element and said valve seat are constrained to be moved together,
second resilient means disposed between the bottom plate means and said valve housing for applying a second spring force to said mandrel assembly for biasing said mandrel assembly, said ball element and said ball cage towards said valve seat, said second spring force being selected to be less than the force of said compression spring means when said ball element is in said open and closed position but greater than the spring force of said first resilient means when said ball valve is in the closed position,
the arrangement being such that in response to an applied force said piston means is moveable to rotate said ball element to an open position and to compress said compression spring means to a compressed state in which a compressed spring force in said compressed state which is greater than the second spring force applied by said second resilient means, and the first resilient means applies said first spring force to said valve seat to bias said valve seat to remain in contact with said ball element in said open position and,
in the absence or removal of the force applied to said piston means, said compression spring means urges said piston means towards said housing cap such that such ball element is rotated by substantially 90° to a just-closed position where said t
Cowie Gavin David
Edwards Jeffrey Charles
Bastianelli John
Expro North Sea Limited
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
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