Double block and bleed ball valves including retainer components

A valve of the double block and bleed type construction comprises a first valve assembly housing a first ball valve and a second valve assembly housing a second ball valve. The first and second ball valves are independently actuable between open and closed positions. Each of the ball valves are held within the particular valve assembly by an annular retainer component. Each valve assembly has a passage through which fluid can pass when the ball valve is in an open condition and also a mating surface which is brought to bear against the mating surface of the other valve assembly to form a valve with a single joint.

BACKGROUND OF THE INVENTION
 The invention to which this application relates is an improved valve
 construction. In particular the invention is related to improvements for
 the type of valve known in the trade as a double block or a double block
 with bleed valve (hereinafter both referred to as a double block valve).
 This type of valve is used in pipelines as an isolation valve and
 comprises first and second ball valve assemblies in an in line
 configuration. The provision of the two ball valve assemblies means that
 if one of the assemblies fails there is still another valve assembly
 operational.
 The double block valve is commonly connected to pipelines in process, oil
 and gas and instrumentation industries such as refineries for carrying
 compressible, incompressible, or combinations of these fluids. The use of
 the valve is well known in the trade and can be provided to allow safe
 isolation of parts of the pipeline to allow repair or maintenance work
 and/or the connection of monitoring and/or injection apparatus. The valve
 is normally provided with a vent facility which is located between the two
 valve assemblies so as to allow for the controlled venting of the fluid
 carried in the pipeline and the collection of samples.
 There are many different designs of double block valve assemblies but
 generally they comprise a valve body in which the valve components are
 held, with a vent formed therein. The valve body is provided with a
 passage therethrough, and into said passage, and from each end thereof,
 are fitted the respective valve assembly components of the ball, seats and
 seals. When the components are fitted into the passage from each end, the
 components are locked in position by the insertion of retaining members
 into each end of the passage. This design of valve has been used for a
 considerable period of time but has several disadvantages, in that the
 valve is relatively long and bulky and also that the valve has at least
 two joints where leakage or failure of the valve can occur. In the example
 described the joints are created between the retaining means inserted at
 each end of the passage, at which failure and leakage can occur. It is
 accepted that the greater the number of joints in the valve then the
 greater the risk of leakage occurring and, when one considers that the
 fluids being carried can be hot, toxic, corrosive and/or combustible, it
 will be appreciated that any leakage can be catastrophic.
 Patent application no. 2271164 discloses an arrangement for a double block
 valve where there is provided a sealing element which is inserted into the
 valve body and which acts as a common element for both of the ball valve
 assemblies. This is claimed to reduce the overall length of the double
 block valve assembly. However the valve according to this patent still has
 at least two joints at which leakage can occur, these being between each
 of the assemblies and the intervening common valve seat.
 GB2064730 describes a butterfly valve arrangement having a pair of
 rotateable flaps internally of the valve which are operated by a single
 actuation means and close simultaneously. A venting arrangement is
 provided in conjunction with the flaps such that the venting arrangement
 is opened to allow for drainage when the two flaps and thus the valve is
 closed. The valve is stated as being for the food and drinks industries,
 and is insubstantial in that a significant fluid pressure build up behind
 either of the flaps may burst same causing catastrophic failure.
 DE3339472 discloses a valve consisting of two independently operable ball
 valves encased within a single housing and further having an adjustable
 resilient elastomeric member between and contacting the ball valve
 assemblies to create a seal therebetween. The resilient member is
 elongated between the ball valves to compress same by means of driving one
 or more arrow-headed members transversally into the member to deform same
 longitudinally. The valve is not formed from two separable assemblies, and
 cannot therefore be used in the gas and oil industries.
 U.S. Pat. No. 4,335,747 describes a valve having two rotateable ball valves
 housed in separate assemblies, one of said ball valves being substantially
 spherical and the other being generally spherical but having a spherically
 arcuate recess which receives a portion of the other substantially
 spherical ball valve. In the closed condition, the partially spherically
 shaped ball valve is prevented from being rotated by the spherically
 shaped ball valve, and therefore not only is the operation of the ball
 valves dependent on one another, the removal of one of the assemblies will
 affect the integrity of the remaining assembly because in the closed
 condition, one ball valve provides support for the other.
 SUMMARY OF THE INVENTION
 The aim of the present invention is to provide a double block valve in
 which the risk of leakage and failure of the same is minimised without
 unduly affecting the length of the same or affecting any of the other
 characteristics of the same and ensuring that the valve meets the
 appropriate safety and manufacturing standards.
 In a first aspect of the invention there is provided a valve comprising a
 first ball valve assembly and a second ball valve assembly, each of said
 first and second ball valve assemblies having a passage therethrough in
 which a first seal, an apertured ball valve and a second seal are
 disposed, said ball valves being independently actuatable between open and
 closed positions to allow fluid flow through the valve when both ball
 valves are in the open condition, characterised in that said first and
 second ball valve assemblies further comprise apertured retainer
 components lockingly inserted into each assembly to retain the ball valve
 component and first and second seals in each assembly and in that the
 assemblies are brought together to mate with one another with their
 respective passages substantially in alignment to form the valve with only
 a single joint. In one preferred embodiment the first and second ball
 valve assemblies are provided as contained modules which are brought
 together and held in position so as to form the said valve with the single
 joint at the interface of the said two modules.
 In one preferred embodiment the assemblies are engaged in location by means
 of external locking means.
 Typically each ball valve assembly is a self contained module. In one
 embodiment the module comprises a body with a passage formed therethrough
 said passage having a narrow end and a relatively wider end through which
 the components of the valve can be packed into the body, said components
 being the first seal, the ball valve, the second seal and the retainer.
 The retainer is typically inserted into engagement with the wider end of
 the passage once the first seal, ball and second seal are inserted into
 the passage and serves to hold the components in the passage and has an
 aperture therethrough to complete the passage through the body.
 Typically the retainer is held in engagement with the body by providing
 threaded portions on the retainer and passage which allows the retainer to
 be screwed into position and also to exert any required packing force on
 the ball and seals against the narrower end of the passage.
 To form the valve according to the invention, two of the ball valve modules
 are brought into mutual position such that the outer faces of the
 retainers, which in one embodiment lie flush with the outer face of the
 respective assembly bodies, are held adjacent one another with the
 respective passages in line, and then the assemblies are engaged in that
 position to form the double block valve.
 It will therefore be appreciated that the only joint in the valve according
 to the invention is that between the adjacent end faces of the two
 modules.
 Typically each of the valve assemblies includes a ball actuation means to
 allow the valve to be moved between open and closed positions. In one
 preferred embodiment a packing retainer is provided for the packing in the
 actuation means stem and said packing retainer is locked in position by
 means of a cam headed locking screw which is positioned adjacent a flat of
 the packing retainer and the cam secured in position so as to prevent
 accidental removal of the packing or loosening due to vibration or other
 means.
 Preferably the stem is provided of a shape and dimension so as to allow low
 emission type packing to be used such as, for example, the packing sold
 under the trade mark Enviroflex, a trade mark of Flexitellic Limited.
 Thus according to an other aspect of the invention there is provided a
 modular valve formed from two valve assembly modules held in engagement,
 each module a self contained valve assembly.
 The valve formed according to this invention allows one of the modules to
 be removed for repair or maintenance without affecting the integrity of
 the other valve module. This is not possible with conventional valves of
 this type.
 A further feature of the valve according to this invention is that a single
 body seal lies within the joint between respective assemblies to prevent
 leakage of fluid through the joint. Typically the body seal will have a
 continuous surface between the end faces of the valve modules which form
 the single joint. One suitable body seal is a metallic lens ring such as
 that sold under the trade mark Techlok.
 In a preferred embodiment there is provided a further seal assembly which
 comprises a sealing element located between the retainers in the assembled
 valve, said sealing element acting to prevent the leakage of fluid from
 the passage of the valve into the joint between the retainers.
 In a further aspect of the invention the valve includes a locking means
 which is located between the end faces of the retainers of respective
 valve assemblies when the valve is assembled, said locking means
 positioned such that relative movement of the retainers within the valve
 when formed is prevented.
 Typically the locking means is a ring which is formed of a material which
 preferably has a higher degree of resilience than the body seal so as to
 allow compression of the locking means prior to the body seal and hence
 act as a means to absorb vibrationery or other forces on the retainers
 from causing the same to move position in the valve. This ensures that the
 unscrewing or loosening of the same during the service of the valves is
 prevented. This locking assembly can also be provided as the sealing
 element to prevent crevice erosion occurring and can be used in any double
 block valve, even with multiple joints.
 In whichever embodiment of the invention the valve is typically provided
 with a vent assembly. Said vent assembly is provided to be operated from
 externally of the valve body and is in connection with the valve passage.
 In one embodiment the vent assembly is connected to one of the valve
 modules and forms an integral part thereof. In an alternative embodiment
 the vent assembly can be located in a member inserted to lie between the
 modules when joined to form the valve. It is however preferred that the
 vent arrangement takes the form as shown wherein the vent assembly is
 connectable with one of a plurality of apertures formed in the passage
 wall. This connection can be a direct connection or alternatively the
 apertures can be connected to a common chamber to which the vent assembly
 or assemblies can be connected in the required location on the valve. This
 is described in the applicant's co-pending patent application.
 In a yet further aspect of the invention there is provided a method of
 assembling a double block valve, said method comprising the steps of
 forming a first ball valve assembly module by forming a body having a
 passage, one end of which is of sufficient size to allow the valve
 components to be moved into the passage, inserting said components,
 comprising a ball, and sealing elements, into the passage in the required
 sequence, trapping the components in the passage by inserting a retainer
 to reduce the size of the said passage end, engaging the ball with
 actuating means to allow movement of the module between valve open and
 closed positions, repeating the process to form a second ball valve
 assembly module, bringing the modules together so that the end faces in
 which the retainers are located are adjacent and the passages in
 respective modules are in line and engaging the modules together to form
 the valve.
 In a preferred embodiment a venting arrangement is fitted to either one of
 the modules or to a member positioned between said modules when engaged.
 Thus the single joint of this invention is formed between any two major
 body components which in combination form the said double block valve.
 Thus, a preferred embodiment of the valve can have the double block valve
 comprising of two full bore valve balls which is compact within the
 International Standard Lengths dictated by ANSI and others.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring now to the drawings there is shown a valve 2 according to the
 invention with the central portion of the passage 4 removed to show the
 components of the valve in section. The passage 4 passes through the
 length of the valve 2 and the valve is typically joined to other
 components such as monitoring instruments and/or a pipeline by means of
 flanges 6,8.
 The valve shown is known as a double block and vent (bleed) valve and
 comprises two ball valve assembly modules 10, 12 and a vent assembly 14.
 The vent assembly is connected to the passage 4 via port 5 and is
 positioned intermediate the balls of the ball valve assembly modules 10,
 12 to allow the controlled venting of fluid from the passage 4 and hence
 the pipeline.
 The modules 10,12 are each provided with a passage 4A, 4B of larger
 diameter in which the valve components are located and so the passage ends
 4A', 4B' are relatively larger to allow the components to be fitted into
 the passage when assembled.
 Each valve module, as shown in FIG. 2 with respect to module 10, includes a
 first seal 14 which is first placed in position in the passage 4A and also
 provides fire retardant features in combination with the second seal 18 as
 shown in FIG. 3D. The ball 16 is then placed in position and is followed
 by the second seal 18. When these components are in position a retainer
 20, with threaded side walls, is screwed into a threaded portion 21 of the
 passage through end 4A', and this serves to retain the components in
 position in the passage as shown in FIG. 1. The retainer has a central
 aperture 23 of substantially the same diameter as the passage 4 so as to
 ensure that there is provided a passage 4 through the valve as required.
 The same process is repeated for module 12 using components 14'-20'. The
 retainers 20,20' are provided in a mutual relationship as shown in FIG. 3B
 to act to lock, form seats for and retain the balls of the ball valves in
 position.
 Each module is provided with an actuating means 24 in connection with the
 ball 16, 16' to allow the valve assembly to be moved between open and
 closed conditions. The actuating means comprises a valve stem 26 (shown in
 detail in FIG. 3A) connected to a packing retainer 28 and a lever 30 to
 allow actuation. The packing retainer is typically required to be
 maintained in the closed position to trap the packing in the stem 26, said
 packing typically low emission packing, and to ensure that the same is not
 accidentally moved, or influenced by vibration, is locked in position by a
 cam headed locking screw 32 which contacts with a flat of the packing
 retainer 28 (see FIG. 3C) in such a manner to ensure that the packing
 retainer cannot be rotated until the cam headed locking screw is first
 released and removed.
 With each of the valve modules formed, the end faces 4A', 4B' of the same
 are brought into engagement and as this is done they trap a body seal 38
 in position as shown and a sealing and locking means 40 in position as
 shown. When in position, external retaining means, not shown, act to clamp
 the two modular valve assemblies together to form the valve according to
 the invention. It will readily be appreciated that the valve formed only
 has one joint 42 and so the opportunity for leakage and/or failure to
 occur is significantly reduced in comparison to the conventional double
 block valves which have at least two joints.
 A further advantage of the valve according to this invention is that the
 valve is formed from two modular assemblies, each of which can be
 disengaged for repair or maintenance without affecting the integrity of
 the other. This therefore means that a module can be removed, taken for
 repair in a clean environment and at the same time replaced with another
 module easily and quickly.
 The valve according to the invention can also be manufactured to meet all
 relevant International Standards such as ANSI B 16.5, ANSI B16.10, ANSI B
 16.34, API 6D, API Spec6FA, API 598, API 607, BS6755, EEMUA182.