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. 2064730 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.

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, said valve comprising a first ball valve assembly and a second ball valve assembly, said first and second assemblies provided with a passage to allow fluid to flow therethrough when open, and wherein the valve assemblies and components therein are held in position, with or without a further valve component, to form a valve with 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. Alternatively the first and second ball valve assemblies are held in a common valve body and enclosed therein by a closing ring or plate component and said single joint is formed between the plate and the body, typically towards one of the ends of the valve thus formed.

In one preferred embodiment the modules and/or other components 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 typically including at least a first seal, a ball, a second seal and a 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 for forming 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.

Specific embodiments of the invention will now be described with reference to the accompanying drawings wherein; Figure 1 illustrates a diagrammatic elevation of a double block valve according to one embodiment of the invention; Figure 2 illustrates the components of a modular valve assembly according to one embodiment of the invention.

Figures 3A -3D illustrate specific features of the invention in greater detail.

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 Figure 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 Figure 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 Figure 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 Figure 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 Figure 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 Figure 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.