Isolation valve assembly

Abstract

An isolation valve assembly having a valve body ( 22 ) provided with an inlet ( 23 ) and an outlet ( 24 ), fluidly connected by a fluid passageway ( 25 ), and an isolation valve ( 26, 27 ) that is operable to selectively open or close the fluid passageway. A vent is fluidly connected to the fluid passageway and a vent valve ( 34 ) is operable to open and close fluid communication between the fluid passageway and the vent. The vent valve comprises a stem ( 36 ) with a sealing member ( 37 ) and is operable between an open position, in which the sealing member is disposed such that the fluid passageway and the vent are fluidly connected and a closed position in which the valve stem extends across the fluid passageway and the sealing member seals the vent from the flow passageway.

1 . A double-block-and-bleed valve assembly for connection between a main flow pipeline and instrumentation, the double-block-and-bleed valve assembly comprising:
 a valve body having an inlet and an outlet fluidly connected by a fluid passageway, the inlet configured to be connected to a main flow pipeline, and the outlet configured to be connected to the instrumentation, the fluid passageway having a substantially cylindrical shape along a majority of a distance between the inlet and the,   first and second isolation valves operable to selectively open or close the fluid passageway,   first and second handles mounted on a first external surface of the valve body, the first handle is configured to operate the first isolation valve and the second handle is configured to operate the second isolation valve,   a vent fluidly connected to the fluid passageway and a vent valve operable to open and close fluid communication between the fluid passageway and the vent,   the vent valve comprising a stem with a sealing member, and the vent valve comprising a housing mounted on a second external face of the valve body, the second external face being adjacent the first external face, wherein the vent valve is operable between an open position in which the sealing member is disposed such that the fluid passageway and the vent are fluidly connected and a closed position in which the valve stem extends across the fluid passageway and the sealing member seals the vent from the fluid passageway;   wherein the vent valve is disposed between the first and second isolation valves;   wherein the sealing member is arranged such that, in the closed position, fluid flowing in the fluid passageway produces a force directly on the sealing member in the direction of its sealing; and   wherein, when the vent valve is in the open position, the passageway between the first and second isolation valves is substantially unobstructed.   
     
     
         2 . A double-block-and-bleed valve assembly according to  claim 1 , wherein, in the closed position, the valve stem extends across the width of the fluid passageway. 
     
     
         3 . A double-block-and-bleed valve assembly according to  claim 1 , wherein the vent is fluidly connected to a side of the fluid passageway that is proximal to the vent. 
     
     
         4 . A double-block-and-bleed valve assembly according to  claim 1 , wherein the vent is fluidly connected to the fluid passageway by a connecting passageway which opens into the fluid passageway. 
     
     
         5 . A double-block-and-bleed valve assembly according to  claim 4 , wherein the connecting passageway opens into a side of the fluid passageway that is proximal to the vent. 
     
     
         6 . A double-block-and-bleed valve assembly according to  claim 4 , wherein the connecting passageway has a longitudinal axis which is substantially straight. 
     
     
         7 . A double-block-and-bleed valve assembly according to  claim 6 , wherein the fluid passageway has a longitudinal axis and the longitudinal axis of the connecting passageway is substantially perpendicular to the longitudinal axis of the fluid passageway. 
     
     
         8 . A double-block-and-bleed valve assembly according to  claim 4 , wherein in the closed position the sealing member closes the end of the connecting passageway that opens into the fluid passageway. 
     
     
         9 . A double-block-and-bleed valve assembly according to  claim 1 , wherein the stem of the vent valve and the fluid passageway are arranged such that when the vent valve is in the closed position there is a clearance between the stem and an inner wall of the fluid passageway so as to allow fluid flowing in the fluid passageway to flow past the stem. 
     
     
         10 . A double-block-and-bleed valve assembly according to  claim 9 , wherein the stem has a curved outer surface. 
     
     
         11 . A double-block-and-bleed valve assembly according to  claim 1 , wherein the vent valve is received in a cavity that extends into the valve body and opens into the fluid passageway. 
     
     
         12 . A double-block-and-bleed valve assembly according to  claim 11 , wherein the cavity is dimensioned to allow the stem and sealing member of the vent valve to pass into the fluid passageway to the closed position. 
     
     
         13 . A double-block-and-bleed valve assembly according to  claim 11 , wherein the fluid vent is fluidly connected to the fluid passageway by a connecting passageway which opens into the fluid passageway and the connecting passageway opens into a side of the fluid passageway that is opposite to the side of the fluid passageway which the cavity opens into. 
     
     
         14 . A double-block-and-bleed valve assembly according to  claim 1 , wherein the vent valve comprises a housing with an axially extending bore, within which the stem is received, the bore is provided with an internal threaded section and the stem is provided with an external threaded section which is engageable with the internal threaded section of the bore such that as the stem rotates relative to the housing, it translates relative to the housing; and the length of the internal threaded section of the bore, the length of the external threaded section of the stem and the diameter of the fluid passageway are arranged such that the stem can be screwed from the open position to the closed position. 
     
     
         15 . A double-block-and-bleed valve assembly according to  claim 1 , wherein the sealing member is arranged such that, in the closed position, fluid flowing in the fluid passageway passes over the sealing member. 
     
     
         16 . A double-block-and-bleed valve assembly according to  claim 1 , wherein in the closed position a surface of the vent valve is exposed to fluid flowing in the fluid channel and a lower surface of the sealing member is disposed within the connecting passageway such that it is shielded from the flow within the fluid passageway. 
     
     
         17 . A double-block-and-bleed valve assembly according to  claim 1 , wherein a terminal end of the inlet configured to be connected to a main flow pipeline, and a terminal end of the outlet configured to be connected to the instrumentation, the fluid passageway is cylindrical from the terminal end of the inlet to the terminal end of the outlet. 
     
     
         18 . An isolation valve assembly comprising:
 a valve body having an inlet and an outlet fluidly connected by a fluid passageway;   first and second isolation valves operable to selectively open or close the fluid passageway;   a vent having an opening into the fluid passageway, such that the vent and the fluid passageway are fluidly connectable;   a vent valve comprising a stem having a sealing member at a terminal end; the vent valve and the vent being located between the first and second isolation valves;   the vent valve being configured to move between an open and a closed position, such that:   in the closed position, the valve stem extends across the width of the fluid passageway such that the sealing member seals the opening of the vent into the fluid passageway, thereby restricting any fluid flow between the fluid passageway and the vent; and,   in the open position, the sealing member is spaced apart from the opening, such that the fluid passageway and the vent are in fluid communication; and,   wherein, when the first and second isolation valves and the vent valve are in the open position, the fluid passageway is unobstructed, such that any flow of fluid through the fluid passageway is unimpeded.   
     
     
         19 . An isolation valve assembly according to  claim 18 , wherein the fluid passageway has a substantially circular cross-sectional shape along its entire length. 
     
     
         20 . An isolation valve assembly according to  claim 18 , wherein when the vent valve is in the closed position, any fluid flowing in the fluid passageway flows past the stem via a clearance gap between the stem and an inner wall of the fluid passageway. 
     
     
         21 . An isolation valve assembly according to  claim 18 , wherein the vent valve comprises a housing having an axially extending bore, the stem of the vent valve being received within the bore; and wherein the bore has an internal surface comprising an internally threaded section, and the stem comprises an external surface having an externally threaded section, the internally and externally threaded sections being engageable. 
     
     
         22 . An isolation valve assembly according to  claim 21 , wherein rotational movement of the stem relative to the housing is converted into translational movement of the stem relative to the housing; and wherein the length of the internally threaded section of the bore, the length of the externally threaded section of the stem and the width of the fluid passageway are arranged such that the stem can be screwed from the open position to the closed position.