Patent Application
20110240156
This invention relates generally to sandwich-type valves used to prevent flow through a pipeline or access connection to a pipeline during hot tapping and plugging operations. More particularly, the invention relates to an improved arrangement of providing double block sealing between the valve member or disc and the valve body.
“Double block and bleed” is a well-known term of art in the pipeline and piping industry that refers to setting two seals in a pipe and opening a bleed port between the seals to ensure that the first seal is holding. Any leakage past the first seal is contained by the second seal and forced to exit through the bleed port. This arrangement also prevents any unwanted buildup of pressure occurs across the second seal and ensures that the pipe is completely sealed.
Sandwich-type valves are typically employed in hot tapping operations. In the typical hot tapping operation, a fitting—usually in the form of a flange—is welded on the exterior of a pipe that has flowing gas or liquid under pressure. A sandwich-type valve is then secured to the flange and a hot tapping machine is secured above the valve. A valve member or disc moves laterally between a closed seated position across the passageway provided by the fitting and an open unseated position free of the passageway. By use of specialized equipment, when the valve disc is in its unseated position, a boring bar with a cutter tool attached may pass through the valve body and cut a hole through the wall of the pipe while gas or liquid continues to flow through it. This hole provides access to the interior of the pipe, such as for inserting equipment to temporary block flow through the pipe while repairs are being made. The valve disc is opened whenever equipment must pass through the valve body and is closed whenever necessary. After repairs are complete, a threaded or non-threaded completion plug is typically inserted as a temporary seal below the sandwich valve so that any equipment secured above the valve may be reclaimed.
Prior-art sandwich-type valves are similar to the one disclosed in U.S. Pat. No. 3,047,226, titled “Valve” and issued to B. Ver Nooy on Jul. 31, 1962. The valve member or disc is contained within the open space of a spacer ring or flange that is secured between two plates. The valve disc is provided with O-ring type seals on its lower and upper face portion and a retainer ring on each face facilitates placement of the O-ring and provides fluid pressure to the groove in which the O-ring is located. When the valve is in its seated position across the ports of the plates, the seals provide sealing engagement with the face surfaces or seats of the plates and prevent fluid flow between the ports. However, fluid pressure above or below the valve disc pushes the valve disc away from one of the seats and toward the other seat. Although this design provides adequate and proper sealing, the dependent arrangement of the seals may create a potential leak path through the seal that is being pushed away from its seat.
An object of this invention is to provide an improved sandwich-type valve in which the movement of one seal does not affect the sealing performance of the second seal. Another object of this invention is to provide a sealing arrangement that energizes substantially instantaneously at low pressure and seals at high pressure. Yet another object of this invention is to provide a sandwich-type that may be applied in surface and subsurface (on-shore and offshore) hot tapping and plugging applications. Still yet another object of this invention is to provide seals that may be re-energized, lubricated, or substantially backed-up in case of an in-service leak. A still further object of this invention is to provide a sandwich-type valve that allows existing valves to be easily retrofitted with the improved features of the valve. Last, an object of this invention is to provide for bleed capability between the seals of the valve.
An improved sandwich-type valve made according to this invention has a substantially flat valve disc located in an open space of a spacer flange. The valve disc is moveable in the open space between an unseated position and a seated position. When in the seated position, the valve disc is disposed across ports located above and below the spacer flange in an upper and lower plate, respectively, and blocks flow between the ports. Sealing engagement is provided by a first and second seal. The two seals move and seal independent of one another.
The first seal is located on the upper surface of the valve disc and is preferably an O-ring type seal. The first seal moves with the valve disc toward and away from the upper plate in response to fluid pressure. This seal provides sealing engagement with the lower face surface or seat of the upper plate.
The second seal is a floating seal that is received by a seat of the lower plate. The second seal moves toward and away from the lower plate in response to fluid pressure and provides sealing engagement with the lower surface of the valve disc and the seat of the lower plate. This movement is independent of that of the first seal and the valve disc. A spring may be provided to bias the second seal in its top position, that is, moving away from the lower plate and toward the valve disc. Means may also be provided to limit the vertical movement of the second seal. The second seal is preferably a double O-ring type seal, with the first O-ring type seal being located on an upper surface of the second seal and the second O-ring type seal being located about a peripheral side surface of the second seal.
Both the first and second seals are capable of providing “bubble tight” sealing performance at low and high pressure. Preferably, the second seal moves away from the lower plate and upward toward the valve disc substantially instantaneously as fluid pressure rises above 0 bars. The first and second seals may be configured so that the fluid pressure that the first seal responds to is a different fluid pressure than what the second seal response to.
A bleed port may be provided in the spacer flange between the first and second seal. The bleed port provides an extra measure of safety and is preferably capable of handling whatever fluid (or gas) escapes past the second seal to ensure that no unwanted buildup of pressure occurs across the first seal.
Preferred embodiments of an improved double block and bleed sandwich-type valve will now be described by making reference to the drawings and the following elements illustrated in the drawings:
The elements listed in the drawings are as follows:
Referring first to
Valve disc 70 is of such a size that when it is in the seated position, it is disposed across the ports 23, 43 to prevent flow between the ports 23, 43. Valve disc 70 may be moved laterally between its seated and unseated positions by any suitable means, including hydraulic means (not shown). Manual means may include a valve stem 15 in communication with valve disc 70 and having a sealed connection 17 with flange 30 (see
To provide double block sealing, a first and second seal 80, 90 is employed. Should either seal 80, 90 fail, the other seal 90, 80 continues to prevent fluid flow between the ports 23, 43. The seals 80, 90 preferably have both low and high pressure sealing capability, with the seals 80, 90 being “bubble tight” at near zero pressure as well as at maximum allowable operating pressures (e.g., 900 psi, 1500 psi). The seals 80, 90 may be re-energized, lubricated, or substantially backed-up in case on an in-service leak without permanent loss of seal integrity.
The first seal 80 is preferably an O-ring type seal disposed in an annular groove 71 located on the upper surface 73 of closure disc 70. A segmented ring 75 facilitates placement of seal 80 into groove 71 and provides for pressure fluid to flow into a dovetail portion 79 of the groove 71. Seal 80 moves vertically upward (or downward) with valve disc 70 and, therefore, toward (or away from) seat 21 in response to fluid pressure. Seal 80 provides sealing engagement with seat 21, thereby preventing fluid flow between ports 23, 43.
The second seal 90 is a floating seal assembly disposed within a seat 45 that is located at the upper end 47 of lower plate 40. Seal 90 moves vertically upward (or downward) in response to fluid pressure. The vertical movement of seal 90 is independent of that of seal 80 and closure disc 70.
Seal assembly 90 may be a ring 107 having two O-ring type seals 91, 97 that provide sealing engagement to prevent fluid flow between ports 23, 43. O-ring type seal 91 is disposed in an annular groove 93 located at the upper end 95 of ring 107. Seal 91 provides sealing engagement with the lower surface 77 of valve disc 70. O-ring type seal 97 is disposed in an annular groove 99 located about the peripheral surface 101 of ring 107. Seal 97 provides sealing engagement with an opposing wall surface 49 of seat 45.
Seal 90 is preferably a light weight seal so that when fluid pressure below the seal begins to exceed 0 bars (that is pressure resulting in movement toward closure disc 70), the seal 90 is substantially instantaneously lifted up toward closure disc 70. Seat 45 may be any shape preferable and may be arranged to limit the vertical movement of seal 90 (see
Additionally, a spring 105 may be added below ring 107 to keep seal 90 biased toward or urging against the lower surface 77 of valve disc 70 (see
Sandwich-type valve 10 may be configured for internal bypass, external bypass, and preferably double block and bleed capability. Referring to
While an improved sandwich-type valve with double block and bleed capability has been described with a certain degree of particularity, many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. A valve made and assembled according to this disclosure, therefore, is limited only by the scope of the attached claims, including the full range of equivalency to which each element thereof is entitled.
