Fluid handling – Destructible or deformable element controlled – Destructible element
Reexamination Certificate
2001-05-24
2002-12-03
Buiz, Michael Powell (Department: 3753)
Fluid handling
Destructible or deformable element controlled
Destructible element
C137S070000, C137S072000, C137S068120, C251S306000
Reexamination Certificate
active
06488044
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally relates to systems for relieving pressure from a pressurized system. More particularly, the present invention relates to a pressure relief apparatus for a system containing a pressurized fluid.
There are many types of systems that process or use a pressurized fluid. To ensure the safety of these types of systems, each such system typically includes a safety device designed to prevent the over-pressurization of the system. In an emergency situation, where the fluid in the system reaches an unsafe level, the high pressure of the fluid acts on the safety device to create an opening to release fluid from the system. Venting fluid to the environment or a safety reservoir through the opening reduces the pressure in the system and prevents another portion of the system from failing due to the high pressure of the fluid.
Examples of commonly used safety devices include rupture disks and explosion panels. These safety devices can be attached to a pressurized system to expose a certain portion of the device to the pressurized fluid in the system. The portion of the device exposed to the fluid is configured to rupture or tear when the fluid reaches a predetermined pressure. The tearing or rupture of the disk or panel creates an opening through which the pressurized fluid flows to reduce the pressure in the system. This type of safety device is, therefore, self-destructing and must be replaced after each use. Typically, to replace one of these safety devices, some disassembly of the system is needed so that the disk or panel can be properly engaged with the system.
Another type of safety device for a pressurized system is a pressure relief valve, which may be a reclosing valve or a non-reclosing valve. Typically, a spring, a pin, or a combination of a spring and pin, is used to hold a moving plug in sealing engagement with the housing of.the device while connected to the pressurized system. When the pressure of the fluid reaches the predetermined safety level in such systems, the force exerted on the plug by the pressurized fluid overcomes the bias of the spring or exceeds the resistance of the pin that holds the plug in place. When either of these events occurs, the pressurized fluid moves the plug to expose an opening through which fluid may escape to relieve the pressure in the system. Reclosing valves will automatically reset once the pressurized fluid at the inlet of the device has reduced sufficiently for the spring or other mechanism to reseat the plug. Non-reclosing valves require that the device be manually reset so that the valve plug is re-engaged with the seal and, if necessary, the pin or other expendable component replaced.
A valve disposed in a pressurized system will often include a strong seal between the body and the plug to limit or prevent fluid from leaking through the valve. One type of seal is a broad band seal (as opposed to a line seal), where a significant area of the typically flexible seal engages a large portion of the plug. As a result, a correspondingly large force is required to break the seal, and the force required to break the seal tends to increase the longer the seal remains engaged with the plug. A valve using this type of seal is not well adapted for low pressure applications, where the force of the fluid may not be capable of breaking the seal. Further, these valves require a large force to seat the seal, which can interfere with the accuracy of the set pressure of the device. In addition, the seals of these valves are located in positions that require extensive disassembly of the valve in the field, which makes seal replacement difficult and can affect the accuracy of the device.
A common type of pressure relief valve is a rotatable valve assembly. A rotatable valve includes a plug that is mounted on a rotatable shaft and may be rotated between a closed position where the plug blocks the flow of fluid and an open position where the plug allows fluid to flow through the valve. The rotation of the plug to the open position may be initiated manually or by another external force. Alternatively, the plug may be mounted on the shaft so that the rotational axis of the plug is offset relative to the center of the plug, so that the pressurized fluid exerts a torque on the shaft and urges the plug to rotate. A device may be coupled to the shaft to prevent the shaft from rotating until the torque on the shaft reaches a certain level, indicating that the pressure of the fluid has reached an over-pressure situation. At that point, the shaft is released and the plug rotates to open the valve and vent the system.
However, the components of these rotatable valve assemblies are specifically designed to provide pressure relief for a specific pressure or narrow pressure ranges. To operate at a range of set pressures, the rotatable valve assembly would require modification of some or all component parts to vary the distance by which the rotational axis of the plug is offset from the center of the shaft. This limits the use of such assemblies in the field and creates inventory problems for valve manufacturers. Moreover, the inability to standardize parts for broad pressure ranges increases the cost of manufacturing the devices.
Another problem with rotatable valve assemblies is that the rotation of the plug does not move the plug out of the fluid flowpath and, thus, the plug obstructs the flow of the venting fluid. The object of the pressure relief device is to quickly reduce the pressure of the system and significant blockage of the fluid flow is undesirable. A low flow resistance factor (Kr) or high coefficient of discharge (Kd) is required. The presently known valve assemblies have the disadvantage of impeding fluid flow in relieving an over pressure situation.
In light of the foregoing, there is a need for a pressure relief apparatus that (1) can be calibrated to provide pressure relief over a wide range of pressures while utilizing standard parts, (2) provides a large flowpath for fluid to vent, (3) has an improved seal in both its working design and for purposes of field replacement, and (4) may be used in low pressure systems as well as high pressure systems.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a pressure relief apparatus that obviates one or more of the limitations and disadvantages of prior art pressure relief devices. The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to a pressure relief apparatus for a system containing a pressurized fluid. The pressure relief apparatus includes a valve having a body that defines a fluid flowpath. A shaft is rotatably disposed in the body and has an exterior end that extends through the body. A plug is mounted on the shaft. The body is engageable with the system to expose the plug to the pressurized fluid. The pressurized fluid acts on the plug to exert a torque on the shaft and rotate the plug from a closed position to an open position. A linkage assembly is engageable with the exterior end of the shaft and is configured to translate the torque exerted on the shaft into an output force. The linkage assembly is adjustable to vary the magnitude of the output force corresponding to a particular shaft torque. A release device is connected to the linkage assembly to prevent the shaft from rotating until the output force exceeds a predetermined limit.
In another aspect, the invention is directed to a pressure relief apparatus for a system containing a pressurized fluid. The pressure relief apparatus includes a valve having a body that defines a fluid flowpath. A shaft is rotatably disposed
Brazier Geof
Dubbeldam Arthur
Dubbeldam Peter
Hitz Michael
BS&B Safety Systems, Inc.
Buiz Michael Powell
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Krishnamurthy Ramesh
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