Fluid handling – Processes – Cleaning – repairing – or assembling
Reexamination Certificate
2000-04-07
2002-08-13
Chambers, A. Michael (Department: 3753)
Fluid handling
Processes
Cleaning, repairing, or assembling
C137S315040, C137S068180, C137S071000
Reexamination Certificate
active
06431196
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally relates to devices for relieving pressure from a pressurized system. More particularly, the present invention relates to a pressure relief device that combines a rupture disk and a pressure relief valve.
Devices that combine a rupture disk and a pressure relief valve are commonly engaged with pressurized systems to provide a safety mechanism that prevents over-pressurization within the systems. In these types of devices, the rupture disk is connected to the pressure relief valve by a fluid passageway. The device is engaged with the pressurized system to expose the rupture disk to the pressurized fluid. The rupture disk, which is configured to burst when exposed to a predetermined fluid pressure, prevents the fluid from flowing through the fluid passageway and into contact with the pressure relief valve.
When the rupture disk bursts in response to a pressure change in the system, fluid flows through the passageway and into contact with the pressure relief valve. The pressure relief valve is similarly configured to open when exposed to a predetermined fluid pressure. Thus, the pressure of the fluid causes the pressure relief valve to open and relieve the system pressure. Typically, the pressure relief valve will reclose after the system pressure decreases sufficiently. By doing so, it prevents the system from losing its entire fluid content.
Combining a rupture disk with a pressure relief valve is advantageous over a pressure relief valve alone because the rupture disk prevents constant exposure of the pressure relief valve to the fluid. This extends the valve life by protecting valve parts from potentially corrosive fluids, permits in-service valve testing without the need to shutdown the system, and prevents the inadvertent release of the fluid by the valve under normal system operating conditions. In addition, it has been found that subjecting a pressure relief valve to constant pressure may affect the pressure at which the pressure relief valve opens and resets.
In the known rupture disk/pressure relief valve combinations, the rupture disk is connected to the pressure relief valve with a mechanical coupling. The rupture disk is typically held within the mechanical coupling using mechanical fasteners such as bolts, threads or pins. The mechanical coupling, in turn, attaches to the pressure relief valve by a threaded, flanged, pin, or bayonet fitting connection to complete a rupture disk/pressure relief valve combination.
One disadvantage of the conventional mechanical coupling to form a rupture disk/pressure relief valve combination is that the burst pressure of the rupture disk may shift if the mechanical fasteners are over-tightened. Furthermore, an over-tightened or under-tightened mechanical coupling may cause leakage past or through the rupture disk. To avoid an uncertainty in the burst pressure and possible leakage, considerable care and control need to be exercised when connecting the rupture disk to the pressure relief valve using mechanical fasteners. In fact, a good design practice results in enlarged dimensions that far exceed the nominal size of a threaded or flanged connection.
Another disadvantage of the conventional mechanical coupling is that the overall length of the combination pressure relief device may not be suitable for certain applications. For example, the space available on refrigeration systems to install the conventional rupture disk/pressure relief valve combination is often limited. Also, certain refrigeration systems, such as those in transportation and aviation applications, require a minimum mass to maximize the fuel efficiency and load-carrying capacity of the transportation vehicle. The mechanical coupling is undesirable in these applications because it adds to the overall length and mass of the combination.
Yet another disadvantage of the mechanical coupling is that the intended rupture disk/pressure relief valve combination can be disassembled, and thereby may lead to incorrect application and installation. For example, an operator may install the pressure relief valve without the rupture disk, or may install only the rupture disk and not the the pressure relief valve. In addition, an operator may improperly combine a rupture disk having a first set pressure with a pressure relief valve having a second, incompatible, set pressure. This would result in non-compliance with applicable code requirements and pose a risk to users of the system. Moreover, a rupture disk/pressure relief valve combination can be code-certified as a “combination device” with an increased flow capacity. Thus, it is desirable to retain the certified combination together for application and installation.
In light of the foregoing, there is a need for a rupture disk/pressure relief valve combination that (1) eliminates conventional mechanical fasteners that may affect the burst pressure and leak tightness of the rupture disk/pressure relief valve combination, (2) minimizes the overall length and mass of the combination device, (3) ensures that the system-required combination of rupture disk and pressure relief valve set pressures is integrated, and (4) enables the certified combination of rupture disk and pressure relief valve to remain together.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a pressure relief device 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 device for a system containing a pressurized fluid. The pressure relief device includes a valve body. The valve body includes an inlet and an outlet defining a flow passage therebetween. A valve mechanism is housed in the valve body and is movable between a closed position where the valve mechanism blocks the flow passage and an open position. A rupture disk is permanently attached to the valve body to prevent the pressurized fluid from flowing through the flow passage until the rupture disk bursts.
In another aspect, the invention is directed to a method for preventing over-pressurization of a system. One of the steps for carrying out the method is providing a pressure relief device that includes a valve body having an inlet and an outlet defining a flow passage therebetween. A valve mechanism is housed in the valve body and is movable between a closed position where the valve mechanism blocks the flow passage and an open position. A rupture disk is permanently attached to the valve body to prevent a pressurized fluid from flowing through the flow passage. In accordance with the method, the pressure relief device is engageable with the system to prevent the pressurized fluid from flowing through the flow passage until the pressure within the system exceeds a predetermined level, thereby causing the rupture disk to burst.
In yet another aspect, the invention is directed to a method of manufacturing a pressure relief device. The method includes the step of providing a valve body that includes an inlet and an outlet defining a flow passage therebetween and has a valve mechanism movable between a closed position where the valve mechanism blocks the flow passage and an open position. The method also includes the step of providing a rupture disk that is configured to burst at a predetermined pressure. The rupture disk is permanently attached to the valve body to prevent a fluid from flowing through the flow passage until the rupture disk bursts.
It is to be understood that both the foregoing general description and the following detailed description are exemplary an
Brazier Geof
Mundt Arnold
BS&B Safety Systems, Inc.
Chambers A. Michael
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
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