Fluid handling – Processes – Involving pressure control
Reexamination Certificate
1999-04-02
2001-09-04
Chambers, A. Michael (Department: 3753)
Fluid handling
Processes
Involving pressure control
C137S552000, C137S552700, C137S554000, C137S469000, C137S476000
Reexamination Certificate
active
06283138
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to pressure relief devices, and more particularly to devices for monitoring their performance.
BACKGROUND OF THE INVENTION
Pressure lines (e.g., pressure vessels and piping systems) are often designed with pressure relief valves located at various locations to protect the pressure line from excess overpressure. The pressure relief valves are self-actuated devices set to open when the pressure in the pressure line exceeds a specified level. When the pressure in the pressure line exceeds the pressure at which the pressure relief valve is set to open, the closure element of the pressure relief valve moves away from the inlet nozzle seat and fluid is allowed to flow out of the pressure line and through the pressure relief valve. This flow of fluid will continue at a sufficient rate to prevent the pressure in the pressure line from rising above a predetermined level or above a specified overpressure. When the pressure in the pressure line is reduced to a level below the pressure at which the pressure relief valve is set to open, the closure element in the pressure relief valve will return to its closed position, i.e. into contact with the inlet nozzle seat, preventing additional flow from the pressure line. Under normal operating conditions, the closure element of the pressure relief valve is in the closed position.
Prior art monitoring devices used in these pressure lines typically employ position transducers mounted on the pressure relief valve to sense the position of the closure element. These position transducers transmit analog signals indicating the position of the closure element with respect to the inlet nozzle. These devices, however, do not store this information and apply the information to determine operating characteristics of the pressure relief valve, such as total flow through the pressure relief valve during a specified time interval when the pressure relief valve is open.
Moreover, in the prior art the presence of leakage flow past the closure element of a pressure relief valve (i.e., flow past the closure element when the closure element is in the closed position) could only be determined by physically examining the valve in its installed position, removing the valve from its installed position, and performing a seat leakage test on a test stand, or by isolating the valve (through the use of appropriate valving) in its installed position, but not in active service, and performing a seat leakage test in situ. Such techniques for determining the presence of seat leakage, however, do not allow for continuous monitoring to detect seat leakage past the closure element while the pressure relief valve is both installed and in service.
In addition, unstable operation of pressure relief valves, i.e. rapid opening and closing of the closure element, can occur when the system pressure rises just to or slightly above the set pressure and then drops, as a result of fluid flowing from the system through the pressure relief valve, as soon as the closure element lifts off the seat permitting the spring to immediately seat the closure element. Such unstable operation, however, can cause physical damage to components of the pressure relief valve. It is therefore desirable to know when such unstable operation occurs so that corrective action may be taken. The prior art practice has been for personnel to listen for the noise, often referred to as “valve chatter,” generated by the closure element being rapidly and repeatedly forced against its seat. This practice, however, is ineffective if no personnel are near the valve at the time the unstable operation occurs or if the location of the valve is beyond earshot of attending personnel.
SUMMARY OF THE INVENTION
In light of the above, a pressure relief valve monitoring device is provided. The monitoring device includes a sensor input module located proximate to a pressure relief valve, a microcontroller located within the sensor input module, and a real time clock/calendar also located within the sensor input module. The monitoring device also includes a number of sensors, including (
1
) a position sensor mounted on the pressure relief valve for measuring the position of the valve's closure element relative to the inlet nozzle seat and for generating a lift signal representative of such position; (
2
) a pressure sensor mounted on the pressure relief valve for measuring the pressure of the pressure system and generating a pressure signal representative of such pressure; and (
3
) a leakage sensor mounted on the pressure relief valve and positioned in close proximity to the inlet nozzle seat and capable of detecting noise generated by leakage of fluid between the inlet nozzle seat and the closure element when the closure element is engaged with the inlet nozzle seat. The microcontroller is configured to receive and store signals from any or all of the three sensors and correlate the receipt thereof with an indication of time from the real time clock/calendar to determine certain characteristics of valve performance. A method for monitoring the operation of the pressure relief valve is also provided.
The present invention provides a monitoring device mounted on or near a pressure relief valve and which will continuously monitor the performance of the pressure relief valve while the valve is in active service. The monitoring device will also convert analog signals received from sensors attached to the valve into digital format, will store the digital information, will detect leakage flow through the pressure relief valve while the valve is in active service, will calculate fluid mass flow through the pressure relief valve when the valve is open and allowing fluid to flow from the pressure line, will detect and warn of unstable operation of the pressure relief valve, and will communicate with a host computer to transmit the information stored by the valve monitoring device and receive information regarding that particular valve from the host computer.
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Friend Ronald George
Jones Michael Allen
Anderson, Greenwood LP
Chambers A. Michael
Kenyon & Kenyon
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