Fluid handling – Processes – Involving pressure control
Reexamination Certificate
2000-01-11
2001-09-11
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Processes
Involving pressure control
C137S102000, C137S492500
Reexamination Certificate
active
06286534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a pressure relief valve system that includes a pilot valve and, more particularly, to such a valve system in which the pilot valve has a radial damper mechanism that when used in conjunction with a pressurized liquid system, permits better control of the opening and closing characteristics of the closure elements in such valves.
Pressure lines, i.e., pressure vessels and piping systems, are frequently designed with pressure relief valves located at various locations therein to protect the pressure line from excessive pressure. These pressure relief valves are selfactuated devices that are set to open when the pressure in the line reaches a predetermined, maximum safe pressure level, typically referred to as the maximum allowable working pressure. When the pressure in the line reaches this maximum allowable working pressure, the closure element of the pressure relief valve moves away from the inlet nozzle and process fluid is allowed to flow out of the pressure line through the pressure relief valve. This fluid flow will continue at a rate sufficient to prevent the pressure in the pressure line from rising above a maximum allowable overpressure.
When the pressure in the pressure line falls below the set pressure of the pressure relief valve, the closure element in the pressure relief valve returns to the closed position, i.e., in contact with the nozzle, which prevents any additional flow from the pressure line.
Pressure relief valves are self-actuated, in that the forces required to open such valves are provided by the fluid at the pressure relief valve inlet. A particular problem exists when the fluid in the pressure line is an incompressible liquid due to the inertia of the incompressible fluid. Frequently, when dealing with incompressible liquids, the valve prematurely closes because the fluid in the pipeline is slow to move forward to hold the closure element open. As soon as the valve closes, however, the pressure in the pipeline again spikes back to the original pressure level thereby causing the valve to re-open. When this occurs, the pressure relief valve may become unstable as the closure element begins to cycle at high frequency which can cause damage to the pressure relief valve and to the system is being protected by the pressure relief valve.
2. Description of the Prior Art
Several methods have been employed to prevent a pressure relief valve from operating in an unstable manner when used in conjunction with incompressible liquid systems. One method is to design the valve to open in a proportional manner such that pressure is maintained at the valve inlet. An example of such a spring-loaded, pressure relief valve is described in U.S. Pat. No. 4,130,130 that issued to R. Stewart on Dec. 19, 1978. Similar technology has been applied to pilot operated pressure relief valves that employ a modulating pilot that controls the opening of the valve closure element in a proportional manner. Examples of such a valve is described in U.S. Pat. No. 4,586,533 which issued to R. Estes on May 6, 1986; U.S. Pat. No. 4,863,098 which issued to L. Kolze on Sep. 5, 1989; U.S. Pat. No. 5,058,624 which issued to L. Kolze on Oct. 22, 1991; and U.S. Pat. No. 5,950,657 which issued to Y. Lai on Sep. 14, 1999. These methods have improved the ability of pressure relief valves to operate in a stable manner when used in conjunction with an incompressible liquid system, however instability can and does still occur under a variety of system operating conditions.
Another approach is to introduce a damper into the pressure relief valve design which serves to reduce the severity of any oscillation and eliminate the oscillation once a steady state condition is achieved after the pressure relief valve has opened. Dampers may include viscous dampers or snubbers, e.g. needle valves or fixed orifices in pilot operated pressure relief valve control lines. An example of a valve having such a damper is described in U.S. Pat. No. 4,799,645 which issued to K. Kramer on Jan. 24, 1989. Dampers are, however, generally costly and difficult to maintain since they are prone to clogging.
The current invention incorporates a new damper concept that can be incorporated into the internal components of a pilot operated pressure relief valve. It serves to reduce cost, eliminate the need for additional special maintenance, and overcome the potential for clogging.
SUMMARY OF THE INVENTION
Against the foregoing background, it is a primary object of the present invention to provide a pressure relief valve system that includes a pilot valve having a radial damping mechanism used in conjunction with a main pressure relief valve.
It is another object of the present invention to provide such a pressure relief valve system that is particularly adapted to control the opening and closing characteristic of its closure element when used in conjunction with a pressurized liquid system.
It is but another object of the present invention to provide such a pressure relief valve system in which the radial damping mechanism comprises at least one radial damping labyrinth ring in the pilot valve to control the rate at which fluid is allowed to enter and leave its damping chamber.
It is still another object of the present invention to provide such a pressure relief valve system in which the control of its closure member by the pilot valve is improved to limit the potential for oscillation of the closure element.
It is yet still another object of the present invention to provide such a pressure relief valve system that is less susceptible to unstable operation when used in conjunction with a pressurized liquid system.
It is but another object of the present invention to provide such a pressure relief valve system that is more resistant to clogged passages.
It is but still another object of the present invention to provide such a pressure relief valve system having a pilot valve with improved control of the main pressure relief valve without added restriction to the fluid flow either into or out of the pilot valve.
To the accomplishments of the foregoing objects and advantages, the present invention, in brief summary, comprises a pressure relief valve system that is particularly adapted to be used with a pressurized system containing a noncompressible fluid. The pressure relief valve system of the present invention includes a main pressure relief valve in communication with the pressurized pipeline and a pilot valve in communication with the main pressure relief valve. The pilot valve includes a pilot valve body, a pressure chamber that is always in communication with the system pressure, and a sense piston reciprocal in the pilot valve body that is exposed to the pressure in the pressure chamber. The sense piston includes damping means to improve control of the opening and closing of the valve system. Preferred damping means include a labyrinth damping ring that extends downward from the sense piston and which is adapted to engage and form a restriction with a radial damping ring on the top of the hydraulic damping plate. The labyrinth damping ring includes at least one downwardly extending ring or projection that is adapted to engage at least one complimentary, upwardly extending, damping ring on annular flat surface positioned below the sense piston. This serves to define a sense piston chamber that provides a damping effect on the operation of the valve system.
REFERENCES:
patent: 4285362 (1981-08-01), Taylor
Anderson, Greenwood LP
Grimes & Battersby LLP
Michalsky Gerald A.
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