Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
1999-05-12
2001-04-24
Huson, Gregory L. (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S489000, C137S492500
Reexamination Certificate
active
06220280
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a pressure relief valve controlled by a pilot valve, and more particularly, to an isolation system for isolating the pilot valve from process media or fluid.
A pressure relief system typically includes a relief valve mounted over a pressure vessel, such as a tank or pipe line, and a pilot valve which controls movement of the relief valve. The relief valve moves to an open position when pressure in the pressure vessel reaches a predetermined maximum level to discharge process media or fluid from the pressure vessel and reduce pressure therein. The relief valve moves to a closed position when enough process media is discharged to reduce the pressure in the pressure vessel to a desired predetermined level.
The pilot valve is typically of a non-flow type wherein process media does not flow through the pilot valve when the relief valve is in a static condition but process media does flow through the pilot valve to move or operate the relief valve. For example, see U.S. Pat. No. 3,664,362, disclosing a non-flow pilot valve, the disclosure of which is expressly incorporated herein by reference in its entirety. Process media flows through the pilot valve and changes a dome pressure of the relief valve to activate a pressure responsive element, such as a piston or diaphragm.
These pilot valves serve their intended purpose in an exemplary manner when the process media is clean. These pilot valves, however, are not suitable for dirty service wherein the process media is dirty and/or contains particulate or foreign matter because the pilot valves have many tight clearances which can be affected thereby. For example, flow passages can be clogged or restricted, sliding surfaces can be damaged and/or bound together, and sealing surfaces can be damaged and/or held apart.
One solution has been to supply an auxiliary source of clean fluid to the dome chamber of the relief valve and chambers of the pilot valve which expose a spool valve so that the process media does not contaminate the dome chamber or the spool valve. See, for example, U.S. Pat. No. 5,027,852, the disclosure of which is expressly incorporated herein in its entirety by reference. This solution, however, still exposes some components of the pilot valve to process media and cannot be used to retrofit existing pressure relief systems without replacing the existing pilot valve. Accordingly, there is a need in the art for an improved pressure relief system wherein a pilot valve is isolated from process media.
SUMMARY OF THE INVENTION
The present invention provides a pilot operated pressure relief system which overcomes the above-described problems of the related art. According to the present invention, the pressure relief system includes a relief valve, a pilot valve, and an accumulator for transmitting pressure changes of process media in a pressure vessel to control fluid in the pilot valve. The relief valve has an inlet in fluid-flow communication with the pressure vessel, an outlet, and a dome chamber. The pilot valve has an inlet port, a control port in fluid-flow communication with the dome chamber, and a discharge port. The accumulator has an inlet in fluid-flow communication with the inlet of the relief valve, an outlet in fluid flow communication with the inlet port of the pilot valve, and an isolator preventing fluid-flow communication between the accumulator inlet and the accumulator outlet to isolate control fluid from process media.
In a preferred embodiment, the accumulator is a piston-type accumulator wherein the isolator is a piston movable within an interior chamber. Alternatively, a bladder-type accumulator can be used wherein the isolator is a bladder movable within an interior chamber. The isolator divides the interior chamber into a first portion in fluid-flow communication with the accumulator inlet and a second portion in fluid-flow communication with the accumulator outlet and is movable in response to fluid pressure in the first and second portions of the interior chamber. Preferably, the pressure relief system further includes a source of pressurized control fluid which is in fluid-flow communication with both the outlet of the accumulator and the inlet port of the pilot valve to prevent the control fluid from dropping below a predetermined pressure level.
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Curtis-Wright Flow Control Corporation
Huson Gregory L.
Krishnamurthy Ramesh
Pearne & Gordon LLP
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