Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
2000-01-19
2001-02-27
Huson, Gregory L. (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S488000, C251S282000, C251S335100
Reexamination Certificate
active
06192924
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a pilot operated safety relief valve, and more particularly to such a pilot operated relief valve in which no process fluid of the pressure vessel on which the relief valve is mounted is exhausted to atmosphere through the pilot valve upon actuation of the pilot valve.
BACKGROUND OF THE INVENTION
A so-called snap action pilot valve such as shown in U.S. Pat. No. 3,664,362 dated May 23, 1972, effects a rapid movement to an open position of the valve member for fluid flow to an exhaust port. Upon cracking of the valve member under fluid pressure from a seated position, the valve member snaps to a full open position as a result of the increased area of the valve member exposed to fluid pressure. A small amount of process fluid from the pressure vessel, such as a tank or pipeline, may be vented to atmosphere through the exhaust port. The valve member reseats upon relieving of the fluid pressure in the pressure vessel.
A limitation for such a pilot valve and other snap acting pilots is the inability to vent the pilot valve to a pressure source above atmospheric and maintain specified performance. The venting of process gas to atmosphere in even small quantities is rapidly becoming unacceptable except for common non-toxic and non-hazardous gases. The pilot valve such as shown in the '362 patent is designed to be referenced to atmosphere for adjusting the relieving pressure and the reclosing pressure and therefore must operate by exhausting to atmosphere. Many installations of pilot operated safety relief valves are multiple valves discharging to a common header. Pilot operated safety relief valve such as shown in U.S. Pat. No. 3,664,362, are not effective in these applications due to potential positive backpressure on the pilot exhaust. The result of backpressure is to cause a possible change in the relieving pressure and the reclosing pressure as the backpressure changes. It is desirable to have a pilot valve that is effective even when a backpressure is present in the exhaust line.
Prior attempts to solve this problem have involved balancing the pilot against backpressure by using conventional sealing techniques. Typically an o-ring or similar seal is installed in an operating spindle opposed to the main pilot seat with the effective piston area equal to the seat area of the main pilot seat. Under these conditions the pilot spindle would be balanced so backpressure at the exhaust port would have no effect on the pilot popping pressure or reseating pressure. However, friction in the seal, regardless of design, has rendered this solution impractical. The spindle forces on a pilot can be very small and any friction on the force train between the spring and the pilot seat can cause significant variation of applied force and unpredictability in the relieving and reclosing pressures.
SUMMARY OF THE INVENTION
The present invention is directed to a pilot operated safety relief valve in which the pilot valve includes a spindle or spindle valve member defining the exhaust valve member for controlling fluid flow to and from the exhaust port. The exhaust port is connected to a header or fluid collection container which may also collect fluid from other safety relief valves or devices. The forces acting on the spindle are balanced against backpressure from the exhaust line or exhaust port without any frictional forces being applied. The forces acting on the spindle are balanced against backpressure by creating an upwardly biased piston effect opposite and equal to the force on the main pilot seat. This has been accomplished by installing a relatively thin and flexible elastomeric or polytetrafluoroethylene (Teflon) diaphragm about the spindle valve member. The diaphragm is installed in such a manner that it is in a neutral position (unstretched) when the spindle is in its uppermost position. As spring load is applied to the pilot to establish the seating force the diaphragm is stretched very slightly as the spindle moves down to the main pilot seat. Essentially no friction forces are applied to the spindle. It is also important that the diaphragm conform very well around the small radius of the spindle when in a down seated position so the effective area is essentially the area of the spindle outside diameter above the diaphragm. The diameter can be altered to optimize the balance with the main seat. It is also important that the diaphragm material does not stick or cold vulcanize to the spindle and create resistance to upward movement during the relieving action. In summary, the invention acts to balance the pilot valve at the relieving pressure with backpressure applied to the exhaust port. The relieving pressure must remain within the tolerance specified for the pilot valve.
It is an object of this invention to provide a pilot operated safety relief valve having a pilot valve that is particularly adapted for utilization in a safety relief system in which a backpressure may occur from the exhaust port or exhaust line.
A further object of the invention is to provide such a pilot valve for a pilot operated safety relief valve in which a snap-action spindle valve member controls the flow of fluid to and from the exhaust port with forces resulting from backpressure from the exhaust port being balanced for acting against the spindle valve member.
A further object of the invention is to provide such a spindle valve member for a pilot valve in which frictional forces acting against the spindle valve member form sealing means upon movement of the spindle valve member are substantially eliminated thereby to permit the pilot valve to easily remain in the specified operating tolerance of the pilot valve for relieving and reclosing.
Other objects, features, and advantages of the invention will be apparent from the following specification and drawings.
REFERENCES:
patent: 2649115 (1953-08-01), Deardorff
patent: 3294111 (1966-12-01), Abercrombie
patent: 3304951 (1967-02-01), Farris
patent: 3406712 (1968-10-01), Weise
patent: 3414008 (1968-12-01), Greenwood
patent: 3512560 (1970-05-01), Weise
patent: 3568706 (1971-03-01), Weise
patent: 3664362 (1972-05-01), Weise
patent: 3726301 (1973-04-01), Schmidt
patent: 4172466 (1979-10-01), Pattarini et al.
patent: 4355657 (1982-10-01), Reip
patent: 4390041 (1983-06-01), Reip
patent: 5099882 (1992-03-01), Smith, III
patent: 5842501 (1998-12-01), Powell et al.
patent: 5941505 (1999-08-01), Nagel
patent: 5954086 (1999-09-01), Ronchi
Higgins Thomas F.
McNeely Michael D.
Browning Bushman
Huson Gregory L.
Krishnamurthy Ramesh
Tyco Flow Control, Inc.
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