Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
2000-03-14
2001-11-20
Chambers, A. Michael (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S492000, C251S038000, C251S043000
Reexamination Certificate
active
06318406
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a pilot operated safety relief valve for a pressure vessel, and more particularly to such a pilot operated safety relief valve in which the pilot valve is an integral portion of the relief valve.
BACKGROUND OF THE INVENTION
Most pilot valves are mounted on the main relief valve with brackets and fluid pressure is transmitted to the pilot valve by suitable tubing. Pilot operated relief valves having tubing connections between the main valve body and the pilot valve body are subject to possible leakage and a high manufacturing cost.
In some instances, such as shown in U.S. Pat. Nos. 4,172,466 and 5,842,501, the pilot valve has been connected directly to the main valve body without the use of brackets and separate tubing lines between the pilot valve body and the main relief valve body. However, the pilot valve body is connected to the main valve body along planar or flat surfaces and possible leaks may occur along such faces or surfaces.
In some instances in which a plate-type main valve member having a diaphragm actuator is provided, a pilot valve has been mounted on a cap on the main valve body over the main diaphragm chamber with the plate-type main valve member connected directly to the diaphragm actuator.
It is desired that a pilot operated relief valve be provided in which the main valve member comprises a piston with a pilot valve axially mounted on a cap for the main valve body adjacent a dome chamber over the piston.
SUMMARY OF THE INVENTION
The present invention is particularly directed to a pilot operated safety relief valve in which the pilot valve is mounted on and supported by a cap on the valve body for the main relief valve. A dome chamber is provided adjacent the cap and the pilot valve extends axially of the main valve member.
The main valve member preferably comprises a piston having a central bore which receives an end portion of an inlet sensing tube and is mounted for reciprocal movement relative to the inlet sensing tube with the end portion of the inlet sensing tube remaining within the central bore. The inlet sensing tube is secured at its outer end to a pilot valve diaphragm and inlet fluid pressure is communicated by the inlet sensing tube to the upper outer side of the diaphragm. A dome chamber is provided between the piston and an end cap on the main valve body which supports the pilot valve. The sensing tube includes a pilot valve member which is positioned in the dome chamber and moves downwardly within the dome chamber upon the inlet fluid pressure reaching a predetermined high amount.
An adjustment spring continuously urges the sensing tube and pilot valve member in an upward position and the spring is positioned within the exhaust chamber between the dome chamber and the inlet sensing chamber. Thus, a single exhaust port for both the spring and exhaust chamber is provided and the normal outwardly extending spring bonnet is not needed. Since the pilot valve member is positioned in the dome chamber and the adjustment spring is positioned in the exhaust chamber between the inlet sensing chamber and the dome chamber, a highly compact pilot valve structure is provided with a minimum of porting between the chambers.
An annular restriction or clearance is provided between the sensing tube and the main piston valve member to provide a restricted fluid communication between the inlet fluid and the dome chamber during normal operation. Relative axial movement occurs between the piston valve member and the sensing tube so that adequate cleaning of the annular restriction is achieved.
Upon a predetermined inlet fluid pressure applied against the pilot valve diaphragm, the diaphragm and sensing tube secured thereto move downwardly against an adjustment spring in the exhaust chamber to an unseated open position of the pilot valve member which is mounted in the dome chamber to communicate the dome chamber to the exhaust chamber for reducing the dome fluid pressure. Upon a reduction in the dome fluid pressure so that the fluid pressure load under the piston is greater than the fluid pressure load over the piston, the piston is moved or lifted from its valve seat to an open position to permit fluid from the pressure vessel to flow from the outlet of the main valve body. Thus, the fluid pressure in the pressure vessel is relieved or reduced from a predetermined maximum amount. Upon a reduction in the inlet fluid pressure from the pressure vessel below a predetermined amount, the reduced inlet fluid pressure to the pilot diaphragm chamber results in return of the diaphragm and inlet sensing tube in an upward or outer direction to the seated closed position of the pilot valve member blocking fluid flow from the dome chamber to the exhaust chamber or vent. Inlet fluid pressure flow to the dome chamber through the relatively small annular clearance between the piston and sensing tube provides an increase in fluid pressure in the dome chamber for movement of the piston valve member toward a closed seated position. For a relatively small increase of inlet fluid pressure, a relatively small decrease of fluid pressure in the dome chamber results in a relatively small movement of the main piston valve member toward a open position. Since proportional increases or decreases in inlet pressure result in proportional decreases or increases in the dome fluid pressure acting against the piston, a modulating action of the pilot valve is provided.
The pilot valve of the present invention fully opens at a maximum 2.5 psig differential across the valve with the dome chamber vented to atmosphere. Such an arrangement is desired in blower applications as the pilot valve normally bypasses downstream piping to provide a low flowing resistance against blower startup.
Minimal frictional resistance is provided against movement of the main piston valve member toward an open position since there is no seal between the piston and sense tube; an annular clearance is provided between the piston and the inlet sensing tube. In addition, the piston is preferably made of a lightweight aluminum material and a U-cup seal activated by dome fluid pressure is provided between the piston and an outer liner to minimize friction during lift or movement of the piston toward an open position when dome pressure is exhausted and reduced to substantially zero pressure.
An object of the invention is to provide a pilot operated safety relief valve in which the pilot valve is integral with the main relief valve.
An additional object of the invention is to provide such a pilot operated safety relief valve having a modulated and flowing pilot valve.
Another object of the invention is to provide such a pilot operated safety relief valve having a strong and sturdy pilot valve particularly adapted for use in low pressure vibrating service, such as blower applications.
A further object is to provide a highly compact pilot valve for a safety relief valve in which the exhaust chamber is positioned between the dome chamber and the inlet fluid sensing chamber with the adjustment spring mounted in the exhaust chamber thereby to provide a minimum of porting between the chambers and a minimal height.
Another object is the provision of such a pilot valve in which an inlet fluid sensing tube secured to an outer diaphragm provides fluid communication of inlet fluid to the outer side of the diaphragm for urging the pilot valve member downwardly for movement to an open position within the dome chamber.
Other objects, features, and advantages of the invention will be apparent from the following specification and drawings.
REFERENCES:
patent: 2619109 (1952-11-01), Garrett et al.
patent: 2890714 (1959-06-01), Greenwood et al.
patent: 3294111 (1966-12-01), Abercrombie et al.
patent: 3477456 (1969-11-01), Powell
patent: 3592224 (1971-07-01), Bois
patent: 4172466 (1979-10-01), Pattarini et al.
patent: 4425938 (1984-01-01), Papa et al.
patent: 4586533 (1986-05-01), Estes
patent: 4615356 (1986-10-01), Reip
patent: 4705065 (1987-11-01), McNeely et al.
patent: 4722361 (1988-02-01), Reip
pat
Browning & Bushman P.C.
Chambers A. Michael
McShane Thomas L.
Tyco Flow Control, Inc.
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