Valves and valve actuation – Mechanical movement actuator – Screw
Reexamination Certificate
2002-07-31
2004-11-02
Keasel, Eric (Department: 3754)
Valves and valve actuation
Mechanical movement actuator
Screw
C251S357000, C251S214000
Reexamination Certificate
active
06811140
ABSTRACT:
FIELD OF THE INVENTION
The subject invention relates to a shutoff valve assembly for handling refrigerant liquids and/or gases.
More specifically, the subject invention relates to a valve assembly comprising a valve body, an internally threaded bonnet, an axially shiftable externally threaded valve stem provided in the bonnet, a hand-wheel, a valve disc, a circular collar provided around the outer surface of the said valve disc, an annular groove provided adjacent to the said circular collar to house the resiliently compressible deformable circular ring, a circular disc provided in the center of the lowermost portion of the said valve disc having a pair of holes, a sealing ring, a retainer plate rigidly fixed to the lower portion of the said valve disc.
The embodiment of the invention resides in an annular resiliently deformable backseat bush fitted in the said annular groove, a conical annular seat provided at the lower end of the said valve stem above the said valve disc wherein the said annular seat is seated against the said resiliently deformable backseat bush to ensure that the refrigerant liquids and/or gases are not allowed to escape in the event of the replacement of gland packing
More specifically, the invention relates to a resiliently deformable back-seat sealing bush, wherein the conical annular seat is seated against the said backseat bush to avoid the leakage of refrigerant liquids and/or gases, while replacing the gland packing.
The other embodiment of the invention resides in the flat face of the sealing ring which is pressed against the flat annular valve seat surface in the valve body.
Yet, another embodiment of the invention resides in the resiliently deformable compressible circular ring provided under the sealing ring providing a full proof sealing.
Another embodiment of the invention resides in the lower conical portion of the valve stem which is rounded at its lower most portion to accommodate the hollow cavity of the innermost portion of the valve disc.
The object of the invention is to avoid the closing down of the system in case of removal or replacement of gland packing, after the same is worn-out besides providing complete leak proof sealing.
Prior Art
Large industrial and commercial refrigeration systems employ refrigerants, such as ammonia, freon and the like, which are circulated through the system at high pressure in gaseous and liquid form.
These refrigerants are costly and a leakage in a large system not only reduces system efficiency but adds to cost of operation. Such systems require relatively large stop valves to control fluid flow. Such valves typically comprised either a one piece cast iron valve body with integrally formed threaded inlet and outlet flow tubes to which threaded pipe ends were connected, or a valve body fabricated of various components secured together by gas or electric welding techniques.
U.S. Pat. No. 86,749 claims a cast iron valve body to avoid such leakage. While cast iron valve bodies, being integral members may reduce the possibilities of leakage, casting is a complex and costly technique requiring separate molds for each valve size.
Conversely, prior art valve bodies fabricated of conventionally welded components are complex in design and methods of fabrication, introduce potential weak spots and are not easily kept clean during manufacture.
Various types of valve spindle stuffing box arrangements were employed to seal against leakage of high pressure past the valve spindle. Also, various valve seating arrangements were employed to ensure proper valve closure. Threaded connections on the valve body, whether casted or welded, very often proved to be prone to fluid loss. Furthermore, valve seat and valve disc designs and valve spindle stuffing box designs, often dictated by the configuration of a cast iron valve body, were susceptible to wear and tear is requiring servicing and replacement of seals to prevent leakage.
Shut-off valves are used in various systems to control the flow of liquids and/or gases and are particularly well suited to control the flow of refrigerants in gaseous and/or liquid states, which are circulated under extremely high pressure in refrigeration system. Such valves typically ranges in size from ¼ inches to 12 inches, when measured with reference to the diameter of the valve's inlet or outlet ports.
A typical shut-off valve generally comprises of a valve housing having an inlet port, an outlet port and an annular valve seat within the housing between the two ports. An externally threaded rotatable valve stem extends through an internally threaded, sealed valve stem opening in the housing and is provided at its lower end with a circular valve disc which is axially movable into and out of engagement with the annular valve seat as the valve stem is rotated between closed-and open positions respectively.
The prior art teaches various forms of sealing means which aim to improve the seal between the valve disc and the annular seat to prevent the undesirable leakage through the valve when the valve is closed. In one known prior art type of disc-type shut off valve used in high pressure refrigeration system, the valve disc located at lower end of the rotatable valve stem takes the form of conical metal member which presses the conical metal valve seat made on the valve body. The chances of leakage at the valve seat where the metal to metal contact is sealing the joint, was very high. The sealing between the valve stem and the valve body is effected by asbestos
on-asbestos sealing material which is tightly packed between the valve stem and the valve body. The sealing material eventually get corroded due to the friction and has to be replaced. It is very difficult to replace the packing when the plant is under pressure. For such replacement, the valve is to be isolated first and then the packing known as gland packing is removed and replaced with fresh material of gland packing.
In conventionally available shut-off valves, the valve disc is connected to the valve stem in such a manner that some space for relative movement is possible between them, so that the valve disc can adjustably position itself on the valve seat. The valve disc has an annular groove and an annular ring. The annular groove is formed around the outer periphery of the lower surface of the valve disc. The annular ring is made up of plastic such as Teflon. The plastic annular sealing ring is held in place on the valve disc by a smaller circular metal retainer plate which is attached to the lower surface of the valve disc and bears against the under side of the sealing ring. The retainer plate is secured to the valve disc by a number of bolts extending through holes in the retainer plate and screw into threaded bolt holes in the valve disc. When the valve is closed, the lower corner edge or flat face of the plastic annular sealing ring bears against the annular conical shaped/flat faced metal valve seat surface in the valve body.
Since, there is high fluid pressure conditions existing at the underside of the valve, when the valve is closed, there is always a possibility of gas or liquid leakage through a space between the rear side of the retainer plate and the front side of the sealing ring, through a second space between the inner edge of the sealing ring and the side edge of the annular groove in the valve disc and through a third space between the rear side of the sealing ring and the bottom of the annular groove in the valve disc. Furthermore, the result of such leakage is that high pressure liquid in the aforesaid second place causes the resilient plastic sealing ring to expand or to be urged laterally or circumferentially outward relative to the groove due to the fluid pressure in the aforementioned second space. With the passage of time, such a phenomenon has the effect of permanently deforming and losing the plastic sealing ring and increasing the possibility of undesirable fluid leakage through the aforesaid flow-paths when the valve is fully closed.
U.S. Pat. No. 4,801,125 teaches the use of stop valve, wher
Keasel Eric
Ladas & Parry
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