GB2109508A

GB2109508A - Gate valve with bonnet relief valve

Info

Publication number: GB2109508A
Application number: GB08230492A
Authority: GB
Inventors: Joseph Robert Santoro; Mike Bonfiglio
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1981-11-16
Filing date: 1982-10-26
Publication date: 1983-06-02
Also published as: DE3240871A1; KR840002080A; SE8205477D0; IT1154031B; JPS5888269A; FR2516625A1; SE8205477L; IT8224178A0; BE895026A

Abstract

A gate valve having an internal relief mechanism (36) comprises a movable valve disc (32) for blocking the main fluid passageway (30) through the valve body (14). The valve disc (32) is provided with a channel (40,42) providing communication between the valve bonnet cavity (34) and with the main fluid passageway (30). The pressure relief mechanism (36) is disposed in the channel (42) of the valve disc (32) and provides for fluid communication between the valve bonnet cavity (34) and the high pressure side of the main fluid passageway (30) such that the pressure in the valve bonnet cavity remains substantially equal to the fluid pressure in the main fluid passageway (30). <IMAGE>

Description

SPECIFICATION Gate valve with bonnet relief valve This invention relates to gate valves and more particularly to gate valves having relief valves incorporated therein.

Typically, gate valves have cavities in the valve bonnet for accommodating the valve stem and valve disc as the valve is opened or closed.

Frequently, these bonnet cavities are in fluid communication with the fluid passing through the valve body so that fluid can enter the bonnet cavity. When the valve is closed, the fluid can become trapped in the bonnet cavity. Normally, trapping of the fluid in the bonnet cavity does not result in a valve failure or leakage from the valve.

However, in valves subjected to high temperature operation, the fluid trapped in the bonnet cavity can generate high pressure due to expansion. This high pressure can result in valve failure including leakage of the fluid from the valve bonnet to the atmosphere. Leakage of this type can be particularly troublesome when the fluid involved is a noxious, corrosive, radioactive, or otherwise dangerous fluid.

It is therefore the principal object of the present invention to provide a valve having a selfactuating mechanism for relieving bonnet cavity pressure when that pressure reaches a predetermined limit.

With this object in view, the present invention resides in a gate valve having a pressure relief mechanism comprising a valve body (14) having a fluid passageway (30) for conducting a fluid therethrough, a valve bonnet (12) disposed on said valve body (14) and defining a bonnet cavity (34) therein, and a valve disc (32) movably disposed in said valve bonnet (34) so as to be capable of selectively opening or closing said fluid passageway (30); characterized by pressure relief means (36) disposed in said valve disc (32) in fluid communication with a first portion and a second portion of said fluid passageway (30) and in fluid communication with said bonnet cavity (34) for selectively maintaining fluid communication between said bonnet cavity (34) and said first portion of said fluid passageway while isolating said bonnet cavity and said first portion of said fluid passageway (30) from said second portion of said fluid passageway (30) thereby preventing overpressurization of said bonnet cavity (34). The pressure relief mechanism provides for communication between the valve bonnet cavity and the high pressure side of the main fluid passageway such that the pressure in the valve bonnet cavity remains substantially equal to the fluid pressure in the main fluid passageway.Thus, the valve bonnet cavity pressure does not exceed the operating pressure of the valve. The invention will become more readily apparent from the following description of a preferred embodiment thereof shown, by way of example only, in the accompanying drawings, wherein: Figure 1 is a cross-sectional view in elevation of the valve; Figure 2 is a view along line Il-Il of Figure 1; and Figure 3 is a view along line Ill-Ill of Figure 2.

Referring to Figure 1, a valve 10 comprises a valve bonnet 12 that may be integral with or attached to a valve body 1 4. A valve stem 1 6 extends through valve bonnet 12 and has threads 1 8 for engaging threads 20 of valve bonnet 1 2 for moving valve stem 1 6 relative to valve bonnet 12. A valve handle 22 is attached to valve stem 1 6 for advancing valve stem 1 6. A packing 24 is disposed in the valve bonnet 12 and around the valve stem 16 to prevent leakage of fluid. A packing retainer 26 is mounted on valve bonnet 12 for maintaining the packing 24 in a tight configuration.

Valve body 14 has a fluid passageway 30 for accommodating the flow of the working fluid. The valve stem 1 6 has a valve disc 32 attached to one end thereof which may be a wedge-shaped metal member. Movement of valve stem 1 6 causes valve disc 32 to be moved out of or into the fluid passageway 30, thus selectively allowing or preventing flow of fluid through fluid passageway 30. In many prior art concepts, valve disc 32 is manufactured to be a single solid member or several individual parts forming a solid member so that when in the position similar to that shown in Figure 1, no fluid can pass through fluid passageway 30. Similarly, when valve disc 32 was raised to allow flow through fluid passageway 30, fluid could also enter bonnet cavity 34 which is the cavity formed within valve bonnet 12.Fluid entering bonnet cavity 34 is usuaily not a problem.

However, when valve disc 32 is returned to a closed position as shown in Figure 1 fluid can be trapped in bonnet cavity 34. In valves used for high temperature service, the fluid trapped in bonnet cavity 34 can become heated to the point that the fluid can exert extreme pressure on packing 24 and on valve bonnet 12. This can lead to leakage of fluid from valve bonnet 1 2 which can be particularly troublesome if the fluid is a dangerous or noxious fluid.

Referring now to Figures 1-3, in order to prevent overpressurization of bonnet cavity 34, valve 10 is provided with a pressure relief mechanism referred to generally as 36 for selectively establishing fluid communication between bonnet cavity 34 and fluid passageway 30 so that the pressure of the fluid in bonnet cavity 34 does not substantially exceed the fluid pressure in passageway 30. Pressure relief mechanism 36 comprises a channel 38 defined between valve body 14 and valve disc 32 and extending to a first bore 40 in valve disc 32. Valve disc 32 also has a transverse second bore 42 that is connected to first bore 40 and extends completely through valve disc 32 to fluid passageway 30 on each side of valve disc 32.

Second bore 42 is constructed to have a portion large enough to accommodate a movable valve member 44 which is capable of preventing flow of a fluid through a portion of second bore 42. Valve member 44 is sized to have a portion that is capable of seating against a section of second bore 42 for blocking flow through that section while allowing flow through the remainder of second bore 42. Valve member 44 may be a dumbbell-shaped member that is capable of blocking the flow of the fluid from one portion of fluid passageway 30 to the other portion of fluid passageway 30 while allowing flow of the fluid from bonnet cavity 34 through channel 38 and first bore 40 and into only one portion of fluid passageway 30 as shown in Figure 1.A sleeve 46 having a third bore 48 may be disposed in second bore 42 for allowing the insertion of valve member 42 during assembly but preventing the dislodging thereof during operation. Third bore 48 establishes fluid communication between fluid passageway 30 and second bore 42. Valve member 44 is slidably disposed in second bore 42 so as to slide in second bore 42 under the influence of the fluid pressure in fluid passageway 30. The construction of pressure relief mechanism 36 is such that it is bidirectional in operation. That is, valve member 44 will move from the high pressure side of valve disc 32 to the low pressure side of valve disc 32 irrespective of which side of valve disc 32 is the high pressure side. In this manner, valve member 44 maintains a fluid conduit between the high pressure portion of fluid passageway 30, through a portion of second bore 42, and to first bore 40.Since first bore 40 is in fluid communication with channel 38 and bonnet cavity 34, fluid communication is thus maintained between bonnet cavity 34 and the high pressure portion of fluid passageway 30. Thus, by being in fluid communication with the high pressure portion of fluid passageway 30, bonnet cavity 34 maintains a pressure substantially equal to that of the high pressure portion of fluid passageway 30 and thereby preventing extreme overpressurization of bonnet cavity 34. In addition, valve member 44 serves as a check valve preventing flow of fluid from one portion of fluid passageway 30 to the other through second bore 42 while allowing fluid flow from bonnet cavity 34 to the high pressure side of fluid passageway 30.

When in the position as shown in Figure 1, valve disc 32 prevents flow of fluid through valve 10 and prevents overpressurization of bonnet cavity 34. Therefore, the invention provides a gate valve having a self-actuating pressure relief mechanism to prevent overpressurization of the bonnet cavity.

Claims

1. A gate valve having a pressure relief mechanism comprising a valve body (14) having a fluid passageway (30) for conducting a fluid therethrough, a valve bonnet (12) disposed on said valve body (14) and defining a bonnet cavity (34) therein, and a valve disc (32) movably disposed in said valve bonnet (34) so as to be capable of selectively opening or closing said fluid passageway (30); characterized by pressure relief means (36) disposed in said valve disc (32) in fluid communication with a first portion and a second portion of said fluid passageway (30) and in fluid communication with said bonnet cavity (34) for selectively maintaining fluid communication between said bonnet cavity (34) and said first portion of said fluid passageway while isolating said bonnet cavity and said first portion of said fluid passageway (30) from said second portion of said fluid passageway (30) thereby preventing overpressurization of said bonnet cavity (34).

2. A gate valve as claimed in claim 1, characterized in that said pressure relief means (36) comprises a first bore (40) in said valve disc (32) in fluid communication to said bonnet cavity, a second bore (42) in said valve disc (32) and extending through said valve disc (32) from said first portion of said fluid passageway (30) to said second portion of said fluid passageway (30); and a valve member (44) slidably disposed in said second bore (42) for selectively isolating said second portion of said fluid passageway (30) from said first portion of said fluid passageway (30) while permitting fluid communication between said bonnet cavity (34) and said first fluid passageway.

3. A gate valve as claimed in claim 1 or 2, characterized in that said pressure relief means (36) further comprises a channel (38) in said valve body (14) providing communication between said bonnet cavity (34) and said first bore (40).

4. A gate valve as claimed in claim 3, characterized in that said valve member is a dumbbell-shaped member (44) capable of isolating one portion of said second bore while permitting fluid communication through the other portion of said second bore (42).