WO1992010699A1

WO1992010699A1 - Sealing device for rotary valve

Info

Publication number: WO1992010699A1
Application number: PCT/US1991/009246
Authority: WO
Inventors: Alberto Aliani
Original assignee: Keystone International Holdings Corp.
Priority date: 1990-12-11
Filing date: 1991-12-11
Publication date: 1992-06-25
Also published as: AU9127891A; IT1242408B; IT9042542A0; IT9042542A1

Abstract

The present invention is directed to a sealing device for a rotary valve. The sealing device of the present invention comprises a bellows seal (6) sealingly disposed about a linearly displaceable actuator shaft (14) between a housing (30) and a linearly displaceable slide (17, 31) to which the actuator shaft (14) is affixed and upon which is carried a rack (4) for cooperation with a pinion (3) for driving a rotating shaft to move the valve closing element between its closed and opened positions. The sealing device of the present invention comprises the bellows sealing system (6) for cooperation with the rack (4) and pinion (3) to transform the linear reciprocating motion of actuator shaft (14) and rack (4) to rotary motion of pinion (3) and the rotating valve closing shaft and closing element. Actuator shaft (14) is inserted through the bellows (6) which provides static seals to flange (30) and bushing (31). The bellows sealing system may thus be employed with rotary valves where it avoids the necessity to use conventional packing or sealing rings which are prone to leakage and failure due to friction with the rotating actuator shaft.

Description

SEALING DEVICE FOR ROTARY VALVE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a sealing device for rotary valves. More specifically, the present invention is directed to an improved rotary valve sealing device comprising a bellows seal system for controlling and eliminating leakage around the actuator shaft.

2. Description of the Background

A rotary valve is a valve whose stem rotates about its axis without linear motion in order to move a closing element between its open and closed positions. Exemplary rotary valves are ball and butterfly valves. Rotary valves generally employ a dynamic sealing

system based on gaskets or rings which seal about the rotating actuator stem in order to prevent leakage of the fluid flowing through the valve to the outside of the valve housing or of the pipe into which the valve is disposed. The gaskets or rings are often made of rubber, teflon, TFE, asbestos, graphite or other similar materials. The gaskets or rings are pressed axially by a bushing and forced radially against the actuator stem.

A serious disadvantage encountered when using the previously described dynamic sealing systems is the wear of the gaskets or rings due to friction with the actuator stem.

Progressive wear of the gaskets or rings causes valve leakage. Leakage may create dangerous conditions at the location of the valve. Leakage and these conditions may result in signifⁱcant damage, especially when the valve is used with dangerous liquids.

Static sealing systems which employ static seals, e.g., bellows sealing systems, are known for use in other fields and with non-rotary valves. In these bellows systems the bellows move linearly by expanding and contracting. The sealing effect toward the outside

SUBSTITUTE SHEET is created by means of static seals at the end of the bellows. These static seals are not prone to the disadvantageous wear typical of the dynamic seals discussed above. However, bellows seals are used only on valves featuring linearly moving stems, i.e., on valves wherein the stems move without rotation around their axes, since the bellows could not withstand the twisting stress due to stem rotation.

Ball and butterfly valves rotate about ninety degrees between the opened and closed positions. This corresponds to the two limit positions wherein the closing elements are perpendicular to the flow direction (valve closed) or parallel to the flow direction (valve opened). There has been a long felt but unfulfilled need for an improved seal system for sealing about the rotating actuator shaft in rotary valves, e.g., in ball and butterfly valves.

SUMMARY OF THE INVENTION

The present invention is directed to a sealing device for rotary valves of the type having a rotating shaft which moves the closing element. More specifically, the present invention is directed to the improvement in such valves comprising means for controlling and

eliminating the leakage around the actuator shaft by use of a bellows seal system.

An object of the present invention is to eliminate the disadvantages of the prior art valve sealing systems, including those discussed above. The seal of the present invention

reduces possible dangerous conditions and minimizes valve maintenance.

In order to achieve this object the present invention employs a static, bellows-type seal with a rotary valve. The bellows seal is disposed about an actuator shaft which moves linearly along the axis of the bellows. Linear movement of the actuator shaft is typically accompanied by rotary motion. The linear movement of the actuator shaft is converted to rotary movement of the valve rotating shaft by a rack and pinion connection. The bellows seal provides a static seal on a first end with a flange in the actuator housing through which

the actuator shaft is disposed and a static seal on a second end with a bushing with which the linearly movable rack moves.

In another aspect, the present invention includes an alarm system to signal possible bellows failure by monitoring the pressure in the interior of the bellows, i.e. , between the bellows and the actuator shaft. The stated advantages and objects of the present invention are comprehensively provided in a sealing device for rotary valves in accord with the present invention. By employing a bellows seal system for controlling and eliminating the leakage around a rotating actuator shaft of a rotary valve, e.g. , a ball or butterfly valve, the advantages of the present invention are achieved. These and other meritorious features and advantages of the present invention will be more fully appreciated from the following detailed description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and intended advantages of the present invention will be readily apparent by the references to the following detailed description in connection with the

accompanying drawings, wherein:

Fig. 1 is a cross-section of a rotary valve including a bellows sealing device in accord of the present invention; and

Fig. 2 is a cross-section along line 2-2 of the valve and sealing device of Fig. 1.

While the invention will be described in connection with the presently preferred embodiment, it will be understood that it is not intended to limit the invention to this

embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included in the spirit of the invention as defined in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The improved rotary shaft sealing device of the present invention comprises a bellows

seal system employed to seal about the actuator shaft of a rotary valve. In general, the actuator shaft will both rotate and move linearly to rotate a valve closing shaft which moves the closing element between its opened and closed positions. A bellows seal system provides

means for controlling and eliminating the leakage about the rotating actuator shaft in rotary

valves, e.g., ball and butterfly valves.

The invention will now be described with reference to the cross-sectional illustrations

in Figs. 1 and 2. The present invention comprises a sealing device 1 for the upper part of a rotary valve. The sealing device 1 is fitted with a flange 2 having holes 5 for fastening the flange to the upper part of the valve body with a static gasket (not shown). The valve includes a shaft on which a pinion 3 is mounted for coupling with a movable rack 4 which

is part of a sliding block 17 placed in chamber 7 in the body 18 of the device 1 which limits the space subjected to the same pressure as that of the flowline. Block 17 is fitted with guides 19 favoring linear movement of block 17 in chamber 7. Block 17 is connected with a threaded shaft 14 screwed into a bushing 31 which is inside and connected to block 17.

Linear movement of threaded shaft 14 is caused by rotation of handwheel 13. Other conventional means of turning actuator shaft 14 may be employed. Exemplary means include

electric actuators, pneumatic cylinders and hydraulic cylinders, all of conventional types. Bellows 6 is placed inside chamber 7 and fitted around actuator shaft 14. The ends of the bellows are affixed by any appropriate means, e.g. , welding, to bushing 31 at one end and at the other end to flange 30 which closes body 18 of the device. Each end of bellows 6 must include a static seal. Inside the bellows there is no pressure of the fluid in the flowline since the bellows is sealed at each end to form a fluid-free chamber between bellows 6 and threaded shaft 14. Sealing is obtained at the bellows ends, preferably by welding. Bellows 6 is pressurized from the outside. Because of outside pressurization, smaller bellows 6 may be employed, thus creating a more compact device. Bellows 6 can extend and contract linearly according to the movement of the actuator shaft 14 and block 17. Outside chamber 7 a smooth section of the threaded shaft 14 is inserted through packing 8 which consists of studs 9, only one of which is illustrated, which press gland 11

towards chamber 12 by means of nuts 10. Packing 8 essentially provides a backup safety

seal for operation in case of failure of the bellows 6.

Port 16 connects the interior of bellows 6 with a non-sealed area 20 of the device.

As illustrated in Fig. 1, port 16 is preferably closed by plug 15. In an alternative embodiment, a sensor for the pressure inside bellows 6 is fitted in place of plug 15. This

sensor detects possible bellows failure by detecting pressure changes in the fluid-free chamber between bellows 6 and shaft 14. During normal operation of the valve, the pressure in port 16 is approximately atmospheric pressure. Upon bellows failure, port 16 becomes pressurized by the valve medium. When coupled with a telemetry means, signals indicating possible bellows failure may be sent to an alarm or control center.

Pinion 3 with rack 4, bellows 6 and threaded shaft 14 provide means for control of

the valve rotating shaft. Using a bellows sealing system, the pressure sensor and port 16 provide means to detect possible failure of the valve sealing elements and particularly of the bellows 6.

The present invention makes it possible therefore to fit a bellows sealing system to

a rotary valve, by transforming the linear motion of shaft 14, not necessarily a threaded shaft, and of the bellows 6 into the rotary motion of the valve closing shaft. Having further included an extra sealing system of the packing type 8 and a pressure sensing device for signaling to a control center ensures improved operation and safety particularly useful in the handling of dangerous fluids.

The device may be constructed of various materials well known to those of skill in the art depending on the fluid circulating in the pipe in which the valves are installed. Particularly useful materials include, e.g., steel, stainless steel, alloy steel and other similar

materials.

The foregoing description of the invention has been directed in primary part to a particular preferred embodiment in accordance with the requirements of the patent statutes and for purposes of explanation and illustration. It will be apparent, however, to those

skilled in the art that many modifications and changes in the specifically described system may be made without departing from the true scope and spirit of the invention. Therefore,

the invention is not restricted to the preferred embodiment illustrated, but covers all modifications which may fall within the scope of the following claims.

Claims

What is Claimed is:

1. A sealing device for use with a rotary valve of the type having a rotating shaft for moving the closing element, said sealing device comprising: a housing;

a linearly movable actuator shaft extending into said housing for creating rotary motion to move said closing element between a closed position and an opened

position; and a bellows seal system for controlling leakage about said actuator shaft.

2. The sealing device of Claim 1 wherein said bellows seal system comprises:

a pinion affixed to said rotating shaft; a rack linearly movable with said actuator shaft for cooperation with said pinion to rotate said rotating shaft about its axis to move said closing element between said opened and said closed positions; and

a bellows disposed about the portion of said actuator shaft extending within said housing for sealing between the interior and exterior of said housing.

3. The sealing device of Claim 1 , further comprising means for detecting leakage or failure of said bellows seal system.

4. The sealing device of Claim 3 wherein said means for detecting comprises a pressure sensing device in fluid communication with the space between said bellows and said actuator shaft.

5. The sealing device of Claim 4, further comprising a port in communication

with the space between said bellows and said actuator shaft and wherein said pressure sensing device is disposed in said port.

6. The sealing device of Claim 1, further comprising a safety packing about said actuator shaft where said actuator shaft exits said housing to ensure sealing along said actuator shaft downstream of said bellows.