WO1992012366A1

WO1992012366A1 - Bi-phase sealing assembly

Info

Publication number: WO1992012366A1
Application number: PCT/US1992/000147
Authority: WO
Inventors: William E. Key; George Wang
Original assignee: Bw/Ip International, Inc.
Priority date: 1991-01-11
Filing date: 1992-01-09
Publication date: 1992-07-23

Abstract

A bi-phase seal assembly (10) for preventing the escape of a fluid which is liquid at pressures above atmospheric and gaseous at atmospheric pressure is proposed which comprises the combination of a mechanical seal (12) and a magnetic fluid seal (14) in tandem. Any escaping gaseous fluid is conducted to a remotely located fluid disposal system, such as a vapor recovery system (48) or a flare (50) to be burned.

Description

BI-PHASE SEALING ASSEMBLY

BACKGROUND OF THE INVENTION

FIELD OF INVENTION

This invention relates to a tandem, bi-phase sealing assembly, for example, the combination of a mechanical seal assembly and a magnetic fluid seal assembly for use in apparatus for handling a fluid which is liquid at a pressure in excess of atmospheric and a gas or vapor at atmospheric pressure. Generally such sealing assemblies are associated with pumping apparatus where the emission of gas or vapor to the atmosphere is not permissible, especially where there are humans, so that the invention can be used to meet the most stringent Federal and local emission standards for pumps.

BACKGROUND DISCUSSION

The use of sealing assemblies to substantially prevent the escape of product fluid along a shaft connecting a rotary device, such as a pump, is well known in the art. Generally the sealing means can be a simple elastomer ring or the like or a more complicated sealing means, such as a mechanical seal. Mechanical seals generally comprise a pair of seal rings, one arranged for rotation with the shaft and the other stationary within the housing. One or both seal rings can be so arranged to be movable axially, toward and away from the other. Both seal rings have a generally planar seal face, the seal face of one seal ring opposing the seal face of the other seal ring. A narrow gap may exist between the two opposing seal faces or they may be in contact. Because of the construction just explained, there is relative rotation between the seal rings. In the majority of seal assemblies, there is slight leakage across the relatively rotating seal rings, which lubricates the seal faces.

In the particular usage encountered, the fluid, if any, escaping across the seal rings becomes a vapor which enters the atmosphere. In general, these emissions are noxious, toxic and hazardous. Thus, near zero leakage arrangements are mandated by government agencies.

THE INVENTION

To accomplish the objectives of a zero-leakage, bi-phase, sealing arrangement, the combination of a primary mechanical seal assembly and a secondary magnetic fluid seal assembly is proposed. The mechanical seal assembly is most effective when operating with liquids, while the magnetic fluid seal assembly is only effective when operating with vapors or gases. When pumping propane, for example, leakage across the faces of the mechanical seal assembly vaporizes and becomes a gas, which gas leakage is sealed from the immediate atmosphere (environment) using a magnetic fluid seal and is vented to a remotely located vapor recovery system or to a remotely located flare where the gas is burned, thus removing the gases or vapors from the work area and the motor. If the leaking fluid is a volatile organic compound (VOC) , it is transformed from a liquid to the gaseous or vapor phase during its transit across the mechanical seal faces. Typical VOCs include light hydrocarbons, for example, ethane, propane and butane, and many chemical compounds. The leaking fluid enters the atmosphere as a noxious, toxic or hazardous compound. Local, state and federal (EPA) regulatory limits are being placed on emissions of VOCs and volatile hazardous air pollutants (VHAPs) . Near zero emission levels are specified for new pumps in the Los Angeles Basin (Los Angeles, San Bernardino, Orange and Riverside counties) . The EPA requires that carcinogenic vapor emissions must be less than one part per million.

THE DRAWING

The single figure of the drawing is an illustration, primarily in section, of a zero leakage, bi¬ phase sealing assembly as constructed according to the invention described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Looking now at the drawing, there is illustrated a bi-phase zero-leakage seal assembly 10, especially adaptable for use with pumps where the product fluid is a liquid at a pressure above atmospheric and a gas or vapor at atmospheric pressure. The assembly 10 comprises a primary mechanical seal assembly 12 and a secondary magnetic fluid seal assembly 14. The seal assemblies 12 and 14 encircle a shaft 16 connecting a pump 18 and a driving motor 20 (both shown schematically) . The shaft passes through a pump housing 22.

The mechanical seal assembly 12 comprises a pair of seal rings 24 and 26, each having opposing seal faces 28 and 30, respectively. The seal ring 24 is fixed against rotation by a pin 32 connected to a flange 34 of the housing 22, while the seal ring 26 is connected for rotation with the shaft 16. One or both seal rings can be axially movable. Here the seal ring 26 is axially movable and is urged toward the seal ring 24 by a coil spring 36, one end of which abuts a stop 38, while the other end engages a spring follower and face holder 40 which urges the seal ring 26 to its operative position. The seal ring 24 is sealed to the housing flange 34 and the housing 22 by means of an elastomeric O-ring seal 42, as illustrated. The housing is provided with a vent chamber 44 and a conduit 46 is provided to a remotely located vapor recovery system 48 or, in the alternative, to a remotely located flare 50 (both shown schematically) , so that any vapors or gaseous leakage passes through the conduit 46 to the remote location of the recovery system or flare.

Connected to the shaft 16 and to the housing flange 34, and in tandem with the primary mechanical seal assembly 12 is the secondary magnetic fluid seal assembly 14. This seal assembly 14 comprises a flanged housing 52 connected to the pump housing 22 through the flange 34. The shaft 16 or an extension thereof, such as a sleeve 54, passes through the housing 22. An annular permanent magnet 56 is fixed within the housing 52 and is radially spaced from the shaft 16. The magnet 56 abuts an annular pole member 58 which extends between the housing 52 and the shaft 16, being slightly radially spaced from the latter and thus defining, with the shaft, a radial gap 60. A ferrofluid 62 occupies the space between the shaft 16 and the pole member 58. The ferrofluid 62 forms the seal with the shaft, permitting the shaft to rotate, but preventing the escape of gaseous fluid or vapor along the shaft from the housing 22 to the immediate atmosphere or environment.

The gap 60 may be on the order of 2 to 12 mil, and a variety of ferrofluids may be employed in the assembly described. Typical ferrofluids would include ferrofluids having a magnetization in gauss ranging from 200 to 1000, and a viscosity of 50 cps to 900 cps, at 27 degrees C. The carrier liquid in the ferrofluid usually comprises a nonvolatile liquid carrier, such as a fluorocarbon, silicone oil, hydrocarbon, ester or other liquid carrier with suspended magnetite particles. Also, a dual seal as described and claimed in U.S. Patent No. 4,407,518 may be used, if desired. It is also to be understood that the primary mechanical seal may be constructed as a cartridge, the components being assembled on a shaft sleeve which surrounds the shaft when the mechanical seal is placed in the bi-phase assembly. Also, other constructions may be used, such, for example, as a bellows seal.

The claims appended hereto are intended to be given their broadest interpretation as permitted by the prior art.

Claims

We Claim:

1. A tandem seal assembly for preventing the escape of product fluid along a pump or machine shaft and out a housing through which the shaft passes to the immediate atmosphere comprising: a primary mechanical seal having a pair of seal rings encircling said shaft, each seal ring having a seal face and oriented such that the seal face of one seal ring engages the seal face of the other seal ring, one seal ring rotating with said shaft and the other seal ring being non-rotating; and a secondary magnetic fluid seal axially spaced from the primary seal and having an annular magnet in contact with a pole piece that is radially spaced from the shaft and that encloses a magnetic fluid encircling said shaft in close proximately to said mechanical seal.

2. A tandem seal assembly as recited in Claim

1, further comprising means to vent any leaking product fluid to a secondary location remote to said seal assembly.

3. A tandem seal assembly as recited in Claim

2, further comprising a disposal means connected to said means to vent any leaking fluid.

4. A tandem seal assembly as recited in Claim

3, wherein said disposal means comprises a recovery system for any leaking fluid.

5. A tandem seal assembly as recited in Claim 3, wherein said disposal system comprises a flare located at said secondary location.

6. A tandem seal assembly as recited in Claim 1, further comprising means to vent any product fluid leaking past said relatively rotating faces to a secondary location removed from said seal assembly.

7. A bi-phase zero-emission sealing assembly encircling a machine shaft, comprising a mechanical seal that is constructed and arranged to substantially prevent the escape of a fluid from a first confined zone about the shaft, which fluid changes from a liquid phase to a vapor phase upon escape therefrom, and a magnetic fluid seal that is in close proximity to said mechanical seal and is constructed and arranged to substantially prevent the escape of any of said fluid in gaseous phase from a second confined zone which escapes thereinto from said first confined zone.

8. A bi-phase seal assembly as recited in Claim 7, further comprising means to vent any gaseous fluid which escapes from said first confined zone to a location remote from said seal assembly.

9. A bi-phase seal assembly as recited in Claim 8, wherein location remote from said seal assembly comprises a vapor disposal means.

10. A bi-phase seal assembly as recited in Claim 9, wherein said disposal means comprises a vapor recovery system.

11. A bi-phase seal assembly as recited in Claim 9, wherein said disposal means comprises a flare where said vapor is burned.