MECHANICAL SHAFT SEAL

Abstract

An improved mechanical shaft seal to give a tight seal between relatively rotating machine parts and prevent the escape of particulate material into the atmosphere or into the mechanical components of the housing under adverse operating conditions. The seal provides a grease chamber that prevents solid particles from reaching the main seal by migration within the mechanical shaft seal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The various features of the invention will become more apparent from the following description of an embodiment of the invention wherein reference is made to drawings.

FIG. 1 is a perspective view of a mechanical shaft seal of the present invention mounted on the side wall of a flap valve.

FIG. 2 is an exploded view of FIG. 1.

FIG. 3 is a cross-sectional view of half of a seal assembly according to the present invention.

FIG. 4 is a cross-sectional view of a grease housing according to the present invention.

FIG. 5 is a cross-sectional view of a rotor sleeve according to the present invention.

FIG. 6 is a cross-sectional view of a gland according to the present invention.

FIG. 7 is a perspective view of an alternative embodiment of a mechanical shaft seal of the present invention mounted on the side wall of a flap valve.

FIG. 8 illustrates a multiple valve configuration.

DETAILED DESCRIPTION

Referring to FIG. 1 and FIG. 2, a mechanical shaft seal embodying the present invention is adapted to be externally and sealingly mounted onto dry-material-handling equipment, such as onto a flap valve (e.g. an Airlock® valve sold by Plattco Corporation (Plattsburgh, N.Y.)), or a flap valve, or a diverter valve or other valve maintaining a pressure differential between two environments. Applications for a mechanical shaft seal of the invention include, but are not limited to, installation around an entry point of a mixer or packer.

Gland 13 for the mechanical shaft seal 19 is exposed to the outside atmosphere and secured to end cap 37, e.g. by fastening bolts 39 through apertures 36. End cap 37 is then attached to the side wall of flap valve 38. Shaft 20 extends from within flap valve 38 and through end cap 37 and mechanical shaft seal 19. A bore through the center axis of the mechanical shaft seal 19 is large enough to accept a rotating shaft 20 and prevents the release of dry material between the mechanical shaft seal 19 and the end cap 37, as well as preventing leaks between the rotating shaft 20 and the bore. No pneumatic lines are required in order to prevent dry material from escaping from the inside of the flap valve.

Referring to FIG. 3, a mechanical shaft seal 19 is comprised of a seal assembly, a rotor sleeve 3, and gland 13. The seal assembly is comprised of grease housing 14, lip seal 17, grease chamber 18, and a single-spring seal 1. The seal assembly is secured to the rotor sleeve 3 via at least one snap ring 6. “Single-spring seal” is defined as a mechanical seal that is capable of rotating with a shaft while maintaining a seal with a stationary seat to prevent the migration of material along the length of the shaft. The seal assembly is exposed to dry material under pressure. The gland 13 is mounted externally and exposed to the atmosphere. Extending along the axis of symmetry of mechanical shaft seal 19 is the rotor sleeve 3 and a rotatable shaft 20. The seal assembly prevents the release of dry material into rotor chamber 21.

The ledge 22 provides a seat for a lip seal 17. The lip seal 17 is preferably made of a fluoroelastomer. Lip seal 17 creates a seal between the inner wall of grease housing 14 and the outer wall of the proximal end of portion 29 of rotor sleeve 3. The ledge 30 provides a step for a stationary seat 2. The stationary seat 2 is preferably made of tungsten carbide or silicon carbide. Stationary seat packing 4 is located in between stationary seat 2, ledge 30, and the inner wall of portion 25 of gland 13. Stationary seat packing 4 secures stationary seat 2 also provides a seal between the seal assembly and chamber 21. Stationary seat packing 4 secures stationary seat 2 against spring seal 1 and provides a seal between chamber 18 and rotor chamber 21. The stationary seat packing 4 is preferably made of a fluoroelastomer. A rotating single-spring seal 1 disposed around portion 29 of rotor sleeve 3 presses against stationary seat 2. The single-spring seal 1 is preferably comprised of “316” stainless steel, Viton® (DuPont), and carbon. An annular groove around the outer wall of the proximal end of portion 29 of rotor sleeve 3 holds a snap ring 6 that secures the rotating single-spring seal 1 against stationary seat 2. The snap ring 6 is preferably made of “302” stainless steel. A back-up ring 5 is disposed around rotor sleeve 3 between snap ring 6 and single-spring seal 1. The back-up ring 5 is preferably made of “316” stainless steel. Snap ring 6 and back-up ring 5 set the operating length of single-spring seal 1. Chamber 18 houses snap ring 6, back-up ring 5, and single-spring seal 1. Chamber 18, which is bounded by the lip seal 17, the inner wall of grease housing 14, stationary seat 2, and the outer wall of portion 29 of rotor sleeve 3, is packed with grease.

Fluoroelastomer O-rings useful in the present invention include those of fluorocarbon rubber (FKM) such as Viton® (DuPont). Grease useful in the present invention includes grease conforming to NLGI 2 (National Lubricating Grease Institute grade 2, corresponding to a worked penetration value of 265-295, using the standard NLGI penetration test apparatus, as is known in the art), which are lubricants exhibiting high viscosity and that are resistant to breakdown. Preferably, the lubricants are Almagard® lubricants, e.g. Almagard 3752 NLGI 2 (Lubrication Engineers, Inc., Fort Worth, Tex.).

Portion 25 of gland 13 and annular collar 27 form an annulus that provides a seat for a sealed bearing 8 disposed around portion 28 of rotor sleeve 3 that bears against portion 26 of gland 13. In order to prevent sealed bearing 8 from moving axially that would result in potential leakage of dry material, sealed bearing 8 is press fit onto portion 28. An annular groove in the outer wall of portion 28 holds a snap ring 7 and an annular groove in the inner wall of portion 26 holds a snap ring 12. Snap rings 7 and 12 secure the sealed bearing 8 against portion 25 of the gland 13. Snap rings 7 and 12 are preferably made of “302” stainless steel.

A plurality of set screws 15 extend radially through the male coupling 23 and female coupling 24 to secure the grease housing 14 to the gland 13. The set screws 15 are preferably made of hardened steel. An annular groove in the male coupling 23 is adjacent to the set screw and holds the grease housing O-ring 16. The grease housing O-ring 16 is preferably made of a fluoroelastomer. A circumferential groove adjacent to the female coupling 24 holds the gland O-ring 11. The gland O-ring 11 is preferably made of a fluoroelastomer.

Referring to FIG. 4, grease housing 14 is cylindrical with a proximal end 36 exposed to the pressurized dry material and a distal end 33. The grease housing 14 is preferably made of “304” stainless steel. Grease housing 14 has a short ledge portion 22 that extends inwards radially at the proximal end 36 of the grease housing 14. Grease housing 14 also has a male coupling 23 integrally connected at the distal end 33 of the grease housing 14.

Referring to FIG. 5, rotor sleeve 3 has a proximal end 34 exposed to the dry material and a distal end 31 exposed to the atmosphere. Rotor sleeve 3 is preferably made of “304” stainless steel. Rotor sleeve 3 includes three main portions: an elongated barrel portion 29 located at proximal end 34, a short barrel portion 28 located at the distal end 31, and an annular collar 27 located between portions 28 and 29. Rotor sleeve 3 has a bore extending axially therethrough, sized to accommodate shaft 20. A plurality of set screws 10 extend radially through the distal end 31 of portion 28. The set screws 10 are preferably made of alloy steel. An annular groove adjacent to the set screws 10 in the inner wall of the rotor sleeve 3 holds the sleeve O-ring 9. The sleeve O-ring 9 is preferably made of a fluoroelastomer.

Referring to FIG. 6, gland 13 has a proximal end 35 which connects to grease housing 14 (FIG. 4) and a distal end 32 exposed to the atmosphere. The gland 13 is preferably made of “304” stainless steel. The gland 13 includes an axially directed portion 26 and a radially directed portion 25 thus giving a segment of such gland, as seen in cross-section, a generally L-shaped appearance. Portion 25 has a short ledge portion 30 that extends inwards radially into the rotor chamber 21. Gland 13 has a bore extending axially therethrough sized to accommodate the rotor sleeve 3 and a plurality of circumferentially-spaced apertures 36 through portion 26. The proximal end 35 of gland 13 has a female coupling 24.

Referring to FIG. 7 and FIG. 8, an alternative embodiment of a flap valve 60 that uses mechanical shaft seal 19 is shown. In this embodiment, flap valve 60 has opening 62 to receive material. Shaft 20 is mechanically linked to a flap (not shown) that is movable to either restrict or allow the flow of material within flap valve 60. Shaft 20 is mechanically linked to lever 64, which is mechanically linked to air cylinder 72 via cylinder shaft 68. Pneumatic supply lines (74A and 74B) are fed by a compressed air system (not shown). In operation the air cylinder is activated and deactivated to control the flow of material through the valve as desired.

FIG. 8 illustrates a flap valve system 80. In embodiment shown, multiple flap valves (here, indicated as 60A and 60B) are arranged in a vertical manner as shown. The multiple valve configuration allows for more precise control of the flow of the material. Preferably, the flap valves are configured to have opposite phases. That is, when flap valve 60A is “open” and allowing material to pass through it, valve 60B is closed, and material accumulates in valve 60B, but can not exit since valve 60B is closed. Then in the next cycle, valve 60A is closed, and valve 60B is open, allowing only the material that had been previously deposited in valve 60B to pass through. The opposite phase relationship can be implemented via a pneumatic control system (not shown) that opens and closes flap valves 60A and 60B with the desired timing sequence. In one embodiment, the multiple valve configuration comprises two flap valves. However, it is possible to use more than two valves without departing from the scope of the present invention.

Although the present invention has been described in connection with a specified embodiment thereof, many other modifications, corrections and applications are apparent to those skilled in the art. Therefore, the scope of the present invention is not limited to the embodiment described herein.

Claims

1. A mechanical shaft seal comprising a rotating seal assembly, a stationary seat, a gland, and a rotor sleeve mounted for rotation therein, said rotor sleeve having an inner wall and an outer wall,said seal assembly comprising a grease housing, a lip seal, a grease chamber, and a single-spring seal,said seal assembly surrounding said rotor sleeve, in sealing engagement with said stationary seat,said seal assembly being secured to said gland,said gland surrounding said rotor sleeve, andsaid rotor sleeve having a bore therethrough to enable said rotor sleeve to surround and sealingly engage a shaft for rotation with said shaft.

2. A mechanical shaft seal according to claim 1 wherein said seal assembly is secured to said rotor sleeve with at least one snap ring

3. A mechanical shaft seal according to claim 1 further comprising a sealed bearing in sealing engagement within said gland and surrounding said rotor sleeve.

4. A mechanical shaft seal according to claim 1, wherein said single-spring seal is comprised of 316 stainless steel, an elastomer, and carbon.

5. A mechanical shaft seal according to claim 1, wherein said grease chamber contains grease having an NLGI grade of 2.

6. A mechanical shaft seal according to claim 1, wherein said stationary seat is made of a substance comprising tungsten carbide.

7. A mechanical shaft seal according to claim 1, wherein said stationary seat is made of a substance comprising silicon carbide.

8. A mechanical shaft seal according to claim 1, wherein said rotor sleeve is comprised of 304 stainless steel.

9. The mechanical shaft seal of claim 8, wherein the rotor sleeve further comprises an annular groove within the inner wall of the rotor sleeve, said annular groove holding a sleeve O-ring.

10. The mechanical shaft seal of claim 9, wherein said rotor sleeve further comprises an annular groove around the outer wall of the rotor sleeve, and a snap ring disposed within said annular groove.

11. The mechanical shaft seal of claim 10, wherein said snap ring is comprised of 302 stainless steel.

12. The mechanical shaft seal of claim 9, wherein said sleeve O-ring is comprised of a fluoroelastomer.

13. The mechanical shaft seal of claim 1, wherein said lip seal is comprised of a fluoroelastomer.

14. A mechanical shaft seal adapted to be used with dry-material-handling equipment, comprising a seal assembly, a stationary seat, a gland, and a rotor sleeve, wherein said seal assembly comprises a grease housing, a lip seal, a single-spring seal, and a grease chamber, said grease housing having a proximal end and a distal end and a bore therethrough to receive said rotor sleeve, said single-spring seal being disposed around said rotor sleeve within an annulus bounded by said grease housing and said rotor sleeve at said distal end of said grease housing, said lip seal being located at said proximal end disposed around said rotor sleeve and between said rotor sleeve and said grease housing, said grease chamber being bounded by said lip seal, said rotor sleeve, and said grease housing, said stationary seat being disposed around said rotor sleeve in sealing engagement with said single-spring seal, said gland having a bore therethrough to receive said rotor sleeve and being coupled with said distal end.

15. A mechanical shaft seal according to claim 14, wherein a sealed bearing is disposed around said rotor sleeve within an annulus bounded by said gland and said rotor sleeve.

16. A method of sealing a rotating mechanical shaft in an environment of dry particulates comprising the steps of: disposing a mechanical shaft seal around said shaft,placing a seal assembly of said mechanical shaft seal into contact with an environment of dry particulates,externally mounting said mechanical shaft seal around an entry point for said shaft into a vessel, andsecuring said mechanical shaft seal onto said vessel.

17. A method for making a mechanical shaft seal comprising the steps of: disposing a gland with a first bore running therethrough around an outer wall of a rotor sleeve,disposing a stationary seat with a second bore running therethrough around said outer wall adjacent to said gland,disposing a single-spring seal around said outer wall adjacent to said stationary seat,placing a lip seal around an inner wall at a proximal end of a grease housing with a third bore running therethrough,inserting said rotor sleeve and said single-spring seal through said third bore into a distal end of said grease housing,joining and securing said gland to said grease housing, andfilling a grease chamber bounded by said lip seal, said inner wall, said outer wall, and said lip seal with grease.

18. A method according to claim 17, further comprising the step of disposing packing material around said outer wall and between said stationary seat and said gland.

19. A method according to claim 17, further comprising the step of disposing a sealed bearing around said outer wall within an annulus bounded by said gland and said outer wall.

20. A method according to claim 17, further comprising the step of disposing a snap ring around said outer wall, whereby said snap ring is positioned to make contact with the single-spring seal, thereby serving to secure the single-spring seal in place.

21. The method of claim 16, further comprising the steps of: connecting a lever to said shaft,connecting an air cylinder to said lever, andactivating and deactivating said air cylinder by controlling the flow of compressed air to the air cylinder.

22. A flap valve system for dry particulates comprising a plurality of flap valves disposed in a vertical arrangement.

23. The flap valve system of claim 22, wherein the plurality of flap valves consists of a first flap valve disposed above a second flap valve, said first flap valve configured to have an opposite phase from the second flap valve.