CA1181779A

CA1181779A - Mechanical seal assembly with integral pumping device

Info

Publication number: CA1181779A
Application number: CA000412567A
Authority: CA
Inventors: William V. Adams
Original assignee: Durametallic Corp
Current assignee: Durametallic Corp
Priority date: 1981-07-13
Filing date: 1982-09-30
Publication date: 1985-01-29
Also published as: ES516197A0; AU8889182A; ES8308983A1; IN156689B; BE894561A

Abstract

MECHANICAL SEAL ASSEMBLY WITH
INTEGRAL PUMPING DEVICE

ABSTRACT
A double or tandem mechanical seal construction having as an integral part thereof a pumping structure for effecting circulation of buffer fluid. The shaft sleeve is provided with surface irregularities thereon, such as a series of circumferentially spaced slots, so that the shaft sleeve functions as a pumping rotor. The surrounding seal stator has supply and discharge ports extending radially therethrough, which ports extend substantially tangentially with respect to the shaft sleeve so that the latter, due to its rotation, will effectively pump and hence circulate the cooling or buffer fluid through the buffer chamber.

Description

MECHANICAL SEAL ASSEMBLY WITH
INTEGRAL PUMPIMG DEVICE

F`IELD OF TEIE INVENTION
This invention relates to a double or tandem mechanical seal construction having a pumping structure integrally associated therewith for effecting circu-lation of a cooling or buffer fluid.
BACKGROUND OF THE INVENTION
Recently there has been greater demand for mechan-ical seal constructions of the double or tandem type to permit continued operation even if one seal should fail.
With this type construction, the stationary seal ring normally has a rotatable seal ring urged into sliding sealing engagement with each axial end thereof. With this double seal arrangement, an intermediate chamber is formed between the two seals in surrounding relationship to the shaft, and a buffer or cooling fluid is supplied to this chamber to cool the seal faces. The buffer fluid is circulated through a closed system by an external auxiliary pump. With this arrangement, the t~o seals operate in tandem when the buffer fluid is at a very low pressure so that the inner seal forms the primary seal, but if the high pressure working fluid leaks into the buffer chamber, then the outer seal prevents leakage. Alternately, buffer fluid can be supplied to the cha~er at a pressure higher than that of the working fLuid, whereby the arrarlgement functions as a double seal for preventing leakage of the working fluid.
One of the common drawbacks of double or tandem seal arrangements is the excessive hea-t generated thereby, and the difficulty of circulating adequate quantities of coolant or buffer fluid through the seal construction. The circulation is normally achieved by an external auxiliar~ pump, but most users object to such system sinc~ the required au~iliary pump increases the complexity and unreliability of the system.
In recognition of this problem, one manufacturer has incorporated a pump within the mechanical seal construction by fixedly securing an elongated pumping sleeve within the seal stator in surrounding relation-ship to the rotatable shaft. This pumping sleeve has a spiral pumping groove formed in the inner peripheral surface thereof. However, the spiral pumpin~ groove and its small cross section creates a severe restriction on the quantity of fluid which can be pumped, and hence the effectiveness of this arrangement is seriously question-able. Further, this pumping sleeve occupies substantial space, whereby the seal construction will not always fit within the stuffing box on some types of equipmentO
Accordingly, this improved mechanical seal con-struction overcomes the above disadvantages. The mechanical seal construction of this invention can be utilized as a dou]~le or tandem seal, and incorporates as an integral part thereof a pumping structure within the interior chamber to effect efficient circulation of substantial quant:ities of buffer fluid for effecting 7~

optimum cooling c,f the seal construction, whereby use of an auxiliary pump ls hence obviated. Further, the pumping structure i5 extremely small and compact, and is formed directly on the seal stator and shaft sleeve, whereby additiona.l components are not required, thereby enabling the seal construction to maintain minimum axial and radial dimensions.
In this improved seal construction, the shaft sleeve i5 provided with surface irregularities, such as circumferentially spaced slots, so that it functions as a pumping rotor. The surrounding seal stator, namely the gland insert, has supply and discharge ports extend-ing radially therethrough, which ports extend substan-tially tangentially with respect to the shaft sleeve so that the latter, due to its rotation, will pump and hence circulate the cooling or buffer fluid through the bu:Efer chamber and through the external circuitry for the fluid.
This improved seal construction additionally is of a balanced construction, that is, the axial forces imposed on the rotating seal rings by the working fluid are imposed over an area which is slightly less than the area of engagement between the seal faces so as to minimize heat generation on the seal faces. The seal construction also preferably utilizes a single large-diameter coil spring in surrounding relationship to the shaft sleeve for urging the seal ring against the stator, thereby minimizing the possibility of hang-up ancl providing the construction with added corrosion resistance, parti,-ularly when used as a tandem arrange-ment.

BRIEF DESCRIPTION OF T~E DRAWINGS
Figure 1 is a central sectional view oE the mechan-ical seal construction as taken along line I-l in E'igure

2.
Figure 2 is a sectional view taken along line II-II
in Figure 1.
Figure 3 is a fragmentary view illustrating the tongue-and-slot connection between the shaft sleeve and the rotatable seal ring.
DETAILED DESCRIPTION
The drawings illustrate a mechanical seal con-struction 10 of t:he double or tandem type as associated with a fluid hanclling apparatus, such as a pump having a housing 11 with a rotatable shaft 12 projecting there-from. The housing 11 defines therein a cylindrical opening 13 (commonly known as a stuffing box) in sur--rounding relationship to the shaft 12 for accommodating therein the seal construction 10.
The seal construction 10 includes an elongated sleeve 1~ which ~,urrounds and is nonrotatably secured to shaft 12, clS by a set screw 17. This sleeve 16 is in turn closely surrounded by an annular gland insert 18, hereinafter referred to as the seal stator. This stator 18, which is prei-erably constructed of carbon, is surrounded by and nonrotatably keyed to a gland 19 which is fixed to the housing 11, as by threaded fasteners 21.
The seal construc-tion 10 includes a pair of face seal arrangements located adjacent the opposite axial ends of the stator 18, one being inwardly of the stator and the other ou1wardly thereof.
Referring f:Lrst to the inward face seal arrange-ment, same is dei~ined by a seal ring 22 (hereinafter referred ~o as the seal rotor) which is positioned ~ '7~'4~

within opening 13 and surrounds the shaft sleeve 16.
Seal rotor 22 has a slot 23 extending axially inwardly from the inner end thereof for slidably accommodating therein a tongue 24 as formed on the inner end of shaft sleeve 16. This arrangement 23-24 enables seal rotor 22 to axially slide and also angularly tilt a limited extent relative to the shaft sleeve. At the same time, this elongated sl.ot 23 and its cooperation with the planar side surface on the tongue 24 prevents localized wear and hence prevents hang-up of the rotor 22.
The other end of seal rotor 22 has a projecting annular flange 26 which surrounds an annular face ring 27, the latter being press fit within the flange 26.
This face .ring 27 has a planar front surface 28 which functions as a seal face and is disposed in rotatable sliding engagement with an opposed planar seal surface or face 29 as formed on the adjacent end of the stator 18.
The rotor 22 is urged outwardly against the stator 18 by a single coil spring 31 which i5 of large diame-ter. Spring 31 is positioned within rotor 22 in sur-rounding relationship to shaft sleeve 16, whereby the outer end of the coil spring bears against an annular shoulder 32 formed on the rotor 22. The other end of coil spring 31 bears against an annular spring retainer 33 which, as illustrated in Figure 1, is L-shaped in cross section. This retainer 33 is adapted to abut against a shoulder 34 formed on the shaft sleeve 16 for limiting the spri:ng expansion. An elastomeric O-ring 36 surrounds shaft sleeve 16 directly adjacent the rearward end of spring ret,ainer 33, whereby the O-ring 36 creates a sealed engageme:nt with an outer diameter 37 on the shaft sleeve 16 and an inner diameter 38 on the rotor 22.
To provide a "balanced" seal, and thereby mi.nimlze contact pressure and hence heat generation be-tween seal faces 28-29, the inner diameter 37 is selected so as to be larger than the inner diameter of the annular seal contact area (that is, the inner diameter of the Lace 28) but smaller t:han the outer diameter of the seal contact area (that is, the outer diameter of face 28).
This thus results in the unbalanced pressure force imposed on the rotor 22 and face ring 27, which unbal-anced force is ri.ghtwardly in Figure 1 and is due to the pressurized worki.ng fluid within stuffing box 13, acting over an unbalanced area which is less than the contact area between the seal faces 28-29. The contact pressure between the seal faces is thus less subject to the influence of the pressurized working fluid and is maintained at a ].ower level so as to minimize wear and heat generation between the seal faces. While achieving such balance is i.tself known in prior seals, neverthe-less the provision of such balance is believed particu-larly crit:ical for a double or tandem seal.
Considering now the outer face seal arrangement as disposed r:ightwaxdly of stator 18, it includes an annular seal ring 41 (that is, a seal rotor) which is spaced from but encircles the other end of shaft sleeve 16 and is nonrotatably but axially slidably connected thereto. Shaft sleeve 16 has an annular collar 42 which projects radially outwardly and one or more pins 43 projecting axial].y therefrom. These pins 43 slide into recesses formed i.n the seal rotor 41 to nonrotatably couple same toget:her, while permitting axial slidable displacement and at least limited tiltability of the ''7~3 seal rotor 41. This collar 42 is fixed to shaft sleeve 16 by a set screw 17. The collar ~2 has a hub portion 44 which is concen-trically interposed between the seal rotor 41 and the shaft sleeve 16. This annular hub ~
has an inner elastomeric O-ring 46 for creating a sealed engagement with the shaft sleeve 16, and an outer elastomeric O-ring 47 for creating a sealed engagement with the seal rotor 41.
The seal rotor 41 has an annular flange 48 project-ing from the inner axial end thereof, and an annular face rin~ ~9 is fixedly press fit within this flange 48.
The face ring 49 defines thereon a planar en~ surface 51 which functions as a seal face and is maintained in rotatable sliding engagement with an opposed flat seal face 52 as formed on the opposed end of stator 18.
Springs 53 urge the seal face 51 into abutting contact with the opposed seal face 52.
This second seal arrangement as created by seal faces 51-52 is also of the "balanced" type, this balance being achieved by providing the O-ring 47 with an outer diameter (aLs defined by the inner diameter of seal rotor 41) which i.s smaller than the maximum diameter of the seal face contact area (as defined by the maximum diameter of face 52) but larger than the minimum diame-ter of the seal :Eace contact area (as defined by the minimum diameter of face 52)o This thus results in an unbalanced pressure force, as imposed on seal rotor ~1 and its face ring 49, acting over an area which is less than the contact area between the seal faces 51-52.
To cool the seal construction, there is an interior annular chamber 56 for receiving cooling or buffer fluid. This chamber 56 is defined between the shaft seal 16 and the s,urrounding stator 18 and rotors 22 and l 7 7~-~

41. Chamber 56 is sealed at opposite ends thereof by O~rings 36 and 47. Fluid is supplied to chamber 56 through an inlet port 57 which extends radially through the gland 19, which port 57 in turn communicates with an inlet passage 58 which extends radially through the stator 18. The fluid from chamber 56 is discharged in a similar manner through an outlet passage 61 which also extends radially through the stator 18 and communicates with A discharge port 62 which extends radially through the gland 19. These ports 57 and 62 are connected to suitable conduits which define a closed external circuit for the cooling or buffer fluid, which circuit conven-tionally has a heat exchanger associated therewith.
To prevent escape of fluid as it flows between stator 18 and gland 19, a pair of O-rings 63 surround the stator lB and sealing:Ly engage the gland 19, which O-rings 63 are disposed axially on opposite sides of the aforesaid ports and passages.
To achieve maximum circulation of fluid through the cha~ber 56, the seal construction is provided with a pumping structure integrated therein. This pumping structure includes the formation of a pumping rotor on the shaft sleeve 16, which pumping rotor in the illus-trated embodiment is formed by a plurality of axially elongated grooves or slots 66 formed in the periphery of the shaft sleeve 16. These grooves 66, as disposed in angularly spaced relationship around the shaft sleeve, are disposed so as to be directly radially aligned with the radially inner ends of passages 58 and 61. In addition, passages 58 and 61 are themselves oriented to extend substantially tangentially with respect to the periphery of the pumping rotor section defined on the shaft sleeve 16. Grooves 66 have an axial length, as ~i~ 7ty~

shown in Figure 1, so that the~ project outwardly a small extent beyond opposite sides of passages 58 and 61 to maximize the effectiveness of the pumping action.
In operation, the coolant or buffer -~luid is supplied through port 57 and passage 58 into chamber 56.
Due to rotation of shaft sleeve 16 and the provision of pumping ~rooves ~;6 thereon, the fluid within chamber 56 is pressurized and circulated throuyhout the chamber 56, and some of this fluid is discharged through the outlet passage 61 so as to be recirculated through the external circuit having a heat exchanger associated therewith.
In this manner, the coolant or buffer fluid can be ade~uately and accurately circulated through the buffer chamber to effect optimum cooling of the seal con-struction, and circulated through the entirety of the circuitry without requiring any external pumping device.
This pumping structure as integrally associated with the mechanical seal construction is extremely compact and solely utilizes existing seal elements inasmuch as the pumping rotor is formed as an integral part of the shaft sleeve 16, and the passages 58 and 61 are tangentially oriented relative to the pumping rotor to optimize the pumping effect. These structural and positional rela-tionships, together with the close surrounding relation ship of the stator 18 with respect to the shaft sleeve 16 so as to define only a narrow annular chamber there-between, hence permits minimization with respect to the radial and axial dimensions of the seal construction, while still permitting effective pumping and circulation of the coolant or buffer fluid.
; When seal construction 10 is used as a tandem seal, such as is conventional, then primary sealing is carried out by the inner seal 28-29 so as to prevent escape of pressure fluid from the stuffing box 13, which fluid may be at a rather high pressure, such as between 300 and 450 psi. On the other hand, the coolant or buffer fluid as supplied to c]lamber 56 is pressurized only slightly above atmospheric, which pressure is sufficient solely to permit the circulation of the fluid. However, if the seal 28-29 should leak, then the pressurized product in stuffing box 13 :Leaks into chamber 56, and the outer seal 51-52 at least temporarily prevents product leak-age.
When used as a doubLe seal, the buffer fluid ispressuri~ed to a level which is approximately 25 psi above the product: pressure, whereupon chamber 56 is at a higher pressure ]evel to effect proper sealing of both seals 28~29 and Cil-52~
While -the disclosed embodiment illustrates the use of slots or grooves 66 for defining a pumping rotor on the shaft sleeve 16, nevertheless the pumping rotor could also be formed b~ utilizing some other type of surface irregularity on the shaft sleeve 16, which surface irregularity should effectively define an annular band which surrounds the shaft sleeve and is in direct relationship with the tangential passages 58 and 61. For example, it is anticipated that an annular knurled band can be provided on the exterior of the shaft sleeve 16, in place of the grooves 66, for effect-ing the desired pumping of the cooling or buffer fluid.
In addition to the :relationships defined above with respect to O-rings 36 and 47 to achieve a "balance" as a result of product pressuxe, the seal construction 10 also has a reverse balance to prevent excessive contact pressure between the sea:L faces (such as faces 28-29) in the event that a high pressure buffer fluid is supplied to chamher 56. To achieve this balance, the outer diameter 38 of seal ring is preferably slightly smaller than the maximum diameter of the seal contact area (tha-t is,, the ma~imum diameter of seal face 29), whereby the unhalanced pressure force imposed on seal rotor 22 by the buffer fluid acts on an area which is less than the seal contact area between the faces 28-29.

Claims

I claim:

l. A mechanical seal construction for sealing a shaft which projects from and is relatively rotatable with respect to a surrounding housing, comprising in combination:
an elongated shaft sleeve nonrotatably and seal-ingly connectible to said shaft in surrounding relation-ship thereto;
an annular seal stator disposed in surrounding relationship to said shaft sleeve and being spaced therefrom by a narrow annular chamber therebetween, said seal stator being nonrotatable with respect to said housing;
said seal stator defining thereon first and second nonrotatable annular seal faces, said first and second seal faces being defined on opposite axial ends of said stator and facing outwardly in opposite directions;
a first seal rotor disposed axially adjacent one side of said stator in surrounding relationship to said shaft sleeve; said seal rotor being nonrotatably fixed to said shaft sleeve and spaced therefrom to define a first annular region therebetween which is in open communication with said annular chamber, and first deformable seal ring means coacting between said shaft sleeve and said first seal rotor for sealingly closing the end of said first annular region;
said first seal rotor having a first rotatable annular seal face formed on one end thereof and main-tained in abutting sliding contact with said first nonrotatable seal face;
a second seal rotor disposed axially adjacent the other side of said stator in surrounding relationship to said shaft sleeve, said second seal rotor being non-rotatably fixed to said shaft sleeve and spaced there-from to define a second annular region therebetween which is in open communication with said annular cham-ber, and second deformable seal ring means coacting between said shaft sleeve and said second seal rotor for sealingly closing the end of said second annular region;
said second seal rotor having a second rotatable annular seal face formed on one end thereof and main-tained in abutting sliding contact with said second nonrotatable seal face; and pump means integrally associated with said stator and said shaft sleeve for effecting recirculation of fluid through said annular chamber, said pump means including inlet and outlet passages extending radially through said stator, the inner ends of said passages where they communicate with said annular chamber being directed substantially tangentially with respect to said shaft sleeve, said pump means also including an annular pumping rotor defined by a portion of said shaft sleeve, said pumping rotor being disposed radially directly adjacent the inner ends of said passages and having an irregular annular surface for effecting pumping of the fluid within said annular chamber.
2. A seal construction according to Claim 1, wherein the irregular annular surface on said pumping rotor is defined by a plurality of grooves or recesses which are formed in said shaft sleeve and are circumfer-entially spaced apart therearound.
3. A seal construction according to Claim 2, wherein the first elastomeric seal ring means sealingly contacts an outer annular surface as defined on said shaft sleeve having a diameter which is greater than the minimum diameter of the annular contact area between said first seal faces.
4. A seal construction according to Claim 3, wherein the first elastomeric seal ring means is seal-ingly engaged with an inner annular surface as defined on said first seal ring rotor which has a diameter which is less than the outer diameter of the annular contact area between the first seal faces.
5. A seal construction according to Claim 2, wherein the housing includes a cylindrical stuffing box opening through which the shaft concentrically projects, said shaft sleeve when mounted on said shaft projecting into said stuffing box opening, said stator being fixed to said housing directly adjacent the outer end of said stuffing box opening, and said first seal rotor being disposed within said stuffing box opening.
6. A seal construction according to Claim 1, including a platelike gland fixed to said housing in surrounding relationship to said stator, said gland and stator having seal ring means coacting therebetween, said gland having inlet and outlet ports extending radially therethrough and respectively communicating with the outer ends of the inlet and outlet passages, said inlet and outlet ports being connected to an external closed circuit for the fluid which circulates through the annular chamber, said external circuit being free of circulation-effecting auxiliary pumping devices.
7. A seal construction according to Claim 1, wherein the stator is of a rigid one-piece construction and has the first and second nonrotatable seal faces formed integrally on opposite ends thereof.
8. A seal construction according to Claim 4, wherein the first elastomeric seal ring means sealingly contacts an outer annular surface as defined on said shaft sleeve having a diameter which is greater than the minimum diameter of the annular contact areas between said first seal faces.
9. A seal construction according to Claim 1, including spring means coacting between said shaft sleeve and said first seal rotor for normally urging said first rotatable seal face into abutting sliding contact with said first nonrotatable seal face, said spring means comprising a single large-diameter coil spring disposed within said first annular chamber in surrounding relationship to said shaft sleeve.
10. A seal construction according to Claim 9, wherein said first seal rotor defines thereon an axially directed shoulder which is disposed in opposed relation-ship to a second axially directed shoulder as defined on said shaft sleeve, said coil spring being axially confined between the opposed first and second shoulders, and a retainer plate positioned between said second shoulder and the adjacent end of said coil spring, said retainer plate having a substantially L-shaped cross-section and including a radially extending ringlike base portion which has one side thereof seated against said second shoulder and the other side thereof in engagement with the end of said coil spring, said retainer plate also including an annular axially projecting rim which is secured to said base portion adjacent the radially outer edge thereof and projects axially away therefrom in the opposite direction from said coil spring, said annular rim at the free axial end thereof being engaged with said first deformable seal ring means.
11. A seal construction according to Claim 10, wherein the first deformable seal ring means sealingly contacts an outer annular surface as defined on a first portion of said shaft sleeve having a diameter which is greater than the minimum diameter of the annular contact area between said first seal faces, said first portion of said shaft sleeve being axially joined to a second portion which is of reduced diameter and defines said second shoulder at the interface therebetween, said coil spring being disposed in surrounding relationship to said second portion of said shaft sleeve.
12. A seal construction according to Claim 1, wherein said first seal rotor and said shaft sleeve are nonrotatably coupled together by axially elongated tongue-and-slot means coacting therebetween adjacent the end of said first rotor which is remote from said stator, said tongue-and-slot means comprising an axially elongated slot formed in said first rotor and an axially elongated tongue which is formed on said shaft sleeve and projects radially therefrom into said slot, both said tongue and said slot defining substantially parallel and axially elongated planar side surfaces for permitting the tongue to be snugly but axially slidably confined within the slot.