AU773785B2 - Mechanical seal - Google Patents

Description

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AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventor(s): Address for Service: FRANCIS WELLS SMITH FRANCIS WELLS SMITH INTELLPRO FeeeT .ep ,RG, R Patent Trade Mark Attorneys 3' \t egE',--r S(-CT- Level 7, Reserve Bank Buil,,ding 102 Adolaide Street s BRISBANE, QLD, 4000 (GPO Box 1339, BRISBANE, 4001) Invention Title: Details of Associated Provisional Application(s) No(s): MECHANICAL SEAL Australian Patent Application No. PQ2511 filed 27 August 1999.

The following statement is a full description of this invention, including the best method of performing it known to me: a a.

MECHANICAL SEAL THIS INVENTION concerns mechanical seals for shafts.

Such seals are widely used in refineries, food processing lines, chemical reactor installations and the like. Much down time in such industries is due to seal failure. Seals commonly fail due to over-heating or admission of abrasive or chemically active reagents.

A multi stage installation may need a variety of pumps to convey feedstock around the plant. A corresponding variety of seals must be stocked by the maintenance department. Greater reliability under a greater range of operating 10 conditions is expected but is difficult to provide with standard components because different feedstocks impose such variable operating problems.

Seals must function when pressures fluctuate, for example, the seal may have to cope with partial vacuum followed by high super atmospheric pressure.

Such changes tend to distort the sealing parts and the internal geometry of the seal.

This invention addresses these problems.

This invention provides mechanical seal for a shaft comprising a seal body defining a seal chamber with mutually spaced end walls, capable of containing liquid for at least partially immersing the working surfaces of the seal, a sleeve in the seal body co-axial with the shaft centre I ine which, in use, rotates with the shaft, an annular, stationary, wear resistant seal located in each end wall surrounding the sleeve, an annular axially slidable spacer surrounding thesleeveand, in use, rotated by the sleeve, with a seal pocket in both end faces of the annular spacer and a rotary annular soft seal in each of the seal pockets arranged to slide axially in the be.

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C. C seal pocket and urged against the adjacent stationary seal by spring means acting between the spacer and the soft seal. The sleeve may be a hook sleeve or a parallel sleeve. It may be collar driven or movement compensator driven.

When the sleeve is compensator driven the drive has a drive pocket which receives a spacer projection which transfers the sleeve rotation to the spacer while allowing axial float.

The stationary seals preferably have annular, flat sealing faces. These may be of hard material such as tungsten carbide. The annular rotatable seals which contact them may be of U-section. They may be of moulded polymers commonly 10 used in seals but may be of metal depending upon the material being handled.

The spacer may be of substantially I-section. The spacer may also be a polymeric moulding. The spring means may be a series of spring pockets in the seal pockets of the spacer. These may be arranged in a ring around the spacer so as to act in the area of the mating faces of the softer and harder seals.

The seal chamber may surround the seal and have means to fix it to the adjacent structure, usually a pump wall or other fluid conveying component. The chamber may have external fins for heat dissipation. The sleeve may have an axial flow fan which rotates with the sleeve applying cooling air flow to the chamber.

The chamber in use contains a liquid lubricant which facilitates sliding movements of the seal parts. This promotes self-centring and recovery of the rotational positions designed for the seal in the event of disturbance by pressure surges.

The chamber may have a sensor which collects data for microprocessor control.

The end wall of the seal body adjacent the moving fluid may have an exterior seal recess containing a seal intended to act as a barrier against fluid borne particles. The seal may be a labyrinth type or a spiral pressure reducer type.

One embodiment of the invention is now described with reference to the single figure of the accompanying drawing which is a section of the seal.

This is shown fitted to the drive shaft of a centrifugal pump impeller.

A cylindrical metal housing 2 has an end wall 4 and an end wall 6 joined oa a by a circular wall with cooling fins 8 and an oil filler 10. Both end walls have a shaft bore 12. End wall 4 has an exterior seal recess 14 which houses a labyrinth seal 16. An adjacent interior recess houses a tungsten carbide ring 18. A corresponding seal is housed in end wall 6. Parallel sleeve 20 passes through the housing 2 and rotates with the shaft and the centrifugal pump impeller (not shown).

15 An annular central seal spacer 22 is a slide fit in the centre portion of the sleeve.

A drive dog 24 projects into a spline 26 in the sleeve ensuring that the spacer rotates with the sleeve. The springs centralise the spacer but the width of the spline 26 allows the spacer to float axially for several mm. Each end wall of the annular spacer has a shallow seal pocket 28. U-section metal seal 30 rides in the pocket and has a sealing face 32 which contacts the tungsten carbide rings 18, 20. The metal seals are urged against the ring by coil springs 34 located in radially disposed bores in the spacer seal pockets. These direct sealing force on the mating faces of the rotary and rings.

The components are removably retained by conventional O-rings housed in recesses one of which is indicated at 36.

A fan 38 is push fit onto the sleeve In use the chamber is filled to the level indicated with a viscous, synthetic oil developed for sealing duty. This conducts heat from the seal surfaces to the chamber walls. Port 40 admits a sensor (not shown) which detects opacity change in the oil.

S•I have found the advantages of the above embodiment to be: 1. The twin polymer or metal seals present two barriers to the conveyed S 10 fluid. If one seal fails the reducing seal will function until the maintenance program prompts inspection.

2. The floating action of the spacer allows the seal to reset spontaneously after a disturbance caused by a pressure surge.

3. The seal surfaces are constantly wet with lubricant.

4. No flushing stream of water is necessaryto keep solids away from the seal.

The housing may be pressurised in order to either balance high pressure pumping operations or to keep very small particles e.g., submicronic lime from migrating across the seal.

Whilst the above has been given by way of illustrative example of the present invention many variations and modifications thereto will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention as herein set forth.

Claims (11)

1. Mechanical seal for a shaft comprising a seal body defining a seal chamber with mutually spaced end walls, capable of containing liquid for at least partially immersing the working surfaces of the seal, a sleeve in the seal body co-axial with the shaft centre line which, in use, rotates with the shaft, an annular, stationary, wear resistant seal located in each end wall surrounding the sleeve, an annular axially slidable spacer surrounding the sleeve and, in use, rotated by the sleeve, with a seal pocket in both end faces of the annular spacer and a rotary annular soft seal in each of the seal pockets arranged to slide axially in the seal pocket and urged against the adjacent stationary seal by spring means acting between the spacer and the soft seal.

2. A seal as claimed in claim 1 wherein the seal pocket is an annular recess in the end of the spacer facing the stationary seal.

3. A seal as claimed in claim 2 wherein the rotary annular seal has a flange which coaxially overlaps the seal pocket.

4. A seal as claimed in claim 1, 2 or 3 wherein the spring means is a series of spring pockets in the seal pocket of the spacer.

A seal as claimed in claim 4 wherein the spring pockets are arranged radially around the spacer so as to act in the mating area of the rotary and stationary seals.

6. A seal as claimed in any one of claims 1 to 5 wherein the end of the seal which is exposed in use to pressure fluctuation is protected by a labyrinth seal.

7. A seal as claimed in any one of claims 1 to 6 wherein the sleeve is a hook sleeve or a parallel sleeve and is collar driven or movement compensator driven.

8. A seal as claimed in any one of claims 1 to 7 wherein the sleeve carries an axial flow fan.

9. A seal as claimed in any one of claims 1 to 8 wherein the housing has a lubricant opacity detector.

A seal as claimed in any one of preceding claims wherein the rotary seals are made of metal or synthetic sealing polymer.

11. A seal substantially as herein described with reference to and is illustrated in the accompanying drawing. DATED this 28 th day of August, 2000 FRANCIS WELLS SMITH By his Patent Attorneys INTELLPRO *s r r r r r r r