GB2286020A - Mechanical shaft seals - Google Patents

Abstract

A double mechanical seal is mounted onto a shaft 2 which is allowed to rotate and onto a stationary housing portion to which the stationary portion of the seal 5 is fixed. The stationary portion has a number of connecting ports 43 and 44 which allow a liquid to be placed between the sets of faces in order to supply lubrication and cooling. An eccentric or other formed shape is produced around one longitudinal axis which produces a reduction in pressure under one port and an increase in pressure under another port, inducing an increase in flow of the liquid. <IMAGE>

Description

MECHANICAL SHAFT SEALS.

This invention reiates to the stationary gland assembly of a mechanical shaft seal.

A mechanical shaft seal may typically comprise of two distinct units, one which rotates with the shaft of the pump or vessel, known as the rotary assembly, and another which is known as the stationary assembly which is fixed to the pump or vessel through which the snaft passes. The stationary portion may be provided with sealing face or faces which mate with a face or faces on the rotary assembly.

Typically where two or more sealing elements are utilised, a liquid is piaced between tie sealing elements to lubricate and cool the sealing faces and in order to form a barrier between the pnmary sealed liquid and the atmosphere.

Mechanical shaft seals have been proposed which posses means to cool tile liquid by moving the liquid through tile seal with a pumping tog whicli revolves with the shaft or ill another example have a stationary pumping ring or a combination of both. These examples incorporate an internal or external screw thread which axially move liquid from one side tu the other, aiod require that the ports in atoci out are axially separated therefore requiring a large amount of axial space.

It has now surprisingly been discovered that sufficient flow of liquid can be produced without the requirement for axially separated ports which preclude the use of pumped barrier liquids where space is limited, without the use of external pumps requiring control mechanisms and creating a safety hazard.

According to this invention, there is provided a stationary assembly which possesses two or more pairs of sealing faces for a balanced or non balanced mechanical seal for sealing a rotatable shaft tu a freed stationary housing, the rotating portion possessing radial faces wnich contact the stationary sealing faces and form a seal there between. Both stationary faces are either arranged as annular rings mounted upon the stationary 'gland' or part of the gland which is fixed to the stationary portion of the pump, vessel or equipment. The gland portion possessing connecting ports which are rotationally separated from each other, but in a similar longitudinal position, which provide connections to be made for a 'barrier liquid' to be used between the pairs of seal faces.Typically the stationary portion has a clearance between its inside diameters and the outside diameters of the rotary portions which pass through the stationary portions. The clearance is created smaller on one side between the ports and larger on the other side, the effect being that the rotation of the shaft creates a low pressure area at one port and a higher pressure area at the other, in order to pull liquid Into the first port and to push liquid out of the second port.

The variance in clearance may be due to an eccentric diameter being created inside the stationary portion.

The variance in clearance may be formed in such a way that the clearance on one side between the ports is at a minimum and the clearance on the other is at a maximum.

The pumping action is not 100% efficient as flow created by the rotation of the shaft creates a pressure surge' where the clearance is reduclng, and a pressure drop where the clearance is increasing, which induces the liquid to not only pass in and out of the ports, but also to 'slip' axially from the higher pressure area back to the lower pressure area, greatly increasing the cooling effect at the sealing faces due to increased flow under them.

The flow may be increased by creating a larger volume of eccentricity both radially and axial.

The invention includes the stationary assembly as defined above, in combination with the rotary or revolving portions.

Specific embodiments of the invention wlll now be described by way of example, and with reference to the accompanying drawings, in which : Figure 1 illustrates a balanced mechanical seal in accordance with the invention, which is shown in longitudinal cross section; Figure 2 illustrates the stationary assembly similar to that forming part of the mechanical seal in figure 1 in which the annular space between the two stationary portions Is opened up with an eccentric diameter to form high and low pressure areas within the eccentric annular space as the rotating portion tums, shown In longitudinal cross section.

Figure 3 illustrates the eccentric annular space similar to that in figure 1, shown in axial cross section, through both the stationary and rotating portions with the ports illustrated through which the liquid is pumped.

Figure 4 illustrates a balanced mechanical seal similar to that in figure 1, shown in axial cross section, in which the space between the rotating and stationary portions is formed in such a 'Say as to give a small volume of liquid between the ports in one section, opening up to give an increased volume between the ports in another section.

Figure 5 illustrates a stationary forming part of the stationary assembly similar to that in figure 2, shown in axial cross section, where the inside diameter is eccentric to the other diameters and to that of the pump axis. The effect being to increase the volume of the eccentricity and thus the flow of liquid.

VVith reference to Figures 1 and 2 , a balanced double mechanical seal is shown generally at 1 and provides sealing between a shaft 2 and a housing 3 and between the stationary portion 4 and the shaft 2, the seal 1 compnses a stationary portion 4 and rotary portions being the external rotary portion 5 and the internal rotary portion 6 The rotary portion 6 consists of a fixed annular ring 9 which is attached to the shaft 2 by grub screws 10 preventing relative axial and rotational movement between fixed annular ring 9 and shaft 2. Incorporated in the fixed annular ring 9 is an annular sealing ring ( '0' Ring ) 11 which seals between the fixed annular ring 9 and the shaft 2.Located in the radial face 12 of the fixed annular ring 9, there are a number of drive pins 13 which prevent relative rotational movement between fixed annular ring 9 and a floating portion 14 of the rotary assembly 6, but allow axial movement in order to keep sealing engagement between the rotary assembly 6 and the stationary assembly 4.

The floating portion 14 of the rotary assembly 6 comprises an annular ring 15, surrounding the shaft 2 and the fixed annular ring 9 to which it is sealed with an annular sealing ring ( 'O Ring ) 16. In the end nearest the stationary assembly is located an annular ring 17 manufactured from a suitable sliding material, possessing a radial sealing face 18. Interspaced between fixed annular ring 9 and the floating portion 14 of the rotary assembly is a plurality of compression springs 19,which abur at one end against radial face 12 of fixed annular ring 9 and at the other end against the bottom of axial holes 20 in a radial face 21 of the floating annular ring 14. These springs urge the floating portion 14 axially away from the fixed annular ring 9 and into sliding contact with the stationary assembly 4.

The Stationary assembly 4 consists of a fixed portion 22, and flexibly mounted portions 7 and 8. The fixed portion 22 of the stationary assembly is sealed against the housing 3 by means of a gasket 23 which seals as the fixed portion is clamped to the housing face by a plurality of studs and nuts 25. In order to seal between flexibly mounted portion 7 and fixed portion 22 there is provided an annular sealing ring ('0' Ring ) 26, in combination with a back-up ring 27. The flexibly mounted portion 7 possesses a radial sealing face 28 for sealing against sealing face 18 of rotary portion. The flexibly mounted portion 8 is sealed against fixed portion 22 by means of an annular sealing ring ('0' Ring ) 29 and possesses a radial sealing face 30 for sealing against a radial sealing face 31 of external rotary portion 5.

The external rotary portion 5 consists of a fixed annular nng 32 which Is attached to the shaft 2 by grub screws 33, preventing relative axial and rotational movement between fixed annular nng 32 and shaft 2. The fixed annular ring 32 possesses a plurality of'dive slots 34 in Its outer diameter. The floating portion 35 of the extemal seal 5 comprises an annular nng 36 surrounding shaft 2 and fixed annular ring 32, into which is fixed an annular ring 37 manufactured from a suitable sliding material and possessing a radial sealing face 31.Projecting from the radial face 38 there are a plurality of 'dnve pegs' 39 which mate with drive slots 34 in the annular ring 32, allowing axial movement but preventing relative rotational movement between fixed annular ring 32 and floating portion 35.

Interspaced between footed annular ring 32 and the floating portion 35, is a plurality of compression springs 40 which abut at one end against radial face 38 and at the other end against the bottom of axial holes 41 in a radial face 42 of fixed annular ring 32. The effect of the springs 40 is to urge the radial sealing face 31 into sliding contact with the stationary sealing face 30.

The space between the shaft 2 and the rotating and stationary components 4,5 and 6 may be filled with a suitable liquid through two ports, 43 and 44. The axial gap 45 between the two flexibly mounted portions 7 and 8 is produced with an eccentric diameter, with the narrowest gap being between the two ports, on one side and the widest gap on the other. As the shaft rotates, the gap increases as it passes under one port and decreases under the other.

The axial gap between the flexibly mounted stationary portions may be produced wah a minimum diameter, in order to clear the rotating shaft on one side of the two holes 43 and 44 and with a maximum diameter on the other.

The process of producing an eccentric diameter may be extended by having the flexibly mounted portions 7 and 8 aiso with there inside diameters eccentric, increasing the flow even more.

Claims (6)

1. A stationary assembly which possesses two or more pairs of sealing faces for a balanced or non balanced mechanical seal for sealing a rotatable shaft to a fixed stationary housing, the rotating portion possessing radial faces which contact the stationary sealing faces and form a seal there between. Both stationary faces are either arranged as annular rings mounted upon the stationary 'gland' or part of the gland which is fixed to the stationary portion of the pump, vessel or equipment.

The gland portion possessing connecting ports which are rotationally separated from each other but in a similar longitudinal position, which provide connections to be made for a 'barrier liquid to be used between tile pairs of seal faces. Typically the stationary portion has a clearance between Its inside diameters and the outside diameters of the rotary portions which pass thorough the stationary portions. The clearance is created smaller on one side between the ports and larger on the other side, the effect being that the rotation of the shaft creates a low pressure area at one port and a higher pressure area at the other, in order to pull liquid into the first port and to push liquid out of the second port.

2. A stationary assembly as claimed in claim 1 in which the clearance is created by producing a eccentric diameter between the flexibly mounted portions into which the ports connect.

3. A stationary assembly as claimed in claim 1 in where a small clearance is created between the rotary and stationary elements on one sector between the ports, using a concentric diameter, with a larger clearance between the ports in the opposite sector.

4. A statIonary assembly as claimed in claim 1 In which the eccentric diameter is also in the inside diameter of the flexibly mounted portions.

5. A stationary assembly as claimed in claim 1 which forms part of a mechanical seal which is mounted on a 'cartridge, being a one piece unit incorporating the internal and external seal elements with the stationary portion.

6. A stationary assembly substantially as described herein with reference to Figures 1 to 5 of the accompanying drawings.