GB2217398A

GB2217398A - Mechanical shaft seal

Info

Publication number: GB2217398A
Application number: GB8808674A
Authority: GB
Inventors: Neil Mcintosh Wallace; Duncan Kinloch Irons
Original assignee: Flexibox Ltd
Current assignee: Flexibox Ltd
Priority date: 1988-04-13
Filing date: 1988-04-13
Publication date: 1989-10-25
Anticipated expiration: 2008-04-13
Also published as: GB2217398B; GB8808674D0

Abstract

A mechanical seal comprises, as usual, a rotating seal element 13 in face-to-face contact with the stationary seal element 14. On both of the seal elements is mounted a respective carrier 15, 19 through the intermediary of a rubber shroud 35, 20. The respective carrier 15, 19 is provided with a restraint disposed radially inwardly the rubber shroud 35, 20 to resist inward "blow-out" or separation of the rubber shroud from the carrier when the mechanical seal is pressurized. <IMAGE>

Description

MECHANICAL SEAL This invention relates to a mechanical seal for use in sealing a rotating shaft extending from a housing containing a fluid product to be retained within the housing.

It has been proposed, in a mechanical seal, to provide the usual rotating and stationary seal elements with rubber or equivalent elastomer or plastics shrouds which serve to mount the seal elements in their carriers. The term "rubber" is used hereinafter for convenience but is to be construed as including any suitable elastomer or plastics material.

With this proposed arrangement it has been found that, due to the fact that the internal diameter of the rubber shrouds is not greater than the balance diameter of the mechanical seal a net force can result from pressurisation of the mechanical seal causing the rubber shrouds and seal rings to be ejected. Also under high pressure conditions the rubber shrouds can extrude inwardly down the back of the seal elements.

It is an object of the present invention to obviate or mitigate these drawbacks.

According to a first aspect of the present invention therefore there is provided a mechanical seal for use in sealing a rotating shaft extending from a housing containing a fluid product to be retained within the housing, the mechanical seal comprising a rotating seal element in face-to-face contact with a stationary seal element and with one or both seal elements being mounted in a respective carrier through the intermediary of a rubber shroud, and the respective carrier providing a restraint radially inwardly of the rubber shroud to resist the aforesaid "blow out" or separation when the rubber shroud is pressurised.

Preferably, the restraint comprises an annular land integral with or connected to the respective carrier and located outside the balance line of the mechanical seal.

As a result of providing the restraining land, the rubber shroud, upon pressurisation, is prevented from extruding down the back of the seal element and this, taken with the fact that the rubber shroud does not extend inwards beyond the balance line, means that the net force applied to the rubber shroud ensures retention of the rubber shroud and its associated seal element in its carrier.

It is also known in mechanical seals to maintain the face-to-face contact between the rotating and stationary seal elements by applying a control fluid against one of the seal elements (usually the stationary seal element) causing it to be axially forced against the other seal element.

Such control fluid is generally supplied from a reservoir incorporating means for forcing the control fluid under pressure against the seal element. The control fluid is generally, but not necessarily, hydraulic fluid.

According to a second aspect of the present invention there is provided a mechanical seal for use in sealing a rotating shaft extending from a housing containing a product fluid to be retained within the housing, the mechanical seal comprising a rotating seal element in face-to-face contact with a stationary seal element, means for applying a control fluid under pressure against one of the seal elements to maintain the face-to-face contact, and means associated with the control fluid application means for indicating a measure of the face wear of the seal elements.

Preferably the indicating means comprises an indicator responsive to the level of control fluid in the reservoir thereby providing the measure of face wear of the seal elements.

Preferably the control fluid reservoir is a hydraulic cylinder and the means for pressurising the control fluid a piston, the area of the latter being a fraction of the loading area of the seal element thereby providing an amplification of the face wear on a scale of the indicating means.

Preferably the piston area is, for example, 1/10th the area of the seal element loading area thereby providing a 10:1 amplification of the face wear on the scale.

The first and second aspects of the present invention may be employed separately or jointly in a given mechanical seal.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Fig. 1 is a fragmentary sectional view of a mechanical seal embodying both aspects of the present invention; and Fig. 2 is a fragmentary sectional view of a modification of the mechanical seal of Fig. 1.

The mechanical seal is fitted between a rotating shaft 10 and a stationary housing 11, say of a pump, to maintain a product fluid within the housing 11.

The shaft 10 has a shaft shroud 12 keyed or otherwise made rotatably fast thereto.

The mechanical seal comprises a rotating annular seal element or ring 13 and a stationary annular seal element or ring 14, both formed for example of carbide, and having respective rubbing faces 13A, 14A in face-to-face contact.

The rotating seal element 13 is supported in a carrier 15 peripherally flanged at 15A to surround the seal element 13 and secured to an annular~ radial flange 16 of the shaft shroud 12 by screws or bolts 17, there being an O-ring seal 18 fitted between the shaft 10, the carrier 15 and the shaft shroud 12.

The stationary seal element 14 is supported in a carrier 19 through the intermediary of an annular rubber shroud 20 of inverted L-configuration. The carrier 19 is peripherally flanged at 19A to surround the rubber shroud 20 and the stationary seal element 14 and is formed with an annular axially-extending land 19B radially inboard of the rubber shroud 20.

The flange 19A and the land 19B thus contain therebetween the rubber shroud 20 and serve to restrain it against inward or outward radial movement.

The carrier 19 has an axial extension 21 housed in an annular recess 22 of the housing 11, there being inner and outer O-ring seals 23, 24 between the -extension 22 and the housing 11. The extension 22 is bored as indicated at 25 at angularly-spaced intervals, each bore 25 receiving a fixed pin 26 secured to the housing 11 whereby the carrier 19 is restrained against rotation but is axially movable.

The rubbing faces 13A, 14A of the seal elements 13, 14 are preloaded hydraulically. This is effected by a hydraulic master cylinder diagrammatically indicated at 27 in communication by a hydraulic line 28 and passage 29 in the housing 11 with the recess or chamber 22. The hydraulic cylinder 27 houses a weighted piston (not shown) to force hydraulic fluid from the hydraulic cylinder 27 along the line 28 and the passage 29 to apply a hydraulic force to the extension 21 to urge the carrier 19 and consequently the stationary seal element 14 against the rotating seal element 13 and so preload the rubbing faces 13A, 14A.

A scale diagrammatically indicated at 30 is associated with the hydraulic master cylinder 27 and is calibrated to provide a measure of the displacement of the seal element 14 in the axial direction as it compensates for wear at the rubbing faces 13A, 14A to retain the seal between the seal elements 13, 14.

The area of the piston in the hydraulic master cylinder 27 is selected to be, say, only 1/both the area of the loading face of the extension 22 to provide a 10:1 amplification of the face wear at 13A, 14A on the scale 30.

Reverting to the rubber shroud 20 this is, in effect, enclosed by the outer flange 19A, the inner land 19B and the seal element 14 so that any tendency of same, upon pressuration of the product fluid, to "blow out", or separate, from its carrier 19 is obviated. This resistance to "blow out" or separation is assisted by the fact that the rubber shroud 20 and the inner annular land 19B are positioned outside the line of balance of the mechanical seal so that the net force resulting from pressurisation causes the rubber shroud 20 to be retained in its housing defined by the radial wall of the carrier 19, the outer carrier flange 19A and the inner carrier land 19B.

A removable distance piece 31 is provided to facilitate easy accurate installation of the mechanical seal, which distance piece 31 is bolted as indicated at 32 to a split drive collar 33 clamped securely on the shaft shroud 12 as indicated at 34.

If a secondary seal is to be provided it is fitted into the space designated "A".

In the modification of Fig. 2, where parts similar to those in Fig. 1 are indicated by the same references, the rotating seal element 13 is also mounted by a rubber shroud 35 to its carrier 15, which rubber shroud 35 is shrouded by the radial wall of the carrier 15, the outer flange 15A and an inner annular land 15B. Like the rubber shroud 20 and the inner annular land 19B, the rubber shroud 35 and its inner annular land 15B lie outside the line of balance of the mechanical seal.

Claims

1. A mechanical seal for use in sealing a rotating shaft extending from a housing containing a fluid product to be retained within the housing, the mechanical seal comprising a rotating seal element in face-to-face contact with a stationary seal element and with one or both seal elements being mounted in a respective carrier through the intermediary of a rubber shroud, and the respective carrier providing a restraint radially inwardly of the rubber shroud to resist inward "blow out" or separation of the rubber shroud from the carrier when the mechanical seal is pressurised.

2. A mechanical seal as claimed in claim 1, in which the restraint comprises an annular land integral with or connected to the respective carrier and located outside the balance line of the mechanical seal.

3. A mechanical seal as claimed in claim 1 or 2, comprising means for applying a control fluid under pressure against one of the seal elements to maintain the face-to-face contact, and means associated with the control fluid application means for indicating a measure of the face wear of the seal elements.

4. A mechanical seal as claimed in claim 3, in which the indicating means comprises an indicator responsive to the level of control fluid in a reservoir thereby providing the measure of face wear of the seal elements.

5. A mechanical seal as claimed in claim 4, in which the control fluid reservoir is a hydraulic cylinder and the means for pressurising the control fluid a piston, the area of the latter being a fraction of the loading area of the seal element thereby providing an amplification of the face wear on a scale of the indicating means.

6. A mechanical seal as claimed in claim 5, in which the piston area is 1/10th the area of the seal element loading area thereby providing a 10:1 amplification of the face wear on the scale.

7. A mechanical seal, substantially as hereinbefore described with reference to the accompanying drawing.