GB2205365A

GB2205365A - Shaft seal safety device

Info

Publication number: GB2205365A
Application number: GB08812899A
Authority: GB
Inventors: Gunter Pietsch
Original assignee: Blohm and Voss GmbH
Current assignee: Blohm and Voss GmbH
Priority date: 1987-06-02
Filing date: 1988-05-31
Publication date: 1988-12-07
Anticipated expiration: 2008-05-31
Also published as: GB8812899D0; SE8802046D0; DE3718411C2; JPS641693A; NL8801403A; SE8802046L; DE3718411A1; SE501938C2; JP2525225B2; NL193466C; GB2205365B; NL193466B

Description

1 Safety Device at a seal Arranqement for Rotatinq Shafts,-in particular

for the Stern Tubes of ShiD ProDulsion Systems The invention relates to a safety device at a seal arrangement for rotating shafts, in particular for the stern tubes of ship propulsion systems, there being two groups of lipped cuffs each comprising at least two lipped cuffs of elastomeric material which are each clamped between two support rings fixed to the housing and arranged in the axial direction alongside one another, with the group of cuffs adjacent the material to be sealed facing towards this medium and with the other group facing towards a chamber which is filled with a liquid lubricant, preferably oil, at the same pressure or at a somewhat higher pressure than the medium to be sealed, and wherein one of the cuffs facing the lubricant chamber serves as a reserve cuff which, in normal operation, is acted on at its front side and also at its rear side by the same pressure of the lubricant, and is thus rendered inactive, but which however is activated on failure of one of the cuffs so 1 so facing the lubricant chamber by blocking off the lubricant supply to the reserve cuff'by means of a blocking member, characterised in that the cuff In a known safety device of this kind (Japanese patent publication 8221/1981) the outermost of the cuffs facing the lubricant chamber is used as the reserve cuff. During normal operation the same pressure prevails at the front and rear sides of this cuff. This is achieved by supplying the lubricant to the rear side of the reserve cuff via a channel which is connected to a pick up container into which the lubricant is pumped from a collection chamber, and in which a pressure is maintained which corresponds to the pressure which acts at the front side on the reserve cuff.

On any eventual breakdown of the cuff adjacent the reserve cuff the aforementioned channel is closed off and the reserve cuff is thereby activated. This complete blockage of the lubricant gives rise to the subsidiary effect that all lubricant supply to the cuff adjacent the failed cuff and facing the medium to be sealed (seawater in stern tube seals) is interrupted.

This leads to the danger of this cuff overheating due to lack of lubrication and thus to the danger of premature failure of this cuff. In addition comes the fact that as the same pressure forms with time on both sides of the failed cuff a vacuum may arise at the rear side of the last cuff facing the medium to be scaled. Experience shows that this vacuum amounts to approximately 0.6 bars for stern tube seals. It acts at the rear side of the narrow active reserve cuff so that a pressure difference of approximately 1.9 bars prevails here when the pressure in the lubricant chamber is set at 1.3 bar which corresponds to the normal rule. A high pressure loading of this kind 9 1 so naturally amplifies the above named negative effect with respect to the life of the reserve cuff.

The invention has set itself the object of overcoming these disadvantages and accordingly of so modifying the known safety device that despite interruption of the lubricant flow a reduced lubricant supply is maintained which prevents the remaining cuffs running dry and also prevents the formation of a vacuum in the rear side chamber of the activated reserve cuff.

In order to solve this problem provision is made, in accordance with the chaiacterising part of claim 1, that the cuff adjacent the outermost of the cuffs facing the lubricant chamber acts as the reserve cuff and is acted on during normal operation at the front side and rear side by the lubricant with a lower pressure than that of the medium to be sealed, and that on failure of the outermost cuff the blocking off of the lubricant takes place in such a way that only the supply of lubricant to the front side is interrupted, the supply of lubricant to the rear side (with the lower pressure) is however maintained.

In accordance with a preferred embodiment of the subject of the invention the two different pressures of the lubricant are generated by the static pressure of the lubricant columns from two collecting containers arranged at different levels above the seal arrangement, with the higher collection container being connected via a line'with the lubricant space and with the lower collection container being connected with the rear side space of the reserve cuff and with the front side space of the reserve cuff via a respective line in ech case, and in that the blocking member is inserted into the line leading to the'front side space.

1 so In this way it is possible with simple means to adapt the pressure of the lubricant to the pressure of the medium to be sealed by vertical adjustment of the collecting containers and also to control the reduced pressure in accordance with the circumstances if it should become necessary to activate the reserve cuff.

In accordance with a further variant provision is made that the blocking member is actuatable by a detector which responds to a pressure rise in the front side chamber of the reserve cuff.

In this way the effectiveness of the safety device can be increased since even small changes of pressure can be detected by the automatic detection system. A further improvement of the safety effect can be achieved, in accordance with the invention, if the reserve cuff and/or the shaft are so formed in the region of the reserve cuff that the reserve cuff is continuously subjected to controlled oscillations during rotation of the shaft in such a way that the lip edge executes pump movements.

Then, as a result of the continuous "pumping" of the sealing lip of the reserve cuff, lubricant is permanently supplied directly to the latter whereby it is adequately cooled and thus protected for its use as the main cuff. Moreover, through the pump effect, a continuous circulating flow of lubricant oil is achieved from the front side space of the reserve cuff via the opened blocking member, the collecting container and back to the rear side space of the reserve cuff. Though this continuous circulating flow any medium which eventually passes the cuffs facing the medium to be sealed is continuously conveyed into the collecting container. From there the medium can be allowed to flow away without difficulty after it has 1 1 so separated out.

As a special method for the production of pump movements it is proposed, in accordance with a further variant, that the shaft surface in the region of the reserve cuff should be formed as an eccentric device with the eccentricity amounting to 4 mm maximum.

The subject of the-invention is illustrated by way of example in schematic form in the drawing, which shows:

Fig. 1 a safety device at a stern tube seal formed as a multiple lip seal as seen in longitudinal section, and Fig. 2 the lubricant arrangement for the stern tube seal of Fig. 1.

In Fig. 1 the reference numeral I designates a multiple cuff seal, the sealing lips of the cuffs MI and M2 of which face the medium to be sealed, in the present case the seawater W, whereas the sealing lips of the cuffs M3 and M4 face the interior of the stern tube which is designated in the following as the lubricant chamber S. The sealing lips of the named cuffs cooperate with the sleeve 2 which is drawn onto the propeller shaft 3 and is connected at one end with the propeller hub via a flange 4 and projects at the other end into the stern tube 5. The cuffs are each clamped between two spatially fixed support rings so that a ring chamber is in each case formed between two cuffs, and indeed the chamber K1 between the cuffs Ml and M2, the chamber K2 between the cuffs M2 and M3, and the chamber K3 between the cuffs M3 and M4.

1 1 so The cuff M3 has in particular a special role since it is used as an inactive reserve cuff, i.e. does not execute any sealing function during normal operation but is activated as a sealing cuff in the event that the cuff M4 fails. The cuff is made inactive in that the chambers K2 and K3 are supplied with lubricant at the same pressure. The supply and take off of the lubricant oil takes place via the passages 6 and 7 indicated by arrows. If the cuff M4 fails then it looses its sealing capability and the reserve cuff M3 is loaded at the front side with the pressure of the lubricating oil from the lubricating space S. In this case the line 7 is closed, as is further explained below, and thus the oil take off out of the chamber K3 is stopped. The lubricant oil pressure in the line 6 is maintained and indeed at a level which lies beneath the pressure of the seawater W.

Thus, the pressure in the lubricant space S acts on the front side of the so activated reserve cuff M3, i.e. a pressure in the present case of approximately 1.3 bar, and the relatively low lubricant oil pressure in the line 6 acts at the rear side, i.e. approximately 0.8 bar. This pressure ensures that vacuum formation in the chamber K2 is reliably avoided.

In the region of the sealing lip of the reserve cuff M3 the sleeve 2 is formed in the manner of an eccentric device, in such a way that the sealing lip of the cuff M3 executes, during rotation of the sleeve 2, a. continuous radial to and fro movement which, as known in such cuffs, has a pumping action in such a way that the lubricant oil in the lines 6 and 7 experiences the flow indicated by the arrows. The eccentricity E may naturally not exceed a certain size and amounts to a maximum of 4 mm.

1 1 1 so 1 The sealing arrangement of Fig. 1 is shown to a smaller scale in Fig. 2 and permits the lubricant arrangement to be recognised. The lines 6 and 7 which are connected to the chambers K2 and K3 respectively are led to a collection cont ainer 8 for the lubricant oil which is arranged lower than the surface WL of the seawater W so that the static pressure in the chambers K2 and K3 is lower than the static pressure of the seawater W.

Into the line to the chamber K3 there is inserted a cut-off member 11 which is open during normal operation and is closed by hand or by a sensor on failure of the cuff M4, i.e. to activate the reserve cuff M3. A second collecting container 9 is arranged higher than the surface WL of the seawater W and is connected via a line 10 with the lubricant chamber S.

This collecting container 9 thus ensures the maintenance of a pressure in the lubricant chamber S which is higher than the static pressure of the seawater W, in the present case approximately 1.3 bar.

1

Claims

P a t e n t C 1 a i m s

Safety device at a seal arrangement for rotating shafts, in particular for the stern tubes of ship propulsion systems, there being two groups of lipped cuffs each comprising at least two lipped cuffs of elastomeric material which are each clamped between two support rings fixed to the housing and arranged in the axial direction alongside one another, with the group of cuffs adjacent the material to be sealed facing towards this medium and with the other group facing towards a chamber which is filled with a liquid lubricant, preferably oil, at the same pressure or at a somewhat higher pressure than the medium to be sealed, and wherein one of the cuffs facing the lubricant chamber serves as a reserve cuff which, in normal operation, is acted on at its front side and also at its rear side by the same pressure of the lubricant, and is thus rendered inactive, but which however is activated on failure of one of the cuffs facing the lubricant chamber by blocking off the lubricant supply to the reserve cuff by means of a blocking member, characterised in that the cuff adjacent the outermost of the cuffs facing the lubricant chamber acts as the reserve cuff and is acted on during normal operation at the front side and at the rear side by the lubricant with a lower pressure than that of the medium to be sealed, and in that on failure of the outermost cuff the blocking off of the lubricant takes place in such a way that only the supply of lubricant to the front side is interrupted, the supply of lubricant 1 1 to the rear side (with the lower pressure) is however maintained.
2. Safety device in accordance with claim 1, characterised in that the two different pressures of the lubricant are generated by means of the static pressure of lubricant columns from two collection containers arranged at different levels above the sealing arrangement, with the higher collection container being connected via a line with the lubricant space, and with the lower collection container being connected with the rear side space of the reserve cuff and with the front side space of the reserve cuff via a respective line in each case, and in that the blocking member is inserted into the line leading to the front side space.

so
3. Safety device in accordance with claim 1 or claim 2, characterised in that the blocking device is actuatable by a detector which responds to a pressure increase in the front side chamber of the reserve cuff.
4. Safety device in accordance with one of the claims 1 to 3, characterised in that the reserve cuff and/or the shaft in the region of the reserve cuff are so formed that the reserve cuff is subjected to continuous controlled oscillations during rotation of the shaft in such a way that the lip edge executes pump movements.
5. Safety device in accordance with claim 4, characterised in that the pump oscillations originate from an eccentric layout of the shaft surface in the region of the reserve cuff.

1 1
6. Safety device in accordance with claim 5, characterised in that the eccentricity amounts to 4 mm maximum.
7. Safety device as described herein with reference to and as illustrated in the accompanying drawings.

so 1 Published 1988 at The Patent Office, State House, 86!71 High Holborn, London WCIR 4TP. Purther copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.