GB2150234A - Underwater sealing of an oil-lubricated shaft bearing - Google Patents

Abstract

For the sealing of an oil-lubricated bearing (2, 3) of a drive shaft (1), a leakage space (20) and an adjoining oil chamber (30) are arranged between a slide ring seal (11, 12) and the bearing. The oil chamber is bounded by two outer lip seals (25, 27) and contains a further, normally unloaded inner lip seal (26). If a water pressure, which is higher than the normally low oil pressure in the oil chamber (30), should build up in the leakage space (20) and a collecting chamber (41) connected therewith, the oil pressure in the forward oil chamber compartment (30b) is increased to about half that of the water pressure. The changing of the pressures in the oil chamber compartments (30a and 30b) activates the inner lip seal (26), which, however, is subjected to only half the pressure difference between the ambient water pressure and the low oil pressure in the bearing. <IMAGE>

Description

SPECIFICATION Underwater sealing of an oil-lubricated shaft bearing The present invention relates to a rotary shaft and oil-lubricated bearing assembly in combination with sealing means to provide underwater sealing of the bearing, the shaft being, for example, a drive shaft such as a propeller shaft.

In the case of floating offshore drilling platforms and for the movement of immersible bodies with tools for working on the seabed, there is a need for drive shaft seals which are reliable in water depths of 30 to 50 metres and even up to about 100 metres.

In a known sealing arrangement for ship propellers a rearward slide ring seal is adjoined by a leakage space with a drainage channel, in front of which is arranged an oil chamber which, with two mutually facing lip seals, serves to seal off an oil-lubricated bearing from the leakage space. Ingressing oil or leakage water can flow out of the oil chamber through a channel when the pressure in the oil chamber is higher than the pressure in the bearing.

However, this arrangement cannot be used for greater water depths as the coincidence of unfavourable circumstances might allow the full external water pressure to impinge on the lip seal immediately behind the bearing and this would be destroyed in a short time hereby, as lip seals are suitable for only a limited pressure difference.

There is thus a need for a sealing arrangement which becomes effective on the failure of the slide ring seal at the water side and which, in spite of a high external water pressure, can provide sealing against the ingress of water into an oil-lubricated bearing.

According to the present invention there is provided a rotary shaft and oil-lubricated bearing assembly in combination with sealing means to provide underwater sealing of the bearing, the sealing means comprising a stationary slide ring cooperable with a rotary slide ring at the shaft, means defining a leakage chamber for water leaking from the slide rings towards the bearing, two outer lip seals axially bounding an oil chamber between the leakage chamber and the bearing and arranged with their lips directed towards each other, at least one inner lip seal axially dividing the oil chamber into two compartments and arranged with its lip directed away from the bearing, and means responsive to a water pressure rise in the leakage chamber to cause oil pressure in the compartment closer to the bearing to be increased to a value substantially half that of the pressure in the leakage chamber.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawing, the single figure of which is a schematic sectional elevation of a shaft and bearing assembly in combination with sealing means for underwater sealing of the bearing, the combination embodying the present invention.

Referring now to the drawing, there is shown a shaft and bearing assembly comprising a drive shaft 1 mounted in a liner 2 of a bearing 3, at the rear end of which is disposed an oil space 4 receiving part of the substantially pressure-free lubricating oil for the bearing. Aflange 5 of a drive propeller is arranged at the free rear end of the shaft 1 extending into the surrounding water and a bush 6, which is fastened by an end flange 7 to the flange 5, sits on the shaft 1.

Arranged at the shaft 1 is a slide ring seal consisting of a first slide ring 11, which turns with the bush 6 or the shaft 1 and is secured by pins 13 to the flange 7, and a second slide ring 12, for example a ring of synthetic carbon, which is resiliently pressed in axial direction against the first slide ring 11. The slide ring 12 is supported through an annular body 14, at the forward side of which engages a compression spring 15, and is secured radially to a body 14 by a ring 16. The non-rotating body 4 is arranged at a spacing within a fixed ring 17 and the gap therebetween is sealed off by a lip seal 18 withstanding a high static pressure.A gap 19, through which water seeping in between the slide rings can flow into a leakage space 20, is disposed between the inner circumferences of the slide rings and the body 14 and the outer circumference of the bush 6.

A seal housing, which is composed of housing rings 21, 22, 23 and 24 is arranged between the slide ring seal and the rearward end of the bearing 3. Lip seals 25, 26 and 27 are clamped between the housing rings. The seals 25 and 27 bound an oil chamber 30, which is sub-divided by the middle seal 26 into a rearward part 30a and a forward part 30b.

The lips of the seals 25 and 27 face each other and the lip of the seal 26 points rearwardly.

Connected to the forward oil chamber part 30b is an oil duct 31, which feeds oil into the chamber 30 under a pressure which is somewhat higher than the oil pressure in the space 4 of the bearing and also higher than the water pressure normally prevailing in the leakage space 20. As a result, the lips of the seals 25 and 27 are pressed against the bush 6 and penetration of oil from the bearing, or water from the space 20, into the oil chamber 30 is prevented.

As illustrated, the feed of the oil through the duct 31 preferably takes place from a high tank 32. If oil circulation through the chamber 30 is desired, the oil can also be fed through a pump at regulable pressure. The oil cools and lubricates the lip seals which, due to the normally small pressure differences between their two sides, are loaded only slightly and therefore have a long service life. The middle seal 26 is completely relieved, since the same pressure is present in both parts of the oil chamber. The seal 26 is constantly well lubricated and cooled through the oil in the chamber 30 so that, in the case of a pressure rise in the rearward chamber part 30a, it can be activated as a reserve seal.

Water ingressing through the slide ring seal into the space 20 is conducted away out of the space through a channel 40 into a collecting chamber 41.

Since the shaft and bearing assembly is arranged at the lowest point in certain equipment, for example a drilling platform, the collecting chamber 41 is disposed at a small height above the sealing device.

From the chamber 41 the water is periodically pumped away through a non-return valve 43 and a duct 44 by means of a leakage water pump.

Preferably, the chamber 41 stands under atmospheric pressure and possesses a ventilation pipe 45. The pump 42 is set into operation by suitable control means in dependence on the filling level.

Although slide ring seals are very reliable, additional protection is needed in the case of sealing for offshore equipment and also in the case of damage arising in the slide ring seal, such as to lead to increase in the pressure of the water in the space 20 to that of the ambient water and thereby also to increase in the pressure in the chamber 41.

A pressure increase in the leakage space 20 effects lifting of the seal 25 off the bush 6 so that leakage water penetrates at high pressure into the rearward part 30a of the oil chamber and loads the seal 26. This could be destroyed very rapidly when the external water pressure acts on its lip, since the forward oil chamber part30b provides only a low pressure sufficient for the sealing of the bearing.

Accordingly, the pressure in the forward oil chamber part 30b is increased to about half the external water pressure in the case of a rise in the pressure in the leakage space 20 above the normal pressure in the forward chamber part 30b. In this manner, the seals 26 and 27 are each loaded only by half the total pressure difference between the surrounding sea water and the bearing.

To increase the oil pressure, a second, higher oil tank 33 is provided. Arranged in the ventilation pipe 45 of the collecting chamber 41 is a water indicator 46, which responds to the liquid rising up to it in the ventilation pipe and, through an electrical circuit, issues signals which indicate a pressure rise in the leakage space 20. One signal can actuate an alarm device (not shown). Another signal acts on a valve 34, which lets oil flow out of the second tank 33 through a duct 35 and into the forward oil chamber part30b. The height of the oil tank 33 is so chosen that it produces in the chamber part 30b an oil pressure which corresponds to about half the external water pressure at the water depth at which the shaft and bearing assembly is normally disposed. The oil tanks 32 and 33 are expediently connected by way of ventilation pipes 36 and 37 with the atmosphere.

A further signal of the water indicator 46 can act, optionally with a time delay, on an inlet valve (not shown) in order to blockfurtherflowofwaterfrom the leakage space 20 to the collecting chamber 41.

At the same time, the pump 42 can be switched off.

The illustrated embodiment with two oil tanks 32 and 33 which are disposed at different heights above the seals is particularly suitable for, for example, a drilling platform with approximately constant depth of immersion of the drive shaft. This arrangement has the advantage that the oil pressure in the forward chamber 30b can be increased reliably and by simple means in an emergency, in which case the valve 34 can also be operable manually.

If only temporary pressure increases in the leakage space 20 occur or if a circulation of the oil through the oil chamber 30 is desired, a return duct (not shown) can be provided from the rearward chamber part 30a. An only temporarily necessary pressure increase in the chamber 30 can be reduced through this return duct, in which blocking devices and a pump (not shown) can be arranged.

In the case of immersible watercraft and underwater tools, in which the supply of oil from appropriately highly positioned oil tanks is hardly possible, the necessary oil pressure adapted to the respective immersion depth can be produced through pumps with pressure regulating equipment. For great depths of water, several normally unloaded seals 26 can be arranged in the oil chamber 30. Use is not restricted to bearings in great water depths as use is appropriate for, for example, different kinds of watercraft, such as merchant ships and tugboats.

In the embodiment hereinbefore described, there is provided, in the oil chamber bounded by the outer lip seals, a further inner lip seal which is not loaded during the normal operation of the sealing device and, in consequence of the lubrication from both sides in the oil chamber, does not exhibit wear even after extended operating periods. If, however, the pressure in the leakage space rises, the rearward lip seal would be raised allowing water to enter the rearward compartment of the oil chamber. This has the effect that the inner lip seal is pressed against the shaft, whereby penetration of the water into the forward compartment of the oil chamber is prevented. The inner lip seal remains effective as long as the pressure prevailing behind it is greater than the pressure in the forward compartment of the oil chamber. If, however, the full water pressure in, for example, 40 metres of water depth (thus an excess pressure of about 4 bar) acts from behind on the inner lip seal, a pressure of about 2 bar acts at its forward side in the forward compartment of the oil chamber. Present at the inner lip seal and at the forward outer lip seal is a pressure difference of two bar, whereby suitable lip seals can remain in service for a lengthy period of time until the exchange of damaged slide ring seals or elimination of a defect in the leakage water drainage.

Claims (9)

1. A rotary shaft and oil-lubricated bearing assembly in combination with sealing means to provide underwater sealing of the bearing, the sealing means comprising a stationary slide ring co operable with a rotary slide ring at the shaft, means defining a leakage chamber for water leaking from the slide rings towards the bearing, two outer lip seals axially bounding an oil chamber between the leakage chamber and the bearing and arranged with their lips directed towards each other, at least one inner lip seal axially dividing the oil chamber into two compartments and arranged with its lip directed away from the bearing, and means responsive to a water pressure rise in the leakage chamber to cause oil pressure in the compartment closer to the bearing to be increased to a value substantially half that of the pressure in the leakage chamber.

2. A combination as claimed in claim 1, comprising first oil storage means connected by a duct to said closer compartment to supply oil to produce in the oil chamber a pressure higher than a given normal water pressure in the leakage chamber and than a given normal oil pressure in the bearing and second oil storage means to supply oil to increase the pressure in at least said closer one of the compartments.

3. A combination as claimed in claim 2, each of the oil storage means comprising an oil storage chamber standing under atmospheric pressure and the second storage means being disposed at a height above that of the first storage means and connected thereby by way of an openable and closable connecting duct.

4. A combination as claimed in any one of the preceding claims, comprising means defining a collecting chamber to collect water removed from the leakage chamber, discharge means to discharge water from the collecting chamber, and a vent duct to place the collecting chamber in communication with the ambient atmosphere, the means responsive to water pressure rise comprising a water indicator so responsive to rise of water in the vent duct as to actuate means to effect said oil pressure increase.

5. A combination as claimed in claim 4, said means defining the collecting chamber comprising a tank disposed at a height above that of the slide rings and lip seals.

6. A combination as claimed in either claim 4 or claim 5 when appended to claim 3, said means actuabie by the water indicator comprising a valve controllable by the indicator to open the connecting duct when said response occurs.

7. A combination as claimed in claim 6, wherein the indicator is arranged to additionally close a water inlet valve for the collecting chamber when said response occurs.

8. A combination as claimed in either claim 6 or claim 7, wherein the indicator is arranged to additionally actuate an alarm device when said response occurs.

9. A rotary shaft and oil-lubricated bearing assembly in combination with sealing means to provide underwater sealing of the bearing, the combination being substantially as hereinbefore described with reference to the accompanying drawing.