Seal system for a stern tube

Abstract

 Seal system (1) for sealing a stem tube (2) with a propeller shaft (5) arranged therein such that it can rotate, wherein use is made of sealing rings and lubricant, such as oil, is fed to the stem tube (2) from an oil reservoir (10) that is some distance above the stem tube (2). A first sealing ring (13) is fitted close to the end of the stem tube that is on the inside and a second sealing ring (14) close to the end where the propeller (7) is located. A space (16) is formed between the second and a third sealing ring (15) on that side of the stem tube (2) where the propeller (7) is located, to which space a suction pump (20) and a vent pipe (17) are connected. At least a fourth sealing ring (21) is fitted next to the third sealing ring (15) for forming a chamber (22) between these sealing rings to which clean water under pressure can be fed for the lubrication of these sealing rings (15, 21).

Description

[0001] The invention relates to a seal system for sealing a stem tube with a propeller shaft that is arranged therein such that it can rotate and is supported by bearings, wherein use is made of sealing rings, each provided with a lip that runs around the propeller shaft and is in resilient contact with the shaft, wherein lubricant, such as oil, is fed to the stem tube by means of a line that is connected to an oil reservoir that is some distance above the stem tube, wherein a first sealing ring is fitted close to the end of the stem tube that is furthest inwards and a second sealing ring is fitted close to the end where the propeller is located and the lips of these sealing rings are oriented towards one another.

[0002] Such a seal system is, for example, disclosed in a brochure by the Applicant entitled "SUPREME Schroefaskokerafdichtingen en Schroefaslagers" ("SUPREME Stem Tube Seals and Propeller Shaft Bearings").

[0003] In the case of this known system the oil in the stem tube is maintained at a pressure that is higher than the outboard water pressure. To this end the reservoir for the oil is installed a certain distance above the water line. Adequate lubrication of the lips of the sealing rings can be obtained by this means. Water is also prevented from being able to penetrate from the outside into the stem tube, which could damage the bearings. However, the pressure exerted by the oil on the lips of the sealing rings can give rise to more rapid wear of the lips or of the bush or the shaft than is desired.

[0004] Furthermore, as a result of the pressure exerted on the oil in the stem tube there is the risk that in the event of some wear on the sealing ring on the propeller side oil can be forced outwards and reach the surface water.

[0005] This will also be able to take place because a certain pumping action is exerted on the oil by the lip of the sealing ring when the shaft rotates.

[0006] An attempt has been made to overcome the drawback of the use of oil by making use of a biodegradable oil or grease. However, the use of the latter is expensive and if grease has got onto the surface water it is not possible to establish immediately that this grease is indeed biodegradable. This can lead to difficulties with the authorities.

[0007] The aim of the invention is, now, to eliminate these drawbacks and to this end it provides for a space to be formed on that side of the stem tube where the propeller is located, to which space a suction pump is connected and a vent pipe that is in communication with the atmosphere, which space is delimited, on the one side, by the said second sealing ring and, on the other side, by a third sealing ring, the lip of which runs in the direction of the propeller.

[0008] What is achieved in this way is that any oil that leaks from the stem tube past the second sealing ring passes into the space that is at atmospheric pressure and from which the oil can be extracted. Thus, no oil can leak outwards into the surface water.

[0009] Preferably, at least a fourth sealing ring oriented in the same direction is fitted next to the third sealing ring to form, between these sealing rings, a chamber to which clean water can be fed under pressure for lubrication of these sealing rings.

[0010] Outboard water that may leak past the third and fourth sealing rings will also pass into the space at atmospheric pressure and will be extracted therefrom. Partly because the oil in the stem tube is at a pressure that is somewhat higher than atmospheric pressure, no water will be able to pass into the stem tube, so that damage to the bearings is prevented.

[0011] Because of the presence of the space at atmospheric pressure between the second and third sealing ring no water under elevated pressure will be able to reach the second sealing ring. As a result, the oil in the stem tube only needs to be at a slight excess pressure.

[0012] According to the invention, therefore, provision can also be made that the oil reservoir is a relatively short distance above the stem tube, which distance, for example, can be between 1 and 2 metres. The installation is appreciably simplified as a result. Of course, a vent pipe is needed, which preferably will extend to above the water line.

[0013] Because of the relatively low excess pressure of the oil in the stem tube, the wear on the lips of the first and second sealing rings bounding the stem tube will be limited.

[0014] A vent pipe will also be connected to the stem tube. What is achieved by this means is that the stem tube is completely filled with oil, so that the bearings cannot be damaged as a result of too little oil in the stem tube.

[0015] By making use of a pump to bring clean water from a reservoir into the chamber between the third and fourth sealing ring, dirty water is prevented from being able to reach the space at atmospheric pressure, which could cause the discharge line thereof and the suction pump to become blocked. Wear on the sealing rings or on the propeller shaft, or on a bush fitted thereon, with which the lips of the sealing rings are in contact, could also occur as a result of dirt in the water.

[0016] In order to achieve good extraction of water and oil from the space at atmospheric pressure, provision will preferably be made that the suction line is connected to the bottom of the space and the vent pipe to the top.

[0017] If the seal system is intended for a vessel with a deep draught, it is possible according to a further development of the invention to fit a fifth sealing ring oriented in the opposing direction in the space at atmospheric pressure against the second sealing ring, which seals the space at atmospheric pressure against the stem tube, such that oil can be fed dropwise from the stem tube to the space between the lips of the second and fifth sealing rings.

[0018] Additional lubrication of the sealing rings and a supplementary seal, i.e. an emergency seal, from the space at atmospheric pressure towards the stem tube is obtained by this means.

[0019] In addition, it can furthermore be provided that a sixth sealing ring is fitted between the third and fourth sealing ring, which sixth sealing ring is oriented in the same direction as the third and fourth sealing ring, so that the space between the third and fourth sealing ring is divided and water under pressure is fed to the chamber between the fourth and the sixth sealing ring and the space between the third and the sixth sealing ring is connected to a water reservoir that is some distance above the stem tube.

[0020] As a result of the presence of the sixth sealing ring, the pressure of the outboard water will be on this sealing ring, so that the third sealing ring, which delimits the space at atmospheric pressure, cannot be exposed to the pressure of the outboard water. Yet further sealing rings can be used to obtain further distribution of the pressure as well. A dirt stop ring can then be fitted closest to the propeller, as is known per se.

[0021] The invention will be explained in more detail with reference to illustrative embodiments shown in the drawing, in which,

Fig. 1 shows, diagrammatically, a first embodiment of a seal system according to the invention; and

Fig. 2 shows, diagrammatically, a system that is suitable in particular for a vessel with a relatively large draught.

[0022] Fig. 1 shows, diagrammatically, a seal system 1 that is installed in a stem tube 2, which is joined to the hull of a vessel at 3 and in which a propeller shaft 5 is supported by means of bearings 4.

[0023] Bushes 6 are located locally on the propeller shaft 5, it being possible for the hub of the propeller to be fixed to the left-hand bush 6 by means of bolts. As indicated in the righthand part of the drawing, a bush 6 can be mounted on a flange 8 joined to the propeller shaft 5.

[0024] The stem tube 2 is filled with oil via a line 9 from the oil reservoir 10 that is a distance H of approximately 1 to a few metres above the stem tube 2 and is provided with a vent pipe 11. The stem tube 2 is provided with the vent pipe 12.

[0025] Oil is prevented from flowing out of the stem tube 2 to the interior of the vessel by means of a first sealing ring 13. The other end of the stem tube 2 is sealed by a second sealing ring 14. There is a third sealing ring 15 opposite the sealing ring 14, so that a space 16 is formed between the sealing rings 14 and 15. The space 16 is, on the one hand, in communication with the atmosphere by means of the line 17 and, on the other hand, with a reservoir 19 by means of the line 18. A suction pump 20 that feeds the fluid sucked in, which can be either oil or water, to a storage tank, which is not shown, is connected to the reservoir 19.

[0026] The sealing rings 13, 14 and 15, and also the sealing rings that are still to be described in more detail, are not directly on the propeller shaft 5 but on the bushes 6 fitted thereon. By this means wear on the propeller shaft 5 is prevented from occurring, whilst the bushes 6 can be replaced if any wear occurs.

[0027] There is a fourth sealing ring 21 next to the third sealing ring 15, so that a chamber 22 is formed to which clean water under pressure can be fed from a reservoir 25 by means of a line 23 and a water pump 24. A vent pipe 26 is also connected to the reservoir 25.

[0028] The sealing rings 15 and 21 are lubricated and cooled with water by this means and surface water, that could be contaminated, is prevented from being able to reach these sealing rings.

[0029] Fig. 2 shows, diagrammatically, a seal system that is suitable in particular for a vessel with a deep draught. Corresponding components are indicated by the same reference numerals as used in Fig. 1.

[0030] A fifth sealing ring 30 is now fitted by the second sealing ring 14 so that a space 31 is produced between the lips of these two sealing rings. Oil is able to flow dropwise from the stem tube 2 to the space 31 via the line 32 using a throttle.

[0031] A sixth sealing ring 33 is fitted between the third sealing ring 15 and the fourth sealing ring 21 so that a chamber 22 is produced to which water under pressure can be fed from the reservoir 25 by means of the pump 24. A space 34 is formed between the sixth sealing ring 33 and the third sealing ring 15, to which clean water can flow form the reservoir 25 via the line 35. This water is thus not under elevated pressure, so that the third sealing ring 15 will be subjected to a lesser load. The space 34, in turn, is in communication with a vent pipe 36.

[0032] The fourth sealing ring 21 can optionally be designed as a dirt stop ring, but there can also be a separate dirt stop ring.

[0033] Valves and the like, which are not shown in more detail, can be fitted in various lines in order, inter alia, to prevent back-flow of medium. Furthermore, there will be stopcocks in the various lines in connection with maintenance and fitting or dismantling of components.

[0034] In the figures the water line outside the vessel in the loaded state thereof is indicated by W. In Fig. 2 an additional sealing ring, that is not indicated in more detail, is also fitted by the sealing ring 13, as is customary in the case of stem tubes.

[0035] Yet further sealing rings can be fitted on either side of the seal system and many other modifications can also be made without going beyond the inventive concept as is indicated in the claims.

Claims

1. Seal system (1) for sealing a stem tube (2) with a propeller shaft (5) that is arranged therein such that it can rotate and is supported by bearings (4), wherein use is made of sealing rings, each provided with a lip that runs around the propeller shaft and is in resilient contact with the shaft, wherein lubricant, such as oil, is fed to the stem tube (2) by means of a line (9) that is connected to an oil reservoir (10) that is some distance above the stem tube (2), wherein a first sealing ring (13) is fitted close to the end of the stem tube that is furthest inwards and a second sealing ring (14) is fitted close to the end where the propeller (7) is located and the lips of these sealing rings are oriented towards one another, characterised in that a space (16) is formed on that side of the stem tube (2) where the propeller (7) is located, to which space (16) a suction pump (20) is connected, and a vent pipe (17) that is in communication with the atmosphere, which space is delimited, on the one side, by the said second sealing ring (14) and, on the other side, by a third sealing ring (15), the lip of which runs in the direction of the propeller (7).

2. Seal system according to claim 1, wherein at least a fourth sealing ring (21) oriented in the same direction is fitted next to the third sealing ring (15) to form, between these sealing rings, a chamber (22) to which clean water can be fed under pressure for lubrication of these sealing rings (15, 21).

3. Seal system according to Claim 1 or 2, characterised in that the oil reservoir (10) is a relatively short distance above the stem tube (2), which distance, for example, can be between 1 and 2 metres.

4. Seal system according to any of the preceding Claims, characterised in that the suction line (18) is connected to the bottom of the space (16) under atmospheric pressure and the vent pipe (17) to the top.

5. Seal system according to one of the preceding claims, characterised in that a fifth sealing ring (30) oriented in the opposing direction is fitted in the space (16) at atmospheric pressure against the second sealing ring (14), which seals the space against the stem tube (2), such that oil can be fed dropwise from the stem tube (2) to the space (31) between the lips of the second and fifth sealing rings (14 and 30, respectively).

6. Seal system according to one of the preceding claims, characterised in that a sixth sealing ring is fitted between the third and fourth sealing ring (14 and 21, respectively), which sixth sealing ring (33) is oriented in the same direction as the third and fourth sealing ring, so that the space between the third and fourth sealing ring is divided and water under pressure can be fed to the chamber (22) between the fourth and the sixth sealing ring (21 and 33, respectively) and the space (34) between the third and the sixth sealing ring (14 and 33, respectively) is connected to a water reservoir (25) that is some distance above the stem tube (2).

Drawing