GB2174156A - A stern-tube seal - Google Patents

Abstract

In a stern-tube seal a displacement pump (22) is arranged in a housing ring (53) at a chamber (14) for drawing off liquids which seep in or flow through the chamber, with the displacement element being driven by a cam (6) located on the shaft (1). The liquids are sucked in through a valve (21) and are discharged via a line (20) and a delivery valve (23) arranged in or close to the seal housing, for example into a further line (24) which rises upwardly and/or has a large flow resistance. <IMAGE>

Description

SPECIFICATION A stern-tube seal The invention relates to a stern-tube seal for a ship or a similar sealing arrangement in which for example an oil lubricated bearing at a propeller shaft is to be sealed against the water and in which both the emergence of oil and also the penetration of water must be prevented.

A number of seal arrangements already exist in which a separation of oil and water is to be achieved with the aid of resilient sealing rings or slide rings. In some of these proposals a chamber partitioned off between seal elements is used, with leaking liquids being caught in the chamber and being led from the chamber into the bilge via a line. In other seal arrangements provision is made for the oil in an oil chamber to be checked via a line and, if necessary, for it also to be changed. As the spatial conditions in the region of the sterntube are very cramped and as only small quantities of liquid are to be conveyed through the lines the line resistances can be so large at the rear seals that liquid no longer flows therethrough.There are also shaft mountings in which a natural downward slope cannot be utilized, for example due to a downwardly inclined shaft end, or due to the arrangement of the drive at the lower end of a leg of a floating platform. The sucking-off of liquids by pumps which have to be mounted some distance away from the rear seal in the ship is frequently not possible because of the relatively large line resistances and also on exceeding the maximum suction head or height.

The problem underlying the invention is thus to generate a forced flow in a liquid medium which is to flow through or flow out of a chamber, at a position, for example at the rear seal arrangement of the stern-tube, at which other pumps can only act with difficulty due to the long lines, or cannot be directly accommodated.

The invention provides that a small displacement pump is accommodated in the seal housing with its working space lying in a line connected with the chamber and with its displacement element being moved by a cam of a shaft. The pump arrangement includes, in addition to a displacement member, a suction valve and a delivery valve. For the sucking-off of, for example, leakage fluid from a leakage chamber the suction valve is expediently arranged directly at the lowest point of the leakage chamber. The delivery valve can likewise be accommodated within the seal arrangement, however depending on the spatial conditions in the seal arrangement and in the stern-tube is also possible to locate it somewhat further away if necessary.

The diameter of a propeller shaft amounts, for larger ships, to approximately 300 to 1000 mm. A piston pump with a stroke of approximately 2 to 5 mm and a piston diameter of 5 to 12 mm is sufficient to remove liquid leakages from a leakage chamber. A cam sufficient for this stroke, or a corresponding eccentricity of the shaft, for example a ring-like part sitting on the shaft, has practically no effect on the shaft and its vibrational behaviour. With the small pump a discharge pressure can be achieved corresponding to a discharge head of 60 m. When the shaft rotates the pump is continuously driven it must therefore be constructed, particularly with regard to its bearings, so that it can also operate in the dry state. The parts of the pump must also be made of material which is resistant to seawater and oil. The displacement pump can also be constructed as a membrane pump.The valves are expediently constructed as automatic check valves (non-return valves).

The pump arrangement has to be constructed in accordance with the operating conditions which are to be expected at a seal and it is possible to deviate from the previously given dimensions and also to arrange several cams on the shaft.

The pump arrangement of the invention is not only suitable for conveying liquid leakages from a leakage chamber into a collection tank, which may optionally be disposed at a higher level, but is also suitable to force a flow through an annular chamber filled with oil, or to generate a higher pressure in a chamber filled with water in order to force a flushing flow of water through the outer seal against the pressure of the surrounding seawater.

Further details of the invention and examples of its use can be seen from the claims and from the embodiments which are described with reference to the drawings.

In the drawings various embodiments are illustrated in simplified and partly schematic form. There is shown: Fig. 1 a longitudinal section through a seal arrangement with a pump at a leakage chamber, Fig. 2 a cross-section through a part of the seal arrangement which contains the pump and the associated valves, Fig. 3 a longitudinal section through the lower half of a seal with slide rings subjected to axial contact pressure and with a pump at the leakage chamber between the slide rings, Fig. 4 a longtidudinal section through the upper half of a seal wherein filtered seawater is forced by means of the pump into an annular chamber, Fig. 5 a rear seal arrangement with membrane pumps wherein one pump removes liquid leakage from a leakage chamber and a further pump conveys the lubricant from an annular chamber under pressure to an oil cooler disposed as a higher level.

In the stern-tube seal shown in Fig. 1 a running sleeve 2 is located on the shaft 1.

The shaft 1 is journalled in a bearing sleeve 3 in the stern boss 4 to which the seal housing 5 consisting of several housing rings 51, 52,53,54 is secured. The housing 5 contains at least one rear lip seal 11 which protects a leakage chamber 14 against the penetration of the surrounding seawater. An annular chamber 15 which contains oil is located between two further lip seals 12,13. The space 16 of the bearing which is likewise filled with oil lies in front of the seal 13. Any liquid leakages penetrating into the leakage chamber 14 through the seals 11 and 12 are led away via a line 20.In accordance with the invention a suction valve 21, a displacement pump 22 and a delivery valve 23 are arranged in the line 20, with the suction valve 21 being located, in accordance with Figs. 1 and 2, at the chamber 14 which is to be emptied, and with the displacement member of the pump 22 being in direct contact with a cam 6 or a corresponding eccentric formation of a part which rotates with the shaft 1, for example the running sleeve 2. When the shaft 1 rotates the pump 22 will continuously suck from the leakage chamber 14 and discharge via the line 20, with the line 20 and a further line 24 after the delivery valve 23 also being able to extend upwardly. A vent line 25 can be provided to the chamber 14 so that no depression can arise in the chamber 14 which would be disadvantageous for the neighbouring seals.

Whereas, in Fig. 1, the suction valve 21 and pump 22 are arranged alongside one another in the axial direction, Fig. 2 shows the arrangement of these parts alongside one another in the peripheral direction which is preferred in order to reduce the constructional dimensions of the seal arrangement. The inlet to the suction valve lies at the lowest point of the annular chamber. It is however also possible to arrange the suction valve at a higher level if a certain quantity of liquid leakage is to remain in the leakage chamber to lubricate the lip seals. Fig. 2 also shows, as a preferred embodiment, the arrangement of the delivery valve in the seal housing near to the pump.

Fig. 2 shows further details of an example of a pump arrangement with a piston pump.

A displacement member consisting of the piston 31 and the push rod 32 is radially displaceable (with reference to the centre of the shaft 1) in a bore 30 of an insert 39, which is for example inserted into a housing ring 53 containing the leakage chamber 14, and is pressed by a spring 32 against the periphery of the running sleeve 2 including the cam 6.

At least the push rod 32 is disposed in a ring 34 of a suitable plastic material which permits dry friction over a longer period of time. A securing ring 35 retains the pump in the bore 30. The suction valve 21 is accommodated in a further bore 36. The sucked-in medium flows through a passage 20a into the working space 30a of the piston 31 and is supplied from the piston through a line 20b to the delivery valve 23 which sits in a bore 37 to which a pressure line (not shown), which in this embodiment would extend outside of the seal housing, is connected via a threaded part 38. The check valves 21,23 are shown as spring loaded ball valves, however other valves which only permit flow in one direction can also be used.

With the double acting slide ring seal of Fig.

3 two slide rings 41,42, for example of artificial carbon, are pressed against a counter ring 40 secured to the shaft 1, with a leakage chamber 44 surrounding the counter ring 40.

The slide rings 41,42 are secured in mounting rings 45,46 which are pressed together by springs 47,48 and are axially displaceable in a bore 43 of the housing ring 55. The suction valve 21 and the pump 22, which is driven by a cam 49 at the periphery of the counter ring 40, are arranged at the leakage chamber 44.

Seawater penetrating for example via the slide ring seal 41 and oil penetrating via the slide ring seal 42 are led away through the pump 22, the line 20 and the delivery valve 23. This arrangement with slide ring seals and a displacement pump which sucks at the leakage chamber is also suitable for large water depths, such as occur for example with a drive at the leg of a floating platform, because they make it possible to convey the leaking liquids to a collecting tank disposed very much higher in the leg.

The seal arrangement of Fig. 4 contains, behind the outer seal 11, a chamber 60 in which cleaned seawater is introduced with a slight excess pressure in order to flush the seal 11 with the expressed clean water and to prevent the entry of contamination into the chamber 60. At the front the chamber 60 is closed in this example by a slide ring seal which is adjoint by a leakage chamber 64 followed, behind a seal 67, by an oil filled chamber of a bearing. A mounting ring 61, to which a slide ring 62 of artificial carbon is secured, is mounted on the shaft 1. A counter ring 63 is axially displaceable on a housing ring 56 and is pressed by springs 65 against the slide ring 62. A seal 66 seals between the counter ring 63 and the housing.

A cam 69 which actuates the displacement pump 62 is formed on the housing ring 61.

Seawater is sucked in through a line 70 via a suction valve 21 and a filter element 71 and is forced by means of the pump 22 into the chamber via the delivery valve 23, with the pressure in the chamber being elevated above that of the surrounding seawater, so that the outwardly directed lip seal 11 is lifted against the seawater pressure away from the shaft 1 and flushing takes place. This avoids abrasive substances penetrating the seal 11 with seawater leading to rapid wear of the slide ring seal.

The stern-tube seal of Fig. 5 corresponds essentially to that of Fig. 1 and the same reference numerals are used for corresponding parts. A pump 22a and 22b with a suction valve 21 and a subsequent delivery valve 23a, 23b is however provided both at the leakage chamber 14 and also at the annular chamber 15 which contains oil. In addition the pumps 22a,22b are shown as membrane pumps which are moved by the cams 6a,6b. The flexible membranes 80 can be pressed against the cams on the shaft either by springs 81 as illustrated or by a spring bias which exists in the membranes themselves.

The pump 22a removes from the leakage chamber 14 any liquid leakages which have penetrated into this leakage chamber and forces them via the lines 20,24 to a higher disposed outlet from which they can flow away, for example into a non-illustrated collecting tank.

The pump 22b draws oil out of the annular chamber 15 and forces it via the lines 74,75 into an oil cooler 76 or into a corresponding tank in which the oil cools and in which contamination may settle out. The oil then flows from the tank 76 back into the annular chamber 15 via the supply line 77. The removal of oil by the pump 22b brings about a continuous oil flow through the annular chamber 15.

A pressure can be maintain in correspondence with the static height of the oil cooler 76 above the seal which is higher than the pressure in the chamber 16 of the bearing and optionally also higher than the seawater pressure.

In addition to the illustrated embodiments for stern-tube seals, the design of which can be changed in various respects and which can be adapted to the sealing reconditions, the invention can also be used with similar seal arrangements and also with seals at vertical shafts. In all these cases it can be advantageous for the pump to be arranged directly at or alongside the chamber from which a liquid medium has to be removed via lines having a significant flow resistance or a corresponding inclination.

Claims (10)

1. A stern-tube seal comprising at least one chamber which surrounds the shaft, which is partitioned off by seal elements, which is provided with a line for the supply or removal of a liquid medium and which is arranged in a seal housing, characterised in that a displacement pump (22, 22a) is accommodated in the seal housing (5) with its working space (30a) lying in a line (20, 70, 74) connected with the chamber (14, 15, 44, 60), with its displacement member (31, 80) being driven against the force of a spring (33) by a cam (6, 49, 69) which is located on the shaft (1) or on a part (2, 40, 61) which rotates with the shaft and with one of its valves (21, 22) being arranged at the chamber (14, 15, 44, 60).

2. A seal in accordance with claim 1, characterised in that the suction valve (21) is arranged at the chamber (14, 15, 44) and the delivery valve (23) is arranged in a line (20, 74) leading away from the chamber.

3. A seal in accordance with claim 2, characterised in that the chamber containing the displacement pump (22) is a leakage space (14,44) for capturing liquids which seep through the seal elements (11,12,41,42) and in that the line (24) which adjoins the delivery valve (23) leads to a collecting tank.

4. A seal in accordance with claim 3, characterised in that a vent line (25) leads into the leakage space (14).

5. A seal in accordance with claim 2, characterised in that the chamber containing the displacement pump (22) is an annular chamber filled with a lubricant for the seal elements (12,13); and in that the line which adjoins the delivery valve (23b) leads to an oil cooler (76) disposed at a higher level; and in that a line (77) leads back into the chamber (15) from the oil cooler.

6. A seal in accordance with claim 1, characterised in that the chamber containing the displacement pump (22) is an annular chamber (60) which is filled with water; and in that the delivery valve (23) associated with the pump (22) lies in a line (70) which supplies water under pressure to the annular chamber (60), with the pressure of the water supplied through the line (70) being higher than the pressure of the sea water surrounding the seal arrangement.

7. A seal in accordance with claim 6, characterised in that the suction valve (21) is connected with the surrounding seawater via a filter (71).

8. A seal in accordance with one of the claims 1 to 7, characterised in that the displacement pump is constructed as a piston pump (22).

9. A seal in accordance with one of the claims 1 to 7, characterised in that the displacement pump is constructed as a membrane pump (22a,22b).

10. A seal substantially as herein described with reference to and as illustrated in any one of the accompanying Figues 1 to 5.