SEALS

Abstract: A gas tight seal comprises a retaining means (5) adapted to be mounted on a partition (l) to surround a rotary component (l0) where it penetrates the partition (l). A pair of annular floating members (3) are located in axially spaced apart relationship by said retaining means (5). Sealing means (9; 20) are provided between the inner periphery of the floating members (3) and the rotary component (l0), these sealing means (9; 20) being arranged to make sealing engagement with the rotary component (l0) when liquid under pressure is introduced into the space (8) between the floating members (3).

Description: This invention relates to seals and in particular seals for use where a rotary component passes through a partition which separates one chamber from another. British Patent Specification GB 2 l09 875B discloses a bulkhead seal which remains substantially inoperative until one side of the bulkhead is flooded, when exposure of the sealing element to the liquid or liquid pressure differential causes it to make sealing engagement. The liquid in the flooded compartment in addition to actuating the seal also lubricates and cools the sealing elements, so that the rotary component passing through the bulkhead may be used without undue risk of premature failure of the bulkhead seal. There is now a requirement to provide a bulkhead seal which, when in operation is gas tight, so that hazards such as gas, smoke or chemical vapours may be confined to one side of the bulkhead. The seal disclosed in GB 2 l09 875B is not suitable for this purpose as it relies on the presence of liquid for actuation, lubrication and cooling. According to one aspect of the present invention a seal for producing a gas tight closure between a rotary component and a partition separating two chambers, where the rotary component penetrates the partition comprises; retaining means adapted to be mounted on the partition so as to surround the rotary component as it passes through the partition, said retaining means being arranged to locate a sealing assembly in a manner which will permit limited radial movement of the rotary component relative to the retaining means, said sealing assembly including an annular floating member the inner periphery of which is dimensioned to provide a small clearance about the rotary component and sealing means adapted to be interposed between the inner peripheral surface of the floating member and the opposed surface of the rotary component, said sealing means being arranged to seal the gap between the floating member and the rotary component and the floating member being arranged to make sealing engagement with the retaining means upon exposure to liquid on one side of the sealing assembly; characterised in that the retaining means defines a pair of axially spaced annular formations, each formation locating a separate sealing assembly in spaced apart relationship to define a annular chamber therebetween, an inlet being provided to the chamber by means of which liquid may be introduced into the chamber to cause the sealing assemblies to come into sealing engagement with the rotary component and the retaining means. In operation, under normal conditions, the sealing elements of the seal disclosed above are not in sealing engagement and will be subjected to little wear as there is little frictional engagement between the sealing elements and rotary component. It is only in an emergency that the chamber between the floating members would be flooded with liquid to bring the sealing elements into sealing engagement and provide a gas tight seal. The liquid which is retained in the annular chamber between the floating members will provide lubrication and cooling of the sealing elements and will also contain any gas that leaks past the sealing elements. As the floating members are free to move radially of the axis of the rotary component, the clearance between its inner surface and the rotary component may be quite small, while still accommodating out-of-centre and angular movement of the rotary component. Furthermore, the sealing action is not dependent on rotation of the rotary component and will consequently function whether the component is rotating or not. Actuation of the seal by introduction of liquid into the space between the floating members, may be controlled manually or automatically by, for example smoke or gas detectors. In addition to providing a gas tight seal the seal of the present invention will also provide a fluid tight seal, in the manner disclosed in British Patent Specification GB 2 l09 875B, in the event that a chamber on one side of the partition is flooded. The sealing means may be arranged to be brought into sealing engagement upon introduction of liquid into the space between the floating members, as a result of the pressure differential exerted by the liquid. Alternatively the sealing means may be brought into action as a result of physical change in the sealing means resulting from its exposure to the liquid, for example the sealing means may swell upon contact with the liquid. Various embodiments are now described, by way of example only, with reference to the accompanying drawings in which: Figure l shows a part-sectional elevation of a seal formed in accordance with the present invention, and Figure 2 shows a part-sectional view of an alternative form of sealing means that may be used in the seal construction shown in Figure l. As illustrated in Figure l, a seal for sealing a ship's bulkhead l where it is penetrated by a propeller shaft l0 comprises a retaining means or housing 5 which is bolted to the bulkhead l by means of a series of circumferentially spaced bolts 7, so that it surrounds the propeller shaft l0. The housing 5 defines a pair of inwardly directed annular recesses ll which are spaced axially with respect to the propeller shaft l0. A pair of annular floating members 3 are mounted one in each of the annular recesses ll, so that they extend radially from the recesses ll. The opposed surfaces l2, l3 of the recesses ll and floating members 3 are lapped, so that when in engagement they will provide a liquid tight seal. A small clearance is provided between the surfaces l2, l3 so as to provide only limited axial movement of the floating members 3. A substantial clearance is provided between the outer periphery l4 of the floating members 3 and the cylindrical surface l5 of the recesses ll so that the floating members 3 are free to move radially to accommodate any axial misalignment of the shaft l0. Each of the floating members 3 surrounds the shaft l0, there being a small clearance between the inner periphery l6 of each member 3 and the shaft l0. The inner periphery l6 of each member 3 is provided with a groove l7 the walls l8 of which are inclined to the axis of the shaft l0. An elastomeric O-ring 9 is slidingly located around the shaft l0, within the groove l7, so that when in the central portion of the groove l7 it will be clear of the surface of the member 3, over most of its circumference. An inlet 2 is provided in the housing 5 and passes through the annular flange 2l which separates the recesses ll opening into the annular space 8, so that liquid under pressure may be introduced into the annular space 8 between the floating members 3. In operation, under normal circumstances, the O-rings 9 will be free to revolve around or with the shaft l0 and will only be in partial, light contact with their associated floating member 3 and will not consequently be subjected to any significant wear. However, in an emergency, liquid under pressure may be supplied from an appropriate source, through inlet 2 into the space 8 between the floating members 3. The pressure of this liquid will force the floating members 3 apart so that the opposed surfaces l2, l3 of the floating members 3 and housing 5 abut and make sealing engagement with one another. The liquid pressure will also force the O-rings 9 into contact with the inclined walls l8 of grooves l7 and the shaft l0 to provide a liquid tight seal between the floating members 3 and shaft l0. The liquid is thus contained in a liquid tight annular chamber between the floating members 3 and forms a gas tight seal between the compartments separated by the bulkhead l. Introduction of liquid into the space between the floating members 3 to effect emergency operation of the seal may be controlled manually or triggered automatically in response to an emergency. Furthermore, should the chamber on one side of the bulkhead become flooded, the pressure of water in that chamber will cause surface l3 the floating member 3 remote from the flooded compartment to move into sealing engagement with surface l2 the housing 5 and the O-ring 9 to engage the opposed surfaces of the groove l7 and shaft l0, to provide a liquid tight seal which will prevent leakage into the chamber on the other side of the bulkhead. In a modification of the above embodiment, the elastomeric O-rings 9 may be located within grooves on the shaft l0, the O-rings 9 and grooves l7 being dimensioned so that as the floating members 3 move into sealing engagement with the opposed surfaces l2 of the housing 5, the inclined walls of the grooves l7 also engage the O-rings 9. In a further modification of the above embodiment the O-rings may be replaced by strips having strands of material, for example nylon which form soft bristles. The strip is located in a recess in groove l7, so that under normal circumstances the strands will sweep lightly over the opposed surface of shaft ll. However when liquid is introduced into chamber 8 the liquid pressure will deflect the strands into the narrow gap between surface l8 of groove l7 and the shaft ll thereby blocking the gap and providing a liquid tight seal. In the embodiment illustrated in Figure 2 in place of the O-rings 9 the groove l7 in the inner periphery l6 of the floating members 3 is packed with a material 20 which will absorb liquid and swell. In this manner under normal operating conditions the floating members 3 will have a clearance on the shaft l0, but when liquid is introduced into the space between the floating members 3, liquid seeping through the gaps between the floating members 3 and shaft l0, will be absorbed by the material 20 which will swell to seal the gaps between the floating member and shaft, thereby forming a fluid tight seal. The packing material 20 may be a natural material such as softwood or may be a suitable synthetic material. The material 20 may be permanently anchored in the groove l7 or may be arranged to leak into the gap between the floating member 3 and shaft l0, so that as it swells, it will seal off the gap. In the latter case, the material may conveniently be a combination of a soluble material with a sealant in the form of fibres or particles which will swell in contact with liquid, so that as the soluble material dissolves the fibres or particles are free to fill the gap between the floating member 3 and shaft l0. In the embodiment described above, the floating members 3 permit free out-of-centre rotation and angular movement of the shaft, so that under normal circumstances, the sealing members would not be subject to undue wear. Preferably the floating members 3 are formed from light material such as a reinforced plastic. In the embodiment illustrated in Figure l, the housing 5 is formed in two halves and is secured together by a series of bolts 6; and the floating members 3 are formed in two halves which are secured together by means of tangential bolts 4. This construction enables the seal to be fitted or replaced without removal of the propeller shaft. However, one piece components may be used where removal of the shaft is not a problem.

Claims: 1. A seal for producing a fluid tight closure between a rotary component (l0) and a partition (l) separating two chambers where the rotary component (l0) penetrates the partition (l), said seal including retaining means (5) adapted to be mounted on the partition (l) so as to surround the rotary component (l0) as it passes through the partition (l), said retaining means (5) being arranged to locate a sealing assembly (3, 9; 20) in a manner which will permit limited radial movement of the rotary component (l0) relative to the retaining means (5), said sealing assembly (3, 9; 20) including an annular floating member (3) the inner periphery (l6) of which is dimensioned to provide a small clearance about the rotary component (l0) and sealing means (9; 20) adapted to be interposed between the inner peripheral surface (l8) of the floating member (3) and the opposed surface of the rotary component (l0), said sealing means (9; 20) being arranged to seal the gap between the floating member (3) and the rotary component (l0) and the floating member (3) being arranged to make sealing engagement with the retaining means (5) upon exposure to liquid on one side of the sealing assembly (3, 9; 20); characterised in that the retaining means (5) defines a pair of axially spaced annular formations (ll), each formation (ll) locating a separate sealing assembly (3, 9; 20) in spaced apart relationship to define a annular chamber (8) therebetween, an inlet (2) being provided to the chamber (8) by means of which liquid may be introduced into the chamber (8) to cause the sealing assemblies (3, 9; 20) to come into sealing engagement with the rotary component (l0) and the retaining means (5). 2. A seal according to Claim l characterised in that the retaining means (5) defines a pair of annular recesses (ll) opening inwardly, the floating members (3) being located between radial walls (l2) of the recesses (ll) and having radially opposed surfaces (l3) which are capable of making liquid tight engagement with the walls (l2) of the recesses (ll), in response to the axial pressure applied to the floating members (3) by exposure to liquid on one side of the floating member (3). 3. A seal according to Claim 2 characterised in that a radially inwardly directed flange portion (2l) separates the two recesses (ll), the inlet (2) to the annular chamber (8) being provided through this flange portion (2l). 4. A seal according to any one of Claims l to 3 characterised in that the sealing means (9) associated with each of the floating members (3) seals the gap between the inner peripheral surface (l8) of the floating member (3) and the opposed surface of the rotary component (l0) as a result of pressure differential exerted by exposure to liquid on one side of the floating member (3). 5. A seal according to Claim 4 characterised in that the inner peripheral surface of each floating member (3) is provided with an annular groove (l7) with inclined walls (l8) and an elastomeric O-ring (9) positioned between the rotary component (l0) and the floating member (3) within the groove (l7) so that when subjected to a pressure differential the elastomeric O-ring (9) will be wedged between one of the inclined surfaces (l8) of the groove (l7) and the rotary component (l0) to form a seal therebetween. 6. A seal according to Claim 5 characterised in that the elastomeric O-ring (9) is located within a groove in the rotary component (l0). 7. A seal according to any one of Claims l to 3 characterised in that the sealing means (20) undergoes a physical change, upon exposure to liquid, this change causing the sealing means (20) to close the gap between the inner peripheral surface (l8) of the floating member (3) and the rotary component (l0). 8. A seal according to Claim 7 characterised in that the sealing means (20) swells upon exposure to liquid. 9. A seal according to any one of the preceding claims characterised in that the retaining means (5) and the floating members (3) are formed in a plurality of arcuate parts which may be secured together about the rotary components (l0).

Inventors: BRISTOW, PETER
Applicants: JOHN CRANE UK LIMITED
Application year: 1986
Main classification: B63H23
IPC codes: B63H23, F16J15