Patent Application
20130113163
The described embodiments relate to a maintenance and emergency run secondary seal capable of operating as both a static and a dynamic seal to support a primary dynamic seal used in drive/propeller shafts for power driven vessels.
Power driven vessels (such as ships and in-board motor boats) include a drive or propeller shaft that connects an engine or transmission inside the vessel directly to a propeller. The propeller shaft extends through a stuffing box or other type of seal at the point it exits the vessel's hull. A primary dynamic seal encircles the vessel's propeller shaft to prevent water from entering the vessel during operation and when stopped. Conventional static maintenance safety seals have been proposed to provide a back-up in case of a typical primary dynamic seal failure. The problem with this type of arrangement is that conventional static seals only block water penetration when activated: use of the vessel is not recommended since the propeller shaft should not freely rotate after static maintenance safety seal activation due to the fact that friction of the engaged seal on the shaft creates heat that can destroy the seal.
Although emergency running safety seals have been proposed and are implemented in some vessels they are typically complex duplications of the primary dynamic seal and are thus not a cost effective solution in many applications.
As a result, there is a continuing need to improve maintenance and emergency run secondary seals that enable both static and dynamic seal functionality with a simplified structure and that can permit ready cost effective retrofitting to existing vessels or installation on new builds.
It is an object of the described embodiments to provide a maintenance and emergency run secondary seal for a vessel having a rotatable shaft that can provide both static and dynamic seal functionality to support a traditional primary dynamic seal in case of failure to enable a safe return to port for repair of a damaged primary seal.
Certain exemplary embodiments can provide a maintenance and emergency run secondary seal mountable to a rotatable shaft, the seal comprising: a housing; a sealing ring having a double-tapered receiving channel located between two exterior surfaces and an interior wear surface, the sealing ring being mounted in the housing; a lantern ring having a double-tapered profile for enabling engagement within the double-tapered receiving channel of the sealing ring to form an air chamber between the sealing ring and the lantern ring at a base of the double-tapered receiving channel; and means for directing and controlling pressurized air to the air chamber to enable three operating positions for the sealing ring: a first position where the sealing ring is spaced from the shaft, a second position where a portion of the interior wear surface of the sealing ring is closed-in on the shaft to enable an emergency run secondary seal to permit shaft rotation and a third position where the sealing ring is in full contact with the shaft to enable a static seal.
Certain exemplary embodiments can also provide a maintenance and emergency run secondary seal for a rotatable shaft having an axial direction, the seal comprising: a housing having an air track for receiving and directing pressurized air, the housing being mountable about the axial direction of the shaft; a sealing ring mounted in the housing and being in fluid communication with the air track of the housing, the sealing ring having an interior wear surface including a center region defined between an outboard edge and an inboard edge; and a lantern ring mounted within the sealing ring, the lantern ring having a plurality of air passages to enable pressurized air to pass through to the sealing ring, wherein the sealing ring being operable from a stand-by position where the sealing ring is spaced from the shaft in rotation; a partially activated position where a portion of the interior wear surface is partially closed-in to the shaft and a fully activated position where the interior wear surface is in full contact with the shaft.
The housing 12 also includes an air inlet 22 and an air track 24 for receiving and directing pressurized/compressed air. The air track 24 extends from the air inlet 22 to the pair of nested rings 16, 18. The sealing ring 16 and the lantern ring 18 are removably mounted in the housing 12 and can be individually serviced and replaced as required by removing the housing cover plate 14.
Further details of the sealing ring 16 are illustrated in the various views of
The size of the grooves 36 can range from 1.5 to 2.0 mm in width and from 1.0 to 1.5 mm in depth depending on the size of the sealing ring 16. The number of grooves 36 varies based on the diameter of the sealing ring 16. The diameter of the sealing ring 16 will vary based on the size of the rotatable shaft 50 mounted in the MERSS 10.
The sealing ring 16 has a double-tapered receiving channel 40 for receiving a matched double-tapered profile 42 of the lantern ring 18 (discussed further in
The sealing ring 16 is made from a hard, self-lubricating, elastomeric polymer alloy designed to reduce friction and frictional heat generation when in contact with a rotating shaft. The elastomeric material used in the seal ring 16 has a high mechanical strength and hardness (in the range of 85 to 95 A), and has appropriate elasticity, tear strength and abrasion resistance to provide a sealing function.
Further details of the lantern ring 18 are illustrated in the various views of
A magnified cross-section of the MERSS 10 mounted about a rotatable shaft 50 (such as a propeller shaft) having an outside surface 52 is illustrated in
Operating Positions
The MERSS 10 has three primary operating positions managed by controlling the displacement of the lantern ring 18 and expansion of the sealing ring 16 using pressurized/compressed air managed by a compressed air pressure generation and control system 54 (see
The three primary operating positions are:
(1) A stand-by (or deactivated) position: defined as the sealing ring 16 being spaced apart from the shaft 50. The MERSS 10 operates in this position when a primary dynamic seal of the vessel is functioning properly. The first deactivated position is illustrated in
(2) An emergency dynamic operating (or partially activated) position: defined as (a) a small center portion 70A of the sealing ring 16 being in slight contact with the shaft 50 as shown in
To deploy the MERSS 10 from the stand-by position to the emergency dynamic operating position compressed air is directed and controlled by the control system 54 to the air inlet 22 through the air track 24 in the housing 12 through the air passages 46 of the lantern ring 18 to deflect the sealing ring 16. By controlling the pressure of the compressed air using the compressed air pressure generation and control system 54, the flow directed through the air track 24 of the housing 12, will close-in the sealing ring 16 to the outside surface 52 of the shaft 50 to form the gap position 72 (
The double-tapered shapes of the lantern ring 18 and sealing ring 16 develops a clamping force between the sealing ring 16 and the engagement surfaces 64 of the housing 12 and cover 14 (see
(3) A secondary static sealing (or fully activated) position: defined as a significant portion 70B of the sealing ring 16 being in contact with the outside surface 52 of the shaft 50 to reduce water leakage to a level that will permit maintenance operations to be performed on a defective primary dynamic seal. The third fully activated position is shown in
To deploy the MERSS 10 from either the stand-by position or the emergency dynamic operating position to the secondary sealing position compressed air from the compressed air pressure generation and control system 54 is directed and controlled by the control system 54 to the air inlet 22 through the air track 24 in the housing 12 through the air passages 46 of the lantern ring 18 to deflect the sealing ring 16 effectively fully press the interior wear surface 30 against the outside surface 52 of the shaft 50 to provide an effectively water tight seal.
To return the MERSS 10 from either the secondary static sealing position or the emergency dynamic sealing position to the stand-by position air is bled from the sealing ring 16 by removing the compressed air flow from the air track 24 in the housing 12 using the compressed air pressure generation and control system 54. This air bleed operation will gradually separate the sealing ring 16 from the shaft 50 to return the sealing ring 16 to the standby position of FIGS. 5A/B.
In summary, embodiments of the MERSS 10 are designed to be used in conjunction with a conventional primary dynamic seal for a vessel's propeller shaft. The MERSS 10 is capable of functioning as a static maintenance safety seal to allow repair of sealing elements of the primary dynamic seal and for use as an emergency secondary dynamic seal that allows the vessel to return to port safely under its own power when the primary dynamic seal is damaged or becomes unserviceable during operation.
In particular, when a vessel is stopped in a safe location and all parts and technical expertise are available for a scheduled repair of a primary dynamic seal, the MERSS 10 can be pressurized to the fully activated position (FIGS. 5E/F) to effect a sufficiently watertight seal around the propeller shaft to allow the primary dynamic shaft seal to be repaired with no (or limited) entry of water into the vessel. However, if there is a failure of the primary dynamic seal while the vessel is sailing and it is not possible to stop and repair the primary seals, the MERSS 10 is pressurized to a lesser degree (FIGS. 5C/D) to effectively act as an emergency dynamic seal to allow the vessel to continue to sail (at a reduced speed) until it returns to port and repair of the primary dynamic seal can be safely performed. The MERSS 10 can function as a back-up primary dynamic seal by controlling the expansion of the sealing ring 16 (as discussed above) to permit shaft rotation and limiting the friction produced by close-in on a rotating shaft versus conventional safety seals requirement that there be no shaft rotation.
