Rotary kinetic fluid motors or pumps – With lubricating – sealing – packing or bearing means having... – For shaft sealing – packing – lubricating or bearing means
Reexamination Certificate
1999-08-04
2001-03-13
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With lubricating, sealing, packing or bearing means having...
For shaft sealing, packing, lubricating or bearing means
C415S180000, C415S230000, C277S390000, C277S930000, C277S943000, C417S423800
Reexamination Certificate
active
06200086
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to mechanical seal assemblies, and more particularly to the control of heat generated in mechanical seal assemblies.
BACKGROUND OF THE INVENTION
Mechanical seal assemblies are used in a wide variety of applications to prevent a fluid from leaking therethrough. For example, mechanical seal assemblies are often used in centrifugal pumps which are used to transport a process fluid. A centrifugal pump typically comprises a rotating shaft with an impeller attached to one end of the shaft for pumping the process fluid. The shaft is driven by a motor either directly or indirectly through a transmission assembly such as a gearbox. As a result, the shaft extends from a motor or gearbox housing to a pump housing which encloses the impeller. The motor or gearbox typically requires lubricated bearings to support the rotating shaft. As a result, the mechanical seal assembly is used to contain lubricant inside the motor or gearbox, thereby preventing leakage into the process fluid.
The mechanical seal assembly typically comprises a rotating member which is attached to or otherwise rotates with the shaft and a stationary member which engages the rotating member to form a mechanical seal therebetween. As the shaft rotates, frictional heat is generated between the stationary and rotating members.
The frictional heat generated between the stationary and rotating mechanical seal members can become severe enough to damage other components located nearby. In certain types of pumps, for example, an inboard bearing journally supports the shaft and is typically located inside the gearbox to receive adequate lubrication. Because the impeller is cantilevered off one end of the shaft, however, it is desirable to locate the inboard bearing as close as possible to the impeller to minimize the overhung load and resulting shaft deflection. When the shaft is rotated, the heat generated by the mechanical seal assembly due to friction may be substantial and detrimental to components located in the immediate vicinity of the mechanical seal assembly. For example, the temperature at the inboard bearing may be elevated such that oil coking occurs, thereby causing premature bearing failure from lack of lubrication.
A previous mechanical seal assembly is known which attempted to address the frictional heat problem by forming a rotating member of the mechanical seal assembly out of ceramic, which is a non-heat-conducting material. While this device did reduce the amount of frictional heat reaching the inboard bearing, the amount of localized heat at the point of contact between the stationary and rotating member increased, thereby decreasing the life of the mechanical seal assembly.
SUMMARY OF THE INVENTION
A mechanical seal assembly has a heat barrier to control the amount of frictional heat conducting therefrom without decreasing the life of the seal.
According to one aspect of the present invention, a seal assembly is provided for a shaft rotatably supported in a bearing. The seal assembly comprises a stationary seal member positioned about the shaft and a mating member mounted on the shaft for rotation therewith and having a face in contact with the stationary seal member at which heat is developed during movement of the shaft. A thermal barrier is disposed between the mating member and the bearing.
In accordance with another aspect of the present invention, a mechanical seal assembly is provided for use with a shaft rotatably journaled in an inboard bearing. The assembly comprises a stationary seal member positioned about the shaft. A mating member is supported for rotation with the shaft and has a face engaging the stationary seal. Frictional heat is generated between the mating member and the stationary seal member as the mating member rotates with the shaft. A thermal barrier is sized to fit between the mating member and the inboard bearing, and comprises a non-heat-conductive material to prevent a portion of the frictional heat from conducting from the mating member to the inboard bearing.
In a preferred embodiment, the mating member comprises thermally conductive material to conduct heat away from the point of contact of the mating member and stationary seal member.
In accordance with yet another aspect of the present invention, a pump is provided for use with a motor. The pump comprises a rotatable shaft adapted to be coupled to the motor, an impeller attached to one end of the shaft, and a housing enclosing a portion of the shaft. A bearing is disposed inside the housing and journally supports the shaft. A mating member is attached to and rotates with the shaft, the mating member being positioned near the bearing. A stationary seal member is positioned to engage the mating member to form a mechanical seal so that frictional heat is generated between the mating member and the stationary seal member when the mating member rotates with the shaft. A thermal barrier is disposed between the mating member and the bearing, the thermal barrier comprising a non-heat-conductive material.
In a preferred embodiment, the pump further comprises a sleeve attached to and rotating with the shaft. The sleeve engages a side of the mating member opposite the thermal barrier and is disposed radially inward of the stationary seal member. The sleeve is formed of a thermally conductive material to transfer a portion of the frictional heat away from the inboard bearing.
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patent: 3411707 (1968-11-01), Zoehfeld
patent: 3652183 (1972-03-01), Pottharst, Jr.
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patent: 4363631 (1982-12-01), Wloka
patent: 4776759 (1988-10-01), Maskell et al.
patent: 5160246 (1992-11-01), Horiuchi
patent: 5186006 (1993-02-01), Petty
patent: 5375852 (1994-12-01), Charhut
patent: 5580216 (1996-12-01), Munsch
patent: 5626460 (1997-05-01), Franke et al.
Look Edward K.
McDowell Liam
Sundyne Corporation
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