Rotary kinetic fluid motors or pumps – With lubricating – sealing – packing or bearing means having... – For shaft sealing – packing – lubricating or bearing means
Reexamination Certificate
1998-03-31
2001-04-03
Verdier, Christopher (Department: 3745)
Rotary kinetic fluid motors or pumps
With lubricating, sealing, packing or bearing means having...
For shaft sealing, packing, lubricating or bearing means
C415S111000, C415S113000, C415S026000, C415S049000, C415S176000, C415S229000, C415S230000, C415S231000, C384S110000, C384S448000, C277S318000, C277S375000, C277S408000
Reexamination Certificate
active
06210103
ABSTRACT:
BACKGROUND TO THE INVENTION
In
FIG. 10
of RAMSAY, there is shown a bearing/seal system for a pump drive-shaft, based on the use of a tapered sleeve. The sleeve is cut with grooves, which, by virtue of the rotation of the sleeve, serve to pressurise a barrier liquid, and to drive the barrier liquid towards the process fluid being pumped. As described, the tapered sleeve arrangement serves as a bearing, which is located advantageously close to the pump impeller, and is a very efficient seal.
In RAMSAY, however, as far as the bearing is concerned, only a journal bearing capability was provided, in that the tapered sleeve was allowed to float axially, along the pump drive shaft. The axial or thrust location of the shaft was handled by a separate ball-bearing.
GENERAL FEATURES OF THE INVENTION
The present invention serves as a rotary-interaction apparatus. In one preferred option, the apparatus is formatted as, and used as, a bearing—either a journal bearing, or a combined journal-and-thrust bearing. In another preferred option, the apparatus is formatted as, and used as, a seal, for example in a pump, for sealing the pump shaft against escape of process fluid.
The apparatus includes a first pair of sleeves, comprising a first rotor sleeve and a first stator sleeve, having surfaces which together define a first surface-to-surface interface between them, the interface being of a first tapered configuration. The interface-surface of the first rotor-sleeve is provided with a first spiral groove, having an entry-mouth in liquid-flow-communication with an entry-chamber, for the supply of barrier-liquid into the groove. The first-spiral-groove is so disposed in the interface-surface of the first rotor-sleeve as to define plain lands of substantial width between adjacent turns of the groove, the lands being of such dimensions and configuration as to comprise, during rotation, a means for creating and supporting a hydrodynamic film of barrier-liquid between the interface-surfaces of the first pair of sleeves.
The apparatus also includes a second pair of sleeves, having characteristics similar to those of the first pair. The exit-mouth of the groove of the second pair of sleeves discharges barrier-liquid into an exit chamber.
Each of the pairs of sleeves may be understood as being derived, individually, from the RAMSAY reference.
Preferably, the first and second pairs of sleeves are arranged in the apparatus with the first and second tapered interfaces thereof in a co-axial, in-line, end-to-end, relative configuration.
As a seal, the two-pairs-of-sleeves apparatus is an excellent means for sealing a rotary shaft in a machine, for example a pump-housing. In a typical impeller-pump, the two sleeves can have an aggregate groove length of well over a foot (12 inches), and a correspondingly long aggregate interface, so the pressure-differential-gradient along the length of the interfaces may be very small.
Basically, the interfaces are not subject to wear under steady running conditions, if the hydrodynamic film remains stable operationally. Besides, as will be explained, any wear that might take place can be compensated for by biassing.
As a seal, it is simple enough, as will be explained, to arrange for the sleeves apparatus to be sealed off from, or to be open to, the process fluid, as operational requirements may dictate. It is also simple enough, as will be explained, for the pressures in the barrier-liquid to be monitored, to be compared with process pressure, to be regulated, etc. in accordance with operational requirements.
As a seal, the apparatus is tolerant of vibrations or sudden loading abuse, and is secure, reliable, and long lasting.
As a bearing, the apparatus makes an excellent bearing for supporting a rotary shaft in a housing or fixed frame. As a bearing, the apparatus is especially suitable for shafts that experience only light journal loads, such as the shafts of impeller-pumps when driven via a torque-only coupling. As a bearing, the apparatus is excellent at coping with vibrations, out-of-balance forces, and abusive factors (such as cavitation, dead-heading, etc), which can arise occasionally, either suddenly and shortlived, or gradually and progressively, and which can lead to a reduction in the length of service life.
As a bearing, the interfaces are lubricated by the barrier-liquid, and the hydrodynamic film ensures that direct contact sleeve-to-sleeve does not occur—at least during normal operation. Occasional abuse might cause the sleeves to touch, but the fact that two pairs of sleeves are present means that the interface area is very large, and occasional touching is insignificant.
Even if prolonged touching did occur, perhaps because of a change in operating conditions, because the interfaces are so large it is unlikely that failure would be immediate. Rubbing interfaces could be expected to last long enough for correction or repair to be planned for, with minimum disruption to the operation of the machine.
As a bearing, the apparatus has a very reliable lubrication system. Of course, if all the barrier-liquid leaks away, the bearing will fail. But it may be noted that the barrier-liquid only needs to be present at the entry chamber: there is no need for the barrier-liquid to be pressurised. Once the liquid enters the first groove, it is picked up by the groove and forced, under gradually increasing pressure, through the grooves and the interfaces, by the action of the groove itself.
It may be noted that in other lubrication systems that involve the circulation of liquid lubricant, the most common cause of failure is the circulation pump; in the present case, the “circulation pump” is actually a built-in facet of the bearing interface.
The barrier liquid may be oil, or may contain a trace of oil, but an aim of the invention is to provide a system that can use water as the barrier liquid. In pumping generally, it is a common requirement that leakage of process fluid to atmosphere is a secondary failure mode: that is to say, that the primary failure mode is that the barrier liquid leaks to atmosphere, or the barrier liquid leaks into the process fluid. In other cases, contamination of the process fluid by the barrier-liquid is paramount. The invention allows water to be used as the barrier-liquid, and enables a number of different failure modes to be engineered into the design, as will be explained, which makes the apparatus of the invention very versatile as to its applicability.
One noteworthy area of application of the invention is in magnetic-drive (mag-drive) pumps, of the kind in which the impeller shaft is placed inside an isolation chamber, and is driven magnetically through the walls of the chamber. In mag-drive pumps, the difficulty has been to separate the process fluid from the lubricant for the impeller-shaft-bearings. The invention permits this to be done in a mag-drive pump in a highly reliable manner, as will be explained.
As a bearing, the apparatus is axially long, which gives a good bearing spread, for stability during running. When the apparatus is used as a seal and a bearing combined, as in an impeller-pump, there is no need for a seal (or at any rate, no need for an axially-long seal) between the seal/bearing apparatus and the impeller on the end of the shaft. In other words, the overhang of the impeller beyond the bearings can be effectively zero. This lack of overhang also makes for excellent stability during running.
Also, the lack of overhang, even though the bearing is long, means the rotary-shaft can be thinner. In rotary machines, the major cost determinant usually is the base diameter of the shaft.
As will be described, it can be arranged that the interface clearance, i.e the clearance that is filled or bridged by the hydrodynamic film, can find its own dimensions; in that case, the slack or play in the bearing is effectively zero, and remains zero throughout the life of the bearing.
The apparatuses as described herein can be expected, under the correct operating conditions, to be unaffected by vibration, cavitation, dead-heading, an
A. W. Chesterton Co.
Rockey Milnamow & Katz Ltd.
Verdier Christopher
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