Abstract:
Liquid ring pumps, of the type having a port structure that extends into an annular recess in an end of the rotor, have several parts that are designed so that they can be used to make pumps having either relatively demanding service requirements or substantially less demanding service requirements. Some of these parts can be substantially exactly the same in both final pump configurations. Others of these parts may be castings that differ substantially only in some subsequent machining in order to adapt them for each final pump configuration. Some of the final pump configurations have more compact mechanical seal structures and/or improved structures for supplying liquid to the seal structures.

Description:
This application claims the benefit of provisional patent application No. 60/186,263, filed Mar. 1, 2000, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to liquid ring vacuum pumps and compressors, and more particularly to constructions for such products which increase the number of parts that can be used in more than one product configuration. For ease of reference, the term “pump” or “pumps” is generally used herein as a generic term for both pumps and compressors. 
     Liquid ring pumps are typically designed so that a single pump design can serve a number of markets. Accordingly, the same basic pump may be used for different applications such as chemical processing, general industrial markets, and so on. Generally, chemical and petrochemical process applications require higher discharge and hydrostatic test pressure (i.e., liquid leakage pressure) capabilities and the use of special mechanical seals. These requirements are often not so stringent in general industrial applications. For example, in the chemical processing industry differential pressures to 30 psig and hydrostatic test pressures to 225 psig are common requirements. In comparison, for general industrial pumps the differential pressure capability required is typically about 15 psig and hydrostatic test is about 75 psig. Also, chemical industry pumps may have to meet certain industry specifications such as those set by the American Petroleum Institute or the Engineering Equipment and Materials Users Association. 
     Because a liquid ring pump may be needed for any of these markets, overall design is often based on meeting specifications for the more demanding chemical process applications. The resulting design is “optimal” for chemical applications, but may be “over-designed” for general industrial applications. Pumps of the type shown in Dudeck et al. U.S. Pat. No. Des. 294,266 (also known as the “SC” type of pump available from The Nash Engineering Company of Trumbull, Connecticut) are an example of this type of known pump design. To meet the more stringent requirements of chemical process applications, these pumps have removable bearing brackets to facilitate access to the mechanical seals. The seals are also provided with an external flush to cool the seal and help reduce erosive damage to the seal components. Features such as these are often not necessary for less demanding general industrial applications. Accordingly, the SC design may be a more costly one than is needed for such less demanding installations. On the other hand, it is also costly to provide completely separate designs that have been optimized for each possible application. 
     (It should be noted here that the SC pumps also use gas scavenging technology of the type shown in Schultze et al. U.S. Pat. No. 4,850,808, which is hereby incorporated by reference herein in its entirety.) 
     In view of the foregoing, it is an object of this invention to provide liquid ring pumps that can economically meet the requirements of several different types of service without all parts of the pump having to be entirely customized to each type of service. 
     It is another object of this invention to provide simplified lubrication of seals which can be used in at least some liquid ring pumps. 
     SUMMARY OF THE INVENTION 
     These and other objects of the invention are accomplished in accordance with the principles of the invention by providing liquid ring pumps having at least several major components that can be used or easily adapted for use in pumps having either of at least two significantly different designs, each of which is adapted to meet a respective one of two significantly different sets of service requirements. For example, although two different pumps may have such variations as different shaft diameter and shaft length between bearings, the two pumps may have several common rough parts such as the rotor, head, cone, and lobe, and may have common finished parts such as the lobe. To accomplish this in the case of the head, for example, that part may be cast with sufficient material in the shaft area so that this material can be machined out either for a relatively large shaft (for a higher pressure pump) or for a relatively small shaft plus a bearing (for a lower pressure pump). Similarly, in the case of the cone, that part may be cast with enough material in the shaft area so that it may be machined out either for the larger shaft or for a relatively small shaft plus mechanical seal components. 
     The pumps of this invention may also be constructed with features that simplify the provision and lubrication of seals, especially for pumps with less stringent seal requirements. For example, at one end of the pump the seals may be located inside the cone of the pump where they can be lubricated by the flow through the above-mentioned gas scavenging structure associated with the cone. At the other end of the pump, the rotor shroud may be perforated to facilitate a flow of liquid from the liquid ring to and past the seals at that end. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified sectional view of an illustrative prior art liquid ring pump. 
     FIG. 2 a simplified, composite, sectional view of portions of two different final pump constructions that can be made using several common or substantially common parts in accordance with the invention. In particular, the upper portion of FIG. 2 shows one of these two final pump constructions, and the lower portion of FIG. 2 shows the other of these two final pump constructions. 
     FIG. 3 is a simplified sectional view showing more of the pump shown in the upper portion of FIG.  2 . 
     FIG. 4 is a simplified sectional view showing more of the pump shown in the lower portion of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The typical prior art liquid ring pump  10  shown in FIG. 1 includes the following principal parts: stationary housing (or lobe)  20 ; stationary head  30  attached to one axial end of lobe  20 ; stationary cone (or port member)  40  mounted on head  30  and projecting into the interior of lobe  20 ; stationary bearing bracket  50  also mounted on head  30 ; stationary bearing bracket  60  mounted on the end of lobe  20  remote from head  30 ; shaft  70  rotatably mounted in bearings  52  and  62  in bearing brackets  50  and  60 , respectively; and rotor  80  mounted on shaft  70  for rotation therewith. As is conventional for liquid ring pumps, lobe  20  is eccentric to shaft  70  and contains a quantity of liquid (e.g., water) which the radially and axially extending blades  82  of rotor  80  form into a recirculating ring of liquid inside lobe  20 . On one circumferential side of pump  10  the inner surface of this liquid ring is moving radially out away from the central longitudinal axis of shaft  70 . Accordingly, on this side of the pump gas is pulled into the spaces between circumferentially adjacent rotor blades  82  via gas intake passages  32  and  42  in head  30  and cone  40 , respectively. On the other circumferential side of the pump the inner surface of the liquid ring is moving radially in toward the central longitudinal axis of shaft  70 . Accordingly, on this side of the pump gas is compressed between circumferentially adjacent rotor blades  82  and then discharged from the pump via discharge passages  44  and  34  in cone  40  and head  30 , respectively. (The connection of discharge passage  34  to the exterior is not visible in FIG. 1, but such a connection is nevertheless present in pump  10 .) 
     A stuffing box  36  is provided in head  30  around shaft  70  to accommodate packing or mechanical seals. Another similar stuffing box  26  is provided in lobe  20  around shaft  70 , again to accommodate packing or mechanical seals. (FIG. 1 actually shows packing in both stuffing boxes  26  and  36 .) Bearing brackets  50  and  60  are removable to facilitate maintenance of the packing or mechanical seals in boxes  26  and  36 . External liquid couplings (not shown) are provided to provide liquid to the packing or mechanical seals for such purposes as lubrication, cooling, contaminant flushing, etc. 
     With the various features that have thus been described, pump  10  is able to meet very stringent service requirements such as those that are often encountered in chemical processing. 
     FIG. 2 shows representative portions of two different pumps that can be constructed using several substantially common parts in accordance with this invention. Above the chain-dotted shaft centerline FIG. 2 shows a portion of a pump  110   a  which is designed to meet relatively stringent service requirements like those met by pump  10  in FIG.  1 . Below the chain-dotted shaft centerline FIG. 2 shows a portion of a pump  110   b  which is designed to meet less stringent service requirements. (The drive ends of the shafts in FIG. 2 are on the left rather than on the right as shown in FIG. 1.) Parts in FIG. 2 that are generally similar to parts in FIG. 1 have reference numbers that are increased by 100 from the reference numbers for the corresponding parts in FIG.  1 . (Although FIG. 1 suggests that the left-hand end of lobe  20  is closed by structure that is integral with the remainder of the lobe, FIG. 2 shows use of a separate end plate  190   a/b  for that purpose.) Also in FIG. 2, parts of pump  110   a  all have reference numbers with the suffix “a”, and parts of pump  110   b  all have reference numbers with suffix “b”. Although a part may thus be shown in FIG. 2 with both suffix “a” and suffix “b”, that part may in fact be one common part (e.g., a common casting with common machining), or one substantially common part (e.g., a common casting with only somewhat different machining). Particular examples of this commonality of parts will be discussed in more detail below. 
     Principal differences between pumps  110   a  and  110   b  in FIG. 2 are as follows: Shaft  170   a  is both longer between bearings  162   a  and  152   a  and larger in diameter than shaft  170   b . A more robust shaft is used in pump  110   a  because the distance between bearings  162   a  and  152   a  is greater and because pump  110   a  is designed for greater pressure. Pump  110   a  has a greater distance between bearings  162   a  and  152   a  for the same reason that pump  10  has a comparable distance between bearings, namely, to allow more room for more elaborate stuffing boxes and mechanical seals, and to facilitate access to those elements. Pump  110   b , on the other hand, can have its bearings  162   b  and  152   b  closer together because pump  110   b  does not need such elaborate stuffing boxes and mechanical seals. Because bearings  162   b  and  152   b  are closer together (and because pump  110   b  is designed for lower pressures), shaft  110   b  can be both shorter and smaller in diameter. At the right-hand end of pump  110   b  bearing  152   b  can be disposed directly in head  130   b  and no projecting bearing bracket comparable to bracket  150   a  is needed at all. In addition, mechanical seal  146   b  can be located inside cone  140   b  in lieu of stuffing boxes  136   a  in head  130   a  and an additional mechanical seal retainer  138   a  mounted on the outside of head  130   a  inside of bearing bracket  150   a . Similarly, at the left-hand end of pump  110   b , bearing  162   b  can be disposed in end plate  190   b . Mechanical seal  126   b  can be relatively close to the shrouded end of rotor  180   b . This is in contrast to the provision in pump  110   a  of more elaborate stuffing box  126   a  and bearing bracket  160   a  and mechanical seal retainer  198   a  mounted on the outside of end plate  190   a.    
     The pump constructions shown in FIG. 2 allow commonality of major components as follows: The same rough parts (e.g., the same castings) can be used for rotors  180   a  and  b , heads  130   a  and  b , cones  140   a  and  b , and lobes  120   a  and  b . The same finished parts (e.g., machined castings) can be used for lobes  120   a  and  b . For example, a generic rotor casting  180  can be made with a sufficiently small shaft opening that it can be machined out either by the relatively small amount required to accept relatively small diameter shaft  170   b  or by the relatively large amount required to accept relatively large diameter shaft  170   a . Similarly, a generic head casting  130  can be made with a sufficient quantity of metal surrounding the central shaft opening so that this metal can be machined out either to receive relatively large diameter shaft  170   a  and to form stuffing box  136   a  or to receive relatively small diameter shaft  170   b  plus bearing  152   b . In either case sufficient head metal remains to completely annularly surround elements  170   a  and  136   a  or elements  170   b  and  152   b . However, not so much metal is provided in that part of generic head  130  that adequate gas intake and discharge passages (comparable to passages  32  and  34  in FIG. 1) are not also provided in head  130 . Generic head  130  is also configured to receive either bearing bracket  150   a  and mechanical seal retainer  138   a  or a much simpler end plate  200   b . As yet another example, a generic cone casting  140  can be made with sufficient material in the shaft area so that this material can be machined out to receive either relatively large diameter shaft  170   a  or relatively small shaft  170   b  plus mechanical seal  146   b.    
     Common finished parts are possible for lobes  120   a  and  b.    
     Examples of principal parts that are not common between pumps  110   a  and  110   b  include shafts  170   a  and  170   b , left-hand end plates  190   a  and  190   b , and the more elaborate bearing brackets  150   a  and  150   b  that have to be provided for pump  110   a . Nevertheless, the ability to construct pumps  110   a  and  110   b  with several principal parts that are common or substantially common is a great cost saving for both pump configurations. 
     FIG. 2 also illustrates other features of the invention which will now be described. As was mentioned earlier, pumps  110   a  and  110   b  may be constructed with gas scavenging like that shown in Schultze et al. U.S. Pat. No. 4,850,808. A passage  220  is provided through cone  140   a/b  into the clearance between the outer surface of shaft  170   a/b  and the inner surface of cone  140   a/b  from just downstream of the compression zone of the pump. Any gas that does not exit from the pump via discharge passage  144   a/b  can flow through passage  220  into the annular clearance inside cone  140   a/b  around shaft  170   a/b . Just downstream from the intake zone of the pump another passage  222  is provided from this clearance through cone  140   a/b . Accordingly, gas that would otherwise be carried over from the compression zone to the intake zone, where it would reduce the intake capacity of the pump, is able to bypass the intake zone and therefore does not reduce the intake capacity. 
     The above-described bypass gas flow is typically accompanied by a substantial flow of liquid from the liquid ring. By constructing pump  110   b  with mechanical seal  146   b  inside cone  140   b  where the mechanical seal comes in contact with this liquid flow, pump  110   b  can take advantage of that flow to cool, lubricate, flush, and otherwise enhance the performance of seal  146   b . No external liquid supply is needed for seal  146   b . This is an additional cost saving and operating improvement of pump  110   b  in accordance with this invention. 
     Similar advantages can be achieved or enhanced at the other axial end of pump  110   b . In accordance with yet another aspect of the invention, holes  232  are provided in the annular shroud  230  at the left-hand end of rotor  180   a/b . Holes  232  allow liquid from the compression side of the liquid ring to flow out into the clearance around shaft  170   b  that is partly occupied by mechanical seal  126   b . On the intake side of the pump holes  232  allow this liquid to re-enter the liquid ring. This flow of liquid cools, lubricates, flushes, and otherwise enhances the performance of seal  126   b . Once again, this reduces or avoids the need for an external liquid supply to seal  126   b , with consequent cost savings and operating improvement for pump  110   b.    
     Although FIG. 2 is useful for facilitating direct comparison of pumps  110   a  and  110   b , more of pump  110   a  is shown in FIG.  3  and more of pump  110   b  is shown in FIG.  4 . In addition to what is shown in FIG. 2, FIG. 3 shows the provision of external liquid supply conduits  240  and  242  for supplying liquid to seals  126   a  and  136   a.    
     FIG. 4 shows more details of particularly preferred constructions of mechanical seals  126   b  and  146   b . In particular, FIG. 4 shows seal  126   b  constructed as a first annular component  126   b   1  mounted on shaft  170   b  for rotation therewith, and a second annular component  126   b   2  mounted on stationary end structure  190   b . Portions of the annular, axial end faces of components  126   b   1  and  126   b   2  abut one another and thereby provide the desired mechanical seal. Liquid (e.g., from apertures  232 ) can reach components  126   b   1  and  126   b   2  (and especially the proximity of their abutting axial end faces) to lubricate, cool, flush, and otherwise help maintain the mechanical seal. Mechanical seal  146   b  similarly includes a first annular component  146   b   1  mounted on shaft  170   b  for rotation therewith, and a second annular component  146   b   2  mounted inside port member  140   b . Portions of the annular, axial end faces of components  146   b   1  and  146   b   2  abut one another and thus provide a mechanical seal. Liquid (e.g., from aperture  220 ) can reach at least portions of components  146   b   1  and  146   b   2  (especially the proximity of their abutting axial end faces) in order to lubricate, cool, flush, and otherwise help maintain mechanical seal  146   b.    
     It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. For example, although the illustrative pumps shown herein have conical (actually frustoconical) port members  140   a/b , the principles of the invention are equally applicable to pumps having port members or structures with substantially cylindrical, radially outer surfaces.