US3076412A - Method and apparatus for maintaining rotating pump seals - Google Patents

Description

Feb. 5, 1963 J. H. HARKER ETAL Filed March 4, 1959 2 Sheets-Sheet 1 EX PA NSION NK 31 TA 2e BOILER R ffi/vefiar-s RAD/A 70R: Ha r'ler Raj 016W Ila/7Z6 52 I FROM mp/Amks @{lfid ji es. 29 25 fig g/ wvvz mu/ METHOD AND APPARATUS FOR MAINTAINING ROTATING PUMP SEALS Filed March 4, 1959 Feb. 5, 1963 J. H. HARKER ETAL 2 Sheets-Sheet 2 Wr/azzeisz f Kai 0 1 awa United States 3,076,412 METHOD AND APPARATUS FOR MAINTAiNlls G ROTATING PUMP SEALS John H. Harker, Park Ridge, Ralph W. Janetz, Park Ridge Manor, and Jack Keyes, Park Ridge, 11]., assrgrrors to Bell & Gossett Company, a corporation of Illinois Filed Mar. 4, 1959, Ser. No. 797,190 3 Claims. (Cl. 103-411) Applications involving the pumping of high-temperature liquids, which are now quite numerous, necessarily require that the pump parts, and this includes the rotating seal, also operate at high temperatures. Thus the seal structure is faced with rigorous conditions at the very outset.

. One pump application particularly subject to failure of the rotating pump seals is found in closed hot water systems for boilers. In these boiler systems the circulating pump is called upon to handle water at temperatures in the range of 185 F. to 250 F. and in many instances the water temperature is as high as 400 F.

In recent years, rotating seal assemblies of a type that has long been successfully employed in the seal wells of centrifugal pump constructions have suffered a severely high rate of failure when used in pumping systems handling high-temperature liquids.

In general the blame for this high rate of seal failures has been directed at the seal structure itself and while various alternative seal structures have been considered, the high failure rate remained and even increased as more applications involving pumping of higher temperature liquids came into being. Numerous instances are known where seal structures have failed after but a single days service.

The principal object of the present invention is to provide a method and apparatus for eliminating the high rate of failure of seal structures employed in pumps used in systems for handling high-temperature liquids.

A further object of the invention is to eliminate destructive overheating of the seal structures by continuously maintaining a supply of liquid in direct contact with the seal structures to ensure proper lubrication and cooling of the seal faces thereof.

Still a further object of the invention is to provide an improved closed hot water system wherein the circulating pump of the present invention is combined with means in the system for trapping air separating from the water in the system.

According to the teachings of the present invention, the failure of the pump seal structures employed in applications involving pumping of high-temperature liquids arises from the ability of high-temperature liquids to more readily release gas and the fact that the shaft rotating in the seal well tends to set up a centrifuging action and drive the liquid in the seal well in an outwardly swirling path in the general direction of shaft rotation. This centrifuging action encourages the release of gas from the liquid; and the liquid, being heavier, tends to occupy the outer region of the seal well and leave a gas pocket surrounding and thermally isolating the seal structure. When this condition exists, the heat generated at the seal is not carried away and the seal quickly overheats and fails.

Heating of the seals is also accelerated in the absence of liquid wetting and lubricating the seal faces.

The central gas pocket condition can arise even with liquids that are not heavily gas laden, since the heat generated locally at the seal tends to vaporize some of the liquid and the vapor is trapped around the seal in the form of a gas pocket.

Thus the solution to the present problem of seal failure is to maintain liquid in'contact with the seal structure, and

g 3,075,412 iQfi g ed Feb. 5., 1963' this is best accomplished by applying reaction forces to liquid tending to swirl in the seal well and thereby prevent, the establishment of a swirling ring of liquid. In the preferred practice of the invention, baffles are interposed in the seal well to disrupt the swirl path of the seal well liquid and the battles are preferably in the form of ribs rigidly secured to the wall structure that borders and defines the seal well.

Other objects and advantages will become apparent during the course of the following description.

In the accompanying drawings forming a part of this specification and in which like numerals are employed to designate like parts throughout the same:

FIG. 1 is a side-elevational view of a centrifugal pump incorporating the teachings of the present invention, with parts broken away and sectioned to facilitate the disclosure;

FIG. 2 is an enlarged sectional view of the seal well region of the pump of FIG. 1;

PEG. 3 is an end view of the pump seal plate of the preferred constructional embodiment;

FIG. 4 is an end view of an alternative seal plate construction in accordance with the invention; and

FIG. 5 is a simplified diagrammatic illustration of a closed hot water heating system to which the invention finds particular application.

For purposes of disclosure the invention is illustrated in its application to a conventional centrifugal pump, designated generally as 10.

The illustrated pump is of the type having a volutecasing 11 formed with a liquid inlet and suction passage 12 and a pressure chamber 13. Numeral 14 designates part of a bracket adapted for connection with a motor support (not shown). A rotatable drive shaft 15 extends through a seal plate 16 that constitutes one end wall of plate 15 includes wall structure 16W surrounding anddefining a seal well 18, and a conventional seal assembly is shown at iii in encircling relation to the shaft. The seal assembly may include a carbon ring 20 slidable relative to the shaft and mounted for rotation therewith. In

- the illustrated construction the seal plate receives a stationary seal ring 21 of Remite or other suitable seal face material that is mounted to present a seal face for engage. ment with the seal face of the rotatable carbon ring 20.

During normal operation of a pump of this type, the

seal well is filled by liquid returning from the pressure chamber along leakage paths such as are indicated by the arrows designated 22. The action of the rotating shaft continuously moves liquid around in the seal Well so that circulation of the seal well liquid continues at a rate normally sufficient to ensure proper cooling of the.

seal structure. It will be understood that the interengaging seal faces of the rings 20 and 21 continuously generate heat by friction, and it is important that liquid occupy the seal well for contacting the seal rings and lubricating and cooling these seal faces.

As explained previously, in recent years the failure rate of seal structures used in centrifugal pumps handling" motion by the action of the shaft rotating in the seal" well and this swirling motion encourages the liquid to, release gas, which is then trapped in a pocket that surrounds the seal structure. Thus the seal well liquid is effectively excluded from contact with the seal and it cannot properly cool and lubricate the seal. Failure results quickly when this gas pocket condition develops in the seal well.

Since the seal failure rate in centrifugal pumps handling high-temperature liquid is common to all presently known commercial pumps, the seal structure itself has been condemned by many in the field, but it will now be apparent that the problem does not reside in the seal construction, but, rather, in the pump arrangements which entertain the development of the gas pocket in the seal well.

Therefore, according to the present invention, the seal structure is cooled by continuously developing reaction forces against liquid tending to swirl outwardly in the seal well in the direction of shaft rotation to continuously divert or deflect such liquid back to the seal structure. Preferably, the reaction forces should be such that the basic centrifuging action never matures into the development of an actual gas pocket.

In the preferred practice of the present invention, the gas pocket is substantially eliminated by providing stationary deflector structure in the form of ribs on the seal plate wall structure that surrounds the seal well, with the ribs projecting into the seal well to intercept the path of liquid tending to swirl around the shaft in the direction of rotation. The number, arrangement, and configuration of the ribs may be variously altered and in many instances will depend mainly upon the running clearances existing in the seal well between the seal plate and the impeller. Any rib arrangement capable of preventing the swirling or centrifuging action of the liquid in the seal well to an extent sufficient to substantially continuously maintain liquid in contact with the seal structure will satisfactorily eliminate the present seal failure problem.

In the preferred construction, best shown in FIGS. 2 and 3, the ribs are shown at 24 and are ararnged in a common radial plane on opposite sides of the shaft to substantially fill a clearance space between the shaft and the outer seal well wall. Only two ribs are shown, as they have proven sufficient, but more can be provided.

In an alternative construction, the ribs 24' are shaped in the general form of inwardly spiralling blades projections across the seal well from the end wall thereof and spiralling inwardly in the direction of shaft rotation to divert and redirect liquid tending to swirl about the shaft along paths leading back to the seal structure, as indicated by the arrows designated 25. The arrangement of these blade-like ribs also acts to baffle the seal well for substantially preventing undesirable swirling of the liquid such as would cause separation of the liquid and gas. It should be understood that while it is preferred that the ribs extend a sufficient distance axially of the seal well to provide a substantially complete baffle, it is contemplated that they be located only at the region of the seal rings such that they would not totally preclude the development of an air pocket but that would nevertheless continuously supply sufficient liquid to the seal faces to effectively cool and lubricate them.

While. many straight-through type high-temperature pumping applications have been seriously hampered by seal problems of the type referred to, one particularly severe problem resides in the closed hot water heating system applications wherein water is handled at temperatures as high as 400 F. One such system is indicated diagramamtically in FIG. as including a hot water boilor 26 connected through a supply line 27 to one or more radiators 28. The circulating pump of the type described herein is connected in the supply line 27 so that the suction side of the pump is as close as possible to the point of no pressure change of the system. The water is returned to the boiler over a return line 29. The supply line includes a boiler fitting 30 which may be of the type illustrated in FIG. 2 of Tidds US. Patent No. 2,500,621, the disclosure of which, to the extent it is not inconsistent herewith, is specifically incorporated by reference. A branch line 31 extends from the boiler fitting 30, which is the point of no pressure change of the system, to a sutiable expansion tank 32 and includes a tank fitting 33 which may be of the type shown in FIG. 2 of Tidds US. Patent No. 2,395,697, the disclosure of which, to the extent it is not inconsistent herewith, is specifically incorporated by reference.

As is explained in these U.S. patents, the boiler fitting and tank fitting arrangements facilitate separation and trapping of air in the expansion tank and it has been found that when the pump construction 10, such as is shown in FIGS. 1-4, is employed as the circulating pump of a closed hot water system that is provided with suitable air separation and trapping equipment for the general purposes described in the aforementioned Tidd' patents, seal failure problems arising from, gas pocket formations in the seal well are eliminated. It will be appreciated, of course, that the invention allows substantial improvement in the seal performance in closed hot water heating systems that do not provide for effective separation and trapping of air, but important additional performance improvements are attributable to the combination of the present pump with the particular type of closed hot water heating system.

It should be understood that the invention finds general application to centrifugal pumps irrespective of the details of the seal structure itself and irrespective of detailed variations in the construction of the impeller and the pressure chamber of the pump.

it should be understood that the description of the preferred form of the invention is for the purpose of complying with section 112, title 35, of the US. Code and that the claims should be construed as broadly as prior art will permit.

We claim:

1. In a centrifugal pump of the type that includes a casing having a liquid inlet leading to a suction passage and a pressure chamber leading to a liquid outlet, said casing having wall structure bordering and defining a seal well with said wall structure having a single opening, a rotatable shaft projecting through said opening and seal well and carrying an impeller for rotation in said casing, and a seal assembly in said seal well and including relatively rotatable seal rings encircling said shaft to provide a seal across said shaft opening of said wall structure to substantially eliminate allfluid fiow from said seal well through said well structure, said pump having a running clearance leakage path existing between said impeller and said seal well Wall structure, said shaft being rotatable in said casing to rotate said impeller and draw liquid through said suction passage for discharge into said pressure chamber with said shaft rotation producing forces tending to swirl liquid in said seal well so as to create a solid liquid annulus that maintains a central gas pocket around said seal rings, means for preventing a gas pocket around said seal rings and including ribs stationarily fixed to said wall structure and projecting through said seal well for deflecting contact with liquid therein tending to swirl about said shaft for redirecting such liquid inwardly to the seal rings, said ribs extending from close proximity to points where said leakage path enters said seal cavity and leading towards the seal rings to prevent the establishment of a solid liquid annulus at any point in said seal well intermediate of said entrance points and said seal rings.

2. In a centrifugal pump of the type that includes a casing having a liquid inlet leading to a suction passage and a pressure chamber leading to a liquid outlet, said casing having wall structure bordering and defining a seal well with said wall structure having a single opening, a rotatable shaft projecting through said opening and seal well and carrying an impeller for rotation in said casing, and a seal assembly in said seal well and including relatively rotatable seal rings encircling said shaft to provide a seal across said shaft opening of said wall structure to substantially eliminate all fluid flow from said seal well through said wall structure, said pump having a running clearance leakage path existing between said impeller and said seal well wall structure, said shaft being rotatable in said casing to rotate said impeller and draw liquid through said suction passage for discharge into said pressure chamber with said shaft rotation producing forces tending to swirl liquid in said seal well so as to create a solid liquid annulus that maintains a central gas pocket around said seal rings, rigid rib structure on said seal well wall and projecting into the path of liquid swirling about said shaft to divert such liquid in different directions, said rib structure providing paths for diverting swirling liquid inwardly to said seal rings for eliminating a gas pocket therearound.

3. In a centrifugal pump of the type that includes a casing having a liquid inlet leading to a suction passage and a pressure chamber leading to a liquid outlet, said casing having wall structure bordering and defining a seal Well with said wall structure having a single opening, a rotatable shaft projecting through said opening and seal well and carrying an impeller for rotation in said casing, and a seal assembly in said seal well and including relatively rotatable seal rings encircling said shaft to provide a seal across said shaft opening of said wall structure to substantially eliminate all fluid flow from said seal well through said wall structure, said pump having a running clearance leakage path existing between said impeller and said seal well wall structure, said shaft being rotatable in said casing to rotate said impeller for drawing liquid through said suction passage and for discharging such liquid into said pressure chamber with said shaft rotation producing forces tending to swirl liquid in said seal well so as to create a solid liquid annulus that maintains a central gas pocket around said seal rings, stationary rib structure fixed to said wall structure and positioned in said seal well for deflecting contact with liquid therein tending to swirl about said shaft for redirecting such liquid inwardly to the seal rings, said rib structure extending from close proximity to points where said leakage path enters said seal cavity and leading towards the seal rings to prevent the establishment of a solid liquid an nulus at any point in said seal well intermediate of said entrance points and said seal rings.

References Cited in the file of this patent UNITED STATES PATENTS 768,911 Schoene Aug. 30, 1904 1,755,430 Crosthwait Apr. 22, 1930 1,832,398 Jennings Nov. 17, 1931 2,395,697 Tidd Feb. 26, 1946 2,402,995 Garraway July 2, 1946 2,500,621 Tidd Mar. 14, 1950 2,777,395 Disbrow Jan. 15, 1957 2,843,404 Janetz July 15, 1958 FOREIGN PATENTS 276,593 Germany July 15, 1914

Claims (1)

1. IN A CENTRIFUGAL PUMP OF THE TYPE THAT INCLUDES A CASING HAVING A LIQUID INLET LEADING TO A SUCTION PASSAGE AND A PRESSURE CHAMBER LEADING TO A LIQUID OUTLET, SAID CASING HAVING WALL STRUCTURE BORDERING AND DEFINING A SEAL WELL WITH SAID WALL STRUCTURE HAVING A SINGLE OPENING, A ROTATABLE SHAFT PROJECTING THROUGH SAID OPENING AND SEAL WELL AND CARRYING AN IMPELLER FOR ROTATION IN SAID CASING, AND A SEAL ASSEMBLY IN SAID SEAL WELL AND INCLUDING RELATIVELY ROTATABLE SEAL RINGS ENCIRCLING SAID SHAFT TO PROVIDE A SEAL ACROSS SAID SHAFT OPENING OF SAID WALL STRUCTURE TO SUBSTANTIALLY ELIMINATE ALL FLUID FLOW FROM SAID SEAL WELL THROUGH SAID WALL STRUCTURE, SAID PUMP HAVING A RUNNING CLEARANCE LEAKAGE PATH EXISTING BETWEEN SAID IMPELLER AND SAID SEAL WELL WALL STRUCTURE, SAID SHAFT BEING ROTATABLE IN SAID CASING TO ROTATE SAID IMPELLER AND DRAW LIQUID THROUGH SAID SUCTION PASSAGE FOR DISCHARGE INTO SAID PRESSURE CHAMBER WITH SAID SHAFT ROTATION PRODUCING FORCES TENDING TO SWIRL LIQUID IN SAID SEAL WELL SO AS TO CREATE A SOLID LIQUID ANNULUS THAT MAINTAINS A CENTRAL GAS POCKET AROUND SAID SEAL RINGS, MEANS FOR PREVENTING A GAS POCKET AROUND SAID SEAL RINGS AND INCLUDING RIBS STATIONARILY FIXED TO SAID WALL STRUCTURE AND PROJECTING THROUGH SAID SEAL WELL FOR DEFLECTING CONTACT WITH LIQUID THEREIN TENDING TO SWIRL ABOUT SAID SHAFT FOR REDIRECTING SUCH LIQUID INWARDLY TO THE SEAL RINGS, SAID RIBS EXTENDING FROM CLOSE PROXIMITY TO POINTS WHERE SAID LEAKAGE PATH ENTERS SAID SEAL CAVITY AND LEADING TOWARDS THE SEAL RINGS TO PREVENT THE ESTABLISHMENT OF A SOLID LIQUID ANNULUS AT ANY POINT IN SAID SEAL WELL INTERMEDIATE OF SAID ENTRANCE POINTS AND SAID SEAL RINGS.

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