US 3413926 A
Description (OCR text may contain errors)
2 Sheets-Sheet 1 Filed Aug. 25, 1967 INVENTOR RICHARD AYSON BY Q 9 Mjw ATTORNEYS Dec. 3 1968 AYSON 3,
CENTRIFUGAL PUMP Filed Aug 25, 1967 2 Sheets-Sheet 2 FIGZ FIGS
INVENTOR RICHARD AYSON BY Cw ATTORNEYS United States Patent 3,413,926 CENTRIFUGAL PUMP Richard Ayson, Aurora, Ill., assignor to General Signal Corporation, a corporation of New York Filed Aug. 25, 1967, Ser. No. 663,317 1 Claim. (Cl. 103--111) ABSTRACT OF THE DISCLOSURE A centrifugal pump employing a taper fit between the impeller and drive shaft, and a seal sleeve for protecting the shaft from the wearing effects of the shaft seal. The sleeve is slidable on the shaft and is biased into abutment with the impeller by a dished ring spring made of coiled flat wire and seated in an annual peripheral groove formed in the shaft.
Background and summary of the invention This invention relates to centrifugal pumps, and particularly to centrifugal pumps employing a taper fit between the impeller and the drive shaft.
In the conventional centrifugal pump, the end of the drive shaft within the volute chamber is provided with a cylindrical portion on which is mounted an impeller which contains a matching cylindrical bore. The pump includes a seal device, of either the mechanical or packing box type, which retards leakage from the volute chamber along the shaft, and, since this device, or foreign particles lodged between it and the shaft, can score and Wear the shaft, it is customary to encircle the shaft with a replaceable protective sleeve. The sleeve is keyed to the shaft and is clamped between the rear surface of the impeller and a shoulder on the shaft when the impeller lock nut is tightened to force the impeller longitudinally along the shaft. With this arrangement, accumulated manufacturing tolerances present no problem since the impeller is free to assume whatever longitudinal position is necessary in order to insure a tight clamp up between the shaft shoulder and the lock nut.
When the conventional pump is in service, the pumped medium sometimes leaks into the small radial clearance between the shaft and the impeller and corrodes the mating surfaces of these parts. This increases the resistance to sliding of the impeller along the shaft and makes it difficult to remove the impeller from the shaft. In cases where the length-to-diameter ratio of the impeller bore is large, removal requires the use of special wheel pullers. This problem can be eliminated by employing a taper fit between the impeller and the shaft, since slight axial displacement of the impeller relatively to the shaft will separate the impeller from its seat, but, in the past, this solution has entailed elimination of the shaft sleeve. The reason for this is that the final position of the impeller relative to the shaft cannot be varied to accommodate manufacturing tolerances. Unless impractical tolerances are used, there is no way to guarantee both positive seating of the impeller, i.e., metal-to-metal contact between the tapered shaft portion and the wall of the tapered impeller bore, and firm clamping of the shaft sleeve between the shaft shoulder and the impeller. Since tolerance buildup in one sense would prevent positive seating of the impeller, and build-up in the opposite sense would give the sleeve freedom to oscillate along the shaft, it is evident that the conventional shaft sleeve arrangement cannot be used in a pump employing a taper fit between impeller and shaft.
The object of this invention is to provide an improved centrifugal pump incorporating both a taper fit between the impeller and the shaft, and a protective seal sleeve 3,413,926 Patented Dec. 3, 1968 for the shaft. In accordance with the invention, the seal sleeve is biased into abutment with the impeller by a dished ring spring formed of flat wire coiled on edge and seated in an annular peripheral groove formed in the shaft. The force and deflection characteristics of this type of spring have been found adequate to maintain a satisfactory static seal between the sleeve and the impeller while affording to the sleeve the degree of freedom required to accommodate tolerance accumulations. Since the sleeve in the improved pump is not part of a rigid connection between the impeller and the shaft, but is biased by a controlled force against the impeller, proper seating of the impeller on the shaft is guaranteed, and detrimental oscillations of the seal sleeve are precluded.
Description of preferred embodiment The preferred embodiment of the invention is described herein with reference to the accompanying drawings in which:
FIG. 1 is an axial sectional view of a typical horizontal axis centrifugal pump incorporating the invention.
FIG. 2 is an enlarged view of the shaft seal shown in FIG. 1.
FIG. 3 is an enlarged sectional view showing the installation of the ring spring.
FIG. 4 is a perspective view of the ring spring.
As shown in FIG. 1, the improved pump comprises a conventional casing 11, cover 12, adapter 13, power frame 14, base 15 and support 16, all of which are held together by bolts, Casing 11 encloses a volute chamber 17 which is provided with an axial inlet 18, and which contains the impeller 19. The impeller is formed with a tapered axial bore which matches and receives the tapered inner end of drive shaft 21, and the impeller and shaft are clamped together by a lock nut 22 which is threaded onto a stud 23 carried by the shaft, and which acts on the impeller through a washer 24. Gaskets 25 and 26, inter-posed between lock nut 22 and washer 24 and between washer 24 and impeller 19, prevent entry of the pumped medium into the impeller bore. A key 27 provides a positive drive connection between shaft 21 and impeller 19.
An insert 28, bolted to adapter 13, carries sealing device 29 which prevents leakage from volute chamber 17 along drive shaft 21. The sealing device 29 may be a mechanical seal or, as shown, a stacked series of packings. In either case, the seal device includesa protective, replaceable sleeve 31 which is free to slide along, but keyed to rotate with, drive shaft 21. At its right end, sleeve 31 carries an O-ring gasket 32 which is forced against the hub of impeller 19 by a ring spring 33 which reacts between drive shaft 21 and the left end of the sleeve. This spring 33 has a dished shape and is formed from a length of steel wire of rectangular cross section which is coiled on edge. It is seated in an annular groove 34 formed in the periphery of shaft 21. A suitable, commercially available spring of this type is marketed by the Ramsey Corporation under the :name Spirolox. The laminated construction of ring 33 permits large deflections without overstressing, but, in order to avoid localized yielding, the right wall of groove 34 is inclined or chamfered as shown in FIG. 3.
Spring ring 33 exerts a controlled force on sleeve 31 which, because of the substantially continuous zone of engagement, is distributed substantially uniformly around the circumference of the sleeve. The magnitude of the controlled force can be varied by changing the thickness of the material from which ring 33 is made, or by changing the number of turns. This controlled force insures positive compression of the static seal defined by O-ring 32, and thus renders the seal effective to prevent the pumped medium from contacting shaft 21.
Although I have illustrated and described one specific embodiment of the invention, it will be understood that the invention can be employed in various other types of centrifugal pumps.
1. A centrifugal pump characterized by (a) a drive shaft having a tapered end portion on which is mounted an impeller containing a matching tapered bore;
(b) a sleeve slidable on but fixed to rotate with the shaft and serving to protect the shaft from the Wearing eifects of a seal mechanism which encircles the shaft and is arranged to prevent leakage along the shaft;
(c) an annular peripheral groove formed in the shaft;
References Cited UNITED STATES PATENTS Wiltley 103-115 McHugh 287--53 Caserta 287-53 Carter 103115 Sence 103-115 RADUAZO, Primary Examiner.