US2641190A - Balanced impeller for centrifugal pumps - Google Patents

Description

June 9, 1953 1-. w. JOHNSON BALANCED IMPELLER FOR CENTRIFUGAL PUMPS Filed NOV. 22, 1949 2 Sheets-Sheet 1 INVENTOR.

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June 9, 1953 Filed NOV. 22', 1949 T. W. JOHNSON BALANCED IMPELLER FOR CENTRIFUGAL PUMPS FIG. 3

2 Sheets-Sheet 2 v IN VEN TOR.

T HOMAS W OHNSON BY Patented June 9, 1953 BALANCED IMPELLER FOR c'ENTRIFUGAL PUMPS Thomas W. Johnson, Parsippany, N. J., assignor to Bendix Aviation Corporation, Teterboro, N. J a corporation of Delaware Application November 22, 1949, Serial-No. 128,813

The present invention relates to centrifugal pumps and particularly to means and methods for balancing the axial reactive forces on the impellers thereof.

r The action of the impeller during the opera- 5 of theinvention. tion of the pump is to hurl the fluid into the de- Referring to the drawin wherein like referlivery chamber from the impeller chamber thereenee characters designate l p r by causing a pressure gradient to exist about Fig. 1 iS an ele p y in section of a the impeller. The effect of this pumping action Centrifugal P p assemblyis to cause more fluid to flow into the pump cas- 8 2 is a perspective view of the impeller, rear ing, and as the action of the impeller is conce upw rdstinuous, the pressure gradient above-mentioned 3 is a View Showing the'lelative magnitude remains continuously across the impeller. Be- 0f the unbalanced areas of e peller. cause of the difference in area of the face of the Referring H W t th draw s d more p rear shroud and the face of the front shroud of ula y to F a Ce t fugal pump generally the impeller, the impeller and shaft are subdesig by he numeral 10 comprises a casjected to an undesirable axial thrust, illg l2 and inlet l4 and outlet is. The casing It is, therefore, one of the objects of the presit contains an impeller chamber 18, having front ent invention to provide a novel method of baland rear walls It and 2|, respectively, and where-' ancing the impeller means whereby the foregoing in the impeller 29 is free to rotate, driven y the disadvantage is eliminated, and to do so in a a t 22 which is coupled to the source of ronovel and effective manner. tary power 24. Casing l2 also contains an outlet Another object of the invention is to provide chamber l8a peripherally disposed about impeller an impeller for a centrifugal pump whereby sevof chamber I8 and communicating therewith. The eral of the power losses now present are elimseal 26 of the shaft 22 is considerably smaller in mated, diameter than inlet conduit 28, which difference Another object of the invention is to provide contributes-to the unbalance of the axial loads on an impeller for a centrifugal pump whereby the impeller as hereinafter explained. A seal shallow grooves of a specified size and number encompasses e aft 2 and prevents leakage on the rear of the shroud act as non-deliver- 3 from the chamber l8. The impeller 20 includes ing centrifugal pumps so as to create a pressure a front shroud 32 and a rear shroud 34 held on the shroud to balance the other fluid forces together by pins 35. Vanes 31 are provided thereon. in the'rear shroud 34 and open from the interior Still another object of the invention is to proof the impeller 20 to the chamber 18 and outlet vide a balanced impeller for a centrifugal pump 35 chamber 18a. 7 I thereby obviating the necessity for thrust bear- During normal operation of the pump, a clearings on the impeller. ance space A between the front shroud 32 of the Another object of the invention is to balance impeller and the front wall IQ of impeller chamth fgrces on t impeller of a t if l pump ber l8, and a clearance space B between the rear in such a manner to permit a shorter overall 40 Shroud 34 0f e i p and the rear Wall 2| pump length of chamber l8 are filled with fluid from the Still another object of the invention is to inoutlet chamber |8a and therefore, the shrouds crease the efficiency of a centrifugal pump by 32 and 34 are subjected to pressure therefrom eliminating the energy losses caused by the longiover the surfaces 36 and 38, respectively (Fig. 3). tudinal pull on the impeller. Referring now to Fig. 2, the rear shroud 34 of Still another object of the invention is to prothe impeller 20 contains a series of relatively vide means of the above-indicated character shallow slots 40 radially disposed about the which shall be simple and economical to manperiphery thereof and extending towards the ufacture and install, yet positive and reliable in shaft 22. The length L of the slots 40 is adjusted operation. as hereinafter explained depending upon the The foregoing and other objects and adrelative unbalance of the impeller. vantages will appear more fully hereinafter from Having thus explained the invention, it will a consideration of the detailed description which now be apparent to those skilled in the art that follows, taken together with the accompanying when a fluid from the inlet I4 is drawn into the drawings, wherein one embodiment of the invenimpeller 20 and hurled against the walls of the 2 Claims. (01. 103-103) tion is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration only, and are not to be construed as defining the limits outlet chamber [8a for ejection through the outlet It, all of the clearance space between the front shroud 32 and on the surface 38 of rear shroud 34. the rear shroud 34 and rear wall 2! of chamber [8 will become filled with fluid which will exercise a pressure on the surface 36 of the front shroud 32 and on the surface 32 of rear shroud 34.

Since the surface 38 is greater than the surface 36, partly because of the greater diameter of the inlet conduit 28 compared to the seal 24 of the shaft 22, the pressure on the rear Shroud 34 would ordinarily be greater than the pres. sure on the front shroud 32 thereby causing an undesirable axial component in the direction of the inlet I4. However, the slots 40 in the rear shroud 34 impart a turning swirling action to the fluid between the face 01 the rear shroud, 34 and the adjacent rear wall IQ of chamber I8, and in effect act as non-delivering centrifugal pumps, with the result that the total pressure on the rear shroud 34 is reduced tending to balance ra her than over ome the pr ssure on the front shroud, 32.

It is to be noted that the invention permits extremely finite balancing of the impeller forces since the shallow grooves 40 may first be cut of insufficient length L to balance the impeller, and the operation tested and then gradually increased in length L after each test run, there. bygradually approaching and ultimately reaching the precise balance point.

There are thus provided means for balancing the forces on the impeller of a centrifugal pump which are simple and economical to manufacture and yet positive and reliable in operation and which obviate the necessity for expensive thrust bearings.

It is further to be noted that the invention accomplishes the balancing of the impeller without the necessity of increasing the overall pump length since the fluid swirling means are contained within the impeller itself without protruding therefrom.

Although only one embodiment and one ap-s plication of the invention has been illustrated and described, other changes in form and relative arrangements of the parts may be made to suit requirements.

What is claimed is:

1. In a centrifugal pump of the type including a casing, an impeller chamber in said casing having front and rear walls, an axial inlet said front wall, an outlet including an outlet chamber peripherally disposed about said im-, peller chamber, and an impeller mounted for rotation in said impeller chamber, said impeller having front and rear shrouds arranged in spaced relationship with the front and rear walls of said impeller chamber and pumping vanes interposed between said front and rear shrouds, said inlet opening into the interior of said im-. peller whereby the rotation of said impeller pumps a fluid from said inlet to said outlet, and said impeller being effected by an unbalanced pressure distribution over the inner and outer surfaces of the front and rear shrouds upon Cal the pumping of a fluid as aforesaid, the improvement comprising a plurality of shallow grooves formed in the outer radial surface of said rear shroud opposite said inlet, said grooves extending radially inwards from the periphery of said rear shroud and effective upon the retation of said impeller to rotate the fluid between said rear shroud and the wall of said impeller chamber adjacent said rear shroud whereby the rotational velocity of the rotating fluid is greatest adjacent the periphery of said rear shroud and the forces produced on the surface of said rear shroud by said rotating fluid are effective to balance the summation of all forces acting on the remaining surfaces of said impeller.

2', In a centrifugal pump of the type including a casing, an impeller chamber in said casing having front and rear walls, an axial inlet in said front wall, an outlet including an outlet chamber peripherally disposed about said impeller chamber, and an impeller mounted forrotation in said impeller chamber, said impeller having front and rear shrouds arranged in spaced relationship with the front and rear walls of said impeller chamber and pumping vanes interposed between said front and rear shrouds, said inlet opening into the interior of said impeller whereby the rotation of said impeller pumps a fluid from said inlet to said outlet, said rear shroud having a greater outer surface than the outer surface of said front shroud whereby a greater force is produced on said rear shroud upon rotation of said impeller to pump a fluid from said inlet to said outlet;- the improvement comprising a plurality of radial grooves formed in the outer surface of said rear shroud, said radial grooves extending inwardly from the periphery of said rear shroud and terminating short of the center thereof, said radial grooves being effective upon the rotation of said impeller to produce a whirling of the fluid between said rear shroud and said rear wall to thereby produce a pressure distribution on the outer SUI. face of said rear shroud decreasing proportionately from a high value adjacent the periphery of said radial grooves toward a lower value adjacent the inner ends thereof whereby the forces on the front and rear shrouds are equalized.

THOMAS W. JOHNSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 633,732 Price Sept. 26, 1899 2,228,207 Forssell Jan. 7, 1941 2,247,813 Huitson July 1, 1941 2,361,521 Yates Oct. 31, 1944 FOREIGN PATENTS Number Country Date 443,332 Germany Apr. 26, 1927 698,291 France s Nov. 17, 1930

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