US2262191A - Pump - Google Patents

Description

l.. F. MOODY Nov. 11, 1941.

L. F. MOODY 2 .Tv h O Q 2 4wd Y s A D R E t N um R h l MN m S 2 E T 2 a rw A 2 .E l j w E Vl L. B

PUMP

Flled June 26 1940 :E in'.

AIR v-f Patented Nov. A11, 1.94.1

UNITED STATES" PATENT OFFICE PUMP Lewis F. Moody, Princeton, N. J. Application June 26, 1949, sei-nino. 942,465

4 Claims.

This invention relates to pumps, and more particularly to means for preventing cavitation and for preserving steady ow in propeller and other centrifugal pumps.

In centrifugal pumps and particularly propeller pumps operated at off-normal discharge capacities, strong whirl of the fluid pumped may Vbe created in the suction space or inlet of the pump and propagated against the flow of the impeller. Such whirl increases towards the axis according to the law of constancy of moment of momentum and creates a void around the axis in the forni a a tubular cavity. Condensable vapor accumulates in such cavity and its sudden condensation under unsteady iiow conditions causes disturbances similar to explosions, generating local pressures which attack the metal of the pump, resulting in pitting of the pump parts with corresponding reduction in their longevity and efficiency. Moreover, the repeated formation and collapse of such .vapor lled space, known as cavitation, interferes with the steady flow operation of the pump and may cause serious vibration.

It is an object of the present invention to provide means which will prevent or reduce the formation of such vapor filled spaces or cavities in the pump suction space, will relieve the high local vacuum, and replace Water vapor with air, and consequently eliminate pitting of the pump parts, surging in the pump discharge and unstable performance of the pump.

More speciiically the present invention comprehends the prevention of the formation of vacuous or vapor lled cavities or spaces about the axis of the suction space of a centrifugal pump by the provision of radial guide vanes and the introduction, preferably through the vanes, of air under atmospheric or higher pressure into such cavities or spaces to break up the formation of the cavities and prevent the detrimental effects of their formation on the pump structure and its performance.

With these and other objects in View, as may appear from the accompanying specication, the invention consists of various features of construction and combination of parts, which will be iirst described in connection with the accompanying drawings, showing a pump of the preferred form embodying the invention, and the features forming the invention will be specifically pointed out in the claims.

In the drawings:

ugal pump of the propeller type constructed in accordance with the present invention.

Figure 2 is a horizontal section on the lin'e 2 2 of Figure 1.

Figure 3 is a detail section of the line 3--3 of Figure 1.

Figure 4 is a vertical section through a modified form of the pumpr showing the invention applied to a centrifugal pump of the closed impeller type.

Figure 5 is a detail section on the line 5-5 of Figure 4.

Referring more particularly to the drawings, Figures l to 3 inclusive show a centrifugal pump of the propeller type in which an open propeller l is provided for pumping the fluid. The propeller I takes or draws the liquid from the suction or inlet space 2 and discharges it into the volute 3, as is usual in such pump construction. Although illustrated in combination with a volute casing pump, the invention is 'equally applicable to propeller pumps having diffusion vanes in place of the volute.

As pointed out above, it sometimes occurs that when a pump of this type is operating at oinormal discharge capacity, particularly, strong Whirl is created in the suction space leading to the propeller I. Such whirl increases toward the axis of the pump. and creates a void or tubular cavity around the axis which becomes vapor filled, resulting not only in the pitting of the pump parts, but also in irregular flow through the pump. The present invention comprehends means for the prevention of the formation or reduction of such voids or tubular cavities or the eliminating of high vacua and the presence of water vapor in such cavities as remain, thus eliminating their detrimental effects, and includes a plurality of radially extending axial guide varies 5 at or near the entrance to the suction space 2.

These varies 5 are stream-lined in cross-section according to the direction of flow of liquid through the suction space 2 so as to cut down and avoid to a certain degree initial whirl in the suction space. One of the vanes, nam'ely the vane 5', is provided with a passage or opening 6 extending longitudinally therethrough which opens out at its discharge and into a chamber 1 formed at the inner junction of the various guide vanes 5. The chamber 1 has its outlet opening upwardly, as shown at 8, in a line with the axis of rotation of the pump. The outer or inlet end Figure 11s a vertical section through a centrif- 55 0f the passage 6 has an air supply pipe 9 con;

nected thereto which may receive air from any suitable source, either direct from the atmosphere or from a source of air under pressure (not shown).

A valve l0 is placed in the pipe 9 and this valve is operated by any approved type of pressure actuated operating means, generically indicated at Il. This pressure actuated valve operating means il may be of any approved type which may be purchased upon the open market, and it has its operating rpressure connection l2 with the pipe 9 between the valve I0 and the outlet 8 so that the member Il Will be controlled and actuated by the pressure at the outlet 8,' or in other words, by the pressure at the axis or vertical center of the suction space 2 Thus, when a tubular cavity or void is formed labout the axis of the suction space 2 the pressure in such Void being considerably below the normal pressure and below atmosphere, will act on the 20 member Il and Aopen 'the valve I0 to `admit air under apressure. greaterA than the prssiire 'in the tubular cavity into the tubular 'cavitythrough the passage 6 and chamber 8. Such air'will break up the tubular cavity and ll the void, thus avoiding cavitation and preservinng the'steady flowof liquid through the pump.

`The breaking up of such tubular cavities or voids in the pump suction will also eliminatesurging and unstable performance of the 'pump and '30 4eliminate vibration, which would be the :result thereof.

Only one of the vanes 5 has been vshown as pro- Avicledyvith the air passage 6, although fourof 4such vanes havebeen shown, but it is to be understood that Aany desired number of vanesmay be provided and that any desired number of 'such rvanes may beprovided with air passages, without departing from the spirit of the present yinvention. Y F40 The modiiied wfor-rn shown indljgure's. 5

, is, Ainessentials, the same as. the form "shown in Figures 1 to 3 inclusive. In 'this latterc'ons'truc- -tion shown in Figures 4 and'fhoweverytheiinvention is shown as' applied't'o' a` centrifugal pump 71"'5 4embodying a vClosed impeller 2U, which receives ther liquid to rbe pumped through"y :suction space '2 I and discharges vit, into the volute ,"22.v y In K.. guide. 'varies 23 are relativelywideiin propo ron to the vg'fiiulmfl thejvaes 5 as shown in FgiirS '1 to s, but itis to be understod'thatitfie of such varies isfafnatter ofdesignfdepen fup'n "theV requirements of fthel particullar` the axis of rotation of the impeller 20 and opens upwardly or inwardly towards the impeller.

Air is supplied to the passage 24 and chamber 25 through a suitable air supply pipe 27, which has a valve 28 therein. The valve 28 is shown as manually operated, but it is to be understood that a pressure actuated valve structure such as shown in Figure 1 may be substituted for the manually operated valve, if it is so desired.

The operation of the modied form of pump is rth'esaine as the operationof the form disclosed in Figures 1 to 3 inclusive.

d It will be understood that the invention is not to be limited to the specific construction or ar- 'rangement of parts shown, but that they may be `widely modified Within the invention dened by the claims.

What is'claimed is:

k1. In a centrifugal pump, means for supplying air to whirl created cavities in the suction space `of the pump comprising, air passage forming means extending into said suction space and having itsoutlet arranged to discharge air into the suction space in an axial direction substantially at thelaxis 4of l,the pump, and means controlled by the pressure of nthe j suction 4,space about `the outlet O fsad airg -nassaee forming means for controllingthedelivery of air into the suction space.

2- In .en eenirfilsal pump; means for supplying `air to whirl created cavities inthe Asuction `space of ih e, pumnemprisina a radial guidera@ in ,sasethelfein @Perline out into theuction space .at @engins means fol: delivering air t0 Said ,airfrassasand means cotmlled bythe pressure means Vforsupplying"air Vto whirl `vcreatedcavities in the pump comprising'a vane 'in said"ca"sing provided 'withan airpassa'geliavi'ng "an inlet: for air irfomthe exterior ofthe casing 'and 'opening 'outjinto the casingatia point 'for "delivering the airto the whirl created cavities, yandineans controlledby th'epreslsure within-the pump'casing `for controlling the'` delivery of air into x"the casing through said passage. ,l

'LEW IS 'F.MOODY.

4. In I'a Centrifugal puinpfincludingacasing,

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