US2581828A - Pump - Google Patents

Description

Jan. '8, 1952 Filed March '7, 1946 H. E. ADAMS 2,581,828

PUMP

2 SHEETSSHEET l FLgl Wags

H. E. ADAMS Jan. 8, 1952 PUMP 2 SHEETSSHEET 2 Filed March 7, 1946 21 Figfi. flux! 2, d M

lPatented Jan. 8, 1952 UNITED STATES PATENT OFFICE PUMP Harold E. Adams, Norwalk, Conn., assignor to Nash Engineering Company, South Nor-walk, Conn., a corporation of Connecticut Application March 7, 1946, Serial No. 652,633

21 Claims.

The present application is a. continuation in part of application Serial No. 493,662 now Patent Number 2,461,865, and deals with an invention relating to the pumping of highly volatile effervescent or glass-laden liquids, such as gasoline, when pumped, for example, from aircraft fuel tanks to engine carburetors.

In the parent application referred to, there is described as a specific application of the invention a fuel booster centrifugal pump mounted directly on the-bottom of or inside of the fuel tank, to deliver fuel under pressure to the main engine fuel pump. In order to prevent vapor lock, the fuel pump has associated therewith a gas removal pump, and the two pumps are so associated and constructed as to deliver bubblefree liquid fuel to the main engine fuel pump.

One object of the present invention is to provide a new and improved pump unit comprising a centrifugal liquid pump and a gas removal vacuum pump constructed and arranged to afford efl'ective gas purging action, and to handle a large quantity of fuel by means of a small compact unit.

In accordance with the present invention, the centrifugal liquid pump has a gas collecting annular chamber or groove communicating with the liquid pump chamber, and encircling the inlet of said liquid pump near the suction end thereof. The entrained gas in the centrifugal pump is centripetally separated from the liquid, collected in said annular chamber, and then conducted to the inlet of the gas removal pump.

One of the features that distinguishes the centrifugal impeller of the present invention from the conventional one is the extreme height or width of the impeller blades at the entrance to the impeller wheel, as compared with the height at the exit. This results in an angle of about 35 between the conical side or end of the impeller and its axis of rotation as compared with the normal impeller wheel angle 75 to 80. The purpose of providing a pump with these extreme proportions is to slow up the liquid as it enters the field of operation of the impeller blades to the point where suflicient time will be allowed during the passage of the liquid from the entrance to the exit of the impeller wheel to permit the free gas or vapor carried y the liquid, to separate out by centripetal action and concentrate around the inner diameter of the wheel, where it may be drawn in by the annular gas collecting groove or grooves, and conducted by the suction connections to the gas removal vacuum pump. This blade dimen- 2 sional feature serves not only to slow down the liquid being pumped, so that a more effective gas separating action is afforded, but also serves to maintain the liquid under a static head during 'its passage through the impeller, so that the flashing of the liquid into vapor is reduced to a minimum.

In designing the entrance angles of the impeller blades, careful consideration is usually given to the calculation of entrance velocities, so that the liquid flows into the field of action of these blades with a minimum of disturbance. In other words. the entrance angle of the blades is usually designed so that the blades follow as closely as possible the lines of flow of the liquid entering under the given velocity and entrance area conditions.

Another characteristic rule usually followed in the design of an impeller is that the velocity of flow of the entering liquid starting from rest in the pool of liquid above the pump must be gradually accelerated after it passes the entrance of the pump in a constantly increasing amount until it finally leaves the exit end of the impeller at its full discharge velocity as imparted to it by the impeller blades. There has been noexception to this rule, the velocity .being accelerated from the entrance immediately adacent the impeller wheel or eye, as it is generally called, through the entrance of the impeller blades themselves, the liquid being accelerated during its entire passage in the field of operation of the blades.

In accordance with the present invention, however, the liquid pump is deslgned so that the liquid after entering the eye of the pump, immediately adjacent to the pump blades, is decelerated rather than accelerated as it is picked up by the'entering blades of the impeller, the entrance velocity of this liquid through this eye being in addition lower than the velocities of the liquids in conventional pumps handling liquids near the boiling point.

- A pump of good impeller design for boiling liquid has previously been considered one having velocities at the impeller eye of the order of from 5 to 8 feet per second, with velocities ahead 01 this ranging down to 3 feet per second, whereas in accordance with the present invention, the impeller is designed to afford velocities at the eye desirably ranged from 2 to 5 feet per second. After the liquid enters the impeller blades, there is still a greater difference in the characteristics between the impeller of the prior art and that of the present invention. In the case of the impeller of the present invention, the velocities at the entrance to the impeller blades desirably drop to a low value of 1 to 2 feet per second, whereas in the convential impeller, these velocities increase from 5 to- 15 feet per second.

There is another basic diflerence .in t.he entrance angle of the blades in the impeller of the present invention as compared with that of the conventional type. As indicated above, the impeller blades of the prior art generally are proportioned so as to meet the entering stream of liquid with a minimum of shock, the blade angle being determined by calculation of flow velocities in conjunction with impeller areas and capacities dealt with. In accordance with the present invention, however, the entrance angles of the impeller blades are designed to handle a volume of flow three or four times the volume of liquid to be handled by the impeller so that volume of gas which is three or more times the volume of liquid discharged from the outlet ends of the impeller blades. a

The designing of the pump to handle .a large proportion of gas and vapor at, the entrance ends, of. the impeller blades, whether or not these gas and vapor proportions are present. takes care of those excessive proportions of gas to liquid when they do occur, and although when handling substantially gas-free liquid theremay be present shock conditions resulting-from the fact that theblades are dimensioned to handle three times this quantity of liquid, the otherwise detrimental eifect of this shock is offset by the slow velocity of the liquid through the impeller, affording ample timefor centrifugal-separation, for condensation of the vapors flashed by the entrance shock conditions, and for concentration of any non-condensible gases, holdingthem near the center of the impeller, where they can be withdrawn through the annular collecting chamber by a suitable vacuum pump connection..

As another feature ofthe present invention, the pump affords relatively long-flow passages from the entering edges of the impeller .blades' to the exit ends thereof. If the liquids were allowed to freely accelerate between the entrance and the exitv by the action of centrifugal force, it would .take about. one-quarter of a revolution of the impeller to effect this transltion.

. In accordance with the present invention, the pump is constructed to hold back the liquid in the impeller ,for approximately three come plete revolutions from 'the' time it passes .the entrances of the bladesuntil. it leaves the exits. By thus holding back-the liquid and retaining. it inthe-passages of.the impeller for three Coma plete revolutions, there is provided. ample-time for the .complete separation of gases and-vapors from the liquid portion of the mixture entering the pump, and for the segregationflof the. gas at the inner-diameter, where, asindicated above, it maybe removed by the vacuum-pump,

-Asanother feature ofthe present invention,

the liquid centrifugah pump -i s of the double suction impeller type, having two annular'gas collecting grooves for the two respective impeller sections, these gas collecting grooves being served by independent suction conduits, each conduit in turn having an independent suction port to a liquid ring gas removal suction pump. This liquid ring suction pump is of two-lobe construction, allowing each lobe to operate independently of the other as far "as its suction connections are concerned, so that each lobe draws vapors and gases from one annular collecting groove, and the other draws vapors and gas from the other collectinggroove. Since these two lobes are independent of each other, this construction is the equivalent of two separate vacuum pumps drawing from two separate annular gas collecting grooves independent of each other. This feature of independent lobes with separate suction connections is important. because if the suction conduits of both annular grooves were joined together 'before they entered a common'vacuum pump, one or the other of the suction conduits leading to the respective annular groove would take more of its share of the total vacuum 'pump capacity at the expense of the other suction conduit. In other words, the suction of the vacuum pump would take the line of least resistance, and it would draw through the annular collecting groove that had the least resistance at the expense of the other annular groove. By separating the two; and connecting each suction conduit to its independent vacuum pump, there is attained full surface for each of the annular gas collecting grooves, regardless of the condition of the other groove.

\ Various other objects, features and advantages of the invention will be apparent from the following particulardescription, and from an inspection of the accompanying drawings, in

which:

Fig. l is a longitudinal section of a pump unit embodying the features of the present invention;

Fig. 2 is a section taken on line 2-2 of Fig. 1;

Fig. 3 is a plan section taken on line 3-3 of Fig. 1,, and showing the two-lobe construction of the vacuum pump with two portions of the rotor broken away to show the separate inlet passages therefore;

Fig. 4 is a plan section taken on line 4 -4 of Fig. 1, and showing the outlet port on the top of the lobe casing, one portion of the lobe cas-j ing being broken away to show the bottom inlet port; and v v Fig. 5 is a perspective of the impeller.

Referring to the drawings, the pump assembly, of the present invention is shown of the fuel submerged typedesigned'for mounting on the bottom or lower sideof an aircraft. fuel tank, andadaptedto be securedtothe bottom wall of said tank by a mounting fiangelll forming part of saidassembly. jTheupumping assembly comprises a booster. centrifugaluliquid pump ll having a centrifugal impeller l2 mountedat the lower .end of ayertical shaft l3l'which. isdriven from .an electric ,motor. enclosed-in a liquid tight casing .il anda gas removal ;vacuum pump 44 with a ro'torlll mounted on-said shaft.

-. j The. complete pumping a'ssen'ibly is 'securedfm position with respect t -the-fueltankv to afford, free gravity flow. of. theliquid fuel from the .tank into the" pumpsectiom For that purpose,the centrifugal liquid pump I I is enclosed in a pas-.5 ine- 1 3 w al -out h '-w U a 2 the p er n1et9 d-;. lf hi communication with the bottom of the fuel tank, and is covered with a strainer t8, while the lower section of said well communicates with bottom suction side 3| of the pump II. The top suction side 32 of the pump ll communicates with the bottom of the fuel tank through a strainer 94.

The liquid fuel is discharged from the centrifugal impeller l2 through a collecting volute and a discharge nozzle 26. Suitable flexible hose connections are made at this point to the fuel line leading to the main engine fuel pump outside the fuel tank.

In order to afford greater pumping capacity with a unit of minimum size, the liquid pump ll is of the double-suction type comprising a combined wheel hub and web'2'l secured to the lower end of the shaft l3 for rotation therewith,- and having afilxed thereto on opposite sides thereof two sets of impeller blades or vanes 29'and 29. "and 29 have'respective axial eyes or suction openings 3| and 32, to which the liquid flows on its way to the inlet ends 33 of the corresponding set of impeller blades.

- The highly volatile and ebullient liquid flows by gravity through the strainers l9 and 64 to the suction eyes 3| and 32 respectively. With the strainers I9 and 64 located above these suctioneyes 3| and 32, some of the bubbles entrained in the liquid may have an opportunity to rise counter to the slow downward flow of liquid, and thus escape to the surface of the fuel in the tank. Some of these bubbles, however, are entrapped with the liquid passing through the eyes 3i and 32 of the impeller l2, and will be engaged by the leading edges 33 of the'impeller blades 28 and 29.

32 with the entering liquid, there will be bubbles evolved when the volatile liquid strikes the revolving leading blade edges 33.

The presence of air or gas bubbles in any appreciable volume will break down the action of a centrifugal pump. This is due to the lowering of the average density of the fluid in the impeller by the presence of the gases and vapors, with the result that sufllcient head cannot be generated by the impeller to fulfill its normal discharge head requirements.

The impeller pumping rate diminishes approximately as the over-all density of the fluid in the impeller is reduced by the presence of bubbles, and it may continue to reduce to a point where all pumping ceases at a given head. In

the case of the aircraft application, the delivery of bubbles in the main engine fuel pump suction is detrimental to the latters pumping action, and the mere presence of the bubbles alone may cause failure of the main engine fuel pump before the actual reduction in pumping volume of the fuel booster pump occurs. In accordance with the present invention, continuous separation, collection and removal of these bubbles from the passages of the impeller is effected, so that the density of the liquid therein will be suilicient to insure flow and full operation of the centrifugal pump.

.The centrifugal blades 29 and 2-9 are arranged and constructed to set up a circulating movement within the passageway defined between each pair of adjoining blades in addition to the radial flow therethrough. When gas bubbles are entrained in the liquid being pumped; these bubbles are urged towards the leading edges .33

These two sets of impeller blades In addition to the bubbles already carried from the eyes 3| and by this circulating movement, and by the action of differential presure between the adjoining blades. There is also the effect of centrifugal force tending to separate the gas bubbles. and to force these bubbles centripetally towards the center portion of the impeller l2, while at the same time allowing the more solid liquid to pass radially outwardly along the pressurized leading face of each impeller blade 28 or 29. The result of these forces is a concentration of separated gas near the entrance of each impeller passageway.

Means are provided for withdrawing this accumulated gas. For that purpose, the pump casing l5 has a lower annular collecting groove 36 near its radially irmermost side in communication with the impeller passageways defined by the lower set of blades 29, and an upper annular collecting groove 37 disposed near its innermost radial side of the casing, and in communication with the impeller passageways defined by the upper set of impeller blades 29. The lower annular gas collecting groove '36 opens up into a gas take-off or suction conduit 40, 4| and 42, leading to an inlet port 43 in a vacuum gas removal pump '44. The upper annular gas collecting groove 31 opens into a gas take-off or suction conduit 45 leading to another inlet port 490i the vacuum gas removal pump 44.

The gas removal vacuum pump 44 is of the liquid ring type, and comprises a rotor- 41 secured to the shaft l3 for rotation therewith, and enclosed in a casing 48. The pump is of the two-lobe type, the separate lobes or displacement chambers in the pump being indicated at their deepest portions as and 5|.

The gas from the pump is discharged from the vacuum pump 44 through upper ports 52 and 53 in the pump to a gas discharge chamber 54, and this gas is then discharged through a port 55 into the tank or source of supply.

The gas centripetally accumulated within the confines of the impeller passages is drawn off by the suction action of the auxiliary gas pump 44 at a rate equal to the formation or accumulation of gas in this region.

The inlet port 43 of lobe 50 derives its suction through conduits 42, 4| and 49, removing air and vapor collected in the bottom collecting ring or groove 3'5, .and this lobe 50 discharges vapors collected from this bottom collecting groove through its discharge port 52, where it in turn discharges into the common discharge chamber 54, and thence through the discharge port 55 to the tank. The other inlet port 45 of lobe 5| derives its suction through the conduit 45, and removes vapors and air collected in the upper annular groove 31. -The discharge from this lobe 5| is through discharge port 53 into the common discharge chamber 54 through the port 55, and into the tank or source of supply.

It should be noted that the two lobes 59 and 5lform separate pumping chambers with one common rotor 41, each chamber having its own inlet and discharge port, so that each lobe operates independently of the otheras far as their suction connections are concerned. By separating these suction connections, there is provided the equivalent of separate independent vacuum pumps for each side of the double-suction pump.

I thus obtaining definite removal of gas from each of the gas from one side of the impeller at the expense of the other side.

As an additional feature of the present invention, the impeller blades 28 and 29 at the entrance to the impeller wheel l2 are of comparatively extreme width to slow up the liquid as it enters the field of operation of the impeller blades, sufliciently to permit the impeller blades to separate centrifugally the free gas or vapor from the liquid and collect it in the annular collecting grooves 88 and 81. To slow up the liquid to this extent, the axially open sides or ends 60 of the impeller describe substantially conical surfaces of revolution about the axis of the impeller shaft l8, each inclined 35 with re- 1 spect to said axis as indicated by the angle A in Fig. 1 compared with the usual impeller angle A of about 75 to 80. The impeller of the present invention thus forms. an included angle of about 110 between both conical surfaces defined by of vapor and gas to liquid, and I do not wish to.

be limited to this specified angle. It might vary from 15 to or more and still be within cer-, tain aspects of the present invention.

As another feature of the present invention,

the pump is proportioned so that the liquid after entering the suction eyes 8| and 82 of the pump immediately adjacent to the impeller blades 28 and 29, is decelerated rather then accelerated as it is picked up by the leading edges of these blades. For that purpose, the cross-sectional flow combined cross-sectional areas of the flow passages in the impeller wheel 12 along the full length of said wheel, and along the leading edges 83 of the combined impeller blades 28 and 29 at the entrance to said passages. These areas are desirably proportioned so that the combined cross-sectional areas at the entrance to the flow passages in the impeller wheel 12 is about twice the cross-sectional vflow area of the suction eye 8| or 32. With such relative pump dimensions, and with the pump operating at a desirable liquid flow velocity of 2 to 5 feet per second at'the suction eye 8|, the velocity of the liquid at the entrance to the impeller blades 28 and 29 drops to 5 a low value of l to 2 feet per second.

As another feature of the present invention, the impeller blades 28 and 29 are proportioned and designed to handle a volume of fluid flow at their entrance end from about three to four times the volume of liquid to be handled by the impeller l2 at its exit end.

The reason for this departure in the proportioning of the impeller blades 28 and 29'from conventional design, is that the pump of the present invention is designed to handle fluids containing large quantities of previously entrained gasas well as gas evolved byshock conditions at the entrance to these blades. These impeller blades- 28 and 29 are therefore proportioned to handle at their inlet a volume of fluid three or more times the volume of liquid discharged into the volute 25 from their exit.

The detrimental shock effect of this disproportionate entrance design, when the 'impeller is shock conditions, or separate and compress anygases or vapors which are diflicult-tdcondense and collectthem in the annular grooves 86 and 81 from which they can be withdrawn through the action of the vacuum pump 44.

As another feature of the present invention, the pump is designed to aflord a relatively long length of time for the passage of the liquid from the entering edges 32 of the impeller blades 28 and 29 to their exit edges. If the liquid were allowed to accelerate freely from entrance to exit by the action of centrifugal force alone, it would take-about $4; of a revolution of the impeller to complete this travel, and this is the usual value for the average conventional centrifugal pump impeller. In the present invention, due to the disproportionate design in-the impel: lerpassages, to handle at least three times the, quantity at the inlet that is provided for at the exit, this larger quantity .of liquid entering the impeller is slowed down in its passage from entrance to exit so that it. takes approximately. three complete revolutions from the time a particle of liquid passes the entrance of the blades to the time it leaves the exit. In addition to this feature, the impeller blades 28 and 29 have their radial outer sections 63 extending. for substantial distances somewhat concentric with respect to the axisof .the impeller l2 asshown in Fig. 2 and circularly, so that the extent of their radial components. at these outer sections is reduced to a minimum.

As'many. changes can be ,made in the aboveapparatus, and many apparently widely difler-t .5- nt embod men of area of the suction eye II or 82 is less than the e 1 ts this invention can be made" without departing from the scope of the claims. it is intended that all matter contained in the: above description or shown in the accompany ing drawings shall be interpreted as illustra- -l( tive and not in a limiting sense.

5 ant is set forth in the appended claims.

handling a clear liquid or approximately onecondense the vapors flashed by blade entrance? .charge connection to the said source of supply.-'

'2. A centrifugal pump comprising a c'entri-fugal impeller of the double-suction type, having two impeller sections with respective inlets, said pump having'anoutlet, a liquid pump chamberfor said impeller, and two annular gas collecting chambers communicating directly with the in'-'- terior' of the liquid pump chambernear saidinlets. respectively, and extending around the axis'of rotation of said impeller, said pump having conduits for leading the collected gases away from said gas collecting chambers. 4

'3; A centrifugal pump comprising "acentrifu-' gal impeller of the double-suction type, having two similar adjoining pumping sections with respective inlets, and a casing enclosing said im-'- peller-and-having-two axially spaced annular gas collecting grooves, said-pump havingan' outlet,- and; a liquid pump chamber for said impeller, said grooves communicating" directly with the liquid .pump chamber near said inlets respectively and-extending around the. axis-p! rotation of said impeller, and-pconduits tor-,leadilng-the gases away from said grooves;

- .4. In combination. acentrifuBal liquid pump comprising aeentriiugah impeller, of the double- 4 suction type having two similar acUoining pump- :ing sections with' respective inlets, and a casing enclosing said .impeller .and having; two. axially spaced. annular, gas collectinggrooves. said pump having an outlet, and-a liquid-pump chamberfor said impeller; said grooves. communicating di- .rectly with. the liquid pump chamber near said inlets respectively andextendins. around the axis 'ofrotation 01 said impeller. a gas removal pump,

.and conduitsbetween said grooves and, the inlet tions to said inlets respectively;

6. The combination as described in claim ,5, in yvhichtheoutlet means oisaid gas removal p ump comprises two separate outlets operatively corresponding to said inlets respectively. v

7. {Thecombin'ation as described in claim 5 in which said gas removal pump is of the twolobesuctionrotary; type,- and said inlets extend into the two lobe sections respectively of said latterpump.

8. T l e eombination as described in claim 5, in which the outlet means of. said gas removal pump comprises two separate outlets operatively corresponding tdsaid inlets respectively, said gas removal pump is of thetwo-lobe suction-rotary type, .and-each of the lobe sections has a corresponding inlet and a corresponding outlet on the suction and discharge sides respectively of said latter lobesection.

.9. In combinatioma pump having an outlet, and comprising a centrifugal, impeller for the double suction type having two similar adiq is pumping sections with respective inlets,

and a casing enclosing said impeller and having a liquid pump chamber for said impeller and two axially spaced annular gas collecting grooves communicating with the liquid pump chamber near said inlets respectively and extending around the axis of rotation of said impeller, a gas removal pump of the two-lobe suction type having two separate inlets leading to the two lobe sections of said latter pump respectively, and two separate outlets communicating with the two lobe sections of said latter pump respectively, and conduits connecting said grooves with said latter inlets respectively.

10. A centrifugal pump comprising a casing, an impeller therein defining with said casing a plurality of liquid flow passages, the inlet and outlet ends of said passages 'being proportioned to handle substantially more 01 the volume of the fluid at said inlet ends as at said outlet ends, said impeller having its blades with circumferential components of substantial length which will cause the liquid in the pump during normal pumping operations to be retained in said passages for about three revolutions or more of said impeller, the gas or vapor carried by the liquid passing through said passages being adapted to separate out from said liquid and to concentrate in said passages at an' annular region extending around the axis of rotation of said impeller and located near and radially outwardly beyond the initial axial. entrance area to said impeller, means for collecting said separated gas or vapor atsaid'region, and means for drawing oi! said separated gas or vapor from said collecting means and away from the pump.

11. A centrifugal pump as described in claim 10, inwhich said impeller blades are curved substantiaily circularly for substantial distances at the radially outer sections to retain the liquid inze pump during normal pumping operation for tieast one revolution of said impeller.

12. A centrifugal pump comprising a casing, an

- impeller therein defining with said casing a plurality of liquid fiow passages, theinlet and outlet ends of said passages being proportioned to handle about three times the volume of fluid at said inlet ends as at said outlet ends, the gas or vapor carried by the liquid passing through said passages being adapted LO separate out from said liquid and to concentrate in said passages at a region around but near the inner periphery oforawing 'off said separated gas or vapor from said collecting means and away from the pump, said collecting means comprising an annular collecting groove in saidcasing in direct communication with said passages in said region, and said drawing means comprising a gas take-oil condult connected to said groove and leading away from the pump. i

13. A centrifugal pump comprising a casing, an impeller therein having blades defining with said casing a plurality of liquid fiow passages, the width of said blades at their entrance end with respect to the width at'their exit end and with respect to the cross-sectional area of the impeller eye or inlet being such, as to slow up the liquid as it enters said passages and to create in said separated gas or vapor in said region defined by said casing, and conduit means for drawing off said gas or vapor from said collecting chamber.

14. A centrifugal pump as described in claim 13, in which said collecting chamber is in the form of an annular groove on the inner side of said casing communicating directly with said passages in said region.

15. A centrifugal pump comprising a casing, an impeller therein having blades defining with said casing a plurality of liquid flow passages, the width of vsaid blades at their entrance end with respect to the width at their exit end being such as to create in said passages an annular region of lowest pressure or density extending around the axis of rotation of said impeller and located near and radially outwardly beyond the initial axial entrance area to said impeller, an annular collecting chamber for the separated gas or vapor in said region defined by said casing, and conduit means for drawing off said gas or vapor from said collecting chamber.

a 16. A centrifugal pump comprising an impeller having rotary impeller blades mounted thereon, the outer edges of said blades on one side describing a substantially conical surface of revolution about the axis of rotation of said impeller inclined approximately 15 to 45 with respect to said axis, a casing for said impeller having its wall opposite said edges conforming close to said and located near and radially outwardly beyond the inlet of said impeller, means for collecting said separated gas or vapor at said region, and means for drawing the collected gas or vapor from said collecting means away from the pump.

17. A centrifugal pump of the double suction.

open impeller type, including an impeller whose' edges on each axially open side describe a substantially conical surface of revolution about the axis of rotation of said impeller inclined to 45 from said axis, thus forming an included angle between both conical surfaces of from 90 to 150, a casing having walls closely conforming to said surfaces of revolutions and defining an inlet to said impeller, an outlet from said impeller, and a pump chamber therebetween, and means for separating the gas and vapor from the liquid in said pump chamber, collecting it, and drawing it away from the pump.

18. A centrifugal pump comprising a casing, an impeller therein having impeller blades mounted thereon and defining with said casing a plu rality of liquid flow passages through said pump, said pump having an outlet and an axial suction inlet having an area in a plane at right angles to the direction of flow therein substantially smaller than the combined cross-sectional areas of said passages at their inlets, to effect decrease in the velocity of the liquid as it passes from said suction inlet to said passage inlets, whereby sufilcient time will be allowed during the flow of the liquid through said passages to permit the free gas or vapor carried by the liquid to separate out from said liquid and to concentrate in said passages at an annular region extending around the axis of rotation of said impeller and located near and radially outwardly beyond the inlet of said impeller, means for collecting said separated gas or vapor at said region, and means for drawing oil said separated as or vapor from said collecting means and away from the pump.

19'. A centrifugal pump as described in claim 18. in which said axial suction inlet area and said combined passage inlet areas are proportioned about one to two. to decrease the velocity of the liquid to about one-half as it passes from said suction inlet-to said passage inlets.

20. A centrifugal pump comprising a casing. an impeller therein defining with said casing a pinrality of liquid flow passages, the inlet and outlet ends of said passages being proportioned to handle about three times the volume of fluid at -said inlet ends as at said outlet ends, the, gas or vapor carried by the liquid passing through said passages being adapted to separate out from said liquid and to'concentrate in said passages at an annular region extending around the axis of retation of said impeller and located near and radially outwardly beyond the inlet of said im-' peller, means for collecting said separated gas or vapor at said region, and means for drawing oi! said separated gas or vapor from said collecting means and away from the pump.

21. A centrifugal pump as described in claim 20, in which means are provided for retaining the liquid in the pump during normal pumping operations for at least one revolution of said impeller.

HAROLD E. ADAMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,780,679 Jennings Nov. 4. 1930 1,901,154 Durdin Mar. 14, 1933 1,989,061 Longenecker Jan. 22, 1935 2,134,686 De lancey Nov. 1, 1938 2,368,528 Edwards Jan. 30, 1945 2,368,530 Edwards Jan. 30, 1945 2,402,398 Harpster June 18. 1946 2,461,865 Adams Feb. 15, 1949

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