US2874642A - Adjustable bypass valve - Google Patents

Description

24,'195-9 v I F.` R. ORRST 237 3 ADJUSTABLE BYPASS VALVE Filed Oct. 5, 1955 4 Sheets-Sheet 2 9 F. R. FbRR'-:sT 2,874,642

ADJUSTABLE BYPASS VALV Filedbct. 5, 1955 I 4 Sheets-Sheet. 3

Feb. 24; 1959 F. R. FORREST 2,874,642

ADJUSTABLE BYPASS VALVE Filed Oct. 5, 1955 4 Sheets-Sheet 4 Uit d tat sltfi O t i lfl t i/P ssa .Th is a ont a anf-pa pp cation of an appliation filedpctober '21, 1953, Serial; No.

i centrifugalpump3 and conventionalvalveto.a propor- 2,874,642 d F h- 24,19 9

Other objects and advantages will appear -from the following description of structures illustrating several em'- bodiments of the nvention, reference being hadto the accompanying drawings, in which: y Fig. 1 is a sectional view ofa-,centrifugal pump assembly embodying the invention; a j a Fig. 2 is a View in cross ,section taken along line II--II ofFig.;1;` t.

Fig; 3 is a, view showing a rack of Fig. 1 in detail; i

Big. ,4 is a fragmenta'y` view in section ,of a` modified embodment ofthe 'invention utilizing a centrifugal pump with a closed impeller; I,

Figt 5 is a view in'section of adouble suction centr fugal pump, embodying theinvention; i i i.

Fig( 6, isa modified embodment of -the invention in whichtthe impeller Vis moved. axially towardand away from the impeller casing to valve theinternal fluid-return passage, the fluid return passage being shown in a;closed positiong ;i i I a .Fig. 7 s a sectional end view taken alonglineVII-VII of Fig. 6; i e V Fig. 8 is a fragmentary view in section of the structure of Fig. 6 showing the fluid return passage in opened position;and V i 4, i

Fig. 9 is a vew in section of a double su'ction centrifugal-pump embodyng the invention-and illustratinga tiorer which Supplies :predetermned iportions. of .the i sev- 'eraLtypes ofs tock Theva1ve.opens and 'lcloses in ;response to a float levelicontrolimechanismjinzthe` proportioner. The valve,,operably positionedwithina connecting ,conduiui Controls `the` `flow of stockin thetconduit `by reducing the efiectivecross.sectional area` presented to theflow. g mg 1:'` i.: ,Dificulty hasiheretof orebeen experiencedin controlling the flow ofstock `toitheproportioner by means of the i, conventional valve. The:.stock, being\ composed, of WQCdfibIS-SUSPCldd'fl a liquid, `nvariably parts' (with sometofjts fibersyinitspassagethrough the .valve. i. The separated fibers become wcdged around the movable valve element and furtherrestrict ;the flow. Thisseparation of thefibers from'the suspending liquidxis referred' tovas stocktdewatering; i The further thewvalve vis. closed within limits, the greatertthe amount of fibersremoved, and the moret/the stoclisdewatered After the valvehas been closed to a position in which it throttles the flow to about one-fourthof normal capacity;stock fibers buildup around the movable' valvetelement andrprevent further openingyor closing ofxthe, va1ve,:a,condition knownas plugging. Whenthis `occurs thepump must be shut)` down and thevalve `'c1eaned.,`; 1.\ i i; This nventionuproposes to solve the `plug'g'g problem 'by providing-,in .a centrifugal .pump, a controlled internal fluidireturnpassage;` 'By makingoneo'f the walls'of the returnipassagea;continually movng part, plugging is avoided. 7\ 1 1, i: i '(1 Accordingly, itis `an object of this invention to'eliminate the aforestated difliculties experienced ;withknown valves by providing a valving apparatus `for a e'e'ntrifugal pump .which controls the:` flow .ofpaper stoekfrom 'zero dseharge to normal ,capacity without plugging. the valve atbelow normal capacity.: u r a Another object of my invention is :to provide in a entrfugalpump a yalvng control, oneowhose operating membersis acontinually movng' partgi ,i

,Anothenobjectl of my invention-is to providea' centi-ifugal paper; stock pump with i an adjustable internal fluid return passage and valve means, `easilyfoperableiand effec tively responsive to automatic controls.

modified .movable wall memben i The centrifugal pump assembly illustrated in Fig. 1 includes a housing-10 which operatively houses a rotatablesingle suction-centrfugal impeller 11 mounted'on one end of a rotatably driven shaft 12. Sh'a'ft IZ nay be rotated by any suitable means (notshown)-. A suitable bearing assembly journals shaft 12. A seal- 13 inter posted-between shaft 12 and-housing 10 prevents fluid leakage along the shaft.` v i i The housing *10 has wall structures 14 which 'define 'a fluid confinjng impeller chamber 15. The fluid confining mpeller chamber 15 is provided with an axal inlet 16,

and' an outlet 17 radally spaced from the inlet 16. Hous i ing 10 is carried by a supporting housing ls which surrounds a section-of housing 10 adjacent'the end of the shaft 12. i p i Impeller 11 isprovided with a hub portion lla, a wall portion 11b and a single set of fluid confining'purnping passageways 19,'which extend through the' impeller 11 and termnate in radally spaced intake and discharge ends'20, 21, respectively.' The intake or suc`tion`end 20 and discharge end 21 are disposed adjacent the' inlet 16 and'theoutlet 17,' respectively, to' complete the passage for the fluid flow through the pumpj i 'The impeller 11 has a plurality of blades 22 each pre sentng a` surface portion 23' on the suc't'ion side of the impeller: "The blades 22 combine with the hub 'portion 11a to*define theintakezo and'join with a surface formed bythe hub portion' 11 and the wall portion`11b to form the 'single set of fluid impelling passages' 19. The "surface portions 23 `are spaced apart from an opposed 'inner`wa1l structure'surface 'portion 24 of housing 10, to defiie' a fluid return passage or'intemal bypass 25 therebetween. The fluid return' passage 25 is of sufficierit capacity to mi'nimize' the discharge of fluidflthrough the outlet 17. Deflectng means shown as a series of radally extending vanes 26 are carried by a ring fastened to 'the housing 10 and positioned circumferentially around the discharge end 21 'of the impeller 11 in radally spaced relation thereto. The vanes 26 aid to reverse the flow of`dis`charged fluid into the fluid return passage 25. t Means cooperating with the housing 10 for varying the axial extent of the communication between'the fluid return passage 25 and the 'intake 20 include an open ended generally cylindrical wall member 28' which-is reciprocably mounted in the wall structure 14 to form the inlet ger/4,6 4

16 with the inner end 29 of the wall member 28 coactingwith the impeller surface portion 23.-- Wall member 28 is sealed in fluid tight relation against housing 10 by means of any suitable known seals such as so-called O-rings '30 to prevent return of fluid from outlet-17 to -inlet 16 aroundthe wall member 28. The inner end 29 maybe formed as an annular lip 31 overlapping the intake 20 of the impeller 11 as shown in the embodiment in Fig. 1, or as atcylindrical lip32 abutting the impeller as shown in the embodiment in Fig. 4. The wall member 28 is reciprocated toward and away from impeller 11 for varying at will the aXial extent of communication betweenthe fluid-return passage 25 and the intake 20.

As shown in Fig. 1, wall member 28 may be reciprocated from the position shown in solid lines to the position shown in broken lines by interaction of pinions 33, with axally. extending racks 34. The racks 34 are affixed with machine screws 35 onto diametrically opposed outersides of the wall member 28 as shown in Fig. 3. The ,wall member 2 8 is held against rotation relative to housing 10 by guide 36 mounted on housing 10 cooperatingiwith a groovein member 28. The pinions 33 are fixed on rotatable rods 37 which have one end journaled in supports 38 .positioned within housing 10. The opposite ends of rods 37 extend outward through and are journaled in the housing 10. These ends are provided with spur gears 39.. The spur gears 39 are engaged by actuating gears 40. :One of the actuating gears 40 is provided with a hand wheel 41 for actuation of the attached actuating gear 40. Rotation of the actuating gear 40 transmits rotary motion through the spur gears 39 and the rods 37 to the pinions 33, which in turn coact with the racks 34 to reciprocate the wall member 28 axally toward and away from the surface portion 23 of theimpeller 11.

4 ;fljheembgdiment in Fig. shows the application of the invention to a double suction centrifugal pump.

'The double suction pump utilizes a double impeller 44 in place of the single suction impeller 11, and in addition uses a' chain drive 45 to reciprocate wall members toequal extents in opposite directions. *As shown in Fig. 5, the inventive structure is duplicated so that each half of the double suction impeller reflects the single suction impeller embodiment shown in Fig. 4. The reciprocating assembly is also a duplication of the previously described single assembly, with the exception of the chain drive which is added to facilitate cooperative adjustrnent of the wall members.

In the embodiment illustrated in Fig. 5, the double suction impeller 44 is mounted on the shaft 212. The housing 210 has wall structures .214 which form an impeller chamber 215 havingtwo axial nlets 216 and an outlet 217. Wall members 228 similar to the wall member 28 of Fig. l are reciprocally mounted in the wall structures 214 to define the nlets 216. Fluid return passages 225 are formed between the wall structures 214 and impeller 44 similar to the fluid return passage 25 of Fig. 1. The wall members 228 are reciprocally mounted in the wall structures in the same way that the wall member 28 is reciprocally mounted in the wall structure in Fig. l. The wall members are reciprocally moved axally toward and away from the impeller 44 to open and close the fluid return passages 225. The chain drive 45 cooperates with the spur gears 239, the actuating gears 240 and the hand wheel 241 to coordinate the reciprocal movement of the wall members 228.

?The following description will' cover the operation of the embodiment of Figs. l and 4.

In operation, the Wall member 28 coutrols the size of the fluid return passage 25 to control the fluid discharge into the outlet V 17. Referring to Fig. 1, the wallmember 28 is in the closed position, therefore the fluid discharge from impeller 11 is completely discharged into; the outlet 17. The pump then delivers its normal Capacity. As the discharge demand is changed to require less than normal Capacity, the wall member 28 is moved 'axally away-"from the surface portion 23 of the impeller 11 by rotating hand wheel 41 to open the internal fluid return passage 25. Fluid is then pumped from the discharge end 21 into the fluid return passage 25 back to the intake 20. The wall member 28 opening can be so constructed as to open sufliciently wide to enable the entire discharge of the iinpeller ll to flow through fluid return passage 25 and reenter the impellers 11 at the intake 20. Under these conditions there is no discharge in outlet 17 beyondthe entrance to fluid return passage25.

The impeller 11 continues to rotate at its normal rotational speed, continually pumping at normal impeller Capacity. The internal surface 24 of housing 10 forms one wall of fluid return passage 25 and the surface portion 23 of the impeller forms the other wall of the fluid return passage. surface portion 23 being a continually rotating part, there is no lodging of solids Suspended in the fluid pumpedin the' fluid return passage 25. This avoids the objections to controlling the discharge means of valves in that plugging or elogging of the valve is eliminated.- Accordingly, the discharge into the outlet 17 can be vared from zero discharge to normal discharge without valve plu'gging.

i The embodiment of' Fg; 5 operates in essentially the same way as the'embodiment of Fig. 1 except that the embodiment of Fg. 5 is' a'double suction pumprather than a single suction pump and has a chain drive to 'co- -ordinate the axial adjustment of the wall members.

'The embodiment illustrated in Fig. 9 shows another application of the invention in a double suction pump. The housing '310 has wall structures 314 which define a fluid confining impeller chamber 315, inlet Channels 370 and an outlet 317. A double suction impeller 344 is mounted on the rotatable shaft 312 and is postioned within the chamber 315. As shown in Fig. 9 the inventive structure is substantially duplicated and in effect'the pump is divided into two adjacent pumping sections. A suitable hearing assembly, not shown, journals theshaft.

Walltmembers 328 are reciprocally mounted in the wall structure 314. Each wall member 328 consists of a. cylindrical shell 371 embr'acing the shaft 312, an annular lip 331 positionable, adjacent the impeller 344, and

a plurality of crcumferentially spaced rad'ally extend-.

ing ribs 372.fo`r mounting the lip 331 on the inner end 374 of the shell 371. In this arrangement the shell 371 can` be in directvcontact with the shaft 3l2 but preferably as shown a shaft sleeve 373 is interposed between the shaft 312 and the shell 371. Such an arrangemert causes wear on the easily replaceable shaft sleeve373 rather than on the shaft 312. Suitable packing means 375 are positioned between a portion of the shell 371 and the shaft 'sleeve 373. i

The inlet 316 intothe chamber 315 is formed by the lip. 331 which fits into an opening in' the wall structure 314. Thetcircumferentially spaced ribs 372 are positionedvwithin the channel 370 formed by the wall structure 314. The channel 370 conducts fluid from the source of fluidbeing pumped to the inlet 316.

A gearrack 334 is attached to -the outer end 376 of the shell 371 of the wallmember 328. Gear means are mounted on the. housing 310 and engage the rack 334 for moving the wall member 328 axally relative to the impeller 344.' The'gear 'means' illustrated consist of pinions 333,ispur.gears .339, actuating gears 340, a hand wheel 341 and a'chan drive 345. i

I The positionof the lip 331 relative to the impeller 344 determinestthe Volume of fluid being recirculated through the fluid return passage and through the impeller 344. The' wall members 328 are reciprocally moved axally relativelyto' the impeller 344 to open and close the 'fluid return passage 325 and henc'e regulate the 'Volume of fluidsbeng.recirculated. The cha'n drive 345 serves to coordinate .therecprocal movement of the wall members 321 relative' to the impeller 344;

e .In operation thefluidi being. pumped enters thechannel .370, flowsbetween the circumferentialiy spacedribs 372,

.yolume of fluid-being vdschargedbytheipump. i i

. Fig. 6. shows' a .modified meansitvcooperating .with the housing 110, for varying thevaxialextent of the communication between 'the fluid returnpassage 125 and the intake 120 in which theoimpeller 111 .can be re'ciprocatedfor varying the axial extentof the ,communication between the fluidreturn passage.12.5 and `the intake 120. The surface portion 123 of impe11er111 is spaced apart from the .opposed inner wallstructureisurface portion 124. to define fluidtretum' passage 125.. Thehousing 110.:has wall .structures114 forming' thelimpeller chamber 115. A wear ring or wallmember 128 is mountedin the wall structure ttotodefine an inleti 116 ir'tothe tchamberlls. A centrifugal single suctionitnpeller 111 having a.fluid confim'ng .pumping passageway 119, which terminates in int'ake andudischarge end-s 120and 121, respectively, is mounted. fort rotation within 'the impeller chamber .115 on a rotatable shaft 112. Theintake 120 and discharge end. 121 are. dposedadjacentimet 116 andtoutleti 117, respectively.) Theshaft112is carried. at-the impeller endi by a hearing assemblyu. A seal assembly 7113 is carried by;the reciprocating :structure 150. The shafti 112 has an externally nsplned section 151. which inter'connectswith an internally splined section of the .driven rotatable element 152. The driving means' (not shown) drives the element 152. The bulk of .the ishaft 112. is v rotatably supported inball: hearings 153 which are` car ried by the reciproca ting structure t 150. The` irecprocatngstructure 150 has a carrier 154 which restston .the bed plate 155. The carrier 154 is tin tongue and groove engagement with' the bed plate 155 andi-sfreeto move axially with respect to the bed plate '155 butnistfixed against rotation. 'The reciprocating .structure150 can be moved axially toward andaway from the housing 110 by rotation of the actuating screw 162.

i `Opening-andclosirig'of the fluid return passage 125 is eflectedbythe hand wheel 161 which` is connected with; and rotates the actuating 'screw 162. iThe hand wheel 161 ;threadingly-` carried at one :end by` the bed plate 155 is afi'ixedat its opposing `end to the `reciprocating-"structure 150. Clockwise rotation ,of the hand wheel 161 will drawthe carriage 154 axially toward the hand wheel 161 opening the fluid return passage 125. Counterclockwise rotation will move 'the carriage 154( away from` the hand wheel 161-c1osing the fluid return passage l25. 'O-rngs 130 `-seal the structure 15 0 10 the housing 110. Fig. 8 shows the position of the impeller 111 with-respect to thewall structure` 114 when -the impeller 111-has' beenmoved -axally away from the wallmember-;128 to open the fluid return passage 125 for' receiving discharged` fluid from the discharge end 121 oi theimpeller 111.- Deflecting means,-showr as housing portion 160, project over the i impeller opening to aid'in defiectng' the discharged fluid into the fluid return passage 125. r i j i The particular "embodments of `theinvention illustratedand described heren are illustrative only. The invention includes` such other modificationsand equivalents as may` readily occur to those skilied -in the art, within the scope of the appended claims. i I u flIt is claimed and desired to secureby Letters Patent: luA variable' flow centrifugal pujn comprising,in combin ationya housinghaving wll'structures forming a fluid corflning chamber, said wall'structures'cooperating to'form an outlet for discharging fluid from saidpump,

tand. a; second inletgaxially.spaced 'from each other'for the admission of fluid into saidchamber, a double suction impeller member rotatably mounted insaid cham'ber iandiycomprising a hub por tion, a 'first set ?of blades'co- ;Operating (with .one end of said hub portion to' dene ;a

first, intake for. receiving fluid to be pumped, "said first ,intake axially facing said first inlet; 'a =second"set;--of

blades cooperating with the other-end of said hub portion to define a second intake for receiving fluid -to 'be ,p'nmped, said. second intake spaced` from said first-intake and axiallyt facing said second inlet, a first-wal1 portion .merging with said one end` of saidhub portionto 'jointly present a first surface extending frornthe innermost point of fluid flow of said impeller adjacent said first` inlet' to the periphery 'of said impeller a second wallportion .merging withsaid other end of said hubporton 'and said first wall portion to jointly present'a s econd surface' .extendingtfrom theinnermost point of fluidflow of said impeller. adjacent said second inlet to 'the periphe ry 'of ,saidmpe11er, saidfirstset'of blades joining with said surfaceto formua single 'set of flud-impellng passages extendingitbetween said E outlet and said first in1et,-sad 'second set. of.bladesjoining wth said second surface to. form asingle. set of fluidimpelling passages extending from said outlet to said second inlet, said impeller mem- ,benand opposingwall structures' definingtherebetween a ,first 'and a 'secondfluid return passageysaid first fluid return passage hydraulically -connectng said outlet to said first intake fort recirculating fluid through said-impeller; said second fluid return passage hydraulicaliy connecting said outlet to said second intake forrecirculating fluid through said impeller, said fluid return passages `being of suflicient capacityto absorb-substantially-the entire Vdischarge offluid through saidoutlet,` means forinovng said wall members-in unson axiallyi relatively to said impeller member, one of said wall members having" its innerend coactingwith saidimpeller to ;vary the extent of axialcommunication between said first fluid return passage and said first -intake,` the other of said wall members having..its inner` end coacting with said impeller fotvaryingthe axial extent of communication between said second fluid return passage and said second intake; 2. A variable flow centrifugal purhpcbmprsng, in combination, ,a housing having wallstructures "formng a fluid confining chamber, said wall strutures cooperating to. form an outlet for dischargingflud from said' pump, two open ended generally cylindricai 'wall' members'reciprocally mounted in sad Wall structures to forrn 'a'first and: asecond inlet ax ially spaed from each other for theadmission of fluidinto said chamber, a'double 'suc` tion mpelle member rotatably mounted `in` said charnber and` comprising a` hub portion,-a 'first set of blades co Operating with one end of said hub por' tion to define a firstiintake for receivingfluidto bepu'mped, said first intake axiallyfacng said first in1et, a second setof blades cooperatingwith the other end oflsaid hubmitonft definea second intakeor reeivingfluid to be pumped, said second intake spaced from' said first intake and axially facing said second inlet, a first wall porton'merg ing with said one endof said-hub portion to ontly present a first i surface extending from the innermost' point of fluidflow of 'said impeller adjacent said first ir'let to thetperiphery of said impeller, asecond wall portion mergirg with said other end of said hub portion and said first wallportion to jointly-pres'ent a second surface' ex tending from theinnermost point of fluid flow of said impeller adjacent said second inlet' to the' 'periphery of said i impeller, said first set of blades joining with said surface to form a single set of fluid impelling passages exten ding between said outlet and said first inlet, said second set of blades joining with said'second surface to form a single set offluid impelling passages e'xtending from said ou -lt iqsaidlsec nd in1ets,aidimpeller member and? opposrrig yvallstructures defining* therebetween a firstrand' a ,secondfluidreturn passage, saidfirst fluid return passage hydraulically connecting said outlet to said first intake for recirculating fluid through said impeller, said second .fl uidreturn passage hydraulically connecting said outlet return passage and said firstoirta'ke, the other of said wall members having its inner end coacting with 'said mpeller for yaryngtheaxial extent of communication .b tween said second fluid return passage and said 'second intake, and means forintercormect'ng said wall members and for reiprocally moving in unison said wall members ax ally in opposing directions 'relatively to said impeller thereby varying the axial distance between said 'impeller member and said inner end of each of said wall members.

3. variable flow` centrifugal ,pump comprising, in combnation, a housing having wall structures forming a fluid confinng chamber, one of said wall structures definng an outlet for discharging fluid from said chamber, a shaft rotatably mounted in said housing and extending through said chamber, said housing defining two adjacent pumpng sections, each of said sections comprising another of said wall structures defining therein a channel, said other wall structure having a wall member reciproca1ly mounted therein and defining an inlet from said channel into said chamber, said wall member'embracing said shaft, an impeller mounted on said shaft for rotatontherewith and havinga hub portion, a set 'of blades cooperating with said hub portion to define an intake for reeevng fluid to be pumped, said intake axially facing sad nlet, an impeller wall 'portion merging with said hub portior to jointly present 'a surface extending from the nnermost point of fiuid flow of said impeller to the periphery of said impeller, said set of blades joining with sad surfaces to form a single set of fluid mpelling passages extending between said outlet and said intake, said mpeller and opposing said wall structure defining therebetween a fluid return passage hydraulically connecting sad outlet to said intake for recirculating fluid through said impeller, said fluid return passage being of suflicient capacity to absorb substantially the entire discharge of fluid from said impeller, means for moving said wall member axially relative to said impeller, the inner end of said wall member coacting with saidimpeller to vary the extent of hydraulic communication between said fluid return passage and said intake, saidimpellers' of each of said sections being positioned back to back on said'shaft to form a double suction impeller member postionable within said chamber.

4. variable flow centrifugal pump comprising, in combnaton, a housing havingwall 'structures forming a fluid confining chamber, one of said wall structures defining an outlet for discharging fluid from said chamber, a shaft rotatably mounted in said housing 'and extending through said chamber, shaft sleeves rotatably mounted on said shaft, said housing defining two adjacent pumping'sections, each of said sections comprising another of said wall structures defining .therein a channel and having a wall member reciprocally mounted therein, said wall member comprising a cylindrical shell'embracing said sleeve, an aunularlip positionable to coact with said impellen and a plurality of circumferentially spaced radally extending ribs formounting said lip in the inner end of said shell, packing means interposed between a portion of said shell and said sleeve, said lip defining an inletibetween said channel and said chamber, an impnerj mountedon said shaft for rotation therewith and havingfa hub portion, said hub portion positioned on said shaft'intermedite ad'sleeves; a set of blades co Operating with said hub portion to define an intake for re'c`eivi`ng fluid'to be pumped, said intake axially facing said' inlet, an impeller wall portion merging with said hub portion to jointly present a surface extending from the innermost point of fluid flow of said impeller to the periphery of said impeller, said set of blades joining with said surface to' form a single set of fluid mpelling passages 'extending between said outlet and said intake, said impeller and opposing 'said wall structure defining therebetween a fluid return passage hydraulically connecting said outlet to said intake for recirculating fluid through said impeller, said fluid return passage being of suflicient capacity to absorb substantially the entire discharge of fluid from said impeller, gear rack means connected to the other end of said shell, an actuating gear mounted on said housing and positioned to operatively engage said rack means for moving said wall member axially relative to said impeller member to vary the extent of hydraulic communication between said fluid return passa'ge and said intake, said impellers of each of said pumping sections being positioned back to `back on said shaft to form a double suction impeller member positionable within said chamber.

5. A variable flow centrifugal pump comprising, in combination, a housing having wall structures forming a fluid confining chamber, one of said wall structures defining an outlet for discharging fluid from said chamber, a shaft rotatably mounted in said housing and extending through said chamber, said chamber defining two adjacent pumping sections, each of said sections comprising another of said wall structures defining a channel and having a wall member reciprocally mounted therein, said wall member comprsing a cylindrical shell embracng said sleeve, an annular lip positionable to coact with said impeller, and a plurality of circumferentially spaced radially extending ribs for mounting said lip on the inner end of said shell, packing means interposed between a portion of said shell and said sleeve, said lip defining an inlet between said channel and said chamber, an impeller mounted on said shaft for rotation therewith and having a hub' portion, said hub portion being positioned on said shaft intermediate said sleeves, a set of blades cooperating with said hub portion to define an intake for receiving fluid to be pumped, said intake axially facing said inlet, an impeller wall portion merging with said hub portion to jointly present a surface extendng from the innermost point of fluid flow of said impeller to the periphery of said impeller, said set of blades joning with said surface to form a single set of fluid mpelling passages extending between said outlet and said intake, said impeller and opposing said wall structure defining therebetween a fluid return passage hydraulically connecting said outlet to said intake for recirculating fluid through said impeller, said fluid return passage being of suficient capacity to absorb substantially the entire dis charge of fluid from said impeller, said impellers of each of said pumping sections being positioned back to back on said shaft to form a double suction impeller member positionable within said chamber, and means for interconnecting said wall members and for reciprocally moving in unison said wall members axially in opposing directions relatively to said impeller thereby varying the axial distance between said impeller member and said lip of each of said wall members to vary the extent of hydraulic communication between said fluid return passages and said intakes.

6. A variable flow centrifugal pump comprising, in combination, a housing having wall structures forming a fluid confinng chamber, one of said wall structures having an open ended generally cylindrical wall member reciprocally mounted therein and describing an inlet for the admission of fluid into said chamber, another of said wall structures describing an outlet spaced from said inlet fondischarging fluid from said chamber, a fluid impeller m mbr rotatably mounted in said chamber and &874342 comprisin'g a plurality of blades having axially extending free ends, a hub portion defining with said blades an intake for receiving fluid to be pumped, said intake axially facng said inlet, and an impeller wall portion merging with said hub portion to jontly present a surface continuous from the axis of said inpeller member to the periphery thereof, said surface joining with said blades to form in said impeller member a single set of fluid impelling passages extending between said inlet and said outlet, said impeller member and said one wall structure defining therebetween a fluid return passage hydraulically connecting said outlet tosaid intake for recirculating fluid through said impeller, said return passagebeing of sufficient capacity to absorb substantially the entire discharge of fluid through said outlet, external means directly engaging said wall member for reciprocally moving said wall member axially relatively to said impeller member to overlap the axially extending free ends of said blades, said external means being independent of responses from said fluid to selectively position and maintain the inner end of said wall member in cooperating alignment with said impeller member for varying the extent of hydraulic communication between said fluid return passage and said intake while said pump is operating.

7. A variable flow centrifugal pump comprising, in conbination, a housing having wall structures forming a fluid confining chamber, one of said wall structures having an open ended generally cylindrical wall member reciprocally mounted therein and describing an inlet for the admission of fluid into said chamber, another of said wall structures describing an outlet' spaced from said inlet for discharging fluid from said chamber, a fluid impeller member rotatably mounted in said chamber and comprising a plurality of blades having axially extending free ends, a hub portion defining with said blades an intake for receiving fluid to be pumped, said intake axiallyefacing said inlet, and an impeller wall portion merging with said hub portion to jointly present a surface continuous from the axis of said impeller member to the perphery'thereof, said surface joining with said' blades to form in said impeller member a single set of fluid impelling passages extendng between said inlet 'and said outlet, said impeller member and said one wall structure defining therebetween a fluid return passage hydraulically connecting said outlet to said intake for recirculating fluid through said impeller, said return passage being of suflicient capacity to absorb substantially the entire discharge of fluid through said outlet, external means mounted on said pump housing engaging said wall mernber for reciprocally moving said wall member axially relatively to said impeller member to selectively establsh and maintain the capacity of said return passage independent of responses from' said fluid while said pump is Operating, said wall member having "an integrally formed annular lip defining its inner end, said inner end of said lip having a curved inner surface in complementary overlapping relation with said axially extending free ends of said impeller member for varying the axial extent of the communication between said fluid return passage and said intake while said pump. is Operating.

8. A variable flow centrfugal pump comprising, in combination, a housing having wall structures forming a fluid confining chamber, one of said wall structures having an open ended generally cylindrical wall member reciprocally mounted therein and describing an inlet for the admission of fluid into said chamber, another of said wall structures describing an outlet spaced from said inlet for discharging fluid from said chamber, a fluid impeller member rotatably mounted in said chamber and comprisng a plurality of blades having axally extending free ends, a hub portion defining with said blades an intake for receiving fluid to be pumped, said intake axially facing said inlet, and an impeller wall portion merging 10 with said hub portion .to jointly present a surface continuous from the axis of said impeller member to the periphery thereof, said surface joining with said blades to form in 'said impeller member a single set of fluid impelling passages .extending between said inlet and said outlet, said impeller member and said one wall structure defining therebetween a fluid return passage hydraulically connecting said outlet to said intake for recirculating fluid through said impeller, said return passage being of sufflcient capacity to absorb substantially the entire discharge of fluid through said outlet, external means engaging said wall member for reciprocally moving said wall member axially relatively to said impeller member to selectively control and maintain the discharge of said pump from maximum to substantially near zero capacity independent of responses from 'said fluid while said pump is operating, said wall member having a cylindrical lip defining its inner end and overlapping said axially extending free ends of said impeller mem-ber for varying the axial extent of the communication 'between said fluid return passage and said intake.

9. A variable flow centrifugal pump comprsing, in combination, a housing having wall structures forming a fluid confining chamber, one of said wall structures having an open ended generally cylindrical wall member reciprocally mounted therein and describing an inlet for the admission -of fluid into said chamber, another of said wall 'structures descrbing an outlet spaced from said inlet for discharging fluid from said chamber, a fluid impeller member rotataibly mounted in said chamber and compris ing a plurality of 'blades having axially extending free ends,

a hub portion defining with said blades an intake for receiving fluid to 'be pumped, said intake axially facing said inlet, and an impeller wall portion merging with said hub portion to jointly present a surface continuous from the axs of said impeller member to the periphery .thereof, said surface joining with said blades to form in said impeller member a single set of fluid impelling pas-sages extending between said inlet and said outlet, said impeller and said one wall structure defining therebetween a fluid return passage hydraulcally connecting said outlet to said intake for recirculating fluid through said impeller, said return passage being of sufficient capacity to absorb substantially the entire discharge of fluid through said outlet, the inner end of said wall member defining a lip having a curved inner surface in eomplementary overlapping relation with said axially extending free ends of said impeller member, said inner end of said wall member coacting with said impeller member for varying the extent of hydraulic communication between said fluid return passage and said intake, and means for reciprocally moving said wall member axially relatively to said impeller member -to selectively control the discharge of said pump from minimum to substantially near zero capacity while said pump is Operating, said means comprising axially extending racks aifixed to the periphery of said wall member, rotatable pinions engaging said racks, and means external to said housing and connected to said pinions for rotating said pinions and reciprocating said racks.

References Cited in the file of this patent UNITED STATES PATENTS 1,556,771 Dupont Oct. 13, 1925 1,846,379 Anderson Feb. 23, 1932 2,239,152 Jacobsen Apr. 22, 1941 2,265,940 Forrest Dec. 9, 1941 2,555,686 Farrelly et al. June 5, 1951 2,786,420 Kenney Mar. 20, 1957 FOREIGN PATENTS 326,866 Germany Nov. 25, 1919 494,649 Germany Mar. 26, 1930 808,796 Germany July 19, 1951

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