US2599927A - Slipper pump - Google Patents

Description

June 10, 1952- w. T. LIVERMORE 2,

SLIPPER PUMP Filed Oct. 6, 1944 2 SHEETS-SHEET l June 10, 1952 w. T. LIVERMORE 2,599,927

SLIPPER PUMP Filed Oct. 6, 1944 2 SHEETS-SHEET 2 IN V EN TOR.

Patented June 10, 1952 UNITED, STATES PATENT OFFICE SLIPPER PUM? William T. Liver-more, Grosse Pointe Farms, Mich. Application October 6, 1944, Serial No. 557,390

11 Claims. 1

This invention relates to rotary pumps and specifically to that type thereof known as slipper pumps.

The rotary elongated vane type of pump is one wherein a rotor mounted for rotation in a pump casing or chamber carries. a plurality of spaced vanes slidablyarranged in rather deep radially extending slots which either extend nearly to the center of the rotor or extend diametrically entirely across said rotor. Although very many different types of constructions for the vane types of pumps have been proposed such type of pumps are-subject to many objections. Unless the vanes extend a very substantial distance into the slots of the rotor, difiiculty is experienced in preventing thevanes from jamming or cocking. As it is...

necessary, therefore, to have the vanes extend quite a substantial distance into the slots of the rotor, the frictional drag of the movement of. the vanes in the slot is quite appreciable. Again due to the distance which the vanes must extend into the rotor slots, the vanes must be of substantial length and, due therefore to their mass, .are forced against the bore of the pump chamber by centrifugal force. with suificient pressure as to cause marked wear upon the-surface of the pump chamber.

Because of the above and other disadvantages of the rotary elongated vane type of pump, the so-called slipper type of pump is frequently employed. By a slipperpump is. meant one in which 7 the fluid propelling members instead of being of appreciable length, considered radially oflthe pump, .are small block-like members, the thicknessof which, that is the dimension considered radially, vis-usually no-greater than and .preferablyis considerablysmaller than the width of the. notch or slot in the rotor in which said slipper is carried. By width is meant the dimension considered circumferentially, or in the direction of rotationof the rotor.

Both the elongated vane and slipper types of pumpsare characterized by the rotor being mounted in a. casing .eitherhaving a pump chamber with a truecylindrical contour that is eccentric with respect to the axis of rotation of the rotor thereby to provide acrescent-shaped workingspace or the inner surfaceofthe pump chamberis in theform of a developed contour usually consisting of a plurality of cylindrical arcswhich merge together. to. form a smooth contour --with .which theuouter facesbf .prODelling members,

Another object is to provide a new and improved construction for a slipper type of pump whereinaportion of the pump chamber is in the form of a cylindrical arc concentric with the cylindrical surface of the rotor and, but very slightly greater than the radius of the rotor therebyto form a seal having a large surface area between the rotor and the inner wall of the pump chamber and located between the outlet and inlet ports of the pump.

A further object is to provide the pump chamber of the pump with a'second cylindrical are also concentric to the cylindrical surface of the rotor through the entire working are between the inlet and; outlet ports whereby the surface area of contact of the leading face of any one of the slippers against the fluid being pumped thereby will be uniform' throughout'th'e entire travel of the slipper through theeffective working arc of the pump.

Another object of the invention is to form the contour of the surface of the pump chamber thereof adjacent to the inlet port and to so locate the port relative thereto that the formation of a vacuum pocket behind a slipper as such slipper enters the inlet port opening will beobviated.

A further object is to form the contour of the pump chamber in'the area adjacent to the cutoff edgelof the outlet port and to so locate the outlet port relative thereto that no fluid will be trapped in advance of a slipper as it passes through the non-working arc of the pump from the outlet towards the inlet of the pump.

Another object is to provide anew and improved construction for the slippers of a slipper type pump of the type wherein the slippers are seated in notches of much greater width than the slipper, whereby fluid will be admitted under pressure to the underside of the slipper andv also toprovide theslipper'with a cut away portion on its outer face thereby to permitthe pressure of the fluid to be exerted on the outer face of the slipper and thus count'er-balancea portion of the fluid pressure on the underfac'e thereof to reduce the frictional drag between the slipper and the inner surface of the pump chamber while at the same time maintaining effective sealing contact between the slipperand the surface ofthe pump chamber.

A further object is to provide anorif ice or opening extending betweenjthe outer andinner faces of a slipper so as to insure that thepressure of the fluid beingpumped will beequal onboth faces of such slipper. v

Another object is to provide a slipper type of pump in which the inner surfaces of thepump chamber are so constructed and arranged. that the outer working faces of the slippers will be formed upon an are having the. same radius of curvature, as the inner surfaces of the pump chamber throughout the working arcof the .pump

. and upon a radius greater than. the, inner surface companyingdrawings forming a part hereo of the pump chamber between the outlet and inlet whereby sealing contact of the slippers along the following edgethereof with the last-mentioned surface of the pump chamber will be se cured.

As a result of considerable experimentalanddevelopment work, I have found that the best efficiency for a slipper type pump is secured if the t notches in which the slippers are mounted in the.

rotor'are wider than the width of the slipper'in order to permit the fluid being pumped by a" slipper in the working arc of the pump to flow past the .leading'edge ofthe-slipper and under the bottom surface thereof, thereby to employ the pressure of the fluid for forcing or-holding the outer face of'the'slipper against the inner surface of the pump chamber withan effective seal. I have found that if the surface of the rotor of the pump contacts with the inner-surface of the pump chamber at the point'of tangency between these two" members with a line contact in accordance with the usual construction of a slipper pump, I the pressure of the fluid in the delivery or outlet sideof the pump is exerted upon the rear or followingedge of the slipper; while suction is exerted: on the leading or forward-edge of the slipper as the slipper is passing through the line of .tangency This tends to cause the slippers to be pulled'forwardly'so that the forward edgeor leading edge contacts with the front wall ofthe notch and as the slipper passes into the working arc, the slipper is then shifted rearwardly to contact with the rear edge of the notch. Consequently, a more-or less continuous shiftingof the slippers from the forward to the rearward edge -of the notch occurs, which produces'fluctuations-in the fluid pressure line that tends to I working side of the pump which completely obviates theseobjectionable features because of the large;area of the seal formed directly between theouter surface of the rotor and the cylindrical inner surface of the pump which is concentric with the cylindrical surface of the rotor and .curvedupona radius that is substantially equal to the radius of curvature of the rotor.

v The above and other objects of the invention, -such as providing a pump of marked efficiency,

. .low' manufacturing and maintenance costs will .appear more fully from the following more de tailed description and by reference to the acf and wherein:

Fig. 1 is a central vertical section through the pump constructed in accordance with the principles of the present-invention,

I Fig; 2 is'a vertical section taken substantially on the line 2-2 of Fig. 1,

7 Fig. 3'is an enlarged fragmentary view of the upger portion of the pump rotor shown in Fig. 1, an r r Fig. 4 isa perspective view of an individual .slipper element showing particularly the recess .in the outer face thereof.

i As shown in the drawings, the numeral ID indicates the outer casing. of. the pump which is provided .with an inlet II and an outlet l2 separated by a wall I3. As clearly shown in Fig. 1, "the inlet conduit terminates in an inlet port [4 I while the outlet conduit terminates in similar port l5.

The casing I is provided with a pump chamber indicated generally by the reference character l6 51in which is rotatably mounted a rotor I! having apair of trunnions I8 and I9 integral therewith. The trunnion I8 is mounted in a suitable bearing bushing20 seated within a bore 2| formed in a boss .22, formed integral with the head 23. The

trunnion I9 is similarly journaled in a bushing 24 seated within an open ended boss 25 formed integral with the head 26, the heads 23, 26 being suitably secured to the pump casing H) in the usual manner by bolts (not shown),

The rotor I1 is provided with a plurality of spaced notches 21 in each .of which isseated a slipper 28 presently to be more fully described. a

Each of the slippers .28 is normally urged in yielding contact. withthe wall I 5 .of .theQpump chamber by a compression spring 29, oneend of which isseated within a small holeZfl-a drilled in the base of each notch2'l. The other end of the spring 29 seats within a similar hole 30 drilled in the bottom face of its respective slipper 28. As

shown in Fig. '1 of the drawings, each slipper '28 is substantially narrowerthan. the width of the notch 21 within which it. is seated so that when the slippers are passing through the working arc of the pump chamber, the fluid under pressure within such working arc may pass into the notch to exert its pressure on the underside of the slipper and hold the same with a firm sealing contact against the wall of the pump. chamber. Forthe purpose. of reducing the pressure exerted by the slipperagainst the wall of the pump chamber, a

small. through hole 3| is drilled through the slipper in alignment with thehole or recess 30 so as to permit the pressure of the fluid within the notch below the slipper to be communicated to and equalizedwith fluid within a U-shaped recess32 formed in the outer face of the slipper. This recess is bounded by a'pair of side walls or 'ribs 33 and a rear wall or rib 34, as shown in Figs. 1 and 2 of the drawings. It will be seen from the 5 foregoing description that when a slipper is passing through the working arc of the pump with the rotor l1 rotating in thedirection of the arrow A .in Fig.1, the fluid trapped in advance of the .slipper will be prevented from flowing past the 5 outer. face of the slipper by the sealing of the outer surfaces of the two side ribs 33 and the rear rib 34 of each slipper; that the pressure of the fluid in advance of the slippery will be com- .municated directly to the recess 32 through the open front thereof and also through the notch 21 and holes 30 and BI to the underside of the slipper so that the pressure both below the under- ;face of the slipper and within the recess 32 on the top face thereof will be equalized.

5 The pumpof the present invention has been 7 particularly designed for use with automotive vehicles wherein smoothness and quietness of operation is. absolutely imperative. If the surface of the, rotor of the pump contacts with the inner 5 surface of the pump chamber at the point of tangency between these two members witha line contact in accordance with the usual construction of a slipper pump, I have found that the pressure of the fluid in the delivery or outlet side of the pump is exerted upon the rear or following edge of the slipper, while suction is exerted on the leading or forward edge of the slipper as the slipper is passing through the line of tangency. This tends to cause the slippers to be pulled forwardly so that the forward edge or leading edge contacts aoemaav ".withthe front wall o'f the notclr'and as theslipper passes :into' the: working arcgatheslipper'ziszthen shifted rearwardly to contact with gthe:rearnedge :of the notch. Consequently, -a *more'or -:less.:con'- -tinuousshift'ing of the-*slippersifrom ther'forward to'the rearward edge ofreachznotch occurs-,flwhich not.ionly causesfluctuationsinthe'fluid' -pressure line that tends to' pro'duce an objectionable hydraulic hammer inwthe pressure line, lbutfithe shifting of the #slippers :also tends; :to rproduce "mechanical 'clicking -noises which are highly ob.- jec'tionable; I have :also found thata smoother, "quieter and more emcient operation: of a slipper type pump isi'obtained 'if the crosssectional "area or the space between" the outer surface of I the rotor-and the: inner surface of .theapump chamber is uniform 'throughout'=the: entire working arc :of the pump between "the Binletvand outlet: thereof. The objectionable shifting ofithe slippers'above described is .2 obviated in Jthe :present invention "by forming that portion \of the surface :of' the pump chamber 16; indicated iby the :reference character :25, and located on the inner sideof :the wall. l3 as a cylindrical arcihaving aradiusr substantially equal to the radius -.of:the5rotor:.l1, it being, of course, understood that the". radius r of the surface 35 wouldi be in:.:the neighborhood ofathousandth'o'f an=inch larger thanzthe radius of therotor so-that' thereiis-a neatizrunninglrfit between the rotorand pump :chamber :at this point, while at the' same timebeinggof sufliciently close fit to=maintaim an effective seal sbetweenv the inlet I lan'd outlet l-'2*of-' the pump. 'The. uniform cross {sectional area oftherpump insthe working arc thereof '-isobtained -by forming thatiportion of f the pump chamber Hi i indicated by: the'refer- -ence-character'l31-also as a cylindrical areby'hav- 'in-g'a radius-R,-wh-iehis equal to=1=+e, whereirL'e indicates the linear" distance between' the .outer face "of 'the' -rotor f1 and the cylindrical -arc;31

As a matter of manufacturing; simplicity and low 'manufacturing cost, the' pump chamber is preferably fabricate'd by the :use rofan ordinary round or cylindrical millingcutter-having a-ra'dius r, the-axisof the cutter being heldin substantiall-yexact alignment with the axis upon which the rotor l1 is to be" rotated, 'while the:cutter.iis rotated to machine the cylindrical surface 35 :to finished-size. The 'milling: cutter' is :thenpreferably'fed-sothat its axis travels inra straight line, for example, along :the line .2:, which will result in -the formationof the surface 38 locatedfibetween the radial linesia and b. Next the cut'ter is then fedso that its-=axis traversesthe circular arc y having'a radius equal to-the distance e indicated inthe drawing. This will: result ::in :the formation oi -the cylindrical surface 531 'having a radius R. equal to 'r+6,--a-n'd locatedlbetweennthe radial lines b' and af. "Finally' thecutteriis fed 'backwardly to its starting point along: the .line a which results-in theformationof the-surface -36-a located between theradi-al lines a and b..

As will-beseen from *the foregoing,=the method of'fabricating thewalls-of the pump; chamber t6 is of marked simplicityas it can be 'performed with an-ordinary stock on-standard z-type-of cylindrical milling cutter and-by: the simple :manipula- "tion of the carriageor a standard :milling --machine =within xthe'skill "of an ordinarymachinist. It-will, of course, beunderstoodi that-the contour of the :pump chamber-could-be formedsby; theause of a specialbreach: ifllthe pumpswere: toehex-constructed in large'quantitiesron a: production :basis. 'In the operation oftheepump mithtthezxrotor H rotating in a counterclockwise direction, as indi- '10 be in-its outermost radialipositionffromwtheaaxis of rotation, and so that there will she no :possibilityofanyfluid beingtrapped as it-werebetween the outer-face of the; slipper and the workingsarc '31 of the pump chamber: l.6 such trapping :would '15 tend to prevent-the rear edge'or rib 34 of thezslip- "per from forming a tight sealing contact with the wall 31.

Byreferenceto-Fig. 1, it will be seensthat-the distance between the twoslippers 28 through whichlthe radial lines-aan'db' pass is such that when the rear or following end of the slipper 28 at the lower right reachestheline b at which 'the' leading'edge' of outlet port 15 terminates, the leading edge of the slipper 28 at lower'left simultaneously reaches the cut-off end of the 'inletport-14, as a result of this constructionthere will always be two succeeding slipperstaking up the pumping function as soon as-the slipperimmediately ahead of them ceasesits 1 pumpingsac- 30 tion. Consequently, with the arrangement'disclosed,:the pump functions; assa multi-stage pump andpumpslip isreduced to a minimum. It-will also lse-obvious that as thedistance between the periphery of the-rotor f1: and the cylindrical sur- :"fabe -31jis= uniform-throughout the pumps working-arc,-.the delivery-oftthelpumpawill. atrallrtimes be unif'orm.

sAnz important-feature .of- :the pump of the present invention :is :that' the-router 'contac'tesurface 40 of. each .-slipperz is curved-Lon an arcrequal to the radius Riofithe cylindricalsurface 1351f; therefore Lthfl i-leading zandifollowing edges: of *therslippers will contact: with the-surface: 3.5: of smaller-radius. Surface; as distinguished from :line, .seals' are athereby; effected .tbetween'. outlet and; inletv ports,

by thesslipperszacross [their-working.:armandlby the @rotonitself; acrossithenon-working are. 7

.The .-springs 28 act iltOflfiSSiSt, the centrifugal sjf0I.0&"iIT; keepingithe slippers snugly seatedagainst the working arcia'l of thesworking chamber-atilow speeds and also tend to prevent'thel'slippersfrom stickingto the-bottom of the notchesafter they havepassed the point of tangency between the rotor an'cl workingchamber. 3

The provision of the recess 32 in the outer lworking' face-of the slippers together with the communication provided-through the hole r3l and counterbore 30 for fluid "between the outer and underfaces of the' slippers will result,- as herein- 0 before described-in a reduction of the-forceor pressure withwhich the-slipper i forced against the surtace of the working chamber of the pump by the-fldid: pressure.

It will be noted thattheoutlet port l=5-termi- 5 natesatthe line b" so as to insure that'the slippers: will= deliver 'fluid to -the outlet port I 5 and outlet-i i 2,ewhile thesli'ppers arestillin their outer- -mostradial positiomand,therefore, delivering the full volume 'offiuid from the working chamber.

ASLthe slippers sweep upwardly from the right handsside of the pump, ass'howninFig, 1, and throught-the discharge-arc of the-pump, the con- .figurationof ithe working faceof the borei6 is such :that the 1 outer. faces of the-slippers pass -'75 into: engagement with 'the concentric are 3-5 be- '7 fore they pass out of communication with the outlet port I and outlet fl 2, as is clearlyiindicated by the position of line a. It will likewise be noted that the end of the are 35, as indicated by the position of line b, is slightly beyond the upper end of the inlet port I I. This results, as hereinbefore explained, in the sealing of the pump'in the non-working are between the inlet H and the outlet [2 being effected between the periphery of the rotor I! and the concentric are 35 of the bore l6. 'Asa result, the slippers are not subjected ,to any suction or pressure effects from either the inlet or outlet of the pump, with the resultant tendency of the slippers, as hereinbefore described, to move backward and forward in their respective notches; It will be noted that the distance between the line a and the cut-off point of the outlet port I5 is greater than the width of the slipper so that there will be no possibility of any fluid being trapped ahead of the slippers as they pass through the concentric non-working are 35 of the working chamber l6.

Although I have described a satisfactory constructional example embodying these various principles of invention, it will, of course, be understood that any changes, variations and modifications thereof may be resorted to without departing from the spirit of the present invention, as set forth in the claims hereunto appended.

I claim: v

1. In a slipper type pump, a rotor having a plurality of spaced notches therein, a slipper freely mounted in each of said notches, the width and thickness of each slipper being less than the width and depth of its respective notch, a pump casing having a working chamber in which said rotor is rotatably mounted and an inlet and an outlet terminating in inlet and outlet ports respectively communicating with said working chamber, and said working chamber being provided with an arcuate sealing surface concentric with the axis of rotation of said rotor located between said outlet and inlet ports, and the radius of said arcuate sealing surface being substantially equal to the radius of said rotor thereby to form a fluid tight seal of relatively large area between the periphery of said rotor andsaid arcuate sealing surface between said inlet and outlet ports, the arc having said radius extending circumferentially into said outlet port a distance at least equal to the width of a slipper.

2. In a slipper type pump, a rotor having a plurality of spaced notches therein, a slipper freely mounted in each of said notches the width and thickness of each slipper being less than the Width and depth of its respective notch, a pump casing having a working chamber in which said rotor is rotatably mounted and an inlet and an outlet terminating in inlet and outlet ports respectively communicating with said working chamber, and said Working chamber beingprovided With an arcuate sealing surface concentric with the axis of rotation of said rotor located between said outlet and inlet ports having substantially the same radius as said rotor, the arcuate surface having said radius extending into said outlet port a distance equal to at least the width of a slipper and extending at least to the beginning of said inlet port thereby to prevent the production of suction and pressure effects upon said slippers as they pass through the non-working zone of the pump between outlet and inlet ports thereof.

3. In a slipper type pump, a rotor having a plurality of spaced notches therein, a slipper freely mounted in each of said notches the width and thicknessv of each slipper ';being less than the width and depth of its respectivelnotcn'aipump casing having a working chamber in which said rotor is rotatably mounted and an inlet and an outlet terminating in inlet and outlet ports respectively communicating with said working chamber, and said working chamber having an arcuate sealing surface concentric with the axis of rotation of said rotor extending entirely across said working chamber between the inlet and outlet of said pump and theradius of which is substantially equal to the radius of said rotor to form a fluid tight seal of relatively larg area between said inlet and said outlet, and said working chamber having an arcuate working surface concentric with said rotor, diametrically opposite to said arcuate sealing surface and the radius'of said second surface being greater than the radius of said rotor to form a working are between said inlet and outlet ports ofuniform cross sectional area, said slippers having an arcuateouter surface with a radius substantially equal to that of said working arc in order to establish a surface seal across the entire'outside area of said slippers through said working arc.

4. Inc, slipper type pump, a rotor having a plurality of spaced notches therein, a slipper freely mounted in each of said notches thewidth V and thickness of each slipper being less than the width and depth of its respective notch, a pump casing having a Working chamber in which said rotor is rotatably mounted and an inlet and an outlet terminating in inlet and outlet ports respectively communicating, with said working chamber, and said working chamber having an arcuate sealing surface concentric with the axis of rotation of said rotor extendingentirely across said working chamber between the outlet and inlet of said pump and the radius of which is substantially equal to. the radius of said rotor to form a fluid tight seal of relatively largearea'between said inlet and said outlet and said working chamber having an arcuate working surface concentric with said rotor diametrically opposite to said sealing surface to form a working are between said inlet and outlet ports of uniform cross sectional area, the concentric are including said working are extending into said inlet port a distance at least'equal to the width of a'slipper.

5. In a slipper type pump, a rotor having a plurality of spaced notches therein, a slipper freely mounted in each of said notches the-Width and thickness of each slipper being less than the Width'and depth of its respective notch, a pump casing having a working chamber in which said rotoris rotatably mounted and an inlet and an outlet terminating in inletand outlet ports respectively communicating with said working chamber, and said working chamber having an arcuate sealing surface concentric with the axis of rotation of said rotor extending entirely across said working chamber between the outlet and the inlet of said pump and the radius of which is substantially equal to the radius of said rotor to form a fluid tight seal of relatively large area between said inlet and said outlet and said working chamber having an arcuate working surface concentric with said rotor, diametrically opposite to said sealing surface to form a working arcbetween said inlet and outlet ports of uniform cross sectional area, the concentric are including said working arc extending into said inlet port a distance at least equal to the width of a slipper and extending at least to the beginning of said outlet por K 6. In a slipper type pump, a rotor having a plurality of spaced notches therein, a slipper freely mounted in each of said notches the width and thickness of each slipper being less than the width and depth of its respective notch, a pump casing having a working chamber in which said rotor is rotatably mounted and an inlet and an outlet terminating in inlet and outlet ports respectively communicating with said Working chamber, and said working chamber having an arcuate working surface concentric to the axis of rotation of said rotor and having a radius greater than the radius of said rotor to form a working are between said inlet and outlet ports of uniform cross sectional area, the concentric arc including said working are extending into said inlet port a distance at least equal to the Width of a slipper.

7. In a slipper type pump, a pump casing having a working chamber and a rotor rotatably mounted therein, said rotor being provided with a plurality of spaced notches, a slipper mounted in each of said notches, each of said slippers having a width and thickness and substantially less than the width and depth of its respective notch, the outer working face of said slipper being provided with an open ended U-shaped contact rib to reduce the cross sectional area of contact between the outer face of said slipper and the working chamber of said pump while retaining the stability characteristics of a full contact surface.

8. In a slipper type pump, a pump casing having a working chamber and a rotor rotatably mounted therein, said rotor being provided with a plurality of spaced notches, a slipper mounted in each of said notches, each of said slippers having a width and thickness substantially less than the width and depth of its respective notch, the outer working face of said slipper being provided along the side edges and the rear edge thereof with a projecting U-shaped rib to form a recess in said outer face open at the front end thereof for the admission of fluid under pressure to the outer face of said slipper as said slipper is passing through the working arc of said pump thereby to reduce the area of surface contact between said slipper and the surface. of the working chamber of said pump as said slipper passes through said working arc while retaining the stability characteristics of a full contact surface.

9. In a slipper type pump, a pump casing having a working chamber, an inlet and an outlet terminating in an inlet and an outlet port respectively and communicating with said working chamber, a rotor having a plurality of spaced notches rotatably mounted within said working chamber, a slipper within each of said notches, each of said slippers having a circumferential width and a radial thickness substantially less than the width and depth of its respective notch, said working chamber having a working or pumping are located between said inlet and said outlet ports through which said slippers pass to pump fluid under pressure from said inlet port to said outlet port and which fluid because of the looseness of each of said slippers in its respective notch is communicated to the underside of each slipper as it passes through said Working arc, the upper face of each slipper being provided with a U-shaped contact rib to reduce the area of surface contact between said slipper and the working surface of said working chamber and the surface of said chamber as said slipper passes through the working arc of said pump while retaining the stability characteristics of a full contact surface, and means for establishing communication between the outer and under-surfaces of said slipper to insure equalization of the fluid pressure on said under and outer surface as said slipper passes through said working are.

10. In a slipper type pump, a rotor having a plurality of spaced notches therein, a slipper freely mounted in each of said notches, the width and thickness of each slipper being less than the width and depth of its respective notch, a pump casing having a working chamber in which said rotor is rotatably mounted and an inlet and an outlet terminating in inlet and outlet ports respectively communicating withsaid working chamber, said rotor having a cylindrical periphery of radius 1', and said working chamber also having an arcuate sealing surface substantially equal to said radius r, concentric to the axis of rotation of said rotor and extending entirely across said working chamber between said outlet and inlet ports and said working chamber having an arcuate working surface diametrically opposite said first named surface extending entirely across said working chamber between said inlet and outlet ports and having a radius R=r+e where e represents the distance across the working arc of the pump between the said second surface and the periphery of said rotor, said slippers having an arcuate outer surface with a radius R=r+e.

11. In a slipper type pump, a rotor having a plurality of equally spaced notches therein, a slipper freely mounted in each of said notches the width and thickness of each slipper being less than the width and depth of its respective notch, a pump casing having a working chamber in which said rotor is rotatably mounted and an inlet and an outlet terminating in inlet and outlet ports respectively communicating with said working chamber, and said working chamber having a cylindrical working surface concentric to the axis of rotation of said rotor and having a radius greater than the radius of said rotor to form a working are between said inlet and outlet ports of uniform cross sectional area the distance between the leading sealing edge of any one slipper to the following sealing edge of the second adjacent leading slipper being at least equal to the circumferential distance between said inlet port and said outlet port across said working arc.

WILLIAM T. LIVERMORE.

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

UNITED STATES PATENTS Number Name Date 886,110 Bromley Apr. 28, 1908 1,123,977 Baker et al. Jan. 5, 1915 1,558,696 Marion Oct. 27, 1925 1,651,336 Wissler Nov. 29, 1927 1,805,063 Wrona May 12, 1931 1,922,951 Hawley Aug. 15, 1933 2,073,215 Mann Mar. 9, 1937 2,149,337 Deming Mar. 7, 1939 2,278,131 Livermore Mar. 31, 1942 2,333,323 Livermore Nov. 2, 1943 FOREIGN PATENTS Number Country Date 1,987 Great Britain 1897 163,200 Switzerland Oct. 2, 1933 270,833 Italy June 22, 1930 468,773 Germany Nov. 22, 1928 561,635 France Aug. 13, 1923

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