US2287318A - Balanced pressure metering pump - Google Patents

Description

F. M INTYRE BALANCED PRESSURE METERING PUMP June 23, 1942'.

Filed March 16, 1939 2 Sheets-Sheetjl June 23, 1942. F. MclNTYRE BALANCED PRESSURE METERING PUMP Filed March 16, 1959 2 Sheets-Sheet 2 Patented June 23, 1942 UNITED STATES PATENT OFFICE BALANCED PRESSURE METERING PUMP Frederic McIntyre, Newton, Mass. Application March 16, 1939, Serial No. 262,079

11 Claims. (Cl. 103 -126) Q The invention herein disclosed is concerned with gear pumps of the flxed delivery type, particularly developed and intended for use in spinning rayon. otherwise known as artificial silk. Such pumps are called metering pumps because they control and regulate the rate of flow to the spinning jets of the coagulable fluid solution to be made into filaments, as well when this solution is delivered from a source of supply at an initial pressure greater than needed to force it through the spinning jets. as when the pump itself raises the pressure from a lower pressure to that required for spinning. In this specification, including the appended claims, the term metering pump will be used with this meaning to identify the generic classification of the invention. The material which is passed through and delivered by the pump may be any of the solutions capable of being made into filaments, including viscose, cellulose acetate, and other materials commonly used for the purpose. Viscose presents certain peculiar problems, and one phase of the invention has particular reference to solving such problems, but the protection which I seek covers all novel structural, mechanical and functional characteristics of the invention whatever may be the particular substance operated on.

The primary object of this invention is to afford means for applying the pressure of the fluid passing through the pump upon the gears in such a way as to balance the pressures tending to spread the gears apart. A further object is to combine such pressure balancing means or provisions with means for effecting adequate and satisfactory lubrication of the gears by the solution, without dead-end ducts or conduits.

' Thegears of such metering pumps may be centered either by shafts to which they are secured, mounted to rotate in bearings in the pump casing, or by fixed studs on which'the gears are mounted to rotate, or by the enveloping walls in which the gears are contained. Heretofore the unbalanced pressures to which the gears are subject in use have made it impracticable to depend on the surrounding walls of the gear chambers for centering and holding the gears in liquid tight meshing contact. The liquid in both the intake and discharge sides of gear pumps exerts a spreading force tending to separate the gears from one another and causing their circumferences at the sides opposite to the meshing point'to bear against the contiguous walls of the chambers, in cases where the gears are not restrained by bearing studs or shafts.

Such 5 pressure causes the outer circumferences of the gears themselves to be reduced by wear, and at the same time to enlarge the chambers by wear of the surrounding walls, sufllciently to change the normal delivery or displacement of the pump. This affects adversely the uniformity of the filaments produced.

The matter of lubrication is another cause of difficulty attending the use of metering pumps. This difiiculty is particularly pronounced with pumps employed in connection with viscose, which has a more deleterious effect on pumps than other spinning compounds and of which the nature is such that pumps admirably suited to other uses, even the other rayon processes, have little. if any, value when applied to the particular purpose of passing viscose at a predetermined rate of flow without interruption for periods of time long enough to be practically useful in commercial production;

By the present invention I have devised a means for conducting the solution through the metering pump so as not only to lubricant the gears satisfactorily, but also to eflect a counterbalancing fluid pressure against the pressure tending to force them apart from one another, and thus enable them to be centered and maintained in tight mesh by the walls of the gear chambers. without serious wear at any point and without dependence on central studs or shafts. In its generic aspect the invention consists in balancing the radial fluid pressures applied to the pump gears so that in effect, and in almost full measure, they float in their chambers. The effect and result of such pressure balancing is to eliminate, in large degree, rubbing pressure contact of the gears with contiguous parts of the pump structure, thereby diminishing wear. Such reduction of wear results whether the walls of the pump chamber or fixed studs or rotating supported shafts are depended on for centering the gears. Hence, although in the present illustrated embodiment of the invention the walls of the chambers establish the meshing locations of the gears, yet the principles of the invention are equally applicable to situations where the gears are centered by studs or shafts.

I have described in the following specification and illustrated in the drawings two forms of pump embodying the principles of this invention. One form, illustrated in Figs. 1-7 inclusive, is de-- signed for use with viscose and embodies provisions for conducting the liquid so as to lubricate the gears and their bearing surfaces satisfactorily, overcoming the difliculties inherent with the use of viscose while effecting satisfactory pressure balance. The other, shown'in Figs. 815 inclusive, embodies equivalent pressure balancing means with provisions for lubrication satisfactorily with the use of cellulose acetate and other compounds which have comparable permanence and lubricating qualities.

In the drawings,

Fig. 1 is a sectional view, taken on its longitudinal center line, of a complete metering pump containing that phase of the invention which combines pressure balancing with provisions for lubricating by such difficult compounds as viscose;

Fig. 2 is an elevation of the outer face of the front plate of the pump casing;

Fig. 3 is an elevation of the inner face of said plate;

Fig. 4 is an elevation of the inner face of the rear side plate of the pump casing;

Fig. 5 is a sectional view taken on line 55 of Fig. 1 showing the center plate and gears in elevation;

Fig. 6 is an elevation of a center plate adapted to be substituted for the center plate shown in the preceding figures and containing an equivalent variation of one feature of construction;

. Fig. 6a is a section of the last mentioned plate taken on line 6a-6a of Fig. 6;

Fig. 7 is a perspective view of the channels by which the liquid is conducted to and from the gear chambers of the pump, such channels being shown in their assembled relationship to one another, the outlines of the casing and gears being likewise shown by lighter lines than those designating the channels;

Fig. 8 is a view similar to Fig. 1 showing another embodiment of the invention;

Fig. 9 is a section taken on line 33 of Fig. 8 and showing the inner face of the front plate in elevation;

Fig. 10 is an elevation of the outer face of the front side plate;

Fig. 11 is a side view of said plate;

Fig. 12 is an elevation of the inner face of the rear side plate;

Fig. 13 is a side view of the rear plate;

Fig. 14 is an elevation of the center plate of the pump shown in Fig. 8;

Fig. 15 is a cross section of said center plate taken on line l5--l5 of Fig. 14;

Fig. 16 is a perspective view of a self lubricating packing washer used in the pump last described to seal the driving shaft of the pump against leakage.

Like reference characters designate the same parts wherever they occur in two or more of the figures.

It will first describe the form of pump shown in Figs. 1-7 inclusive. In its main structural characteristics this pump is generally similar to the pumps shown in my prior Patents 1,785,386 of December 16, 1930, and 1,972,271 of September 4, 1934. That is, it comprises a casing made up of a massive, rigid front or driving side plate N, a center plate II and a rigid massive rear side plate l2, all detachably secured together by screws l3. Inlet and outlet ports I and I5 are formed in the outer sides of the front and back side plates respectively, from which conduits (of special character, later described) lead to spaces or chambers l1 and i3 inwhich the pump gears l3 and 20 respectively are located; and one of the gears is driven by a shaft having a connection outside of the pump casing with power delivering means. But the pump contains numerous other features unlike the disclosures of my prior patents in which particularly this invention resides. r

The center plate does not extend the full length of the side plates, but is long enough only to enclose and seal the gear chambers adequately. The space between the side plates in line with the ports l4 and I5 is occupied by a spacing disk It which has studs on opposite sides occupying recesses in the side plates and serves to take the thrust of the nipples by which the pump is supported when in service and through which the solution is conducted. Studs 2i and 22 are mounted tightly in the back plate and project from the inner face thereof. The stud 22 thus projects a distance equal to, or very slightly less than, the thickness of the center plate. Stud 2| projects a distance slightly greater than this. enough to provide an end thrust bearing for the driving shaft. In the outer side of the front plate there is a cavity 23 from which an opening 24, coaxial with the gear chamber l1. when the pump is fully assembled, extends to the inner face of this Plate. A driving shaft 25 passes through the cavity 23 and the opening 24 into end thrust bearing with stud 2| and coupled engagement with the gear IS. The enlarged inner end of this shaft loosely fits the opening 24, and carries fingers 26 projecting from its peripheral part into holes in the gear to provide the coupling through which the shaft imparts rotation to the gear.

The outer portion of the shaft fits rotatably a bearing in a sleeve 21 which has an enlarged flange 28 on one end secured to the outer face of the side plate ill by screws 29. Sleeve 21 has also an external bearing 30 coaxial with the shaft bearing, on which an external drive'gear 3| is rotatably mounted. The latter gear carries retaining keys 32 entering, and fitted to travel freely in, a groove which surrounds the protruding outer end of the sleeve, and a yoke 33 slotted to receive a non-circular tongue 34 on the outer end of the shaft 25, through which torque is transmitted from the gear to the shaft. Both the keys and yoke are secured to the outer side of the gear by screws 35.

A seal to prevent outward leakage, along the shaft, of the solution being pumped, or inward leakage into the pump of oil or air, is provided by a metal sealing plate 36 and a metal sealing disk 31, both of which surround the shaft. Plate 36 is contained within a recess in the flange 23 and overlies the cavity 23, being pressed into leakage tight contact with the surface of the side plate I 0 around such cavity by the flange 28 when the screws 23 are tightened up. Disk 31 is connected flexibly to the shaft to rotate with it and is pressed into close contact at its outer side with the inner face of plate 36 by the pressure of the fluid passing through the pump and by spring tongues 33 offset from a ring 39 which reacts against a shoulder on the shaft. These sealing members 36 and 31 have flat contact surfaces and are provided with means formaintaining between such surfaces a lubricating film of the liquid being pumped. A passage 40 constituting a part of the conduits previously referred to, is formed in the front side plate ID from the inlet port I to the cavity 23 and directs the inflowing liquid toward the plane of contact between the sealing members. A groove 4| in the side of this cavity.

opposite to passage 40 extends to the bottom of the cavity.

The studs 2| and 22 are not relied on to provide bearings for the gears, in addition to properly locating the center plate. Instead, holes in the gears which they occupy may be large enough to provide greater clearance than that between the outside circumferences of the gears and. the enveloping walls of the chambers in the center plate. whereby the gears have their bearings on, and are centered by, such walls.

In the periphery of the opening 24 in the front side plate I there is a groove or passageway 42 leading through to the inner face of the plate and connecting with a curved groove 43 in said inner face by means of a radial groove 44. The groove 43 is concentric with the gear chamber ll when the parts of the pump are in their cor- 1 rectly assembled relationship and the radius of its outer bounding wall is equal, or approximately equal, to the radius of the bounding wall of chamber l1, while its radial width is preferably equal, or approximately equal, to the radial length and depth of the gear teeth and intermediate tooth spaces. It is located at the opposite side of the center of gear l9 from the part of the gear which meshes withthe gear 20.

For convenience of this explanation, the locations of the gears with reference to the side plates when the pump is assembled, are designated by the broken lines I9 and 20 in Figs. 3 and 4, while the corresponding location of the central hole in the gear 20, wherein stud 22 is received, is indicated in Fig. 3 by the broken line 45.

There is also formed in the inner face of the front side plate l0 an arcuate groove 46 of outer radius approximately equal to the radius of gear chamber 18 and of approximately equal width to the groove or channel 43. This groove is located at the side of the axis of gear 20 away from the meshing point of the gears, although not exactly opposite to the meshing point. It is joined with a groove 47 which in its outer part is substantially radial to the axis of gear 20 and in the inner part is generally tangential to a cylinder projected from the hole in the gear, and it crosses the rim of the hole and terminates approximately on the center line CL of the gears.

The back plate contains a connected series of grooves 48, 49, 50 and in its inner face. The groove or part 48 of this series is coaxial with the gear l9 when the parts are assembled, and is of substantially equal outside radius with the gear chamber II. It is located at the side of the gear axis away from the meshing point. The groove portion 49 is radial. or approximately so; the groove 50 passes around the stud 2| in close proximity thereto; and the part 5| extends tangentially from the part 50 to a termination in register with the intake space between the gears and gear chambers, such space being designated 52 in Fig. 5.

Another arcuate groove 53 is formed in the inner face of the back plate. This groove is coaxial with the gear 20, at the opposite side of the axis from the meshing point of the gears and substantially equal in outer radius to the gear chamber I8. 54 which extends across the area overlaid by gear 20 into register at its inner end with the discharge or outlet space 55 between the gears and gear chambers at the side of the center line opposite to the space 52.

A groove or channel 56 is formed in the stud 22 at the side thereof away from the meshing point of the gears and registers with a passage 51 through the substance of the back plate leading to the exhaust port l5.

Itis joined at one end to a groove The relationship of these grooves to one another when the parts of the pump are assembled is shown in perspective by Fig. 7. The grooves 43 and 48 lie adjacent to the opposite end planes of the gear 19 and subtend in part the same angle around the axis of that gear. Similarly the grooves 46 and 53 lie adjacent to the opposite end planes of the gear 20 and subtend in part the same angle around the axis of that gear. With rotation of the gears in the direction of the arrows, applied adjacent to their locations in Figs. 3-7, the course of the solution is as follows:

From the inlet port l4 through passage 48 to the outer part of the cavity 23, around the sealing ring 31 and through the groove 4| to the inner part of the cavity; thence through groove 42 and channels 44 and 43 to the outer side of the gear chamber II; thence across the gear chamber through the tooth spaces of gear I!) to the connected groove series 48, 49, 50 and 5| to the space 52, which corresponds to the usual intake point of pump gears. The liquid is thence carried in divided paths by the teeth of the two gears around the chambers to the discharge space 55, whence it is carried by the groove 54 to the circumferential groove 53. The flow then crosses the gear chamber through tooth spaces of gear 20 to the circumferential groove 46, and thence travels by the tangential groove 41 to the channel 56, and through the latter to the passage 51, and thence to the discharge port 15. The direction of flow is graphically indicated by arrows applied adjacent to these grooves and passages in Figs. 3, 4 and '7. In flowing through the channels 44, 49, 5|, 54 and 41, the liquid passes in contact with the opposite faces of both gears, constantly bathing these faces with fresh viscose and supplying the gears with a constantly renewed film of viscose by which they are lubricated in traveling over the stationary faces of the side plates which close the ends of the gear chambers. The tops or crests of the gear teeth and surrounding walls of the chambers are lubricated by the films of viscose applied to the teeth as they pass through and between the spaces and 52.

The entire delivery of the pump passes through the grooves hereinbefore described. There are no other channels for carrying the solution directly to the space 52 and away from the space 55. Consequently these grooves are made as channels sufiiciently wide and deep to provide the requisite flow capacity. In a pump designed for a delivery of .586 c. 0. per revolution, the grooves are 1%" in both width and depth. But these dimensions can be widely varied to suit the conditions of pumps of different dimensions and capacities and for liquids of dillerent viscosities.

The pressure balancing effect referred to at the beginning of this specification is accomplished by the arrangement and distribution of the arcuate grooves. In the particular embodiment here shown. the groove 43 extends through an arc of to the right from the center line CL and through an arc of to the left of this line. The groove 48 is (in the position shown in Fig. 4) wholly at the left of the center line and extends through an arc of 60. Hence, as the sideplates are located face to face when assembled, groove 48 is directly opposite to so much of the groove 43 as appears at the right of the center line in Fig. 3. As these groove portions are also opposite to the spaces 52 and 55 across the axis of gear I 8, the liquid conducted through them exerts force radially on the gear in opposition to the radial force exerted by the liquid in these spaces.

left of the center line (as seen in Fig. 4), while groove 46 extends through an arc of 60 between points at and 15 respectively from the center line at the left side thereof, as seen in Fig. 3. Thus, when the side plates are placed face to face, groove 45 is exactly opposite to that portion of the groove 53 which comprises sixty angular degrees from the closed extremity thereof, and both these groove portions are opposite to the discharge space 55 across the axis of gear 20. In the operation of the pump the unit pressure of the liquid in these grooves is the same as in the discharge space 55 and causes radial force to be exerted on the gear in opposition to that exerted by the liquid in the discharge space. Similarly the liquid in the part of groove 53 at the left i with reference to Fig. 4) of the center line transmits pressure radially to gear in opposition to that exerted by the liquid in the intake space 52; and that in the part of groove 43 at the left (with reference to Fig. 3) of the center line transmits pressure radially to gear 19 in opposition to that exerted by the liquid in the discharge space.

The arcs of the gears to which pressures are thus transmitted through the grooves are here shown as wider than the arcs exposed to the pressures in the intake and discharge spaces; enough wider to produce resultant pressures on the gears toward one another sufficiently great to balance in suitable degree the pressures tending to force them apart. As a result, (and since the liquid entrapped between the teeth is released by means later described) the gears are held in close mesh and substantially no pressure contact with the surrounding chamber walls except such as follows from application of the rotative driving force. In other words, forcible contact of the gears on their outer circumferences with the chamber walls is prevented and wear greatly reduced. More generically stated, a pressure effect is obtained on both gears, which overcomes wholly, or in large measure, the forces universally present in gear The specific values for the angular dispositions and lengths of the arcuate grooves stated herein are illustrative only; and variations may be made within the scope of the invention according to different conditions of service for which pumps embodying the invention are: designed. In general, the grooves are designed to transmit pressure into numbers of tooth spaces proportional to the number of teeth exposed to pressure at the points 52 and 55 and to the pressures existing at those points. It is essential, however, that properly proportioned channels be provided for flow of the solution, arranged according to the principles of the arrangement here shown, to produce pressure effects on the gears substantially as described; that is, the channels must transmit pressures in counterbalancing relation to the fluid pressures acting on the gears in the intake and discharge spaces. But an exact or complete balance is not needful. A substantial counterbalancing effect is sufficient.

The'formation shown at 58 in Fig. 3 is a groove sunk into the inner face of the front plate, preferably being formed in the end of a plug 58a set into this plate with its end face flush with the inner face of the plate. This groove has separated ends located beside the points where the gears come into full mesh when rotating in the direction indicated by the arrows. From these points the groove leads to the space 55 clear of the gears. with gears which operate without backlash, as these do, the teeth of each come into bearing on both sides with flanking teeth of the other before arriving at the line of centers and before penetrating to full depth into the space between such flanking teeth. The liquid in such space is then entrapped and would be put under tremendous pressure by further penetration of the entering tooth if no means for relieving the pressure were provided. The groove here described affords relief, enabling entrapped liquid to pass into the discharge space 55 and thence to the delivery port of the pump. Plug 55a may be removed or displaced back from the face of the plate when such face is ground and lapped in reconditioning the pump after long continued wear, enabling the original depth of groove 58 to be preserved.

As previously stated, the chamber walls rather than the studs have the function of locating and guiding the gears. So far as that function is concerned therefore, the studs could be omitted and the central holes in the gears filled by plugs, if other suitable means are provided for properly locating the plate with relation to the relieving groove 58. But in this design the studs constitute means for properly locating the spacer plate, and the stud 2| serves further as an abutment for the driving shaft 25 by protruding from the rear side plate a distance slightly greater than the thickness of the gear IS. The stud 22 provides a location for the channel 55; and both studs together establish the line of centers with respect to which the gear chambers in the center plate may be alined, making it unnecessary to fit the connecting screws [3 to the corresponding holes in the center plate so closely and exactly as would be necessary if they were relied on for alining that plate. And the studs serve, equally as well as plugs of any other character, to substantially fill the holes in the gears and prevent accumulation of stagnant viscose in such holes. But pressure balancing grooves such as herein disclosed may be used with equal effect and benefit in pumps where the gears are located by stationary studs or are fixed to shafts rotating in bearings to reduce pressure and wear between the gears and studs or between the gear shafts and the shaft bearings.

Instead of forming the arcuate grooves 43, 46, 48 and 53 in the faces of the side plates, the equivalents of such grooves may equally well be formed in the center plate. Figs. 6 and 6a show a modified construction in which this is done. Here the edge of the gear chamber IT at the side of the center plate Ila next to the front Plate is cut away at 45a forming a channel which extends from a point 44a where it communicates with the channel 44 in the front side plate a distance equal to the length of groove 43; and the edge of the chamber next to the back plate is cut away at 48a axially opposite to a portion of the channel 43a, forming a second channel which opens into the radial groove 49. Likewise the opposite edges of the outer part of the gear chamber l8 are cut away at 46a and 53a to form channels corresponding to the grooves 46 and 53, which communicate, respectively, with the grooves 41 and 54, and with each other through tooth spaces of the gear. For manufacturingv 'one important difference.

2,287,318 purposes it is easier, and a less expensive operation, to form such channels or enlargements in the gear cavities in the center plate than to cut curved grooves in the faces of the side plates.

Equivalent pressure balancing means to that here described are applicable also to pumps designed for use with solutions which are not liable to solidify when allowed to stagnate, such as cellulose acetate. Figs. 8-15 inclusive show a pump of this character having essentially the same parts as the pump first described, but in which there is a direct passage 59 leading from the inlet port [4 to a port 60 in the inner face of the front side plate Ifla, and a direct passage 6| from a port 62 in the inner face of the rear side plate l2a to the discharge port IS; the ports 60 and 62 communicating respectively with the intake space 52a and the discharge space 550 of the center plate llb, as in my said prior patents. A relief cavity 58b corresponding to the groove 58 of the previous description is sunk into the face of the rear side plate and communicates with the space 55a and outlet port 62.

A groove or channel 63 is cut in the inner face of the rear side plate l2a in communication with the space 55a and cavity 58b. It extends across the zones overlaid by the pump gears, (the relative positions of which are indicated by the broken lines [9 and 20 in Figs. 9, 10 and 12), to terminations outside of the circumferences of these zones. The edges of the gear cavities in the center plate are beveled or cut away at the side which comes next to the rear plate when the pump casing is assembled. Such edge bevels are shown at 64 and 65 in Figs. 14 and 15. They are located in segments of the cavity walls away from the pitch point of the gears in locations which bring one end of each across one end portion of the channel 63. Thus when the pump is assembled, the bevels 64 and 65 provide arcuate channels leading from the end portions of the channel 63 and communicating with the tooth spaces of the gears over an are at the opposite side of a diameter of each gear from the spaces 52a and 55a. The system of channels thus created receives the spinning solution and transmits pressure therethrough to the outer arcs of the gears, the angular extent of which is made sufiicient to effect a balance, or any desired approach to a balance, or an overbalance, of the pressures tending to force the gears apart.

The channel 63 also brings the solution into contact with one face of each gear and extends in a line running near to the studs suitably located to cause the entire surface, or any desired part of the surface, of each gear on the end next to the back plate to be lubricated by the solution.

There is also a groove or channel 66 in the inner face of the front side plate which crosses (and thereby communicates with) the outlet space 550. and conducts a lubricating supply of the solution to the end faces of the gears next to the front plate.

It will be noted that the pressure balancing provisions last described are collateral to the channels through which the solution is carried into and out of the pump. They illustrate the principles of means which may be used for this purpose in any pump used with fluids which cause no ill effects from stagnation.

The driving shaft and means for sealing it are similar to those previously described, except for The sealing means comprises a metal plate 36 overlying the cavity graphite.

5 sealing disk 31a surrounding the shaft and coupled to it by a ring 39. But instead of lubricating the contact surfaces of such plate and disk by the fluid, I provide between them a washer 61. The adjacent surfaces of the plate and disk,

and the washer, are dry. 'There is no access of Y the solution to these surfaces. However, the washer itself is self lubricating. It is made of an agglomerate of metal and particles of graphite intermingled in a manner which gives the effect of cohesion in the metal part of the washer, while the particles of graphite are distributed so as to give the effect of satisfactory lubrication at the surfaces. In this structure the agglomerated metal serves as a binder for the lubricating Such composite structures of copper, iron or other metal and graphite are known and are produced commercially by different processes. I have used this known material in making the washer 61 herein shown. But the use of a washer of that character in the environment and combination here disclosed, or equivalent combinations, is new; and I claim such novel combination.

as a phase of the present invention. This phase of the invention comprises a floating washer between contiguous shoulderson a shaft and a casing structure respectively, which washer has strength to resist crushing or fracture in such circumstances, and makes non-frictional contact with contiguous metal surfaces.

Like the pumps described in my prior patents, the pumps here shown are made and finished with extreme accuracy. The inner faces of the side plates and both faces of the center plate ar finished with an accuracy closely approaching that of a true optical fiat and their contact faces are truly parallel when the connecting screws are tightened. The gearsare made with end faces finished fiat with an accuracy equal to that of the center plate and their teeth are generated so accurately that they mesh without backlash, and the extremities of the teeth of each practically bottom in the spaces of the other. Clearances sufficient for lubricating films of the liquid, but not great enough to permit leakage, are provided between the faces of the gears and side plates and between the outer circumferences of the gears and the chambers in the center plate. These clearances may be from .0001" upward, depending on the viscosity of the liquid handled by the pump. To secure accuracy in clearances of such minute values, with interchangeability of parts manufactured in quantity production, the thicknesses of center plate and gears are held to a tolerance of .000025 (one forty-thousandth of an inch), while the diameters and center distance of the gears and gear chambers, and the dimensions of the gear teeth, are held to tolerance of .00005" (one twenty-thousandth of an inch).

In assembling these pumps, the gear chamberinto which driving shaft 25a enters and a metal 7 on a film of oil with respect to the gears so as to avoid rubbing contact with the teeth before the connecting screws 13 are tightened. This may be easily done by filling the pump with heavylubricating oil and turning the gears. The screws are then tightened and the oil is completely washed out.

The foregoing description shows some of the forms in which the invention may be embodied. Other forms are within my contemplation and within the scope of protection sought by the following claims.

What I claim and desire to secure by Letters Patent is:

1. A metering pump having a casing with internal merging gear chambers, intake and outlet spaces at opposite sides of the merging portions of said chambers and external inlet and discharge ports, pump gears occupying said chambers with clearances sufllcient for rotation and insuflicient to permit substantial leakage of fluid around the gears meshing together between said intake and outlet spaces, the casing having an internal channel leading from the inlet port to a limited portion of the circumference of one gear diametrically opposite to the meshing point between the gears, a second channel leading from said portion of the circumference of said gear to the intake space of the gear chambers, a third channel leading from the outlet space of the gear chambers to the outer peripheral part of the other gear, and a fourth channel leading from said peripheral part of the last named gear to the discharge port of the pump.

2. A pump as set forth in claim 1, in which portions of said channels extend across end faces of the gears and are open to permit lubricating application of the fluid being pumped upon said gear faces. a

3. A gear pump of the metering type comprising side plates, a center plate having merging gear chambers, and pump gears rotatably fitted within said chambers in mesh with each other, the pump having inlet and outlet ports communicating with said chambers at points near to, and at relatively opposite sides of, the meshing point of the gears, one of said side plates having a channel in its inner face running from the outer part of the circumference of one of the gears to a space within the center plate immediately adjacent to said meshing point, there being an arcuate space between said side plate and center plate in communication with said channel through which fluid may pass from the channel into pressure transmitting relation with the periphery of such: gear, and said arcuate space being closed at both ends to prevent leakage flow between the same and the before named points near the meshing points of the gear.

4. A gear pump of the metering type comprisinga casing having internal merging gear chambers and spaces at opposite sides of the line of centers of the chambers, and also having inlet and outlet. ports communicating respectively with said spaces, gears fitted rotatably in said chambers in meshing relation with each other and in substantially leakage preventing proximity with the walls of said chambers, said gears being adapted when rotating to carry liquid-from one of said lateral spaces and deliver it to the other, and the casing having internal channels leading from the space into which liquid is so delivered by the gears to limited arcs of the circumferences of the gears remote from said space, whereby the pressure of the fluid is transmitted from said space and exerted radially on the gears in opposition to the pressure effect in said space tending to separate the gears from one another, said channels extending in part across the faces of the gears and being open to such faces so as to wet them with the liquid.

5. A gear pump comprising a center plate having communicating chambers adapted to receive gears, side plates flanking the center plate and extending across said chambers, gears fitted rotatably'in said chambers meshing with one another, and a driving shaft passing through one of the side plates into coupled relation with one of the gears; the side plates having an intake port in one, an outlet port in the other, and interior passageways leading from the inlet port to one end face of one of said gears, thence to the circumference of that gear, thence from the same circumference of the same gear across the opposite end face thereof to the intake point of the gear chambers, across the end face of the other gear to the circumference thereof from the discharge point of the gear chambers, from the circumference of the second named gear across its face to a point within its circumference, and thence through said gear to the outlet, said passageways where they cross the faces of the gears being open to such faces and adapted to supply thereto a lubricating film of the solution being pumped.

6. A metering pump comprising a casing having internal gear chambers merging with one another, gears mounted rotatably in said chambers and meshing with one another, and a drive shaft entering the casing coaxially with one of the gears into coupled connection with such gear; the casing having external inlet and outlet ports, internal spaces at the intake and outlet sides respectively of the intermeshing gears opening into the merging portions of said chambers, and passageways between the external inlet port and the internal space at the intake side of the gear chambers, on the one hand, and between the internal space at the outlet side of the gear chambers and the external outlet port, on the other hand, said passageways including channels bounded by the end faces of the gears arranged to cause all of the fluid propelled by the pump to flow through them in series, and to bring the fluid into contact with said gear faces for lubricating them.

7. A metering pump having merging internal gear chambers, intermeshing pump gears occupying such chambers with clearances insufficient to permit substantial leakage of artificial silk solution between the gears and the enveloping chamber walls, the pump having inlet and outlet ports and interior spaces contiguous to the meshing point of the gears, one of which spaces is in communication with the inlet port and the other with the outlet port, and having internal arcuate channels concentric with the gears and open to the peripheral parts of the gear chambers at the opposite sides of the centers of the respective gears from the meshing point, the ends of said. arcuate channels being closed against communication circumferentially of the gears with said interior spaces, and the casing having channels connecting each of said arcuate channels with one of said interior spaces and extending across the end face of the adjacent gear, and being open at the side next to said end face whereby to apply the solution to said face.

8. A metering pump comprising a casing having tangentially merging gear chambers, intermeshing gears occupying said chambers rotatably, the casing having internal intake and outlet spaces contiguous to the meshing point of the gears at opposite sides thereof, external ports for intake and discharge of fluid, arcuate channels coaxial with the gears open throughout their peripheral length to the peripheral portions of the chambers at the sides thereof opposite to the meshing point of the gears, and being closed at their .ends against peripheral communication with said internal spaces, and channels leading in series from the intake port to the arcuate channel contiguous to one of said gears, and thence to said internal intake space, and from the internal outlet space to the arcuate channel contiguous to the other gear and thence to the discharge port.

9. A gear pump particularly adapted for controlling the flow of solutions employed in the manufacture of artificial silk, consisting of side and center plates, intermeshing gears contained in the center plate between the side plates, and a drive shaft passing through one of the side plates into coupled connection with one of the gears, the side plates having intake and outlet ports and the center plate having intake and outlet spaces contiguous to, and at opposite sides of, the meshing point of the gears, in communication with the respective ports, the side plates having passageways in their inner faces extending across and being open to the contiguous end faces of the gears, and arcuate channels communicating with said passageways and open to limited areas of the gear circumferences at the opposite side of the centers of the respective gears from the meshing point, for leading the solution into contact with such faces and transmitting pressure to the outer peripheral portions of the gears in opposition to the pressure existing in said spaces. I

10. A gear pump having intake and discharge ports, intermeshing gears, and interior passageways leading respectively from the intake port to the gears at one side of the intermeshing teeth, and from the opposite side of the intermeshing teeth to the discharge port, the passageway from the intake port being arranged to conduct entering fluid across and in contact with one end face of one gear, from a point within the circumference thereof to a circumferential are at the opposite side of the center of said gear from said intermeshing teeth, and thence across the opposite end face of the gear to a point beside and contiguous to said intermeshing teeth.

11. A gear pump having external intake and discharge ports, intermeshing gears, interior intake and outlet spaces contiguous to, and at relatively opposite sides of, the meshing teeth, and interior channels leading from said intake port to said intake space and from said outlet space to said discharge port, said channels being arranged in courses which conduct the fluid being pumped into lubricating contact with the opposite end faces of the gears and into pressure exerting communication with limited circumferential arcs of the gears at the opposite sides of their respective centers from said interm-eshing teeth.

FREDERIC McINTYRE.

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