US2714856A

US2714856A - Rotary pump or motor

Info

Publication number: US2714856A
Application number: US139190A
Authority: US
Inventors: Thomas C Kane
Original assignee: Commercial Shearing Inc
Current assignee: Commercial Shearing Inc; Commercial Shearing and Stamping Co
Priority date: 1950-01-18
Filing date: 1950-01-18
Publication date: 1955-08-09
Anticipated expiration: 1972-08-09
Also published as: DE897203C

Description

T. C. KANE ROTARY PUMP OR MOTOR Aug. 9, 1955 2 Sheets-Sheet 1 Filed Jan. 18, 1950 INVENTOR 7/70/7788 C/(ane Aug. 9, 1955 T. c. KANE ROTARY PUMP OR MOTOR- 2 Sheets-Sheet 2 Filed Jan. 18, 1950 I'Ig. 6.

500 IRRM.

w w w W m w 0 w w w w i w I 1 H /MP w 1 w M W m zM I u {0/ 6 M Q. m Q w w m P. w mr/ I G .2 m w I 8 w s x Z o O A 4 w A a ll%hir 0 o m m w kwkwqmwi w SQMW a Pressure b72511 INVENTOR Thomas 61 Kane 0 w l/ 1M8 United States Patent 0 RQTARY PUMP 0R MOTOR Thomas C. Kane, Mahoning County, Ohio, assignor to The Commercial Shearing & Stamping C0,, Youngstown, Ohio, a corporation of Ohio Application January 18, 1950, Serial No. 139,190

23 Claims. (Cl. 103-126) This invention relates to pumps and motors with rotary impellers, and particularly to means for sealing the ends of the impellers.

A gear pump, for example, has a pair of impellers in the form of meshing gears and a case extending closely around a portion of the periphery of each impeller to cooperate with the impeller teeth in trapping fluid on the low-pressure side of the pump and carrying it around to the high-pressure side of the pump. The meshed teeth prevent any substantial return flow between the impellers as a result of the pressure differential between the outlet and inlet sides of the pump, and end plates are provided to limit the return flow between the ends of the impellers, which are rotating, and the case, which is stationary. The problem is to adjust the plates enclosing the impeller ends tightly enough to prevent a substantial return flow and loosely enough to prevent the impellers from being seized and stopped. The problem is complicated by the fact that since the impellers are preferably made of steel the end plates are preferably made of bronze to reduce wear and drag, and bronze has a higher coeflicient of thermal expansion than the main body of the casing, which is preferably made of iron or steel. As a result, if the peripheral edges of the plates are enclosed in the casing, as shown, for example, in Patent No. 1,972,632 to Patton, the plates either expand longitudinally against the casing and become bowed relative to the impeller ends with the result that the impellers are seized and stopped, or the peripheral clearance of the plates must be increased to such an extent as to allow an excessive return flow to develop along the plate edges, which lessens the efficiency and maximum pressure developed by the pump. Further difli- CllllIlCS arise in the case of enclosed end plates which are arranged to float relative to the impeller ends, with the opposite faces of each plate subject topressure of fluid from the outlet side of the pump for the purpose of creating a net pressure tending to urge the plates against the impeller ends at all times. The difficulty with known forms of floating plates is that the fluid pressures on the rear faces of the plates remain high most of the way across the rear faces from the outlet to the inlet side of the pump while the fluid pressures on the front faces of the plates against the revolving impeller ends fall off rapidly between the high-pressure outlet and the low-pressure inlet sides of the pump. This results in an unbalance of pressures tending to force the floating plates so hard against the impeller ends near the inlet side of the pump that seizure develops when the pump operates at full power for even short periods. This problem is recognized in the aforesaid Patton Patent No. 1,972,632 but the solution of Patton is not applicable to reversible pumps and does not overcome the above-mentioned difficulties resulting from longitudinal thermal expansion of the plates.

In view of the difliculties of using enclosed end plates it is conventional to sandwich the impellers and a central casing member surrounding the impeller teeth between a nr ...d

Era-tented Aug. 9, 1%55 pair of bronze plates, and to enclose the outer faces of the plates between a pair of outer casing members. The peripheries of the plates are not enclosed in the casing, which eliminates the causes of bowing, and the fixed width of the central casing member determines the clearance between the bronze plates and the impeller ends, which eliminates the pressure problems of floating plates. While this conventional form of pump or motor is workable it requires great accuracy in manufacture and adjustment, and at best its performance character istics are limited, particularly with respect to the maximum pressure which it can develop or utilize.

I have invented a new form of rotary pump and motor construction which is less difficult tomanufacture and affords better performance characteristics than the constructions heretofore in use. I provide novel plates for engaging the ends of the rotary impellers and the plates are mounted in a novel way in the case. The periphery of each plate has alternating relieved and unrelieved portions so that the unrelieved portions closely engage a surrounding part of the casing and oppose return flow around the periphery of the plate, and the relieved portions are spaced from the casing and permit the plate to expand radially as it becomes heated instead of becoming bowed relative to the impeller ends as a result of longitudinal compression in the casing. It is thus practicable to enclose the plates within the casing in movable relation to the impeller ends. The space between the rear face of each plate and the adjacent end casing member is partially open to fluid from the outlet side of the pump in order to counterbalance the pressure of other fluid from the outlet side of the pump entering between the front face of the plate and the adjacent rotary impeller ends, and substantial balance of the opposed pressures on each portion of each plate is achieved by the use of a system of seals between the rear face of theplate and the casing. A series of fluid pockets are created by these seals and the pressure in each pocket is so balanced against the pressure on the opposite face of the plate that a pump or motor constructed in accordance with my invention can develop or operate under substantially higher pressures without danger of seizure than other forms of pumps and motors of the same size. A further advantage of my plates is that they are symmetrical, including the system of seals on their rear faces, and permit reversal of flow through the pump or motor, in contrast, for example, with the end plates disclosed in the aforesaid Patton Patent No. 1,972,632. Another advantage is that my end plates may be of substantial thickness and may be repeatedly refinished and reused without lowering the performance of the pump. Moreover, the balance of pressures across the plates equalizes the wear on the plates and increases their period of use before there is any need for refinishing.

An additional feature of the construction of my invention is that the end plates are fitted over the ends of the adjacent bearings for the rotary impellers, which centers the plates relative to the impeller axes, and the unrelieved portions of the plate peripheries engage the central casing member and center it relative to the impeller axes. In this way the central casing member is aligned in the desired closely spaced relationship to the outer periphery of the impellers without the use of any of the multiple dowels conventionally employed for this purpose. The elimination of dowels simplifies fabrication and assembly and improves accuracy of alignment by eliminating the accumulation of error resulting from boring numerous dowel holes. The use of my end plates for alignment purposes also improves the resistance of the assembled pump or motor to rough handling Without loss of alignment. Conventional dowels must each take the stress of a blow or shock in shear at the precise point of juncture where the casing members come together and hence are readily deformed so that the pump or motor becomes misaligned. My end plates, on the other hand, have surfaces of considerable area engaging the central casing member and bearing shells and a shock or blow acts in compression on these surfaces and is not sufliciently concentrated on any small area to cause deformation and misalignment. A further advantage of mounting the plates on the bearing shells with portions of their peripheries engaging the central casing member is that the ends of the seals on the rear faces of the plates can extend against the central casing member and bearing shells to block leakage around the ends of the seals, and the arrangement of the plates around the bearing shells prevents leakage of fluid into the space enclosed by the shells.

Further novel features and advantages of the rotary pump and motor of my invention will become apparent from the following detailed description and in the accompanying drawings. I have shown in the drawings, for purposes of illustration only, a present preferred embodiment of my invention, in which:

Figure l is a sectional view of a rotary pump and motor taken through the impeller axes;

Figure 2 is a sectional view taken on the line IIII in Figure 1;

Figure 3 is a view of an end plate showing its front face which engages the impeller ends;

Figure 4 is a view of the rear face of the plate illustrated in Figure 3;

Figure 5 is a sectional view on the line V-V in Figure 3;

Figure 6 is a chart of comparative performances at 500 R. P. M.; and

Figure 7 is a corresponding chart of comparative performances at 1200 R. P. M.

Referring in detail to the drawings, there is provided a pump 10, which is also usable as a motor, having a pair of

meshing gear impellers

11 and 12 between a pair of

end plates

13 and 14 with a central casing member 15 enclosing the outer peripheries of the impellers and plates. Ports 15a and 15b through the casing member 15 serve interchangeably as inlet and outlet ports for the pump. The

plates

13 and 14 and easing member 15 are enclosed between a pair of

end casing members

16 and 17, and bolts 18 extend through

casing members

15 and 17 and screw into casing member 16 to hold the casing members together in tightly sealed relation. The inner side of the casing member 17 lies in a continuous flat plane except for a pair of cylindrical depressions into which bearing shells 19 and 20 are tightly fitted, with their ends projecting from the casing member 17. Needle bearings 21 within the shells 19 and 20 rotatably support hollow

cylindrical hubs

22 and 23 projecting integrally from the

impellers

11 and 12, respectively.

The plate 14 has a pair of

openings

24 and 25 through which the

hubs

22 and 23 extend, and these openings are countersunk on the rear face of the plate to provide

counterbores

26 and 27 fitting closely around the projecting ends of the bearing shells 19 and 20 (Fig. 1). The front face of the plate 14 (Fig. 3) is in the form of a figure 8 with flat surfaces fitting closely against the adjacent impeller ends and with two pairs of grooves 28, which are conventional and serve to carry fluid compressed between the meshing impeller teeth back to the outlet side of the pump, regardless of the direction of rotation of the impellers. The rear face of the plate 14 (Figure 4) is also in the form of a figure 8 with flat surfaces paralleling the adjacent flat surface of the casing member 17 and with a channel 29 between the

counterbores

26 and 27, and four

channels

30, 31, 32 and 33 separating the semicircular outer ends of the figure 8 from its central portion. Rubber-

like seals

34, 35, 36, 37 and 38 are received in the

respective channels

29, 30, 31, 32 and 33. Each seal is as long as the corresponding channel and rises at least slightly above the top of the channel. The seals need not be as wide as the channels in order to operate effectively if neoprene, the preferred material, is used. The depth of each channel is less than the projection of the bearing shells 19 and 20 from the casing member 17 so that the shells close one end of each of the channels 30-33 and both ends of channel 29. The other ends of the channels 2933 are closed by casing member 15. When the pump 10 is in operation the seals wedge between edges of the channels and adjacent surfaces of the casing members and shells and set up different pressure areas on the rear face of the plate. For example, considering the outlet of the pump to be on the left side of the plate 15 as shown in Figure 4, the high-pressure fluid from the pump outlet would be confined in the left central area bounded by the

seals

29, 30 and 32, the pressure of the fluid along the right central area bounded by the

seals

29, 31 and 33 would be close to the pump inlet pressure, and fluid pressure on the two outer areas bounded by the seals 3031 and 3233 would have an intermediate value between the outlet and inlet pressures. This intermediate pressure approaches the outlet pressure because the relieved periphery of the plate, hereinafter described in more detail, permits relatively highpressure fluid to flow from the front face of the plate near the outlet side of the pump, over the edge of the plate and into the said outer areas of the rear face of the plate. Fluid is thus pocketed against each of said areas of the rear face of the plate, with the pockets nearest the ports each opening into the adjacent port across the periphery of the rear face of the plate between

seals

34 and 36 in the case of the pocket between those seals, and between seals and 37 in the case of the pocket between the latter seals. The resultant rear face pressures hold the plate against the impeller ends with sufficient force to prevent substantial backflow along the impeller ends but are so balanced against the opposing pressures across the opposite face of the plate as to avoid seizure of the plate against the impellers.

The periphery of the plate 14 is relieved on both sides of the opposite ends of the plate, as indicated at 39, 40;

41 and 42 in Figure 4. The unrelieved peripheral portions of the plate form lands 43 and 44 at opposite ends of the plate, and lands 45, 46, 47 and 48 on the opposite side edges of the plate. The said lands engage the central casing member 15 in a snug sliding fit. The relieved portions 39-42 are spaced substantially from the casing member 15 and permit the plate to bow out in a radial direction along its relieved periphery instead of warping and buckling in a direction parallel to the impeller axes when the plate, which is preferably of bronze, thermally expands at a greater rate than the casing member 15, which is preferably of iron. The minimum amount of such spacing of the relieved peripheral portions 3942 is generally a function of the size of the plate, its thermal expansion coeflicient, and the expected range of operating temperatures, and in any event must be definitely larger than the amount of spacing which might result from mere dimensional variations within manufacturing tolerances. Moreover, the plate 14 is centered relative to the axes of the

gears

11 and 12 by the bearing shells 19 and 20 engaging the plate counterbores 26 and 27, and the plate 14 through its peripheral lands 43-48 serves to center the central casing member 15 relative to the impeller axes so that the impeller teeth will be kept in uniformly close alignment with the adjacent surface of the casing member 15 (Figure 2).

The plate 13 corresponds identically with the plate 14 in construction, mounting and operation, and aids in aligning the central casing member 15. The end casing member 16 cooperates with the plate 13 in the same manner as the opposite end casing member 17 with the plate 14, but

5 differs from the member 17 in that it mounts a drive shaft 49 which is keyed to the impeller 11 and is adapted to drive or be driven by suitable means (not shown). Conventional means 50 seal the shaft 49 to prevent escape of fluid between the shaft and the casing member 16. The

plates

13 and 14 work equally well with impellers having straight or helical teeth.

The comparative performance of a pump constructed in accordance with my invention and a pump having the same size impellers but conventional side plates sandwiched between the casing members in fixed relation to the impellers, is illustrated in the charts shown in Figures 6 and 7. The full lines show the performance characteristics of my new pump and the dotted lines the corresponding characteristics of the conventional pump. At speeds such as 1200 R. P. M., illustrated in Figure 7, the relatively high pump delivery reduces the percentage losses in performance caused by return flow through the pump, but even so it will be observed that the delivery (G. P. M.) of the conventional pump falls off rapidly at higher pressures even with increasing power input whereas the delivery of my new pump remains almost ideally steady in the higher pressure ranges with only a slight drop in efficienc At lower speeds such as 500 R. P. M., illustrated in Figure 6, the performance of my new pump is better by a wide margin than that of the conventional pump, which cannot develop nearly as high amaximum pressure as my new pump and falls off rapidly in efficiency and delivery as it approaches its limited maximum pressure.

The invention is applicable to pumps and motors with rotary impellers other than gears, including those such as vane pumps with single impellers. While I have shown and described a present preferred embodiment of the invention it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

I claim:

1. A rotary machine of the class described, comprising a rotary impeller, a plate against an end of the impeller, and a case enclosing the impeller and plate, with a portion of the case fitting closely around a portion of the periphery of the impeller to trap fluid therebetween and with the periphery of the plate extending alternately in contact with and substantially spaced from the case adjacent said portion of the case, whereby during operation of the machine the contact between the plate periphery and case opposes flow of fluid along the periphery of the plate and the spacing between the plate periphery and case permits the plate to expand relative to the case without buckling relative to the adjacent impeller end.

2. A rotary machine of the class described, comprising a rotary impeller, a plate against an end of the impeller, and a case enclosing the impeller and plate, with a portion of the case fitting closely around a portion of the periphery of the impeller to trap fluid therebetween and with the periphery of the plate extending alternately in contact with and substantially spaced from the case adjacent the said portion of the case, there being at least two said spacings each extending continuously along substantial lengths of the plate periphery with said contact along the plate periphery disposed between the two spacings, whereby during operation of the machine the contact between the plate periphery and the case opposes flow of fluid along the periphery of the plate and the spacings between the plate periphery and the case permit the plate to expand relative to the case without buckling relative to the adjacent impeller end.

3. A rotary machine of the class described, comprising a rotary impeller, a plate against an end of the impeller, and a case enclosing the impeller and plate, with a portion of the case fitting closely around a portion of the periphery of the impeller to trap fluid therebetween and with the periphery of the plate extending alternately in contact with and substantially spaced from the case adjacent the said portion of the case, there being at least two said contacts spaced along the plate periphery with at least one said spacing extending continuously along a substantial length of the plate periphery therebetween, whereby during operation of the machine the contacts between the plate periphery and case oppose flow of fluid along the periphery of the plate and the spacing between the plate periphery and case permits the plate to expand relative to the case without buckling relative to the ad jacent impeller end.

4. A rotary machine of the class described, comprising a rotary impeller, a plate against an end of the impeller, and a case enclosing the impeller and plate, with a portion of the case fitting closely around a portion of the periphery of the impeller to trap fluid therebetween and with the periphery of the plate extending alternately in contact with and substantially spaced from the case adjacent the said portion of the case, there being several said contacts spaced apart along the plate periphery with a plurality of said spacings extending continuously along substantial lengths of the plate periphery between said contacts, whereby during operation of the machine the contacts between the plate periphery and case oppose flow of fluid along the periphery of the plate and the spacings between the plate periphery and case permit the plate to expand relative to the case without buckling relative to the adjacent impeller end.

5. A rotary machine of the class described, comprising a pair of rotary impellers, a plate against the ends of the impellers, a case with a chamber receiving the impellers and plate, said chamber having a pair of surfaces respectively curved around at least part of the periphery of each impeller to trap fluid therebetween and having extension of said surfaces curved around the respective parts of the plate periphery adjacent the said parts of the impeller peripheries, spaced portions of each of said parts of the plate periphery in contact across the width of the plate with said extended surfaces of the case, and with other portions of each of said parts of the plate periphery spaced from the said extended surface to an extent insuring definite clearance beyond manufacturing tolerances along substantial continuous lengths of the plate periphery, whereby during operation of the machine the contacts between the plate periphery and case oppose flow of fluid along the periphery of the plate and the spaces between the plate periphery and case permit the plate to expand thermally relative to the case without buckling relative to the adjacent impeller ends.

6. A rotary machine of the class described comprising a pair of meshing rotary impellers, a plate against the impellers at corresponding ends thereof, and a case enclosing the impellers and plate, with a portion of the case fitting closely around part of the periphery of each impeller to trap fluid between the impellers and case, and with the periphery of the plate extending alternately in contact with and substantially spaced from the case adjacent said portion of the case closely fitting around the periphery of each impeller, whereby during operation of the machine the contact between the plate periphery and case opposes flow of fluid along the periphery of the plate and the spacing between the plate periphery and case permits the plate to expand relative to the case without buckling relative to the adjacent impeller ends.

7. A rotary machine of the class described comprising a pair of cooperating rotary impellers, a plate in the form of a figure 8 against corresponding ends of the impellers with the impeller axes generally concentric with the respective circular portions of the figure 8, and a case enclosing the impellers and plate, with a portion of the case fitting closely around part of the periphery of each impeller and with a pair of semi-circular portions of the periphery of the plate each extending closely adjacent the said part of the periphery of one of the impellers, with the ends of each of said semicircular portions of the plate periphery in contact with the case adjacent the places Where the impeller peripheries leave and resume close engagement with the case before and after meshing, in order to control flow of fluid around the semicircular portions of the plate periphery from the high-pressure to the lowpressure side of the impellers, and with intermediate parts of said semicircular portions of the plate periphery substantially spaced from the case in order to accommodate thermal expansion of the plate radially of the impeller axes so that the plate will not buckle and seize against the impellers.

8. A rotary machine of the class described comprising a pair of cooperating rotary impellers, a plate in the form of a figure 8 against corresponding ends of the impellers, impeller shafts journaled in the plate with the impeller axes generally concentric with the respective circular portions of the figure 8, and a case enclosing the impellers and plate, with a portion of the case fitting closely around part of the periphery of each impeller and with a pair oi: semicircular portions of the periphery of the plate each extending closely adjacent the said close-fitting part of the periphery of one of the impellers, with the ends of each of said semicircular portions of the plate periphery in contact with the case adjacent the places where the impeller peripheries leave and resume close engagement with the case before and after meshing, in order to to control flow of fluid around the semicircular portions of the plate periphery from the high-pressure to the lowpressure side of the impellers, with the center of each of said semicircular portions of the plate periphery also in contact with the case to align the plate in the case, and with intermediate parts of said semicircular portions of the plate periphery between said ends and centers substantially spaced from the case in order to accommodate thermal expansion of the plate radially of the impelle'. axes so that the plate will not buckle and seize against the impellers.

9. A rotary machine of the class described comprising a pair of meshing rotary impellers, a plate against corresponding ends of the impellers, and a case enclosing the impellers and plate, the impellers being journaled in the plate and the plate being shiftable in the case axially of the impellers, with a portion of the case fitting closely around part of the periphery of each impeller to trap fluid between the impellers and the case, and with the periphery of the plate extending alternately in contact with and substantially spaced from the case adjacent said closefitting portion of the case, said contact being a slidable contact under at least some operating conditions whereby during operation of the machine, the contact between the plate periphery and case opposes flow of fluid along the periphery of the plate and aligns the impellers relative to the case while the spacing between the plate periphery and case permits the plate to expand relative to the case without buckling against the adjacent impeller ends.

10. A rotary machine of the class described comprising a pair of meshing rotary impellers, a plate against corresponding ends of the impellers, a case having a first section enclosing the impellers and the periphery of the plate and having a second section enclosing the rear face of the plate away from the impellers, means detachably securing the two sections of the case together, the first section having semicircular portions in close-fitting engagement with the impellers to trap fluid therebetween and in contact with adjacent portions of the plate periphery, and the plate being shiftable in the first section of the case axially against the impellers and having a pair of openings therethrough which are concentric with the respective impeller axes and which are counterbored from the rear face of the plate, roller bearings carrying the impellers and having nonrotating outer elements secured in the second section of the case and extending into the counterbored portions of the openings through the plate, and sealing means connecting the rear face of the plate and the second section of the case to control fluid pressures on the rear face, said sealing means being received in channels in the rear face of the plate Which are substantially shallower than the counterboring, and said sealing means and channels extending between the counterbores and also generally radially thereof toward portions of the plate periphery in contact with said semicircular portions of the case.

11. A pressure plate for corresponding ends of a pair of cooperating impellers in a rotary machine of the class described, comprising a metal body having a front face adapted to abut the impeller ends, a pair of openings to receive the impeller shafts, and a rear face channeled between said openings to receive a length of rubberlike sealing means to oppose flow of fluid across the rear face between the impeller axes.

A pressure plate for corresponding ends of a pair of cooperating impellers in a rotary machine of the class described, comprising a metal body having a front face adapted to abut the impeller ends, a pair of openings to receive the impeller shafts, and a rear face having channels therein extending from said openings to the outer periphery of the plate to receive lengths of rubberlike sealing means to control flow of fluid across the rear face, said openings being counterbored from the rear face to a substantially greater depth than the channels in the rear face.

13. A pressure plate for corresponding ends of a pair of cooperatin impellers in a rotary machine of the class described, comprising a metal body in the general form of a figure 8, the body having a front face adapted to abut the impeller ends, a pair of openings through the plate to receive the impeller shafts, and a rear face having a channel across it between said pair of openings and other channels from opposite sides of said openings to the outer periphery of the plate, the portions of the outer periphery at the ends of said other channels being of greater radius from the respective centers of the adjacent openings than intermediate portions of the outer :eriphery adjacent the outer ends of the plate, said channels being adapted to receive lengths of rubberlike sealing means to oppose flow of fluid along the rear face around the major arc surrounding each opening from adjacent one side to adjacent the other side of the center line of the openings at the center of the plate.

14. A pressure plate for corresponding ends of a pair of cooperating impellers in a rotary machine of the class described, comprising a metal body in the general form of a figure 8, the body having a front face adapted to abut the impeller ends, a pair of openings through the plate to receive the impeller shafts, and a rear face having a channel across it between said pair of openings and other channels from opposite sides of said openings to the outer periphery of the plate, the portions of the outer periphery at the ends of said other channels being of greater radius from the respective centers of the adjacent openings than intermediate portions of the outer periphery adjacent the outer ends of the plate, said channels being adapted to receive lengths of rubberlike sealing means to oppose flow of fluid along the rear face from adjacent one side to adjacent the other side of the center line of the pair of openings at the center of the plate.

15. A pressure plate for corresponding ends of a pair of cooperating impellers in a rotary machine of the class described, comprising a metal body in the general form of a pair of joined rings arranged as a figure 8, the body having a front face adapted to abut the impeller ends, a pair of openings through the rings to receive the impeller shafts, and a periphery along the outer edges of the unjoined portions of the rings having alternating sections of substantially different radius from the centers of the respective rings, for the purpose of spacing the peripheral sections of smaller radius from a surrounding case while the other sections of larger diameter engage'the case so that thermal expansion of the plate in the case can be accommodated without buckling the plate against the adjacent impeller.

16. A pressure plate for corresponding ends of a pair of cooperating impellers in a rotary machine of the class described, comprising a metal body in the general form of a pair of joined rings arranged as a figure 8, the body having a front face adapted to abut the impeller ends, a pair of openings through the rings to receive the impeller shafts, and a periphery around the outer edges of the unjoined portions of the rings having sections of relatively large radius from the respective centers of the rings where a line through said centers intersects the said outer periphery and substantially where a line through each of said centers normal to the first-mentioned line intersects the said periphery on both sides of each ring and having sections of less radius from the respective centers of the ring between each of the sections of relatively large radius where the first-mentioned line intersects the periphery and the other sections of relatively large radius. r j

17. A pressure plate for corresponding ends of a pair of cooperating impellers in a rotary machine of the class described, comprising a metal body in the general form of a pair of joined rings arranged as a figure 8, the outer periphery of the unjoined portion of each ring including sections of two different radii from the center of the ring, said body having a front face adapted to abut the impeller ends, a pair of openings to receive the impeller shafts, and a rear face having channels indented therein to receive lengths of rubberlike sealing means for controlling flow of fluid across the rear face, said openings being counterbored from the rear face to a greater depth than said channels, and said channels extending from the respective counterbored openings to sections of the periphery of relatively great radius.

18. A rotary machine of the class described comprising a case with inlet and outlet ports, at least one impeller rotatably mounted in the case in the path of fluid passing through the case between said ports, a pressure plate enclosed in the case and having a front face bearing against an end of the impeller and a generally parallel rear face extending closely adjacent an interior surface of the case, said plate. being shiftable axially against said end of the impeller, whereby a greater fluid pressure is developed between the impeller and front face of the plate adjacent one port than adjacent the other during operation of the machine, and means forming a pair of separate fluid-retaining pockets. between the rear face of the plate and the said interior surface of the case, one pocket extending across part of the area of the rear face adjacent one port and opening into said port across a portion of the outer periphery of the rear face adjacent that port and the other socket extending across another part of the area of the rear face adjacent the other port and opening into the said other port across another portion of the outer periphery of the rear face adjacent the said other port, said means sealing the boundaries of the respective pockets around said areas of the rear face except along said portions of the outer periphery of the rear face adjacent the ports and including lengths of resilient rubberlike material which are pressed between the rear face of the plate and said interior case surface and which have ends terminating adjacent the respective portions of the outer periphery of the rear face of the plate adjacent the ports, whereby the fluid pressures in said pockets substantially equalize the pressures across the front face of the plate against the end of the impeller during operation of the machine.

19. A rota1y machine of the class described comprising a case with inlet and outlet ports, a pair of meshing impellers journaled in the case in the path of fluid passing through the case between said ports, a pressure plate enclosed in the case and having a front face bearing against one end of each impeller and a generally parallel rear face extending closely adjacent an interior surface of the case, said plate being shiftable axially against the adjacent ends of the impellers, whereby a greater fluid pressure is developed between the impellers and front face of the plate adjacent one port than adjacent the other during operation of the machine, and means forming a pair of separate fluid-retaining pockets between the rear face of the plate and the said interior surface of the case, one pocket extending across part of the area of the rear face adjacent one port and opening into said port across a portion of the outer periphery of the rear face adjacent that port and the other pocket extending across another part of the area of the rear face adjacent the other port and opening into the said other port across another portion of the outer periphery of the rear face adjacent the said other port, said means sealing the boundaries of the respective pockets around said areas of the rear face except along said portions of the outer periphery of the rear face adjacent the ports and including lengths of resilient rubberlike material which are pressed between the rear face of the plate and said interior case surface and which have ends terminating adjacent the respective portions of the outer periphery of the rear face of the plate adjacent the ports, whereby the fluid pressures in said pockets substantially equalize the pressures across the front face of the plate against the ends of the impellers during operation of the machine.

20. A rotary machine of the class described comprising a case with inlet and outlet ports, a pair of meshing impeller gears rotatably mounted in the case in the path of fluid passing through the case between said ports, a pressure plate in the general form of a figure 8 enclosed in the case and having a front face bearing against one end of each gear and a generally parallel rear face ex tending closely adjacent an interior surface of the case, bearing means for the gears extending in sealed relation through two openings through the plate, said plate being shiftable axially against the adjacent ends of the gears, whereby a greater fluid pressure is developed between the gears and front face of the plate adjacent one port than adjacent the other during operation of the machine, and means forming a pair of separate fluid-retaining pockets between the rear face of the plate and the said interior surface of the case, one pocket extending across part of the area of the rear face adjacent one port and opening into said port across a portion of the outer periphery of the rear face adjacent that port and the other pocket extending across another part of the area of the rear face adjacent the other port and. opening into the said other port across another portion of the outer periphery of the rear face adjacent the said other port, said means sealing the boundaries of the respective pockets around said areas of the rear face except along said portions of the outer periphery of the rear face adjacent the ports and including lengths of resilient rubberlike material which are pressed between the rear face of the plate and said interior case surface, and which are received in and substantially coextensive with channels indented across the rear face of the plate, one channel extending between said two openings through the plate and other channels respectively extending between the outer periphery of the plate and one of the said openings through the plate, the said other channels each terminating adjacent one of the ends of said portions of the outer periphery of the rear face of the plate adjacent the ports, and the periphery of the plate being in close-fitting engagement with the case where the said other channels extend to the outer periphery of the rear face, whereby the fluid pressures in said pockets substantially equalize the pressures across the front face of the plate against the ends of the gears during operation of the machine.

21. A rotary machine of the class described comprising a case with inlet and outlet ports, a pair of meshing impeller gears rotatably mounted in the case in the path of fluid passing through the case between said ports, a pressure plate in the general form of a figure 8 enclosed in the case and having a front face bearing against one end of each gear and a generally parallel rear face extending closely adjacent an interior surface of the case, bearing means for the gears extending through two openings through the plate, the plate being shiftable axially against the adjacent ends of the gears, whereby a greater fluid pressure is developed between the gears and the front face of the plate adjacent one port than adjacent the other during operation of the machine, and means forming a plurality of separate fluid-retaining pockets between the rear face of the plate and the said interior surface of the case, one pocket extending across part of the area of the rear face adjacent one port and opening into said port across a portion of the outer periphery of the rear face adjacent that port, another pocket extending across another part of the area of the rear face adjacent the other port and opening into the said other port across another portion of the outer periphery of the rear face adjacent the said other port, and other pockets respectively adjacent the opposite ends of the plate and extending across different portions of the remaining other areas of the rear face of the plate, said means including lengths of resilient rubberlike material which are pressed between the rear face of the plate and said interior case surface and which are received in channels indented across the rear face of the plate, one channel extending between said openings generally in a plane through the gear axes and other channels extending from opposite sides of each of said openings to the outer periphery of the plate in a direction generally normal to said plane, the outer periphery of the plate being in close-fitting relation with the case where each channel extends to the outer periphery of the rear face, and the outer periphery of the plate being spaced substantially from the case adjacent each of said pockets at the opposite ends of the plate to permit passage of fluid between the latter pockets and the opposite portions of the front face of the plate and also to accommodate thermal expansion of the plate in the case, said pockets serving to substantially equalize the pressures across the front face of the plate against the ends of the gears during operation of the machine.

22. Apparatus according to claim 21 in which said pockets and channels are arranged symmetrically with respect to the plane through the gear axes and the gears are reversible for flow between the ports in either direction.

23. A rotary machine of the class described comprising a case with inlet and outlet ports, a pair of meshing impeller gears journaled in the case in the path of fluid passing through the case between said ports, a pressure plate in the general form of a figure 8 enclosed in the case and having a front face bearing against one end of each gear and a generally parallel rear face extending closely adjacent an interior surface of the case, said plate having two openings transversely therethrough countersunk from the rear face, bearing means for the gears including a pair of cylindrical members snugly received at one end in said countersunk openings, said plate being shiftable axially against the adjacent ends of the gears, whereby a greater fluid pressure is developed between the gears and front face of the plate adjacent one port than adjacent the other during operation of the machine, and means forming a pair of separate fluid-retaining pockets between the rear face of the plate and the said interior surface of the case, one pocket extending across part of the area of the rear face adjacent one port and opening into said port across a portion of the outer periphery of the rear face adjacent 0 that port and the other pocket extending across another part of the area of the rear face adjacent the other port and opening into the said other port across another portion of the outer periphery of the rear face adjacent the said other port, said means sealing the boundaries of the respective pockets around said areas of the rear face except along said portions of the outer periphery of the rear face adjacent the ports and including lengths of resilient rubberlike material which are pressed between the rear face of the plate and said interior case surface and which are received in and substantially coextensive with channels indented across the rear face of the plate, one channel extending between said countersunk openings and other channels extending from each of said countersunk openings to the outer periphery of the plate adjacent the ports, the outer periphery of the plate being in close-fitting relation with the case where each of said other channels extends to the outer periphery of the rear face, whereby the fluid pressures in said pockets substantially equalize the pressures across the front face of the plate against the ends of the gears during operation of the machine.

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