US2391811A - Multistage centrifugal pump - Google Patents

Description

@126, 25, 1945. E W|LHELM 2,391,813.

MULTISTAGE CENTRIFUGAL PUMP Filed Nov. 6, 1943 4 Sheets-Sheet l a 3945 E. A. WILHELM MULTISTAGE CENTRIFUGAL PUMP Filed Nov. 6, 1945 4 4 Sheets-Sheet 5 Fawn MAW K v Lil-)1 nag Dec. 25, 1945. E. A. WILHELM MUL'IISTAGE CENTRIFUGAL PUMP 4 Sheet-Sheet 4 Filed NOV. 6, 1943 Patented Dec. 25, 1945 2,391,811 K MULTISTAGE CENTRIFUGAL rpm Edward A. Wilhelm, straul. Minn., assignor to Waterous Company, St. Paul, Minn., a corporation of Minnesota Application November 6, 1943, Serial No. 509,244

11 Claims.

My invention relates to an improvement in centrifugal pumps, wherein it is desired to provide a novel two stage pump, the stages of which may be arranged either in series or in parallel.

In pumps of the centrifugal type designed for use on fire engines and the like, it is desirableto construct the pump as flexible as possible so that it may adopt itself for use under varying conditions. For example in some instances it is desired to pump a relatively large volume of water at a relatively low pressure. In other instances it is desirable to pump a relatively smaller quantity of water at a high pressure. The present pump is designed to accommodate itself to the varying conditions.

A feature of the present invention lies in the provision of a centrifugal pump having a pair of impellers which may be arranged either in series or in parallel. When a relatively large volume of fluid is to be pumped the impellers are arranged to operate in parallel, each impeller pumping a substantially equal amount of water. When the impellers are arranged in series only approximately one-half of the volume of water is pumped and the output of one impeller is fed to the intake of the other impeller. The pressure, however, is substantially double that developed when the impellers are arranged in parallel.

A feature of the present invention lies in the provision of a two impeller centrifugal pump controlled by a single valve. Due to the fact that each impeller is normally provided with an intake and an outlet, it is ordinarily necessary to manually operate a series of valves so as to permit the output of one impeller to enter the intake of the other, to close the normal outlet of the first impeller and to close the normal inlet of the second impeller. In my construction but a single valve is provided for manual operation, thereby greatly simplifying the operation of my pump.

A feature of the present invention lies in the provision of automatically operable valves, and in so connecting the impellers that these valves operate automatically to close the outlet of the first impeller and to close the intake of the second impeller when the impellers are arranged in series. This operation is accomplished by means of pressure normally developed within the pump casing and permits semi-automatic operation of the system.

A feature of the present invention lies in the construction of the pump casing. The pump casing is normally constructed so that substantially one-half of the casing may be disconnected from the other half thereof, thereby exposing all of the construction details on the interior of the pump. As a result any portion of the pump is rendered readily accessible for repair or replacement.

These and other objects and novel features of my invention will be more clearly and fully set forth in the following specification and claims.

In the drawings forming a part of my specification:

Figure 1 is a top plan view of my pump in its entirety showing the arrangement of parts thereupon.

Figure 2 is a side elevational view of the pump illustrated in Figure l of the drawings, showing further details of construction thereof.

Figure 3 is an end elevational view of the pump showing the drive mechanism for the pump.

Figure 4 is an enlarged top plan view of the pump casing showing the arrangement of parts within the casing in dotted outline.

Figure 5 is a transverse sectional view through the manually operable valve for changing the operation from parallel connecting impellers to series connected impellers.

Figure 6 is a cross-sectional view taken on a substantially vertical plane, the position of which is indicated by the line 66 of Figure 1.

Figure 7 is a sectional view taken on substantially the line 1-1 of Figure 4.

Figure 8 is a diagrammatic view showing the valve arrangement when the pump impellers are arranged in parallel. s

Figure 9 is a diagrammatic view similar to Figure 8 showing the valve arrangement when the impellers are arranged to operate in series.

The pump A is constructed externally, as best illustrated in Figures 1, 2, and 3 of the drawings. A relatively wide intake manifold I0 is terminally flanged at H for attachment with the transition joint l2 connected to any suitable tubular connection leading to a source of fluid supply. A cap I 3 may close the end of the transition joint l2 when-the pump is not in use. The joint I! is flanged at It and the flanges II and H are connected together in any suitable manner such as by the bolts I5. I

A similar intake manifold IG' projects from the opposite end of the pump A. The manifold I6 is terminally flanged at I l to abut the flanged end I9 of the transition joint 20 which connects the relatively wide and shallow manifold 16 with a circular connecting end 2|. A closure cap 22 may be secured over the end of the transition joint 20 to close the same when the pump is not in use.

Obviously either or both of the intake manifolds may be connected by suitable tubular conduit means to a source of fluid supply. If but one -manifold is in use at any time, the remaining manifold is sealed by means of the corresponding transition Joint cap l3 or 22.

The lower portion of the pump body is integrally cast with the manifolds i and II. The upper section 23 of the pump body is bolted to the lower portion thereof by means of connecting bolts 24. The upper portion 33 of the pump is separated from the lower portion 23 thereof along the axis of the transversely extending impeller shaft 2! so that this shaft 28 and the impellers supported thereon may be readily removed once the upper half of the pump casing has been separated from the lower portion II of the pump.

An aligned outlet conduit 21 extends longitudinally of the pump A above the level of the intake manifolds I0 and ii. This outlet manifold 21 is provided with flanged ends 29 and 3. which are desi ned for attachment with transition Joints 3i and 32, respectively, which in turn are connected to control valves. The transition joint 3| is provided with an end flange 33 which abuts against the flange 28 and is secured thereto by bolts 34 or other suitable means. The transition Joint 3i is shown of bifurcated form having flanged ends 35 arranged to abut the flanged ends 38 of the shut-oil valves 31. These valves 31 are provided with outlet ends 39 which are normally closed by caps 40 when the pump is not in use.

The transition Joint 32 is provided with a flanged end 4| arranged to abut the flange 30 of the outlet manifold 21 and to be secured thereto by any suitable means such as bolts 42. The transition joint 32 is likewise provided with a flanged end 43 which may be bolt connected in abutting relation to the flanged end 43 of the shut-off valve 35. The valve II is provided with an outlet II which is normally closed by a cap 41 when the pump is not in use. While I have illustrated a bifurcated double transition Joint on one end of the pump A, and a single transition Joint 32 at the other end thereof, obviously these transition Joints could be reversed, or both joints could be similar and either of the single or double type to provide the required number of pump outlets at the most convenient points.

The pump A is operated through any desired drive mechanism and is shown provided with a gear casing 49 designed to enclose the necessary drive gears. For example, a pinion Iii on the end of the impeller shaft 26 may be gear connected by the idle gear I to a suitable drive gear.

not illustrated, mounted upon the drive shaft II. The drive shaft 52 is connected to any suitable source of power supply.

As best illustrated in Figure 1 of the drawings, a relief valve 53 may be connected at any point to the outlet manifold 21 so as to by-pass fluid when a predetermined maximum pressure is attained within the pump. This relief valve assists in preventing a sudden surge in the various outlet lines of the pump when one of the outlets is closed. The relief valve 53 also acts to by-pass fluid when the maximum desired pressure within the pump is exceeded due to the closure of most or all of the outlet lines.

With reference to Figures 4, 6, and 7 of the drawings, it will be noted that each of the intake manifolds is centrally divided so'that the intake to each pump impeller is separated for some distance from the intake of the other impeller. In Figure 4 of the drawings, att nti n is called to the fact that the hidden portions of the construction forming a part of the upper section of the pump are shown in relatively short dotted lines. The hidden portions of the lower section of the pump illustrated in Figure 4 are illustrated with longitudinal dashes so that the hidden upper portions may be distinguished from the hidden lower portions of the pump.

With reference now to Figure 4 of the drawings. the intake manifold II is provided with a central dividing partition wall 84 which extends from a point adjacent the flanged end Ii to the impeller casing portion of the pump casing. As illustrated the partition 54 branches to provide two separate manifold walls II and II which conduct the fluid flow therethrough into the intake chambers 51 and 58 respectively. In other words,

the intake manifold I II is divided into two separate conduits 60 and I, the flrst of which leads into the impeller intake chamber 51, while the other of which leads into the impeller intake chamber 50.

The intake manifold II is likewise connected to the intake chambers 51 and n. The manifold Ii is provided with a central partition wall 62 which divides the manifold into spaced conduits 83 and 64. The conduit 63 leads directly into the intake chamber 51 at a point opposite to the connection of the conduit I0 with this chamber. The conduit 64 is similarly connected with the inlet chamber 5! at a p int opposite the connection of this chamber with the intake conduit ti. A valve 65 is provided in the conduit 83, however, this valve is best illustrated in Figure 5 of the drawings.

As best illustrated in Figure 6 of the drawings the impeller shaft It supports a pair of axially spaced impellers l6 and 01. These impellers are of any desired or preferred shape, being provided with impeller vanes not speciflcally illustrated in the drawings. The impeller includes a hub is and is likewise provided with a substantially cylindrical flange II in spaced relation to the hub. The flange II is designed to engage against the inner surface of a wear ring H which is provided with a central ring-shaped wall I2 which extends into communication with the enlarged portion 13 of the impeller shaft 26. The ri portion I! thus provides a central bearing for the shaft 28 between theimpellers; while the wear ring Ii provides a bearing end seal for the rear side of the impeller 86. Spaced apertures 14 are provided through the impeller between the hub is and the flange II so as to release any fluid which might leak through the sealbet'ween the impeller and the wear ring I l The portion of the pump housing sections 23 and 25 encircling the impellers II and 81 form volutes I! and 18, respectively, for these impellers. In the construction illustrated, best shown in Figure 7, the voiute begins at a point substantially vertically above the shaft 23 and terminates in upwardly and'longitudinally extending discharge p l1 and II. Thus as the volute I rotates, fluid enters through the coaxial intake 80 of the impeller and is forced by the impeller longitudinally and upwardly through the discharge passage 11.

The impeller 81 is virtually identical with the impeller 88. This impeller 01 is provided with a hub ll to hold the impeller upon the shaft and is provided with a spaced substantially cylindrical flange I! designed to engage the inner surface of the wear ring ll. Vanes, not speciflcally illustrated in the drawings, force fluid entering the 2,391,811 3- intake "as outwardly mm the: awhiclrl radually merges-into the discharge' passage 1 9.

Openings 84 through the 1 impellivprevent fluid from becoming'trappedbetween the impeller'and the weaning-u;

The impeller 661s provided'with a cylindrical bearing surface 85- outwar'dly-of the intake pas-- sage 30,, which is supported by a; wear ring 86.

Similarly, the impeller 61 is' provided with an.

exi'gemal bearing. surface. 81 which is supported bya wearrlng 89. mounted in the impeller casing. The impellers are thus securely mounted and rotate at a high rate of speed.

hubs 9I and 92. Packing 93 is provided about the shaft 26 within the hub 9| and this packing is held in sealing relation between the. shaft and the hub by means of a split collar 94 provided with a split cylindrical sleeve 95 arranged to bear against the packing 93. The split'co-llar 94 is held in place by studs or cap screws 96.

Packing 91 is provided between the shaft 26 and the hub 92 and this packing is urged in sealing relation between the hub and shaft by a split collar 99, which is held in place by studs or cap screws I00. Very little leakage may take place through the walls of the pump casing about the shaft 26.

One end of the shaft 26 is supported by bearings IOI mounted in a bearing housing I02, sup ported in spaced relation to the pump housing sections by brackets I03. A flinger ring I04 en-' circles the shaft 26 to close the inner end of the bearing housing I02, while the outer end thereof is closed by means of a closure plate I05, securely bolted to the housing I02. A plug I06 or grease connection is provided in the plate I05 and may act to provide a means of lubricating the bearing and also of gaining access to the shaft, and for applying a tachometer to the end of the shaft. The other end of the shaft 26 is supported by the gear housing 49 which is secured by brackets I01 to the pump housing. Bearings I09 and I I are provided between the gear housing 49 and the shaft, and a flinger ring I I l acts to close the inner end of this gear housing. The outer end of the gear housing is provided with a closure plate H2 which is provided with a removable plug or grease fitting II3 to permit lubrication of the bearings and to provide access to the end of the shaft.

As was previously described the pinion 50 is mounted on the shaft 26 and is positioned between the bearings I 09 and H0. The idle gear I is mounted upon a stub shaft H4 in the gear housing in the manner best illustrated in th drawings. I

With reference now to Figure 4 of the drawings, it will be noted that the impeller discharge passages 11 and 19 extend upwardly and outwardly,

being guided by the curved casing walls II5 and I I6 into the opposite sides of the discharge manifold 21. The manner in which the passages 11 and 19 merge or blend into the discharge manifold 21 is perhaps best illustrated in Figure 1 of the drawings. As a result the fluid flowing into the discharge manifold flows into the same oil travelling at substantially rightangles thereto,

discharge conduit with equalfacility. As a result the fluid entering either or both intake manifolds I0 and I6 may flow through the'associated' intake chambers 51 and59, through the impellers 66 and 61, through the volute discharge passages 11 and. 19, and into the discharge manifold 21 in such a way that the fluid may flow from either end of the discharge manifold with equal ease. Parallel operation of the pump takes place in this action just described.

With reference now to Figure 5 of the drawings, it will be noted that the by-pass conduit II 1 extends into communication with the inlet conduit 64. This conduit I I1 is illustrated in Figures 4, 5,

and 7 of the drawings and communicates upwardly'through a conduit II 9 in the upper pump section 23 with the volute discharge passage 19. As a result a continuous passage is provided from the volute discharge passage 19 to the intake passage 64 of the second impeller, The valve is so mounted as to rotate on a substantially vertical axis and selectively close either the intake passage 64 or the by-pass passage II 1.

When in one extreme position, illustrated in full lines in Figure 5 of the drawings, the intake chamber 59 of the impeller 66 is in communication with the discharge passage 19 of the volute 16. When the valve 65 is in the position illustrated in dotted outline in Figure 5 of the drawings, the volute discharge passage 10 is sealed from the intake passage 64 and the intake passage 64 is connected to the source of fluid supply.

As best illustrated in Figures 4 and 7 of the drawings, an automatically operable valve I20 is provided at the end of the volute discharge passage 19. When this valve I 20 is closed the discharge 11 of the volute 16 is not connected to the discharge ou'tlet manifold 21. As may be seen from Figure 4 of the drawings, the valve I20 closes oil the discharge passage within the curved casing wall II6 so that the volute 16 is not connected directly with the discharge. The valve I20 is illustrated as being hinged along its upper edge at I2I.

A valve I22. similar to the valve I20, is hingedly mounted along its upper edge I23 within the intake passage 6|. When the valve I 22 is closed, it abuts against the transition joint I2 and closes off the adjacent intake passage. When open,

.fluid may be drawn from a suitable source of fluid supply.

' The operation of the pump A is believed obvious from the foregoing description, and is diagrammatically illustrated in Figures 8 and 9 of the drawings. When the valve 65 is open, or in the position illustrated in dotted outline in Figure 5 of the drawings, fluid may enter any or all of the suction passages 60, 6|, 63, and 64. Certain of these passages may be closed,.as by caps I3 or 22 mounted upon the ends of the transition joints I2 and 20, respectively. However, the fluid may be drawn through any open intake passage into the suction room 59 of the impeller 66 and into the suction room 51 of the impeller 61. Fluid entering the impeller 66 is urged ,through the volute 15 and the volute discharge passage 11, through .the curved casing portion II5 entering the outlet or discharge manifold 21 at substantially right angles thereto. This fluid under pressure may be withdrawn through any open passage connected to the discharge manifold 21, either flowing through the transition joint 3|, the transition joint 32, or both of these joints, as the case may be,

and thus: mayjbe removed from either end of Fluid entering the impeller 81 is forced through the volute l5 and through the volute discharge passage 19 from which it fiows, through the curved casing portion H6 .to enter the outlet or discharge manifold 21 at substantially right angles thereto. This fluid may flow from the discharge passage from either or both endsthereof.

It will therefore be seen that when the valve 65 is in the open position, or in the dotted outline position of Figure 5, the impellers 68 and 61 operate in parallel and force a relatively high volume of water from the discharge manifold 21 at a relatively low speed.

When it is desired to pump a smaller volume of water at a higher pressure from the discharge manifold, the valve 65 is rotated into the position shown in full lines in Figur 5 of the drawings, thereby closing the intake passage 84 leading to the impeller 66. Under such conditions the fluid is drawn through the inlet passage 60, 83, or both of these passages into the intake chamber 51 of the impeller 61. Fluid is then urged through the impeller 61 into the volute 15 and into the volute discharge passage 19. Due to the opening of the passages I I1 and H9 in the pump casing by the valve 65, the fluid leaving the impeller 61 through the discharge passage 1! has two possible courses to travel. The first course is through the curved casing portion ll! into the discharge manifold 21. Considerable pressure is necessary to force fluid through this discharge manifold under normal operating conditions. The second possible course of travel is through the passages I I9 and I I! to the inlet pas-' sage ll, leading to the intake chamber 59 of the impeller 86. There is relatively no back pressure retarding the flow of fluid in this direction, and in fact the rotation of the impeller 66 has a tendency to draw water from the intake chamber 59 as fast as this chamber is filled. Therefore the main flow of fluid leaving the volut I8 through the discharge passage 19 will pass through the passages H9 and H1 into the intake ll of the volute 68. i

Due to the flow of fluid from the discharge of the first volute to the intake of the second, pressure will be built up within the intake chamher I which is communicated through the intake passage 8|, thereby tending to close the valve I22. For example. if each volute is capable of producing a discharge pressure of 125 pounds per square inch, this pressure will be communicated through the intake chamber 59 to .the inlet passage I. As a result fluid under pressure will be found in the passage 5|, which is resisted only by intake pressure and therefore the automatically operable valve I22 will quickly swing tightly closed and remain closed during series operation of the pump.

As the pressure entering the impeller 80 is already at 125 pounds per square inch, fluid will be discharged into the volute 15 and into the volute discharge passage 11 at substantially 250 pounds per square inch pressure. This pressure will be communicated through the casing portion ll into the discharge manifold 21. Simultaneously the fluid under pressure will be communicated through the passage III to hold the valve I20 in tightly closed position. The valve I20 will remain closed throughout series operation of the pump, as there is but 125 pounds per square inch pressure on one side of the valve and substantially twice this pressure on the other side thereof. Obviously these pressures are only stated for the purpose of illustration.

Thus with reference to Figure 9 of the drawings, when the valve 85 is turned into position to close the intake passage M and to open the pa:- sase Ill, the fluid will flow from the outlet of the first impeller 61 to the inlet of the second impeller 66. The remaining inlet passage ii will be automatically closed as will the valve i2. between the outlet of the impeller I! and the inlet of the impeller 88. The volume of fluid pumped by the pump will obviously be decreased to substantially one-half the amount pumped during parallel operation as indicated in Figure 8, but the outlet pressure of the fluid will be substantially doubled. As soon as the valve is turned into the position illustrated in dotted outline in Figure 5, the outlet pressure will be substantially cut in half but the volume of fluid pumped will be substantially doubled.

The convenient form of construction of my pump A permits quick repair or replacement of any of the parts thereof, due to the fact that the upper half of the pump casing can be removed from the lower half thereof to expose the impeller shaft, the impellers, and the various internal mechanisms. The impellers themselves can be readily removed when necessary, together with the impeller shaft 26. The valve arrangement is such that the operation of a single valve will automatically change the operation of the impellers from parallel operation to series operation and vice versa, the remaining necessary valves operating automatically as a result of the operation of the single valve 85.

In accordance with the patent statutes, I have described the principles of construction and operation of my pump, and while I have endeavored to set forth the best embodiments thereof, I desire to have it understood that obvious changes may be made within the scope of the following claims without departing from the spirit of my invention.

I claim:

1. A centrifugal pump comprising a pair of impellers, a volute for each of said impellers, a discharge for each of said volutes, a pair of inlet manifolds to said impellers, means connecting said inlet manifolds, a passage connecting the outlet of one of said volutes to the intake of the impeller in the other of said volutes, a valve in said last named passage operable selectively to connect said impellers in series by opening said passage and simultaneously closing an inlet manifold or in parallel by closing said passage and simultaneousl opening said inlet manifold, and valve means in the intake manifold to the impeller in the other of said volutes to close and to disconnect the intake manifolds.

2. A centrifugal pump comprising a first impeller, a first volute therefor, a first discharge passage therefrom, and a first intake manifold to said impeller, a second impeller, a second volute therefor, a second discharge therefrom, and a second intake manifold to said second impeller, a passage connecting said first discharge passage to said second intake manifold, valve means in said passage, said valve selectively opening said passage and simultaneously closing said second intake manifold, and vice versa, means connecting said first and second inlet manifolds, and valve means selectively closing the connection between said first and second inlet manifolds.

3. A centrifugal pump comprising a first impeller, a-first intake manifold leading thereto, a first discharge passage leading therefrom, a second impeller, a second intake manifold leading thereto, a second discharge passage leading therefrom, a passage connecting said first discharge passage with said second intake manifold, valve means in said last named passage, said valve means operable selectively to open either said passage or said second intake manifold, means connecting said intake manifolds, and valve means in said connecting means to selectively close the connection between said first and second intake manifolds.

4. A centrifugal pump comprising a first impeller, a, first inlet manifold leading thereto, a first discharge passage leading therefrom, a second impeller, a second inlet manifold leading thereto, a second discharge passage leading therefrom, passage means connecting said first discharge passage to said second inlet manifold, valve means in said connecting passage, said valve means operable selectively to open either said passage means or said second intake manifold, means connecting said inlet manifolds, and check valve means in said connecting means to close said second inlet manifold from said first manifold when the pressure in said second inlet manifold exceeds the pressure in said first inlet manifold.

5. A centrifugal pump comprising a first impeller, an inlet manifold leading thereto, a discharge passage leading therefrom, a second impeller, a second inlet manifold leading thereto, a second discharge passage leading therefrom, means connecting said first discharge passagetto said second inlet manifold, valve means in said connecting passage, said valve means operable selectively to open either said passage means or said second intake manifold, means connecting said inlet manifolds, check valve means in said last named connecting means operable when the pressure in said second inlet manifold exceeds the pressure in said first named inlet manifold to close the connection therebetween, means connecting said discharge passage, and check valve means in said last named connecting means operable when the pressure in said second discharge passage exceeds that in the first discharge passage to close the connection between said discharge passage.

6. A pump comprising a first pumping element, an intake passage thereto, a discharge passage therefrom, a-second pumping element, a second intake passage thereto, a second outlet passage therefrom, a passage connecting said first discharge passage with said second intake passage,

and valve means in said last named passage, said valve means operable selectively to open either said last. named passage or said second intake passage.

7. A pump comprising a first pumping element, a first intake passage thereto, a first outlet passage therefrom, a second pump element, a second intake passage thereto, a second discharge passage therefrom, a connecting passag connecting said first discharge passage with said second intake passage, valve means in said connecting means, said valve means operable selectively to open either said passage means or said second intake manifold, means connecting said first and second intake passages, and valve means operable to close said last named connecting means to cut off said second intake passage from said first intake passage.

8. A pump comprising a first pumping element,

a first inlet passage thereto, a first discharge passage therefrom, a second pumping element, a second inlet passage thereto, a second discharge passage therefrom, means connecting said first discharge passage with said second inlet passage, valve means in said connecting passage, said valve means operable selectively to open either said passage means or said second intake manifold, connecting means connecting said first and second inlet passages, valve means in said connecting passage operable when the pressure in said second inlet passage exceeds the pressure in said first inlet passage to close said valve, connecting means connecting said discharge passage, and means operable when the pressure in said second discharge passage exceeds the pressure in said first discharge passage to close said connecting means.

9. A pump comprising a first pumping element, a pair of first inlet manifolds leading thereto, a first discharge passage leading therefrom, a second pumping element, a pair of second inlet manifolds leading thereto, a second discharge passage leading therefrom, a passag connecting said first discharge passage with one of said second inlet manifolds, valve means selectively operable to connect either said connecting passage or said one inlet manifold to said second pumping element so that said second pumping element may receive-fluid either from the discharge of said first pumping element or from said one inlet manifold of said second pair of inlet manifolds, means connecting said one inlet manifold of said second pair of inlet manifolds with one inlet manifold of said first pair of inlet manifolds, means connecting the other manifolds of said pairs of inlet manifolds, and valve means in said last named connecting means operable when pressure in the other inlet manifold of said second pair of inlet manifolds exceeds the pressure in said first inlet manifolds.

10. A pump comprising a first pumping element, a first inlet chamber associated therewith, a first double ended inlet manifold connected to said first inlet chamber, a first discharge passage leading from said first pumping element, a second pumping element, a second inlet chamber associated therewith, a second double ended inlet manifold connected to said second inlet chamber, a second discharge passag connected to said second pumping element, a connecting passage connecting said first discharge passage with said second inlet chamber, valve means selectively connecting said second inlet chamber either with said connecting passage or with one end of said second double nded inlet manifold, a, common intake connection connecting the other ends of said first and second double ended inlet manifolds, and valve means in said common intake connection and operable when the pressure in said second inlet chamber exceeds the pressure in said first inlet manifold to clos the connection therebetween. 11. A pump comprising a first pumping eleent, a first inlet chamber associated therewith, a first double ended inlet manifold connected to said chamber, a first discharge passage connected to said first pumping element, a second pumping element, a second inlet chamber connected to said second. pumping element, a second double ended inlet manifold connected to said second inlet chamber, a second discharge passage connected to said second pumping element, apassage connecting the discharge of said first pumping element to said second intake chamber, a

valve means selectively closing the passage from said second inlet chamber to said connecting p33- sage or to one end of said second double ended intake manifold, means connecting the other ends of said double ended inlet manifolds, check valve means operable when the pressure in said second inlet chamber exceeds the pressure in said first double ended inlet manifold to close the connection between said double ended inlet manifolds, means connecting said discharge passages, and valve means in said connecting means operable when the discharge pressure of said second pumping element exceeds the discharge pressure of said first pumping element to close the connection between said discharge passages.

EDWARD A. WE-HEIM.

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