US2144613A - Priming system for centrifugal pumps - Google Patents

Description

Jan. 24, 1939. F. s. BROADHURST PRIMING SYSTEM FOR CENTRIFUGAL PUMPS Filed March 19, 1935 4 Sheets-Sheet l 47? mars.

Jan. 24, 1939. F4 S BROADHURST PRIMING SYSTEM FOR CENTRIFUGAL PUMPS Filed March 19, 1935 4 Sheets-Sheet 2 III Jan.24,1939.' F s BROADHURST PRIMING SYSTEM FOR CENTRIFUGAL PUMPS Y Fiied March 19, 1935 4 Sheets-Sheet s (iv/M ww,

Jan. 24, 1939. F. s. BROADHURST PRIMING SYSTEM FOR CENTRIFUGAL PUMPS 4 Sheets-Sheet 4 Filed March 19, 1935 Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE Frank S. Broadhurst, Watertown, Mass, assignor to De Laval Steam Turbine Company, Trenton, N. J., a corporation of New Jersey Application March 19, 1935, Serial No. 11,867

9 Claims.

This invention relates to a priming system for centrifugal pumps.

The present application is, in part, a continuation of my applications Ser. Nos. 457,309 and 457,311, filed May 29, 1930.

In cases where there is no supply of liquid available to prime a centrifugal pump by gravity flow, or where it is undesirable or impossible to prime the pump by the use of an auxiliary water pump, it has been customary to provide the centrifugal pump with an air pump in the same casing to evacuate the main pump and so render it self-priming. A system, of this character isvery unsatisfactory for several reasons, among which may be mentioned the fact that the centrifugal pump is driven for an appreciable time without priming, which may result in damage to labyrinthine packing, the fact that there is absorption of considerable power by the air pump which is running throughout the operation of the main pump, and the fact that scoring and plugging of the air pump may occur due to grit,

dirt, seaweed, etc. in the water being pumped, some of which is passed through the air pump for L sealing purposes.

It has also been customary to prime centrifugal pumps on the delivery side, sometimes with the provision of float valves or the like designed to prevent the passage of liquid to a vacuum .,pump after the centrifugal pump is primed and operating. The valves, under such conditions, are exposed to high pressures and are liable to damageby impact and blocking by solid or semisolid material jammed against them, for example', in the handling of sewage.

In general pumping and particularly in the pumping of driven wells, air is carried into the centrifugal pump with the liquid. This air is separated by the centrifugal action of the pump and accumulates adjacent the shaft. When the accumulation reaches such extent as to substantially cut off the intake passages, the pump will lose its'prime and with previous priming systems it would be necessary to shut down the pump, reprime, and then restart-the pumping operations.

It is the broad object of the present invention to provide an automatic priming system for centrifugal pumps which overcomes the various obas an ejector or eductor for evacuating the suction bells and the interior of the impeller of the centrifugal pump, the air pump being automatically stopped after the centrifugal pump is primed. The air pump thus ,operates only for short periods, primarily during the starting of the main pump, and accordingly, if a wet type of pump is used, a small supply of clean water sufiices for sealing purposes, since there is no substantial loss by evaporation due to heating. If the pump is of the dry type and is provided with a water jacket, the same saving of water, in this case used for cooling, is accomplished.

In accordance with the present invention, the priming is also of such nature as to remove the air separated in the centrifugal pump. Specifically this is effected by drawing off the air adjacent the axis of rotation in a continuous fashion and in such manner that while the air is removed, removal of liquid from the same place is substantially avoided.

The use of special devices in accordance with the present invention permits the handling of liquids containing relatively large quantities of gas such as, for example, water pumped from a driven well. In such case, provision is made not only to separate the larger quantities of air drawn from the well, but also sand and dirt which may be carried with the water and which would be detrimental to the centrifugal pump.

A further modification of the invention is desirably used when sewage is being handled. Since the priming system necessarily, according to the present invention, involves automatic valves, it is absolutely essential that such valves be protected against the presence of solid or semi-solid material in the sewage. In accordance with this modification of the invention, clean water is introduced into the system in such fashion as to prevent the sewage from ever coining into contact with the priming elements. The present invention also involves the provision of a driving motor control arrangement which prevents operation of a centrifugal pump unless the pump is primed.

' V More specific objects of the invention relate to the provision of various means whereby proper action of the priming system is insured, and will be clear from the following description read in conjunction with the accompanying drawings, in which:

Fig. 1 illustrates diagrammatically a preferred embodiment of the invention applicable for general pumping use;

, Fig. 2 is a similar'diagram of a modified form 'of the invention applicable particularly ,where; large quantities of gas and/or dirt is contained "in the water being supplied to the pump as, for

example, in the pumping of driven wells;

Fig. 3 is a further diagram of similar character showing the application of the invention to the pumping of sewage;

Fig. 4 is a diagrammatic sectional view showing certain elements of thepriming system in their relationship to a centrifugal pump;

Fig. 5 is a sectional view showing a fioat controlled valve used for controlling the removal of the major portion of the air in priming;

Fig. 6 is a sectional view of a float valve designed particularly for the continuous removal of accumulated air from the system;

Fig. 7 is a sectional view of a vacuum controlled shut-off valve arranged to operate in conjunction with the stoppage of the vacuum producing device to prevent loss of prime;

Fig. 8 is a sectional view showing a vacuum controlled valve arranged to control the flow of either cooling or sealing water to the vacuum pump to permit fiow to occur only when the pump is operating; and

Fig. 9 is a sectional view showing a float controlled switch for insuring that the centrifugal pump is operated only when primed.

Referring first to Fig. 4, there is diagrammatically illustrated a motor 2 driving the rotor 4 of a centrifugal pump, which pump is provided with a pair of suction bells 6 receiving liquid from the intake 6. The liquid is discharged into the usual discharge volute it). In all of the arrangements here considered, it will be assumed that the intake communicate with a source below the level of the pump so that vacuum priming is necessary, there being provided in the delivery connections the conventional check valves which close when the pumps are idle and hence permit evacuation and priming.

Extending downwardly into each of the suction hells 6 there is a pipe l2the lower end i4 of which opens closely adjacent the shaft or shaft sleeves. The lower end of the pipe is so positioned relatively to the shaft that it will be exposed by the liquid to the air accumulating around the shaft whenever there is even a relatively small quantity of air present. The pipes l2 are additionally provided with small openings I6 located immediately inside the upper portions of the suction bells. When the pump is stationary, these openings permit the priming to occur to such extent as to completely fill the suction bells with water which, of course, would not be the case if the only openings in the pipes were closely adjacent the shaft. Under the last circumstances, priming could not be completed until after the pump was running. Pipes l2 are of moderately large size so that the air may bubble freely upwardly in them and in the vertical pipe l6 with which they connect.

As is customary in centrifugal pumps, the

glands are sealed by water introduced under pressure through pipes such as illustrated at 26. In single stage pumps it is conventional to introduce such gland sealing water; otherwise air will be drawn intothe pump along the shaft. In multistage arrangements of pumps, however, the pumps following the first are not generally provided with sealing water for the glands because a pressure greater than atmospheric exists about the shafts. However, in a multistage arrangement in accordance with the present invention, the pumps forming stages later than the first are also desirably provided with water seals; otherwise, during the priming procedure,

substantial quantities of air will enter through the glands and along the shafts. Such provision of sealing water in the second stage of a two-stage arrangement is indicated in Fig. 1. For satisfactory operation of the present priming system it is desirable to maintain not less than 10 pounds per square inch on these glands.

Referring now particularly to Fig. 1, which shows an arrangement suitable for general purposes wherein only relatively small quantities of air enter with the water, there are illustrated four centrifugal pumps 22, 24, 26 and 26, the last of which forms a second stage following the first stage provided by the pump 26. The pumps 22 and 24 and the first stage pump 26 are provided with priming arrangement embodying pipes l2, as described above in connection with Fig. 4.

The intakes 6 of the pumps 22, 24 and 26,

are connected to a common inflow pipe 32 which takes liquid from a supply below the level of the pumps. The passage from the first to the second stages of the multistage arrangement is indicated at 30. At the end of the pipe 32 beyond the last pump connected thereto there is provided a stand-pipe 34 of substantial height above the pumps and of substantial cross-sectional area. This stand-pipe, for example, may be of the order of five or more feet, and extends above the fioat controlled switch I36 later described, to a height greater than fluctuations of liquid level which might occur in the stand-pipe due to transient conditions. Adjacent the upper end of this stand-pipe there is located a float-controlled valve, the details of which are shown in Fig. 5. This valve comprises a chamber 36 in which is located a fioat 46 carried'by a pivoted lever which is connected by a link 42 with an adjustable lever 44 carrying a valve member 46 arranged to engage a seat surrounding an opening 46. Closure of this valve is effected when the fioat is raised.

Above the opening 46 there is located a rubber ball check 56 carried in a housing 5| which has an exit connected through a pipe 52 to a vacuum line 54.

The chamber 36 is provided with an outlet 66 communicating with a pipe 66 connected to the upper end of the stand-pipe 34. The opening 66 is above the normal level of liquid in the chamber 36 when the fioat is in its uppermost position and the valve 46 is closed. Accordingly large quantities of .air or'gas may pass through the valve without disturbance of the liquid level thus preventing chattering and damage to the valve 46. Y

A pipe 46 connected to the side of the standpipe 34 joins it with the lower portion of the chamber 36 through a removable strainer 42 which prevents the entrance of solid materials into the valve to avoid any passage oi solid particles to the valve members or seats.

At the upper end of each of the pipes I 6, of which there is one corresponding to each pump that may be used in conjunction with a single I priming system, there is located a fioat valve 66 forated plate 16. The chamber 66 communicates with the vacuum line 54 through a pipe 12. The lower end of the valve 60 is provided with a removable strainer I4 which prevents solid particles passing through the pipe I8 from entering the chamber 62.

The vacuum line 54 used in conjunction with .a multiple pump arrangement is preferably substantially horizontal and is located preferably less than twelve'inches above the valves 36 and 80. If separate vacuum lines extend to the various pumps from the vacuum tank 80, all of these stantially reduced due to this additional height.

It may be remarked that even though the checks are designed to prevent the passage of liquid to a vacuum tank, such result cannot be completely achieved and small quantities of water seeping through the valves accumulate in the vacuum tank.

The discharge volute of a higher stage of amultiple stage arrangement is preferably connected by a pipe I6 controlled by a valve I8 with the intake of the first stage in order to remove continuously any air which may accumulate in the volute. The valve I8 is of 'such nature that it is merely cracked in order to prevent any substantial circulation of liquid and only achieve the removal of accumulated gas. The same typeof arrangement is used when the multiple stage arrangement comprises separate pumps or a plurality of impellers in a single casing.

The vacuum tank 80 is connected by a pipe 82 with a control valve 84 which is in turn connected by a pipe 88 to the vacuum producing device which, in the present case, is shown as a dry vacuum pump 88. The vacuum producing device, however, may be of any suitable form, for example, a wet vacuum pump, an ejector or eductor or the like. The dry type of vacuum pump,

however, is illustrative of certain desirable or necessary features and is hence herein disclosed.

The vacuum tank 80 is of suitable size to avoid starting and stopping of the vacuum pump at short intervals. In a typical installation, a tank 24" in diameter and 40 in height was found ample.

The valve 84 is illustrated in detail in Fig. 7. It comprises upper and lower chambers between which there islocated a diaphragm I00. The pipe 82 communicates with a tube 92 having an upturned end providing a seat for a valve member 94 which is guided in a bore 98 andconnected by a yoke 98 with the diaphragm I00. The outlet pipe 80 communicates with the chamber above the diaphragm. The chamber below the diaphragm is connected through a, tube 90 to the vacuum tank 80, preferably at some distance from the connection of pipe 82 into this tank, to avoid the effect of fluctuations at the outlet. The operation of this valve will be described hereafter. From the structural standpoint, it may be pointed out that-the seat and valve arrangement which is illustrated is very desirable, since dirt will fall off both the seat and valve and thus there is avoided leakage due to improper seating.

88. The arrangement is conventional and need not be described in detail. It is sufficient to state that the arrangement is such and the switch I04 is so adjusted that the motor I08 is stopped when the vacuum in the tank reaches a predetermined value and is restarted when the vacuum drops to another predetermined value. For example, the pump may be stopped when a vacuum of 27 to 28 inches is attained and started when the vacuum drops to 20 to 23 inches. Adjustment is made to give minimum operation of the vacuum pump and, consequently, minimum power consumption. The tank 80, in other words, acts as a storage for vacuum and prevents short period intermittent operation and stoppage of the motor I08, which preferably operates for a short time and then remains stopped for a long period before restarting.

I The pump 88 which is illustrated is of a dry type, for example, the Fuller rotary type, and requires cooling by means of circulating jacket water. This jacket water comes from a pressure supply, for example, a municipal water supply, through a pipe I I and is controlled by the manually operable valve H2. It then enters a valve I I4 and passes from this valve through piping I I6 to the jacket of the pump.

Details of the valve I I4 are illustrated in Fig. 8. The intake pipe H0 communicates through an upturned tube I20 with the lower chamber of the valve below the diaphragm I24. As in the case of the valve shown in Fig. '7, the upturned end of the tube I20 forms a seat with which cooper atesa valve I22 secured to the diaphragm I24. The upper chamber II4 of this valve communi cates through a tube I I 8 with the vacuum line 88.

The water from the jacket passes through piping I28 to a water jet eductor I28, the discharge from which passes through .a rubber faced check valve I30 to the line 32. The eductor I28 is designed to draw off accumulated liquid from the bottom of the vacuum tank 80 through a loop seal I32 and a rubber faced check valve I34, the arrangement being such as to maintain substantially no liquid in the tank 80. Undue rise of liquid in this vacuum tank may be determined from a sight glass I36. The purpose of the loop seal I32 is to prevent the withdrawal of air from the vacuum tank by the eductor I28 after the accumulated liquid is removed from thetank.

Connected to the stand-pipe I34 above the level of the uppermost of a series of centrifugal pumps is a float controlled switch I38 connected to the stand-pipe through piping I40 and I42. The details of this switch are indicated in Fig. 9. It comprises a chamber in which is located a float I44 connected to the inner plate I46 of a sylphon which serves merely as a fulcrum which does not require packing. The plate of the sylphon has attached thereto a switch arm I48 which, when the fioat is in its upper position, closes a contact at I50 and maintains energized, through suitable connections, the no-voltage release of the starter for the one'or more motors used to drive the centrifugal pumps. This switch is used to prevent the operation of the pumps when they are not primed, namely, before the liquid level in the stand-pipe initially rises above the tops of the pumps or when, for example, the supply fails. Any drop of liquid level below this switch I 38 will result in tripping the no-voltage release and the motor I88 stopped, this motor is started through proper manual control of the starting box I88. Prior to its starting, the pressure in the vacuum tank 88 and all of the connections will be atmospheric. As a consequence, the spring I28 will be holding the valve member I22 of valve II4 against its seat, closing of! the flow of jacket water to the pump. The valve 84 may be in an immaterial, neutral position, since atmospheric pressure will exist uoth above and below the diaphragm I88. As soon as the vacuum pump begins to operate, a partial vacuum is produced in line 88 and, because of the connection of piping II8 adjacent the pump, a vacuum is produced above the diaphragm of valve I I4, thus lifting the valve member I22 from its seat against the tension of spring I28 and permitting the fiow of jacket water to begin. This flow of jacket water produces a partial vacuum in eductor I28, thereby almost immediately removing any water which may have accumulated in the bottom of vacuum tank 88.

The production of the partial vacuum in pipe 88 produces a corresponding partial vacuum above diaphragm I88, the pressure below which will exceed this so that the valve. member 84 will be lifted from its seat and the tank 88 thereby put in open communication with the pump 88. As evacuation of the tank 88 proceeds, the check valves 88 and 88 will be raised from their seats and, since the floats in both valves 38 and 88 are in lower position, evacuation of stand-pipe 84 and pipes I8 will take place. Because of the large cross-sectional area of the stand-pipe 34,

the major portion of the air from the intake piping will be drawn through the stand-pipe and through large valve 38. At the same time the pump casings will be evacuated through the pipes II and valves 88. The liquid level will eventually rise in the stand-pipe 84 and in the centrifugal pumps, eventually substantially filling the suction bells of these pumps due to the provision of the holes I8 in the pipes I2. The liquid level in stand-pipe 34 will pass the switch I38, causing contact to be made at I58 and thereby putting the starters for the centrifugal pump motors in condition to be manually operated, and will finally rise in valve88, lifting the float 48 and thereby forcing the valve member 48 to close the seat 48. Likewise, after the liquid level rises through pipes I8 and in valves 88, it will seat the floats 84 to close oil the outlet openings of the valves 88. Accordingly, except for -accidental seepage,,no liquid will enter the vacuum line 84.

As soon as the valves 38 and 88 are closed off, as just described, the further operation of the vacuum pump will serve merely to exhaustthe vacuum line 84, vacuum tank 88, and their connections, until eventually a pressure is reached at which the vacuum switch I84 will stop the vacuum pump motor I88. The pump 88, if it is of the usual dry type, will almost immediately open the connections 88 and H8 to the atmosphere.

With the first resulting inflow of air into the upper chamber of valve 84, the pressure above the diaphragm I88 will rise as compared with the pressure below it (which will be that of the tank 88) and consequently the valve member 84 will be snapped down upon its seat and thus act as a check preventing the entrance of air into the'vacuum tank 88. Accordingly, the vacuum so produced is maintained. Simultaneously with the stopping of the pump 88, the upper chamber of valve H4 is also opened to the atmosphere and, as a consequence, thevalve member I22 is seated,

cutting off the flow of jacket water and, of course,

' the flow of water through the eductor I28. The

check'valve I34 will immediately close and prevent backward flow of waterinto the vacuum tank. As a result, the vacuum in this tank will be maintained except for the influx of air or other gas which may occur through the line 54.

As was remarked, as soon as the liquid level rises above valve I38, the centrifugal pumps may be started. As soon as a multistage pump is started, the priming of the stage or stages subsequent to the first is effected, since the air will be driven out by the liquid from the first stage through the piping I8 and will be recirculated into the first stage to be removed from adjacent the shaft thereof by the lower ends of the pipes I2.

As soon as sufllcient air accumulates in any one of the valves 88 to cause its float 84 to drop, the air which is permitted to pass will flow past the ball check 88 to the vacuum line 54 and thence to tank 88. In operation no substantial movements of the floats 84 will occur, but there will be a more or less constant seepage of air past these floats into the vacuum tank. The

same type of action occurs in connection with the large valve 38 at the upper end of t e standpipe. Since the passage 48 of this val e is made quite large to accommodate the large quantities of air which must be removed from the intake connections for initial priming, the valve member 48 will be held to its seat by a substantial upward pressure. This accounts for the necessity for using the linkage to insure opening of the valve when the level of liquid is 36 drops. The linkage also insures tight closure as the liquid rises, preventing any entrance of material which might later disturb seating.

By reason of the gradual accumulation of air in the vacuum tank, the pressure therein will gradually rise until it reaches the adjusted pressure at which the vacuum switch I84 will again close to start the motor I88. The restarting of the motor will effect substantially the same operations as before described, with the exception that it will run only for a short time suflicient to again reduce the pressure in tank 88 and its immediate connections to that at which the switch I84 opens and motor I88 again stops. During this short period of operation the eductor I28 operates to remove any accumulated water from the bottom of tank 88. Under conditions such as Just described, eventhough rather unusually large amounts of air enter with the pumped liquid, the vacuum pump operates only for very short periods, perhaps operating only for a few minutes or a fraction of a minute in an hour, depending entirely upon the amount of air which enters the system in relation to the size of the tank 88 and the pressure limits of operation. As a result, there is very little wear and tear on the vacuum pump and its motor, no waste of jacket water, and very little consumption of power.

Entirely similar controls may be used in conjunction with a wet type of vacuum pump which utilizes water for sealing purposes. A valve identical with II4 may control the flow of sealing water; Again, there will be no waste of mate, since flow will occur only when the pump re-'- quires it. In the case of a wet pump the suction may be taken from the bottom of the tank to remove air and water together. A valve such as II 4 may also be used where water is necessary for the operation of any other vacuum producing devices which may require it only during their periods of operation.

' The switch I38 is located below the lowest level of liquid which might be expected in the standpipe 34 during normal operation. Since there is some air in the top of this stand-pipe, transient conditions in the piping, for example, upon the starting of the pumps, may result in substantial change of level of the liquid in the stand-pipe.

. Any such normal changes, however, will not affeet the switch I38 and hence the centrifugal pumps will continue to operate. It is very necessary or desirable, however, to have the switch I 38 present in order to prevent any possibility of operation of the centrifugal pumps for a substantial period in an unprimed condition, this being particularly the case when the arrangement is used in an isolated pumping station. If anything happens to the priming system, the liquid level will drop below the switch I38, immediately tripping the no-voltage release of the centrifugal therein is avoided, since the air is not bubbled up through the liquid in the valve 36 but passes over the surface of the liquid from the opening 56 which is located above the normal liquid level.

The purpose of check valves 50 and 68 in valves 36 and 60 is primarily to avoid any ,possibility of reverse flow of air if a vacuum drawn by a centrifugal pump should exceed that in the tank 80. If the check valves were not present and such condition occurred, air would immediately rush to the shafts of the centrifugal pumps, resulting in immediate loss of prime. Likewise, the check valve 50 will prevent general disturbance by preventing any drop of liquid in the stand-pipe 34. While the check valves serve this particularly useful purpose where a j 'fully applicable to a single pump, multiple arrangements of pumps being referred to herein merely to indicate the added difiiculties which may arise due to multiple operation.

The use of pipes I2, such as shown in Fig. 4, extending closely adjacent-the shaft in conjunction with valves such as 60 for preventing passage of liquid to a vacuum producing device, is advantageous in a semi-automatic system as, for example, where, the pump is used in connection with various bilges in ships with valve connecti'ons so that it can be manually connected to one or the other of the bilges. 'In such case it is possible to pump one bilge dry and'switch over to another bilge without stopping the pump, the priming taking place while the pump is operating. This, of course, is true only where the pumps are of such character that they may run unprimed for limited periods without damage. The provision' for preventing starting in unprimed condition is essential where packing clearances are small so that damage would immediately ensue.'

If .driven wells 1 are being pumped, or the pumping is being done from any other source from which the water carries considerable quantities of air and/or dirt, it is desirable to separate both the air and the dirt preliminarily to the passage of the liquid to the pump, not only to avoid the entrance of grit or other material into the pump, but also to avoid the necessity-for removing the large quantities of air from the pump by means of the present priming system. In other words, it is desirable that the priming elements associated immediately with the pump should take care only of what might be regarded as incidental accumulation of air in small quantities. A system designed specifically for pumping driven wells is indicated in Fig. 2.

The arrangement of this figure consists essentially of very substantial enlargement of the stand-pipe of the system previously discussed and the removal of solid materials as well as air in the enlarged stand-pipe which is now located tially complete removal of air, it is necessary that the velocity of the stream of liquid be quite low. Accordingly, the stand-pipe takes the form of a settling chamber I54. Conveniently, the vacuum tank is built as part of the settling chamber and is indicated at I68, there being a downwardly convex bottom to the vacuum tank from which accumulated water may be drawn oil through the loop I92 by the eductor I86.

The pumped liquid enters the settling chamber at I52, the entrance being immediately above the upwardly concave bottom I56. In order to substantially completely eliminate the entrance of solid material into the intake pipe I62 of the centrifugal pump I64, there is provided a ba-flie arrangement as indicated at I58 and I60, I60 forming, in efiect, a roof over a housing provided by the baflie I58 surrounding the connection between pipe I62 and the settling chamber. The flowing liquid passes between the bailies I58 and I60. These bailles are quite effective in removing floating debris. A plurality of pumps may draw their supplies from a single settling chamber.

The pump I64 is connected through the valve I66, precisely similar to valve 60, to the vacuum tank I68. The pipes I69 have the same form as the pipes I2 previously discussed and extend downwardly to the shaft to remove the accumulated air or gas. The valve I10 has the same form as valve 36 and is connected through the piping I12, I14 and I16, respectively, to the vacuum tank I68, a portion of the settling tank above-the normal liquid level therein, and a portion of the settling tank below the normal liquid level therein. As a consequence, the air which separates in the settling tank and floats upwardly passes through the pipe I14 over the surface of the liquid in valve I10 and, through dropping of the float valve therein, escapes past the check valve into the vacuum tank.

The vacuum is produced by the pump I82 connected to the vacuum tank I88 through piping I18, which is controlled by the diaphragm check valve I 88 corresponding to 84. The cooling water to the pump I82, if it is of the dry type, or the sealing water if it is of the wet type, enters it through the vacuum controlled valve I84 corresponding to I I4 and the water leaving the vacuum pump operates the eductor I88 and passes through the check valve I88 to the lower portion of the settling chamber. The loop I82, together with its check valve I98, have the same function as their counterparts in the'previous modification. The low level switch I94 is identical with I38 and serves the same purpose of stopping the pump in case the liquid falls to a dangerous low level. The pump I82 is driven by motor 284 controlled through starting box 288, to which is connected the vacuum switch I98 connected to the vacuum tank through line I98. function of chamber I54, the operation is substantially identical with that described in connection with the previous modification.

Fig. 3 discloses a modification of the invention particularly adapted to the handling of sewage. In the handling of sewage, it is absolutely necessary to insure the most direct passage of the material being pumped through a centrifugal pump to avoid clogging. Accordingly there is preferably provided a side inlet pump as indicated at 288, which is driven by a motor 2I8 receiving the sewage through entrance pipe 288 and discharging through 2 I2. Obviously, only one side of this pump need be provided with a sealing gland to which water is fed through pipe 2 I4.

Connected to the inflow passage adjacent the pump and lined up with the approach pipe is a stand-pipe M8, to the upper end of which there is connected by piping 2 IT a valve 2 I8 of the same form as valve 86 previously described. The top of the valve 2I8 is connected through pipe 282 to a vacuum tank 88. It will be noted that the parts which are common to both Figs. 1 and 3 are designated, for convenience of reference, by the same reference numerals.

The bottom of the valve 2I8 is connected through an enlarged pipe 228 having a loop seal 222 to the lower portion of the stand-pipe 2I8. The pipe 228 is preferably of relatively large diameter as compared with the connections leading. thereinto, in order to provide for free flow. It is essential that no sewage should'enter the pipe 228 or the valve 2I8 since otherwise rapid clogging would occur, putting the priming system out of operation. In order to insure against the entrance of sewage, the discharge from the eductor I28 is led through pipe 226 and check valve 228 to the upper end of the pipe 228 immediately below the strainer 230 located in the lower porseal 222 definitely prevents the backing of sewage into the pipe 228 against the inflowing clear water, it will be clear that it is .virtually impossible for any sewage to get into the valve 2I8.

The low level control valve 224 is not connected to the stand-pipev but to the pipe 228, which contains clear water. However, since the level in Except for the separating pipe 228 rises and falls with that in the stand-pipe 2I8, the function of the switch 224 is the same as in the preceding modifications to close down the centrifugal pump motor when the liquid level dangerously falls. The connections of switch'224 to pipe 228 are of small diameter to prevent disturbances in the switch when fluctuations occur in the stand-pipe.

'valves such as 86 and88, stand-pipes can be provided of such height that the barometric head of water therein would sufflce to prevent the passage of liquid to the vacuum producing device. Arrangements of this character, however, are not generally applicable because of the considerable height which is necessary if substantial vacua are used for the priming.

It will be obvious that various modifications may be made within the scope of the invention. While the various valves, for example, are shown as of specific forms, it will be clear that various other types of float valves may be used in place of those shown and likewise instead of the diaphragm controlled valves other types may be used. The diaphragm types are particularly advantageous, however, since closure and opening are effected under the applications of substantial forces whereby there is secured not only certainty of operation but there are avoided detrimental pulsations, wear and leakage which make unsatisfactory, and result in the rapid destruction of, conventional check valves.

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

1. In combination, a centrifugal pump comprising a casing having intake and discharge pw sages therein, a, shaft mounted in the casing, and an impeller carried by the shaft; 9. motor driven vacuum pump; connections between the vacuum pump and an intake passage of the centrifugal pump, said connections opening in the intake passage closely adjacent the shaft whereby the vacuum pump may evacuate and thereby prime the centrifugal pump; a float valve arrangement in said connections adapted to pass air but prevent the passage of liquid; a vacuum switch communicating with the connections between the vacuum pump and the valve and arranged to stop the motor upon the attainment of a predetermined vacuum in the connections; and a vacuum tank of substantial capacity communicating with the connections between the vacuum pump and the valve, said tank being of such size relative to normal accumulation of gas at said valve during pumping that operating periods of the vacuum pump are short compared with its periods of rest.

2. In combination, a centrifugal pump comprising a casing having intake and discharge passages therein, a shaft mounted in the casing, and

an impeller carried by the shaft; 9. motor driven vacuum pump; connections between the vacuum pump and an intake passage of the centrifugal pump,- said connections opening in the intake passage closely adjacent the shaft whereby the tank of substantial capacity communicating with the connections between the vacuum pump and the valve said tank being of such size relative to normal accumulation of gas at said valve during pumping that operating periods of the vacuum pump are short compared with its periods of rest.

3. In combination, a centrifugal pump comprising a casing having intake and discharge passages therein, a shaft mounted in the casing, and an impeller carried by the shaft; a vacuum producing device; connections between the vacuum producing device and an intake passage of the centrifugal pump, said connections opening in the intake passage closely adjacent the shaft whereby substantially complete removal of gas from said intake passage may be efiected while the pump is running, and also opening in the upper portion of the intake passage whereby the intake passage may be substantially filled with liquid while the pump is stationary; means in said connections adapted to pass gas but prevent the passage ofliquid; vacuum controlled means for stopping operation of the vacuum producing device upon the attainment of a predetermined vacuum in the connections between the vacuum producing device and the first mentioned means; said vacuum controlled means stopplng operation of the vacuum producing device only when the pressure in the connections between the vacuum producing device and the first mentioned means is considerably less than the lowest pressure on the other side of the first mentioned means.

4. In combination, a centrifugal pump comprising a casing having intake and discharge passages therein, a shaft mounted in the casing, and

an impeller carried by the shaft, said pump being arranged to take liquid from a supply located below it so that the pressure in the intake thereof is less than in the supply; a vacuum producing device; connections between the vacuum producing device and an intake passage of the centrifugal pump, said connections opening in the intake passage closely adjacent the shaft whereby substantially complete removal of gas from said intake passage may be eiiec'ted while the pump is running; means in said connections adapted to pass gas but prevent the passage of liquid: vacuum controlled means for stopping operation of the vacuum producing device upon the attainment of a predetermined vacuum in the connections between the vacuum producing device and the first mentioned means; and a vacuum tank of substantial capacity communicating with the connections between the vacuum producing device and the first mentioned means; said vacuum controlled means stopping operation of the vacuum producing'device only when the-pressure in.

the connections between the vacuum producing device and the first mentioned means is considerably less than the lowest pressure on the other side of the first mentioned means; and said tank being of such size relative to' normal accumulation of gas at said first mentioned means during pumping that operating periods of the vacuum producing device are short compared with its 5 periods of rest.

5. In combination, a centrifugal pump, a vacuum producing device, connections between the vacuum producing device and the centrifugal pump through which the former may evacuate 10 and thereby prime the latter, said connections including a diaphragm controlled check valve, one side of the diaphragm of which communicates with the suction of the vacuum producing device and the other side of which communicates with 15 the connections on the centrifugal pump side of the check valve.

6. In combination, a centrifugal'pump, a vacuum producing, device, connections between the vacuum producing device and the centrifugal g0 pump through which the former may evacuate and thereby prime the latter, means for supplying liquid to the vacuum producing device, and means operated 'bysuch liquid leaving the vacuum producing device to remove liquid from said 25 connections.

7. In combination, a multiple stage centrifugal pump, a vacuum producing device, connections between the vacuum producing device and the first stage of the centrifugal pump, and a con- 3 nection between the discharge side of a subsequent stage of the centrifugal pump to the intake of the first stage to let gas out of said subsequent stage into the intake of the first. I

I 8. In combination, a centrifugal pump, a vacuum producing device, connections between the vacuum producing device and the centrifugal pump through which the former-may evacuate and thereby prime the latter, said connections ineluding a stand-pipe connected to the intake pas- A sage of the centrifugal pump, a float valve arranged below the top of said stand-pipe and .adapted to pass air but prevent the passage of liquid to the vacuum producing device, a connection between the float valve and'the stand-pipe 45 above the normal high level of. liquid therein,

a connection between thefioat valve and the stand-pipe below the normal high level of liquid therein, and means for introducing clean water into the last named connection.

9. In combination, a centrifugal pump, a vac- 50 uum producing device, connections between-the vacuum producing device and the centrifugal pump through which the former may evacuate and thereby prime the latter, said connections 55 including astand-pipe connected to the intake passage of, the centrifugal pump. a float valve arranged below the top oi. said stand-pipe and adapted to pass air but prevent the passage of liquid to the vacuum producing device, a connection between the float valve and the stand-pipe above the normal high level of liquid therein, a connection between the float valve and the standpipe below the normal high level of liquid therein, and means for introducing the last named connection, said last named connection including a loop seal. FRANK S. BROADHURST.

clean water into

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