US2275501A - Priming system for centrifugal pumps - Google Patents

Description

March 10, 1942. F. s. BROADHURST PRIMING SYSTEM FOR CENTRIFUGAL PUMPS 2 Sheets-Shet 1 Filed March 8, 1939 W M a m 5 w m A hwfi" No j fii w T.

March 10, 1942. F. s. BROADHURST PRIMING SYSTEM FOR CENTRIFUGAL PUMPS 2 Sheets-Sheet 2 Filed March 8, 1959 l l I H Illl ff IPA 5Y6.

Patented Mar. 10, 1942 Frank S.Broadhurst, Watcrtown, Mass, assignor to De Laval Steam Turbine Company, Trenton,

N. J a corporation of New Jersey Application March8, 1939, Serial No. 260,470 2 Claims. (01. 103-113) This invention relates to a priming system for centrifugal pumps, and particularly to a priming system adapted for pumps handling sewage or similar liquids, such as paper pulp discharged from digestors, containing large quantities of solid or semi-solid materials.

The vacuum priming of centrifugal pumps for handling sewage is attended with great difiiculties by reason of the solid or semi-solid materials in the sewage which will rapidly clog any passages of restricted size which are necessary in the case of vacuum priming. Furthermore; it is practically impossible to keep such materials outof float valves, check valves or the like, with the result that heretofore it has been considered practically essential that a centrifugal pump for the handling of sewage should be located below the level of the supply so that priming cantake place by gravity.

Inmy application Serial No. 260,469 filed of even date herewith, there are disclosed various modifications of a priming system of vacuum type designed to insure effective priming of centrifugal pumps which are handling liquids permitting the use of restricted passages. The advantages of the priming systems describedin said application are primarily in that the vacuum pumping apparatus is normallyoperated only in starting up the system and: thereafter. is. standing by without operation merely to serve in the case of an emergency created by an influx of an abnormal amount of gas with the liquid handledby the pump. Specifically, the improved systems involve the utilization of the centrifugal pump itself for continuously priming the system, i. e., continuously removing gas which tends to separate out within the pumps. The systems of said application require some modification to be applicable to the handling of sewage or other liquids containing large floating masses of solid or semisolid materials.

Broadly stated it is the object of the present invention to adapt the priming systems of said copending applicaticnto the handling of sewage in such fashion that not only may vacuum priming be applied to sewage pumps, but so that continucus removal of gasmay be effected, specifically with substantially no operation of the vacuum pumping means used for the initial priming of the system. As will be evident hereafter, while initial priming is of a vacuum type, the system thereafter is substantially a flooded one, the flooded condition being maintained by the pump action.

Subsidiary objects of the invention relate to the provision of devices for protection of the priming system against surges of sewage or the like beinghandled by the pumps. One feature of the invention is the application of a gas cushion to definitely stopany possibility of the entrance of liquid into any small passages. In the preferred system, the sewage in no case is able to enter any small passage, with the sole exposure of any part of the vacuum priming system to the sewage being. in a passage of very rapid flow of the sewage where the sewage is exerting an ejector action on the connections so that'there is substantially no tendency whatever toward clogging.

The various objects of the invention will be clear from the following description, read in con-. junction with the accompanying drawings, in which:

Figure 1 is a diagrammatic view, partially in section, illustrating one embodiment of the invention;

Figure 2 is a wiring diagram showing certain control arrangements; and

Figure 3 is a diagrammatic View of a modification of the invention.

Referring first to Figure 1, there are illustrated therein motors 2 and 2' driving centrifugal pumps 4 and 4' drawing through Venturi passages 6 and 6' and valves 8 and 8. sewage from a common source indicated at M. The sewage enters the pumps through a large pipe l2, which has flaring communication passages l0 and valves 8 and 8'. The upward flare of these passages is provided for the purpose of insuring against clogging. It will be understood, of course, that the invention is applicable to a single pump, but two have been illustrated for the purpose of indicating certainadvantageous operations which may occur when a plurality of pumps are drawing liquid from a common source or even different example, of the order of 20to inches asis V customary in connection with all passages used in the handling of sewage. Likewise the approaches to the pumps are of similar ample size to insure the proper handling of any materials which may enter with thesewage. To the top of the standpipe l6 there is connected a pipe 18 controlled by a valve 20 adapted to be operated by a solenoid 22. The arrangement is such that when the solenoid is energized it will close the valve 20. The pipe l8 communicates with the upper portion of i a vacuum tank 24. With this tank there communicate vacuum switches 26 and 28 serving for the control of motors 30 and 30' driving vacuum pumps 32 and 32 which are submerged in oil. The vacuum switches are providedin duplicate for safety purposes.- One of them may, for example, be effective to start the I 0' With the,

Thus the former will normally be the controlling 4 system, while the latter serves to effect its control only under emergency conditions." Both of these f" f should be of the snap type, as indicated, to avoid any instability of operation, i. e., eachsho'uld,

tend to start and stop the operation of substantially different values of pressure within the tank.

The two vacuum pumps 32 and 32' are proi. type A-shaped core indicated at 60 having a coil 62 on its'crossbar portion grounded at one end and connected at its other end to the electrode 56.

is a wiring diagram of the electrical connections. The two electrodes 56 and 58 constitute the controlling electrodes for a relay which is illustrated as of the well known Bender-Warrick induction This type of relay is provided with an The upper connecting element of the core is provided with a coil 64 permanently connected to an alternating power line. The legs of the core are adapted to attract an armature 66 which is con- Vided to give a factor of safety. The vacuum pumps are illustrated as of the Imo type, i. e., comprising a plurality of screws arranged to be motor driven and sealed to provide air pumping passages by means of oil contained in a tank indicated at 33. Pumps of this type are positive pumps capable of handling large quantities of air which may be separated from the recirculating oil by means of a screen arrangement indicated at 38, and thence pass upwardly through a pipe 4|] which may pass to a device for further insuring separation and avoiding loss of oil. These pumps, while using oil for sealing purposes, would be classified as dry pumps, since they are apt to be damaged by a non-lubricating liquid such as water. Accordingly, their connections 34 and 34 tothe vacuum tank 24 are at the top of that tank. These connections are provided with'check valves 35' and 36' designed to close Whenever the pumps stop.

A second connection to the upper end of the standpipe I6 is made by means of a pipe 42, within which is a check valve 43 and which is arranged to be controlled by a valve 44 actuated by a solenoid 46 so as to be closed whenever the solenoid 46 is energized. The pipe 42 is branched as indicated at 48 and 46' in the event that more than one centrifugal pump is being primed, the branch 48 communicating with a belt chamber 50 surrounding the throat of the venturi 6-which is provided with longitudinal-slots indicated at 52. These slots are preferably provided with sharp edges for the purpose of cutting any materials in the sewage which may tend to stick to the slots. The, belt 56 is preferably made readily removable so that it and the slots may be readily periodically cleaned. The venturi 6' is provided with a similar belt 56 and slots 52. When cleaning is to take place, oneof the valves 8 may be closed while the other valve remains open so that all of the sewage may be .handledby one or more of the other pumps. Valves 49 and 49"may be interposed in the branches 48 and 48 to close them while such cleaning is being effected so as not to interfere with the normal operation of the system. y

The control of the priming is effected solely through the medium of electrical connections to electrodes 54, 55, 56=and 58 located at various levels as indicated in the drawings. These electrodes maybe of the well known type used for level indications in sewage comprising insulating shells having openings therein so that the liquid may contact with the metallic electrodes within the shells. Such electrodes are commonly used and function very reliably to insure contacts when theyare submerged in the liquid, despite the presence of floating materials therein.

The connections of these electrodes and their function in the control of the system will be best understood from consideration of Figure 2, which ventionally illustrated as adapted to close a single contact at 68 and thereby connect the electrodes 56 and 58 together, and a pair of contacts at 10 adapted to cause the removal of a short circuiting connection for the no-voltage release of the starter 12 for the pump motors 2 and 2, this being accomplished through a suitable relay which is not shown.

A second Bender-Warrick type of relay is used in connection with the electrode 55 and also comprises an A-shaped core 74 having a coil 76 on its crossbar portion grounded at one end and connected at its other end to the electrode 55. The

upper connecting element of the core is provided with a coil 15 permanently connected to the alternating current power line. The legs of this core are adapted to attract an armature 11, which is conventionally illustrated "as adapted to close a pair of contacts at 78. adapted to cause energization of the solenoid 22 which controls the valve 20.

A third Bender-Warrick type of relay is illustrated at 19 having its crossbar coil connected to identical with those previously described, it is i1- lustrated only in diagrammatic fashion.

While the tank 24 is not intended to receiveany liquid; it is impossible to avoid accumulation of liquid therein due to spray and also to condensation. Accordingly, there is provided a Water jet air pump indicated at 80 adapted to draw accumulated liquid from the tank 24 through the connection 82. This jet air pump is supplied with.

pressure water through 84 and discharges through the line '86 into the upper end of the standpipe l6. As will be obvious from the description of the operation hereafter, accumulation of any:

liquid within the tank 24 will be very slow so that the jet pump 86 need be operated only at long intervals, operation being effected merely by opening the valve of the supply line 84. A suitable gauge glass may be provided to indicate the amount of accumulation in the tank. It is imarmatures will then be unattracted by the fieldmembers of the relays and consequently soleholds 22 and 46 will be deenergi'zed and their corresponding valves 20 and 4!] opened. Upon clos- 'lng the supply line, .since atmospheric pressure will exist in the tank 24, the vacuum pumps will be operated to draw a vacuum in the tank 24 and hence throughout the system, the usual check valves on the delivery sides of the pumps being closed. At this time, the no-voltage release coil of thestarter for the'motors 2 and2 will be deenerg1zed byreason. of the short circuiting al rangement, .and consequently .these motors can-= merges the electrode 58 nothing occurs because the. electrode circuit is .open at 68. As soon as l the liquid reaches the level of the electrode 56, however, the circuitof the secondary coil 62 will be closed, Prior to this, the crossbar of the core which carries the coil 62 will have served asthe short circuiting path for the flux due to the energizing coil 64 and attraction of the armature 65 will not have taken place. Upon completion of the circuit of the coil 62, however, a countermagnetomotive force is created opposing the flux through the crossbar so that the flux due to the coil 64 will tend to take apath through the armature 66, attracting this armature and closing the contacts at 68 and 10. As soon as the contact 68 is closed, the electrode 58 is thrown in parallel with the electrode 56 and will additionally tend to maintain the closed condition of the relay. At the same time, the short circuiting connection is removed from the no-voltage release of the motor starter.

The pumps are now primed and the motors are ready to start. Starting may be effected bya hand control of the starter; or, alternatively, the arrangement may be readily made such that upon energization of the no-voltage release coil the motors will start automatically. Since the specific arrangements for automatically starting the motors are no part of the present invention, this may be considered as embodied in the diagrammatic illustration of thestarter at 12. Itmay be remarked that where reference is made to a single starter it will be obvious that there may be provided separate starters for the. various motors, the control connections being made in parallel fashion for the various starters.

The arrangement of electrodes 56 and 58 prevents unstable operation. When the pumps are started it is likely that a downward surge will occur in the standpipe I6. If. the electrode 56 is spaced sufficiently above the electrode 58, however, the surge will not uncover the electrode 58, and consequently the pump motors will continue to run. The height between these two electrodes, therefore, defines a region through which fluctuations of liquid level may occur without disturbance to the motor circuits. Whenever the liquid level drops below the electrode 58, the motors will immediately stop, due to short circuiting of the no-voltage release or releases, and will not then be started until the electrode 56 is submerged.

During the starting of the motors or even before they are started, if some delay is involved either automatically or manually the continued drawing of a vacuum in the upper end of pipe l6 will submerge electrode 55. As soon as this occurs, the action of the relay 14 will cause closweet the valve 20, and thereafter a higher vacuum may be drawn in the tank 24 until the vacuum pumps are stopped under the action of one of the switches 26 or 28.

As soon as starting occurs, the valves 49 and 49" may be opened. By reason of theprovision of the Venturi passages; at 6 and 6', an ejector action is created at the slots 52 and a partial vacuum is drawn through the pipe 42 to tend to further exhaust the upper end of the standpipe [6. The design of the venturi is preferably such that a vacuum will be drawn which will cause the liquid level in the standpipe to rise above the electrode 55 to .some predetermined maximum degree such as, for example, four feet. The maximum extent of the rise produced by this ejector action should not permit the liquid level to rise .to the level of the electrode 54.

By reason :of the provisionof the ejectors by means of the Venturi passages, continuous removal of gas is effected automatically so as to maintain the liquid level in the standpip l6 well above the critical level. defined by the. electrode 55, which would open communication to the vacuum tank. Gas which accumulates in the upper end of .th'estandpipe will be immediately removed so as to maintain the level of liquid in thestandpipeat a normal height.

It will be obvious that in accordance with the above, normal operation will occur Without any reopening of the valve to permit passage of gas to the vacuum tank. Under unusual conditions when the level drops to clear electrode reopening of this valve may occur and this may even be accompanied by stopping of the motors if the level falls below electrode 58. In the normal operation of the system, the vacuum pumps willnot operate except in the initial priming and will stop automatically after the liquid level submerges the electrode 55 and after drawing a high vacuum in the tank 24. Even if substantial amounts of gas pass to the tank 24, therefore, in the event that valve 20 opens, the vacuum pumps will not restart until the. pressure in the tank rises sufficiently to cause actuation of one of the switches 26 and 28.

It will be obvious that during normal operation the outlets l8 and 42 are well protected against the sewage Within the standpipe. Surges, however, are likely to occur which, without suitable precautions, might carry sewage into these pipes, clogging them and preventing operation of the controlling valves. Accordingly, provision is made to insure against any possibility of rise of the sewage to the top of the standpipe and to this end the electrode 54 is provided, immersion of which will cause energization of the solenoid 46 to close the valve 44 by action of relay [9. Thus if a surge occurs, the valve 26 will already be closed and the valve 44 will close the instant the liquid reaches the electrode 54, which is well below the top of the standpipe I6. With both the valves 20 and 44 closed, there will be a sub stantial volume of gas in the upper end of the standpipe, and as the surge takes place this cushion of gas will be compressed by the liquid acting as a piston to such extent that the liquid can never reach the top ofthe standpipe. Since the cross-section of the standpipe is quite large,

and the pipes l8 and 42 may be quite small, it will be obvious that this gas would have to be compressed to an enormous pressure before the liquid could reach these pipes. As soon as normal conditions are reestablished, and the liquid drops below the level of 54, the valve 44 will drop open to permit continuation of the ejector action.

It will be seen from the above that priming takes place continuously without. either entry of gasto the vacuum tank or operation of the vacuum pumps except under starting and emergency conditions.

If desired, the electrode controlling circuits may be variously arranged. For example, instead of using a separate electrode 55, the operation of the valve 20 may be tied in with control of the pump motors in such fashion that the valve 20 will be closed when electrode 56 is submerged and reopened only when electrode 58 is cleared. While a holding circuit is shown only for .the motor controlling means, itwill be obvious that with the addition of anotherelectrode there may be provided a holding arrangement for control of valve 20 in such fashion that it will close when the liquid reaches one level, but will not be reopened until the liquid drops substantially below that level.

Figure 3 discloses a modified form of apparatus designed for the handling of sewage or similar materials and embodying the principles of the invention. A centrifugal pump 90 of the type used for handling materials of this sort receives its supply through an elbow 92 of large radius communicating with its intake indicated at 94. Extending upwardly from the top of the elbow 92 there is a standpipe 96, which should be of substantial cross-section to prevent any possibility of its becoming clogged. The upper end of this standpipe communicates through a line I02 in which is interposed a valve 98 operated by a solenoid I00 with a vacuum pumping apparatus which may be of the type described in connection with Figure 1, comprising an oil chamber I04 containing either one or two screw vacuum pumps driven by one or more motors I06.

Extending downwardly through the top of the standpipe 96 are electrodes I08 and H0, the forother electrode IIO terminates a substantial distance from the elbow 92, but well below the point of communication of the line I02 with the standpipe. These electrodes I08 and H0 are connected to relays in a fashion similar to the connections of the electrodes illustrated in Figure 2, which connections will be obvious from a descriptionof the operation and need not be described in detail.

In the operation of this modification, when the vacuum pumps are started, liquid is drawn into the intake connections and into the elbow 92, the conventional discharge check valve being closed at this time.

The liquid rises in the standpipe I08 above the level of the intake of the pump until it reaches the level of the electrode H0. The submerging of this electrode immediately energizes the solenoid I00 to close the'valve 98 so that no further rise of the liquid in the standpipe may occur. At the same time, the pump motor may be automatically started or put in condition for manual starting and the'vacuum pumps may be stopped. It is, of course, possible to interpose a vacuum tank with connections for insuring a high degree of vacuum therein, but this may be generally dispensed with. I

As the centrifugal pump operates, accumulating gas may rise in the standpipe 96 and the liquid level in the standpipe will drop. Connec tions are provided, however, such that restarting of the pumps, opening of the valve 99 and stopping of the centrifugal pump will. not occur unless the liquid level clears the lower end of electrode I08, i. e., the blade II2. Eventually, gas may accumulate to such extent that the liquid level drops substantially to the bottom of the standpipe. But any further accumulation of gas will be prevented automatically by the flow past the standpipe and there will be maintained normally despite any abnormal influx of gas a sufiicient level of liquid to maintain the electrode I08 submerged. Thus, in normal operation the pump is maintained primed, the rapid flow through the elbow being sumcient to carry in dispersed form any gas into the centrifugal pump so that it will be handled by the pump without loss of prime.

The standpipe 96 in this modification is primarily to submerge the eye of the pump and to take care of surges. Initially, the liquid level should be raised well above the pump so that the downward surge occurring on starting will not uncover the electrode I08. The standpipe is also provided to insure that an upward surge of the liquid will meet an air or gas cushion in the upper end of the standpipe to prevent any possibility that sewage or similar liquids will enter the connection I02. As indicated, valve 98 is normally closed, but even in starting, an upward surge will close that 'valve as soon as the liquid reaches the level of electrode IIO. An extremely high degree of compression would be necessary in the upper end of the standpipe to cause any liquid to enter the connection I02. 1

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

1. In combination, a centrifugal pump; means providing a chamber connected to the intake passage of the centrifugal pump for accumulation of gas contained in the liquid being pumped; means connected to the upper portion of said chamber for evacuating said chamber to raise liquid therein to a level above the intake passage to thereby prime the'pump; means for interrupting the action of said evacuating means when the liquid reaches a predetermined level in said chamber; means to eifect further removal of gas by an ejector action of liquid being handled by said pump and to thereby raise the liquid level above said predetermined level; means for efiecting renewed action of said evacuating means only when the liquid level drops substantially below said predetermined level; and means for completely closing the evacuating connections to said chamber if the liquid rises to a level above that attained by said ejector action, thereby to provide an air cushion in the upper portion of said chamber to prevent the carrying over of liquid into said evacuating connections.

2. In combination, a centrifugal pump; means providing a standpipe connected to the intake passage of the centrifugal pump for accumulation of gas contained in the liquid being pumped; means for evacuating said standpipe to raise liquid therein to a level above the intake passage thereby to prime the pump; means for interrupting the operation of said evacuating means upon attainment of a predetermined liquid level in said standpipe; means toeffect removal of gas accumulating in said standpipe, after attainment of said'predeterminedlevel, by an ejector action of liquid being handled by said pump; and means for closing off communication between the standpipeand the last mentioned means if the liquid rises to a predetermined level above said predetermined level. I I

' FRANK S. BROADI-IURST.v

Images