US2202757A - Apparatus for use in the manufacture of paper - Google Patents

Description

May 28, 1940. K. DAMMANN APPARATUS FOR USE IN THE MANUFACTURE 0F PAPER Filed Feb. l5, 1938 5 Sheets-Sheet 1 IILMH.

INVENTOR. Q'Yfm warm? 72 ATTORNEY K. DAMMANN May 28, 1940.'

APrARA'rUs FOR UsE IN THE MANUFACTURE oF PAPER Filed Feb. l5, 1938 5 Sheets-Sheet 2 INVENToR.

ATTORNEY K. DAMMANN 2,202,757

APPARATUS FDR USE IN THE MNUFACTURE 0F PAPER May 28, 1940.

5 Sheets-Sheet 3 Filed Feb. l5, 1958 mmvron y /fflamma ATTORNEY May 28, 1940.' K. DAMMANN 2,202,757

APPARATUS kFOR USE IN THE MANUFACTURE 0F PAPER Filed Feb. 15, 1938 5 Sheets-Sheet `4 7 l 9 El n- E ElE- Y Ir 9 l 3.9

26 32 Z NVENTOR May 28. 1940- K. DAMMANN l ,2,202,757

APPARATUS FOR USE IN THE MANUFACTURE 0F PAPER Qw; INVENToR.

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ATToRA/ EY 7 Patented May V28, 17940 UNITED STATES PATENT OFFICE APPARATUS FOR,` USE IN THE MANUFAC- TURE OF PAPER 10 Claims.

My invention relates broadly to the manufacture of paper and more particularly to a control method and apparatus for varying the speed of centrifugal pumps for delivering paper pulp from a paper machine stock chest to the screen.

yIn processes of paper making, the expeditious and uniform handling of paper stock in the form of pulp has long been a problem, and imperfections in the finished products can be traced directly-to variations in the handling of the pulp stock, particularly by pumps, and in the feeding of the pulp stock in thernishing steps. In the application of a centrifugal pump to the purpose of pumping paper pulp from a paper machine stock chest to the paper machine feed box, I have found that the quantity of discharge from the pump varies according to the height of the pulp stock in the machine stock chest and. to changes in consistency or freeness, or both, in the pulp stock'. By consistency is meant lthe absolute degree of density in the mass with regard to the proportions of solid bre and ve' 'hicle; and by freeness is meant the relative firmness inthe mass, or its degree of resistance under pressure and thus its inclination to flow through the pump.

I have also found that a controlled, variable l speed, centrifugal stock pump is of the utmost limportance in the manufacture of paper because the required headfof delivery of the pump varies according to the consistency, freeness and sizing o1' the pulp stock. In order that a uniform product be obtained, a constant delivery of pulp to the paper machine'is imperative, and therefore, a constant head, or pressure, over the machine feed gate in the head box must be maintained.

One of the objects of my invention, therefore, is to provide a control arrangement for the feeding of pulp stock to a paper making machine at uniform rate, regardless of its characteristics and of the amount of machine feed required.

Another object of my invention is to provide a construction of movable overflow gate controlled in accordance with the rate of delivery of stock for maintaining an approximately constant head of stock in the head box.

A further object lof my invention is to provide a movable overflow gate in combination with means for controlling thespeed of the delivery pump for maintaining a substantially constantv head of stock in the head box.

Still another object of my invention is to pro-r vide a novel method of controlling the level of pulp stock in a head box fed by a centrifugal Dump.

A still further object of my invention is to provide a method of controlling the level of pulp stock in a head box fed by a centrifugal pump involving a first, direct control of the level in accordance with the rate of delivery df stock 5 to the box, and a second, indirect control of the level by control of the rate of delivery of stoc by the centrifugal pump.

Still another object of my invention is to provide control means for regulating the speed of a centrifugal pump to maintain a constant level in a head box fed by the pump, the level being subject to change due to variation in the de- ,livery of the pump accompanying variations in the characteristics of the stock.

A further object of my invention is to provide control means for regulating the speed of a centrifugal pump in combination with the control circuit of a driving electric motor, mechanically connected with the pump, whereby the pump is reduced to its lowest operating speed before stopping the driving motor.

Another object of my invention is to provide vsupporting means operative under shut-down conditions for relieving the actuating mechanism of my invention of undue pressure, and for maintaining the same in balanced condition.

Still another object of my invention is to provide an electrical control system for a centrifugal pump feed system in -a paper making apparatus which is capable of functioning either in connection with an alternating current power supply system or a direct current power supply system.

Other and further objects of my invention re- -side in the systems and apparatus herein disclosed, and will be clearly understood by reference to the following specifications and to the accompanying drawings, in which:

Figure 1 is a diagrammatic showing of a gen- 40 eral arrangement of apparatus for paper making and indicating the embodiment of my invention with respect to the machine-feed head box and the centrifugal pump feeding the same; Fig. 2 is a'top plan view of the head box showing the control apparatus of my invention; Fig. 3 is .a side elevation view of the head box shown in plan in Fig. 2; Fig. 3A is a detail view in elevation taken at the line 3A-3A in Fig. 3; Fig. 4 is `an end elevation view.. of the head box, and shows the machine feed` gate at the outlet from the box; Fig. 5 is va-vertical sectional view of the head box taken/.fat line 5 5 in Fig. 2 and showing particularly the action at the adjustable overflow gate of my invention; Fig. 6 is an elevation view of the pilot valve structure with the valve chamber shown in section; Fig. 'I is a partial vertical sectional view thereof takenon line 1-1 in Fig. 6; Fig. 8 is a top plan view thereof,

` partially in section as at line 8-8 in Fig. 6;' Fig.

nism and a constant speed motor as indicated in l Fig. l; and Fig. 12 is a schematic diagram of the electrical connections in the modified control arrangement shown in Fig. 11.

In' normal operation with a homogeneous stock, the discharge pressure or head, and the quantity of stock delivered will vary with the speed of a centrifug-al pump; and by controlling the speed under a given discharge pressurefthe quantity of stock delivered may be regulated, or by controlling the speed with a constant quantity of stock demanded the discharge pressure may be regulated. When pumping paper pulp stock, however, orany similar pulp stock, it is found that the above stated conditions do not always obtain because the stock may not be homogeneous but may vary in consistency, free--v ness, and sizing, the latter referring to constituents of paper pulp stock which partially determine its quality. In such cases the discharge pressure of the centrifugal pump is subject to variation and for a given speed of operation the' pump will accordingly deliver varyingamounts of stock. In accordance with my invention, the speed of the pump is varied in accordance with the characteristics of the stock, as evidenced by variation in the delivery head, so that a substantially constant quantity of stock is delivered by the pump under asubstantally constant head to the machine-feed head box.

In order that the pump may be run for the most part at an economical constant speed, I provide a primary control of the level of -stock in the head box in the form of a movable overflow gate which permits a greater overflow as the rate of discharge of the" pump increases andless overflow as the rate decreases, without affecting the speed of the pump. Any appreciative variation in the quantity discharged, and consequent variation of the level in the head box, operates the pump control system for increasing or decreasing the pump speed, as may be required. In this manner, a substantially constant head and uniform quantity of stock delivered are maintained, regardless of the characteristics of the pulp stock and ofthe amount of machine feed required, within the practical capacity of the pump.

Referring to the drawings in-more detail, in

Fig. l reference character I indicates the beater chest where the fibrous raw material is reduced to pulp, motor 2 being employed to drive beaters 3 and also a pump 4 for transferring the ApulpA stock to a jordan 5, driven by motor6, wherein mixing is effected with desired bleaches, sizing materials and the like. The jordan delivers the stock to a machine chest 1 before its controlled delivery to the paper machine through the machine-feed head box 8. 'I'he box 8 is provided with an adjustable outlet or machine-feed gate 9 through which the pulp passes to a make-up waterbox I wherefrom it is pumped to the screen II and taken to the finishing machines.

aaoamsv From the chest I the pulp is drawn into centrifugal pump I2 and discharged through pipe I4 to the head box 8. An overflow gate I5 having a movable section I6 divides the head box 8 Ainto twochambers; pipe I4 discharges into the filled chamber 8a, and the other chamber 8b constitutes an overflow chamber'connected by return pipe I1 with the chest 1. The pump I2, as shown in Fig. 1

is driven by a constant speed -motor I'8 through i a variable speed transmissionat I9. Control motor is connected with the variable speed transmission for regulating theoperation thereof with respect to the motor I8 and pump I2. Motors I8 and 20 are controlled by the circuit means shown in Fig. 10, as will hereinafter be set forth in detail.

Referring now to Figs. 2-5 showing the structure of the head box 8, in more detail, means are provided for automatically controlling the movable gate section I6. vA corrugated float 2l is mounted on lever arms 23 which are fixed to shaft 24 mounted in bearings25 on the top edge of the box 8. Theiloat 2l may be formed of corrugated sheet metal or molded material, in the form of a closed elongated body substantially cylindrical in outline, and may be fixedly or revolvably mounted in the lever arms 23. The corrugated wall makes the float structure rigid, and is easily maintained in clean condition for insuring the proper operation of the system.

The oat 2I controls a pilot valve 26 through an adjustable lever arrangement which includes an arm 21 fixed to the shaft 24, an adjustable link 28, 29, and lever 30. The armA 21 is provided 'Y with a counter-weight 3| for the float assembly. and has a series of apertures 21a for selectively connecting with the yoke member 28 of the adjustable link. Lever -30 likewise is provided with a series of apertures, 30a, for selectively connecting with the bolt member 29 of the adjustable link. The leverage derived from float 2I may thus be determined, by connecting the link 28, 29, in selected apertures in arm 21 and lever 39. It will be noted that the shaft 24 and the pivot 30h, of lever 30, are arranged so that the leverage adjustmeni is facilitated and the adjustable link 28, 29, may be maintained substantially vertical,

reference being had particularly to Fig.- 3.

The pilot valve 26 'is shown in more detail in Figs. 6-9,` and comprises a cylindrical valve. chamber 32 and-a piston valve 34 which is connected Vwith and controlled by lever 39 at 30c, as shown.

The valve chamber 32 has a uid pressure inlet '32a at the middle thereof, and an exhaust 32h at one end which communicates with the opposite end through duct 32e, Fig. 6. Vaive'34 is a type of D valve forming a sealed chamber communicating with the pressure inlet 32a and normally in central position. When valve 34 is shifted upwardlyby a rise of float 2|, pressure is communicated from Vthe inlet 32a to an outlet 32d connected with pipe 35, a second outlet pipe 36 and duct 32e being connected with the'exhaust 32h at the same time! 34 is shifted downwardly by a fall of float 2|, duct 32d is opened to the exhaust 32h and pres- Alternatively, when valve sure is communicated from the inlet 32a to theA f comprises the yoke member 28 andr bolt member 29. Adjustment is effected by means of nuts 28a on the bolt member 29, which may be set to clamp the yoke member 28 within a wide range of 'u 2,202,757 adjustment. 'I'he valve 34 is biased in its central position by coil springs 31, the force of which may be regulated by nuts 38 on the axial supporting bolts 39. Bearing plates 48 are provided on opposite sides of the lever 38 to equalize the spring pressure. Pivot 30h is initially set by adjustment of bolt 4I by nuts 42 to establish the central position of the valve 34 with the desired bias of springs 31. The pilot valve 26 including the actuating lever 30 is mounted in a suitable framework on the outer wall of the head box 8, as indiciated. I

Referring again to Figs. 2-5, the movable gate section I6 is supported by links 43 from lever arms 45 fixed to shaft 46 which is mounted in bearings 41 on the upper edge of the head box 8 similarly to bearings 25 for shaft 24. An actuating lever 48, fixed to shaft 46 is connected through link 49 with the piston 50 of a hydraulic device actuated by pressure controlled by the pilot valve 26. Outlet pipe connects to cylinder 5| of the hydraulic device above the piston and pipe 36 connects below the piston. Accordingly, a rise of fioat 2| causes a differential of pressure in cylinder 5| with pressure greater in pipe 35 and on the top of the piston 58. Gate I6 therefore is moved to a lower position to permit a greater overflow of stock to reduce the head in the chamber 8a until it again stands at then desired level.

Conversely a fall of float 2| causes the gate section I6 to be raised by effecting a differential of pressure in cylinder 5I greater on the lower side of the piston 58. In this connection, it may be noted that fall of the float may be due to the stopping of pump 'I2 in which case the system is shut down. Control being no longer required, it is desirable to relieve the apparatus of strain and accordingly I provide an arm 52 xed to shaft 24 and arm 53 fixed to shaft 46 substantially in the relation shown in Fig. 3, and of such length that the ends thereof will overlap. When the pump I2 is stopped, the stock in box 8a recedes through the pump to the level in the machine chest 1, and thereby allows float 2| to fall to near its limit of movement. As the pilot valve.

26 is actuated accordingly, piston 58 and gate section I6, rise, as above noted, and also arm 53, which meets the end of arm 52 and supports it as piston 58 continues to rise. Pilot valve 26 and float 2| are actuated through arm 52 and brought to and maintained in normal position. 'Ihe entire control arrangement is now in aV balanced condition. As soon' as pump I2 is started again, the stock will slowly rise against float 2|, and when float y2| is raised above its normal position pilot valve 26 is actuated, as has been described, and the regulator is again in operation.

The foregoing control arrangement constitutes the primary control of my invention and is operative independently withinpredetermined limits of variation' in the stock level. Connected for parallel operation with piston 58, I provide an electric control switch 54 which is actuated from the piston by rod 56 rigidly connected with the piston by arm 51. Rod 56 is supportedl in guides 58, which are conveniently formed as ex` tensions at the ends of cylinder 5I, and has a lug 59 secured thereto for operation of the switch lever 68. The switch 54 is so constructed that limited movement of the lug 59 is permitted without operation of the switch contacts, the switch being maintained normally in open circuit condition and adapted to close either of two circuits as the lug 59 rises or drops beyond its free limits, as will be more fully set forth.

The control arrangement shown schematically in Fig. 10 is provided in combination with a two-phase, three wire, alternating current power supply and a constant speed, pump driving m0- tor I8. 'I'he control system employs the control motor 20, an auxiliary source of power 6|, and control switches and relays as shown. The motor I8 is adapted to be started through a switch system indicated generally at 62 which includes a multiple switch 63 for connecting the motor to the power lines through resistors 64, 65, 66, and a multiple switch 61 for shunting the resistors as the motor gains speed. Overload relays 68 and 69 are provided in two, of the lines to the motor I8 with their contacts in circuit with the auxiliary power source 6| for disconnecting the control system and releasingthe line switches 63 and 61.

It will be understood that three-phase alternating current, or any suitable supply circuit for the motor used at I8, may be provided in conjunction with the control circuit of my invention:

More particularly the control circuit ofv my invention includes a separate starting switch 18, a main control switch 1I, and the automatic control switch 54, connected with the source 6| for operating the motor 28 with respect to the motor I8, and the conditions of stock in the system. The switch 1I has two positions which may be termed Stop and Run, one set, 12, of two contacts being closed in the former position while two sets, 13, and 14, of two contacts each are actuated in the latter'position. With the main control switch 1I in run position, the starting switch 18 connects the actuating winding 15 of linel switch 63 with the source 6| through line switch control contacts 61a, contacts 13 and conductor 16. Simultaneously, the actuating winding '18 of a slow acting relay is energized in shunt with the winding 15 and operates after a short interval to close contacts 19 to energize the actuating winding 88 of line switch 61. Meanwhile, the push-button starting switch 18 may be released, as holding contacts 63a are closed upon operation of winding 15 and maintain the circuit throughl windings 15 and 18 until operation of the slow acting relay. The control contacts 61a are opened and holding contacts 8| for relay 88 are closed upon actuation of the line switch 61, the relay windings 15 and 18 being deenergized at contact 61a, opening line switch 63 and contacts 19. Motor I8 is thus directly connected with the power lines and running at constant speed, subject to being disconnected by release of relay 88 controlling switch 61.

With switch 1I in run position, the source 6| is connected with one contact of each pair of contacts, 82, 83, in the automatic control switch 54 through contacts 13 and conductor 16. 'I'he other contact of the upper pair 82 in switch 54 connects through contacts 14 and limit switch 84 with one of the controlling terminals of reversible motor 28, the neutral terminal of which is connected back to the source 6|. Thus, with switch arm thrown upwardly to close contacts 82, motor 20 will drive in one direction, in this instance to alter the variable speed transmission I9 for driving the pump I2 at a greater speed. The limit switch 84 is-controlled by the variable spee'd transmission I9, and opens within a range determined bythe upward limit of the range of variation in the transmission I9.

The Iotheigcontact o-f the lower pair 483 in IB switch 5e' connects through relay contacts 05 with the other controlling terminal of reversible motor 20, so that with switch arm 60 lowered to c1ose,contacts 83, motor 20 will drive in reverse direction to lower the speed of pump I2. The relay contacts 85-t0gether with contacts 86 which are connected in shunt with contacts 13-are controlled by Winding 81 energized by the source 6I through limit switch 89, which is closed in the normal operation of the system. Limit switch 89 like the switch 84, is controlled by the variable speed transmission I9, and Opens within a range determined by the lower limit of the range "of variation in the transmission I9; thus, the two switches, 84 and 89, cannot be open at the same time.

The automatic operation of switch 54 is therelfore evident: decrease in the delivery ofthe pump, due to a stock of less freeness or of greater consistency, will result in operation of the pilot valve 26 to control the position of the movable gate section and to actuate switch 54, closing contacts 82, and resulting in a higher pump speed to increase the delivery of the p ump; whereas, increase in the delivery as shown by a higher head of stock in the box 8 causes the vreverse effect by closing contacts 83 which results in a decrease of the pump speed and, accordingly, adecrease in the delivery therefrom. In either event, the pump speed is maintained constant at a new rate which provides a substantially constant level of stock in the head box 8 under the conditions of adjustment.

When it is desired to cease operations, the main control switch 1| is thrown to stop position, relay 60 being held energized through contacts 86 until themotor 20 has set the variable speed transmission I9 for driving the pump I2 at the slowest speed. This is effected by means of the stop. contacts 12 which are effectively in shunt with the contacts 83 'on switch 54, and connect the motor 20-with the source 6| for regulating the transmission I9. In this connection, however, unlike that through contacts 83, there is no automatic opening of contacts 12 and the motor 20 runs until limit switch 69 is opened, which deenergizes winding 81, releasing contacts 85 in circuit with the motor 20, and contacts 86 in circuit with relay winding 80 which results in release of lin'e switch 61. Motors 20 and I8 are thus stopped, and the only further action in the system is the operation of arm 53v to raise f arm 52 and the float 2| to balanced condition, as described.

By virtue of the control arrangement for stopping as above described, the transmission |9 is conditioned so that motor I8 may be started under small load, with the pump I2 driven at its slowest speed and under a low head of stock. As contacts 82 on automatic switch 54 are usually closed under these conditions, the load is gradually increased automatically until normal operation is attained.

Similar results may be obtained in accordance with my invention by employing a variable speed i driving motor directly connected with the pump I2, as indicated diagrammatically in Fig. 11. Either direct or alternating current variable speed motors may be-employed, but in Fig. l2 I have 'preferably shown the control system of my invention in combination with a directY current variable speed motor with the control motor at 20 adapted to control the speed thereof for regulating the operation of the pump I2.

The control arrangement shown in Fig. 12, as'

well as the driving motor 90, derives its power control of the relay 95, for shunting the several ythe speed of motor 90 and pump-I2.

from the line source. The motor 90 is compound wound and includes armature 90a, series connected field 90b, and shunt connected'eld 90e. The starting system indicated generally at 9| includes a resistance 92 connected in the armature circuit to be progressively decreased in the starting operation. Speed control is effected by means of resistance at 93 in the shunt iield circuit, the resistance being under the control of control motor 20.

Motor 90 `is started by operation of push-button v switch 94, thus' energizing relay windings 95 and 96 through the normally closed contacts of stop switch 91. Relays 95 and 96 are energized by line voltage throughA a shunt switch 98 but upon the operation of relay 95, delayed with respect to the operation of relay 96, switch 98 is opened and a resistor 99 is left in circuit with the relay' windings to decrease the current therein. Operation of relay 95 is retarded by dashpot |00, or other suitable means, in order that the voltage on motor 90 will be progressively increased over a period of time. Resistor 92 is provided with a series of tap connections, 92a, adapted to be contacted in order by a shunt-connector I| underv sections of the resistor. One side of the power source is connected with the shunt-connector I0 I which thus serves' also as a line switch with respect to the shunt eld 90e. It will be shown that the shunt field is alwaysA connected to the power supply at line voltage, for'slowest speed in the motor 90 at thestart. The shunt-connecterIM also connects with contact |03 to shunt the starting switch 94 and hold relays 95 and 96 energized. Operation of relay 96'opens contacts |04 which vare connected in shunt with contacts 83 on the automatic control switch 54, and closes contacts which are in series with contacts 82 on switch 54. Motor operates limit switches 84 and 89, similarly as motor 20 in Fig. 10. In eiect, the operation of the control system of Fig. 12 is substantially identical with that of the system of Fig. 10, the speed of pump I2 being controlled directly at motor 90, Fig. 11, rather than through the variable speed transmission I9, Fig. l. Briefly, a lowering of stock in the head box 8 causes contacts 82 on switch 54 to close which completes the circuit to one of the controlling terminals of reversible motor 20' through contacts |05 and limit switch 84, motor 20' operating to increase the resistance in circuit lat 93 which results in increase of speed at motor 90 and pump I2. Conversely, rising of stock in the head box will cause contacts 83 to close, completing the` circuit to the other controlling terminal of reversible motor 2 0 through limit switch 89, motor 20' operating in reverse direction to decrease the resistance in circuit at 93 and lower Operation of motor 90 may be stopped by pressing button switch 91v which deenergizes - relay windings 95 and 96. Motor 90 is immediately disconnected from the source at the shunt-connector IOI, and the shunt at |03 on the starting switch 94 is removed. However, motor 20' is energized through contacts |04 and limit switch 89, and operates to set resistance 93 for the slowest speed. of operation of motor 90, which is zero resistance in circuit, at which stage limit switch 89 opens and disconnects motor 20'. Thus the condition of thev system for starting is such that motor 90 and pump I2 will have the slowest speeds within the range of adjustment. lAs contacts 82 on switch 54 are usually closed under such condif tions, however, motor will be promptly energized to increase the speed of motor 90 and pump I 2 to normal, the progression from the start being even and without surges in speed such as would result in improper delivery of stock and unsatisfactory operation of the control system.

Similar control means may be provided in conjunction with a variable speed alternating current driving motor, or with any variable speed centrifugal pump driving arrangement, the control motor, as at 20 and 20', being adapted in all such arrangements to control mechanism affecting the speed of the pump I2.

Thus, -while I have defined my.v invention in certain preferred embodiments, I desire it understood that modifications maybe made therein, and that no limitations upon my invention are intended, exceptas are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In a pumping system for supplying a unif form demand of pulp stock, a centrifugal pump,

a head box having a partition for dividing said bo'x into a head chamber connected with the discharge side of said pump and an overflow chamber connected with the intake side of said pump, a movable gate section forming an upward extension of said partition between said chambers,

adjustable connection between said float and said pilot valve for determining the normal position of said gate section relative to said float for maintaining the level of stock at the desired head.

5. In a pumping system for supplying a uniform demand of pulp stock, a centrifugal pump adapted for use Withpulp stock, a head box connected with the discharge side of said pump, a

and means controlled by changes in the level of stock in said head chamber due to changes in the rate of delivery of stock caused by changes in the consistency and freeness of the pulp stock which affect the capacity of said pump for varying the position of said movable gate section for regulating the rate of overflow of stock vthereover in accordance with variation in the head of stock on the discharge side of said pump resulting from said variations in the characteristics of the pulp stock.

2. In a pumping system, apparatus as set lforthv in claim 1 wherein said means for varying the position of the movable gate section comprises a float supported on the stock in said head chamber, a pilot valve controlled by said float, and hydraulic actuating means controlled by said pilot valve and connected with said gate section.

3. In a pumping system, a head box having a head chamber andan overflow chamber, a movable overflow gate section between said chambers, a float mounted by lever arms in said head charnber and adapted to be supported by the stock in said chamber, means controlled by said float and connected with said gate section and operable to vary the position of the movable gate section above and below a normal position as the level of stock falls and rises, respectively, an arm connected with the said lever arms, and means connected with said gate` section and engageable with said arm with the gate section substantially displaced above its normal position corresponding to a low position of said float under shut down conditions for raising said float out of contact with the residual stock in said head chamber.

v4. In a pumping system, a head box having av return duct from said head box to the intake side of said pump, means controlled by limited changes in the level ofstock in said head box due to variations in the` rate of delivery of stock for varying the rate of return of stock from the discharge to the intake of said pump through said duct, and means controlled by excessive changes in the level of stock in said head box due to variations in the rate of delivery of stock for regulating the speed of said pump and thereby the rate of delivery of stock from said pump in counteraction of said vari-ations in the rate ofdelivery, said variations in the rate of delivery of stock by said centrifugal pump being due to variations in the consistency and freeness of the pulp stock affecting the capacity of said centrifugal pump, the last said means including an electric control system having a two-position switch mechanicaly connected with the aforesaid means for varying the rate of return of stock and actuated in conjunction therewith, and electric circuit means controlled by said switch and operative to effect variation in the speed of said pump for altering the rate of delivery therefrom.

6. In a pumping system, apparatus as set forth in claim 5 and including in said means for regulating the speed of vsaid pump a constant speed motor for driving said pump and a variable speed transmission `between said motor and said pump; said electric circuit means including a reversible motor connected with said transmission for varying its operation with respect to said pump, and accordingly the speed of the pump.

'7. In a pumping system, apparatus as set forth in claim 5 and including insaid means for regulating the speed of said pump a variable speed motor for driving said pump, and a separate speed control element for said motor; said electric circuit means including a reversible motor connected with said element for varying its operation with respect to said motor and accordingly the speed of said motor and said pump.

8. In a pumping system, apparatus as set forth in claim 5 and including in said electric lcircuit means, switch contacts connected in shunt with the contacts in a selected position of said twoposition switch and operable under shuttingdown conditions in said system for actuating said electric circuit means for effecting low speed driving conditions with respect to said pump.

9. In a pumping system, apparatus as set forth in claim 5 and including in said means for regulating the speed of said pump a constant speed motor for driving said pump and a variable speed transmission between said motor and said pump; said'electric circuit means including a reversible motor conneeted with said transmission for varying its operation with respect to said pump, and accordingly the speed of the-pump, and switch contacts connected in shunt with the contactsin claim 5 and including in said means for regu-` connected in shunt with the contacts in aselected position of said two-position switch and operable under vshutting-down conditions in said system for energizing said reversible motorior adjusting said speed control element for slowest I speed operation of said motor upon restarting.

v KARL DAMMANN.

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