USRE20471E - Motor contooiung device - Google Patents

Description

Aug. 17, 1937. c. R. KELTY MOTOR CONTROLLING DEVICE Original Filed March 28, 1925 I '4 Sheets-Sheet l I I I I I l I I I I I L Imam/for.- i. 6%az'ZeslhllTeiiy ,MMa W An 17, 1937. c. R. KELTY 20,471

MOTOR CONTROLLING DEVICE Original Filed March 28, 1925 4 4 Sheets-Sheet 2 as 82 so 77 I v r I I c. R. KEL TY MOTOR CONTROLLIYNG DEVICE Rle. 20,471

Aug. 17, 1937.

Original Filed March 28, 1925 4'Sheets-Sheet 5 Aug. 17, 1937'. c. R. KELTY Re. 20,471

\ MOTOR CONTROLLING DEVICE Original Filed March 28, 1925 4 Sheets-Sheet 4 89 OPEN 97 I iwzienifar: Cfiaz'Ze-s lifieZ? I Reissued Aug. 17,1937

por ation of Delaware Original No.

No. 19,183, March 28,

23 Claims.

.This invention aims to provide a simple and efficient motor controlling device.

In the accompanying drawings wherein is shown, merely for illustrative purposes, one embodiment of my invention;

Fig. 1 is an elevation with certain parts in section illustrating the controller applied to a gate valve;

Fig. 2 is a vertical section of the controller shown on a somewhat larger scale than in Fig. 1;

Fig. 3 is a sectional plan view taken on the line 3-3 of Fig. 1;

Fig. 4 is a plan section taken on the line 4--4 of Fig. 2; Fig. 5 is a diagram of the motor circuit wiring;

and

Fig. 6 is a detail side elevation of the limit switches and their supporting means. 1

- The motor controlling device of the present invention is capable of a variety of uses but, for convenience, I have elected to show, in the accompanying drawings, its application to the control of a relatively large gate valve operating means.

In the drawings, referring particularly to Figs.

1 and 2, a casing l is provided for enclosing the operative parts of the controller and, mounted in close proximity to said casing by bolts 2, is an electric motor 3. The motor'3 has a shaft 4 to which is keyed and secured, by screw 5, a 7 coupling member 6. A drive shaft 1 is journalled to rotate in the casing l in suitable bearings 8 herein arranged at the opposite end of the casing from said motor and desirably in axial alignment with the motorshaft 4 from which it herein is positively driven in one direction and frictionally driven in an opposite direction as will hereinafter be explained. The motor shaft 4 herein terminates in the coupling 6 and, interposed between 49 said coupling and the drive shaft 1, is a clutch including a clutch body 9 secured by screws in to said shaft coupling.- This clutch body has a relatively thick base II which is provided with a recess I2 to receive the shouldered end l3 of the drive shaft 1, thus insuring the proper alignment of the latter shaft with the shaft 4.

From the base H, there extends, parallel-with the shaft 1, a cylindrical shell l4 arranged to enclose the clutching devices, herein comprising 50 metal disks including a series l5 constituting clutch body friction plates and a series 16, which alternate with and engage plates 15, constituting drive shaft'friction plates. The friction plates l5 are somewhat larger than the plates I6 and 55 the rims thereof which project beyond the latter MOTOR CONTROLLING DEVICE Charles R. Kelty, Milton; Mass., assignor to Cutler-Hammer, Ine.,

PATENT OFFICE Milwaukee, Wis., a cor- 1,908,763, dated May 16, 1933, Serial 1925. Renewed September 29, 1932. Application for reissue June 21, 1937, Serial No. 149,502 1 are notched desirably at opposite points II to engage keys I8 shown most clearly in Figs. 2 and 4 set into the interior face of the shell l4 and permitting axial but not'radial movements of said plates l5 relatively to said shell. Alternate plates [6 are, on the other hand, permitted at times, as when slipping of the clutch is desired, to rotate relatively to said shell but are prevented from rotating relatively to the shaft 1 by one or more keys is in said shaft and engaging notches 20 in the inner portion of the plates [6.

A" friction plate thrust washer 2| is interposed between the series of friction plates and the clutch body 9 and a second thrust washer 22 is arranged against the opposite end of said series of friction plates and constitutes a seat for a spring 23. This spring encircles the drive shaft 1 and provides sufiicient tension upon the several plates of the clutch to insure the transmission of rotary motion from the motor shaft 4 to said drive shaft 1 under normal conditions. Adjust-' ing means are provided for varying the tension 'of the spring 23 as required, said adjusting means including a spring retainer 24 which iscounterbored or recessed at 25 to receive and position said spring concentric with the shaft 1. The retainer 24 has a hub portion 26 bored to receive and fit the shaft 1.

The shaft I is screw-threaded at '21 and is provided with a nut or collar 29 correspondingly screw-threaded and arranged to be moved longitudinally of said shaft 1 to exert more or less pressure through said hub 26, spring retainer 24, and the spring 23 upon the disks of said clutch. A screw 30 is arranged in the nut 29 for the purpose of locking the same in its adjusted position on the shaft. Mounted upon the shaft, between the nut 29 and the hub 26, is. a. flanged hub 3| which is splined at 32 to provide for axial movement with respect to said shaft but preventing relative rotary movements therebetween.

The shell 14 is internally threaded, at its upper end, as at 33, and a cover 34 has screw-threaded engagement therewith for closing said upper end of the shell, said cover having rotatable engagement with the hub 25, and completely enclosing the friction elements of the clutch. As previously stated, the clutch, including the friction disks l5 and I6,.is capable of operating the shaft 1 from the shaft 4 under normal conditions, but said clutch is desirably so. adjusted and set that, when a predetermined resistance or obstruction to the operation of the shaft I is encountered, the shaft 1 is permitted to stop movement while the driving shaft thereof conbe hereinafter explained. r With the arrangement thus far described, the

shaft 1 will be frictionally operated in either di- 5 rection by the reversing of the poles of the motor 3 but it is sometimes desirable to provide a positive drive in one direction and a friction drive in the opposite direction and, to this end, ratchet means are interposed between said shaft 4 and the shaft 1 which will positively impart motion to the latter in one direction but will slip when necessity requires during the operation of the shaft 4 in an opposite direction. Herein the ratchet means comprises a seriesbf ratchet teeth 35 formed upon the outer face of the cover 34,;which teeth are engaged by a pawl 36 carried by the flange, and yieldingly maintained in contact with the teeth by a spring 31, the inner end'of said pawl being beveled to conform with the incline of the teeth 35.

It is obvious that the transmitting mechanism, herein interposed between the shaft 1 and the shaft 4, is capable of many uses but, for convenience, is herein applied to the operation of a gate valve 38 shown most clearly in Fig. l. The valve 38 comprises a housing 39 within which a gate 49 is arranged for reciprocation from closed position, in-dotted lines in said figure, to open position and vice versa.

A valve stem 4| is connected with said gate to reciprocate within a suitable gland 42 which prevents leakage around said stem. The stem' 4| is screw-threaded and engages a rotary nut 43 appropriately journaled in a bracket 44 extending herein from the housing of the coritroller, said controller being, in turn, supported at 45 upon the valve housing 39. The nut 43 has an annular flange 46 engaging herein, ball bearingmembers 41 and 48 which constitute end thrust bearings to prevent axial movement ofsaid nut. A gear 49 is secured to the sleeve 43 to rotate, therewith and, in the example shown, motion is imparted to the gear 49 from the shaft 1 through a small pinion 59 and intermediate gear 5| shown most clearly in Figs. 1 and 3. The diameters of the gears of this train are of such a ratio as greatlyto reduce the speed of the nut 43 and increase the power applied thereto whereby a relatively small motor will be able to effect 50 the opening and closing operations of the gate 49. The intermediate gear 5| is pivotally arranged upon the housing to .permit its withdrawal from engagement of one at least of the gears 59 and 49 when manual operation of the valve is desired, which manual operation may be effected through the operation of a hand wheel 52secured to the upper face of the wheel 49. To facilitate movements of the intermediate gear 5| from its operative to its inoperative position and vice versa, said gear is rotatablymounted upon a stud 52 herein eccentrically connected 'with a shaft 53, which latter is rotatably mounted in a suitable bearing 54 formed in the housing I.

The upper end of the shaft 53 is shouldered at 55 to form a seat for said shaft at the upper end of the bearing 54.

When manual operation of the valve is desired, the rotation of the shaft 53 causes the eccentric stud 52 to swing the gear 5| out of intermeshing relation with the pinion 50 and gear 49, where it may remain until further use thereof is required. The train of gears just described is suitably protected by gear coverings 59 and 60 secured together by appropriate screws such as 6| shown most clearly in Fig. 1.

to properly seat and close said 20,471 tinues its operation for a time at least, as will By reason of the construction hereinbefore described, the motor 3, when operating in one direction, will effect a positive opening of the valve by acting through the coupling 6, clutch body 9, shell l4, top 34 and the aforesaid ratchet means, to operate the shaft 1 and, throughthe train of gears and nut 43, raise the gate 40. Upon reversing the operation ofthe motor 3, the nut 43 will be rotated in an opposite direction by means of said friction clutch including the friction disks l5 and I6 and, should any obstruction to the closing operation of said valve, be encountered, the friction'disks will be permitted to slip without causing injury to the operating instrumentalities of the valve or to the valve itself. A similar slipping action of said clutch will likewise take place when the valve 4|] reaches its seat, the pressure upon the friction plates being preferably sufficient valve but insufiicient to cause any injury to said operating mechanism. During the opening of the valve 38, obstructions are seldom encountered; therefore it is safe to employ positive driving means including thepawl 36 and ratchet 35 which impart a hammerlike blow to the gate to start it from its seat.

When the valve has been opened to the extent desired, the motor 3 may be brought to a. stop by opening the power circuit thereof but, for convenience, means have been provided for automatically throwing a switch when said gate reaches a predetermined position. In this connection means including'a limit switch 6| are disposed in the path of a movable member of the device for example, the screw stem 4|, to be engaged thereby, or asherein shown, by an extension 62 thereof when the gate 49 is opened a predetermined amount. The switch 6| is herein shown as embodying a movable self-closing switch member 63 adapted to engage contacts 64 and 65 and thereby close the electric circuit including said contacts and hereinafter more fully explained.

The movable switch'member 63 and the contacts' 64 and 65, shown most clearly in Fig. 6, are herein secured to a depending portion 66 of an adjustable frame 61 vertically adjustable in a bracket 68 carried by the portion 60 of the gear covering; The member 63 is shown supported upon a spring depressed stud E3 mounted between the contacts 64 and 65 upon an insulating block 63 the latter being adjustably secured upon the depending portion 65. The member 63 projects into the path of an adjustable abutment (i3 adjustably secured to the extension 62. When the abutment 63 is approaching the limit of its valve opening movement, it is arranged to engage and raise the switch member 63, thus breaking connection between the switch member 6| and contacts 64 and 65 and stopping the motor 3.

To close the valve, operation of the motor 3 isdesirably reversed and, when this reverse movement is started, the clutch, including the disks l5 and I6, is brought into play to revolve the nut 43 in a reverse direction and thus start the valve stem 4| on its closing movement. The initial closing movement of the stem 4| permits the switch 6| to close in readiness to be acted upon during the next opening operation thereof.

To initiate the starting operation of the motor 3 in opening or closing the valve, starting switches are preferably provided which may be manually held temporarily closed but, in order to render the device automatic, at least as to the stopping of the motor when certain conditions arise, .means are provided whereby, when the motor has reached a predetermined speed, other means are set into operation which maintain the motor circuit closed until either the end of the valve stroke To this end, I employ centrifugal circuit closing means including herein two levers 69, shown most clearly in Figs. 2 and pivotally secured at 18 in brackets 1I connected to a sleeve 12 herein forming a part of the flange 31 which surrounds the clutch casing or sleeve I4. The levers 88 have weighted ends 18 arranged upon one side of the pivots 18 and switch arms 14 arranged at the opposite sides of said pivots.

Springs 15 are interposed between the levers 69 and said sleeve and normally retain the weights 13 in their contacted or inner positions but, upon rotation of said sleeve, the weights 13 are thrown outwardly by centrifugal force against the action of the spring 15 and cause switch blades 16, carried by the arms 14, to contact with circular bands 11 and 18 desirably arranged parallel and in spaced relation upon the outer face of said sleeve but insulated therefrom by appropriate insulating material shown at 18.

18. are constantly engaged by spring pressed brushes 88 and 8|, respectively, which are mounted in the housing I in insulating sleeves or bushings 82.

Springs 83 yieldingly retain said brushes in contact with their respective bands during the rotation of, the latter. The outer ends of the brushes 88 and 8| are connected by wires 84 and 85 constituting a part of a motor controlling circult and, by this arrangement, said motor controlling circuit 12 is revolving at a speed suflicient to retain the blades 18 of the centrifugal switches in contact with said bands, but the moment said sleeve slows down or stops, the springs 15 thereof act to withdraw the blades 18 from the bands and thereby open'the motor controlling circuit with the result that the motor comes to a stop. By connecting the switch 6| with the said motor controlling circuit including the wires 84 and 85,

it will be evident that, upon disconnecting the member 63 from the contacts 84 and 85, the motor will come to rest and that, by adjusting the abutment 63 or the said switch BI or the standard 81, the stopping of said motor may be effected at just the desired moment.

To obtain a clearer idea of the wiring ofthe motor controlling and feed circuits, a substantially complete electrical diagram is shown in Fig. 5.

' In this figure,

three main wires of the motor circuit, herein a three phase system so-called. Inserted in said circuit, are magnetic reversing switches, herein two, 88 and 88. The switch 88 has blades 8| (30 and 82 connected together by insulating sections 83 to operate simultaneously to electrically connect the two sets of terminals 84 and 85 and 88 and 85'. An armature 96, arranged between the blades BI and 82, but insulated-therefrom, is arranged to be acted upon herein by an electromagnet 91 to draw the blades 8| and 82 which are herein shown pivotally connected respectively with, the terminals 84 and 88' into contact respectively with the terminals 85 and 85' and 70 thereby close the motor circuit and supply current to the motor and, so long as the current continues to pass through the magnet 81, the switch 88 will remain closed and cause current to pass through the conductors 81 and 88, switch 75 blades 8| and 82, conductors 88 and 88 to said 4. These levers are ,The other contact will be closed when the sleeve 88, 81' and 88 constitute the.

motor to form the ends thereof indicated by the reference character I88 in said Fig. 5.

As previously stated, the initial starting of the motor 3 is effected by temporary circuit closing means, said means being preferably provided at a main control station which I have indicated at A, Fig. 5. At this station I provide, for convenience, a panel I8I wherein is mounted a push button I82 for connecting contacts I88 and I84. The push button I82 is normally held out of contact with said contacts by a spring I85. One of the contacts, herein I88, has connection, through a conductor I88, with the magnet 81. I83 is herein shown connected with a conductor I81, the latter extending to one of the main feed wires of the motor circuit, herein the wire 81. The other end of the coil of the magnet 81 is connected, through conductors I88, I88 and H8, with a second wire of said motor circuit, herein the wire 88 whereupon, when the push button I82 is pressed to connect the contacts I83 and I84,-current will be supplied from the feed wires through the magnet 91, energizing the same and causing the magnetic switch, including the switch blades SI and 82, to close the motor circuit through the switches 88 and 88 to the motor.

In the circuit including the push button I82,

which I will designate as the motor starting circuit for opening the valve 38, I preferably insert a stop switch I I I which, when open, prevents starting of the motor from any other point, thus permitting work to be done upon said circuit and connected parts without danger of injury. This switch, however, is normally closed or, at least, it is closed by hand prior to the operation of the motor which may then be effected by closing the push button switch I82. It is obvious that the circuit, including said push button and the magnet 81, will remain closed only so long as pressure is maintained upon said push button.

Therefore, to supplement the push button switch I82, and to maintain the motor controlling circuit closed, after the initial closing has been effected, means herein including an automatic switch is operated to close the circuit including the magnet 81. This means preferably includes the Switchblade 82 and a conductor I I2, herein connected with one of the contacts of said blade, for example, the contact 94' so that, when said blade is moved to engage the contact 95' to close the motor circuit, current will pass from the feed. wire 81, through said blade, conductor H2, and conductor II3, to the conductor I88, thence through the magnet 81, conductors I88, I88 and H8 to the other feed wire 85, thereby completing the motor controlling circuit through the magnet and short circuiting that portion of the starting circuit that includes the push button It will now be apparent that the magnet 81 will remain energized regardless of the opening of the switch I82, until other means are brought into play to open the motor controlling circuit to deenergize said magnet and cause the blades 8| and 82 to return to their open positions shown in Fig. 5. To accomplish the last mentioned function, I arrange in said motor controlling circuit, the limit switch GI hereinbefore described as being operated bythe valve stem I on its valve opening movement. 'This'limit switch, shown in detail in Fig. 6 and in diagrammatic form in Fig. 5, is normally held in its closed position by spring means and, when in such position, completes the motor controlling circuit whereby the said magnet 91 will remain energized, even after pressure upon the push button I02 has been removed, until the limit switch 6| is opened net I26, attracting the armature I25 and causing the blades I I8 and I2I to engage their respective terminals in emit current to operate the motor 3 in a reverse direction to that hereinbefore explained.

In this case, as in the case with the push button I02, the I25, the element I3I connected with one side of said magnet, also elements wires 81, 86, III), III, II4, I09 and I32 connected with the ot er side or the magnet I26 will remain said main feed circuit and transclosed so long as pressure is maintained upon the buttton I21. This button I2! is, h

' means of this circuit called the motor control circuit, the electro-magnet I26 will remain ener- During the valve closing operations, obstructlons are very often encountered which would, if movement of the gate 40 thereof were not stopped,

extending from said light,

indicator to a terminal I38 herein located with a similar terminal I 39 in the path of the limit 5 nected. To complete the indicator circuit, the

terminal I39 has connection through a wire I4Il, with a second feed wire herein the wire 85, thus completing the circuit through the indicator I34 I and causing the same to show red as hereinbefore stated when the valve has reached the selected stage in its opening movement. The indicator I35 is connected by wire I4I, through the conductor I01, with the main feed wire 81. A wire I42 also connects said indicator 5 with one pole I43 of a normally open limit switch I44, herein held open by a spring I45. A second pole I46 of said switch has connection with the conductor I40 leading to the feed wire 8G. Any appropriate limit means may be, provided to close the switch I44 when the valve reaches its closed position and thus indicate this fact at the remotecontrol station. The switch I44 is, for convenience, arranged in the path of an abutment I41 herein adjustably mounted upon the extension 25 62 of the valve stem 4|, so that, when the latter is in its retracted position representing the closed position of the valve gate 40 (see Fig. 6), it will have moved said switch I44 into contact with the terminals I43 and I46 and maintain it in this 30 position so long as the valve remains closed.

From the foregoing description, it will be apparent that, among other functions, the driven device, herein embodying a gate valve may be operated either manually or by power; that the power operating instrumentalities may be set in motion in either direction by the manual closing of switches, thereby supplying current to the operating motor and, at the same time, bringing into play, m'otor controlling devices which sup- 40 plement the starting devices and maintain the motor in operation for selected or predetermined periods and, when these periods have terminated, in automatically bringing the motor toa stop. Furthermore the meeting of an obstruction, which 45 offers predetermined resistance at any interme-' diate stage in the operation of the device, not taken care of by the limit devices, automatically brings into play instrumentalities which also cause the motor to stop before injury is done to 0 the driving mechanism; or the motor may be manually stoppedat any stage and again started from that point to operate in either direction regardless of the direction in which it was then running.

55 Although I have disclosed and discussed in detail one full and complete embodiment of my invention, it is to be understood that the inven tion is not limited thereto.

I claim:

valve, motor operating means for said valve, positive drivingmeans for opening said valve including a ratchet, friction closing means arranged to slip. when said valve meets an obstruction, and centrifugal switch means operated by said motor.

2. In combination, a valve, operating means for said valve, positive driving means interposed between said operating means and said valve for ef- 70fecting movement thereof in one direction, slip drive means interposed between said operating means and said valve, adapted to yield when the valve encounters an obstruction at any point in the operation thereof in an opposite direction, 75 and centrifugal means functioned by said oper- 1. In an apparatus of the class described, a

ating means after said valve has come to a stop, to out off power to said operating means.

3. In combination, a valve, power operating means for said valve including a motor, and means interposed between said motor and said valve including a centrifugal switch, for automatically shutting off the current to said motor following the application of a predetermined closing tension'to said valve.

4. In combination, a valve, a motor for operating said valve, limit means controlled by said motor for stopping said valve at one limit of its movement, centrifugal means for stopping said valve at substantially any stage of its operation toward the other limit thereof, and indicators arranged at a remote distance from said valve to indicate when said opposite limits are reached.

5. In a device for operating valves, in combination, a motor, a driven member, friction driving means interposed between said motor and said driven member to slip when predetermined resistance to operation of said driven member is encountered, and motor control devices rendered effective upon a predetermined deceleration of said driven member to stop said motor.

6. Ina device for operating valves, in combination, a motor, a driven member, a friction clutch interposed between said motor and said driven member to slip when predetermined resistance is encountered, a motor controlling circuit, and a centrifugal switch arranged to be operated by said clutch when the latter is rotating at a selected speed to maintain said motor controlling circuit closed, said switch being arranged automatically to open said controlling circuit upon predetermined slipping of said clutch.

7. In a device for operating valves, in combination, a motor, a driven member, a friction clutch interposed between said motor and said driven member to slip when predetermined resistance is encountered, a motor controlling circuit, a centrifugal switch arranged to be operated by said clutch when the latter is rotating at a selected speed to maintain said motor controlling circuit closed, said switch being arranged automatically to open said controlling circuit upon predetermined slipping of said clutch, and means including said friction clutch to stop further movements of said motor when said controlling circuit is opened.

8. In a device for operating valves, in combination, an electric motor, a main feed circuit for said motor, a controlling circuit for said motor,

a starting circuit for said motor, a driven member, friction driving means interposed between said motor and said driven member, manually operable switch means for closing said starting and main feed circuits, automatic switch means arranged automatically to close with the closing of said main feed circuit, and centrifugalswitch means normally operated by said friction driving means, to maintain said controlling circuit closed but arranged, upon a predetermined slipping of said friction clutch and a consequent reduction in centrifugal force thereof, to open said controlling circuit and stop said motor.

9. A device for operating valves, including a reversible motor, a feed circuit for said motor, manual switch means to start said motor in either direction, manual switch means to stop said motor at any stage of its operations in either direction, centrifugal switch means automatically operated upon the closing of said feed circuit to supplement said manual switch means in maintaining said feed circuit closed, and. means to stop said motor at selected stages of its operation.

10. A device for operating valves, including a reversible motor, a feed circuit for said motor, manual switch means to start said motor in either direction, manual. switch means to stop said motor at any stage of its operations in either direction, centrifugal switch means automatically operated upon the closing of said feed circuit to supplement said manual switch means in maintaining said feed circuit closed, limit switch means to stop said motor at selected stages of its operation, and means effectual upon the encountering of predetermined resistance to the operations of said motor, to stop the same.

11. The combination with a valve mechanism, of a. motor for actuating the same, a torque limiting coupling connecting said mechanism and motor, and centrifugal means for automatically de-energizing said motor when slippage occurs in the torque limiting coupling.

12. A valve-operating mechanism comprising a valve, a drive mechanism therefor, a motor for actuating said drive mechanism, a friction clutch interposed between said motor and said mechanism, and a centrifugal .switch connected to the latter to stop said motor when slippage occurs in the friction clutch.

13. A valve-operating mechanism comprising a drive-shaft for engaging the valve to be operated, a motor connected to the drive shaft by means of a friction coupling, a power supply circuit for the motor, a centrifugal switch associated with the drive shaft for completing the motor supply circuit while the drive shaft is turning and switch means for shunting the centrifugal switch to start the motor.

14. A valve-operating mechanism comprising a valve, a gear wheel operatively connected with said valve, a drive shaft cooperatively engaged with said wheel, a motor coupled with said drive shaft, a friction clutch and a delayed motion device respectively arranged to transmit valve opening and closing movements from said motor to said gear wheel, a normally open centrifugal.

switch mounted on said drive shaft, an electric control circuit for said motor including said 'centrifugal switch, means for engaging said motor, and means utilizing centrifugal force for opening and closing said switch.

15. A valve-operating mechanism comprising, in combination, a valve, a gear wheel operatively connected with said valve, a drive shaft cooperatively engaged withsaid gear wheel, a motor coupled with said drive shaft, a friction clutch including a delayed motion device for connecting said motor and drive shaft and adapted, upon the slipping of said clutch, to produce a hammer-like blow to start said valve, a centrifugal switch mounted on said drive shaft, and an electric circuit including said centrifugal switch for controlling operations of said motor.

16. A valve-operating mechanism comprising a valve, a drive shaft for transmitting movement to said valve, a motor, a friction clutch having driving and driven members for connecting said motor with said drive shaft, adelayed motion device interposed between the driving and driven members of said friction clutch to limit slippage between said members in one direction, a centrifugal switch effective upon the slowing down of said drive shaft to stop said motor, an electric circuit including said centrifugal switch cooperating to contact said motor with a source of electrical energy, and means for shunting said centrifugal switch to start said motor.

17. A valve-operating mechanism comprising a drive shaft for cooperatively engaging the valve to be operated, a reversible motor, a friction clutch for connecting said motor and drive shaft, a centrifugal switch mounted on said drive shaft for stopping the motor when the drive shaft stops, an electric circuit including said switch for controlling the circuit to said motor, and means for shunting said centrifugal switch.

18. A valve-operating mechanism comprising a drive shaft for cooperatively engaging the valve to be operated, a reversible motor, a friction clutch for connecting said motor and drive shaft, a centrifugal switch mounted on said drive shaft for stopping the motor when the drive shaft stops, an electric circuit including said switch for controlling the circuit to said motor, and means for shunting said centrifugal switch to start said motor in a forward direction.

19. A valve-operating mechanism comprising a drive shaft. for cooperatively engaging the valve to be operated, a reversible motor, a friction clutch for connecting said motor and drive shaft, a centrifugal switch mounted on said drive shaft for stopping the motor when the drive shaft stops, an electric circuit including said switch for controlling the circuit to said motor,

and means for shunting said centrifugal switch to start said motor ina reverse direction.

20. A valve-operating mechanism comprising a drive shaft operatively connected with the valve, a motor, a centrifugal switch for controlling the motor, a magnetic. switch in circuit with said 7 motor, an electric circuit including said centrifugal switch and the coil of said magnetic switch, and means to shunt said centrifugal switch.

21. A valve-operating mechanism comprising a drive shaft operatively connected with the valve, a reversible motor, a friction clutch for connecting said motor with said drive shaft, forward and reverse electric motor circuits each including a magnetic switch, manual means to close said forward and reverse circuits, and means in circuit with one of said motor circuits arranged automatically to shunt one of said manually closed circuits when said shaft has attained a predetermined speed.

22. A valve-operating mechanism comprising a reversible motor, forward and reverse circuits for said motor, manually operable starting switches for each of said circuits, a drive shaft operated by said motor, a magnetic switch for each of said circuits, and a centrifugal switch on said shaft and in circuit with one of said magnetic switches arranged to shunt one of said manually operable switches when said drive shaft has obtained a predetermined speed.

23. A valve-operating mechanism comprising a

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