US2267688A - Control device - Google Patents

Description

Dec; 23, 1941. w 5 LANDON 2,267,688

CONTROL DEVICE Original Filed Ocfc. 24, 1935 nillllllll in mi /1% INVENTOR A10 ATTORNEY Patented Dec. 23, 1941' UNITED- STATES PATENT OFFlCE CONTROL DEVICE Walter S. Landon, Detroit, Mich., assignor to Detroit Lubricator Company, Detroit, Mich., a corporation of Michigan Application October 24, 1935, Serial No. 46,480 Renewed October 11, 1939 12 Claims. (01.236-48) My invention relates generally to fluid flow end, the bore 14 leading into an axially aligned,

control devices and more particularly to thermorelatively small bore 15 at its lower end. The static valves for controlling flow of fluid fuel to bores I4 and 15 provide a seat 16 for cooperating burners. with the conical face 11 of a controlling means One of the objects of my invention is to prowhich is shown as a valve member 18 and which vide a fuel supply control device having a new is disposed for reciprocal movement in bore 14. and improved arrangement of the operating parts The valve member I8 has an upper end portion thereof. extending into the casing and has a lower end Another object of my invention is to provide portion of reduced diameter, as at 18, which coa new and improved snap-acting thermostatic operates with the wall of bore 14 to provide an control device for controlling the supplying of annular chamber 88. The casing 66 is provided fuel to a burner and to provide a device of this with an inlet 8| and an outlet 82 for connection character. having a new and improved snap-actin a fluid fuel line (not shown) and preferably ing, motion transmitting mechanism for transthe inlet and outlet are oppositely disposed and mitting motion from a thermostatic power elelocated in side walls 68 and 69, respectively, and ment to a flow controlling means. also located adjacent bottom wall 61. The inlet Another object of my invention is to provide a ill and t erout e 8 y e e ed y ho w snap-acting control device which is sensitive and bosses 83 and 84, respectively, which may be inefficient in operation and one in which frictional tegral with the casing and be-internally threaded and other forces tending to oppose movement for connection in a fluid fuel sup y line. A of the snap-acting mechanism are minimized bore 85 connects the inlet passage 8| and the without sacrificing the efliciency or effectiveness at e y Small e 15 0f e V e b of thesnap-acting mechanism. the bore 85 preferably being inclined downwardly The invention consists in the improved confrom passage 8| and being intersected by the struction and combination of parts to be more 5 relatively small bore 15. The outlet passage 82 fully described hereinafter and the novelty of is in communication with the annular chamber which will be particularly pointed out and dis- 0 by a bore 88 which is prefer inclined tinctly claimed. downwardly from chamber 88 and communicates In the accompanying drawing, to be taken as With u et Passage 32 oh h the casing a part of this specification, I have fully and he valve member 18 is actuated by a thermoclearly illustrated my invention, in which draw- S c P wer a s e e ent which includes a i temperature responsive actuator which is carried Fig. l is a view shown in vertical cross section by. and re va e w th he Cover 12 s a t y of a control device embodying my invention; s t i'ee Cover 72 is P ed t an D- Fig. 2 is a view shown in cross section taken 35 Wardly extending hollow Portion 37 n w c the along the, line 2-4 of Fig. 1; thermostatic actuator. is disposed, the actuator Fig. 3 is a view in cross section taken along including an expansible-collapsible element 88 the line 3-3 of Fig. l, and which may be a substantially cylindrical, cir- Fig. 4 is a view showing certain parts of the cumferentially corrugated, resilient, metallic belcontrol device in perspective. 40 lows. The bellows 88 is arranged for movement Referring to the drawing by characters of refn a V c d ect and has s pp and erence, the numeral 66 designates the casing of l r d hermetically s d an s ured t0 the device, the casing preferably being a hollow, d Wall 01 plate members 88 and e p substantially rectangular casting having a bot- 1y. In the end or upp Wall 9| Ofthe hollow tom wall 61, side walls 68 and 69, and end walls co er portion the e is pro ded a c r y in and 1|. The upper end of the casing is closed isp sed per re for r vi a tubular h p by a cover 12 which may be secured to the casing supportin and connecting member 92 which has by screws or other suitable attaching means. An an external annular flange 92 for abutment extended portion 13, preferably integral with botagainst the inner face of the end wall 9|. An tom wall 61, extends upwardly therefrom, the ppe e por n of t e ubula member 92 extended portion 13 preferably being located projects above the end wall 9|, externally 0f the substantially midway between the end and side sin nd is threaded o re eive a n 94 y walls of the casing. The extended portion I3 means of which the supporting member 92 may is provided with a relatively large, vertically exbe secured to the wall 9|. Between the wall 8| tending bore 14 which opens through its upper and flange 92 there may be provided a washer or gasket, if desired. The upper end wall 89 of the bellows 88 is provided with a centrally disposed aperture for receiving a lower and reduced end portion of the supporting member 92, the lower end of the reduced portion being peened over to rigidly secure the end wall 89 to the supporting member 92. A thrust member 93 is screw threaded to a supporting member 94. The lower or movable end wall 90 is provided with a centrally disposed aperture for receiving the supporting member 94 whose inner end is peened over to secure the parts together.

The thermostatic power element includes a bulb 95 for heat transfer relation with the heated medium which, for example, may be water in a boiler of a hot water supply system. A supporting member 99 has a bore for receiving an end portion of the bulb '95 which is sleeve fitted thereinto and the supporting member 96 also has a relatively small bore 91 in which is screw threaded one end of an open ended tube 98 which extends longitudinally through the bulb 95. The tube 98 connects the interior of bulb 95 with the relatively small bore 91. Intersecting bore 91 externally of the bulb there is a. bore in which is threaded an end portion of a conduit 99. The other end of the conduit 99 is threaded into the bellows supporting member 92, the conduit 99 thus connecting the interior of bulb 95 and the interior of the bellows 88. A flexible conduit or sheath I is preferably provided for enclosing conduit 99 to protect the same against injury. Opposite ends of the flexible conduit I00 may be inserted in apertures in the bulb and bellows supporting members and may be secured and sealed therein by solder, or other suitable sealing material. The bulb, bellows, and connecting conduit may be charged, preferably under a vacuum, with ethyl alcohol, or any other suitable expansible-contractible fluid.

Disposed within the bellows 88 there is a 'coil spring ml which tends to expand bellows 88. The upper end of spring IOI preferably seats against a retainer member I02, the lower face of the retainer having an extended portion for receiving and preventing undue side. movement of the upper end of spring IOI. The upper face of the retainer I02 is provided with a plurality of upwardly extending, spaced lugs I03 and the lower face of fixed end wall 89 is formed with a round an upwardly directed, extended portion formed on the movable end wall 90 of the bellows. The upwardly extending tubular portion of lower retainer I05 has an end wall I0I in which there is provided a centrally disposed aperture through which the shank of a screw I08 extends. The screw I08 is carrried by the upper retainer I02 and has a head disposed within the tubular portion I08 of lower retainer I05. The aperture in end wall I0! is made sufliciently large such that there will be no frictional engagement between the screw and retainer, but is smaller than the diameter of the head of screw I08 so that the latter cannot pass therethrough. The

ber I8, and this transmitting means includes three levers or movable operating members I09, H0, and III which levers are shown in Fig. 4. The lever I09 may be termed the main lever and the levers H0 and III may be termed auxiliary levers. The main lever I09 extends horizontally and longitudinally of the rectangular shaped casing 66 and isdisposed adjacent the upper end thereof. Preferably the main lever I09 is formed having substantially parallel, reenforcing side flanges H4 which, when the lever is in operative position, extend downwardly from the lever proper, or horizontally extending portion designated by the numeral H5. The side flanges H0 extend beyond the horizontal portion H5, at one end of the lever, and are provided with aligned apertures H6 for receiving apivot pin or bearing shaft I I1 whose opposite ends may be supported in the opposite side walls 68 and 89 of the casing 66 and preferably adjacent end wall 10. Opposite end portions of the shaft III are preferably inserted and supported in aligned removable closure plugs I I8 which may be threaded into side walls 68 and 89. In the horizontally disposed lever portion I I5 there is preferably provided a downwardly extending, conical shaped indentation I20 for receiving the pointed end of the thrust member 93 which seats therein. Preferably the point of engagement of the thrust member 93 and lever I09 is' at a point between the pivot point of lever I09 and the valve member I8.

In the bottom wall 61 of the casing there is provded a threaded bore I2I whose axis is substantially in alignment with the thrust member 93 and in which there is screw threaded the shank I22 of an adjustable supporting member I23 which supports the lower end of a forceexerting means or coil spring I24. The upper end of the spring I2I seats against the underside of the main lever I09 and surrounds the downwardly extending indented portion I20 which serves to prevent undue lateral movement of the upper end of the spring. The spring I24 is under compression and opposes movement of the thrust member and this spring may be termed the range spring for by changing the force exerted by this spring the temperature range of operation of the device can be changed accordingly.

The main lever I09 extends from its pivot point adjacent the end wall 10, toward opposite end wall II and overlies the upper end of valve member 18 in spaced relation thereto. The end of the lever I09 which is disposed toward end wall H has an arm or portion I25 which extends substantially perpendicularly and downwardly from horizontal portion I I5 and whose lower end portion I26 is preferably bent or offset, and in a manner so that it extends downwardly at an angle to portion I25 and back toward valve member 18 or end wall. Carried by the lever I09 and fixed to the offset portion I26 there is a bearing or engaging pin I21 which extends downwardly and toward end wall II and which preferably has a pointed end for seating in a conical recess, provided in aseating or retainer member threaded into a closure plug I32, which in turn is threaded into the end casing wall lI adjacent bottom wall 61. By means of the screw I3I it will be seen that the compression force of spring I29 can be adjusted, and the force exerted by this spring determines the temperature differential that will be obtained as well as acting to aid in actuating the valve member I8. The point of engagement between pin I21 and member I23 is adapted to move over center either side of a line extending from the point of pin I3I through the pivot point of lever [.09. When the pointed end of pin I2! is above the above mentioned centerline, the force exerted by spring I29 will tend to pivot lever I09 in a counterclockwise direction while when the point of pin I21 is moved below the center line the force of spring I29 will tend to pivot lever I09 in a clockwise direction. Located above the main lever I09 for engagement with its upper face there is'a stop member I32 which may be in-the form of a pin or shaft and have its opposite ends supported in the opposite 'the auxiliary lever I I0 is formed having'longitudinal side reenforcing flanges I33 which, when the lever is in operative position, extend upwardiy, and preferably the width of lever H0 is made such that its upturned side flanges I33 are positioned between the downwardly extending side flanges II4 of main lever I 09. The sideflanges I33 are provided with aligned apertures I34 adjacent one end of the auxiliary lever I I0, for receiving the pivot pin or shaft III. In the lever proper, or horizontally disposed portion designated by the numeral I35, there is an aperture I through which spring I24 extends, and running into aperture I36 and extending toward the free end of the lever there is provided a slot I31 for receiving the valve member 18. The valve member I0 has oppositely disposed flattened portions I39 adjacent its upper end which provide upper and lower shoulders I40 and HI, respectively. The width of the slot I3! is made such that the lever will engage the upper shoulder I40 and also so that it is freely movable without frictional engagement with the oppositely disposed flattened portions I39. The lever IIO extends beyond the valve member 18 toward end wall II, and at a point between its free end and the slot I31 there is provided an opening I43 preferably of rectangular form through which extends the downwardly extending portion I25 of the main lever I09. Preferably the lever I I0 has an upwardly disposed offset portion I44 at its free end and in which there is provided a slot I45 which runs out of the end of the lever I I0 to thus provide a bifurcated lever end.

The cover 12 is provided with two laterally positioned threaded bores for receiving parallelly extending threaded screws I40 and I41 which may be termed maximum and minimum stop members, respectively and which together with the stop member I32 comprise an abutment means. Lower end portions of the screws project downwardly into the casing, the lower end of screw I49 being disposed for engagement with the upper face of the auxiliary lever IIO. The other or minimum stop screw I41 extends through the slot I45 in the end of leverl I0 and has a head on its lower end which is adapted to engage with the underside of the lever to limit its downward movement. This screw can be set so as to permit the valve to positively stop flow of fluid through the valve port, or can be set in a position so as to obtain a minimum desired fluid flow. Preferably locking nuts are provided and threaded on the upper ends of screws I46 and I4! externally of the casing, and preferably the upper or externally projecting portion of the screws are enclosed by a cap member I50. The stop members I32, I45 and I4! thus provide parallel spaced stop surfaces.

Disposed within the casing 66 and immediately beneath the auxiliary lever H0 is the auxiliary side flanges or tabs I52 at one end" thereof and which may be provided with aligned apertures I53 for receiving the shaft or pivot pin I I I. The

lever III is also preferably provided with longitudinally extending, substantially parallel reenforcing flanges I54 which extend upwardly when the lever III is in operative position. In the lever proper, or horizontally extending portion and which is designated by the numeral I55, there is provided an opening or aperture I55 through which the range spring I24 extends. The lever III is provided with a slot I51 which runs out of its free end and which receives the flattened portion of the valve member I8. The slot I51, like the slot I45 in the upper auxiliary lever H0, is sufficiently wide such that the lever is freely movable without frictional engagement with the flattened portions I39 of the valve member, the width also being such that the lever is adapted to engage the lower shoulder I40 formed on the valve member. At its free end the lever III is preferably provided" with upturned flanges or abutting portions I58 whose upper ends are adapted to engage the underside of the auxiliary lever IIO.

Surrounding the spring supporting member I23 and'the range spring I24 there is a coil spring I52 which has its lower end bearing against the bottom wall 51 of the casing and has its upper end bearing against the underside of the lower auxiliary lever III. The spring I62 is operable to maintain the auxiliary levers H0 and II I in engagement and opposes clockwise movement of the levers. Carried by the main lever I09 there is a vertically extending screw or engagement means I60 which is screw threaded into the horizontal portion II 5 of the lever and which extends through aperture I35 in lever H0 and toward lower auxiliary lever III. The lower end of the screw I is adapted to engage the upper face of lever III and when the lever I09 is in engagement with stop member I32 the screw I60 is set so that its lower end is spaced from lever III.

By this arrangement it will'be seen that the main lever I09 will pivot in a clockwise direction a predetermined distance before it will engage and cause lever III to be pivoted, the lever I09 thus gaining momentum before it acts to pivot auxiliary lever III against the opposition of spring I62.

The operation of the herein described control device is as follows: When the operating parts are in the position shown in Fig. 1, with main lever I09 against its stop I32 and with upper auxiliary lever IIO against the maximum stop screw I46, the valvemember I8 is in open position, and is being held in open position solely by the spring I62 acting through auxiliary levers H and III. Also, when the Valve member I8 is in open position the point of engagement between the supporting member I21 and the spring end member I28 is above center so that the differential spring I29 is opposing the power element. Assume now that the device is set to have an operating range between 155 F. and 143 F.

,When the temperature of the bulb 95 becomes 155 F. the force exerted by the expanded fluid, plus the force exerted by spring IOI, will exceed the opposing forces comprising the force of atmospheric pressure, the force exerted by range spring I24, and the force of diflerential spring I29 and when this occurs'the main lever I09 will begin to pivot in a clockwise direction. Because of the space between the end of adjustment screw I60 and the lever III, the main lever I09 will move through a corresponding arc before it engages'and causes lever I II to move and during which travel it gains momentum by the breakdown of spring forces. When the main lever I09 engages and causes lever III to pivot in a clockwise direction the upper auxiliary lever IIO follows lever III by reason of its weight and the weight of the valve and thus valve member I8 .moves toward closed position. When the main lever has moved to the point where the point of engagement between its bearing member I21 and the abutment member I28 mov'es below center, then the force of spring I29 acts with the power element and lever I09 is pivoted clockwise with a snap-action. Upon a predetermined movement of the lower auxiliary lever III, it engages with the lower shoulders on the valve member IB and through such engagement the valve member is held in closed position, assuming that the minimum stop screw I4! i set to permit the valve to seat. When the temperature of the bulb 95 decreases to 143 F. the force exerted by the expansible-contractible fluid, plus the force exerted by spring IOI becomes less than the sum of the opposed forces and the main lever begins to pivot in a counterclockwise direction. During this movement spring I62 acts to maintain lever III in engagement with the adjustment screw Hill of the main lever and also engages and causes lever IIO to be pivoted in a counterclockwise direction. However, initial movement of levers H0 and II I is not transmitted to the valve member I8 because of the lost motion connection between the levers and the valve member. When the main lever I09 has moved such that the point of engagement of its bearing member I'Z'l and the-abutment member I28 moves above center. then the differential spring I29 acts against the power element and the main lever is pivoted counterclockwise with a snap-action. The spring I62 causes the auxiliary levers to follow the main lever and when the upper auxiliary lever engages the upper shoulders of the valve member the valve member is moved upwardly or to an open position determined by the position of maximum stop screw I46. When the minimum stop screw I41 is set to limit downward movement of the valve member I8 so as to obtain a. minimum flow, the operation of the device is substantially as described above except that when the lever IIO engages the head of the stop screw M1 the lower auxiliary lever I II continues to pivot through its lost motion so that the auxiliary lever III moves out of engagement. In this position the upper auxiliary lever H0 is in engagement with the upper shoulders of the valve member while the lower auxiliary lever is held against the lower shoulder of the valve member. When the main lever begins to pivot in a counterclockwise direction the valve member remains stationary until the lower auxiliary lever III engages the upper auxiliary lever and causes the same to pivot. By this time the main lever'is moving with a snapaction and the auxiliary levers follow the main lever under the force of spring I62 until lever IIO engages the maximum stop screw I46.

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

1. In a control device having a power element for actuating a controlling means, a supporting means, a main lever fulcrumed on said supporting means andpivoted in one direction by said power element for actuating said controlling means, said lever having an inactive position, resilient means opposing pivotal movement of said main lever by said power element, and an auxiliary lever for engaging and moving said controlling means and movable by said power element through movement of said main lever and engagement of said levers, said auxiliary lever being in spaced relation to said main lever when said main lever is in its inactive position, said resilient means being so positioned relative to said main lever that the force exerted by said resilient means decreases upon movement of said main lever so that said main lever will gain momentum before engaging said auxiliary lever.

2. In a control device having a power element for actuating a control member, a supporting means, a main lever member pivotally mounted on said supporting means and pivotal in one direction by said power element, spring means engaging said main lever member, the point of engagement between said main lever member and said spring means being movable overcenter, a second spring means acting on said lever member to pivot said lever member in the opposite direction, an auxiliary lever member pivotally mounted on said supporting means and carrying said control member, a stop means for limiting movement of said main lever member in one direction, a stop means for limiting movement of said auxiliary lever member in said main lever member one direction, and an engagement means carried by one of said lever members for engagement with the other of said lever members, said engagement means being out of engagement with the other of said lever members when the lever members are against their respective stop means so that the main lever member has a predetermined initial movement before it engages to move said auxiliary lever member.

3. In a control device, a casing having a passageway for fluid, a valve member for controlling flow through said, passageway, a lever member fulcrumed within said casing and having a lost motion connection with said valve member, said lever member being operable upon predetermined movement ior engaging and moving said valve member in one direction, spring means operable to pivot said lever member, a second lever member fulcrumed in said casing and having a lost motion connection with said valve member, said second-named lever member being operable upon predetermined movement to engage and move said valve member in the opposite direction, and a power element for moving said second-named lever member.

4. In a control device, a casing having a passageway for fluid, a valvemember for controlling flow through said passageway, a lever member fulcrumed within said casing and having a lost motion connection with said valve member, said lever member being operable upon predetermined movement for engaging and moving said valve member in one direction, spring means operable to pivot said lever member, a second lever member fulcrumed in said casing and having a lost motion connection with said valve member, said second-named lever member being operable upon predetermined movement to engage and move said valve'member in the opposite direction, a power element for moving said second-named lever member, a stop member for engagement with one of said lever members, to limit movement of said valve member toward open position, and a second stop member for engagementwith said one lever member for limiting movement of said valve member in a valve closing direction.

5. In a control device having a casing with a passageway for fluid controlled by a valve member, a lever member fulcrumed in said casing and carrying said valve member, said lever member having a lost motion connection with said valve member and operable to engage and move engagement with saidvalve member, said secondnamed lever member having a lost motion connection with said valve member and operable when pivoted in one direction to move said valve member toward closed position, resilient means operable to maintain said lever members in engagement and vfor moving said valve member toward open position, an overcenter means'within said casing operable when moved overcenter in one direction to pivot said second-named lever member to move said valve member toward closed position, means operable to move said overcenter means in said one direction, and resilient means operable to movesaid overcenter means in the opposite direction.

6. In a control device having a casing with a passageway for fluid controlled by a valve member, a lever member fulcrumed in said casing and carrying said valve member, said lever member having a lost motion connection with said valve member and operable to engage and move said valve member, a second lever member fulcrumed in said casing and engageable with said first-named lever member to hold the same in engagement with said valve member, said secondnamed lever member having a lost motion connection with said valve member and operable when pivoted in one direction to move said valve member toward closed position, resilient means operable to maintain said lever members in engagement and for moving said valve member toward open position, an overcenter means within said casing operable when moved overcenter in one direction to pivot said second-named lever member to move said valve member toward closed position, means operable to move said overcenter means in said one direction, resilient means operable to move said overcenter means in the opposite direction. a stop member for engaging said first-named lever member to limit movement of said valve member in one direction,

said valve member, said lever member having a a lost motion connection with said valve member and being pivotal for movingv said valve member, a second lever member fulcrumed in said casing and having a lost motion connection with said valve member, said second-named lever member being pivotal in one direction for engaging said valve member to urge the same toward closed position, said second-named lever member being pivotal in the opposite direction to engage said first-named lever member, spring means acting on said second-named lever member and operable to hold said first-named lever member in engagement with said valve member to hold said valve memberin an open position, a main lever member fulcrumed within said casing and pivotal for engaging and moving said second-named lever member in a valve closing direction, said main lever member having an active and an inactive position and being out of engagement with said second-named lever member when in its inactive position, a spring engaging said main lever member with the point of engagement being movable over center for quickly moving said main lever member to its active and inactive positions, spring means operable to move said main lever member to its inactive position, and a power element operable to move said main lever member to its active 1 position. l

8. In a control device, a ,casinghaving a passageway for fluid, a reciprocal valve member controlling flow through said passageway, a lever member fulcrumed in said casing and carrying said valve member, said lever member having a lost motion connection with said valve member andpivotal to move said valve member toward open position, a second lever member disposed immediately beneath said first-named lever member and having a lost motion connection with said valve member, said second-named lever ,member being pivotal in one direction to engage said first-named lever member and being pivotal in the opposite direction to engage and urge said member to move said valve member toward closed position, spring means operable to move said main lever member to its inactive position, and an element operable to pivot said main lever member to its active position.

9. In a control device having a power element for actuating a control member, a supporting means, a main lever member pivotally mounted on said supporting means and movable by said power element for actuating said control member, spring means acting on said lever member,

the point of engagement between said spring to engagement therewith, said main lever member and said spring being moved overcenter by said power element prior to movement of said control member by said auxiliary lever member so that said main lever member will be in motion upon its operation of said control member thereby to impart a quick movement to said control member.

10. In a control device having a power element, a controlling m ans, a supporting means, a main lever member pivotally mounted on said supporting means and movable by said power element in one direction, spring means engaging said main lever member with the point of engagement being movable overcenter, resilient means for moving said main lever member in a direction opposite to said one direction, an auxiliary lever member pivotally mounted on said supporting means,'said auxiliary lever member having a lost motion connection with said controlling means and being operable for engaging and moving said controlling means toward one position, a second auxiliary lever member pivotally mounted on said supporting means and having a lost motion connection with said controlling means, said second-named auxiliary lever member being arranged to engage said firstnamed auxiliary lever member, and spring means acting on said second-named auxiliary lever member and operable to move said auxiliary lever members and said controlling means toward said one position, said second-named auxiliary lever member being moved in the opposite direction through engagement therewith or said main lever member for movement of said controlling means toward a second position.

11. A control device comprising a supporting means, an auxiliary lever member journaled on said means, a control means movable upon movement of said lever member, a coil spring opposing movement of said lever member, a main lever member journaled concentrically with and extending parallel to said auxiliary lever member, means to transmit movement from said main lever member to said auxiliary lever member, a spring acting on said main lever'member, said auxiliary lever member having an aperture therethrough for transmission of the force of said second-named spring to said main lever member, stop means cooperable with said auxiliary lever member to space said auxiliary lever member from said main lever member, and a power element alined with said aperture and acting on said main lever member to move said main lever member'in opposition to said second-named spring.

12. A control device comprising a supporting means, a main lever member journaled on said supporting means, an auxiliary lever member journaled concentrically with and extending parallel to said main lever member, a coil spring under compression and acting on said main lever member, said auxiliary lever member having an aperture therethrough for transmission of the force of said spring to said main lever member, stop'means to limit movement of said main lever member by said spring, a coil spring under com- .pression and acting directly on said auxiliary lever member to move said auxiliary lever member toward said main lever member, stop means to limit movement of said auxiliary lever member toward said main lever member, a power element operable to move said main lever member away" from said first-named stop means and to move said auxiliary lever member away from said second-named stop means, a thrustmember for said power element alined with said aperture and engaging said main lever member, means to transmit the movement of said main lever member to said auxiliary lever member, and control means operatively connected to one of said lever members and movable upon movement of said auxiliary lever member.

WALTER S. LANDON.

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