US1965543A - Control device - Google Patents

Description

July 3, 1934. L. w. EGGLESTON ET AL 1,965,543

CONTROL DEVICE Filed Aug. 29, 1931 Patented July 3, 1934 CONTROL DEVICE Lewis W. Eggleston and EarnestJ. Dillman, De-

troit, Mich., assignors `to Detroit Lubricator Company, Detroit, Mich.,

Michigan a corporation of Application August 29, 1931, Serial No. 560,164

28 Claims. (Cl. 200-83) Our invention relates to new and useful improvements in control devices operable automatically in response to predetermined variations in an actuating force created by temperature, pressure, hygrostatic, or other conditions.

An object of our invention is to provide a )control device operable to effect a quick action for actuating a controlling means upon the occurrence of a predetermined condition.

Another object is to provide means for adjusting the differential operation of the control device.

Another object is to provide a devicewhich in one embodiment is adjustable `for response to pressures bothabove and below atmospheric pressure. l

Another object is to provide a device which is of simple construction and efllcient in operation.

The invention consists in the improved construction and combination of parts) to be more fully described `hereinafter 'and the novelty of which will be particularly pointed out and distinctly claimed.

In the accompanying drawing, to` be taken as a part of this specification. wehave fully and clearly illustrated a preferred embodiment of our invention, in which drawing- Figure 1 is a view in front elevation of the conirol device embodying our invention, with a cover er.l closure member removed, certain parts being broken away and certain parts being shown in vertical, central section;

Fig. 2 is a view in vertical section on the line 2-2 of Fig. 1, showing the cover member in position, and

Fig. 3 is a detailv in vertical section showing certain of the parts in full and in dotted lines at their respective extremes of movement.

Referring to the drawing by characters of reference, 1 designates generally a casing of base member, preferably of metal, having a substantially vertical rear wall member 2, from the marginal edge or Vperiphery of which extendsy a forwardly' projecting surrounding flange or side wall member 3, the member ,2 preferably being substantially circular and the member 3 cylindrical.

A cover or closure member 3 is preferably provided for thecasing and which has a peripheral flange which overlaps the fiange 3. Extending acoss or bridging the interiory of the casing is a substantiallyI horizontal'supporting member 4 having a horizontal web 5 from which depend front and rear flanges 6, 7, the ends of the front `ange `6 terminating in lugs 8 which seat in sockets or recesses 9 formed-in the front edge of the wall or flange 3. The member 4 may be secured to the rear wall 2 by a screw 10 or the like, which serves with lugs 8 to fix rigidly the member4 in the casing. Depending from the front and rear sides of the member 4, substantially midway of its length and preferably 'from the lower edges of flanges 6, 7, are spaced, substantially parallel supporting arm or bearing members 11, 12 re.- spectively, which terminate at their lower ends in knifeA edgesv 1,3 defining fulcrum supports or pivot points for a purpose to be described. The lower ends `of members l1, 12 are preferably joined and held rigidly together by a tie rod 14 or the like.

Fulcrun'ied on the knife edges 13 and seating vupwardly thereagainst intermediate its ends, is

ing arms 16 provided in their upper faces with seats or sockets 17 which receive the knife edges 13. At one end ofthe lever 15 is a transverse depending flange 18 having an upwardly extending lug 19 projecting above the plane of the lever andto which is secured a coil spring or other resilient means 20, preferably having its end portion 21 hooked through an aperture in the lug 19. Secured to the free end of the spring which extends upwardly through an aperture 21m in th web of the supporting member 4, is an adjustment means 22, preferably comprising a screw member 23 having its head engaged in the end coils of the spring 20, as at 24, and being threaded tightly into a longitudinal, internally threaded tation. Threaded on the member 26 is a nut 29, i y preferably cylindrical and knurled to provide a 95- `finger grip, which seats on the boss 28 so that rotation of the nut 29 regulates the tension of the spring 20. At the other end of the lever l5 is an upstanding flange or arm 30 having a substantially conical socket or seat 31 formed there- 100 in in its iner face. Pivotally seated Ain the socket 31 isone end, preferably. pointed or conical, as at 32, of a rod orforce transmitting thrust, member 33, having its'othe'r end 34, also preferably pointed or corneal, seated for pivotal move- 105 ment in a substantially conical recess or socket 35 formed in the end portion of a depending lever member 36. The member 36 has a transverse re inforcing flange 37 extending downward from its upper end, and'aiso has at its. upper end a. iat- 1 10 Cil eral, forwardly extending arm 38 terminating in an ear or projection 39 substantially parallel to flange 37. Extending through alined apertures in the flange 37 and ear 39 is a shaft or rod 40 having its ends fixed in the supporting member flanges 6, 7 such that the lever member 36 is pivotally supported from or fulcrumed on the shaft 40. The member 36 extends downward through a slot 41 in the forward edge of the lever 15 between the lever fulcrum and the end flange 30, and has in its rear vertical edge a slot 42 which receives the lever 15, the substantially horizontal top and bottom edges of the slot 42 defining stop means to limit the swing of the lever 15. Secured to the lever member 36, preferably intermediate its ends, is one end of a coil spring or resilient means 43 preferably having its end hooked through adjacent apertures in member 36, as at 44. The other end of spring 43 is preferably sej cured to adjustment means 45 similar to the adjustment means 22, and comprising a screw member 46 having its head fixed in end coils of spring 43 and being fixed to a slide member 47 `of polygonal cross-section, preferably triangular,

which is reciprocable through a triangular guide,

aperture 48 inthe side wall or flange 3 such that the member 47 is held against rotation. Threaded on the member 47 and bearing against the outer face of wall 3, is an adjustment nut 49, preferably cylindrical and knurled to provide a finger grip. Extending along the rear edge of the lever 15 is a reinforcing flange 50 having an upwardly extending operating arm 51 which terminates in an operating finger or projection 52, for a purpose to be described.

Positioned beneath the lever 15 and operatively connected thereto is a power means 53 for actuating the lever. The means 53 comprises a supporting member 54 having a lateral flange 55 which seats against the outer face of wall 3 and is secured thereto by screws 55a or the like. Supported-on the top, inner face of flange 55 is al resilient, expansible-collapsible element 56, preferably a substantially cylindrical, circumferentially corrugated, metallic bellows which projects upwardly through an aperture in the Wall 3. The lower or bottom edge of the element 56 is secured and tightly sealed to the member 54, preferably by inserting and soldering the marginal edge thereof in a circular recess in the member 54, as at 57. The top end of the element 56 is closed by a head or end wall member 58, the periphery of which is secured and sealed, as by solder, to the top edge of element 56, as at 59. The head 58 and the member 54 have oppositely positioned bosses 60, 61 respectively, which receive and center the opposite ends of a coil spring 62 held under compression and normally tending to expand the element 56. Secured and sealed in a central aperture in the head 58 is a plunger member 63 which extends into the element 56 and projects upwardly therefrom, terminating at its upper end in a substantially'conical or pointed end portion 64. The portion 64 seats in a substantially conical socket or recess 65 formed in the underface of the lever 15 adjacent the fulcrum points 13 andlongitudinally between the lever fulcrum and the .lever member 26. The spring 62 and the resilience of the element 56, which 1 is in substantially inert or neutral condition, together serve in conjunction with the springs 20 and 43 to maintain the lever 15 in engagement with the knife edges 13. Through the member 54 is a bore or passage 66 which is of reduced in the position of Fig..

diameter, as at 67, to form a guideway which receives the free inner end 68 of the plunger' member 63 to guide the reciprocable movement of the plunger member. The interior of the element 56 is in communication with the passage 66 through one or more ports 68LL in the member 54.

Extending between and fixed at its ends to the supporting membersll, 12 above the operating arm 51, is a rod or shaft 69 on which is journaled a carrier or supporting member 70 having at its front and rear ends depending flanges 71, 72 which are apertured to receive the shaft 69. The rear flange 72 has a depending lug 73 which ex-v tends into the path of movement of the operating finger 52. The lug 73 is normally urged into engagement with the finger 52 by a light spring member 74 coiled about the shaft 69 and having one end 75 engaging the carrier member, and having its other end 76 seated on or bearing against a forwardly extending lug 77 on the arm member 12. Secured to the carrier member 70 is a clip member 78 having oppositely disposed pairs of resilient curved fingers 79 which receive and support, transversely to shaft 69, a switch means 80, preferably a sealed glass tube containing contacts 81, 82 and a globule of mercury which acts on tilting of the tube to make and break circuit between the contacts. Connected to the contacts are lead wires 83 having their free ends secured to terminal posts 84 on a block 85 by screws 86. The block, which is of insulating material, is preferably fixed to the casing rear wall by a screw 87 or the like. The carrier member 70 is preferably provided with a stop arm 88 cooperable with a lug 89 projecting forwardly from the supporting member 12 above the lug 77 to limit clockwise rocking or tilting of the carrier member 70.

Cooperable with the switch means is an operating means 90 for actuating the switch means irrespective of the operation of the lever 15. The means 90' comprises a housing or supporting member 91 having a lateral surrounding flange 92 which is secured to the casing side wall 3 by screws 93 or the like. Tightly sealed and secured to the inner face of the member 91 by solder or the like, as at 94, is a resilient, expansible-collapsible member 95 which extends through an aperture in the wall 3. The member 95 is preferably in the form of a cylindrical, circumferentially corrugated, metallic element or bellows having its free end closed and sealed by a head or end wall member 96 which is soldered or otherwise sealed at its periphery to the element. Through the web of member 4 directly beneath the bellows member 95 is an internally threaded aperture 97, in which is adjustably threaded a `spring seat member 98 which is substantially cupshaped and receives the lower end of a compression spring 99, preferably of the coil type, which seats at its upper end against the bellows head 96 to regulate the degree of internal pressure necessary to expand the bellows. Secured and sealed in a central aperture 100 in the head 96.is a plunger member 101 which extends downward through the coil spring 99, and a guide aperture 101*l in the end wall of member 98, terminating adjacent to the top of the carrier member 70 at one side of the shaft 69, so that on expansion of the bellows the plunger member will engage the carrier member and rook or tilt the switch tube. Through the member 91 is a passage 102 which is of reduced diameter, as at 103, to receive the inner end of the plungermember 101 to guide the same in reciprocation. The interior of the bellows 95 is in 1 the shoulders formed ,by the reduction in thev passage diameters to limit the expansion of respective bellows. l

The operation of the device is as follows, that shown being particularly adapted for control` ling the operation of a compressor motor in refrigeration system. The device is connected in the system with the leads 83 joined to the motor leads so that the switch means will make and break the motor circuit, with the passage 102 of the operating means 90 connected by suitable conduit means into the high pressure side* of the system, preferably at the condenser, and with the passage 66 of the power-means 53 connected by suitable conduit means to the, low pressure side of theysystem, for example, at the evaporator. The operating means comprises asafety means forv breaking the motor lcircuit if the pressure goes too high, and therefore the member 98 is adjusted to regulate the compresthe sion o f spring 99 acting to resist expansion ofthe bellows Aso that upon occurrence of the predetermined desired maximum pressure in the high side, the plunger member 101 will be `moved downward by the bellows expansion into engagement with the carrier member 70 totilt the same counterclockwise of Fig. 1 about the shaft 69 to flow the mercury away from contacts 81, 82 and break the motor circuit. It will be noted that this movement of member 70 is only opposed by the light spring 74, which in normal operation acts to tilt 'the tube 80 clockwise on shaft 69 when the carrier member '70 is released by the operating finger 52. The device is now adjusted by the sleeve nut 29 to determine the operating range of the device, that is, the predetermined desired low side pressure at which the motor circuit will be broken in the tube 80, this pressure increasing as the nut 29 is turned to place increasing tension in the spring 20. The

cutting in of the motor or the pressure in the low side which will make circuit in the tube 80 is determined by the tension in the differential spring 43, which-is adjusted by the sleeve nut 49. It is to be particularly noted that due to the fact that when the lever 15 is in its up position, as in Fig. 1 the longitudinal centerline of pin 33, or the line through its points of engagement with lever 15 and lever member' 36, includes or is alined with the fulcmm of the lever 15, Yso

that the Whole force of the spring 43 acts longitudinally of the lever 15 at its fulcrum, and therefore exerts no turning movement on the lever, that is, exerts no force either tending to or in opposition to movement of lever 15. Therefore,

' the adjustment or variation in the tensionl of spring 43 does notaifect or vary the setting of the spring 2O andthe predetermined pressure which will cause tilting of the tube 80 to break the circuit. Assuming that the range spring 20 has been set to exert a resistance to operation ofthe power means 53 of, say, four pounds, and the differential spring-43 for a. differential of, say, two pounds, that is, a change of pressure inthe power means 53 of two pounds between the pressure to actuate the lever 15 in one direction, and that to actuate the lever in the opposite direction, a force of six pounds on plunger member 63 will be required to move the lever from the full line position of Fig. 2 to the position of Fig. 1,

and a drop in pressure to four pounds after the levervhas been moved to the position of Fig.v 1

will cause actuation of the lever to the full'linc position of Fig. 2 under the force of spring 20.

. With the lever 15 in its down position, Fig. 2 full lines, the circuit to the motor will be broken in tube A80, and when the pressure in the low side builds up suiiiciently to cause the bellows 56'to exert an upward pressure on the `plunger member 63 Lof six pounds, the combined resistance of springs 20 and 43'will be overcome. the lever 15 starts to move, the angle at which the pin 33 acts on the lever 15 will decrease, and

As soon as therefore the downward or resisting component of force of spring 43 acting through pin 33 will decrease. The inherent resilience of the springe 20 and 43 and the lever arms of the forces which they exert in opposition to movement ofthe lever is such that although the inherent tensile force of spring 43 decreases and the inherent tensile force of the spring 20 increases on movement of the lever, the force exerted by the spring 43 in opposition to movement of the lever decreases at a greater rate than the rate of increase of resstance of spring -20 to movement of the lever. Therefore,.from the instant of movement of lever 15 under the force of means 53 there will be an un- "increased, and preferably a decreased, resistance to operation of the lever, so that the force which" will start or initiate movement of the lever\will cause movement of the lever completely through its rangeof movement, that is, until it strikes the top edge of the stop slot 42, as in Fig. l. The

movement of the lever takes place without any in-- crease in force by the power means 53 and with a sudden, quick, or snap action, without any overcenter movement of parts, which action is due to the unincreased and preferably decreased resistance exerted by `the sum of 'the forces of,l

springs 20 and 43 as the lever moves from the full line position of Fig. 2 to the position of Fig. l. As the ever moves counterclockwise, the i'ln- -ger 52 will swing toward the left, facing Fig. 1,

of the spring 20 and the resilient force ofthe bellows 56 remain substantially constant for al1 positions of the lever 15. The lever 15 will remain in the position of Fig. 1 and the tube 80V in circuit closing position as long as the pressure in the system is above the four pound setting atv which the circuit is desired to be broken.

When the pressure in the systemdrops to four pounds, the upward force on the Alever exerted by thepower means 53 will be overcome by the force of spring 20, the spring 43 not exerting any force tending to move the lever. As soon as the lever moves, however, a component of the forcey of spring 43iwill act through the lever against the means' 53, and this component will increase at a uniform, substantially constant rate for each increment of clockwise movement of the lever. -It will therefore be noted that as soon -as t-he force exerted by the power means 53 .decreases suiciently to permit movement of the lever by the spring 20, .thespring 43 comes into play with aconstantly increasing force in opposition to the power means, and the lever will be moved quickly and with a sudden, substantially snap action to the full line or down position of Fig. 2. As the lever moves downward, the finger 52 will engage and carry the lug 73 with it toward the right of Fig. 2, rotating the carrier member and tube 8() counterclockwise about shaft 69 to break contact at the contacts 81, 82.

The device is also adjustable by the nut 29 for response to sub-atmospheric pressures due to the spring 62, which being under compression normally tends to move the lever upward or counterclockwise. When the tension in spring 20 is relieved by nut 29 such that the turning moment of spring 62 is greater than that of spring 20, then a vacuum will be required in the power means 53 to permit spring 20 to act to move the lever downward. It is therefore apparent that the device may be set to respond to predetermined desired absolute pressures both above and below'atmospheric pressure and with any predetermined desired differential over the range of operation of the device..

As further illustrative of the operation of the device, the following example sets forth the forces, disregarding friction, which exist in the full line position of Fig. 2 and in the position of the elements, as in Fig. 1, when the device is set to operate on any infinitesimal increase above zero pounds pressure (gauge) and with the smallest possible differential. With the tension in the spring 43 set to exert a force at point 44 of 2.11 pounds, the spring force transmitted by lever member 36 to the thrust member 33 at point 35, will be 0.964 pounds, as the distance between points 40 and 44 is 0.969 inches and the distance from point 40 to point 35 is 2.125 inches. Since the thrust member 36 is acting on the lever 15 at an acute angle, a component of. the force oi' spring 43 will oppose movement of lever 15 to the position of Fig. 1, which downward component will be 0.2 89 pounds at the end of lever 15, as the| angle of application of the spring force thereon is substantially 16 degrees 45 minutes. This component transferred to the'center line of the power means 53 is 2.74 pounds, because the dis-l tance or lever arm from knife edges or fulcrum 13 to point 30 is 2.367 inches, and lthe distance between the fulcrum and the power means is 0.25 inches. The spring 20 will be adjusted to exert a tension of 2.85 pounds on the lever at point 19, which force transferred to the center line of means 53 is 5.70 pounds, since the distance between the fulcrum and point 19 is 0.5 inches. Therefore, the total downward force at the means 53 and opposing operation ofthe lever 15 thereby is 8.44 pounds in this instance. The upward force normally acting through plunger member 63 on the lever 15 is equal to the sum of the expansive forces of element 56 and of spring 62. The bellows element in the full line position of Fig. 2 is compressed from neutral, inert position 0.035 inches and exerts an upward force of one pound. The spring 62 which has a resistance to compression of 12.5 pounds per inch scale, has been compressed so that in the full line position of Fig. 2 it is exerting an up force of 7.44 pounds. It will therefore be apparent that the system is in balance, the sums respectively of the up and of the down forces being 8.44 pounds, so that any force exerted by the power means will start upward movement of the lever. Upon movement of the lever to the position of Fig. 1, the system will still be in balance, so that the force in or exerted by the means 53 is still in' excess and has been suicient to carry the lever completely through its range of movement. As noted above, the force of spring 43 in the Fig. l position of the elements is acting longitudinally of lever 15 and in line with the fulcrum, that is, is in a dead center position, so that spring 43 is exerting neither an up or a down force on the lever. The movement of lever 15 to the position of Fig. 1 has stretched spring 20 so that it is now exerting a tension of 3.5 pounds at point 19, which force transferred to the center line of element 53 is 7.0 pounds. This force tending to move the lever downward is, however, balanced' by the spring 62, the bellows element having expanded 0.035 inches to neutral position, as the spring has been permitted likewise to expand 0.035 inches. From the foregoing' particular example, which is illustrative solely, it will be apparent that the range of the device may be readily adjusted by regulation of the tension in spring 20, and-that any desired differential may be obtained by adjusting or regulating the force of spring 43.

Although we have described the device for the purpose of illustrating the operation thereof as embodied in a refrigerating system, it is obvious that the device is equally capable of use in heating or other systems or apparatus in which a control device responsive to pressure is desirable or necessary. It is further to be noted that the device may be utilized to control valve means or the like in lieu of the switch means shown, for example, by operatively connecting the operating arm 51' to the movable element of the valve means, as will be obvious to one skilled in the art. The power means 53, although described above as responsive directly to a pressure condition, is

equally operable in response to a force created Y by temperature or atmospheric conditions, for example, by connecting and sealing a bulb or the like to the passage 66, the bulb being charged with a suitable volatile or other fluid responding by expansion and contraction to the desired controlling or controlled condition.

What we claim and desire to secure by Letters Patent of the United States is l. A device of the character described, comprising a reciprocable controlling means, a lever havinga rigid arm projecting therefrom into operative engagement with and for actuating said controlling means, power means operable to move said lever in one direction, range determining means exerting a predetermined resistance to operation of said controlling means by said power rigid member in one direction to move said lever.

in said opposite direction.

2. A device of the character described, lcomprising a controlling means, a lever fulcrumed intermediate its ends, means on said lever having operative engagement with and for actuating said controlling means, a plunger engaging said lever adjacent its fulorum,lmeans acting on said plunger and operable in response to variation in fluid pressure to move said plunger, range determining means engaging said lever adjacent one end thereof and opposing movement thereof byv said plunger, a rigid member having one end supported independently of said lever and having its other end in pivotal engagement with said ferential determining means acting through said Irigid memberv and in conjunctionwith said opposing means tol oppose movement of said lever by said plunger.

3. A device of the character described, comprising a controlling means, a lever having means in operative engagement with and for actuating said controlling means, a plunger engaging said lever, means acting on said plunger and operable in response to variation in iluid pressure to move said lever in one direction, range determining means exerting a predetermined resistance to operation of said lever by said responsive means and normally acting to, move said lever, in the opposite direction, a rigid member having 'one end supported independently of saidy lever and having its other end in pivotal engagement with said lever, and differential determining means acting normally to maintain s aid member in engagement with said lever, said last-named means initially assisting said yresistance means inlboth directions of movement of said lever.

4. In a device of the character described, a lever having a fulcrum support, means acting on said lever and operable in response to variation in fluid pressure to move said lever in one di- ,rection, range determining means resisting operation of said responsive-means and' normallyy acting to move said lever in the opposite direction, a spring acting on said lever in opposition to said range determining means, means to adjust the resultant force of said range determining means and said spring, abutment means on said lever, a member movable longi-7 tudinally of y said lever and positioned between saidfulcrum support and said abutment means,

a rigid member positioned betweenand in engagement with said movable member and said abutment means, and differential determining means acting through said movable memberland said rigid member-to resist operation offssaid responsive means in conjunction with said lresisting means. i

5. A device ofthe character described, vcomprising a controlling means, a lever, means operatively connectingsaidlever and said means, power means operable to move said lever in one direction, range determining means in engagement with and resisting operation of said lever by said power means and normally acting yto move said lever in the opposite.direction, a second lever having a fulcrum support, means extending transversely to said second-,named lever and interconnecting said levers, and differential determining means acting through Asaid secondnamed lever and in conjunction with said firstnamed resisting means to resist operation of said first-named lever by said power means.

6` A device of the character described, comprising a movable controlling means, a lever',1

means projecting from said lever for transmitting movement from said lever to said means,

power means operable to move said lever in one direction, range determining means resisting operation of said lever by said power means and normally acting to move said lever in the opposite direction, a second leverA having a ffulcrum support, a rigid thrust member extending trans- 0 versely to said second-named lever and operatively connecting said levers, and differential determining means acting through said secondnamed lever andin conjunction with said rstnamed resisting means to resist operation of said first-named lever by said power means.

'7. lA device of the character described, comprising a controlling means, a lever, means operatively connecting said lever and said means, power meansv operable to move said lever in one direction, range determining means resisting operation of said llever by said power l,means and normally actingto move said lever in the opposite direction, a second lever having a fulcrum support, said levers having oppositely positioned sockets, a rigid member positioned between said levers and having its ends seated in said sockets, and diterential determining means acting through said second-named lever and inconjunction with said first-named resisting means to resist operation of said first-named lever by said power means, said last-namedmeans serving to maintain the ends of said member seated in said sockets. g

8. In a device of the character described, a lever having a fulcrum support, power means operable to move said lever in one direction, range determining means resisting said power means, a second lever extending transversely to said first-named lever and having a fulcrum support,` said second-named lever having stop means to limitmovement of said first-named lever, a rigid member operatively connecting said levers, and

.differential determining means acting through said second-named lever and in conjunction with said first-named resisting means to resist said power-means.

9. In a device of. the character described, a lever, power means operable to move said lever in one direction, meansresisting operation oi said power means, a second lever extending transversely to said first-named lever, said mst-named lever having a transverse arm, a rigid member positioned between and having its opposite ends engaging said arm and said second-named lever, means acting through said'second-named lever and in conjunction with said rst-named resisting means to resist said power means, and stop means to limit movement of said first-named lever by said power means.

10. In a device of the character described, a 1

lever having a fulcrum and a range of move-- ment, power means operable to move said lever,A

lever is stopped when the resistance of said second-named means acting inopposition to said power means is substantially zero. i

11. A device of the character described, com- .prising a controlling means, a1 lever having a rigid operating arm operatively connected to said controlling means, power means operable to move said lever in one direction, a range spring exerting a predetermined resistance to operation of said power means and operable to move said lever in the opposite direction, a second lever, a rigid thrust member interconnecting said levers and normally positioned atan acute angle to said first-named lever and transversely to said second-named lever, and a differential-deter'- mining spring having one end ilxedL relative to the fulcrums of said levers and acting on said second-named lever to exert a `component of its force through said thrust member in opposition to movement of said lever by said power means.

12. A device of the character described, comprising a controlling means, a lever operatively connected to and for actuating said means, power means to move said lever in one direction, spring means having one end iixed relative to the fulcrum of said lever and exerting its force in opposition to said power means, a second lever extending transversely to said first-named lever, a thrust member interconnecting said levers, and a second spring means having one end fixed relative to the fulcrums of said levers and having its other end engaging said second-named lever whereby a component of the force of said second-named spring means acts in conjunction with said first-named spring means to oppose said power means. v

13. A device of the character described, comprising a controlling means, a lever operatively connected to and for `actuating said means, power means to move said lever in one direction, spring means opposing said power means, a second lever extending transversely to said first-,named lever, a thrust member interconnecting said levers, a second spring means having o 1e end fixed relative to the fulcrums of said lev ers and having its other end engaging said second-named lever whereby a component of the force of said second-named spring means acts in conjunction with said rst-named spring means to oppose said power means, and means engageable by said rstnamed lever to limit movement of said iirstnamed lever by said power means.

id. A device of the character described, comprising a controlling means, means to move said controlling means in one direction, a lever operatively connected to and for actuating said controlling means in the opposite direction, power means to move said lever in one direction, spring means opposing said power means, a second lever extending transversely to said first-named lever, a thrust member interconnecting said levers, a second spring means having one end fixed relative to the fulcrums of said levers and having its other end engaging said second-named lever whereby 'a component of the force of said second-named spring means acts in conjunction with said rst-named spring means to oppose said power means, and means to limit move.- ment of said first-named lever by said power means.

15. in a device of the character described, a casing containing a supporting member having depending arm members, a lever fulcrumed on said arm members, a coil spring having one end xed to one end of said lever and normally tending to tilt said lever in one direction, an adjustment means extending through and bearing against a wall of said casing and fixed to the free end of said spring whereby to adjust the force of said spring acting on said lever, power means engaging said lever on the opposite side of saidarm members from said coil spring and being operable to tilt said lever in the opposite direction, a depending lever member pivotally supported at its upper end and positioned between said power means and the free other end of said lever, Vstop means to limit movement of said lever by said spring and bysaid power means, a rigid thrust member interconnecting the said other end of said lever and the free end or" said lever member, a dierential spring having one end ixed to said lever member and being operable through said thrust member to oppose movement of said lever in conjunction with said coil spring, and adjustment means extending through and bearing against a wall of said casing and being xed to the free end of said differential spring whereby to adjust the force of said diierential spring acting on said lever.

16. A device of the character described, comprising a casing having a rear wall and a iorwardly extending surrounding flange, a substantially horizontal internal supporting member extending across said casing and having spaced depending arm members terminating in downward directed knife edges, a lever having oppositely positioned bearing seats seating upwardly against said knife edges, powerr means extending through said liange and engaging the underside of said lever, spring means having one end engaging said flange and having its other end acting on said lever in opposition to said power means to maintain said lever seated against said knife edges, a rod extending between and secured to said arm members above said lever, a switch tube, a carrier member supporting said switch tube and journaled on said rod, an operating arm on said lever operatively engaging said carrier member to tilt said tube, a rod extending between and secured to said arm members above said lever, a lever member pivotally supported on and depending from said second-named -rod, a thrust member extending between said lever and said lever member, and spring means secured at one end to said flange and having its other end fixed to said lever member whereby a component of force of said second-named spring means acts to resist operation of said lever by said power means.

i7. ln a device of the character described, a lever, means exerting a force in opposition to movement of said lever, means having a comfil ponent of force normally acting to move said lever, and means operable to overcome the i'orce of said rst-named means whereby the component of force oi said second-named means is ree to move said lever.

18. In a device of the character described, a lever, means exerting a force in opposition to movement or" said lever, means having a component of force normally acting to move said lever, means determining the opposing force of said first-named means, and means operable to overcome the force of said rst-named means whereby the component of force of said secondnamed means is free to move said lever.

19. In a device of the character described, a lever, stop means for said lever, resilient means normally acting to maintain said lever against said stop means,l means responsive to sub-atmospheric pressure and operable to overcome said resilient means, resilient means acting on said lever in opposition to said resilient means to determine the force of said first-named resilient means, a

thrust member pivotally engaging said lever, and spring means acting on said thrust member, the line of action of said spring means on said thrust member passing through the lever fulcrum whereby said spring means normally exerts a zero force in opposition to said rst-named resilient means,

said thrust member being movable by said lever whereby a component of force of said spring means acts to move said lever.

20. A device of the character described, comprising a tiltably supported carrier member, a switch tube supported by said member, an arm member operable to tilt said carrier member, a

lever engageable with said arm member, means normally urging said arm member into engagement with said lev'er, means resisting movement of said lever, and power means operable to overcome said resisting means and to move said lever. 21. A device of the character described, comprising a carrier member, a shaft supporting said member for rocking movement, switch means carried by said member, .an arm member secured to said carrier member, a lever engageable with said arm member, a leaf spring secured on saidshaft and having one end fixed and having its other end cooperable with said arm member to urge said arm member into engagement with said lever, means resisting movement of said lever, and power means operable to overcome said resisting means and to move said lever.

22. A device of the character described, comprising a tiltably supported carrier member, a

-switch tube supported by said member, an arm member operable to tilt said member, a lever en gageable with said arm' member, means normally urging said arm member into engagement with said lever, means resisting movement of said lever, power means operable to overcome said resisting means and to move said lever, and means operable to overcome said rst-named means and to hold said member in predetermined position.

23. A device of the character'described, comprising a controlling means, means to move said controlling means in one direction, means operable to overcome said second-named `means to move said controlling means in the opposite direction, a lever operatively connected to and for actuating said controlling means in the opposite direction, power means to move said lever in one direction, spring means -opposing 'said power means, a second lever extending transversely to said first-named lever, a thrust member inter-I connecting said levers, and a second spring means having one end iixed relative to ,the lever fulcrums and having its other end engaging said second-named lever whereby a component of the force of said second-named spring means acts in conjunction with said first-named spring means to oppose said power means.

24. A device of the character described, comprising a controlling means, a lever, a lost-motion connection between said lever and said controlling means, power means operable to move said lever, means resisting operation of said power means, a rigid member having one end sup-v ported independently of said lever and having its other end engaging said lever, means acting through said rigid member and in conjunction vn'th said resisting means to oppose operation of said controlling means by saidpower means, and means 1to move said controlling means to and to hold said controlling means in predetermined position irrespective of operation of said power means. l

25. A device of the character described, comprising a casing, a supporting member in the casing, switch means carried by said member, a lever having a lost-motion connection to said means, meansV resisting operation of said lever, power means supported by said casing and operatively engaging said 'lever for moving said switch means, a second power means supported by said casing, an adjustable abutment member carried by said supporting member, a spring positioned between said abutment member and said second power means and acting to determine the operation of said second power means, and means for directly connecting said second power means independently of said lever and said switch means. l

26.""A device of the character described, comprising a controlling means, a lever having an arm extending transversely thereto, said arm having operative connection with said controlling means, power means operable to move said lever, spring means opposing said power means, a second lever extending transversely to said iirstl named lever intermediate the ends thereoffsaid first-named lever having an abutment member in opposed relation to said second-named lever, a thrust member positioned between said abutment member an'd said second-named lever and operatively connecting said levers, and a second spring means acting through said second-named lever whereby to exert a component of its force in conjunction with the force of said iirst-named spring means in opposition to movement of said first-named lever by said power means.

27. A device of the character described, comprising a controlling means, a lever fulcrumed intermediate its ends and operatively connected to and for actuating said means, spring means acting on said lever at one side of the fulcrum, a plunger acting on said lever on the other side of the fulcrum, spring means acting through said plunger in opposition to said rst-named spring means, pressure responsive means cooperable with said plunger and operable to vary the force exerted'by said plunger, a second lever, means interconnecting said levers, and spring means acting through said second-named lever in opposition to said responsive means.

28. A device of the character described, comprising a base member having forwardly extending spaced flange portions, a supporting member rigidly secured to said base member between said ange portions and having depending spaced arm members, a lever fulcrumed at its side edges intermediate its ends on said arm members, power means carried by one of said flange portions and operatively engaging said lever, spring means having one end engaging the other of said flange portions and having its other end acting on said lever in opposition to said power means, a shaft carried by said supporting member, switch means, a carrier member supporting said switch means and rockably supported by said shaft, a rod supported by said supporting member, a depending lever member supported by said rod and extending adjacent to and between the ends of said lever, a thrust member extending between said lever and said lever member, and spring means having one end fixed to said base member and having its other end engaging said lever member.

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