US2393455A - Pressure switch - Google Patents

Description

Jan. 22, 1946. L BEEMAN 2,393,455

PRESSURE SWITCH med Aug. 2o, 1941 2 sheets-sheet 1 Lyle Beeman INVENTOR.

BY Y 40 40 I l' ATToR/YEY.

Jan. 22? 1946. BEEM A N 2,393,455

` PRESSURE swITcH Filed Aug. 20, 1941 2 Sheets-Sheet 2 FIG. 9.Y FIGJU.

l Ti n 40' y 59 I 1 I 4l' I; 5 65, 7

, l v Ly F1513. INVENTOR- BY MM Ze Beeman Patented Jan. 22, 1946 UNITED STATES PATENT OFFICE PRESSURE SWITCH vLyle Beeman, Ann Arbor, Mich.

Application August 20, 1941, Serial No. 407,545

(Cl. 20G-83) 9 Claims.

This invention relates to pressure switches and particularly to automatic switch actuators of the snap action type.

One object of the present invention is to provide a sturdy reliable pressure switch of simple, compact and inexpensive design.

Another object is to provide an improved automatic snap-action mechanism of simple compact form for the actuation of switches and the like.

Other more specific objects and advantages will appear from the following description of two illustrative embodiments of the present invention.

In the accompanying drawings:

Figure 1 is an enlarged view in side elevation, partly in section, of a pressure switch constructed in accordance with the present invention, showing the relative positions of the switch actuator parts when the switch is closed.

Fig. 2 is a top plan view with the cover broken away.

Fig. 3 is a horizontal sectional view with the cover and terminal block removed.

Fig. 4 is a fragmentary vertical sectional view showing the relative positions of the switch actuator parts when the switch is open.

Fig. 5 is a fragmentary vertical sectional view in a plane extending lengthwise of the differential adjustment spring shown in plan in Fig. 3.

Fig. 6 is a fragmentary vertical sectional view taken along the line 6-6 of Fig. 2.

Figs. '7 and 8 are views in side elevation of a modified form of switch actuator embodying the present invention and showing the relative positions of parts when the switch is `closed and open respectively.

Fig. 9 is a top plan view.

Fig. l0 is also a top plan view with the clapper shown in Fig. 9 removed.

Fig. l1 is a fragmentary sectional view taken along the line I I-I I of Fig. '1.

Fig. l2 is a fragmentary sectional view taken along the line I2-I 2 of Fig. 7.

Fig. 13 is a fragmentary side elevation showing a modified means for regulating the stroke of the clapper.

The pressure switch illustrated in Figs. l to 6 is shown enclosed in a housing having a bottom.

III- whose corners II are preferably rounded to reduce the maximum dimensions thereof, and a single pair of opposite upright side walls I2 each perforated. as at I3, to receive a conventional electric conduit (not shown). Each of the side walls I2 is preferably extended about the rounded corners to stiften the housing and to leave large openings I4 at the front and back thereof through which ready access may be had to thehousing to facilitate wiring. The housing I0 is closed by an appropriate flanged cover I5 adapted to seat over the upper ends of the side walls II and having depending panels I6 disposed to overlie and close the openings I4.

The bottom of the housing contains a large circular opening I1 covered by a substantially circular internal plate I8, which serves as a convenient mounting for the switch actuating mechanism to be later described. A dished disk I9, externally applied to the bottom of the housing, cooperates with a flexible diaphragm 20, interposed between the housing and disk, to form a pressure chamber 2| adapted to be connected to a source of actuating pressure through an appropriate threaded nipple 22. The nipple 22 is preferably disposed centrally of the housing bottom I0. The plate I8, diaphragm 20, and disk I9 are releasably secured to the housing by appropriate means, such as a series of screws 23 which preferably extend downwardly therethrough and into threaded engagement with the disk I9.

A terminal block 24 of suitable insulating mate'- rial is preferably mounted in the upper rear p0rtion of the housing and attached to the opposite side walls I2 thereof by screws 25. The block provides support for two appropriate switches, each comprising in this instance a pair of stationary contacts 26 and a pair of coacting movable contacts 21. Each stationary contact 26 is carried by a conductor strip 28, attached by screws 29 to the base of a recess 30 formed in the top ofthe block 24, each strip 28 also carrying an appropriate terminal screw 3 I, Each pair of movable contacts 21 are mounted at opposite ends of a bridge vpiece 32 of conducting material perforated intermediate its ends to receive the reduced end 33 of a push rod 34 of insulating material on which it is retained by a cotter pin 35. Each push rod `34 extends downwardly through the block 24 and is guided therein for lengthwise movement. s

A compression spring 36 mounted on the lower end of each rod 34 reacts against the bottom of the block 24 to yieldably retain the rod in rthe lowermost position shown in Fig. 1 with the movable contacts 21 in engagement with the stationary contacts 26, so that the switches are normally closed. Both switches are opened by forcing the rods 34 upwardly, so as to lift the movable contacts 21 from the stationary contacts 26. A stationary bar 31 of insulating material overlying the recesses 30 in the block 24, provides a 1imiting stop for the upward travel of th'e rods 33 and the pairs of movable contacts carried thereby.

In the device shown, snap action mechanism is provided for simultaneously applying to the lower ends of both rods 34 an upwardly directed driving blow to thereby effect a quick opening movement of the movable contacts 21 away from the stationary contacts, the springs 36 functioning to maintain the desired pressure between the several switch contacts until the instant of delivery of the opening driving blow. Mechanism for that purpose may assume various forms but that shown has proven entirely satisfactory and, as indicated, can be Compactly arranged in the lower part of the housing in such manner as to leave ample space above it for easy and convenient wiring.

The snap action mechanism shown comprises a clapper 38 in the form of a stiif metallic strip having one end 39 reduced to form a knife edge, which is engaged in the grooved horizontal edge 40 of a lug 4I to provide a fulcrum for the clapper, The lug 4I in this instance comprises a suitably bent extension of the plate I8 The opposite end of the clapper 38 is laterally extended to form a driving head 42 disposed beneath the lower ends of the push rods 34. A pair of appropriate tension springs 43 serve to hold the clapper 38 against its fulcrum 40 and to actuate the clapper. In this instance each of the springs 43 is inthe form of a spring rod laterally bent to foreshorten the same and thereby render it lengthwise resilient, each having a hook at one end rockably engaged in a perforation 44 in the clapper head 42 and a hook at the other end rockably engaged in a notch 45 in the end of a carrier lever 45.

The carrier lever 46 extends lengthwise of and beneath the clapper 38, one end being recessed, as at 41, to clear the lug 4| and the fulcrumed end 39 of the clapper, and to provide fingers 48 in the ends of which the notches 45 are formed. The ngers 48 are upwardly bent so as to position the notches 45 at a level adjacent that of the fulcrum 40, and the ends thereof are preferably reduced to a knife edge so as to reduce the area of contact with the hooked ends of the springs 43. The opposite end of the carrier lever 46 is fulcrumed on the horizontal edge 49 of a lug 50 comprising a suitably bent extension of the mounting plate I8, and for that purpose that end of the lever is provided with a series of oppositely bent fingers 5| or otherwise fashioned to rockably receive the fulcrum edge 49. The head 42 of the clapper is preferably recessed, as at 52, to clear the lug 50.

It will of course be understood that the line of action of the springs 43 may be represented by the dotted line a-a (Fig. l) extending through the points of contact of each spring with the elapper head 42 and carrier lever 46, and that when this line of action is below the fulcrum 40 of the clapper 38, the head 42 of the clapper is urged downwardly, whereas, when this line of action is above the fulcrum 4U, the head of the clapper is urged upwardly. It will also be understood that the 'carrier lever 4S is vertically swingable upon its fulcrum 49 for the purpose of shifting this line of spring action to a position above or below the :fulcrum 4D. That is to 'say,with the carrier -lever 45 in the lower position of Fig. 1, the springs `43 retain the Vclapper head 42 in ,the depressed position shown, but the instant that the line of action of the springs 43 is shifted'upwardly past thefulcrum 40, by upwardmovement Yof the carrier lever 46, the clapper head 42 is instantly forced upwardly by the springs 43 in a manner to apply an upward driving action against the lower ends of the push rods 34, and the switches are thereby promptly opened, It will be noted that this snap action occurs only at the instant that the tips of the fingers 48 arrive at a predetermined point above the iulcrum 49,

Similarly, during downward movement of carrier lever from the upper position shown in Fig. 4 the line of action of the springs 43 is shifted to a position below the fulcrurn 45, at which point the springs 43 act to instantly return the clapper head 42 to the depressed position of Fig. l, thereby permitting the switches to promptly close under the action ci springs 36. curs only at the instant that the tips o the ngers 48 arrive at a predetermined point below the fulcrum 40. The snap closing action and the snap opening action thus occur et different points vertically spaced in the range of motion of the carrier lever. This feature provides a natural diiferential between the points at which the switches open and close, a feature which is highly desirable in automatic switches, such as those designed to respond to temperature, fluid pressure or the like.

In the device shown in Figs. l to 6, the switchesI are caused to respond to uid pressure by rcndering the carrier lever 4S responsive to the pressure in the chamber 2l. For this purpose the carrier lever 46 is connected to a disk 53 cen- Lili.

trally seated on the diaphragm 2G, the disk in this instance carrying a central stud 54 which projects upwardly therefrom through an appropriate opening in the mounting plate 3 and which is provided with a threaded central re cess threaded to receive a screw 55 whose head is loosely engaged in a perforation formed in thel lever 46 midway of the length thereoi.

The upward thrust of the disk 53, induced by the fluid pressure against the diaphragm 2U. is opposed by resilient means preferably such as 'will now be described. In the device shown in Figs. 1 to 6 the resilient means shown is in the form of a leaf spring preferably comprising two superimposed relatively wide thin leaves of spring steel 56 extending across the housing bcneath the carrier lever 46. The use of a plurality of thin leaves affords a high degree of ilexibility and resilient capacity. One end of the leaf spring bears upwardly against the overhanging end of the lug 5U and is positioned by a vertical screw 51 anchored in the lug 53 and engaged in an end slot 58 of the spring. The other end of the spring bears upwardly against the lower end of a Stop screw 59 screwed into the overhangingr end of the lug 4I. The spring` 55 is preferably normally bowed downwardly and at its mid-point bears downwardly against the upper end of the stud 54 so as to press the disk 53 downwardly against the diaphragm 20. A spacer washer 6D is preferably interposed between the spring 56 and the carrier lever 45.

The arrangement is such that, as the pressure in the chamber 2l increases, the disk 53 and carrier lever 46 are forced upwardly against the in- .creasing resistance of the spring 56 until the finger tips of the lever 4S reach that predetermined point above the fulcrum 40 where the liml of action of the springs 43 is above the fulcrum, at which point the clapper head 42 swings wardly with a snap action and drives the push rods 34 and movable switch contacts 21 into open switch position in the4 manner above described.

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It will be noted that this snap action cei This switch opening snap action occurs as the pressure in the chamber 2| increases to a predetermined degree dependent upon the degree of resistance offered by the leaf spring 56 which of course may be regulated by adjustment of the screw 59. Thereafter, as the pressure in the chamber 2| reduces, the carrier lever 46 and disk 53 move downwardly under the thrust of the leaf spring 56, until the tips of the fingers on the lever 46 reach that predetermined position below the fulcrum 40 where the line of action of the springs 43 has passed below the fulcrum 40, at which point the clapper head 42 swings downwardly with a snap action and the switches close in the manner above described. 'I'he degree of lower pressure in the chamber 2| at which this snap action occurs is of course also normally dependent on the position of adjustment of the screw 59.

It will thus be noted that degree of pressure at which the above described device functions to open the switch and the lower degree of pressure at which the device functions to close the switch may both be simultaneously raised or lowered by adjustment of the screw 59. It is highly desirable in many conditions of use that the difference between these switch-opening and switchclosing pressures, commonly' known as the differential, be also regulatable at will. In the device shown in Figs. 1 to 6 this is accomplished by the use of an adjustable spring arranged to oiTer increasing resistance against the action of the leaf spring 56 as the carrier lever 46 moves downwardly so as to vary the degree of pressure at which the switch-closing action occurs relative to the degree of pressure at which the switchopening action occurs and independently of the screw 59.

The spring shown for that purpose comprises a strip of springy steel 6| bent intermediate its ends with the bent portion 62 seated on the mounting plate I8. One end of the spring 6| is retained in position by an adjustment screw B3 extending therethrough and screwed into the plate I8, while the other end 64 extends upwardly against the leaf spring 555 and is bifurcated to straddle the stud 54. The arrangement is such that in the upper position of the lever 46 and Y leaf spring 56 the spring 6| offers little or no resistance to the downward thrust of spring 56 so that it has little or no eiect upon the degree of fluid pressure required to effect a switch-opening action, but during a downward movement of the lever 45 the spring 6| oil'ers a rapidly increasing resistance to the downward thrust of the spring 55, thereby causing the switch-closing action to occur at a uid pressure higher than would be required if the spring 6| were not present. The tension in the spring 6| may of course be regulated by adjustment of the screw 63 to thereby regulate the effect thereof on the spring 56 and thereby vary the degree of fluid pressure at which the switch-closing action will occur.

It will thus be noted that an automatic snap action mechanism has been provided for pressure switches and the like which comprises` an exceptionally small number of simple inexpensive parts arranged in an extremely compact manner i-n a housing of small size so as to leave ample space therein for convenient wiring, It will also be noted that by reason of the small lateral dimensions of the housing together with the central disposition of the nipple 22 coincident with the central axis of the housing, very little space is required to permit rotation of the housing and nipple while screwing the nipple into a iluid pressure outlet. This is highly desirable from an assembly standpoint.

A snap-action mechanism similar in many respects to that hereinabove described is shown in Figs. '7 to 12. It may be enclosed in an appropriate housing, such for instance as that shown in Figs. 1 and 2 and may be employed to operate a suitable switch mechanismlike that hereinabove described; although in this instance the mounting plate I8 thereof is shown attached to a casting I9 containing a fluid pressure chamber 2 covered by a diaphragm 20', and the head 32' of the clapper 38 is arranged to operate a remote switch or the like through a push rod 34' vertically arranged above the clapper head.

The clapper` 38 is substantially like the clapper hereinabove described having a knife edge 39 at one end engaged in the grooved horizontal edge 40' of the fulcrum lug 4| carried by the mounting plate I8', the clapper being actuated and controlled by a pair of tension springs 43 respectively engaged at one end with the clapper head 42' and at the other end with the tips of the fingers 38' of the carrier lever 46 in the manner hereinabove described.

In this instance the carrier lever 46 is rockably supported at one end by a` lug 65 struck up from the mounting plate I8', that end of the carrier lever 46 having a reduced extension 66 loosely projecting through the lug 65 to position the lever. I'he carrier lever 46 is also secured at a point midway of its ends to a suitable spring 56 which functions to yieldably retain the same in the lower position shown in Fig. 7.

In this instance the spring 56 comprises a small rod of spring steel bent into U-shape with the legs 61 thereof disposed at opposite sides of the lever 46' and projecting into openings provided in upstanding lugs 68 formed on the mounting plate I8. The loop end 69 of the spring 55' is engaged beneath a screw 59 adjustably threaded through the overhanging portion of the lug 4|. The means shown for securing the spring 56 to the lever 46' comprises a pair of clamp bars 10 respectively disposed above and below the lever and spring and bound together by suitable means such as a screw 55 extending therethrough and through the center of the lever 46'.

As in the device hereinabove described the carrier lever 46 is actuated and controlled by the fluid pressure in the chamber 2| through a disk 53 seated on the diaphragm 20 and carrying an upright thrust element 54. In this instance the element 54 is socketed to loosely receive the lower end of the screw 55', the screw 'being rockably engaged with the base of the socket so as to provide a flexible thrust transmitting connection between the disk 53 and the lever 46.

The clapper head 42 is limited in its downward movement by the lugs 65 and 68 and in its upward movement by an appropriate stop 1| attached to the upturned end 12 of a spacer plate 13 interposed between the mounting plate I8 and diaphragm 20. The spacer plate 13 is cut away to 'accommodate the disk 53'.

The device of Figs. 7 to 12 functions in a manner substantially similar to that of Figs, 1 to 6. As the Ipressure in the chamber 2| increases the disk 53 and carrier lever 46 are forced upwardly against the increasing resistance of' the spring 56 until the line of action of the springs 43' passes above the fulcrurn 40, at which point the springs 3' impart to the clapper head 62 a quick upward driving action against the push bar 34'; and as the pressure in the chamber 2 l thereafter reduces, the lever 55S' lowers under the thrust of the spring E5' until the line of action of the springs 3' passes below the fulcrum li, at which point the springs 4S' impart to the clapper head 42 a quiet: downward swing to its initial lower position.

As in the device rst above described, the degree of pressure at which the clapper head drives upwardly is always higher than the degree of pressure at which the clapper head drives downwardly, and both pressures at which these actions occur may simultaneously raised or lowered by adjustment of the screw 59 to thereby increase or decrease the tension in the spring 56. Provision is also made for varying the diierential or difference between the pressures at which these actions occur and in the device shown in Figs. 7 to i2 this is accomplished by means quite different from the means employed for the purpose in the device first above described.

In the device of Figs. 7 to l2 adjustment of ie differential is effected by adjusting the position assumed by the clapper head 4?. when at rest, the specific means shown for the purpose comprising a screw 'l5 carried by the clapper head 42 and arranged to engage a iXed stop element, such as the xed end extension G6 of the lever 46, when the clapper head 42' swings downwardly. By adjustment of the screw T5 the position of the clapper head 42 when in its lower rest position may be conveniently regulated.

, By way of explanation, it will of course be understood that the position of the line of action of the springs i3 is determined, not alone by the position of the tips of the fingers 38 on the carrier lever but also by the position of the clapper head so that a raising or lowering of a rest position or the clapper head, necessarily requires a change in the extent to which the nger tips of the carrier lever 4G must be moved in order to shift the line of action of the springs 1113 past the V Fulcrum 119i or dead center point. hereiore if, for example, the screwl 'l5 be adjusted so as to raise the clapper head 42 away from the lugs 65 and 68 when in its lower rest position, a shorter upward movement of the lever QG is required to shift the line of action of the past the dead center position than would be required if the clapper head 42 were seated in a lower position against the lugs 65 and And in view of this shorter movement an upward snap action of the clapper 42 will of course occur at a lower pressure in the chamhe 2E than would be required for a greater movement. Therefore by adjusting the screw 'l5 the degree oi pressure required to effect an upward snap action of the olapper head 42 may be regulated relative to and independently of the degree of pressurD at which the downward snap action will occur and also independently of the position of the screw 59.

Fig. i3 illustrates a modified means for adjusting the stroke of the clapper 38 in such manner as to vary the degree of pressure required to efiect a downward snap action of the clapper, wi rout arresting the higher degree o pressure required to effect an upward snap aotion of the olapper. The ieans shown for this purpose comprises a relatively stiff resilient strip of metal 'it fixed to the clapper 38 and having an elevated end portion 'i8 disposed to overlie the clapper head 42'. The end portion 18 of the strip is disposed to engage and operate the push rod 34', and it also cooperates with the stop 'H' to limit the upward stroke of the clapper head l2 and to position the latter in its upper rest position. A screw' 15', extending through the end portion T8 of the strip and in threaded engagement with the clapper head 42', is operable to regulate the position of the portion 18 toward and from the clapper head. When the screw 15' is rotated in such direction as to draw the portion 'I8 toward the clapper head, the latter assumes a relatively high position when the portion 'I8 engages the stop ll', but when the screw 15 is rotated in such direction as to withdraw the portion 18 from the clapper head, the latter assumes a somewhat lower position when the portion 10 engages the stop ll. In this way the upperrest position of the clapper head 42 maybe regulated to thereby regulate the fluid pressure required to effect a downward snap action of the cla-pper 38.

Various changes, may be made in either embodiment of the invention hereinabove specically described without departing vfrom or sacrificing the advantages of the invention as defined in the appended claims.

I claim:

l. In a pressure switch the combination of a housing, switch mechanism mounted in the top thereof, a ciapper having an end movable to actuate said switch mechanism, means in said housing providing a fulcrum for the other end oi said olapper, actuating means for said clapper, a carrier in said housing movable to shift the line of action of said actuating means from one side to the other of said iulcrum to thereby effect a snap action movement of said clapper, a laterally resilient spring supported at its ends and having an intermediate portion acting on said carrier to urge the latter in one direction, fluid pressure means at the base of said housing below said clapper for moving said carrier in the opposite direction against the resistance of said spring, said spring being disposed wholly within the bottom of said housing below said clapper.

2. In a fluid pressure switch a snap action mechanism therefor comprising the combination of a clapper having a switch-actuating movable end, means providing a fulcrum for the other end of said clapper, actuating means f or said clapper, a carrier movable to shift the line of action of said actuating means from one side to the other of said fulcrum to thereby effect a snap action movement of said clapper, a laterally resilient spring comprising a plurality of laterally resilient strands, said spring being supported at its ends and having an intermediate portion acting on said carrier to urge the latter in one direction, and fluid pressure means for moving said carrier in the opposite direction against the resistance of said spring, said spring and last named means being disposed below said clapper,

3. In a snap action mechanism for the operation of switches and the like the combination of a clapper having a. movable end, means providing a fulcrum for the other end of said clapper, a lever having a movable end disposed adjacent said fulcrum, tension means connected with the movable end of said lever and with the movable end of said clapper to actuate the latter, a leaf spring supported at its ends and having an intermediate portion acting on an intermediate portion of said lever to urge the same in one direction, said leaf spring being disposed below said clapper, and means acting on said lever to move the same against the resistance of said spring to thereby shift the line of action of said tension means from one side to the other of said fulcrlm and thereby eiect a snap action movement of said clapper. e

4. In a snap action mechanism for the operation of switches and the like the combination of a clapper having a movable end, means providing a fulcrum for the other end of said clapper, tension means connected with the movable end of said clapper for operating the same, a carrier movable to shift the line of action of said tension means from one side to the other of said fulcrum to thereby effect a snap action movement of said clapper, a laminated leaf spring urging said carrier to move in one direction, and other means for moving said carrier in the opposite direction, said spring and last named means being disposed below said clapper.

5. A snap action mechanism comprising the combination of a clapper having a movable end, means providing a fulcrum for the other end of said clapper, actuating means therefor, a carrier movable to shift the line of action of said actuating means from one side to the other of said fulcrum to thereby effect a snap action movement of said clapper, a laterally resilient spring supported at its ends and having an intermediate portion acting on said carrier to urge the same in one direction, and means for moving said carrier in the opposite direction against the resistance of said spring, said spring and last named means being disposed below said clapper.

6. A snap action mechanism comprising the combination of a clapper having a movable end, means providing a fulcrum for the other end thereof, actuating means connected to the movable end of said clapper, a carrier movable to shift the line of action of said actuating means from one side to the other of said fulcrum to thereby eilect a snap action movement of said clapper, means for moving said carrier in one direction, a laterally resilient spring supported at its ends below said clapper and having an intermediate portion acting on said carrier to resist the action of said last named means, and means for adjusting one end of said spring to thereby vary the resistance offered thereby,

'7. A snap action mechanism comprising a clapper having a movable end, means providing a fulcrum for the other end thereof, actuating means connected to the movable end of said clapper, a carrier movable to shift the line of action of said actuating means from one side to the other of said fulcrum to thereby effect a snap action movement of said clapper, pressure responsive means operable to shift said carrier in one direction to eiect snap action movement of said clapper in one direction at a, predetermined pressure, a laterally resilient spring supported at its ends and having an intermediate portion acting on said carrier to resist the action of said last named means and to eiect snap action movement of said clapper in the opposite direction f at a lower predetermined pressure, means for adjusting said spring to vary the pressures at which both of said snap actions occur, and additional means for modifying the eiect of said spring to vary the pressure at which one of said snap actions occurs.

8. A snap action mechanism comprising a clapper having a movable end portion, means providing a fulcrum for the other end portion thereof actuating means connected to the movable end portion of said clapper, a movable carrier operable to effect relative movement between said fulcrum and said actuating means to position the line of action of the latter on one side or the other of said fulcrum alternatively and thereby effect a snap action movement of said clapper in one direction or the other alternatively, pressure responsive means operable to move said carrier to effect snap action movement of said clapper in one direction at a predetermined pressure, resilient means opposing the action of said pressure responsive means and operable to effect a snap action movement of said clapper in an opposite direction at a lower predetermined pressure, and a leaf spring opposing the action of said resilient means and adjustable to vary the pressure at which one of said snap action movements occurs.

9. A snap action mechanism comprising a clapper having a movable end portion, means providing a fulcrum for the other end portion of said clapper, actuating means for said clapper, a carrier movable to effect relative movement .between said fulcrum and said actuating means so as to position the line of action of the latter on one side or the other of said fulcrum alternatively thereby to effect a snap action movement of said clapper in one direction or the other alternatively, means for moving said carrier in one direction to effect a snap action movement of said clapper at one point in one direction, resilient means opposing the action of said last named means and operable to effect a snap action movement of said clapper at another point in an opposite direction, and means adjustably mounted on said clapper for regulating the range of movement of said clapper to thereby vary the point at which one of said snap action movements occurs.

LYLE BEEMAN.

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