US2345276A

US2345276A - Thermoelectric safety device

Info

Publication number: US2345276A
Application number: US421855A
Authority: US
Inventors: Lourdes V Mccarty
Original assignee: Milwaukee Gas Specialty Co
Current assignee: Milwaukee Gas Specialty Co
Priority date: 1941-04-25
Filing date: 1941-12-06
Publication date: 1944-03-28
Anticipated expiration: 1961-03-28

Description

March 28, 1944. 1 v, MCCARTY THERMOELECTRIC SAFETY DEVICE original Filed Aprilvzs, 1941 2 Sheets-Sheet l /////1. lll

INVENTOR. Zaza/@56S 'LPMCQQ/ my l 124/10 IS Y www3/M114 V March 28, 1944.

L. V, MCCARTY THERMOELECTRIC SAFETY DEVICE Original Filed April 25 1941 2 sheets-sheet 2 Fotentec Mar, 28, 1944 UNITED STATES PATENT OFFICE THERMOELECTRIC SAFETY DEVICE Lourdes V. McCarty, Milwaukee, Wis., assigner to Milwaukee Gas Specialty Company, Milwaukee, Wis., a corporation of Wisconsin Original application April 25, 1941, Serial No.

390,247. Divided and this application December 6, 1941, Serial No. 421,855

i Claims.

This invention relates to thermoelectric safety devices for heating and other apparatus, and has particular relation to a thermoelectric safety shutoff valve.

The pnesent application is a division of my co pending application Serial No. 390,247, tiled April 25, 1941.

One of the main objects of the present invention is to provide an improved safety shutoff valve of the class described, and, more particularly, a safety shutoff valve having an improved form of valve actuator means, an improved form ci thermoelcctric generator energized holding means for the valve actuator means, and an improved form of reset means for resetting the valve to open or operating position and the armature of the thermoelectric generator energized holding means to attracted position.

Another object of the invention is to provide, in a device of the class described, structural improvements and improvements in the relation between the parts of the device to the end of permitting effective sealing of the electromagnet and armature within the electromagnet chamber and from the gaseous iuel, and to the further end of permitting' arrangement of the valve stem at an angle to the armature stem.

It is also an object of the invention to provide a device which is of simple and inexpensive construction, and a device composed of relatively few parts and adapted for convenient assembly and eiectively to accomplish the results set forth.

Further objects and advantages of the invention Will appear from the following detailed description taken in connection with the accompanying drawings, in which:

Figure 1 is a fragmentary and more or less diagrammatic view showing an embodiment of the invention in a pilot burner and main burner gas supply system;

Figure 2 is a vertical longitudinal section through the thermoelectric control and safety shutoff device shown in Figure l Figure 3 is a fragmentary vertical section taken on the line 3-3 of Figure 2; and

Figure 4 is a fragmentary vertical transverse section taken on the line 4 4 of Figure l.

Referring now to the drawings, in Figure 'i the burner l is any suitable or preferred main burner. It may be. the main burner for a room or space heater, or it may be the burner for a water heater, or for a iioor furnace, an oven burner, one or more top burners for a gas range, or any other burner. A fuel supply pipe il leads to the burner it for the delivery of gaseous or (Cl. libia-336) other fuel thereto-for example, through a mira ing chamber i2 to which air is admitted in the usual way, as wel] understood in the art.

interposed in the fuel supply pipe li is the thermoelectric control and safety shutoii device indicated in its entirety at l5 in Figure l. The device I5 is responsive to the pilot burner i6. It may also be responsive to a control device il' shown, for purposes of illustration in Figure i, as a thermostaticaliy actuated switch which, in the case of a hot water heater, may be subject to the temperature of the Water in the tank, or, in the case of a room or space heater or floor furnace, may be mounted in appropriate position within the room or other space heatedL by the burner ID. Instead of being in the form of a thermostatically actuated switch, the control device il may be of a character to operate, for example, upon the occurrence of an abnormal pressure in the tank of a hot water heater, or upon the occurrence of any other abnormal, defective or insufficient functioning of the apparatus. The room or space or portion of the apparatus or system to the tem perature or other condition of which the control device Il is subject is indicated more or less dia grammatically by dgt and dash iines i8 in Figure l.

The pilot burner IE, which is located in juxtaposition to the main burner lll to maintain a pilot iiame for igniting the main burner, is supplied with gaseous fuel by a pilot supply pipe i9 which is shown as leading from the housing or case of the thermoelectric control and safety shutoi device I5. This may vary within the scope ci the present invention.

Referring now in detail to the thermoelectrlc control and safety shutoff device i5, the housing or case 22 for this device has an inletat 23 and an. outlet at 24. The inlet 22 opens into the interior of the housing, and a partition or wall 5 separates the interior of the housing from the outlet 24. The partition 'i5 has an opening into which is threaded a retaining ring 26 which secures a valve seat member 2l in place. The valve seat member 2 deiines amopening 2t for placing the interior of the housing 22 in communication with the outlet 24. The upper end of the valve seat member 2i is provided with an annular valve seat 29 upon which the shut-oir valve disc 30 is adapted to seat to shut oi' the supply of fuel l to the burner I. A gasket may be provided at 3 i.

Contiguous sections of the fuel supply pipe il are connected to the inlet at 23 and to the outlet at 2i as shown in Figure i. A cover 34 is removably secured upon and closes the top of the housing 22. The cover 34 is shown as secured to the housing 22 by screws 35, and a cover gasket may be provided at 36.

The electromagnetic operator for the valve or controlling member, and the valve, valve lever, and energy storing means constitute a unitary assembly which is carried by the cover 34, preferably resiliently, as will hereinafter appear. This assembly is enclosed within the housing 22 when the cover 34 is applied, and is removable from the housing by removing the cover.

The electromagnetic operator includes an electromagnet consisting of a magnet frame 40 shown as of generally U-shaped form, although this may vary. The coil 4I is shown as wound around one leg of the magnet frame, and the end of the other leg of the magnet frame is shown as turned at v42 to position generally parallel to the armature 43 to present a relatively large pole face to the armature.

The ends of the magnet frame 40 extend through openings in a sealing plate 44, the margin of which is turned or flanged laterally to receive a sealing cover 45 between which and the plate 44 the pole faces of the magnet frame 40, the armature 43, and the energy storing means are enclosed and sealed. The armature 43 is hinged by hinge means 48 to a spacer 50 fixed to or integral with the sealing plate 44. The hinge means 48 hinges the armature 43 in position adjacent the pole faces of the magnet frame, and the hinge means 48 is preferably of spring character to maintain the armature in the desired position. The cover 45 is removably secured to the sealing plate, for example by screw 52, and the cover, when in place, may limit movement of the armature away from the electromagnet.

The magnet frame 40 is mounted on and carried by a mounting plate 56 which has a downturned lug 51 positioned against the back of the downturned end 42 of the magnet frame. Screws (not shown) secure the-sealing plate 44 to the downturned lug 51 on the mounting plate 56. A sealing gasket is preferably provided at 59.

The armature 43 and the downturned end 42 of the magnet frame have registering openings 62. A plunger 63, movable endwise in these openings, is secured to the center of a flexible diaphragm 64 by a diaphragm pin 65. The diaphragm 64 is clamped in place to the back of the downturned lug 51 on the mounting plate 56 by a retaining plate 66 which may be secured in place by screws and cooperating nuts (not shown), or otherwise as desired. The retaining plate 66 and the downturned lug 51 on the mounting plate 56 have registering openings, and the diaphragm 64 seals the space between the sealing plate 44 and the cover 45 against the entry of deleterious matter through the openings 62.

A valve or controlling member operating lever is hinged at 'l2 by a pair of hinge springs 13 to lugs on the sealing plate 44 at opposite sides of the lever, or to lugs on a mounting plate secured in place with the sealing plate. The opposite ends of the hinge springs 13 are secured, for example, to lateral lugs (not shown) on the operating lever 1D. The lever 10 has a lug 16 offset upwardly therefrom, and the valve disc member 3U or controlling member is secured to this lug 16 by a valve disc screw 18. The reduced outer end of the lug i6 engages in a slot 19 in the downturned lug 89 on the mounting plate 56.

Engagement of the reduced outer end of the lug 16 with the lug 80 at thebottom of the slot i9 serves to prevent undue separation of the valve 7.5

disc 30 from the mounting plate 56 and electromagnetic operator assembly, particularly when the assembly is removed from the housing 22.

At its opposite end the lever 1U is provided centrally between its opposite sides with a downwardly offset lug 82 having a pointed end for engagement at 83 with the adjacent end of the diaphragm pin 65. The lever 10, being hinged or fulcrumed close to the pointed engagement at 83 with the plunger 63, provides for imparting relatively great movement to the valve disc 30 with relatively slight movement of the plunger 63. IThe mounting plate 56 has an opening 65, and a relatively light coiled spring 66 is disposed toextend through this opening and between the magnet frame 49 and the lever 10 for returning the valve disc 30 to closed position upon deepergization of the electromagnet. The thermoelectric control and safety shutoff device is preferably positioned vertically in use, as shown in Figures 1 and 2, in which case I contemplate returning the valve disc 30 to closed position by gravity and without the use of a spring, such as the spring 86, or by gravity in conjunction with the spring 86, or otherwise as desired. A circular raised portion 81 on the lever 10 engages in the lower end convolution of the spring 86 for holding the lower end of the spring in place and against lateral displacement.

It will be noted that the gas pressure within the housing 22 acting upon the top of the valve disc 30 holds the valve disc to its seat 29. When the valve is closed it requires the greatest force to lift it or move it from its seat 29, and as the valve disc 39 is lifted or moved away from its seat, the drop in pressure across the valve cause a rapid drop in the force required to continue movement of the valve disc 30 to full open position.

The energy storing means is shown as comprising a pair of flat leaf springs su and 92 normally disposed in substantially parallel relation. The upper ends of these leaf springs 9u and 92 are attached to the armature 43, for example, by a screw 93 threaded into an armature bushing 94, which bushing 94 in turn is suitably secured or fixed to the armature 43. Spacers are provided at 95, one between the armature 43 and the spring and the other between the spring 90 and the spring 92. A retaining clamp 96 is provided between the spring 92 and the head of the screw 93.

An adjusting pressure screwr 98, threaded through the spring 90 near its lower end, has endwise engagement with the plunger 63 preferably extending into an axial opening in .the plunger as shown in Figure 2. A second adjusting pressure screw |66 is threaded through the spring 92 near its lower end, and the pointed inner end of the screw |00 is adapted to engage or contact the spring 99 after initial tensioning of the spring 90, as will presently appear. In that the spring 99 alone is tensioned in the initial movement of the armature from retracted to attracted position, the pointed inner end of the screw |00 is normally spaced from or out of contact with the spring 90, as shown more or less diagrammatically in Figure 2, The screws 98 and 409 are adjustable to adjust the action of the device and may be locked in adjusted positions as desired, tension clamps being indicated more or less diagrammatically at 92 and i133 respectively. The spring 92 has an opening 94 which operates over the head of the screw 96 to permit movement of the spring 92 toward 'the spring and free of the spring 99 in the initial movement of the armature to attracted position,

By reference to Figure 3 it will be seen that the pilot valve member 200, which is adapted to shut off or control the supply of fuel to the pilot burner, is urged toward its seat and toward a closed position by a coiled spring 201. The valve member 200 will be in open position only when the pilot light is burning, and, when in open position, the fuel for the pilot burner passes from the housing 22 through an opening 202, and thence through the opening defined by the valve seat member and through openings 203 and an outlet 204 into the pilot supply pipe 19 leading to the pilot burner 16.

The cover 34 has a boss provided with a bore 206. A magnet support 201 and a lever support 208 are clamped in place in the inner end of the bore 206 by a generally cup-shaped member 210 threaded at its inner end into the outer end of the bore 206. A flexible diaphragm 212 clamped in place marginally between the members 201 L and 208 carries an actuator element in the form of a diaphragm pin 214. A dowel pin may be provided at 215. A lever 216 is fulcrumed at 211 on the lever support 208 and has one end positioned to be actuated by the diaphragm pin 214, and its other end is positioned to actuate the plunger or stem 220 for the valve member 200.

An electromagnet is housed within the member 210 and comprises a magnet frame 221, shown of generally U-shaped form, and an energizing The magnet frame 22| is attached by a coil 222. sleeve member 223 to the center of the raised bottom portion f the magnet support 201. An armature stem 224 passes slidingly through the sleeve 223, and has an armature mounted on its outer end preferably for relative movement on the stem 224 so that the armature may accommodate itself to the pole faces of the magnet frame when in attracted position. The inner end of the armature stem 224 contacts the diaphragm 2 I 4,

A flexible diaphragm 230 is secured marginally in the outer end of the member 210 by a retainer ring 232, and a reset button 234 ls secured at 235 to the center of the diaphragm 230. The reset button projects slidingly through an opening 236 in the outer end of the member 210. When the button 234 is engaged by the nger and pressed inwardly, it moves the armature 226 to attracted position, and the accompanying inward movement of the stem 224 swings the lever 216 in a clockwise direction about its fulcrum 211, the engagement of the lever 216 with the valve stem 220 moving the valve 200 to open position against the action of the spring 201 as the reset button is pressed inwardly.

For purposes of illustration, the thermoelectric generator, which is energized by the heat of the pilot flame for supplying thermoelectric current to the thermoelectric operating circuit for energizing the electromagnet for the main burner valve aswell as the electromagnet for the pilot burner valve, is shown more or less diagrammatically as a thermopile comprising a plurality of therrnocouples-three being shown-connected in series. This, of course, may vary within the scope of the present invention, any thermoelectric generator which will generate the required thermoelectric current being contempated within the'scope of the appended claims.

Suiiice it for purposes of the present application to state that each of the three thermocouples of the thermoelectric generator 1 I5 comprises the usual or any suitable elements 116 and 111 of different thermoelectric characteristics, each pair of said elements being joined at 118 to provide the hot junctions which are placed in position to be heated by the pilot flame as long as the pilot iiame is burning. Any other suitable thermoelectric or electric generator may be employed.

The lead conductors for the thermoelectric generator may be of the type more fully disclosed in Oscar J. Leins Patent No. 2,126,564, granted August 9, 1938, or the construction of the thermoelectric leads may be of any other suitable or preferred form.

For the purpose of this description suflice it to state that the thermoelectric lead conductors may comprise, as shown fragmentarily in Figure 4, an inner lead conductor and an outer tubular lead conductor 126 surrounding the inner lead conductor, The inner lead conductor is insulated from the outer lead conductor, for instance, by a wrapping of insulation 121 on the inner'lead conductor. One terminal of the thermoelectric generator is shown more or less diagrammatically as connected to the outer tubular lead conductor 126. The other terminal of the thermoelectric generator is shown as connected at 130 to the inner lead conductor 125.

A quick detachable or removable connection is preferably provided between the electromagnet for the main Valve of the thermolectric control and safety shutoff device and the ends of the

leads

125 and 126 opposite the ends which are connected to the thermoelectric generator. This removable lead connection may be of the form disclosed in the copending application of Richard K. Engholdt, Serial No. 328,923, filed April l0, i940. Sufhce it, for purposes of this description, to state that the inner lead 125 has a connector cone 128 which seats in the correspondingly recessed outer end of the terminal tip 130, and is clamped in contact therewith by a connector sleeve 132. The adjacent end of the outer tubular lead conductor 126 is grounded to the cover 34 of the housing through a bushing 133 and the connector sleeve 132 to the internally threaded boss 134 on the cover 34.

One end of the coil 41 (Figure 2) is secured to the under side of the cover 34 lby a binding screw 140, and thereby is grounded to the cover and thus connected to the outer lead conductor 126. The other end 142 of the coil 41 is connected to a terminal post 143 fixed in a boss 144 on the cover 34 and insulated therefrom by a terminal bushing 145". The terminal tip 130, which is insulated from the cover by an insulator bushing 148, is connected in circuit with a second terminal post by a connector strip |52. An insulator strip is provided at 153 (Figure 4) The terminal post 150 is fixed in a boss 155 on the cover 34 and is insulated therefrom by a terminal insulator 156. An insulating terminal'board 158 is mounted across the tops of the bosses 144 and 155, suitable washers being provided at 159, and the upper ends of the terminal posts l43 and 150 being peened over or otherwise formed to secure the terminal board in place.

Where a thermostat or other condition responsive device is employed as indicated at 11 in Figure l, the

leads

162 and 163 for this device are connected to the terminal .posts 143 and 150 by suitable binding screws 165. The thermostat or other condition responsive device 11 is thus placed in series circuit relation with the thermoelectric generator and the coil 41 of the electromagnet for the main valve.

To secure accurate positioning of the valve disc 30 or other controlling member with respect to the valve seat 29 or cooperating part, and independently, for example, of the attachment of the cover 34 to thehousing 22, I provide a resilient mounting for the electromagnetic operator assembly. This resilient mounting comprises vertically elongated screws or posts having their heads disposed beneath the vmounting plate S and their shanks extending up relatively loosely through openings in the mounting. plate. The upper ends of the screws or posts H5 have threaded engagement (not shown) with the cover 341, and springs H8 are coiled about the respective posts and interposed between the cover B and the mounting plate 56. When the cover 34 is applied, the electromagnetic operatoris positioned Within the housing 22 and the mounting plate 5S seats upon horizontal `seating surfaces one of which is indicated at la@ in the interior of the housing 22, thus assuring accurate positioning of the valve disc with respect to its valve seat 29. The cover 36 may be clamped in place, and any improper lt of the cover or non-conformity in the clamping of the same in place will not disturb the proper positioning of the valve disc 3G. screws or posts H5 are spaced below the mounting plate 56 and are positioned in recesses i8? 'in the housing 22.

The magnet frames and armatures are preferably formed of an alloy of relatively low magnetic' reluctance, and the operating circuit for the de vice is preferably of low resistance characteristics.

The energizing coil 222 for the pilot valve electromagnet is preferably connected in parallel circuit relation with the electromagnet for opening the main valve and for holding same open. This permits the thermostat or other condition responsive device at Il, for example, to operate to deenergize the electromagnet for the main valve without deenergizing the electromagnet for the pilot valve. When the pilot light is extinguished, both the main valve and the pilot valve operate to closed position. The spring closes the valve 20|) when the electromagnetther'efor is deenergized, and through the stem or plunger 220, lever ZIB, diaphragm pin 2m, and armature stem 224 moves the armature to retracted position and the reset button to its outwardly projected position as shown in Figure 3. When the reset lbutton is pressed inwardly in resetting or cooking the device, the armature is moved to attracted position, and assuming that the electromagnet for the pilot valve is sufliciently energized by the heat of the pilot ame on the thermoelectric generator, the armature will be held magnetically in attracted position, thus holding the pilot valve open as long as the pilot light is burning.

As thus described, the pilot generator shown, for example, at l le inl Figure l, supplies the thermoelectric current for energizing the electromagnet for the .pilot valve as well as the thermoelectric current for energizing the electromagnet for the main valve.

The operation of the device is as follows:

Assume that the pilot light is lighted and heating the "hot" junctions H8 of the thermoelectric generator to supply the operating thermoelectric current to the circuit for energizing the two electromagnets, and that the thermostat or other condition responsive device at l1 lias operated to open or disable the thermoelectric circuit to deenergize the electromagnet foi` the main burner verve. The armature llt is then positioned in re The heads and the lower ends of the' tracted position with an air gap between it and the magnet -frame by the screw 98 and plunger 63 pushing against the diaphragm pin 65 and point 83 on the valve lever 10, the armature and energy storing springs and 92 being positioned substantially as shown -in Figure 2. The main valve disc 30 will be closed upon its seat 29 to shut oi the supply of fuel to the main burner, and will be held closed by the pressure of the gas within the housing 22.

Now, when the thermostat or other condition responsive device il operates to close or enable the thermoelectric circuit for the electromagnet for the main burner valve, the heat oi the pilot flame on the thermoelectric generator will supply thermoelectric current for energizing the main burner valve electromagnet.

When this electromagnet is energized the armature i3 is pulled toward the pole faces of the magnet frame by the magnetic attraction. The lower end of the energy storing spring 90 is held against following the armature by engagement of the adjusting pressure screw 98' with the plunger 53 which, in turn, is prevented from moving by the gas pressure acting on the valve disc S6, said valve disc being operatively connected to lthe spring 9@ by means of the adjusting screw 98, plunger S3, fulcrum 83, pivot point l2, and lever lt. As a result, the spring t@ is tensioned by a scissors-like action or separation of the lower end of the armature it from the lower end of the spring 9b.

The lower end of the second spring 92 being free, follows the movement of the armature 53 without tensioning of the second spring in the initial movement of the armature to attracted position. As the armature i3 moves toward the pole faces of the magnet frame and after initial tensioning of the spring lill,r the pressure adjusting screw lil, carried by the spring 92 contacts the spring 9B. Further movement of the armature 43 toward attracted position thereupon further tensions the spring 99 and, at the same time, tensions or stores up energy in the second spring 92. At the time when the movement of the armature i3 to attracted position is tensioning only the spring 90, the magnetic attraction is least, and when the movement of the armature is tensioning both springs 9G and 92, the armature is closer to the magnet frame and the magnetic attraction is greater. The tension in the leaf springs 9G and 92 is built up or energy is stored until the combined tension or energy in both springs is sufcient to lift or open the valve discSll against the gas pressure, whereupon the stored energy operates to open the valve quickly and effectively to set up the supply of fuel to the burner l0. As the valve disc 30 begins to lift or open, the pressure across it drops and leaf spring t continues to lift the valve andmoves away from the spring .Q2-that is, the point of the pressure screw lil@ loses contact with the spring 9D.

The position of the armature G3 when the valve disc 3D is being lifted depends upon the gas pressure across the disc-that is, the greater the gas pressure the further the armature moves toward the pole faces of the magnet frame before the valve disc begins to open. The force or energy in the leaf springs 9@ and 92 must exceed the combined force of the gas pressure and other counteracting forces before the valve disc 30 can be opened. It should be borne in mind that neither spring 90 nor S2 is stressed when the valve disc 30 is in the closed position-that is, The spring @t is slightly on the valve seat.

stressed when the valve disc is in the open position. This is caused by the pressure drop across the valve, the weight of the valve, and the force of spring 86. However, spring 92 is not tensioned at this time because the point of the screw is not in contact with the spring 90. The energy storing means presents to the armature in all positions thereof in its movement to attracted positiony a resistance less than the magnetic attraction between the electromagnet and the armature at the corresponding position of the armature, and therefore the energy storing means does not prevent or obstruct movement of the armature to attracted position.

From the foregoing it will be apparent that as long as the thermoelectric generator is heated by the pilot flame, the main valve will be opened and closed automatically by the condition responsive or equivalent means.

If, for any reason, the pilot burner is extinguished with the thermostatic or other condition responsive switch at I1 closed, the resulting discontinuance of the thermoelectric current results in deenergization not only ofthe electromagnet for the pilot burner valve but deenere gization of the electromagnet for the main burner valve. The armatures are thereupon actuated to retracted position, which results in closing of the'main burner valve and pilot burner valve completely to shut off the supply of fuel. When the pilot burner is reignited, the heat of the pilot flame will energize the electromagnet for the main burner valve whereupon, assuming that the thermoelectric circuit for this valve is closed, the valve will be automatically operated to open position in the manner already described. The pilot burner valve selected for illustration requires manual resetting of the same to open position, Ibut the use of a pilot burner valve which will open automatically is contemplated.

I have determined, by experiment, that in one preferred embodiment of the invention the ratio of the air gap with the armature in retracted position to the'length' of air gap with the armature in attracted position is preferably approximately over three times the ratio of pull with the armature in attracted position to the pull with the armature in retracted position.

The embodiment of the invention shown in the drawings is for illustrative purposes only, and it is to be expressly understood that said drawings and the accompanying specification are not to be construed as a definition of the limits or scope of the invention, reference being had to the appended claims for that purpose.

I claim: I

l. In a device of the character described, a'

phragm, and an armature attached to said stem, the latter cooperating with said diaphragm for flexing said diaphragm downward when said armature is attracted by said electromagnet and said dished support accommodating upward flexing of said diaphragm when said armature is in retracted position away from said electromagnet.

2. In a device of the character described, a

housing having its lower wall dished upward providing a substantially rigid support spaced inward from the periphery of said lower wall, a flexible diaphragm extending across the lower end of said housing providing a fluid tight seal therefor and disposed beneath said support for upward flexure thereinto, an electromagnet comprising a U-shaped frame disposed with its bight portion seating on said support, a. sleeve member securing said frame to said support, a stem slidable through said sleeve disposed in said housing and entirely above said diaphragm, and an armature attached to said stem above said electromagnet, said stern cooperating with said diaphragm for flexing said diaphragm downward when said armature is attracted by said electromagnet and said dished support accommodating upward flexing of said diaphragm when said armature is in retracted position away from said electromagnet.

3. In a device of the character described, a housing having its lower wall dished upward providing a substantially rigid support spaced inward from the periphery of said lower wall, a flexible diaphragm extending across the lower end of said housing providing a iluid tight seal therefor and disposed beneath said support for upward ilcxure thereinto, an electromagnet mounted on said support within said housing, a stem mounted in said housing i'or rectilinear movement disposed entirely above said diaphragm, an armature attached to said stem, the latter cooperating with said diaphragm for ilexing said diaphragm downward when said armature is attracted by said electromagnet and said dished support accommodating upward flexing of said diaphragm when said armature is in retracted position away from said electromagnet, a second flexible diaphragm extending across the upper end of said housing providing a fluid tight seal therefor, and a reset button secured to said second diaphragm and guided in the upper end of said housing for resetting said armature to attracted position by pressing downwardly on said button.

4. In a device of the character described, a housing having its lower wall dished upward providing a substantially rigid support spaced inward from, the periphery of said lower wall, an

.electromagnet comprising a U-shaped frame disposed with its bight portion seating on said support, a sleeve member securing said frame to said support, a stem slidable through said sleeve, and an armature attached to said stem above said electromagnet to be held in attracted position thereby.

LGURDES V. MCCARTY.