US2648732A - Hermetically sealed pressure switch - Google Patents

Description

1953 G; A. STARBIRD 2,648,732

HERMETICALLY SEALED PRESSURE SWITCH Filed April 16, 1951 INVENTOR. 1e 1; 6502654. STARE/R0 Patented Aug. 11 1953 HERMETICALLY SEALED PRESSURE SWITCH George A. Starbird, Agoura, Calif., assignor to Meletron Corporation, a. corporation of California Application April 16, 1951, Serial No. 221,259

3 Claims. 1

My invention relates generally to pressureresponsive switches, and more particularly to a pressure-responsive switch having the electrical contact elements located within a hermetically sealed chamber that is unaffected by variations in operating pressures so as to maintain optimum switching conditions.

Pressure-responsive switches are utilized in a wide variety or control systems, and have extensive application in high altitude aircraft to control motor driven mechanisms in accordance with a selected pressure relationship, as for example that existing between the cabin pressure and the reduced external pressure. Devices of this type include two major components, a pressure-operated actuator mechanism and an electrical contact switch of conventional design. In prior pressure-responsive switches, the electrical switch has been exposed to one or the other of the operating pressures, and as can be understood, may thus be subjected to a wide pressure variation.

As is well known in the electrical switch art, there is a direct relationship between the pressure and the dielectric strength of air. At reduced pressures there may be excessive arcing at the switch contacts causing pitting and a possible fire hazard. In addition, the moisture vapor of the air may be condensed upon a pressure or temperature change so as to collect around the switch contacts. This leads to further trouble such as insulation deterioration or fungus growth experienced under tropical conditions, and may render the switch completely inoperative. When it is further considered that many such switches are located in inaccessible positions on aircraft, it can be seen that expensive upkeep work may be necessitated unless the electrical switch contacts are properly protected. It can also be understood that a heavy and complex structure is highly undesirable in a device of this character and must be avoided particularly in aircraft installations.

It is therefore a major object of my invention to provide an improved pressure-responsive switch of light weight and durable construction which will overcome the aforementioned operational difficulties.

It is also an object of my invention to provide an improved pressure-responsive switch having the electrical switch located within a hermetically sealed chamber so as to be unaffected by changes in the operating pressures.

A further object of my invention is to provide an improved pressure-responsive switch which may be easily adjusted and accurately calibrated to maintain a predetermined operating relationship between two different pressure conditions.

It is another object of my invention to provide a switch of the character described having a hermetically sealed chamber adapted to be pressurized with an inert gas for maintaining the electric switch under optimum operating condi-- tions, unaffected by external moisture, dirt or other harmful substances.

A still further object of my invention is to provide a device of the character described having a light weight pressure-balanced housing construction which is capable of withstanding substantial pressure changes and yet remain sensitive to slight operating variations therein.

These and other objects and advantages of my invention will become apparent from the following detailed description of a preferred form thereof, and from an inspection of the accompanying drawings, in which:

Fig. 1 is an end elevation of a preferred embodiment of my improved pressure-responsive switch;

Fig. 2 is a vertical section taken along the longitudinal axis of the preferred device showing the operating plate in a position to actuate the switch button; and

Fig. 3 is a vertical section similar to Fig. 2 with the operating plate and switch button shown in a normal position.

Referring now to the drawings and particularly to Fig. 1 thereof, the numeral Hi indicates generally a cylindrical housing which encloses a preferred embodiment of my device. The housing ID includes a horizontally disposed rigid shell II which is closed by a flexible end wall or diaphragm I2 and a central flexible diaphragm l3 to define an inner chamber Id. An electrical switch l5, preferably of the miniature snap-acting type, is mounted within the chamber 14 and is provided with an operating lever or button l6 which faces the central diaphragm iii. The button i6 is movable towards or away from the switch i5 to open and close electrical contacts within the switch, and is normally spring-urged to an outwardly projecting position. As can be understood, with the button 18 in its normal position the electrical circuit through the switch [5 may be either open or closed, depending upon the desired construction of the latter.

At the opposite end of the shell H from the diaphragm i2 is a cap or rigid outwardly convex end wall I! which defines with the central diaphragm 13 a pressure chamber 58 that is adapted to be connected to a selected pressure source. Since the cap I! is rigid while the diaphragm i3 is flexible, it can be seen that pressure variations within the chamber [8 will tend to cause movement of the diaphragm along the axis of the housing It. This movement of the diaphragm E3 is utilized; to, actuate the switch button it for opening and closing the electrical contacts of the switch [5.

Likewise, it can be seen that since the flexible diaphragm i2 is exposed to the ambient; or ex; ternal pressure without the housing it, variations eration of the device is concerned, it is desired to control the operation of the switch: in f esponse to the pressure differential behyveen the ambient pressure and the pressure within the i v i tl'iep s'su'r'e t v'ithin' the chamber i i be unaffected by pressure variationsi'n either ofthe operating pressures. Td accomplish thisipend I provide linkingthe diap h ragms" i2 and; 13 together forunitar of parallel mevement; Thus the diaagrfrs i2 and l-3 operate in effect as a single hragm" wait and maintain a constant volume t the-c amber menumoving axially of the housing seer response to the pressure differ ential between the chamber and; the ambient pressure.

The shell H- is" formed as a th'iinwalled rigid member having a pair or annular internal shouldersZU andZ-l pressed therein to provide opposed satsfor the diaphragrns t2 and 53, respectively. Preferably the diaphragn'i's l2 and it are formed as flexible metal disks curted-concavely towards the chamber in opposed relationship, and having substantially equalareas to create a balanc'e'd'total pressure thereon. Fhe edges of the diaphragms l2 and it" are brazed or otherwise suitably secured to theshell: M to seal thechamb'e'l' t4; and the center portion or" each. diaphragm is supported by an expansible arcuate rim'portion 22 st). as to. befr-ee for av greater amount or movement along. the axis of the shell it. use. of theexpansible rim portion 22- permits a greater fiexure of the diaphragmcenterswithout exceeding the! elastic. limits of the diaphragm material. and henc'epriovide's for a moreacc'urate calibration of the device.

Extending; axially. through the chamber iii. is .a linking; means vsuchasa shaft25 which centrally connects thediaphragms l2 and. 3; for unitaryv orcparalll movement. To support the shaft 25' an;internally.threadediboss or. sleeve 26 is mounted:. on. the: diaphragm. threaded. socket; or cap. 21. is similarly. mountedo'nx the, diaphragm. l 3;-

within the sleeve Z'ii. and socket 2!v so asto lock the di'aphragms l2" and: I3; together. An operatingplate or circular-disk 3hisfixed-to theshaft 25: adjacent the switch l5 and extends radially a suflicient distance to engage the switch operating 2e aficsocket 2-1, the operating platec'e is moved At the same time it is desiredthat The l2 and an internally.

The shaft. 25; is provided. with: threaded. end: portions 253 which. engage.

. l-l and the chamber M is; evacuated and fill axially with respect to the operating button [6 Thus a simple means is provided for calibration of the device after assembly. After a proper adjustment of the device is obtained, the shaft 25 may be soldered or otherwise sealed within the sleeve 26. to fix the adjustment and prevent any pressure leakage across. the diaphragiinm.

In order to connect the chamber IS with an operating pressure source, the cap I! has a central opening 35 defined by an inturned flange 36. coupling boss 31 is welded within the flange 36 and projects outwardly for threaded engagement with the end of. a conduit 38 which leads from the se efc ted press is source. The outer edges of the cap ii are; ne'd to form a rim 39 which fits tightly within the end of the shell i l and is sealed into place by brazing or similar operation to seal the chamber 58 from external pressure As can be understood, since the cap member 17 is of rigid ens mcti n. he pr ssufew ibi the. chambe 8 W c Qnb" n he le ble pb ee i 13, and. he'mbvemfit of he'lat e i W ciirately tenet: the' pressure (inferential existing between the he' arnbient' pressure.

nted' upon one end of a Supports, a e s es s tei t the leads" 41- to clos'i the n i l 38. Above the fiangefiiii, a base 1 g 5,5} secure th-eis'h ell H to' projectupwar de s, ior'a able electricconnector 15 To com-plat tl assembly ensat on this-secure place; onthe base mastery fast -n us such as the bolts 5?. Preferably the c'onne 5 S:is

of the so -call ed AN type, and in any e v V be of typ'e'providing aherm'etic se betwec chamber 'M; and the outside of t e; shell H; B the' connecjtor and-the gasket- 5+ pr i d' pre sure seals into the chamberft-,- and there is littleor no possibility of; pre sure leakagetherein In the manufacture of i'i pto'veziswitch a capillary.connection58 is'passedthrou'gl'r the'sh withan inert as. Thch'oiceofa suitable inert gas andth'e' pressurization-of the chanrber M an be determined largely by c -he" anticipated-condi" tionsunder which the dev'i'ce is to be uses; Moderate pressurization will be suitable for-most uses, and will provide dielectric conditions such that therewill not be any arcing at the contacts of the switch I5 or any deteriorationof the. switch because of moisture condensation, fungus growth: or: other well-known d'ifiicu'lties.

In. operation; the pressure within the chamber M.-will be unaffected by variations in th op'erat ing pressures. The diaphragms l2 and mete. as a unitary. structuretbecause. of the provision of the. linking means 25;- and the volume of the: chamber. [141. remainscon'stant; In Fig} 2-I have illustrated. the condition underwhich the pressure within the chamber i3 is greaten than thatv of the ambient plxessurewithout the diaphragm I2. Under thiscondi'ti'or'r the pressure acting againstthe diaphragm- [3- overcomes; the eves sure acting against dia hragm l2; and both; diaphragms are flexedtowards" the right-hand" endof the housing lli, Th Shaft iifiinovesaxi 1y and the operating plate at pushes the switch" button [6 inwardly to set the switch contacts into either an on or ofi position. In Fig. 3 I have illustrated the condition under which the ambient pressure exceeds the pressure within the chamber I8. The diaphragms l2 and I3 are flexed to the left and the operating plate 38 moves therewith, to allow the switch operating button 16 to return to its normal outwardly projecting position, and causes the switch contacts to be set in the opposite position to that of Fig. 2,

In the foregoing I have shown and described a preferred embodiment of my invention which is simply and durably constructed and is fully capable of accomplishing the objects and advantages of the invention. However, many changes of design and construction will be apparent to those skilled in the art, and I do not wish to be limited to the details herein described, except as defined in the appended claims.

I claim:

1. A switch of the class described which includes: a rigid housing having an open end; an outer flexible diaphragm closing said housing and sealed therewith; an inner flexible diaphragm mounted within said housin parallel to said outer diaphragm and having an area substantially equal to that of said outer diaphragm, said inner diaphragm dividing said housing into a first sealed chamber closed by said inner and outer diaphragms and a second sealed chamber Icetween said inner diaphragm and the closed end of said housing, said second chamber being adapted to be connected to a selected fluid pressure source; a linking shaft disposed axially through said first chamber and extending outwardly through said outer diaphragm, said shaft being threadedly connected to said inner and outer diaphragms for axial adjustment therealong while holding said diaphragms spaced a constant distance apart for unitary parallel movement to maintain a substantially constant volume in said first chamber; switch means mounted in said first chamber and externally connectible through the wall of said housing, said switch means having an operating member operable to open and close switch contacts upon axial movement thereof; and a generally circular operating plate secured to said linking shaft adjacent said switch operating member to move said member in response to movement of said diaphragms, said plate rotating with said shaft as the latter is turned to adjust the axial position of said plate, whereby the operating range of said switch may be adjusted, and said plate at all times presents an area to said operating member.

2. A switch of the class described which includes: a rigid tubular housing; a rigid cap member sealed to one end of said housing and adapted to be connected to a selected fluid pressure source; an outer flexible diaphragm sealed at the other end of said housing and having an inwardly concave center portion capable of limited axial movement; an inner flexible diaphragm sealed across the interior of said housing to divide said housing into a first chamber closed by said diaphragms and a second chamber closed by said inner diaphragm and said cap member, said inner diaphragm being substantially equal in area to said first diaphragm and having an op posed concave center portion capable of limited axial movement; a linking shaft disposed axially through said first chamber and extending outwardly through said outer diaphragm, said shaft bein threadedly connected to said inner and outer diaphragms for axial adjustment therealong while holding said diaphragms spaced a constant distance apart for unitary parallel movement to maintain a substantially constant volume in said first chamber; switch means mounted in said first chamber and having an operating button facing one of said diaphragms and operable to open and close switch contacts upon axial movement thereof; a sealed external connector mounted in the wall of said first chamber and connected to said switch means; and a generally circular operating plate secured to said linking shaft for movement therewith and extending outwardly therefrom to engage said switch operating button and move said button in response to the movement of said diaphragms as the pressure difierential between the pressure of said second chamber and the ambient pressure changes, said plate being adjustable axially with respect to said button by external rotation of said shaft, and presenting an area to said button at all times regardless of the rotation of said shaft.

3. A switch of the class described which includes: a first chamber having a pair of movable walls at opposite ends thereof, said chamber being hermetically sealed; a second chamber adjacent said first chamber and closed by a rigid housing and one of the movable walls of said first chamber, said second chamber being adapted to be connected to a suitable fluid pressure source; an internally threaded socket centrally mounted on said one movable wall and opening into said first chamber; an internally threaded sleeve centrally mounted in the other of said movable walls; a threaded rod extending through said sleeve, through said first chamber, and into said socket, said rod being axially adjustable with respect to said movable walls by rotation of said rod, and holding said walls spaced a constant distance apart regardless of the axial position of said rod; switch means mounted in said first chamber and externally connectible through the wall of said first chamber; and a generally circular plate mounted on said rod for movement therewith, said plate at all times presenting an operating area to the actuating member of said switch means regardless of the rotation or axial position of said plate.

GEORGE A. STARBIRD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,480,495 Mejean et a1 Aug. 30, 1949 2,481,612 Nicholson Sept. 13, 1949 FOREIGN PATENTS Number Country Date 307,059 Germany Oct. 17, 1919

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