US2452221A

US2452221A - Fluid blast arc extinguishing circuit breaker

Info

Publication number: US2452221A
Application number: US612777A
Authority: US
Inventors: Arnold E Brock
Original assignee: PACIFIC ELECTRIC Manufacturing CORP
Current assignee: PACIFIC ELECTRIC Manufacturing CORP
Priority date: 1945-08-27
Filing date: 1945-08-27
Publication date: 1948-10-26
Anticipated expiration: 1965-10-26

Description

A. E. BROCK FLUID BLAST ARC EXTINGUISHING CIRCUIT B REAKR Filed Aug. 27, 1945 'Y oct. 26, 194s.

INVENTOR. ARNOLD EBRO cx. BY

Patented Oct. 26, 1.948

'UNITED STATELS PATENT OFFICE FLUID BLAST ARC EXTINGUISHING CXRCUIT BREAKER fornia Application August 2'?, 1945, Serial N0. 612,777

(Cl. 20S-148) 7 Claims. l

My present invention relates to high voltage circuit breakers, and more particularly to an improved means by which an arc drawn between the circuit controlling contacts of the circuit breaker may be effectively interrupted, irrespective of its current value, by a blast of air or other arc extinguishing fluid and it has for its object to provide an improved are extinguishing means for circuit breakers of the iiuid blast type by which an arc established between the circuit interrupting contacts of the circuit breaker may be effectively and eiciently extinguished, irrespective of its current value, with a minimum of arc extinguishing uid.

Another object of the invention is to provide an improvement in circuit breakers of the iiuid blast typewhich will prevent the building up of a back pressure by the generation of gases in an arc at the point of contact separation.

Another object of the invention is to provide i? an arc extinguishing device for use with the circuit controlling contacts of a fluid blast circuit breaker in which means are provided for the venting of any excessive gas pressure that might interfere with the extinction of an arc therebetween at the time of circuit interruption.

A further object of the invention is to provide a new and novel contact arrangement for circuit breakers of. the axial blast arc extinguishing type in which one of the contacts is provided with a pressure responsive by-pass or valve means that will operate in the event of a sustained arc to relieve any excessive pressure caused by arc generated gases and permit a substantially normal flow of arc extinguishing iluid through the arc at the time of circuit interruption.

Other objects and advantages of the invention will be evident to those skilled in the art, and pointed out hereinafter in the following description taken in connection with the accompanying drawing, wherein there is shown by way of illustration and not of limitation preferred embodiments of my invention.

In the drawing;

Figure 1 is a fragmentary vertical elevation showing my invention as applied to a circuit breaker of the type employing the so-called axial blast principle for the extinction of any arc established between its contacts upon circuit interruption,

Figure 2 `is a'fragmentar-y sectional view taken along'line II-'II of Figure 1, looking in direction of arrows,

Figure 3 is a similar fragmentary sectional View taken along line III-III of Figure 1,

Figure l is a fragmentary sectional view showing a modified form or the invention as applied to a circuit breaker of the type employing the socalled transverse blast principle for `the extinction ci any arc established between the contacts thereof, and

Figure 5 is a fragmentary sectional view taken along line V-V of Figure 4, looking in direction ci arrows.

rEhe use of a blast of air or other fluid as an arc extinguishing medium in circuit breakershas long been considered, but up to the present time no satisfactory arrangement has been found that will operate successfully under all the various current values at which interruption of a circuit may be necessary. This is believed to be due to the fact that once the circuit breaker has been designed, the physical dimensions of the chamber surrounding the zone of arc interruption become fixed, while at the same time the current values of the arc to be extinguished may vary greatly. in other words, in the prior arrangements the blasts of arc extinguishing fluid employed operate in a substantially uniform manner under all conditions and do not take into account the possible variations in the current values of the arc. As a result, at low current values the blastvof arc extinguishing iuid or air is only slightly heated and there is, therefore, establisheda low pressure area behind the point of arcing between the separating contacts, which hinders arc interruption. This low pressure area also tends to promote-a restriklng of the arc, due to the fact that it does not permit the building up of suiilcient dielectric effect within the blast of arc extinguishing fluid to extinguish the arc. Similarly, when an arc or" high current value is interrupted, the arc extinguishing gases are heated to a higher temperature and expand to such an extent that there is orten established a reversal of now of arc extinguishing gases between the separating contacts. This retards the biast of arc extinguishing iiuid and results in a high ionisation thereof which likewise prevents arc extinction andthe ultimate interruption of the circuit.

in view of the above, it `has been necessary in the past to compromise between the different op erating conditions that result from the interruption of a circuit at diilerent current values. In this direction two methods have been used. The rst has been to provide a large volume biast passageway in which the arc is drawn, and the second has been to conne the arc in a restricted chamber having a relatively narrow passageway and provide a large exhaust outlet at or immediately beyond the point of arcing. The first of these methods requires the use of excessive quantities of arc extinguishing fluid, and while the latter meth-od is more economical in the use of the arc extinguishing fluid and has met with some success, it is still open to the objection that a blocking pressure is often built up within the restricted passageway at the point of contact separation that seriously interferes with the free new of the arc extinguishing fluid through the passageway, which tends to decrease the ecency oi the circuit breaker and lower its maximum current interrupting capacity.

In accordance with the present invention, I provide an arc extinguishing arrangement in which the establishment of such a blocking pressure by the arc generated gases is avoided, and in which a blast of arc extinguishing fiuid, having a substantially constant pressure and velocity, may be used at all times regardless of the current value at the time of the circuit interruption. This enables the use of a small volume of the arc extinguishing fluid and also avoids the need for a compromise in performance to meet different conditions oi current value at the time of circuit interruption. This operation, with a constant pressure and velocity, regardless of current value at the time of interruption, is ob-ained in accoi-dance with the preferred embodiment of the invention by providing a fluid blast passageway which is expandable, or in which the velocity and/ or volume of are extinguishing fluid flowing therethrough may vary in response to gas pressures that may result from temperature changes caused by the arc between the separating contacts during circuit interruption.k It has been found to be a fact that the interrupting capacity of circuit breakers employing an arc extinguishing fluid blast for interrupting an arc between its contacts is limited by any condition that will permit the generation of excessive heat in an arc drawn between its separating contacts, which will result in a reverse flow of the arc extinguishing fluid through its arc extinguishing chamber. This is true even though the reversal of ilow of the arc extinguishing iiuid may be only temporary, and often the interrupting capacity or" the circuit breaker is limited to a value far below the maximum rated capacity thereof. This is explained by the fact that any reversal of flow or blocking pressure that will interfere with the normal blast of the arc extinguishing iiuid through the arc will prevent a proper cooling of the highly ionized gases that are generated in any arc drawn between the separating contacts when a circuit is being interrupted.

In the accompanying drawing, I have shown preferred arrangements, wherein the circuit controlling contacts of a circuit breaker are disposed in arc extinguishing chambers that are provided with pressure responsive or valved relief outlets through which the fluid blast and/or arc generated gas pressure may escape from the zone of arcing and thus prevent the building up of any blocking pressure within the contact enclosing chamber, which might interfere with a normal flow of the arc extinguishing fluid between the separating contacts.

In Figures 1, 2 and 3 of the drawing there is shown, in detail, an embodiment of the invention as applied to a circuit breaker of the so-called axial blast type. In circuit breakers of the axial iiow uid blast type the arc extinguishing luid introduced either through one of the contacts to the arcing space formed therebetween upon contact separation, or the arc extinguishing fluid is charged into a chamber surrounding the separable contacts, so that when the contacts separate, this arc extinguishing fluid may exhaust under pressure axially outward through one of the contacts. The device here shown is of this latter type and, in its preferred form, it contemplates the employment of a substantially cylindrical stationary Contact Ii? with which an axially movable contact II cooperates. The stationary contact III has a truncated conical contact surface I 2 at its inner end with which a conical contact surface I3, formed upon the contact I I, cooperates. In this way there is provided a restricted throat Ill at the inner end of the contact Iii through which an arc extinguishing fluid may discharge outwardly through the stationary Contact Id. As here shown, the contacts i!) and II are enclosed within a fluid pressure containing,- chamber I5 that is formed thereabout by a tubular member It which carries suitable end closure members II. Only one of the end forming members II is here shown, but it will be understood that a similar end closure member I'I, at the lower end of the chamber I5, will be provided with a packing or stuihng box through which the operating rod or shank of the movable contactl il may move in a sealed manner. The stationary contact I0 is mounted within the chamber I5 and is secured to the closure member I' by means of an externally threaded bushing I8 that has a somewhat larger discharge conduit located in alignment with the restricted throat lli at the inner end of the contact I0. This bushing I8 extends through the end closure member il and is secured by means of a threaded conduit forming member i9 which may lead tothe atmosphere or to a suitable flame and sound quenching muiiler. Within the central opening through the cylindrical stationary contact Iii, and also in register with the restricted throat I4 at the inner end thereof, there is an annular valve-like member 20 which has a somewhat more restricted throat-like aperture 2 I through which, under normal operating conditions, the blast of arc extinguishing fluid will be discharged. This annular valve-like member 2i? is supported for axial movement, with respect to the restricted throat I4, by means of a cage-like support 22 which, as is more clearly shown in Figure 2, has radial arms 23 that hold it centrally within the contact I0. This cage-like member 22 also carries a cylindrical sleeve 2d which is held in spaced relation with the inner wall of the stationary contact I Il by the radial arms 23, so as to form an auxiliary or Icy-pass conduit 25 through which gases may exhaust when the valve-like member 2i! is moved away from the restricted throat or orifice I4 of the stationary contact I6. Mounted within the cylindrical sleeve 2t there is a compression `spring 2G which operates to bias the valve-like member 2d in a position against the rim of the restricted throat It so that upon contact separation, the blast of arc extinguishing fluid will be caused to normally exhaust through the throat-like aperture 2l thereof. At this point it will be noted that the movable contact Il is provided with a highly refractory arcing tip 27 which is resistant to pitting and/or burning away in the event of a sustained arcing.

In operation, with the chamber I5 charged with an arc extinguishing fluid, it will be seen that when the moving contact II is moved away from the stationary contact I0, as in interrupting a circuit, any arc drawn between the respective contact surfaces I2` and|3 orthese contacts'will be subjected to a'blast of arc extinguishing fluid which will normally exhaust centrally throughy the throat-like aperture 2| of theValve-like member 1`20 'and outwardly to 1 thev atmosphere or a mulcr, as abovesuggest'ed. S'However; should the current value of this arcbe 'ofsucha value as would result'in excessive heating, randa-consequent excessive generation. of ionized gases that might set lup a bloclring'pressure at the `point of contact separation which would interfere ..with 'the free flow 4of cool arc extinguishing fluid through thev arc, the annular valve-l-ikermember 20 Vwill bemoved .upwardly in response to this excessive pressure andthus permit-thisexcessive gas pressure to escape outwardly therearound and to l the atmosphere or muiler through .the annular auxiliary orfby-pass conduit`25.` Under normal operating conditions it is anticipated'that thearc extinguishing. fluid'will be 'maintained 'in the' chamber l5 at a pressure somewhere between 80 andv 100 pounds per square inch, and the spring 2li-will be so arranged and designed as to permit a valve opening movement of the annular valvelike member 20 whenever the pressure atv the restricted throat I4 of the stationary contact I0 approachesto Within 50 to 75 per cent of the pressurevalue normally maintained within the chamber l5. However, these values may vary under diierent conditions of operation. Inran actual test,v with contacts constructed -as 'here illustrated, it was found possible, with thevalve member 20 set to respond at a pressure of from 40to V60 pounds-per square inch, to interrupt a current of 4000 amperes at 15000 volts within one-half a cycle'withV an air pressure of 80'pounds, whereas without the annular valve member, an air pressure of 160 `pounds per square inch was required to obtain a comparable performance at this currentvand voltage. Therefore, it is apparent that by controlling the exhaust of hot gases from the arcing zone to the atmosphere or muffler, under conditions responsive to the current values of the are, a considerable saving in the pressure and quantity of the arc extinguishing :duid results.

Reference is now made to Figures y4 vand 5 of the/drawing,l wherein the invention vis shown as embodied in a circuit breaker of the so-called transverse .blast type. In circuit breakers of this latter type, the cooperating contacts are lgenerally arranged to separate and draw'any arc established therebetween within a relatively narrow arc chute which ares'outwardly so as to permit a rapid vexhaust and cooling of the iluid blast and arc generated gases. In these figuresl ofthe drawingy a stationary contact 28, with which a movable contact 29 is adapted to cooperate, are shown as Varranged to engage and disengage each other within a chamber or arc chute forming housing.' 30. The movable contact 29 is of bladelike'conguration,l andl the stationary contact 28 carries a plurality of yielding contact viingers v3l that engage the opposite sides of the movable contact-29. The stationary Contact 28, with its yielding-contact fingers 3 I is xed within the chamber of'arc chute forming housing 30 and opposite thereto the housing 30 has a relatively small opening-32 through whichA the'moving contact 29.may travel in moving into and out of circuit making engagement with the yielding contact fingers 3| of thestationary contact28. Immediatelyv above the.r path ofrtravel of themoving contactf29there is--a .fluid directing conduit 33 through which -a blast of arc-extinguishing iluid maybe discharged into the cl'iarnber.v or :arc chute iforming'fhousing 30 transversely to the path `of any: arc that-may be established between' the moving contact 29 andthe yielding. contact' v`lingers .31 f of the .stationary. contacts. Dlrectly.oppos'ite Ito thereon'- duitf 33 the. Varc .chuteiforming housingz: ls= flared outwardly, as'a.t134,wsofas to provide fontherapl`d exhaust.A of has passed through. thefpath ofanynarc'establi'shed f between :the :..contacts 'L18-land; 29 i. LTo' `:accelerate the :breaking-tup. of :anys persister-ritirare, the :dared portion 534. of i thef'arc Achute forming housing 30. `is also 'generallyLprovided .with:.a: plurality 'of lspaced Vand radially extending :baffle forming-.- members 5:35 which operate. tobreak .up the arc intowsrnallerA segmentsaandifthus provide fora more leicientcoolingzof, the'hot'zarczgeneratede'gases.k 'Arranged.outwardlyzf-beyondf theiiiared portioniu` oftheibame formingmembersl withinizthe housingiSU,.theresisearconduit or muler 36 intotwhich .thel cooled @gases iare.flclischarged` and inaliy exhausted; towtheratmosphere: `iThis: arrangement, vas .sof farv described, is wel1' v:known: and understoodnbyf those fskilled in.the.-.art,;and while it is capable"oninterrupt-ingecircuits athig-h voltages .and'scurrent values, J it iris :open-:.toithe objection that its :current'interruptingcapacity is 'limited to a4 relatively.: narrow rangeiofs'c-urrent values. This` diculty is 'believed to be;duef.tothe fact thatv the hot gas; coniiningi:housing-:ElliA .makes no allowances for 1 variations x in..` gas wprcssuresl which `result fromzthe. interruption .ofaicircuit .at

diierent currentvalues.V .'Inaccordancez-wlthjthc present invention, this: is: overcome bygproviding the arc;.chutea formingirhousingtallfwithi .faxmeans that will relieve the: arc achutaiiorr'thecchamber thus formed` about the;V arcing ,'.zone between the separating contacts, of :.any; back :pressure ,that might interfere with the vfree andseectiveflow. vof the arc extinguishing iiuidV through anyarc .which may be drawn between the; stationary contact 28 and the moving contact;29v ininterrupting areircuit. Thisfmeanaas here4 show.n,imay be` in the form'of ari-auxiliary vent-or exhaustA outlet 3'l that will permit theescape'ofv arc generated'gases from the arochuteat the point ofgcontact separation whenevera back-pressure, vinA excess of that whichV Would'preventf-an :effective-flow ofthe arc extinguishing fluid,focc,urs. Thelauxiliarysvent. orv exhaustoutlet 3T maybelocated in one or bothsides of` the arc, chute forminghousing. 30 anchas is more Vclearly shownyin-Figure 5. of the drawing, these auxiliary-vents or exhaust outletsi37 are provided with pressure responsivevalve .members38 that are,yieldinglyzffbiased v4into sealing-` relation with: thezauxiliary ventsr.or-exhaust-` outletss. 3 "l, 4by meansv ofisprings 39. .-Preferablyf these vents or exhaustoutlets 3`l are'located; closely adjacentthe point of-contact separation where the-highest gas pressures areY initially generated. The-.vents or exhaust. outlets -31 are shownf as vdisposed -in the sides of-,thefarc formingfhousing adjacent-the inner ends of thexbaiflev formngfmembers where an accumulation. .ofi ihotf. gasesfmight ;1 eiectively set-up; .an back; pressure: that would interfere with, if ,not entirelystop, the How of, the arc extinguishing gases throughl thefchamberorarc chuteforming housing 30. `It is believed.:.that ;the,4 operation of this embodiment` oithe invention will -be yclearly understoodv from thel 'operationr abovel described in connection fwith the embodiment of the invention shown in Figure .1. Therefore,"it-appears only. necessary towhere add: that .the springs 1139,'

whichwoperate` .tofseat .the twovalvemembers 38' within; the;.auxiliary 1. ventzori exhaustuoutletsll 31,.

the 1 arc 'exting-uishlng fi'luidcafter 'uit herev shown' as disposed one at each side of the arc chute forming housing 39, may be calibrated or designed so as to permit a response of their respectivevalve members 38 at different pressure values and, as a result, the Yarc extinguishing characteristics ofthe arrangement shown may be rendered eiective to extinguishan arc established between the separating

contacts

28 and 23 overa Widerrange of current values. i While I have described and illustrated Yspeciiic forms vofthe invention, I desire to have it understood that the invention is not limited to the specific arrangements disclosed,l but may be einbodied in other waysthat will suggest themselves to persons skilled in the art and all such changes as come within the scope of the appended claims are-tobe considered as part of vthis invention.

Having thus described my invention, what I claim and desireto secure by Letters Patent is- 1. In a uid .blast arc extinguishing circuit breaker, the combination-of a contact enclosing chamber adapted to maintain a iiuid under pressure having an exhaust outlet at one end, a stationary contact of cylindrical configuration extending into said chamber and forming a continuation of said exhaust outlet through which a liiuid under pressure within said chamber flow to said exhaust outlet, said cylindrical contact having its inner end formed to provide an open annular contact surface, .a cooperating :3:7

axially `movable contact having a cooperating contact surface adapted to engage the annular contact surface of said cylindrical contact and -close the opening therethrough, an annular valvelike member disposed within and in back of the annular contact surface of said cylindrical con'- tact having a restricted centrally disposed opening through which a blast of arc extinguishing uid may flow when said contacts are moved out of engagement* with each other, a cylindrical sleeve forl supporting said movable valve-like member centrally in spaced relation with the inner walls of the cylindrical contact and forming an outer annular passageway leading to the exhaust outlet of said Contact enclosing chamber, and means for yieldinglymaintaining said movable valve-like member in position where a blast of arc extinguishing fluid will be normally directed through its central opening and permitting movement thereof in the event oi a predetermined arc generated gas pressure to allow the generated gases 'to' flow -aroundl the outside thereof and through said annular passageway to the exhaust outlet of said chamber.

2. In a fluid blast `arc extinguishing circuit breaker, the combination of a contact enclosing chamber adapted to maintain a fluid under pressure having an exhaust outlet at its end, a stationary cylindrical Contact mounted within and forming a continuation of the exhaust outletoi said chamber through which a fluid under pressure within said chamber may flow to said exhaust outlet, said cylindrical contact having its inner end formed to provide a truncated conical contact surface, a cooperating axially movable contact having a conical contact surface adapted to engage-the truncated conical contact vsurface of said cylindrical contact'and close the opening therethrough, a movable valve-like member disposedcentrally within said cylindrical contact having 'a centrally disposed and. restricted openlng through which a blast of arc extinguishing uid. may flow when said contacts are moved out ofv engagement with each other, means for supporting said movable valve-like member centrally in spaced relation-with the inner walls of the cyl l Contact, and spring means for yieldirigly maintaining said movable valve-like member in a position with respect to the truncated conical contact surface o said cylindrical contact where a blast of arc extinguishing fluid will be normally directed through its central opening and permitting movement thereof in the event of an abnormal back pressure clue to arc generated gases which will allow said generated gases to flow around the outside thereof and to said exhaust inlet.

3. In a fluid blast arc extinguishing circuit breaker, the combination of, a substantially cylindrical contact forming member having an annular contact surface at its end and a passageway extending centrally therethrough ior the exhaust oi an arc extinguishing fluid, a second contact member adapted to engage said annular contact surface and operating to close the passageway through saidl cylindrical contact when said contacts are in circuit making engagement with each other, a pressure confining chamber surrounding said contacts at their point ci separation adapted to be charged with an arc extinguishing iluid medium under pressure, said cylindrical contact being mounted in a wall oi said chamber and forming an exhaust conduit 'for said arc extinguishing fluid, a passageway dividing means disposed within said cylindrical Contact and forming an outer auxiliary passageway therethrough, and a pressure responsive valve means cooperating with said passageway dividing means operating to prevent a now of said arc extinguishr; ing fluid through said auxiliary passageway under normal arcing conditions and permitting said arc extinguishing iiuid to exhaust through said auxiliary passageway under abnormal arcing conditions.

4. In a iiuid blast arc extinguishing circuit breaker, the combination of a substantially cylindrical stationary Contact forming member having an annular Contact surface at its end and a passageway extending centrally therethrough for the exhaust of an arc extinguishing fluid, a movable contact adapted to engage said annular contact surface and substantially close the passageway through said cylindrical stationary contact when said contacts are in circuit making engagement with each other, a pressure confining chamber surrcunding said contacts at their point of separation adapted to be charged with an arc extinguishing iluid medium under pressure which will exhaust therefrom to extinguish any arc established between said contacts when they separate to open a circuit, said cylindrical stationary contact being mounted in a wall of said chamber and forming an exhaust conduit for said arc extinguishing uid, a cylindrical partition forming means disposed within said cylindrical contact and forming an annular auxiliary passageway therein, a pressure responsive valve means cooperating with said cylindrical passageway dividing means operating to prevent a flow of said arc extinguishing iiuid through said outer annular passageway under normal arclng conditions and permitting said arc extinguishing uid to exhaust through said annular passageway under abnormal arcing conditions, said pressure responsive valve means being adapted and arranged to operate and open said auxiliary passageway at a pressure below that which would maintain a blocking pressure oi ionized gases sufficient to prevent an extinction of the arc by a flow of said arc extinguishingk fluid through said cylindrical contact.

5. n a fluid blast arc extinguishing circuit breaker, the combination of a substantially cylindrical contact having an annular contact surface at one end and a fluid blast exhaust passageway extending centrally therethrough, a movable contact adapted to move axially with respect to said cylindrical contact and close the fluid blast exhaust passageway through said cylindrical contact when said contacts are in circuit establishing engagement with each other, a chamber surrounding said contacts from which an arc extinguishing fluid under pressure may exhaust through said cylindrical contact to extinguish an arc established between said contacts when said contacts separate, means forming an annular concentrically arranged vent passageway within the fluid blast exhaust passageway through said cylindrical contact, an axially movable valve member having a centrally located throat-like opening for the passage of fluid under pressure from said chamber upon separation of said contacts, said annular valve member being positioned to normally close said annular vent passageway, and spring means for maintaining said annular valve member in its vent passageway closing position and adapted to permit axial movement of said annular valve member to open said vent passageway for the escape of ionized gases generated by an arc between said contacts at a pressure below that which would establish an exhaust blocking pressure within the throat-like aperture of said valve member.

6. In a iluid blast arc extinguishing circuit breaker, the combination of a substantially cylindrical contact having an annular contact surface at one end and a fluid blast exhaust passageway extending centrally therethrough, a movable contact adapted to move axially with respect to said cylindrical contact and close the fluid blast exhaust passageway through said cylindrical contact when said contacts are in circuit establishing engagement with each other, a chamber surrounding said contacts from which an arc extinguishing fluid under pressure may exhaust through said cylindrical contact to extinguish an arc established between said contacts when said contacts separate, means forming an annular concentrically arranged vent passageway within the iluid blast exhaust passageway through said cylindrical contact, and axially movable valve member having a centrally located throat-like opening for the passage of fluid under pressure from said chamber upon separation of said contacts, said annular valve member being positioned to normally close said annular vent passageway, and spring means for maintaining said annular valve member in its vent passageway closing position and adapted to permit axial movement of said annular valve member to open said vent passageway for the escape of ionized gases generated by an are between said contacts at a pressure substantially corresponding to the pressure of the arc extinguishing fluid flowing between said contacts, whereby a blocking of the flow of arc extinguishing fluid between said separating contacts due to any back pressure at said throat-like opening will be avoided.

7, In a fluid blast arc extinguishing circuit breaker, the combination of a contact enclosing chamber adapted to maintain a fluid under pressure having an exhaust outlet at one end, a cylindrical contact member mounted within and having its central opening communicating with the exhaust outlet of said chamber through which a fluid under pressure within said chamber may ilow to said exhaust outlet, said cylindrical contact having its inner end formed to provide an annular contact surface, a cooperating movable contact having a contact surface adapted to engage the annular contact surface of said cylindrical contact member and close the central opening therethrough, an annular valve member disposed centrally within said cylindrical contact having its central opening disposed to form a restricted passageway through which a blast of arc extinguishing fluid may flow when said contacts are moved out of engagement with each other, means for supporting said valve member centrally in spaced relation with the inner walls of said cylindrical contact member, and means for yieldingly maintaining said valve member in a position with respect to the annular contact surface of said cylindrical contact member, where a blast of arc extinguishing fluid will be normally directed through its central opening, but permitting an operation movement thereof, which will allow arc generated gases to flow around it and to said exhaust inlet in the event of an abnormal gas pressure due to arcing between said contacts.

ARNOLD E. BROCK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,944,403 Clerc Jan. 23, 1934 2,063,173 Lange Dec. 8, 1936 2,084,885 Biermanns i June 22, 1937 2,367,934 Flurscheim Jan. 23, 1945 2,380,817 Woolard July 31, 1945 2,399,412 Webb Apr. 30, 1946