US3435166A

US3435166A - Gas blast circuit breaker with improved resistor switch

Info

Publication number: US3435166A
Application number: US508005A
Authority: US
Inventors: Philip Barkan
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-11-16
Filing date: 1965-11-16
Publication date: 1969-03-25
Anticipated expiration: 1986-03-25

Description

P. BARKAN March 25, 1969 GAS BLAST CIRCUIT BREAKER WITH IMPROVED RESISTOR SWITCH Sheet Filed Nov. 16, 1965 INVEN TOR. PHIL/P BAR/(AN, Maw/7" A Tram/5y March 25, 1969 P. BARKAN 3,435,155

GAS BLAST CIRCUIT BREAKER WITH IMPROVED RESISTOR SWITCH Filed Nov. 16, 1965 Sheet 2 of 2 //v VENTOR. PHIL/P BARK/w,

ATTORNEY United States Patent US. Cl. 200-148 Claims ABSTRACT OF THE DISCLOSURE Discloses a gas blast circuit breaker of the type in which a movable main contact is connected through a mechanical linkage to a movable resistor switch contact. A main blast valve downstream from the main contacts and the resistor-switch contacts controls the flow of arcextinguishing gas past both sets of contacts. A resistorswitch blast passage communicates with the main exhaust passage downstream of the main contacts and upstream of the main blast valve and contains normally-closed secondary flow control means that is opened late in an interrupting operation to allow flow through the region of the resistor-switch contacts. The secondary flow control means blocks flow through the resistor-switch blast passage during the period when the main blast valve is first opened, and this allows a high speed blast to be quickly established past the main contacts upon main blast-valve opening without detraction by fiow through the resistor-switch blast passage.

This invention relates to a gas blast circuit breaker of the type that comprises a voltage-controlling resistor shunting its main contacts and, more particularly, relates to an improved resistor switch for interrupting the flow of current through said resistor after the main contacts have been separated.

The general type of circuit breaker that the present invention is concerned with is illustrated in US. Patent 3,l33,l76-fiSchneider, assigned to the assignee of the present invention. In this circuit breaker, there is a tank filled with high pressure gas and a pair of separable main contacts in the tank. When the contacts are separated, a main arc is drawn and a blast of gas is caused to flow through the region of the main arc. This blast passes through a main exhaust passage that contains a previously-closed blast valve that had been opened to initiate the blast.

Shunting the main contacts is a voltage-controlling resistor and a resistor switch connected in series with the resistor. The resistor switch comprises a pair of relatively movable contacts that are separated to draw an are at a predetermined instant after the main contacts have been separated. To aid in extinguishing the resistor-switch are, a secondary blast of gas is caused to flow through the region of this arc. This secondary blast flows through a resistor-switch blast passage that communicates with the main exhaust passage through which the main blast of gas flows. Both the secondary blast and the main blast are controlled by the blast valve in the main exhaust passage.

It is desirable that the pressure in the main exhaust passage be reduced to a value no higher than 53% of the tank pressure immediately upon opening of the blast valve so that the main blast immediately attains its desired high velocity, i.e., sonic velocity, through an interrupting orifice located in the main exhaust passage. It has been discovered, however, that the time required for the pressure in the exhaust passage to drop to the required low level after blast-valve-opening has been somewhat longer than expected and desired.

An object of the present invention is to reduce the time required for the pressure in the main exhaust passage to ice drop to the desired low level after opening of the main blast valve.

Another object is to prevent the secondary blast, which flows through the resistor-switch arcing region and into the main exhaust passage, from interfering with the rate at which the pressure drops in the main exhaust passage immediately after the main blast valve is opened.

Still another object is to provide a resistor switch in which there are no substantial pneumatic forces acting on its contacts until after they have parted.

In carrying out the invention in one form, I normally block communication between the resistor-switch blast passage and the main exhaust passage. This is done with a normally-closed valve located in the resistor-switch blast passage. This latter valve is opened upon separation of the resistor switch contacts, but such valve-opening occurs substantially after the main contacts have been separated and the main blast valve has been opened. The initiation of the secondary gas blast, which flows through the arcing region of the resistor switch, is delayed until about the time the resistor switch contacts are opened.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a sectional view through a circuit interrupter embodying one form of the invention.

FIG. 2 is a sectional view through a resistor switch forming a part of the circuit interrupter of FIG. 1. The resistor switch is shown in its closed position.

FIG. 3 is another sectional view of the resistor switch but showing the switch in an open position.

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3.

Referring now to FIG. 1, the circuit breaker shown therein is of the general type disclosed and claimed in US. Patents No. 2,783,338Beatty and No. 3,133,176-- Schneider, assigned to the assignee of the present invention. This circuit breaker comprises an enclosed interrupting chamber 11 defined, in part, by a metallic casing 12 which is filled with a pressurized arc-extinguishing gas, such as air.

A pair of elongated

conductive studs

15 and 20 project into the casing 12 from diametrically-opposed points, and each of these studs carries a suitable stationary contact assembly 16 at its inner end. Suitable cylindrical insulators 17 are provided about the studs to support them on the metal casing 12 and to insulate them from the casing 12. Cooperating with each stationary contact assembly 16 is a movable contact 28 pivotally mounted upon a stationary pivot 29. These pivots 29 are supported upon stationary brackets 31 which are integral with one end of a stationary operating cylinder 32. Suitable means (not shown) are provided for transferring current between the movable contacts 28 and the brackets 31, so that the brackets 31 together with the cylinder 32 form a conductive path electrically interconnecting the two movable contacts 28.

The cylinder 32, at its lower end, is suitably supported from a generally cylindrical housing 33, which, in turn, is suitably secured at its lower end to the metal casing 12.

For producing a gas blast action for extinguishing the arcs which are established by separation of the contacts 16 and 28, the housing 33 is provided with a normallyclosed annular exhaust passage 36 which leads from the interrupting chamber 11 to the surrounding atmosphere. The housing 33 at its upper end is formed with a pair of generally diametrically-opposed nozzle-type electrodes 38 defining inlets to the exhaust passage 36. The entrance portion of each nozzle 38 is referred to hereinafter as an orifice, which has an orifice opening 37. 'For controlling the flow of arc-extinguishing gas through the nozzle electrodes 38 and through the exhaust passage 36, there is provided at the lower end of the exhaust passage 36 a cylindrically-shaped reciprocable blast valve member 40 which slides smoothly in a surrounding tubular housing 41 integrally formed in the housing 33. In FIG. 1, the valve member 40 is shown in its closed position where its lower end abuts against a cylindrical valve seat 34. The valve member 40 is normally maintained in this closed position of FIG. 1 by the action of a suitable spring (not shown) and by the action of the pressurized gas within the passageway 36. This gas produces upon the valve member 40 an unbalanced force urging the valve member 40 downwardly into its closed position.

Since the chamber 11 is normally filled with pressurized gas, it will be apparent that when the valve member 40 is opened by upward movement (by means not shown), gas in the chamber 11 will flow at high speed through the nozzles 38 and out the passage 36 past the valve member 40 to atmosphere, as is indicated by the arrows E and -F shown in FIG. 1. Opening movement of each of the contact members 28 first establishes an are between the ends of the contacts 28 and 16. Shortly thereafter, however the blast of gas which has been flowing through the nozzle 38, as indicated by the arrow B, forces the upstream terminal of the arc onto an upstream electrode 44, which is electrically connected to the stationary contact 16. As opening motion of the movable contact 28 continues, the gas blast forces the downstream terminal of the arc to transfer from the movable contact 28 to the nozzle 38, which is electrically connected to the movable contact 28. The gas blast then impels the downstream terminal of the are through the orifice opening and nozzle onto a projecting electrode 45. The arc then occupies the position generally shown at 46. When the arc is in this position, the arc column extends through the orifice opening 37 and is subjected in the orifice region to an intense high Velocity blast. This blast is eitective to cool and deionize the arc and to prevent reignition thereof at an early current zero.

4 For operating the blast valve 40 and the movable contacts 28, a combined operating mechanism preferably of the fluid-actuated type shown in the aforementioned Beatty patent is provided within the cylinders 32 and 33. The details of this operating mechanism form no part of the present invention and, hence, such details are not shown in the present application. An adequate understanding of the present invention may be had it it is understood that the operating mechanism acts during an opening operation to drive a piston rod shown at 58 upwardly. It also acts to open the blast valve 40. The piston rod 58 is coupled to the contacts 28 (by means soon to be described), and, hence, such movement of the piston rod serves to drive the contacts 28 open. At a predetermined instant after the contacts 28 have been opened, the then-open blast valve 40 is driven closed by the operating mechanism, as is described in detail in the aforesaid Beatty patent. This closing of the blast valve prevents further loss of gas from the interrupting chamber 11.

The means for coupling the piston rod 58 to the main contacts 28 comprises a cross head 59 and two sets of connecting links 60. The cross head 59 is rigidly secured to the piston rod 58 by suitable clamping means, whereas the connecting links 60 are pivotally connected at 61 and 62 to the cross head and movable contacts, respectively.

In the position of FIG. 1, the movable contacts 28 are biased into closed position by means of overcenter compression springs 64. Each of these springs 64 has one end pivotally supported at 65 on a stationary projecting portion of one of the brackets 31. At their inner ends, the springs 64 are pivotally supported on the cross head 59. These overcenter springs 64 tend to urge the contacts closed while the cross head 59' is to the left of a reference line connecting the pivots 65. But when the cross head is moved upwardly beyond this reference line (as occurs during a contact-opening operation), the overcenter springs thereupon tend to urge the contacts in a contactopening direction. This action coupled with that of the operating mechanism acts to hold the contacts 28 in a fully open position until the opearting mechanism is subsequently operated to close the contacts 28.

Shunting each pair of main contacts 16, 28 is a voltagecontrolling resistor 70. This resistor is schematically shown as a resistive element wound about a cylindrical insulating core 70a. This core is suitably supported on its

conductive stud

15 or 20. In the schematic illustration of FIG. 1, this core is supported by a conductive web 72 that electrically interconnects one terminal of the resistor element 70 and the stationary contact 16. The other terminal of the resistor element 78 is electrically connected to a stationary contact 73 of a resistor switch 75.

The resistor switch 75 comprises, in addition tothe stationary contact 73, a movable contact 74 that is carried by a pivotally-mounted tubular arm 77 of the resistor switch. Referring to FIGS. 2 and 3, the illustrated stationary contact 73 is of a generally spherical form, and the movable contact 74 is of an annular ring-shape form. The ring-shaped contact 74 is slidably supported on the tubular arm 77, and a suitable compression spring 78 urges the ring-shaped contact 74 toward its fully-extended position of FIG. 3. The spring 78- serves as a wipe spring which permits a limited amount of overtravel of the tubular arm 77 after

contacts

74 and 73 engage during a closing operation. Suitable flexible braid schematically shown at 81 in FIG. 3 electrically interconnects the movable contact 74 and its movable supporting arm 77. When the movable arm 77 is moved away from the stationary contact 73 during an opening operation, a shoulder 83 on the movable arm strikes a projection 830 on the movable contact 74, after which movable contact 77 moves in an opening direction with the movable arm 77. During initial opening movement of arm 77, the contact 74 remained stationary, being held against contact 73 by wipe spring 78.

For mounting the tubular arm 77 on the stationary housing 33, a tubular extension 79 is provided on the tubular arm 77 This tubular extension 79 projects from the arm 77 at a right angle thereto and is rotatably mounted on the housing 33 in a hollow boss 80 integral with housing 33. The hollow boss 80* contains a central passage 82 in which the extension 79 is journaled. A radially-extending passage 84 connects this central passage 82 with the main exhaust passage 36 .when the tubular arm 77 is moved out of its closed position of FIG. 2.

The extension 79 on the switch arm 77 is a tubular part that has a radially-extending port 86 therein. When the resistor switch 75 is closed, as in FIG. 2, this port 86 is blocked off by the cylindrical wall of the passage 82 which closely surrounds the extension 79. But when the resistor switch is moved into the open position depicted in FIG. 3, extension 79 is rotated to such an extent that port 86 moves into alignment with radially-extending passage 84. This permits pressurized air to flow through tubular arm 77, tubular extension 79 and

passages

86 and 84 into the main exhaust passage 36. In effect, the rotatably-mounted tubular extension 79 with the port 86 therein constitutes the movable element of a

control valve

79, 86, 84 for controlling communication between the interior of the tubular switch arm 77 and the main exhaust passage 36. This

control valve

79, 86, 84 is referred to hereinafter as a secondary valve.

When the tubular arm 77 of the resistor switch is pivoted in a downward direction from its closed position of FIG. 2 toward its open position of FIG. 3, an arc is drawn between the

contacts

73 and 74. After a predetermined amount of initial opening movement of the tubular arm 77, the

control valve

79, 86, 84 is opened, and a blast of gas is permitted to flow from the pressurized chamber 11 through the tubular arm 77, the tubular extension 79, ports 86, 84-, and into the main exhaust passage 36. This blast of gas follows a path illustrated by the arrows K of FIGS. 3 and 4, and it acts in a known manner to assist in extinguishing the arc that is formed between

resistor switch contacts

73 and 74. The passage for this gas blast is referred to hereinafter as the resistorswitch blast passage 87. The blast itself is referred to hereinafter as a secondary gas blast.

Each of the resistor switches 75 is operated to its open position only after the two sets of main contacts 16, 28 have been separated for a predetermined length of time. For effecting such operation of the resistor switches 75, a conventional operating mechanism, diagrammatically indicated at 90, is provided. This operating mechanism 90 connects the movable arm 77 of each switch to the cross head 59 that operates the main movable contacts 28. This operating mechanism 90 is coupled to the cross head 59 through a rod 92 secured to the cross head. The mechanism 90 is connected to the switch arm 77 through a linkage that comprises a rotatable shaft 93, a driving crank 94, a driven crank 95, and a link 96 connected between the two cranks. The driving crank 94 is keyed to the shaft 93 and the driven crank 95 is fixed to the extension 79 of the switch arm 77. The link 96 is pivotally connected to driving crank 94 at one end and at its other end is connected through a suitable universal joint 98 to the driven crank 95.

When the cross head 59 of FIG. 1 is moved in an upward direction to open the movable main contacts 28, it acts near the end of its contact-opening stroke to drive the link 96 in a downward direction. Such downward motion is transmitted to link 96 through

components

92, 90, 93 and 94. Downward motion of link 96 drives crank 95 downwardly, thereby rotating switch-arm-extension 79 and pivoting switch arm 77 in a direction to open the

resistor switch contacts

73, 74. The operating mechanism 90 of FIG. 1 delays this opening motion of the switch arm 77 until the cross head 59 enters a predetermined position near the end of its opening stroke.

:It is to be noted that the two resistor switches 75 are operated substantially simultaneously since they are mechanically connected together through their common rotatable shaft 93. The shaft 93 is rotatably mounted on metallic casing 12 by means of stationary bearing brackets 99 that are fixed to metal casing 12.

In prior circuit breakers of the general type disclosed in this application, the resistor-switch blast passage has been in permanent communication with the main exhaust passage 36. This may be seen, for example, in FIG. 3 of the aforementioned Schneider Patent 3,133,176. A disadvantage of this type of arrangement, heretofore unrecognized, is that fiow through the resistor-switch blast passage can interfere with the immediate development of the desired high velocity flow in the main gas blast. In this connection, recall that the main gas blast is initiated by the opening of the normally closed main blast valve 40. When the main blast valve is initially opened, pressure in the enhaust passage 36 begins to drop. In order to achieve the desired sonic velocity through the orifice opening 37, pressure in the exhaust passage should be no more than 53% of the pressure in the chamber 11. A finite time is required before the pressure in the exhaust passage can be reduced to this level; and in some cases, it does not drop to this level until after the main cont-acts have parted. The result is that the gas velocity in the region of the contacts 16, 28 when they part is not as high as that ultimately obtainable, and this lower velocity delays transfer of the are off the contacts and into its position between the electrodes 44 and 45 and also delays effective blasting of the are by the high velocity blast.

In prior arrangements, the flow of high pressure gas into the exhaust passage 36 through the resistor switch blast passage 87 during the period immediately following opening of the main blast valve 40 has retarded the rate of drop of pressure in the exhaust passage 36. In the circuit breaker of my invention, I prevent any such interference with the rate of pressure drop in the exhaust passage 36 by providing the normally-closed

control valve

79, 84, 86 between the resistor-switch bl-ast passage -87 and the main exhaust passage 36. During the early stages of the opening operation of the overall circuit breaker, this normally-closed

control valve

79, 84, 86 blocks any flow through the resistor-switch blast passage 87 into the main exhaust passage 36, thereby allowing pressure in the main exhaust passage 36 to be reduced without interference from flow through the resistor swi-tch blast passage. It is only when the resistor switch 75 is released and allowed to open near the end of the opening operation for the main contacts 16, 28 that flow through the resistor-switch blast passage is permitted by the

valve

79, 86, 84. By this time, the pressure in the main exhaust passage has already been reduced to the desired low level to produce flow at sonic velocity through the orifice opening 37 and the desired rapid transfer of the arc to its position between electrodes 44 and 45.

The delay in initiating the secondary blast, i.e., the flow through the resistor-switch blast passage 87, does not significantly interfere with the electrical performance of the resistor switch 75 because flow through this passage performed no useful function prior to separation of the contacts. With my arrangement, I eliminate this unnecessary flow, but yet have the desired flow available when it is needed, i.e., upon separation of the resistor switch contacts. Not only does this reduce the period of time required for the main gas blast velocity to rise to the desired sonic level through orifice opening 37, as explained hereinabove, but it also reduces the consumption of pressurized air resulting from each circuit breaker operation.

When the main blast valve 40 closes, it prevents the further flow of gas from the pressurized chamber 11 to the surrounding atmosphere. Closing of this blast valve 40 does not occur until the are between the

resistor switch contacts

73, 74 has been extinguished.

It should be noted that when the contacts of the resistor switch are closed, as shown in FIG. 2, the same pressure prevails in the resistor-switch blast passage 87 as in the surrounding pressurized chamber 11. This is the case because the ring-shaped contact 74 is purposely made in such a shape that there is a passage present between the

contacts

74 and 73 when these contacts engage. This passage 100 affords communication between the resistorswitch blast passage 87 and the surrounding chamber 11 when the

contacts

73, 74 are closed.

It is important that the contacts of resistor switch 75 part at a precisely controlled instant after the main contacts 16, 28 part. This timing should not be significantly afiected by flow or pressure conditions adjacent the resistor switch components. My resistor switch has a number of features that prevent its performance from being significantly affected by flow and pressure conditions adjacent its components. One of these features is that the

flow control valve

79, 84, 86 remains closed during the period prior to separation of the

resistor switch contacts

73, 74, and thus there is no How during this period through the resistor-switch blast passage 87 to develop unpredictable forces on the movable con-

tact arm

77, 79. Another feature is that a drop in pressure in the exhaust passage 36 does not appreciably affect the force tending to open the resistor

switch contact arm

77, 79. Because the

valve

79, 84, 86 is a rotary valve, a pressure differential on opposite sides of its movable valve element 79 exerts no substantial force tending to operate the valve element; and thus its operation is essentially insensitive to the magnitude of the pressure differential existing between resistor-switch blast passage 87 and the main exhaust passage 36. Thus, the pressure in the main exhaust passage 36 can be drastically reduced, as by opening of the blast valve 40, without producing any significant additional forces tending to rotate the extension 79 or to pivot the movable contact arm 77 There are additional pneumatic forces on the movable contact arm 77 when a substantial flow occurs through the

valve

79, 84, 86, but in a preferred embodiment of the invention substantial flow is delayed until after the contacts 73, 7 4 part. .Thus, during the interval prior to contactpart, which is the crucial interval that should be precisely controlled in duration, these additional forces are not present. After the

contacts

73, 74 part, these additional forces are of minor significance.

Although I have shown the

flow control valve

79, 84, 86 completely blocking communication between the resistor-switch blast passage 87 and the main exhaust passage 36, I may in some cases permit a small amount of leakage past the valve or may provide a small permanently-open passage through the valve that allows a minor flow to occur before the valve itself opens. This leakage or minor flow is, however, maintained low enough so that its initiation, upon opening of the main blast valve 40, does not result in any significant additional forces on the movable resistor switch contact arm 77. Even though such a valve might permit this leakage or minor flow to occur when in its position of FIG. 2, it is still considered to be a normally-closed valve since the amount of flow permitted when in the position of FIG. 2 is very small compared to that permitted when in its open position of FIG. 3.

While [I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing frommy invention in its broader aspects; and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker of the gas blast type comprising:

(a) a normally pressurized chamber,

(b) a pair of separable main contacts, one of which is movable, within said chamber for establishing a main are when said main contacts are separated,

(c) an exhaust passage leading from the region of said main arc to the exterior of said chamber,

((1) a normally-closed blast valve for controlling flow through said exhaust passage and said main arcing region,

(e) means for opening said blast valve at about the same time said main contacts are separated to cause an arc-extinguishing blast of gas to flow through said arcing region and said exhaust passage,

(f) a voltage-controlling resistor normally connected electrically in parallel with said separable main contacts,

(g) means for controlling the current flowing through said resistor when said main contacts are separated comprising a normally-closed resistor switch,

( h) said resistor switch comprising separable resistor switch contacts, one of which is movable, connected in series with said resistor,

(i) means comprising a mechanical linkage interconnecting said movable resistor switch contact and said movable main contact for separating said resistor switch contacts after said main contacts have been separated for a predetermined period, whereby to establish a resistor-switch arc,

(j) secondary flow control means for causing a secondary gas blast to flow through the region of said resistor switch arc,

(k) said secondary flow control means comprising:

-(i) a resistor-switch blast passage communicating with said exhaust passage upstream from said blast valve,

(ii) a normally-closed secondary valve substantially blocking communication between said resistor-switch blast passage and said exhaust passage during the period when said blast valve is first opened,

(iii) and means for opening said normally-closed secondary valve upon separation of said resistor switch contacts and substantially after said main contacts have separated and said blast valve has opened, whereby to produce a secondary gas blast through said resistor-switch blast passage in the region of said resistor switch arc.

2. The circuit breaker of claim 1 in which said means for opening said normally-closed secondary valve is operable in response to a contact-separating operation of said resistor switc'h contacts.

3. The circuit breaker of claim 1 in which said secondary valve is a rotary valve comprising a rotatable valve element that controls flow therethrough, and said resistor switch comprises a movable contact-controlling part coupled to said rotatable valve element for producing valve-opening motion thereof when said movable contact-controlling part is moved to effect contact-opening motion of said resistor switch contacts.

4. The circuit breaker of claim 1 in which said resistor switch comprises:

(a) a movable arm carrying one of said resistor switch contacts,

(b) means for mounting said one resistor switch con tact on said arm for limited relative movement with respect to said arm,

(c) wipe spring means for causing said one resistor switch contact to remain in engagement with said other contact until said arm moves a predetermined distance in a switch-opening direction,

(d) means for parting said resistor switch contacts upon movement of said arm through said predetermined distance,

(e) and means for delaying opening of said secondary valve while said arm is moving through said predetermined distance.

5. An electric circuit breaker of the gas blast type comprising:

(a) a normally pressurized chamber,

(b) circuit interrupting means comprising a movable main contact in said chamber for establishing an are,

(c) an exhaust passage leading from the region of said arc to the exterior of said chamber,

((1) a normally-closed blast valve in said exhaust passage openable to produce a gas blast that assists circuit interruption,

(e) a voltage-controlling resistor connected in parallel with said circuit interrupting means for facilitating interruption,

(f) a resistor switch comprising normally-closed separable resistor switch contacts connected in series with said resistor, one of said resistor switch contacts being movable,

(g) means comprising a mechanical linkage connected between said movable main contact and said movable resistor switch contact for separating said resistor switch contacts after said circuit interrupting means has been operated for a predetermined time, whereby to establish a resistor switch arc,

(11) secondary flow control means for causing a secondary gas blast to flow throuhg the region of said resistor switch arc,

(i) said secondary flow control means comprising:

(i) a resistor-switch blast passage communicating with said exhaust passage upstream from said blast valve,

'(ii) a normally-closed secondary valve substantially blocking communication bet-ween said resistor-switch blast passage and said exhaust passage during the period when said blast valve is first opened,

(iii) and means for opening said normally-closed secondary valve upon separation of said resistor switch contacts and substantially after said main contacts, have separated and said main blast valve has opened.

References Cited UNITED STATES PATENTS Thieme 200-148.8 Forwald 20082.1 Oppel ZOO-148.2 Baker 200-1482 ROBERT S. MACON, Primary Examiner.

US. Cl. X.'R. 200-144, 145, 11