US2550507A - Condition responsive, timing, and sequencing circuit control - Google Patents

Description

A. WELLMAN April 24, 1951 Filed May 51, 1946 Z M 4 2 M M lw h 3 I W 7 1H5 ill Wi 4 m l Ilia a a 1 22. ,1 o E 2 B 0 I 2 I m 1 CRITICAL LOCKOUT PERIOD,

coouus PERIOD seas cwsso--1 HEATING PERIOD His Attorney.

Patented Apr. 24, 1951 CONDITION RESPONSIVE, TIMING, AND

IRCUIT CONTROL SEQUENCING 0 Albert Weilman, Scotia,

N. Y., assignor to General Electric Company, a corporation of New York I Application May 31, 1946, Serial No. 673,338

13 Claims. lCl. 158-28) The invention relates to condition responsive, timing, and sequencing circuit control particularly of a type suitable for the automaticcontrol of electrically operated oil burners or the like.

7 One of the objects is to provide an improved form of multi-selective circuit control system capable of operating in response to different predetermined condition, time, and sequence control conditions to provide timed starting and restarting, continued running, stopping, and safety lockout of electrically operated oil burnersor the like.

. Another object is to minimize the essential automatic condition responsive, timing and sequencing switching elements involved by so combining, and interlocking their respective functions as to obtain a more eificient and less expensive form of multi-selective switching and safety interlocking mechanism capable of insuring proper, reliable and safe control of conventional electrically operated oil burners in automatic domestic heating service under both normal and abnormal conditions.

Another object is to so combine a condition responsive reversely movable interlocking control member with a sequential circuit controlling, electrically heated thermal timer in controlling both the operation of the timer and the selective energization of an electroresponsive device as to meet the essential control and safety requirements encountered in oil burner control or other similar control service.

Another object is to provide an improved form of interlocking and safety circuit control mechanism for quickly and selectively responding only to the initial changes in a widely variable temperature condition such as produced upon initiation and termination of combustion of an oil burner. It is a particular object of my invention to provide such an interlocking and safety circuit control mechanism which is adaptable for use with a regulated air bellows form of temperature responsive device.

Further objects and advantages of the invention will become apparent from the following description of the accompanying drawing in which Fig. 1 is a schematic perspective View of a condition responsive timing and sequencing circuit control embodying the improvements of the present invention in a preferred form suitable for oil burner control service, Fig. 2 is a timesequence diagram of the various condition responsive, timing, and sequencing control functions provided by the improved control and Fig. 3 is a fragmentary view showing schematically the relative positions of the lookout sequence control parts under different conditions of operation.

As shown schematically in Fig. l, the invention is applied to control an oil burner H] which fill may be of a conventional type operated by an electric motor indicated by winding H. able oil pumping mechanism enclosed within the pump casing l2 as well as a combustion air blower within the blower casing l3 are both operated when the driving motor I l is energized. As indicated, oil is supplied under pressure through pipe M to atomizing nozzle l5 and combustion air is supplied through conduit l8 and air supply tube H for mixing with the atomized oil to project a combustible mixture into a combustion chamber l8 defined by the-wall l9. Under normal burner operating conditions, this combustible mixture is ignited by means of ignition transformer 2i and the high-voltage spark electrodes 22. However, under some abnormal conditions, combustion may not be successfully established during a limited starting period and it then becomes imperative that further operation of the oil burner be stopped. Otherwise a dangerous explosion might occur due to the accumulation of a relatively large amount of unburned atomized oil in the combustion chamber. The present invention provides improved means for selectively and positively differentiating in an im'- proved manner between the normal establishment of combustion and the failure to estab-' lish combustion while the motor II is initially energized during the limited starting period.

Burner motor H is energized from suitable electric supply lines Ll, L2, preferably under control of an electroresponsive relay 23 having an operating winding 24 energized from the lowvoltage secondary of a transformer 25. Relay 23 is operated under the control of an improved timing and sequencing switch mechanism indicated generally by the reference character 26 which is combined in interlocking relation with an improved combustion responsive device indicated generally by the reference character 21. A master control switch in the form of a conventional room thermostat 28 or the like is provided for initiating and terminating burner operation to regulate a predetermined condition such as the room temperature.

The timing and sequencing mechanism 26 is provided with a movable thermal timing element 30 having an electric heater 3| supported in heating relation with the thermal element 30 by bracket 32 mounted on a projection 33 from the base 34. The thermal timin main supporting element 35 is shown as of the bimetallic type fixed at lower end and carrying at its upper end contact plate on which switching contacts 36 are mounted back to back so as to abut selectively with the cooperating switch contacts 31 Switch contact 31 is resiliently carried by a spring strip 48 mounted on the arm 4| which in mounted by the flexible strip of magnetic material and is movable into magnetic attractive relation with the permanent magnet 46 that is carried by the switch plate 35, being suitably secured thereto as by screw 45. Thu a releasable holding means is provided by magnet and arm 4| for maintaining contact 3? in resilient abutment with contact 35 during a predetermined movement of the switch plate 35 by the thermal element 30 due to the heating thereof until arm 4| engages the extension 41 of adjustable stop 48 to release arm 4| from magnet 46. Thus the adjustment of stop 48 by adjusting screw 49 regulates the heating period of thermal element 30.

Switch contact 38 is carried by a flexible strip 50 extending from the base 34 to position contact 33 so as to engage with contact 36 during the predetermined heating of the thermal element 35. To eliminate diniculties due to chattering of room thermostat 28, the switch plate 35 also may carry contact 5| into abutting engagement with contact 52 carried by the flexible strip 53 extending from the base 34 thermostat 28 for a limited interval during the starting of burner H).

The combustion responsive device 21 in the improved form shown air-filled bellows 55 mounted on a connection base 55 and interconnected through tube 51 with a temperature bustion chamber l8. An operating arm 59 is pivotally mounted on the pin 60 to engage with and be operated by the finger 6| extending from the closed end of the bellows 55. arm 58 is opcrabl connected with the switching interlock member 52 that is movably mounted by means of bracket 63 and the resilient mounting spring 64 extending from a fixed support 65 having a motion limit stop 66.

As explained more in detail hereinafter the interlocking member 62 is provided with a projecting finger 69 for cooperating with the extension ?5 of switch plate 35, an interlocking finger 7| for cooperating with the bent-over extension 52 of the flexible strip 53 and an adjustably mounted interlocking finger "I3 for cooperating with the extension 14 of the movable magnetic arm 4|. Also, interlocking member 62 carries a finger 15 for engaging with arm 16 to separate the normally closed switch contacts T! and thereby open the primary circuit of the ignition transformer 2| after combustion is established.

An improved automatic air pressure control valve mechanism 89 is provided for regulating the air pressure to which the bellows 55 is subjected both before heating of the bulb 58 in response to combustion and also during the heat- As shown, a conventional form adjusting screw 86 into and out of engagement with the tire valve stem 81.

The improved pressure control operates as follows: When the bulb 58 is cooling, bellows 55 contracts due to the decreased internal air pressure below atmospheric and a suitable spring 88 moves lever 59 to carry the head of adjustable screw 89 into engagement with the forked end of the pressure control lever 84 so as to engage adjustable screw 86 with valve stem 87 and thereby open the tire valve 8|. As a result, the air pressure inside of bellow 55 becomes equalized with the outside air pressure and bellows 55 then can expand sufficiently to reclose tire valve 8|. In this way a predetermined equalized pressure is always provided inside the bellows 55 when bulb 58 is cooled.

When bulb 58 is heated, the resulting increase of internal air pressure causes bellows 55 to expand relatively quickly until the knob 90 on lever 59 engages adjusting screw 9| and tilts lever 84 to press adjusting screw 86 against valve stem 81 to open valve 8| andthereby release some of the increased pressure inside of bellows 55. When the pressure inside bellows 55 is thus released, valve 8| is automatically reclosed. In this way, even though bulb 58 is finally heated to a relatively high temperature, the pressure inside of bellows 55 is always prevented from increasing beyond a predetermined maximum value. Consequently, by means of the improved pressure regulating valve mechanism bellows 55 is able to respond relatively quickly to a relatively small increase or decrease of the temperature of bulb 58 to effect reverse operations of interlocking member 62. This in turn enables a very quick and positive response of bellows 55 to the establishment or termination of combustion to be obtained.

The combustion responsive device 21 is describe Operation With the various parts in their respective positions shown in Fig. 1, the oil burner |0 is started into operation upon closure of the master control switch 28. Thi first closes a time delay heating circuit extending from the secondary of transformer 25 through relay winding 24, conductor I55, master switch 28, conductor |0|, switch plate 35, abutting contacts 36 and 31, strip 45, arm 4|, strip 42, support 43, conductor I52, heater 3| and conductors I03 and H14 to the opposite terminals of the transformer winding. Due to the current limiting action of electric heater 3|, the resulting limited energization of relay winding 24 is below the pick-up value and hence is ineffective to cause response to the relay to close contact 23. However, heater 3| begins to heat thermal timing element 30 to produce movement of the upper end thereof to the left as indicated by the arrow I-I. Magnet 46 holds plate 4| in attractive relation therewith so as to maintain contacts 36, 31 n abutment during a predetermined heating period of element. As' ndi a ed in F 2, th s h ati g er od e tends from the initial starting time To when master switch 28 closes its contacts to time T2 when contact 31 becomes separated'from contact 36 due to engagement of arm M with the extension 4'! of the adjustable stop 48. During this heating period, thermal element 30 carries plate 35 to abut contact 36 with contact 38 at a time indicated in Fig. 2 as Tl. Thus during a relatively short interval between time TI and time T2 contact 36 is maintained in abutment with both contacts 31 and 38. 1

' Upon abutment of contact 36 with contact 33 at time TI a parallel circuit is closed shunting the electric heater 3|. This parallel circuit extends from contact 36 through contact 38, strip 50, and a suitable current limiting resistor i 35. With resistor Hi thus connected in parallel or shunt with the electric heater 3 i, the relay winding 24 now becomes sufficiently energized to pick up and eflect operation of relay contact 23 from its normally opened position in which it is shown to the closed position to start operation of burner Hi.

Upon closure of relay 23 the oil burner operating motor H is energized from supply line Ll. through conductor Hi1, relay 23, conductor tilt, the energizing winding of motor ll and conductor I09 and the usual safety limit switches lie. Also, the closure of relay 23 energizes the igni tion transformer 2!, the circuit extending through conductor Hi, normally closed ignition control switch contacts ll, conductor H2, the primary ignition transformer 2i, and conductors H3 and i539 and limit switch till. With both motor H and ignition transformer it thus energized upon closure oi relay 23 at time Tl in the diagram of Fig. 2, the subsequent operation oi. oil burner iii should successfully establish combustion within a limited time thereafter. During this limited time contacts 5! and 52 bypass the master switch 23 to insure against the difficulties that might result from chattering of the room thermostat contacts.

Let us assume that combustion is initially established at time E, as shown in diagram of Fig. 2, during the cooling period of thermal element 38. At this time relay 23 is maintained effectively energized entirely by the shunt circuit including resistor I95 since thermal element 3!! had previously moved contact plate 35 in the direction of the arrow suiiiciently to pull arm 4|, through the agency of magnet 4%, into engagement with adjustable stop 4'! and thereby release the arm from the magnetic attraction of magnet .6. Thereupon arm M and strip 49 are biased by resilient strip 22 to move to the right until extension I l engages with the sloping cam surface lfia of the adjustably mounted cam 33 so as to carry arm 6! entirely out of attractive relation with magnet 46 and contact 31 out of abutment with contact 36 and thereby open the circuit through electric heater 3i and thus terminate the heating period and initiate the cooling period of thermal element 39 at time T2.

With combustion established at time E as assumed, the bulb 58 will quickly become heated to expand bellows 5-5 and thereby relatively quickly operate interlocking member 62 upwardly so as to move arm ll to the left due to carnming action of the sloping surface 13a on extension it and thus return arm ll into the position indicated by the dotted lines in Fig. 3 to be attracted by magnet All when the latter returns-to itsnormal starting position as shown in Fig. 3. The further upward movement of member 63 also will position finger 69 in the path of extension ill, finger H in the path of the projection l2 and engage finger T5 with the arm it to separate contact 11 and thereby deenergize the ignition transformer 21. Thus as thermal element 30 continues to cool, finger ll engages with extension 12 to separate contacts 5|, 52 and thereby remove the by-pass circuit around the master control thermostat 28. Shortly thereafter, projection I0 engages the finger 59 so as to block further movement of plate 35 to the right even though thermal element as continues to cool. Consequently, contact 3% is maintained in abutment with contact 38 by the blocking engagement of finger 69 with extension in in response to establishment and maintenance of combustion during the cooling period or thermal element 30.

Under assumed conditions, when combustion is once successfully established and maintained during the cooling period of thermal element 38, the burner motor ii is thereafter operated under the joint control of the combustion responsive device 2?, master control switch 2b and relay 23. Thus, in case for any reason combustion should fail after time T3, the improved control insures an automatic restart of the burner in the following manner: Upon the initial cooling of bulb 58 bellows be relatively quickly responds to move interlocking member 62 downwardly and thus disengage finger its from extension 1!) and thereby free plate 35 for snapaction movement contact 3"! due to the resilient biasing action provided by the cooling of thermal element 30.

Such reengagement of contacts 3% and 31 after termination of combustion is obtained solely due to the {act that when finger B9 disengages extension it to release plate 35 for snap action movement, the cam surface 53a of interlocking finger is still engages extension it of arm il as indicated by the dotted lines in Fig. 3 and thus holds arm t! in a position to again be at tracted and thereby held by magnet 56 and consequently maintain contact 3i in engagement with contact 36. Upon the release of plate 35, contact 36 disen'gages contact 38 and thereby opens the maintaining circuit through resistor for relay 23. As a result relay 23 returns to its open position and deenergizes burner motor H.

Upon the snap action reengagement oi contacts 36 and 31 just described, the electric heater 3! again is energized and thermal element 36 again is heated to restart burner operation in precisely the same timed cycle as described above. Furthermore, exactly the same automatic restart operation is obtained in case of voltage failure of the power supply lines Li, L2, wheneverthe power failure is of sumcient duration to produce a. response or the combustion responsive device 2? to slow down or stop the burner operation and thereby cool bulb 53.

In case a normal burner operation has con-- tinued sufficiently to satisfy the demands of the master control thermostat 28, the opening of the thermostat contacts will deenergize relay 23 and thus stop further burner operation at time Trc shown in Fig. 2. In this case, contact 36 is returned into engagement with contact 31 and magnetite into attractive relation with arm M in exactly the same manner as previously. de-

scribed. Thus the improved control is ready to to reengage contact 38 with V restart the burner whenever the master switch 28 again recloses its contacts.

Let us now assume that due to some fault of the burner it, combustion is not successfully established during the cooling time or" thermal element 36. In this case interlocking member 62 will remain in its initial position during the entire starting cycle time since bulb 58 is not heated and bellows 55 is not expanded. Hence, the adjustable interlock stop 73 is maintained in its initial lockout position shown in full lines in Fig. 3 to engage with extension H without exerting any cumming action thereon that would tend to return arm il into attractive relation with magnet 43. Consequently arm 4! when released at time T2 moves in accordance with its bias provided by resilient strip 2 as adjusted by screw 4 to a lookout position that is out of attractive relation with magnet 4G when thermal element 39 has cooled as shown by the dot-dash lines of Fig. 3. Thus, when element 39 has cooled extension is will engage with the flat end of interlocking member 52 but arm 43! will not be magnetically attracted or held by magnet 15 and thus contact 37 will not abut contact 36. In this way the improved control is automati cally locked out when combustion is not successfully established by a predetermined time L that is before the end of the cooling time T3.

T0 restart burner operation after such an automatic lock-out and after the burner fault producin the look-out has been corrected, the manual push-button H5 is operated to engage the extension H6 with arm 45 to move this arm into magnetic attractive relation with magnet 46. At the same time extension iii engages with strip to so as to move contact out of the range of movement of contact 35. Only a momentary operation of the reset button H5 is required since arm 4| will at once be held by magnet es and pushbutton it 5 may then be returned to its initial position by spring H8 to restore the whole control again to its normal operating condition.

t will be understood that in case a non-chattering type of room thermostat 28 is employed, then the thermostat automatic shunting contact control comprising the contacts 5!, 52 may be omitted if desired. Likewise, in case deenergization of the burner ignition system is not desired after combustion is established, the ignition control switch 7? also may be omitted. Furthermore, while the preferred form of air pressure responsive bellows combustion responsive mechanism has been disclosed for operating the interlocking control member 62, it will be understood that this control 52 may, if desired, be operated by any other suitable forms of combustion responsive devices such, for example, as a conventional expansible tube and rod or the like.

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

1. A condition responsive timing and sequence control having in combination circuit control means including a switch for closing a circuit, means for closing said switch upon termination of a predetermined condition including a condition responsive device, a thermal timing element having an electric heater in said circuit for opening said switch upon a redetermined heating of said element, and interlocking connections b tween said device and said element for maintaining said switch op n upon non-response of said device to said condition during cooling of said element.

2. An electrically operated burner control having in combination burner starting means including a switch for closing a circuit essential for burner operation, means for closing said switch upon termination of operation of the burner including a combustion responsive device and a thermal timing element having an electric heater in said circuit, means for opening said switch after a predetermined heating of said element, and means interlocking said combustion responsive device and said thermal timing ele: ment for maintaining said switch open to lock out said burner starting means upon non-response of said device to combustion during cooling of said element.

3. An electrically operated burner control havin in combination burner startin means including a switch for closing a circuit essential for burner operation, means for closing said switch after a heating cycle operation of the burner establishing combustion including a, combustion responsive device and a thermal timing element having an electric heater in said circuit, interlocking connections between said device and said element for opening said switch upon a predetermined heating of said element and for maintaining said switch open to lock out said burner starting means upon non-r spouse of said device to combustion during cooling of said element, and manually Operable means for reclosing said witch to restart burner operation.

A condition responseve timing and sequence control having in combination control means ineluding abutting contacts for closing a circuit, means biasing one or" said contacts to open said circuit, timing means including a reversely movable thermal timing element carrying the other of said contacts and having an electric heater in said circuit and provided with releasable magnetic holding means for maintaining said one contact in abutment with said other contact until after a predetermined heating of said element, and sequencing mean including a condition responsive device and cam operated interlocking means responsive thereto fo controlling said one contact to maintain said contacts out of abutment upon non-response of said device to a predetermined condition during cooling of said element and for abutting said contacts upon termination of said condition after cooling of said element.

5. A condition responsive timing and sequence ci'cuit control system having in combination a first circuit having abutting contacts for closing said circuit, timing means including a reversely movable thermal timing element carrying one of said contacts and having an electric heater in said first circuit and provided with releasable means for maintaining the other of said contacts in circuit closing abutment with said one contact until after a predetermined heating of said element, a condition responsive device having connections for controllin the other of said contacts to maintain said contacts out of abutment upon non-response of said device to a predetermined condition during cooling of said element, a second circuit having abutting contacts for closing said second circuit, one carried by said element into circuit closing abutment with the other upon said predetermined heating of said element and interlocking means operated by said condition responsive device for maintaining said second circuit controlling contacts in abutment in response to occurrence of said condition during said cooling of said element and for main taining said first circuit closing contacts out of abutment until termination of said condition.

6. A condition responsive timing and sequence control having in combination electroresponsive condition control means having energizin means including a circuit and a switch for closing and opening said circuit, means for closing said switch including a condition responsive device and a thermal timing element having an electric heater in said circuit, and means interconnecting said condition responsive device and said thermal timing element for opening said switch after a predetermined heating of said element and for maintaining said switch open upon non-response of said device to a predetermined condition during cooling of said element.

7. A condition responsive timing and sequence control having in combination a circuit including an electric heater and a switch for closing and opening said circuit, electroresponsive means dependent upon closure of said circuit for establishing a predetermined condition and having a maintaining circuit, means for closing said switch including a condition responsive device responsive to said condition and a thermal timing element heated by said heater, and interconnecting means between said condition responsive device and said thermal timing element for controlling said maintaining circuit upon establishment of said condition and having correlated connections for opening said switch again after a predetermined heating of said element and for maintaining said switch open until termination of said condition after cooling of said element or upon non-establishment of said condition during cooling of said element.

8. A condition responsive timing and sequence control having in combination circuit control means including an elongated reversely movable thermally responsive timing element having an electric heater and having switching means for sequentially closing one circuit and opening another circuit including said heater during a heating interval and for sequentially opening said one circuit and reclosing said other circuit during .a cooling interval, means including an electroresponsive device for normally establishing a condition during closure of both said circuits and maintaining said condition established upon continued closure of said one circuit, and a condition responsive device having cam interlocking means associated with said timing element for controlling said switching means to maintain said one circuit closed upon establishment of said condition before the end of said cooling interval and for preventing reclosing of said heating circuit upon cooling of said element only after failure to establish said condition before the end of said cooling interval.

9. A condition responsive timing and sequence control having in combination means including an electroresponsive device for normally establishing and maintainin a condition during effective energization of said device, circuit means including parallel circuits for effectively energizing said device only upon closure of both said circuits and the simultaneous passage of current through both circuits of said device and upon subsequent continued closure of one of said circuits, means for closing the other or said circuits including an electrical timer operable responsively to said closure or" the other of said circuits and having a first switching means for maintaining said other circuit closed only forfan interval and a second switching means for closing said one circuit before the end of said interval to effectively energize said electroresponsive device, and means including a condition responsive device having one interlocking means for maintain-' ing said second switching means closed to maintain said device effectively energized upon establishment of said condition before the end of a second interval and another interlocking means for maintaining said first switching means ineffective to reclose said other circuit after failure to establish said condition before the end of said second interval.

10. A condition control system having in com bination a first switch, a thermal timing operating element for closing said switch during heating of said element and opening said witch during cooling of said element, a condition responsive device having interlock means for maintainin said first switch closed during the occurrence of a predetermined condition, a second switch having correlated operating means including said condition responsive device and said thermal ele: ment for closing said second switch only after opening said first switch upon the termination of said predetermined condition and maintaining said second switch open after the non-occurrence of said condition, said thermal element having releasable holding means for maintaining said second switch closed for an interval after said closing of said first switch during said heating of said element, an electric circuit under control of said second switch and including in series a master switch an electric heater for said thermal element and an electroresponsive device having means for controlling said condition, and a resistor for shunting said heater upon closure of all said switches to effectively energize said electro responsive control device to establish said condition and maintain said device efiectively energized to maintain said condition under joint control of said master switch and said first switch upon opening of said second switch.

11. A condition responsive timing and sequencing control mechanism having in combination three movable switch members having contacts for selectively controlling two parallel circuits. a master switch for controlling the closure of said circuits by said switch members, time delay operating means for one of switch members including a reversely movable thermally responsive operating element having an electric heater energized under control of said master switch upon closure of one of said circuits for heating said element to operate said one switch member with a time delay after closure of said one circuit and to contact a second of said switch members to close the other of said circuits, releasable means under control of said operating element for maintaining the third of said switch members in contact with said one switch member to maintain said one circuit closed until the end of a limited heating interval for said operating element after said other circuit is closed, and condition responsive means having a movable interlocking memher for cooperating upon the occurrence of a predetermined condition before the end of a secone. interval beginning at the termination of said first interval with said operating element to maintain said one and said other switch members in contact upon cooling of said operating element,

and means under joint control of said condition responsive means and said operating element for controlling the reestablishment of tween said one switch switch member after cooling contact bemernber and-said third of saidel'ement and dependent upon the occurrence or absence of said condition before the end of said second interval.

12. A variable temperature responsive timing and sequence control having in combination control means including abutting contacts for closing a circuit, means biasing one of said contacts ing the other of said contacts and having an electric heater in said circuit and provided with recontact until after a predetermined heating of said element, and sequence control means including an initial reverse temperature change responsive device and cam interlocking means for con trolling said one contact to maintain said contacts out of abutment upon non-response of said device to a predetermined initial reverse tem perature change during cooling of said element and for reabuttins, said contacts only upon occurrence of an opposite initial reverse temperature change after cooling of said element.

13. A temperature change responsive timing and sequencing control, having in combination electroresponsive temperature control means having energizing means including a circuit and a switch for closing and opening said circuit, means for closing said switch includng a temperature 12 change responsive device and a thermal timing element having an electric heater in said circuit and having correlated connections including a magnet carried by said element for holding said switch closed and a stop positioned to engage said switch for opening said switch after a predetermined heating of said element and means including a movable stop member positioned by said taining said switch open upon non-response of said device to a predetermined temperature change during cooling of said element.

ALBERT WELL-MAN.

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

UNITED STATES PATENTS Number Name Date 1,674,051 McCabe June 19, 1928 2,076,967 Shaw Apr. 13, 1937 2,102,656 Vaughn Dec. 21, 1937 2,135,829 McGoldrick Nov. 8, 1938 2,231,209 Dillman Feb. 11, 1941 2,346,284 Baak Apr. 11, 1944 2,367,059 Rothwell et al Jan. 9, 1945 2,384,372 Eaton Sept. 4, 1945 2,408,047 Cunningham Sept. 24, 1946

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