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Publication numberUS2941308 A
Publication typeGrant
Publication date21 Jun 1960
Filing date27 Jul 1956
Priority date27 Jul 1956
Publication numberUS 2941308 A, US 2941308A, US-A-2941308, US2941308 A, US2941308A
InventorsCobb Clifton A, Williams James T
Original AssigneeWhirlpool Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Laundry drier heater element control
US 2941308 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

9 June 21, 1960 c. A. COBB ETAL 2,941,308

LAUNDRY DRIER HEATER ELEMENT CONTROL Filed July 27, 1956 3 Sheets-Sheet 1 E I ns n36 INVENTORS CLIFTON A. COBB JAMES T. WILLIAMS ATTO R June 21, 1960 c. A. COBB ETAL LAUNDRY DRIER HEATER ELEMENT common 3 Sheets-Sheet 2 Filed July 27, 1956 & ME H E lwllh ruTwmw l 1 4? I: It 116% BO 140 a 166 i] F Ill/Iggy] INVENTORS CLIFTON A. COBB JAMES T. WILLIAMS BY uvr% ATTORNEYS United States Patent LAUNDRY nnrER HEATER ELEMENT CONTROL Clifton A. Cobb and James T. Williams, St. Joseph, Mich, assignors to Whirlpool Corporation, a corporation of Delaware Filed July 27, 1956, Ser. No. 600,541

18 Claims. (CI. 3448) The present invention relates to improvements in domestic clothes driers and especially to an operating control which operates in response to the pressure of the air flowing through the drier air circuit system.

Clothes driers of the domestic type generally employ a clothes containing chamber in which the clothes are placed while being subjected to a circulating heating air which causes an evaporation of the moisture therein to dry the clothes. The container is usually in the form of a rotating drum and an intake conduit having a heater therein directs warm air to the drum and a discharge conduit leads the air away from the drum. A powered fan is usually provided to provide a circulation of air through the drum. During circulation the air may pick up lint from the clothing. A lint trap may be provided at the discharge conduit to catch the lint and prevent the lint from being discharged into the room.

During continuous operation especially with certain types of clothing or garments, the lint trap may catch an excess amount of material thereby slowing the flowage of air through the conduit below a safe level so as to cause an overheating of the heating elements in the intake conduit. If the heating elements are not turned off damage to the machine may occur and a conflagration of the combustible materials in the neighborhood of the drier, such as the oil for the bearings, the waste lint which may be caught in the corners of the machine or even the clothing within the drier may catch on fire. It is also important that the other operating elements such as the blower fan do not overheat and that the air heater does not reach a dangerous temperature for any reason.

Another problem which is encountered in drier operation is the control of the heating elements. With a substantial flow of air through the drier, heat from heating elements of considerable size must be supplied. If these elements are electrical in nature, to suddenly throw them on the supply circuit will create too high a current fiow and will very likely blow a fuse. Further the heaters must be capable of bringing the heating chamber quickly up to the appropriate temperature and then be controllable to maintain the chamber at the proper temperature during operation.

It is therefore an object of our invention to provide a simplified reliable safety mechanism which will automatically turn ofi the heating elements for the clothes drier when an emergency condition is encountered.

Another object of the invention is to provide a control mechanism for the heating elements which will automatically function to either turn ofi the heating elements or signal the operator when a reduced flow of air through the drier occurs to prevent overheating of the elements.

Another object of the invention is to provide an improved control mechanism for the heater elements which is capable of being used to vary the number of heating elements used in accordance with the temperature in the air heating chamber and in accordance with the amount of air flowing through the drier.

Another object of the invention is to provide a control mechanism for the heaters of a drier in which a plurality of heaters are provided and an automatic time delay is used for placing the various heaters into operation.

A still further object of the invention is to provide an improved simplified and more reliable time delay mechanism which is operated by the air circulating through the clothes drier.

Another object of the invention is to pro'vide a mechanism for simply and quickly turning ofi? the heaters at the end of operation or for an emergency condition with expensiveout the provision of additional switches or equipment.

A further object of the invention is to provide a safety mechanism which will turn off operating elements of the machine automatically when the lint filter is filled with lint.

A further object of the invention is to provide improved and simplified electrical circuits which will reduce the' number of switches and operating elements required and the size of the elements and switches to perform a starting and stopping of the machine as well as a means for ter minating operation as a safety measure.

Other objects and advantages will become more apparent to those skilled in the art with the following specification and appended drawings, in which:

Figure 1 is an elevational view of the clothes drier taken from the rear of the drier with portions of the cab-' inet broken away and with parts of the interior shown schematically to illustrate the operating elements of the machine;

Figure 2 is a side elevational view of the machine with portions of the cabinet broken away to better show the important and basic operating elements, with portions of the elements being shown schematically;

Figure 3 is a plan view of the improved time delay mechanism of the present invention;

- Figure 4 is a vertical sectional view taken along the line IV-IV of Figure 3;

Figure 5 is a vertical sectional view taken along line V-V of Figure 4;

Figure 6 is a sectional view taken along line VI-VI of Figure 4;

Figure 7 is an enlarged detailed sectional view taken along line VII-VII of Figure 4;

Figure 8 is a diagrammatic View of the circuit employing the preferred embodiment of the principles of the invention;

Figure 9 is a circuit diagram of an alternative circuit which may be used; and,

Figure 10 is another diagram of an alternative embodiment of a circuit that may be used.

The features and principles of the invention are shown in the drawings and described in the present description as the means being incorporated in a domestic type clothes drier. Although this construction afifords and partakes of the advantages and attainments of the invention, it is to be understood that the methods and proc esses of the invention and the features thereof may be utilized in various other types of mechanisms and in various other circumstances without departing from the vided which functions to contain the clothes while they are being subjected to the heated drying air. The drum .12 is supported for rotation on a horizontal axis on a shaft 14 suitably secured to the end of the drum and the shaft or axis 14 is suitably supported in a bearing 16 which may be of the cantilever type. Secured to the shaft 14 is a driving pulley 18, and for purposes of rotating the drum to tumble the clothes therein a belt 20 Patented June 21, 1960 is trained over the pulley 18 which may be a V-pulley and the belt be a V-type belt. The lower end of the belt is trained over a small pulley 22 which is carried 3 a speed reduction idler. shaft 24 -which may be spring base. also support'sthe vertical post 38 which carries. the

drum support bearing16 in its: upper end and which carries the bearing for the idlershaft 24. a

The V-belt 28 also passes over a small pulley 40 which is mounted on the drive shaft 42 of a fan 44. The fan is. mounted in a small housing or fan scroll 46 which is suitably supportedon' the bulkhead 54 within the cabinet so as to be secured adjacent to the rotating drum 12. The fan scroll 46 is anenclosure for the fan and is provided with a discharge opening 48 through which the air is discharged. The fan scroll is provided with an intake opening 50 which leads axially to; the hub of the fan and through which air passes from the drier drum. to be centrifugally discharged. by the fan through the-.

fan scroll and out through the discharge opening; 48 where it passes into the surrounding air such as into the room.

The discharge opening 48 leading from the fan scroll 46 leads outwardly through the rear wall 49 of the cabinet. to-a lint basket 51; The lint basket 51'. is formed of screen or like material which is provided with a multiplicity of small air flow openings so as to permit the normal passage of an air stream but to filter lint from the air. The air being discharged from the air circuit of thedrier must first pass through this lint basket be fore escaping to the room and therefore any lint picked up enroute, such as from the clothing within the drier drum, will be caught andv not be permitted to escape into the-room; This lint basket is removably secured back of the drier drum and must be cleanedat periodic intervals. At times the lint removed. from the clothes will exceed the expected amount or the operator will forget to clean the lint basket and thus the flow of; air from the fan scroll 46 will be impeded. When the flow of air decreases below a. safe level the present invention employs a mechanism as will be ,describedlater to automatically terminate the operation of the heater elements and to actuate an alarm to thereby prevent damage to the machine and to alert the operator as to what has occurred.

The fan as is illustrated in the present drawings serves as a suction fan to draw air through the drier drum 12 and the intake opening 50 is in constant communicationwith the interior of the drum through an annular perforate area 52 of the drum. The perforate annular area 52 in the rear of the drum 12 which leads to theinterior thereof also provides a means of constant communication to the interior of the drum for the air intake or admission conduit 56 which. leads the warm air to circulate within the rotating drum 12.

The heater box 59 carries heating elements 57 and 58 which are shown as resistance electrical coils but also may be in the form of gas heating elements and are. used in order to raise the temperature of the air which passes into the rotating drum. v

,The heating elements if electrical in form as shown at 57 and 58 are operated by control switch. such asa relay as will be described later in. connection with Figure 5. ;If they are gas operated they will be electrically controlled by a solenoid valve, not shown. i I

Although the preferred embodiment of the drawings utilizes a fan 44 which is on the. discharge side of the rotating drum 12 to provide a suction to draw air in through the air circuit, whichconsists of the air intake conduit 219, air admission conduit 56, the. (111 1 and the fan scroll 46, the fan may be placed in other locations with respect to the drier mechanism. For example" in the location shown in Figure 1, the portion of the.

enclosure 46 which has been called the fan scroll will be under pressure from the fan forcing the air ahead of it out the discharge opening 48 and the interior of the drier drum 12 and the air intake conduit 219 and the air admission conduit 56 and heater box 59 will be under a slight suction or vacuum as the air is drawn into the drier drum due to the suction of the fan 44. If the fan 44 is omitted and Ya substitute fan is placed at the admission conduit 56 the entire system will be under a slightpressure, due to the air being forced through the drum aud'out, the discharge chamber. The build up in pressure due to. the air being forced ahead of the fan is due to the frictional resistances, and change of size of air passageways of the system.

ambient or room air and the air within the drum within the air intake conduit 219 within the admission conduit: 56,, and within the fan scroll 46. The present invention contemplates utilizing this pressure differential in, order to detect the quantity of flow of air through the machine and in order to control a signal and the air heater in response to the quantity of flow.

It is to be understood therefore that in the specification and claims when the pressure within the air circuit or air system is spoken of the position of the fan in the embodiment shown in the drawings is given by way of example and not by way of limitation. The pressure differential which in, the present embodiment is due to higher pressure within the discharge conduit could be sensed'in a difierent part of the air circuit and could be. dueto a lower pressure within the circuit if the fan' for circulating air were located in a difierent portion of the aircircuit. 7 h

The control mechanism is shown generally at 60 in Figures land 2 and is shown in detail in Figures 3 through 7. The control mechanism is shownin the location illustrated relative to the. cabinet 10 for purposes of the present description only and maybe mounted at any location within the cabinet or at some portion remote from the cabinet. The control is apressure responsive time delay mechanism and it is essential that it be connected in some way to the air circuit of the air system which creates the flow of air through. the drier. In the illustration the control mechanism 60 is shown mounted within the drier cabinet at a place handy to the fan scroll 46. The flexible connecting tubing 62 will communicate the pressure within the fan scroll 46 to the control mechanism. v i 7 As is shown in the detail drawing of Figure 4, the control mechanism consists primarily of an actuating member which is operated by a pressure diiferential member.

The actuating member'is shown in the. form of a thin ex ble diaphragm which is circular in shape and which, may be formed of athin pliable material such as rubber. The central portion ofthe diaphragm is reinforced by thin reinforcing metal disks 68 and 70 clamped to either side. In addition to these reinforcing disks an additional disk 72 is clamped on the top side to engage theoperating members of the switches as the diaphragm is moved due to pressure differential. To clamp the disks 68, 70 and 72 to either side of the diaphragm, a reduced shank 74 of a switch actuating pin 76 is pro jected through a hole in the center of the reinforcing disks and the diaphragm. To secure the switch actuating pin in place with the pin extending vertically upright, a fastening member 79 such as a speed nut is secured beneath the diaphragm to the shank 74 of the pin 76.

The diaphragm is mounted within a housing 78 which is comprised of an upper dish-shaped portion 80 and a lower dish-shaped portion 82. The portions 80 and 82 have outer flanged edges which are brought together to clamp the outer edge of the diaphragm 66 therebetween. To secure the upper and lower members of the housing 78.together and to clamp the edge of the diaphragm firmly therebetween the lower flange 86 is bent over the upper flange.

The lower dish-shaped portion 82 of the housing forms a closed or sealed chamber 88 beneath the diaphragm 66; This chamber is sealed with the exception of a vent opening 90, which is normally closed but which may be opened to outside air, and with the exception of the tubing 62 which leads to the air circuit system of the drier. The housing 78 is provided with a hollow boss 110 over which the tubing 62 may be slid for easy connection.

The vent opening 90 comprises a hole through the lower. dish-shaped portion 82 of the housing in which is mounted a rubber grommet 92. Against the outer face of the grommet is positioned a valve head 94 carried on a valve stem 98. The valve stem 98 acts as the armature or movable core of a solenoid, the coil of the solenoid being shown at 102. The valve stem or core 98 is slidably mounted in a metal bearing member 100 secured within a sleeve 101 in the coil 102. Electrical leads 104 and 106 lead'to the coil from a suitable switching arrangement which will be described later to supply electricity -to the solenoid coil 102. The valve stem 98 is normally held during operation in its closed position by the solenoid against the action of a coil spring 111 which connects to the valve head 94 and is connected at its other end to the metal bearing member 100 secured within the coil.

When the coil of the solenoid is deenergized, the valve stem will be drawn downwardly to move the valve head 94 away from the opening 90 to open the sealed chamber 88. When the coil of the solenoid is energized the valve will again move to closed position. The solenoid as a whole is supported on a bracket 108 suitably mounted on the housing 78.

In normal operation therefore, the vent opening 90 is sealed and the closed chamber 88 beneath the diaphragm actuating member 64 is subjected to the pressure of the air circuit of the drier as communicated to the closed chamber 88 via the tubing 62.

The diaphragm or actuating member 64 is shown in Figure 4 in its first or starting position before being subject to pressure from the air circulating system of the drier. When this air pressure is admitted to the closed chamber 88, the pressure on the lower face of the diaphragm will begin moving the diaphragm upwardly. The boss 110 leading from the tubing 62 to the closed chamber-88 has a small circular bore 112 through the center which is the communicating hole leading from the tubing 62 to the chamber 88. This hole is considerably smaller in cross-sectional area than the diaphragm and therefore the air will bleed up into the chamber 88 slowly to cause the "diaphragm to move slowly upwardly. This slow upward movement of the diaphragm will create a time delay during which the diaphragm engages its sequence of switches. Thus through normal operation the starting up of the drier and the circulation of air therethrough will cause a slow upward movement of the actuating member or diaphragm 64.

The chamber 114 above the diaphragm is exposed to atmosphere and the upper portion of the housing is not sealed. Various openings in the upper portion of the housing are present because of the switch connections and in addition a vent opening 116 may be specifically provided to expose the upper face of the diaphragm 64 to the atmosphere.

As the diaphragm moves upwardly it engages a sequence of three switches. The switches 1, 2 and 3 are labeled by enclosed numbers 1, 2 and 3 and this also indicates the sequence of operation of the switches. The

first switch as will be later described in detail with the circuit diagram of Figure 8, operates a first heating element 57 within the heater box 59 and the second switch 2 places in circuit the second heater element shown at 58 in Figure 1. The third switch is not operated in normal operation but is an emergency switch and is connected to an audible or visual signal.

Switches 1 and 2 are similar in construction with the body of switch 1 incorporating a beam member 118 having upturned ears 120 and 122 which pivotally support the beam as is shown in the detail sectional view of Figure 5. Extending through holes in the ears is a pintle bar 1'24 which also extends through downwardly turned support ears 126 and 128 from a support member riveted to the circular plate 130 which forms the upper part of the housing 78 and which is attached thereto by screws 132, 132.

The forward end of the beam carries a shaped leaf spring 134 to which is connected a T-bar 136 that serves to bridge the electrical conducting strips 138 and 140. As is shown in the Figure 3 and Figure 6 the leaf spring 134 is arranged to resiliently carry the T-bar 136 for engagement with and to bridge the conducting strips 138 and'140. The conducting strips are shown in Figure 3 with 140 being the power terminal or the hot strip supplied by the power input terminal 142. The strip 138'supplies the terminal 144 which leads to the heater element. Thus when the T-bar 136 bridges the strips 140 and 138 the electricity will flow from the strip 140 to the strip 138 and to the heating element, the circuit having been completed. The beam 118 which carries the switch bridging T-bar 136 is rocked by a coil compression spring 146 which is secured to the lower face of the beam 118. The lower end of the spring 146 rests on top of the diaphragm 64 and is in direct engagement with the reinforcing disk 72 which is secured to the actuator diaphragm 64. Therefore as soon as the diaphragm 64 begins moving upwardly, the spring 146 will become compressed until the beam 118 swings in a counterclockwise direction as shown in Figure 4 to snap the bridging elements across the conductor strips 138 and 140. The switch moves upwardly with a snap action rather than with a slow action which would cause an arcing across the contacts because of the permanent magnets 148 at the free end of the beam 118. When the pressure in the spring 146 becomes sufiiciently large the end of the beam will break away from the magnet and the switch will snap shut. It will be recognized that overcenter or toggle type switch linkage may be utilized instead of the magnet arrangement shown. Through the center of the magnet 148 extends an adjustment screw 158 which bears downwardly against the beam 118 and which is adjustable to adjust the spacing between the beam and the magnet to reduce or increase the resistance necessary to swing the beam 118. This adjustment is made in accordance with the requirements of the system as dictated by the strength of the actuator diaphragm 64 and of the spring 146.

When the switch member 1 has been closed, switch member 2 is next closed to close the circuit of the second tir actuator diaphragm164 must have moved up to the o tediine jposition of Figure 4 by compressing spring 1 46'until it reaches and beginsto compress the spring 160. The spring 16d is secured beneath the end of the beam 162'whichsupports switch 2. The beam 162 of switch 2 also'carries at its end a leaf spring 164 which supportsja Tbar 166. The T-bar is movable upwardly with the rocking of the beam 162 to create a bridge across contact'strips 140. and 168as is shown in Figure 3. Strip 140 is continuous from the terminal 142 and is the power stripandwhen the T-bar 166 bridges across from the power strip to the strip 168 electrical current is fed to the terminal 170 which leads to the second heating ele ment 5.

'"Thes'witch-carrying beam 162 is shown in the switchclosed position in'Figure 4. In this position theend of thebeam 162 is separated from its magnet 172, the magnet also being provided with an adjustable spacing member 174. The beam itself is supported by upturned ears 176,. only one of which isshown since the construo tions is similar to that of the beam 118 shown in detail inFigure 5, The upturned car 176 is connected to the ear 178 ;o f the support by a pintle bar 180 whichextends through holes in the ears.

'When'the coil compression springs 146 and 160 have been sufficiently compressed to close the respective switches 1' and 2, the resistance of the springs will be such to; hold the'actuating diaphragm 64 in a static position since their resistance will equal the force of the air pressur'efin theclosed chamber 88 beneath the diaphragm. Therefore only an increase in pressure which is in excess of a normal amount will cause a further upward movem e 1 1 t of the diaphragm. This excessive amount of pressurewill becaused only by an abnormal operating condition such as occurs if the lint basket becomes stopped to slow down thecirculation of air below a safe volume. In the normal operating position the switch actuating pin 76 .will be'in the dotted line position of Fig. 4.v Howevenwhen' an excessive pressure builds up within the drier to cause the actuating diaphragm64 to compress the springs146 and 160 'an abnormal amount, the switch actuating pin 76 will move upwardly to close the switch 3. "Switch 3 closes the circuit to a signal mechanism to warn the operator of the clogged lint screen. Since a reduced fiow of 'air would cause a sudden increase" in temperature of the heatingelements anda possibility of the'goccurrence of a fireand at least damage to themachine, it is important that the heating elements be immediately'turned 01f. It will be understood that although electrical heating elements are shown in the preferred embodiment, the

mechanism can be employed with gas heaters wherein solenoid valves are used to supply gas to the heaters. The solenoid valves will therefore be controlled to turn off the gas of the heater instead of the heater being turned directly oif by being taken out of the electrical circuit.

It will also be understood that although switch 3 is shown in the circuit and isdescribed herein as being connected to a signal mechanism, other operating elements of the drier could be operated by switch 3 and if desired the entire machine could be turned off or only select elements of the machine turned off in addition to or instead of operating the signal. Switch 3 is shown'in'detailin Figures 3 and 7. As is shown in Figure 7 the switch incorporates a cantilevered leaf spring switch arm 182 which carries a switch'contact 184; extreme end of the switch arm'1fi6 is biased upwardlyby the normal tension of the spring against an adjustment screw 188 which is adjustably threaded into the plate 130. Adjustment of the screw 188.contro1s the spacing between the terminal 184 and the electrical strip 140. "This will of course control pressure required for theswitch actuating pin 76 to move the contact 184 against the ele'ctrical 'strip140.' As the pin 76 moves up wardly and engages the leaf spring 182', the terminal; 184'will be pushed against theconduc'tin'g strip l lfl to close the circuitto'the't'erminal'190} Terminal l90 com-f pletes the circuit, as will be shown'l'ater in connectionwith the" circuit dia ram, to the alarm whi h maybeinform of a buzzer in order to alert the operator of the reduced air flow creating a build' up of-pres'sure'withinthedfier. v

'With reference to the circuit diagram 0i Figure; 8- it; will be seen that electricity is suppliedior ope'r'ating the.

machine-through the usual 220 volt line wherein the leads are labeled L larid L The" neutral line is labeledwith. N. The heater elements "shown at 57 and-'58 are con nected across the 220 volt line whereaslthe other operat ingrnechanism is connected from the neutral-to one 'ot thelines to operate on volts; The drier is prefer-- ably automatic in nature and as such iscontroiled by a time cycle switch which is not shown. in detail sincei. it is not absolutely essential to the operation ofsthis iiivention and if usedmay be of various types known as the art. The switch generally is operated by timer motor' as is labeled in the circuit diagram and operation oflthe. timer motor is begun by manually turning or .settingthc switch until the timer switch is closed to icomlpleteifthe circuitthrough the timer motor. The timer motor. then begins operating automatically and will sequentiallysep'a'- rate the contact from the power contact 192 and later separate contact 194 from the power contact 192 to' stop. the machine. Separation of the-first contact 190mm; the power contact"192 will turn offithe heatereler'nent's and separation ofcontact 19.4.will terminate operation. of the machine by stopping the drier motor. ThellOzvol-t circuit through thetimer switch to the timer. motor and d'rie'r'motor is completed through a door sv'vitichz 19.7 which may or maynot ,be provided but if provided breaks the circuit to'stop the drier motor and timer motonantoe matically when the door ,15, as shown in,Fig. 2,.of the, drier is opened. When thedoor is againclosed .thecir: cult is completed to reconvene operation of the timer motor and drier motor.

Bringing the contacts 190, and 192 of the timer switch together also completes the circuit, through. the valve. solenoid .96which is in series circuitwith the fan bone: ing safety switch and ithe heater box safety switch.196 and .198, respectively. The heater box safety switchjs a heat responsive switch which will be set to, open when an excessive heat is encountered within the ,heatenbox 59- as is shown in Figure 1. During normal operation this switch will remain closed and complete the circuit through thevalve solenoid 96 -but only on excessive temperatures as .are encountered with some mechanical break: down of the machine will the switch open to automatical ly open the circuit tothe valve solenoid. This of course will vent theunder surface of the diaphragm causing it to drop and open the switches to theheater elements;

The fair housing safety switch 196 is mounted ina suitable location in close adjacency .to the tan 44, If something goes wrong with the fan 44 causingitto over.- heat, the zfan housin g safety switch 196 which is a thermo: responsive switch set to .open at excessive temperatures, will break the circuit to the valve solenoid 96. However, during normal operation the safetyswitch 196,will re- 'ma'in closed.

As previously described the valve solenoid 96 inoperative position closes the vent hole 90 to seal the chamber 66 below' the diaphragm actuator .64. Thus -the ,dia phragm actuator will keep switches v1 and 2 closed, but if the circuit to the valve solenoid is opened, the r di aphragm actuator 64 will drop, opening the switches to the"heaterelements;v Y i i As the machine, is started, the circuit is completed thrcnlgh the drierfmotora'nd ltimer motor and aspressmfe builds up due to operationof the fan, diaphragm switdhesf l and "2 will' "sequentiallyclose, Asthe flfirst switch l lqs s s" s a p i F 4f .1 t s. atesspla [in circuit. the machine continues td' operate (ii aphragm actuator 64 continues to move upwardly against the compression of the springs 146 and 160 until it closes switch 2. When the switch 2 closes the heater element 58 will be placed in circuit. Since the heater elements are placed in the circuit over a spaced period of time,

a heavy load will not be thrown on the circuit at one time to blow the fuses. Further, as the heater element heats its resistance increases so that the current flow in the first heater will have dropped by the time the second heater is placed in the circuit. The time delay between these heaters may be adjusted and varied as for example from about two to ten seconds, and this may be controlled by various factors such as controlling the size of the opening 112 leading into the sealed chamber 88 below the actuator diaphragm 64 or changing the size of diaphragm and housing.

It is to be noted that an operating thermostat 200 is in circuit with the second heater element 58 and during normal operations While switches 1 and 2 of the diaphragm delay control 60 are closed, the thermostat 200, which may be placed at any convenient location in the air stream passing through the drier, will open and close the second heater element 58 in accordance with the demand of the heat and in accordance with the adjustment to which the thermostat is set. Thus heater element 57 will keep operating at its maximum load and at peak efiiciency permitting the entire unit to operate at maximum efliciency throughout its operation.

If the lint trap fills up so as to cause an abnormal build up of air pressure which indicates the reduction of. flo-w of air through the drier, switch 3 of the diaphragm delay control switch 60 will close. This will complete the circuit, as will be seen in Figure 8, through the lint buzzer sounding an alarm .to alert the operator to what is occurring. The operator can immediately remove the lint from the lint trap to permit operation to continue but if the operator does not do so the heating elements will gradually overheat until the heater box safety switch 198 opens to thereby deenergize the valve solenoid 96 which vents the chamber 88 beneath the diaphragm 64 to permit the diaphragm to immediately drop to open the switches 1 and 2 to thereby take the heating elements out of the circuit.

An alternative arrangement is shown in Figure 9 wherein the diaphragm delay control 60 is connected across the 110 volt instead of the 200 volt circuit to operate relay switches. This permits utilization of switches of a smaller amperage rating and decreases the general cost of the system. As willbe seen in Figure 9, the diaphragm delay control in this case is placed in circuit only by operation of the timer switch and is not continually in the circuit as in the case of the circuit of Figure 8. When the contacts 202 and 204 are connected to the power contact 206, the timer motor and drier motor are first placed in circuit through the door switch. The diaphragm delay control is also thus placed in the circuit and as the drier begins to operate and pressure builds up due to the circulation of air, the diaphragm delay control switches 1 and 2 will sequentially close. As the first switch closes, the circuit through the first relay coil 199 will be first closed, closing its relay switch to place the heater element 57 in the circuit. As the diaphragm actuator 64 continues to rise the switch contact 2 will next close completing the circuit through the second relay 197 which closes its relay switch to complete the circuit through heating element 58. The operating thermostat which is in series with the second relay switch will complete the circuit through the heating element 53. Both relay coils are connected in series circuit with the fan housing safety switch 196 and the heater box safety switch 198 and as these switches are normally closed, the relays will be immediately placed in circuit. These switches as will be recalled will remain closed unless the fan housing or the heater box reaches an excessive temperature whereupon the switches will open as a safety measure and will release the relay switches to take the heater coils 57 and 58 out of the circuit. This arrangement permits omission of the valve solenoid 96. Again, the contact 3 of the diaphragm delay control will not close unless excessive pressure builds up within the air circuit system of the drier and if this occurs and switch contact 3 closes the lint buzzer will sound to alert the operator as to what has occurred.

With reference to Figure 10 another circuit arrangement is shown. In this circuit centain details are changed for the sake of economy and for certain operational objectives. As the timer switch is closed, power contact 210 is connected to contacts 212 and 214. Contact 212 closes the circuit to the timer motor and the drier motor through the door switch. The contact 214 closes the circuit to the diaphragm control and as pressure builds up within the drier, switch 1 of the diaphragm control 60 will be closed. It is to be especially noted that a simplified model of the diaphragm control is herein employed with switch 2 omitted. In this instance the only time delay which will occur will be in the closing of the first switch and there will be no time delay between placing the heating elements in circuit. The two heating elements are placed in circuit at the same time and are both connected to the relay switches 216 which are operated by relay coil 218. When the diaphragm control switch 1 closes, the relay coil 218 will immediately be in circuit with the heater box safety switch and the fan housing safety switch which are in their closed position. This circuit arrangement also permits omission of the valve solenoid 96.

The diaphragm control of Figure 10 still retains the contact 3 which is in circuit with the lint buzzer and if a stoppage of the air flow occurs, the buzzer alarm will sound by virtue of switch contact 3 being closed.

Although the operation of the mechanism will be now understood from a description of the structure and operation of the various parts an over-all description of operation will be helpful in understanding the objectives and attainments of the invention. The drier is first placed in operation by a manual starting of the timer switch as is shown in Figure 8. This closes the circuit to the drier motor 34 and to the timer motor shown in the circuit. As the motor 34 starts, it operates the fan 44 as shownin Figure 1 to build up a pressure within the fan scroll 46 and to draw air through the drier drum 12 and through the air intake conduit 219 and admission conduit 56. As

1 the air circulates through the drum it passes over the heater elements 57 and 58 to be increased in temperature. As the pressure builds up in the fan scroll 46 air flows through the tubing 62 into the time delay element control 60. As is shown in Figure 4 the air will build up pressure in the closed chamber 88 to cause the actuator diaphragm 64 to be slowly raised. As the diaphragm raises it pushes upwardly on the spring 146 until the beam 118 separates from the magnet 148 to bring the T-bar 136 across the electrical strips 140 and 138. This completes the circuit to the first heating element 57. As the actuator diaphragm 64 continues to raise, it next closes switch 2 by engaging the spring and causes the beam 162 to rock in a clockwise direction as is shown in Figure 4. As the T-bar 166 is brought across the contact strips 140 and 168, the circuit is completed to the second heater element 5-8.

The actuator diaphragm 64 will remain in this position unless an excessive pressure is created within the discharge conduit 46 such as by stopping of the lint trap 51. This excessive pressure will cause an increase raising of the actuator diaphragm 64 until the switch actuator pin 76 closes switch 3. This will complete the circuit to a buzzer or an alarm to alert the operator as to what has occurred. If the condition is not corrected the heater box 59 will overheat or the fan scroll 46 will overheat and the safety switches therein will open the circuit to the valve solenoid shown generally at 96 in Figure 4. When this circuit is open the valve head 94 moves downwardly to open the vent 90. This immediately bleeds air from the closed 1 1 chamber 88 permitting thediaphragrn 64*to drop thus immediately opening the. switches 1 and Z'ofthe time. delay element control andltaking the. heating elements "57 a'nd'58 out of circuit to preventidanger of a fireor prevent damage to. the. operating mechanism.

Thusit willibe seen that we have provided a control mechanism for a heater which meets thexobjectives hereinbefore set forth. Theamechanism is simple and reliable in operation and.presents.-an improved time delay mechanism: which operates from the air, pressure differential which. occurs with operation of the drier system. The mechanism. positively prevents the dangers of fires and prevents damage-to the equipment by automatically turning off the heater. in case.of a decreased'fiow ofair throughv the machine. Further, the time delay mechanismplaces the. heater. elements in circuit in sequence so a s to prevent ausevereload being thrown on the circuit at one time- Themechanism issprovided with a simplified inexpensive-air escape-.vent-which functions to quickly and surelyturnoff the heater elementsin cases of emergency as determined-by the safetycontrol switches; The entire mechanism-utilizes a minimumnumber of switches and the structure is simpleand foolproof in construction and will tope'rate over longwperiods of time with aminirnum of attention and without adjustment.

We have, in-the drawings andspecification, presented a 'detailed disclosure of thepreferred embodiments of our invention, butit is to be understood that we do not intend to limit theinvention to the specific formdisclosed but intend tocover all-modifications, changes-and alternative constructions and methods falling within the scope of the principles taught byour invention.

We claim as our invention:

1: A; mechanism for controlling the .operationof a "clothesfdrier including-a drier chamber, operating elements, and air admission-and discharge-conduits with a fanto driveair through the air circuit including the conduits and drier chamber, the control mechanism comprising an actuating member movable in response to a pressure differential between atmospheric air to which one side is exposed and air within'thedrier circuit to whichthe other side is exposed, a housing for said actuatin'g-member movably supporting. said member therein, 'said h ousing exposing one side of "said actuating member toatrnospheiea conduit crmriected tc the housing and exposing the other sideof said actuating member to the air circuit of the drier, a first switch positioned to be engauged by the actuating member as it moves in response to pressuredifferential, a second switch'spaced from the 'firstswitch to be engaged by said actuating member after the first switch is engaged by further movement of the actuating member, andfirst and second electrically opcrate-d drier elements performing drier "operating function s when actuated and connected in circuit with said first andsecond switches so asto be operated sequentially with movement of the actuating member in response to a flow of air within the drier.

2. A mechanism for controlling the operation of a clothes drier comprising a drier chamber in which clothes are contained during a drying operationduring which they are exposed to acirculation of heated air, and air admission conduit leading to said clothes chamber, a discharge conduitjleading away from said clothes chamber, sa'id conduits and chamber providing an air circuit for the movement ofair through the drier, a controlhousing, a diaphragm extending across the interior of said control sensi g to divide one end of said housing into a closed chamber and the other -end-into an open; chamber exposedto atmosphere, saiddiaphragm movable in response to a pressure differential between the-closed chambei'fafid the: open chamber, an airjconduit connected. be t n'the aircircuit of thedrier and the closed chamber .of said; control housing, saidair conduit having a cross section less than the cross sectional areaoi -the diaphragm toacreateaz relatively slow movement of-the diaphragm with -flow{of. airythrough said conduit a firstswitch me beengaged thereby, a-second switch-,meansspaeedifrom the first switch to-be subsequently. engaged by continued; movement ofthe'diaphragm, and a first and-second elecq trically. operated means operative to performdrying fun tions :whenactuated and connected respectivelynin'circmj with said firstand second switches to be sequentially oppera'tedbythe actuation of the switches bythe actuating diaphragmas it moves ,inresponse to a pressure change withinthe drier chamber to. manifest. a flow-of air. through; the drier circuit.

3'; Axmechanism for use in connection withtheoperag tion of a: clothes drier which includes .a drier chamber and communicating air admission and discharge. conduits with a fantomove air through the air circuit including the conduits anddrier chamber, themechanism comprise ing -an' Iaetuatingmember movable'in response. to a pres; sure 'ditferentialon opposing. sides, a supportfonsaid actuating .member connected to expose one side of the actuating member to the pressure. within the air circuit and to expose-the other side of-the actuating member-:10 atmosphericair, said actuating -member moving withz'a changeofpressure within the air circuit when air is flow ing-through the drier chamber, a first switch in the path of said actuating member to be operated thereby, axSCCr ond switch-in the pathof said actuating. member to.-.be operatedby saidactuating member after said first switch, resilient switch operatingmeans located between the-first switch and :the actuating member and adapted to be en.- gaged bythe actuatingmemb'er to operate said first switch; means-between the second switch and actuating member to operate the second switch after-the first switch, said resilient switch operating means compressing witlr con tinued movement ofnthe actuating member as the actuating member moves to operate the secondswitch', and first-and second electrically operated means connected in circuit with said switches to berespectively operated in asequential manner by operationof the first and secend switches withmovement ofthe actuating -member.

4. A mechanism forusein connection with the operation of a clothes drier including a drier-chamber-and air admission and discharge conduits with a fan to move air through the air circuit of thedr'ie'r including-said conduits and drier chamber, the mechanism comprising fluid operatedtime delay apparatus operative-between zero time and aswitch operating time, means for connectingthe -timedelayapparatus to said air circuit-to expose the time delay-apparatus to changein pressure Within the air circuit to cause operation thereof, the switch operatively connected tothe time delay apparatus to be operated thereby at the switch operating time electricallyoperated means connected to said switch to be operatedthereby after a flow of air through the drier chamber has begun, and anemergency time delay-return mechanism connected to the time de1ay apparatus and;operative to return the time delay mechanism :to zero time and-to return the switch tounOperated-position.

5. A mechanism for use in connection with'the'op'eration=of a clothes-drier including a clothes drying drum and --air' admission and-discharge conduits with a fan to move the airthrough the air circuit including the conduits and drier drum, the mechanism comprising 'a fluid-pressure differential-operated time delay mechanism, means-for connecting the time delay mechanism :to the air 'cir'cuittoexpose the time delay apparatus to change in pressure in the air circuit with a flow of air through 'said drie r-drum,- an operating switch connected to the :mea-n's responsive .to' a change; of, conditionwith-in ;..the

drier, and time delay return apparatus connected to the time delay mechanism and operative to return the time delay to zero time and connected to said condition responsive apparatus and operative upon the presence of a condition change within the drier to deactuate said switch.

6. A mechanism for use in connection with the operation of a clothes drier including a drier chamber and air admission and discharge conduits with a fan to move air through an air circuit including the conduits and drier chamber, the mechanism comprising an actuating member movable in response to a pressure differential between two operating surfaces thereof, a housing for enclosing said actuating member and creating a closed chamber on one operating surface of the actuating member, means connecting said closedchamber to the air circuit of the drier to subject the chamber to the pressure within said air circuit and cause movement of the actuating member with a change in air pressure due to flow of air through the drier chamber, switch means positioned to be engaged by the actuating member after travel of the actuating member from a first position to asecond position due to said pressure differential, means responsive to a change in condition within the drier and operatively connected to said actuating means to return the actuating means to first position with said change in condition to deactuate the switch, and an electrically operated means connected to said switch to be operated thereby after a flow of air through the drier chamber is inaugurated.

7. A mechanism for use in connection with the operation of a clothes drier including a drier chamber and air admission and discharge conduits with a fan to move air through an air circuit including said conduits and drier chamber, the mechanism comprising an actuating member subject to a pressure differential across operating surfaces and movable between a first and a second position, a housing for said actuating member providing a closed chamber surrounding one of said operating surfaces to atmosphere, means to connect said closed chamber'of the housing to the air circuit of the drier to expose the actuating member to change in pressure within the air circuit as air is caused to flow through the drier chamber to move the actuating member to said second position, 'an air vent leading to said closed chamber and positioned in said housing to permit the closed chamber to be vented to atmosphere, valve means operatively connected to said vent and being operative to permit the actuating means to be returned to said first position when the closed chamber is vented to atmosphere, and drier control means positioned to be actuated by said actuating member when the actuating member moves between first and sceond positions.

8. A mechanism for controlling the operation of a .clothes drier comprising a drier chamber in which the clothes are contained while being subjected to a heated drying air, an air admission conduit leading to the clothes chamber, a discharge conduit directing air away from the clothes chamber, a fan operatively associated with said conduits to move air through said drying chamber,

an actuating member movable in response to a pressure differential across operating surfaces thereof, a housing for said actuating member providing a closed chamber for one .of said operating surfaces and a chamber exposed to atmosphere for the other of said operating surfaces, means to connect said closed chamber to the drier air ,circuit including said conduits and drier chamber, a

valve controlled air vent leading to said closed chamber .and'adapted to be opened to vent the chamber to atrnosphere, means responsive to a temperature of operatng elements of the drier and operatively connected to the valve air vent to open said vent upon the temperature reaching an unsafe level to permit the actuating member to be returned to starting position, switch means positioned to be engaged by the actuating member when 14 moved by a pressure differential, said switch means being disengaged when said air vent is opened, and electrically operated means -in circuit with said switch to be operated in response to the flow of air through the drier chamber.

9. A mechanism for controlling the operation of a clothes drier including a drier chamber and air admission and discharge conduits with a fan to move air through an air circuit including said conduits and drier chamber, the mechanism comprising a housing having a closed chamber at one end and a vented chamber at the other end, a diaphragm extending across said housing and having one surface exposed to the closed chamber and the other surface exposed to the vented chamber, means to connect said closed chamber to the air circuit of the drier to expose the diaphragm to pressure changes with the flow of air through the drier, switch means operated by the diaphragm as it is moved between a first and second position by a pressure differential, an electrically operated means connected in circuit with the switch to be operated upon actuation of the switch by the diaphragm, an air vent in said housing communicating between the closed chamber and the atmosphere, a solenoid operated valve operative to seal said vent or to be actuated to open the vent and expose the closed chamber and diaphragm to atmospheric air to return the diaphragm to a first position, and means for operating said solenoid to vent the clothes chamber and deactuate the switch by the diaphragm moving to the first position.

10. Mechanism for controlling a clothes drier comprising a drier chamber in which clothes are contained while being subjected to a circulating drying air, an air circuit for the drying air including an intake conduit leading to the chamber, a discharge conduit leading from the chamber, means for moving air through said air circuit, an air heater located in the intake conduit to raise the temperature of the air, a lint trap positioned in the discharge conduit to capture lint which is picked up by the circulating air, actuating means responsive to a pressure differential between operating surfaces, a housing having actuating means dividing the housing into two chambers with a closed chamber on one side of said actuating means and a vented chamber on the other side of said actuating means, means for connecting said closed chamber of the housing to the air conduit to subject one side of the actuating means to the pressure of the air within said air conduit, switch means in the path of said actuating means, said switch means operatively connected to the air heater to terminate operation of the heater when engaged by the actuating means, and means resisting movement of the actuating means to be overcome by a predetermined pressure within the air circuit due to stoppage of the lint trap which reduces the flow of air below a predetermined level.

11. A mechanism for controlling a clothes drier including a drier chamber with a connecting intake air conduit and a connecting discharge conduit to complete an air circuit for the drier, the mechanism comprising a pres sure responsive actuating member movable by a pressure differential between operating surfaces thereof, a housing for said pressure responsive actuating member form ing a closed chamber on one side of the member and open chamber on the other side of the member, means connecting said closed chamber to the air circuit of the drier, the pressure of the air within the drier causing movement of the pressure responsive member between a first and a third position, first switch means operative by said actuating member, spring means between said first switch means and said actuating member to operate the switch when the actuating member moves to a second position between said first and third positions, said spring resisting movement of the actuating member and normally preventing movement to a third position, a lint trap positioned in the discharge conduit to capture lint which is picked up by the circulating air, and a second switch actuated bysaid actuating member when the mem- QLmQYes, to third position against; the. resistance of said sprin'g due to the change in pressure from a,reduction of air fiow as a result of an aggregation of anrexcessive amountoflint in said lint trap. f i 12 A'mechanism for controlling a clothes drier comprising a drier chamber in which clothes are contained while being subjected to a circulatingdrying air, anair circuit for the drying air including. an intake conduit leading", to the chamber, a discharge. conduit. leadingaway from the chamber, apair of heating elements in said intake conduit, a pressure responsive actuatingmember, ahousing for saidactuatingmember.providing a closed chamber on one-side of said actuating member, means for connecting said closed chamber to the air circuit of the drier with a. change in air pressure. within the air circuit causing movement of the actuating member, a first switch positioned in the path of the actuating memberto be operatedthereby, and a second switch spaced fromsaid first switch to beactuated by the actuating member at a time later than, said first switch, saidfirst switchconnected to said first heaterelernent and .a sec,- ondiswitch connected to the second heaterleleme'nt to cause a sequential operation of said .heater. elements v.as the air. pressure builds up within the. air circuitofthe drier.

1 3. A- .mechanism torcontrolling a clothes drier, comprising an intake airconduit for supplying .air to the drier, an exhaust conduit for directing air away from the, drier,

a; drier chamber between said conduits and in communication therewith for containing the clothes .subjected to the circulated drying air, a plurality of heaters positioned in the: intake air conduit to increase the temperature of the: air entering thedrierin accordancewith the number of heaters in operation, switches for each ofthe heater elements to selectively control the number of h eater-elemerits in operation, and air pressure responsivemeans connected to the air circuit for the drier chamber-and operatively connected to theswitches and operating the switches selectively in accordance with the'airpressure within the drying circuit to increase thenumber of heaters 'in operation with the increase in air pressure and to decrease the number-of heatersinoperation with the decrease in. air pressure to indicate a reduced flow of air through the drier air circuit.

14. A mechanisrn for controlling a clothes drier comprising =a drier chamber inwhich clothes are contained while-being being subject to a circulated drying air, an air circuit for the drying air including anintake conduit-leading to thedrying chamber, a discharge conduit leading from the drying chamber, =a pressure responsive diaphragm operated by a pressure differential across its operating surfaces, a housing for said diaphragm providing a closed chamber for one side of the diaphragm and avented chamber fortheopposite side, meansttor connecting .said closed'chamber of :the housing'to. the air-circuit of the drier to subject the diaphragm to the pressure within the drier air circuit, a valve vent means-connected to said closed chamber to vent the air therein to atmosphere to cause a return of the diaphragm'to its original pos-ition,'afirst, second, and third switch means sequentially positioned in the pathof movement of the diaphragm, first and second air heaters-positioned in the intake conduit for the drier,'said first and second switches connected to said first and second heaters, said heaters being sequentially operated as the switches are engaged by the moving diaphragm, resilient means to. prevent movement of the diaphragm to a third positionin engagemer t with said third switch, a signal means to indicate the presence of a conditionto an operator, said third switch connectedto said signal means,"operating' means connected to said vent means to vent said closedchamber and permit movement of the diaphragrnto its origirral position to move-out ofengagement with said;first,' secand third W -t.l ,;;audfi n ,tr n pcsi ionedvin the:

dischargeconduit of the drier, said lint trap capturing lint picked up by the circulating air and causing a stoppage; of airflow and increased pressurewith an'excess arnount of, lintto move the diaphragm to the third position to operate thesignal to enable the operator todisconnect' the: heater elements preventing overheating thereo'fw a reduced, flow.of airfrom the stoppage ofi-the lint trap.

15.. A mechanism for controlling a clothes drier hava ingadrier chamber in which clothes are contained while being dried, anair circuit for the drying air including an intake conduit leading to. the dryingchamber, a discharge conduit leading from the drying chamber, affanmeans' to. move air through. the airci-rcuit, a mechanism comg prising a heater element located in the intake conduitloi the. drier for increasing the, temperature of the-airpa'n actuating, member operable by a pressure difierential acrosslits operating surfaces, a housing for said actuating member presenting a closed chamber on one sideof said actuating member and a vented chamber on the otherside of said actuating .member, means t cOnnectsaid closed chamber to. the air circuit of thedrier, a switch means connectediinscircuit with the air heatermechanisrrr positionedin the pathofsaid actuatingg memberto be operable thereby when the change in pressurethe air circuitcausesmovement of the operating rnern; ber, an electrically operated valve controlledpventleading to said closed chamber to permit movementot h actuating member to its a return position, a temperature responsive o s ns tiet wi ch c ted adja en said fan and operative to open said vent upon the fan reaching an unsafe predetermined temperature to causemoyement of the actuator to return position to discontinue opera; tion of the heater due to the increased temperat re of the fan,

16. A mechanism for controlling a'clothes drier comprising an air circuit for clothes drying airincludingan intake conduit, adischarge conduit, and a drying chamber between said conduits in communication therewith for containing the, clothes during a dryingope'ration, fan means for moving air through said aircircuit, aheater positioned in the intake conduit to raise the temperature of the air entering the drier chamber, heater switchimeans electrically connected to said heater to control the operation thereof, a switch actuator member operableby a pressure difierential between operating surfaces thereof, means to expose one surface of said actuating member to the pressure within said air circuit including a housing providing a closed chamber on one surface of said actuating member in communication with said air circuita'nd a-vented chamber on the opposing side of said-actuating member, vent means for said closed chamber to vent the chamber to atmosphere permitting a return of 'the actuating member to the return position, said heater operating switch being in the path' of movement of the actuating member when moved to actuated position, and a teinperi'ature responsive. heater safety switch positioned inclos'e proximity to said heater and operatively connected t'o said vent to open said vent and permit a returnof'the actuating member to return position' upon; the heater reaching an unsafe temperature to thereby deactivate said heater switch and terminate operation of; the heater.

17 A mechanism for controlling a clothes drier having'a drier chamber in which clothes are contained wliile being subjected'to a circulatingdrying air, an air'circuit for the drying air including an intake conduit leading to the chamber, a discharge conduit leading ifrorn the chamher, a fan for moving 'air through said airlcircuitlthe mechanism comprisingv first and second relay; control located in the intake conduit to the drier, first'andsec- 0nd, relay coils operatively connected to said 'and WOJJd relay. control switches, first and second rel ay operated switches operatively connected to said first and second heating elements, and a temperature responsive thermostat positioned in close adjacency to said heating elements and having a switch in the circuit of said first heating element to open the circuit thereto when the temperature of the heating elements reaches a predetermined level, said pressure operated time delay mechanism connected to said air circuit to cause sequential operation of the heater elements upon the beginning of a circulation of air to said drier chamber.

18. A mechanism controlling a clothes drier having a drier chamber in which clothes are contained while being subjected to a circulated drying air, an air circuit for the drying air including an intake conduit leading to the chamber, a discharge conduit leading from the chamber, air circulating means adapted to move air through said drier chamber, first and second heater elements positioned in said intake conduit, a thermostat positioned in close adjacency to said heater elements, a thermostat switch connected in circuit with one of said heater elements, a relay switch connected in the circuit of both of said heater elements, a pressure responsive control switch operatively connected to said air circuit operable with increased pressure in said air circuit, a relay coil in circuit with said pressure responsive switch and connected to said relay switch to operate the heater elements with the build up in pressure in said conduit, and means to open said pressure responsive switch to terminate operation of said heaters upon the increase of said pressure in the air circuit above a predetermined to prevent overheating of the heating elements with a reduced flow of air due to stoppage of flow of air in the discharge conduit.

References Cited in the file of this patent UNITED STATES PATENTS 1,217,229 Smith Feb. 27, 1917 2,004,448 Kelley June 11, 1935 2,360,915 Vermilya Oct. 24, 1944 2,550,118 Kauffman Apr. 24, 1951 2,577,104 Butler Dec. 4, 1951 2,604,313 Grantham July 22, 1952 2,608,003 Tucker Aug. 26, 1952 2,644,246 Robinson July 7, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,941,308 June 21 1960 Clifton A. Cobb et a1.

It is herebfi certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 11, line 62, for "and" read an column 13 line 41:0 after "faces" insert and exposing the other of said line 53, for "sceond" read second operating surfaces Signed and sealed this 10th day of January 1961.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 2,941,308

Clifton A Cobb et a1\ June 21 1960 It is herehfl certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 11, line 62, for "and" read an column 13 line 40 after "faces" insert and exposing the other of said line 53 for "sceond" read second operating surfaces Signed and sealed this 10th day of January 1961.,

(SEAL) Attest:

KARL H. AXLINE Attesting Oflicer ROBERT C. WATSON Commissioner of Patents

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Classifications
U.S. Classification34/552, 219/481, 34/82, 200/83.00R
International ClassificationD06F58/28, D06F58/20, D06F58/22
Cooperative ClassificationD06F58/28, D06F58/22
European ClassificationD06F58/22, D06F58/28