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sept, 17, '1946. c. M. HELYAR 2,407,743 ' AIR DRAFT TIMING AND VOLUME CONTROL y Filed April so,v 1942 2 Sheçts-Sheet l sept. 17, 1946.` c. M, HELYAR ' ` 2,407,743 AIR DRAFT TIMING AND VOLUME CONTROL Filed April 30, 1942 ' 2 Sheets-Sheet 2' .5 Patented Sept. 17, 1946 2,407,743 ` UNITED \ STATES 'PATENT oFFIcE 2,407,743 , AIR DRAFT TIMING AND VOLUME CONTROL charles M. Heiyar, saint vital, Manit'oba, canada Application April 30, 1942,)Serial No. 441,248 12 Claims. (ci. 110-__72) 2 My invention relates to an air draft timing and volume control assembly particularly but not ex clusively for automatic stokers, designed to be lo cated within the air duct leading to the retort thereof, an object of this invention being to pro vide a device of the character described, by the V means being provided to regulate the volume of air fed to the dormant ?re bed. l As a result, the Violent kindling action of a full head of air under forced draft, can, and some times does have the elfect of extinguishing the ?re completely, blowing the remaining incandes use of which, at the commencement of each cycle of stoker operation, the fuel bed will be given an cent particles up the chimney. When this ex treme is not reached, a considerable quantity of opportunity to kindle without the intervention of a forceddraft, until there is su?icient incan 10 ?y-ash is blown about inside the ?re box to set tle on the castings and effectively insulate the descence and burning strength in the fuel bed to same against the transmission of heat.. Warrant the introduction of a gradually increas Dealing with the effect upon a ?re bed, of the ing volume of air. shutting off of the fan at the conclusion of a _ f_l furtheruobject of my invention is to provide an assembly of the character herewithin de scribed, by ther use of- which, at the conclusion cycle of stoker operation, I would explain that 15 two conventional expedients are followed in con struction and installation. The A?rst is to pro vide a heavily weighted damper within the air duet leading to the retort, so that immediately of raicycle of stoker operation, the fuel bed may continue to drawa natural draft through the st'oker air duct for a predetermined period of ti1_ne,_suchk draft being however, gradually ob str-uctedand eventually closed off. V 20 ural chimney draft. The vother is to provide no damper in the duct, which permits of the con tinuance of a natural draft after the stopping j A Vfurther object of my invention is to provide an assembly of the character herewithin described which is of eminently simpli?ed construction, can readilyV be installed by service men following sim pli?ed-instructions, can readilyV be adjusted to the conditions of any stoker, Will give long service andlcannot readily become out of order. With the above more important objects in view after the fan stops, the damper will drop, being suf?ciently heavy to resist being lifted by nat of the fan. 25 _ - _ The ?rst expedient results in the ?re being suddenly banked at a moment when valuable vol atiles are being liberated, these volatiles thus, being deprived of 'the necessary oxygen required and such other minor objects as may appear as 30 to ignite the same. With the second expedient, a ?re can burn itself out before the next cycle the speci?cation proceeds, my invention consists essentiallyV in _the arrangement and construction of stoker operation commences. immediately following the commencement of a > 0.9 Di cycle of stokeroperation so as to give the fuel bedan opportunity to kindle while in its initial attenuated state, thereafter permitting the pas ing*V and Volume control assembly, in situ with both dampers closed. ' , i sage of a “nursing”'draft as the heat of the fuel AÂFigure 2 is similar to Figure 1 but showing both dampers fully open. » ~ _ * ' 4,0 , Figure 3 is an end elevation of my assembly. ' i Figure 4 is a -perspective detail illustratingthe » Figure 5 is a detail illustrating my airdischarge 1 - v - > v:Figure 6- is a perspective detail illustrating the structure -employed -tov adjust my ~measuring damper. ~ ~ ~ In the drawings like characters of reference I bed increases and the ?re grows stronger, and from there gradually increasing as more coal is fed- structure' employed to adjust my control damper. elbow and associated valve; i the passage of air from the fan for a short period scribed, reference being had to the accompanying drawings, in which: , . Figure 1 is a side elevation of my air draft tim - My assembly is therefore designed to 'obstruct of; parts all asV hereinafter more particularly de 45 , . .._ In conventional stoker practice, it should _be understood that a fixed damper `is, provided in the forced air duet, the damper being adjusted to each particular job. As an arbitrary exam ple, it may be .said that such damper is adjusted to cut off four ?fths of the area of the duet. ' It therefore follows, that When a thick -and indicate corresponding parts in the different ?g 50 possibly dense?fueI bed has been `built up,- that ures._1- I; - _ I ~ V,according to conventional practice in the con struction and operation of automatic stokers, the fan is synchronised to start up simultaneously such fuel bed will resist the penetration of a forced draft. It is therefore necessary to in crease the volume of air so as to overcomeiob-i -but this` cannot be done with a fixed with the _motor operating the coal feed screw, no 555 structions, damper andÂ consequently valuable products of 2,407,743 3 combustion liberated, cannot dissipate their full thermal efficiency owing to lack of oxygen. With my assembly, when a fixed, dense and hot fuel bed has been created, I am able to overcome the resistance to the passage of air by permitting an increase in the volume of air which will pass through the duct, a vo1ume which is only limited by the capacity of the fan and thus the fuel bed-of anautomatic stoker to which my assembly *has _I'been ?tted, will never be over nourished or unclernourished with air to impair its thermal efficiency. In view of the foregoing brief résumé compar ing my assembly with conventional Apractice, -a therewith similarly to the quadrant plate 1. A sleeve 26 similar to the sleeve 8 is freely mount ed on the trunnion between the plate 2.5,and the wall, ..a IQuadrant lock 21 similar to .the quadrant lock 9 being secured for rotation with the sleeve so that the foregoing parts may ybe caused to rotate as a unit, résumé which could be considerably tampli?ed, I will proceed to describe the construction of my assembly. 4 the trunnions projecting on either side of this vane, also being journalled _in the frame 23, the opposite side wall of the duct, or both. The trunnion 24 projects beyond the wall 6 similarly to the trunnion 5, a quadrant plate 25 being secured to the end thereof for rotation , .At any convenient point upon the length of a stoker duct I, I locate an intermedially jour nalled volume regulating damper 2 capable of , Upon the 'sleeve =2~6 isa trip rod 28 of the con 115 figuration best illustrated in the accompanying Figure "6, capable of intercepting the lever 29 Lbest :illustrated in Figures 1, 2 and 6, provided with the right angled portion 29', which lever is 'journalled in the bearing 33, being angulated 20 adjacent the bearings and therefore projecting through the wall 16 `'into the interior of the duct where it angles Ebackwardly as 'II have indicated sealing one side of the duct from theother com pletely. ,It is generally found convenien't l.w-hen at Sl in Figures land `l`2,1ina1l5y 2beinganlgulated inserting ga damper Vin a Vduct to frame Vthe same a'sçby means -of the'frame 3, which, however, yI do Anot 'claim Âto be part vof my invention. A as fat 32, transversely lof the duct Vand >as best illustrated fin Figure 5 extending lfreely through a transverse drilling in the headf-33of the 'valve 2G so that rotation of Ithe lever in a clockwise small A-stop 4 may -also 1be provided to prevent rotation of the damper 2 in a counterclockwise direction with respect'to the accompanying “Fig direction beyondthe limits imposed bythe stop. ures A-1 and 2, will liftthe-valve. 4'One-of the trunnions 5 of ythe damper '2 pro jectssubstantially*beyond the side "wall 35 of the electric-coil :in fthrough?which- current is designed duct, a qu-adrant plate l'l being secured to *the to pass upon the commencement of -a cycle ~'of end thereof for rotation therewith and vwith `the plate. A s`1eeve'8 ``is also f-reely `mounted upon the trunnions between the Quadrant plate'l and the wallv'ü, a radial. Quadrant lock 19 of Lthefconñgura ti'on clearly fillustrated 'in the Vaccompany'ing- Fig . Secured to thewall 46 below the A-ring 114 *isian stoker operation to heat the ring *Hi andthe heat motor 1,!2, and finally, those parts of _?the-*fore 35 ure zlfbeing secured -for rotation with the sleeve 8; lThis'Quadrant lock, itwill be seenfterminates at~~the=lower 'end' thereof in a reverse-'angulated portion 1!!! lprovided with the set-screw ll Which is -capableofficlamping onto the larcuateedge'o'f the -pl'a-te 'I atanydesiredpoint -so that the sleeve and Lthe'trunnions, and-consequently the -damper going structure which?are positioned upon the outer Vsideof the duct l, lare enclosed Withinthe housing the end wall '36 of this -housingfbe ing providedv with'the air Aescapeaperture131 'for the -purpose-presently tolbe described. ' Proceeding now todescribe theoperation ”of my assembly, I Would explain =that irmnediately upon Ithe commencement of a »'cycle of stoker operation, the -co'il 434 `=commences to heat up `and radiatei-tsiheat 1against the ring M. fHoweverfa . ~ certainvilength of time will elapselbefore *the-ring iSecure'd a-t _its inner -end to theb sleeve 8 Vis a 4,5 has absorbedsu?icient heat-to transmit -an'yfto bi-metallic heat -`motor 'IE-formed of spiral bi theibi-'me'tallicfheat motor or coil [2 'and'during metal tape and `'substantially like la spiral-type that time, the *fuel bed in the fstoker retort çis thermostat. SšIPheouter end '5,3 of Jthe --motor 172 kinding :naturally *rather than vbeing Lblown is -anchored -atfa convenient point upon fthe pe apart vand struggling against =a Violent >drašft of rimeterof a-fairly bymassive heat retaining 'ring [4 which surrounds "the motor, thisring being 'Eventually, the _coil -or ib-i-metal tape 'of' the preferably imade of cast iron or-some other isub motor 12 commences 'to `lengtlfien and unwind too, moves as a unit. air. s'tance capable of l`retaining Vheat fairly efficient ly. This'ring is clamped tojthe wallšü. i hn?offsetlportion l'â of'V the ring :Id/is provided _ withlthe passage Plt, .Which passage -opens :onto the i internal ,circumference . of the>ring ,at :one .end thereof, right angling at uthe other .end thereof as I have indicated by :the chain-line ,ring AElin Figure lgand by the parallel chain lines :ll' in Figure 5, and opening upon the posterior surface IB of the offset portion and in alignment with _an air _discharge `port IQ which includes an aper ture (not shown) in the wall 6 and .an upwar'd ly directed elbow Vprovided `with the 'vertically movablevalve'zü. V . - V''Also within the duct l but spaced vfrom the damper 2 'and upon the retort side thereofis an Vair ?evv responsive vane 2! normally Vbiassed to the .position'illustrated in vFigure 1, andalso preferab-ly mounted Within a frame 22 similar Vto the frame 3, a stop 23 being provided similar =to the stop 4. ' » . a ~ - opening Lthe damper ' 2 v'very s'lowly and gradually permitting air therepast. ` f ' ~ - 'k 'Thesair lflowing therepast will graduaHyac quire su?icient?volume'to 'lift? the lya'ne 2 I, and-at this point, I would speciñcally-explain, as willjbe clearly noted from Figures ~1 and 2,-that the vane lZI does not entirely seal the duct `| -asdoesthe damper 2l When closed, the upper and 'lowerhori zorit'alwedges 53% and `39 of the -vane 12l providing , the'nfarrow itr'ansverse Vspaceslltil>V and 'M Kat'top and'bottom through 'lwhich?aksmall 1volume of air may @pass without raisingfth'efdamper, ' =At alcertainrstage,V after the fuel "bed has ibe comef replenished~with coal `andthe šsame' ist-giving off its products o_f combustion freely, the- control damper '2 will 'have-f'rotated almost as far as I havelshown in the Laccompanyingi'Figure '21, thus permitting the passage of a certain volume-ofb airto' `liftthe vane 2l» almost as far as `~I_ -have shown it jin fthe same figure. f VThe accumulated heat fwithin'fth'e ringl |f4hand the-continued radia `This vane will :preferably be mounted to swing about a line .above its central horizontal axis, 75 tionof heat from~the coil '34, will-eventual-l-ylmove 2,407,743 6 the control damper still further as for example, plate and vane, I am able to provide accurately. for every installation. In conclusion, although the title of this speci fication directs my invention to its use for auto matic stokers, I desire to explain that the same Would also be practicable and useful in certain other industrial arts such for example as in the drying of a mass of material varying in density. I therefore do not Wish this speci?cation to be 10 interpreted as limiting my rights under thispat to the position as actually illustrated in the ac companying Figure 2 at Which point the in creased volume of air Will cause the vane 2| to rise still further, and to the point actually shown where the trip rod 28 will intersect the lever 29, rotating the same to a small extent and causing the valve 20 to open. Opening of the Valve 20 -permits the escape of air through the port l9, through the passage IG to impinge upon the motor [2 tending to cool the same, thereby contracting it and causing the i damper plate 2 to rotate slowly in the opposite ent to the use of my invention on automatic stokers but only as limited by the appended claims. ` and closing direction. In this way, it will be seen Since various modi?cations can be made in my that I have provided an accurate means for gov 15 invention as hereinabove described and many ap erning and controlling the maximum volume of ' parently widely different embodiments of same air to be permitted into the retort. Air dis made Within the scope of vthe claims Without de charged through the port l 9 may escape through parting from such spirit and scope, it is intended the aperture 31 in the end Wall 36 of my casing that all matter contained in the accompanying 35. . 20 speci?cation shall be interpreted as illustrative As I have previously indicated, a considerable only and not in a'limiting sense and I desire only volume of air at Substantial pressure is required such limitations placed thereon as are speci?cally to penetrate through a dense, thick fuel bed--a expressed in .the accompanying claims. greater volume, that is, than Would ever practi What I claim as my invention is: cably be permitted With a ?xed damper, the po 25 1. An air draft timing and volume control for sition of Which is a compromise to provide at automatic stokers, comprising in combination least reasonable efficiency under a variety of ?re With the air duct thereof a rotatable volume reg bed conditions. ulating damper and a rotatable ?ow responsive Therefore, it is to 4'be understood that When a vane normally biassed to one position and mov-I fuel bedis Well ?lled with coal, giving up its vola 30 able from such position by an amount dependent tiles freely, my control damper 2 is in such posi on the flow therepast, said vane being positioned tion that it is permitting a greater volume of air in spaced relationship with respect to said volume' to pass and force its way through the bed than regulating damper, within said air duct and upon Would be the case with a ?xed damper, the air the downstream side of said regula-tlng damper, discharge port I 9 and associated valve being pro 35 the area of said vane being less than the right vided to check the damper 2 against ipermitting angled .tr-ansverse area of said duet, a heat motor the admission of an even greater, and excessive connected to said regulating damper and gov Volume of air, as the motor |2 gets hotter and erning the movement thereof so as to permit an increases in length. ~ increased ?ow therepast as the temperature of At the conclusion of a cycle of stoker operation, 40 said motor increases, a coil for heating said motor at Which time the fan comes to rest, it Will be upon the commencement of a cycle of stoker op recognized that -my control damper 2 is open to eration, means for cooling said motor upon dthe the maximum extent, and the same will only close opening of said vane to a predetermined extent, at a very slow rate of speed, as the heat motor a trunm'on rotatable With at least said damper and the heavy cast ring 14 surrounding it, give or said vane, a pl-ate secured for' rotation .to and up their heat so that a brisk natural Vdraft may With said trunnion, a loose sleeve on said trun continue to be indrawn into a ?re bed, the oxy nion, and means projecting from said sleeve, said gen therein being utilized to ignite the volatiles as means being secured for unitary movement to they continue to be liberated but at a decreas and With said sleeve for looking said plate -and ing rate. 50x said sleeve in a plurality of selected positions so Referring to the adjusting means associated that said plate and sleeve may rotate as a unit. With my damper and vane and including the 2. An air draft timing and volume control com Quadrant plates 'I and 25 et seq. respectively, it prising in combination with an air duct, a volume will readily be understood by reference to the ac regulating damper, a ?ow responsive vane nor companying Figures 1 and 4 for instance, that mally biassed to one position and being inovableA rotation of the quadrant lock 9 in a clockwise di from such position by an amount dependent on rection following the loosening of the screw ll, the ?ow therepast, said vane being positioned in around the quadrant plate, Will increase the ten spaced relation With respect to said volume regu sion of the motor L2. Conversely, rotation of the arm 9 in the opposite direction, will slacken the 60 lating damper, within said air duct, a heat motor connected to said regulating damper and gov motor, and in this connection, I desire to ex erning vthe movement thereof so as to permit an plain that I generally prefer that my motor be increased ?ow therepast as the temperature of so adjusted that the damper 2 is caused to bear said motor increases, means for periodically heat against the stop 4 with a certain amount of pressure When in closed position, so that it will 65 ing said motor, and automatically operable means for cooling said motor upon the movement of not commence to rotate immediately the bi-metal said vane from its normal position a predeter tape of the motor commences to deform respon mined extent. sive to the adjacent heat source. 3. An air draft timing and volume control com prising in combination With an air duct, a volume charge lvalve l9, it will readily be recognized that 70 regulating damper, a ?ow responsive vane nor rotation of the quadrant lock 21 on the quadrant As to my flow responsive vane 2l and air dis plate 25, together With the sleeve 26 and the trip rod 28, will control the point at Which the-'valve 20 opens responsive to the action of the rod 29, and so, With these adjustments on each of my mally biassed to one position -and being movable from such position by an amount dependent on the. ?ow therepast, said vane being positioned in spaced relation with respect to said volume regu 75 lating damper, Within said -air duct, said vanebe 2,407,743 7 8 a heat radiating ring around Asaid motor, means ing located upon the downstream 'side of said regulating damper, a heat'motor connected to said regulating damperfand governing the 'move for periodically heating said ring 'and thereby ment thereof so .as to 'permit 'an 'increased flow said “motor, and means for cooling said motor upon the movement of 'said'vane from its normal therepast as 'the .temperature 'of said motor in position 'a predetermined extent. _ 7. An air 'draft timing'and volume vcontrol 'com prising in combination with an air duct, 'a'volu'me tor, an air discharge :port in said air duct Acon regulating damper, a flow responsive vane nor structed land arranged to 'direct its discharging mally biassed to one position and being movable air onto 'said motor, .together With 'an 'associated normally closed valve, and `means designed so vas 10 from said position by an amount dependent upon the flow therepast, said vane being positioned in to `open said valve and permit air from within spaced relation With respect to said'volume resu said duet to impinge upon and cool Vsaid motor lating damper, Within said duot, said vane being When said vane is moved from its normal position located upon the 'downstream side of *said regu apredetermined extent. lating damper, `a heat motor connected to said 4. An air draft timing and volume 'control com regulating damper and governing the movement prising in combination With an air duet, a volume thereof so as to permit an increased flow lthere regulatin'g damper, 'a flow responsive vane nor past as the temperature of said motor increases, mally biassed to one position .and being movable a heat radiating ring around said motor, means from "said _position by an .amount dependent 'on .the flow therepast, said vane being positioned in 20V for periodically heating said ring and thereby said motor, and an Vair discharge port in said spaced relation with respect to said volume regu air duct constructed and arranged to direct itsV lating damper, within said duct, said vane being discharging lair onto 'said motor together With positioned upon the down-stream side >of said reg an associated valve normally 'closing said ducts, ulating damper, 'a heat motor connected to said creases, means for periodically 'heating Lsaid mo regul'ating damper and governing the movement 25 said valves being operable to open position by the movement of said vane from its normal position thereof so as to permit an increased ?ow there a predetermined extent, thereby permitting air from within said duct to impinge upon said motor past a's the temperature of said motor increases, means for periodically heating said motor and an air discharge port 'in said air duct constructed to cool the same. and arranged to direct its discharging air onto 30 said motor together 4with an associated valve nor `8. An air draft timing and Volume control com prising in lcombination with an air duct, a volume regulating damper, a ?oW responsive vane nor mally biassed to one position, 'and being movable mally closing said 'ducts, said valve being oper a'bl'e to open position by the movement of said from such position by an amount dependent on vane fromv its normal position a predetermined extent xt'hereby permitting the air from within 35 .the flow .therepast, said vane being positioned in spaced relation With respect to said volume regu said duct to impinge upon said motor to cool the lating damper, Within said duet, said vane being same. 5. An air draft timing and volume control com prising in combination withra'n 'air duct, ”a volume regu'lating damper, a ?ow responsive vane nor mally biassed .to one position and being movable from said position by an amount dependent upon the ?ow 'therepast, said vane being positioned in spaced relation with respect to said volume regu lating damper, within said duct, said vane being positioned upon the downstream side 'of said reg ulating damper, a heat motor connected to Vsaid regulating damper and governing the movement located upon the downstream side of said regu lating damper, a heat motor connected to said 40 regulating damper and governing the movement V thereof so as to permit an increased flow there past `as the temperature of said motor increase's, a heat radiating ring around said motor, means for periodically heating said ring and thereby said motor, an air discharge port in the form of an elbow in one wall of said duct constructed and `arranged to direct its discharging air onto said motor, a valve normally closing said port Within said duct, a lever connected to said valve, said past las-'the temperature of said motor in'creases, 50 lever being rotated by the movement of said vane when the latter is moved from its normal posi means for periodically heating said motor, *an air tion a predetermined extent to open said valve discharge port in the form of an elbow in one thereby permitting the escp'e of air from within Wall of sai-d duet constructed and arranged .to said duet-through said port to impinge upon said direct its discharging lair onto said motor, a valve normally closing said port within lsaid duct, *a , motor and cool the same. 9. An air draft 'timing and volume control com lever connected to said valve, said lever being prising in combination With an air duct, a volume rotated by .the movement of said vane when the regulating damper, a ?ow responsive vane nor latter is moved from its normal position a pre mally biassed 'to one position and being movable determined extent to open said valve, thereby permitting the escape of air 'from within'said duct 60 from such position by an amount dependent upon the flow therepast, said vane being positioned in through said port to impinge upon said motor thereof so as to permit an increased 'flow there and cool the same. 6. An air 'draft timing and volume control 'com prising in combination `Vwith lan air duet, a volume regulating damper, a flow responsive Vvane nor mally biassed 'to ,one position land being movable from said position by an amount dependent on the ?ow therepast, said vane being positioned in spaced relation with respect to said volume regu lating damper, within said Vduct, said vane being positioned upon the downstream side of said reg' spacedrelation with respect to said volume regu lating damper, Within said duet, said vane being positioned upon the downstream side of said reg ' ulating damper, said vane being supported on projecting trunnions, a plate secured for rotation to one of said trunnions, -a sleeve on the trunnion ulating damper, a heat' motor connected to said to which said plate is connected, said sleeve being interposed between said vane and said plate, a radial lock Vs'ecuring saidl plate 'to 'said sleeve, a trip rod also secured to said sleeve, a heat motor connected to said regulating damper .and gov regulating damper and governing the movement erning the movement thereof so as to permit an increased ?ow therepast as the vtemperature of past as the temperature of said motor increases, 75 said motor increases, means for periodically heat of same so .as to permit an _increased ?ow there 2,407,743 10 ing said motor, an air discharge port in .the form of an elbow in one wall of said duct constructed and arranged .to direct its discharged air onto said motor, a valve normally closing said port within said duct, a leverl connected to said valve, said lever being engaged'by said trip rod upon the rotation thereof, together with said lock, plate and vane, a predetermjifned extent to open said valve and permitting :the passage of air from within t_said duct through said elbow to impinge on said motor and cool the same. ing .the movement of said damper so as to permit an increased ?ow therepast as the temperature of said motor increases, a heat radiating ring around said motor, an air discharge _port in the wall of said duct constructed and arranged to direct itsy discharging air onto said motor, a valve normally closing said port, means for periodically heating said ring and thereby said motor, and automatically operable means for opening said 10 valve to permit air to escape through said port 10. An air draft timing and volumeV control volume' comprising regulating in combination damper positioned With an air therewithduct, a f' in, a heat motor connected .to said damper upon '1 the external side of said ,duct and governing the i' and impinge on said motor .to cool the same and thereby move said damper towards or into the closed position following the opening of said damper a predetermined extent. 12. An air draft timing and volume control comprising in combination with an air duct, a volume regulating damper, a ?ow responsive vane creased flow .therepastiasrthe temperature of said .f_ normally biassed .to one position and being mov motor increases, an air discharge port in .the wall able from such position by an amount dependent of said duct constructed and arranged to direct on the ?ow .therepast, said vane being positioned its discharging air ont'o said motor, a valve nor in spaced relation with respect .to said volume mally closing said port, means for periodically; damper, within said air duct, said vane heating said motor, afnd automatically operablefff" regulating being positioned upon the downstream side of means for opening said valve to permit air to es-@r said regulating damper, a heat motor connected cape through said portjand impinge on said motor_ :_ to said regulating damper and governing the to cool same and thereby move said damper -to-jx movement thereof so as .to permit an increased wards or into the closed position following .th opening of said damper a predetermined maxi-fff ?ow therepast as the temperature of said motor movement of said damper so as to permit an in- f] mum extent. _ 11. An air draft timing and volume contro comprising in combination with an air duct, volume regulating damper positioned within saidf'f' air duet, a heat motor connected to said damper upon .the external side of said duct and govern increases, means for periodically heating said motor, means for cooling said motor upon the movement of said vane from its normal position a predetermined extent, the area of said vane` being less than .the right angled transverse area of said duct. i CHARLES M. HELYAR.