US2349368A - Damper construction - Google Patents

Description

c. 1.. MYERS DAMPER CONSTRUCTION 4 Sheets-Sheet 1 Filed Aug. 16, 1941 fzderdbr CHARLES L.MYER$ ay 23, 1944-. c Y S DAMPER CONSTRUCTION Filed Aug. 16, 1941 4 Sheets-Sheet 2 Izdenior.

CHARLES L.MYERs WW 5e 7 flan/rea C. L. MYERS DAMPER CONSTRUCTION Filed Aug. 16, 1941 4 Sheets-Sheet 3 .ZiuJenior CHARLES L MYERS May 23, 1944. Q MYERS 2,349,368

DAMPER CONSTRUCTION Filed Aug. 16, 1941 4 Sheets-Sheet 4 (Olden/Z01 CHARLES L. MYERS Patented May 23, 1944 UNITED STATEfi PATENT GFFICE.

DAMPER CONSTRUCTION Gharles L. Myers, Philadelphia, Pa.

Application August 16, 1941, Serial No. 407,135

17 Claims.

This invention relates generally to dampers for boilers and the like and more particularly to an improved construction of damper in the form of a roller type flexible curtain which is adapted to be partially or fully drawn across the duct in which it is installed to control the gas or air flow therethrough.

Among the principal objects of the present invention is to provide an adjustable damper which requires little space for installation, which maybe installed in old, as well as new, boiler units with a minimum of change and expense, and which provides greater capacity from boilers through conservation and control of the available draft, and reduces draft loss and increases the capacity and efficiency of the boiler unit with which the damper is associated.

Another object is to provide a damper which is equally adapted for installation in boiler uptakes, forced draft ducts, Icy-pass flues and other such passages that normally require dampers, the damper of the present invention being designed, when installed, for example, in the uptake connection, to prevent the flow of excess gas to the stack during low load or banking periods and retain heat for useful purposes that is ordinarily wasted. When installed in the air supply duct this damper prevents the flow of air to the furnace durin banking periods, while when installed, for example, in a by-pass the damper insures all of the gas going to the heat recovery unit with consequent improved recovery of the gas and greater reduction in the induced power requirements.

More specifically, it is an object of the present invention to provide a damper in the form of a roller type flexible curtain which is adapted to be drawn into any desired adjusted position to accurately control the flow of gas (or air) through the duct, the curtain being operative in association with a sustaining grille to definitely and positively seal against passage of gas (or air) through all of that part or area of the duct which is traversed by the damper curtain.

Further specific objects are to provide the damper curtain with means operatively associated therewith for (1) insuring automatic cleaning of the curtain surface of the damper of dust and ash which tend to accumulate in dampers and interfere with their eflicient operation; (2) modifying the flow characteristic of the damper to insure against disproportionately high rates of flow for each small adjustment of the damper, particularly when the damper apthe flow of gas (or air) in either direction through the duct in which the damper is installed by the employment of a dual construction of curtain; and (4) permitting installation and actuation of the damper curtain in ducts disposed in vertical, horizontal and inclined positions, as well as facilitating operation of the curtain when the same is itself disposed in any of said positions.

Still other objects and advantages of the invention, as Well as economies effected thereby, Will be apparent more fully hereinafter, it being understood that the present invention consists substantially in the combination, construction, location and relative arrangement of parts, all as described in detail hereinafter, as shown in the accompanying drawings and as finally pointed out in the appended claims. In the accompanying drawings, which are illustrative of preferred embodiments of the principles of the present invention- Figure 1 is a general diagrammatic view in perspective illustrating a damper constructed and installed in accordance with and embodying the principles of the present invention;

Figure 2 is a vertical sectional view of a damper installed in a horizontal duct;

Figure 3 is a front elevational view of a damper of the general type shown in Figures 1 and 2;

Figure 4 is a vertical sectional view of a dual construction of damper;

Figure 5 is a front elevational View on an enlarged scale of the lower section of the damper unit equipped with V-ports for controlling the flow characteristic when the curtain approaches fully closed position;

Figure 6 is a vertical sectional View taken substantially on the line 5-6 of Figure 5;

Figure '7 is a perspective View of part of the lower movable roller of the damper curtain;

Figure 8 is a detail showing a preferred manner of securing one end of the curtain to the upper winding roller of the damper unit;

Figure 9 is a sectional detail view at one side of the lower end of the damper unit showing the side guide channel for the bottom roller and the means for sealing the side edge of the curtain on the downstream side thereof;

Figure 10 is a vertical sectional view showing a special installation of the damper of the present invention, the damper curtain in this case having means operatively associated therewith for selectively sealing it on either its downstream or upstream side;

Figure 11 is a sectional view of an installation proac'hes its fully Closed p tion; (3) controlling for dampin a vertically extending flue or duct;

Figure 12 is a partial front elevational view of a modified unit for damping a vertically extending flue or duct;

that the damper unit of the present invention consists of a flexible curtain l0, one end of which is secured to and adapted to be wound about a roller while its opposite end is secured, as at l2, to a fixed part of the casing I3 in which the roller I I is journalled. The curtain is withdrawn from the roller to an extent sufiicient to form an intermediate looped portion and within the freely extending bight end of this looped portion of the curtain is disposed a second roller 5 of a weight suflicient to maintain the extended curtain relatively taut in all adjusted positions of the curtain. The curtain I0 is formed of any suitable heat and fire-resistant material having the requisite flexibility and durability, such as asbestos reinforced with metal, or closely woven metal mesh suitably impregnated with asbestos or the like.

Operatively associated with the roller curtain I0 is a grille I6 which is designed and functions to support the curtain against the pressure of the draft through the duct ll in which the damper unit is installed. It will be observed that in the arrangement shown in Figure 1 the grille I6 is disposed upon the downstream side of the damper curtain. In certain installations, however, for example, as shown in Figure 10, such grille may be disposed upon both the downstream and upstream side of the curtain. In every case, the

grille I6 is of a size and shape corresponding to the transverse dimensions of the duct or flue in which it is immovably installed, the side edges of the grille being each framed with parallel chan nel members |8|8 which present their open sides toward each other to provide a pair of opposed guides for side edges of the curtain l0 and its roller weight 5. In this connection it will be noted, however, that the channel members I8 are each of a width to provide ample clearance of the looped curtain therein because satisfactory operation of the damper is not dependent upon a tight fit of the curtain in such channel guides. Indeed, proper operation requires that the upstream panel IQ of the curtain be free of contact with the upstream fianges 2|)2|l of the channel guides, it being an important characteristic of the present invention that only the downstream panel 2| of the curtain be in actual contact with the downstream flanges or sealing strips 22-22 of the guide channels and with the intervening grille l6. Thus, as the effective length of the curtain I0 is varied by winding it about or unwinding it from the upper roller II, the downstream panel 2| of the curtain is caused to overlie the grille to the extent desired without rubbing of this panel relatively to the grille. Thus, there is no frictional resistance to overcome between the grille and the portion of the downstream panel of the curtain in contact with the grille, the lower weighted end of the curtain being merely laid upon or lifted from the grille as the effective curtain length is increased or decreased by rotation of the winding roller II in proper direction. It will be understood, of course, that by increasing the effective length of the curtain the damping action is increased, and vice versa.

The upper winding roller H is encased within a suitable housing l3 preferably removably mounted outside of the duct in which the damper is installed, the roller |3 being provided with suitable trunnions (not shown) which are journalled in suitable bearings provided in opposite ends of the casing IS. The roller may be operated manually by any suitable mechanism or by an electric motor drive, such as that designated generally by the reference numeral 23.

In the operation of the damper as hereinbefore described, the opposite side edges of the downstream panel 2| of the curtain will be pressed against the downstream flanges 22-22 of the guide channels for the curtain due to the pressure of the draft through the duct, in consequence of which said panel 2| of the curtain forms a tight seal against passage of the gas or air) through the portion of the duct so sealed by the damper. The draft flow is then only through the open area between the free lower end of the looped curtain and the lower frame member 24 of the grille, the extent of this open area being easily and accurately controlled by operating the curtain to vary its effective length. Due to the fact that the upstream panel |9 of the looped curtain is not in contact with the upstream flanges 20-28 of the curtain guide channels (see Figure 2), this panel is free of any frictional resistance during positional adjustment of the curtain such as is effected upon rotating the upper winding roller II in one direction or the other. In fact, the draft through the duct is free to pass about the side edges of the upstream panel l9 and into the space between the panels |9 and 2| of the curtain to thereby exert a positive pressure against the upstream surface of the panel 2| throughout its entire extent, thus insuring sealing of this panel 2| against the grille Hi and its side sealing strips 22-22. A further advantage of having the flow pass into the space between the upstream and downstream panels l9 and 2| of the curtain will appear hereinafter.

In order to control more accurately the draft flow characteristic and to insure a flow of controlled minimum value when the curtain is all but closed, this invention contemplates the provision of special means for gradually decreasing or increasing the flow as the curtain approaches or recedes from its fully closed position. This means is best shown in Figures 2, 3, 5 and 6 wherein it will be observed that the bottom frame member 24 of the grille I6 is provided upon the downstream side thereof with a plate 25 which is notched, as at 26, at longitudinally spaced intervals to form a plurality of ports. These ports are preferably V-shaped so that as the looped end of the damper curtain overlies the notched plate 25 during the last stage of its closing movement, free communication between the upstream and downstream sections of the duct H is progressively and gradually decreased to the zero value. Conversely, as the damper commences to move to open position from its fully closed position, these V-ports 26 accord increasingly large apertures between the closed-01f sections of the duct, thereby providing a gradually increasing and accurately controlled minimum flow to suit almost any requirement and condition.

Dampers are frequently installed under con ditions wherein they are exposed tolarge quantitles of dust and :ash which tends to accumulate in 'the damper and interiere with its proper operation. :Inorder toobviate suchaccumulationnf dust, ash, grit and like substances between the convolutions and 'over'the exposed surfaces of the .damper curtain of the present invention, :an arrangement may be employed such as is illustrated in Figure 2.- In this arrangement, a brush 2-1 is mounted in the top member or :header of theicasing I 3, the bristles -28 of this brush loeing in contact with the outer surface of the curtain l throughout substantially its entire width. :If desired, a spring (not shown) :may -be .-interposed between the brush backing and the :casing top member to exert a positive pressure of the brush against the curtain H] as the latter .is wound upon or unwound from the roller H. Any dust which accumulates upon the exposed surface -.of the curtain is thus :br-ushed oil and discharged into the duct H from which it maybe readily removed.

In conjunction with this means for "brushing the ,eXposed or outer surface of the curtain free of accumulated dust, means also may be employed for maintaining the inner surfaces :of the curtain free of dust, etc., this latter means fleeing operable somewhat on .the I principle of a vacuum cleaner. As most clearly appears in Figures 2, .6, '7 and 9, the weight roller 15, which is supportedin the looped vend of the curtain, is preferably of hollow construction with the walls thereof provided with a plurality of slots or openings v29.. These slots or openings afford communication between the interior of the roller 15 and the space between the panels [9 and 2.! .of the looped curtain. .Also, inasmuch as the opposite ends of. the roller L5 are spaced from the ,base walls 38-30 of the side guide channels..l.8-|.8 see Figure .9), the interior .of the roller 15 is in free communication with thezone of the duct H which is open to .free how therethrough.

Inasmuch as .the space between the panels 19 and 2! of the curtain .is subjected to .a pressure greater than that prevailing in the open .zone of the duct immediately below the weighted :end of the curtain, a pressure .differentialexists which favors a flow of gas (.or air.) from the space between the panels of the curtain to the open zone of the duct beneath the curtain. .Also, the

flow from the space .between the panels I9 and 2! past the open ends .of the hollow roller [51nduces a flow from the interior of the roller outwardly through said open ends thereof, which is additive to the flow resulting from the aforesaid pressure differential. The velocity of this resultant flow (designated by the arrows .in Figures 6 and 9) is sufficient to carry dust and ash from between the curtain panels, to the interior of the roller l5 and thence by way of the open ends of the latter into the duct Il thus automatically maintaining the inner surfaces of the curtain free of any accumulation of ash, dust and the like.

It will 'be apparent that frequent adjustment of the curtain damper results in correspondingly frequent flexures of the curtainadjacent its anchored end 1'2 (see Figure 1). In order to increase the fiexing life of the curtain in the anchored region thereof, an arrangement such as is best shown in Figure 2 is preferably employed. In such arrangement, the casing '13 in which is housed the upper winding roller is provided with a wall having a plurality of angularly related sections .3 I, Y32 and 33 which underlie the flexing all) portion :of the curtain. The fixed end of the latter is secured only to thewall section 3|, the portions :of the curtain which overlie the sections 32 and :33 being relatively free of these sections so that as the curtain is moved into adjusted position :flexing of the .anchored end thereof may occur along transverse lines located at the spacedpoints :34 and .35. Thus, longer flexing life of the anchored end of the curtain is assured.

Figure :8 illustrates on an enlarged scale the means :for securing .the curtain to its winding roller 1 i as shown in Figure 2, it being, of course, understood that any suitable means may be em-' ployed for this purpose. In the means illustrated in Figures 2 and 8, the curtain I0 is initially provided with a hem .36, and this hem is then in-. serted in a longitudinal slot 31 provided in the roller H. Thereafter, a key 38, in the form of a r-rod or ibar, is projected into the hem through theopen end .of the roller ll, thus spreading the hem of the curtain and preventing its withdrawal from the roller. Inasmuch as the key is of a length equal to that of the roller, the curtain .is secured to the roller with uniform distribution of strain over the entire width of the curtain. Removal of the curtain from the roller 1 I is easily and readily effected upon withdrawal of the key 38 from the curtain hem.

Dampers of the art to which the present inven-' tion relates are most generally employed in applications where the flow is in a, single direction. The damper construction shown in Figures 1 and 2 is particularly designed for such unidirectional flow. However, there are many cases wherein the flow under certain conditions of operation may :tend :to be in a direction reverse from normal, which reverse flow is, of course, undesirable because resulting in loss in efliciency. In order to 'seal the duct against this undesirable reverse flow, the damper of the present invention may be employed in a modified arrangement such as is shownin Figures 3 and 4 and in Figure 10'.

the arrangement of Figures 3 and 4, the damper is of the dual type and consists essentially ;of .a pair of roller curtains 40 and 4| each of which operates in the manner and is of substantially the same construction as the single type damper hereinbefore described. The curtains ill and 4| are installed in the duct 42 in tandem relation, that is, with the looped panels thereof all in parallel relation and closely associated as best shown in Eigure i. The outer ends of the curtains lil and '4! are respectively secured,

as at 23 and 451, to the casing 45, while the "inner ends of the curtains are respectively secured to the upper winding rollers 43 arid 44 These1atter rollers are journalled for rotation in the casing 8-5, corresponding ends of these rollers being axiallyextended beyond the casing and fitted with intermeshing gears fisand '41 which are operative to synchronize the rotation of the rollers 43 and M to insure simultaneous and'un'iform adjustment of the pair of curtains MI and 41. Any suit able means, such as the electric motor drive 48, may be employed for operating the rollers 43' and Mi l it 'heing apparent that rotation of one roller in a given direction results in corresponding rotation of the other roller in the opposite direction. Thus. the curtains 40 and GI maybe simultaneously adjusted in position to vary the opening in the duct 42. .(Dperatively associated with the pair'of curtai-ns are :the grilles 49 and 49 the vertical side edges of which are framed with side'guide chain nels"5l3-.5il similar to those hereinbefore described.' The grilles ND-49 are, of course, disposed upon the outer sides of the curtains, that is,- adjacent the panels and 52 thereof which have their ends fixed to the casing 45. Also, each curtain is provided with a lower weight roller 53 supported in the fold of the curtain, this roller 53beingin all material respects functionally and structurally similar to the roller l5 hereinbefore described. Also, each of the curtains 40 and 4| has operatively associated therewith a notched plate, such as plate 25 of Figures 3, 5 and 6, for controlling the draft flow characteristic as the curtain approaches or recedes from its fully closed position.

Assuming the direction of flow to be in the direction of the full line arrow of Figure 4, it will be apparent that only the panel 5| of the curtain 46 will be sealed against its grille 49 and the downstream sealing strips of its side guide channels.- The side edges of all the remaining panels will be freely disposed, so that the curtains 46 and 4| may be vertically adjusted in position without requiring any panel thereof to be rubbed against a resisting surface. When the direction of gas flow is in the opposite direction, that is, in the direction of the dotted arrow of Figure 4, the panel 52 of the curtain 4| is the only one that is sealed against the grille 49 and its downstream sealing strips. Consequently, regardless of the direction of draft through the duct 42, the damper curtains may be freely adjusted to close off any area of the duct desired without injuriously rubbing the sealing panel against its associated grille.

i Figure illustrates a modified arrangement of installation for sealing against reverse gas flow under certain special conditions of operation, this installation involving the use of a single unit damper of the present invention. In the application of Figure 10 the normal flow through the stack 53 is in the direction of the full line arrow. Thedamper unit including the looped curtain 54 is arranged in an inclined plane across the stack and is provided with a grille 55 and associated sealing strips adjacent the panel 56 of the curtain at the downstream side of the damper unit. The curtain may be positionally adjusted as hereinbefore described to control the normal flow through the stack.

When it is desired, however, to flow the gas to the stack via, for example, an economiser and induced draft fan, in the direction of the dotted arrow, thereby by-passing the damper unit, it becomes necessary to seal off the stack in the region of the damper to preclude any possibility of recirculation of the gas through the economizer. To effect this desired objective, a grille 51 and associated sealing strips are provided adjacent the panel 58 of the curtain on the normal upstream side of the damper unit. Accordingly, when the damper curtain is in fully closed position (as shown by the dotted lines of Figure 10) the upstream side of the unit seals the stack against reverse flow therethrough. It will be understood that during conditions of reverse flow the damper would remain in its adjusted position, usually full closed, and no attempt would be made to readjust the damper position until normal flow condition is again obtained. In order to determine the condition of flow existing at i any time, various indicating means not herein shown because well understood and known in the art may be employed, such as a differential draft gage or the like.

Figures 11 to show arran ements for controlling the vertical flow of gas by dampers constructed in accordance with the present invention, the damper curtains in such cases being operable in horizontal planes. In the simpler ar rangement of Figure 11, the stack 66 extends ver-' tically toprovide for a vertical flow. The damper installed in such stack includes'the looped curtain 6| as in the previously described installations, one end of which is secured, as at 62, to the housing for the winding roller 63, the opposite end of the curtain being secured to this latter roller. Disposed in the looped end of the curtain is a roller 64 to which is suitably secured, by means of a cable 65, a counterweight 66. The cable 65 travels over a sheave 61 journalled upon a bracket 68 fixed to the stack as shown. The cable 65 is, of course, connected to' opposite ends of the roller 64 by any suitable means, as,'f0r example, a yoke (not shown). Or, a pair of counterweights may be employed, each secured by its own cable to either end of the roller 64.

It will be apparent that the weight of the counterweight acting on the roller 64 will tend to draw the latter outwardly away from winding roller 63 and thus maintain the curtain in taut condition transversely across the stack 60. In order toadjust the damper curtain to vary the flow permitted through the stack, the winding roller 63 is provided at one end thereof with a worm gear 69 which is in 'mesh with a worm 10 adapted to be rotated in one direction or the other by a chain or cable operated pulley H. It will be apparent that upon operation of the pulley H in one direction the curtain'fil will be wound about the roller 63, against the action of the counterweight 66, to shorten the efiective length of the'curtain transversely of the stack, while when the pulley is operated in the reverse direction, the counterweight 66 acts on the roller 64 to unwind the curtain from the roller 63 and thus increase the effective length of the curtain. It will be understood, of course, that the damper curtain is provided upon its downstream side with a grille and associated sealing strips for sealing the panel of the curtain against flow therethrough.

Figures 12 to 15, inclusive, show a preferred arrangement of damper unit for controlling flow through a vertical stack 12. In this latter arrangement, the damper curtain I3 is disposed in a manner similar to that shown in Figure 11, the opposite ends thereof being respectively-secured to the casing, as at M, and to the operating winding roller 75. The draw roller 16, which is disposed in the looped end of the curtain, operates in the same manner and for the same purpose as the roller 64 of Figure 11. Also, as in the latter case, the upstream side of the damper unit is provided with the grille 11 and sealing strips 11a characteristic of the present invention.

Tofacilitate operation of the horizontally dis: posed curtain 13, the draw roller 16 is provided at either end thereof with trunnions 18 suitably journalled in ball-bearings I9 mounted within the adjoining ends of the roller 76. Fitted upon each of these trunnions 18 is a wheel having a sloped rim 8|, as shown. These wheels 80 travel along a pair of parallel tracks 82 disposed to either side and extending longitudinally of the curtain in the region of its upstream panel 13*. The tracks are complementally inclined with respect to the wheel rims in consequence of which the draw roller 16 and accordingly the damper curtain are automatically centered at all times between the side walls of the stack and at the same time permit expansion and contraction of the parts under varying conditions of stack temperature.

The damper curtain 13 is operated by means of an electric motor 83 or the like, the shaft of which is coupled to the operating roller '55 by a chain drive 84. As appears most clearly in'Figure 14,. the operating roller 15 and the draw roller 16 are connected together by a pair of cables 85 which pass over sheaves 86 suitably supported adjacent the draw roller end of the damper. One end of each cable 85 is adapted to bewound about a drum 8']! operatively associated and rotatable with the operating roller 15, while the opposite end of each cable is secured to the outer end of the draw roller 16, as at 88, the arrangement being such that as the damper curtain is wound about its winding roller T the draw roller it is drawn inwardly to reduce the effective length of the damper curtain, the cables on the spindle drums 81 being at the same time unwound to increase the lengths .thereof to compensatefor the shortening of the curtain length.

Conversely, as the curtain is unwound from the operating roller upon reversing the operation of the latter, the cables 85 are wound upon the spindle drums and so draw the roller 16 outwardly to increase the effective length of the damper curtain. In all cases, the damper curtain is thus maintained in relatively taut condition transversely of the stack 12.

It will be understood, of course, that the present invention may be modified in other respects than as indicated hereinbefore and may beemployed in installations other than as described all without departing from the real spirit or general principles thereof. For example, the damper of the present construction is adapted for use and may be installed in the ducts of air-conditioning systems not only to regulate and control the flow of air therethrough and so improve "the efi'iciency of operation of the system, but alsoto close ofi the duct in which it is installed inthe event of fire, thus precluding the possibility of the duct serving as a conduit for fire. In fact, the damper of the present invention may be 'employed in any system wherein it is desired to control or interrupt entirely the flow of gas or air through a conduit. Accordingly, it is intended to claim the invention broadly, as well as specifically, as indicated in the appended claims.

What is claimed as new and usefulis:

1. A damper for controlling the draft through a flue comprising, in combination, a flexible curtain looped to provide a bight end which is adapted to be drawn transversely across the flue opening, the free ends of the looped curtain being respectively secured to a stationary part and to a winding roller disposed to one side of said flue, a roller disposed in the bight end of. said looped curtain for maintaining the same extended across the flue in taut condition, means for operating stream face of the looped end of said damper curtain, said plate being provided with spaced notches each of gradually increasing width opening toward the free edge of the plate.

3. A damper for controlling the draft'through aflue comprising, in combination, a flexible curtain of a'width adapted to fit snugly between the opposite side walls of the flue and adapted to be drawn across the flue opening to close off more or less of the latter, said curtain being doubled upon itself to provide a pair of spaced parallel panels, a roller supported in the looped portion between said panels, a winding roller connected to one free end of said curtain and about which the latter is adapted to be wound to vary the effective length of the doubled portion of the curtain, means for anchoring the other'free end of said curtain in fixed position, meansfor operating said winding roller to wind or unwind the curtain thereon or therefrom, and a .casing for commonly housing said winding 'roller'and the fixedly anchored end of the curtain, said casing being mounted externally of the flue and being provided with an opening in communication with the interior of the flue through which the doubled portion of the curtain is projected.

'4. A damper for controlling the draft through a flue comprising, in combination, an extensible curtain of flexible material adapted to be drawn across the flue'opening to close'off more "or less of the latter, and baffle means fixedly positioned in the flue for operative association with the free end of the curtain for controlling the flowcharacteristic of the damper as said curtain approaches its fully closed position,

5. A damper for controlling the draft through a flue comprising, in combination, a curtain of flexible material adapted to be adjustably extended across the flue opening to close 01f more or less of'the latter, and a bafliing plate fixedly positioned in the flue and disposed in parallel relation to the plane of the curtain, the free end of the latter being adapted to overlap said plate .as the curtain approaches its fully closed position, said plate having a series of openings'thereinof gradually increasing width opening toward the free edge of the 'plate'whereby to providedraft ports through the flue which vary in areadepending upon the extent of overlap of the curtain with respect to said plate.

6. A damper for controlling the .draft' through a flue comprising, in combination, a curtain of flexible material adapted to be adjustably extended across the flue opening to close off. more or less of the latter, said curtain being doubled upon' itself to provide a pair of spaced, substantially parallel panels joined together by a looped portion disposed interiorly of the flue, means operatively'associated with the opposite ends of the curtain to vary the effective length of the doubled portion thereof, a hollow roller disposed in the looped end .of the curtain for maintaining the spaced panel sections thereof extended across the flue in relatively taut conditioma stationary grille fitted within said flue and disposed on the .downstream side of said curtain, and sealing strips provided along opposite edges of said grille against whichthe side edgesof the downstream panel-of the curtain engage under the pressure of the draft exerted thereagainst, the opposite .ends .of the roller being spaced'from the embracing side walls of the flue ,and said roller being provided with openings in. the Wall thereof .aifording. communicatingpassageS between the exposed .portionof the flue and the space between the panel sections of the curtain whereby to utilize the flow through the flue to rid the last-mentioned space of any dust and the like tending to accumulate therein.

7. A damper for controlling the draft through a flue comprising, in combination, a curtain of flexible material adapted to be adjustably extended across the flue opening to close off more or less of the latter, said curtain being doubled upon itself to provide a pair of spaced, substantially parallel panels joined together at their inner ends by a looped portion, means at the outer ends of said panels operative to vary the effective lengths thereof, said means including a winding roller about which one end of the curtain is adapted to be Wound and unwound, and means at the inner looped end of the curtain for maintaining the same relatively taut during all adjusted positions thereof, said last-mentioned means facilitating the drawing by the draft of accumulated dust and the like from the space between the panel sections of the curtain and discharging the same into the region of the flue which is not closed off by the damper curtain.

8. A damper for controlling the draft through a flue comprising, in combination, a curtain of flexible material adapted to be adjustably extended across the flue opening to close off more or less of the latter, said curtain being doubled upon itself to provide a pair of spaced, substantially parallel panels joined together at their inner ends by a looped portion, means at the outer ends of said panels operative to vary the efiective lengths thereof, said means including a winding roller about which one end of the curtain is adapted to be wound and unwound, means at the inner looped end of the curtain for maintaining the same relatively taut during all adjusted positions thereof, and means operatively associated with the winding roller aforesaid to rid the curtain of dust and the like which may tend to accumulate on the exposed outer surface of the curtain.

9. In a damper construction of the character defined in claim 8 wherein said last-mentioned means is in the form of a brush disposed in wiping engagement with the exposed outer surface of the curtain'and which is operative, as the curtain is wound upon said winding roller, to free said surface of dust and the like accumulating thereon.

10. A damper for controlling the draft through a flue comprising, in combination, a flexible curtain adapted to be adjustably extended across the flue opening to close 01f more or less of the latter, said curtain being doubled upon itself to provide a pair of closely spaced, substantially parallel panels joined together at their inner ends by a looped portion, means at the outer ends of said panels operative to vary the elfective lengths thereof whereby to change the area of the flue opening in the plane of the curtain, a pair of grilles fitted in the flue and disposed upon opposite sides of the doubled curtain, and sealing means associated with each of said grilles and operative to seal one or the other of said panels against flow about the side edges thereof depending upon the direction of the flow through the flue.

11. A damper for controlling the draft through a flue comprising, in combination, flexible curtain means adapted to be adjustably extended across the flue opening to close off more or less of the latter, means at the outer ends of said curtain means for varying its effective length and so change the effective area of the flue opening, a pair of grilles fitted in the flue and embracing therebetween said curtain means, and means associated with each of said grilles and operativ to seal said curtain means against flow about the side edges thereof depending upon the direction of the flow through the flue.

12. A damper construction of the character defined in claim 11 wherein said curtain means is in the form of a pair of doubled curtains each providing a pair of closely spaced, substantially parallel panels, the outermost panel sections of each curtain having their free ends fixedly anchored to one Wall of the flue while the innermost panel sections of each curtain have their ends severally secured to Winding rollers journalled upon said flue wall, the said innermost panel sections being each adapted to be wound on or unwound from said winding rollers upon rotation of the latter and the outermost panel sections being each adapted to be rolled off of or on to its associated grille to vary the area of the grille covered by the curtain.

13. A damper for controlling the draft through a flue comprising, in combination, a flexible curtain looped to provide a bight end which is adapt- "ed to be drawn transversely across the flue opening, the free ends of'the looped curtain being secured respectively to a stationary part on the flue wall and to a winding roller journalled upon said flue wall, a movable roller disposed in the bight end of the looped curtain,'a grille disposed upon the downstream side of the curtain against which the downstream section of the looped curtain is forced by the pressure of the draft exerted thereagainst, and means operatively associated with the movable roller aforesaid to exert a pull thereon transversely of the flue whereby to maintain the looped curtain in taut, extended condition.

14. A damper construction of the character defined in claim 13 wherein said curtain is disposed for operation in a substantially horizontal plane and wherein said last-mentioned means includes a counterweight operatively connected to said roller.

15. A damper construction of the character defined in claim 13 wherein said curtain is disposed for operation in a substantially horizontal plane and wherein said last-mentioned means includes a cable extending between the two rollers which is operative to exert an outward pull upon the movable roller simultaneously as the winding roller is rotated to increase the effective lengths of the extended curtain and which is operative to permit retraction of said movable roller as the winding roller is rotated to decrease the effective lengths of the curtain.

16. A damper construction of the character defined in claim 13 including a pair of guide tracks disposed upon opposite sides of the extended our tain, and wheels journalled upon opposite ends of said roller and movable along said guide tracks to support said roller for movement in a fixed plane extending transversely of the flue.

1'7. A damper construction of the character de fined in claim 13 including apair of oppositely sloped parallel guide tracks disposed upon opposite sides of the path of movement of the curtain, and wheels carried by said roller at opposite ends thereof and movablealong said guide tracks to support said roller for-movement in a fixed plane extending transversely of the flue, said wheels having track-engaging runs which are sloped in correspondence with the slope of the tracks whereby to automatically insure centering of the roller between said tracks.

"CHARLES L. MYERS.

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