US 3164455 A
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Description (OCR text may contain errors)
Jan. 5, 1965 Filed June 29, 1961 K. L. WESTLIN AIR CLEANING APPARATUS 4 Sheets-Sheet 1 .24 |6N w I Ill \,|4
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KARL L. WESTLIN ATTORNEY Jan. 5, 1965 K. L. WESTLIN 3,
AIR CLEANING APPARATUS Filed June 29, 1961 4 Sheets-Sheet 2 4- DIRTY AIR IN INVENTOR.
KARL L. WESTLI N ATTORNEY Jan. 5, 1965 K. L. WESTLIN 3,164,455
AIR CLEANING APPARATUS Filed June 29, 1961 4 Sheets-Sheet 3 28f 3&1
INVENTOR. KARL L. WESTLIN ATTORNEY 4 Sheets-Sheet 4 KARL L. WESTLIN ATTORNEY Jan. 5, 1965 K. L. WESTLIN AIR CLEANING APPARATUS Filed June 29, 1961 United States Patent Q 3,164,455 AIR CLEANING AYPARATUS Karl L. Westlin, Louisville, Ky., assignor to American Air Filter Company, Inc, Louisvilie, Ky., a corporation of Delaware Filed June 29, 1961, Ser. No. 120,716 TClaims. (Cl. 55273) terior of the pockets under normal air flow conditions in communication with theclean air chamber, and under reverse air flow conditions for cleaning the pockets in communication with a reverse air source; and means for I reversing the air flow through a portion of the pockets in sequential fashion. I
Various arrangements have been devised to reverse the air flow through those pockets to becleaned, and to prevent the dust dislodged during pocket cleaning from being redeposited on adjacentpockets. One well known -arrangement moves an air discharging 'traveler,- connected to a separate blower, along theopen ends of successive pockets to provide the reverse air flow, and blanks ofli one or more pockets adjacent to the pocket being cleaned. The pockets which-aie blanked offreduce the capacity of the cleaner.' The provision of a traveler which must seal tightly against the open ends ofthe pockets presents substantial mechanical problems. Other deficiencies of such consideraan arrangement will also be appreciated from a tion of the apparatus required therefor. v I,
Thus among the objects of the invention is ,the provision of a pocket type air cleaner: which utilizes atmospheric air in connection with a'particula'r valve arrangement, instead of an air discharging traveler, for effecting a reverse air flow for'pocket cleaning purposes;swhich includes means for operating the valve arrangement in a manner causing an abrupt reversalin air flow for pocket cleaning purposes and. a contrasting slow reversal in air flow after the pocket has been cleaned; which doesnot require auxiliary or secondary blower means to provide the reverse air; and in which no pockets areblanked off from'air flow so that as the cleaning of successive pockets is initiated, the maximum energy available for snapping or popping the pockets is utilized. I a
In accordance with the invention, the interioror clean side of each pocket is connected to a chamberlthrough which cleankair flows inone direction while thepocket is filtering air, and through which atmospheric air flows in the opposite or reverse direction when the pocket itself is being cleaned. To effect this, each chamber has a nor- 3,164,455 Patented Jan. 5, 1965 to effect the reverse air flow very'abruptly and to restore normal air flow in a gradual. movement.
Other features and details of the invention will be appreciated from the following description taken in connection with the accompanying drawing illustrating one form of apparatus embodying the principles of the invention by way of example, and wherein:
FIGURE 1 is a front view, with some detail deleted, of an air cleaner embodying the invention;
FIGURE 2 is a partly broken side view of the air cleaner of FIGURE 1;
FIGURE 3 is a partly broken top view of the air cleaner of FIGURE 1;
FIGURE 4 is a face view of an inner retainer for supporting one of the pockets or sleeves from collapsing during normal air flow;
FIGURE .5 is an edge view of the retainer of FIG URE 4;
FIGURE 6 is a face View of an outer retainer for sup-' porting one of the pockets during reverse air flow thereview illustrating'the genenal structural arrangement, of,
several chambers of the air flow control box; a
FIGURE 11 is a partly broken, face view ofa valve and certain associated parts for the atmospheric air inlet of a chamber; I
FIGURE 12 is a fragmentary horizontal sectional view corresponding to one taken along line 1212 of FIGURE 11 with certain details omitted for clan'ty;
FIGURE 13 is a horizontal sectional view correspondi ing to one taken along line 1313 of FIGURE 11 illustrating a valve controlling cam follower in solid linesin a position holding the outer valve closed, and an adja cent valve controlling cam follower in dotted lines in a position which permits opening of the outer valve; and" FIGURE 14 is a fragmentary vertical section corresponding to one taken along the line 14-14 of FIG- URE '1 illustrating a bracket and support means for the endless band.
The air cleaner (FIGURES 1-3) basically comprises; a dust chamber or box generally designated 2 into the upper part of which dust'laden gas or air is introduced; a series of filter pocket assemblies 4 (shown in dotted line outline form in FIGURE 2) mounted in spaced sidernally closed atmospheric air inlet, and a normally open clean air outlet in communication with the suction source; Both the atmospheric inlet and clean air outlet have at, terconnected valve members arIangedso that when the atmosphericairinlet is open, the clean air outlet is closed, I
and vice versa. A traveling endless band controls the positions of the'valves in'a sequence wherein successive pairs of adjacent chambers'are opened to ,-atmospheric air and closedto the suction source to obtain the reversal bers occurs while the pockets on both sides of the pair continue to receive normal air flow therethrough; The
valves and control means are arranged to'move the valves by-side relation across the lower part of the dust box with their front ends being open and aligned in the plane of the front wall of the dust box; dust hoppers 6 in the form of inverted .pyram-ids underlying the dust box; an air flow first set in communication with companion; individual chambers of the second set, or a-lternatively 'to close the two sets of chambers to each other andtoopen'the, first set to atmosphere; and a travelingtendlessband arrangement'10 mounted on the control box front and operate ing the valve arrangement in a manner that successive of one.
J pairs .of pockets are subjected to reverse cleaning purposes while the normal airflow. I j I j With this general arrangement, and for the moment air flow for i excepting those pockets being cleaned by reverse airflow,
the direction of air flow throughthe apparatus is as shown remaining pockets receive 1 by the dotted arrows of FIGURE 2. Dust laden air drawn into theupper portion of the dust box passes downwardly into the spaces between the adjacent pockets,
through the pocket fabric to the interior of thepockets (causing the dirt'tojbe deposited on'the outside of .the pocketfabric), then into and through the control box first chambers (i.e., those chambers in registry with the front open ends of -.thepockets),and through the control box second chambers connected by a clean air'rnanifold'to the suction source (not shown). 7
As to those pockets being cleaned, the valve arrangement closes the openings between the first and second chambers and opens the first chambers to atmosphere.
Thus' the suction source induces a reverse. flow of air through the first chambers from atmosphereand through the pocket fabric from inside to outside, this reverse air then passing to a pocket undergoing normal air flow and to the suction source. The reversal of air flow is abruptly effected by means to be hereinafter detailed so that the pocket is popped or slapped smartly against an outer support retainer to dislodge the dirt accumulated on the outer face of the pocket fabric. I V i v 3 "The pockets are subjected to reverse air flow cleaning in pairs so that the dirt dislodged from the opposing inner faces of apair of. pockets, is not redeposited, on another open ended dust lter pocket or envelope held therebe- The pocket assemblies are mounted in spaced face-to-face relation across the lower portion of the dust box in upstanding positions parallel to the opposite side walls 14 and 16. The vertically extending front and rear openends of the pockets are aligned along the front and 7 rear of the'dust box. The rear open ends of the pockets pocket butfalls downthrough the space between'the ad;
jacent pockets being' cleaned into the dust hopper. The
actuation of the valve arrangement to effect reverse" flow cleaning of successive pairs of pockets is accomplished flby" movement of-the endless band'past the actuating means of the valve arrangement, the endless "band holding the valve arrangement in a normal; air flow position for the chambers 'forall pockets except a pair. Since the valve arrangement for each first chamber is independent of the valve arrangement for other. chambers, movement of the endless band causes reverse flow to one pocket to end at about the same time that reverse flow begins in the second pocket ahead in the direction of movement of the endless I 'bandg That is, the interval of time during which each pocket is subjected to reverse air flow overlaps, or coincides'in part at least, with the intervals of time during which the immediately preceding and succeeding pockets are subjected to reverse air flow so that the second pocket of one pair to receive reverse air flow continues toreceive reverse air flow asthe first pocket of the next successive.
. pair is subjected to reverse air flow; Thus as the-clean- .ing of pairs of pockets progresses, that dirt dislodged from the leading face of a pocket as it firstreceives reverse air flow and which is then normally redeposited to a degree on the opposing-face of'the next successive pocket (which is undergoing normalair flowlwill be dislodged I v and. fall into'the hopper when 'that next successive pocket receives reverse air, flow with the preceding pocket also continuing to receive reverse air flow. Stating it in another Way, it maybe considered that in -a pair of pockets undergoing reverse air flow there are four filtering faces and:
that of the four faces one is a leading face, one trailing face, and two are opposed-inner faces. T hen the dirt 1 dislodgedfrom the leading face will be redeposited to some degree on the opposing face of the next successive pocket, the dirt dislodged from the pairoff'opposing inner faces will fall downwardly into the hopper, and the trail-- ing' facewill have had its dirt load previously dislodged when itwas in thetposition of an opposing inner face.
Referr'ing nowin'som'e detail to the structure of the" apparatus, the dust'box 2 includes: a top wall 12; side walls 14' and 16;"a rear wall lld having a series of'verticallyfextending; openings through which the pocket assenb ":blies are inserted and removed; an :upper front wall 2i fthe'lower portion of the front of the dust box having the 'does not include the channel" spacers.
tion of air flow reverses,
are closed; by individual vertically disposed channels 26 (best .seen in FIGURES 3 and 9) secured to the rear wall 7 18 to close the vertical openings in the rear wa'll through which access to the individual pocket assemblies is had. As shown in FIGURE 9, the inner faces of the channels 26 carry gaskets 28 which seal'the rear open ends of the pockets. The periphery of the front open end of each pocket assembly seats against a rectangular gasket 36 which frames 'the'control box openings which are in registry with the front open ends of the pockets.
Turning now to the details of the pocket assemblies (FlGURES4-8), the inner retainerfor each pocket is afrectangular, open-face, open-edge structure comprising a pair of screen covered frames 32 spaced apart by a series of vertically spaced channels 34 extending horizontally from the front to the rear edges of the retainer.
The screen 36 covering the opposite open faces and the top and bottom edges maybe /2" mesh hardware cloth or the like. The front and rear vertical ends of the retainer are not covered byxthe screen 36.
The outer" retainers (FIGURES 6 7) are generally similarto the inner retainers insofar as they comprise a pair of spaced apart perimetric frames 38 and have open faces and edges. The frames are held apart attheir cor- 1 nersJby spacers 44 -It is notedhowever that the screen 42 covering the opposite faces of the outer retainer has openings which preferably are considerably larger than V the openings of the inner-retainer grid, and that the outer retainer isicdnsiderably thicker than the inner-ones and Thus when the inner retainer is received within. the outer retainer with the fabric envelope or sleeve between the retainers, there will be a space of say /zi between one faceof the inner retainer and the opposing face of the outer retainer. This space between the opposing faces of the inner and outer retainers permits apprecable displacement of the filtering surface when reverse air flow to the pocket begins so that dirt-may be knocked off as well as blown off.
The filtering medium for each pocket assembly is selected'to provide a suitable filtering surface for the type of dust to be encountered, The selected material is made into asleeve 44' (FIGURES 3 and 8) having opposite open ends. The sleeve length is sufficiently in excess of the length of the inner and outerretainers that the oppo-' site. ends of the, sleeves may be turned backwardly to form short hems 46 overlying theffront and rear edges of the outer retainer; The circumferential dimension of the sleeve is slightly larger than the interior of the outer frame so that the ends of the sleeve may be stretched to form the hems and so thatsthere is sufiicient material to accommodate the-displacement of the filtering surface between the openwork faces of the retainers as the direc- Passing. now to thetconstruction of thecontrol box a,
' as .noted previously it basically comprises two; sets of vertically extending chambers'alternating with each other and "provided with valve means for controlling the communication between the chambers and atmosphere. As perhaps best shown in FIGURESB and19, the chambers 48 of the first set (which registerjwith the pocket assemblies) areopen at their rear to the interiors of the pockets,
and each chamber 48 is provided with a vertically ex- All except gap after sliding off the trailing edge of the last plate preceding the gap, will be abrupt.
As previously noted, the valves 52 and 66 for each chamber are both pivotally connected to the levers 68 so by indicating a closed position of these valves. The two valves 52 shown spaced slightly from the front wall 51 are intended to represent open outer valves associated with the two pockets being cleaned. The bottom of the first set compartments or chambers are closed by bottom wall 54 (FIGURES 2 and 9) at the level of the pocket assembly bottom.
The chambers 56 (FIGURES 2, 3, 9) of the second set extend below the bottom wall 54 of the first set chambers to communicate with the suction manifold 58 in the control box lower portion, which is in turn connected through clean air outlet duct 60 to the suction source. The vertical wall 62 between each first chamber 48 and its companion second chamber 56 is bent along a vertical line so that it angles into the second chamber as shown in FIGURE 9 and terminates in a vertical right angle member defining one side of the vertical slot opening 64 between each of the companion chambers. An inner valve 66 which is also a long shallow channel, closes this slot opening 64 at the same time that outer valve 52 opens slot 50 in the control box front wall 51 when the reverse air flow is initiated.
I The valve arrangement (FIGURES 9-13) for each first that they operate together. The bight of the outer. valve 52 is connected to the levers by upper and lower swivel connections 83 (FIGURE 12), the levers then extending through horizontal slots 90 in the bight to similar swivel 1 connections 92 on the inner valve. Each inner and outer chamber and its companion second chamber includes the innerand outer valves 66 and 52, a pair of vertically spaced cranks .or levers 68 to whichboth valves are pivotally secured, a vertical shaft '70 rotatably carried on the exterior of the control box front wall and to which the levers 68'are rigidly secured, spring means biasing the shaft and levers toward a position in which the inner valve 66 is closed and the outer valve 52 isiopen, and cam follower means in the form of member 72 rigidly secured to and projecting from the shaft 70 with its outer end riding against the endless band arrangement 10 so that the valve assembly is normally held in a position opposite its biased position. 7
As shown in some detail in FIGURE 11, each shaft 79 is carried for limited rotation by a series of vertically spaced bearings '74 secured to the front Wall 51 of the control box. Both the upper and lower levers 68 have collars 76 welded. thereto which receive the ends of the shaft 7 ti and are suitably secured thereto by means of an Allen screw or the like. The bias means for the valve,
assembly includes upper and lower torsion springs 78 having one end secured to the control box front wall and ,the opposite offset end 80 projecting into a hole in the lever 63 adjacent the, collar '76.
The chain follower 72 is rigidly secured to the middle ofthe. shaft it? and has a free outer end provided with a central notch 82. The forked outer end normally bears against a series of small plates 84 secured to the outside face of the endless chain it) so that outer valve 52 is held closed and inner valve 66 held open. However, the plates 84 are omitted from a number of chain links to provide the gap 86 corresponding to the width of two first valve is provided with gasket material, such as felt, on its seating face, the felt on the outer valve serving also to seal around the slots 934) through which the levers pass.
The endless chain 19 extends horizontally across the front of the control box (FIGURE 3) and is driven at a suitable speed by an electric motor 94 through a gear reducer )6, both mounted at one end of the front of the control box. To insure that the chain 10 does not sag, and is not displaced outwardly by the chain follower force bearing against the inner flight of the chain, a series of U-shaped brackets 98am spaced along the front of the control box to carry a chain guide plate 100 (FIGURE 14) underlying both flights of the chain, and a bar 162 extending along the outer face of the inner flight as illustrated.
A summary explanation of the operation of the air cleaner, and of the control box and valve arrangement in particular, is perhaps best understood in connection with FIGURE 9 wherein one first chamber and its companion second chamber are designated 48a and 56a respectively, and the other first chamber and its companion second chamber are designated 48b and 56b respectively. Air flow through the upper pocket 4a of FIGURE 9 is in a normal direction in the sense that it is passing through and two companion second chambers. The gap in the L plates permits the followers to move outwardly under the t force of the torsion spring '78 with the central notch 82 straddling the chain and results in the inner valve 66 closing and the outer. valve 52 opening. It will be noted I that, as shown in FIGURES 9 and 13, the followers are bent along several vertical lines toward their outer ends so that when the follower end is engaged by the first plate 84 following a gap, the movement of the valve assembly to the position closing the outer valve 52 and opening the inner valve as will be effected easily and gradually. However, the opposite movement of the valve assembly, occurring when the follower springs outwardly into a the pocket from outside to inside with the filtering surface pressed against the inner retainer screens as illustrated. The dirt taken out of the air is of course lodged on the exterior surface of the pocket. The cleaned air then flows through first chamber 48a in a direction indicated by the arrows and into companion chamber 56a through opening 64a. The cleaned air flows downwardly through companion chamber 56a to the suction manifold and thence to the suction source for discharge. The how of air through all pockets associated with control box chambers having the valves in the position shown for chamber 48a will be the same.
' Now as to the lower pocket, i.e., the one associated with chamber 4%, in this case the gap 86 in the plates on the chain has permitted the follower 72b to move outwardly so that outer valve 5215 has moved to an open position and inner valve 65:) has moved to a closed position; As a result atmospheric air is drawn through opening Siib and through first chamber 48b in a reverse direction to the interior of the pocket where it causes the filtering surfaces to slap outwardly against the outer retainer where it is held as illustrated. It will be appreciated that while only pocket 4b is shown as undergoing reverse air flow in FIGURE 9, an adjacent pocket is also undergoing reverse air flow since the gap $6 in the chain plates is of length to encompass two followers at any one time. The dirt dislodged from that face of the pocket 4b 'is determined in accordance with the dust load encountered. This may be readily controlled in one way by the rate of chain travel, in another way by providing more gaps in the total chain length, and further ways will occur to those skilled in the art. 7
Several features of the invention are believed worthy of some emphasis. The preferred valve arrangement described results in movement-ofthe valves from a normal air flow position to areve'rse air flow position very abrupt- 1y as the follower 72 springs outwardly, but the return movement of the'valves to their normal air flow position is relatively gradual. Since there is space between the faces 'ofthe inner and outerretainers fordisplacement of'thefiltering surface, it is forcibly slapped outwardly by the reverse air fiow with the dirt dislodged from the exterior of the surface in an'effective manner. However, since the fabric is displaced inwardly against the inner retainer in a gradual manner, the possibility of any dirt still on the fabric being shaken through the fabric and carried into the clean air stream is minimized.
The provision of separate chambers and a separate valve arrangementfor each pocket permits an operation wherein all of the pockets function to cleanthe air or else are undergoing cleaning themselves. I hat is,'none of the pockets are blanked oil. While this in itself is advantageous from a capacity standpoint, it also results in a higher negative static pressure in the pockets when their cleaning is to start than if the pockets had been blanked otf. Therefore, there is a more forceful inrush of air and a sll-arperlslap of the fi'rter surface against the outer retainer than'if the pockets had been blanked off from the suction source and had, as a result, a static pressure substantially equivalent to-that existing on the dirty air side of the pockets.
Since the described appanatus uses atmospheric airas a source of reverse air, it does'not require a separate forced draft of secondary air to clean the pockets. thus avoids the problems inherent in providing an air discharging traveler which should tightly seal against successive pocket ends for satisfactory, operation.
In a consideration'of' the merits of the invention, it-
should' also be pointed out that while the term reverse means by which the cleaning of the pockets is effected,
' the factor which is perhaps most important in the pocket cleaning operation is the forcefulness of the slap of the filtering surface when reverse air flow is initiated since the dirt is dislodged more by being knocked off than by being blown off. It will thus be appreciated that the provision of support means for the filtering surface which permits measurable displacement thereof upon reverse fiow initiation is of appreciable significance in the apparatus.
The provision of an arrangement wherein the pockets havetheirrear ends against the rear wall prevents pas sage of dislodged dirt around the rear end of a pocket and its redeposit upon some pocketundergcingnormal air flow. Re-entrainment below the bottom edges of the pockets may be minimized by baffles depending from the lower edges of the pocket assemblies.
ing the trailing gap are so spaced that, as the chain moves along, the intermediate plate and the first plate following the trailinggap will f concurrently engage the cam v followers associated with the pair 'of pockets undergoing reverse air flow to restore the respective. valve arrangemerit to a normal air' flow position while the plate im-.
inediately preceding the leading gap holds that particular valve arrangement in a normal airflow position. Then as the chain moves farther along, the pair of adjacentlcam followers engaged bythe plate immediately'preceding the leading gap and'the i .termediate plate disengage there fromand. spring outwardly into the leading and trailing gaps respectively to subject the correspondin poclcets to lie-entrainment 'over the tops of the pockets is of course prevented by the. general downward flow of air through the dust box.
. 8 7 reverse air flow. The primary benefit of this modified arrangement, i.e.', the split gap arrangement, is that each pocket is subjected to two reverse air flow slaps during eachpassage of the gap portion of the chain therepast since normal air fiow is restored to the leading pocket of a pair undergoing reverse air flow before it subsequently occupies the position of a trailing pocket undergoing reverse air flow. Thus an alternating condition is set up wherein the reverse air flowvto the successive pairs of adjacent pockets alternates with normal air flow to all pockets.
end; an air control box on the front side of said dust box having a set of first chambers in registry with and connected to said open front ends of said pockets and a' set of companion second chambers alternating with said first set, said second chanibersbeing connectedin common with a suction source; valve means for each first chamber operable, in a first position to open each first chamber to its companionisecond chamber and to close each first chamberto atmosphere, and in an alternate position to close each first chamber to its companion second chamber and to open each first chamber to atmosphere; and means for operating the valve means of. each successive first chamber to said alternate position for a time interval overlappingrat least a part of the time intervals during which the valve meansof the immediiately precedingand air flow cleaning more or less accurately describes the succeeding adjacent first'chambers are insai positions whereby a reverse flow of air is induced through alternate those successive pairs of filters pockets connected with said first chambers handing-valve means in said alternate position. I f j ,2. In the air cleaner specified in=claim 1: said valve operating means include means for moving said valve means from said first position to said alternate position in an abrupt. movement, and for restoring said'valve means to said first position in a substantially slower movement. Y e
3. An air cleaner as specified in claim l wherein: said dust'laden air is admitted into the upper-portion of said dust box;isaid filter pockets are disposed in the lower portion of said dust box so that a substantially unobstructed space is provided thereabove; and means are provided for sealing the rear end of each of said filter pockets with therear wall ofvsaiddust box to prevent air tlow therearound during said reversal of airflow. 1
Y be cleaned and a series of separate outlets on one side ,of said casing; a corresponding series of filter envelopes between said inlet and said outlets for filtering air passing therethrough from outside to inside, each having one open end connected to an outlet opening; auxiliary cas ang means mounted on said one side of said main casing and forming a series of alternating chambers including a set of first chambers registering with said outlet openings, and a set of second chambers in common communication with a suction source, each first chamber having a companion second chamber; means defining a first open- 9 phere; valve means for said first and second openings; and means for periodically operating the valve means of successive pairs of adjacent first chambers from a first position wherein said first opening is open and said second opening is closed to an opposite position wherein said first opening is closed and said second opening is open whereby said successive pairs of adjacent first chambers receive a reverse flow of air from atmosphere While 7 the remaining first chambers are in communication with their companion second chambers.
6. In an air cleaner: a dust box into which dust laden air is admitted into the upper portion thereof and flows downwardly: :a series of upstanding filter sleeves disposed in spaced side-by-side relation across the lower portion of said dust box, each sleeve having an open end at the front side of said box and a closed end sealed with the rear side of said box; an air control box having a series of separate alternating chambers on the front side of said dust :box including a set of first chambers registering with and connected to the front open ends of said sleeves, and a set of alternating companion second cham- 'bers in communication with a suction source and normally open to said first chambers; and means for periodically opening successive pairs of adjacent first chambers to atmosphere and closing them to their companion second chambers to induce a reverse fiow or air trom atmosphere through the connected sleeves, While simultaneously maintaining the remaining first chambers and companion second chambers open to each other and closed to atmosphere, the time interval during which each first chamher is open to atmosphere overlapping the time intervals during which the immediately preceding and succeeding adjacent first chambers are open to atmosphere.
7. In an air cleaner: means forming a main casing into which dust laden air is admitted, and an auxiliary casing having a set of first chambers alternating with a set of companion second chambers, said first chambers being in communication with the interior of said main casing and said second chambers being in communication with a suction source; a series of horizontally spaced, vertically disposed filter envelopes having one open end anranged in said main casing so that each of said envelopes has its interior in communication with a corresponding first chamber; valve means for each first chamber operable, in a first position to open each first chamber'to its companion second chamber and to close each first chamber to atmosphere, and in an alternate position to close each first chamber to its companion second chamber and to open each first chamber to atmosphere; and means for operating said valve means for each successive first chamber from said first to said alternate to said first position concurrently with the operation of the valve means of the immediately preceding first chamber in the same sequence, and then from said first to said alternate to said first position concurrently with operation of the valve means of the immediately succeeding first chamber in that same sequence.
References Cited in the file of this patent UNITED STATES PATENTS 2,682,316 Kaufmann June 29, 1954