Abstract:
An apparatus for collection of yard debris combines a vacuum pick up with a blower unit, a separator, and a detachable accumulator with an attached roller to support the accumulator upon detachment from the separator. The apparatus collects and entrains debris in an airflow induced at the vacuum pickup, impels the debris to the separator which removes the debris from the airflow, and deposits it in the accumulator which is supported by a roller to aid subsequent dumping when the accumulator is detached.

Description:
RELATED US APPLICATIONS 
   This application is a Continuation In Part of and claims priority to, co-pending U.S. application Ser. No. 11/453,579, which is a Continuation-In-Part of co-pending U.S. application Ser. No. 11/145,289, filed Jun. 3, 2005, which is a division of U.S. application Ser. No. 10/846,029, filed May 14, 2004, now U.S. Pat. No. 6,904,742, which is a Continuation-In-Part of and claims priority to, U.S. application Ser. No. 10/724,316, filed Nov. 26, 2003, now U.S. Pat. No. 7,114,317, which is a division of U.S. application Ser. No. 10/045,123, filed Nov. 9, 2001, now U.S. Pat. No. 6,658,833, which claims benefit of U.S. provisional application Ser. No. 60/247,456, filed Nov. 9, 2000. This application is also related to co-pending U.S. application Ser. No. 11/648,982 and Ser. No. 11/649,105 filed on even date Jan. 3, 2007 as divisions of U.S. application Ser. No. 11/145,289. 

   FIELD OF THE INVENTION 
   This invention relates to an apparatus for collection and reduction of yard debris in thick layers and deep piles. 
   BACKGROUND 
   Homeowners, commercial-property owners, and companies who provide care for lawns have an ongoing challenge of how to remove leaves, grass clippings, and other debris from lawns, gardens and paved surfaces, particularly when the debris accumulates to a depth of over an inch. Several companies now manufacture and sell combination vacuum-chipper-shredder machines intended for this purpose. Some U.S. patents illustrating the range of these machines are as follows: U.S. Pat. Nos. 5,931,396 and 5,799,365, both assigned to MTD Products; 5,381,970 and 5,231,827, both assigned to Garden Way Incorporated; and 5,642,864, assigned to Simplicity Manufacturing, Inc. However, the dilemma with many prior-art units is that while they are reasonably adapted to vacuum a thin layer of debris from the ground, they do not function well when there is a thick layer of leaves or other debris. When there is a covering of several inches of leaves, the collector duct merely pushes a stack of leaves ahead of the unit instead of drawing the leaves into the machine. If the collector duct is raised to be able to take leaves from the top of the overlayer, it is no longer so effective in collecting the leaves and other debris close to the ground. Accordingly, while the available machines are somewhat effective in removing the thin layers of debris, the task of collecting thick layers of debris, particularly deep piles of leaves, remains quite problematic. Typical prior art machines, such as those shown in U.S. Pat. Nos. 5,799,365 and 5,231,827, have a vacuum pick-up opening wherein the plane of the opening is parallel to the ground, while the device shown in U.S. Pat. No. 5,642,864 has its opening disposed at an angle of about 45 degrees with respect to the ground. Such devices are poorly adapted to the tasks for which machine assistance is needed most. 
   Many existing machines depend primarily on flow of air to lift and entrain the leaves and other debris for transport through chipper shredder devices, and then to blow the reduced debris into accumulation units. To separate the debris from the air in which it is entrained, the machines rely on some form of filtration, with either fabric bags or screens. However, as leaf fragments and other debris collect on the filter, resistance to the flow of air increases, diminishing the air flow rate, and thereby, reducing the effectiveness of the vacuum pick-up opening. 
   OBJECT OF THE INVENTION 
   It is an object of the present invention to provide a machine which effectively removes deep piles of leaves and other debris. In preferred embodiments, the thin layer of residual debris which might otherwise be left for later removal in another step is cleanly removed at the same time. 
   Another object of the invention is to provide a unit combining a front-facing vacuum-assisted opening with a rotor which serves to impel heavy leaves and debris toward a vacuum slot while creating air flow close to the surface to be cleaned in a direction which is generally parallel to that surface for picking up finer debris. 
   Another object of the invention is to provide a rotor-vacuum combination which both frontally engages piles of leaves and other debris and also brushes the leaves and other debris from the surface to be cleaned while entraining the debris in an air stream whence the debris may be reduced in size. 
   Another object of the invention is to provide a means for separating the air stream with entrained debris into a solids-depleted stream and a solids-enriched stream for collection and disposition of the debris. 
   It is another object of the present invention to remove deep piles of leaves and other debris. 
   Another object of the invention is to provide a means of breaking twigs into shorter fragments to alleviate plugging of collector-unit airflow systems by longer twigs frequently co-mixed with leaves and other lawn debris. 
   Another object of the invention is to provide a reduced-height air-solids separator to permit greater operator visibility toward the front of a collector machine during operation. 
   Yet another object of the present invention is to provide a debris-accumulation container achieving greater ease of dumping collected debris. 
   Another object of the invention is to provide a unit which engages and lifts lawn thatch, entrains it in an air stream, and then separates the thatch from the air stream and retains the thatch in an accumulation container for convenient disposal. 
   Another object of the invention is to provide an improved air-solids separator which can be adapted to a debris-collecting motor vehicle or towable vehicle. 
   Still another object of the invention is to substantially increase the throughput rate for lawn debris. 
   Another object of the invention is to provide a low-cost but durable means for removing lawn thatch. 
   Yet another object of the invention is to provide a convenient container for receiving multiple loads from the debris-accumulation container, hauling the debris to a disposal point, and dumping it easily. 
   SUMMARY OF THE INVENTION 
   These objects are provided by an apparatus for collection and reduction of yard debris comprising a combination of a frontally facing rotor-assisted vacuum pick up, a chipper-shredder-blower unit which (i) induces an airflow for entraining the debris collected at said pick up; (ii) reduces the debris entrained in the airflow to a more manageable volume and (iii) impels the reduced debris to a free-flow-separator device for removing the debris from the air in which it is entrained. 
   More particularly, this invention relates to an apparatus for collecting yard debris comprising: a frame having a shredder blower unit mounted thereupon; a collector-rotor mounted on the frame comprising impeller elements adapted to: (i) engage a surface, (ii) collect yard debris thereupon, and (iii) impel the yard debris toward the shredder blower unit; an air-solids separator mounted on the frame operatively connected to the shredder blower unit for separating the yard debris into a debris-enriched stream and a debris-depleted stream by action of body forces thereupon; and an accumulation chamber adapted to receive the debris-enriched stream from the air-solids separator; wherein the collector rotor means is configured for substantially untrammeled engagement with yard debris having a depth of at least about two (2) inches. 
   In another aspect this invention relates to an apparatus for collecting yard debris comprising: a frame; a shredder blower unit mounted on the frame; a collector rotor mounted on the frame comprising impeller elements adapted to: (i) engage a surface, collect yard debris thereupon, and (ii) impel said the debris toward the shredder blower unit; an air-solids separator mounted on the frame operatively connected to the shredder blower unit for separating the yard debris into a debris-enriched stream and a debris-depleted stream; and an accumulation chamber adapted to receive the debris-enriched stream from the air-solids separator; wherein the collector rotor is configured for substantially untrammeled engagement with yard debris having a depth of at least about two (2) inches. 
   In still another aspect this invention relates to an apparatus for collecting yard debris comprising: (A) a frame; (B) a shredder blower unit mounted on the frame; (C) a collector rotor mounted on the frame comprising impeller elements adapted to: (i) engage a surface, collect yard debris thereupon, and (ii) impel the yard debris toward the shredder blower unit; (D) an air-solids separator means mounted on the frame operatively connected to the shredder blower unit for separating the yard debris into a debris-enriched stream and a debris-depleted stream by action of body forces thereupon; and (E) an accumulation chamber adapted to receive the debris-enriched stream from the air-solids separator. 
   Yet another aspect of this invention relates to an apparatus for collecting and reducing yard debris comprising: (A) a frame adapted for movement in a principal direction upon a surface; (B) a first duct mounted on the frame having an entrance and an exit; (C) a collector-rotor assembly comprising: a collector-rotor body disposed at the entrance to the first duct having a substantially horizontal axis of rotation generally normal to the principal direction; and a plurality of impeller elements mounted upon the collector-rotor body, wherein the impeller elements extend radially from the collector-rotor body by at least about one quarter of an inch and are adapted to: (i) sweep over the surface, (ii) collect yard debris thereupon, and (iii) impel the yard debris toward the duct entrance, wherein the collector-rotor assembly and the first duct are configured for substantially untrammeled frontal engagement with yard debris having a depth of at least about two (2) inches; (D) a second duct mounted upon the frame having an entrance and an exit; (E) a shredder blower unit, disposed between the exit to the first duct and the entrance to the second duct, adapted to: (i) provide suction at the entrance of the first duct; (ii) induce a flow of air through the first and second ducts; and (iii) reduce yard debris entrained in the flow of air as it passes through the shredder blower unit; (F) an air-solids separator disposed at the exit to the second duct for separating the reduced yard debris in the flow of air induced by the shredder blower into a debris-enriched stream and a debris-depleted stream; (G) an accumulation chamber mounted on the frame adapted to receive the debris-enriched stream from the air-solids separator; and (H) a power source mounted on the frame adapted to provide power to the shredder blower unit and the collector rotor. 
   In a preferred embodiment of the invention the impeller elements extend radially at least about an inch from the collector-rotor body. 
   In another preferred embodiment the collector-rotor assembly comprises a substantially gas-impervious impediment to unrestricted flow of air into the first duct and extends substantially athwart the entrance to the first duct. 
   A preferred collector-rotor assembly comprises three impeller elements generally equispaced around the collector-rotor body. 
   A more preferred collector-rotor assembly further comprises fillets extending between adjacent impeller elements for limiting carriage of yard debris around the collector-rotor assembly; wherein the fillets partially define generally concentric interrupted annular cavity spaces between adjacent impeller elements. 
   In a more preferred embodiment of this invention, a housing serves to limit the flow of air between the housing and the collector-rotor assembly without substantially impeding air flow along the surface under the collector-rotor assembly and into the entrance of the first duct; wherein this housing: (i) is disposed above the collector-rotor assembly, (ii) is an arcuate portion of a generally cylindrical shell spanning an upper portion of the collector-rotor assembly concentric to the axis of rotation of the collector-rotor body, and (iii) engages each of the impeller element tips in flow-limiting proximity seriatim. 
   In another preferred embodiment, vertically extending seals are carried on the frame adjacent to the ends of the collector-rotor assembly for limiting axial flow of airflow into the rotor assembly. 
   In another embodiment, vertically extending seals carried on the ends of the collector-rotor assembly limit axial flow of airflow into the rotor assembly. 
   In a preferred embodiment, the housing means defines a frontal opening extending from the surface vertically to a height of at least four inches and a suction opening under the rotor extending rearwardly from the front of the apparatus at least to a line below the axis of rotation of the collector-rotor body. 
   In another preferred embodiment, the impeller elements mounted on the collector-rotor body are configured to allow intermittent rearward rushes of air under the forward side of the rotating rotor body into the entrance to the first duct, and pulsed forward rushes of air under the first duct and into the first duct entrance, thereby alternatingly collecting principally bulky yard debris from the forward side of the rotor body during the rearward rushes of air and enhancing collection of residual debris from the surface during the pulsed forward rushes of air. 
   A preferred embodiment of the invention further comprises an air-slot defined within the housing between the upper lip of the housing and the entrance to the first duct for allowing flow of air in a direction opposed to the direction of rotation of the collector-rotor body and into the first duct and therein stripping leaves and debris from the rotating rotor assembly. 
   In another embodiment, the entrance to the first duct generally spans the length of the collector-rotor body, and the duct converges rearwardly such that the convergence angle throughout the duct is generally less than 100 degrees. 
   In one embodiment, the shredder blower unit comprises a rotatable shaft having shredder elements mounted thereupon, wherein the axis of rotation of the shaft is parallel to the principal direction. 
   In a preferred embodiment of the invention, the air-solids separator comprises: (A) a first passage for accepting the flow of air bearing entrained reduced yard debris from the second duct; (B) a separation chamber adapted to receive the flow of air from the first passage; (C) a second passage adapted to exhaust the debris-depleted stream from the separation chamber into the atmosphere; and (D) a baffle for: (i) generally inhibiting secondary flow from the accumulation chamber; and (ii) impeding re-entrainment of fine particulates in the debris-depleted stream as it is discharged to the atmosphere; wherein the baffle is disposed to permit passage of entrained reduced yard debris into the accumulation chamber while impeding passage of fine particulates of reduced yard debris in air exhausted from the separation chamber through the second passage. 
   In a more preferred embodiment, the air-solids separator separates the reduced yard debris in the airflow induced by the shredder blower into a debris-enriched stream and a debris-depleted stream by action of body forces thereupon, wherein the separator comprises: (A) a separation chamber; (B) a first declivously extending curvilinear passage for conducting the flow of air bearing the entrained reduced yard debris from the second duct into the separation chamber, wherein the separation chamber adjoins the declivously extending curvilinear passage and is adapted to receive and direct the flow of air bearing debris from the declivously extending curvilinear passage in a direction generally tangential to the perimeter of the separation chamber; (C) a generally centrally located upwardly extending second passage for exhausting the debris-depleted stream from the separation chamber into the atmosphere; (D) a baffle extending generally outwardly from a central point below the entrance to the second passage, wherein the baffle is disposed generally below the exit from the declivously extending curvilinear first passage; and (E) an opening around the baffle into the accumulation chamber; wherein the baffle is disposed to permit passage of entrained reduced yard debris in the debris-enriched stream into the accumulation chamber while impeding secondary flows of air containing finely reduced debris fragments from re-entering the separation chamber. 
   In an embodiment, the shredder blower unit further comprises a chipper knife adapted to chip branches. 
   In another embodiment, the power source further comprises a means for supplying power to wheels mounted on the frame, thereby powering forward movement of the apparatus. 
   In one embodiment, the air-solids separator means further comprises an enclosure having at least one filtering element, and the airflow passes through the filtering element, leaving the yard debris retained in the enclosure. 
   Another aspect of the invention relates to an apparatus for collecting yard debris comprising: (A) a frame adapted for movement in a principal direction upon a surface; (B) a duct mounted on the frame having an entrance and an exit; (C) a collector-rotor assembly comprising: a substantially impervious collector-rotor body disposed and extending substantially athwart the entrance to the duct and having a substantially horizontal axis of rotation generally normal to the first direction; and a plurality of impeller elements mounted upon the collector-rotor body, extending radially from the collector-rotor body by at least about one quarter of an inch, and having approximately equal radial extensions from the axis of rotation of the collector-rotor assembly, wherein the impeller elements are adapted to: (i) sweep over the surface, (ii) collect yard debris thereupon, and (iii) impel the yard debris into the duct entrance; (D) a housing disposed adjacent the entrance to the duct for limiting the flow of air between the housing and the collector-rotor assembly without substantially impeding air flow along the surface under the collector-rotor assembly and into the entrance of the duct, wherein the housing: (i) is disposed above the collector-rotor assembly; (ii) engages each of the impeller element tips in flow-limiting proximity seriatim; and (iii) is configured to permit substantially untrammeled frontal engagement of the collector-rotor assembly with yard debris having a depth of at least about two (2) inches; (E) an air-movement device connected to the exit of the duct and adapted to: (i) provide suction at the entrance of the duct, and (ii) induce a flow of air through the duct; and (F) a power source mounted upon the frame adapted to provide power to the air-movement device and the collector rotor. 
   In a preferred embodiment of the invention, the tips of the impellers further comprise pliable blades that are yieldable to hard objects encountered on the surface, but are sufficiently stiff to sweep debris from the undulating surface. 
   In a more preferred embodiment, the tips of the impellers comprise radially extending raker teeth adapted to engage and impel debris objects on the surface toward the duct entrance. 
   In a further embodiment, the housing comprises an arcuate portion of a generally cylindrical shell spanning an upper portion of the collector-rotor assembly generally concentric to the axis of rotation of the collector-rotor body, and which is disposed in flow-limiting proximity to at least one tip of one of the impeller elements during at least about one fourth of the time of each revolution of the collector-rotor assembly. 
   In an embodiment, the duct is disposed such that a space at least ½ inch thick is preserved between the bottom of the duct and the surface, permitting forward air flow toward the duct entrance. 
   In a preferred embodiment, the cross-sectional area of the channel through the duct measured normal to the center flow line of the airflow through the duct remains generally constant along the center flow line. 
   In a further embodiment, the collector-rotor assembly and the entrance of the duct are disposed along the advancing front of a lawnmower having a cutting path of a defined width. 
   In a preferred embodiment, the collector-rotor assembly impels the yard debris into the mowing chamber within the mowing enclosure of the lawnmower. 
   In a more preferred embodiment, the air-movement means achieves an airflow volume of at least about twenty cubic feet per minute per inch of collector-rotor assembly length. 
   In another preferred embodiment the present invention relates to an apparatus for separating entrained lawn debris from a transporting air stream by action of body forces thereupon comprising: (A) an apparatus for delivering a stream of air bearing entrained lawn debris; (B) a first passage having an entrance and exit, having the entrance adapted to receive the stream of air bearing entrained lawn debris, and the passage adapted for conducting the flow of air bearing entrained lawn debris from the entrance to the exit; (C) a separation chamber having a generally cylindrical outer wall section, with the separation chamber: (i) connected to the exit from the first passage; and (ii) adapted to: (a) receive and direct the stream of air bearing entrained lawn debris from the first passage in a direction primarily tangential to the generally cylindrical outer wall section of the separation chamber, and (b) separate the stream of air bearing entrained lawn debris into an outerly located debris-enriched stream and an innerly located debris-depleted stream; (D) an upper bulkhead to the separation chamber having defined therein, a generally centrally located second passage having an entrance and an exit, with the generally centrally located second passage adapted for: (i) receiving the innerly located debris-depleted stream from the separation chamber through the entrance, and (ii) conducting the innerly located debris-depleted stream to the exit and discharging it into the atmosphere; (E) the bulkhead of said separation chamber further: (i) extending generally horizontally from the second passage generally outwardly to the substantially cylindrical outer wall, and (ii) being disposed at generally the same height as the entrance to the second passage; (F) a baffle extending generally outwardly from a central point below the entrance to the second passage, wherein the baffle is disposed generally below the exit of the first passage, and the outer periphery of the baffle is spaced inwardly from the generally cylindrical outer wall section; and (G) an opening around the baffle into the interior of an accumulation chamber below the baffle; wherein the baffle is disposed to permit passage of entrained yard debris into the accumulation chamber while impeding passage of fine particulates of reduced yard debris from the accumulation chamber into the debris-depleted stream discharged from the separation chamber through the second passage. 
   Preferably, the plane of the said baffle periphery is disposed below the lowermost portion of the upper bulkhead by a distance of less than about 0.6 times the inside diameter of the separation chamber. 
   In another preferred embodiment, the baffle periphery is disposed below the lowermost portion of the entrance to the second passage by a distance of less than about 0.6 times the inside diameter of the separation chamber. 
   In one embodiment the upper bulkhead of the separation chamber further comprises a substantially planar surface generally normal to the axis of the substantially cylindrical outer wall and has an opening comprising the entrance of the second passage. 
   In another embodiment, the upper bulkhead of the separation chamber further comprises a generally semi-toroidal surface and has an opening comprising the entrance of the second passage. 
   Preferably, the upper bulkhead has as its substantially only interruptions, openings comprising the exit of the first passage and the entrance of the second passage. 
   In a more preferred embodiment, the first passage extends declivously from its entrance toward its exit and directs the stream of air bearing entrained lawn debris into the separation chamber. 
   Preferably, (A) the first passage is curvilinear in a plane generally perpendicular to the axis of the generally cylindrical outer wall section, (B) the outer wall of the curvilinear passage is disposed approximately coincident with the generally cylindrical outer wall section of the separation chamber, and (C) the generally cylindrical outer wall section of the separation chamber is disposed at least about three inches outward from the perimeter of the entrance to the second passage. 
   In a preferred embodiment, the generally cylindrical outer wall section of the separation chamber is disposed at least about five inches outwardly from the perimeter of the entrance to the second passage. 
   In a preferred embodiment, the baffle further comprises an upright cone having its apex pointing toward the entrance of the second passage. 
   Preferably, the cone periphery and the outer wall section of the separation chamber are generally circular. 
   In a preferred embodiment, the opening around the periphery further comprises an annular opening between the periphery of the baffle and the outer wall section of the separation chamber. 
   Preferably, the vertical distance from the apex of the cone to the plane of the entrance of the second passage is less than about 0.6 times the diameter of the entrance to the second passage. 
   In one embodiment, the accumulation chamber is approximately cylindrical and has a slidable opening in a plane at an angle of about 75 degrees to about 90 degrees to the axis of the cylinder. 
   In a preferred embodiment, the stream of air bearing entrained lawn debris swirls around the separation chamber with a tangential perimeter velocity of at least about 2000 feet per minute, causing the entrained reduced lawn debris to move toward the generally cylindrical outer wall of the separation chamber by action of body forces thereupon. 
   Preferably, the radial distance from the baffle periphery to the outer wall of the separation chamber is less than about one fourth of the inside diameter of the separation chamber, measured in approximately the same plane as the plane of the baffle periphery. 
   In another embodiment, the accumulation chamber further comprises a flexible bag-like container, such as a paper bag or a plastic bag. 
   In still another embodiment, the device for delivering a stream of air bearing entrained lawn debris further comprises a lawnmower having a discharge duct connected to the entrance of the first passage. 
   In another aspect, this invention relates to a free-flow apparatus for separating entrained lawn debris from a transporting air stream by action of body forces thereupon comprising: (A) an apparatus for delivering a stream of air bearing entrained lawn debris; (B) a first passage having an entrance and exit, with the entrance adapted to receive the stream of air bearing entrained lawn debris, and the passage adapted for conducting the stream of air bearing entrained lawn debris from the entrance to the exit; (C) a separation chamber having a generally frusto-conical outer wall section, with the separation chamber: (a) connected to the exit from the first passage; and (b) adapted to: (i) receive and direct the stream of air bearing entrained lawn debris from the first passage in a direction primarily tangential to the frusto-conical outer wall section of the separation chamber, and (ii) separate the stream of air bearing entrained lawn debris into an outerly located debris-enriched stream and an innerly located debris-depleted stream; (D) a generally centrally located second passage having an entrance and an exit, and being adapted for (i) receiving the innerly located debris-depleted stream from the separation chamber through the entrance, and (ii) conducting the innerly located debris-depleted stream to the exit and discharging it into the atmosphere; (E) an upper bulkhead to the separation chamber having defined therein a generally centrally located second passage having an entrance and an exit, with the upper bulkhead extending from the second passage generally outwardly to the generally frusto-conical outer wall section; (F) a baffle extending generally outwardly from a central point below the entrance to the second passage, and disposed generally below the exit of the first passage, wherein the outer periphery of the baffle is disposed inwardly from the generally frusto-conical outer wall section, and below the uppermost portion of the first passage by a distance of less than 1.2 times the inside diameter of the separation chamber proximate the baffle; and (G) an opening around the baffle into the interior of an accumulation chamber below the baffle; wherein the baffle is disposed to permit passage of entrained yard debris into the accumulation chamber while impeding passage of fine particulates of reduced yard debris from the accumulation chamber into the air discharged from the separation chamber through the second passage. 
   In a preferred embodiment, (A) the first passage is curvilinear in a plane generally perpendicular to the axis of the generally cylindrical outer wall, (B) the outer wall of the curvilinear passage is disposed generally coincident with the generally frusto-conical outer wall section of said separation chamber, (C) the bulkhead is disposed at generally the same height as the entrance to the second passage, and (D) the generally frusto-conical outer wall section of the separation chamber is disposed at least about three inches radially outward from the perimeter of the entrance to the second passage. 
   Preferably, the first passage comprises substantially the only passage for conducting air flow into the separation chamber, and the second passage comprises substantially the only passage for conducting the innerly located debris-depleted stream out of the separation chamber. 
   In a preferred embodiment, the device for delivering a stream of air bearing entrained reduced lawn debris further comprises a shredder blower. 
   In another aspect, this invention relates to a free-flow apparatus for separating entrained lawn debris from a transporting air stream by action of body forces thereupon comprising: (A) an apparatus for delivering a stream of air bearing entrained lawn debris; (B) a primary-separation duct having an entrance and exit, wherein the entrance is adapted to receive the stream of air bearing entrained lawn debris, the duct is adapted for conducting the stream of air bearing entrained lawn debris from the entrance to the exit; and the primary-separation duct has a generally curvilinear outer surface spanning an arc of at least about
 
arc cosine(RI/RO)
 
circumferentially along its length, having the primary-separation duct adapted to direct the stream of air bearing entrained lawn debris to flow generally circumferentially along its length and initiate separation of the stream of air bearing entrained lawn debris into an outerly located debris-enriched stream and an innerly located debris-depleted stream, wherein
         RI=radius of curvature for the generally curvilinear inner surface of the primary-separation duct, and   RO=radius of curvature for the generally curvilinear outer surface;       

   (C) a secondary-separation chamber connected to the exit from the primary-separation duct and having a generally annular outer wall defining a primary axis generally co-incident with the center of curvature of the generally annular outer wall, the functions of the secondary-separation chamber further comprising (i) receiving and directing the streams of air bearing entrained lawn debris from the primary-separation duct in a direction generally tangential to the generally annular outer wall of the secondary-separation chamber, (ii) directing the outerly located debris-enhanced stream from the primary-separation duct to flow adjacent to the outer wall of the secondary-separation chamber, (iii) directing the innerly located debris-depleted stream from the primary-separation duct to flow radially inward of the debris-enriched stream, and (iv) further separating the streams of air bearing entrained lawn debris into an upwardly and inwardly directed debris-depleted stream and a downwardly and outwardly directed debris-enriched stream; (D) a generally centrally located passage having an entrance and an exit, and being adapted for: (i) receiving the upwardly and inwardly directed debris-depleted stream from the secondary-separation chamber through the entrance, and (ii) conducting this stream to the exit and discharging it into the atmosphere; (E) a baffle extending generally outwardly from a central point below the entrance to the passage, having the outer periphery of the baffle spaced inwardly from the generally annular outer wall; and (F) an opening around the baffle into the interior of an accumulation chamber below the baffle; wherein the baffle is disposed to permit passage of entrained yard debris in the downwardly and outwardly directed debris-enriched stream into the accumulation chamber while impeding passage of fine particulates of reduced yard debris from the accumulation chamber into air discharged from the separation chamber through the passage. 
   Preferably, the baffle periphery is disposed below the uppermost portion of the primary-separation duct by a distance of less than 1.2 times the inside diameter of the secondary-separation chamber having a generally annular outer wall, with this inside diameter being measured in the plane of the baffle periphery. 
   More preferably, the baffle periphery plane is disposed below the uppermost portion of the entrance to the passage by a distance of less than about 0.6 times the inside diameter of the secondary-separation chamber having a generally annular outer wall, with this inside diameter being measured in the plane of the baffle periphery. 
   In one embodiment, the axis of curvature of the primary-separation duct is disposed generally coincident with the primary axis. 
   Still another aspect of this invention relates to a free-flow apparatus for separating entrained lawn debris from a transporting air stream by action of body forces thereupon comprising: (A) an apparatus for delivering a stream of air bearing entrained lawn debris; (B) a separation chamber having an upper bulkhead and an outer wall; (C) a first passage having an entrance and exit, having the entrance adapted to receive the stream of air bearing entrained lawn debris, and being adapted for conducting the stream of air bearing entrained lawn debris from the entrance to the separation chamber and directing the stream of air bearing entrained lawn debris into the separation chamber in a direction primarily tangential to the outer wall of the separation chamber; wherein the separation chamber is adapted to separate the stream of air bearing entrained lawn debris into an outerly located debris-enriched stream and an innerly located debris-depleted stream; (D) a generally centrally located second passage having an entrance and an exit, wherein the generally centrally located second passage is adapted for: (i) receiving the innerly located debris-depleted stream from the separation chamber through the entrance, and (ii) conducting the innerly located debris-depleted stream to the exit and discharging it into the atmosphere; (E) a baffle extending generally outwardly from a central point below the entrance to the second passage; having the outer periphery of the baffle spaced inwardly from the outer wall; and (F) an opening around the baffle into the interior of an accumulation chamber below the baffle, having the baffle disposed to permit passage of the innerly located debris-depleted stream into the second passage while impeding passage of fine particulates of reduced yard debris from the accumulation chamber into the air discharged from the separation chamber through the second passage; wherein the overall height of the apparatus from the uppermost portion of the apparatus to the plane of the outer periphery of the baffle is less than about 1.2 times the inside diameter of the separation chamber proximate the baffle periphery. 
   Preferably, the connection of the exit of the first passage into the separation chamber is disposed below the upper bulkhead. 
   In a preferred embodiment, the first passage is curvilinear in a plane generally perpendicular to the axis of the outer wall and has its concave surface generally concentric about the axis. 
   Yet another aspect of this invention relates to a free-flow apparatus for separating entrained lawn debris from a transporting air stream by action of body forces thereupon, comprising: (A) an apparatus for delivering a stream of air bearing entrained lawn debris having a flow rate of at least about 300 cubic feet per minute; (B) a primary-separation duct having an entrance and exit, with the entrance adapted to receive the stream of air bearing entrained lawn debris, and the duct adapted for conducting the stream of air bearing entrained lawn debris from the entrance to the exit; wherein the primary-separation duct (i) has a generally curvilinear outer surface spanning an arc of at least about
 
arc cosine RI/RO
 
circumferentially along its length and has a radius of curvature of its generally curvilinear outer surface less than about 36″, (ii) measures at least about 4″ perpendicular to its plane of curvature and at least about 2″ in the radial direction, and (iii) is adapted to direct the stream of air bearing entrained lawn debris to flow generally circumferentially along its length and initiate separation of the stream of air bearing entrained lawn debris into an outerly located debris-enriched stream and an innerly located debris-depleted stream, wherein
         RI=radius of curvature of the generally curvilinear inner surface of the primary-separation duct, and   RO=radius of curvature of the generally curvilinear outer surface;       

   (C) a secondary-separation chamber less than about 36″ in diameter and connected to the exit from the primary-separation duct and having a generally annular outer wall defining a primary axis generally co-incident with the center of curvature of the generally annular outer wall, the secondary-separation chamber further comprising a shape for (i) receiving and directing the streams of air bearing entrained lawn debris from the primary-separation duct in a direction generally tangential to the generally annular outer wall of the secondary-separation chamber, (ii) directing the outerly located debris-enhanced stream from the primary-separation duct to flow along the outer wall of the secondary-separation chamber; (iii) directing the innerly located debris-depleted stream from the primary-separation duct to flow radially inward of the debris-enriched stream; and (iv) further separating the streams of air bearing entrained lawn debris into an upwardly and inwardly directed debris-depleted stream and a downwardly and outwardly directed debris-enriched stream; (D) a generally centrally located passage at least 4″ in diameter and having an entrance and an exit, and having the perimeter of the entrance located at least 2″ radially inward from the generally annular outer wall of the secondary-separation chamber, wherein the generally centrally located passage is adapted for: (i) receiving the upwardly and inwardly directed debris-depleted stream from the secondary-separation chamber through the entrance, and (ii) conducting the upwardly and inwardly directed debris-depleted stream to the exit and discharging it into the atmosphere; (E) a baffle extending generally outwardly from a central point below the entrance to the passage, having the outer periphery of the baffle spaced at least 1″ inwardly from the generally annular outer wall, and having the outer periphery disposed less than 15″ below the entrance to the passage; and (F) an opening around the baffle into the interior of an accumulation chamber below the baffle; wherein the baffle is disposed to permit passage of entrained yard debris in the downwardly and outwardly directed debris-enriched stream into the accumulation chamber while impeding passage of fine particulates of reduced yard debris from the accumulation chamber into air discharged from the separation chamber through the passage. 
   A preferred embodiment of this invention relates to an apparatus for collecting and reducing twig-containing yard debris comprising: (A) a frame adapted to be advanced over a surface; (B) a duct mounted on the frame having a duct entrance and a duct exit; (C) a twig-arrestor mounted on the frame; (D) a collector-rotor assembly comprising: (i) a rotating collector-rotor body rotatably mounted on the frame adjacent: the surface, the twig-arrestor means, and the duct entrance; (ii) a plurality of impeller elements mounted upon the collector-rotor body extending radially from the collector-rotor body by at least about one half inch and defining crenels and merlons having at least one circumferential alignment of crenels, the impeller elements being adapted to: engage yard debris disposed on the surface, impel the yard debris toward the duct entrance and transport twigs encountered on the surface against the twig-arrestor; the twig-arrestor protruding into the circumferential alignment of crenels and, in combination with the impeller elements mounted upon the rotating collector-rotor body, constituting a device for fracturing twigs transported against the twig-arrestor by the impeller elements by impact therewith, (E) a blower unit operatively connected to the duct and adapted to induce a flow of air through the duct and provide suction at the duct entrance; (F) a source for providing power to the blower unit; and (G) a source for providing power to the collector-rotor assembly. 
   Another embodiment of this invention relates to an apparatus for collecting and reducing twig-containing yard debris comprising: (A) a frame adapted to be advanced over a surface; (B) a duct mounted on the frame having a duct entrance and a duct exit; (C) a collector-rotor assembly comprising: (i) a rotating collector-rotor body rotatably mounted on the frame adjacent the surface and the duct entrance, having a length generally spanning the duct entrance; and (ii) a plurality of impeller elements mounted upon, and distributed along the length of, the rotating collector-rotor body, the impeller elements extending radially from the collector-rotor body by at least about one half inch, and being adapted to engage yard debris disposed on the surface and impel the yard debris toward the duct entrance, and transport twigs encountered on the surface about the axis of the collector-rotor body; the cylindrical volume swept amongst the impellers and generally coinciding with the length of the collector-rotor body defining rotor-occluded volume (ROV); (D) a member for fracturing twigs being transported about the axis of the collector-rotor body by the impeller elements, the member being mounted on the frame and protruding into the rotor-occluded volume; (E) a blower unit operatively connected to the duct, adapted to induce a flow of air through the duct and provide suction at the duct entrance; (F) a source for providing power to the blower unit; and (G) a source for providing power to the collector-rotor assembly. 
   Yet another embodiment of this invention relates to an apparatus for collecting and reducing twig-containing yard debris comprising: (A) a frame adapted to be advanced over a surface; (B) a duct mounted on the frame and having a duct entrance and a duct exit; (C) a twig-breaking device including a twig arrestor disposed adjacent the duct entrance and a plurality of impeller elements movably mounted on the frame, the impeller elements defining crenels therebetween and being adapted to: (i) engage yard debris disposed on the surface, and (ii) impel the yard debris encountered on the surface against the twig arrestor; (D) the twig arrestor comprising at least one fracturing member: (i) protruding into the crenels; and (ii) adapted to break twigs being transported against the fracturing member by engagement therewith; (E) a blower unit operatively connected to the duct adapted to induce a flow of air through the duct and provide suction at the duct entrance; (F) a source for providing power to the blower unit; and (G) a source for providing power to the impeller elements. 
   An apparatus for collecting and reducing twig-containing yard debris comprising: (A) a frame adapted to be advanced over a surface; (B) a duct mounted on the frame having a duct entrance and a duct exit; (C) a collector-reducer assembly comprising: (i) a rotating collector-rotor assembly rotatably mounted on the frame adjacent the surface and disposed at the duct entrance, comprising: a rotating collector-rotor body; a plurality of impeller elements mounted upon the rotating collector-rotor body, the impeller elements extending radially therefrom and being adapted to engage and impel yard debris disposed on the surface toward the duct entrance, and transport twigs encountered on the surface about the axis of rotation of the rotating collector-rotor body; (ii) a twig-fracturing member for breaking twigs, the twig-fracturing member being mounted on the frame adjacent the rotating collector-rotor body and adapted to, upon rotation of the rotating collector-rotor assembly, pass between the plurality of impeller elements so as to engage and fracture twigs being transported about the axis of rotation of the rotating collector-rotor body by the impeller elements; (D) a blower unit operatively connected to the duct, adapted to induce a flow of air through the duct and provide suction at the duct entrance; (E) a source for providing power to the blower unit; and (F) a source for providing power to the rotating collector-rotor assembly. 
   In another embodiment of the invention, the impeller elements comprise polymeric lath elements. 
   In another embodiment of the invention, the impeller elements comprise metallic lath elements. 
   In still another embodiment of the invention, the impeller elements comprise pivotably mounted flail elements. 
   In a further embodiment, the pivotably mounted flail elements have T-shaped cross-sections. 
   In still another embodiment, the pivotably mounted flail elements comprise circumferentially extending breaker bars and longitudinally extending blocker plates. 
   In another embodiment, the pivotably mounted flail elements comprise iron-based flail elements adapted to: (A) engage twigs in deep yard debris, (B) transport the twigs about the axis of rotation of the rotating collector-rotor body, (C) urge the twigs against the twig-fracturing member, (D) break the twigs into twig fragments, and (E) impel the twig fragments toward the duct entrance. 
   In another embodiment, the pivotably mounted flail elements further comprise bushings encompassing a flail pivot shaft and adapted for reducing interference of adjacent flails with each other. 
   In another embodiment, the pivotably mounted flail elements extend at least to the surface. 
   In another embodiment, the pivotably mounted flail elements extend below the surface. 
   In another embodiment, the impeller elements comprise members projecting radially from the rotating collector-rotor body and extending axially along a portion of the length of the rotating collector-rotor body. 
   In another embodiment, the members are generally planar. 
   In another embodiment, the members are generally helical. 
   In still another embodiment, the members are generally helical and adapted to urge yard waste away from the ends of the rotating collector-rotor assembly toward the central portion of the rotor. 
   In another embodiment, the impellers on the rotating collector-rotor assembly comprise radially extending pegs. 
   In another embodiment, the impellers on the rotating collector-rotor assembly comprise both axially extending plates and radially extending pegs. 
   In another embodiment, the impellers on the rotating collector-rotor assembly comprise radially extending pegs of at least two differing lengths defining merlons and crenels between the merlons. 
   In another embodiment, the rotating collector-rotor assembly rotates such that debris is swept under the axis of rotation of the rotating collector-rotor body as the apparatus is advanced over the surface. 
   In another embodiment, the flow of air is exhausted and directed against the surface forward of the collector/reducer assembly. 
   In another embodiment, the collector-rotor assembly is encompassed by a housing comprising side support plates, a rear seal plate, and an upper housing. 
   In another embodiment, flexible seal strips restricting peripheral airflow into the housing are attached to the side support plates and the rear seal plate. 
   In another embodiment, flexible seal strips restricting peripheral airflow into the housing are attached to the side support plates and to the twig arrestor mounted on the frame. 
   In another embodiment, a single power source provides power to the blower unit and the rotating collector-rotor assembly. 
   In another embodiment, the fracturing member protrudes radially into the rotor-occluded volume at least about one half inch. 
   In another embodiment, at least one of the crenels is at least about one inch deep, measured in the radial direction. 
   In another embodiment, at least one of the fracturing members protrudes into the crenel at least about ¾ inch, measured radially from the tips of adjacent merlons. 
   In another embodiment, the fracturing member is at least about ⅛ inch in diameter. 
   In another embodiment, the fracturing members are spaced apart from each other no more than about one foot. 
   In another embodiment, the merlons are plates having thicknesses of at least about 1/16 inch measured circumferentially. 
   Another embodiment comprises a rotary brush located at the duct entrance. 
   Another embodiment further comprises a counterrotating brush located at the duct entrance. 
   Another embodiment further comprises adjustable-height wheels adjacent the rotating collector-rotor assembly adapted for supporting the rotating collector-rotor assembly at adjustable heights above the surface whereby the degree of engagement of the impeller elements with the surface may be controlled. 
   In another embodiment, the rotating collector-rotor assembly is rotatably attached at the entrance of the duct which is mounted on the frame, and the duct has sufficient rigidity to operationally support the rotating collector-rotor assembly while the rotating collector-rotor assembly engages the surface and debris. 
   Another embodiment comprises yieldable rotor blade tips attached to the impellers. 
   Another embodiment comprises raking tips attached to the impeller elements. 
   In another embodiment, the blower unit is a chipper shredder. 
   In another embodiment, the shredder rotor of the chipper shredder is mounted on the crankshaft of an internal-combustion engine. 
   In another embodiment, the blower is a shredder blower. 
   In another embodiment, the axis of the engine crankshaft is oriented generally parallel to the direction of motion as the apparatus is advanced over the surface. 
   Another embodiment further comprises an adjustable duct-closure device for restricting airflow through the duct. 
   In another embodiment, the adjustable duct-closure device is a pivotable damper. 
   In another embodiment, the adjustable duct-closure device is a sliding-gate device. 
   As another embodiment, the twig-fracturing member is a rod. 
   In another embodiment, the twig-fracturing member is a block. 
   In still another embodiment, the twig-fracturing member is a block. 
   In yet another embodiment, the twig-fracturing member is metallic. 
   In another embodiment, the twig-fracturing member is polymeric. 
   In another preferred embodiment of the present invention, an apparatus for collecting yard debris on a surface comprises: (A) a frame; (B) a blower unit mounted on the frame and adapted to induce entraining air flow; (C) a collector-rotor assembly comprising a collector-rotor body rotatably mounted on the frame and impeller elements mounted upon the collector-rotor body adapted to: (i) engage the surface and yard debris thereupon, and (ii) impel the yard debris toward the entraining air flow; (D) a duct for conducting the yard debris in entraining air flow to the blower; (E) an air-solids separator operatively connected to the blower unit for separating the yard debris into a debris-enriched stream and a debris-depleted stream; (F) a detachable accumulation container adapted to receive the debris-enriched stream from the air-solids separator; and (G) the detachable accumulation container having at least one attached wheel adapted to support the accumulation chamber upon detachment of the accumulation chamber from the frame. 
   In still another embodiment of the invention, an apparatus for collecting yard debris on a surface comprises: (A) a chassis frame; (B) a blower unit mounted on the chassis frame and adapted to induce entraining air flow; (C) a collector-rotor rotatably mounted on the chassis frame adapted to: (i) engage the surface and yard debris thereupon, and (ii) impel the yard debris toward the blower unit; (D) a conduit for conducting yard debris in the entraining air flow from the collector-rotor to the blower unit; (E) an air-solids separator operatively connected to the blower unit for separating the entraining air flow into a debris-enriched stream and a debris-depleted stream; (F) a detachable accumulator adapted to receive the debris-enriched stream from the air-solids separator; and (G) the detachable accumulator having at least one attached roller adapted to support the accumulator upon detachment of the accumulator from the frame. 
   In another embodiment, the roller attached to the detachable accumulator does not bear against the surface when the detachable accumulator is not detached from the apparatus. 
   In another embodiment, the roller device attached to the detachable accumulator is spaced from the surface when the detachable accumulator is not detached from the apparatus. 
   In yet another embodiment, the roller device attached to the detachable accumulator comprises at least two attached wheels adapted to support the accumulator upon detachment of the accumulator from the frame. 
   In another embodiment, the apparatus for collecting yard debris further comprises a ramp for raising the detachable accumulator from the surface as the detachable accumulator is being attached to the apparatus. 
   In still another embodiment, the apparatus for collecting yard debris further comprises a ramp for raising the detachable accumulator from the surface as the detachable accumulator is being pushed forward into attachment with the apparatus. 
   In another embodiment, the detachable accumulator has a polyhedral shape. 
   In yet another embodiment, the detachable accumulator has a generally hexahedral shape. 
   In another embodiment, the detachable accumulator has a generally heptahedral shape. 
   In still another embodiment, the detachable accumulator is adapted to be detachably sealed to the air-solids separator. 
   In yet another embodiment, the detachable accumulator and the air-solids separator have matching tongue-and-groove surfaces enabling the detachable accumulator to be slidably sealed to and supported by the air-solids separator. 
   In another embodiment, the entrance ends of grooves on the air-solids separator are downwardly flared to facilitate engagement of the tongue rails on the accumulator with the grooves. 
   In another embodiment, the apparatus further comprises a fastener adapted for securing the detachable accumulator in functional engagement with the air-solids separator. 
   In still another embodiment, the apparatus comprises a mechanical-advantage fastener adapted for securing the detachable accumulator in functional engagement with the air-solids separator. 
   In yet another embodiment, the detachable accumulator can be releasably latched to the air-solids separator. 
   In another embodiment, the separator separates entrained yard debris into a debris-enriched stream and a debris-depleted stream by action of body forces thereupon. 
   In another embodiment, the separator has sidewalls inclined upwardly and inwardly at from about 5 degrees to about 25 degrees from the vertical. 
   In another embodiment, the debris-depleted stream from the air-solids separator is exhausted into the atmosphere frontwardly. 
   In another embodiment, the debris-depleted stream from the air-solids separator is exhausted into the atmosphere sidewardly. 
   In another embodiment, the debris-depleted stream exhausted from the air-solids separator is directed against the surface forward of the collector-rotor. 
   In another embodiment, the detachable accumulator has a perimetral frame detachably sealed to an accumulator-support frame pivotably mounted to the air-solids separator. 
   In yet another embodiment, the accumulator-support frame pivotably mounted to the air-solids separator can be sealingly latched to the air-solids separator. 
   In still another embodiment, the detachable accumulator has a perimetral frame detachably sealed to an accumulator-support frame pivotably mounted to the chassis frame. 
   In another embodiment, the detachable accumulator and the accumulator-support frame have matching tongue-and-groove attachment surfaces enabling the detachable accumulator to be slidably sealed to and supported by the accumulator-support frame. 
   In another embodiment, a maneuvering handle is attached to the detachable accumulator. 
   In another embodiment, the apparatus comprises at least one auxiliary handle attached to the detachable accumulator for lifting the detachable accumulator. 
   In another embodiment, the accumulator has one or more transparent panels affording observation of the debris level within the accumulator. 
   In another embodiment, the accumulator has one or more translucent panels affording observation of the debris level within the accumulator. 
   In another embodiment, the accumulator has one or more adjustable legs adapted for supporting one end of the accumulator. 
   In another embodiment, the apparatus has a duct connecting the blower unit to the air-solids separator. 
   Another aspect of the invention relates to an apparatus for collecting yard debris on a surface in which the apparatus comprises: (A) a frame; (B) a blower unit mounted on the frame adapted to induce entraining air flow adjacent the surface and collect the yard debris in the entraining air flow; (C) a flow conduit for conducting the yard debris in entraining air flow to the blower; (D) an air-solids separator operatively connected to the blower unit for separating the yard debris in the entraining air flow into a debris-enriched stream and a debris-depleted stream; and (E) a detachable accumulator adapted to receive the debris-enriched stream from the air-solids separator; with the detachable accumulator having a polyhedral shape and being adapted to be detachably sealed to the air-solids separator. 
   In another aspect, this invention relates to a free-flow apparatus for separating entrained yard debris from a transporting air stream by action of body forces thereupon comprising: (A) a curvilinear primary separation duct having an outer wall, an interior wall, an entrance for accepting a stream of air bearing entrained yard debris, and an exit; (B) a secondary separation chamber having a roof and a substantially frusto-conical outer peripheral wall with an opening therethrough, the outer wall of the curvilinear primary separation duct being generally tangential to the frusto-conical outer peripheral wall of the secondary separation chamber in one location adjacent the opening, the interior wall of the curvilinear primary separation duct defining an acute angle with the frusto-conical outer peripheral wall at a location generally opposed to the one location adjacent the opening in which the outer wall of the curvilinear primary separation duct is generally tangential to the frusto-conical outer peripheral wall of the secondary separation chamber; (C) the secondary separation chamber being adapted to receive the stream of air bearing entrained yard debris from the exit of the curvilinear primary separation duct; (D) the secondary separation chamber being partially encompassed horizontally by the curvilinear primary separation duct; (E) the secondary separation chamber being adapted to separate the stream of air bearing entrained yard debris into an exteriorly located debris-enriched stream and an interiorly located debris-depleted stream by action of body forces thereupon; (F) an accumulation chamber located below the secondary separation chamber for receiving the exteriorly located debris-enriched stream; (G) a baffle centrally disposed between the secondary separation chamber and the accumulation chamber for inhibiting secondary flow from the accumulation chamber into the secondary separation chamber and impeding re-entrainment of fine particulates from the accumulation chamber into the debris-depleted stream; and (H) the roof of the secondary separation chamber having defined therein a substantially centrally located passage adapted to exhaust the interiorly located debris-pleated stream to the atmosphere. 
   In another embodiment, the outer peripheral wall of the secondary separation chamber flares downwardly and outwardly. 
   In another embodiment, the outer peripheral wall of the secondary separation chamber is generally vertical. 
   In still another embodiment, the opening through the outer peripheral wall of the secondary separation chamber has a generally trapezoidal configuration. 
   In yet another embodiment, the outer peripheral wall of the secondary separation chamber flares downwardly and outwardly at from about 5° to about 25° from the vertical. 
   In another embodiment, the outer wall of the primary separation duct is inclined downwardly and outwardly at from about 5° to about 25°from the vertical. 
   In still another embodiment, the outer peripheral wall of the secondary separation chamber flares downwardly and outwardly and the outer wall of the primary separation duct is inclined downwardly and outwardly at from about 5° to about 25° from the axis of the frusto-conical portion of the secondary separation chamber. 
   In yet another embodiment, the stream of air bearing entrained yard debris flows through the primary-separation duct into the secondary-separation chamber through the opening defined in the outer peripheral wall of the secondary separation chamber. 
   In another embodiment, the height of the uppermost extent of the primary-separation duct above the uppermost extent of the secondary-separation chamber is no more than 50% of the height of the secondary-separation chamber. 
   In still another embodiment, the centrally located passage through the roof through which air is exhausted from the secondary separation chamber directs air discharged therefrom forwardly. 
   In yet another embodiment, the debris-depleted stream from the secondary separation chamber is exhausted into the atmosphere frontwardly. 
   In another embodiment, the debris-depleted stream from the secondary separation chamber is exhausted into the atmosphere sidewardly. 
   In another embodiment, the secondary separation chamber is thermoformed. 
   In still another embodiment, the primary separation duct further comprises an adjustable duct-closure device for minimizing airflow through the primary separation duct. 
   In yet another embodiment, the adjustable duct-closure device is a pivotable damper. 
   In another embodiment, the adjustable duct-closure device is a sliding-gate device. 
   In another embodiment, the accumulation chamber is mounted on a motor vehicle. 
   In still another embodiment, the accumulation chamber is towably mounted on wheels. 
   In another preferred embodiment, the present invention relates to a free-flow apparatus for separating entrained yard debris from a transporting air stream by action of body forces thereupon comprising: (A) a device for delivering a stream of air bearing entrained yard debris; (B) a vessel having an outer vessel wall and an opening therethrough, a roof, and a bottom; (C) a duct having an outer duct wall, an interior duct wall, a duct entrance, and a duct exit, the duct being disposed generally horizontally about an upper portion of the vessel; (D) a portion of the outer duct wall of the duct adjacent the duct exit being generally tangential to the outer vessel wall of the vessel in one location adjacent the opening, and a portion of the interior duct wall of the duct adjacent the duct exit defining an acute angle with the outer vessel wall at a location generally opposed to the one location adjacent the opening; (E) the duct being adapted to: (i) receive the stream of air bearing entrained yard debris through the duct entrance, (ii) conduct the stream of air bearing entrained yard debris from the duct entrance to the duct exit, and (iii) direct the stream of air bearing entrained yard debris into the vessel in a direction generally tangential to the outer vessel wall; (F) the roof having defined therein a substantially centrally located passage with a passage entrance and a passage exit; (G) a baffle extending generally outwardly from a point below the passage entrance, the baffle separating the vessel into an upperly located separation chamber and a lowerly located accumulation chamber, the outer periphery of the baffle being spaced inwardly from the outer vessel wall; (H) the separation chamber being adapted to separate the stream of air bearing entrained yard debris into an outerly located debris-enriched stream and an innerly located debris-depleted stream; (I) the substantially centrally located passage being adapted for: (i) receiving the innerly located debris-depleted stream from the separation chamber through the passage entrance, and (ii) discharging the innerly located debris-depleted stream into the atmosphere; and (J) the baffle being disposed to impede movement of fine particulates from the accumulation chamber into the innerly located debris-depleted stream. 
   In another embodiment, the duct is disposed generally horizontally with an upper portion of the vessel. 
   In still another embodiment, the duct is curvilinear and partially encompasses an upper portion of the vessel horizontally. 
   In yet another embodiment, a portion of the outer vessel wall of the separation chamber is frusto-conical and flares downwardly and outwardly. 
   Another aspect of the invention relates to an apparatus for separating entrained yard debris from a transporting air stream by action of body forces thereupon comprising: (A) a duct having an outer wall, an interior wall, a duct entrance for accepting a stream of air bearing entrained yard debris and a duct exit; (B) a separation chamber having a roof and a substantially frusto-conical outer peripheral wall with an opening therethrough, the outer wall of the duct being generally tangential to the frusto-conical outer peripheral wall of the separation chamber in one location adjacent the opening, the interior wall of the duct defining an acute angle with the frusto-conical outer peripheral wall at a location generally opposed to the one location adjacent the opening in which the outer wall of the duct is generally tangential to the frusto-conical outer peripheral wall of the separation chamber; (C) the separation chamber being adapted to receive the stream of air bearing entrained yard debris from the duct exit; (D) the separation chamber being partially encompassed horizontally by the duct; (E) the separation chamber being adapted to separate the stream of air bearing entrained yard debris into an exteriorly located debris-enriched stream and an interiorly located debris-depleted stream by action of body forces thereupon; (F) an accumulation chamber located below the separation chamber for receiving the exteriorly located debris-enriched stream; (G) a baffle centrally disposed between the separation chamber and the accumulation chamber for inhibiting secondary flow from the accumulation chamber into the separation chamber and impeding re-entrainment of fine particulates from the accumulation chamber into the debris-depleted stream; and (H) the roof of the separation chamber having defined therein a substantially centrally located passage adapted to exhaust the interiorly located debris-pleated stream to the atmosphere. 
   In another embodiment, the means for delivering a stream of air bearing entrained yard debris further comprises: (A) a frame adapted to be advanced over a surface; (B) a conduit mounted on the frame and having a conduit entrance and a conduit exit; (C) a blower unit operatively connected to the conduit exit and adapted to induce a flow of air through the conduit and provide suction at the conduit entrance; the conduit exit being operatively connected to the duct entrance. 
   In still another embodiment, the substantially centrally located passage through the roof through which air is exhausted from the separation chamber directs the debris-depleted stream exhausted therefrom toward the conduit entrance. 
   In still another embodiment, the debris-depleted stream from the separation chamber is exhausted toward the conduit entrance. 
   In another aspect, this invention relates to an apparatus for lifting and collecting lawn thatch comprising: (A) a frame adapted for movement in a principal direction upon a surface; (B) a duct mounted on the frame having a duct entrance and a duct exit; (C) a collector-rotor assembly comprising: a collector-rotor body disposed at the duct entrance having a substantially horizontal axis of rotation generally normal to the first direction; and a plurality of yieldable dethatching elements mounted upon the collector-rotor body, the dethatching elements being adapted to: (i) sweep over the surface, (ii) penetrate, engage and lift thatch thereupon, and (iii) impel the lifted thatch toward the duct entrance, the yieldable dethatching elements extending radially from the collector-rotor body by at least about one half of an inch; the collector-rotor assembly and the duct being configured for substantially untrammeled frontal engagement with yard debris having a depth of at least about two (2) inches; (D) a conduit having a conduit entrance and a conduit exit; (E) a blower unit, disposed between the duct exit and the conduit entrance, adapted to: (i) provide suction at the duct entrance entraining the lifted thatch; and (ii) induce a flow of the entrained lifted thatch through the duct and the conduit; (F) an air-solids separator operatively connected to the conduit exit for separating the entrained lifted thatch into a thatch-enriched stream and a thatch-depleted stream; (G) an accumulator operatively connected to the air-solids separator and adapted to receive the thatch-enriched stream from the air-solids separator; (H) a power source operatively connected to the blower unit and adapted to provide power to the blower unit; (I) a power source operatively connected to the collector-rotor assembly adapted to provide power to the collector-rotor assembly; and (J) a mechanism for adjusting the degree of engagement of the yieldable dethatching elements with the surface. 
   A preferred embodiment of this invention relates to an apparatus for lifting and collecting lawn thatch comprising: (A) a frame; (B) a first duct mounted on the frame having a first-duct entrance and a first-duct exit; (C) a second duct having a second-duct entrance and a second-duct exit, with the second-duct entrance operatively connected to the first-duct exit; (D) a rotating collector-rotor assembly comprising a collector-rotor body rotatably mounted on the frame having yieldable dethatching elements mounted thereupon adapted to: (i) sweep over a surface, (ii) penetrate, engage and lift thatch from among standing shafts of grass on the surface, and (iii) impel the lifted thatch toward the first-duct entrance; (E) a blower unit operatively connected to the first and second ducts and adapted to: (i) induce air flow adjacent the first-duct entrance entraining the lifted thatch; and (ii) induce a flow of the entrained lifted thatch through the first and second ducts; (F) an air-solids separator operatively connected to the second-duct exit and adapted for separating the entrained lifted thatch into a thatch-enriched stream and a thatch-depleted stream; (G) an accumulator adapted to receive the thatch-enriched stream from the air-solids separator; (H) a power source operatively connected to the blower unit and adapted to provide power to the blower unit; and (I) a power source operatively connected to the rotating collector-rotor body and adapted to provide power to the rotating collector-rotor body. 
   In another embodiment, the tips of the yieldable dethatching elements comprise elements for engaging an irregular surface, including pliable blades being yieldable to hard objects encountered on the surface, but being sufficiently stiff to sweep debris from irregularities present in the surface. 
   In another embodiment, the tips of the yieldable dethatching elements comprise rows of radially extending raker teeth adapted to engage and impel debris objects on the surface toward the duct entrance. 
   In still another embodiment, the yieldable dethatching elements comprise flexible polymeric lath elements. 
   In yet another embodiment, the yieldable dethatching elements comprise flexible metallic lath elements. 
   In another embodiment, the yieldable dethatching elements comprise pivotably mounted flail elements. 
   In another embodiment, the apparatus further comprises an arrestor wherein the pivotably mounted flail elements are iron-based, and the flail elements are adapted to: (A) engage twigs in deep yard debris, (B) transport them about the axis of rotation of the rotating collector-rotor, (C) force the twigs against the arrestor, (D) break the twigs into twig fragments, and (E) impel the twig fragments toward the duct entrance. 
   In still another embodiment, the yieldable dethatching elements comprise coil-connected dethatching tines. 
   In still another embodiment, the yieldable dethatching elements comprise coil-connected raking tines. 
   In another embodiment, the collector-rotor comprises axially extending plate members. 
   In still another embodiment, the apparatus further comprises yieldable rotor blade tips attached to rigid impeller elements. 
   In yet another embodiment, the apparatus comprises raking tips attached to rigid impeller elements. 
   In another embodiment, the blower is disposed between the first-duct exit and the second-duct entrance. 
   In another preferred embodiment, the present invention relates to a flail for rotatable mounting on a shaft on a rotatably mounted collector rotor comprising: (A) a transversely extending bushing having a generally cylindrical journal therethrough; (B) a flail body member joined to the bushing comprising a generally planar striker plate extending outwardly from the bushing member and lying in a plane generally perpendicular to the axis of the journal; (C) a blocker plate joined to the flail body member extending outwardly and lying in a plane generally parallel to the axis of the journal; and (D) the total transverse width presented by the blocker plate being less than the transverse length of the bushing, and the outward length of the striker plate exceeding the outward length of the blocker plate. 
   In another preferred embodiment, the present invention relates to an adaptor kit for mounting on a vehicle comprising: (A) a positionable suction head; (B) a conduit operatively connected to the positionable suction head and having a conduit exit; (C) a device for generating a flow of air inwardly through the suction head while collecting a stream of entrained yard debris; (D) a separation chamber having an outer chamber wall, a roof, and an opening for receiving the stream of entrained yard debris, the roof having defined therethrough a substantially centrally located passage; (E) a duct having a duct entrance, an outer duct wall, and a duct exit connected to the opening, the duct being adapted for: (i) accepting the stream of entrained yard debris from the conduit, (ii) conducting the stream of entrained lawn debris from the duct entrance to the opening in the separation chamber, and (iii) directing the stream of entrained lawn debris into the separation chamber in a direction primarily tangential to the outer chamber wall; (F) the separation chamber being adapted to separate the stream of entrained lawn debris into an outerly located debris-enriched stream and an innerly located debris-depleted stream; (G) the substantially centrally located passage being adapted to exhaust the debris-depleted stream from the separation chamber into the atmosphere; (H) an accumulation chamber mountable on a vehicle for receiving the debris-enriched stream; and (I) a baffle located between the separation chamber and the accumulation chamber for inhibiting secondary flow from the accumulation chamber into the separation chamber and impeding re-entrainment of fine particulates from the accumulation chamber into the debris-depleted stream, the separation chamber having an opening around the baffle into the accumulation chamber permitting passage of the outerly located debris-enriched stream from the separation chamber into the accumulation chamber. 
   In a further embodiment, the duct is disposed generally horizontally with the separation chamber. 
   In another embodiment, the duct is at least partially curvilinear and partially encompasses the separation chamber horizontally. 
   In still another embodiment, the device for generating a flow of air inwardly through the suction head comprises a blower fan. 
   In yet another embodiment, the blower fan is operatively connected to the conduit exit and the duct entrance. 
   In another embodiment, the device for generating a flow of air is a chipper shredder. 
   In still another embodiment, the device for generating a flow of air is a shredder blower. 
   In yet another embodiment, the vehicle is a motor vehicle. 
   In another embodiment, the vehicle is a collection truck. 
   In still another embodiment, the vehicle is a towable collection apparatus adapted to be towed behind a motor vehicle. 
   In yet another embodiment, the towable collection apparatus further comprises a utility trailer. 
   In another embodiment, the accumulation chamber is detachable from the device for generating a flow of air inwardly through the suction hood. 
   Another aspect of the invention relates to a towable collection apparatus adapted to be towed behind a motor vehicle comprising: (A) a towable accumulation chamber; (B) a positionable suction head; (C) a flexible transport hose operatively connected to the positionable suction head and having a hose exit; (D) a device for inducing a flow of air inwardly through the suction head while collecting a stream of entrained lawn debris; (E) a separation chamber having an outer chamber wall, a roof, and an opening for receiving the stream of entrained lawn debris, the roof having defined therethrough a substantially centrally located passage with a passage entrance and a passage exit; (F) a duct having a duct entrance, an outer duct wall, and a duct exit connected to the opening, the duct being adapted for: (i) accepting the stream of entrained yard debris from the flexible transport hose, (ii) conducting the stream of entrained lawn debris from the duct entrance to the opening in the separation chamber, and (iii) directing the stream of entrained lawn debris into the separation chamber in a direction primarily tangential to the outer chamber wall; (G) the separation chamber being adapted to separate the stream of entrained lawn debris into an outerly located debris-enriched stream and an innerly located debris-depleted stream; (H) the substantially centrally located passage adapted to exhaust the debris-depleted stream from the separation chamber into the atmosphere; and (I) a baffle located between the separation chamber and the towable accumulation chamber for inhibiting secondary flow from the towable accumulation chamber into the separation chamber and impeding re-entrainment of fine particulates from the towable accumulation chamber into the debris-depleted stream, the separation chamber having an opening around the baffle into the towable accumulation chamber permitting passage of the outerly located debris-enriched stream from the separation chamber into the towable accumulation chamber. 
   In another aspect, this invention relates to an apparatus for collecting yard debris disposed on a surface comprising: (A) a chassis frame; (B) a blower unit mounted on the chassis frame and adapted to (i) induce air flow adjacent a surface, and (ii) entrain yard debris disposed on the surface in an entraining air stream; (C) a conduit having a conduit entrance and adapted for conducting the yard debris in the entraining air stream from the surface to the blower unit; (D) an air-solids separator operatively connected to the blower unit for separating the entraining air flow into a debris-enriched stream and a debris-depleted stream; (E) an accumulator adapted to receive the debris-enriched stream from the air-solids separator; and (F) a passage having a passage entrance and a passage exit, wherein: (i) the passage entrance is operatively connected to and adapted to receive the debris-depleted stream from the air solids separator, (ii) the passage is adapted to conduct the debris-depleted stream along its length, and (iii) the passage exit is adapted to direct the debris-depleted stream toward the conduit entrance. 
   In another embodiment, the passage exit is adapted to direct the debris-depleted stream to a location proximate the conduit entrance. 
   In a preferred embodiment of this invention, an apparatus for collecting and reducing yard debris comprises: (A) a frame adapted for movement in a principal direction upon a surface; (B) a converging duct mounted on the frame having an entrance and an exit; (C) a collector rotor assembly comprising: (i) a collector rotor body disposed at the entrance to the converging duct having a substantially horizontal axis of rotation generally normal to the principal direction, and (ii) a plurality of impellers mounted on the collector rotor body, with the collector rotor assembly having an effective radius defined by rotation of the tips of the impellers about the horizontal axis, the collector rotor assembly being adapted to impel yard debris toward the entrance of the converging duct; (D) a second duct having an entrance and an exit, wherein the entrance thereof is in flow communication with the exit of the converging duct; (E) a blower unit adapted to induce flow of yard debris through the converging duct and the second duct; (F) a motor operatively connected to the blower unit and adapted to provide power to it; (G) a drive operatively connected to the collector rotor assembly and adapted to provide power to it; and (H) a wheel partially supporting the apparatus, forwardly mounted on the frame rearward of the collector rotor assembly, with the frame and collector rotor assembly being cantilevered forwardly thereof. 
   In another embodiment, the apparatus has two bearings mounted on the frame, with the collector rotor assembly rotatably mounted between them and the wheel mounted on the frame generally behind the bearings. 
   In a further aspect of the invention, the apparatus has a pair of side plates, each mounted on the frame adjacent one of the bearings, with the wheel mounted on the frame between the side plates. 
   In another embodiment, the apparatus comprises a pair of side plates, each mounted on the frame adjacent one of the bearings, with a wheel mounted in non-occluding relationship with the converging duct entrance and the collector rotor assembly. 
   In yet another embodiment, the wheel of the apparatus is adjustably mounted on the frame for movement toward and away from the surface. 
   In another embodiment, the apparatus comprises two wheels forwardly mounted on the frame rearwardly of the collector rotor assembly and between the side plates. 
   In another aspect of the invention, the apparatus further comprises two bearings mounted on the frame with the collector rotor assembly rotatably mounted therebetween, the location at which each forwardly mounted wheel is mounted on the frame being located generally behind the bearings. 
   In another embodiment, the present invention relates to an apparatus comprising a second wheel forwardly mounted on the frame rearwardly of the collector rotor assembly, each of the wheels being mounted on an axle, with the axle being pivotable in a generally horizontal plane. 
   In another preferred embodiment, the apparatus for collecting and reducing yard debris comprises: (A) a frame adapted for movement in a principal direction upon a surface; (B) a converging duct mounted on the frame having an entrance and an exit; (C) a collector rotor assembly comprising: (i) a collector rotor body disposed at the entrance to the converging duct having a substantially horizontal axis of rotation generally normal to the principal direction, and (ii) a plurality of impellers mounted on the collector rotor body, with the collector rotor assembly having an effective radius defined by rotation of the tips of the impellers about the horizontal axis, with the collector rotor assembly being adapted to impel yard debris toward the entrance of the converging duct; (D) a pivotable hood mounted on the frame disposed above the collector rotor assembly, wherein the hood is pivotable between a first position in which the hood is generally horizontal and an upward position; (E) a second duct having an entrance and an exit, with the entrance thereof in flow communication with the exit of the converging duct; (F) a blower unit adapted to induce flow of yard debris through the converging duct and the second duct; (G) a motor operatively connected to and adapted to provide power to the blower unit; and (H) a drive operatively connected to and adapted to provide power to the collector rotor assembly. 
   In a further embodiment, the hood is pivotable between a lower position and an upward position. 
   In a further preferred embodiment of the apparatus, air-flow ingress to the entrance of the converging duct is provided above the collector rotor body when the hood is pivoted into the upward position. 
   In another embodiment, the apparatus further comprises a forwardly and downwardly projecting ramp mounted on the frame longitudinally adjacent to and downwardly of the entrance to the converging duct. 
   In a further embodiment, the forwardly and downwardly projecting ramp is flexible. 
   In still another preferred embodiment, an apparatus for collecting and reducing yard debris comprises: (A) a frame adapted for movement in a principal direction upon a surface; (B) a converging duct mounted on the frame having an entrance and an exit; (C) a collector rotor assembly comprising: (i) a collector rotor body disposed at the entrance to the converging duct having a substantially horizontal axis of rotation generally normal to the principal direction, and (ii) a plurality of impellers mounted on the collector rotor body, with the collector rotor assembly having an effective radius defined by rotation of the tips of the impellers about the horizontal axis, and the collector rotor assembly being adapted to impel yard debris toward the entrance of the converging duct; (D) two bearings mounted on the frame and the collector rotor body rotatably mounted therebetween; (E) a pair of side plates, each mounted on the frame adjacent one of the bearings, the radial distance from its associated bearing to the periphery of the portion of each side plate below and forward of its associated bearing not exceeding the effective radius of the collector rotor assembly by more than about 1 inch; (F) a second duct having an entrance and an exit, wherein the entrance thereof is in flow communication with the exit of the converging duct; (G) a blower unit adapted to induce flow of yard debris through the converging duct and the second duct; (H) a motor operatively connected to the blower unit and adapted to provide power to the blower unit; and (I) a drive operatively connected to the collector rotor assembly and adapted to provide power to it. 
   In a most preferred embodiment of this invention, an apparatus for collecting and reducing yard debris comprises: (A) a frame adapted for movement in a principal direction upon a surface; (B) a converging duct mounted on the frame having an entrance and an exit; (C) a collector rotor assembly comprising: (i) a collector rotor body disposed at the entrance to the converging duct having a substantially horizontal axis of rotation generally normal to the principal direction, and (ii) a plurality of impellers mounted on the collector rotor body comprising a plurality of flexible polymeric spikes mounted thereon and projecting generally radially therefrom, with the collector rotor assembly having an effective radius defined by rotation of the tips of the impellers about the horizontal axis, and the collector rotor assembly being adapted to impel yard debris toward the entrance of the converging duct; (D) two bearings mounted on the frame, with the collector rotor assembly rotatably mounted therebetween; (E) a pair of side plates, each mounted on the frame adjacent one of the bearings, the radial distance from its associated bearing to the periphery of the portion of each side plate below and forward of its associated bearing not exceeding the effective radius of the collector rotor assembly by more than about 1 inch; (F) a pivotable hood mounted on the frame disposed above the collector rotor assembly, wherein the hood is pivotable between a first position in which the hood is generally horizontal and an upward position; (G) a second duct having an entrance and an exit, wherein the entrance thereof is in flow communication with the exit of the converging duct; (H) a blower unit adapted to induce flow of yard debris through the converging duct and the second duct; (I) a motor operatively connected to the blower unit and adapted to provide power to the blower unit; (J) a drive operatively connected to the collector rotor assembly and adapted to provide power to the collector rotor assembly; and (K) a wheel supporting the apparatus, forwardly mounted on the frame rearwardly of the collector rotor assembly, the frame and the collector rotor assembly being cantilevered forwardly thereof. 
   In a preferred embodiment, the impellers of the apparatus comprise a plurality of flexible polymeric rake assemblies secured to the collector rotor body, with each flexible polymeric rake assembly having a plurality of flexible polymeric raking fingers extending therefrom, these flexible polymeric raking fingers extending generally radially from the collector rotor body. 
   In another preferred embodiment, the apparatus further comprises a plurality of flexible metallic rake assemblies secured to the collector rotor body, each metallic rake assembly having a plurality of flexible metallic raking fingers extending therefrom, the flexible metallic raking fingers extending generally radially from the collector rotor body. 
   In another embodiment, the apparatus further comprises an access means for permitting access to the interior of the second duct, with the access means adapted for permitting removal of debris clogged in the second duct. 
   In still another embodiment, the apparatus further comprises an access means for permitting access to the interior of the converging duct, with the access means adapted for permitting removal of debris clogged in the converging duct. 
   In another preferred embodiment, the apparatus for collecting and reducing yard debris comprises: (A) a frame adapted for movement in a principal direction upon a surface; (B) a converging duct mounted on the frame having an entrance and an exit; (C) a collector rotor assembly having a substantially horizontal axis of rotation generally normal to the principal direction, with the collector rotor assembly comprising: (i) a collector rotor body disposed at the entrance to the converging duct, and (ii) a plurality of impellers mounted on the collector rotor body comprising a plurality of flexible polymeric spikes mounted on the collector rotor body and projecting generally radially therefrom, with the collector rotor assembly being adapted to impel yard debris toward the entrance of the converging duct; (D) a second duct having an entrance and an exit, with the entrance thereof in flow communication with the exit of the converging duct; (E) a blower unit adapted to induce flow of yard debris through the converging duct and the second duct; (F) a motor operatively connected to and adapted to provide power to the blower unit; and (G) a drive operatively connected to and adapted to provide power to the collector rotor assembly. 
   A further embodiment of the apparatus comprising a multiplicity of perforate mounting plates secured to the collector rotor body, with flexible polymeric spikes extending through the perforate mounting plates. 
   A preferred embodiment of the invention relates to a container adapted for receiving, transporting and dumping yard debris, comprising: (A) a frame; (B) a plurality of walls defining a cavity mounted on the frame including at least: an outwardly displaceable wall, and an opposing wall; (C) a duct mounted on the frame having an entrance and an exit; (D) a blower unit operatively connected to the duct and adapted to induce a flow of air-entrained yard debris into the entrance thereof and through the duct; (E) an air-solids separator disposed on the frame in flow-receiving communication with the exit of the duct and adapted for separating the air-entrained debris into a debris-enriched stream directable into the container and a debris-depleted stream discharged to the atmosphere; and (F) a flexible dislodgement liner adapted to be disposed in an accumulation configuration extending between the displaceable wall and the opposing wall and generally spanning the interior of the container, an upper portion of the flexible dislodgement liner being releasably secured adjacent an upper portion of the opposing wall and adapted to be urged toward the outwardly displaceable wall. 
   A further embodiment relates to the container, wherein a portion of the flexible dislodgement liner is fastened to the frame adjacent to the outwardly displaceable wall. 
   In another embodiment, the outwardly displaceable wall is removably attached to the frame and is adapted for removal from the frame for emptying the container. 
   In a preferred embodiment of the container, an upper portion of the flexible dislodgement liner is releasably secured adjacent an upper portion of the opposing wall in the accumulation configuration and the container further comprises a passageway through a wall of the container, a retractor cord having a portion thereof secured outside the container, being threaded through the passageway, having another portion thereof secured to the flexible dislodgement liner; and wherein the flexible dislodgement liner is movable between (i) the accumulation configuration and (ii) a deployment configuration in which the upper portion of the flexible dislodgment liner is released and urged toward the outwardly displaceable wall; the retractor cord being adapted to urge the flexible dislodgement liner toward the opposing wall upon release of the flexible dislodgement liner. 
   In another embodiment, a pulley is disposed on the retractor cord adjacent the passageway in the container and is adapted to facilitate movement of the retractor cord through the passageway. 
   In yet another embodiment, a turning block is disposed on the retractor cord adjacent the passageway in the container and is adapted to facilitate movement of the retractor cord through the passageway. 
   In one embodiment, the retractor cord is elastically extensible to a length exceeding its untensioned length by at least 25%. 
   In another embodiment, the retractor cord is attached to a spring. 
   In still another embodiment, the retractor cord is attached to a weight. 
   In another preferred embodiment, the container further comprises a rib secured to the flexible dislodgement liner urgeable into a position adjacent the junction of the opposing wall with the frame, and adapted to urge the flexible dislodgement liner to return to the accumulation configuration generally spanning the interior of the container upon release of the flexible dislodgement liner. 
   In another embodiment, the container further comprises a pair of spaced lateral walls spanning between the outwardly displaceable wall and the opposing wall. 
   In another embodiment of the container, the flexible dislodgement liner generally spans between the spaced lateral walls and extends between the displaceable wall and the opposing wall, with an upper portion of the flexible dislodgement liner being (i) releasably secured adjacent an upper portion of the opposing wall and (ii) adapted to be urged toward the outwardly displaceable wall. 
   In another embodiment of the container, a tensioning member is operatively connected to the upper portion of the flexible dislodgement liner and is adapted for urging the upper portion of the flexible dislodgement liner toward the outwardly displaceable wall. 
   In another embodiment of the container, one portion of the tensioning member is operatively attached to the upper portion of the flexible dislodgement liner in the accumulation configuration, and another portion of the tensioning member is releasably deployed toward the outwardly displaceable wall. 
   In a further embodiment of the container, the flexible dislodgement liner generally spans between the spaced lateral walls and extends between the displaceable wall and the opposing wall, with a first portion of the flexible dislodgement liner being releasably secured adjacent an upper portion of the opposing wall, and further having portions of the flexible dislodgement liner extending upwardly along each of the spaced lateral walls and being releasably secured adjacent upper portions of the spaced lateral walls, and the first portion of the flexible dislodgement liner being adapted to be urged toward the outwardly displaceable wall. 
   In still another embodiment of the container, the air-solids separator comprises a free-flow apparatus for separating yard debris from the entraining air flow by action of body forces thereupon. 
   In a preferred embodiment of the invention, a container adapted for receiving, transporting and dumping yard debris comprises: (A) a frame; (B) a plurality of walls defining a upwardly opening cavity mounted on the frame including at least an outwardly displaceable wall and an opposing wall; and (C) an upwardly opening flexible plicating dislodgement liner generally spanning the interior of the cavity and extending at least between the displaceable wall and the opposing wall, a peripheral portion thereof being releasably secured adjacent an upper portion of the opposing wall and adapted to be urged toward the outwardly displaceable wall. 
   In a further embodiment of the invention, a peripheral portion of the flexible plicating dislodgement liner is adapted for manual grasping and urging toward the outwardly displaceable wall. 
   In another embodiment, the outwardly displaceable wall is hingedly connected to the frame and a portion of the flexible dislodgement liner is fastened to the outwardly displaceable wall. 
   In another embodiment of the container, a portion of the flexible plicating dislodgement liner is fastened to the outwardly displaceable wall. 
   In a preferred embodiment, a portion of the flexible plicating dislodgement liner is fastened to an upper portion of the outwardly displaceable wall. 
   In another preferred embodiment, the lower end of the outwardly displaceable wall is pivotably attached to the frame, and the outwardly displaceable wall is adapted to be pivoted outwardly and downwardly. 
   In another preferred embodiment, the container further comprises a pair of spaced lateral walls spanning between the outwardly displaceable wall and the opposing wall. 
   In another embodiment of the container, the flexible plicating dislodgement liner generally spans between the spaced lateral walls and extends between the displaceable wall and the opposing wall; wherein portions of the flexible plicating dislodgement liner extend upwardly along each of the spaced lateral walls and are releasably secured adjacent upper portions of the spaced lateral walls. 
   In still another embodiment of the container, the flexible plicating dislodgement liner is plicated at the junctions of the spaced lateral walls with the frame when the flexible plicating dislodgement liner is in the accumulation configuration. 
   In another embodiment of the container, the interior of the flexible plicating dislodgement liner is a web structure having sufficient burst strength to support the weight of a volume of organic yard debris corresponding to the volume of the container. 
   In yet another preferred embodiment, the container further comprises ramps securable to the outside of one of the walls of the container, with the ramps being adapted for having a wheel-supported debris accumulator rolled up the ramp, and facilitating dumping of the accumulator contents into the container. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a typical apparatus made in accordance with the present invention and showing certain principal features of the apparatus. 
       FIG. 2  is a side view of the apparatus of  FIG. 1  with a portion of the apparatus shown in cross section view along the lines of  2 - 2  of  FIG. 1 . 
       FIG. 3  is a top view of a portion of the apparatus of  FIG. 1  with the transfer duct  92  removed at cross-section view along the lines of  3 - 3  in  FIG. 2  to show elements of power supply to the chipper shredder and the collector rotor. 
       FIG. 4  is a close-up view of the apparatus in  FIG. 2  showing airflow around the lower collector lip. 
       FIG. 5  is a front view of the chipper shredder shown as a cross section view along the lines of  5 - 5  of  FIG. 2 . 
       FIG. 6  is a cross section view of the chipper shredder taken along lines  6 - 6  in  FIG. 5  and showing the interaction of the swing hammers with the inwardly protruding teeth. 
       FIG. 7  is a perspective isolated view of the inwardly protruding teeth shown at  82  in  FIG. 5 . 
       FIG. 8  is a perspective view of the primary separation loop shown in  FIG. 1 . 
       FIG. 9  is a cross sectional view of the separator and hopper as viewed along lines  9 - 9  in  FIG. 2 . 
       FIG. 10  is a perspective isolated view of the collector rotor shown in  FIG. 1 . 
       FIG. 11  is a schematic perspective view of the collector duct shown in  FIG. 2 , including notation for design parameters. 
       FIG. 12  is a schematic view of raking tips that can be used with the collector rotor shown in  FIG. 10 . 
       FIG. 13  is a cross-section view similar to a portion of  FIG. 2 , but showing a forward location of a stripping slot which admits air to strip leaves from the rotor. 
       FIG. 14  is a cross-section view of a variation of the collector rotor shown in  FIG. 13  in which flat fillets have been replaced with convex fillets. 
       FIG. 15  is a cross-section view of a variation of the collector rotor shown  FIG. 14  showing an alternative design for fabricating the collector rotor with convex fillet shapes. 
       FIG. 16  is a schematic top-view diagram of the primary-separation duct showing mathematical notations for calculating minimal arc of curvature for effective separation of air and lawn debris. 
       FIG. 17  is a side view of a riding lawnmower having a collector assembly and a separator of this invention. 
       FIG. 18  is a cross-section view of selected portions of the riding lawnmower shown in  FIG. 17 . 
       FIG. 19  is a perspective view, partially in phantom, of an improved apparatus made in accordance with the present invention showing certain principal features of the apparatus. 
       FIG. 20  is a side view of the apparatus of  FIG. 19  with a portion of the apparatus broken away and shown in cross-section view, additionally illustrating an optional adjustable duct-closure device. 
       FIG. 20A  is a side view of the apparatus of  FIG. 19  additionally illustrating an optional adjustable sliding-gate duct-closure device mounted in a segment of the compact transfer duct. 
       FIG. 21  is a cross-section view of the collector module on the front of the apparatus of  FIG. 19 . 
       FIG. 22  is a cross-section view along the lines of  22 - 22  in  FIG. 21  showing a close-up view of the twig-breaker components and the interaction of the twig-breaker sweeps with the twig-arrestor elements. 
       FIG. 23  illustrates an alternative embodiment of the collector module in which a rotary brush is mounted rearward of the collector duct. 
       FIG. 24  illustrates still another embodiment of the collector module with a twig-breaking-rotor assembly forward of the collector duct, and a rotary brush rearward of the collector duct. 
       FIG. 25  is a cross-sectional view along the lines of  25 - 25  in  FIG. 20  showing the primary-separation duct, the secondary-separation chamber, the baffle, and the receiver grooves supporting the accumulator. 
       FIG. 26  is a cross-section view along the lines of  26 - 26  in  FIG. 25 , showing the hold-down clamp which holds the accumulator in place during operation of the apparatus. 
       FIG. 27  is a side view of an improved accumulator with attached wheels and an accumulator-maneuvering handle, and a sliding tongue-and groove mount for supporting the accumulator. 
       FIG. 27A  is a partial side view of the apparatus of  FIG. 19  illustrating a detachable accumulator bag secured to the lower portion of the separator. 
       FIG. 28  illustrates yet another embodiment of the collector module in  FIG. 19 , with the module having a rotor with swinging flails which perform raking and de-thatching functions. 
       FIG. 29  is a cross-section view along the lines of  29 - 29  in  FIG. 28 , illustrating the mounting of the flails on the collector rotor. 
       FIG. 30  is a perspective phantom view of a flail, illustrating the bushing and the “T” cross section of the flail. 
       FIG. 31  is a side view of an embodiment of the machine, in which a duct transports the air discharged from the separator forward to the vicinity of the collector rotor. 
       FIG. 32  is a partial phantom side view illustrating the height-adjusting mechanism for the adjustable-height wheels. 
       FIG. 33  is a partial cross-section view along the lines of  33 - 33  in  FIG. 32 , illustrating the sliding support blocks on which the adjustable-height wheels are mounted. 
       FIG. 34  is a perspective view illustrating the twig-breaker sweeps with crenels, merlons, and crenel furrows. 
       FIG. 35  is a partial side view illustrating the downwardly flaring mouth of the receiver groove, which functions as a ramp for engaging and raising the leading edge of the accumulator as the accumulator is pushed forward. 
       FIG. 36  is a partial side view illustrating another embodiment in which the accumulator-support frame pivots downward to receive the tongue rails on the accumulator. 
       FIG. 37  is a partial side view illustrating flexible seal strips for restricting peripheral inflow of air into the collector. 
       FIG. 38  is a partial cross-section view illustrating a reduced-height separator mounted on a debris-collecting truck. 
       FIG. 39  is a partial top view illustrating tangential approach of the primary-separation duct to the secondary-separation chamber of the reduced-height separator. 
       FIG. 40  is a side view of an improved apparatus of the present invention, with a portion of the apparatus shown in cross-section view illustrating a duct flange, an improved housing, and adjustable-height wheels. 
       FIG. 41  is a cross-section view of the collector module on the front of the apparatus of  FIG. 40 , showing an improved housing over the twig-breaking rotor assembly and adjustable-height wheels positioned rearward of the rotor assembly. 
       FIG. 42  is a cross-section view similar to  FIG. 41 , but with the improved housing pivoted upward to allow the rotor assembly to engage deep leaves. 
       FIG. 43  is a top view according to lines  43 - 43  in  FIG. 42 , showing placement of the adjustable-height wheels behind the rotor assembly. 
       FIG. 44  is a partial cross-section view of the twig-breaking rotor assembly, with spike dethatcher rods mounted on the assembly. 
       FIG. 45  is a frontal view along lines  45 - 45  in  FIG. 44  of the spike dethatcher rods. 
       FIG. 46  is a partial cross-section view of the twig-breaking rotor assembly, showing an alternate form of raker teeth positioned under and trailing the twig-breaker sweep. 
       FIG. 47  is a perspective view of a section of raker teeth shown in cross-section view in  FIG. 46 . 
       FIG. 48  is a cross-section view of the flange shown at line  48 - 48  in  FIG. 40   
       FIG. 49  is a perspective view of a waste transporter, including ramp boards for elevating the accumulator into emptying position. 
       FIG. 50  is a partial cross-section view of the waste transporter in  FIG. 49 , but with the ramp boards deployed and the accumulator being pushed upward. 
       FIG. 51  is a partial cross-section view of the waste transporter in  FIG. 50 , but with the accumulator resting on the side of the transporter and being emptied into the transporter. 
       FIG. 52  is a cross-section view of the filled waste transporter in  FIG. 51 , but with the side hinged downward for emptying. 
       FIG. 53  is a cross-section view of the waste transporter in  FIG. 52 , with the liner sheet which had draped the sides and ends of the transporter having been pulled away from the transporter to empty the contents of the transporter. 
       FIG. 54  is a partial cross-section view of a retractor cord passing around a pulley on the transporter in  FIG. 53 . 
       FIG. 55  is a partial cross-section view of a retractor cord passing around a turning block on the transporter in  FIG. 53 . 
       FIG. 56  is a cross-section view of a transporter containing waste-collection bags and previously filled bags standing beside the transporter. 
       FIG. 57  is a cross-section view of a filled accumulator having an air-solids separator disposed thereupon, and with the displaceable sidewall removed for emptying the contents of the accumulator. 
       FIG. 58  is a cross-section view showing a variation of the waste transporter in  FIG. 53 , in which the liner sheet had not draped the ends of the transporter, but had spanned from one end wall to the other end wall, and has been pulled away from the transporter to empty the contents of the transporter. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1 , deep collector  22  rests on surface  24  bearing deep yard debris  26  comprising primarily leaves, twigs, clippings and other materials such as usually accumulate on lawns, sidewalks and patios in the vicinity of trees in the autumn. Frame  28  of deep collector  22  comprises right side support plate  30 , left side support plate  32 , base-plate  34 , and control handle structure  36 . Upper housing  38  spans from right side support plate  30  to left side support plate  32 . Rotor shaft  40  journaled between left and right side support plates  30  and  32  carries a plurality of rotor blades  42 , each of which is preferably substantially gas impervious and bears a rotor tip which, in  FIG. 1 , may be a substantially gas impervious flexible rotor blade tip such as that indicated at  44 . Rotor pulley  46  mounted on rotor shaft  40  engages drive belt  48 , which also engages idler pulley  50  mounted on lever arm  52  pivotably mounted on right side support plate  30 . Drive pulley  54  is connected to motive means  146  for powering deep collector  22 . By pivoting lever arm  52  clockwise, idler pulley  50  tightens drive belt  48 , drawing it into firm engagement with rotor pulley  46  and drive pulley  54 , rotating rotor shaft  40  bearing rotor blades  42  and flexible rotor blade tips  44 , which engage surface  24  upon rotation of rotor shaft  40 . A shaft with rollers  47  can be raised and lowered on the side support plates  30  and  32  to conversely lower and raise the rotor blade tips  44  relative to surface  24 . 
     FIG. 3  shows details of power delivery to chipper-shredder unit  66  and drive pulley  54 . Conventional engine  146  disposed on base plate  34  has engine crankshaft  148  extending into chipper-shredder unit  66 , chipper shredder rotor  74  being mounted on said engine crankshaft. Engine drive belt  150  engages engine drive pulley  152  disposed on engine crankshaft  148  and second pulley  154  disposed on first power shaft  156 . Reducing-angle drive  158  disposed at the intersection of first power shaft  156  and second power shaft  160  transmits power to drive pulley  54 . 
   As shown in  FIG. 2 , as rotor blades  42  are driven counterclockwise, flexible rotor tips  44  proximately engage upper housing  38  impeding substantial passage of air between upper housing  38  and rotor blades  42 . As the arc of upper housing  38  is at least a significant fraction of the included angle between adjacent rotor blades  42 , a substantial seal to passage of air is provided above rotor shaft  40  throughout much or all of the rotation cycle of said rotor shaft. In preferred embodiments, rotor shaft  40  is at least about 2″ above surface  24 , facilitating engagement of rotor blade tips  44  with deep yard debris  26  having a depth considerably greater than 2″. In more preferred embodiments, upper lip  58  on upper housing  38  will be at least about 4″ inches above surface  24  permitting engagement with yard debris  26  having a depth of that order of magnitude. In more preferred embodiments, upper lip  58  of upper housing  38  will be disposed at least about 8″ inches above surface  24 , more preferably at least about 12″. Yard debris  26  engaged between adjacent rotor blade tips  44  is thereby impelled rearwardly toward collector duct  60  defined between upper collector shell  62  and lower collector shell  64 . Suction is supplied to collector duct  60  by chipper-shredder unit  66  which may be of any conventional construction such as that shown in U.S. Pat. No. 5,931,396. For typical yard debris having a depth of several inches, we have obtained good results with units providing at least about 20, preferably over 40, cubic feet per minute (cfm) of air flow per inch of width of the suction intake. While it is desirable to have considerable shredding action to reduce the volume of the debris collected, even the minimal amount of shredding provided by a sufficiently powerful fan can be adequate for effectively collecting leaves. 
   As generally indicated at  68  in  FIG. 2 , as flexible rotor blade tip  44  moves toward lower collector lip  70  between right side support plate  30  and left side support plate  32 , flows of air having substantial components nearly parallel to surface  24  are induced in close proximity to surface  24 . As shown in  FIG. 4 , as lower collector lip  70  is spaced from surface  24 , forwardly and upwardly directed air flow generally indicated at  69  around lower collector lip  70  provides enhanced vacuuming effect at surface  24  during the period in which flexible rotor tips  44  are moving from the point of engagement with surface  24  toward lower collector lip  70 . Ideally, the lowermost portion of lower collector lip  70  is spaced from surface  24  by a height of about one tenth to about three quarters of the height of the opening to collector duct  60 . Particularly enhanced suction at surface  24  and air flow parallel to surface  24  occurs as each flexible rotor blade  44  draws into closest proximity with surface  24 . 
   In some preferred embodiments, suction in collector duct  60  comprises a steady level of suction having superimposed therewith pulsed suction, this combination of steady and pulsed suction providing excellent ability to both induce flow of fine yard debris through collector duct  60  while also impelling heavier yard debris through said collector duct toward chipper-shredder unit  66 . Pulsing of the suction applied to collector duct  60  is thought to result from the variable opening created between flexible rotor blade tips  44  and surface  24  as flexible rotor blades  44  sweep rearwardly toward lower collector lip  70 , attaining high velocity in collector duct  60  prior to rotor blade  42  and flexible rotor blade tip  44  coming into closest proximity with surface  24 , and high suction as rotor blade  42  and flexible rotor blade tip  44  come into closest proximity with lower collector lip  70 . 
   Variable stripping slot  72  defined between upper housing  38  and upper collector shell  62  admits a flow of air into voids between rotor blades  42 , aiding in removal of yard debris contained therebetween and reducing cycling of yard debris around rotor shaft  40 . Ideally, the width of variable stripping slot  72  is sized to provide enough of an impulse to remove debris which might otherwise be carried around with the rotor, without unduly compromising the vacuum flow used for removal of fine debris from the ground. We have found that a width of from about one tenth to about three quarters of the height of the opening to collector duct  60  is suitable for a 5 HP unit. We have also found that fillets  73  installed between adjacent rotor blades  42  aid in reducing the amount of debris which might otherwise be carried around with the rotor. 
   Airflow induced by chipper-shredder unit  66  entrains yard debris  26  and transports said yard debris through collector duct  60  and into chipper-shredder unit  66 .  FIGS. 5 ,  6 , and  7  show features of a preferred embodiment of chipper-shredder unit  66 . A shredder rotor  74  with swing hammers  76  and fan blades  78  rotates in chipper-shredder enclosure  80 . Swing hammers  76  swing past inwardly protruding teeth  82 , reducing the size of leaves and other entrained debris. An advantage of reducing the volume of the collected leaves and other debris with the invention is to make it possible to store a considerable mass of debris, reducing storage space while reducing the tendency for wind to disperse the leaves. Branches may be introduced into chipper-shredder enclosure  80  through chipper shredder opening  84  and chipped by chipper knives  86 . Reduced debris passes through elongated gaps in swing hammer screen  88  and outward through chipper-shredder exhaust port  90 . 
   Entrained debris from chipper-shredder unit  66  is impelled through transfer duct  92  to separator  94  which separates entrained debris from the entraining air. As shown in  FIG. 8 , debris entrained in air passes from transfer duct  92  into separator  94  through separator inlet duct  96 . Primary separation occurs in primary separation duct  98  as the flow of air is redirected inwardly, while inertial forces urge debris solids toward perimetral wall  100  of primary separation duct  98 , thereby forming a solids-depleted inner layer and a solids-enriched outer layer. Primary separation duct  98  directs the flow of air-entrained yard debris downwardly as it enters secondary separation chamber  102  in  FIG. 9 , impelling downward flow of both solids-depleted inner air layer generally indicated at  104  and solids-enriched outer layer generally indicated at  106  through transfer opening  108  between primary separation duct  98  and secondary separation chamber  102 . 
   As shown in  FIG. 9 , solids-depleted inner air layer generally indicated at  104  flows downwardly in innermost portion of transfer opening  108 , while solids-enriched outer layer generally indicated at  106  flows downwardly along first perimetral wall  100  into secondary separator chamber  102 . Rotating airflow indicated generally at  110  swirls around secondary separation chamber  102 , further separating debris into solids enriched outer layer  106 , which passes along second perimetral wall  112  of secondary separation chamber  102  into hopper  114  below. If desired, bag  113  may be placed in hopper  114  in order to collect retained debris  124  directly in bag  113 . To be most effective, this rotating airflow moves with a tangential velocity of at least about 2000 feet per minute measured close to second perimetral wall  112 , causing the entrained reduced lawn debris to move outwardly toward second perimetral wall  112  of secondary-separation chamber  102  by action of body forces thereupon. Second perimetral wall  112  may consist of some combination of cylindrical and frusto-conical surfaces, and is referred to as a frusto-conical outer wall section. Swirling continues in hopper  114 , while infundibulate baffle  116  impedes secondary flows of air containing finely reduced debris fragments from re-entering secondary separation chamber  102 . In secondary separation chamber  102 , solids-depleted inner air layer generally indicated at  105  migrates upwardly along the axis of secondary separation chamber  118 , through exhaust entrance  120 , which passes through upper bulkhead  121 , and exits through exhaust passage  122  to the atmosphere. Infundibulate baffle  116  is suspended below secondary separation chamber  102  by supporting rods  117  or by other supporting means. If desired, deflector  125  can be placed adjacent to exit  123  of exhaust passage  122  to direct airflow generally indicated at  127  away from person operating apparatus. 
   As most of the separation is achieved by the action of body forces on the particles of entrained debris, the flow through the separator is substantially unimpeded—in contrast to those units in which filtration is primarily relied upon to remove the particulate debris from the air-stream in which it is entrained. Hence, this separator is referred to as a free-flow apparatus. Even though a minimal filter may be placed in the exhaust stream from the separator if so desired, the flow through the separator is substantially free of obstructions which might limit the flow of air significantly if filtration were relied upon for primary removal of heavy debris. Thus, the invention provides a machine which effectively separates the reduced yard debris from the air in which it is entrained, and which can be operated effectively for an extended period without either stopping to clear a filter in the separator, or experiencing decreased pick-up efficacy because of reduced air flow rate occasioned by partial blockage of a filter area. 
   Since the apparatus of the invention separates the debris from the air stream without relying primarily on a filter element, another aspect of the invention is to be able to collect the reduced debris in an impervious receptacle. Thus, the receptacle may be a barrel-like container, a fabric bag of limited permeability, a plastic bag, or a paper bag.  FIG. 27A  illustrates a polymeric bag, paper bag or generally air impervious fabric bag  113  secured to the lower portion of second perimetral wall  112  of separator  394  by a band  115 . One may also deploy a flexible container, such as a plastic or paper bag, within a rigid barrel-like container.  FIG. 9  illustrates a polymeric bag, paper bag, or generally air impervious fabric bag  113  deployed within barrel-like hopper  114 . 
   Another aspect of the invention is that it provides a machine having a separator and collector container low enough in height that the operator will be able to see over the separator in order to operate the machine effectively, while the collector container still has substantial capacity for accumulating debris. Accordingly, it is preferable that the overall height of the apparatus from the uppermost portion of the apparatus to the outer baffle periphery be less than about 1.2 times the inside diameter of the separation chamber as measured proximate the baffle periphery. It is further preferable that the plane of the baffle periphery be disposed below the lowermost portion of the upper bulkhead by a distance of less than about 0.6 times the inside diameter of the separation chamber. In some configurations, it is preferable that the baffle periphery be disposed below the lowermost portion of the entrance to the exhaust passage by a distance of less than about 0.6 times the inside diameter of the separation chamber. 
   Further in  FIG. 9 , upon being filled with retained debris  124 , hopper  114  may be opened by sliding apart upper and lower flanges  126 , allowing retained debris  124  accumulated therein to be discarded. Thus, another feature of the invention is in providing a debris-collection receptacle which can be emptied quickly and easily. 
     FIG. 10  further displays construction of collector rotor  128  comprising rotor shaft  40 , rotor blades  42 , flexible rotor blade tips  44 , adjusting nuts  130  for adjusting flexible rotor blade tips  44  for proper engagement with surface  24 , and left seal disc  132  and right seal disc  134  for assisting in rigidifying of rotor blades  42  while substantially impeding axial air flow into spaces between rotor blades  42 . 
     FIG. 11  shows a preferred configuration for collector duct  60 , having a collector duct entrance  136 , a collector duct exit  138 , and a convergence angle Φ preferably less than about 120°. In preferred embodiments, convergence angle Φ will be less than 110°. In more preferred embodiments, convergence angle Φ will be less than 100°, most preferably less than 80°. In other preferred embodiments, the cross sectional area of collector duct  60  measured in planes (generally indicated at  140 ) perpendicular to central flow line (generally indicated at  142 ) will be approximately constant along length of collector duct  60 . In more preferred embodiments, cross sectional area at any point along collector duct  60  will be within about 15 percent of the average of the minimum and maximum values. 
     FIG. 12  displays optional raking tips  144  which may be attached to rotor blade  42 , enabling use of deep collector  22  for raking debris from a grass-covered surface such as a lawn or other crinose surface such as Astroturf®. 
     FIG. 13  illustrates stripping slot  72  in a closed position and forward stripping slot  151  in upper housing  38  being located in a preferred forward position. The advantage of forward placement of stripping slot  151  is that air bleed into collection duct  60  occurs for only a fraction of the rotor revolution, instead of being almost continuous as with open rear stripping slot  72 . Rear upper housing segment  153  spans the equivalent of about two thirds of the arc distance between adjacent rotor tips  157 . Rotor blade tips  157  move in individual proximity with rear upper housing segment  153  for about two thirds of the revolution cycle, and air bleeds through forward stripping slot  151  for only about one third of the cycle. It appears that more of the air admitted to collection duct  60  comes from flows  163  along surface  24  and less from stripping slot  151 , resulting in believed greater efficiency in collecting debris from surface  24 . It also appears that air flow through forward stripping slot  151 , through rotor cavity  159 , and into collection duct  60  has more action in stripping leaves from rotor cavity  159  than would air flowing through rear stripping slot  72  and into cavity  159 . However, even with airflow through forward stripping slot  151 , rotational secondary flows were detected as generally indicated at  161 . These secondary flows appeared to enable leaves to stay in rotor cavities  159  and carry over to open front  162  of the housing, where they were re-deposited on surface  24 . 
     FIG. 14  illustrates convex fillets  164  being used instead of flat fillets  73  shown in  FIG. 2 . Convex fillets  164  define thinner rotor cavities  166  that are generally concentric with rotor shaft  40  and which exhibit greatly reduced or no detectable macro-scale eddy flows upon airflow through forward stripping slot  151 . One could use fillets having generally concentric, generally convex surfaces having a number of small flat, dimpled, or other shaped surfaces, and still achieve a generally convex cavity space. The shape and dimensions of said convex fillets should be chosen such that any substantial, detectable local flows generally indicated at  168  move rearward from forward stripping slot  151  to collection duct  60 . Forward carryover and re-deposition of leaves were greatly reduced with use of convex fillets  164 . 
   An alternative construction of rotor  170  is illustrated in  FIG. 15 . One skilled in the art will recognize that as an alternative to constructing rotor  128  with blades  42  as in  FIG. 10 , and convex fillets  164  as in  FIG. 14 , one could employ a tubular member  172  concentric with rotor shaft  40  and having means  174  for attaching rotor blade tips  44  ( FIG. 10 ) or raking tips  144  ( FIG. 12 ). 
     FIG. 16  is a schematic top-view diagram of separator  94  shown in  FIGS. 8 and 9 . Primary-separation duct  98  has a radius RO of its curvilinear outer surface  100 , a radius RI of its curvilinear inner surface  101 , and a minimum arc of curvature Θ for effective separation of debris-laden air generally indicated at  99  into a solids-enriched outer layer generally indicated at  106  and a solids-depleted inner layer generally indicated at  104 . Both layers pass through transfer opening  108  into secondary separator chamber  102  in  FIG. 9 , and then solids-depleted inner air layer passes upward through exhaust passage  120  in  FIG. 16 . Minimum arc of curvature for effective separation Θ is related to the radii of curvature by the expressions:
 cosine Θ=RI/RO; and Θ=arc cosine RI/RO. 
     FIG. 17  illustrates riding lawnmower  176  having collector assembly  178  mounted at advancing entrance  180  of mower deck  182 . Leaf fragments and grass clippings are separated from entraining air by separator  94  and retained in hopper  114 . 
     FIG. 18  depicts a cross section view of selected portions of riding lawnmower  176  shown in  FIG. 17 . Leaves and other debris are impelled by collector rotor  170  into mowing chamber  186  within the mowing enclosure  188 , where they are reduced by mower blades  190 . Fan  192  induces airflow under collector rotor  170 , through mowing chamber  186 , first air duct  194 , and second air duct  196 , and into separator  94 , entraining leaf fragments, grass clippings, and other debris into hopper  114 . 
   In  FIGS. 19 and 20 , compact collector  322  rests on surface  24  bearing deep yard debris  26  comprising primarily leaves, twigs, clippings, and other materials such as usually accumulate on lawns, sidewalks, and patios in the vicinity of trees in the neighborhood. Reference numbers for this embodiment are derived by adding 300 to the comparable reference numbers in  FIGS. 1 ,  2 , and  3 . Compact frame assembly  328  of compact collector  322  comprises collector frame assembly  200  and motor accumulator frame assembly  201 . Collector frame assembly  200  includes compact right side support plate  330 , compact left side support plate  332  as well as compact upper housing  338  and compact collector duct  360  spanning the space therebetween. Motor accumulator frame assembly  201  comprises engine base  334 , upper reinforcing braces  202 , accumulator-support frame  203  and handle frame structure  204 . Collector frame assembly  200  is connected to motor accumulator frame assembly  201  via compact collector duct  360  which is also connected to chipper-shredder enclosure  80  borne by engine casting  205  resting on engine base  334  bearing handle frame structure  204 . Lower reinforcing braces  206  connect compact left and right side support plates  330  and  332  to engine base  334  while upper reinforcing braces  202  join handle frame structure  204  to engine base  334 . Power from engine  146  is transmitted to drive wheels  207  by drive axle  208  borne on engine base  334  by bearings, not shown, and operably connected to the transmission (not shown) in engine base  334 . Adjustable-height wheels  209  are adjustably supported on compact left and right side support plates  330  and  332  by height-adjusting mechanisms  210 ; so that the spacing of flexible rotor blade tips  44  above surface  24  can be adjusted to accommodate varying heights of lawn and thatch above surface  24 . Accumulator  212 , borne on accumulator-support frame  203 , and reduced-height separator  394  are operatively connected to chipper-shredder enclosure  80  as in previous embodiments. 
   The embodiment shown in  FIGS. 19 ,  20 ,  21 ,  22  and  31  comprises twig-breaking-rotor assembly  214 , twig-breaker bar  216 , seal plate  220  and compact upper housing  338  disposed between compact right side support plate  330  and compact left side support plate  332 . Compact collector duct  360  fastened to compact side support plates  330  and  332  may sealingly engage compact upper housing  338 . Compact right and left side support plates  330  and  332  are joined to each other by the ends of compact upper housing  338 , compact collector duct  360 , and twig-breaker bar  216 . Right and left compact side support plates  330  and  332 , seal plate  220 , and compact upper housing  338  constitute compact collector housing  303 . 
   Chipper-shredder exhaust port  90  of chipper-shredder unit  66  is connected to compact transfer duct  392  leading to primary-separation duct  398 , and thence to secondary-separation chamber  402  emptying into accumulator  212 . Engine drive belt  450  passes around a pulley (not shown) on the engine camshaft (not shown), adjustable idler pulley  215 , and around countershaft-input pulley  217  mounted on countershaft  218 . Rotor drive belt  348  passes around countershaft drive pulley  354  mounted on countershaft  218 , around rotor pulley  346 , and under rotor-actuator idler pulley  350 . Pulling rotor-actuator handle  222  tightens rotor-actuator cable  224 , which pivots lever arm  352  about fulcrum  353 , pressing rotor-actuator idler pulley  350  onto rotor drive belt  348  and thereby tightening rotor drive belt  348 . Inspection cover  226  closes an opening (not shown) in the front of compact collector duct  360  which can be used for clearing clogs if encountered. Adjustable-height wheels  209  (also illustrated in  FIGS. 32 and 33 ) are supported on sliding support blocks  211  connected to threaded adjustment rods  228  which pass through threaded frame blocks  213 . Adjustable-height wheels  209  can be moved up and down by turning threaded adjustment rods  228 , thereby adjusting the height of twig-breaking-rotor assembly  214  above surface  24 . A shredding rotor (not shown but similar to that illustrated in  FIGS. 5-7 ) inside chipper-shredder enclosure  80  is mounted on the drive shaft (not shown) of engine  146 . 
     FIGS. 21 and 22  present more-detailed views of twig-breaking-rotor assembly  214 , and twig-breaker bar  216 . Twig-breaker-rotor body  234  may be formed from any sufficiently rigid structure such as a length of pipe fastened or welded to twig-breaker-rotor shaft  236  and revolving therewith. Fastened to the surface of twig-breaker-rotor body  234  are twig-breaker sweeps  238  fabricated from any suitably rigid material such as heavy-gauge sheet metal having crenels  240  formed therein. Preferably crenels  240  will be about 1½″ wide and 1⅜″ deep on 5-inch centers, leaving merlons  242  about 3½-inch in length between crenels  240 . Crenels may be defined either by a combination of long and short (measured in the radial direction) impellers/sweeps or by absence and presence of impellers/sweeps, with short or absent impellers/sweeps corresponding to crenels. To modify the performance of the twig-breaking-rotor assembly  214  for the variety of conditions that may be encountered, twig-breaker sweeps  238  may be fitted with either flexible rotor blade tips  44  or optional raking tips  144  as illustrated in  FIG. 12 . Raking tips  144  are well adapted for raking a lawn and for removing thatch from a lawn. Raking tips  144  may be made from a stiff but yieldable sheet material, such as for example, polycarbonate or other plastic sheet material about 1/16″ thick, or from spring-steel sheet material about 3/64″ thick. Flexible rotor blade tips  44 , such as might be made from multi-layer rubberized fabric material about 0.2″ thick (as used for conveyor belts), are gentler in treatment of the surface from which debris is to be removed. Stripping slot  372  may be provided in compact upper housing  338  as a means of admitting countercurrent inflow of air. It has been found that airflow countercurrent to the direction of rotation of twig-breaking-rotor assembly  214  may reduce the amount of debris carried around the axis of twig-breaking-rotor assembly  214  and propelled forwardly of compact collector  322  by either flexible rotor blade tips  44  or raking tips  144 . Variable flow-adjusting plate  241 , movable forward and rearward, may be provided as a means of regulating the amount of air inflow. Variable flow-adjusting plate  241 , shown in rearward closed position in  FIG. 21 , may be moved frontward to admit counter-current inflow of air. 
   Rotor-occluded volume (ROV)  239  is defined as a cylinder swept amongst the twig-breaker sweeps  238  (impellers) having a length generally equal to the axial length of twig-breaker-rotor body  234 . Twig-breaker bar  216 , formed from a length of metal angle or other sufficiently rigid material, is attached at one end to compact right side support plate  330  and at the other to compact left side support plate  332 . Twig-arrestor elements  244  made from rigid material such as threaded rod or cut-off bolts are fastened to twig-breaker bar  216  and are aligned with and protrude into crenels  240  of rotatably moving twig-breaker sweeps  238 , twig-arrestor elements  244  preferably being of sufficient length that the bottoms  243  of crenels  240  pass in close proximity to the tips of twig-arrestor elements  244 . In operation therefore, as twig-breaking-rotor assembly  214  turns, twigs carried by merlons  242  defined by twig-breaker sweeps  238  on twig-breaker-rotor body  234  encounter twig-arrestor elements  244  and are broken or sheared by combined action of merlons  242  and twig-arrestor elements  244 . Accordingly, it can be appreciated that by virtue of twig-arrestor elements  244  protruding into ROV  239 , twigs carried by twig-breaker sweeps  238  will engage twig-arrestor elements  244  and be urged against twig-arrestor elements  244  and be comminuted into twig fragments as result of breaking action created between any relevant twig-arrestor elements  244  and two circumjacent crenel edges  246 . Multiple twig-breaker sweeps  238  present on twig-breaker-rotor body  234  define crenel furrows  245  in  FIG. 34  consisting of circumferentially aligned (as hereinafter defined) sequential crenels  240  disposed around turning twig-breaker-rotor body  234  and coinciding with twig-arrestor elements  244 . Alternatively, at least one crenel edge  246  passes at least one twig-arrestor element  244  in shearing proximity, causing a shearing break of the twigs borne by twig-breaker sweep  238 . Twig-breaker sweeps  238  are preferably sized to engage twigs found in deep yard debris  26  to be collected, bring them into rotor cavity  247 , carry them about the axis of twig-breaking-rotor assembly  214 , and present them to twig-arrestor elements  244 , causing the twigs to be fractured as twig-breaker sweeps  238  rotate past twig-arrestor elements  244 , leaving twig fragments which are suitably sized to pass through compact collector duct  360  to chipper-shredder enclosure  80  without clogging. If constructed of the preferred materials and powered by a 10 HP engine, compact collector  322  is capable of collecting and shredding not only leaves and twigs, but also other lawn debris such as pine needles, pinecones, sweet gum balls, hickory nuts, acorns, nutshells, and even aluminum beverage cans. While the invention is herein illustrated with generally axially aligned twig-breaker sweeps  238 ; other-shaped rigid twig-breaker impeller elements such as rods, studs, blocks, plates and other forms may be fastened to the surface of twig-breaker-rotor body  234 , and other spacings and arrangements of impeller elements such as spirals, “V” shapes, etc. can be used as well, so long as a crenel furrow  245  is “circumferentially aligned” so that crenels  240  span a plane perpendicular to the axis of rotation of twig-breaking-rotor assembly  214  coinciding with each twig-arrestor element  244 . Similarly, while a hook-like shape is herein illustrated for each twig-arrestor element  244  protruding into ROV  239  and circumferentially aligned crenel furrows  245 , other twig-breaker arrestor shapes such as studs, rods, plates and blocks are also suitable. 
   For one embodiment of compact collector  322  illustrated in  FIGS. 19 and 20  suitable for residential and light commercial applications, the width between compact side support plates  330  and  332  can be about 26 inches, with an airflow rate through the machine of about 865 CFM and twig-breaking-rotor assembly  214  turning at about 400 rpm, which with a 4-inch-radius rotor, achieves an impeller tip velocity of about 9.5 mph. As twig-breaking-rotor assembly  214  approaches layer or pile of leaves  26 , impeller velocities of this order are quite effective in agitating the leaves, dispersing them in incoming flows of air generally indicated at  68 , and impelling them toward compact collector-duct entrance  436 . 
     FIG. 23  illustrates an embodiment having a compact brush collector  248 . Rotary brush  250  is mounted rearwardly of compact collector-duct entrance  436  and is partially encompassed by brush housing  252 . Strip brushes  254  attached to brush shaft  256  rotate under power from belt and pulley means not shown. Compact right and left side support plates  330 ,  332  and cavity roof  258  bound frontally open cavity  260  forward of rotary brush  250 . Cavity roof  258  constrains the flow path of incoming air, resulting in flows of air generally indicated at  68  generally parallel to surface  24 . Divider vane  262 , formed at the junction of brush housing  252  and trailing surface of compact collector duct  360 , separates brush cavity  263  from the airflow space in compact collector duct  360 . In operation, as compact brush collector  248  moves forward with compact collector  322 , debris  26  from surface  24  is swept toward compact collector-duct entrance  436  by clockwise rotating rotary brush  250 . 
     FIG. 24  illustrates an augmented embodiment of the invention pictured in  FIG. 23 , in which twig-breaking-rotor assembly  214  comparable to one in  FIGS. 21 and 22  is mounted forward of compact collector-duct entrance  436 , and twig-breaker bar  216  is mounted rearward of twig-breaking-rotor assembly  214 . As twig-breaking-rotor assembly  214  turns counterclockwise and rotary brush  250  turns clockwise, both rotors sweep debris toward compact collector-duct entrance  436 . Twig-breaking-rotor assembly  214  reduces twigs that would tend to cause clogging of compact collector duct  360 , and rotary brush  250  sweeps residual debris from surface  24 . 
     FIG. 25  illustrates a reduced-height separator  394 . Reference numbers for this embodiment are derived by adding 300 to the related reference numbers in  FIGS. 8 and 9 . Primary-separation duct  398 , comparable in function to primary separation duct  98  which was disposed above secondary separation chamber  102  in the embodiment shown in  FIG. 9 , is reconfigured to partially encompass secondary-separation chamber  402  horizontally, rather than being displaced vertically above it. In the reduced-height embodiment, entrained debris flowing from primary-separation duct  398  enters secondary-separation chamber  402  through transfer opening  408  in chamber perimetral wall  412 , instead of through upper bulkhead or roof  421  as in  FIGS. 1 ,  2 ,  8 , and  9 . As shown in  FIG. 39 , outer duct perimetral wall  400  of primary-separation duct  398  approaches chamber perimetral wall  412  of secondary-separation chamber  402  at an acute angle, and preferably is tangent to chamber perimetral wall  412  at the line of contact. Likewise, inner duct wall  401  of primary-separation duct  398  also approaches chamber perimetral wall  412  at an acute angle, and preferably is tangent to chamber perimetral wall  412  at the line of contact. This reconfiguration into a generally horizontal configuration of primary-separation duct  398  at generally the same level as secondary-separation chamber  402  reduces the height of separator  394  and permits the operator improved forward view to the front of the apparatus. 
   Advantageously, outer duct perimetral wall  400  of primary-separation duct  398  of reduced-height separator  394 , as well as chamber perimetral wall  412  of secondary-separation chamber  402 , are both inclined inwardly and upwardly about 12° from the vertical. These inclined walls exert downward force on the air-stream entraining the lawn-debris solids, directing the stream of solids-enriched air to flow toward accumulator  212  below baffle  416 . In operation, when constructed in accordance with the parameters preferred herein, after the incoming stream of solids has traveled about 360° around the perimeter of secondary-separation chamber  402 , the solids-enriched stream has generally passed below the edge of baffle  416 . 
   With primary-separation duct  398  partially encompassing secondary-separation chamber  402  generally horizontally and having inclined perimetral walls, reduced-height separator  394  achieves very good separation of lawn debris from the air stream. Furthermore, the inclined-sidewall construction of secondary-separation chamber  402  facilitates manufacture of said chamber, as a thermoformed or molded piece with tapered sidewalls releases readily from a mold. 
   In operation, even though the chipper shredder provides a significant reduction in volume of the yard waste collected, the volume of yard waste collected is generally so large that frequent trips to a collection point will be required, such as for example to street side for municipal collection or to a compost heap. The effort involved in removing the accumulator, transporting the contents of the accumulator to the collection point and reattaching the accumulator can be a significant part of the effort involved in the cleanup.  FIGS. 25 ,  26  and  27  illustrate an improved mechanism for engagement of upwardly opening detachable accumulator  212  with reduced-height separator  394 , allowing accumulator  212  to be easily removed from and easily replaced on reduced-height separator  394  when dumping the contents. Surrounding the top of accumulator  212  is a rectilinear perimetral frame constructed of four rigid angles  264 , which may be integrally molded in the plastic with accumulator  212  or may be a separate fitting made of metal such as aluminum or steel. Horizontal portions (tongue rails)  265  of these rigid angles  264  slip into flared receiver grooves  266  in accumulator-support side bars  268 , thus forming a slidable tongue-and-groove arrangement. Horizontal portions  265  thereby define “tongue rails.” Accumulator-support side bars  268  may be supported by handle frame structure  204  or may be fastened to the underside of reduced-height separator  394  or may be formed integrally therewith, wherein reduced-height separator  394  may be supported by handle frame structure  204  having control handle structure  336  located behind reduced-height separator  394 . Accumulator-support side bars  268  may be made from any sufficiently rigid material, preferably a material with low-to-moderate coefficient of friction permitting low-effort sliding of tongue rails  265  in flared receiver grooves  266 . To connect accumulator  212  to reduced-height separator  394  for operation, leading edges  283  of tongue rails  265  are aligned with flared receiver grooves  266  on each side of accumulator-support frame  203 , and as accumulator  212  is pushed forward, tongue rails  265  slide into flared receiver grooves  266  directing accumulator  212  into position. Concurrently, seal bar  270  fastened to the top of rear frame angle  272  moves forward until it engages accumulator-support rear bar  273 . Similarly as shown in  FIG. 27 , upon closure leading edge  283  of front angle  274  presses against front groove  275  in accumulator-support front bar  277 . Thus, accumulator top frame  276  is in close contact with accumulator support bars  268 ,  273 ,  277  around its full perimeter, effectively sealing accumulator  212  with reduced-height separator  394  and reducing air and dust leakage from accumulator  212 , which in operation may sustain an operating pressure of about 3 to 5 inches of water. Clamp handle  278  is pivotably mounted on reduced-height separator  394  and is pivotably joined to one end of pivotably mounted linking bar  279  intermediate its length. The other end of linking bar  279  is pivotably joined to “L”-shaped presser bar  280  bearing clamp foot  281  at one end, the other end of “L”-shaped presser bar  280  being pivotably joined to reduced-height separator  394 . As accumulator  212  comes into close proximity with its operating position under reduced-height separator  394 , to urge it into its final sealing position, clamp handle  278  is rotated counter-clockwise forcing linking bar  279  to move downwardly while rotating counterclockwise causing “L”-shaped presser bar  280  to pivot counter-clockwise and thereby pressing clamp foot  281  against seal bar  270  urging accumulator  212  into position. Since this linkage can have considerable mechanical advantage, positioning of accumulator  212  is greatly facilitated, and accumulator  212  is retained securely during operation. 
   Similarly during operation, accumulator  212  can be quickly removed for dumping. With one motion, the operator opens clamp handle  278 , reversing the actions above and releasing accumulator  212 . With a second motion, the operator may pull accumulator-maneuvering handle  282  rearward, sliding tongue rails  265  out of flared receiver grooves  266 . To facilitate dumping of accumulator  212 , auxiliary handles  284  may be fitted generally opposed to each other as illustrated in  FIG. 27 , one on the rear of accumulator  212 , the other on the front. Alternatively, auxiliary handles  284  may be fitted on the sides or bottom of accumulator  212 . Accordingly, dumping accumulator  212  is simple, as the operator simply turns accumulator  212  upside down and lifts it away from the accumulated debris contained therein using auxiliary handles  284 . As mentioned, replacing accumulator  212  on reduced-height separator  394  is also simple and quickly accomplished, greatly easing the entire process of removing, emptying and replacing accumulator  212  as compared to the cumbersome and time-consuming procedures required with bags and zippers utilized on current commercially available machines, and while greatly alleviating the amount of dust dispersed during the dumping process. 
   To further ease the process of replacing the accumulator, flared receiver grooves  266  may have downwardly flaring mouths  285  at their rearwardmost extension, as illustrated in  FIG. 26 , to facilitate entry of the leading edges  283  of rigid angles  264  into flared receiver grooves  266  to enable the operator to simply push the empty accumulator  212  forward and into place under reduced-height separator  394 . Ideally the extent of the downward flare  285  will make it possible for the operator to urge accumulator  212  home without lifting as in  FIG. 35 . 
   In still another embodiment as illustrated in  FIG. 36 , accumulator-support frame  203  comprised of accumulator-support side bars  268 , accumulator support rear bar  273 , and accumulator-support front bar  277 , is pivotably mounted on reduced-height separator  394  at forwardly located hinges  267 . Flared receiver grooves  266  are formed in accumulator-support frame  203  to receive tongue rails  265  on accumulator  212 . Latch  269  is mounted on reduced-height separator  394  and, as illustrated in  FIG. 36 , is rotatable from a clockwise retaining position to a counterclockwise separation position in which accumulator-support frame  203  may be pivoted downward and tongue rail  265  on accumulator  212  may be slid rearwardly out of flared receiver groove  266  to allow transport of yard waste in accumulator  212  independently of the remainder of compact collector  322 , as for example in transport to the curb. When latch  269  is rotated from the clockwise retaining position to the counterclockwise separation position, retaining ledge  271  formed on latch  269  is moved out of engagement with accumulator-support rear bar  273  and/or rear frame angle  272  of accumulator top frame  276 , allowing accumulator-support frame  203  to pivot downwardly (clockwise) so that accumulator  212  may be removed as tongue rails  265  on accumulator  212  slide rearwardly out of flared receiver grooves  266 . Accumulator wheels  286  move rearward and downward to surface  24  and support the weight of accumulator  212 . After emptying, accumulator  212  is remounted by introducing leading edge  283  of tongue rails  265  into flared receiver grooves  266 , sliding accumulator  212  frontward, and pivoting accumulator-support frame  203  upwardly (counterclockwise) so that retaining ledge  271  may be moved under the rearmost portion of accumulator-support frame  203  and/or rear frame angle  272  as latch  269  is rotated clockwise, thereby retaining accumulator  212  in position for continued operation. Additionally, if desired, open bag (shown in phantom lines)  219  may be deployed within accumulator  212  in order to receive and retain debris  124  directly in bag  219 . 
   On a machine sized for residential or light commercial usage, cylindrical hopper ( 114 ) illustrated in  FIG. 9  might have a height of 22 inches and an average inside diameter of 22.6 inches with a capacity of about 38 gallons, requiring very frequent dumping. To reduce dumping frequency, higher capacity is desirable. However, gaining capacity by increasing the hopper height would diminish the operator&#39;s forward view. A marked increase in capacity can be obtained by making accumulator  212  in a generally polyhedral or hexahedral shape and by using only slightly larger dimensions as in  FIGS. 19 ,  20  and  27 . If polyhedral accumulator  212  is 24 inches wide, 24 inches front to back, and 24 inches high, with a 4.25×3.75×24-inch wedge eliminated from the lower front corner to achieve clearance for drive wheels  207 , a capacity of about 59 gallons can be obtained. Thus, changing from the barrel shape of  FIGS. 1 and 2  to the generally hexahedral (or technically, heptahedral) shape of  FIGS. 19 ,  20 , and  27  increased the capacity by about 55%, with little increase in the gross utilized volume. This gain in capacity was achieved without increasing either the width or length of compact collector  322 . Largely because of the reduced height achieved with reconfigured primary-separation duct  398 , operators perceived the overall machine as being significantly smaller and more compact than the earlier embodiment. 
   In operation, the importance of increased accumulator volume becomes readily apparent. If sized as suggested, polyhedral accumulator  212  may hold about 20 pounds of shredded leaves per batch. For an 8,000-square-foot yard receiving about 1000 pounds of leaves per year, about 78 trips to the curb would be required with barrel-shaped hopper  114 , but only about 50 with polyhedral accumulator  212 . 
   To further facilitate transport to the curb or other collection point, accumulator wheels  286  and accumulator-maneuvering handle  282  may be provided on accumulator  212 , as illustrated in  FIG. 27 . Adjustable legs  288  may be added to the end of accumulator  212  opposite accumulator wheels  286  for instances when the operator might want to use accumulator  212  for other transporting purposes. Addition of accumulator wheels  286  and accumulator-maneuvering handle  282  to accumulator  212  greatly eases dumping of the contents. The operator simply separates accumulator  212  from compact collector  322  and rolls it to the dumping area, and then rolls empty accumulator  212  back to compact collector  322 . 
   Damper  312  may be provided in compact transfer duct  392  as illustrated in  FIG. 20  to facilitate removing accumulator  212  from compact collector  322  without either stopping rotation of engine  146  on which chipper-shredder unit  66  is mounted, or causing debris to be blown from accumulator  212  by air currents coming from chipper-shredder unit  66  through reduced-height separator  394 . Damper  312  is disposed within compact transfer duct  392  and is fastened to pivotable shaft  313  extending through opposing duct walls  314  of compact transfer duct  392 . Exteriorly of compact transfer duct  392 , one end of damper lever arm  315  is fastened to one end of pivotable shaft  313 , while an axially spring-loaded latch pin  316  is mounted on opposing end of damper lever arm  315 . Open-position detent  317  and closed-position detent  318  are provided in duct wall  314  of compact transfer duct  392  for engagement by spring-loaded latch pin  316  mounted on damper lever arm  315 . In order to alleviate debris buildup on pivotable shaft  313  and damper  312  while damper  312  is pivoted clockwise in open position  319 , pivotable shaft  313  may be rotatably supported preferably adjacent concave wall  320  of curvilinear compact transfer duct  392 . Damper  312  is adapted to restrict airflow through compact transfer duct  392  upon pivoting damper lever arm  315  counterclockwise into closed position  321 . Before removing accumulator  212  from compact collector  322  for dumping, engine  146  may be slowed to idle speed, spring-loaded latch pin  316  is pulled outward in order to release spring-loaded latch pin  316  from engagement with open-position detent  317 , damper lever arm  315  is rotated counterclockwise to closed position  321 , spring-loaded latch pin  316  is released and engages closed-position detent  318 , securing damper  312  in closed position  321 . Upon replacement of accumulator  212  on compact collector  322 , the reverse steps are followed to rotate damper  312  clockwise to open position  319  in order to resume operating airflow. Use of the damper thus allows repetitive removal and replacement of accumulator  212  from/on compact collector  322  without stopping and restarting engine  146  each time. Alternatively, a sliding-gate closure device (such as that pictured at  323  in  FIG. 20A  and well-known for adjusting flow rates in air ducts) or other duct-closure device may be used for similar effect. 
   Advantageously, accumulator walls  290  may be made at least partially from a transparent substance such as polycarbonate; enabling the operator to see when accumulator  212  is getting full and will need to be dumped. Alternatively, one or more transparent panel(s) may be placed in otherwise translucent or opaque accumulator wall(s)  290 , affording visible inspection of fill depth. 
   Compact collector  322  offers advantages over the earlier embodiment of  FIGS. 1 and 2  in being smaller, simpler, and less costly to manufacture. Countershaft  218  and pulleys  354  and  217  provide an appropriate speed of about 400 rpm for twig-breaking-rotor assembly  214  without using an expensive reducing-angle drive. Compact collector duct  360  can be rugged enough to support the weight of twig-breaking-rotor assembly  214 , greatly simplifying construction and reducing usage of metal, thereby alleviating the need for the cost and weight of a separate fabricated frame. A 4-inch-radius twig-breaking-rotor assembly  214  can be smaller, less visually obtrusive, lighter-weight, and easier to maneuver than the 7.5-inch-radius collector rotor  128  illustrated in  FIG. 10 , yet perform very well in collecting deep piles of leaves. Reduced-height separator  394  illustrated in  FIG. 25  having primary-separation duct  398  partially encompassing secondary-separation chamber  402  horizontally along with inclined chamber perimetral wall  412 , may be less costly to manufacture than the bi-level configuration illustrated in  FIGS. 1 and 2 . 
   Severe-service rotor  292  illustrated in  FIGS. 28 and 29  is a modification of collector rotor  128  in the embodiment shown in  FIGS. 1 and 2  and may be adapted for improved ruggedness in applications involving encounters with hard objects such as large stones, curbs and walks. Severe-service rotor  292  is constructed having the configuration shown, with pivotable flails  293  made from metal or other durable material and which may have “T” cross-sections as shown in  FIG. 30 . In  FIG. 29 , pivotable flails  293  are pivotably supported on flail-pivot shaft  294 , which is mounted on twig-breaker-rotor body  234  by shaft-retaining brackets  295 . Each individual pivotable flail  293  may comprise flail bushing  296  encompassing flail-pivot shaft  294  permitting free pivoting of flail  293  while reducing side-to-side movement of flail tips  297  that could permit flail backing plates  298  of adjacent pivotable flails  293  to interfere with each other. Flails without flail backing plates  298  can be used. However, it is preferred to use flails having flail backing plates  298  or other means to restrict free flow of air between adjacent flails, thereby directing air flow under severe-service rotor  292  to more effectively engage and entrain debris  26  encountered on surface  24 . In operation, pivotable flails  293  operate as swing hammers and reduce airflow through rotor-occluded volume (ROV) generally indicated at  239  of the turning severe-service rotor  292 , thereby providing thatch-removal action and enhancing the collection of debris. 
   In  FIG. 28 , severe-service rotor  292  is fitted with two sets of pivotable flails  293  and two sets of twig-breaker sweeps  238 . Such a rotor is well adapted for raking debris and removing thatch when many twigs are present. Alternatively, for removal of thatch along with debris when few twigs are present, a severe service rotor can be made with only pivotable flails  293 , omitting both twig-breaker sweeps  238  and also twig-breaker bar  216 . Similarly, a machine whose primary purpose is dethatching, i.e., to lift, remove, and accumulate thatch, can optionally employ pivotable flails  293  to the exclusion of twig-breaker sweeps  238  and twig-breaker bar  216 , or any convenient combination thereof may be employed, with a preponderance of flails being preferred. Alternatively, coil-connected dethatching/raking tines can be used as dethatching and/or raking members mounted on severe-service rotor  292 . Examples of coil-connected dethatching/raking tines are illustrated in U.S. Pat. No. 3,564,823 (FIGS. 3-5 and 7-8), U.S. Pat. No. 3,545,187 (FIGS. 1-3), U.S. Pat. No. 3,512,345 (FIGS. 1-3), and U.S. Pat. No. 2,989,833 (FIGS. 6-7), and are incorporated herein by reference. A machine fitted with a severe-service rotor, a blower, a separator, and an accumulator provides greatly enhanced collection, separation and accumulation capabilities as compared to currently available dethatching machines without a blower assist. 
   In another embodiment, the function of twig-breaker sweeps  238  can be achieved with flails of sufficient mass such that the flails engage twigs found in deep yard debris  26 , bring them into rotor cavity  247 , carry them past the axis of severe-service rotor  292 , and present them to twig-arrestor elements  244 ; as pivotable flails  293  pass twig-arrestor elements  244 , the twigs are fractured and suitably sized to pass through compact collector duct  360  to chipper-shredder enclosure  80 . 
   In many communities, ordinances or other regulations have been enacted restricting use of so-called “leaf blowers,” at least partially out of concern that these devices disperse large amounts of fine particulates into the atmosphere. To alleviate possible entrainment of microscopic particles, the embodiment of the machine of the present invention shown in  FIG. 31  is fitted with air-recycle duct  300  having diffuser  301  fitted thereto for directing exhaust air discharged from separator exit  423  toward surface  24  forward of compact twig-breaking-rotor assembly  214 , where the suction provided by chipper-shredder unit  66  entrains lawn debris and transports it into compact collector-duct entrance  436 . By directing exhaust air discharged from separator exit  423  against surface  24  just forward of compact twig-breaking-rotor assembly  214 , that is, to a location proximate the compact collector-duct entrance  436 , suspension of microscopic particles in the atmosphere (such as might occur if air discharged from reduced-height separator  394  simply were dispersed upward into the atmosphere) can be alleviated. 
   In some cases, peripheral inflow of air around the sides and rear of compact collector housing  303  might interfere with recycle of the gas stream discharged from air-recycle duct  300  by displacing recycle air and limiting the amount of recycle air that would otherwise enter compact collector housing  303  and compact collector duct  360 . To ameliorate this problem, flexible seal strips  302  illustrated in  FIG. 37  may be attached to seal plate  220  and/or twig-breaker bar  216  and to compact side support plates  330  and  332  of compact collector housing  303  to restrict or reduce peripheral inflow of air into compact collector duct  360 . In  FIG. 23  similar flexible seal strips  302  may be attached to brush housing  252  and compact side support plates  330  and  332  in order to restrict peripheral inflow of air into this embodiment of compact collector housing  303 . 
   Reduced-height separator  394  illustrated in  FIG. 25  is well suited for use on debris-collecting trucks  305  and trailers used to collect yard debris in many municipalities. As partially illustrated in  FIG. 38 , current trucks (and trailers not shown) used for this purpose typically have large debris-collecting vacuum hoses  306  connected to large blower fans  307  which impel the collected debris through ducts and/or hoses  308  to an accumulation chamber  309  having an opening covered with a primitive filter  310  such as an expanded-metal screen. In operation, large debris-collecting vacuum hose  306  is suspended above pile of lawn debris  26  to be collected so that air rushing into vacuum hose  306  entrains debris  26 , transports it to large blower fan  307 , and carries it through subsequent duct or hose  308  into accumulation chamber  309  with the air passing upward through filter  310 , typically resulting in a cloud of shredded debris passing through filter  310  into the atmosphere or onto the street and near-by or passing vehicles. In many cases, municipalities will incur significant additional expense dispatching street sweepers to collect the scattered debris after the debris-collecting trucks and trailers pass. In contrast, use of separator  394  of the present invention on a truck or trailer, either in conjunction with chipper-shredder unit  66  or without, can largely alleviate scattering of debris. The air-entrained debris is directed through large duct or hose  308  mounted on debris-collecting truck  305  or trailer, thence through separator  394  into accumulation chamber  309 , such that, as described previously, solids-enriched outer layer generally indicated at  406  passes around baffle  416  and into accumulation chamber  309 , while the solids-depleted inner layer generally indicated at  405  passes out separator exit  423  and into the atmosphere, thereby greatly alleviating the fine particulates otherwise discharged. Separator  394  separates even relatively fine debris from the entraining air stream, allowing the reduced debris  407  to be retained in accumulation chamber  309 , while solids-depleted air  405  exhausted to the atmosphere will exhibit greatly reduced concentration of particulate matter as compared to present practices employing relatively gross mechanical filters. To alleviate passage of debris through filter  310  in this embodiment, filter  310  may be replaced by or augmented with a generally impermeable enclosing material or with a permeable enclosing material having pores sufficiently small that fine particulates are generally retained in accumulation chamber  309 . While this embodiment is illustrated and discussed with large trucks and/or trailers used by municipalities, the invention is equally applicable to lighter-weight trucks, such as pickups, and smaller trailers, such as utility trailers, normally purchased for home and farm use. 
     FIGS. 40-43  illustrate an improved high-throughput collector version  522  of the present invention, providing greatly improved throughput rate and greater capacity to engage and process deep yard debris. This high-throughput collector operates in a substantially similar fashion as the previously described versions, but has increased accessibility to exceedingly deep yard debris. As shown in  FIGS. 41-43 , the forward edges  526  of right support plate  530  and left support plate  532  closely conform to the effective radius  534  of collector rotor  528  defined by the sweep of rotor blades  542  on rotation of collector rotor  528 , the forwardly portion of right support plate  530  and left support plate  532  preferably extending less than one inch beyond the effective radius of collector rotor  528 , at least in those portions thereof forward of and below rotor shaft  540 . Preferably, adjustable-height wheels  509  mounted on height-adjusting mechanism  510  are located rearwardly of collector rotor  528  and are disposed between right support plate  530  and left support plate  532  behind collector rotor  528 . Alternatively, caster wheels may be used for ease of maneuvering the collector. With the forward edges  526  closely conforming to the effective radius  534  of collector rotor  528 , and with adjustable-height wheels  509  disposed rearward of collector rotor  528 , high-throughput collector  522  generally affects only those portions of yard debris immediately forward of collector rotor  528 , thereby creating a deep corridor of debris  536  through which high-throughput collector  522  passes. 
   As illustrated in  FIGS. 41 and 42 , upper housing  538  is pivotably mounted between right support plate  530  and left support plate, with lower housing surface  539  of upper housing  538  generally conforming to the effective radius  534  of collector rotor  528  when in the lowered position illustrated in  FIG. 41 , but allowing collector rotor  528  to fully engage deep yard debris  26  having a depth exceeding the diameter of collector rotor  528  when pivoted upwardly as illustrated in  FIG. 42 . When upper housing  538  is rotated upwardly, it appears that increased airflow is provided to collector duct  560  passing above collector rotor  528 , as well as passing below the collector rotor. In this fashion, improved high-throughput collector  522  is adapted to engage and entrain extremely deep piles of leaves  26  in the air stream induced in collector duct  560  upon actuation of chipper shredder unit  580 . With upper housing  538  pivoted upward, and with the increased airflow, high-throughput collector  522  rapidly engages deep piles of leaves, dispersing the aggregated leaf pile into single leaves and small clumps of leaves that are readily entrained in the high-volume air flow. 
   In  FIGS. 44 and 45 , twig-breaker sweeps  238  are mounted upon twig-breaker-rotor body  234  and pass between twig-arrestor elements  244  in  FIG. 41  upon rotation of collector rotor  528 . Polymeric dethatching spikes  545  having enlarged retention heads  546  pass through apertures  547  in L-shaped perforate mounting plate  548  secured to twig-breaker sweeps  238  by retention bolt  550 . Preferably, dethatching spikes  545  will have stiffness comparable to trimmer cord used in flexible line trimmers. Suitable dethatching spikes  545  will have a diameter of approximately 0.155 inches and a length of approximately 2 inches. In use, adjustable-height wheels  509  will be adjusted for dethatching, such that when high-throughput collector  522  is disposed upon a flat hard surface such as a concrete driveway or sidewalk, dethatching spikes  545  will touch the hard surface but pass over it without substantial deflection. As described hereinafter in Example 18, polymeric dethatching spikes  545  are extremely effective in removing thatch and are quite durable for extensive use. 
     FIGS. 46 and 47  illustrate alternative raking elements  552  constructed from either spring steel or suitably resilient polymer having body portion  554  with mounting slots  556  formed along upper edge  557  thereof and flexible raking teeth  558  adjoining body portion  554 . For ease in mounting and installation, alternative raking elements  552  will be adapted such that body portion  554  may be disposed generally perpendicular to the radius of collector rotor  528 , while flexible raking teeth  558  will extend in a generally radial direction. In many cases, it will be desirable to form flexible raking teeth  558  with inclined raking tips  559  extending forwardly in the direct of rotation of collector rotor  528 . 
   In cases of aggressive dethatching, particularly in moist conditions when buildup of debris in transfer duct  592  may occur, it may be desirable to provide means of access to the interior of transfer duct  592  to facilitate convenient cleanout. As shown in  FIG. 48 , flanges  584  and  586  have been provided on upper and lower transfer duct sections  588  and  590  respectively. Since upper transfer duct section  588  in  FIG. 40  is removably secured to separator  394 , upon unfastening flanges  584  and  586 , access is provided to the entirety of curved portion  594  of transfer duct  592 , where the tendency for accumulation is greatest; so that compacted wet yard debris may be easily removed from transfer duct  592 . 
   In operation, it has been found that high-throughput collector  522  shown in  FIGS. 40-43  provides such a high throughput rate that even an accumulator  212  having a capacity of 8 cubic feet is filled with finely reduced leaves within a minute of operation. Accordingly, transportation and bagging of collected yard debris is facilitated by use of collection cart  600  illustrated in  FIGS. 49-56 , in which access to collection cart  600  having displaceable sidewall  602  is facilitated by ramps  604  mountable on collection cart  600  and adapted to receive accumulator wheels  286 . Desirably, leading edge  283  of accumulator  212  will have front angle  274  formed thereupon to engage upper periphery  606  of collection cart  600 , allowing accumulator to be pivoted about upper periphery  606  for dumping of the contents  608  of accumulator  212  into collection cart  600  as illustrated in  FIGS. 50 and 51 . To facilitate unloading of collection cart  600 , free edge  610  of flexible liner  612  is releasably secured to opposing sidewall  614  of collection cart  600 , with the remainder of flexible liner  612  extending downwardly along the inside of opposing wall  614 , across bottom  616 , and up displaceable sidewall  602  to upper portion  618  thereof to which it is secured. Preferably the width of flexible liner  612  extends from front wall  620  to rear wall  622  of collection cart  600 . Portions of flexible liner  612  also advantageously extend upward along front wall  620  and rear wall  622 , whereupon plications are formed as illustrated at  615 , or seams are sewn as illustrated at  617  in  FIG. 49 . An alternative variation of overlapping plications is that the flexible liner  612  simply crumples upon itself when lowered into the collection cart  600 . Upon displacement of displaceable sidewall  602  leaving opening  603  as shown in  FIG. 52 , free edge  610  of flexible liner  612  may be released from opposing sidewall  614  of collection cart  600  and drawn toward displaceable sidewall  602  as shown in  FIG. 53  to clear the interior of collection cart  600  in one motion. Flexible plicating liner  612  illustrated in  FIG. 49  is suitably made from any of a variety of flexible sheet-like materials, including woven fabric such as painters&#39; cloth and canvas, ripstop nylon fabric, filament-reinforced film-covered polymeric tarps, polymeric film, and nonwoven tarps such as spunbonded nonwoven fabric. 
   Another variation of flexible liner is illustrated at  612 A in  FIG. 58 , wherein the liner extends from the front wall to the rear wall without extending upward along the front wall or the rear wall. The flexible liner  612 A so illustrated is suitably made from polymeric sheet-like material having sufficient lengthwise flexibility that it folds at the junctions of the displaceable side wall  602  and the opposing sidewall  614  with the bottom  616 , but having sufficient crosswise stiffness that the lateral edges move in close proximity to the front wall  620  and the rear wall  622  upon emptying the collection cart  600 , thereby achieving effective removal of debris from the cart. Examples of polymeric sheet materials suitable for this variation of flexible liner  612 A are extruded polyethylene and polypropylene having thicknesses of about 0.050 inch. 
   As shown in  FIGS. 49-55 ,  57 , and  58 , rod or rib  624  extending generally from front wall  620  to rear wall  622  of collection cart  600  is secured to flexible liner  612  or  612 A adjacent the junction  626  between opposing sidewall  614  and bottom  616  to assist in urging flexible liner  612  or  612 A into position after dumping. Elastic retraction cords  628  are secured to rod  624  inside flexible liner  612  or  612 A adjacent the junction of opposing sidewall  614  and bottom  616 . Elastic retraction cords  628  pass through opposing sidewall  614 , turning blocks  630 , or alternatively as shown in  FIG. 54  pulleys  632 , thence upwardly along the exterior of opposing sidewall  614  and are secured in an upper position  634  so that flexible liner  612  or  612 A may be conveniently returned to position inside collection cart  600  subsequent to removal of the yard waste therefrom. In an alternate arrangement, retraction cords are attached to springs, which are attached at upper position  634 . In still another alternate arrangement, retraction cords pass through pulleys attached at upper position  634 , and then are attached to weights. 
     FIG. 57  illustrates an alternative container construction in which separator  694  is disposed over accumulator  640  having removable sidewall  642  formed therein. Flexible liner  644  is releasably secured to upper periphery  646  of opposing sidewall  648  and extends downwardly along opposing sidewall  648  and across bottom  650  of accumulator  640 , being secured to bottom  650  adjacent junction  652  between opening  654  and bottom  650  of accumulator cart  640 , such that upon removal of displaceable sidewall  642  as shown in  FIG. 57  and release of flexible liner  644  from upper periphery  646  of opposing sidewall  648 , flexible liner  644  may be drawn outwardly toward opening  654  and beyond to facilitate emptying of accumulator  640 . Preferably the width of flexible liner  644  extends from one end wall to other end wall  656  of accumulator  640 ; so that upon removal of displaceable sidewall  642  as shown in  FIG. 57 , free edge  658  of flexible liner  644  may be released from opposing sidewall  648  of accumulator  640  and drawn toward opening  654  to clear the interior of accumulator  640  in one motion. 
   Further in  FIG. 57 , an edge-reinforcing rod  662  is attached to the free edge  658  of the flexible liner  644 . A first portion  665  of a rope  666  is attached to the edge-reinforcing rod  662 , and a second portion  667  of the rope  666  is releasably attached to the end wall  656  of the accumulator  640  via a release clip  668 . Alternatively, the first portion  665  of the rope may be secured to the free edge  658  of the flexible liner  644 . Upon removal of the displaceable sidewall  642  from the opening  654 , the second portion  667  of the rope  666  is freed from the release clip  668  and is used to draw the edge-reinforcing rod  662  and the free edge  658  of the flexible liner  644  toward the opening  654  and beyond, thereby exerting a rolling action on the debris contents  670  and emptying the debris contents from the accumulator  640 . Alternatively to the free-flow separator  694  pictured, the flexible liner  644  will also function effectively with a container having a top-mounted screen separator. Accumulators as herein described with either free-flow separators or screen separators may be used with lawnmowers for collecting grass clippings, leaves, and other lawn waste. As can be seen from the drawings, flexible liner  612 ,  612 A or  644  functions effectively with a displaceable sidewall that is either hinged and pivots outwardly as illustrated in  FIGS. 49 ,  52 ,  53 , or that is removable as illustrated in  FIGS. 57 and 58 . 
     FIG. 56  illustrates an alternative construction in which a plurality of bags  660  may be secured to upper portions of the interior  664  of collection cart  600  for easy filling and removal after filling. 
   Example 1 
   A commercially marketed machine made according to the design shown in U.S. Pat. No. 5,642,864 was used to collect leaves on a lawn and shred them. The machine had an intake opening about 25 inches long and 4 inches wide with the damper at its maximum open position. The opening was inclined forward at about 45 degrees to the ground, giving an effective opening height of about 2.8″. The chamber behind the damper was a solid rectangle in shape and about six inches front to back. A straight rectangular duct led from an opening in one end of the chamber to the center of a chipper-shredder-blower having its axis of rotation perpendicular to the direction of forward movement. The blower discharged into a large bag made of thick cloth and having a mesh-covered opening for venting entraining air. A zipper opening was provided for emptying collected debris. 
   A covering of fresh, dry leaves about three to six inches deep was present on the lawn. In addition, piles of leaves about six to twelve inches thick were also present. The machine was advanced into a pile of leaves, but the front opening pushed the leaves ahead of it instead of drawing the leaves into the opening. The machine was adjusted to raise the front opening to its maximum height, but it still pushed leaves ahead of it. Collection of leaves from the thinnest coverings on the lawn was attempted, but the machine still had a strong tendency to push leaves ahead of it. The damper was disconnected and opened as wide as possible, but still with little improvement in leaf collection. 
   In the belief that the machine performance was limited by low air flow caused by leaf build-up on the mesh opening and resultant flow restriction, the zipper opening was partially opened in the hope of allowing more air flow. Leaf pick-up by the vacuum slot improved somewhat, but was still unsatisfactory. In addition, a stream of leaf fragments blew through the zipper opening, as expected. 
   The conclusion was that the machine might work marginally well with a very thin layer one or two leaves thick, up to perhaps about an inch in depth, but this approach would require using the machine multiple times throughout normal leaf fall. 
   Example 2 
   Following the experience of example 1, collecting leaves with a conventional 26-inch, two-stage snow blower was attempted to see if the auger-feed mechanism would function with leaves. Indeed, the auger readily fed even the deepest piles of leaves into the second-stage blower, which blew them 10-15 feet away. However, this approach left a thin layer of leaves and other debris on the lawn where the pick-up auger had passed. 
   The conclusion was that a machine with a similar auger-feed pick-up would collect even deep piles of leaves. However, the user would need to go over the lawn a second time with a different machine to collect the thin layer of residual leaves and other debris. 
   Example 3 
   A machine of the current invention was built according to the drawings in  FIGS. 1-11 . A Yard Man 5-horsepower chipper-shredder-vacuum machine built by MTD Products was purchased; the chipper-shredder unit and attached drive motor were removed from the purchased machine; and then they were mounted on the base plate of the current machine. The machine width between the left side support plate and the right side support plate was 24.″ The collector rotor diameter was 15″, and it turned 65 revolutions per minute. The front, upper edge of the housing over the rotor was about 13½″ above the support surface. The lowermost portion of the lower collector lip was about 1″ above the supporting surface when measured with the machine sitting on a concrete slab. The collector duct had an entrance opening 2½″ high and 24″ wide with a cross sectional area of 60 square inches, an exit opening about 6″ high and 9″ wide with a cross sectional area of about 54 square inches, and a convergence angle of 76°. The stripping slot was closed. The 5-horsepower engine turned 3450 revolutions per minute. The channel of the primary separation loop measured 4″ wide and 8″ high and ended with a constricted opening 1¾ wide and 8″ high upstream of the downward sloping entrance to the secondary separation chamber. The effective curvature of the loop was about 305°, and the outside radius of curvature was about 10⅝″. The inside diameter of the secondary separation chamber was about 23″. The radial clearance between the perimeter of the baffle and the wall of the secondary chamber was about 1⅜″, and the baffle perimeter was about 7″ below the transfer opening. The exhaust port was 7″ in diameter, and the airflow through the machine was about 540 cubic feet per minute (cfm) (22.5 cfm per inch of machine width). The effective hopper volume (below the baffle) was about 40 gallons. 
   Leaves were spread on a lawn in thicknesses varying from about 2″ to about 10″. The machine was set into operation and advanced through the leaves. Leaf overlayers of all thicknesses were readily collected, and no pushing of leaf piles ahead of the machine occurred. The volume of the leaves was reduced, and the leaf fragments were retained in the hopper. The entraining air exited through the separator exhaust passage, carrying with it only fine dust. Some leaves and debris were left in the wake of the machine, meaning that the machine was proving to be exceptionally effective in removing deep piles of leaves but left some finer debris behind. It appeared that the airflow was not quite great enough to get optimum cleaning. Also, it was observed that when the machine was pulled backward, the cleaning was more thorough, suggesting that the collector rotor should be turning faster. 
   Another observation was that some leaves were remaining with the collector rotor and carrying over the top of the rotor, being impelled onto the grass in front of the machine, or blown by side winds onto part of the lawn which had already been cleaned. 
   Example 4 
   The machine of Example 3 was modified as follows: In order to increase the air flow rate, (1) the engine speed was increased from 3450 to 3680 revolutions per minute; (2) the constriction in the primary separation loop was removed, leaving the channel size throughout the loop at 4″ wide and 8″ high; (3) the transfer opening was enlarged to about 100 square inches; and (4) the separator exhaust port was enlarged from 7″ to 9⅛″ diameter. The airflow rate was then measured at 1000 cubic feet per minute (41.7 cfm per inch of machine width). The collector rotor speed was increased from 65 to 276 revolutions per minute. In order to reduce the number of leaves carried over the top of the turning collector rotor, the stripping slot was opened to 1″. The diameter of the baffle in the separator was reduced, leaving an annular radial clearance of about 2⅜″ between the baffle perimeter and the outside wall of the secondary chamber. The perimeter of the baffle was 5¼″ below the ceiling of the secondary separation chamber. 
   The machine was operated in leaf overlayers of 3″ to 12″ and readily removed the leaves. No leaves and little other debris were left in the path of the machine, and carryover of leaves over the top of the collector rotor was reduced. The separator retained the leaf fragments and exhausted air containing only a small amount of very fine dust, and was judged to operate quite satisfactorily. It was considered remarkable that in the deep piles of leaves the machine could be moved forward into the leaves at a pace and with a concomitant leaf-feed rate that began to overload the shredder, but the collector rotor, collector duct, and separator continued to function well. 
   Example 5 
   In order to achieve more aggressive raking action to lift leaves and other debris from the lawn surface, the continuous but flexible rubberized rotor blade tips  44  were replaced with rake-like teeth shown in  FIG. 12 . To make these teeth, pieces of polycarbonate sheet plastic approximately 6″ wide by 23⅜″ long and 1/16″ thick were sawn with parallel cuts spaced every ½″, sawing from the long edge of the sheet 3″ to the center of the sheet. The saw kerfs were about 1/32″ wide; so that minimal airflow between adjacent teeth would occur. The tips of the “teeth” were bent about 30°. This bending was done with the polycarbonate sheet at room temperature. A strip of raker teeth was bolted to each of the rotor blades such that the teeth extended radially 5/16″ beyond the edges of the seal discs on the ends of the rotor. By adjusting the height of the front-support rollers, the tips of the raker teeth were set about 1/16″ above a flat concrete surface. 
   The machine was then operated on a lawn. The raker teeth readily removed leaves, hickory nuts, shells, dead grass, and even some live grass, especially if the machine was allowed to run in one place very long without moving. The conclusion is that one could adjust the machine to rake as aggressively as desired. 
   Another observation was that carryover of leaves, nuts, etc. over the top of the rotor was increased, perhaps due to the positive rake angle of the teeth. 
   Example 6 
   After seeing leaves carried over the top of the collector rotor and discharged frontward in Example 5, an attempt was made to eliminate this carryover. The existing stripping slot was closed, and a new forward slot was cut in the arcuate housing as shown in  FIG. 13 . The slot was about 1 1/16″ wide and began about 9⅝″ forward of the closed stripping slot, as measured along the arc of the housing cover. Since the remaining continuous housing spanned approximately two thirds of the arc between two adjacent sets of raker teeth, a substantially impervious blade would be in close proximity to the housing two thirds of the time of each revolution of the rotor (Two ninths of the time for each individual blade; two thirds of the time cumulative for the three blades through one rotation). Thus, the blades moving under the housing would prevent significant reverse flow of air from occurring for roughly ⅔ of the time during a rotor revolution. Conversely, reverse flow (from the new slot to the collecting duct) was permitted for about ⅓ of a rotor revolution. Furthermore, the slot was placed such that when one rotor tip (or row of raker teeth) had just passed the new stripper slot and allowed reverse air flow through the slot and into the collector duct, the following rotor tip would be in general proximity to the lower collector lip  70 . Thus, flow through the stripping slot occurred during a phase of the rotor revolution when diminished airflow would have been passing into the collector duct from the supporting surface anyway. The intent of this design was to minimize lost vacuuming effectiveness by trying to maintain as much airflow as possible along the lawn surface and into the collector duct. 
   Unfortunately, this change achieved little reduction in the amount of leaf carryover. 
   Example 7 
   With the machine fan operating, and with the collection rotor stopped in the position shown in  FIG. 13 , a thread on the end of a wire was used as a “tell tale” to detect the directions of air movement in the space between the two blades forming a flow space adjacent to the new stripping slot and the collector duct. The airflow directions are sketched approximately in  FIG. 13 , showing there was a very strong reverse eddy. The presence of this eddy may help explain how there could still be strong carryover of the leaves, as this secondary air flow probably prevented stripping the leaves out of the cavity between the adjacent blades, even with the flat fillets in place. 
   To overcome the leaf carryover in the eddies, convex fillets were substituted for the flat ones, as shown in  FIG. 14 . The outer surfaces of the fillets were about 1½″ radially inward of the tips of the raker teeth and about 1¼″ radially inward of the perimeters of the rotor seal discs. Testing with the “tell tale” showed that the eddy flow had been eliminated, and that all of the detectable localized airflows in the reduced cavity were in the rearward direction—from the new stripping slot and toward the collection-duct entrance. Operation of the machine on a lawn showed that leaf carryover had in fact been greatly reduced. However, there was still some carryover of nuts and shells. 
   Example 8 
   In an attempt to stop the carryover of nuts and shells, raker blades were made having teeth bent with a negative rake angle. The intent was to make sure the positive rake angles of the first raker teeth were not responsible for retaining the nuts on the rotor and enhancing carryover. However, upon operation of the machine on the lawn, carryover of nuts and shells with forward discharge continued. Notably, leaf pickup was not as effective as with the positive rake angle. 
   In the possibility that the carryover was simply a momentum effect, the collector rotor speed was reduced in half—from 276 to 138 rpm (with a rotor peripheral velocity of 433 feet per minute, or 4.9 miles per hour. The carryover of nuts, shells, and other dense debris almost completely stopped. The raker blades with positive rake angle were re-installed, and the carryover was still absent, while virtually complete removal of leaves and other debris from the lawn was achieved. 
   Example 9 
   The bag-holder assembly of a Simplicity riding lawnmower model 12FCH42 was removed, and the hopper and separator were removed from the machine described in Examples 3 and 4. The hopper and separator were set on the back base plate of the Simplicity machine and were connected to the air duct which had been connected to the lawnmower bag-holder assembly. The Simplicity machine had a blower mounted on the right end of the 42-inch mower deck, and the duct transported air, clippings, and leaf debris from the blower to the entrance of the separator inlet duct. The blower delivered 770 cfm of entraining air, and the separator exhaust port was 9⅛″ in diameter. 
   The lawnmower was operated on a lawn having a thin covering of leaves, and the grass had grown about 1½ inch since its previous cutting. The mower blades cut the grass and did some chopping of the leaves, and the blower directed the debris to the separator. The separator performed well, retaining the debris in the hopper and exhausting the air virtually free of debris fragments. 
   Example 10 
   To evaluate the possibility that the machine could also function as a snow blower, the elbow in the transfer duct  92  was disconnected from the separator  94  and directed to one side of the machine. Without making any further changes, the machine was started and advanced into fresh snow about 3 to 4″ deep. The combination rotor and vacuuming action successfully lifted the snow, which passed through the collector duct, into the shredder-blower, and out the discharge (transfer) duct. 
   Example 11 
     FIG. 23  illustrates a compact brush/collector module which can be mounted on the front of a self-propelled chipper-blower unit such as that illustrated in  FIG. 19  to produce a smaller, more compact, and less expensive embodiment of the invention. In this particular example, the engine, mounting platform, self-propelled drive, and rear wheels were adapted from a 10 horsepower DR® LAWN VAC sold by Country Home Products in Vergennes, Vt., and the unit was fitted with a chipper/shredder from a model VCB 258 Mighty Mac® Vacuum-Chipper-Bagger supplied by MacKissic in Parker Ford, Pa. 
   Rearwardly of the collector duct, a brush rotor was fitted with the brush housing as illustrated in  FIG. 23 . The rotor was constructed as a 4-inch-radius brush in which three strip brushes were mounted along a ⅝-inch-diameter shaft. Each strip brush consisted of a metal “U” strip clamped around a wire on which crimped propylene bristles of about 0.030- to 0.045-inch diameter had been looped. Each resulting strip brush had about fifty-two 3⅜-inch and fifty-two 1½-inch bristles per inch. The resulting rotor was similar to the rotary brush used in Precision Pro 26″ Push Sweeper (Model SW 26PUSHD) supplied by Gleason Consumer Products, Milwaukee Wis. When used to clean a lawn surface having a leaf covering between three and six inches deep, the operator found the machine easy to handle and maneuver, leaving a thoroughly cleaned surface. However, in those cases when long twigs mixed with leaves were encountered, the collector duct sometimes plugged. In cases where twigs were especially numerous, the machine could clog as frequently as every few feet. This clogging could be at least partially alleviated by removing most of the larger twigs beforehand, but even this removal still left the machine somewhat susceptible to clogging. In many cases, the number of twigs encountered may be so excessive that it is impractical to remove a sufficient number of twigs to achieve substantially unhindered operation. 
   It had been anticipated that by placing the frontally open cavity ahead of the brush, air rushing into the cavity might have high enough velocity to entrain leaves and impel them into the collector duct, the air flow rate through the machine being over 800 cfm. However, videotape of the machine approaching a tall pile of leaves surprisingly showed that very few leaves were dislodged by the air stream. 
   Example 12 
   The machine of Example 11 was fitted with the new rotor mounted ahead of the collector duct as illustrated in  FIG. 24 . The rotor was constructed from a length of heavy iron pipe to which twig-breaker sweeps were bolted. The sweeps were formed as illustrated in  FIGS. 21 and 22  from sheet metal having crenels 1½ inches wide and 1⅜ inches deep on five-inch centers formed therein leaving 3½-inch merlons between crenels. As illustrated in  FIGS. 21 and 22 , a breaker bar having iron hooks formed from ⅜-inch rods was fastened on the side support plates rearward of the rotor such that the hooks on the breaker bar coincided with the crenels in the twig-breaker sweeps. Accordingly, as the rotor turned, the merlons passed between the hooks creating a breaking or shearing action between each hook and two adjacent edges for shortening the twigs borne by the twig breaker sweeps. In operation, the sweeps on the rotor engaged twigs found in the pile of yard waste to be addressed, brought them into the rotor housing, carried them about the axis of the rotor, and presented them to the hooks so that the twigs fractured and were suitably sized to freely pass through the collector duct to the chipper shredder. 
   In operation, when a nest of about a dozen representative twigs of roughly a quarter inch in diameter by 6 to 15 inches long was laid on a pile of leaves, this embodiment equipped with the twig-breaking rotor, the twig-breaker bar, and the brush advanced easily into the pile of leaves, readily breaking the twigs into short pieces which passed up the collector duct without clogging. When used to address typical yard waste including numerous brittle twigs up to about two feet in length and up to approximately half an inch in diameter, the machine operated quite successfully without clogging, cleaning the overall lawn quite thoroughly. 
   When tested on an area covered with pine needles to a depth of about 4 to 6 inches, the machine was quite effective in removing these needles and shredding them into fragments about half an inch to 3 inches in length, which were easily separated from the air stream by the separator in  FIG. 19 . This achievement is considered particularly significant, as pine needles present a significant challenge to most, if not all, previously known lawn-vacuuming machines. Further, the machine proved quite capable of collecting and shredding pinecones as well as mixtures of twigs, leaves, pinecones, and pine needles. In some cases, particularly with wet flexible leaves, leaves wrapped around the rearward lip of the collector duct, causing partial clogging of the duct and requiring the machine to be advanced more slowly than would otherwise have been desired. 
   Example 13 
   The machine of Example 12 was modified as illustrated in  FIGS. 20 and 21  by removing the brush and providing a steel plate extending from the top edge of the twig-breaker bar to the rearward lip of the collector duct and from the left side support plate to the right side support plate; so that in operation, the flow of air was channeled through the frontal rotor opening, past the twig-breaker bar, and into the collector duct. Surprisingly, it was found that the machine with only a twig-breaker rotor was fully capable of removing leaves even to a depth of 10 inches or more at a forward speed of approximately 7/10 of a mile per hour, cleaning the lawn thoroughly. As before, this embodiment of the invention remained fully capable of gathering and shredding loblolly pinecones up to four inches in length and three inches in diameter, and could even pick up and shred aluminum soft-drink cans. 
   Example 14 
   A compact collector machine was constructed by reconfiguring the separator such that the primary-separation duct  398  wrapped around the separation chamber in a coplanar arrangement as illustrated in  FIGS. 25 and 39 , lowering the overall height of the separator by eight inches and thereby giving the operator an improved forward view. As discussed previously, the perimetral walls of the primary-separation duct and of the separation chamber were inclined upwardly and inwardly by about 12 degrees. The performance of this reduced-height separator was at least fully comparable to that of the larger embodiment. 
   Example 15 
   Height-adjusting wheels were fitted to the side support plates close to the ends of the collector rotor, as shown in  FIGS. 32 and 33 . Turning the threaded rods moved the slide blocks up and down, raising and lowering the attached wheels and permitting incrementally variable adjustment of the collector rotor height above the lawn surface. Height adjustment made it possible to adjust the degree of engagement between the impeller elements and the surface to accommodate varying lawn conditions and tasks. For instance, when the machine was used to rake leaves on a taller, thicker lawn, the collector rotor tips were raised to about two to three inches above ground level. For removing thatch from around the grass shoots, the collector rotor was set low enough for raker teeth mounted on the collector rotor to engage and lift the thatch. While the machine was initially envisioned for raking leaves and other debris, an unexpected benefit was that the machine was quite effective in cleanly lifting thatch, separating it from the entraining air stream, and retaining it in the accumulator. 
   Example 16 
   In operation, the embodiment shown in  FIGS. 1 and 2 , when equipped with raker teeth made as described in Example 5 and configured as illustrated in  FIG. 12 , had a limited service life, particularly when hard objects were encountered. A severe-service rotor is constructed having the configuration shown in  FIGS. 28 and 29 , with pivotable flails made from metal or other extremely durable material and having “T” cross-sections as shown in  FIG. 30 . In operation, the suitable flails operate as swing hammers and reduce airflow through the occluded volume of the turning rotor while providing both collecting and dethatching action. 
   Example 17 
   An air-recycling-duct attachment as illustrated in  FIG. 31  is fitted to the compact collector to direct the exhaust stream from the separator to the collector rotor. By virtue of the recycling action and direction of the exhaust stream groundwardly, there is achieved reduced upward ejection of particulates into the environment. 
   Example 18 
   An apparatus was constructed similar to that shown in  FIGS. 40-43  having side support plates as shown in  FIGS. 41 and 42  with leading-edge radii only about ¼ to ½ inch greater than the swing radii of the flexible rotor blade tips  44 , and the height-adjusting mechanisms  210  and the adjustable-height wheels  209  located in positions rearward of the collector housing seal plate  220  and inboard of the side support plates. The improved apparatus could be advanced into piles of leaves more than twelve inches deep and exhibited improved ability to engage and feed leaves into collector duct  360 . The moving flexible rotor blade tips passed close to the leading edges of the side support plates, and dispersed the leaves which were then drawn into collector duct  360 , forming a clean path through the pile of leaves without disturbing leaves disposed laterally adjacent to the path of the apparatus. In addition, the apparatus having the forward wheels inboard of the side support plates exhibited improved maneuverability around trees, foundations, fences, and other obstacles as are commonly encountered in typical landscaping situations. 
   Example 19 
   An apparatus was constructed having a pivotable upper housing similar to that illustrated in  FIGS. 41 and 42  installed over the rotor assembly, with sufficient pivot friction between the housing side pieces and the side support plates to hold the housing in place once pivoted to the desired position. When used to engage piles of leaves less than about six inches in depth, the housing was placed in the lower position of  FIG. 41 . Leaves, nuts, shells, and other yard debris carried around the rotor past the duct entrance were flung from the rotor tips, striking the inside of the semi-arcuate housing to be deflected forward and downward into the path of the advancing machine. 
   When used to collect very deep piles of leaves, the upper housing was pivoted upward as shown in  FIG. 42 , the leaves being surprising readily collected at depths substantially exceeding the height of the rotor. With an 8″ rotor, piles of leaves having the maximum depth available, about 22″ in depth, were readily collected. 
   On a machine substantially similar to that shown in  FIG. 19 , when the upper housing  338  was removed, it was surprisingly found that machine could then achieve a much faster leaf feed rate in very deep piles of leaves without clogging the collector duct  360 . When a “telltale” as described in Example 7 was held near the collector duct entrance above the rotor, the movement of the string showed that a substantial volume of air flowed over the top of the rotor assembly and rearward into the collector-duct entrance  436  counter to the direction of rotation of the rotor assembly, resulting in increased entrainment of leaves in the resulting air flow while retaining substantial air flow under the rotor assembly along the ground, such that even leaves immediately adjacent the ground were collected and entrained in the flow of air through the duct, along with leaves higher in the pile which also passed under the rotor assembly. 
   Example 20 
   The apparatus of Example 19 was further modified by fastening a seal strip of rubberized-fabric conveyor-belt material to the underside of the twig-breaker bar, as shown at  302  in  FIG. 37 . When operated with this ramp-like seal strip in place to collect nuts, shells, and other relatively dense debris disposed on a flat surface, the lower edge of the seal strip barely touching the flat surface, dense debris was effectively impelled upward and into the collector-duct entrance, leaving the flat surface thoroughly cleaned. Thus, when the machine was used to clean flat surfaces such as concrete driveways, very little debris was left on the surface. 
   Example 21 
   To remove thatch from lawns, sections of raker teeth are formed from resilient material as shown in  FIG. 47  and fitted under the twig-breaker sweeps  238  as shown in  FIG. 46 . The length and thickness of the “teeth” are selected such that the teeth will flex slightly when encountering rigid objects while remaining yielding enough to cause only minimal damage to the live grass, yet stiff enough to be effective in removing the thatch. When such teeth were constructed from 1/16″ polycarbonate, it was demonstrated that such teeth were effective in dethatching with only minimal damage to the live grass, even though some of the teeth broke at the bend line with usage, perhaps due to weakening stress lines resulting from the cold forming method used to shape the angles in the sections. Materials having sufficient durability for this application include thin spring steel and polymeric materials such as polycarbonate formed by methods not unduly weakening the inherent properties of the material. 
   Example 22 
   Alternative sections of raking “spikes” were made as illustrated in  FIGS. 44 and 45 . Sections of aluminum angle having cross sections 1″×1″×⅛″ thick were drilled and countersunk to receive polymeric spikes spaced apart ⅜″ center to center. The two-inch-long spikes were cut from 0.155-inch-diameter MAXI EDGE (WLM-1155) line-trimmer cord supplied by Arnold Corporation, P.O. Box 703, Shelby, Ohio, 44875. The fixed ends of the spikes were heated and pressed into the countersinks to retain the spikes in the aluminum angle during operation. Pieces of the line-trimmer cord were cut to the lengths of the aluminum sections, laid over the melted ends of the spikes, and then melted and formed in a flat ribbon along the length of the aluminum sections and over the melted heads of the spikes. This procedure retained the spikes quite rigidly. The aluminum angles were bolted to the trailing sides of the twig-breaker sweeps. These sections of raking spikes were quite effective in removing thatch from lawns and have proved quite durable. The dethatching aggressiveness of the spikes is adapted by varying the diameter, length, and material of the spikes. During operation, the adjustable-height wheels are raised and lowered to adjust the engagement and aggressiveness of the spikes with the turf. 
   Example 23 
   Surprisingly, it was found that the machine could be used to remove sawdust from a yard with sparse grass. However, the moisture-laden combination of the dense sawdust and topsoil eventually resulted in a buildup in the transfer duct  392  leading from the blower to the separator. To facilitate cleanout, the forward end of the transfer duct and the discharge of the chipper shredder unit were fitted with flanges, as illustrated in  FIGS. 40 and 48 . For quick removal of the duct for cleanout purposes, the bolts are moved from the flanges, the flanged connection is separated, and the duct is slipped forward, slipping the rearward end of the duct out of the primary separation duct  398  in  FIG. 40 . 
   Example 24 
   After high-throughput improvements were made to the machine as described in the examples above, approximately 70 cubic feet of leaves (before volume reduction) could be collected in less than one minute in many cases. Accordingly, the 8-cubic-foot accumulator filled in less than one minute; so the time required to pull the accumulator to the curb, dump it and return, now became the productivity-limiting step. To increase machine efficiency, a dump wagon was built to receive the shredded debris from the accumulator. The wagon is illustrated in  FIGS. 49-56 . 
   Manually dumping the accumulator box in the wagon was awkward for a single person or even for two able-bodied workers. Two wooden ramps were made so the accumulator could be rolled up to one side of the wagon and pivoted on the top edge of the wagon to dump the contents into the wagon. The ramps had flanges formed at the edges, both to stiffen the ramps and to restrain the accumulator to keep it from slipping off the ramps. Handles were fastened to the side of the wagon, and angle brackets to the underside of the upper ends of the ramps. The angle brackets were slipped into the handles to hold the ramp boards in place. Unloading the wagon was accomplished by either inverting and lifting the wagon away from the waste, or by folding one side down and raking out the waste. 
   For use in municipalities which require bagging of lawn waste, six paper bags are placed in plastic stabilizing forms and set in the wagon box to receive the lawn waste, as illustrated in  FIG. 56 . After filling, the bags are removed from the plastic forms and tied at the tops to be transferred to the municipality. 
   Example 25 
   As an improved means of unloading the wagon in Example 24, a liner sheet was fastened along the top of a fold-down side thereof, the remainder being draped over the edges of the other side and the ends, and on the bottom of the box as illustrated in  FIGS. 49-53 . To empty the filled wagon, the fold-down side was pivoted downward as in  FIG. 52 . The edges of the liner sheet, which were draped over the other side and the ends of the box, were grasped and pulled outward toward the declining side as in  FIG. 53  to deposit the contents on the ground. Thereafter, an extensible elastic cord fastened to the outside of the opposite side of the box and to the liner sheet urges the liner sheet back toward the box upon release of the liner sheet. The extensible elastic cord passes through a pulley or over a low-friction turning block to enable easier retraction. Alternatively, a small cord attached to a spring or weight is used to retract the liner sheet. A rod or rib attached to the liner sheet and the elastic cord at the junction of the bottom of the box with the opposite side of the box aids replacement of the liner sheet in the box. In many cases, it is not necessary to drape the liner sheet over the ends of the box, but only over the two opposing sides and the bottom. For a wagon having a removable side, the liner sheet is attached to the bottom of the box adjacent to the removable side and is draped across the bottom, up the opposite side, and over the top of the opposite side.