Duct cleaning method

A method and apparatus for cleaning ducts such as used in HVAC systems includes as part of the apparatus a propeller having pitched, flexible blades for rotatably engaging the interior duct surface for dislodging soot and propelling a cloud of soot along the duct to an evacuation point. The method includes establishing a temporary block in the duct, moving the propeller along the duct for dislodging soot and generation a dust cloud, and evacuating the duct by drawing the soot cloud created by the propeller.

BACKGROUND OF THE INVENTION 
The present invention relates to cleaning ducts, for example ducts forming 
part of heating, ventilation, and air conditioning (HVAC) systems. 
In a typical commercial or residential structure, a HVAC system includes 
heating and air conditioning units located in a machinery room with 
ventilating ducts extending to individual spaces throughout the structure. 
The HVAC system includes air filters to remove dirt entrained in the air 
stream entering and circulating throughout the system. Nonetheless, dirt 
and soot do enter the system even if only in small quantities and in time 
accumulates on the interior surfaces of the ventilating ducts requiring 
periodic cleaning. 
The present invention provides a new and improved method and apparatus for 
duct cleaning and overcomes the limitations of existing techniques. 
SUMMARY OF THE INVENTION 
According to the invention, HVAC duct installations including permanent 
systems as well as temporary installations such as flexible ducting are 
cleaned of dirt and soot accumulations along their interior surfaces by 
means of a rotating propeller having a series of flexible, pitched blades 
fitted to a hub and having a circular fan area with a diameter greater 
than the actual diameter of cylindrical ducts and greater than the major 
dimension of square and rectangular ducts. The rotary propeller blades are 
formed of suitable material such as woven nylon and are secured to the hub 
at a predetermined pitch so that when rotated within a duct, the blade 
tips engage the interior duct surface and dislodge soot and dirt. The 
pitched blades also create a downstream air flow within the duct in the 
vicinity of the propeller which entrains dislodged dirt and creates a 
cloud of dirt moving through the duct ahead of the rotating propeller. 
According to a method aspect of the invention, a vacuum source is applied 
to the duct downstream of the operating propeller for evacuating the duct 
and maintaining an air flow which enables the cloud of dirt to remain air 
borne until it leaves the duct through the vacuum source. 
The propeller is fitted to and powered by a suitable rotary drive such as a 
flexible drive cable which is fed by an operator down into the duct. 
In accordance with the method aspect of the invention, a section of ducting 
is prepared for cleaning by inserting a blocking device into the duct for 
establishing or defining a duct section to be cleaned and for blocking 
flow of air downstream beyond the block. Ordinarily the block is 
established at a convenient location in the duct system as for example 
just downstream of an access or inspection opening forming part of the 
duct. The block itself is preferably an inflatable ball or sphere which is 
easy to install and remove and which when inflated acts as a barrier to 
flow of a cloud of soot beyond the block. A source of vacuum is then 
applied to the isolated duct section by means of a special fitting secured 
to the inspection opening. Next, the cleaning propeller enters the 
isolated duct through a convenient opening such a ceiling air outlet 
upstream of the block and begins dislodging interior soot and dirt and 
propelling a cloud of dust down the duct. The vacuum source evacuates the 
duct drawing the cloud of dust from the duct until the propeller reaches 
the block. This basic operation is repeated until the entire duct system 
is cleaned of soot and dirt. 
Flexible ducting is widely used in HVAC systems because of its low cost and 
ease of installation. Typically, flexible ducting consists of an outer 
plastic layer, an inner layer of insulation such as fiberglass, an inner 
plastic liner defining the inner surface of the duct through with 
conditioning air passes and an inner spiral spring engaging the inner 
surface of the duct and maintaining the cylindrical shape of the flexible 
duct. The propeller cleaning apparatus and method of the invention are 
particularly suited to cleaning such flexible ducting. The rotating 
propeller blades being themselves flexible readily conform to the soft 
inner liner of the duct as they wipe soot and dirt from its inner surface. 
Additionally the propeller tips do not pierce or otherwise damage the the 
integrity of the liner. The vacuum source is applied to an end of the 
flexible duct to evacuate the duct and collect the cloud of dirt generated 
by the propeller. 
The invention may be practiced in several ways, the preferred embodiment 
being a dedicated vacuum cleaner capable of evacuating lengthy sections of 
HVAC duct systems and of sufficient capacity for collecting the required 
volume of soot, together with a cleaning propeller and its driving 
mechanism, a versatile blocking device, and the necessary fittings for 
connecting the vacuum source to fixed and flexible duct systems. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide a method and apparatus for 
cleaning ducts, especially HVAC system ducts. 
It is an object of the invention to provide an apparatus for dislodging 
soot from HVAC ducts, entraining the soot in an moving air cloud, and 
evacuating the duct to remove the soot. 
It is a further object of the invention to provide a duct cleaning 
apparatus including a rotating propeller having flexible blades for 
dislodging soot from a duct and for generating an air flow for entraining 
the soot enabling removal of the soot from the duct by means of a vacuum 
cleaner. 
It is a further object of the invention to provide a method and apparatus 
for cleaning rigid as well as flexible ducts. 
It is a further object of the invention to provide a method for cleaning 
ducts in which a section of duct is isolated by blocking air flow beyond 
the isolated section, dislodging and propelling soot downstream toward the 
block location, and evacuating the duct at the block location. 
It is a further object of the invention to provide a method and apparatus 
for cleaning HVAC systems in which cleaning is performed section by 
section of the system without the need to secure the system. 
It is another object of the invention to provide a method and apparatus 
which is relatively quiet so as not to unduly disturb or annoy occupants 
of a building undergoing HVAC system cleaning.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1--3 of the drawing, the apparatus of the invention 
includes a propeller 10 having a hub 12 and blades 14. 
In a preferred form, the hub may be fabricated of lightweight material such 
as aluminum or plastic and is preferably a cylindrical block 16 with an 
axial bore 18 for connection to a rotary cable 20 and with peripheral 
channels 22 equally spaced along the hub circumference 24 for receiving 
the propeller blades. The peripheral channels are formed at a 
predetermined angle or pitch with respect to the axis of rotation of the 
hub. Channel pitch determines blade pitch. The channels as shown in FIG. 3 
are preferably cylindrical with a portion of each cylinder bore 26 
intersecting the hub circumference to define channel openings 28 for 
receiving propeller blades. 
The propeller blades 14 are preferably formed of a length of strip material 
such as woven nylon which is flexible, does not inflict damage or wear on 
either flexible or sheetmetal ducting and which produces relatively low 
noise levels particularly when cleaning sheetmetal ducts. The propeller 
strips are folded about a mounting shaft 30 and are inserted into the 
peripheral channels and there project radially from the hub in the form of 
propeller blades 14. The propeller, when rotating, defines a fan area 
encompassing the internal surfaces of a HVAC duct including circular, 
square, or rectangular ductwork. 
The hub is fitted to a rotatable, flexible cable 20 which rotates the 
propeller and moves the propeller along the length of duct being cleaned. 
The flexible cable includes an inner wound steel rotary drive shaft 32 and 
outer protective casing 34 normally handled by an operator in deploying 
the propeller. Suitable fittings 36 secure the rotary portion of the cable 
to the propeller hub. 
In accordance with a method aspect of the invention, a section of ducting 
40 as shown in FIG. 5 is prepared for cleaning by inserting a blocking 
device 42 into the duct for establishing or isolating the duct section for 
cleaning. The block confines the flow of dislodged soot to the isolated 
section and enables evacuation of soot from the section. Ordinarily the 
block is established at a convenient location in the duct system as for 
example just downstream of an access or inspection opening 44 forming part 
of the duct. The block itself is preferably an inflatable ball or sphere 
which is easy to install and remove and which when inflated acts as a 
barrier to flow of a cloud of soot beyond the block. A source of vacuum is 
then applied to the isolated duct section by means of a special fitting 46 
secured to the inspection opening. The fitting includes a cover plate 48 
and nipple 50 for mounting over the inspection opening and for attachment 
to a vacuum hose 52. Next, the cleaning propeller enters the isolated 
section of duct through a convenient opening such a ceiling or wall grille 
54 upstream of the block. The propeller is fed into the duct at the end of 
the rotary cable and begins rotating with the tips of the propeller blades 
engaging and dislodging soot and dirt from the duct interior. The 
propeller generates an air flow downstream ahead of the pitched propeller 
blades thereby entraining and propelling a cloud of soot and dust down 
through the duct interior toward the block. The vacuum source V evacuates 
the isolated section of duct drawing the cloud of dust from the duct 
through the inspection opening until the propeller reaches the block. This 
basic operation is repeated until the entire duct system is cleaned of 
soot and dirt. 
As described the propeller may be described as "pushing" the cloud of air 
and soot ahead of the propeller and away from the operator as it moves 
forward through a duct. By reversing the direction of rotation of the 
rotary cable, an air flow to the rear of the propeller is generated so 
that the cloud of dirt can be "pulled" backward through the duct toward 
the operator. This aspect of the invention allows considerable latitude in 
locating the system block with respect to the vacuum source. For example, 
the block may be located some distance along a duct beyond an inspection 
opening enabling the operator to "push" a cloud of soot ahead of the 
propeller from access opening to the evacuation point, and, after 
reversing propeller pitch, to "pull" a cloud of dust and soot back through 
the duct from the block point to the evacuation point. 
The propeller cleaning apparatus and method of the invention are 
particularly suited to cleaning flexible ducting used in HVAC systems. 
Such ducts 55 (FIG. 4) include an outer plastic layer 56, an inner layer 
of insulation 58 such as fiberglass, an inner plastic liner 60 defining 
the inner surface of the duct through with conditioning air passes and an 
inner spiral spring 62 engaging the inner surface of the duct and 
maintaining the cylindrical shape of the flexible duct. The rotating 
propeller blades being themselves flexible readily conform to the soft 
inner liner of the duct as they wipe soot and dirt from its inner surface. 
Additionally the propeller tips do not pierce or otherwise damage the the 
integrity of the liner. The vacuum source is applied to an end of the 
flexible duct to evacuate the duct and collect the cloud of dirt generated 
by the propeller. 
The invention provides an effective system for methodically and effectively 
removing soot and dirt from HVAC equipment with minimal need for removing 
system components, minimal disruption of building routine, while entirely 
confining the dislodged soot within removal equipment. Operation of the 
system is within the capability of building maintenance personnel for 
routine maintenance of HVAC equipment.