Abstract:
A blower module which is sufficiently quiet to be placed in occupied buildings and not require the construction of a separate blower building; each blower module is a cylinder having conic drip cap on its top, a positive displacement blower, typically, a rotary piston or Roots type blower, and electric or otherwise powered motor to drive the blower, a labyrinth passage outlet silencer, and a labyrinth passage inlet silencer; and the blower module being shaped for sanitation, mechanical containment, noise abatement and stacking one blower on top of another.

Description:
BACKGROUND OF THE INVENTION 
     In the field of moving materials, it is often necessary to move bulk materials such as grain, sand, or other bulk material having small particle size. While the bulk materials can be moved by mechanical means, such as shovels, conveyer belts, and such where the device moving the bulk materials carries the bulk material from one location to another location these methods can be impractical and risk contaminating the bulk material. The simplest method for moving such bulk materials is to use gravity. An outlet located at the bottom of the container or bin containing the bulk material is opened and the bulk material is allowed to flow out. While this method is very useful, the bulk material must first be raised into the container or bin so that gravity can act upon it. Typically, the movement provided by gravity is limited and at some time the bulk material must again be raised to a position that gravity can again act on the bulk material. 
     Blower packages are also used in soil remediation and other processes. 
     It has become common to move such bulk materials using airflow to carry the material from one location to another location within a conduit. This method is referred to as pneumatic conveying. This method is especially useful as the conduit can be routed in a fashion that occupies, or requires very little space. 
     In the processing of bulk material having relatively small particle size, the bulk material must frequently be moved from one location to another quickly and efficiently. A commonly used method is to inject compressed air or gas into the conduit at the beginning of the system to push the bulk material through the conduit. This method is commonly referred to as dilute-phase, pressure, pneumatic conveying. Using either of these methods, the bulk material can be moved horizontally or vertically over some distance quickly and efficiently. Another commonly used method is to evacuate a container that is connected to the conduit at the end of the system, drawing air or gas through the conduit to pull the bulk material through the conduit. This method is commonly referred to as dilute-phase, vacuum, pneumatic conveying. 
     To move the bulk material in a dilute-phase, pressure, pneumatic conveying system, a blower must produce a sufficient volume of compressed air at a sufficient pressure to move the bulk material and keep the bulk material moving in the conduit. Similarly, in a dilute-phase, vacuum, pneumatic conveying system, to move bulk material, a blower package must remove sufficient volume of air to produce a sufficient vacuum to move the bulk material and keep the bulk material moving in the conduit. When the volume and/or pressure or vacuum of air is insufficient to keep the bulk material moving, the conduit can become obstructed as the bulk material settles from the air stream and is no longer being moved. An obstructed conduit creates a stoppage of flow which usually requires the intervention of workers to clear and would thus slow if not stop the transfer process, if not other processes that depend from the transfer process. 
     While the use of airflow to move bulk materials is efficient, it is not without problems. Blower packages used are often very large assemblies of components including: A structural base, an inlet filter/silencer, outlet filter/silencer, blower, motor, drive, drive guard, piping &amp; fittings, and support brackets all assembled in an unsanitary, exposed fashion. One of the primary problems is that the blower package is very noisy. Most blower packages create sufficient noise that they must be housed in a separate room so that the sound does not injure the employees. Separate rooms create additional expense of the building, use more floor space, and require longer piping to provide or evacuate the air from the point of use. Longer piping results in greater airflow restriction which, directly results in wasted energy consumption over the useful life of the system. 
     Much of the blower noise is caused rapid movement of air through the blower and by the mechanical action of the blower acting upon the air. The mechanical noise of displacing the air often is transmitted through both the inlet and outlet of the blower to connecting piping, then radiates to the exterior environment. Conventional wisdom has been to use chambered silencers or absorptive filters to absorb the sound waves coming from the blower. While this method does reduce noise, it all too often does not sufficiently reduce the noise to allow the blower package to be placed in an occupied space. Additionally, a large percentage of the noise radiates from the blower housing and can only be reduced by some means of secondary containment that permits air to flow in contact with the blower housing to dissipate heat, generated by its operation. 
     Placement of a blower in a separate building, while removing the noise from the occupied area, causes increased pressure losses and a reduction in the volume of air produced by the blower. Frequently the loss of pressure and volume is sufficient so that a larger blower and/or greater horsepower motor must be used thereby increasing costs and energy requirements. 
     SUMMARY OF THE INVENTION 
     The invention relates to a modular blower and housing for creating a pressure differential for movement of air or gas. More particularly, the invention is a unique blower package for producing a large volume of compressed air which is often used to push bulk materials through a conduit; or for producing a partial vacuum which is often used to pull bulk materials through a conduit. 
     The invention described herein is a blower package which consolidates the function of several necessary components into a sanitary unit that is sufficiently quiet to be placed in occupied places and not require that it is remotely located. Each blower module is a cylinder having conic drip cap on its top. Each module contains a positive displacement blower, typically, a rotary lobed or Roots type blower, connecting drive components and electric or otherwise powered motor to drive the blower, a labyrinth passage outlet silencer, and a labyrinth passage inlet silencer. When used to provide positive pressure air, the module also has an inlet air filter which also provides some absorptive silencing. Multiple modules may be stacked one atop another to increase the blower output without using more floor space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall view of the exterior of a blower module. 
     FIG. 2 is a partial cut away view showing the overall construction of a blower module and its major components. 
     FIG. 3 is an overhead cross sectional view of one of the labyrinth passage silencers taken from line  3 — 3  of FIG.  2 . 
     FIG. 4 is a cross sectional view of one of the labyrinth passage inlet silencers taken from line  4 — 4  of FIG.  3 . 
     FIG. 5 is a cross sectional view of one of the labyrinth passage outlet silencers similar in cut location to the inlet silencer cross-section shown in FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The blower module  10  is a cylindrical housing  12 , has a conic drip cap  14 , a bottom conic cap  15 , an access door  16 , an inlet labyrinth silencer  18 , and an outlet labyrinth silencer  20 . Contained within the cylindrical housing  12  is a blower  22  and its associated drive motor  24 . The inlet labyrinth silencer  18  and the outlet labyrinth silencer  20  may be exchanged if the invention is used in a partial vacuum application instead of a compressed air application. 
     The cylindrical housing  12  is the outer housing of the blower module  10  and may be formed from any suitable material such as plastic or metal. The cylindrical housing  12  material must be sufficiently malleable to be formed into a cylindrical shape using commonly available mechanisms and more importantly should have sufficient strength to allow multiple blower modules  10  to be stacked one atop another. Similarly, the drip cap  14  and access door  16  must share the same properties. Additionally, the access door  16  should be sealed when closed to achieve the maximum effectiveness of the invention. It has been found that 12 gauge sheet iron has suitable properties for fabrication of the cylindrical housing  12 , the drip cap  14  and the access door  16  and is readily available and relatively inexpensive. 
     The access door  16  is preferably hinged and/or bolted for easy access to the interior of the cylindrical housing  12 . When the access door  16  is closed, there is a door seal (not shown) between the access door  16  and the cylindrical housing  12 . The door seal helps eliminate air leakage through the access door  16  opening during operation. Was air to flow through the access door  16  opening during operation, the air would decrease the efficiency of the blower module  10  and would also create noise obviating the quieting advantages of the blower module  10 . The space container within the cylindrical housing  12  forms an air plenum  17  which moderates and feeds air to the blower  22 . The drip cap  14  and the bottom conic cap  15  must have similar properties to the cylindrical housing  12  and is preferably constructed from the same material. 
     The blower  22  is a conventional blower and may be a centrifugal, screw type, or any other type of blower capable of producing sufficient quantity of fluid movement at sufficient volume and pressure. The blower  22  draws air from the plenum  17  and outputs the pumped air to the inlet port  41  of the output silencer  20 . It is preferred that the blower  22  be a positive displacement blower such as a rotary lobed or Roots type. Blowers  22  of this type are readily available in a variety of sizes and may be selected from multiple sources in the marketplace. The drive motor  24  may be any power source having sufficient power to drive the blower  22  of the selected size. Preferably, the drive motor  24  is a totally enclosed fan cooled electric motor. Electric motors of this type are well known in the art and available in numerous sizes and configurations from multiple sources such as General Electric, Westinghouse, Baldor and others. 
     A preliminary air filter  26  may be located external to the cylindrical housing  12  for additional filtration. When used it is attached to pass air through a passage  27  in the cylindrical housing  12 . The preliminary air filter  26  may function to filter particulate and other debris from the intake air. The preliminary air filter  26  also provides some silencing of the intake air stream. The preliminary air filter  26  is a conventional absorptive type air filter that may be of any conventional construction, such as, pleated paper, felt or foam having the properties of low flow restriction. The preliminary air filter  26  is also readily accessible for maintenance as it can collect a substantial amount of particulate and may need to be changed quite often. A secondary air filter  28  is located attached to the blower  22  inlet port. The secondary air filter accepts the pre-filtered air from the preliminary air filter  26  provides further filtration and sound absorption. The secondary air filter  28  is designed to filter smaller particles than the preliminary air filter  26  since the coarser particles have already been removed from the air stream. The secondary air filter  28  is also designed to filter particulate that may be generated from the drive components contained within the air plenum  17 . The secondary air filter  28  also provides some silencing of the intake air stream. The secondary air filter  28  may be a conventional absorptive type air filter. The secondary air filter  28  may be constructed of any suitable filtration media having the properties of low flow restriction and removable of sufficiently small particles and may be constructed in any suitable form such as, pleated paper or foam, with or without oiling. 
     The labyrinth inlet silencer  18  is a cylindrical extension formed in the upper terminus of the cylindrical housing  12  and has as its top the drip cap  14 . The bottom plate  30  is installed parallel to the drip cap  14  and also is formed in a conic shape. The baffles, generally,  32  are located concentrically within the cylindrical housing  12  and about the outlet port  34  as more clearly shown in FIG. 3 or FIG.  4 . Each baffle  32  is a ring extending from the bottom panel  30  to the drip cap  14  and is sealingly affixed thereto. Each baffle also has a transfer port  36  formed passing there through. Each baffle  32  is located in a spaced apart relation to the adjacent baffles  32  or cylindrical housing  12 . Each respective transfer port  36  is located so that it is not aligned with an adjacent transfer port  36 . 
     The labyrinth outlet silencer  20  is configured similar to the inlet silencer with a conical bottom plate  15  and a conical top plate  40  spaced above and parallel to the bottom plate  15 . Concentric baffles  32  are located within the outer cylindrical housing  12  in a spaced apart relation to the outer cylindrical housing  12  or another baffle  32 . Each baffle  32  is a ring extending from the bottom plate  15  to the top plate  40  and is sealingly affixed thereto. Transfer ports  36  are located in each respective baffle  32  and each transfer port  36  is angularly spaced from the adjacent transfer ports  36  or the outlet port  42 . 
     As both the labyrinth inlet silencer  18  and the labyrinth outlet silencer  20  function in an identical manner, their operation will be discussed together. 
     The first passive noise reduction is provided by the labyrinth silencer  18 ,  20  is the line of sight silencing. More particularly, any noise produced by the blower  22  propagates linearly from the blower  22 . Any such noise entering the labyrinth silencer  18 ,  20  is obstructed by the labyrinth from propagating through the labyrinth silencer  18 ,  20 . This process prevents the radiation of sound waves from the blower  22  into the environment outside of the cylindrical housing  12  reducing the ambient noise in the work area. 
     The second active noise reduction is provided by the resonance of the column or flowing air in the labyrinth silencers  18 .  20 . As a blower  22  is operated, it will transmit discrete pulsed air into both the intake and output streams of air. The pulses are usually caused by the blower moving the air in discrete packets. This is most easily exemplified where the blower  22  is a single cylinder piston type blower or compressor. It is easier to see that in a piston type blower that as the piston descends within its cylinder, that a column of air is set into motion to fill the cylinder. When the cylinder is full and the inlet valve closes, the column of air is abruptly stopped and will often dissipate its energy in the form of noise, having a frequency corresponding to the number of reciprocations the piston makes per unit time. The noise produced from the rapid starting and stopping of the column of air is propagated outwardly from the source. When this noise is propagated into the labyrinth silencer  18  or  20  the sound waves are reflected from the baffles  32 . The baffles  32  cooperating with the transfer ports  36  to provide destructive interference of this propagated noise. That is, the baffles  32  are so spaced and the transfer ports  36  are so arranged to cause the cancellation of sound waves of a particular frequency that enters the labyrinth silencer  18  or  20 . While the noise cancellation has been explained with reference to a piston type blower  22 , it is understood that the noise cancellation will work with other types of blowers  22  such as a rotary piston or Roots type blower. 
     While the exact size and spacing of the baffles  32  is intended to provide as many opportunities for noise cancellation as is practical, the cross-sectional area of the passage for air flow through the baffles  32  and the transfer ports  36  must be of sufficient area as to minimize the restriction of air flow through the labyrinth silencer  18 ,  20 . While the exact size and spacing of the baffles  32  and location of the transfer plates can be calculated, it has been found, however, that placing approximately four baffles  32  having an approximate height of nine inches and diameters of approximately twelve, eighteen, twenty-four, and thirty inches within a thirty-five and five-eighths inch cylindrical housing  12  provides ease of fabrication, cost advantages and sufficient noise reduction when the blower  22  is a two lobed Roots type blower driven by a standard 1750 RPM electric motor. At times, the noise reduction may be enhanced by slightly changing the blower  22  speed by changing the size of the drive pulleys on either the drive motor  24  or the blower  22 , or both. Changing the speed of the blower  22  will change the basic frequency of the blower noise to better match the noise cancellation frequency of the labyrinth silencer  18  or  20 . 
     Additionally it has been discovered that the inlet labyrinth silencers  18  not only cancel noise at selected frequencies, but also, set up and enhance a vibration in the air column at a basic frequency. The intake column of air will vibrate between the inlet passage  27  and the plenum  17  in the cylindrical housing  12 . When the basic frequency of the air column coincides with the frequency of the blower  22  inlet opening frequency, an increase in air pumped is noted. This is apparently caused by the moving column of air pulsing into the open blower  22  intake port and being stopped not by the inlet valving, but, by interior parts of the blower thereby providing a charge to the blower that is above ambient pressure. 
     Similarly, the outlet labyrinth silencer  20  not only cancels noise in the output air of the blower  22 , but also, enhances the vibration in the air column at a basic frequency. The output air column will vibrate between the outlet of the blower  22  and the outlet port  42 . When the basic frequency of the air column coincides with the frequency of the blower  22  outlet opening frequency, an increase in air pumped is noted. This increase is apparently caused by the moving column of air pulsing out from the open blower  22  port and scavenging additional air from the blower  22 . 
     An additional benefit of the inlet and outlet labyrinth silencers  18 ,  20  is that they provide a mechanism of dampening the pulsation generated by the blower  22  by virtue of the volume of compressible air contained within the labyrinth silencers  18 ,  20  and the air plenum  17 . 
     In its operation, one or more blower modules is installed in its selected location and connected to a power supply and input or output from the blower module  10  port  42  is connected into the processing system. Each blower module  10  has been previously fabricated off site and can be transported to the site and installed by persons of ordinary skill. This allows the blower modules  10  to be installed by the employees of the customer or local subcontractors which reduce the cost of installation by not requiring the manufacturer to send an installation team to the site. When space is at a premium, multiple blower modules  10  can be stacked one atop another to best utilize the available floor space. Additionally, stacking multiple modules  10  allows the input or output of multiple modules  10  to be merged where it is advantageous to use multiple modules rather than one large blower module  10 . 
     After installation, each module can be independently controlled remotely for starting and stopping as needed in a compressed air application. When the blower module  10  is started, electrical power is applied to the drive motor  24  which turns the blower  22 . As the blower  22  attains operating speed, air is drawn into the blower  22  through the secondary air filter  28  which in turn draws air from the plenum  17  and from the inlet labyrinth silencer  18 . This in turn allows air to be drawn in through the preliminary air filter  26 . When the blower  22  reaches operating speed, the pulsations of the air column stabilize at the basic frequency and the inlet silencer  18  cooperates with the pulsing air column to cancel the noise from the blower  22 . Additionally, the pulsations cooperate with the baffles  32  in the inlet silencer  18  to urge additional air into the plenum, and thus into the blower  22  to increase the amount of air reaching the blower  22 . 
     Similarly, when the blower  22  reaches operating speed, the air in the output silencer  20  begins to pulsate in response to the blower  22  speed. The pulsations interact with the baffles  32  and the labyrinth in the output silencer to cancel the output noise and smooth the air flow. Additionally, the pulsations cooperate with the baffles  32  in the outlet silencer  20  to urge additional air out of the blower  22  and through the outlet port. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize changes may be made in form and detail without departing from the spirit and scope of the invention.