Patent Publication Number: US-7722333-B2

Title: Portable dry air compressor system

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to air compressors. More particularly, the present invention relates to a multi-function dry air compressor system. 
   Electrical power handling equipment, such as transformers, often include a tank filed with oil in which the power handling devices or coils are disposed. The gas volume or ullage above the oil in the tank is often filled with dry air to avoid a moist air atmosphere that contaminates the oil due to oxidation and/or moisture absorption. Dry air for this purpose is generally air having a dew point of less than approximately −30° F. at one atmosphere pressure, which corresponds to a moisture content of approximately less than 235 ppm v/v. During installation or maintenance of the electrical power equipment, a high volume of the dry air is required. 
   To date, the dry air has generally been supplied from high pressure, refillable cylinders. However, the use of dry air cylinders has numerous drawbacks. The dry air cylinders need to be replaced on a regular basis. The cylinders are typically transported in pyramid trailers, rental cradles or semi-tube trailers. The trailers generally require a large vehicle for towing and need special hazmat endorsements prior to transport. Emptied cylinders require change over at an off-site location, thereby requiring transportation time between the electrical equipment site and the change over location. Once the cylinder trailer has arrived at the change over location, approximately 15-21 empty cylinders must be removed from the trailer and replaced by full cylinders, each full cylinder weighing approximately 200 pounds. Such change over often takes several hours such that the complete change over process, including transportation time, takes 10 or more hours which can cause significant delays during the installation or maintenance. Furthermore, the emptied cylinders also have to be returned to the vendor for refilling, resulting in additional time and costs. 
   In addition to using the dry air to fill the transformers or other electrical equipment, the dry air cylinders are also often used to supply breathable air to workers working in and around the transformers. In view of the criticality of the breathable air source, it is necessary to replace the cylinders more frequently to ensure the cylinders do not inadvertently empty, thereby leaving the workers without a sufficient supply of breathable air. 
   Accordingly, there is a need to supply dry air to a remote location that is cost effective and eliminates the need for frequent refilling of cylinders. 
   SUMMARY OF THE INVENTION 
   One aspect of the invention provides a portable air compressor assembly comprising a compressor configured to supply pressurized air along a first path at a first pressure. The compressor assembly further comprises at least first and second outlet valves. A first outlet path extends between the first outlet valve and the first path and a second outlet path extends between the second outlet valve and the first path. A first regulator is positioned along the first outlet path and is configured to regulate the pressure of air at the first outlet valve to a first outlet pressure distinct from the first path pressure. A second regulator is positioned along the second outlet path and is configured to regulate the pressure of air at the second outlet valve to a second outlet pressure distinct from the first path pressure and the first outlet pressure. 
   In a further aspect of the invention, the first outlet pressure is approximately 4 psi, a suitable pressure for filing of electrical power handling equipment, and the second outlet pressure is approximately 7 psi, a suitable pressure for the provision of breathable air. 
   In a further aspect of the invention, the compressor system further comprises a third outlet valve, a third outlet path extending between the third outlet valve and the first path, and a third regulator positioned along the third outlet path and configured to regulate the pressure of air at the third outlet valve to a third outlet pressure distinct from the first outlet pressure and the second outlet pressure. The third outlet pressure is approximately 120 psi. 
   In another aspect of the invention, a dryer assembly is positioned along the first path such that the air passing from the first path to the outlet paths has a dew point of less than approximately −30° F. at one atmosphere pressure, which corresponds to a moisture content of approximately less than 235 ppm v/v. 
   In another aspect of the invention, a filter assembly is positioned along the first path such that the air passing from the first path to the outlet paths meets at least the requirements for Grade D breathing air described in ANSI/Compressed Gas Association Commodity Specification for Air, G-7.1-1989. 
   Additional features and advantages of the present invention will be understood from the drawings and detailed description that follow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
       FIG. 1  is a side elevation view of a portable compressor system according to a first embodiment of the present invention. 
       FIG. 2  is a front elevation view of the portable compressor system of  FIG. 1 . 
       FIG. 3  is a rear elevation view of the portable compressor system of  FIG. 1  with the rear doors open. 
       FIG. 4  is a schematic diagram of the portable compressor system of  FIG. 1 . 
       FIG. 5  is a front elevation view of a safety switch assembly of the portable compressor system of  FIG. 1 . 
       FIG. 6  is a front elevation view of the compressor of the portable compressor system of  FIG. 1 . 
       FIG. 7  is a perspective view of a portion of the filter and dryer system of the portable compressor system of  FIG. 1 . 
       FIG. 8  is a front elevation view of the outlet valve assembly of the portable compressor system of  FIG. 1 . 
       FIG. 9  is an elevation view of the backup air system of the portable compressor system of  FIG. 1 . 
       FIG. 10  is a schematic diagram of a portable compressor system that is an alternate embodiment of the present invention. 
       FIG. 11  is a side elevation view of a portable compressor system according to an alternate embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 
   Referring to  FIGS. 1-9 , a portable compressor assembly  10  that is a first embodiment of the present invention will be described. As shown in  FIGS. 1-3 , the compressor assembly  10  includes a portable trailer  12  including an enclosure  14  supported on a base structure (not shown). The enclosure  14  and base structure are supported on wheels  16  or the like and a draw bar  18  extends from the front of the base structure and is configured to be connected to a vehicle for towing. A forward support  20 , which may or may not include a wheel, is moveable between a supporting position as shown and a retracted position for towing of the trailer  12 . The trailer  12  is desirably small enough that the trailer  12  may be transported without any special hazmat endorsements and may even be small enough to be towed by a car. A storage box  22  may be provided on the draw bar  18  for external storage. 
   The enclosure  14  is illustrated as a rectangular structure with opposed front and back panels, right and left side panels and a top surface, however, the enclosure  14  can have various configurations and is not limited to the illustrated configuration. The enclosure  14  can be manufactured from various materials including metals, plastics or composite materials. The enclosure  14  structure is preferably configured to dampen sound to minimize noise emanating from the enclosure  14 . Sound dampening material, for example, insulative material, may also be provided to further reduce noise. The enclosure  14  includes various vents or louvers (not shown) to permit air flow through the enclosure  14 . 
   The enclosure  14  of the present embodiment includes right side door panels  24  and rear door panels  26  for accessing the interior space of the enclosure  14 . Other door configurations or access configurations, for example, a flip top assembly, may also be utilized. The enclosure  14  also supports an external control panel  30  and an external outlet valve assembly  40  (see  FIGS. 1 and 8 ). The control panel  30  is associated with a central controller  28 , for example, a central processing unit (CPU) or the like. Various buttons or switches  32  are provided in the control panel  30  to facilitate external control of the controller  28 . A cover  34  may be provided to close the control panel  30 . The valve assembly  40  of the present embodiment provides three outlet valves  42 ,  44  and  46  with each outlet valve configured for connection to a hose or the like. More or fewer outlet valves may be provided. A pressure indicator  43 ,  45  and  47  is associated with each outlet valve  42 ,  44  and  46  and indicates the pressure available through the respective outlet valve  42 ,  44 ,  46 . 
   In the present embodiment, flow to outlet valve  42  is regulated to approximately 4 psi such that the air therefrom is suitable for use in filling transformers or the like. Flow to outlet valve  44  is regulated to approximately 7 psi such that the air therefrom is suitable for breathing air. Flow to outlet valve  46  is regulated to approximately 120 psi such that the air therefrom is suitable for use with pneumatic tools or the like. Regulation of each of the valves will be described in more detail hereinafter. 
   Referring to  FIG. 5 , the portable compressor assembly  10  of the current embodiment is powered by connection of a three phase safety switch  56  to an external power supply (not shown). The safety switch  56  has an external connector (not shown) configured for connection to the external power supply. For example, connection cords (not shown) with a first end associated with the safety switch  56  and a second free end may be stored in the external storage box  22 . The cord free ends include connection assemblies, for example, muller clips, whole lugs, or bare wire leads, for connection to a power source. In applications in which the portable compressor assembly  10  is utilized to fill electrical equipment, the electrical system may be configured to accommodate a 208V, 3 phase power source such that the compressor assembly  10  may be connected directly to the available power supply. The safety switch  56  preferably includes an in-phase monitor  57  to ensure that the power source is correctly connected to the compressor assembly  10 . 
   The compressor assembly  10 ′ in  FIG. 11  includes a fuel powered generator  58  that is electrically connected with the compressor assembly  10 ′ and is configured to power the various components and systems thereof. The generator  58  may be provided with electrical outlets or the like (not shown) to power other equipment that is not part of the compressor assembly  10 ′. In all other aspects, the compressor assembly  10 ′ of  FIG. 10  is substantially the same as that of the compressor assembly  10  of  FIG. 1 . 
   Referring to  FIGS. 4 and 6 , an air compressor  60  is positioned within the enclosure  14 . The compressor  60  is configured to intake air generally at atmospheric pressure through inlet passage  61 , compress the air, and outlet high pressure air via outlet passage  63 . The compressor  60  can have various configurations, for example, the compressor  60  can be a reciprocal compressor, a rotary screw compressor, a rotary vane compressor, a centrifugal compressor or any other configuration; a single stage or multi-stage compressor; a variable speed or direct drive compressor; and an oil-flooded or oil-free compressor. A suitable compressor  60  is, for example, the illustrated V15 rotary vane compressor manufactured by CompAir of the United Kingdom. The compressor  60  is associated with the controller  28  and is controlled thereby. 
   Compressed high pressure air from the compressor outlet  63  travels through a filter assembly  64  via conduit  65 . The filter assembly  64  is generally configured to remove oil droplets and particles or debris from the high pressure air flow. For example, the filter assembly  64  preferably includes primary and secondary oil separators (not shown). The filter assembly  64  may include additional filters, for example, charcoal filters or coalescing filters. The filter assembly  64  may be a single unit with multiple filter elements or may be separate units, each configured to filter a different substance. In the illustrated embodiment, the filter assembly  64  is formed as integral components of the V15 compressor  60 , but such is not required. 
   The compressed air exiting the filter assembly  64  is typically hot and moist from the compression process. To remove some heat and moisture, the compressed air travels via conduit  65  through an aftercooler  66  which passes a cooling fluid, for example, air or a liquid, about the compressed air to condense the air and thereby remove heat and moisture. In the illustrated embodiment, the aftercooler  66  is formed integrally with the V15 compressor  60 . Alternatively, the aftercooler  66  may be positioned downstream from the compressor  60 . 
   The compressed air travels from the aftercooler  66  to a reserve tank  68  via conduit  67 . Reserve tank  68  receives and stores compressed air such that a desired pressure, for example, around 150 psi, builds up in the tank  68 . In the illustrated embodiment, the reserve tank  68  is formed integral within the V15 compressor  60 , but may alternatively be formed as a stand alone structure. 
   In the illustrated embodiment, a dryer assembly  70  and a secondary filter assembly  72  are positioned downstream from the reserve tank  68 . The positioning of the various components may be rearranged without departing from the spirit and scope of the invention. As illustrated, the compressed air travels via conduit  69  to a dryer assembly  70  (see  FIG. 7 ). The dryer assembly  70  can include a deliquescent, refrigerant, regenerative, absorptive dryer or a combination thereof and is configured to further remove moisture from the compressed air such that dry air, having a dew point of less than approximately −30° F. at one atmosphere pressure, which corresponds to a moisture content of approximately less than 235 ppm v/v, is provided at conduit  71 . Such dry air is typically sufficiently dry for use in filling the electrical equipment, for example, a transformer. Depending on the operating conditions, the air may be dryer or moister than this given dew point. 
   The illustrated embodiment the dried air traveling via conduit  71  to a secondary filter assembly  72  configured to remove any remaining particulate or other impurities. While the filter assembly  72  is illustrated after the dryer assembly  70 , it may alternatively be provided before or both before and after the dryer assembly  70 . Furthermore, the secondary filter assembly  72  may be a single unit with multiple filter elements or may be separate units, each configured to filter a different substance. In the illustrated embodiment, the dryer assembly  70  and secondary filter assembly  72  are both incorporated in a breathing air purifier manufactured by Domnick Hunter Inc. of Charlotte, N.C. and marketed as model number BA-DME060. The air purifier includes a WS-50 water separator, an AA-0080G high efficiency grade AA filter to further reduce oil and water content, an activated carbon filter to remove odors and oil vapor, a 4 stage absorptive dryer, a BAH101 catalyst purifier configured to remove carbon monoxide and an AR-0080G filter which removes any particulate that carries over from the absorptive materials. While the various filters  64  and  72 , cooler  68  and dryer  70  are illustrated in a given order, the invention is not limited to such order and each of the components may be otherwise positioned. Additionally, the invention is not limited to the specific components identified herein, and more or fewer components may be utilized to clean and dry the air. 
   It is desirable that the secondary filter assembly  72  removes any remaining particulate such that the air traveling therefrom via conduit  73  meets at least the requirements for Grade D breathing air described in ANSI/Compressed Gas Association Commodity Specification for Air, G-7.1-1989, which includes: oxygen content (v/v) of 19.5-23.5%; hydrocarbon (condensed) content of 5 milligrams per cubic meter of air or less; carbon monoxide (CO) content of 10 ppm or less; carbon dioxide content of 1,000 ppm or less; and lack of noticeable odor. 
   A sensor  74  is provided in conduit  73  and is configured to monitor the purity of the air. The sensor  74  can be configured to monitor various impurities including, but not limited to, particulates, carbon monoxide, or nitrogen. The sensor  74  is connected to the controller  28 . In the event the controller  28  receives a signal indicating that an undesirable level of an impurity has been detected, the controller  28  is configured to initiate an emergency sequence as described hereinafter. While a single sensor  74  is illustrated, more than one sensor  74  may be provided and the sensors may be provided at various locations. 
   Provided the air remains sufficiently pure, the clean, dry air flows through a control valve  76 , that is normally open, to a manifold  80 . The manifold  80  directs the clean, dry air along three conduits  90 ,  100  and  110  to the three outlet valves  42 ,  44  and  46 , respectively. While a manifold is described herein, other piping configurations may be used. Air traveling along conduit  90  is passed through a pressure regulator  92  that is configured to regulate the air pressure available at outlet valve  42  to approximately 4 psi. The air pressure is indicated on the associated pressure indicator  43 . Filling of transformers and the like generally requires low pressure, high volume dry air which is available at outlet valve  42 . 
   Air traveling along conduit  100  similarly passes through a regulator  102  that is configured to regulate the air pressure available at outlet valve  44  to approximately 7 psi. The air pressure is indicated on the associated pressure indicator  45 . Furthermore, the air is passed through a water mister  107  that slightly increases the moisture level in the breathable air at outlet valve  44 . While the dry air may be suitable for breathing, extended exposure may cause drying and discomfort for workers breathing the air. It is desirable that the mister  107  add moisture such that the dew point is approximately −10° F. at one atmosphere pressure, which corresponds to a moisture content of approximately 735 ppm v/v. 
   Air traveling along conduit  110  also passes through a regulator  112  that is configured to regulate the air pressure available at outlet valve  46  to approximately 120 psi. The air pressure is indicated on the associated pressure indicator  47 . Furthermore, the air is passed through a lubricator  117  that adds oil or another lubricator to the air such that the air at outlet valve  46  is suitable for use with pneumatic tools or the like which might be damaged by dry air. As such, the portable compressor assembly  10  provides each of the three air sources which may be desired at a transformer filling site or other application. The supply of air is continuous based on operation of the compressor  60  and does not require down time for travel or filling of dry air cylinders. Each of the regulators  92 ,  102  and  112  may be regulated by hand, or alternatively, may be set and regulated automatically using the controller  28 . 
   As indicated above, the controller  28  is preferably configured to initiate an emergency sequence in the event of a failure. Such failures may include, but are not limited to, a loss of power, a compressor malfunction, or an unacceptable level of impurities in the air supply. In the event of an emergency situation, the controller  28  is configured to set off an alarm. The alarm preferably includes both a visual indicator, for example, strobe light  50 , and an audible indicator, for example, siren  52 . The visual and audible indicators increase the likelihood that a worker remote from the compressor assembly  10 , for example, inside of a transformer, will notice the alarm. 
   The controller  28  is further configured to shut down the compressor  60 , if it is not already shut down, and close the control valve  76  such that any remaining pressurized air in the reserve tank  66  does not flow through the conduits  90 ,  100 ,  110 . A blow down valve  78  may be opened to remove any pressure remaining in the system. 
   To ensure that workers have sufficient breathable air to remove themselves from an enclosed work environment, a back-up dry air supply  120  is provided within the trailer  12 . The back-up dry air supply  120  includes one or more tanks  122  pre-filled with breathable, pressurized dry air. The tanks  122  are connected to the manifold  80  via conduit  126 . Each of the tanks  122  is typically valved off at valve  124 . Upon notification of an emergency situation, a worker can open one or more of the valves  124  to allow the flow the back-up air. The back-up air flows through conduit  126 , through manifold  80  and to the conduits  90 ,  100 ,  110 . The back-up air traveling through conduit  100  will also receive moisture from mister  107 . 
   To maximize the duration of breathable air, it is preferred that workers stop demand of the filling air and tool air through outlet valves  42  and  46 . To ensure that workers terminate use of the filling air and tool air, the embodiment illustrated in  FIG. 10  includes solenoid valves  95  and  115  in conduits  90  and  110 , respectively. Upon activation of the emergency sequence, the controller  28  is configured to close valves  95  and  115  such that only conduit  100  is open and all back-up air is limited to use as breathable air through outlet valve  44 . To further automate the system, in the embodiment illustrated in  FIG. 10 , each of the valves  124  is replaced with a solenoid valve  124 ′ such that the controller  28  can automatically open one or more of the back-up air tanks  122  upon activation of the emergency sequence. 
   While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention.