Abstract:
A moisture removal apparatus for a vehicular compressed air storage system includes a canister of mist-eliminating mesh that collects moisture and oil droplets in the air and exhausts them through a gravity drain. The mesh coalesces droplets of both water and oil vapor in the air stream, and is not contaminated by either. The mist eliminating canister can be a stand-alone device through which compressed air is delivered to a pressure tank, or may be integrated into a pressure tank for space efficiency.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of provisional U.S. Patent Application Ser. No. 61/007,567, filed Dec. 13, 2007. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a vehicular compressed air storage system, for operating air brakes for example, and more particularly to an apparatus for removing excessive moisture from the stored air. 
     BACKGROUND OF THE INVENTION 
     Commercial vehicles are commonly equipped with a compressed air storage system for operating air brakes and other pneumatically activated devices. An air compressor driven by the vehicle engine supplies compressed air to one or more storage vessels, which in turn are coupled to the air brakes and other pneumatically activated devices. Since excessive ambient moisture in the compressed air can be harmful to air brakes and other pneumatically activated devices, most compressed air storage systems include a moisture removal mechanism. 
     One of the most common and cost effective ways to remove moisture from a compressed air storage system is to drive the compressed air through a desiccant material such as silica gel or active alumina that adsorbs moisture on its surface. At some point, the desiccant material becomes saturated and the adsorbed water must be removed through a regeneration procedure. However, the problem with this approach is that air supplied by an oil-lubricated compressor invariably contains a certain amount of blow-by oil mist that contaminates the desiccant material so that it will no longer adsorb moisture or regenerate. This condition can be forestalled to some degree by installing an oil filter upstream of the desiccant, but both the oil filter and the desiccant material must, as a practical matter, be periodically replaced to keep the brakes and other pneumatically activated devices free of excessive moisture. Accordingly, what is needed is a more reliable and maintenance-free apparatus for removing excessive moisture in a motor vehicle compressed air storage system. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved vapor droplet removal apparatus for a motor vehicle compressed air storage system in which potentially moisture-laden air supplied to a canister by an oil-lubricated compressor is passed through a mist-eliminating mesh that removes moisture and oil mist in the air. The mesh coalesces droplets of both water vapor and oil vapor in the air stream, and is not contaminated by either. The coalesced moisture and oil are collected in a sump area of the canister, and are periodically exhausted through an electrically activated drain. The drain may be a gravity drain installed in the sump area, but is preferably a siphon drain installed in a dry portion of the canister. The canister may be a stand-alone device through which compressed air is delivered to a separate pressure tank, or may be integrated into a pressure tank for space efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a vehicle compressed air storage system including a stand-alone mist elimination canister according to a first embodiment of this invention; 
         FIG. 2  depicts the stand-alone mist elimination canister of  FIG. 1 ; 
         FIG. 3A  depicts a stand-alone mist elimination canister according to a second embodiment of this invention; 
         FIG. 3B  is a top view of the stand-alone mist elimination canister of  FIG. 3A ; 
         FIG. 3C  is an isometric view of the stand-alone mist elimination canister of  FIG. 3A ; and 
         FIG. 4  depicts a combined pressure tank and mist elimination canister according to a third embodiment of this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , the reference numeral  10  generally designates a commercial truck such as a semi-tractor. The frame  12  of the tractor  10  supports the powertrain  14  and various air storage system canisters  16 - 20 . The air storage system includes a compressor  22 , a stand-alone mist elimination canister  16 , a primary air storage tank  18 , and a secondary air storage tank  20 . In a typical application, the compressor  22  is an engine-driven component, and includes a pneumatically operated unloading or bypass device  24  for controlling the compressor load to regulate the air pressure in one or more of the canisters  16 - 20 . Alternately, the compressor  22  may be driven an electric or hydraulic motor with a speed or on/off control for controlling the compressor load. 
     In the embodiment of  FIG. 1 , the air hose  26  couples the output of compressor  22  to the inlet  28  of a mist elimination canister  16 . A governor  30  responsive to the pressure in canister  16  is coupled to the compressor-unloading device  24  to regulate the air pressure in canister  16  to a prescribed pressure range. The air supplied to canister  16  flows through a mist elimination mesh  32  disposed within the canister  16 , and the de-misted air is then delivered from the canister outlet  34  to the primary and secondary canisters  18  and  20  by one or more air hoses  36 . Typically, the canisters  18  and  20  include inlet check valves (not shown) for preventing leakage of the stored air in the event of an upstream pressure loss. The primary canister  18  supplies pressurized air to an air brake controller  38 , and the secondary canister  20  supplies pressurized air to other pneumatically activated devices such as load levelers, air horns, and so on. 
       FIG. 2  shows the mist elimination canister  16  of  FIG. 1  in further detail. Referring to  FIG. 2 , the mist elimination mesh  32  is preferably disposed in a central portion of canister  16  intermediate the two end caps  40  and  42 . The governor  30  and a safety relief valve  45  are located upstream of the mist elimination mesh  32 , and a screen  43  is disposed downstream of the mist elimination mesh  32  at the canister outlet  34 . Coalesced water vapor and oil vapor is purged from the canister  16  by a manual drain  44  and/or an automatic drain  46  that is remotely activated. The mist elimination mesh  32  preferably comprises a loosely intertwined weave of fine metal wire with multi-filament yarn knitted into the weave. A suitable material is commercially available from Knitwire Products or Amistco Separation Products, Inc. Minute particles of oil and water dispersed in the inlet air collect on the surface of the mesh  32  and coalesce into droplets and flow to the bottom of the canister  16  where they are purged through the drains  44  and/or  46 . The air exiting the canister outlet  34  is substantially free of oil vapor and water vapor particles, and is supplied to the primary and secondary canisters  18  and  20  as dry air suitable for use in air brakes and other pneumatically activated devices. 
       FIGS. 3A-3C  depict a second embodiment of a stand-alone mist elimination canister  16 ′ that is configured for vertical installation instead of horizontal. This embodiment differs from the embodiment of  FIGS. 1-2  in at least three other respects as well. First, the governor  30  and safety relief valve  45  are omitted; second, the automatic gravity drain  46  of the first embodiment is replaced with an automatic siphon drain; and third, an internal baffle is added to enhance mist elimination. 
     Referring to  FIGS. 3A-3C , the mist elimination mesh  32  is disposed in a central portion of canister  16 ′ intermediate the upper and lower end caps  40  and  42 . High pressure air from compressor  22  enters canister  16 ′ via an inlet  28  located below the mist elimination mesh  32 , and is directed laterally along the inner periphery of the canister  16 ′ by a baffle  48  disposed just below the mist elimination mesh  32 . The baffle  48  imparts a swirling motion to the inlet air for improved mist elimination in the mesh  32 , and additionally collects and drains off some of the moisture and oil vapor that comes out of suspension when it impacts the baffle surface. The vapor-laden air flows upward though the mist elimination mesh  32 , and exits the canister  16 ′ via an outlet  34  formed in the upper end cap  40 . In this embodiment, the outlet  34  accommodates an internal screen for capturing any foreign matter. 
     The coalesced water vapor and oil vapor collects in a sump  50  formed in the lower end cap  42 , and is periodically purged by an automatic siphon drain comprising a siphon tube  52 , a through-fitting  54  formed in the side of the canister  16 ′ opposite the inlet  28 , and an electrically activated valve module  56 . As seen in  FIG. 3A , the siphon tube  52  is coupled to the internal end of through-fitting  54 , and extends into the sump  50 . As seen in  FIGS. 3B-3C , canister  16 ′ includes a bracket  58  for mounting the canister  16 ′ on a suitable vehicle frame, and the valve module  56  is mounted on a leg of the bracket  58 . The valve module  56  includes an electrical connector  60 , an inlet port  62  coupled to the external end of through-fitting  54  by a suitable length of tubing  64 , and an outlet port  66 . Conveniently, the outlet port  66  can be coupled to a vented canister (not shown) so that the expelled water and oil can be collected and appropriately recycled. Since the valve module  56  is remote from the sump  50 , it is easily accessible for maintenance, and is not subject to damage or deterioration from contact with frozen liquids. 
       FIG. 4  depicts a multi-compartment canister  70  that combines the functionality of mist elimination canister  16  and primary (or secondary) canister  18  of  FIG. 1 . Reference numerals used in  FIGS. 1-2  have been reused where appropriate. In this case, the air hose  26  from compressor  22  is coupled to the inlet  72  of canister  70 , and an air hose  74  couples the outlet  76  of canister  70  to the secondary air storage canister  20 . The inlet  72  is formed in end cap  78 , the outlet  76  is formed in end cap  80 , and a metal baffle  82  (a third end cap, for example) is welded to the inner periphery of the canister  70  intermediate the end caps  78  and  80  to form upstream and downstream compartments  84  and  86 . The mist elimination mesh  32  is disposed in the upstream compartment  84  (i.e., the wet compartment), and coalesced oil and water is purged from compartment  84  by the manual and/or automatic drains  88  and  90 . Air exiting the upstream compartment  84  enters the downstream compartment  96  through a check valve  92  mounted in the baffle  82 . Thus the upstream compartment  84  serves the function of mist elimination canister  16  and the downstream compartment  86  serves the function of primary (or secondary) canister  18 . 
     In summary, the present invention provides a reliable and maintenance-free apparatus for removing excessive moisture in a motor vehicle compressed air storage system. There are no oil filters or desiccant canisters to periodically replace, and proper operation of the system no longer depends upon adherence to a specified maintenance schedule. While the invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the siphon drain arrangement depicted in  FIGS. 3A-3C  may be used with the other canister embodiments, and so forth. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.