Patent Publication Number: US-2007113738-A1

Title: Purge-control polymer-membrane-type air drier system

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a purge-control polymer-membrane-type air drier system in which air is introduced inside a polymer membrane to dehumidify air thereby controlling purging from a polymer-membrane-type air drier.  
      A polymer membrane comprising polymer through which vapor is permeable is placed in a casing. Wetted compressed air is supplied into the polymer membrane to allow only vapor to permeate therethrough to provide dehumidified air. Such polymer-membrane-type air drier is known.  
      The polymer-membrane-type air drier having no moving part is small, light and durable without electric energy, and provides high dew point which is advantageous. The polymer-membrane-type air drier is installed in various types of equipment.  
      In such a polymer-membrane-type air drier, for continuous dehumidification, it is necessary to keep outside of the polymer membrane in low partial pressure outside the polymer membrane. Thus, dried air is partially decompressed to decrease relative humidity and sent outside a polymer membrane to generate pressure difference in vapor. Thereafter, dried air is purged together with vapor which permeates through a polymer membrane. It is generally employed.  
      In the purged air, dehumidified and compressed air is partially employed. Considerable amount of dehumidified and dried air which could reach to about 30% is consumed without use for primary purpose to cause energy loss.  
      If air which is dehumidified and dried is not consumed, it will not necessary to purge dried air. For example, in JP3,276,784B2 and JP3,429,698B2, depending on whether or not dried air from a polymer membrane is used for primary purpose or discharge pressure of dried air, an electric signal is forwarded to a control device by a flow sensor or pressure-detecting means to allow an outlet of purged air to open and close with an electromagnetic valve.  
      There are some disadvantages in the device in which an electric signal and control device are used.  
      (a) The structure becomes complicate to increase cost.  
      (b) Inspection, maintenance and adjustment need a lot of time.  
      (c) Waiting power is required, which is uneconomical. It is likely to cause fire. It is not usable depending on the field of application.  
      (d) It is difficult to discharge and stop purging. Energy is uselessly consumed.  
     SUMMARY OF THE INVENTION  
      In view of the disadvantages in the prior art, it is an object of the present invention to provide a purge-control polymer-membrane-type air drier system in which a control valve is automatically operated via a selector valve based on pressure of discharged dried air depending on whether or not dried air from a polymer-membrane-type air drier is used thereby purging dried air in the polymer-membrane-type air drier without use of electric signals or control device and stopping purging.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features and advantages of the invention will become more apparent from the following description with respect to embodiments as shown in accompanying drawings wherein:  
       FIG. 1  is a diagram showing the first embodiment of a system according to the present invention in which an air tool is used;  
       FIG. 2  is a diagram showing the first embodiment of a system according to the present invention in which the air tool is not used;  
       FIG. 3  is a diagram showing the second embodiment of a system according to the present invention in which an air tool is used; and  
       FIG. 4  is a diagram showing the third embodiment of a system according to the present invention in which the air tool is not used. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT  
       FIG. 1  shows the first embodiment according to the present invention in which an air tool  5  is used.  
      For simplification, the internal structure and description of a polymer-membrane-type air drier  1  are omitted. Air which flows into an inlet  2  of a polymer-membrane-type air drier  1  is dehumidified and forwarded from an outlet  3  of the sir drier  1  via a selector valve  4  to an air tool  5  in which dried compressed air is used such as an air cylinder. Dehumidified air  1  is partially sent from a purging outlet  6  to a purge-control valve  7  and discharged therefrom as purged air  8 .  
      The selector valve  4  such as a directional control valve has a through hole  9  which connects the outlet  3  to the air tool  5 , and a branching hole  10  which communicates with the through hole  9 . The branching hole  10  has a ball valve  12  which is pressed by a spring  11  to close the branching hole  10  and communicates with a guide hole  13  and a remaining-pressure discharge hole  14 .  
      The purge-control valve  7  such as a sluice valve has a sliding valve element  19  in a tubular body  17  having radial holes  15 , 16  which extends radially and a communicating hole  18  which extends radially to coincide with the radial holes  15 , 16 . The sliding valve element  19  is forced upward by a spring  20 .  
      The sliding valve element  19  moves upward in the tubular body  17  by the spring  20  with no load to allow the communicating hole  18  to communicate with the radial holes  15 , 16 .  
      The guide hole  13  of the selector valve  4  is connected to an upper space of the tubular body  17  of the purge-control valve  7 . While dehumidified air from the polymer-membrane-type air drier  1  is used in the air tool  5 , static pressure of dehumidified air in the through hole  9  of the selector valve  4  is low, so that the ball valve  12  is pushed upwards by the spring  1  to make it impossible for the radial holes  10  to communicate with the guide hole  13 .  
      As shown in  FIG. 1 , the sliding valve element  19  of the purge-control valve  7  is kept to rise by the spring  20  to allow the communicating hole  18  to communicate with the radial holes  15 , 16 , so that air from the purging outlet  6  is discharged.  
      In  FIG. 2 , the air tool  5  is not used to allow static pressure of dehumidified air in the selector valve  4  between the outlet  3  and the air tool  5  to become greater. Dehumidified air partially flows from the branching hole  10  to the purge-control valve  7  via the guide hole  13  to push the ball valve  12  down against the spring  11 . Thus, the sliding valve element  17  lowers to push the spring  20  to make it impossible for the radial holes  15 , 16  to communicate, so that purging stops.  
      When the ball valve  12  of the selector valve  4  is pushed down to allow the guide hole  13  to communicate with the through hole  9 , the remaining-pressure discharge hole  14  is closed by the ball valve  12 , so that the guide hole  13  is blocked off air.  
       FIGS. 3 and 4  show the second embodiment of the present invention in which a selector valve  4  is provided in front of a polymer-membrane-type air drier  1 , which only differs from  FIGS. 1 and 2 . The same numerals are allotted to the same members as those in  FIGS. 1 and 2  and its description is omitted  
      The foregoing merely relates to embodiments of the invention. Various changes and modifications may be made by a person skilled in the art without departing from the scope of claims wherein: