Abstract:
Provided is a water-cooled air compressor which is capable of restraining lowering of the performance of a plate type compressor for heat-exchanging compressed air from a compressor body, with cooling water due to clogging of gaps between plates in the heat-exchanger by dust or the like, incorporating a first solenoid valve and a second solenoid valve connected respectively in a cooling water supply pipe line and a cooling water discharge pipe line of the heat-exchanger, an air feed pipe line connecting between a compressed air supply pipe line on the outlet side of the heat-exchanger and the cooling water discharge pipe line, a third solenoid valve and a check valve connected in the air feed pipe line, a discharge pipe line connected in a discharge pipe line  18  so as to branch therefrom, a fourth solenoid valve connected in the discharge pipe line, and a control device for controlling opening and closing of the first to fourth solenoid valves.

Description:
[0001]    The present application claims priority from Japanese application JP2007-161839 filed on Jun. 19, 2007, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a water-cooled air compressor having a plate type heat-exchanger, and in particular to a water-cooled air compressor capable of preventing a plate type heat-exchanger from being clogged by foreign matter. 
         [0003]    These years, there has been more and more increased the demand that air compressors are small-sized. The air compressor is mainly composed of a motor, a compressor body, a step-up gear and an incorporated dryer which occupy large spaces within the air compressor, and also includes a water-cooling type heat-exchanger which also occupies a relatively large space therein. 
         [0004]    In view of the above-mentioned circumstance, instead of shell-and-tube type heat exchangers which have been conventionally used widely, plate type heat-exchangers which are small-sized and which have a high performance are more prosperously used as heat-exchangers for cooling compressed air in order to satisfy the above-mentioned demand (refer to, for example, JP-A-2006-249934). 
       SUMMARY OF THE INVENTION 
       [0005]    The plate type heat-exchangers each of which comprises a plurality of washboard-like plates which are stacked one upon another, are roughly classified into two types, that is, a packing type in which the plates are sealed together with packing therebetween, and a brazing type in which plates are integrally incorporated with one another by brazing. 
         [0006]    The former packing type heat-exchanger is advantageous since it can be disassembled so as to facilitate the internal cleaning thereof, but it is disadvantageous since it is expensive, so as to possibly cause a risk of leakage through the packing and so forth. Thus, the brazing type heat-exchangers are widely used at present as the plate type heat-exchangers. 
         [0007]    The plate type heat-exchanger is small-sized and is excellent in its performance. However, gaps between plates is relatively small, that is, it is about 2 to 3 mm, and accordingly, foreign matter such as dust having entered into a water cooling system is possibly built up in the plate type heat-exchanger, the flow of cooling water is hindered, and accordingly, the performance of the heat-exchanger would be lowered so that the heat-exchanger should be frequently cleaned. 
         [0008]    In order to prevent the clogging gaps between the plates by foreign matter such as dust, there may be carried out in general the method that a strainer is arranged on the inlet side of the water cooling system in the plate type heat-exchanger so as to separate the foreign matters such as dust from cooling water by the strainer, and thereafter, the cooling water is fed into the heat-exchanger. As stated above, the gaps between the plates in the plate type heat-exchanger is about 2 to 3 mm which is relatively smaller than diameters of tubes, which are about 6 to 20 mm, in a conventional shell-and-tube type heat-exchanger. Thus, even foreign matter such as dust contained in the cooling water, which has not yet caused any problem in the shell-and-tube type heat-exchange would cause the problem of clogging the gaps between the plates, resulting in lowering of the performance of the heat-exchanger. 
         [0009]    In order to eliminate the above-mentioned problem, a strainer is arranged upstream of the plate type heat-exchanger so as to separate foreign matter such as dust from cooling water. However, should a strainer having an extremely fine mesh size with a high degree of accuracy for separation be used, the strainer would be clogged at an early stage. In order to avoid the clogging, the accuracy for separation has been set to a moderate value. 
         [0010]    Thus, microscopic foreign matter such as dust, sludge or the like contained in the cooling water which is in general fed from a cooling tower may pass through the strainer, and as a result, the foreign matter clogs gaps between the plates in the plate type heat-exchanger, causing a problem of lowering the performance of the heat-exchanger. 
         [0011]    The present invention is devised in view of the above-mentioned problems, and accordingly, an object of the present invention is to provide a water-cooled air compressor which is capable of suppressing the lowering of the performance of the heat-exchanger caused by clogging of gaps between the plates in the heat-exchange with foreign matter such as dust. 
         [0012]    To the end, according to a first aspect of the present invention, there is provided a water-cooled air compressor incorporating a plate type heat-exchanger for heat-exchanging between compressed air from a compressor body and cooling water, characterized by the provision of a first solenoid valve and a second solenoid valve which are provided respectively in a cooling water supply pipe line and a cooling water discharge pipe line of the heat-exchanger, an air feed pipe communicating between a compressed air supply pipe line provided on the outlet side of the heat-exchanger, and the cooling water discharge pipe line, a third solenoid valve and a check valve which are provided in the air feed pipe line, a discharge pipe line which is connected the cooling water supply pipe line of the heat-exchanger so as to branch therefrom, a fourth solenoid valve provided in the discharge pipe line, and a control device for controlling the opening and closing of the first to fourth solenoid valves. 
         [0013]    According to a second aspect of the present invention, in the first aspect of the present invention, the control device comprises a storage portion storing therein timings with which there is carried out operations of closing the first solenoid valve, closing the second solenoid valve, opening the third solenoid valve and opening the fourth solenoid valve in the mentioned order, and a computing portion for delivering opening and closing signals to the first to fourth solenoid valves with the timings stored in the storage portion, in response to a stop signal as to the compressor body. 
         [0014]    According to a third aspect of the present invention, in the first aspect of the present invention, the control device comprises a storage portion which stores therein timings with which there is carried out operations of closing the first solenoid valve, closing the second solenoid valve, opening the third solenoid valve and opening of the fourth solenoid valve in the mentioned order, and a set operating time of the compressor body, and a computing portion for delivering opening and closing signals to the first to fourth solenoid valves in response to a stop signal as to the compressor body in the case that an operation time of the compressor body exceeds the set operation time stored in the storage portion. 
         [0015]    Further, according to a fourth aspect of the present invention, in the first aspect of the present invention, the cooling water supply pipe line and the cooling water discharge pipe line of the heat-exchanger are provided respectively with pressure detectors, and the control device comprises a storage portion which stores therein timings with which there is carried out operations of closing the first solenoid valve, closing the second solenoid valve, opening the third solenoid valve and opening the fourth solenoid valve in the mentioned order, and a set pressure differential between the cooling water supply pipe line and the cooling water discharge pipe line, and a computing portion for computing a pressure differential from output signals from the pressure detectors, and for delivering opening and closing signals to the first to fourth solenoid valves with the timings stored in the storage portion in response to a stop signal as to the compressor body in the case that the pressure differential exceeds the set pressure differential. 
         [0016]    According to the present invention, foreign objects such as dust which has been built up in the cooling water passages in the plate type heat-exchanger can be removed away from the cooling water passages with the use of a part of compressed air in response to a stop of the compressor, thereby it is possible to enhance the workability as to the removal of the foreign matter. As a result, the performance of the plate-type heat-exchanger can be restrained from being lowered, thereby it is possible to enhance the performance of the overall compressor. 
         [0017]    Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a configuration view illustrating a water-cooled air compressor in an embodiment of the present invention; 
           [0019]      FIG. 2  is a view illustrating a configuration of a plate type heat-exchanger, as an example, which is used in the air compressor in the embodiment of the present invention; 
           [0020]      FIG. 3  is a time-chart for controlling the water-cooled air compressor according to the present invention; and 
           [0021]      FIG. 4  is a configuration view illustrating a water-cooled air compressor in another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    Explanation will be made of a water-cooled air compressors according to the present invention in the form of preferred embodiments with reference to the accompanying drawings. 
         [0023]      FIGS. 1 and 2  show a water-cooled compressor in an embodiment of the present invention, in which  FIG. 1  is a configuration view illustrating the water-cooled air compressor in the embodiment of the present invention, and  FIG. 2  is a configuration of a plate type heat-exchanger, as an example, used in the water-cooled air compressor in the embodiment of the present invention, and  FIG. 3  is a control time chart for the water-cooled air compressor in the embodiment of the present invention. 
         [0024]    Referring to  FIG. 1 , there is shown a water-cooled air compressor unit  1  which incorporates a compressor body  2  driven by a motor  3 . The compressor body  2  is connected thereto on its suction side with an air suction pipe line  4  which is provided on its suction side with a suction filter  5 . 
         [0025]    The compressor body  2  is connected on its discharge side with a compressed air inlet port of a plate type heat-exchanger  7  through the intermediary of a compressed air discharge pipe line  6 . The plate type heat-exchanger  7  is connected thereto at its compressed air outlet port with a compressed air supply pipe line  8  in which a check valve  9  is provided. 
         [0026]    The plate type heat-exchanger  7  comprises a plurality of plates  7 A,  7 B,  7 C which are stacked one upon another, as shown in  FIG. 2 , so as to define therebetween compressed air passages  7 D and cooling water passages  7 A alternately in the stacking direction of the plates. 
         [0027]    Referring again to  FIG. 1 , the water cooling passages in the plate type heat-exchanger  7  are connected on the inlet side of the cooling water passages with a cooling water pipe line  10  in which a first solenoid valve  11  and a strainer  12  are connected. The cooling water passages in the plate-type heat-exchanger  7  is connected thereto on the outlet side of the cooling water passages with a cooling water discharge pipe line  13  which is connected therein with a second solenoid valve  14 . 
         [0028]    A compressed air supply pipe line  8  on the outlet side of the plate type heat-exchanger  7  and a cooling water discharge pipe line  13  on the outlet side of the plate type heat-exchanger  7  are connected to each other through the intermediary of an air feed pipe line  15  in which a third solenoid valve  16  and a check valve  17  for preventing compressed air from counterflowing from the cooling water discharge pipe line  13  into the compressed air supply pipe line  8  are connected being arranged in the mentioned order as viewed in the direction from the compressed air supply pipe line  8  to the cooling water discharge pipe line  13 . 
         [0029]    The cooling water supply pipe line  10  on the inlet side the plate type heat-exchanger  7  is provided with a discharge pipe line  18  which branches therefrom. The discharge pipe line  18  is connected therein with a fourth solenoid valve  19 . 
         [0030]    The first solenoid valve  11  in the cooling water supply pipe line  10 , the second solenoid valve  14  in the cooling water discharge pipe line  13 , the third solenoid valve  16  in the air feed pipe line  15  and the fourth solenoid valve  19  in the discharge pipe line  18 , which are stated above, are controlled by a control device  20  so as to be opened and closed. The control device  20  comprises a storage portion  20   a  storing therein opening and closing timings of the first solenoid valve  11 , the second solenoid valve  14 , the third solenoid valve  16  and the fourth solenoid valve  19 , and a computing portion  20   b  which receives the opening and closing timings stored in the storage portion  20   a  in response to a stop signal as to the compressor body  2 , and which delivers opening and closing signals for the first solenoid valve  11 , the second solenoid valve  14 , the third solenoid valve  16  and the fourth solenoid valve  19 , to the first solenoid valve  11 , the second solenoid valve  14 , the third solenoid valve  16  and the forth solenoid valve  19 . 
         [0031]    Explanation will be made of the opening and closing timings of the first solenoid valve  11 , the second solenoid valve  14 , the third solenoid valve  16  and the fourth solenoid valve  19 , as an example, with reference to  FIG. 3 . 
         [0032]    During the operation of the compressor body  2 , the first solenoid valve  11  and the second solenoid valve  14  are opened while the third solenoid valve  16  and the fourth solenoid valve  19  are closed. In this condition, when the compressor body  2  comes to a stop, the opening and closing control is carried out as follow: the control device  20  closes at first the first solenoid valve  11  at a time t 1  (corresponding to the time of stopping of the compressor body  2 ) in response to a stop signal A as to a compressor body  2 , which is delivers from a controller (which is not shown) for the compressor, and then closes the second solenoid valve at a time t 2 . Thereafter, the control device  20  opens the third solenoid valve  16  at a time t 3 , and then, opens the fourth solenoid valve  19  at a time t 4 . 
         [0033]    The reason why the second solenoid valve  14  is closed at the time t 2  after the first solenoid valve  11  is closed is such that the cooling water is caused to remain in the cooling water passages within the plate type heat-exchanger  7 , and the residual pressure in the cooling water system is lowered as possible as it can. 
         [0034]    Next, explanation will be made of the operation of the water-cooled air compressor in the embodiment of the present invention with reference to  FIGS. 1 to 3 . 
         [0035]    Referring to  FIG. 1 , the compressor body  2  which is driven by the motor  3  compresses the atmospheric air which is sucked up through the suction filter  4 , up to a predetermined pressure, and discharges the thus compressed air. The compressed air having a high temperature, and discharged from the compressor body  2  is heat-exchanged with the cooling water in the plate-type heat-exchanger  7 , and thereafter, is discharged outside of the unit  1  by way of the check valve  9 . At this time, as shown in  FIG. 2 , the first solenoid valve  11  and the second solenoid valve  14  are opened while the third solenoid valve  16  and the fourth solenoid valve  19  are closed. 
         [0036]    Referring again  FIG. 1 , in the plate type heat-exchanger  7  which carries out heat-exchange between compressed air at a high temperature and the cooling water, the cooling water flows through the first solenoid valve  11  for opening and closing the cooling water pipe line  10  and the strainer  12  for removing foreign matter contained the cooling water, and thereafter flows into the cooling water passages in the plate type heat-exchanger  7 . The cooling water is heat-exchanged with the compressed air at a high temperature within the plate type heat-exchanger  7 , and thereafter, is discharged through the cooling water pipe line  13  and the fourth solenoid valve  14 . 
         [0037]    Next, when the controller (which is not shown) for the compressor stops the operation of the compressor body  2 , the control device  20  receives a stop signal A as to the compressor body  2 , and as shown in  FIG. 3 , closes the first solenoid valve  11  at the time t 1  which is the same time as that of stopping of the compressor body  2 , thereafter closes the second solenoid valve  14  at the time t 2  with a slight lag from the time t 1  in order to causes the cooling water to remain within the cooling water passages in the plate type heat-exchanger  7 . The reason why the second solenoid valve  12  is closed with a slight lag with respect to the first solenoid valve  11  is such that it is desirable to lower the residual pressure in the cooling water system as possible as it can. 
         [0038]    Thereafter, in response to an instruction from the control device  20 , the third solenoid valve  16  in the air feed pipe line  15  is opened at the time t 3  as shown in  FIG. 3 , and accordingly, air is fed into the cooling water passages in the plate type heat-exchanger  7  by way of the check valve  17  with the use of the residual pressure in the compressor body  2 . Next, in response to an instruction from the control device  20 , the fourth solenoid valve  14  in the discharge pipe line  18  is opened at the time t 4  as shown in  FIG. 3 . Accordingly, the cooling water which has remained in the plate type heat-exchanger  7  powerfully counterflows through the cooling water passages in the plate type heat exchanger  7 , and spouts therefrom, thereby it is possible to push out foreign matters such as dust clogging the cooling water passages in the plate type heat-exchanger  7 . Thereafter, the control device  20  causes the first solenoid valve  11 , the second solenoid valve  14 , the third solenoid valve  16  and the fourth solenoid valve  19  to return to their original open and closed positions. 
         [0039]    In view of the above-mentioned embodiment, foreign object such as dust clogging the cooling water passages in the plate type heat-exchanger  7  can be removed and pushed away therefrom with the use of a part of the compresses air in response to a stop of the compressor, and accordingly, it is possible to enhance the removal of foreign matter. As a result, the performance of the plate type heat-exchanger  7  can be restrained from being lowered, thereby it is possible to enhance the performance of the overall compressor. 
         [0040]    It is noted in the above-mentioned embodiment in which a part of the compressed air is fed into the cooling water passages in the plate type heat-exchanger  7  in response to a stop of the compressor in order to remove and push out foreign matter such as dust clogging the cooling water passages in the plate type heat-exchanger  7 , the supply of the air into the cooling water passages in the plate type heat-exchanger  7  may be made every stop of the compressor. 
         [0041]    It is noted, in the above-mentioned embodiment in which the control device  20  is provided in addition to the controller for the compressor itself, that the control device  20  may be incorporated in the controller for the compressor. 
         [0042]    Further, as another embodiment of the present invention, there may be provided the configuration that the operation time of the compressor is monitored, and if the operation time exceeds a set time, the air is fed into the cooling water passages in the plate-type heat-exchanger  7 . In this case, the computing portion  20   b  receives the operating time from the controller for the compressor and controls the opening and closing timings of the first solenoid valve  11 , the second solenoid valve  14 , the third solenoid valve  16  and the fourth solenoid valve  19  when the operation time exceeds the set time which has been stored in the storage portion  20   a  in the control device  20  in response to a stop signal as to the compressor, as shown in  FIG. 3 . 
         [0043]    Referring to  FIG. 4  which is a configuration view illustrating a water-cooled air compressor in another embodiment of the present invention and in which like reference numerals are used to denote like parts to those shown in  FIG. 1  in order to abbreviate detailed description thereto, the water-cooled type air compressor in this embodiment will be explained. 
         [0044]    In this embodiment, the cooling water supply pipe line  10  and the cooling water discharge pipe line  13  of the plate type heat-exchanger  7  are connected respectively therein with pressure detectors  21 ,  22 , and accordingly, there may be provided the configuration that the air is fed into the cooling water passages in the heat-exchanger  7  in response to a stop as to the compressor if a difference between pressures detected by both pressure detectors  21 ,  22  exceeds a set value which has been previously set. In this configuration, the set value has been stored in the storage portion  20   a  of the control device  20  while the computing portion  20   b  calculates a difference between pressures detected by the pressure sensors  21 ,  22 , and accordingly, the opening and closing timings of the first solenoid valve  11 , the second solenoid valve  14 , the third solenoid valve  16  and the fourth solenoid valve  19  may be controlled, as shown in  FIG. 3 , in response to a stop signal as to the compressor if the pressure difference exceeds the set value. 
         [0045]    In the above-mentioned embodiment in which the cooling water supply pipe line  10  and the cooling water discharge pipe line  13  of the plate type heat-exchanger  7  are connected therein respectively with the pressure detectors  21 ,  22 , it is noted that a pressure differential detector may be connected between the cooling water supply pipe line  10  and the cooling water discharge pipe line  13  so that a detection signal is delivered from the pressure differential detector to the control device  20 . Further, the cooling water supply pipe line  10  may be connected therein with a flow detector from which a detection signal is delivered to the control device  20 . 
         [0046]    In the above-mentioned embodiments in which foreign object such as dust clogging the cooling water passages in the plate type heat-exchanger  7  can removed and pushed away therefrom with the use of a part of the compressed air in response to a stop of the compressor, it is possible to enhance the cleaning performance as to the removal of foreign object from the plate type heat-exchanger. As a result, the performance of the plate type heat-exchanger  7  can be restrained from being lowered, thereby it is possible to enhance the performance of the overall plate type heat-exchanger  7 . Further, the intervals as to the cleaning of the plate type heat-exchanger  7  can be prolonged, thereby it is possible to enhance the workability and safety thereof. 
         [0047]    It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.