CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2008-0017669, filed Feb. 27, 2008, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hot air blower, and more particularly, to a hot air blower including a pressure regulation valve for adjusting an air pressure supplied into a burner of the hot air blower at an appropriate pressure. 
     2. Description of the Prior Art 
     In general, hot air blowers are used to provide hot air into a closed space such as a plant or remove moisture from a green house such as a vinyl house, a cow house, and so on. 
     The hot air blowers may be classified into an electric heat exchange type of applying electricity to a heater or a hot-wire coil to heat sucked air to a high temperature and then discharging the hot air to the exterior using the blower, or a combustion heating type of combusting fuel in a combustion chamber to heat air and discharge the heated air using a blowing fan. 
       FIGS. 1 and 2  show a typical example of the combustion heating type hot air blower, among the hot air blowers. 
     The combustion heating type hot air blower includes a blower body  10  having a fuel tank  12  disposed at its lower part a combustion chamber  20  disposed in front of the blower body  10  and over the fuel tank  12 , a burner assembly  22  having an injection nozzle  22   a  installed at a rear part of the combustion chamber  20  to inject fuel and an ignition plug  22   b  for igniting the fuel, a vane pump  28  connected to the burner assembly  22  via a fuel supply line  24  and generating a predetermined pressure to supply fuel, a blower fan  32  for blowing air into the combustion chamber  20 , and a drive motor  30  for rotating the blower fan  32 . 
     The vane pump  28  is merely an example of an air compression pump, and other kinds of air compression pumps may be installed in the blower. 
     In addition, the blower includes a controller (not shown) for controlling the entire operation, a pair of wheels  14  installed at a lower end of the blower body  10  to enable movement of the blower, a stopper  16  installed opposite to the wheels  14 , and a handle  18  installed at an upper part of the blower body  10 . 
     Further, as shown in  FIGS. 3A and 3B , the blower includes a pressure regulation valve  40  installed at one side of the vane pump  28  to supply introduced air through an air suction port  10   a  at an appropriate pressure. The pressure regulation valve  40  is positioned on a path through which the compressed air generated by the vane pump  28  moves to the burner assembly  22 . 
     The pressure regulation valve  40  adjusts a supply pressure of the air compressed by the vane pump  28  to supply the air into the injection nozzle  22   a  of the burner assembly  22  at an appropriate pressure. 
     Hereinafter, the above constitution will be described in detail. 
     First, the vane pump  28  includes a rotor  35  rotated by the drive motor  30 , a front housing  28   d  installed at one side of the rotor  35 , and a rear housing  28   e  installed opposite to the front housing  28   d . The rotor  35  constitutes a compression part of the vane pump  28 . 
     In addition, a chamber  37  in which air flows is formed between the front housing  28   d  and the rear housing  28   e.    
     Further, the front housing  28   d  and the rear housing  28   e  have separation projections  28   f  and  28   g  projecting from their inner surfaces toward each other, respectively. The separation projections  28   f  and  28   g  are adhered to each other via a gasket  28   h  to divide the chamber  37  into an introduction chamber  37   a  and a compression chamber  37   b.    
     Furthermore, the rear housing  28   e  has the air suction port  10   a  in communication with the introduction chamber  37   a.    
     The introduction chamber  37   a  includes a filter  36  for filtering foreign substances included in the air passing therethrough. 
     In addition, as shown in  FIG. 3B , an introduction hole  28   a  is formed in the front housing  28   d  corresponding to the introduction chamber  37   a  to introduce the air passed through the filter  36  into the rotor  35 . 
     Further, a discharge hole  28   b  is formed in the front housing  28   d  corresponding to the compression chamber  37   b  to discharge the air compressed by the rotor  35  to the compression chamber  37   b.    
     The compression chamber  37   b  also has a filter  38  to filter foreign substances included in the compressed air discharged through the discharge hole  28   b.    
     An air line  28   c  is formed around the compression chamber  37   b  to convey the compressed air to the burner assembly  22 . 
     In addition, the pressure regulation valve (or a relief valve)  40  is installed at the rear housing  28   e  to lower the pressure of the compressed air discharged from the vane pump  28 . The pressure regulation valve  40  is installed in a hole  42  formed in the rear housing  28   e  so that the compressed air is discharged through the hole  42 . 
     The air in the compression chamber  37   b  lowered to a predetermined value by the pressure regulation valve  40  is conveyed to the burner assembly  22  through the air line  28   c.    
     A partition wall  28   j  is formed in the compression chamber  37   b  to divide the chamber  37   b  into a space in which the air line  28   c  is formed and a space in which the pressure regulation valve  40  is installed. A relatively small through-hole  39  is formed in the partition wall  28   j . Therefore, it is possible to prevent the air of pressure higher than the predetermined value from being discharged through the air line  28   c.    
     In addition, a pressure gauge and a plug  41  are installed at the rear housing  28   e  adjacent to the through-hole  39  to close a pressure gauge port for measuring the pressure of the compressed air. 
     The pressure regulation valve  40  is installed in the hole  42 , and includes a ball  43 , a spring  44 , and a pressure regulation screw  45 . 
     Therefore, when the pressure regulation screw  45  is tightened, the spring  44  is compressed to prevent displacement even at a high pressure. When the pressure regulation screw  45  is loosened, the spring  44  is released to cause displacement even at a lower pressure. 
     Hereinafter, a process of reducing the pressure of the air compressed by the vane pump  28  using the pressure regulation valve  40  and supplying the air into the injection nozzle  22   a  will be described. 
     The exterior air introduced into the air suction port  10   a  is introduced into the rotor  35  of the vane pump  28  via the filter  36  in the introduction chamber  37   a  and the introduction hole  28   a , and the air compressed by the rotor  35  is discharged through the discharge hole  28   b  to move to the compression chamber  37   b  via the air filter  38 . 
     As described above, the compressed air moved into the compression chamber  37   b  passes through the through-hole  39  and then moves to the air line  28   c  to be supplied into the injection nozzle  22   a  of the burner assembly  22 . 
     A manufacturer can adjust the pressure of the air discharged from the vane pump  28  using the pressure regulation valve  40  to supply the air into the injection nozzle  22   a  at a uniform pressure. 
     In addition, the compressed air supplied into the injection nozzle  22   a  moves along the air line  28   c  to suck fuel in the fuel tank  12  to supply the fuel into the injection nozzle  22   a . When the air pressure is high, the amount of the sucked fuel is increased, and when the air pressure is low, the amount of the sucked fuel is reduced. 
     Therefore, when the compressed air is supplied into the injection nozzle  22   a  at a high pressure, a heating value is raised, and when the compressed air is supplied at a low pressure, a heating value is lowered. 
     That is, the pressure of the compressed air discharged from the vane pump  28  is different according to the hot air blower. For example, when the pressure regulation valve  40  is set to be opened at 7 psi, even when the pressure of the compressed air supplied into the injection nozzle  22   a  of the burner assembly  22  is higher than 7 psi, the compressed air is supplied into the injection nozzle  22   a  at the pressure of 7 psi. 
     For example, when the pressure of the compressed air discharged from the vane pump  28  installed in the hot air blower is 10 psi, the pressure regulation valve  40  is opened to reduce the pressure of the compressed air in the compression chamber  37   b  to 7 psi and then supply the compressed air to the injection nozzle  22   a . Even when the pressure of the compressed air discharged from the vane pump  28  installed at another hot air blower is 9 psi, the pressure regulation valve  40  reduces the pressure to 7 psi and then supplies the compressed air to the injection nozzle  22   a.    
     As described above, since the conventional hot air blower is set to a fixed pressure by the manufacturers, it is difficult for a user to adjust the pressure of the compressed air according to necessities. 
     That is, since the conventional hot air blower includes a single pressure regulation valve set to a certain discharge pressure, it is difficult for a user to adjust the pressure of the compressed supplied to the burner assembly. 
     As a result, when it is needed to reduce a heating value of the conventional hot air blower, operation of the hot air blower must be stopped. 
     In addition, in order to adjust the heating value generated in the combustion chamber, an expensive two-stage electronic pump may be installed instead of the vane pump. However, in this case, manufacturing cost of the hot air blower is increased, and installation of the two-stage electronic pump complicates the structure of the hot air blower. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a hot air blower capable of selectively adjusting the pressure of compressed air to appropriately adjust a heating value generated in the hot air blower. 
     The present invention provides a hot air blower including: a fuel tank for storing fuel; an air compression pump for sucking air and compressing the air; a pressure regulation valve installed at the air compression pump to reduce the pressure of the compressed air; a burner assembly for receiving the fuel from the fuel tank and the air from the air compression pump; and a combustion chamber for receiving the fuel from the burner assembly and combusting the fuel, wherein the pressure regulation valve includes a high pressure regulation valve and a low pressure regulation valve, and a valve opening/closing means is installed at the low pressure regulation valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front view of a conventional hot air blower; 
         FIG. 2  is a plan view of the conventional hot air blower; 
         FIG. 3A  is a perspective view of a conventional pressure regulation valve; 
         FIG. 3B  is a cross-sectional view of the conventional pressure regulation valve of  FIG. 3A ; 
         FIG. 4  is a perspective view of a hot air blower including a pressure regulation valve in accordance with a first exemplary embodiment of the present invention; 
         FIG. 5  is an enlarged perspective view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention; 
         FIG. 6  is an exploded perspective view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention; 
         FIG. 7  is a further exploded perspective view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention, showing a closed state of the valve; 
         FIG. 9  is a cross-sectional view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention, showing an open state of the valve; 
         FIG. 10  is an exploded perspective view of a pressure regulation valve in accordance with a second exemplary embodiment of the present invention; and 
         FIG. 11  is a partial cross-sectional view of a hot air blower in accordance with a third exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. Like reference numerals designate like elements throughout the conventional invention. 
     First Embodiment 
       FIG. 4  is a perspective view of a hot air blower including a pressure regulation valve in accordance with a first exemplary embodiment of the present invention;  FIG. 5  is an enlarged perspective view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention;  FIG. 6  is an exploded perspective view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention;  FIG. 7  is a further exploded perspective view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention;  FIG. 8  is a cross-sectional view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention, showing a closed state of the valve; and  FIG. 9  is a cross-sectional view of the pressure regulation valve in accordance with a first exemplary embodiment of the present invention, showing an open state of the valve. 
     Similar to the conventional art, the hot air blower of the first embodiment includes a blower body  10  having a fuel tank  12  disposed at its lower part, a combustion chamber  20  disposed in front of the blower body  10  and over the fuel tank  12 , a burner assembly  22  having an injection nozzle  22   a  installed at a rear part of the combustion chamber  20  to inject fuel and an ignition plug  22   b  for igniting the fuel, a vane pump  28  connected to the burner assembly  22  via a fuel supply line  24  and generating a predetermined pressure to supply fuel, a blower fan  32  for blowing air into the combustion chamber  20 , and a drive motor  30  for rotating the blower fan  32 . (See  FIG. 1 ) 
     Of course, relative positions between the fuel tank  12 , the blower body  10 , the combustion chamber  20 , the burner assembly  22 , the vane pump  28 , the drive motor  30 , and so on, may be varied, if necessary. 
     The vane pump  28  includes a rotor  35  rotated by the drive motor  30 , a front housing  28   d  installed at one side of the rotor  35 , and a rear housing  28   e  installed opposite to the front housing  28   d . The rotor  35  constitutes a compression part of the vane pump  28 . (See  FIGS. 3A and 3B ) 
     In addition, a chamber  37  in which air flows is formed between the front housing  28   d  and the rear housing  28   e.    
     Further, the front housing  28   d  and the rear housing  28   e  have separation projections  28   f  and  28   g  projecting from their inner surfaces toward each other, respectively. The separation projections  28   f  and  28   g  are adhered to each other via a gasket  28   h  to divide the chamber  37  into an introduction chamber  37   a  and a compression chamber  37   b.    
     Furthermore, the rear housing  28   e  has an air suction port  10   a  in communication with the introduction chamber  37   a.    
     In addition, an introduction hole  28   a  is formed in the front housing  28   d  corresponding to the introduction chamber  37   a  to introduce the air passed through a filter  36  into the rotor  35 . 
     Further, a discharge hole  28   b  is formed in the front housing  28   d  corresponding to the compression chamber  37   b  to discharge the air compressed by the rotor  35  to the compression chamber  37   b.    
     The compression chamber  37   b  also has a filter  38  to filter foreign substances included in the compressed air discharged through the discharge hole  28   b.    
     An air line  28   c  is formed around the compression chamber  37   b  to convey the compressed air to the burner assembly  22 . 
     Here, the filters  36  and  38  may be selectively employed, not necessarily. 
     As shown in  FIGS. 4 to 9 , the hot air blower in accordance with the present invention includes a high-pressure regulation valve  40  and a low-pressure regulation valve  200 , which are disposed adjacent to the compression chamber  37   b  of the rear housing  28   e . The low-pressure regulation valve  200  includes a valve opening/closing switch  100  for opening/closing the low-pressure regulation valve  200 . 
     Among them, the high-pressure regulation valve  40  is set to be opened when a high-pressure is applied, and the low-pressure regulation valve  200  is set to be opened at a pressure lower than that of the high-pressure regulation valve  40 . 
     The pressure regulation valves may use the conventional pressure regulation valves or other general relief valves. 
     Meanwhile, since the high-pressure regulation valve  20  has been described in the description of the prior art, the description will not be repeated. 
     Similar to the high-pressure regulation valve  40 , the low-pressure regulation valve  200  also project backward from the rear housing  28   e , and includes a discharge port  110  having a hole  47 , a ball  211  installed in the hole  47  of the discharge port  110  to open/close the hole  47 , a spring  212  resiliently supporting the ball  211 , and a pressure regulation screw  213  coupled to the discharge port  110 . 
     Therefore, a predetermined discharge pressure of the compressed air can be set by adjusting an insertion length of the pressure regulation screw  213  and a compression length of the spring  212 . 
     Hereinafter, the valve opening/closing switch  100  will be described with reference to  FIGS. 4 to 9  in detail. 
     As shown in  FIGS. 4 to 7 , the valve opening/closing switch  100  includes a valve body  130  coupled to the discharge port  110 , and a rotation drive part  150  rotatably coupled to one side of the valve body  130 . 
     As shown in  FIGS. 6 and 7 , the valve body  130  includes a hollow coupling pipe  131  fitted onto the discharge port  110  by a fastener  120  formed at a side part thereof, a discharge groove  132  formed in a longitudinal direction of the coupling pipe  131 , a coupling part  133  disposed opposite to the discharge port  110  and having a diameter larger than that of the coupling pipe  131 , and an inclined surface  134  formed along a periphery of the coupling part  133 . 
     Here, a coupling hole  136  is formed in a center of the coupling part  133  so that a fixing rod  153  of the rotation drive part  150  is fixed thereto, and stoppers  135  are formed at both ends of the inclined surface  134  so that the rotation drive part  150  is rotated to a predetermined angle. 
     Meanwhile, a handle  151  is formed at a rear surface of the rotation drive part  150  to allow a user to grip the handle  151 , and a coupling body  152  projects from a front surface of the rotation drive part  150  to be coupled to the coupling part  133  of the valve body  130 . 
     In addition, a packing member  154  is fixed to a front end of the fixing rod  153  of the rotation drive part  150 , and a guide projection  155  projects from the surface, on which the fixing rod  153  is formed, to be in contact with the inclined surface  134 . 
     Further, a resilient member  156  is installed between the coupling part  133  and the packing member  154 . 
     The packing member  154  opens and closes the hole  47  of the discharge port  110  with a pressure set by the resilient member  156 . 
     Hereinafter, an example in which the high-pressure regulation valve  40 , the low-pressure regulation valve  200  and the valve opening/closing switch  100  are installed at the vane pump  28  will be described. 
     Here, the vane pump  28  is merely an example of an air compression pump, other kinds of air compression pumps may be installed. 
     The high-pressure regulation valve  40  and the low-pressure regulation valve  200  are set to be opened at different pressures. For example, in this embodiment, the high-pressure regulation valve  40  is set to be opened when the compressed air is higher than 7 psi, and the low-pressure regulation valve  200  is set to be opened when the compressed air is higher than 5 psi. 
     Of course, the high-pressure regulation valve  40  and the low-pressure regulation valve  200  can be freely set the magnitude of the discharged compressed air. 
     First, when the hot air blower  10  in which the high-pressure regulation valve  40  and the low-pressure regulation valve  200  set to different pressures are installed is operated, the air introduced through the air suction port  10   a  passes through the introduction hole  28   a  to be introduced into the vane pump  28  and then compressed, and the compressed air discharged from the vane pump  28  moves to the injection nozzle  22   a  of the burner assembly  22  along the air line  28   c  to suck the fuel stored in the fuel tank  20  to supply the fuel. 
     Here, if the valve opening/closing switch  100  is set to close the discharge port  110  of the low-pressure regulation valve  200 , when the compressed air of 10 psi is discharged from the vane pump  40  to the compression chamber  37   b , the high-pressure regulation valve  40  set to 7 psi is opened to uniformly supply the compressed air to the injection nozzle  22   a  at 7 psi. 
     Therefore, the compressed air discharged from the vane pump  28  is discharged through the high-pressure regulation valve  40  to be supplied to the injection nozzle at 7 psi. 
     The fuel in the fuel tank is supplied by the pressure of the compressed air to be combusted to obtain a large amount of heat. 
     Referring to  FIG. 8 , the valve opening/closing switch  100  is set to close the discharge port  110  of the low-pressure regulation valve  200 . 
     Meanwhile, in the case that the temperature in the space is substantially increased so that decrease of the heating value is needed, when the valve opening/closing switch  100  is rotated to open the discharge port  110  of the low-pressure regulation valve  200 , the low-pressure regulation valve  200  set to 5 psi is opened to reduce the pressure of the compressed air in the compression chamber  37   b  to 5 psi to supply the compressed air into the injection nozzle  22   a  of the burner assembly  22 . 
     That is, when a user rotates the handle  151  of the rotation drive part  150  to reduce the heating value of the hot air blower, the guide projection  155  of the rotation drive part  150  is raised along the inclined surface  134  of the valve body  130  so that the rotation drive part  150  moves in a direction spaced apart from the valve body  130  as shown in  FIG. 9 . 
     At this time, the stopper  135  formed at the inclined surface  134  stops rotation of the guide projection  155  of the rotation drive part  150  such that the rotation drive part  150  rotates to an appropriate angle. 
     As described above, rotation of the rotation drive part  150  pushes the packing member  154  of the valve opening/closing switch  100  toward the rotation drive part  150  to open the hole  47  of the discharge port  110 . 
     Therefore, the ball  211  and the spring  212  in the discharge port  110  of the low-pressure regulation valve  200  are pushed to open the discharge port  110  to discharge the compressed air, and the discharged compressed air is discharged to the exterior of the valve opening/closing switch  100  through the discharge groove  132  of the valve body  130 . 
     In this embodiment, while the high-pressure regulation valve  40  is nearer to the air line  28   c  than the low-pressure regulation valve  200 , there is no affection even when their positions are changed. 
     Second Embodiment 
       FIG. 10  is an exploded perspective view of a pressure regulation valve in accordance with a second exemplary embodiment of the present invention. Description of the same elements as the first embodiment will not be repeated. 
     In the second embodiment, a guide projection  141  is formed at a coupling part  133  of a valve body  130 , not forming an inclined surface  134  at the valve body  130 . 
     In addition, a guide hole  160  is formed in a coupling body  152  of a rotation drive part  150  such that the guide projection  141  is movably coupled thereinto. The guide hole  160  has a horizontal hole  161  formed in a longitudinal direction of the coupling body  152  and vertical holes  162  extending from both ends of the horizontal hole  161  in vertical opposite directions. 
     In the second embodiment, a user can rotate a handle  151  of the rotation drive part  150  to vary a coupling position between the guide projection  141  and the guide hole  160 , and then move the handle forward or backward, and then rotate the handle  151  to lock the handle  151 , thereby opening and closing the discharge port  110  of the pressure regulation valve  200  using the valve opening/closing switch  100 . 
     Since other elements and operation of the other elements are the same as the first embodiment, description thereof will not be repeated. 
     Third Embodiment 
       FIG. 11  is a partial cross-sectional view of a hot air blower in accordance with a third exemplary embodiment of the present invention. 
     As shown in  FIG. 11 , the third embodiment is the same as the first embodiment, except that a low-pressure regulation valve  200  and a valve opening/closing switch  100  are installed at an air line  28   c  connecting the compression chamber  37   b  and the burner assembly  22 . 
     In  FIG. 11 , a pressure reduction housing  49   a  is installed on the air line  28   c  to form a pressure reduction chamber  49 , and the low-pressure regulation valve  200  is installed at the pressure reduction housing  49   a.    
     Provided that the high-pressure regulation valve  40  is set to 7 psi and the low-pressure regulation valve  200  is set to 5 psi, when the compressed air of 10 psi is supplied into the compression chamber  37   b , first, the high-pressure regulation valve  40  installed at the compression chamber  37   b  is opened to be reduced to 7 psi to enter the air line  28   c.    
     Here, when the valve opening/closing switch  100  closes the low-pressure regulation valve  200 , the compressed air of 7 psi moves to the burner assembly  22 , and when the valve opening/closing valve  100  opens the low-pressure regulation valve  200 , the low-pressure regulation valve  200  is opened to reduce the pressure of the compressed air to 5 psi to move the compressed air to the burner assembly  22 . 
     In the first to third embodiments, while the valve opening/closing switch  100  is employed as a valve opening/closing means, a cap (not shown) may be employed as a valve opening/closing means by simply and manually pushing or pulling the cap, even though it is inconvenient. 
     As can be seen from the foregoing, the pressure of compressed air can be selectively regulated by a high-pressure regulation valve and a low-pressure regulation valve, which have different opening pressures, so that a heating value of a hot air blower can be readily adjusted to increase efficiency of the hot air blower. 
     Therefore, it is possible to readily adjust a heating value of the hot air blower and increase efficiency of the hot air blower. 
     While this invention has been described with reference to exemplary embodiments thereof, it will be clear to those of ordinary skill in the art to which the invention pertains that various modifications may be made to the described embodiments without departing from the spirit and scope of the invention as defined in the appended claims and their equivalents.
Provided is a hot air blower comprising a fuel tank for storing fuel, an air compression pump for sucking air and compressing the air, a pressure regulation valve installed at the air compression pump to reduce the pressure of the compressed air, a burner assembly for receiving the fuel from the fuel tank and the air from the air compression pump, and a combustion chamber for receiving the fuel from the burner assembly and combusting the fuel, wherein the pressure regulation valve includes a high pressure regulation valve and a low pressure regulation valve, and a valve opening/closing means is installed at the low pressure regulation valve.