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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to concrete fence wall installation technology and more particularly, to a concrete pile installation apparatus, which facilitates installation of concrete piles, saving much concrete pile installation labor and time. 
     2. Description of the Related Art 
     Conventionally, a concrete fence wall is established, as shown in  FIG. 1 , by: making pile holes on the ground at selected locations, and then mounting concrete piles  1  in the pile holes, and then inserting concrete slabs  3  into the longitudinal grooves  2  of each two adjacent concrete piles  1 . According to this method, concrete piles are individually installed in the pile holes. During installation, rule and wire are used to assist vertical angle and horizontal position measurement. This method has drawbacks as follows:
     1. Concrete piles are to be installed individually. Rule and wire must be used to assist vertical angle and horizontal position measurement, requiring much labor and time and increasing the installation cost.   2. If one concrete pile  1  biased in one respective pile hole  4  due to a human error, as shown in  FIGS. 2 and 3 , the operators will be unable to insert concrete slabs  3  into the longitudinal grooves  2  of the corresponding concrete piles  1  accurately. In this case, the concrete pile  1  must be removed from the respective pile hole  4  and re-installed.   

     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a concrete pile installation apparatus, which comprises a pile clamping unit that has stop plates arranged at different elevations and hand wheel-controlled clamping blocks disposed corresponding to the stop plates and operable to clamp concrete piles for installation and rollers that facilitate adjustment of the position of concrete piles. By means of the concrete pile installation apparatus, multiple concrete piles can be installed at a time, saving much concrete pile installation labor and time. 
     It is one object of the present invention to provide a concrete pile installation apparatus, which further comprises two racks that use hydraulic cylinders and rollers to support the pile clamping unit, allowing adjustment of the pile clamping unit and the clamped concrete piles vertically as well as horizontally. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the installation of a concrete fence wall according to the prior art. 
         FIG. 2  is a schematic drawing showing one concrete pile biased in the pile hole according to the prior art. 
         FIG. 3  is a schematic drawing showing a concrete pile biased and concrete slab installation failed according to the prior art. 
         FIG. 4  is an exploded view of a concrete pile installation apparatus in accordance with the present invention. 
         FIG. 5  is a schematic drawing showing an application status of the present invention. 
         FIG. 6  is a schematic drawing of a part of the present invention, showing one concrete pile supported in the pile clamping unit and adjusted. 
         FIG. 7  is a schematic top view of a part of the present invention, showing a concrete pile clamped in the pile clamping unit. 
         FIG. 8  is a schematic drawing of the present invention, showing the pile clamping unit supported on the racks and adjusted horizontally. 
         FIG. 9  is an exploded view of an alternate form of the rack in accordance with the present invention. 
         FIG. 10  is a schematic front view of the present invention, showing an operation status of the alternate form of the rack. 
         FIG. 11  is a schematic side view of the present invention, showing an operation status of the alternate form of the concrete pile installation apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 4-8 , a concrete pile installation apparatus in accordance with the present invention is shown comprising two racks  20  and a pile clamping unit  10 . 
     The pile clamping unit  10  comprises an upper beam  101 , a lower beam  102 , a plurality of stop plates  15  symmetrically fixedly located on each of the upper and lower beams  101 ; 102 , a plurality of plurality of screw holders  11  symmetrically fixedly located on each of the upper and lower beams  101 ; 102  corresponding to the stop plates  15 , a screw rod  12  rotatably mounted in each of the screw holders  11 , a clamping block  13  fixedly located on one end of each screw rod  12 , a hand wheel  14  fixedly located on the other end of each screw rod  12  and operable to rotate the associating screw rod  12  and to further move the associating clamping block  13  toward or away from the associating stop plate  15  for clamping a concrete pile  1  or releasing the clamped concrete pile  1 , a plurality of rollers  16  pivotally mounted on the upper beam  101  and respectively disposed between the stop plates  15  and the screw holders  11  at the upper beam  101 , and two side plates  17  symmetrically disposed at two opposite lateral sides and supportable on the racks  20 . Each rack  20  comprises a flat top  21 , two vertical hydraulic cylinders  22  mounted on the flat top  21  and a roller  23  supported on the vertical hydraulic cylinder  22  and movable up and down by the vertical hydraulic cylinders  22 . The two side plates  17  of the pile clamping unit  10  are supported on the rollers  23  of the racks  20 . 
     When in use, as shown in  FIG. 6 , place the pile clamping unit  10  horizontally on the ground, and then set concrete piles  1  between the stop plates  15  and the clamping blocks  13  respectively for enabling the concrete piles  1  to be supported on the rollers  16  and adjusted to the desired position, and then operate the hand wheels  14  to rotate the associating screw rods  12  and to further move the associating clamping blocks  13  toward the associating stop plates  15 , thereby clamping the concrete piles  1 . Thereafter, use a steel rope  18  and a crane to lift the pile clamping unit  10  and the clamped concrete piles  1 , as shown in  FIGS. 5 and 8 , for enabling the concrete piles  1  to be inserted vertically into respective pile holes  4  on the ground. At this time, the two side plates  17  of the pile clamping unit  10  are respectively supported on the rollers  23  of the racks  20 . Thereafter, operate the vertical hydraulic cylinder  22  to adjust the elevation of the rollers  23  and the pile clamping unit  10 , thereby adjusting the insertion depth of the concrete piles  1  in the respective pile holes  4 . Further, because the pile clamping unit  10  is supported on the rollers  23  of the racks  20 , adjustment of the horizontal position of the pile clamping unit  10  is easy. 
     As stated above, the pile clamping unit  10  can clamp multiple concrete piles  1  at a time. Subject to the functioning of the rollers  16  and the vertical hydraulic cylinder  22  and rollers  23  of the racks  20 , the clamped concrete piles  1  can be adjusted vertically as well as horizontally to the accurate position. Therefore, the invention facilitates accurate and rapid installation of concrete piles, saving much installation labor and time. 
       FIGS. 9-11  show an alternate form of the rack practical for use in the installation of a non-linear or arched concrete fence wall. According to this alternate form the rack  30  comprises a flat top  31 , two vertical hydraulic cylinders  32  mounted on the flat top  31 , and a roller  33  supported on the top end of the reciprocating rod  320  of each vertical hydraulic cylinder  32  and movable up and down the reciprocating rod  320  of the vertical hydraulic cylinders  32 , a pile holder  34  for holding a concrete pile  1 , and two supplementary rollers  35  located on the bottom side of the pile holder  34  and respectively supported on the rollers  33  at the reciprocating rods  320  of the vertical hydraulic cylinders  32 . During application, as shown in  FIGS. 10 and 11 , a concrete pile  1  is supported on the pile holder  34 . By means of rotating the rollers  33 , as shown in  FIG. 10 , the concrete pile  1  can be adjusted leftwards or rightwards to the desired position. By means of rotating the supplementary rollers  35 , as shown in  FIG. 11 , the concrete pile  1  can be adjusted forwards or backwards to the desired position. 
     Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

Summary:
A concrete pile installation apparatus includes a pile clamping unit having stop plates arranged at different elevations and hand wheel-controlled clamping blocks disposed corresponding to the stop plates and operable to clamp concrete piles for installation and rollers that facilitate adjustment of the position of concrete piles, and two racks that use hydraulic cylinders to support the pile clamping unit and to adjust the elevation of the pile clamping unit and the clamped concrete piles.