the present invention will be clearer from the following description when viewed together with the accompanying drawings , which show , for purpose of illustration only , the preferred embodiments in accordance with the present invention . referring to fig1 and 2 , a hydraulic tool 8 in accordance with the present invention which is capable of performing external - pulling or internal - pulling operation for an object to be assembled or disassembled comprises a control valve 2 with one end connected with an oil storage member 1 . the other end of the control valve 2 is connected with an oil pressure tank 3 which is provided with an adjustment threaded portion 4 on the outer surface thereof . screwed on the adjustment threaded portion 4 is a bracket 5 with a plurality of radially - arranged slide rails 51 facing downward . plural clamping jaws 6 with articulated joints are disposed in the respective slide rails 51 , and disposed at one end of the oil storage member 1 is a hand - operated hydraulic pump 801 . therefore , one end of a shaft portion 91 of the bolt 9 is screwed with an axial shaft 41 at one end of the oil pressure tank 3 , and another end of the bolt 9 is connected with a shaft 71 of a to - be - assembled object 7 ( here it is a bearing for example ), namely , by pressing each of the clamping claws 6 against the object 7 . when the oil pressure tank 3 moves backward , it can simultaneously pull out the shaft 71 of the object 7 connected to the end of the axial shaft 41 , thus reversely pushing the object 7 onto the shaft 71 , as shown in fig1 , 2 and 2 a . on the other hand , each of the clamping jaws 6 mounted on the bracket 5 can also clamp the bottom of the outer periphery p of the object 7 . meanwhile , the axial shaft 41 at one end of the oil pressure tank 3 pushes the shaft 71 of the object 7 downward ( as shown in fig3 , 4 and 4 a ), thus pulling out the object 7 . this is an example of an external - pulling application . an internal - pulling embodiment of the present invention is shown in fig5 , 6 and 6 a and comprises hooks 6 ′ inserted in the axial shaft 41 at one end of the oil pressure tank 3 with the adjustment threaded portion 4 . the hooks 6 ′ are to be clamped against the bottom b of the inner periphery i of the central hole 72 of the object 7 to be disassembled to pull the object 7 upward . meanwhile , each of the hooks 6 ′ is pressed against a peripheral component 73 around the object 7 , thus pulling out the object 7 , and this is called an internal - pulling operation . fig7 - 11 show the control valve 2 disposed at one end of the oil storage member 1 . a valve body 21 of the control valve 2 is defined with an oil circuit . in an opening 211 at an outer portion of the oil circuit are disposed a steel ball 81 , an elastic member 82 and a plug 83 , and in an opening 212 of another outer portion of the circuit are disposed a pin 84 , a steel ball 85 or plural washers 86 and a socket 87 for insertion of the pin 84 and accommodation of the steel ball 85 . in the meantime , a connecting member 88 with a protrusion 881 and two arc - shaped concaves 882 on an inner surface thereof facing the valve body 21 is assembled on the control valve 2 ( as shown in fig1 ). extended from the outer surface of the connecting member 88 opposite the protrusion 881 is a hexagonal rod 883 to be engaged with a handle 89 . the bearing seat 891 of the handle 89 is fixed to a corresponding surface of the valve body 21 through a plurality of screws . when the hydraulic tool with the oil storage member 1 and the control valve 2 are used to perform an external - pulling or internal - pulling operation , the oil circuit of the control valve 2 is provided with different oil passages capable of adjusting oil flow to the oil pressure tank 3 desirably to the states of non - operation , forward movement and backward movement to achieve the desired external - pulling or internal - pulling function . a state of non - operation represents a state in which the oil pressure tank 3 is not working , a state of forward movement means a state in which the oil pressure tank 3 is moving forward , and a state of backward movement means a state in which the oil pressure tank 3 is moving backward . the state of non - operation of the oil pressure tank 3 is shown in fig1 a and 13 . the handle 89 is moved to the center such that the oil from an inlet 11 of the oil storage member 1 will flow through a return passage 213 , a return chamber 214 , and a return hole 215 and back into the oil storage member 1 via an inlet 12 thereof . the state of forward movement of the oil pressure tank 3 is shown in fig1 b and 14 . the handle 89 is moved toward a side so that the oil from the inlet 11 of the oil storage member 1 flows into the oil pressure tank 3 via a first oil passage 22 ( as shown in fig1 ) to push a piston 31 of the oil pressure tank 3 outward . accordingly , the axial shaft 41 connected at the end of a piston rod 32 is also pushed outward ( as shown in fig1 ). at the same time , when the pressure of the oil flowing into the oil pressure tank 3 reaches a maximum value , the oil will flow through an oil chamber 33 inside of the piston rod 32 to a second oil passage 23 ( as shown in fig1 ), then flow through a third oil passage 24 into the return passage 213 , and finally flow back into the oil storage member 1 via a fourth oil passage 25 at one end of the inlet 12 . the forward movement of the oil pressure tank 3 can perform an external - pulling operation for the object 7 to be disassembled ( as shown in fig3 , 4 and 4 a ). the state of backward movement of the oil pressure tank 3 is shown in fig1 c and 17 . the handle 89 is moved toward another side so that the oil from the inlet 11 of the oil storage member 1 will flow into a sixth oil passage 27 at one end of the oil pressure tank 3 via a fifth oil passage 26 and flow into the piston rod 32 ( as shown in fig1 ) and then into an oil chamber 34 at the other end of the oil pressure tank 3 , thus pushing the piston 31 together with the axial shaft 41 connected at the end of the piston rod 32 backward ( as shown in fig1 ). at the same time , the oil of an oil chamber 35 at the front end of the oil pressure tank 3 can flow out via an outlet 36 ( as shown in fig1 ) to a seventh oil passage 28 ( as shown in fig1 ) of the control valve 2 and then flow through an eighth oil passage 29 at one end of the inlet 12 of the oil storage member 1 and back into the oil storage member 1 . the backward movement of the oil pressure tank 3 controlled by the control valve 2 is used to perform an internal - pulling operation ( as shown in fig5 , 6 and 6 a ) for the object 7 or to assemble the object 7 onto the shaft ( as shown in fig1 , 2 and 2 a ). the hydraulic tool 8 can be assembled differently to meet the requirements of internal - pulling or external - pulling . the oil circuit of the control valve 2 is provided with different oil passages capable of adjusting oil flow to the oil pressure tank 3 desirably to the states of non - operation , forward movement and backward movement to achieve the desired external - pulling or internal - pulling function . hence , the hydraulic tool 8 has a wider application scope and is capable of assembling and disassembling the object . while various embodiments in accordance with the present invention have been shown and described , it is clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention .