Length-adjustable hydraulic lifting appliance and use method

Abstract

The invention belongs to the technical field of lifting devices, and particularly relates to a length-adjustable hydraulic lifting appliance and a using method. The hydraulic lifting appliance comprises an oil cylinder, the oil cylinder comprises an upper cylinder cover, an upper cylinder body, a lower cylinder body and a lower cylinder cover which are sequentially connected, a connecting body is fixed between the upper cylinder body and the lower cylinder body, a piston rod penetrates through the connecting body, the lower end of the piston rod extends out of the lower cylinder cover, one end, extending out of a lower end cover, of the piston rod is connected with a lifting lug, and a nut is fixed to the upper end of the piston rod. A spring is connected between the nut and the connecting body, a piston is fixed to the piston rod and located in the lower cylinder body, the space below the piston in the lower cylinder body is a cavity A, the space above the piston in the lower cylinder body is a cavity B, an oil inlet pipe and an oil return pipe are connected between the cavity A and the cavity B, a stop valve is installed on the oil inlet pipe, and a one-way valve is installed on the oil return pipe. And hydraulic oil in the one-way valve flows from the cavity B to the cavity A. According to the length-adjustable hydraulic lifting appliance and the using method, a workpiece can be directly leveled when being hung in the air, and the adjusting precision is high.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hoisting devices, in particular to a hydraulic lifting device with adjustable length and a use method. BACKGROUND

[0002] At present, in the heavy equipment manufacturing industry, many large workpieces need to be assembled, and the horizontal degree of the workpiece is required to be high during the assembly process. The workpiece must reach the horizontal degree required by the technology after being hoisted, such as the horizontal degree being less than 1mm, otherwise the workpiece may not be smoothly assembled. For the parts with small weight, less than 30-40 tons, a hand-operated hoist can be hung on the hoisting wire rope to adjust the workpiece, but for the workpiece with a weight of about 100 tons, it is difficult to use the hand-operated hoist because the hand-operated hoist with a weight of more than 40 tons is heavy, the chain is long, and the installation and use are complicated and low in efficiency. Generally, for the workpiece with large weight, a pair of custom-made steel wire ropes are usually used, and the length error between each steel wire rope is small, but even so, the lifting personnel need to try hoisting several times to adjust the workpiece to the appropriate horizontal degree. SUMMARY

[0003] In order to solve the above problems existing in the prior art, the purpose of the present application is to provide a hydraulic lifting device with adjustable length and a use method, which can directly adjust the workpiece when the workpiece is suspended in the air, and the adjustment precision is high.

[0004] The technical scheme adopted by the present application is as follows: A hydraulic lifting device with adjustable length, comprising an oil cylinder, the oil cylinder comprises an upper cylinder cover, an upper cylinder body, a lower cylinder body and a lower cylinder cover connected in sequence, a connecting body is fixed between the upper cylinder body and the lower cylinder body, a piston rod is arranged in the connecting body, the lower end of the piston rod extends out of the lower cylinder cover, a lifting lug is connected to one end of the lower end of the piston rod, a nut is fixed to the upper end of the piston rod, a spring is connected between the nut and the connecting body, a piston is fixed to the piston rod, the piston is located in the lower cylinder body, the space below the piston in the lower cylinder body is an A cavity, the space above the piston in the lower cylinder body is a B cavity, an oil inlet pipe and an oil return pipe are connected between the A cavity and the B cavity respectively, a stop valve is installed on the oil inlet pipe, a check valve is installed on the oil return pipe, and the flow direction of the hydraulic oil in the check valve is from the B cavity to the A cavity.

[0005] When the piston is subjected to an external downward force, the pressure in the A cavity increases, and since the liquid is incompressible, the piston will not move downward. When the stop valve is opened, the A cavity and the B cavity are connected to form a loop, the oil flows from the A cavity into the B cavity, and the piston moves downward. After moving to the appropriate position, the stop valve is closed, and the piston remains at the current position. At this time, the lifting lug moves downward by a certain distance, so that the workpiece connected with the several oil cylinders is adjusted, and after adjusting the several oil cylinders connected with the workpiece, the workpiece can be adjusted to be horizontal.

[0006] The present application can accurately control the distance of the lifting lug moving downwards by controlling the opening time of the stop valve, can directly level when the workpiece is suspended in the air, does not need to drop the workpiece on the ground, and is high in efficiency.

[0007] The inner diameter of the oil inlet pipe is small, so the speed of the hydraulic oil flowing from the A cavity into the B cavity is slow, and the stop valve can adjust the flow, and the moving speed of the piston is completely controlled. The moving speed of the piston is slow, the movement of the piston is more easily controlled, and the workpiece levelness can be adjusted more accurately.

[0008] When the pressure of the A cavity is greater than that of the B cavity, the one-way valve is in a closed state, and the oil return pipe cannot form a loop. When the external force on the piston is unloaded, the pressure of the A cavity disappears, the spring starts to reset, and the piston moves upwards. At this time, the pressure of the B cavity is greater than that of the A cavity, the one-way valve is opened, the oil return pipe forms a loop, the oil flows from the B cavity back to the A cavity, and the piston is completely reset. Therefore, the piston of the present application can be automatically reset without manual operation; after the piston is reset, the extension length of the oil cylinder piston rod can be adjusted by opening the stop valve again.

[0009] The present application is simple to install, convenient to operate, large in lifting weight, large in adjustable range, high in adjustment accuracy, can directly level when the workpiece is suspended in the air, does not need to drop the workpiece on the ground, and is high in efficiency. Especially for the workpiece which is large in weight and large in diameter, the advantage is more obvious; and a larger load oil cylinder can be easily designed, becoming a series product.

[0010] As a preferred scheme of the present application, the oil inlet pipe is further connected with a speed reduction pipe, and the speed reduction pipe is reciprocatingly bent.

[0011] A speed reduction pipe is installed on the oil cylinder oil inlet pipe, and has the following effects: the design load of the oil cylinder in the present application is 40 tons, which will cause the oil flow speed to be very fast and not easy to control; the speed reduction pipe is formed by cold bending a seamless steel pipe with an inner diameter of 0.9-1 mm, and the unfolded length is about 1700 mm. The small hole diameter and long length of the speed reduction pipe can effectively reduce the oil flow speed. After taking this measure, according to the calculation result, the flow speed is 1 mm per second when the piston moves downwards 1 mm, that is, the moving speed is 0.5 mm per second; in addition, the stop valve can adjust the flow, and the moving speed of the piston is completely controlled. If the lifting load is 20 tons, the piston moving speed is 0.25 mm per second after calculation, the movement of the piston is more easily controlled, and the workpiece levelness can be adjusted more accurately. The speed reduction pipe is installed in the pipe clamp, and can protect the speed reduction pipe.

[0012] As a preferred scheme of the present application, the inner diameter of the speed reduction pipe is 0.9-1 mm.

[0013] As a preferred scheme of the present application, a sealing element is arranged between the connecting body and the piston rod, between the piston and the lower cylinder body, and between the piston rod and the lower cylinder cover. The connecting body is a composite material with self-lubricating effect and certain hardness, which prevents the piston from being damaged by hard contact with the cylinder cover and the cylinder body.

[0014] As a preferred scheme of the present application, a shield is further included, the shield comprises a shield body, the upper cylinder body, the lower cylinder body and the speed reduction pipe are sleeved in the shield body, and the side surface of the shield body is connected with an upper shield plate and a lower shield plate respectively. The upper shield plate and the lower shield plate are assembled on the shield body by screws. The shield protects the valves and pipelines on the oil cylinder. The outside of the shield can be painted with load-bearing specifications.

[0015] As a preferred scheme of the present application, an indicating space is left between the upper shield plate and the lower shield plate, a steel ruler is fixed on the shield body, the steel ruler is located in the indicating space, and the lower end of the piston rod is connected with an indicating device, the other end of the indicating device extends into the indicating space.

[0016] As a preferred scheme of the present application, the indicating device comprises a pointer seat, the pointer seat is installed on the lower end of the piston rod, and a pointer is connected to the pointer seat, the other end of the pointer extends into the indicating space.

[0017] The pointer and the pointer seat are riveted together. When the piston moves, the pointer also moves. The steel ruler is installed on the shield. When the stop valve is opened, the moving distance can be observed by the pointer. The steel ruler with a scale value of 0.5 mm can more accurately control the moving distance of the piston. The oil cylinder 1 in the present application has a design stroke of 100 mm, which is sufficient to compensate for the difference in the levelness of the workpiece caused by the length error of the steel wire rope and the deviation of the lifting point.

[0018] As a preferred scheme of the present application, the pointer seat comprises two semicircular structures, the two semicircular structures are connected by screws, the lower end of the piston rod is provided with a groove, the pointer seat is sleeved in the groove, one of the semicircular structures is provided with an extension rod, and the other end of the extension rod is connected with the pointer.

[0019] As a preferred scheme of the present application, the inner diameter of the oil return pipe is 3-5 mm.

[0020] A method for using a hydraulic lifting device with adjustable length, comprising the following steps: S1: The hydraulic lifting device is used in pairs, and before use, it is confirmed that the stop valve of the oil cylinder is in a closed state; a plurality of oil cylinders are evenly distributed around the workpiece, and are connected to the workpiece by a steel wire rope and a shackle; S2: After lifting the workpiece, the operator checks the levelness of the workpiece by using a level, finds the position of the highest point of the lower plane, and notifies the operator standing on the workpiece, and the operator finds the oil cylinder closest to the highest point of the lower plane of the workpiece; S3: open the stop valve of the oil cylinder closest to the highest point of the lower plane of the workpiece, move the piston downward, and close it according to the order of the monitor, observe the distance of the pointer movement, compare it with the actual distance of the workpiece, and adjust the remaining oil cylinders until the levelness of the lower plane of the workpiece meets the installation requirements.

[0021] The beneficial effects of the present application are: 1. The present application can accurately control the distance of the lifting lug moving downward by controlling the opening time of the stop valve, and can directly level the workpiece when it is suspended in the air without landing it on the ground, which is efficient.

[0022] 2. The inner diameter of the oil inlet pipe is small, so the speed of hydraulic oil flowing from the A cavity into the B cavity is slow, and the stop valve can adjust the flow, and the piston moving speed is completely controlled. The piston moving speed is slow, and the movement of the piston is more easily controlled, and the levelness of the workpiece can be adjusted more accurately. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the front view of the present application; Figure 2 is the left view of the present application; Figure 3 is the top view of the present application; Figure 4 is the front view of the oil cylinder; Figure 5 is the left view of the oil cylinder; Figure 6 is the sectional view of the oil cylinder; Figure 7 is the partial structure diagram of the oil cylinder; Figure 8 is the working principle diagram of the oil cylinder; Figure 9 is the structure diagram of the piston rod; Figure 10 is the installation diagram of the sealing element; Figure 11 is the front view of the indicating device; Figure 12 is the left view of the indicating device; Figure 13 is the top view of the indicating device; Figure 14 is the lifting schematic diagram of the workpiece.

[0024] In the diagram: 1-Cylinder; 2-Seal; 3-Guard; 4-Steel ruler; 5-Indicating device; 11-Upper cylinder head; 12-Upper cylinder body; 13-Lower cylinder body; 14-Lower cylinder head; 15-Connecting body; 16-Piston rod; 17-Lifting lug; 18-Inlet pipe; 19-Return pipe; 31-Guard body; 32-Upper guard plate; 33-Lower guard plate; 51-Pointer seat; 52-Pointer; 161-Nut; 162-Spring; 163-Piston; 164-Groove; 181-Stop valve; 182-Reduction tube; 183-Pipe clamp; 191-Check valve. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the invention can be combined with each other.

[0027] like Figures 1-8 As shown, the adjustable-length hydraulic lifting device of this embodiment includes a cylinder 1. The cylinder 1 includes an upper cylinder cover 11, an upper cylinder body 12, a lower cylinder body 13, and a lower cylinder cover 14 connected in sequence. A connecting body 15 is fixed between the upper cylinder body 12 and the lower cylinder body 13. A piston rod 16 passes through the connecting body 15. The lower end of the piston rod 16 extends out of the lower cylinder cover 14. A lifting lug 17 is connected to one end of the piston rod 16 extending out of the lower cylinder cover. A nut 161 is fixed to the upper end of the piston rod 16. The nut 161 is connected to the connecting body... A spring 162 is connected between 15. A piston 163 is fixed on the piston rod 16. The piston 163 is located inside the lower cylinder 13. The space below the piston 163 in the lower cylinder 13 is chamber A, and the space above the piston 163 in the lower cylinder 13 is chamber B. An oil inlet pipe 18 and an oil return pipe 19 are connected between chamber A and chamber B, respectively. A shut-off valve 181 is installed on the oil inlet pipe 18, and a check valve 191 is installed on the oil return pipe 19. The flow direction of the hydraulic oil in the check valve 191 is from chamber B to chamber A.

[0028] When the piston 163 is subjected to downward external force, the pressure of the A cavity increases, and the piston 163 cannot move downward due to the incompressibility of the liquid. When the stop valve 181 is opened, the A cavity and the B cavity are communicated to form a loop, and the oil liquid flows from the A cavity into the B cavity, and the piston 163 moves downward. After moving to a suitable position, the stop valve 181 is closed, and the piston 163 is kept at the current position. At this time, the lug 17 moves downward by a certain distance, so that the workpiece connected with the plurality of oil cylinders 1 is adjusted, and after adjusting the plurality of oil cylinders 1 connected with the workpiece, the workpiece can be adjusted to be horizontal.

[0029] The present application can accurately control the distance of the lug 17 moving downward by controlling the opening time of the stop valve 181, and can directly adjust the workpiece to be horizontal when the workpiece is suspended in the air, without the need of landing the workpiece, and the efficiency is high.

[0030] The inner diameter of the oil inlet pipe 18 is small, so that the speed of the hydraulic oil flowing from the A cavity into the B cavity is slow, and in addition, the stop valve 181 can adjust the flow, and the moving speed of the piston 163 is completely controlled. The moving speed of the piston 163 is slow, and the movement of the piston 163 is more easily controlled, and the horizontal degree of the workpiece can also be adjusted more accurately.

[0031] When the pressure of the A cavity is greater than that of the B cavity, the one-way valve 191 is in a closed state, and the oil return pipe 19 cannot form a loop. When the external force on the piston 163 is unloaded, the pressure of the A cavity disappears, and the spring 162 starts to reset, and the piston 163 moves upward. At this time, the pressure of the B cavity is greater than that of the A cavity, the one-way valve 191 is opened, the oil return pipe 19 forms a loop, the oil liquid flows back from the B cavity to the A cavity, and the piston 163 is completely reset. Therefore, the piston 163 of the present application can be automatically reset without manual operation; after the piston 163 is reset, the extension length of the piston rod 16 of the oil cylinder 1 can be adjusted again by opening the stop valve 181.

[0032] The present application is simple to install, convenient to operate, has large lifting weight, large adjustable range, high adjustment precision, can directly adjust the workpiece to be horizontal when the workpiece is suspended in the air, does not need to land the workpiece, and the efficiency is high. Especially for the workpiece with large weight and large diameter, the advantage is more obvious; and a larger load oil cylinder 1 can be easily designed to become a series product.

[0033] Further, the oil inlet pipe 18 is further connected with a speed reduction pipe 182, and the speed reduction pipe 182 is reciprocatingly bent. The inner diameter of the speed reduction pipe 182 is 0.9-1 mm.

[0034] A speed reduction pipe 182 is installed on the oil inlet pipe 18 of the oil cylinder 1, and has the following functions: the oil cylinder 1 in the present application is designed to bear a load of 40 tons, which results in a very fast flow rate of oil and is difficult to control; the speed reduction pipe 182 is formed by cold bending a seamless steel pipe with an inner diameter of 0.9-1 mm, and has a length of about 1700 mm after being unfolded; the small diameter and long length of the speed reduction pipe 182 can effectively reduce the flow rate of oil. After taking this measure, according to the calculation results, the flow rate is 1 mm of the piston 163 moving downward per second, i.e. a moving speed of 0.5 mm / s; in addition, the stop valve 181 can adjust the flow rate, and the moving speed of the piston 163 is completely controlled. If the hoisting load is 20 tons, the calculation results show that the moving speed of the piston 163 is 0.25 mm / s, and the piston 163 is more easily controlled, and the workpiece levelness can also be adjusted more accurately. The speed reduction pipe 182 is installed inside the pipe clamp 183, and can protect the speed reduction pipe 182.

[0035] As shown in Figure 10 , sealing members 2 are arranged between the connecting body 15 and the piston rod 16, between the piston 163 and the lower cylinder body 13, and between the piston rod 16 and the lower cylinder cover 14. The connecting body 15 is a composite material with self-lubricating effect and a certain hardness, and has the function of preventing damage caused by hard contact between the piston 163 and the cylinder cover and the cylinder body.

[0036] In the present application, the stop valve 181, the one-way valve 191 and the joint in the oil cylinder 1 are standard parts, which can be easily purchased; the sealing member 2 needs to be customized. The upper cylinder cover 11, the upper cylinder body 12, the connecting body 15, the lower cylinder body 13, the lower end cover, the lifting lug 17, the piston 163 and the piston rod 16 are all made of forged high-strength alloy steel material, such as forged steel 35crMo and 40Cr.

[0037] Further, as shown in Figure 1 , the present application further comprises a protective cover 3, the protective cover 3 comprises a protective cover body 31, the upper cylinder body 12, the lower cylinder body 13 and the speed reduction pipe 182 are sleeved in the protective cover body 31, and the side surface of the protective cover body 31 is connected with an upper protective plate 32 and a lower protective plate 33, respectively. The upper protective plate 32 and the lower protective plate 33 are assembled on the protective cover body 31 by screws. The protective cover 3 has the function of protecting the valves and pipelines on the oil cylinder 1. The outside of the protective cover 3 can be painted with load-bearing specifications.

[0038] The upper protective plate 32 and the lower protective plate 33 are left with an indicating space therebetween, a steel ruler 4 is fixed on the protective cover body 31, the steel ruler 4 is located in the indicating space, and an indicating device 5 is connected to the lower end of the piston rod 16, and the other end of the indicating device 5 extends into the indicating space.

[0039] Specifically, as shown in Figures 11-13 , the indicating device 5 comprises a pointer seat 51, the pointer seat 51 is installed at the lower end of the piston rod 16, a pointer 52 is connected to the pointer seat 51, and the other end of the pointer 52 extends into the indicating space.

[0040] The pointer 52 and the pointer seat 51 are riveted together. When the piston 163 moves, the pointer 52 also moves together. The steel ruler 4 is installed on the shroud 3. When the stop valve 181 is opened, the moving distance can be observed through the pointer 52. The steel ruler 4 is selected with a 0.5mm scale value, so that the moving distance of the piston 163 can be more accurately controlled. The stroke of the oil cylinder 11 in the present application is designed to be 100mm, which is sufficient to compensate for the workpiece level difference caused by the length error of the wire rope and the deviation of the lifting point.

[0041] As shown in Figure 9 The pointer seat 51 includes two semicircular structures connected by screws. The lower end of the piston rod 16 is provided with a groove 164, and the pointer seat 51 is sleeved in the groove 164. One of the semicircular structures is provided with an extension rod, and the other end of the extension rod is connected with the pointer 52.

[0042] The inner diameter of the oil return pipe 19 is 3-5mm.

[0043] As shown in Figure 14 The use method of the adjustable length hydraulic lifting device of the present embodiment includes the following steps: S1: The hydraulic lifting device is used in pairs, that is, 4 are used as a group or 2 are used as a group. Before use, it is confirmed that the stop valve 181 of the oil cylinder 1 is in a closed state; several oil cylinders 1 are evenly distributed around the workpiece, and are connected with the workpiece by a wire rope and a shackle.

[0044] S2: After lifting the workpiece, the monitor checks the levelness of the workpiece with a level, finds the position of the highest point of the lower plane, and notifies the operator standing on the workpiece. The operator finds the oil cylinder 1 closest to the highest point of the lower plane of the workpiece.

[0045] S3: Open the stop valve 181 of the oil cylinder 1 closest to the highest point of the lower plane of the workpiece, move the piston 163 downward, and close it according to the order of the monitor, and observe the moving distance of the pointer 52 and compare it with the actual descending distance of the workpiece. Because the cylinder body of the oil cylinder 1 is inclined, the moving distance of the piston 163 and the vertical descending distance of the workpiece have an angle relationship, which can be used to find the method faster for the next adjustment. Continue to measure the levelness of the workpiece according to this step, and adjust the remaining oil cylinders 1 until the levelness meets the installation requirements.

[0046] The oil cylinder 1 is a one-way oil cylinder 1, that is, the piston 163 can only move downward under load and cannot move upward. When the adjustment fails, it needs to be corrected by adjusting other oil cylinders 1. The stroke of the piston 163 in the present application is designed to be 100mm, which has a large error correction margin.

[0047] The present application is not limited to the above-mentioned optional embodiments, and anyone can derive other various forms of products under the inspiration of the present application, but regardless of any changes in shape or structure, any technical solutions falling within the scope defined by the claims of the present application fall within the protection scope of the present application.

Claims

1. An adjustable-length hydraulic lifting device, characterized in that: The cylinder (1) includes an upper cylinder cover (11), an upper cylinder body (12), a lower cylinder body (13), and a lower cylinder cover (14) connected in sequence. A connecting body (15) is fixed between the upper cylinder body (12) and the lower cylinder body (13). A piston rod (16) is inserted through the connecting body (15). The lower end of the piston rod (16) extends out from the lower cylinder cover (14). A lifting lug (17) is connected to one end of the piston rod (16) that extends out of the lower cylinder cover. A nut (161) is fixed to the upper end of the piston rod (16). The nut (161) is connected to the connecting body (15). There is a spring (162), and a piston (163) is fixed on the piston rod (16). The piston (163) is located in the lower cylinder (13). The space below the piston (163) in the lower cylinder (13) is chamber A, and the space above the piston (163) in the lower cylinder (13) is chamber B. The inlet pipe (18) and the return pipe (19) are connected between chamber A and chamber B respectively. A shut-off valve (181) is installed on the inlet pipe (18), and a check valve (191) is installed on the return pipe (19). The flow direction of the hydraulic oil in the check valve (191) is from chamber B to chamber A.

2. The adjustable-length hydraulic lifting device according to claim 1, characterized in that: The oil inlet pipe (18) is also connected to a deceleration pipe (182), which is bent back and forth.

3. The adjustable-length hydraulic lifting device according to claim 2, characterized in that: The inner diameter of the speed reduction tube (182) is 0.9 to 1 mm.

4. The adjustable-length hydraulic lifting device according to claim 1, characterized in that: A seal (2) is provided between the connecting body (15) and the piston rod (16), between the piston (163) and the lower cylinder body (13), and between the piston rod (16) and the lower cylinder cover (14).

5. The adjustable-length hydraulic lifting device according to claim 1, characterized in that: It also includes a protective cover (3), which includes a protective cover body (31), an upper cylinder body (12), a lower cylinder body (13) and a deceleration tube (182) fitted inside the protective cover body (31), and an upper protective plate (32) and a lower protective plate (33) connected to the sides of the protective cover body (31).

6. The adjustable-length hydraulic lifting device according to claim 5, characterized in that: An indicator space is left between the upper guard plate (32) and the lower guard plate (33). A steel ruler (4) is fixed on the guard body (31). The steel ruler (4) is located in the indicator space. The lower end of the piston rod (16) is connected to an indicator device (5). The other end of the indicator device (5) extends into the indicator space.

7. The adjustable-length hydraulic lifting device according to claim 6, characterized in that: The indicating device (5) includes a pointer seat (51), which is installed at the lower end of the piston rod (16). A pointer (52) is connected to the pointer seat (51), and the other end of the pointer (52) extends into the indicating space.

8. The adjustable-length hydraulic lifting device according to claim 7, characterized in that: The pointer seat (51) includes two semicircular structures connected by screws. The lower end of the piston rod (16) is provided with a groove (164). The pointer seat (51) is fitted into the groove (164). One of the semicircular structures is provided with an extension rod. The other end of the extension rod is connected to the pointer (52).

9. The adjustable-length hydraulic lifting device according to claim 1, characterized in that: The inner diameter of the return oil pipe (19) is 3-5 mm.

10. A method of using an adjustable-length hydraulic lifting device, comprising using the adjustable-length hydraulic lifting device as described in claim 7, characterized in that: Includes the following steps: S1: Hydraulic lifting tools are used in pairs. Before use, first confirm that the shut-off valve (181) of the oil cylinder (1) is closed. Distribute several oil cylinders (1) evenly around the workpiece and connect them to the workpiece with wire rope and shackle. S2: After the workpiece is lifted, the monitoring personnel use a level to check the levelness of the workpiece, find the position of the highest point of the lower plane, and notify the operator standing on the workpiece. The operator finds the oil cylinder (1) closest to the highest point of the lower plane of the workpiece. S3: Open the shut-off valve (181) of the cylinder (1) closest to the highest point of the lower plane of the workpiece, let the piston (163) move downward, and close it according to the command of the monitoring personnel. At the same time, observe the distance the pointer (52) moves and compare it with the actual descent distance of the workpiece. Then adjust the remaining cylinders (1) until the level of the lower plane of the workpiece meets the installation requirements.

Images