Ladder for manhole lifting

Abstract

Provided is a manhole lifting ladder that is easy to install on a manhole and has good usability while ensuring a moving space during lifting and lowering. **Solution**: The present invention is a manhole lifting ladder that is detachably installed on a manhole side flange to which a lid member for closing the opening of the manhole is fixed by screw fastening. The ladder includes a plurality of ladder units in which cross bars connected between a pair of columns are curved outward along the inner peripheral surface of the manhole, and an arcuate fixed flange portion that is connected to a pair of columns of one ladder unit and extends outside the curved cross bar. Each ladder unit is provided with connecting portions at its upper and lower ends for connecting to other ladder units, and the individual ladder units are configured to be connected to form one ladder. The fixed flange portion is provided with insertion holes corresponding to bolt insertion holes of the manhole side flange, and is fixed to the manhole side flange by screw fastening through the insertion holes.

Description

Technical Field

[0001] The present invention relates to a ladder for manhole lifting used in maintenance work of factories and facilities.

Background Art

[0002] For example, in factories and facilities such as oil plants and petrochemical plants, maintenance work is carried out to inspect the condition of equipment such as tanks for dirt, corrosion, damage, etc., and to clean the dirt, repair the corroded and damaged parts. Manholes may be installed as entrances and exits to the interior of the equipment, and workers descend from the manhole and enter the tank to perform maintenance work.

[0003] Ladders are used to enter or exit the equipment inside the manhole (enter and exit the tank). When performing maintenance work, workers, for example, lower a rope ladder from the opening of the manhole or attach the ladder device described in Patent Document 1. After the maintenance work, the used ladder is removed so that no ladder used inside the equipment remains.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the case of a rope ladder, it is difficult to move up and down because the operator has to support his own body only by arm strength. Also, since the rungs (steps) swing, they deviate from the position directly below the ascending / descending operator, making it easy to miss stepping on the rungs. For this reason, there were problems with the stability and safety during ascending and descending.

[0006] In addition, the length of the ladder to be used is required to be the height from the bottom of the tank where the worker stands down to the opening of the manhole in order for the worker to enter the tank inside the equipment. When using one ladder as in Patent Document 1, the higher the height from the bottom of the tank to the opening of the manhole, the longer the ladder needs to be. However, for example, if there are obstacles above or near the manhole, there is a problem that it is difficult to install the ladder.

[0007] Furthermore, since the shape of the ladder in Patent Document 1 is linear in the width direction, when installed in a cylindrical manhole, a gap is formed between the circumferential surface of the manhole and the ladder. The larger the formed gap, the narrower the moving space for the worker ascending and descending the ladder. Since the worker ascends and descends while wearing a fall prevention device such as a helmet or a full harness, it is necessary to appropriately secure the moving space during ascending and descending.

[0008] Therefore, an object of the present invention is to provide a ladder for ascending and descending a manhole that can secure a moving space during ascending and descending and is easy to install on the manhole.

Means for Solving the Problems

[0009] (1) The ladder for manhole lifting of the present invention is detachably installed on a manhole side flange to which a lid member for closing the opening of the manhole is fixed by screw fastening. The ladder for manhole lifting includes a plurality of ladder units in which a cross bar connected between a pair of columns is curved outward along the inner peripheral surface of the manhole, and an arc-shaped fixed flange portion connected to a pair of columns of one ladder unit and extending outside the curved cross bar. And the ladder unit is provided with connecting portions for connecting to other ladder units at the upper and lower ends, and can be configured such that individual ladder units are connected to form one ladder. The fixed flange portion is provided with insertion holes corresponding to the bolt insertion holes of the manhole side flange, and can be configured to be screwed and fixed to the manhole side flange through the insertion holes.

[0010] (2) In the above (1), the fixed flange portion can be configured to be connected to the ladder unit located on the opening surface of the manhole so that the cross bar is located above the opening of the manhole in a state of being fixed to the manhole side flange.

[0011] (3) In the above (1), the insertion holes of the fixed flange portion can be configured to be larger than the bolt insertion holes and formed in an elliptical shape that is long toward the outer side in the circumferential direction of the manhole.

[0012] (4) In the above (1), the fixed flange portion can be configured to include a plate-like member provided with insertion holes, and a pair of connecting members extending from the plate-like member toward each column, with one end fixed to the column and the other end fixed to the plate-like member. And each connecting member can be configured such that a plurality of fixing portions with the column are provided in the longitudinal direction.

[0013] (5) In the above (1), with one ladder unit inserted from the opening of the manhole being held, the lower end of another ladder unit is connected to the upper end of the held one ladder unit. After the connection, the other ladder unit is lowered to sequentially connect a plurality of ladder units. By fixing the fixed flange portion provided on the ladder unit located on the opening surface of the manhole to the manhole-side flange, one ladder can be configured to be installed in the manhole.

Effect of the Invention

[0014] According to the present invention, it is possible to provide a ladder for manhole lifting and lowering that is easy to install in a manhole while ensuring a moving space during lifting and lowering.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

[0017] (Embodiment) Figures 1 to 5 are diagrams showing embodiments according to the present invention. Figure 1 is a diagram showing a ladder for manhole lifting according to the present embodiment, and Figure 2 is a diagram showing a plurality of ladder units 1A, 1B, 1C, 1D and a fixed flange portion 30 that constitute the ladder for manhole lifting.

[0018] The ladder 1 for manhole lifting is configured such that a plurality of ladder units are connected to form one ladder. For example, as shown in Figure 1, the ladder units 1A and 1B can be connected and configured. That is, the ladder 1 for manhole lifting according to the present embodiment is subdivided into a plurality of ladder units as shown in Figure 2. When in use, each ladder unit can be carried to the manhole, and the individual ladder units can be connected and assembled while being installed in the manhole. After use, it can be disassembled into each ladder unit and removed.

[0019] Each of the ladder units 1A, 1B, 1C, 1D includes a pair of columns 10A, 10B and a crossbar 20 connected between the pair of columns 10A, 10B, and the crossbar 20 is curved along the inner circumferential surface of the manhole 100 (toward the outside). The curved shape of the crossbar 20 corresponds to the diameter (opening diameter) of the manhole to be installed. It is also possible to provide a groove for anti-slip on the crossbar 20.

[0020] Each of the columns 10A, 10B is provided with connecting portions 11A, 12A, 11B, 12B for connecting to other ladder units at the upper and lower ends. Holes through which bolts are inserted are formed in the connecting portions 11A, 12A, 11B, 12B. By aligning the holes in the connecting portions of each ladder unit and performing screw fastening using bolts and nuts, the ladder units 1A, 1B, 1C, 1D can be connected and fixed to each other.

[0021] The ladder units 1A, 1B, 1C, 1D have different lengths of the columns 10A, 10B and different numbers of the crossbars 20, and the ladder 1 for manhole lifting can be used by arbitrarily combining ladder units of different lengths or ladder units of the same length.

[0022] Note that the ladder unit 1C is a ladder unit in a state where the fixed flange portion 30 is not attached to the ladder unit 1A. Insertion holes 13A and 13B for screw-fastening to the connecting members 32 and 33 of the fixed flange portion 30 with bolts and nuts are provided in each of the pair of support columns 10A and 10B, respectively.

[0023] The ladder unit 1A is provided with a fixed flange portion 30. The fixed flange portion 30 is connected to the pair of support columns 10A and 10B of one ladder unit constituting the manhole lifting ladder 1, extends outside the curved cross bars 20, and is formed in an arc shape. The fixed flange portion 30 includes an arc-shaped plate member 31 and connecting members 32 and 33.

[0024] The plate member 31 of the fixed flange portion 30 has a predetermined thickness and is formed in an arc shape substantially the same as the inner peripheral diameter of the opening of the manhole side flange 120. The width in the direction toward the outer side in the circumferential direction is formed to be substantially the same as or slightly larger than the width of the manhole side flange 120 shown in FIG. 3 described later.

[0025] The plate member 31 of the fixed flange portion 30 is provided with insertion holes 34 and 35 corresponding to the bolt insertion holes 121 of the manhole side flange 120. The fixed flange portion 30 is screwed and fixed to the manhole side flange 120 through the insertion holes 34 and 35 in a state of surface contact with the manhole side flange 120.

[0026] The connecting members 32 and 33 are long members. One end side is fixed to the support columns 10A and 10B, and the other end side is fixed to the plate member 31. The connecting members 32 and 33 can be formed in an L shape, for example, and the side walls are fixed to the support columns 10A and 10B by screw fastening. Insertion holes 321 and 331 corresponding to the insertion holes 13A and 13B are provided in the side walls, respectively. And the bottom portion extending horizontally from the side wall is fixed to the upper surface of the plate member 31.

[0027] FIG. 3 is a diagram for explaining the fixed flange portion 30 of the manhole lifting ladder 1 and the attached state of the manhole lifting ladder 1. In the example of FIG. 3, in order to explain the mode in which the manhole lifting ladder 1 is installed (fixed) to the manhole, among the manhole lifting ladders 1 composed of a plurality of ladder units, only the ladder unit 1A provided with the fixed flange portion 30 is illustrated, and other ladder units are omitted.

[0028] As shown in FIG. 3, the manhole lifting ladder 1 of the present embodiment is detachably installed on the manhole when entering a tank from a manhole provided in equipment such as a tank in a factory or facility such as an oil plant or a petrochemical plant. The manhole is an opening for maintenance work for inspecting the conditions such as dirt, corrosion, and damage inside equipment such as a tank as described above, and for cleaning dirt, repairing corrosion, and damaged parts. A lid member 110 for closing the opening of the manhole is fixed by screw fastening and is closed.

[0029] The worker removes the lid member 110 of the manhole, inserts the ladder unit 1A into the opening of the manhole, and fixes the fixed flange portion 30 to the manhole side flange 120. The worker aligns the bolt insertion holes 121 of the manhole side flange 120 with the insertion holes 34 and 35 of the fixed flange portion 30, inserts bolts into the insertion holes 34 and 35, and attaches nuts to the bolts protruding from the lower surface of the manhole side flange 120 through the bolt insertion holes 121 and tightens them with screws. Thereby, the ladder unit 1A, that is, the manhole lifting ladder 1 including at least the ladder unit 1A can be installed on the manhole.

[0030] In the A-A view (enlarged) of FIG. 3, the horizontal rung 20 of the manhole lifting ladder 1 is curved outward along the inner peripheral surface of the manhole, and the gap between the horizontal rung 20 and the inner peripheral surface of the manhole is reduced. That is, the worker can approach the inner peripheral surface of the manhole by the curved horizontal rung 20 during lifting and lowering. For this reason, a moving space during lifting and lowering is secured, and a smooth lifting and lowering operation can be performed.

[0031] As described above, in the manhole lifting ladder 1 of this embodiment, since the horizontal rungs 20 are curved outward along the inner peripheral surface of the manhole, the gap formed between the inner peripheral surface of the manhole and the ladder can be reduced, ensuring a movement space for the worker. Also, since the individual ladder units are connected to form one ladder, the required number of ladder units can be assembled according to the height from the opening to the bottom of the manhole and easily installed.

[0032] And since the fixed flange portion 30 is fixed using the manhole-side flange 120, the installation work of the ladder can be easily performed.

[0033] Note that, as shown in FIG. 3, the fixed flange portion 30 is connected to the ladder unit 1A located on the opening surface of the manhole such that a part of the horizontal rung 20 is positioned above the opening of the manhole in a state of being fixed to the manhole-side flange 120.

[0034] As described above, the worker removes the lid member 110, installs the ladder, and enters the tank. Conventionally, since the ladder was not arranged above the opening of the manhole, the worker had to insert the foot toward the horizontal rung located below the opening of the manhole and perform the tank entry operation of stepping directly into the manhole from the opening surface of the manhole. In this case, since there was no place for the worker to grasp above the opening of the manhole, the worker could not stably rely on the ladder, and the tank entry operation was likely to be unstable.

[0035] However, in the manhole lifting ladder 1 of the present embodiment, in the ladder unit 1A located on the opening surface of the manhole, the fixed flange portion 30 is installed below a part of the horizontal bar 20 so that the horizontal bar 20 is located above the opening of the manhole. That is, since the fixed flange portion 30 is installed on the ladder unit 1A such that a part of the horizontal bar 20 is disposed above the fixed flange portion 30, a part of the horizontal bar 20 can be positioned above the opening of the manhole. For this reason, while gripping the horizontal bar 20 disposed above the opening of the manhole, a person can rely on the manhole lifting ladder 1, and a stable tank entry operation can be realized.

[0036] FIG. 4 is a diagram for explaining the attachment state between the elliptical insertion holes 34 and 35 of the fixed flange portion 30 and the manhole side flange 120.

[0037] The insertion holes 34 and 35 are formed larger than the bolt insertion holes 121 of the manhole side flange 120, and are formed in an elliptical shape that is long toward the outer circumferential direction of the arc-shaped plate member 31, in other words, an elliptical shape that is long toward the outer circumferential direction of the manhole.

[0038] As shown in FIG. 4, the bolt insertion holes 121 of the manhole side flange 120 are aligned with the insertion holes 34 and 35 of the fixed flange portion 30 and screwed with bolts and nuts. However, the insertion holes 34 and 35 are formed larger than the bolt insertion holes 121 and in an elliptical shape that is long toward the outer circumferential direction of the manhole. For this reason, while maintaining the state in which the bolt insertion holes 121 are exposed from the insertion holes 34 and 35, the fixed flange portion 30 (the manhole lifting ladder 1) can be moved inward or outward in the radial direction of the manhole opening.

[0039] The inner diameter of the manhole may decrease due to factors such as the pressure acting on the manhole and aging deterioration. The positions of the bolt insertion holes 121 of the manhole-side flange 120 may also shift due to changes in the inner diameter of the manhole. Therefore, when aligning the insertion holes 34, 35 of the fixed flange portion 30 with the bolt insertion holes 121 of the manhole-side flange 120 provided around the opening of the manhole, the cross bar 20 may get too close to or too far from the inner peripheral surface of the manhole. If the cross bar 20 gets too close to the inner peripheral surface of the manhole, the gap between the inner peripheral surface of the manhole and the cross bar 20 becomes narrow, making it difficult to grip the cross bar 20 or hook the foot. Also, if the cross bar 20 gets too far from the inner peripheral surface of the manhole, the moving space during lifting and lowering becomes narrow.

[0040] Therefore, by forming the insertion holes 34, 35 of the present embodiment into an elliptical shape that is larger than the bolt insertion holes 121 of the manhole-side flange 120 and longer toward the outer side in the circumferential direction of the manhole, the fixed flange portion 30 can be moved inward or outward in the radial direction of the manhole opening while maintaining the state where the bolt insertion holes 121 are exposed from the insertion holes 34, 35. Thereby, the ladder 1 for manhole lifting (fixed flange portion 30) can be fixed to the manhole-side flange 120 while adjusting the gap between the cross bar 20 and the inner peripheral surface of the manhole.

[0041] For example, in the example of FIG. 4, if the fixed flange portion 30 is moved inward in the radial direction with respect to the gap A between the cross bar 20 and the inner peripheral surface of the manhole, the gap A1 between the cross bar 20 and the inner peripheral surface of the manhole becomes wider (A1 > A). Also, if the fixed flange portion 30 is moved outward in the radial direction with respect to the gap A between the cross bar 20 and the inner peripheral surface of the manhole, the gap A2 between the cross bar 20 and the inner peripheral surface of the manhole becomes narrower (A > A2).

[0042] In addition to cases where it becomes smaller due to pressure acting on the manhole, aging deterioration, etc., simply considering the gap between the inner peripheral surface of the manhole and the horizontal bar 20 and the movement space during lifting and lowering, while adjusting the gap between the horizontal bar 20 and the inner peripheral surface of the manhole, the ladder 1 for manhole lifting (fixed flange portion 30) can be fixed to the manhole-side flange 120.

[0043] Fig. 5 is a diagram for explaining the attachment method of the ladder 1 for manhole lifting of the present embodiment.

[0044] As shown in Fig. 5, the ladder unit 1C is inserted from the opening of the manhole and temporarily held by the worker X. Next, the worker Y sets the ladder unit 1A with the fixed flange portion 30 above the ladder unit 1C, and the worker Z brings the connecting portions 11A, 12A, 11B, 12B of the ladder unit 1A and the ladder unit 1C into contact and connects them with bolts and nuts (fastening members). Then, the ladder unit 1A connected to the ladder unit 1C is lowered, and the fixed flange portion 30 is brought into contact with the manhole-side flange 120. The bolt insertion holes 121 are exposed in the insertion holes 34, 35 of the fixed flange portion 30 and screwed to the manhole-side flange 120 with bolts and nuts.

[0045] In the example of Fig. 5, the attachment method of the ladder 1 for manhole lifting in which two ladder units 1A and 1C are connected is described as an example. However, while holding the ladder unit 1C inserted from the opening of the manhole, another ladder unit 1C or ladder units 1B and 1D can be sequentially connected, and finally, the ladder unit 1A with the fixed flange portion 30 arranged on the opening surface of the manhole can be connected.

[0046] As described above, the manhole lifting ladder 1 of the present embodiment is configured such that one ladder unit inserted from the opening of the manhole is held, the lower end of another ladder unit is connected to the upper end of the held one ladder unit, and after the connection, the other ladder unit is lowered to sequentially connect a plurality of ladder units. The fixing flange portion 30 provided on the ladder unit located on the opening surface of the manhole is fixed to the manhole side flange 120, so that one ladder is installed in the manhole.

[0047] In the above example, the mode of installing the manhole lifting ladder 1 by three workers has been described. However, for example, when inserting and holding the ladder unit 1C from the opening of the manhole, a chain block can be attached to the cross bar 20 of the ladder unit 1C, and the ladder unit 1C inserted from the opening of the manhole can be temporarily held by the chain block. In this case, worker Y sets the ladder unit 1A with the fixing flange portion 30 above the ladder unit 1C, and worker X can abut the connecting portions 11A, 12A, 11B, 12B of the ladder units 1A and 1C and connect them with bolts and nuts (fastening members). Thus, it is possible to install the manhole lifting ladder 1 of the present embodiment even with two workers.

[0048] As described above, the present embodiment has been described. However, when a sufficient working space can be secured around the manhole, the manhole lifting ladder 1 in a state where a plurality of ladder units are connected and assembled in advance can also be installed at the opening of the manhole. In this case, the assembled manhole lifting ladder 1 can be lifted using a lifting device such as a crane and inserted and installed from the opening of the manhole.

[0049] In addition, a curing material can be attached to the lower end portion of the manhole lifting ladder 1 (the lower end portion of the lowermost ladder unit) as a corrosion countermeasure. As the curing material, for example, a gasket or the like provided between the manhole flange 120 and the lid member 110 can be used.

[0050] In addition, according to the size (inner diameter) of the manhole, a plurality of fixed flange portions 30 of different sizes are prepared, and by attaching fixed flange portions 30 of different sizes to the ladder unit, it is possible to install the manhole lifting ladder 1 composed of the same ladder unit for manholes of different sizes.

[0051] In addition, part or all of the materials of each ladder unit 1A, 1B, 1C, 1D may be any metal material such as iron, stainless steel, steel, or a combination thereof. Also, although the cross bars 20 of the ladder unit 1A are made of round steel, it is not limited to this.

[0052] In addition, the fixed flange portion 30 shown in FIGS. 3 and 4 has two insertion holes, i.e., insertion holes 34 and 35, but is not limited thereto, and may have one insertion hole or three or more insertion holes.

[0053] Also, the length of the cross bar 20 of the flange fixing portion 30 is a size applicable to various manholes, but is not limited to one. Preferably, it is from 18 inches to 24 inches. More preferably, it is 20 inches.

[0054] In addition, in this embodiment, it is assumed that the worker is a human, but at least one of the workers may be a machine (including AI) or an operator.

[0055] FIG. 6 is a diagram showing a modified example of the manhole lifting ladder of this embodiment. As shown in FIG. 6, the fixed flange portion 30A has a plurality of insertion holes 321 and 331 formed in the connecting members 32 and 33 in the longitudinal direction, and can be applied to each ladder unit composed of manholes of different diameters, in other words, cross bars 20A and 20B of different diameters (arcs). Regarding other configurations, they are the same as those of the fixed flange portion 30.

[0056] The connecting members 32 have insertion holes 321a, 321b, 321c corresponding to the insertion hole 13A of the support column 10A, which are arranged longitudinally at a predetermined interval on the L-shaped side wall. Similarly, for the connecting member 33, insertion holes 331a, 331b, 331c corresponding to the insertion hole 13B of the support column 10B are arranged longitudinally at a predetermined interval on the L-shaped side wall.

[0057] In the example of FIG. 6, a fixing flange portion 30A is fixed to a ladder unit composed of a horizontal bar 20A having an arc with a diameter R corresponding to a manhole with a diameter R. In this case, the fixing flange portion 30A is fixed to the support column 10A through the insertion hole 13A of the support column 10A and the insertion hole 321a of the connecting member 32. Similarly, the fixing flange 30A is fixed to the support column 10B through the insertion hole 13B of the support column 10B and the insertion hole 331a of the connecting member 33.

[0058] On the other hand, for a ladder unit composed of a horizontal bar 20B having an arc with a diameter R1 (<R) corresponding to a manhole with a diameter R1, the fixing flange portion 30A is fixed through insertion holes 321b, 331b closer to the plate-like member 31 than the insertion holes 321a, 331a.

[0059] In the fixing flange portion 30A of this modification, in a pair of connecting members 32, 33 connected to the ladder unit, a plurality of insertion holes 321, 331, which are fixing portions with the support columns 10A, 10B, are provided longitudinally. Therefore, each ladder unit composed of horizontal bars 20A, 20B with different arcs corresponding to the diameter of the manhole can be connected to one fixing flange portion 30A. It is not necessary to prepare different fixing flange portions 30 corresponding to the diameter of the manhole, and the number of parts can be reduced.

[0060] In FIG. 6, a mode in which three insertion holes are formed in each of the connecting members 32, 33 is illustrated, but it can be configured such that two or more insertion holes (fixing portions with the support columns 10A, 10B) are formed.

Explanation of Reference Numerals

[0061] 1 Ladder for manhole lifting 1A, 1B, 1C, 1D Ladder unit 10A, 10B Struts 11A, 12A, 11B, 12B Connecting parts 20 Crossbars 30 Fixed flange part 31 Plate-like member 32, 33 Connecting members 321, 321a, 321b, 321c Insertion holes (fixing parts) 331, 331a, 331b, 331c Insertion holes (fixing parts) 34, 35 Insertion holes 110 Cover member 120 Manhole side flange 121 Bolt insertion hole

Claims

1. A ladder for manhole lifting and lowering, which is detachably installed on a manhole side flange where a lid member for closing the opening of the manhole is fixed by screw fastening, comprising a plurality of ladder units in which cross bars connected between a pair of struts are curved outward along the inner peripheral surface of the manhole, and an arc-shaped fixed flange portion connected to the pair of struts of one of the ladder units and extending outside the curved cross bar, wherein the ladder unit is provided with connecting portions for connecting to other ladder units at the upper and lower ends, and the individual ladder units are configured to be connected to form one ladder, the fixed flange portion is provided with insertion holes corresponding to bolt insertion holes of the manhole side flange, and is characterized in that it is fixed to the manhole side flange by screw fastening through the insertion holes. A ladder for manhole lifting and lowering.

2. The ladder for manhole lifting and lowering according to claim 1, characterized in that the fixed flange portion is connected to the ladder unit located on the opening surface of the manhole so that the cross bar is located above the opening of the manhole in a state of being fixed to the manhole side flange.

3. The ladder for manhole lifting and lowering according to claim 1, characterized in that the insertion holes of the fixed flange portion are larger than the bolt insertion holes and are formed in an elliptical shape that is long toward the outer side in the circumferential direction of the manhole.

4. The fixed flange portion includes a plate-shaped member provided with the insertion holes, and a pair of connecting members extending from the plate-shaped member toward each strut, with one end fixed to the strut and the other end fixed to the plate-shaped member, and the connecting member is characterized in that a plurality of fixing portions with the strut are provided in the longitudinal direction. The ladder for manhole lifting and lowering according to claim 1.

5. With one ladder unit inserted from the opening of the manhole held, the lower end of another ladder unit is connected to the upper end of the held one ladder unit, and after connection, the other ladder units are lowered to sequentially connect a plurality of the ladder units, and the fixed flange portion provided on the ladder unit located on the opening surface of the manhole is fixed to the manhole side flange, whereby one ladder is installed in the manhole. The ladder for manhole lifting and lowering according to claim 1.

Images