Bag type blind plate pressing device and pressure testing method

Abstract

The invention relates to a bag type blind plate pressurizing device and a pressure testing method, and relates to the field of sealing performance testing, the bag type blind plate pressurizing device comprises a bag, a mounting plate, a pressurizing pipeline and a gas pipeline, the mounting plate is fixedly connected with one end of the bag, the pressurizing pipeline and the gas pipeline are both fixedly connected with the mounting plate, the gas pipeline is communicated with the bag, the pressurizing pipeline penetrates through the bag, and the gas pipeline is fixedly connected with the gas pipeline. And extends to the other end of the bag. The device has the beneficial effects that water is injected into the cavity through the pressurizing pipeline, so that water injection pressure testing can be conveniently carried out, and water resources are saved. For the factors that the roundness and the ovality of the tank wall manhole in the initial stage are not consistent with those of the design, and deformation occurs in the later operation process, the bag type blind plate pressing device can well seal and press the manhole. After the pressurizing device is used for testing pressure, the testing is similar to the testing of production oil inlet, the leakage after the oil inlet is put into production is avoided, and the tank is prevented from being cleaned again.

Description

Technical Field

[0001] The invention relates to the field of sealing performance testing, and in particular to a bag-type blind plate pressure testing device and a pressure testing method. Background Art

[0002] After the construction of the storage tank is completed, it is necessary to carry out regular tank opening and maintenance work to avoid tank failure due to tank defects, causing environmental pollution and other abnormal events.

[0003] The overhaul of a storage tank mainly includes re-coating the anti-corrosion coating of the storage tank, inspection or replacement of related accessories, as well as electrical rectification, updating and inspection of instruments, and maintenance of fire protection facilities. After the overhaul of the storage tank is completed, the manhole on the tank wall needs to be sealed with a blind plate, so it becomes the most important static sealing point during the operation of the storage tank. After the storage tank is put into production, if a leak is found at the static sealing point, in order to cure this problem, the storage tank must be cleaned again, the blind plate sealing gasket of the storage tank must be replaced, and the leakage fault must be eliminated before the blind plate can be reinstalled and put into production, which will delay the commissioning time of the storage tank and cause huge economic losses. Therefore, it is imperative to test the sealing performance of the blind plate to the manhole during the overhaul stage and develop a reliable pressure test device.

[0004] In the same industry, the pressure test of other sealing points such as the manhole of the tank wall is to inject the same volume of water into the storage tank for static pressure test, so as to achieve the purpose of no leakage after the storage tank is officially put into production. However, because the storage tank is a huge container, it is built by butt welding of steel plates. Under the influence of foundation sinking, earthquakes, wind, gravity and oil products for a long time, the storage tank has different degrees of deformation. As a result, the manhole of the tank wall has become non-circular and has welds. In the case of irregular shapes, it is difficult for traditional pressure devices to achieve sealing, which makes it difficult to carry out the pressure work of the blind plate. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to detect the sealing performance of the manhole of the tank wall.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a bag-type blind plate pressing device, comprising a bag, a mounting plate, a pressing pipe and a gas pipe, wherein the mounting plate is fixedly connected to one end of the bag, the pressing pipe and the gas pipe are both fixedly connected to the mounting plate, the gas pipe is connected to the bag, and the pressing pipe passes through the bag and extends to the other end of the bag.

[0007] The beneficial effects of the present invention are as follows: before the pressure-relief device is placed in the manhole of the tank wall, the bag is in a relaxed state and can be quickly and easily placed in the manhole. After the bag is pressurized by the air pump, the bag is tightly attached to the inner wall of the manhole under the action of the internal gas expansion force, so that the manhole forms a closed cavity between the bag and the blind plate. The cavity is filled with water through the pressure-relief pipeline, so that water injection pressure testing can be carried out conveniently, saving water resources. In the face of factors such as the initial roundness and ovality of the tank wall manhole design not being consistent with the design, and deformation during the later operation process, the bag-type blind plate pressure-relief device can better seal and pressurize the manhole.

[0008] In addition, after the overhaul of the storage tank is completed and the oil is put into production, if the problem of oil leakage from the blind plate of the manhole on the tank wall is found again, the tank needs to be cleaned again and the blind plate gasket needs to be replaced. After the pressure test using the pressure test device of the present invention, it is similar to the test of oil inlet before production, avoiding leakage after oil inlet and production, avoiding cleaning the tank again, thereby saving the manpower cost and time cost of repair and maintenance.

[0009] Based on the above technical solution, the present invention can also be improved as follows.

[0010] Furthermore, the pouch is a cylindrical bag body, and the pouch is provided with three annular protrusions in sequence along its axial direction.

[0011] The beneficial effect of adopting the above further solution is that three layers of annular protrusions are set on the side wall where the bladder contacts the inner wall of the manhole for sealing. The medium in the pressure test space can be sealed at multiple levels to better achieve the sealing function. The bladder is used as the main sealing component. The inflated bladder is also highly tolerant when facing irregular shaped sealing spaces and can adapt to the sealing function under various working conditions.

[0012] Furthermore, a shut-off valve is provided on the pressure-pressing pipeline.

[0013] The beneficial effect of adopting the above further scheme is: a shut-off valve is set on the pressure test pipeline, and after the pressure in the closed cavity between the bladder and the blind plate is increased to 1.5 times the working pressure, the valve is closed to form an independent sealed space in the sealed cavity, reducing the influence of other factors on the pressure test results.

[0014] Furthermore, a pressure gauge is provided on the pressure-pressing pipeline, and the pressure gauge is located between the shut-off valve and the mounting plate.

[0015] The beneficial effect of adopting the above further scheme is: after the bag is installed, the pressure test pipeline is connected to the pressure test pump, and the pressure rise and fall in the sealing cavity is observed online through the pressure gauge. A precision pressure gauge can be selected here to facilitate accurate observation of the pressure drop in the sealing cavity.

[0016] Furthermore, a pressure relief valve is provided on the gas pipeline.

[0017] The beneficial effect of adopting the above further solution is: when the pressure is too high during the pressure increase process or after the pressure test is completed, the pressure relief valve is opened to relieve the pressure in the bladder.

[0018] Furthermore, it also includes a safety anti-blowout device, which is installed on the mounting plate and is used to position with the device to be tested.

[0019] The beneficial effects of adopting the above further scheme are: the risk is relatively high during the pressure test, and there is a risk of the pressure device spraying out and injuring people due to excessive pressure. A safety anti-spraying device is set to position the mounting plate and the device to be tested to prevent the pressure device from spraying out due to excessive pressure.

[0020] Furthermore, the safety anti-blowout device includes a plurality of bolt assemblies, and the plurality of bolt assemblies are arranged at intervals along the circumference of the mounting plate. Each of the bolt assemblies includes a bolt and a nut, the nut is fixedly connected to the mounting plate, and the bolt is radially arranged along the mounting plate and threadedly connected to the nut.

[0021] The beneficial effect of adopting the above further scheme is: using multiple bolt ends to extend radially and abut against the inner wall of the manhole, using the radial force of the bolts to position the mounting plate, so as to achieve the purpose of preventing the bag from spraying out.

[0022] Furthermore, the plurality of bolt assemblies are evenly distributed along the circumference of the mounting plate.

[0023] The beneficial effects of adopting the above further solution are: the multiple bolt assemblies are evenly distributed, the mounting plate is evenly stressed, and the reliability is high.

[0024] The present invention also provides a pressure testing method, which is implemented by using the bag-type blind plate pressure testing device, and includes the following steps:

[0025] Step 1: Place the bag into the manhole of the device to be tested, and make the mounting plate perpendicular to the axis of the manhole;

[0026] Step 2, inflating the bag through a gas pipeline until the bag fits tightly against the inner wall of the manhole;

[0027] Step 3: inject water into the cavity between the bladder and the blind plate through a pressure pipe to increase the pressure until the pressure in the cavity reaches 1.5 times the maximum working pressure of the device under test, and maintain the pressure for 30 minutes;

[0028] Step 4: drain the water in the cavity through the pressure pipe, release the gas in the bag through the gas pipe, and take out the bag.

[0029] The beneficial effect is: by injecting water into the cavity through the pressure-pressing pipeline, water injection pressure testing can be conveniently carried out, saving water resources. In the face of factors such as the initial roundness and ovality of the manhole in the tank wall not being consistent with the design, and deformation during the later operation, the bag-type blind plate pressure-pressing device can better seal and pressurize the manhole. In addition, after the overhaul of the storage tank is completed and the oil is put into production, if the problem of oil leakage from the blind plate of the manhole in the tank wall is found again, it is necessary to clean the tank again and replace the blind plate gasket. After the pressure test using the pressure-pressing device of the present invention, it is similar to testing the oil inlet before production, which avoids leakage after the oil is put into production and avoids cleaning the tank again, thereby saving the manpower cost and time cost of repair and maintenance.

[0030] Furthermore, before step three, the method further includes: rotating a plurality of bolts of the safety anti-blowout device so that the ends of all the bolts are pressed tightly against the inner wall of the manhole.

[0031] The beneficial effect of adopting the above further scheme is: before the pressure test, the position of the mounting plate is fixed by using the safety anti-blowout device to avoid the pressure device from blowing out and ensure the safety of personnel.

[0032] The beneficial effects of the present invention are:

[0033] 1. The bag-type blind plate pressure device has a high adaptability to the manhole of the tank wall, and is highly tolerant of manhole deformation and uneven butt welds. It can adapt to manholes of different sizes and meet the safety pressure test requirements. Compared with traditional water injection pressure testing, it reduces resource waste and complicated water injection procedures, and greatly saves economic costs and labor investment.

[0034] 2. A safety anti-blowout device consisting of multiple bolt assemblies is installed externally to avoid accidents in which the pressure device flies out and injures people due to high pressure between the bag and the sealed cavity.

[0035] 3. Before the tank is put into operation, the oil filling situation of the tank can be simulated to verify the sealing of the manhole, so that the blind plate gasket can be adjusted in time to avoid cleaning the tank again. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a front view of a bag-type blind plate pressing device of the present invention;

[0037] Figure 2 It is a left view of a bag-type blind plate pressing device of the present invention;

[0038] Figure 3 A top view of a bag-type blind plate pressing device of the present invention;

[0039] Figure 4 The present invention is a schematic diagram of a bag-type blind plate pressing device in use.

[0040] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0041] 1. Bladder bag; 2. Mounting plate; 3. Pressure pipe; 4. Gas pipe; 5. Shut-off valve; 6. Pressure gauge; 7. Pressure relief valve; 8. Safety anti-blowout device; 100. Manhole; 200. Blind plate. DETAILED DESCRIPTION

[0042] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0043] like Figure 1-Figure 4 As shown, this embodiment provides a bag-type blind plate pressing device, including a bag 1, a mounting plate 2, a pressing pipe 3 and a gas pipe 4, the mounting plate 2 is fixedly connected to one end of the bag 1, the pressing pipe 3 and the gas pipe 4 are both fixedly connected to the mounting plate 2, the gas pipe 4 is connected to the bag 1, the pressing pipe 3 passes through the bag 1, and extends to the other end of the bag 1.

[0044] Before the pressure-relief device is placed in the manhole of the tank wall, the bag 1 is in a relaxed state and can be quickly and easily placed in the manhole 100. After the bag 1 is pressurized by the air pump, the bag 1 is tightly attached to the inner wall of the manhole 100 under the action of the internal gas expansion force, so that the manhole 100 forms a closed cavity between the bag 1 and the blind plate 200. The cavity is filled with water through the pressure-relief pipe 3, so that water injection pressure testing can be carried out conveniently to save water resources. In the face of factors such as the initial roundness and ovality of the manhole on the tank wall that do not conform to the design, and deformation during the later operation process, the bag-type blind plate pressure-relief device can better seal and pressurize the manhole. In addition, after the overhaul of the storage tank is completed and the oil is put into production, if the problem of oil leakage from the blind plate of the manhole on the tank wall is found again, the tank needs to be cleaned again and the blind plate gasket needs to be replaced. After the pressure test using the pressure-testing device of the present invention, it is similar to testing the oil inlet before production, so as to avoid leakage after the oil inlet is put into production and avoid cleaning the tank again, thereby saving the manpower cost and time cost of repair and maintenance.

[0045] Specifically, Figure 4 As shown, in order to allow the pressing pipe 3 to pressurize the cavity at the other end of the bag 1, the bag 1 is designed as an annular sealed bag body, and the pressing pipe 3 passes through the hole of the annular structure, so as not to affect the sealing of the bag 1.

[0046] Specifically, the bag 1 is made of rubber material.

[0047] Optionally, the mounting plate 2 is a plate of any shape. In a specific example, the mounting plate 2 is a circular plate.

[0048] On the basis of any of the above solutions, the pouch 1 is a cylindrical bag body, and the pouch 1 is provided with three annular protrusions in sequence along its axial direction.

[0049] The side wall where the bag 1 contacts the inner wall of the manhole 100 is provided with three layers of annular protrusions for sealing. The medium in the pressure test space can be sealed at multiple levels to better achieve the sealing function. As the main sealing component, the bag 1 after being inflated also has high tolerance when facing irregular shaped sealing spaces, and can adapt to the sealing function under various working conditions.

[0050] Specifically, the three annular protrusions refer to the shape of the outer contour formed after the bladder 1 is inflated.

[0051] On the basis of any of the above solutions, a shut-off valve 5 is provided on the pressure pipe 3 .

[0052] A shut-off valve 5 is provided on the pressure testing pipeline 3. After the pressure in the sealed cavity between the bladder 1 and the blind plate 200 is increased to 1.5 times of the working pressure, the valve is closed to form an independent sealed space in the sealed cavity, thereby reducing the influence of other factors on the pressure test results.

[0053] On the basis of any of the above solutions, a pressure gauge 6 is further provided on the pressure-pressing pipeline 3 , and the pressure gauge 6 is located between the shut-off valve 5 and the mounting plate 2 .

[0054] After the bag 1 is installed, the pressure test pipe 3 is connected to the pressure test pump, and the pressure rise and fall in the sealing cavity is observed online through the pressure gauge 6. A precision pressure gauge can be used here to accurately observe the pressure drop in the sealing cavity.

[0055] Based on any of the above solutions, a pressure relief valve 7 is provided on the gas pipeline 4 .

[0056] When the pressure is too high during the pressure increase process or after the pressure test is completed, the pressure relief valve 7 is opened to relieve the pressure of the bladder 1.

[0057] On the basis of any of the above solutions, it further comprises a safety anti-blowout device 8, wherein the safety anti-blowout device 8 is installed on the mounting plate 2 and is used for positioning with the device to be tested.

[0058] There is a high risk during the pressure test, as there is a risk of excessive pressure and the pressure device spraying out and injuring people. A safety anti-spraying device 8 is provided to position the mounting plate 2 and the device to be tested to prevent the pressure device from spraying out due to excessive pressure.

[0059] Optionally, the safety anti-blowout device 8 can be threadedly connected, clamped or radially tightened to the manhole of the equipment to be tested.

[0060] On the basis of any of the above schemes, specifically, the safety anti-blowout device 8 includes a plurality of bolt assemblies, and the plurality of bolt assemblies are arranged at intervals along the circumference of the mounting plate 2, each of the bolt assemblies includes a bolt and a nut, the nut is fixedly connected to the mounting plate 2, and the bolt is radially arranged along the mounting plate 2 and is threadedly connected to the nut.

[0061] The ends of the multiple bolts are extended radially and abut against the inner wall of the manhole 100, and the radial force of the bolts is used to position the mounting plate 2, so as to prevent the bag 1 from spraying out.

[0062] Specifically, the bolt head of the bolt is arranged radially outward, and the bolt head abuts against the inner wall of the manhole 100, so the contact area is large and the reliability is high.

[0063] Specifically, the safety anti-spraying device 8 is coaxially arranged with the sac bag 1 .

[0064] Based on any of the above solutions, the plurality of bolt assemblies are evenly distributed along the circumference of the mounting plate 2 .

[0065] The multiple bolt assemblies are evenly distributed, the mounting plate 2 is evenly stressed, and the reliability is high.

[0066] This embodiment also provides a pressure test method, which is implemented by using the bag-type blind plate pressure testing device, and includes the following steps:

[0067] Step 1: Place the bag 1 into the manhole 100 of the device to be tested, and make the mounting plate 2 perpendicular to the axis of the manhole 100;

[0068] Before the bladder 1 is inflated, it is in a relaxed state and can be easily inserted into the manhole 100 of the tank wall. Note that the bladder 1 must be installed "straight", that is, the end face of the bladder 1 is perpendicular to the axis of the manhole 100, so as to ensure better sealing performance.

[0069] Step 2, inflating the bag 1 through the gas pipe 4 until the bag 1 is tightly fitted to the inner wall of the manhole 100;

[0070] An air pump is used to inflate the bag 1 through the gas pipeline 4, so that the three annular protrusions on the bag 1 fit tightly with the inner wall of the manhole 100 without any obvious gap.

[0071] Step 3: inject water into the cavity between the bag 1 and the blind plate 200 through the pressure pipe 3 to increase the pressure until the pressure in the cavity reaches 1.5 times the maximum working pressure of the device under test, and maintain the pressure for 30 minutes;

[0072] The equipment to be tested is a storage tank or other equipment with a manhole. When the pressure in the cavity reaches 1.5 times the maximum working pressure of the storage tank, the pressure is maintained for 30 minutes to observe if there is no pressure drop, and the external sealing surface is checked for leakage to be qualified.

[0073] Step 4: drain the water in the cavity through the pressure pipe 3, release the gas in the bag 1 through the gas pipe 4, and take out the bag 1.

[0074] Water is injected into the cavity through the pressure-testing pipe 3, so that water injection pressure test can be conveniently performed to save water resources. In the face of factors such as the initial roundness and ovality of the manhole in the tank wall not being consistent with the design, and deformation during the later operation, the bag-type blind plate pressure-testing device can better seal and pressurize the manhole.

[0075] In addition, after the overhaul of the storage tank is completed and the oil is put into production, if the problem of oil leakage from the blind plate of the manhole on the tank wall is found again, the tank needs to be cleaned again and the blind plate gasket needs to be replaced. After the pressure test using the pressure test device of the present invention, it is similar to the test of oil inlet before production, avoiding leakage after oil inlet and production, avoiding cleaning the tank again, thereby saving the manpower cost and time cost of repair and maintenance.

[0076] In particular, as in step 3, due to leakage of the sealing surface between the bag 1 and the manhole 100, a pressure drop occurs, and the bag 1 needs to be rotated around the axis of the bag 1. Repeat steps 1 to 4 and re-test the pressure. If necessary, sealant can be used to enhance the sealing effect (i.e., fill the space between the outer wall of the bag 1 and the manhole 100 with sealant) and perform the pressure test.

[0077] Furthermore, before step three, the method further includes: rotating a plurality of bolts of the safety blowout prevention device 8 so that the ends of all the bolts are pressed tightly against the inner wall of the manhole 100 .

[0078] Before the pressure test, the safety anti-blowout device 8 is used to fix the position of the mounting plate 2 to prevent the pressure device from blowing out and ensure the safety of personnel.

[0079] Specifically, when tightening the multiple bolts of the safety anti-spout device 8, first tighten one bolt every 90° to make the four bolts press against the inner wall of the manhole 100, and then tighten the bolts at other positions to ensure uniform tightening force. When tightening the bolts, it should be noted that the bolts in each direction must be evenly stressed, otherwise the bladder will fall out during the pressure test.

[0080] In the description of the present invention, it should be noted that the orientations or positional relationships indicated by the terms "axial", "radial", "circumferential", etc. are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0081] In the description of the present invention, “plurality” means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0082] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0083] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0084] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A bag-type blind plate pressing device, characterized in that: The invention comprises a bag (1), a mounting plate (2), a pressure pipe (3) and a gas pipe (4), wherein the mounting plate (2) is fixedly connected to one end of the bag (1), the pressure pipe (3) and the gas pipe (4) are both fixedly connected to the mounting plate (2), the gas pipe (4) is communicated with the bag (1), and the pressure pipe (3) passes through the bag (1) and extends to the other end of the bag (1).

2. A bag-type blind plate pressing device according to claim 1, characterized in that: The pouch (1) is a cylindrical bag body, and the pouch (1) is provided with three annular protrusions in sequence along its axial direction.

3. The bag-type blind plate pressing device according to claim 1, characterized in that: The pressure-pressing pipeline (3) is provided with a cut-off valve (5).

4. A bag-type blind plate pressing device according to claim 3, characterized in that: The pressure-pressing pipeline (3) is also provided with a pressure gauge (6), and the pressure gauge (6) is located between the cut-off valve (5) and the mounting plate (2).

5. The bag-type blind plate pressing device according to claim 1, characterized in that: The gas pipeline (4) is provided with a pressure relief valve (7).

6. A bag-type blind plate pressing device according to any one of claims 1 to 5, characterized in that: It also comprises a safety anti-blowout device (8), which is installed on the mounting plate (2) and is used for positioning with the device to be tested.

7. A bag-type blind plate pressing device according to claim 6, characterized in that: The safety anti-blowout device (8) comprises a plurality of bolt assemblies, wherein the plurality of bolt assemblies are arranged at intervals along the circumference of the mounting plate (2), each of the bolt assemblies comprises a bolt and a nut, wherein the nut is fixedly connected to the mounting plate (2), and the bolt is arranged radially along the mounting plate (2) and is threadedly connected to the nut.

8. The bag-type blind plate pressing device according to claim 7, characterized in that: The plurality of bolt assemblies are evenly distributed along the circumference of the mounting plate (2).

9. A pressure testing method, characterized in that: The method is implemented by using the bag-type blind plate pressing device according to any one of claims 1 to 8, comprising the following steps: Step 1: Place the bag (1) into the manhole (100) of the device to be tested, and make the mounting plate (2) perpendicular to the axis of the manhole (100); Step 2, inflating the bag (1) through the gas pipeline (4) until the bag (1) is tightly fitted to the inner wall of the manhole (100); Step 3: inject water into the cavity between the bag (1) and the blind plate (200) through the pressure pipe (3) to increase the pressure until the pressure in the cavity reaches 1.5 times the maximum working pressure of the device to be tested, and maintain the pressure for 30 minutes; Step 4: drain the water in the cavity through the pressure pipe (3), release the gas in the bag (1) through the gas pipe (4), and take out the bag (1).

10. A pressure testing method according to claim 9, characterized in that: Before step three, the method further includes: rotating a plurality of bolts of the safety anti-spout device (8) so that the ends of all the bolts are pressed tightly against the inner wall of the manhole (100).

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