KR102322573B1 - the Device for Monitoring Buried Pipe - Google Patents

Abstract

The present invention relates to a monitoring device for collecting inside information of a buried pipe which collects information in a buried pipe through an information collection unit of a monitoring device installed in the buried pipe to transmit the information to a control center on the ground to efficiently maintain and manage the buried pipe, thereby reducing maintenance and management costs. The monitoring device for collecting inside information of a buried pipe comprises: a leakage prevention member (210) inserted into and mounted on a punching groove (1a) of a buried pipe (1); a case body (220) having a dual structure with an outer case (221) mounted on the leakage prevention member and an inner case (225) provided in the outer case; an information collection unit (230) including a camera provided on the lower end of the outer case (221) and a measurement device provided on the lower end of the inner case (225) to collect information in the buried pipe; a wiper member (240) provided on the outer circumference of a camera dome for protecting the camera to clean the camera dome; a driving means (250) provided on the inside of the outer case (221) to drive the wiper member (240); and a pressing support member (270) provided on the outer circumference of the outer case (221) to support the units while pressing the leakage prevention member (210).

Description

A monitoring device for collecting information inside a buried pipe {the Device for Monitoring Buried Pipe}

The present invention collects the information in the buried pipe through the information collection unit of the monitoring device installed inside the buried pipe and transmits it to the control center on the ground, so that the efficient maintenance of the buried pipe is performed, thereby reducing the maintenance cost. It relates to a monitoring device for collecting information inside the tube.

The buried pipe includes a sewage pipe for collecting sewage and rainwater and transporting it to the sewage treatment plant and discharge area, and determines the drainage area and treatment area to form a sewage pipe network underground. In addition, the buried pipe includes a buried wastewater discharge pipe to discharge the wastewater produced by the wastewater producer.

If such a buried pipe is not continuously maintained and managed, the function of the sewage treatment facility deteriorates due to aging and cracks occur, the soil and cement paste of the ground layer covering the buried pipe will flow into the buried pipe. can be imported.

In addition, the transport function is weakened by the soil and organic sediment flowing into the buried pipe, so that rainwater overflows, soil and groundwater contamination due to sewage leakage, and cavities may occur in the ground. Due to this, it may cause a sinkhole, which may cause personal injury and property damage.

In addition, it may cause serious environmental pollution due to the inflow of wastewater that has not been purified or more than an appropriate amount discharged from a wastewater discharge pipe that is not properly maintained.

Accordingly, in order to regularly determine whether the buried pipe is damaged, whether internal soil is deposited and whether the cement pool is inflowed, to determine the adequacy of construction and whether there is a flow obstruction, generally through the inside of the manhole buried at a certain distance, limited by manpower set up to be managed.

However, there may be cracks that have already been created inside the buried pipe, and there is a possibility that harmful gases may remain. In this way, the input of manpower on the site for maintenance in a state where the internal condition of the buried pipe is not accurately judged can cause casualties.

In addition, in a state where the internal condition of the buried pipe is not accurately determined, the introduction of a robot such as a self-propelled car instead of a person may cause property damage due to robot loss.

In particular, a flow rate meter and a gas concentration meter (hereinafter referred to as a meter) are installed in wastewater pipes, which are difficult to manage because manpower is input one by one. However, in order to avoid fines and negligence caused by the discharge of wastewater, cases in which an outsider manipulates the measuring device without permission are constantly occurring. As such, there is an increasing number of cases of unauthorized damage and occupation of underground pipes such as gas pipes and power pipes by exploiting the conditions of the buried pipes that are difficult to grasp with the naked eye.

Korean Patent Publication No. 10-1813913 Korean Patent Publication No. 10-1275117

The present invention for solving the above problems has the following objects.

The present invention can install the monitoring device with a simple operation in installing the monitoring device that collects the information inside the buried pipe, can prevent leakage of water to the installation site in case of rain, and provide information in the buried pipe in real time. It aims to provide a monitoring device for collecting information inside a buried pipe that collects and provides.

An object of the present invention is to prevent environmental pollution by allowing the camera to be installed and collected from outside the buried pipe, to prevent unauthorized manipulation by outsiders, and in particular to control the unauthorized discharge of wastewater in real time.

The present invention is to collect internal information of a buried pipe, and has a double structure with a leak prevention member inserted and seated into a perforated groove of the buried pipe, an outer case seated with the leak prevention member, and an inner case provided inside the outer case An information collection unit for collecting information inside the buried pipe, including a case body having a case body having A wiper member provided to clean the camera dome, a wiper driving means provided inside the outer case to drive the wiper member, and a central connection case interconnecting the inner case and a flexible pipe connected to the ground; It is provided on the outer periphery of the outer case and is provided as a pressure support member for supporting the outer case while pressing the leak prevention member to achieve the above object.

The information collection unit is characterized in that it consists of a camera that provides real-time photographing of the conditions inside the buried pipe, and a measuring device that collects data values by measuring the flow rate, water level, and gas concentration in the buried pipe.

The wiper member is composed of an arc-shaped tube so that the washer liquid is supplied to the inside, a brush provided in a portion close to the camera dome, and a spray nozzle for spraying the washer liquid flowing into the tube into the camera dome, Both ends are characterized by being fastened with a connecting pipe, respectively.

The wiper driving means is provided with a driving part for operating the wiper and a washer fluid supply part for supplying the washer fluid, wherein the driving part has a driving pulley on the axis of the forward/reverse motor and a driven pulley as a connection pipe. The wiper member repeatedly operates a certain section to wash the surface of the camera dome by the forward and reverse driving of It is characterized in that it is provided as a supply pipe to supply the washer fluid to the wiper member.

And the pressure support member is made to be detachably attached to the rail provided in the outer case, the pressure cylinder is provided at both ends of the frame, the pressure cylinder is interconnected by a handle, each end of the pressure cylinder is provided at the bottom It is characterized in that it is fastened with the applied pressure plate to press the leak prevention member.

The pressure plate is provided with a first differential pressure plate directly connected to the pressure cylinder and a second differential pressure plate provided at the lower end of the first pressure plate to be pressed, and a wedge-shaped protrusion is further provided at the lower end of the first and second pressure plates. It is characterized by being equipped.

As described, the present invention has the effect of reducing maintenance costs by collecting and providing information inside the buried pipe in real time through the information collection unit, and the maintenance work is carried out in a state in which the situation inside the buried pipe is known in advance. It has various effects such as the effect of preventing human casualties, preventing unauthorized manipulation by outsiders, and preventing environmental pollution by preventing unauthorized discharge of wastewater.

1 is a view for explaining the configuration of a monitoring device for collecting information on a buried pipe according to an embodiment of the present invention.
2 to 3 are diagrams for explaining the internal configuration of a monitoring device for collecting information on a buried pipe according to an embodiment of the present invention.
Figure 4 is a view for explaining a modified embodiment of the leak prevention member.
Figure 5a. 5b is a view for explaining the configuration of the wiper member.
6 is a view for explaining the installation state of the monitoring device for collecting information on the buried pipe according to an embodiment of the present invention.

Hereinafter, a structure of a monitoring device for collecting information on a buried pipe according to an embodiment of the present invention will be described with reference to the accompanying drawings.

In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the terms to be described later are terms set in consideration of the functions in the present invention, and these terms may vary according to the intention or custom of the producer producing the product, and definitions of terms should be made based on the content throughout this specification.

(Example)

1 to 2 are diagrams for explaining a monitoring device for collecting information on a buried pipe according to an embodiment of the present invention.

That is, the monitoring device 200 according to the embodiment of the present invention includes a leak prevention member 210 that is inserted and seated into the perforated groove 1a of the buried pipe 1, and an outer case 221 that is seated as the leak prevention member. and a case body 220 having a double structure as an inner case 225 provided inside the outer case.

In addition, an information collection unit 230 for collecting information inside the buried pipe, including a camera provided at the lower end of the outer case 221 and a measuring device provided at the lower end of the inner case 225 , and a camera for protecting the camera A wiper member 240 is provided on the outer periphery of the dome to clean the camera dome.

And the wiper driving means 250 provided inside the outer case 221 to drive the wiper member 240, and the inner case 225 and the flexible pipe 170 connected to the ground are interconnected. A central connection case 260 is provided.

and a pressure support member 270 provided on the outer periphery of the outer case 221 to support the units while pressing the leak prevention member 210 .

In more detail, the leak prevention member 210 is made of a soft material such as rubber, urethane, synthetic resin, etc. to prevent water leakage into the perforated hole 1a drilled in the buried pipe 1 for the installation of the monitoring device. It is preferable to configure

As shown in FIG. 3, the leak prevention member 210 is inserted into the support part 211 and the perforated hole 1a of the buried pipe 1 so that the case body 220 is assembled and seated inside the insertion part ( 212) and the water leakage prevention pad 214 extending to both ends of the insertion part 212 and surrounding the outer circumferential surface of the pipe 1 is integrally formed.

At this time, an assembly groove 213 is provided at the center of the integrally formed support part 211 and the insertion part 212 so that the case body 220 is assembled.

In addition, the leak prevention pad 214 is preferably formed in an arc shape so as to be in close contact with the outer periphery of the pipe 1, and the inner side of the leak prevention pad 214 is made to be in surface contact with the outer periphery of the pipe, but one main part A leak prevention protrusion 215 that is in line contact with the outer periphery is formed.

That is, the leak prevention member 210 is assembled with the insertion part 212 into the perforated hole 1a in an interference fit manner to prevent primary leakage, and the leak prevention pad 214 is installed on the outer circumferential surface and surface of the buried pipe (1). The contact and leakage prevention protrusion 215 is in line contact to prevent secondary leakage.

As shown in the accompanying drawings Fig. 4, on the inner peripheral surface of the assembly groove 213, the outer peripheral surface of the insertion part 212 is in full contact with the perforated hole 1a of the buried pipe, an expansion protrusion 216 for expanding the insertion part. is formed

And the insertion part 212 is expanded on the inner circumferential surface of the assembly groove 213 to form a cutout 217a so as to be completely in close contact with the perforated hole 1a of the buried pipe.

That is, when the assembly part 223 of the case body 220 is inserted into the assembly groove 213, it is assembled while pushing the expansion protrusion 216 to the outside, and at this time, the insertion part 212 is inserted through the cutout 217a. By extending to the outside, it is possible to minimize the gap of the perforated hole (1a).

In addition, the insertion portion 212 is expanded at the intersection of the insertion portion 212 and the leak prevention pad 214 to form a cutout 217b so as to be completely in close contact with the perforated hole 1a of the buried pipe. .

The leak prevention member 210 is installed in the pipe 1 using a fastener together with a pressure plate 275 to be described below.

Meanwhile, the case body 220 has an inner case 225 and an outer case 221 having a double structure so as to have a space on the outer periphery of the inner case.

The outer case 221 includes a body 222 having a space 222a for accommodating the wiper driving means 250 inside, and an assembly groove ( It is provided with an assembly part 223 that is inserted into the 213).

And it is preferable that the assembly portion 223 is configured to be smaller than the outer diameter of the body 222, and the upper end of the body 222 is provided with a cover 224 to seal the space portion 222a.

At this time, an inner tube 223a protruding upward is integrally formed inside the assembly part 223 , and the inner diameter of the inner tube is preferably formed to be the same as the outer diameter of the inner case 225 . This is to minimize the gap between the inner case 225 and the inner tube 223a to prevent moisture from entering the space 222a through the gap.

In addition, it is preferable that at least two or more pipe connection sockets 224a for drawing out a pipe for replenishing a power supply wire and washer fluid are formed in the cover 224 .

On the other hand, the inner case 225 is assembled to the inside of the outer case 221, the upper end is assembled so that the inner diameter and airtightness of the cover 224 are maintained, and the lower end is airtight with the inner tube 223a of the assembling unit 223. It is assembled to be maintained, and the lower end of the inner case 225 is assembled to maintain airtightness with the camera dome 232 .

And on the inside of the upper end of the inner case 225, a step 225a for assembling a sealing cover for closing the inner case when not in use or a flexible pipe that is installed close to the ground and connecting the central connection case 26 is formed.

On the other hand, the information collection unit 230 is provided at the lower inner side of the inner case 225 and provides an image by photographing the inside of the buried pipe 1 in real time, the camera 231 and the assembly unit of the outer case 221 ( 223) is installed at the bottom of the buried pipe and consists of a measuring device 235 that measures the flow rate and water level of the fluid flowing inside the buried pipe, and the gas concentration in the pipe to collect data values. (See FIG. 4)

The wiper member 240 is installed on the outside of the camera dome 232 and rotates repeatedly for a certain section while spraying the washer liquid to the camera dome, so that the surface of the camera dome 232 is washed to secure a view.

The wiper member 240 includes an arc-shaped tube 241 so that the washer liquid is supplied to the inside, a brush 242 provided in a portion close to the camera dome, and the washer liquid introduced into the tube to the camera dome. It consists of a nozzle (243).

And both ends of the tube 241 are coupled with connection pipes 244a and 244b, respectively, and the connection pipe 224a is interlocked with the driving unit 251 of the wiper driving means 250 and installed, and the connection pipe 244b ) is installed in conjunction with the supply pipe 257 for supplying the washer fluid.

The connection pipes 244a and 224b pass through the inner tube 223a and flow into the inner tube, and a longitudinal pulley 252b is provided at the end of the connection tube 224a.

And the connection pipe 224b is connected to the connection port 257a of the supply pipe 257, and a bearing b is provided between the connection pipe 244b and the connection port 257a so that the connection pipe 244b is connected to the connection port. It is made to rotate only the connecting tube in the inserted state.

In addition, it is preferable that the connection pipes 244a and 244b passing through the inner tube 223a are provided with bearings for smooth rotation.

Meanwhile, the wiper driving means 250 includes a driving unit 251 for operating the wiper and a washer fluid supply unit 256 for supplying washer fluid.

The driving unit 251 is provided with a driving pulley 252a on the axis of the forward and reverse motor M and a driven pulley 252b as a connection pipe 244a and interconnected by a belt V to connect the forward and reverse motor 251. The wiper member 240 repeatedly operates a predetermined section by the forward and reverse operation of the camera to clean the surface of the camera dome 232 .

And the washer fluid supply unit 256 is provided with a washer fluid reservoir 256 in which the washer fluid is stored, a pump 256a for supplying the stored washer fluid, and a supply pipe 257 connecting the pump 256a and the connection pipe 244b. and the washer fluid is supplied to the wiper member 240 .

The central connection case 260 interconnects the flexible pipe 170 installed close to the ground and the inner case 225, and is seated on the upper end of the inner case 225 with the lower end of the body 261 and is attached to the fastener. A connection flange 261 fastened by the is formed, and a pipe connection socket 262 into which the auxiliary pipe P1 is fitted is formed in the central recess.

At this time, the number of the pipe connection sockets 262 is preferably formed at least two or more, and it is preferable to form the same quantity as the pipe connection sockets 224a formed of the outer case 221 .

In addition, the pipe connection socket 224a of the outer case 221 and the pipe connection socket 262 formed in the central connection case 260 are preferably configured to communicate with each other by coupling the auxiliary pipe P1.

On the other hand, the pressure support member 270 is made to be detachably attached to the rail (221a) provided in the outer case (221).

That is, the pressure cylinders 273 are provided at both ends of the frame 272, the pressure cylinders are interconnected by a handle 271, and each end of the pressure cylinder 273 has a pressure plate 275 provided at the bottom. and is coupled to press the leak prevention member 210 .

The pressure plate 275 is provided with a first differential pressure plate 275-1 directly connected to the pressure cylinder 273, and a second differential pressure plate 275-2 provided at a lower end of the first pressure plate.

At this time, wedge-shaped projections 275-1a and 275-2a are further provided at the lower ends of the first and second pressing plates.

And in a state in which the central connection case 260 assembled on the upper part of the inner case 225 is removed, and the leak prevention packing 281 is seated on the top of the step 225a of the inner case 225, the sealing cover ( 280) When it is fastened with a fastening member in the state of being seated, it is completely closed.

And it is possible to block the inflow of moisture, dirt, etc. to the inside by inserting the leak-proof packing into the pipe connection socket 224a of the outer case 221 by force fitting.

When re-using, the central connection case 260 can be reassembled and used with the sealing cover and leak-proof packing removed.

Hereinafter, the installation and operation of the monitoring device 200 according to the configuration of the above-described embodiment will be described.

First, the monitoring device 200 according to the embodiment of the present invention is installed in the buried pipe 1, but the buried pipe is to be formed with a perforated hole (1a) for installing the monitoring device.

The perforated hole 1a is perforated in the field, and the perforation must be equal to or larger than the outer diameter of the insertion part 212 of the leak prevention member 210 .

At this time, depending on the outer diameter of the buried pipe, there is a difference in the curved portion of the perforated hole 1a, so that a gap is generated with the insertion part 212 of the leak prevention member 210, and water leakage may occur, but the leak prevention member of the present invention ( Since the leak prevention pad 214 is further extended to the outer periphery of the insertion part, leakage of the gap is prevented.

In this way, after the water leakage preventing member 210 is seated in the perforated hole 1a, the case body 220 is installed, and the assembly part 223 of the outer case 221 is the assembly groove of the water leakage preventing member 210. Inserted into the 213 and the body 222 is installed to be seated on the top of the support portion 211 of the leak prevention member (210).

At this time, the information collecting unit 230 , the wiper member 240 , and the wiper driving means 250 must be installed in the inner case 225 and the outer case 221 .

After the installation is completed in this way, the leak prevention pad 214 is passed through the upper end of the first differential pressure plate 275-1 of the pressure support member 270 provided on the outside of the outer case 221 using a fastening member, and It is fastened through the surface of the buried pipe (1).

When the handle 271 of the pressure support member 270 is rotated in the above state, the pressure cylinder 273 descends and is compressed by the first differential pressure plate 275-1 and the second differential pressure plate 275-2 to prevent leakage. The pad 214 is pressed, and the leak prevention pad 214 is in close contact with the surface of the buried pipe 1 to minimize the gap, thereby preventing water leakage.

On the other hand, the central connection case 260 is assembled to the upper part of the inner case 225, and the leak prevention packing P2 is positioned therebetween and fastened with a fastening member to prevent leakage of the connection part.

And the electric wire for applying the power of the wiper driving means 250 provided inside the outer case, the electric wire of the information collection unit 230, and the pipe supplying the washer liquid to the washer liquid reservoir are the pipe connection sockets 224a formed in the cover 224. It can be drawn out and introduced into the pipe connection socket 262 of the central connection case 260 and discharged to the ground.

At this time, the pipe connection socket 224a and the pipe connection socket 262 are connected to the auxiliary pipe P1 to prevent moisture from entering.

On the other hand, the upper end of the central connection case 260 is assembled with the flexible pipe 170 connected to the ground.

The monitoring device 200, which has been installed as described above, collects the internal condition of the buried pipe through the information collection unit 230, that is, the flow rate of the fluid, the level of the fluid, the concentration of gas in the buried pipe, and transmits the collected information to the ground. sent to the control center of

In particular, when it is difficult to secure a view of the camera due to odors and dirt in the buried pipe, the wiper driving means 250 operates and the wiper 240 cleans the camera dome, so there is an advantage of always providing a clean image.

And, since the leak prevention member 210 is installed so as to be completely in close contact with the buried pipe 1, it is prevented from leaking to the part where the monitoring device is installed in case of rain.

In particular, when the body case 220 is assembled with the leak prevention member 210, the assembly part 223 of the outer case 221 is inserted while pushing the extension protrusion 216 of the insertion part to the outside, at this time the insertion part 212. The outer circumferential surface of the tube expands into the perforated hole of the buried pipe, resulting in an action to maintain airtightness.

The present invention described above can collect information on the buried pipe in real time, so it is possible to prevent human damage when manpower is input due to the maintenance of the buried pipe, and in particular, it is possible to prevent environmental pollution by detecting the unauthorized discharge of wastewater.

As mentioned above, although preferred embodiments of the present invention have been described with reference to the accompanying drawings, those of ordinary skill in the art to which the present invention pertains can implement the present invention in other specific forms without changing the technical spirit or essential features. You will understand that it can be Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

210: leak prevention member 211: support part
212: insertion part 213: assembly groove
214: leak prevention pad 220: case body
221: outer case 225: inner case
230: information collection unit 240: wiper member
250: wiper driving means 251: wiper driving unit
255: washer fluid supply unit

Claims (11)

To collect internal information of the buried pipe (1),
A leak prevention member 210 inserted and seated into the perforated groove 1a of the buried pipe 1,
A case body 220 having a double structure as an outer case 221 seated as the leak prevention member and an inner case 225 provided inside the outer case;
an information collection unit 230 for collecting information inside the buried pipe, including a camera provided at the lower end of the outer case 221 and a measuring device provided at the lower end of the inner case 225;
A wiper member 240 provided on the outer periphery of the camera dome for protecting the camera and cleaning the camera dome;
a wiper driving means 250 provided inside the outer case 221 to drive the wiper member 240;
Buried pipe internal information collection comprising a; a pressure support member 270 provided on the outer periphery of the outer case 221 to support the outer case 221 while pressing the leak prevention member 210 for monitoring devices. The method of claim 1,
The leak prevention member 210,
The support part 211 on which the case body is seated and the insertion part 212 inserted into the perforated hole 1a of the buried pipe are integrally formed, and an assembly groove 213 is formed inside so that the case body is inserted,
A monitoring device for collecting information inside a buried pipe, characterized in that it includes a leak prevention pad 214 that extends in all directions of the support and surrounds the buried pipe. 3. The method of claim 2,
The inside of the leak prevention pad 214 is in line contact with the buried pipe at the same time as the surface contact, so that the leak prevention protrusion 215 for preventing water leakage is further included. 3. The method of claim 2,
The inner peripheral surface of the assembly groove 213 has an extension protrusion 216 for expanding the insert so that the outer peripheral surface of the inserting part 212 is completely in close contact with the perforated hole 1a of the buried pipe. Monitoring device for collecting inside information. 5. The method of claim 2 or 4,
The inner circumferential surface of the assembly groove 213 for collecting information on the inside of the buried pipe, characterized in that the insertion part 212 is expanded and a cutout 217a is further included so as to be completely in close contact with the perforated hole 1a of the buried pipe. monitoring device. 3. The method of claim 2,
The insertion part 212 and the leak prevention pad 214 are intersected at the intersection of the insertion part 212 is expanded so that the cutout 217b is further included so as to be in full contact with the perforated hole 1a of the buried pipe. A monitoring device for collecting information inside a buried pipe, characterized by. The method of claim 1,
The information collection unit 230 includes a camera 231 that provides real-time photographing of the internal situation of the buried pipe,
A monitoring device for collecting information inside a buried pipe, comprising a meter (235) for collecting data values by measuring the flow rate, water level, and gas concentration in the buried pipe. The method of claim 1,
The wiper member 240 is
It consists of an arc-shaped tube 241 so that the washer liquid is supplied to the inside, a brush 242 provided in a portion close to the camera dome, and a spray nozzle 243 for spraying the washer liquid flowing into the tube into the camera dome. , A monitoring device for collecting information inside a buried pipe, characterized in that both ends of the pipe (241) are fastened with connection pipes (244a, 244b), respectively. 9. The method of claim 1 or 8,
The wiper driving means 250 is provided with a driving part 251 for operating the wiper and a washer fluid supply part 256 for supplying the washer fluid,
The driving unit 251 is provided with a driving pulley 252a on the axis of the forward and reverse motor M and a driven pulley 252b as a connection pipe 244a and interconnected by a belt V to connect the forward and reverse motor 251. is made to clean the surface of the camera dome 232 by repeatedly operating the wiper member 240 for a certain section by the forward and reverse operation of
The washer fluid supply unit 256 is provided with a washer fluid reservoir 256 in which the washer fluid is stored, a pump 256a for supplying the stored washer fluid, and a supply pipe 257 connecting the pump 256a and the connection pipe 244b. A monitoring device for collecting information inside a buried pipe, characterized in that the washer fluid is supplied to the wiper member (240). The method of claim 1,
The pressure support member 270,
It is made to be detachable with the provided rail (221a) of the outer case (221),
Pressurizing cylinders 273 are provided at both ends of the frame 272, the pressurizing cylinders are interconnected by a handle 271, and each end of the pressurizing cylinder 273 is fastened with a pressurizing plate 275 provided at the bottom. A monitoring device for collecting information inside a buried pipe, characterized in that it presses the leak prevention member 210 . 11. The method of claim 10,
The pressure plate 275 is
A first differential pressure plate 275-1 directly connected to the pressure cylinder 273 and a second differential pressure plate 275-2 provided at the lower end of the first differential pressure plate are provided to perform pressurization, and the first, A monitoring device for collecting information inside a buried pipe, characterized in that the wedge-shaped projections (275-1a) (275-2a) are further provided at the bottom of the secondary pressure plate.

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