Multi-stage bidirectional telescopic structure of scraper conveyor, scraper conveyor tail and scraper conveyor

Abstract

The invention discloses a multi-stage bidirectional telescopic structure of a scraper conveyor, a scraper conveyor tail and a scraper conveyor. The multi-stage bidirectional telescopic structure comprises a main cylinder body, a first-stage piston assembly and a second-stage piston assembly, the first-stage piston assembly is axially arranged in the main cylinder body, the left end of the first-stage piston assembly extends out of the main cylinder body, and the outer wall of the right end of the first-stage piston assembly and the inner wall of the right end of the main cylinder body form a cavity B. The second-stage piston assembly is axially arranged in the first-stage piston assembly, and the right end of the second-stage piston assembly extends out of the right end of the main cylinder body. A cavity C is formed by the outer wall of the left end of the second-stage piston assembly and the inner wall of the left end of the first-stage piston assembly, a cavity A is formed by the inner wall of the left end of the second-stage piston assembly and the inner wall of the right end of the first-stage piston assembly, a high-pressure liquid flow channel communicated with the cavity B is formed in the axis direction of the second-stage piston assembly, and a first high-pressure liquid inlet and outlet hole communicated with the cavity B is formed in the right end of the main cylinder body. A second high-pressure liquid inlet and outlet hole communicated with the cavity A is formed in the left end of the main cylinder body. The multi-layer structure is adopted, the outer diameter is small, the thrust is large, and the problems that a single-layer oil cylinder in a narrow space is large in outer diameter and small in thrust are solved.

Description

Technical Field

[0001] The invention relates to the technical field of well transportation equipment, and in particular to a multi-stage bidirectional telescopic structure of a scraper, a scraper tail, and a scraper conveyor. Background Art

[0002] The scraper chain composed of chains and scrapers running in the middle groove of the scraper conveyor for underground working face of coal mines is gradually lengthened during the coal transportation process due to the force on the chain, and the gap between the middle grooves also changes frequently. The scraper chain needs to be tensioned. Therefore, the scraper conveyor is designed with a retractable telescopic tail, which is retracted and extended by the configured telescopic push cylinder. After the scraper chain becomes loose, it is retracted and tensioned by the telescopic tail. With the development of intelligent coal mines and the demand for efficient transportation of scraper conveyors, it is required that the scraper conveyor can judge the state of the scraper chain in real time and tension it in time to avoid the accumulation of the scraper chain, which causes hanging and other factors that affect the transportation efficiency. In the prior art, the telescopic tail push cylinder of the scraper conveyor for underground working face of coal mines has a small installation space, a large cylinder volume, and a small telescopic thrust, which is difficult to meet the use requirements. Summary of the invention

[0003] In order to solve the technical problems existing in the above-mentioned technology, it is necessary to provide a multi-stage bidirectional telescopic structure of a scraper.

[0004] A multi-stage bidirectional telescopic structure of a scraper, comprising a main cylinder body, a primary piston assembly, and a secondary piston assembly; the primary piston assembly is slidably installed in the main cylinder body along the axis of the main cylinder body, the right end outer wall of the primary piston assembly and the right end inner wall of the main cylinder body form a cavity B, and the left end of the primary piston assembly extends out of the main cylinder body, the secondary piston assembly is slidably installed in the primary piston assembly along the axis of the primary piston assembly, the left end outer wall of the secondary piston assembly and the left end inner wall of the primary piston assembly form a cavity C, the left end inner wall of the secondary piston assembly and the right end inner wall of the primary piston assembly form a cavity A, and the right end of the secondary piston assembly extends out of the right end of the primary piston assembly and the right end of the main cylinder body, a high-pressure liquid flow channel connected to the cavity B is opened along the axial direction of the secondary piston assembly, the right end of the main cylinder body is provided with a first high-pressure liquid inlet and outlet hole connected to the cavity B, and the left end of the main cylinder body is provided with a second high-pressure liquid inlet and outlet hole connected to the cavity A.

[0005] Preferably, the first-stage piston assembly includes a first-stage piston rod body, a first-stage piston rod connecting seat, and a first-stage piston head; the first-stage piston rod body is installed in the main cylinder body along the axis of the main cylinder body, the first-stage piston rod connecting seat is fixed at the left end of the first-stage piston rod body, and the first-stage piston head is fixed at the right end of the first-stage piston rod body. The outer wall of the first-stage piston head slides in contact with the inner wall of the main cylinder body, and the right end outer wall of the first-stage piston head and the right end inner wall of the main cylinder body form a cavity B.

[0006] Preferably, a guide hole is provided along the axial direction of the first-stage piston head.

[0007] Preferably, the secondary piston assembly includes a secondary piston rod body, a secondary piston rod connecting seat, and a secondary piston head; the secondary piston rod body is installed in the primary piston rod body along the axis of the primary piston rod body, the right end of the secondary piston rod body extends out of the right end of the main cylinder body along the guide hole, the secondary piston rod connecting seat is fixed to the right end of the secondary piston rod body, the secondary piston head is fixed to the left end of the secondary piston rod body, the outer wall of the secondary piston head is slidably fitted with the inner wall of the primary piston rod body, the left end inner wall of the secondary piston head and the right end inner wall of the primary piston rod body form a cavity A, and the left end outer wall of the secondary piston head and the inner wall of the primary piston rod connecting seat form a cavity C.

[0008] Preferably, it also includes a displacement sensor assembly, which includes a connecting tube, a displacement sensor probe, and a displacement sensor magnetic ring; the connecting tube is installed in the primary piston rod body along the axis of the primary piston rod body, the left end of the connecting tube is connected to the primary piston rod connecting seat, the displacement sensor magnetic ring is built into the inner wall of the right end of the connecting tube, the displacement sensor probe is installed in the secondary piston rod body along the axis of the secondary piston rod body, and the right end of the displacement sensor probe is connected to the secondary piston rod connecting seat.

[0009] Preferably, a first hydraulic pipe and a second hydraulic pipe are installed on the outside of the main cylinder body, and a first high-pressure liquid inlet and outlet connecting seat is installed on the first hydraulic pipe, and the first high-pressure liquid inlet and outlet connecting seat is connected to the first high-pressure liquid inlet and outlet hole; a second high-pressure liquid inlet and outlet connecting seat is installed on the second hydraulic pipe, and the second high-pressure liquid inlet and outlet connecting seat is connected to the second high-pressure liquid inlet and outlet hole.

[0010] Preferably, a primary piston rod seal is provided on the inner wall of the left end of the main cylinder body and the inner wall of the right end of the primary piston rod body.

[0011] Preferably, a secondary piston rod seal is provided on the outer wall of the secondary piston head and the inner wall of the guide hole.

[0012] It is also necessary to provide a scraper tail.

[0013] A scraper tail comprises a tail body and a tensioning device installed on the tail body, wherein the tensioning device comprises the above-mentioned multi-stage bidirectional telescopic structure of the scraper.

[0014] It is also necessary to provide a scraper conveyor.

[0015] A scraper conveyor comprises a scraper head, a middle trough, and the scraper tail described above, wherein the scraper head, the middle trough, and the scraper tail are connected in sequence.

[0016] Compared with the prior art, the multi-stage bidirectional telescopic structure of the scraper, the scraper tail and the scraper conveyor provided by the present invention adopt a multi-layer structure and a built-in displacement sensor. The outer diameter of the cylinder body is small and the thrust is large. It is used on the telescopic tail of the scraper conveyor on the underground working face of a coal mine, which solves the technical problem of using a single-layer cylinder with a large outer diameter and low thrust in a narrow space. It has a built-in displacement sensor and is equipped with a bidirectional hydraulic lock with a pressure sensor, which realizes the digitization of the cylinder operation and provides data support for the automatic control of the telescopic tail. Good results have been achieved in its application on the underground working face of a coal mine. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0018] Figure 1 It is a schematic diagram of the cross-sectional structure of the present invention.

[0019] Figure 2 For the present invention Figure 1 Schematic diagram of the side structure.

[0020] Figure 3 It is a structural schematic diagram of the first-stage piston assembly of the present invention.

[0021] Figure 4 It is a structural schematic diagram of the secondary piston assembly of the present invention.

[0022] In the figure: main cylinder body 01, first-level piston assembly 02, first-level piston rod body 21, first-level piston rod connecting seat 22, first-level piston head 23, guide hole 24, second-level piston assembly 03, second-level piston rod body 31, second-level piston rod connecting seat 32, second-level piston head 33, cavity B04, cavity C05, cavity A06, high-pressure liquid flow channel 07, first high-pressure liquid inlet and outlet hole 08, second high-pressure liquid inlet and outlet hole 09, displacement sensor assembly 10, connecting pipe 101, displacement sensor probe 102, displacement sensor magnetic ring 103, first hydraulic pipe 20, first high-pressure liquid inlet and outlet connecting seat 201, second hydraulic pipe 30, second high-pressure liquid inlet and outlet connecting seat 301, two-way hydraulic lock 40, first-level piston rod seal 50, second-level piston rod seal 60, displacement sensor connecting seat 70, data cable 80. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be understood that the terms "upper", "middle", "outer", "inner", "lower" and the like indicating directions or positional relationships are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0025] Please see Figures 1 to 4 In one embodiment, the present invention provides a multi-stage bidirectional telescopic structure of a scraper, comprising a main cylinder 01, a first-stage piston assembly 02, and a second-stage piston assembly 03; the first-stage piston assembly 02 is slidably installed in the main cylinder 01 along the axis of the main cylinder 01, the right end outer wall of the first-stage piston assembly 02 and the right end inner wall of the main cylinder 01 form a cavity B04, and the left end of the first-stage piston assembly 02 extends out of the main cylinder 01, the second-stage piston assembly 03 is slidably installed in the first-stage piston assembly 02 along the axis of the first-stage piston assembly 02, the left end outer wall of the second-stage piston assembly 03 and the right end inner wall of the main cylinder 01 form a cavity B04, and the left end of the first-stage piston assembly 02 extends out of the main cylinder 01, The left end inner wall of the first piston assembly 02 forms a cavity C05, the left end inner wall of the second piston assembly 03 and the right end inner wall of the first piston assembly 02 form a cavity A06, and the right end of the second piston assembly 03 extends out of the right end of the first piston assembly 02 and the right end of the main cylinder body 01, and a high-pressure liquid flow channel 07 connected to the cavity B04 is opened along the axial direction of the second piston assembly 03, the right end of the main cylinder body 01 is provided with a first high-pressure liquid inlet and outlet hole 08 connected to the cavity B04, and the left end of the main cylinder body 01 is provided with a second high-pressure liquid inlet and outlet hole 09 connected to the cavity A06.

[0026] During operation, the main cylinder 01 is fixed and does not move. When it needs to be extended, the high-pressure liquid enters the cavity B04 along the first high-pressure liquid inlet and outlet hole 08, and at the same time, the high-pressure liquid also enters the cavity C05 through the high-pressure liquid flow channel 07, prompting the first-stage piston assembly 02 to extend to the left, and the second-stage piston assembly 03 to extend to the right, realizing two-way synchronous movement; at this time, the volume of cavity B04 and cavity C05 increases, the volume of cavity A06 decreases, and the high-pressure liquid in cavity A06 is discharged through the second high-pressure liquid inlet and outlet hole 09. When it needs to be shortened, the high-pressure liquid enters the cavity A06 along the second high-pressure liquid inlet and outlet hole 09, pushing the first-stage piston assembly 02 to move to the right end and the second-stage piston assembly 03 to move to the left end, realizing two-way synchronous movement; at this time, the volume of cavity B04 and cavity C05 decreases, the volume of cavity A06 increases, and the high-pressure liquid in cavity B04 and cavity C05 is discharged through the first high-pressure liquid inlet and outlet hole 08.

[0027] Among them, the cylinder thrust F = (the cross-section of cavity B + the cross-section of cavity C) × the high-pressure liquid pressure in cavity B and cavity C. The cross-section of cavity C (C²π / 4) is more than 50% of the cross-section of cavity (B³π / 4). Compared with a single-layer cylinder, the thrust generated by cavity C is increased, and the thrust of the cylinder with the same outer diameter is increased by more than 50%.

[0028] In one embodiment, the first hydraulic pipe 20 and the second hydraulic pipe 30 are installed on the outside of the master cylinder 01, wherein a two-way hydraulic lock 40 with a pressure sensor is installed at the inlet end of the first hydraulic pipe 20 and the second hydraulic pipe 30, and the pressure sensor installed on the two-way hydraulic lock 40 with the pressure sensor outputs the pressure of the high-pressure liquid in the cavity B04 and the cavity C05. The first high-pressure liquid inlet and outlet connector 201 is installed on the first hydraulic pipe 20, and the first high-pressure liquid inlet and outlet connector 201 is connected to the first high-pressure liquid inlet and outlet hole 08; the second high-pressure liquid inlet and outlet connector 301 is installed on the second hydraulic pipe 30, and the second high-pressure liquid inlet and outlet connector 301 is connected to the second high-pressure liquid inlet and outlet hole 09.

[0029] Specifically, the primary piston assembly 02 includes a primary piston rod body 21, a primary piston rod connection seat 22, and a primary piston head 23; the primary piston rod body 21 is installed in the main cylinder body 01 along the axis of the main cylinder body 01, the primary piston rod connection seat 22 is fixed to the left end of the primary piston rod body 21, and the primary piston rod connection seat 22 can be fixed to the left end of the primary piston rod body 21 by bolts to facilitate disassembly and installation. The primary piston head 23 is fixed to the right end of the primary piston rod body 21, and the outer wall of the primary piston head 23 is slidably fitted with the inner wall of the main cylinder body 01, and the right end outer wall of the primary piston head 23 and the right end inner wall of the main cylinder body 01 form a cavity B04. Correspondingly, when the high-pressure liquid enters the first high-pressure liquid inlet and outlet hole 08 through the first hydraulic pipe 20 and the first high-pressure liquid inlet and outlet connecting seat 201, the high-pressure liquid will enter the cavity B04, and rely on the high-pressure liquid to push the first-level piston head 23 to move axially to the left, prompting the first-level piston rod body 21 to drive the first-level piston rod connecting seat 22 to extend to the left end; when the high-pressure liquid enters the second high-pressure liquid inlet and outlet hole 09 through the second hydraulic pipe 30 and the second high-pressure liquid inlet and outlet connecting seat 301, the high-pressure liquid will enter the cavity A06, and rely on the high-pressure liquid to push the first-level piston head 23 to move axially to the right end, prompting the first-level piston rod body 21 to drive the first-level piston rod connecting seat 22 to contract to the right end, and the high-pressure liquid in the cavity B04 will enter the first high-pressure liquid inlet and outlet connecting seat 201 and the first hydraulic pipe 20 through the first high-pressure liquid inlet and outlet hole 08 and be discharged.

[0030] Of course, in order to better guide the secondary piston assembly 03, a guide hole 24 is provided along the axial direction of the primary piston head 23. Correspondingly, a corresponding circular hole is also provided at the right end of the main cylinder body 01, and a seal is installed between the secondary piston assembly 03 and the circular hole to ensure sealing.

[0031] Specifically, the secondary piston assembly 03 includes a secondary piston rod body 31, a secondary piston rod connecting seat 32, and a secondary piston head 33; the secondary piston rod body 31 is installed in the primary piston rod body 21 along the axis of the primary piston rod body 21, the right end of the secondary piston rod body 31 extends out of the right end of the main cylinder body 01 along the guide hole 24, the secondary piston rod connecting seat 32 is fixed to the right end of the secondary piston rod body 31, and the secondary piston rod connecting seat 32 can be fixed to the right end of the secondary piston rod body 31 by bolts to facilitate disassembly and installation. The secondary piston head 33 is fixed to the left end of the secondary piston rod body 31, the outer wall of the secondary piston head 33 is slidably fitted with the inner wall of the primary piston rod body 21, the inner wall of the left end of the secondary piston head 33 and the inner wall of the right end of the primary piston rod body 21 form a cavity A06, and the outer wall of the left end of the secondary piston head 33 and the inner wall of the primary piston rod connecting seat 22 form a cavity C05. Correspondingly, when the high-pressure liquid enters the first high-pressure liquid inlet and outlet hole 08 through the first hydraulic pipe 20 and the first high-pressure liquid inlet and outlet connecting seat 201, the high-pressure liquid will enter the cavity C05, and rely on the high-pressure liquid to push the secondary piston head 33 to move axially to the right, prompting the secondary piston rod body 31 to drive the secondary piston rod connecting seat 32 to extend to the right end; when the high-pressure liquid enters the second high-pressure liquid inlet and outlet hole 09 through the second hydraulic pipe 30 and the second high-pressure liquid inlet and outlet connecting seat 301, the high-pressure liquid will enter the cavity A06, and rely on the high-pressure liquid to push the secondary piston head 33 to move axially to the left end, prompting the secondary piston rod body 31 to drive the secondary piston rod connecting seat 32 to contract to the left end, and the high-pressure liquid in the cavity C05 will enter the first high-pressure liquid inlet and outlet hole 08 through the high-pressure liquid flow channel 07, and then be discharged through the first high-pressure liquid inlet and outlet connecting seat 201 and the first hydraulic pipe 20.

[0032] In one embodiment, a displacement sensor assembly 10 is also installed, wherein the displacement sensor assembly 10 includes a connecting tube 101, a displacement sensor probe 102, and a displacement sensor magnetic ring 103; the connecting tube 101 is installed in the primary piston rod body 21 along the axis of the primary piston rod body 21, and the left end of the connecting tube 101 is connected to the primary piston rod connection seat 22, and can be fixed by bolts. The displacement sensor magnetic ring 103 is built into the inner wall of the right end of the connecting tube 101, and the displacement sensor probe 102 is installed in the secondary piston rod body 31 along the axis of the secondary piston rod body 31, and the right end of the displacement sensor probe 102 is connected to the secondary piston rod connection seat 32, and can be fixed by bolts. The displacement sensor magnetic ring 103 installed on the connecting tube 101 moves axially relative to the displacement sensor probe 102 assembled on the secondary piston rod connection seat 32, and outputs the obtained displacement data through the data line 80 connected to the displacement sensor probe 102 and the displacement sensor connection seat 70 installed outside the main cylinder body 01.

[0033] In one embodiment, in order to ensure a good sealing effect during axial movement, a primary piston rod seal 50 is provided on the left inner wall of the main cylinder body 01 and the right inner wall of the primary piston rod body 21 .

[0034] In one embodiment, in order to ensure a good sealing effect during the axial movement, a secondary piston rod seal 60 is provided on the outer wall of the secondary piston head 33 and the inner wall of the guide hole 24 .

[0035] In one embodiment, the present invention provides a scraper tail, including a tail body and a tensioning device installed on the tail body, wherein the tensioning device includes a multi-stage bidirectional telescopic structure of the scraper.

[0036] In one embodiment, the present invention provides a scraper conveyor, comprising a scraper conveyor head, a middle trough, and a scraper conveyor tail, wherein the scraper conveyor head, the middle trough, and the scraper conveyor tail are connected in sequence.

[0037] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A multi-stage bidirectional telescopic structure of a scraper, characterized in that: It includes a main cylinder body, a first-stage piston assembly, and a second-stage piston assembly; the first-stage piston assembly is slidably installed in the main cylinder body along the axis of the main cylinder body, the right-end outer wall of the first-stage piston assembly and the right-end inner wall of the main cylinder body form a cavity B, and the left end of the first-stage piston assembly extends out of the main cylinder body, the second-stage piston assembly is slidably installed in the first-stage piston assembly along the axis of the first-stage piston assembly, the left-end outer wall of the second-stage piston assembly and the left-end inner wall of the first-stage piston assembly form a cavity C, the left-end inner wall of the second-stage piston assembly and the right-end inner wall of the first-stage piston assembly form a cavity A, and the right end of the second-stage piston assembly extends out of the right end of the first-stage piston assembly and the right end of the main cylinder body, a high-pressure liquid flow channel connected to the cavity B is opened along the axial direction of the second-stage piston assembly, the right end of the main cylinder body is provided with a first high-pressure liquid inlet and outlet hole connected to the cavity B, and the left end of the main cylinder body is provided with a second high-pressure liquid inlet and outlet hole connected to the cavity A.

2. The multi-stage bidirectional telescopic structure of the scraper according to claim 1 is characterized in that: The first-stage piston assembly includes a first-stage piston rod body, a first-stage piston rod connecting seat, and a first-stage piston head; the first-stage piston rod body is installed in the main cylinder body along the axis of the main cylinder body, the first-stage piston rod connecting seat is fixed at the left end of the first-stage piston rod body, and the first-stage piston head is fixed at the right end of the first-stage piston rod body. The outer wall of the first-stage piston head slides and fits with the inner wall of the main cylinder body, and the right end outer wall of the first-stage piston head and the right end inner wall of the main cylinder body form a cavity B.

3. The multi-stage bidirectional telescopic structure of the scraper according to claim 2 is characterized in that: A guide hole is provided along the axial direction of the first-stage piston head.

4. The multi-stage bidirectional telescopic structure of the scraper according to claim 3 is characterized in that: The secondary piston assembly includes a secondary piston rod body, a secondary piston rod connecting seat, and a secondary piston head; the secondary piston rod body is installed in the primary piston rod body along the axis of the primary piston rod body, the right end of the secondary piston rod body extends out of the right end of the main cylinder body along the guide hole, the secondary piston rod connecting seat is fixed to the right end of the secondary piston rod body, the secondary piston head is fixed to the left end of the secondary piston rod body, the outer wall of the secondary piston head is slidably fitted with the inner wall of the primary piston rod body, the left end inner wall of the secondary piston head and the right end inner wall of the primary piston rod body form a cavity A, and the left end outer wall of the secondary piston head and the inner wall of the primary piston rod connecting seat form a cavity C.

5. The multi-stage bidirectional telescopic structure of the scraper according to claim 4 is characterized in that: It also includes a displacement sensor assembly, which includes a connecting tube, a displacement sensor probe, and a displacement sensor magnetic ring; the connecting tube is installed in the primary piston rod body along the axis of the primary piston rod body, the left end of the connecting tube is connected to the primary piston rod connecting seat, the displacement sensor magnetic ring is built into the inner wall of the right end of the connecting tube, the displacement sensor probe is installed in the secondary piston rod body along the axis of the secondary piston rod body, and the right end of the displacement sensor probe is connected to the secondary piston rod connecting seat.

6. The multi-stage bidirectional telescopic structure of the scraper according to claim 1 is characterized in that: A first hydraulic pipe and a second hydraulic pipe are installed on the outside of the main cylinder body. A first high-pressure liquid inlet and outlet connecting seat is installed on the first hydraulic pipe, and the first high-pressure liquid inlet and outlet connecting seat is connected to the first high-pressure liquid inlet and outlet hole; a second high-pressure liquid inlet and outlet connecting seat is installed on the second hydraulic pipe, and the second high-pressure liquid inlet and outlet connecting seat is connected to the second high-pressure liquid inlet and outlet hole.

7. The multi-stage bidirectional telescopic structure of the scraper according to claim 2 is characterized in that: A primary piston rod seal is arranged on the left inner wall of the main cylinder body and the right inner wall of the primary piston rod body.

8. The multi-stage bidirectional telescopic structure of a scraper according to claim 3 is characterized in that: The outer wall of the secondary piston head and the inner wall of the guide hole are both provided with secondary piston rod seals.

9. A scraper tail, characterized in that: It comprises a tail body and a tensioning device installed on the tail body, wherein the tensioning device comprises the multi-stage bidirectional telescopic structure of the scraper conveyor as described in any one of claims 1-8.

10. A scraper conveyor, characterized in that: It comprises a scraper head, a middle trough, and the scraper tail as claimed in claim 9, wherein the scraper head, the middle trough, and the scraper tail are connected in sequence.

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