A municipal garden drainage overflow anti-backflow device

Abstract

The present invention relates to the technical field of drainage control equipment, specifically a municipal garden drainage overflow and backflow prevention device, comprising a drain outlet, a backflow prevention drainage channel, a horizontal discharge pipe and a truncated cone-shaped hydrophobic transmission channel. The pressure of accumulated water is converted into mechanical power through a stepped overflow control chamber and multiple rows of overflow holes, driving a hydraulic moving mechanism and a horizontal threaded assembly to link the lifting gate to adjust the drainage volume. The power block in the stepped overflow control chamber is pushed by the water pressure, and the rack-gear transmission controls the interval lifting tooth plate to achieve adaptive opening and closing of the gate. The present invention utilizes the gravity of accumulated water in combination with a mechanical structure, responds quickly and does not require external energy, effectively preventing overflow and backflow problems during heavy rainfall. At the same time, the structure is stable and suitable for the ecological drainage needs of municipal gardens.

Description

Technical Field

[0001] The invention relates to the technical field of drainage control equipment, in particular to a municipal garden drainage overflow and backflow prevention device. Background Art

[0002] Municipal garden drainage is a crucial component of the urban drainage system, designed to address rainwater drainage and ecological water circulation issues in areas such as gardens, green spaces, parks, and plazas, while also balancing landscape aesthetics and functionality. Characteristics of municipal garden drainage include an emphasis on natural infiltration and retention, a reduction in hard drainage infrastructure, and the promotion of rainwater resource utilization. Drainage facilities must be coordinated with the landscape (e.g., invisible drains and natural rain gardens). Adopting the sponge city concept, permeable pavement and sunken green spaces are employed to reduce runoff. Unlike municipal road drainage, garden drainage prioritizes localized absorption and dispersed discharge.

[0003] The existing municipal garden drainage system has a drainage capacity suitable for rainwater discharge in most cases. However, it cannot effectively cope with sudden heavy rainfall. In other words, when such a situation occurs, the drainage holes are prone to overflow and backflow. The main reason is that sudden heavy rainfall causes a large amount of rainwater to enter the drainage channel instantly. In addition, the existing drainage channel gate control valve is mostly manually controlled. When encountering sudden rainfall, it is difficult to control the gate to open to an appropriate size in a short time, which will cause rainwater overflow and backflow.

[0004] Therefore, in view of the above-mentioned problems, this technical solution proposes a municipal garden drainage overflow anti-backflow device. Summary of the Invention

[0005] The purpose of the present invention is to provide a municipal garden drainage overflow anti-backflow device to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A municipal garden drainage overflow anti-backflow device comprises a plurality of drainage outlets opened in the municipal garden area, the bottom of the drainage outlet is connected with a vertically distributed anti-backflow drainage channel, the bottom end of the anti-backflow drainage channel is connected with a horizontal discharge pipe arranged underground through an arc-shaped connecting pipe, rainwater or irrigation water on the ground is discharged through the horizontal discharge pipe, a truncated cone-shaped hydrophobic transmission channel for diffusing the inflowing wastewater is provided inside the anti-backflow drainage channel, the bottom end of the truncated cone-shaped hydrophobic transmission channel is connected with the arc-shaped connecting pipe, and an opening is opened between the truncated cone-shaped hydrophobic transmission channel facing the water flow direction inside the horizontal discharge pipe and the anti-backflow drainage channel. A set of stepped overflow control chambers is provided, and the vertical cross-section of the stepped overflow control chamber is set as an inverted right-angled triangle structure. A plurality of rows of overflow holes are arranged at intervals along the straight line track of the inclined surface of the truncated cone-shaped hydrophobic transmission channel on one side of the stepped overflow control chamber close to the truncated cone-shaped hydrophobic transmission channel. The overflow holes are distributed at intervals in the vertical height. When the water is discharged inside the truncated cone-shaped hydrophobic transmission channel, as the water delivery volume increases, the water accumulation height inside the truncated cone-shaped hydrophobic transmission channel increases to the corresponding overflow hole. Part of the wastewater is injected into the stepped overflow control chamber along the overflow hole. At the same time, the vertical height corresponding to the overflow hole height inside the stepped overflow control chamber is increased. A group of hydraulic moving mechanisms are provided on each side of the arc surface. The output end of the hydraulic moving mechanism extends to the outside of the anti-backflow drainage channel and is elastically connected to a horizontal threaded component. Adjacent horizontal threaded components are vertically spaced. One side of all horizontal threaded components is meshed and connected to a group of lifting components. The bottom of the lifting component is connected to a lifting gate provided inside and outside the horizontal discharge pipe. The lifting gate is used to adjust the axial water flow inside the horizontal discharge pipe. The hydraulic moving mechanism uses the wastewater input at the overflow hole to apply horizontal thrust to it, and then drives the horizontal threaded component to move outward, and then drives the lifting component to control the lifting gate at the bottom to rise, so as to Expand the drainage volume inside the horizontal discharge pipe. As water is injected into the overflow hole at a higher position, the hydraulic moving mechanism at the corresponding height is driven to operate, thereby controlling the lifting gate to open a larger amount of water inside the horizontal discharge pipe. When the accumulated water inside the stepped overflow control chamber is discharged outward, the upper hydraulic moving mechanism gradually increases its horizontal pressure. At this time, under the rebound force of the corresponding horizontal threaded component, the horizontal threaded component is controlled to move back, thereby controlling the lifting component to descend to the corresponding distance, thereby realizing adaptive water overflow control according to the drainage volume inside the anti-backflow drainage channel, preventing drainage in a short time and the occurrence of overflow and backflow problems.

[0008] Compared with the existing technology, the beneficial effects of the present invention are: by utilizing the gravity of accumulated water in conjunction with a mechanical mechanism arranged on the outside of the anti-backflow drainage channel, the amount of water flowing inside the horizontal discharge pipe is automatically adjusted according to the amount of accumulated water, thereby adaptively controlling the water discharge amount to prevent overflow and backflow problems during instantaneous drainage. Compared with the drainage control structure with manual or electric control, it has the advantages of fast response speed, high degree of automation and energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a schematic diagram of the planar distribution structure of a municipal garden drainage overflow and backflow prevention device placed in a municipal garden area;

[0010] Figure 2 This is a schematic diagram of the vertical cross-sectional distribution structure of a municipal garden drainage overflow and backflow prevention device placed in a municipal garden area;

[0011] Figure 3 This is a partial three-dimensional structural diagram of a municipal garden drainage overflow and backflow prevention device;

[0012] Figure 4 This is a partial side view of the structure of a municipal garden drainage overflow and backflow prevention device;

[0013] Figure 5 This is a partial top view structural diagram of a municipal garden drainage overflow and backflow prevention device;

[0014] Figure 6 This is a schematic diagram of the three-dimensional structure of a truncated cone-shaped drainage transmission channel in a municipal garden drainage overflow and backflow prevention device;

[0015] Figure 7 This is a schematic diagram of the main internal structure of a truncated cone-shaped drainage transmission channel in a municipal garden drainage overflow and backflow prevention device;

[0016] Figure 8 This is a schematic diagram of the local distribution structure of a power block placed in a power buffer hole in a municipal garden drainage overflow and backflow prevention device;

[0017] Figure 9 for Figure 3 Schematic diagram of the enlarged structure of A;

[0018] Figure 10 for Figure 5 Schematic diagram of the enlarged structure of B;

[0019] Figure 11 for Figure 6 Schematic diagram of the enlarged structure of C in the middle;

[0020] Among them: drain outlet 10, anti-backflow drainage channel 11, horizontal discharge pipe 12, V-shaped water collection channel 13, frustum-shaped hydrophobic transmission channel 14, stepped overflow control chamber 15, rectangular gate 17, rectangular gate 18, outer frame 19, water retaining bar 20, overflow hole 21, power buffer hole 22, power block 23, corrugated bar 24, buffer rod 25, rack 26, driving gear 27, driven gear 28, positioning shaft 29, connecting block 30, telescopic rod 31, buffer sleeve spring 32, telescopic rod positioning plate 33, gear positioning plate I 34, interval type lifting gear plate 35, tooth groove section 36, extension rod 38, slider 39, slide 40, gear shaft 41, gear positioning plate II 42. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0022] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships 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 limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0023] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0024] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0025] See also Figure 1-Figure 7 、 Figure 11A municipal garden drainage overflow anti-backflow device includes a plurality of drain outlets 10 opened in the municipal garden area, the bottom of the drain outlet 10 is connected with a vertically distributed anti-backflow drainage channel 11, the bottom end of the anti-backflow drainage channel 11 is connected to a horizontal discharge pipe 12 arranged underground through an arc-shaped connecting pipe, and rainwater or irrigation water on the ground is discharged through the horizontal discharge pipe 12. A truncated cone-shaped hydrophobic transmission channel 14 for diffusing the inflowing wastewater is provided inside the anti-backflow drainage channel 11, and the bottom end of the truncated cone-shaped hydrophobic transmission channel 14 is connected to the arc-shaped connecting pipe, and the truncated cone-shaped hydrophobic transmission channel 14 is connected to the anti-backflow drainage channel 11 in the direction of water flow inside the horizontal discharge pipe 12. A set of stepped overflow control chambers 15 are provided between the channels 11. The vertical cross-section of the stepped overflow control chamber 15 is set as an inverted right triangle structure. The stepped overflow control chamber 15 is close to the side of the truncated cone-shaped hydrophobic transmission channel 14 and is provided with multiple rows of overflow holes 21 at intervals along the straight line track of the inclined surface of the truncated cone-shaped hydrophobic transmission channel 14. The overflow holes 21 are distributed at intervals in the vertical height. When the truncated cone-shaped hydrophobic transmission channel 14 is drained, as the water delivery volume increases, the water accumulation height inside the truncated cone-shaped hydrophobic transmission channel 14 increases to the corresponding overflow hole 21. Part of the wastewater is injected into the stepped overflow control chamber 15 along the overflow hole 21. At the same time, in the stepped overflow control chamber 15, the water accumulation height inside the truncated cone-shaped hydrophobic transmission channel 14 increases to the corresponding overflow hole 21. A group of hydraulic moving mechanisms are provided on one side of the vertical arc surface at the height of the overflow hole 21 inside the cavity 15. The output end of the hydraulic moving mechanism extends to the outside of the anti-backflow drainage channel 11 and is elastically connected to a horizontal threaded component. The adjacent horizontal threaded components are vertically spaced apart. One side of all the horizontal threaded components is engaged with a group of lifting components. The bottom of the lifting component is connected to a lifting gate arranged inside and outside the horizontal discharge pipe 12. The lifting gate is used to adjust the axial water flow inside the horizontal discharge pipe 12. The hydraulic moving mechanism uses the wastewater input at the overflow hole 21 to apply a horizontal thrust to it, and then drives the horizontal threaded component to move outward, and then drives the lifting component to control the bottom. The lifting gate is raised to expand the drainage volume inside the horizontal discharge pipe 12. As water is injected into the overflow hole 21 at a higher position, the hydraulic moving mechanism at the corresponding height is driven to operate, thereby controlling the lifting gate to open a larger amount of water inside the horizontal discharge pipe 12. When the accumulated water inside the stepped overflow control chamber 15 is discharged outward, the upper hydraulic moving mechanism gradually increases its horizontal pressure. At this time, under the rebound force of the corresponding horizontal threaded component, the horizontal threaded component is controlled to move back, thereby controlling the lifting component to descend to the corresponding distance, thereby realizing adaptive water overflow control according to the drainage volume inside the anti-backflow drainage channel 11, preventing drainage in a short time and the occurrence of overflow and backflow problems.

[0026] In the embodiment of the present invention, the top of the truncated cone-shaped hydrophobic transmission channel 14 is connected to the bottom of the drain outlet 10 through the V-shaped water collection channel 13. At the same time, a filter screen is provided on the upper surface of the drain outlet 10 to prevent larger impurities (weeds, branches, etc.) on the ground from entering the anti-backflow drainage channel 11 and causing blockage.

[0027] The outer side of the truncated cone-shaped hydrophobic transmission channel 14 and the inner side of the anti-backflow drainage channel 11, except for the stepped overflow control chamber 15, are set as a sealed structure. At the same time, because the vertical cross-section of the stepped overflow control chamber 15 is set as an inverted right-angled triangle structure, the amount of water accumulated inside the stepped overflow control chamber 15 will increase synchronously with the increase of height;

[0028] A circle of water retaining strips 20 is installed on the top of the overflow hole 21 located on one side of the inner wall of the conical hydrophobic transmission channel 14. The water retaining strips 20 are used to prevent the wastewater falling along the inside of the conical hydrophobic transmission channel 14 from flowing into the stepped overflow control chamber 15 along the overflow hole 21, that is, to prevent the waste liquid from being transferred to the inside of the stepped overflow control chamber 15 during normal drainage when there is no water accumulation.

[0029] In one embodiment of the present invention, the lifting gate includes a rectangular gate 17 opened inside the horizontal discharge pipe 12, and a rectangular gate 18 is vertically installed in the rectangular gate 17. The top of the rectangular gate 18 is connected to the bottom of the lifting assembly. That is, the depth of the rectangular gate 18 in the rectangular gate 17 is controlled by the lifting assembly to adjust the amount of water flowing in the horizontal discharge pipe 12.

[0030] The sliding contact surfaces of the rectangular gate 18 and the rectangular gate 17 are provided with sealing gaskets to prevent leakage of water inside the horizontal discharge pipe 12;

[0031] It should be noted that the initial height of the lifting gate is determined according to the daily drainage conditions inside the garden, and it is sufficient to ensure that it can meet daily routine drainage.

[0032] As a preferred embodiment of the present invention, see Figure 8 The hydraulic movement mechanism includes a power buffer hole 22 opened in the inner wall of the stepped overflow control chamber 15. A power block 23 is sealed and slidably connected inside the power buffer hole 22. The wastewater input into the stepped overflow control chamber 15 through the overflow hole 21 exerts horizontal pressure on the power block 23, and then controls it to slide along the inside of the power buffer hole 22. A buffer rod 25 is installed in the middle of the side wall of the power block 23 facing the outside of the stepped overflow control chamber 15. The buffer rod 25 is sealed and movable through the stepped overflow control chamber 15 to be connected to the horizontal threaded assembly outward, thereby controlling the movement of the horizontal threaded assembly;

[0033] Specifically, the side of the power block 23 in contact with water is set to an arc-shaped structure, which is used to increase the concentrated contact pressure between the power block 23 and the water. At the same time, the outer surface of the power block 23 in contact with the water is provided with evenly distributed corrugated strips 24. The corrugated strips 24 are used to reduce the resistance of the power block 23 during the initial contact with water, that is, to increase the thrust of the instantaneous contact between the wastewater and the power block 23 to a certain extent.

[0034] As a preferred embodiment of the present invention, see Figure 3-Figure 5 、 Figure 9 The horizontal threaded assembly includes a rack 26 fixedly connected to the outer end of the buffer rod 25, and the bottom side of the rack 26 is meshed with an active tooth 27. The end of the rack 26 away from the buffer rod 25 is installed with a telescopic rod 31 through a connecting block 30. The end of the telescopic rod 31 telescopically passes through a telescopic rod positioning plate 33. A buffer sleeve spring 32 is set on the telescopic rod 31 located between the telescopic rod positioning plate 33 and the end of the rack 26. When the buffer sleeve spring 32 is in a free state, the rack 26 is controlled to move in a direction away from the telescopic rod positioning plate 33, that is, the power block 23 is controlled to stay at the inlet of the power buffer hole 22. When the power block 23 is subjected to horizontal wastewater thrust, the rack 26 is controlled to move toward the telescopic rod positioning plate 33, and the telescopic rod 31 slides along the inside of the telescopic rod positioning plate 33. At the same time, when the rack 26 moves, it drives the active tooth 27 at the bottom to rotate. When the horizontal thrust is lost, the rebound force of the buffer sleeve spring 32 is used to reset the power block 23.

[0035] Specifically, gear shafts 41 are installed at both ends of the driving gear 27, one end of which is rotatably connected to a gear positioning plate II 42 fixed at the bottom on the horizontal discharge pipe 12, and the other end is connected to a driven gear 28. The end of the driven gear 28 away from the driving gear 27 is connected to a positioning shaft 29, and the end of the positioning shaft 29 is rotatably connected to a gear positioning plate I 34 fixed at the bottom on the horizontal discharge pipe 12. That is, when the rack 26 drives the driving gear 27 to rotate, the driven gear 28 is synchronously driven to rotate. One side of all the driven gears 28 is threadedly connected to the lifting assembly;

[0036] The lifting assembly includes an interval type lifting gear plate 35 fixedly mounted on one side of the top of the rectangular gate 18. The interval type lifting gear plate 35 has a set of tooth groove sections 36 on the side facing the driven gear 28. In the initial state, the tooth groove section 36 is placed at the bottom, and its top is engaged with the driven gear 28 at the bottom. As the rack 26 at the bottom moves outward, the driving gear 27 and the driven gear 28 are controlled to rotate, and then the tooth groove section 36 is driven to rise upward. After the rack 26 moves to the maximum stroke, the tooth groove section 36 moves to the side of the driven gear 28 on the upper side and engages with it. Then, as the water in the stepped overflow control chamber 15 increases, it gradually drives the driven gear 27 and the driven gear 28 to rise upward. The rack 26 here moves outward, and then controls the driven gear 28 to rotate and drive the tooth groove section 36 to continue to move upward. At this time, the rectangular gate 18 at the bottom of the interval lifting tooth plate 35 is driven to continue to rise until the rack 26 here moves to the maximum stroke, and then the water accumulation in the stepped overflow control chamber 15 continues to increase. This process is repeated until the rectangular gate 17 is opened to the maximum water flow, realizing the adaptive anti-backflow overflow function. Similarly, as the water accumulation in the stepped overflow control chamber 15 decreases, the rebound force of the buffer sleeve spring 32 at the end of the rack 26 is used to gradually control the tooth groove section 36 to fall, that is, drive the rectangular gate 18 to descend.

[0037] As a preferred embodiment of the present invention, see Figure 10 In order to maintain the stability of the spaced lifting gear plate 35 during lifting, a plurality of longitudinally spaced extension rods 38 are connected to one side of the spaced lifting gear plate 35. A slider 39 is installed at the end of the extension rod 38. A slide groove 40 is opened on the side wall of the gear positioning plate I 34 corresponding to the end of the slider 39. The slider 39 slides along the inside of the slide groove 40, thereby maintaining the stable lifting of the spaced lifting gear plate 35.

[0038] Specifically, the slider 39 and the slide groove 40 are configured as a T-shaped structure to increase the limiting force when the two slide.

[0039] As a preferred embodiment of the present invention, the bottoms of the telescopic rod positioning plate 33, the gear positioning plate I34, and the gear positioning plate II42 are all connected to an outer frame 19 installed on the outside of the horizontal discharge pipe 12, and the rectangular gate 18 also passes through the outer frame 19 in a lifting manner.

[0040] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A municipal garden drainage overflow anti-backflow device, comprising a drain outlet (10) opened in a municipal garden area, wherein the bottom of the drain outlet (10) is connected to a vertical anti-backflow drainage channel (11), and the bottom end of the anti-backflow drainage channel (11) is connected to an underground horizontal discharge pipe (12) through an arc-shaped connecting pipe, characterized in that: A truncated cone-shaped hydrophobic transmission channel (14) is provided in the anti-backflow drainage channel (11), the top end of which is connected to the drainage outlet (10) via a V-shaped water collection channel (13); A set of stepped overflow control chambers (15) are provided between the truncated cone-shaped hydrophobic transmission channel (14) and the anti-backflow drainage channel (11). The stepped overflow control chambers (15) have a vertical cross-section in the form of an inverted right triangle, and a plurality of rows of overflow holes (21) are provided on a side thereof close to the truncated cone-shaped hydrophobic transmission channel (14). A hydraulic moving mechanism is provided in the stepped overflow control chamber (15) corresponding to each row of overflow holes (21), and the hydraulic moving mechanism comprises a power buffer hole (22) on the inner wall of the stepped overflow control chamber (15), a power block (23) sealingly sliding in the power buffer hole (22), and a buffer rod (25) connected to the power block (23); the contact surface of the power block (23) with water is arranged in an arc shape and is provided with a corrugated strip (24), and the outer end of the buffer rod (25) is connected to a horizontal threaded assembly; The horizontal thread assembly includes a rack (26), a driving tooth (27), a driven tooth (28), a buffer sleeve spring (32) and a telescopic rod positioning plate (33); one end of the rack (26) is connected to the buffer rod (25), and the other end is connected to the telescopic rod (31) through the buffer sleeve spring (32); the driving tooth (27) meshes with the rack (26) and drives the driven tooth (28) to rotate, and gear shafts (41) are installed at both ends of the driving tooth (27), one end of the gear shaft (41) is rotatably connected to the gear positioning plate II (42) fixed at the bottom on the horizontal discharge pipe (12), and the other end is connected to the driven tooth (28), and the end of the driven tooth (28) away from the driving tooth (27) is connected to the positioning shaft (29), and the end of the positioning shaft (29) is rotatably connected to the gear positioning plate I (34) fixed at the bottom on the horizontal discharge pipe (12), and one side of the driven tooth (28) is threadedly connected to the lifting assembly; The lifting assembly includes a spaced lifting tooth plate (35), the side wall of which is provided with a tooth groove section (36), and the tooth groove section (36) is movably engaged with each driven tooth (28) to drive the rectangular gate (18) to rise and fall; The buffer sleeve spring (32) is sleeved on the telescopic rod (31) between the telescopic rod positioning plate (33) and the rack (26); The hydraulic moving mechanism is linked to a lifting assembly via a horizontal threaded assembly, and the bottom of the lifting assembly is connected to a lifting gate for adjusting the amount of water flowing through a horizontal discharge pipe (12); A water retaining bar (20) is installed on the top of the overflow hole (21) of the truncated cone-shaped hydrophobic transmission channel (14), and the water retaining bar (20) is used to prevent wastewater from flowing into the stepped overflow control chamber (15) in a non-water accumulation state.

2. A municipal garden drainage overflow anti-backflow device according to claim 1, characterized in that: The lifting gate comprises a rectangular gate (17) in a horizontal discharge pipe (12) and a rectangular gate (18) slidingly matched therewith, and the top of the rectangular gate (18) is connected to the lifting assembly.

3. A municipal garden drainage overflow anti-backflow device according to claim 2, characterized in that: The corrugated strips (24) of the power block (23) are evenly distributed along the direction of water flow.

4. A municipal garden drainage overflow anti-backflow device according to claim 3, characterized in that: One side of the spaced lifting gear plate (35) is connected to an extension rod (38), and a slider (39) is provided at the end of the extension rod (38). A T-shaped slide groove (40) for the slider (39) to slide is provided on the corresponding gear positioning plate I (34).

5. A municipal garden drainage overflow anti-backflow device according to claim 4, characterized in that: The bottoms of the telescopic rod positioning plate (33), the gear positioning plate I (34), and the gear positioning plate II (42) are all connected to an outer frame (19) installed on the outside of the horizontal discharge pipe (12), and the rectangular gate (18) is lifted and lowered through the outer frame (19).

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