Bridge cantilever deformation detection device

Abstract

The invention relates to the technical field of bridge construction, and comprises a detection mechanism installed on a bridge cantilever body, the detection mechanism comprises square pipes detachably installed at the two ends of the bridge cantilever body, and communicating pipes located at the center positions of the square pipes are fixedly installed on the outer walls of the two square pipes correspondingly; the device comprises two square pipes, centering clamping assemblies are installed in the two square pipes, the square pipes are installed on a bridge cantilever body through the centering clamping assemblies, communicating pipes are located at the center of the height of the bridge cantilever body, hoses are installed at the bottom ends of the two communicating pipes in a communicating mode, and a differential pressure sensor is installed between the two hoses. The square pipe and the bridge cantilever body are detachably connected through the centering clamping assembly, the communicating pipe is forced to be located in the center of the height of the bridge cantilever body all the time after installation, manual installation deviation is eliminated, and detection is conducted through the differential pressure sensor.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, specifically a device for detecting the deformation of a bridge cantilever. Background Technology

[0002] Bridge cantilever deformation mainly refers to the relative shear slip between adjacent cantilever segments during the construction and subsequent operation of bridges constructed using the cantilever assembly method. This slippage is caused by factors such as prestress relaxation, concrete shrinkage and creep, or interface material creep. This deformation typically manifests as slow slippage following a gradual decrease in the interfacial interlocking force between segments. Although the initial amplitude is small, it is prolonged and may accumulate over time. Failure to monitor it in a timely manner can lead to safety hazards such as decreased structural stability. Therefore, long-term, high-precision real-time monitoring of shear deformation between bridge cantilever segments is a crucial step in ensuring bridge construction quality and operational safety.

[0003] In existing technologies, detection devices for shear deformation between bridge cantilever segments have significant defects in the installation and positioning process. For example, document CN216869525U discloses a device for measuring shear deformation between assembled bridge cantilever segments. The monitoring method is based on the principle of connecting pipes and relies heavily on manual operation to fix the monitoring points. During installation, human error can easily cause the monitoring points to be located inaccurately at the center of the cantilever height. For instance, if the connecting pipe is installed off-center from the cantilever height, it will directly cause a deviation in the measurement benchmark of the initial liquid column height difference. The error will accumulate over time in subsequent deformation calculations, seriously affecting the accuracy and long-term validity of the monitoring data and limiting its practical application in bridge engineering. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a bridge cantilever deformation detection device, which solves the problem that human error during installation can cause the monitoring point to be unable to be accurately located at the center of the cantilever height, thus affecting the accuracy of the monitoring data.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A bridge cantilever deformation detection device includes a detection mechanism installed on the main body of the bridge cantilever. The detection mechanism includes square tubes detachably installed at both ends of the main body of the bridge cantilever. A connecting pipe located at the center of the square tubes is fixedly installed on the outer wall of each of the two square tubes. A centering clamping assembly is installed inside each of the two square tubes. The square tubes are installed on the main body of the bridge cantilever through the centering clamping assembly, and the connecting pipe is located at the center of the height of the main body of the bridge cantilever. A flexible hose is connected to the bottom end of each of the two connecting pipes, and a differential pressure sensor is installed between the two flexible hoses.

[0007] Furthermore, the centering clamping assembly includes a bidirectional lead screw rotatably disposed inside a square tube. The square tube has through grooves corresponding to the threaded sections at both ends of the bidirectional lead screw. The bidirectional lead screw is threaded with spaced threaded sleeves. A limiting block is fixedly connected to the threaded sleeve and slidably disposed in the through groove. A clamping assembly located outside the square tube is fixedly connected to one side of the limiting block.

[0008] Furthermore, the clamping assembly includes a base fixedly connected to the limiting block, a support plate fixedly connected to the base, a nut fixedly connected to the support plate, a screw threadedly connected to the inner ring of the nut, a sliding groove provided on the base, a slider slidably disposed in the sliding groove, a pressure plate fixedly connected to one side of the slider, one end of the screw rotatably connected to the pressure plate via a bearing, and a rotating head fixedly connected to the end of the screw away from the pressure plate.

[0009] Furthermore, a worm gear is fixedly connected to the bidirectional lead screw, and a worm that meshes with the worm gear is rotatably mounted on the square tube via a bearing. One end of the worm is fixedly connected to an adjusting head located on the outside of the square tube.

[0010] Furthermore, the base is provided with scale lines, which are used to detect the position of the pressure plate. On one side surface of the pressure plate, there are mutually perpendicular and spaced grooves, which form friction protrusions on the surface of the pressure plate.

[0011] Furthermore, a contact plate is fixedly connected to one side of the square tube, and the side of the contact plate away from the square tube and the side of the base away from the square tube are located on the same plane.

[0012] Furthermore, the connecting pipe is provided with a pipe cap to seal the connecting pipe, the connecting pipe has a small ventilation hole, and a liquid passage pipe is connected to the bottom of the connecting pipe. The end of the flexible tube away from the differential pressure sensor is connected to the liquid passage pipe.

[0013] Furthermore, a mounting base is provided on the outer wall of the square tube, and an edge is fixedly connected to the mounting base. Screws for fixing the mounting base to the square tube are passed through the edge. The connecting pipe is placed inside the mounting base, and a slot for the liquid pipe to pass through is opened at the bottom of the mounting base.

[0014] Furthermore, a slide rod is slidably provided on the top of the mounting base, passing through the mounting base. A pressure block that presses against the pipe cover is fixedly connected to the bottom end of the slide rod. A spring sleeved on the outside of the slide rod is provided between the pressure block and the mounting base.

[0015] Furthermore, the differential pressure sensor integrates a control display, which is signal-connected to the differential pressure sensor for displaying and transmitting pressure difference changes.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. In this invention, the square tube and the main body of the bridge cantilever are detachably connected by the centering clamping component. After installation, the forced connecting pipe is always at the center of the height of the bridge cantilever body, eliminating human installation deviation.

[0018] 2. In this invention, the screw is driven to rotate by a rotating head, and the displacement of the pressure plate is quantified by the scale lines on the base. The travel of the pressure plate can be precisely controlled, so that the clamping assembly can adapt to the size differences of different bridge cantilever bodies. The grooves on the surface of the pressure plate form regular friction protrusions, which reduce the contact area but increase the pressure, enhance the interlocking effect, and ensure a firm connection. It can flexibly adapt to bridge cantilever bodies of different thicknesses and shapes, greatly expanding the application scenarios.

[0019] 3. In this invention, since the forced connecting pipe is always located at the center of the height of the bridge cantilever body, the differential pressure sensor measures the initial pressure difference between the two connecting pipes through a flexible tube, and the initial pressure difference is zero or close to zero as the reference data. When the bridge cantilever body segment deforms, the two connecting pipes are relatively displaced with the bridge cantilever body segment, resulting in a change in the height difference of the liquid column in the connecting pipe. The differential pressure sensor measures the pressure difference after deformation in real time, calculates the pressure difference change, and the control display integrated with the differential pressure sensor displays the pressure difference and change curve in real time. The data is transmitted to a remote terminal via Bluetooth / Wi-Fi to realize automated monitoring. Attached Figure Description

[0020] Figure 1 This is a perspective view of the present invention;

[0021] Figure 2 This is a perspective view of the testing mechanism of the present invention;

[0022] Figure 3 This is a perspective view of a partial cross-section of the square tube in this invention;

[0023] Figure 4 This is a perspective view of the clamping assembly of the present invention;

[0024] Figure 5 This is a perspective view of a partial structure of the present invention;

[0025] Figure 6 This is a perspective view of the mounting base of the present invention.

[0026] The meanings of the reference numerals in the attached diagram are as follows: 1. Bridge cantilever body; 2. Square tube; 21. Through groove; 22. Contact plate; 3. Connecting pipe; 31. Pipe cap; 32. Small ventilation hole; 33. Liquid pipe; 34. Mounting base; 35. Edge; 36. Groove; 37. Slide rod; 38. Pressure block; 39. Spring; 4. Centering clamping assembly; 41. Two-way lead screw; 42. Screw sleeve; 43. Limiting block; 44. Clamping assembly; 441. Base; 442. Support plate; 443. Nut; 444. Screw; 445. Slide groove; 446. Slider; 447. Pressure plate; 448. Rotating head; 449. Scale line; 4410. Groove; 4411. Friction protrusion; 45. Worm gear; 46. Worm; 47. Adjusting head; 5. Hoses; 6. Differential pressure sensor; 61. Control display. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0028] The component designations used in this document, such as "first" and "second," are merely for distinguishing the described objects and do not have any sequential or technical meaning. The terms "connection" and "linkage" used in this invention, unless otherwise specified, include both direct and indirect connections (linkages). In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0029] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0030] Reference Figure 1-6A bridge cantilever deformation detection device includes a detection mechanism installed on the main body 1 of the bridge cantilever. The detection mechanism includes square tubes 2 detachably installed at both ends of the main body 1 of the bridge cantilever. A connecting pipe 3 located at the center of the square tube 2 is fixedly installed on the outer wall of the two square tubes 2 respectively. A centering clamping component 4 is installed inside each of the two square tubes 2. The square tubes 2 are installed on the main body 1 of the bridge cantilever through the centering clamping component 4 and the connecting pipe 3 is located at the center of the height of the main body 1 of the bridge cantilever. A flexible hose 5 is connected to the bottom end of the two connecting pipes 3 respectively. A differential pressure sensor 6 is installed between the two flexible hoses 5.

[0031] As an optimization solution, such as Figure 2-3 As shown, the centering clamping assembly 4 includes a bidirectional lead screw 41 rotatably disposed inside the square tube 2. The square tube 2 has through grooves 21 corresponding to the threaded sections at both ends of the bidirectional lead screw 41. The bidirectional lead screw 41 is threaded with spaced threaded sleeves 42. A limiting block 43 is fixedly connected to the threaded sleeve 42 and is slidably disposed inside the through groove 21. A clamping assembly 44 located outside the square tube 2 is fixedly connected to one side of the limiting block 43.

[0032] Specifically, by driving the bidirectional lead screw 41 to rotate, the threaded sleeves 42 at both ends of the bidirectional lead screw 41 move in opposite directions, causing the limiting block 43 to slide in the through groove 21, so that the threaded sleeves 42 move linearly and avoid radial deflection. The limiting block 43 drives the clamping assembly 44 to move closer to or further away from the bridge cantilever body 1 in sync, so as to realize the connection and separation between the square tube 2 and the bridge cantilever body 1. During the connection, the forced connecting pipe 3 is always in the center position of the bridge cantilever height, eliminating human installation deviation.

[0033] As an optimization solution, such as Figure 2-4 As shown, the clamping assembly 44 includes a base 441 fixedly connected to the limiting block 43, a support plate 442 fixedly connected to the base 441, a nut 443 fixedly connected to the support plate 442, a screw 444 threadedly connected to the inner ring of the nut 443, a sliding groove 445 provided on the base 441, a slider 446 slidably arranged in the sliding groove 445, a pressure plate 447 fixedly connected to one side of the slider 446, one end of the screw 444 being rotatably connected to the pressure plate 447 through a bearing, and a rotating head 448 fixedly connected to the end of the screw 444 away from the pressure plate 447.

[0034] Specifically, the rotating head 448 drives the screw 444 to rotate. With the cooperation of the nut 443, the screw 444 rotates and moves forward, pushing the pressure plate 447 to drive the slider 446 to move along the slide groove 445. The cooperation between the slider 446 and the slide groove 445 limits the pressure plate 447. The stroke of the pressure plate 447 is controlled by the thread lead of the screw 444, so that the stroke of the pressure plate 447 can be varied to adapt to different bridge cantilever bodies 1.

[0035] As an optimization solution, such as Figure 3 As shown, a worm gear 45 is fixedly connected to the bidirectional lead screw 41, and a worm 46 that meshes with the worm gear 45 is rotatably mounted on the square tube 2 via a bearing. One end of the worm 46 is fixedly connected to an adjusting head 47 located on the outside of the square tube 2.

[0036] Specifically, the hexagonal adjusting head 47 is compatible with a universal wrench, which facilitates the control of the rotation of the worm 46. The worm 46, through its cooperation with the worm wheel 45, enables the rotation of the bidirectional lead screw 41. The cooperation between the worm wheel 45 and the worm 46 changes the torque, making adjustment easier. At the same time, the self-locking characteristics of the worm wheel 45 and the worm 46 prevent backlash caused by vibration, ensuring stable clamping force.

[0037] As an optimization solution, such as Figure 4 As shown, a scale line 449 is provided on the base 441. The scale line 449 is used to detect the position of the pressure plate 447. A groove 4410 is provided on one side surface of the pressure plate 447. The groove 4410 forms friction protrusions 4411 on the surface of the pressure plate 447.

[0038] Specifically, the scale line 449 is laser-engraved on the side of the base 441 to indicate the displacement of the pressure plate 447 and synchronously adjust the stroke of the pressure plate 447. The scale line 449 quantifies the displacement of the pressure plate 447, realizes standardized control of the clamping force, and adapts to different bridge cantilever bodies 1. The grooves 4410 that are perpendicular to each other and spaced apart are milled to form regular friction protrusions 4411. The contact area is reduced but the pressure is increased, and the friction effect is good, which enhances the interlocking effect and makes the pressure plate 447 and the bridge cantilever body 1 firmly connected.

[0039] As an optimization solution, such as Figure 2 As shown, a contact plate 22 is fixedly connected to one side of the square tube 2. The side of the contact plate 22 away from the square tube 2 and the side of the base 441 away from the square tube 2 are located on the same plane.

[0040] Specifically, the contact plate 22 and the outer side of the base 441 are designed to be coplanar. During installation, they simultaneously fit against the side of the bridge cantilever body 1 to form a three-point positioning. The three-point contact automatically corrects the parallelism between the axis of the square tube 2 and the center line of the bridge cantilever body 1, making installation convenient.

[0041] As an optimization solution, such as Figure 5 As shown, the connecting pipe 3 is provided with a pipe cap 31 to seal the connecting pipe 3, and a small ventilation hole 32 is opened on the connecting pipe 3. A liquid passage pipe 33 is connected to the bottom of the connecting pipe 3, and the end of the hose 5 away from the differential pressure sensor 6 is connected to the liquid passage pipe 33.

[0042] Specifically, the cap 31 seals the top of the connecting pipe 3 with an O-ring, the small vent 32 balances the air pressure, the liquid pipe 33 is connected to the hose 5 with a quick-connect fitting, and the small vent 32 allows the gas to flow slowly, eliminating the liquid column height error caused by temperature changes.

[0043] As an optimization solution, such as Figure 5-6 As shown, a mounting base 34 is provided on the outer wall of the square tube 2. An edge 35 is fixedly connected to the mounting base 34. A screw for fixing the mounting base 34 to the square tube 2 is passed through the edge 35. The connecting tube 3 is placed inside the mounting base 34. A slot 36 for the liquid pipe 33 to pass through is opened at the bottom of the mounting base 34. A slide rod 37 is slidably provided on the top of the mounting base 34 and passes through the mounting base 34. A pressure block 38 is fixedly connected to the bottom end of the slide rod 37 and is pressed against the tube cap 31. A spring 39 is provided between the pressure block 38 and the mounting base 34 and is sleeved on the outside of the slide rod 37.

[0044] Specifically, the preload of spring 39 causes pressure block 38 to continuously press the tube cap 31. By pulling slide rod 37 to squeeze spring 39, pressure block 38 is separated from tube cap 31, and connecting tube 3 can be removed. Connecting tube 3 is easy to install and remove and convenient to use.

[0045] As an optimization solution, such as Figure 6 As shown, the differential pressure sensor 6 integrates a control display 61, which is connected to the differential pressure sensor 6 for displaying and transmitting pressure difference changes.

[0046] Specifically, the signal from the differential pressure sensor 6 is transmitted to the control display 61, and the LCD screen of the control display 61 displays the pressure difference and its change curve in real time. It supports Bluetooth / Wi-Fi data transmission and displays and transmits pressure difference changes.

[0047] Working principle:

[0048] S1. Install two square tubes 2 at both ends of the bridge cantilever body 1. Rotate the worm gear 46 to make it cooperate with the worm wheel 45 to drive the double-acting screw 41 to rotate. The screw sleeves 42 at both ends of the double-acting screw 41 move in opposite directions, causing the limiting block 43 to slide along the through groove 21, so that the clamping assembly 44 moves closer to the bridge cantilever body 1 in sync, realizing the detachable connection between the square tube 2 and the bridge cantilever body 1. Before this, according to the actual situation of the bridge cantilever body 1, drive the screw 444 to rotate and push the pressure plate 447 to move. Quantify the displacement of the pressure plate 447 through the scale line 449. After installation, the forced connecting pipe 3 is always in the center position of the height of the bridge cantilever body, eliminating human installation deviation.

[0049] S2. Pull the slide bar 37 to compress the spring 39 and move the pressure block 38 upward. Place the connecting pipe 3 in the mounting seat 34 on the outer wall of the square pipe 2. The liquid pipe 33 passes through the bottom groove 36 of the mounting seat 34. Release the slide bar 37 and use the elastic force of the spring 39 to reset the pressure block 38 and press it onto the pipe cover 31 to realize the installation of the connecting pipe 3.

[0050] S3. Inject an appropriate amount of liquid into the two connecting pipes 3 and let it stand until the liquid level is stable. The small ventilation hole 32 at the top of the connecting pipe 3 balances the air pressure and eliminates the liquid column height error caused by temperature changes. Since the forced connecting pipe 3 is always at the center of the height of the bridge cantilever body, the differential pressure sensor 6 measures the initial pressure difference value of the two connecting pipes 3 through the hose 5. If the bridge cantilever body is not deformed and is relatively flat, the initial pressure difference value is zero or close to zero. The initial pressure difference value is used as the reference data.

[0051] S4. When the bridge cantilever body segment deforms, the two connecting pipes 3 move relative to the bridge cantilever body segment, causing the height difference of the liquid column in the connecting pipes 3 to change. The differential pressure sensor 6 measures the pressure difference value after deformation in real time and calculates the pressure difference change. The control display 61 integrated in the differential pressure sensor 6 displays the pressure difference and change curve in real time, and transmits the data to the remote terminal via Bluetooth / Wi-Fi to realize automated monitoring.

[0052] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalent elements of the claims are intended to be included within this application. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0053] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A device for detecting the cantilever deformation of a bridge, characterized in that: The system includes a detection mechanism installed on the main body of the bridge cantilever (1). The detection mechanism includes square tubes (2) that are detachably installed at both ends of the main body of the bridge cantilever (1). A connecting pipe (3) located at the center of the square tube (2) is fixedly installed on the outer wall of each of the two square tubes (2). A centering clamping assembly (4) is installed inside each of the two square tubes (2). The square tubes (2) are installed on the main body of the bridge cantilever (1) through the centering clamping assembly (4), and the connecting pipe (3) is located at the center of the height of the main body of the bridge cantilever (1). A flexible hose (5) is connected to the bottom end of each of the two connecting pipes (3). A differential pressure sensor (6) is installed between the two flexible hoses (5).

2. The bridge cantilever deformation detection device according to claim 1, characterized in that: The centering clamping assembly (4) includes a bidirectional lead screw (41) rotatably disposed in a square tube (2). The square tube (2) has through grooves (21) corresponding to the threaded sections at both ends of the bidirectional lead screw (41). The bidirectional lead screw (41) is threaded with spaced threaded sleeves (42). The threaded sleeves (42) are fixedly connected with a limiting block (43) slidably disposed in the through groove (21). A clamping assembly (44) located outside the square tube (2) is fixedly connected to one side of the limiting block (43).

3. The bridge cantilever deformation detection device according to claim 2, characterized in that: The clamping assembly (44) includes a base (441) fixedly connected to a limiting block (43), a support plate (442) fixedly connected to the base (441), a nut (443) fixedly connected to the support plate (442), a screw (444) threadedly connected to the inner ring of the nut (443), a sliding groove (445) provided on the base (441), a slider (446) slidably arranged in the sliding groove (445), a pressure plate (447) fixedly connected to one side of the slider (446), one end of the screw (444) being rotatably connected to the pressure plate (447) through a bearing, and a rotating head (448) fixedly connected to the end of the screw (444) away from the pressure plate (447).

4. The bridge cantilever deformation detection device according to claim 2, characterized in that: A worm gear (45) is fixedly connected to the bidirectional lead screw (41), and a worm (46) that meshes with the worm gear (45) is rotatably provided on the square tube (2) through a bearing. An adjusting head (47) located outside the square tube (2) is fixedly connected to one end of the worm (46).

5. The bridge cantilever deformation detection device according to claim 3, characterized in that: The base (441) is provided with scale lines (449), which are used to detect the position of the pressure plate (447). The pressure plate (447) has grooves (4410) that are perpendicular to each other and spaced apart on one side surface. The grooves (4410) form friction protrusions (4411) on the surface of the pressure plate (447).

6. The bridge cantilever deformation detection device according to claim 3, characterized in that: A contact plate (22) is fixedly connected to one side of the square tube (2). The side of the contact plate (22) away from the square tube (2) and the side of the base (441) away from the square tube (2) are located on the same plane.

7. The bridge cantilever deformation detection device according to claim 1, characterized in that: The connecting pipe (3) is provided with a pipe cap (31) to close the connecting pipe (3), and a small ventilation hole (32) is opened on the connecting pipe (3). A liquid passage pipe (33) is connected to the bottom of the connecting pipe (3), and the end of the flexible hose (5) away from the differential pressure sensor (6) is connected to the liquid passage pipe (33).

8. The bridge cantilever deformation detection device according to claim 7, characterized in that: A mounting base (34) is provided on the outer wall of the square tube (2). An edge (35) is fixedly connected to the mounting base (34). A screw for fixing the mounting base (34) to the square tube (2) is provided on the edge (35). The connecting tube (3) is placed inside the mounting base (34). A slot (36) for the liquid pipe (33) to pass through is opened at the bottom of the mounting base (34).

9. A bridge cantilever deformation detection device according to claim 8, characterized in that: The top of the mounting base (34) is slidably provided with a slide rod (37) passing through the mounting base (34), and the bottom end of the slide rod (37) is fixedly connected to a pressure block (38) pressing on the pipe cover (31). A spring (39) sleeved on the outside of the slide rod (37) is provided between the pressure block (38) and the mounting base (34).

10. A bridge cantilever deformation detection device according to claim 1, characterized in that: The differential pressure sensor (6) integrates a control display (61), which is signal-connected to the differential pressure sensor (6) for displaying and transmitting pressure difference changes.

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