A soil tensiometer with automatic air exhaust and water replenishment

Abstract

The present invention relates to a soil tensiometer with automatic exhaust and water replenishment, comprising a protection mechanism, a control system, a clay head, an organic glass tube and a first sealing mechanism; the first sealing mechanism is provided with a water replenishment hole, a water level hole, a pressure collection hole and an exhaust hole; one end of the water replenishment pipe extends into the organic glass tube through the water replenishment hole, and the other end is connected to the water replenishment valve and the water storage mechanism in sequence, and the magnetic float water level controller extends into the organic glass tube through the water level hole; one end of the pressure collection pipe extends into the organic glass tube through the pressure collection hole, and the other end is installed with a pressure sensor; one end of the exhaust pipe extends into the organic glass tube through the exhaust hole, and the other end runs through the protection mechanism, and is provided with an exhaust valve above. The soil tensiometer of the present invention can monitor the effective moisture content in the soil for a long time, in real time and accurately, and can effectively prevent plants from being damaged by drought or excessive irrigation, so as to achieve the purposes of saving water resources, reducing labor costs, protecting the ecological environment, etc.

Description

Technical Field

[0001] The invention relates to a soil tensiometer capable of automatically exhausting and replenishing water, and belongs to the technical field of soil moisture monitoring. Background Art

[0002] The soil tensiometer is a device that can directly and accurately monitor soil moisture. It uses soil water potential to accurately reflect the degree to which soil moisture can be effectively absorbed and utilized by crops from an energy perspective. Traditional soil tensiometer equipment is mainly composed of microporous clay heads, plexiglass tubes, vacuum gauges and other components, and the microporous clay heads are connected to the plexiglass tubes. When used, the microporous clay head of the device is inserted into the soil to a certain depth, and the plexiglass tube is filled with airless water. When the soil moisture becomes dry due to the reduction of crop water absorption and evaporation, the soil water and the airless water in the plexiglass tube will be exchanged under the action of energy difference. The soil absorbs water through the microporous clay head. Because the plexiglass tube cannot achieve absolute complete sealing, the airless water in the plexiglass tube of the soil tensiometer will be exchanged into the soil in small amounts. When it is reduced to a certain extent, it will cause the measurement data accuracy, and artificial water replenishment and exhaust are required to maintain normal monitoring, which greatly limits the use of this facility. Patent CN115541849 A discloses a soil tension sensor device with self-diagnosis and self-calibration, the soil tension sensor device comprises: a fluid box, a fluid pipeline, a first solenoid valve, a second solenoid valve, a soil tension sensor, a porous ceramic medium, a pressure sensor, a liquid level sensor, a drive control unit, a data processing unit, a data storage unit, and a data sending and receiving unit; the fluid box is connected to the soil tension sensor through a fluid pipeline, the liquid in the fluid box enters the liquid cavity of the soil tension sensor, a porous ceramic medium is inserted below the liquid cavity, the porous ceramic medium contacts the soil, and the liquid in the liquid cavity exchanges water with the soil through the porous ceramic medium to achieve water potential balance; the sensor device is self-checked by relying on the local data received by the data processing unit in the soil tension sensor device, thereby driving the start and stop of the vacuum pump and the solenoid valve in the soil tension sensor device, and automatically diagnosing and calibrating the soil tension sensor device. The overall structure is complex, and multiple sensors are required for precise control, and the preparation and maintenance costs are high. Summary of the invention

[0003] The invention provides a soil tensiometer with automatic air exhaust and water replenishment, which solves the problems that the existing soil tensiometer needs manual water replenishment and air exhaust, and the existing soil tensiometer with automatic water replenishment and air exhaust has a complex structure and high manufacturing and maintenance costs.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A soil tensiometer with automatic exhaust and water replenishment comprises a protection mechanism, a control system, a clay head, an organic glass tube and a first sealing mechanism, wherein the organic glass tube and the first sealing mechanism are arranged in the protection mechanism, the clay head is installed together with the organic glass tube, and the organic glass tube is sealed by the first sealing mechanism; the first sealing mechanism is provided with a water replenishment hole, a water level hole, a pressure collection hole and an exhaust hole; one end of the water replenishment pipe passes through the water replenishment hole and extends into the organic glass tube, and the other end is connected with the water replenishment valve and the water storage mechanism in sequence, and a magnetic float water level controller passes through the water level hole and extends into the organic glass tube; one end of the pressure collection pipe passes through the pressure collection hole and extends into the organic glass tube, and a pressure sensor is installed at the other end; one end of the exhaust pipe passes through the exhaust hole and extends into the organic glass tube, and the other end passes through the protection mechanism and is provided with an exhaust valve above; the magnetic float water level controller, the water replenishment valve, the pressure sensor and the exhaust valve are respectively installed together with the control system.

[0006] Further, preferably: the protection mechanism includes a cylindrical upper part, a conical lower part and a top cover, the top of the cylindrical upper part is provided with a water storage bracket, and the middle and lower part is provided with a circuit bracket; the aperture of the conical lower part matches the plexiglass tube to seal the conical lower part, and the top cover is threadedly connected to the cylindrical upper part to seal the cylindrical upper part.

[0007] Further, preferably: a fixing ring is arranged inside the cylindrical upper part.

[0008] Further, preferably: the conical lower part is provided with a conical sealing ring.

[0009] Further, preferably: the control system includes a microcontroller, a transmission module and a power supply module, and the microcontroller, transmission module and power supply module are interconnected through a circuit board, the microcontroller is connected to the water supply valve and the exhaust valve, and is used to control the switches of water supply and exhaust; the microcontroller is connected to the pressure sensor for data acquisition; the microcontroller is connected to the magnetic float switch water level controller, which collects the water level information in the plexiglass tube, converts the water level information into a signal for controlling the water supply valve and the exhaust valve, and controls the opening and closing of the water supply valve and the exhaust valve through the microcontroller, and the power supply module supplies power to the entire device.

[0010] Further, preferably: the first sealing mechanism is a rubber plug.

[0011] Further, preferably: the first sealing mechanism includes a rubber stopper, a sealing cover and a sealing gasket, the lower part of the rubber stopper is inserted into the plexiglass tube, the upper part of the rubber stopper and the sealing cover are fixed together by threads, the height of the sealing cover is higher than the height of the threaded part of the rubber stopper, and the rubber stopper and the upper part of the plexiglass tube can be covered inside, and the sealing gasket is arranged between the sealing cover and the rubber stopper.

[0012] Further, preferably: the magnetic float water level controller includes a hollow support rod, a magnet and a float with a magnetic ring, the magnet is installed at the bottom of the hollow support rod, the float with the magnetic ring is an annular cylinder, which is sleeved on the hollow support rod, and the magnet is connected to the control system by a wire, and the wire is arranged in the hollow support rod.

[0013] Further, preferably: a second sealing mechanism is provided at one end of the hollow support rod extending out of the first sealing mechanism, the second sealing mechanism includes a threaded cover and a sealing gasket, the threaded cover is provided with a wire hole, the inner wall of the wire hole is provided with an elastic sealing layer, the threaded cover is threadedly fixed to the hollow support rod and the sealing gasket is pressed tightly.

[0014] Based on the traditional soil tensiometer, the present invention aims at the problem of artificial water replenishment and exhaust. The overall design adds a magnetic float water level controller (with a magnetic ring), a water storage mechanism, an automatic valve and other devices. The magnetic ring on the magnetic float water level controller is used to fit and open, and the water replenishment and exhaust switches are controlled at the same time. The exhaust port is opened to discharge the gas in the organic glass tube, thereby realizing the exhaust function. The water storage mechanism is at the top of the device, and the water flows into the vacuum glass tube from the pipeline by the gravity of the water, thereby realizing the water replenishment function until it is filled with water, the magnetic ring is opened, and the water replenishment and exhaust switches are controlled at the same time, thereby completing the automatic water replenishment and exhaust work. This whole process does not require manual operation, which not only saves labor costs, but also ensures the long-term monitoring accuracy of the equipment. This invention creates the most suitable soil moisture range for scientific drought prevention, waterlogging, water-saving irrigation and other crop planting, greatly reduces maintenance costs, and expands the scope of use.

[0015] The automatic exhaust and water replenishment function of the soil tensiometer of the present invention can ensure accurate monitoring of the moisture content in the soil and always keep it within the suitable growth range of plants. When used in conjunction with the intelligent irrigation system, it can effectively prevent plants from being harmed by drought or excessive irrigation, ensure that the growth rate and yield of plants are always in the optimal soil moisture environment, and achieve the purposes of saving water resources, reducing labor costs, and protecting the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0018] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0019] Figure 3 for Figure 2 A magnified view of part A;

[0020] In the figure, 1 is a circuit bracket, 2 is a pressure sensor, 3 is a water supply valve, 4 is a water supply pipe, 5 is a rubber plug, 6 is a hollow support rod, 7 is a float, 8 is a magnet, 9 is a water storage mechanism, 10 is a microcontroller, 11 is a circuit board, 12 is a transmission module, 13 is a top cover, 14 is a water storage bracket, 15 is a power module, 16 is an exhaust valve, 17 is an exhaust pipe, 18 is a pressure collection pipe, 19 is a fixing ring, 20 is a cylindrical upper part, 21 is a plexiglass tube, 22 is a conical lower part, 23 is a clay head, 24 is a wire, 25 is a sealing pad, 26 is a sealing cover, 27 is a threaded cover, 28 is an elastic sealing layer, and 29 is a sealing gasket. DETAILED DESCRIPTION

[0021] 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. Example 1

[0022] like Figure 1 As shown, a soil tensiometer with automatic exhaust and water replenishment includes a protection mechanism, a control system, a clay head 23, an organic glass tube 21 and a first sealing mechanism, wherein the organic glass tube 21 and the first sealing mechanism are arranged in the protection mechanism, the clay head 23 and the organic glass tube 21 are installed together, and the organic glass tube is sealed by the first sealing mechanism;

[0023] The function of the first sealing mechanism is to ensure the vacuum state of the upper organic glass tube 21. Generally, a rubber plug 5 is used. The rubber plug 5 has the following advantages: (1) The rubber plug 5 has good air tightness and very low air permeability, and can well prevent the penetration of gas or liquid; (2) The rubber plug 5 also has good high temperature resistance, ozone resistance and weather resistance, and can maintain its sealing performance in various environments; (3) The rubber plug 5 has high chemical stability and can resist corrosion from a variety of media; (4) The water absorption rate of the rubber plug 5 is small, which helps to maintain its original shape and size, thereby improving the sealing effect. Through holes are set on the rubber plug 5, which are a water supply hole, a water level hole, a pressure collection hole and an exhaust hole in sequence.

[0024] One end of the water supply pipe 4 passes through the water supply hole and extends into the organic glass tube 21, and the other end is connected to the water supply valve 3 and the water storage mechanism 9 in sequence; the magnetic float water level controller passes through the water level hole and extends into the organic glass tube 21; one end of the pressure collection pipe 18 passes through the pressure collection hole and extends into the organic glass tube 21, and the other end is installed with the pressure sensor 2; one end of the exhaust pipe 17 passes through the exhaust hole and extends into the organic glass tube 21, and the other end passes through the protection mechanism and is provided with the upper exhaust valve 16; the magnetic float water level controller, the water supply valve 3, the pressure sensor 2 and the exhaust valve 16 are respectively installed together with the control system.

[0025] The organic glass tube 21, the rubber stopper 5, the aperture of the inserted hose inside the rubber stopper 5, the water supply valve 3, and the exhaust valve 16 are all in an airtight sealed state, ensuring that the system is in a sealed state and reducing the error effect of air on the measurement result.

[0026] Pressure sensor 2 can measure gas or liquid pressure with a measurement range accuracy of -1~0Mpa, and is used to monitor soil negative pressure.

[0027] The exhaust valve 16 generally adopts a normally closed device with stable working performance and rapid response. When the organic glass tube 21 needs to be replenished with water, it can quickly exhaust and restore to normal water supply capacity in a short time. The magnetic float water level controller realizes automatic exhaust by monitoring and controlling the water level. The exhaust valve 16 should have a relatively high air closing pressure and have sufficient capacity to completely exhaust the air in the organic glass tube 21 to improve the water delivery efficiency.

[0028] The water supply valve 3 generally adopts a highly automated, stable and reliable electromagnetic device. The magnetic float water level controller realizes automatic water supply by monitoring and controlling the water level. When the water level drops to the magnetic ring, the valve core will automatically open to allow water to enter the organic glass tube 21, and continue to supply water until the water level is restored.

[0029] The working mechanism of the magnetic float water level controller is generally divided into two states: closed and open. When the water level leaves the magnetic ring, the exhaust valve 16 / water supply valve 3 is closed to stop exhaust / water supply. When the water level drops to the magnetic ring, the exhaust valve 16 / water supply valve 3 is opened to open the exhaust / water supply.

[0030] The water supply pipe 4, the pressure collection pipe 18 and the exhaust pipe 17 are generally made of elastic plastic hoses, which will not be deformed when passing through the rubber plug 5. Of course, water pipes made of other materials can also be used as long as the pipeline can pass through the rubber plug 5 with good sealing performance.

[0031] The magnetic float water level controller includes a hollow support rod 6, a magnet 8 and a float 7 with a magnetic ring. The magnet 8 is installed at the bottom of the hollow support rod 6. The float 7 with a magnetic ring is an annular cylinder, which is sleeved on the hollow support rod 6. The float 7 can slide on the hollow support rod 6 under the action of buoyancy and gravity. The magnet 8 is connected to the control system through a wire 24, and the wire 24 is arranged in the hollow support rod 6.

[0032] The control system includes a microcontroller 10, a transmission module 12 and a power module 15, and the microcontroller 10, the transmission module 12 and the power module 15 are connected to each other through a circuit board 11;

[0033] The microcontroller 10 is connected to the magnetic float water level controller, collects the water level information in the organic glass tube 21, and converts the water level information into a signal for controlling the water supply valve 3 and the exhaust valve 16;

[0034] The microcontroller 10 is connected to the water supply valve 3 and the exhaust valve 16 to control the switch of water supply and exhaust; the microcontroller 10 is connected to the pressure sensor 2 to collect the pressure value;

[0035] The protection mechanism includes a cylindrical upper part 20, a conical lower part 22 and a top cover 13. The top of the cylindrical upper part is provided with a water storage bracket 14, the water storage mechanism 9 is arranged on the water storage bracket 14, the middle and lower part is provided with a circuit bracket 1, and the control system is arranged on the electric stove; the aperture of the conical lower part 22 matches the organic glass tube 21, the conical lower part 22 is sealed, and the top cover 13 is threadedly connected with the cylindrical upper part 20 to seal the cylindrical upper part 20. The protection mechanism provides an installation position for the water storage mechanism 9 and the control system on the one hand, and can effectively protect the relevant equipment from environmental hazards on the other hand, and improve the service life and accuracy.

[0036] A fixing ring 19 is disposed inside the cylindrical upper portion 20 . The fixing ring 19 can more effectively and stably mount the protection mechanism and the organic glass tube 21 together.

[0037] The main structure of the water storage mechanism 9 is a water storage bag, which is made of environmentally friendly materials and is placed in the threaded cover 27 on the top of the protection mechanism to form a closed cavity. The water storage bag is provided with a screw-type cover that can be unscrewed for easy water replenishment. The lower end is connected to a water replenishment hose, which is connected to the organic glass tube 21 through the water replenishment valve 3.

[0038] The operation process of the soil tensiometer of this embodiment is as follows:

[0039] According to the drawings, assemble the soil tensiometer, adjust the stone removal state, drill holes, and fix the soil tensiometer of this embodiment in the soil to be measured.

[0040] At the beginning, the plexiglass tube 21 is filled with water, and the float 7 with the magnetic ring floats on the upper part of the plexiglass tube 21 under the action of buoyancy, and is separated from the magnet 8; the pressure sensor 2 measures the pressure in the plexiglass tube 21 in real time, and processes and analyzes the collected data, converts the collected humidity analog quantity into digital information, and sends it to the transmission module 12, and then the transmission module 12 sends the humidity data information to the remote terminal.

[0041] Through the interaction between the clay head 23 and the soil, the free water in the organic glass tube 21 contacts the soil water through the clay head 23, and the water potential balance is achieved after the exchange. When the soil becomes dry, the soil absorbs the moisture inside the organic glass tube 21 through the clay head 23, causing the pressure inside the organic glass tube 21 to change. The pressure sensor collects the pressure change data and converts the data into digital information representing the soil moisture, and sends it to the transmission module 12, and then the transmission module 12 sends the moisture data information to the remote terminal. During operation, the water content in the organic glass tube 21 will gradually decrease, and the float 7 will move downward under the action of gravity and magnetic force. When the float 7 and the magnet 8 are adsorbed together, the water level in the organic glass tube 21 will drop below the line, and a signal will be generated through the wire and transmitted to the microcontroller 10. The microcontroller 10 will open the water supply valve 3 and the exhaust valve 16 to replenish water and exhaust air. Water will enter the organic glass tube 21 under the action of gravity, and the gas in the organic glass tube 21 will be discharged through the exhaust pipe 17. The float 7 will overcome the gravity and magnetic force under the action of buoyancy, separate from the magnet 8, and move upward to achieve automatic water supply and exhaust. When the water supply and exhaust reach the set time, the water supply valve 3 and the exhaust valve 16 will be closed.

[0042] The invention has a simple structure and is easy to operate; it has a high degree of automation and does not require manual operation; it is stable and reliable and can replenish water according to actual needs; and it is easy to install and maintain. Example 2

[0043] like Figure 2 and 3 As shown, the soil tensiometer mainly uses the pressure change in the organic glass tube 21 to measure the moisture of the soil, so the sealing of the organic glass tube 21 mouth plays an important role.

[0044] It is basically the same as Example 1, except that:

[0045] The conical lower part 22 of the protection mechanism is provided with a conical sealing ring. The protection mechanism needs to prevent water vapor in the soil from entering. The contact sealing between the conical lower part 22 and the organic glass tube 21 alone has a small contact area and a poor sealing effect. The conical sealing ring can effectively increase the contact area and improve the sealing effect. In the specific setting, the height of the conical sealing ring needs to be set according to the actual situation, and it cannot be too high to cause difficulty in installing and fixing the protection mechanism.

[0046] Although the rubber plug 5 has a good sealing performance with the organic glass tube 21, the sealing effect of relying solely on the elasticity of rubber is not good, especially since the rubber plug 5 is provided with four through holes, which further reduces its sealing effect. To solve the above problem, in this embodiment: the first sealing mechanism includes a rubber plug 5, a sealing cover 26 and a sealing pad 25, the lower part of the rubber plug 5 is inserted into the organic glass tube 21, the upper part of the rubber plug 5 is fixed together with the sealing cover 26 by threads, the height of the sealing cover 26 is higher than the height of the threaded part of the rubber plug 5, and the rubber plug 5 and the upper part of the organic glass tube 21 can be covered therein, and the sealing pad 25 is arranged between the sealing cover 26 and the rubber plug 5.

[0047] In this embodiment, the rubber plug 5 is modified. The lower part is consistent with the traditional rubber plug 5, and the upper part is a combination of an external thread and a sealing cover 26 with an external thread. The pipeline in the through hole on the rubber plug 5 is further compressed, which can effectively improve the sealing box. At the same time, the thread + extrusion fixing method is more stable during use than the single extrusion fixing method, and it is not easy to cause the sealing performance to decrease.

[0048] The hollow support rod 6 of the magnetic float water level controller extends out of the organic glass tube 21, and the sealing problem needs to be considered. The traditional sealing relies on the installation seal between the magnet 8 and the lower part of the hollow support rod 6. The magnet 8 and the lower part of the hollow support rod 6 are immersed in water for a long time, which is easy to reduce the sealing problem, thereby affecting the overall sealing of the organic glass tube 21. In this embodiment, a second sealing mechanism is provided at one end of the hollow support rod 6 extending out of the first sealing mechanism. The second sealing mechanism includes a threaded cover 27 and a sealing gasket 29. The threaded cover 27 is provided with a wire hole, and the inner wall of the wire hole is provided with an elastic sealing layer 28. The threaded cover 27 is threadedly fixed to the hollow support rod 6, and the sealing gasket 29 is pressed tightly.

[0049] The combination of the threaded cover 27, the sealing gasket 29 and the elastic sealing layer 28 can effectively seal the gap between the hollow support rod 6 and the pressure collection hole and the gap between the wire and the threaded cover 27, thereby improving the overall sealing performance and thus increasing the service life.

[0050] After field experiments, the structure of this embodiment has more accurate measured data than the structure of Example 1, and the service life of the equipment is increased by more than 50%, which has a good effect.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A soil tensiometer with automatic exhaust and water replenishment, characterized in that: It includes a protection mechanism, a control system, a clay head, an organic glass tube and a first sealing mechanism, wherein the organic glass tube and the first sealing mechanism are arranged in the protection mechanism, the clay head is installed together with the organic glass tube, and the organic glass tube is sealed by the first sealing mechanism; the first sealing mechanism is provided with a water supply hole, a water level hole, a pressure collection hole and an exhaust hole; one end of the water supply pipe passes through the water supply hole and extends into the organic glass tube, and the other end is connected to the water supply valve and the water storage mechanism in sequence, and the magnetic float water level controller passes through the water level hole and extends into the organic glass tube; one end of the pressure collection pipe passes through the pressure collection hole and extends into the organic glass tube, and the other end is installed with a pressure sensor; one end of the exhaust pipe passes through the exhaust hole and extends into the organic glass tube, and the other end passes through the protection mechanism and is provided with an exhaust valve; the magnetic float water level controller, the water supply valve, the pressure sensor and the exhaust valve are respectively installed with the control system; The protection mechanism comprises a cylindrical upper part, a conical lower part and a top cover, a water storage bracket is arranged on the top of the cylindrical upper part, and a circuit bracket is arranged on the middle and lower part; the aperture of the conical lower part matches the organic glass tube to seal the conical lower part, and the top cover is threadedly connected to the cylindrical upper part to seal the cylindrical upper part; a fixing ring is arranged inside the cylindrical upper part; a conical sealing ring is arranged on the conical lower part; the control system comprises a microcontroller, a transmission module and a power supply module, the microcontroller, the transmission module and the power supply module are interconnected through a circuit board, the microcontroller is connected to the water supply valve and the exhaust valve to control the switch of water supply and exhaust; the microcontroller is connected to the pressure sensor to process and analyze the collected data; the microcontroller is connected to the magnetic float switch water level controller to collect the water level information in the organic glass tube, convert the water level information into a signal to control the water supply valve and the exhaust valve, and the water supply valve and the exhaust valve are opened and closed by the microcontroller, and the power supply module supplies power to the entire device; The magnetic float water level controller comprises a hollow support rod, a magnet and a float of a magnetic ring, wherein the magnet is installed at the bottom of the hollow support rod, the float of the magnetic ring is an annular cylinder, which is sleeved on the hollow support rod, and the magnet is connected to the control system by a wire, and the wire is arranged in the hollow support rod; The first sealing mechanism comprises a rubber stopper, a sealing cover and a sealing gasket, wherein the lower part of the rubber stopper is inserted into the organic glass tube, the upper part of the rubber stopper is fixed to the sealing cover by threads, the height of the sealing cover is higher than the height of the threaded part of the rubber stopper, and the rubber stopper and the upper part of the organic glass tube are covered therein, and the sealing gasket is arranged between the sealing cover and the rubber stopper; A second sealing mechanism is provided at one end of the hollow support rod extending out of the first sealing mechanism. The second sealing mechanism includes a threaded cover and a sealing gasket. The threaded cover is provided with a wire hole. The inner wall of the wire hole is provided with an elastic sealing layer. The threaded cover is threadedly fixed to the hollow support rod and the sealing gasket is pressed tightly.

Images