Hydrostatic bearing air supply system capable of continuously supplying air

Abstract

The invention relates to the technical field of bearings, and provides a hydrostatic bearing gas supply system capable of continuously supplying gas, the hydrostatic bearing gas supply system comprises a first gas supply subsystem and a second gas supply subsystem, the first gas supply subsystem comprises a first pipeline, a first valve, a first reaction mechanism, a second reaction mechanism and a degassing structure, the first reaction mechanism is internally provided with a reactant, and the second reaction mechanism is internally provided with a second pipeline; the first valve and the degassing structure are arranged on the first pipeline; the second gas supply subsystem is connected with the first gas supply subsystem; the first valve is used for being opened when the second gas supply subsystem breaks down, reactants in the first reaction mechanism enter the second reaction mechanism to be subjected to chemical reaction, water vapor and oxygen are generated, and the degassing structure is used for consuming oxygen and generating superheated steam. According to the hydrostatic bearing gas supply system capable of continuously supplying gas, high-temperature and high-pressure water vapor and oxygen are generated through chemical reaction, the oxygen is consumed through the degassing structure, a pure water vapor working medium is provided for the hydrostatic bearing, and normal operation of the hydrostatic bearing is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of bearing technology, and in particular to a hydrostatic bearing air supply system with sustainable air supply. Background Technology

[0002] Bearings are one of the core components of power machinery. Hydrostatic bearings have the characteristics of high load-bearing capacity and low friction loss. Compared with traditional hydrostatic oil-lubricated bearings, the oil supply system can be eliminated and mechanical losses can be reduced. In particular, when high-pressure gas inside the power system is used as the bearing working medium, the power system can be simplified and energy efficiency can be improved. However, when the gas supply system fails or the high-pressure gas is suddenly cut off, the load-bearing capacity of the hydrostatic bearing drops sharply, causing the rotor to collide with the hydrostatic bearing and causing damage to the hydrostatic bearing.

[0003] In this situation, a backup gas source needs to be configured. When the high-pressure gas supply to the system is interrupted, the system should immediately switch to the backup high-pressure gas source to maintain the bearing load for a period of time until the equipment stops operating. Generally, the bearing working fluid can be pre-pressurized and stored in a gas tank as a backup gas source. This method does not rely on complex real-time pressurization equipment and has good reliability. However, when using high-temperature, easily phase-change gas as the working fluid for hydrostatic bearings, the high-pressure working fluid in the gas tank will liquefy after dissipating heat to the outside, causing the temperature and pressure of the working fluid inside the tank to drop and turn into a liquid phase, thus failing to serve as a backup gas source. Based on this, providing a new hydrostatic bearing gas supply system has become an urgent problem to be solved in the industry. Summary of the Invention

[0004] This invention provides a hydrostatic bearing air supply system with sustainable air supply, which solves the defect in the prior art that hydrostatic bearings cannot operate normally when the air supply system suddenly fails.

[0005] This invention provides a sustainable gas supply system for a hydrostatic bearing, comprising: a first gas supply subsystem, including: a first pipeline, a first valve, a first reaction mechanism, a second reaction mechanism, and a degassing structure; the first reaction mechanism, the second reaction mechanism, and the first pipeline are connected sequentially; the first reaction mechanism contains reactants; the first valve and the degassing structure are disposed on the first pipeline, with the degassing structure located between the second reaction mechanism and the first valve; and a second gas supply subsystem connected to the first pipeline, with its two ends respectively used for connecting to a gas source and a hydrostatic bearing; wherein, the first valve is used to open in case of a failure in the second gas supply subsystem, allowing water vapor from the second gas supply subsystem to enter the second reaction mechanism; when the temperature in the second reaction mechanism reaches a first preset value, the first reaction mechanism and the second reaction mechanism are connected, and the reactants in the first reaction mechanism enter the second reaction mechanism to undergo a chemical reaction, generating water vapor and oxygen; the degassing structure is used to consume oxygen and generate superheated steam, which enters the hydrostatic bearing.

[0006] According to the present invention, a hydrostatic bearing gas supply system with sustainable gas supply is provided, wherein the first reaction mechanism includes: a first container containing reactants and filled with high-pressure gas, the first container being connected to the second reaction mechanism; and a gas supply assembly connected to the first container, the gas supply assembly being used to supply high-pressure gas to the first container.

[0007] According to the present invention, a hydrostatic bearing gas supply system for sustainable gas supply includes: a gas cylinder containing high-pressure gas; a second pipeline connected at both ends to the gas cylinder and the first container, and a second valve provided on the second pipeline.

[0008] According to the present invention, a hydrostatic bearing gas supply system with sustainable gas supply is provided, wherein the second reaction mechanism includes: a third pipeline connected to the first container, wherein a third valve is provided on the third pipeline; and a second container connected to the first pipeline and the third pipeline, wherein the second container is in a vacuum state, and the reactants and water vapor undergo a chemical reaction in the second container.

[0009] According to the present invention, a hydrostatic bearing gas supply system with sustainable gas supply is provided, wherein the first gas supply subsystem further includes: a temperature sensor disposed in the second container for detecting the temperature inside the second container; a controller for controlling the third valve to open when the temperature inside the second container reaches the first preset value, and the controller is further used to control the first valve to open when the second gas supply subsystem malfunctions.

[0010] According to the present invention, a hydrostatic bearing gas supply system with sustainable gas supply is provided, wherein the degassing structure is a metal hydride porous medium.

[0011] According to the present invention, a hydrostatic bearing gas supply system for sustainable gas supply further includes a first pressure sensor disposed in the first container, the first pressure sensor being used to detect the pressure in the first container; the controller is further used to control the second valve to open when the pressure in the first container is less than a second preset value.

[0012] According to the present invention, a hydrostatic bearing gas supply system with sustainable gas supply is provided, wherein the second gas supply subsystem includes: a fourth pipeline, the two ends of which are respectively used to connect to the hydrostatic bearing and a gas source, and the first pipeline is connected to the fourth pipeline; and a check valve disposed on the fourth pipeline.

[0013] According to the present invention, a hydrostatic bearing gas supply system with sustainable gas supply is provided. The second gas supply subsystem further includes a second pressure sensor, which is disposed in the fourth pipeline and located between the check valve and the hydrostatic bearing. The second pressure sensor is used to detect the pressure in the fourth pipeline. The controller is used to control the first valve to open when the pressure in the fourth pipeline is less than a third preset value.

[0014] According to the present invention, a hydrostatic bearing gas supply system for sustainable gas supply is provided, wherein the second gas supply subsystem further includes a third pressure sensor disposed in the fourth pipeline and located between the gas source and the check valve, the third pressure sensor being used to detect the pressure in the fourth pipeline; the controller is further used to control the third valve to close when the pressure in the fourth pipeline is greater than or equal to the third preset value.

[0015] The hydrostatic bearing gas supply system provided by this invention, by setting up a first pipeline, a first valve, a first reaction mechanism, a second reaction mechanism, and a degassing structure, can generate high-temperature and high-pressure water vapor and oxygen through chemical reaction when the second gas supply subsystem fails. The oxygen is then consumed by the degassing structure, providing pure water vapor as the working fluid for the hydrostatic bearing. This ensures the normal operation of the hydrostatic bearing and avoids damage to the hydrostatic bearing due to rotor collision when the second gas supply subsystem fails. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of the hydrostatic bearing air supply system with sustainable air supply provided by the present invention.

[0018] Figure label: 11. First pipeline; 12. Degassing structure; 13. First container; 14. Third pipeline; 15. Second container; 16. Gas cylinder; 17. Second pipeline; 21. Fourth pipeline; 22. Check valve; 23. Second pressure sensor; 24. Third pressure sensor; 30. Inlet pipe; 101. Rotor; 102. Hydrostatic bearing; 111. First valve; 131. Reactant; 132. First pressure sensor; 141. Third valve; 151. Temperature sensor; 171. Second valve. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] The following is combined with Figure 1 The present invention describes a hydrostatic bearing air supply system with sustainable air supply.

[0021] like Figure 1 As shown, in an embodiment of the present invention, the continuously supplying gas system for the hydrostatic bearing includes a first gas supply subsystem and a second gas supply subsystem. The second gas supply subsystem is used to supply gas to the hydrostatic bearing 102 during normal operation. The first gas supply subsystem is used to supply gas to the hydrostatic bearing 102 in the event of a failure of the second gas supply subsystem. In this embodiment, the working fluid of the hydrostatic bearing 102 is pure gaseous water vapor.

[0022] like Figure 1 As shown, the rotor 101 is sleeved inside the static pressure bearing 102, and there is a gap between the rotor 101 and the static pressure bearing 102. After the water vapor provided by the first air supply subsystem and the second air supply subsystem enters the static pressure bearing 102, it is discharged through the gap between the rotor 101 and the static pressure bearing 102.

[0023] In this embodiment, the first gas supply subsystem includes: a first pipeline 11, a first valve 111, a first reaction mechanism, a second reaction mechanism, and a degassing structure 12. The first reaction mechanism, the second reaction mechanism, and the first pipeline 11 are connected in sequence, and the first pipeline 11 is connected to the second gas supply subsystem. The first valve 111 and the degassing structure 12 are both disposed on the first pipeline 11, and the degassing structure 12 is located between the second reaction mechanism and the first valve 111. The first reaction mechanism contains reactant 131.

[0024] Specifically, when the second gas supply subsystem malfunctions or the gas supply is suddenly cut off, the first valve 111 is opened, and water vapor from the second gas supply subsystem enters the second reaction mechanism through the first pipeline 11. When the temperature inside the second reaction mechanism reaches a first preset value, the first reaction mechanism connects with the second reaction mechanism, and reactant 131 from the first reaction mechanism enters the second reaction mechanism. When reactant 131 comes into contact with water vapor, a violent chemical reaction occurs, producing high-temperature, high-pressure water vapor and oxygen. When the high-temperature, high-pressure water vapor and oxygen flow along the first pipeline 11 to the degassing structure 12, the oxygen undergoes a catalytic oxidation reaction with the metal hydride in the degassing structure, generating metal oxides and superheated steam. The metal oxides remain in the degassing structure 12, and the superheated steam pressure decreases, entering the hydrostatic bearing 102 as the working fluid during the operation of the hydrostatic bearing 102. This ensures that the hydrostatic bearing 102 can operate normally when the second gas supply subsystem malfunctions or the gas supply is cut off, preventing the rotor 101 from colliding with the hydrostatic bearing 102 and causing damage to the hydrostatic bearing 102.

[0025] In this embodiment, reactant 131 can be hydrogen peroxide. Hydrogen peroxide reacts violently with water vapor to generate high-temperature, high-pressure water vapor and oxygen.

[0026] The hydrostatic bearing gas supply system with sustainable gas supply provided in this embodiment of the invention, by setting up a first pipeline, a first valve, a first reaction mechanism, a second reaction mechanism and a degassing structure, can generate high-temperature and high-pressure water vapor and oxygen by chemical reaction when the second gas supply subsystem fails. The oxygen is consumed by the degassing structure, providing pure water vapor working medium for the hydrostatic bearing, ensuring the normal operation of the hydrostatic bearing, and avoiding damage to the hydrostatic bearing due to rotor collision when the second gas supply subsystem fails.

[0027] In an embodiment of the present invention, the degassing structure 12 is a metal hydride porous medium, in which the metal hydride can undergo a catalytic oxidation reaction with oxygen.

[0028] Specifically, when high-temperature, high-pressure steam and oxygen pass through the porous medium, the oxygen reacts with the metal hydride to generate stable metal oxides and steam, releasing heat. This further raises the temperature of the steam, forming superheated steam—pure gaseous steam. The steam's pressure decreases as it passes through the porous medium, creating a working fluid suitable for the operation of the hydrostatic bearing 102. The superheated steam then enters the hydrostatic bearing 102, supplying it with gas. Optionally, the metal hydride can be titanium hydride, magnesium hydride, etc.

[0029] In this embodiment, the volume and porosity of the porous medium are related to the amount of oxygen produced by the chemical reaction. The porous medium must be able to completely consume the oxygen produced by the chemical reaction within a set time, and must ensure that when high-temperature and high-pressure water vapor passes through the porous medium, the pressure of the water vapor can be reduced to the pressure range within which the hydrostatic bearing 102 operates normally.

[0030] like Figure 1 As shown, in an embodiment of the present invention, the first reaction mechanism includes a first container 13 and a gas supply assembly. The first container 13 contains reactant 131, and high-pressure gas is filled above the reactant 131. The first container 13 is connected to the second reaction mechanism. The gas supply assembly is connected to the first container 13 and is used to supply high-pressure gas to the first container 13.

[0031] Specifically, when the temperature inside the second reaction mechanism reaches the first preset value, i.e., the reaction temperature of hydrogen peroxide, the reactant 131 in the first container 13 enters the second reaction mechanism to undergo a chemical reaction. As the chemical reaction occurs, the pressure inside the second reaction mechanism increases. The purpose of filling the first container 13 with high-pressure gas is to ensure that the reactant 131 can still enter the second reaction mechanism under the action of the high-pressure gas when the pressure inside the second reaction mechanism increases. When the pressure inside the first container 13 decreases, the gas supply component supplies gas to the first container 13 to stabilize the pressure inside the first container 13, ensuring that the reactant 131 can enter the second reaction mechanism.

[0032] Furthermore, in an embodiment of the present invention, the gas supply assembly includes a gas cylinder 16 and a second pipeline 17. The gas cylinder 16 stores high-pressure gas, and the two ends of the second pipeline 17 are respectively connected to the gas cylinder 16 and the first container 13 to supply gas to the first container 13, thereby stabilizing the gas pressure at the top of the first container 13. A second valve 171 is provided on the second pipeline 17, which is used to control the opening and closing of the second pipeline 17.

[0033] like Figure 1As shown, in an embodiment of the present invention, the second reaction mechanism includes a third pipeline 14 and a second container 15. The third pipeline 14 is connected to the first container 13, and a third valve 141 is provided on the third pipeline 14. The second container 15 is connected to the first pipeline 11 and the third pipeline 14, and the reactant 131 and water vapor undergo a chemical reaction in the second container 15.

[0034] Specifically, before reactant 131 enters the second container 15, the second container 15 is in a vacuum state. When the second gas supply subsystem malfunctions, the first valve 111 opens, and water vapor from the second gas supply subsystem enters the second container 15 through the first pipeline 11. When the temperature inside the second container 15 reaches a first preset value, the third valve 141 opens, and hydrogen peroxide enters the second container 15 through the third pipeline 14. Hydrogen peroxide reacts violently with the water vapor, generating high-temperature, high-pressure water vapor and oxygen. The high-temperature, high-pressure water vapor and oxygen flow along the first pipeline 11. When passing through the degassing structure 12, the oxygen undergoes a catalytic oxidation reaction with the metal hydride within the degassing structure, generating metal oxides and water vapor. The catalytic oxidation reaction is exothermic, further increasing the temperature of the water vapor to form superheated steam. After passing through the degassing structure 12, the pressure of the water vapor decreases, forming a gaseous working fluid that satisfies the operation of the hydrostatic bearing 102. Superheated steam enters the hydrostatic bearing 102 as the working fluid during operation, ensuring normal operation of the hydrostatic bearing 102 in the event of a failure in the second air supply subsystem.

[0035] It should be noted that in this embodiment, the first valve 111 can be a switch valve, and the second valve 171 and the third valve 141 are check valves.

[0036] like Figure 1 As shown, in an embodiment of the present invention, the first gas supply subsystem further includes a temperature sensor 151 and a controller. The temperature sensor 151 is disposed inside the second container 15 and is used to detect the temperature inside the second container 15. The controller is used to control the third valve 141 to open when the temperature inside the second container 15 reaches a first preset value, and the controller is also used to control the first valve 111 to open when the second gas supply subsystem malfunctions.

[0037] Specifically, when the second gas supply subsystem malfunctions, the controller opens the first valve 111, allowing water vapor from the second gas supply subsystem to enter the second container 15 via the first pipeline 11. The temperature sensor 151 monitors the temperature inside the second container 15 in real time. When the temperature inside the second container 15 reaches a first preset value, i.e., the temperature required for the hydrogen peroxide reaction, the controller opens the third valve 141, allowing reactant 131 from the first container 13 to enter the second container 15 and undergo a chemical reaction upon contact with the water vapor.

[0038] like Figure 1As shown, in an embodiment of the present invention, the continuously supplying hydrostatic bearing gas supply system further includes a first pressure sensor 132, which is disposed in the first container 13. The first pressure sensor 132 is used to detect the pressure in the first container 13. When the pressure in the first container 13 is less than a second preset value, the controller controls the second valve 171 to open, and the gas cylinder 16 supplies gas to the first container 13. When the pressure in the first container 13 is greater than or equal to the second preset value, the controller controls the second valve 171 to close.

[0039] like Figure 1 As shown, in an embodiment of the present invention, the second air supply subsystem includes a fourth pipeline 21 and a check valve 22. The two ends of the fourth pipeline 21 are respectively used to connect to the hydrostatic bearing 102 and the air source, the first pipeline 11 is connected to the fourth pipeline 21, and the check valve 22 is disposed on the fourth pipeline 21.

[0040] Specifically, under normal circumstances, check valve 22 is open, and the gas source supplies gas to the static pressure bearing 102 via the fourth pipeline 21. When the fourth pipeline 21 malfunctions or the gas source is cut off, the pressure between check valve 22 and the static pressure bearing 102 in the fourth pipeline 21 is greater than the pressure between check valve 22 and the gas source in the fourth pipeline 21, and check valve 22 closes. Opening the first valve 111 allows water vapor in the fourth pipeline 21 to enter the second container 15 via the first pipeline 11.

[0041] like Figure 1 As shown, in an embodiment of the present invention, the second gas supply subsystem further includes a second pressure sensor 23, which is disposed in the fourth pipeline 21 and located between the check valve 22 and the static pressure bearing 102. For ease of description, the section of the pipeline between the gas source and the second check valve 22 in the fourth pipeline 21 is named the first section of the pipeline, and the section of the pipeline between the second check valve 22 and the static pressure bearing 102 is named the second section of the pipeline. The second pressure sensor 23 is used to detect the pressure in the second section of the pipeline. When the pressure in the second section of the pipeline is less than a third preset value, it indicates that the gas source is cut off, and the controller controls the first valve 111 to open so that the water vapor in the fourth pipeline 21 can enter the second container 15.

[0042] like Figure 1 As shown, in an embodiment of the present invention, the second gas supply subsystem further includes a third pressure sensor 24. The third pressure sensor 24 is disposed in the fourth pipeline 21 and located between the gas source and the check valve 22. That is, the third pressure sensor 24 is disposed within the first section of the pipeline. The third pressure sensor 24 is used to detect the pressure within the first section of the pipeline. When the gas supply is restored, the gas pressure within the first section of the pipeline gradually increases. When the pressure in the first pipeline reaches or exceeds the second preset value, the controller closes the second valve 141, and the first container 13 stops supplying reactant 131 to the second container 15, interrupting the reaction. The controller then closes the third valve 141, stopping the supply of reactant 131 from the first container 13 to the second container 15. At this time, the controller closes the first valve 111, and the check valve 22 opens under the pressure difference, allowing the gas source to supply gas to the static pressure bearing 102. During normal gas supply, reactant 131 can be added to the first container 13, the second container 15 can be cleaned, and the degassing structure 12 can be replaced, enabling online maintenance of the first gas supply subsystem without requiring system shutdown.

[0043] like Figure 1 As shown, in an embodiment of the present invention, the continuously supplying gas system for the static pressure bearing further includes an inlet pipe 30, which is connected to the first pipe 11, the fourth pipe 21, and the static pressure bearing 102. When the gas source supplies gas to the static pressure bearing 102, the water vapor supplied by the gas source enters the static pressure bearing 102 through the fourth pipe 21 and the inlet pipe 30; when the first gas supply subsystem supplies gas to the static pressure bearing 102, the water vapor enters the static pressure bearing 102 through the first pipe 11 and the inlet pipe 30.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these 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 the present invention.

Claims

1. A hydrostatic bearing air supply system with sustainable air supply, characterized in that, include: The first gas supply subsystem includes: a first pipeline, a first valve, a first reaction mechanism, a second reaction mechanism, and a degassing structure. The first reaction mechanism, the second reaction mechanism, and the first pipeline are connected in sequence. The first reaction mechanism contains reactants. The first valve and the degassing structure are disposed on the first pipeline, and the degassing structure is located between the second reaction mechanism and the first valve. The second air supply subsystem is connected to the first pipeline, and the two ends of the second air supply subsystem are respectively used to connect to the air source and the static pressure bearing. The first valve is used to open when the second gas supply subsystem fails, so that the water vapor from the second gas supply subsystem enters the second reaction mechanism. When the temperature in the second reaction mechanism reaches a first preset value, the first reaction mechanism is connected to the second reaction mechanism, and the reactants in the first reaction mechanism enter the second reaction mechanism to undergo a chemical reaction, generating water vapor and oxygen. The degassing structure is used to consume oxygen and generate superheated steam, and the superheated steam enters the hydrostatic bearing.

2. The hydrostatic bearing air supply system with sustainable air supply according to claim 1, characterized in that, The first reaction mechanism includes: A first container, containing reactants and filled with high-pressure gas, is connected to a second reaction mechanism. A gas supply assembly, connected to the first container, is used to supply high-pressure gas to the first container.

3. The hydrostatic bearing air supply system with sustainable air supply according to claim 2, characterized in that, The gas supply assembly includes: A gas cylinder containing high-pressure gas; The second pipeline is connected at both ends to the gas cylinder and the first container, respectively, and a second valve is provided on the second pipeline.

4. The hydrostatic bearing air supply system with sustainable air supply according to claim 3, characterized in that, The second reaction mechanism includes: A third pipeline is connected to the first container, and a third valve is provided on the third pipeline; The second container is connected to the first and third pipelines. The second container is under vacuum, and the reactants and water vapor undergo a chemical reaction inside the second container.

5. The hydrostatic bearing air supply system with sustainable air supply according to claim 4, characterized in that, The first gas supply subsystem also includes: A temperature sensor is installed inside the second container to detect the temperature inside the second container; The controller is used to control the third valve to open when the temperature inside the second container reaches the first preset value. The controller is also used to control the first valve to open when the second gas supply subsystem fails.

6. The hydrostatic bearing air supply system with sustainable air supply according to claim 1, characterized in that, The degassing structure is a metal hydride porous medium.

7. The hydrostatic bearing air supply system with sustainable air supply according to claim 5, characterized in that, It also includes a first pressure sensor, which is disposed inside the first container, and the first pressure sensor is used to detect the pressure inside the first container; The controller is also used to control the second valve to open when the pressure in the first container is less than a second preset value.

8. The hydrostatic bearing air supply system with sustainable air supply according to claim 5, characterized in that, The second gas supply subsystem includes: The fourth pipeline has two ends for connecting to the hydrostatic bearing and the air source, respectively, and the first pipeline is connected to the fourth pipeline. A check valve is installed in the fourth pipeline.

9. The hydrostatic bearing air supply system with sustainable air supply according to claim 8, characterized in that, The second air supply subsystem also includes a second pressure sensor, which is disposed in the fourth pipeline and located between the check valve and the hydrostatic bearing. The second pressure sensor is used to detect the pressure in the fourth pipeline. The controller is used to control the first valve to open when the pressure in the fourth pipeline is less than a third preset value.

10. The hydrostatic bearing air supply system with sustainable air supply according to claim 9, characterized in that, The second gas supply subsystem also includes a third pressure sensor, which is installed in the fourth pipeline and located between the gas source and the check valve. The third pressure sensor is used to detect the pressure in the fourth pipeline. The controller is also used to control the third valve to close when the pressure in the fourth pipeline is greater than or equal to the third preset value.

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