A hydraulic system with a dual-redundant relief valve

Abstract

The application discloses a kind of overflow valves with dual redundancy in hydraulic system, and the overflow valve includes: including shell, first overflow mechanism, second overflow mechanism, piston, piston spring, first inlet, second inlet;The first inlet and the second inlet are arranged on the bottom surface of the shell;A transverse piston cavity is arranged above the first inlet and the second inlet, the piston cavity is provided with a variable diameter at a stepped cavity, and the longitudinal cross-sectional area of the A side of the piston cavity is less than the longitudinal cross-sectional area of the B side;The A side of the piston cavity is communicated with the A side of the piston cavity above the first inlet, and the B side of the piston cavity is communicated with the B side of the piston cavity above the second inlet, and the B side of the piston cavity is provided with an internally threaded connection area;The A side of the piston cavity is provided with a longitudinal first overflow passage above, and the A side of the transverse piston cavity is communicated below the first overflow passage;The B side of the piston cavity is provided with a longitudinal second overflow passage above, and the B side of the transverse piston cavity is communicated below the second overflow passage;The application can effectively deal with measures to cause accidents.

Description

Technical Field

[0001] The present application relates to the technical field of hydraulic system applications, and in particular to a double-redundant overflow valve in a hydraulic system. Background Art

[0002] Safety relief valves are essential components in hydraulic systems, providing safety protection. When the hydraulic system pressure exceeds a specified threshold, the relief valve opens, discharging some of the hydraulic fluid into the hydraulic tank, thereby reducing the system pressure and preventing accidents caused by excessive pressure. However, if a relief valve malfunctions during hydraulic system operation, it can no longer guarantee the safety of the hydraulic system. Existing relief valves generally exhibit two fault states. Fault state 1: When the relief valve's main spool wears continuously, it can become sluggish or even become stuck in the closed position, preventing it from opening properly. This prevents the hydraulic system from properly unloading, leading to excessive system pressure and potentially serious consequences such as hydraulic line ruptures, hydraulic equipment, or actuator damage. Fault state 2: When the relief valve's main spool repeatedly operates, breaking or bending the return spring, preventing the valve from closing, the hydraulic system cannot maintain or limit pressure. Pressure cannot be fully applied to the terminal actuator, or cannot be applied at all. This disrupts the hydraulic system's normal operation and, in severe cases, can cause irreversible accidents.

[0003] When a hydraulic system is operating, if the relief valve has the above two faults, it will cause the hydraulic system to malfunction, the actuator to fail to bear the load, and even cause a major safety accident. Therefore, how to improve the safety margin of the relief valve and ensure the normal operation of the hydraulic system is an urgent problem to be solved. Summary of the Invention

[0004] The present application provides a double-redundant overflow valve in a hydraulic system, which can be used to solve the technical problem that after a overflow valve fails, it can only be replaced immediately, which affects the work progress.

[0005] The present application provides a double-redundant overflow valve in a hydraulic system, the overflow valve comprising:

[0006] It includes a housing, a first overflow mechanism, a second overflow mechanism, a piston, a piston spring, a piston end cover, a second end cover, a first liquid inlet, a second liquid inlet, a piston cavity, and a liquid outlet;

[0007] The shell is in a cubic shape, with a first liquid inlet and a second liquid inlet provided on the bottom surface. Both liquid inlets are oriented longitudinally, and the pressure at both locations is the same.

[0008] A lateral piston cavity is arranged above the first liquid inlet and the second liquid inlet, the piston cavity is provided with a variable diameter at a step cavity, the longitudinal cross-sectional area of the A side of the piston cavity is smaller than that of the B side; wherein, one side of the first liquid inlet is regarded as the A side; one side of the second liquid inlet is regarded as the B side;

[0009] The A side of the piston cavity is connected to the B side of the piston cavity above the first liquid inlet; the B side of the piston cavity is connected to the B side of the piston cavity above the second liquid inlet, and the B side of the piston cavity is provided with an internal thread connection area;

[0010] A longitudinal first overflow passage is arranged above the A side of the piston cavity, and the first overflow passage is connected to the A side of the lateral piston cavity below; a longitudinal second overflow passage is arranged above the B side of the piston cavity, and the second overflow passage is connected to the B side of the lateral piston cavity below, and the first overflow passage and the second overflow passage are provided with an internal thread connection area above;

[0011] A longitudinal liquid outlet is arranged above the shell, the liquid outlet is arranged between the first overflow passage and the second overflow passage, the liquid outlet is connected to the first overflow passage and the second overflow passage through a through-type lateral passage, and the lateral passage is provided with an internal thread connection area on both sides; the lateral passage is located above the piston cavity; the second end cover is provided with an external thread connection area, and the two second end covers are installed on the left and right sides of the lateral passage through threaded connection.

[0012] Further, the first overflow mechanism includes a first steel ball, a first spring, a first overflow passage, and a first end cover; wherein, the first steel ball and the first spring are installed in the first overflow passage, the first spring is located above the first steel ball, and the first end cover is located above the first spring; the first end cover is provided with an external thread and is connected to the internal thread above the first overflow passage; the central axis of the first steel ball, the first spring, and the first overflow passage coincides with the central axis; when the first spring is in a compressed state, the first steel ball blocks the first overflow passage under the action of the spring force.

[0013] Further, the second overflow mechanism includes a second steel ball, a second spring, a second overflow passage, and a first end cover; the second steel ball and the second spring are installed in the second overflow passage, the second spring is located above the second steel ball, and the first end cover is located above the second spring; the first end cover is provided with an external thread and is connected to the internal thread above the second overflow passage; the central axis of the second steel ball, the second spring, and the second overflow passage coincides with the central axis; when the second spring is in a compressed state, the second steel ball blocks the second overflow passage under the action of the spring force.

[0014] Further, the piston is a stepped piston, horizontally placed, with a variable diameter, the same shape as the inner shape of the horizontal cavity, the force receiving areas of the two ends of the piston are S1 and S2 respectively, the force receiving area S1 of the A side is smaller than the force receiving area S2 of the B side; the piston is installed in the horizontal piston cavity, the piston end cover is provided with external threads, connected with the internal threads of the piston cavity and arranged on the B side of the piston passage; the piston can move linearly along its axis in the cavity under the action of hydraulic pressure and spring force, used for switching between the first overflow mechanism and the second overflow mechanism.

[0015] Further, the overflow pressures of the two overflow mechanisms can be adjusted for pressure adjustment; the opening pressures of the two overflow mechanisms are the same.

[0016] Both the first overflow mechanism and the second overflow mechanism have independent overpressure overflow functions, and when the pressure is not over, the first steel ball and the second steel ball will block the first overflow passage and the second overflow passage under the action of the spring force.

[0017] Further, when the overflow valve is working normally, the liquid pressures p0 received by the two ends of the piston are the same.

[0018] At this time, the spring compression amount x1 satisfies the equation S1*p0+kx1=S2*p0, so the forces received by the two ends of the piston are the same at this time, the first overflow mechanism is put into work, and the second overflow mechanism does not work; wherein the spring elastic coefficient of the piston is k, and the compression amount x1 under the normal working condition of the hydraulic system; the force receiving areas of the two ends of the piston are S1 and S2 respectively.

[0019] Further, when the pressure of the hydraulic system exceeds the set opening pressure, the overpressure oil enters from the first liquid inlet, flows along the first overflow passage, opens the first steel ball and the first spring of the first overflow mechanism, and finally flows back to the tank from the liquid outlet along the horizontal passage to realize pressure relief.

[0020] Further, when in the first fault state, the system pressure exceeds the rated working pressure, the first overflow mechanism is blocked and cannot release the overpressure oil, and the system pressure continues to rise, at this time, p0 in the equation S1*p0+kx1=S2*p0 continues to increase.

[0021] When P0 increases to P1, since S1<S2, at this time the equation becomes S1*p1+kx1<S2*p1, the hydraulic pressure received by the B side of the piston is greater than the combined force of the hydraulic pressure received by the A side and the spring force, the piston moves to the A side under the action of the unbalanced force, when P1 increases to P2, under the action of the pressure P2, the piston continues to move to the A side to the position where the second overflow passage is just opened, the overpressure oil enters from the second liquid inlet, flows along the second overflow passage, opens the second steel ball and the second spring of the second overflow mechanism, and finally flows back to the tank from the liquid outlet along the horizontal passage to realize pressure relief, ensuring the safety of the system.

[0022] Further, when in the second failure state, the first spring breaks, at this time the first overflow mechanism is in the open state, the liquid pressure on the side of piston A drops to p3, the pressure on the side of piston B remains unchanged, still p0.

[0023] At this time, the equation S1*p0+kx1=S2*p0 becomes the inequality S1*p3+kx<S2*p0, then the hydraulic pressure on the side of piston B is greater than the combined force of the hydraulic pressure on the side of piston A and the spring force, the piston moves to the side A under the action of the unbalanced force until it moves to the limit position on the side A; at this time, the first overflow passage and the first liquid inlet are blocked by the piston, the first overflow mechanism is cut off, and the second overflow mechanism is put into the system; when the system pressure exceeds the set pressure, the overpressure oil enters from the second liquid inlet, flows along the second overflow passage, pushes open the second steel ball and the second spring of the second overflow mechanism, and finally flows back to the tank from the liquid outlet along the transverse passage to realize pressure relief, ensuring the safety of the system.

[0024] Further, if the piston spring breaks before the first spring, k in the equation S1*p0+kx1=S2*p0 becomes 0, and the equation becomes the inequality S1*p0<S2*p 0， The piston moves to the limit position on the side A under the action of the unbalanced force, and at this time the state changes to the working state in the second failure state.

[0025] When the system is working normally, only the first overflow mechanism participates in the work; when the first spring breaks or the first steel ball is stuck, the first overflow mechanism is automatically cut off from the hydraulic system, and then the second overflow mechanism is put into work to continue to realize the overpressure overflow function, ensuring the safety of the system; the two overflow mechanisms have a time sequence logical relationship and cannot be put into the system at the same time, so the safety margin of the hydraulic system is doubled, which is beneficial to improve the reliability of the hydraulic system; in addition, the present application has a simple structure and strong applicability, can be used in hydraulic systems with different functions, and does not need electric control, improving the reliability of the present application itself. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a cross-sectional view of the present application in the normal working state.

[0027] Figure 2 is a cross-sectional view of the present application in the first failure state.

[0028] Figure 3 is a cross-sectional view of the present application in the second failure state.

[0029] In the figure: (1) housing; (2) first spring; (3) first end cover; (4) second spring; (5) first steel ball; (6) second steel ball; (7) piston spring; (8) piston; (9) second end cover; (10) piston end cover; (21) liquid outlet; (22) first overflow passage; (23) second overflow passage; (24) first liquid inlet; (25) second liquid inlet; (26) transverse passage; (27) piston cavity. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present application more clear, the embodiments of the present application will be described in further detail below with reference to the drawings.

[0031] Firstly, the embodiments of the present application will be introduced below with reference to the drawings.

[0032] The present application is characterized in that: comprising a housing 1, a first overflow mechanism, a second overflow mechanism, a piston 8, a piston spring 7, a piston end cover 10, a second end cover 9, a first liquid inlet 24, a second liquid inlet 25, a piston cavity 27, a liquid outlet 21;

[0033] The housing 1 is in a cuboid shape, and a first liquid inlet 24 and a second liquid inlet 25 are arranged on the bottom surface. The two liquid inlets are both in a longitudinal direction, and the pressure at the two liquid inlets is the same.

[0034] A transverse piston cavity 27 is arranged above the first liquid inlet 24 and the second liquid inlet 25. The piston cavity 27 is a stepped cavity provided with a variable diameter. The longitudinal cross-sectional area of the A side of the piston cavity 27 is smaller than that of the B side. The side of the first liquid inlet 24 is regarded as the A side, and the side of the second liquid inlet 25 is regarded as the B side.

[0035] The first liquid inlet 24 is connected to the A side of the piston cavity 27, and the second liquid inlet 25 is connected to the B side of the piston cavity 27. The B side of the piston cavity 27 is provided with an internal thread connection area.

[0036] A longitudinal first overflow passage 22 is arranged above the A side of the piston cavity 27. The first overflow passage 22 is connected to the A side of the transverse piston cavity 27 below. A longitudinal second overflow passage 23 is arranged above the B side of the piston cavity 27. The second overflow passage 23 is connected to the B side of the transverse piston cavity 27 below. The first overflow passage 22 and the second overflow passage 23 are provided with an internal thread connection area above.

[0037] A longitudinal liquid outlet 21 is arranged above the shell 1, the liquid outlet 21 is arranged between the first overflow passage 22 and the second overflow passage 23, the liquid outlet 21 is communicated with the first overflow passage 22 and the second overflow passage 23 through a through horizontal passage 26, the horizontal passage 26 is provided with an internal thread connection area on both sides; the horizontal passage 26 is located above the piston cavity 27; the second end cover 9 is provided with an external thread connection area, and the two second end covers 9 are installed on the left and right sides of the horizontal passage 26 through threaded connection;

[0038] The first overflow mechanism includes a first steel ball 5, a first spring 2, a first overflow passage 22 and a first end cover 3; the first steel ball 5 and the first spring 2 are installed in the first overflow passage 22, the first spring 2 is located above the first steel ball 5, and the first end cover 3 is located above the first spring 2; the first end cover 3 is provided with an external thread and is connected with the internal thread above the first overflow passage; the central axes of the first steel ball 5, the first spring 2 and the first overflow passage 22 coincide; when the first spring 2 is in a compressed state, the first steel ball 5 blocks the first overflow passage 22 under the action of the spring force;

[0039] The second overflow mechanism includes a second steel ball 6, a second spring 4, a second overflow passage 23 and a first end cover 3; the second steel ball 6 and the second spring 4 are installed in the second overflow passage 23, the second spring 4 is located above the second steel ball 6, and the first end cover 3 is located above the second spring 4; the first end cover 3 is provided with an external thread and is connected with the internal thread above the second overflow passage 23; the central axes of the second steel ball 6, the second spring 4 and the second overflow passage 23 coincide; when the second spring 4 is in a compressed state, the second steel ball 6 blocks the second overflow passage 23 under the action of the spring force;

[0040] The overflow pressures of the two overflow mechanisms can be adjusted to adjust the pressure; the opening pressures of the two overflow mechanisms are the same.

[0041] The first overflow mechanism and the second overflow mechanism both have independent overpressure overflow functions; when the pressure is not over, the first steel ball 5 and the second steel ball 6 block the first overflow passage 22 and the second overflow passage 23 under the action of the spring force.

[0042] The piston 8 is a stepped piston and is horizontally placed, has a variable diameter, and has the same shape as the horizontal cavity; the force receiving areas of the two ends of the piston are S1 and S2 respectively, and the force receiving area S1 of the A side is smaller than the force receiving area S2 of the B side; the piston is installed in the horizontal piston cavity 27, the piston end cover 10 is provided with an external thread and is connected with the internal thread of the piston cavity 27 and is arranged on the B side of the piston passage; the piston 8 can move linearly along its own axis in the cavity under the action of the hydraulic pressure and the spring force, and is used for switching between the first overflow mechanism and the second overflow mechanism.

[0043] The inner surfaces of all passages are finely processed to improve the surface roughness level and reduce the flow resistance.

[0044] The shell 1, the piston 8, the first steel ball 5 and the second steel ball 6 are subjected to suitable surface treatment to improve wear resistance.

[0045] The first liquid inlet 24 and the second liquid inlet 25 are connected to the oil supply pipeline in a detachable manner to ensure good sealing performance at the connection; the pressure of the two liquid inlets is the same; the liquid outlet 21 is connected to the oil return pipeline in a detachable manner to ensure good sealing performance at the connection.

[0046] The threaded connection adopts sealing and threaded anti-loosening measures, and the mode is not limited. The working principle of the present application is as follows: when the present application is in a normal working state, the liquid pressure p0 on both ends of the piston 8 is the same. At this time, the spring compression amount x1 satisfies the equation S1*p0+kx1=S2*p0, so that the force on both ends of the piston 8 is the same at this time, and the piston 8 is in the position as shown in the figure, at this time, the first overflow mechanism is put into the system, and the second overflow mechanism is withdrawn from the system. Figure 1

[0047] When the hydraulic system pressure exceeds the set opening pressure, the overpressure oil enters from the first liquid inlet 24, flows along the first overflow passage 22, pushes open the first steel ball 5 and the first spring 2 of the first overflow mechanism, and finally flows back to the oil tank from the liquid outlet 21 along the transverse passage 26 to realize pressure relief and ensure system safety. The flow path of the overpressure oil inside the shell 1 is shown by arrows in the figure. Figure 1

[0048] When in the first fault state, the system pressure exceeds the rated working pressure, the first overflow mechanism is blocked and cannot release the overpressure oil, so the system pressure continues to increase, and in the equation S1*p0+kx1=S2*p0, p0 continues to increase; when P0 increases to P1, since S1<S2, at this time the equation becomes an inequality S1*p1+kx1<S2*p1, the hydraulic pressure on the B side of the piston 8 is greater than the combined force of the hydraulic pressure and the spring force on the A side, and the piston 8 moves to A under the action of the unbalanced force, when P1 increases to P2, the piston 8 continues to move to A to the position where the second overflow passage 23 is just opened, at this time the overpressure oil enters from the second liquid inlet 25, flows along the second overflow passage 23, pushes open the second steel ball 6 and the second spring 4 of the second overflow mechanism, and finally flows back to the oil tank from the liquid outlet 21 along the transverse passage 26 to realize pressure relief and ensure system safety; the flow path of the overpressure oil inside the shell 1 is shown by arrows in the figure. Figure 2

[0049] ​​​When in the second failure state, the first spring 2 breaks, at this time the first overflow mechanism is in the open state, the liquid pressure on the side of the piston 8A drops to p3, the pressure on the side of the piston B remains unchanged, still p0; at this time the equation S1*p0+kx1=S2*p0 becomes the inequality S1*p3+kx<S2*p0, then the hydraulic pressure on the side of the piston 8B is greater than the combined force of the hydraulic pressure on the side of the piston A and the spring force, and the piston moves to the side A under the action of the unbalanced force, when P1 increases to P2, at this time under the action of the pressure P2, the piston continues to move to the side A to the position where the first overflow passage 22 and the first liquid inlet 24 are blocked by the piston 8, the first overflow mechanism is cut off, and the second overflow mechanism is put into the system; when the system pressure exceeds the set pressure, the overpressure oil enters from the second liquid inlet 25, flows along the second overflow passage 23, pushes open the second steel ball 6 and the second spring 4 of the second overflow mechanism, and finally flows back to the tank from the liquid outlet 21 along the transverse passage 26 to realize pressure relief, ensuring the safety of the system; the flow path of the overpressure oil in the housing 1 is as shown by the arrows. Figure 3

[0050] In some cases, the piston spring 7 in the present application breaks before the first spring 2, then k in the equation S1*p0+kx1=S2*p0 becomes 0, and the equation becomes the inequality S1*p0<S2*p 0， The piston 8 moves to the limit position on the side A under the action of the unbalanced force, then the state changes to the working state in the second failure state, and does not affect the function of the present application.

[0051] The above-described embodiments of the present application do not constitute a limitation on the protection scope of the present application.​

Claims

1. A double-redundant overflow valve in a hydraulic system, characterized in that: The relief valve comprises: It comprises a housing (1), a first overflow mechanism, a second overflow mechanism, a piston (8), a piston spring (7), a piston end cover (10), a second end cover (9), a first liquid inlet (24), a second liquid inlet (25), a piston cavity (27), and a liquid outlet (21); The housing (1) is in a cubic shape, and a first liquid inlet (24) and a second liquid inlet (25) are provided on the bottom surface. Both liquid inlets are oriented in the longitudinal direction, and the pressure at the two locations is the same. A transverse piston cavity (27) is provided above the first liquid inlet (24) and the second liquid inlet (25). The piston cavity (27) is a stepped cavity with a reduced diameter. The longitudinal cross-sectional area of ​​the piston cavity (27) on the A side is smaller than the longitudinal cross-sectional area of ​​the piston cavity (27) on the B side. The side of the first liquid inlet (24) is considered as the A side; the side of the second liquid inlet (25) is considered as the B side. The upper portion of the first liquid inlet (24) is connected to the A side of the piston chamber (27), and the upper portion of the second liquid inlet (25) is connected to the B side of the piston chamber (27). The B side of the piston chamber (27) is provided with an internal thread connection area. A longitudinal first overflow passage (22) is provided above the A side of the piston chamber (27), and the lower portion of the first overflow passage (22) is connected to the A side of the transverse piston chamber (27); a longitudinal second overflow passage (23) is provided above the B side of the piston chamber (27), and the lower portion of the second overflow passage (23) is connected to the B side of the transverse piston chamber (27); an internal thread connection area is provided above the first overflow passage (22) and the second overflow passage (23); A longitudinal liquid outlet (21) is provided above the housing (1), and the liquid outlet (21) is provided between the first overflow passage (22) and the second overflow passage (23). The liquid outlet (21) is connected to the first overflow passage (22) and the second overflow passage (23) via a through-type transverse passage (26), and internal thread connection areas are provided on both sides of the transverse passage (26); the transverse passage (26) is located above the piston cavity (27); the second end cover (9) is provided with an external thread connection area, and the two second end covers (9) are installed on both sides of the transverse passage (26) through threaded connection; The first overflow mechanism comprises a first steel ball (5), a first spring (2), a first overflow passage (22), and a first end cover (3); wherein the first steel ball (5) and the first spring (2) are installed in the first overflow passage (22), the first spring (2) is located above the first steel ball (5), and the first end cover (3) is located above the first spring (2); the first end cover (3) is provided with an external thread and is connected to the internal thread above the first overflow passage; the central axial axes of the first steel ball (5), the first spring (2), and the first overflow passage (22) coincide with each other; when the first spring (2) is in a compressed state, the first steel ball (5) blocks the first overflow passage (22) under the action of the spring force; The second overflow mechanism comprises a second steel ball (6), a second spring (4), a second overflow passage (23), and a first end cover (3); the second steel ball (6) and the second spring (4) are installed in the second overflow passage (23), the second spring (4) is located above the second steel ball (6), the first end cover (3) is located above the second spring (4), and the first end cover (3) is provided with an external thread connected to the internal thread above the second overflow passage (23); the central axis of the second steel ball (6), the second spring (4), and the second overflow passage (23) coincides with the central axis; when the second spring (4) is in a compressed state, the second steel ball (6) blocks the second overflow passage (23) under the action of the spring force; The piston (8) is a stepped piston, placed horizontally, with a variable diameter, and the outer shape is the same as the inner shape of the horizontal cavity. The force-bearing areas at both ends of the piston are S1 and S2 respectively, and the force-bearing area S1 on the A side is smaller than the force-bearing area S2 on the B side; the piston is installed in the horizontal piston cavity (27), and the piston end cover (10) is provided with an external thread, which is connected to the internal thread of the piston cavity (27) and is arranged on the piston passage B side; the piston (8) can move linearly along its own axis in the cavity under the action of liquid pressure and spring force, and is used for switching between the first overflow mechanism and the second overflow mechanism.

2. The relief valve according to claim 1, characterized in that The overflow pressure of the two overflow mechanisms can be adjusted to adjust the pressure; the opening pressure of the two overflow mechanisms is the same; The first overflow mechanism and the second overflow mechanism both have independent overpressure overflow functions. When there is no overpressure, the first steel ball (5) and the second steel ball (6) block the first overflow passage (22) and the second overflow passage (23) under the action of the spring force.

3. The relief valve according to claim 1, characterized in that When the overflow valve works normally, the liquid pressure p0 at both ends of the piston (8) is the same; At this time, the spring compression amount is x1, which satisfies the equation S1*p0+kx1=S2*p0. At this time, the forces on both ends of the piston (8) are the same, and the first overflow mechanism is put into operation, while the second overflow mechanism is not operated. Among them, the elastic coefficient of the piston spring (7) is k, and the compression amount is x1 when the hydraulic system is working normally. The force areas on both ends of the piston are S1 and S2 respectively.

4. The relief valve according to claim 3, characterized in that When the pressure of the hydraulic system exceeds the set opening pressure, the overpressure oil enters from the first liquid inlet (24), flows along the first overflow passage (22), pushes open the first steel ball (5) and the first spring (2) of the first overflow mechanism, and finally flows back to the oil tank from the liquid outlet (21) along the transverse passage (26) to achieve pressure relief.

5. The relief valve according to claim 4, characterized in that: When in the first fault state, when the system pressure exceeds the rated working pressure, the first overflow mechanism is blocked and cannot release the overpressure oil, the system pressure continues to increase. At this time, p0 in the equation S1*p0+kx1=S2*p0 continues to increase; When P0 increases to P1, since S1 is less than S2, the equation becomes an inequality S1*p1+kx1<S2*p1. The liquid pressure on the B side of the piston (8) is greater than the resultant liquid pressure on the A side and the spring force. The piston (8) moves toward the A side under the action of the unbalanced force. When P1 continues to increase to P2, under the action of the pressure P2, the piston (8) continues to move toward the A side to a position where the second overflow passage (23) is just opened. At this time, the overpressure oil enters from the second liquid inlet (25), flows along the second overflow passage (23), pushes open the second steel ball (6) and the second spring (4) of the second overflow mechanism, and finally flows back to the oil tank from the liquid outlet (21) along the transverse passage (26) to achieve pressure relief, thereby ensuring system safety.

6. The relief valve according to claim 4, characterized in that When in the second fault state, the first spring (2) breaks, and the first overflow mechanism is in a normally open state. The liquid pressure on the piston (8) side A drops sharply to p3, while the pressure on the piston B side remains substantially unchanged, still at p0. At this time, the equation S1*p0+kx1=S2*p0 becomes the inequality S1*p3+kx<S2*p0, then the liquid pressure on the piston 8B side is greater than the resultant force of the liquid pressure on the A side and the spring force, and the piston moves toward A under the action of the unbalanced force until it moves to the extreme position on the A side; at this time, the first overflow passage (22) and the first liquid inlet (24) are blocked by the piston (8), the first overflow mechanism is cut off, and the second overflow mechanism is put into the system; when the system pressure exceeds the set pressure, the overpressure oil enters from the second liquid inlet (25), flows along the second overflow passage (23), pushes open the second steel ball (6) and the second spring (4) of the second overflow mechanism, and finally flows back to the oil tank from the liquid outlet (21) along the transverse passage (26) to achieve pressure relief, ensuring system safety.

7. The relief valve according to claim 6, characterized in that If the piston spring (7) breaks before the first spring (2), then k in the equation S1*p0+kx1=S2*p0 becomes 0, and the equation becomes the inequality S1*p0<S2*p 0， The piston (8) moves to the A side to the limit position under the action of the unbalanced force, and the state at this time is converted into the working state of the second fault state.

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