Bidirectional cartridge valve

Abstract

The invention relates to the technical field of hydraulic transmission control, in particular to a two-way cartridge valve which comprises a cartridge valve lower cavity A, a valve port, a cartridge valve upper cavity B, a main valve spring, a valve element B / B1 seal, a B1 control cavity, a valve element, a valve element A1 / B1 seal, an A1 control cavity, a valve element A / A1 seal, a balance cavity A + A and a pilot control assembly. The cartridge valve lower cavity A is communicated with the cartridge valve upper cavity B through a valve port, and the valve element can move in the axial direction to control opening and closing of the valve port; according to the scheme, the design of a traditional floating ring is canceled, the area difference between the balance cavity A + A and the lower cavity A of the cartridge valve is adopted to form closing resultant force, meanwhile, the symmetrical conical structure of the valve port is optimized, two-way flowing of liquid flow is achieved, and the overflowing capacity is improved by more than 50%; under the condition of 5 bar pressure drop, the overflowing capacity reaches 150% of that of an international standard cartridge valve, the problem that a traditional cartridge valve is optimal in one-way overflowing due to the fact that the overflowing area is sacrificed by a floating ring is solved, and the two-way efficient circulation requirement of a high-pressure large-flow system is met.

Description

Technical Field

[0001] This invention relates to the field of hydraulic transmission control technology, and in particular to a bidirectional cartridge valve. Background Technology

[0002] Cartridge valves, also known as logic valves, cone valves, or two-way valves, have been used for over 50 years. The hydraulic industry manufactures these components according to the installation and connection dimensions conforming to international standard cartridge valves (DIN ISO 7368). Rexroth (Germany), ATOS (Italy), Vickers (USA), and Yuken (Japan) all have sales markets in China. A number of large-scale hydraulic companies producing logic valves have also emerged in China, such as Beijing Huade, Jiangsu Hengli, Shaanxi Duolun, Yuken (Yuci), Shandong Taifeng, and Taiwan (Tengen).

[0003] Traditional cartridge valves, due to their floating ring design, must sacrifice flow area. Companies like Rexroth in Germany have floating ring area ratios as high as 50%, while other hydraulic companies have floating ring area ratios between 30% and 50%. This floating ring area ratio creates an area difference between the upper and lower chambers, further forming a pressure drop at the valve port and establishing the dynamic conditions for the valve core to open and close. However, the force on the valve core is also affected by many factors such as pump source pressure, load pressure, return oil pressure, and unloading oil pressure. Therefore, a shuttle valve and a check valve pilot control unit are added, which complicates the cartridge valve control cover and reduces the flow capacity of the cartridge valve to "help" the valve core to open and close.

[0004] Oil Gear Corporation of the United States produces a type of cartridge valve with different cap sizes. Unfortunately, this type of cartridge valve does not conform to international standards. It achieves faster closing and more reliable closing control by increasing the outer dimensions of the valve cup, valve cavity, and valve body. However, due to the size difference between cartridge valves of the same specification, it is difficult to promote and apply it.

[0005] To address this, the present invention proposes a bidirectional cartridge valve that achieves bidirectional flow, improved flow capacity, and a combination of structural simplification and compatibility by eliminating the float ring, designing a balance chamber, and using a stepped seal. Summary of the Invention

[0006] Technical problems solved: traditional cartridge valves suffer from poor flow rate and complex control issues.

[0007] To address the shortcomings of existing technologies, this invention provides a bidirectional cartridge valve, thereby solving the technical problems mentioned in the background section.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A bidirectional cartridge valve includes a lower chamber A, a valve port, an upper chamber B, a main valve spring, a valve core B / B1 seal, a B1 control chamber, a valve core, a valve core A1 / B1 seal, an A1 control chamber, a valve core A / A1 seal, a balance chamber A+A, and a pilot control assembly. The lower chamber A and the upper chamber B are connected via the valve port. The valve core is axially movable to control the opening and closing of the valve port, allowing bidirectional flow of fluid between the lower chamber A and the upper chamber B. The balance chamber A+A surrounds the lower chamber A, and the hydraulic action area of ​​the balance chamber A+A is larger than that of the lower chamber A. The valve core eliminates the traditional float ring design, unifying the terms "inlet valve," "outlet valve," "internal flow valve," and "external flow valve."

[0010] In one possible implementation, valve core A / A1 seal, valve core A1 / B1 seal, and valve core B / B1 seal are sequentially arranged on the outer side of the valve core; valve core A / A1 seal isolates the lower chamber A of the cartridge valve from the control chamber A1, valve core A1 / B1 seal isolates the control chamber A1 from the control chamber B1, and valve core B / B1 seal isolates the upper chamber B of the cartridge valve from the control chamber B1.

[0011] In one possible implementation, the pilot control assembly includes a pilot proportional cone valve BB spring, a pilot proportional cone valve control port BB, a control high pressure P, a pilot proportional cone valve T port, a pilot proportional cone valve AA spring, and a pilot proportional cone valve control port AA; the pilot proportional cone valve control port AA is connected to the A1 control chamber, the pilot proportional cone valve control port BB is connected to the B1 control chamber, the control high pressure P provides a pressure oil source for the pilot control assembly, and the pilot proportional cone valve T port is used for oil return.

[0012] In one possible implementation, the pilot control component is compatible with a 2-position 4-way solenoid directional valve, a 2-position 4-way proportional directional valve, or a pilot proportional cone valve, and controls the valve core movement by adjusting the pressure difference between the A1 control chamber and the B1 control chamber through an external control signal.

[0013] In one possible implementation, the hydraulic action area of ​​the balance chamber A+A is 1.2-1.5 times that of the hydraulic action area of ​​the lower chamber A of the cartridge valve.

[0014] In one possible implementation, the main valve spring is sleeved on the outside of the valve core to ensure that the valve core is in a closed state when the hydraulic system is stopped or powered off.

[0015] Beneficial effects compared to existing technologies:

[0016] 1. In this solution, by eliminating the traditional float ring design and using the area difference between the balanced chamber A+A and the lower chamber A of the cartridge valve to form a closing force, and simultaneously optimizing the symmetrical conical structure of the valve orifice, bidirectional flow of liquid is achieved and the flow capacity is increased by more than 50%. Under a pressure drop of 5 bar, the flow capacity reaches 150% of the international standard cartridge valve, solving the problem of traditional cartridge valves sacrificing flow area and achieving optimal unidirectional flow due to the float ring, thus meeting the bidirectional and efficient flow requirements of high-pressure, high-flow systems.

[0017] 2. In this solution, a stepped isolation design using valve core B / B1 sealing, valve core A1 / B1 sealing, and valve core A / A1 sealing, combined with external control pilot logic replacing the internal control shuttle valve, simplifies the control structure and improves reliability. It eliminates the complex "internal control, internal discharge" and "external control, external discharge" control methods of traditional cartridge valves, simplifies the control cover and channels, reduces potential failure points, and ensures consistent bidirectional sealing performance with a leakage rate ≤0.1mL / min@31.5MPa, making it suitable for various media such as oil and water.

[0018] 3. In this solution, by adopting the external installation dimensions that conform to the international standard DIN ISO 7368, and shortening the valve core opening and closing time (20%-30% shorter than traditional valves), both compatibility and response speed are achieved. It can directly replace existing standard cartridge valves, which is convenient for promotion and application. At the same time, it can reduce hydraulic shock and water hammer through a smooth opening and closing process, thereby improving the stability of the hydraulic system. It is suitable for industrial scenarios with high-frequency response and bidirectional load. Attached Figure Description

[0019] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0020] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0021] Legend: 1. Lower chamber A of cartridge valve; 2. Valve port; 3. Upper chamber B of cartridge valve; 4. Main valve spring; 5. Valve core B / B1 seal; 6. B1 control chamber; 7. Valve core; 8. Valve core A1 / B1 seal; 9. A1 control chamber; 10. Valve core A / A1 seal; 11. Balance chamber A+A; 12. Pilot proportional cone valve BB spring; 13. Pilot proportional cone valve control port BB; 14. Control high pressure P; 15. Pilot proportional cone valve T port; 16. Pilot proportional cone valve AA spring; 17. Pilot proportional cone valve control port AA. Detailed Implementation

[0022] Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention can also be implemented in various different forms, and therefore the present invention is not limited to the embodiments described below. In addition, for the purpose of more clearly describing the present invention, parts not connected to the invention will be omitted from the drawings.

[0023] The technical solution in this application embodiment is to solve the problems mentioned in the background art, and the overall idea is as follows:

[0024] Example:

[0025] Please refer to Figure 1 As shown in the figure, this embodiment introduces a specific structure of a bidirectional cartridge valve. The bidirectional cartridge valve adopts a modular design, and the overall structure is symmetrically distributed along the axial direction, from top to bottom (with... Figure 1 Based on the orientation, it can be divided into two main parts: the main valve chamber assembly and the pilot control assembly. Each component works together through precision machining and sealing design.

[0026] I. Overall Structure and Positional Connections

[0027] (I) Core Valve Body Structure Layout

[0028] Main valve chamber assembly (core fluid control area):

[0029] The lower chamber A1 of the cartridge valve is located at the bottom of the valve body and is directly connected to the low-pressure side of the external hydraulic system or the return oil circuit of the actuator. Its inner port is connected to the valve port 2 (the valve port 2 is a conical sealing surface), and it cooperates with the conical surface structure of the valve core 7 to form a flow switch node. The upper chamber B3 of the cartridge valve is located at the top of the valve body and is connected to the high-pressure side of the external hydraulic system or the inlet oil circuit of the actuator. It is isolated from the B1 control chamber 6 by the valve core B / B1 seal 5.

[0030] The valve core 7 is the core moving part of the main valve chamber. It has a stepped cylindrical structure that runs through the entire main valve chamber. Its lower conical surface cooperates with the valve port 2 to achieve a seal. The valve core A / A1 seal 10, valve core A1 / B1 seal 8, and valve core B / B1 seal 5 are arranged sequentially on the outer side of the middle part, dividing the main valve chamber into three independent chambers (the lower chamber A1 of the cartridge valve and the A1 control chamber 9 are isolated by the valve core A / A1 seal 10), the A1 control chamber 9 and the B1 control chamber 6 are isolated by the valve core A1 / B1 seal 8, and the B1 control chamber 6 and the upper chamber B3 of the cartridge valve are isolated by the valve core B / B1 seal 5.

[0031] The balance chamber A+A11 surrounds the lower outer side of the valve core 7, forming an annular cavity structure. Its hydraulic action area is designed to be larger than the action area of ​​the lower chamber A1 of the cartridge valve. It is connected to the lower chamber A1 of the cartridge valve through an internal oil circuit, forming the basic force source for valve core closure. The main valve spring 4 is sleeved on the outer side of the middle part of the valve core 7, with its upper end abutting against the shoulder of the valve body and its lower end pressing against the boss of the valve core 7, always providing downward preload force.

[0032] Pilot control assembly (valve spool drive control area):

[0033] Located above the main valve chamber, it is connected to the main valve chamber through an internal oil circuit; it controls the high-pressure P14 as a pilot power source, which is connected to the inlet of the pilot proportional cone valve through an external pipeline, and its pressure is usually 1.2-1.5 times the maximum working pressure of the system.

[0034] The pilot proportional cone valve control port AA17 is connected to the A1 control chamber 9 through an internal channel, and the pilot proportional cone valve control port BB13 is connected to the B1 control chamber 6. The return oil of both is connected to the system return oil tank through the pilot proportional cone valve T port 15. The pilot proportional cone valve AA spring 16 and the pilot proportional cone valve BB spring 12 are respectively installed on the outside of the valve stem of the two pilot cone valves to provide reset force. Their stiffness is designed according to the system working pressure (usually 5-10 N / mm).

[0035] (II) Sealing and Isolation Design

[0036] All seals are made of polyurethane or fluororubber, with the appropriate formula selected based on the type of medium (oil or water).

[0037] The valve core A / A1 seal 10 has a U-shaped ring structure, with the inner side fitting the outer circle of the valve core 7 and the outer side embedded in the valve body groove to prevent liquid from leaking from the lower chamber A1 of the cartridge valve to the A1 control chamber 9.

[0038] The valve core A1 / B1 seal 8 is a combined seal (including an O-ring and a retaining ring), which isolates the A1 control chamber 9 and the B1 control chamber 6 to prevent mutual interference of control pressures;

[0039] The valve core B / B1 seal 5 has a Y-ring structure, which is adapted to the high-pressure environment of the B1 control chamber 6 and prevents liquid cross-contamination between the upper chamber B3 of the cartridge valve and the B1 control chamber 6.

[0040] II. Mechanism of Component Collaboration

[0041] (I) Core Force Balance System

[0042] The bidirectional cartridge valve breaks away from the traditional reliance on floating rings by designing the area of ​​the balance chamber and control chamber, thus constructing a completely new force balance logic:

[0043] The hydraulic action area (S1) of the balance chamber A+A11 is greater than the hydraulic action area (S2) of the lower chamber A1 of the cartridge valve, and S1 = 1.2-1.5S2 (optimized according to the system pressure level); when there is no external control pressure, the pressure oil (P) in the lower chamber A1 of the cartridge valve a The pressure oil (with P) acting on S2 balances chamber A+A11. a An equal force (F = P) acts on S1, forming an upward resultant force (F = P). a×(S1-S2)), push the valve core 7 to press against the valve port 2, and achieve natural closure;

[0044] The preload force (F_spring) of the main valve spring 4 further enhances the reliability of the shut-off. Its design value must cover the residual pressure effect when the system is shut down, and ensure that the valve core 7 is leak-free in the power failure / shutdown state.

[0045] Control chamber A1 9 and control chamber B1 6 drive valve core 7 to move through a pressure difference: When control chamber A1 9 is connected to the control high pressure P14, it generates a downward thrust (F). a1 =P×S a1 When control chamber 6 of B1 is connected to control high voltage P14, it generates an upward thrust (F). β1 =P×S β1 ), via F a1 With F β1 The difference controls the opening and closing degree of valve core 7;

[0046] (II) Synergistic Effect of Sealing Systems

[0047] Three seals form a "stepped isolation":

[0048] The valve core A / A1 seal 10 prevents low-pressure oil in the lower chamber A1 of the cartridge valve from entering the A1 control chamber 9, thus avoiding interference with the control pressure accuracy;

[0049] Valve core A1 / B1 seal 8 isolates control chamber A1 9 from control chamber B1 6, ensuring that the pressure of the two control chambers can be adjusted independently;

[0050] The valve core B / B1 seal 5 prevents high-pressure oil from entering the upper chamber B3 of the cartridge valve into the control chamber B1 6, ensuring that the pressure in the control chamber is not affected by fluctuations in the main oil circuit.

[0051] The three components work together to make the main valve chamber and the control chamber completely independent, laying the foundation for "bidirectional flow" - traditional cartridge valves cause a conflict between sealing and flow area due to the floating ring design, while this design achieves bidirectional sealing without sacrificing flow capacity through the structured layout of the sealing components.

[0052] (III) Driving logic of pilot control components

[0053] The pilot-operated proportional cone valve acts as a "pressure-to-force conversion element," controlling the movement of the valve core 7 via electromagnetic force.

[0054] The AA spring 16 and BB spring 12 of the pilot proportional cone valve are reset elements. Their stiffness determines the opening pressure threshold of the pilot valve (usually the stiffness of the AA spring is slightly greater than that of the BB spring to ensure priority closure when power is off).

[0055] Control port AA17 is linked with control chamber 9 of A1, and control port BB13 is linked with control chamber 6 of B1. The on / off state of the two control ports is adjusted by electromagnetic force to realize the switching of high pressure P14 and return oil pilot proportional cone valve T port 15.

[0056] It is compatible with various pilot valve types (2-position 4-way solenoid directional valve, proportional directional valve, etc.). The core is to adjust the pressure difference of the A1 / B1 control chamber through external control signals, replacing the complex logic of the traditional "internal control shuttle valve".

[0057] III. Detailed Explanation of Valve Body Working Process

[0058] (a) Off state (initial / power off state)

[0059] When there is no controlled pressure:

[0060] The pressure oil in the lower chamber A1 of the cartridge valve simultaneously enters the balance chamber A+A11. Since S1>S2, the upward resultant force pushes the valve core 7 to press against the valve port 2. The preload of the main valve spring 4 is superimposed on this resultant force to ensure that the valve port 2 is completely sealed. At this time, the upper chamber B3 of the cartridge valve is completely isolated from the lower chamber A1 of the cartridge valve, and no liquid flows through.

[0061] When the pilot valve is de-energized:

[0062] The high pressure P14 enters the A1 control chamber 9 through the pilot proportional cone valve control port AA17, generating a downward pressure F. a1 =P×S a1 The combined force of the main valve spring and the balance chamber further enhances the closing reliability of the valve core 7. At this time, the B1 control chamber 6 returns oil through the pilot proportional cone valve T port 15, without upward thrust, and the valve core 7 is in a "rigidly closed" state, which is suitable for system pressure holding or emergency shutdown scenarios.

[0063] (II) Opening process (pilot valve energized state)

[0064] Electromagnetic force driven stage:

[0065] After the pilot proportional cone valve solenoid is energized, the electromagnetic force overcomes the preload of spring 16 AA, connecting the pilot proportional cone valve control port AA17 with the pilot proportional cone valve T port 15—the oil in control chamber 9 of A1 returns to the oil tank through the pilot proportional cone valve T port 15, F a1 The electromagnetic force gradually disappears; simultaneously, the electromagnetic force compresses the BB spring 12, controlling the high voltage P14 to enter the B1 control cavity 6 through the control port BB13, generating an upward thrust F. β1 =P×S β1 ;

[0066] Valve core movement stage:

[0067] When F β1When the combined force of the balancing chamber and the spring force of the main valve are greater than the combined force of the balancing chamber and the spring force of the main valve, the valve core 7 moves upward and the valve port 2 gradually opens. The liquid can flow from the lower chamber A1 of the cartridge valve to the upper chamber B3 of the cartridge valve (forward) or from the upper chamber B3 of the cartridge valve to the lower chamber A1 of the cartridge valve (reverse). The specific direction is determined by the pressure difference between the lower chamber A1 of the cartridge valve and the upper chamber B3 of the cartridge valve (the side with higher pressure flows to the side with lower pressure).

[0068] Because the floating ring is eliminated, the flow area of ​​valve port 2 is significantly increased (the equivalent area is 55% larger than that of a conventional cartridge valve). Under a pressure drop of 5 bar, the flow rate can reach 150% of that of a conventional valve, and the flow capacity is consistent in both directions (the reverse flow capacity of a conventional valve is reduced by 30%-50% due to structural limitations).

[0069] Flow regulation phase:

[0070] If a proportional directional valve is used as the pilot valve, the pressure increment rate of control chamber 6 in B1 can be controlled by adjusting the magnitude of the electromagnetic force (0-100% linear output). When the pressure rises in a curve, the valve core 7 opens at a gradually faster speed, avoiding the hydraulic shock caused by the "sudden opening" of the traditional valve (the shock pressure can be reduced to less than 1 / 3 of that of the traditional valve).

[0071] (III) Shutdown process (pilot valve de-energization transition)

[0072] Electromagnetic force decay stage:

[0073] When the pilot valve solenoid is de-energized, the electromagnetic force gradually decreases, the pilot proportional cone valve AA spring 16 resets and pushes the pilot valve core to close the pilot proportional cone valve control port AA17, and at the same time the pilot proportional cone valve BB spring 12 resets and closes the pilot proportional cone valve control port BB13; the control high pressure P14 re-enters the A1 control chamber 9 through the pilot proportional cone valve control port AA17, and the oil in the B1 control chamber 6 flows to the pilot proportional cone valve T port 15 through the pilot proportional cone valve control port BB13;

[0074] Valve core reset stage:

[0075] The pressure in control chamber 9 of A1 gradually increases, F a1 Increase and exceed the residual thrust of control chamber 6 in B1, valve core 7 in F a1 Under the combined action of the main valve spring force and the balance chamber force, the valve moves downward and the valve port 2 gradually closes. Because the pressure change decreases in a curved manner, the closing process of the valve core 7 is smooth (the closing time is shortened by 20%-30% compared to traditional valves), avoiding water hammer caused by sudden cutoff of liquid flow.

[0076] (iv) The principle of bidirectional flow

[0077] Traditional cartridge valves, due to their float ring design, achieve "optimal unidirectional flow," resulting in a sharp reduction in flow area during reverse flow. This design, however, achieves bidirectional equivalent flow through the following innovations:

[0078] The valve port 2 adopts a symmetrical conical structure. The flow paths on the lower chamber A1 and upper chamber B2 of the cartridge valve are completely symmetrical, with no difference in the "liquid inlet / liquid outlet" structure.

[0079] The force design of the balance chamber A+A11 is only related to the valve core closing and is independent of the flow direction. Regardless of whether the flow is A→B or B→A, the resultant force of the balance chamber always ensures that the valve core is closed when there is no control pressure, without affecting the switching of the flow direction.

[0080] The sealing components (valve core B / B1 seal 5, valve core A1 / B1 seal 8, valve core A / A1 seal 10) adopt a bidirectional sealing structure (both Y-rings and U-rings are bidirectional in action), and the sealing performance is consistent under both positive and reverse pressure (leakage is ≤0.1mL / min@31.5MPa).

[0081] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A bidirectional cartridge valve, characterized in that, Includes a cartridge valve lower chamber A (1), valve port (2), cartridge valve upper chamber B (3), main valve spring (4), valve core B / B1 seal (5), B1 control chamber (6), valve core (7), valve core A1 / B1 seal (8), A1 control chamber (9), valve core A / A1 seal (10), balance chamber A+A (11), and pilot control assembly; the cartridge valve lower chamber A (1) and the cartridge valve upper chamber B (3) are connected through the valve port (2), and the valve core (7) The valve core (7) can move axially to control the opening and closing of the valve port (2), allowing bidirectional flow of liquid between the lower chamber A (1) and the upper chamber B (3) of the cartridge valve; the balance chamber A+A (11) surrounds the outside of the lower chamber A (1) of the cartridge valve, and the hydraulic action area of ​​the balance chamber A+A (11) is greater than the hydraulic action area of ​​the lower chamber A (1) of the cartridge valve; the valve core (7) eliminates the traditional floating ring design and unifies the "inlet valve", "outlet valve", "internal flow valve" and "external flow valve".

2. A bidirectional cartridge valve as described in claim 1, characterized in that, The valve core (7) is provided with valve core A / A1 seal (10), valve core A1 / B1 seal (8), and valve core B / B1 seal (5) in sequence on the outside. The valve core A / A1 seal (10) isolates the lower chamber A (1) of the cartridge valve from the A1 control chamber (9), the valve core A1 / B1 seal (8) isolates the A1 control chamber (9) from the B1 control chamber (6), and the valve core B / B1 seal (5) isolates the upper chamber B (3) of the cartridge valve from the B1 control chamber (6).

3. A bidirectional cartridge valve as described in claim 1, characterized in that, The pilot control assembly includes a pilot proportional cone valve BB spring (12), a pilot proportional cone valve control port BB (13), a control high pressure P (14), a pilot proportional cone valve T port (15), a pilot proportional cone valve AA spring (16), and a pilot proportional cone valve control port AA (17). The pilot proportional cone valve control port AA (17) is connected to the A1 control chamber (9), the pilot proportional cone valve control port BB (13) is connected to the B1 control chamber (6), the control high pressure P (14) provides a pressure oil source for the pilot control assembly, and the pilot proportional cone valve T port (15) is used for oil return.

4. A bidirectional cartridge valve as described in claim 3, characterized in that, The pilot control component is compatible with a 2-position 4-way solenoid directional valve, a 2-position 4-way proportional directional valve, or a pilot proportional cone valve. It controls the movement of the valve core (7) by adjusting the pressure difference between the A1 control chamber (9) and the B1 control chamber (6) through an external control signal.

5. A bidirectional cartridge valve as described in claim 1, characterized in that, The hydraulic action area of ​​the balance chamber A+A(11) is 1.2-1.5 times that of the hydraulic action area of ​​the lower chamber A(1) of the cartridge valve.

6. A bidirectional cartridge valve as described in claim 1, characterized in that, The main valve spring (4) is sleeved on the outside of the valve core (7) to ensure that the valve core (7) is in the closed state when the hydraulic system is stopped or powered off.

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