Hydraulic valve block and hydraulic unit for closed loop applications

Abstract

A hydraulic valve block (100) for a hydraulic unit comprises a high pressure port (2), a low pressure port (3), a pilot valve (10) with a pilot valve spool and a bypass valve (30) with a bypass valve spool. The pilot valve connects a control line (25) to a drain area (60) in an initial position. The pilot valve switches to a shifted position by means of a force which is dependent on the pressure level at the low pressure side, in which shifted position the pilot valve conducts pressure from the high pressure port to the control line. The bypass valve (30) switches from a closed position, in which a fluid connection between the high pressure port and the low pressure port is disabled, to an open position, in which a fluid connection between the high pressure port and the low pressure port is enabled, if the control line (25) connected to an opening surface of the bypass valve is not connected to the high pressure port.

Description

Technical Field

[0001] The present invention relates to a hydraulic valve system for hydraulic units, particularly for hydraulic units used in closed-loop hydraulic applications. Background Technology

[0002] In closed-loop hydraulic applications, a minimum low pressure is typically required to be maintained while the hydraulic unit is operating. Maintaining this minimum low pressure becomes problematic when a shock load occurs, causing a sharp rise in pressure on the high-pressure side of the closed hydraulic circuit. For example, such a shock load can occur if an operating hydrostatic propulsion unit is suddenly subjected to a high-level load, such as encountering high resistance or partial blockage. A practical example is hydraulically driven drilling operations when the drill bit is stuck underground.

[0003] When such a shock load occurs, the pressure on the high-pressure side of the hydrostatic propulsion unit rises sharply, causing high loads on the hydrostatic lines, seals, and other parts of the hydrostatic system. On the low-pressure side, the pressure drops due to the high hydraulic fluid flow required to resist the shock load. These pressure drops can be very high, and the feed pump often cannot compensate for the flow required on the high-pressure side, thus potentially damaging the hydrostatic system when a shock load occurs. This event, which causes a sharp rise in pressure on the high-pressure side and a sharp drop in pressure on the low-pressure side, is commonly referred to as a "low-loop event." To prevent damage to the hydrostatic unit during such a low-loop event, it is desirable to maintain / ensure a minimum low pressure level on the low-pressure side.

[0004] Publication DE 10 2018 205 194 A1 (US 2018 / 0291797 A1) describes a hydraulic circuit in which a bypass valve can bypass the high-pressure side and the low-pressure side when the low-pressure drop at the low-pressure side is below a predetermined minimum pressure (i.e., a predetermined minimum pressure to be maintained). However, when a high-speed low-pressure drop occurs, the system may not react quickly enough because the bypass valve is held in its closed position by the low pressure and only opens when the low-pressure hydraulic pressure acting on the bypass valve spool is below the spring force acting in the bypass opening direction.

[0005] EP 2 975 34 A1 describes a method for a braking hydrostatic actuator having a pump with adjustable displacement driven by an internal combustion engine and a hydraulic motor connected to the hydraulic pump via two lines in a closed circuit. The hydrostatic actuator also has a hydraulic valve block for connecting the high-pressure side to the low-pressure side, the hydraulic valve block including a bypass valve designed as an electrically controllable proportional valve.

[0006] Those skilled in the art will deduce that when the low pressure level is slightly below the predetermined minimum pressure level, the remaining spring force required to open the bypass valve is very small, possibly insufficient to fully open the bypass valve. This is because the spring force decreases as the spring is depressurized, and thus a balance between the spring force and the hydraulic force may occur before the bypass valve reaches its fully open position. The reaction speed of moving the bypass valve spool from the closed position to the open position is also slow, as this depends on the incremental force between the spring force and the low pressure, which is below the predetermined minimum pressure level, in order to open the bypass valve to avoid low-loop events. Summary of the Invention

[0007] Therefore, the object of the present invention is to provide a hydraulic system in which a minimum low pressure is ensured and maintained during the operation of the hydraulic unit, wherein the response time of the hydraulic system should be short and the response speed of the hydraulic system should be high in order to avoid low-loop events. At the same time, the hydraulic system should be designed to be cost-effective and robust.

[0008] This objective is achieved by a hydraulic valve block according to claim 1, wherein a preferred embodiment of the hydraulic valve block according to the invention is given by a dependent claim directly or indirectly dependent on claim 1. This objective is also achieved by a hydraulic unit according to claim 10 or a hydraulic system according to claim 11, both of which use the hydraulic valve block according to the invention.

[0009] The hydraulic valve block according to claim 1 is provided for a hydraulic unit that can be used in closed hydraulic circuit applications. The hydraulic valve block according to the invention includes a high-pressure port, a low-pressure port, a pilot valve with a pilot valve spool, and a bypass valve with a bypass valve spool. Thus, the pilot valve can be connected to the high-pressure port of the hydraulic valve block via an inlet and to a discharge area via a discharge port. The outlet of the pilot valve is connected to a control line leading to the bypass valve. The pilot valve spool is held in an initial position, wherein the outlet is connected to the discharge area by means of a pilot valve spring acting on its first front side. According to the invention, the pilot valve spool can be moved to a displaced position by means of hydraulic pressure, the relative strength of which depends on the pressure level at the low-pressure port of the hydraulic valve block. In the displaced position of the pilot valve, pressure from the high-pressure port via the inlet can be transmitted to the control line. Here, the relative strength of the force displaced by the pilot valve spool depends on the low pressure level and acts on the second front side of the pilot valve spool, and also resists the force of the pilot valve spring, thereby pushing the pilot valve spool to the initial position.

[0010] The bypass valve spool of the bypass valve according to the invention includes a first open face connected to the high-pressure side of the hydraulic valve block and a closed face connected to the control line. On the closed face, a bypass valve spring also acts in the closing direction of the bypass valve spool. The bypass valve according to the invention can be switched from a closed position to an open position, in which the fluid connection between the high-pressure port and the low-pressure port is disabled, and in the open position, the fluid connection between the high-pressure port and the low-pressure port is enabled. If the opening force applied by the high pressure to the open face of the bypass valve spool is greater than the sum of the closing forces on the closed face, the bypass valve spool shifts to the open position. Therefore, the sum of the closing forces is the combination of the pressure acting on the closed face in the control line and the force applied by the bypass valve spring. Therefore, when the hydraulic system (where a hydraulic valve block is used) has no (or no) pressure, the bypass valve is held in the closed position only by the bypass valve spring because there is no pressure at the bypass valve spool. The same applies to hydraulic valve blocks not connected to a hydraulic unit.

[0011] Under normal operating conditions, i.e., when the low pressure level is higher than the predetermined minimum pressure level, the pilot valve spool is held in its displaced position because the pressure acting on it is higher than the pilot valve spring force. In the displaced position, the pilot valve directs pressure from the high-pressure port to the control line via the inlet, and then to the closed surface of the bypass valve spool. Therefore, when the hydraulic valve block and hydraulic unit according to the invention are under normal operating conditions, high pressure is conducted to both the first open surface and the closed surface of the bypass valve spool. However, on this closed surface, the bypass valve spring also acts, applying an additional force such that the bypass valve is firmly held in the closed position and the connection between the high-pressure side and the low-pressure side is not activated because no pressure differential acts on the bypass valve spool, even though the pressure surfaces at the closed and open sides are of equal size.

[0012] When the pressure drop at the low-pressure side of the hydraulic valve block, at the low-pressure port, falls below a predetermined threshold of the minimum pressure level, the pilot valve spool shifts back to its initial position because the force exerted by the pilot valve spring on the pilot valve spool is higher than the hydraulic pressure on the opposite pilot valve spool side (depending on the low pressure level). The pilot valve spring force is higher when the hydraulic pressure at the low-pressure side is below the minimum pressure level threshold. In this initial position, i.e., under conditions below the permissible minimum low pressure, the control line is fluidly connected via the pilot valve spool to a relatively low-pressure area, for example, to a reservoir in the housing of the hydraulic unit or to a tank. In other words, according to the invention, the sum of the forces at the closed face of the bypass valve spool is lower than the opening force generated by the high pressure at the open face of the bypass valve spool, causing the bypass valve spool to shift to its open position, in which bypass between the high-pressure port and the low-pressure port of the hydraulic valve block is enabled.

[0013] At least those skilled in the art can deduce from the above that the bypass valve according to the invention always switches by means of hydraulic pressure from the high-pressure side, so that small reductions in low pressure at the minimum permissible low pressure level are quickly detected, and the hydraulic valve block according to the invention can react quickly when a large moving force is applied to the bypass valve spool, because high pressure generates these switching forces under any operating condition.

[0014] As can also be deduced from the above, the control line transmitting control pressure to the closing surface of the bypass valve spool can be discharged to a low-pressure area, allowing the hydraulic reaction force against the opening force of the bypass valve to be reduced to a minimum in a short time. This results in a high force difference between the opening and closing forces at the two front surfaces of the bypass valve spool in each case, enabling a rapid and quick response to move the bypass valve spool. In this case, and in a preferred embodiment, the closing hydraulic pressure acting on the closing front surface via the control line is greater than the opening pressure surface on the bypass valve spool, thereby enhancing the closing force acting on the bypass valve spool. Therefore, when the pressure at the low-pressure port is higher than the minimum low-pressure level, the hydraulic pressure powered by the high pressure acting on the closing surface of the bypass valve spool is greater, or even higher, than the closing pressure surface (closing front surface) to open the bypass valve.

[0015] In another embodiment of the invention, a second opening pressure surface is arranged on the opening side of the bypass valve spool and fluidly connected to the low-pressure side. In this case, the closing pressure surface on the bypass valve spool should be larger than the opening high-pressure surface on the opposite side of the bypass valve spool to compensate for the additional fluid pressure generated by the low pressure on the second opening surface. In one specific embodiment, if the two opening pressure surfaces are located at the bypass valve spool, they may be of equal size. This embodiment is suitable for closed-loop applications in which the hydraulic unit connected to the hydraulic valve block according to the invention can operate in both motor and pump modes. As is known at least to those skilled in the art, the high-pressure side and the low-pressure side will change with the change of the operating mode of the hydraulic unit, for example, from motor mode to pump mode.

[0016] If the hydraulic block according to the invention is used in such a hydraulic unit, another selective switching valve is arranged upstream of the pilot valve. In each mode, this selective switching valve ensures that high pressure is directed to the inlet of the pilot valve, while low pressure is directed to the second face of the pilot valve spool, so that the low pressure can act as a counterforce against the displacement force of the pilot valve spring. This selective switching valve can be a two-position four-way valve, wherein each face of this selective switching valve refers to an inlet. Such switching valves are known to those skilled in the art and therefore require no further explanation.

[0017] When a switching valve is used in the hydraulic valve block according to the invention, the hydraulic valve block can also be used in a hydraulic unit. For example, this also requires changing the pressure side in hydraulic propulsion applications that can be driven in two directions. By using a switching valve, the hydraulic valve block according to the invention increases the functionality and range of use for a variety of hydrostatic applications. When the two closed faces at the bypass valve spool, on which two pressure levels can act simultaneously, are of equal size, the function of the hydraulic valve block according to the invention is enabled under all operating conditions, and rapid response and rapid actuation time can be maintained independently of operating conditions.

[0018] Although, as described above, the switching force of the pilot valve spool is preferably applied directly by the low pressure, those skilled in the art will at least imagine that this force can be generated in other ways based on the low pressure level present at the low-pressure port. For example, the pilot valve spool can be actuated by a solenoid using a signal from a pressure sensor located on the low-pressure side. Another possibility is a lever or spring mechanism whose switching force is directly related to the low pressure level. However, in a preferred embodiment of the invention, the displacement force acting on the pilot valve spool is generated directly by guiding the low pressure on the switching face of the pilot valve spool.

[0019] In another embodiment, the pilot valve is a proportional valve, positioned based on the low pressure level at the low-pressure port and movable, such that high pressure from the high-pressure port is directed proportionally toward the bypass valve via the control line. In this embodiment, a reaction time is maintained. However, the switching speed of the pilot valve is slightly reduced to prevent excessive pressure on the low-pressure side when the bypass valve is opened, thus enabling bypass between the high-pressure and low-pressure ports.

[0020] In another preferred embodiment, the force of the pilot valve spring is adjustable. By doing so, the minimum low pressure level at which the hydraulic unit and / or hydraulic system should operate can be adjusted. Adjusting the spring force allows setting the minimum threshold for the low pressure required to displace the pilot valve spool. Typically, this adjustment is made when the hydraulic system is put into service. However, readjustment at a later time is also conceivable.

[0021] Furthermore, the bypass valve spring can be configured such that its force is also adjustable to ensure that the bypass valve spool is in its closed position when the low pressure is above the minimum permissible pressure level. However, the bypass valve spring force should not be too high, so as not to slow down the opening speed of the bypass valve.

[0022] In a preferred embodiment, the pressure surface on the closed side of the bypass valve spool is larger than the two open surfaces on the opposite side of the bypass valve spool to ensure rapid closure of the bypass and to ensure the closed position of the bypass valve. However, depending on system parameters, an orifice may be placed thereto to suppress fluid flow through the control line, resulting in a lower frequency of opening and closing the loop in the event of a low-loop event and also leading to a rapid return to stable operating conditions. Therefore, such an orifice in the control line will have a damping effect on the switching of the bypass valve, especially when the closed pressure surface on one side of the bypass valve spool is configured to be larger than the two open surfaces on the opposite side of the bypass valve spool. According to the invention, this condition is particularly applicable to embodiments using a switching valve in a hydraulic valve block.

[0023] As disclosed above, the hydraulic valve block according to the invention is particularly suitable for hydraulic units provided for closed-loop applications, wherein the hydraulic valve block according to the invention can be used in hydraulic pumps or hydraulic motors. Similarly, such pumps and motors have axial or radial configurations and can be equipped with devices for changing displacement volume. Here, at least those skilled in the art will associate this with axial hydraulic piston units of the rotating swashplate type or curved shaft type configurations. However, the invention also covers radial piston pumps with or without variable displacement volume control. Furthermore, even though only rotary hydraulic devices have been mentioned for the foregoing, the hydraulic valve block according to the invention is also suitable for hydraulic linear actuators, such as bidirectional hydraulic cylinders. Attached Figure Description

[0024] The preferred embodiments shown in the accompanying drawings are for illustrative purposes only and should not limit the scope of the inventive concept or protection. The following drawings illustrate:

[0025] Figure 1 : A schematic diagram of the hydraulic valve block according to the present invention in an unpressurized state.

[0026] Figure 2 : In normal operating condition of the hydraulic unit Figure 1 An embodiment of the hydraulic valve block according to the present invention.

[0027] Figure 3 The basis for being in an operating state when a low-loop event occurs. Figure 1 A schematic diagram of an embodiment of a hydraulic valve block.

[0028] In the accompanying drawings, the same parts are indicated by the same reference numerals for easier readability. Detailed Implementation

[0029] For example, Figure 1 A hydraulic valve block 100 according to the invention in an unpressurized state is shown, having an unconnected pressure port. This is merely an example.Figure 1 The hydraulic port on the left is designated as high-pressure port 2, and Figure 1 The pressure port on the right is selected as the low-pressure port 3. Two high-pressure ports 2 are connected by a high-pressure line 4, and two low-pressure ports 3 are connected by a low-pressure line 6. Three valves are arranged between the two pressure lines 4 and 6, the uppermost of which is a switching valve 50 with a high-pressure inlet 51 and a low-pressure inlet 52. When the high-pressure port 2 is interchanged with the low-pressure port 3, each face of the selective valve spool 54 references one of the pressure levels at inlet 51 or inlet 52 to move the switching valve spool 54. At least those skilled in the art will deduce from the switching valve 50 that when the pressure port changes pressure level, the switching valve 50 is switched to its second position (not shown), ensuring that pressure from the high-pressure port 2 is always directed to the high-pressure outlet 56, and low pressure is directed from inlet port 2 to the low-pressure outlet port 57.

[0030] The two outlet ports 56 and 57 of the switching valve 50 are connected to the pilot valve 10, wherein the high-pressure outlet 56 of the switching valve 50 is connected to the pilot valve inlet 11, and the outlet port 57 of the switching valve 50 is connected to the second front end 17 of the pilot valve spool 14 of the pilot valve 10. The pilot valve spring 15 is located on the first front end 16 of the pilot valve 10. Figure 1 As shown, the pilot valve spring 15 holds the pilot valve 10 in its initial position. The pilot valve 10 also has a discharge port 12, which is connected to a low-pressure area, in this case, to tank 60 or a discharge area. The pilot valve 10 also includes an outlet 13, which is connected to a control line 25 leading to the bypass valve 30.

[0031] The control line 25 is connected to a closed surface 38 on one front side of the bypass valve core 34 of the bypass valve 30, on which the bypass valve spring 35 is also arranged. Two opening faces 36 and 37 are provided on the opposite side of the bypass valve core 34, wherein the first opening face 36 is connected to the high-pressure line 4, and the second opening face 37 is connected to the low-pressure line 6. Because... Figure 1 The hydraulic valve block 100 shown is depicted in a non-pressurized state, with the bypass valve spring 35 pushing the bypass valve 30 into a closed position, thus disabling the bypass between the high-pressure line 4 and the low-pressure line 6. Simultaneously, since there is no pressure in either the low-pressure line 6 or the high-pressure line 4, the pilot valve spring 15 holds the pilot valve 10 in its initial position, i.e., the pilot valve spool 14 controls the connection between the pressure line 25 and the discharge area 60, ensuring that no pressure can act on the closed face 38 of the bypass valve spool 34.

[0032] exist Figure 2In this embodiment, the hydraulic valve block 100 according to the invention is depicted in an operating state where the low pressure level is above a minimum, and below that minimum, any low pressure compensation should be initiated. This means that the low pressure guided by the switching valve 50 on the second front of the pilot valve 10 generates a higher hydraulic pressure than the spring force applied to the opposite first front 16. Therefore, the pilot valve spool 14 is moved to its displaced position, and the pilot valve guides the hydraulic pressure from the high-pressure side (i.e., high-pressure port 2) into the control line 25. The pressure in the control line 25 then acts on the closed front 38 of the bypass valve spool 34. On the same closed surface 38, the bypass valve spring 35 also applies a closing force to the bypass valve spool 34. On the opposite side, the high pressure from the high-pressure line 4 acts on the first open front 36, which is smaller than the closed front 38, thus the bypass valve spool 34 is held in its closed position and the bypass valve 30 is closed, i.e., bypass between the high-pressure line 4 and the low-pressure line 6 is disabled.

[0033] Figure 3 Another operating state of the hydraulic valve block 100 according to the invention is depicted. The pressure in the low-pressure line 6 is below a predetermined threshold, i.e., in the event of a low-loop event. The switching valve 50 remains in contact with... Figure 1 and Figure 2 At the same position depicted, however, pilot valve 10 is again in the initial position because the low pressure guided to the second face 17 of pilot valve spool 14 does not generate a sufficiently high hydraulic pressure to overcome the spring force of pilot valve spring 15. Therefore, control line 25 is discharged to discharge area 60, causing the hydraulic pressure on the closing surface 38 of bypass valve spool 34 to be reduced to a minimum, and only bypass valve spring 35 exerts a closing force on bypass valve spool 34. Since the first opening face 36 of bypass valve spool 34 is still connected to high-pressure line 4, a higher opening force is generated on bypass valve spool 34, pushing it into its open position, where hydraulic bypass from high-pressure line 4 to low-pressure line 6 is activated.

[0034] As long as the hydraulic pressure on the second face 17 of the pilot valve spool 14 is insufficient to overcome the spring force of the pilot valve spring 15 to move the pilot valve spool 13 to the shift or switching position, the bypass valve spool 34 remains in the open position. When the hydraulic pressure on the second face 17 of the pilot valve spool 14 is high enough to overcome the force of the pilot valve spring 15, the pilot valve spool 14 is brought to the switching position, and the hydraulic pressure from the high-pressure port 2 is directed via the pilot valve 10 and control line 25 to the closing face 38 (the larger pressure face) of the bypass valve spool 34, and thus the bypass valve 30 closes immediately after the low pressure level in the low-pressure line 6 exceeds a predetermined / pre-adjusted minimum low pressure threshold.

[0035] Therefore, as can be seen from the figure, by adjusting the spring force of the pilot valve spring 15, the threshold of the minimum pressure level can be maintained at the pressure level of the low-pressure line 6. According to the present invention, this pressure level can be set at any time, especially when the hydraulic system is connected to the hydraulic valve block.

[0036] Furthermore, according to the present invention, those skilled in the art will find it potentially advantageous to configure and adjust the bypass valve spring 35 so that the bypass valve switching adapts to other system parameters of any hydraulic system equipped with the hydraulic valve block 100.

[0037] Furthermore, those skilled in the art will conclude that if the hydraulic valve block 100 and the system operate only in one direction and do not change the operating mode—in other words, if the high-pressure line 4 is never interchanged with the low-pressure line 6—then the switching valve 50 can be omitted. It is readily apparent to those skilled in the art that when the operating mode of the hydraulic system changes, for example from motor mode to pumping mode (when the high-pressure line 4 is interchanged with the low-pressure line 6), the same working principle as described above is achieved through the pilot valve 10 and the bypass valve 30. In this case, the switching valve 50 is switched so that pressure from the high-pressure port 2 is directed to inlet 11, and hydraulic pressure from the low-pressure port 3 is directed to the second face 17 of the pilot valve spool 14.

[0038] In summary, the hydraulic system equipped with the hydraulic valve block of this invention provides users with a reliable, robust, and cost-effective system that ensures optimal bypass opening when the minimum low pressure level in the hydraulic system is weakened, enabling low-pressure compensation to avoid damage to the hydraulic system. In practice, this automatic adjustment / control is continuous because the hydraulic system frequently experiences shock loads. To prevent frequency / pressure oscillations within the hydraulic system during shock loads, orifice 27 can be implemented to control line 25 to suppress these pressure oscillations.

[0039] Based on the foregoing discussion, the accompanying drawings, and the claims, it will be apparent that the hydraulic valve block 100 according to the invention offers numerous advantages over the prior art. Those skilled in the art will further understand that various other modifications can be made to the device without departing from the spirit and scope of the invention. All such modifications and variations fall within the scope of the claims and are intended to be covered by them. It should also be understood that the examples and embodiments described herein are for illustrative purposes only, and various modifications or variations suggested therein by those skilled in the art are included within the spirit and scope of this application.

[0040] List of reference numerals

[0041]

Claims

1. Hydraulic valve block (100) for a hydraulic unit provided for use in a closed hydraulic circuit application, the hydraulic valve block comprising a high pressure port (2), a low pressure port (3), a pilot valve (10) with a pilot valve spool (14) and a bypass valve (30) with a bypass valve spool (34), wherein, - the pilot valve (10) is connected to the high pressure port (2) by a pilot valve inlet (11), to a drain area (60) by a drain port (12) and to a control line (25) by a control outlet (13), the pilot valve spool (14) is held in an initial position in which the control line (25) is connected to the drain area (100) by means of a pilot valve spring (15) acting on a first face (16) thereof, wherein the pilot valve spool (14) is slidable into a displaced position and pressure from the pilot valve inlet (11) is transmittable to the control line (25) by means of a force the strength of which depends on a pressure level at the low pressure port (3) acting on a second face (17) of the pilot valve spool (14) against the force of the pilot valve spring (15); - the bypass valve spool (34) comprises a first opening face (36) connected to the high pressure port (2) and a closing face (38) to which the control line (25) is connected and on which a bypass valve spring (35) acts in a closing direction, wherein the bypass valve (30) is switchable from a closed position in which a fluid connection between the high pressure port (2) and the low pressure port (3) is disabled to an open position in which the fluid connection between the high pressure port (2) and the low pressure port (3) is enabled if an opening force exerted on the first opening face (36) of the bypass valve spool (34) by the high pressure is higher than a sum of a closing force exerted on the closing face (38) by a pressure in the control line (25) and a force of the bypass valve spring (35).

2. The hydraulic valve block (100) of claim 1, wherein, The bypass valve spool (34) comprises a second opening face (37) connected to the low pressure port (3).

3. The hydraulic valve block (100) of claim 2, wherein, The first opening face (36) and the second opening face (37) on the bypass valve spool (34) have equal sizes.

4. The hydraulic valve block (100) according to any one of claims 1 to 3, wherein The second face (17) of the pilot valve spool (14) is fluidly connected to the low pressure port (3).

5. The hydraulic valve block (100) according to any one of claims 1 to 3, wherein, The force on the second face (17) of the pilot valve spool (14) is exerted by a solenoid (18).

6. The hydraulic valve block (100) according to any one of claims 1 to 3, wherein The pilot valve (10) is a proportional valve.

7. The hydraulic valve block (100) according to any one of claims 1 to 3, wherein The force of the pilot valve spring (15) and / or the force of the bypass valve spring (35) is adjustable.

8. The hydraulic valve block (100) according to any one of claims 1 to 3, wherein An orifice (27) is located in the control line (25).

9. The hydraulic valve block (100) according to any one of claims 2 to 3, wherein, A two position switch valve (50) is fluidly connected to the high pressure port (2) and the low pressure port (3) for selection and to transmit high pressure from the high pressure port (2) to the inlet (11) of the pilot valve (10) and low pressure from the low pressure port (3) onto the second face (17) of the pilot valve spool (14).

10. A hydraulic unit (200) for closed circuit applications, the hydraulic valve block (100) according to any one of claims 1 to 9 being connected to the hydraulic unit (200) at respective high pressure and low pressure ports of the hydraulic unit.

11. A hydraulic system (300) comprising a hydraulic motor (210) and a hydraulic pump (220) connected via a working line to form part of a closed circuit, the system further comprising a hydraulic valve block (100) according to any one of claims 1 to 9.

12. The hydraulic system (300) of claim 11, wherein, The hydraulic valve block (100) is attached to the hydraulic motor (210) or the hydraulic pump (220).

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