DE102017219942A1 - Valve arrangement for hoist control with a pressure regulator - Google Patents

Abstract

The invention relates to a valve arrangement (30), wherein a control valve (50) and a pressure control device (70) are provided, which are connected in parallel to a first and a second working port (31; 32), wherein the control valve (50) has a load reporting port (30). 58) having a first, a second, a third and a fourth position (51; 52; 53; 54).
According to the invention, in the second position (52) the first working port (31) is fluidically connected via the control valve (50) to a first return port (34), wherein in the second, third and fourth positions (52; 53; 54) Connection between the control valve (50) and the first inlet port (33) is blocked by the control valve (50), wherein the pressure regulating device (70) is connected to a first inlet port (33).

Description

The invention relates to a valve arrangement according to the preamble of claim 1 and a hydraulic drive system with such a valve arrangement.

From the EP 1 672 225 B1 a valve assembly is known, which is used to control the hoist of an agricultural tractor. The spool has four positions. In one position, the hoist is raised. In another position cylinder of the hoist is hydraulically clamped. In another position, the hoist is lowered. In the last position, the hoist can move freely. The pressure in the cylinder chambers of the hoist cylinder is influenced by pressure relief valves, whereby only one of the two pressure relief valves is adjustable. Further, a pressure compensator is provided, with which the pressure of a continuously adjustable control panel in the control valve is adjusted to a predetermined value, so that the movement speed of the cylinder depends essentially solely on the position of the control panel.

An advantage of the present invention is that loads connected to the cylinder can be raised and lowered single or double acting. Both the speed of movement and the force of the cylinder should be adjustable. In particular, the pressure should optionally be adjustable in one of the two cylinder chambers and indeed in the widest possible limits. Jerky movements of the cylinder should be avoided. The entire valve assembly should be particularly simple. Next is to be avoided that the hoist lowers when the delivery pressure of the pump for the desired stroke itself is not sufficient. Any uncontrolled or unwanted movement should be avoided. The above advantages should also be exploitable in exceptional applications of tractor hitch, for example, even if the hoist is used to raise the tractor during maintenance. Here, especially when lowering again, jerky movements can occur which should be avoided.

According to the independent claim, it is proposed that, in the second position, the first working connection is fluidically connected via the control valve to a first return connection, wherein in the second, the third and the fourth position a connection between the control valve and the first inlet connection is blocked by the control valve is, wherein the pressure regulating device is connected to the first inlet port. In the EP 1 672 225 B1 missing one of the second position comparable position of the control valve. Further, in the third position, ie when lowering the hoist, the fluid flow from the pump via the control valve is passed. In addition, the pressure relief valves have the EP 1 672 225 B1 no connection to the first inlet connection. Therefore, you can only lower the pressure in the associated working lines, but not increase up to the delivery pressure of the pump, as is possible with the pressure control device according to the invention.

The first to fourth positions are preferably formed differently from each other. The first and / or the second working port may each be assigned a pressure sensor with which the pressure at the relevant working port can be measured. In the first position, a continuously adjustable control panel is preferably arranged in the connection from the first inlet connection to the second working connection. This control panel, as well as all other control panels mentioned below, are preferably formed by a spool of the control valve. In the second and the fourth position, a continuously adjustable control panel is preferably arranged in the respective connection to the first return port. Between the first inlet connection and the first valve, a pressure compensator can be arranged, which is set up such that the pressure difference between the pressure at the load-signaling connection and the pressure downstream of the pressure compensator can be regulated to a predetermined value. The control valve is preferably designed as a slide valve. The corresponding control slide is preferably designed so that the fluid connections according to the invention can be adjusted by displacement of the control slide relative to the surrounding housing. The valve means is typically used with a pressurized fluid, which is preferably a liquid and most preferably hydraulic oil.

In the dependent claims advantageous refinements and improvements of the invention are given.

It can be provided that the control valve has a fifth position, in which a connection between the control valve and the first inlet port is blocked by the control valve, wherein the first and the second working port are fluidically connected to a first return port. The fifth position corresponds functionally to the clearance position of the EP 1 672 225 B1 , In the fifth position, a continuously adjustable control panel is preferably arranged in the connection from the second working connection to the return connection. In the fifth position, the load-indicating connection can be connected or blocked with a first return connection. In the latter alternative is preferably the below addressed shuttle valve used. It may be provided a sixth position of the control valve, which has the same connections as the fifth position, said control panel is fully open.

It can be provided that the first, the second, the third, the fourth and optionally the fifth position of the control valve are arranged side by side in the stated order. In an adjustment of the control valve in one direction, the positions mentioned will thus pass through one another in the order named. With this arrangement, a particularly simple and inexpensive construction of the spool.

It can be provided that the pressure regulating device comprises at least one pressure reducing valve, which in each case has a second inlet connection, a second return connection and an outlet connection, wherein the pressure at the outlet connection can be regulated to the first setpoint pressure by either a fluidic connection from the outlet connection to the second inlet connection or is opened to the second return port, wherein the second return port is fluidly connected to a first return port, wherein the second inflow port is at least indirectly connected to the first inflow port. With such pressure reducing valves, the pressure at the outlet port is adjustable within wide limits, which are defined by the pressure at the second inlet port and the pressure at the second return port. In addition, pressure reducing valves can be used, which are produced as standard valves in large quantities and accordingly offered inexpensively. The at least one pressure reducing valve is preferably each electrically adjustable. It is preferably designed in the form of a Einschraubventils. It is conceivable that the pressure regulating device for the first and the second working port each has a separate pressure reducing valve whose output port is directly fluidically connected to the relevant working port.

It can be provided that at least one, preferably each pressure reducing valve is associated with a first check valve, which is arranged between the first inlet port and the respective second inlet port, wherein it allows only a fluid flow from the first inlet port to the respective second inlet port. This prevents pressurized fluid from flowing back to the pump via the second inlet connection if the delivery pressure of the pump is insufficient to maintain the load acting on the cylinder.

It can be provided that the pressure control device comprises a single pressure reducing valve, wherein a switching device is provided, via which the output port of the pressure reducing valve is selectively fluidically connectable to the first or the second working port, said two compounds are shut off at the same time. The switching device is typically less expensive than a pressure reducing valve, so that costs are saved. In addition, the proposed blocking position can be easily realized with the switching device. This is used for example in the fifth and sixth position of the control valve, in which the pressure control is not needed and would even disturb. The switching device can be formed by a 3/3-way valve. But it is also conceivable to use two parallel 2/2-way valves. The aforementioned directional control valves are preferably designed in seat construction, if a leak-free closure is desired.

It can be provided that the load-signaling connection of the control valve is fluidically connected in the second position to the second working port, in the third position to a first return port and in the fourth position to the first working port, the load-reporting port being at least indirectly connected to a delivery pressure regulator of a pump is fluidically connectable. With this design of the load feedback, it is not necessary that the pressure control device can adjust the pressure zero. It can therefore be designed inexpensively. Said indirect connection to the delivery pressure regulator can take place via a shuttle valve cascade, to which further hydraulic consumers are connected, which can be supplied with pressurized fluid by the pump.

It can be provided that the load-signaling connection of the control valve in the second position and / or the third position and / or the fourth position is blocked by the control valve, wherein a shuttle valve is provided which fluidly connected on the input side to the load-indicating connection and the output connection of the pressure-reducing valve is, wherein the change-over valve on the output side with a delivery pressure regulator of a pump is at least indirectly fluidly connectable. This simplifies the production of the control valve, in particular the spool. In the positions in which the load-signaling connection is blocked, the load message is generated by the pressure-reducing valve via the shuttle valve.

It can be provided that a second check valve is assigned to each of the first and / or the second working connection via which the relevant working connection is connected to a first return connection, wherein the second check valve allows only fluid flow from the respective first return port to the respective work port. This avoids that forms in one of the cylinder chambers a vacuum. As soon as a negative pressure arises in one of the cylinder chambers, pressurized fluid is sucked out of the tank.

Protection is also claimed for a hydraulic drive system which is equipped with a valve assembly according to the invention, wherein a double-acting cylinder is connected to the first and the second working port, wherein a tank is connected to the at least one first return port, wherein a pump is provided with which pressure fluid from the tank to the first inlet port can be conveyed, wherein the pump has an adjustable displacement volume, wherein a delivery pressure regulator is provided, with which a delivery pressure of the pump by adjusting the displacement volume of the pump to a second target pressure is einregelbar. Said cylinder is preferably part of a hoist of an agricultural tractor. A corresponding hoist is for example from the EP 2 870 842 B 1 known. The cylinder may be assigned a position sensor with which the position of the cylinder is at least indirectly measurable. Preferably, the position sensor is formed by a rotation angle sensor, which is arranged on a rotary joint of said hoist. The cylinder can be connected in each case via a load-holding valve to the first and / or the second working port, in order to avoid uncontrolled movement of the loaded cylinder due to leaks.

It can be provided that the second desired pressure depends on the pressure at the load-signaling connection or on the output-side pressure at the changeover valve. The second setpoint pressure is preferably a predetermined pressure difference above said pressure at the load reporting port or at the shuttle valve.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

• 1 eine erste Ausführungsform eines hydraulischen Antriebssystems mit einer erfindungsgemäßen Ventilanordnung;
• 2 eine zweite Ausführungsform eines hydraulischen Antriebssystems mit einer erfindungsgemäßen Ventilanordnung; und
• 3 eine zweite Ausführungsform der Umschaltvorrichtung.

The invention will be explained in more detail below with reference to the accompanying drawings. It shows:

• 1 a first embodiment of a hydraulic drive system with a valve assembly according to the invention;
• 2 a second embodiment of a hydraulic drive system with a valve assembly according to the invention; and
• 3 a second embodiment of the switching device.

1 shows a first embodiment of a hydraulic drive system 10 with a valve arrangement according to the invention 30 , The valve arrangement 30 has a first and a second work connection 31 ; 32 , an inlet connection 33 and multiple return ports 34 , The valve arrangement 30 is typically formed by a valve block or a valve disc on which said connections are made in the form of separate connection bores. However, it is also conceivable that the valve arrangement is part of a larger hydraulic circuit, wherein said connections are formed by specific locations within the corresponding hydraulic line system. Preferably, only a single first return port is provided, wherein the in 1 shown return paths within the valve assembly 30 be merged.

To the first inlet connection 33 is a pump 11 connected, which has an adjustable displacement volume, wherein it is preferably formed by an axial piston pump, which is most preferably designed in a swash plate design. The pump 11 sucks pressurized fluid out of a tank 14 and conveys it under pressure to the first inlet connection 33 , The pump 11 is a delivery pressure regulator 12 assigned. This can be done by means of a control pressure 19 For example, a hydraulic swing cylinder in the pump 11 Press, with which the displacement volume is adjusted. The delivery pressure regulator 12 becomes the delivery pressure 13 the pump 11 fed as actual value. Next is the delivery pressure regulator 12 a load reporting pressure 39 supplied within the valve assembly 30 is generated. Unless the pump 11 next to the in 1 illustrated cylinder 15 supplied further hydraulic consumers, the load reporting pressure 39 On the input side abut a shuttle valve cascade, wherein the output of the shuttle valve cascade the delivery pressure regulator 12 is supplied. Typically, the delivery pressure regulator controls 12 the delivery pressure to a second setpoint, which is a predetermined pressure difference above the load reporting pressure or the output pressure of the shuttle valve cascade. The output pressure of the shuttle valve cascade is the highest pressure from the input side pressures on the shuttle valve cascade. In addition, the delivery pressure regulator 12 also one Power limitation effect, so that the pump 11 and / or their drive are not overloaded.

To the first and second work connection 31 ; 32 is a double-acting cylinder 15 connected, wherein a parallel connection of several double-acting cylinder is also conceivable. The cylinder 15 is preferably part of a hoist 16 an agricultural tractor, although other mobile machines can be equipped with a comparable hoist. The cylinder 15 is a position sensor 17 associated with the position of the cylinder 15 at least indirectly measurable. Preferably, the position sensor 17 formed by a rotation angle sensor, which at a hinge of the hoist 16 is arranged.

The valve arrangement 30 includes a control valve 50 and a pressure regulating device 70 , Opposite the EP 1 672 225 B1 is the peculiarity of the pressure control device 70 in that instead of pressure relief valves, a pressure reducing valve 80 is used. In principle, it is conceivable to use two separate pressure reducing valves 80 each to an associated first or second working port 31 ; 32 are connected. For cost reasons, however, it is preferable to have a switching device 70 to use, with a single pressure reducing valve 80 optionally with the first or the second working connection 31 ; 32 is connectable. In the present case, the switching device 74 from a 3/3-way valve 72 formed, which is designed in slide construction. The 3 / 3 -way valve 72 is biased by means of at least one spring in a central locking position, wherein it is movable by means of electromagnets in the other two positions to produce said fluid connections.

The pressure reducing valve 80 has an output connection 83 , a second inlet connection 81 and a second return port 82 , The output connection 83 is as explained above with the working ports 31 ; 32 connectable. The second return connection 82 is with a first return port 34 fluidly connected. The second inlet connection 81 is with the first inlet connection 33 fluidly connected via a first check valve 71 , which exclusively a fluid flow from the first inlet connection 33 to the second inlet connection 34 allows. The first set pressure 84 is adjusted by means of an electromagnet. This can act as shown directly on the valve spool, where it can alternatively influence the biasing force of the spring, depending on whether an increasing or a falling characteristic is desired. The valve spool of the pressure reducing valve will also be the pressure at the outlet port 83 applied. If the pressure force exceeds the effective force from the magnetic and spring force, the output connection to the second return connection becomes 82 connected. If the pressure falls below the effective force from the magnetic and the spring force, the output connection with the second inlet connection becomes 81 connected. The result is pressure at the output port 83 so that the forces mentioned are in equilibrium.

Opposite a pressure relief valve has the pressure reducing valve 80 the second inlet connection 81 , via the pressure fluid to the cylinder 15 can flow, which is not possible with the known pressure relief valve. This results in the risk that the cylinder moves in a way that is not the setting of the control valve 50 equivalent. The control valve according to the invention 50 is accordingly designed so that such unwanted movements are avoided.

The control valve 50 in the present case has a first, a second, a third, a fourth, a fifth and a sixth position 51 - 56 , where the fifth and the sixth position 55 ; 56 optional. The positions 51 - 56 are preferably arranged side by side in the order given, so that the corresponding valve slide is easy to produce. Alone in the first position 51 there is a connection from the first inlet connection 33 via the control valve 50 to the second work connection 32 , In all other positions 52 - 56 is the connection between the first inlet connection 33 and the control valve 80 through the control valve 80 locked, so that the pressure fluid in these positions exclusively via the pressure control device 70 to the cylinder 15 can flow, only the cylinder 15 backflowing pressure fluid via the control valve 50 to a first return port 34 flows. In the third position 53 , which is designed as a blocking position in which the cylinder 15 not moved at all, no pressure fluid flows to a first return port 34 , In this position is preferably also the pressure reducing valve 80 by means of the switching device 74 from the work connections 31 ; 32 separated.

In the first position 51 should the to the cylinder 15 connected load at a high speed by utilizing the pumping capacity of the pump 11 be raised against gravity. In this operating state is typically no force control by means of the pressure control device 70 required. This is therefore preferably by means of the switching device 74 from the work connections 31 ; 32 separated. In the first position 51 there is a continuously adjustable control panel 57 in the lead. The pressure drop at this control panel 57 is preferably by means of a pressure balance 37 adjusted to a constant value, allowing the movement speed of the cylinder 15 essentially solely by the position of the control panel 57 depends. The pressure balance 37 is between the first inlet connection 33 and the control valve 50 connected. It is in the closing direction of the pressure between the pressure compensator 37 and the control panel 57 applied. In the opening direction, it is the force of a preloaded spring and the pressure downstream of the control panel 57 which is connected to a load-signaling connection 58 of the control valve 50 is applied. In the second to sixth position is the pressure balance 37 not effective because the flow path from the first inlet port 33 via the pressure balance 37 to the control valve 50 from the control valve 50 Is blocked.

The second position 52 is set, for example, when the desired position of the cylinder 15 by means of the first position 51 is reached, the load should be held only force-controlled or slowly raised further. The switching device 74 is adjusted so that the pressure reducing valve 80 the pressure at the second working connection 32 regulates. The continuously adjustable control panel 57 is in the second position 52 in the return between the first work connection 31 and a first return port 34 , It is adjusted so that the desired movement speed results. The corresponding setting is load-dependent. The regulated pressure at the second working connection 32 will also be connected to the load report port 58 connected, where there is essentially no pressure fluid via the delivery pressure regulator 12 can drain away.

The fourth position 54 Functionally corresponds to the second position 52 , where only the direction of movement is reversed. Accordingly, the pressure reducing valve 80 preferably via the switching device 74 with the first work connection 31 connected. The second work connection 32 is via the continuously adjustable control panel 57 with a first return port 34 connected. At the load report connection 58 the regulated pressure is at the first work connection 31 on.

The third position 53 is a blocking position in which the cylinder 15 hydraulically clamped. The connection between the control valve 50 and the first and second working ports, respectively 31 ; 32 is accordingly each by the control valve 50 blocked. The switching device 74 is preferably adjusted so that the connection between the pressure reducing valve 80 and the first and second working ports, respectively 31 ; 32 each is locked. The load report connection 58 is via the control valve 50 with a first return port 34 connected, so that at the load-signaling connection 58 essentially no pressure is applied. As a result, the pump is running 11 essentially depressurized.

By means of the fifth position 55 Can the to the cylinder 15 connected load can be lowered alone by the action of gravity at a defined speed. The second work connection 32 , whose pressure is typically working against gravity, is accordingly a continuously adjustable control panel 57 in the control valve 50 with a first return port 34 connected, with the first work connection 31 via the control valve 50 essentially unthrottled with a first return port 34 connected is. The load report connection 58 is also via the control valve 50 with a first return port 34 connected so that the pump 11 essentially depressurized.

At the sixth position 56 it is an extreme position of the fifth position 55 , in which the corresponding, continuously adjustable control panel 57 is completely open. That to the cylinder 15 connected hoist 16 can move accordingly freely. The sixth position 56 is shown separately, since it is set comparatively frequently, for example, when a mower is mounted on the hoist, the weight of which is fully supported in the mowing operation on the ground.

The load report connection 58 is present directly to the delivery pressure regulator 12 connected. The delivery pressure 13 is preferably adjusted to a second desired pressure by a predetermined pressure difference above the pressure of the load reporting port 58 lies. The first embodiment is characterized in that in all positions of the control valve 50 a defined pressure at the load-signaling connection 58 is applied.

Attention is still on the two second check valves 36 , each to an associated first and second working port 31 ; 32 are connected, wherein they only a fluid flow from an associated first return port 34 to the relevant work connection 31 ; 32 let it go. As a result, a so-called Nachsaugung is realized, which is effective, for example, when the cylinder 15 in the sixth position 56 of the control valve moves very fast. Then can pressure fluid from the tank 14 over the relevant second check valve 36 be sucked into the enlarging cylinder chamber, so that no vacuum is formed there. In normal operation, the second check valves 36 sealed fluid-tight.

Next is on the two pressure sensors 35 to indicate, with which the pressures at the first and at the second working port 31 ; 32 are measurable.

It is understood that the pressure sensors 35 ; the position sensor 17 , the control valve 50 , the switching 74 and the pressure reducing valve 80 to an electronic control device 18 are connected to the desired movement of the hydraulic drive system 10 to control.

2 shows a second embodiment 10 ' a hydraulic drive system with a valve arrangement according to the invention 30 , The first and the second embodiment are identical except for the differences described below, so that in this regard to the comments on 1 is referenced. In the 1 and 2 are the same or corresponding parts marked with the same reference numerals.

In the second embodiment, the load message at the load pressure port 58 of the control valve 50 changed so that there is a much simpler valve spool. In the first and the third position 51 ; 53 the load message is unchanged from the first embodiment. In the second, the fourth, the fifth and the sixth position 52 ; 54 ; 55 ; 56 the existing in the first embodiment Lastmeldeverbindungen are simply locked, so that via the control valve 50 no load feedback occurs. In return, the shuttle valve 38 introduced, on the input side of the pressure at the load-sensing connection 58 and the pressure at the output port 83 the pressure reducing valve 80 is applied. In the second, the fourth, the fifth and the sixth position 52 ; 54 ; 55 ; 56 Accordingly, the pressure at the output port is immediately 83 the pressure reducing valve 80 to the delivery pressure regulator 12 reported. In the second and fourth positions 52 ; 54 is this type of load feedback functionally equivalent to the load feedback according to the first embodiment. In the fifth and sixth positions 55 ; 56 is a pressure reducing valve for the desired load feedback 80 required, which can adjust the pressure zero. Such a pressure reducing valve 80 is complicated and expensive, so that for cost reasons, the first embodiment with the slightly more expensive valve slide is preferred.

3 shows a second embodiment of the switching device 74 ' , This can according to the switching device 1 and 2 replace, and in particular in those cases where a fluid-tight closure of the first and the second working port 31 ; 32 should be possible. Instead of the 3/3-way valve are two separate 2/2-way valves 73 provided, each between the output terminal 83 the pressure reducing valve and the associated first and second working port 31 ; 32 are switched. The 2 / 2-way valves are each designed as a seat valve, which is closed fluid-tight. Although it would be conceivable to perform a 3/3-way valve in the seat design, but this is more expensive than the execution 3 ,

Preferably, in any operating state of the hydraulic drive system, both 2/2-way valves 73 open. The three remaining switching combinations correspond to the switching positions of the 3/3-way valve in 1 and 2 ,

LIST OF REFERENCE NUMBERS

10

hydraulic drive system (first embodiment)

10 '

hydraulic drive system (second embodiment)

11

pump

12

Delivery pressure regulator

13

Delivery pressure of the pump

14

tank

15

cylinder

16

hoist

17

position sensor

18

control device

19

actuating pressure

30

valve assembly

31

first work connection

32

second work connection

33

first inlet connection

34

first return connection

35

pressure sensor

36

second check valve

37

pressure compensator

38

shuttle valve

39

Load-sensing pressure

50

control valve

51

first position

52

second position

53

third position

54

fourth position

55

fifth position

56

sixth position

57

control panel

58

Load-sensing connection

70

Pressure control device

71

first check valve

72

3/3-way valve

73

2/2 way valve

74

Switching device (first embodiment)

74 '

Switching device (second embodiment)

80

Pressure reducing valve

81

second inlet connection

82

second return connection

83

output port

84

first target pressure

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1672225 B1 [0002, 0004, 0007, 0022]
• EP 2870842 [0015]

Claims (11)

Valve arrangement (30) having a first and a second working port (31; 32), a first inlet port (33) and at least one first return port (34), wherein a control valve (50) and a pressure regulating device (70) are provided, which in parallel the first and the second working port (31; 32) are connected, wherein the pressure regulating device (70) is arranged so that at least selectively either the pressure at the first or at the second working port (31; 32) can be regulated to a predetermined first target pressure (84) wherein the control valve (50) has a load sensing port (58) having first, second, third and fourth positions (51; 52; 53; 54), wherein in the first position (51) the first Working connection (31) via the control valve (50) with a first return port (34) is fluidly connected, wherein the first inlet port (33) via the control valve (80) with the second working port (32) fluidly connected is, wherein the second working port (32) via the control valve (80) to the load-signaling port (58) is fluidly connected, wherein in the third position (53), a connection between the control valve (50) and the first and the second working port (31; 32) is in each case blocked by the control valve (50), wherein in the fourth position (54) the second working port (32) is fluidically connected via the control valve (50) to a first return port (34), characterized in that in the second Position (52) the first working port (31) via the control valve (50) with a first return port (34) is fluidly connected, wherein in the second, the third and the fourth position (52; 53; 54) a connection between the control valve (50) and the first inlet port (33) is blocked by the control valve (50), wherein the pressure regulating device (70) is connected to the first inlet port (33). Valve arrangement according to one of the preceding claims, wherein the control valve (50) has a fifth position (55) in which a connection between the control valve (50) and the first inlet port (33) from the control valve (50) is locked, the first and the second working port (31; 32) are fluidically connected to a first return port (34). Valve arrangement according to one of the preceding claims, wherein the first, the second, the third, the fourth and optionally the fifth position (51-55) of the control valve (50) are arranged side by side in the order given. Valve arrangement according to one of the preceding claims, wherein the pressure regulating device (70) comprises at least one pressure reducing valve (80) each having a second inlet port (81), a second return port (82) and an outlet port (83), wherein the pressure at the outlet port (80) 83) can be adjusted to the first setpoint pressure by opening either a fluidic connection from the outlet connection (83), to the second inlet connection (81) or to the second return connection (82), the second return connection (82) being connected to a first return connection (34). is fluidically connected, wherein the second inlet port (81) is at least indirectly connected to the first inlet port (33). Valve arrangement after Claim 4 wherein at least one, preferably each pressure reducing valve (80) is associated with a first check valve (71) which is arranged between the first inlet port (33) and the respective second inlet port (81), wherein it exclusively a fluid flow from the first inlet port (33) to the relevant second inlet port (81). Valve arrangement after Claim 4 or 5 wherein the pressure control device (70) comprises a single pressure reducing valve (80), wherein a switching device (74; 74 ') is provided, via which the outlet port (83) of the pressure reducing valve (80) is selectively connected to either the first or the second working port (31 ; 32) is fluidically connectable, both said compounds are shut off at the same time. Valve arrangement according to one of the preceding claims, wherein the load reporting port (58) of the control valve (50) in the second position (52) with the second working port (32), in the third position (53) with a first return port (34) and in the fourth position (54) to the first working port (31) is fluidly connected, wherein the load reporting port (58) with a delivery pressure regulator (12) and a pump (11) is at least indirectly fluidly connectable. Valve arrangement after Claim 7 in which the load-signaling connection (58) of the control valve (50) in the second position (52) and / or the third position (53) and / or the fourth position (54) is blocked by the control valve (50), wherein a shuttle valve (50) 38) is provided, which is the input side to the load-sensing connection (58) and the output port (83) of the pressure reducing valve (80) fluidly connected, the shuttle valve (38) on the output side with a delivery pressure regulator (12) of a pump (11) at least indirectly fluidly connectable is. Valve arrangement according to one of the preceding claims, wherein the first and / or the second working port (31; 32) in each case a second check valve (36) is assigned, via which the relevant working port (31; 32) is connected to a first return port (34) wherein the second check valve (36) allows only fluid flow from the respective first return port (34) to the respective working port (31; 32). A hydraulic drive system (10, 10 ') having a valve assembly (30) according to any one of the preceding claims, wherein a double-acting cylinder (15) is connected to the first and second working ports (31; 32), to which at least one first return port (15). 34), a tank (14) is connected, wherein a pump (11) is provided, with which pressurized fluid from the tank (14) to the first inlet port (33) can be conveyed, wherein the pump (11) has an adjustable displacement volume, wherein a Delivery pressure regulator (12) is provided, with which a delivery pressure (13) of the pump (11) by adjusting the displacement volume of the pump (11) is adjustable to a second desired pressure. Hydraulic drive system according to Claim 10 , backward on Claim 7 or 8th wherein the second set pressure depends on the pressure at the load-sensing port (58) or at the output-side pressure at the shuttle valve (38).

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