CN214366961U - Flushing device, hydraulic pump, closed hydraulic system and concrete pump truck - Google Patents

Abstract

A flushing device for a closed hydraulic system, a hydraulic pump, the closed hydraulic system and a concrete pump truck are provided. An irrigation device comprising: a shuttle valve including two inlets and one outlet and selectively communicating a lower pressure one of the two inlets to the outlet; a relief valve connected to an outlet of the shuttle valve, wherein the relief valve opens only when a pressure from the shuttle valve is above a predetermined pressure during normal operation. The flushing device also comprises a logic valve, wherein the logic valve comprises a logic valve spool, the logic valve is connected to the overflow valve, and the logic valve spool can be switched between a first position and a second position, and in the first position, the logic valve does not influence the normal work of the overflow valve; in the second position, the logic valve keeps the spill valve closed.

Description

Flushing device, hydraulic pump, closed hydraulic system and concrete pump truck

Technical Field

The disclosure relates to the field of hydraulic pressure, in particular to a flushing device for a closed hydraulic system, a hydraulic pump, the closed hydraulic system and a concrete pump truck.

Background

The hydraulic power system of the concrete pump truck has two basic forms: open hydraulic systems and closed hydraulic systems. The closed hydraulic system is composed of a hydraulic pump, a hydraulic oil cylinder, a radiator, a filter and the like, the whole system is compact in structure, high in efficiency and stable in performance, but the temperature of hydraulic oil is continuously increased because the hydraulic oil serving as a medium in the closed hydraulic system is circulated repeatedly in the system, and the whole hydraulic system is further influenced. In order to solve the problem, in the prior art, a flushing valve is arranged for the hydraulic pump, so that the low-pressure oil way is communicated with the flushing valve, part of hydraulic oil in the low-pressure oil way flows back to the radiator through the flushing valve, and the temperature in the closed hydraulic system is reduced, so that the purpose of heat dissipation is achieved.

In practice, as the hydraulic pump is alternately switched between opposite oil delivery directions, significant pressure fluctuations occur in closed hydraulic systems, in particular at the initial moment of the oil delivery direction switching process. Therefore, how to effectively alleviate or solve the pressure fluctuation generated in the oil path conveying direction conversion process of the closed hydraulic system has become a technical problem to be overcome in the industry.

SUMMERY OF THE UTILITY MODEL

The present disclosure is directed to overcoming or reducing at least one or more of the problems or disadvantages in the related art as set forth above.

Therefore, at least one object of the present disclosure is to provide a flushing device for a closed hydraulic system, which can reduce pressure fluctuations generated during switching of an oil feeding direction of the closed hydraulic system with a simple configuration at low cost.

According to one aspect of the present disclosure, there is provided a flushing device for a closed hydraulic system comprising a hydraulic pump and a hydraulic consumer, the hydraulic pump being alternately switchable between a first and a second opposite conveying direction, the flushing device comprising:

a shuttle valve including two inlets and one outlet and selectively communicating a lower pressure one of the two inlets to the outlet;

a relief valve connected to an outlet of the shuttle valve, wherein the relief valve opens only when pressure from the shuttle valve is above a predetermined pressure during normal operation;

wherein the flushing device further comprises a logic valve comprising a logic valve spool, the logic valve being connected to the excess flow valve and the logic valve spool being switchable between a first position in which the logic valve does not affect the normal operation of the excess flow valve and a second position; in the second position, the logic valve keeps the spill valve closed.

In one embodiment, the relief valve includes a relief valve spool having a pressure receiving end facing the valve seat and a back pressure end facing away from the valve seat, and a valve seat, the flushing device includes a back pressure oil passage communicating an outlet of the shuttle valve to the back pressure end of the relief valve, the logic valve is disposed in the back pressure oil passage, blocks the back pressure oil passage when the logic valve is in the first position, and communicates the back pressure oil passage when the logic valve is in the second position.

In one embodiment, the logic valve is in the second position only at an initial moment of a switching process of the hydraulic pump from one of the first and second conveying directions to the other of the first and second conveying directions.

In one embodiment, the logic valve spool is formed with a communicating portion that blocks back pressure oil passages on both sides of the spool of the logic valve when the logic valve spool is in the first position, and a blocking portion that communicates the back pressure oil passages when the logic valve spool is in the second position.

In one embodiment, the logic valve spool includes a cylindrical portion, the communication portion includes an annular slot formed on the cylindrical portion, and the blocking portion includes a cylindrical surface of the cylindrical portion.

In an exemplary embodiment, the logic valve spool is formed with an intermediate block portion, two communication portions formed on both sides in the axial direction of the intermediate block portion, and two end block portions located on the opposite side of the two communication portions from the intermediate block portion.

In an alternative embodiment, the logic valve spool is formed with a communication portion and two blocking portions located on both axial sides of the communication portion.

In one embodiment, the shuttle valve has a neutral position in which pressure from both inlets is throttled and communicated to the outlet.

In one embodiment, the intermediate blocking portion of the logic valve spool blocks a back pressure oil path when the shuttle valve is in the intermediate position.

In one embodiment, the shuttle valve includes a shuttle valve spool including a depressed shuttle valve communication portion at a center, shuttle valve blocking portions at both sides of the shuttle valve communication portion, and a throttling portion between the shuttle valve communication portion and the shuttle valve blocking portions, the throttling portion having a cross-sectional dimension slightly smaller than a cross-sectional dimension of the shuttle valve blocking portions but larger than the cross-sectional dimension of the shuttle valve communication portions.

In one embodiment, the logic valve further comprises springs disposed at both ends of the logic valve spool, respectively.

In one embodiment, the switching action of the logic valve is actuated by a pressure signal applied to both sides of the logic valve spool.

In one embodiment, the pressure signal is derived from a control pressure that causes the hydraulic pump to switch the conveying direction between the first conveying direction and the second conveying direction.

According to another aspect of the present disclosure, a hydraulic pump is provided which is alternately switchable between opposite first and second delivery directions, the hydraulic pump comprising a flushing device as described in any of the previous embodiments.

According to yet another aspect of the present disclosure, there is provided a closed type hydraulic system including: the hydraulic pump of any preceding embodiment; and a hydraulic load.

According to still another aspect of the present disclosure, there is provided a concrete pump truck including: the closed hydraulic system of any preceding embodiment.

The flushing device for the closed hydraulic system, the hydraulic pump, the closed hydraulic system and the concrete pump truck directly reduce pressure fluctuation generated by the closed hydraulic system in the process of converting the oil path conveying direction, and fundamentally reduce damage caused by the pressure fluctuation so as to prolong the service life of the whole system.

Other disclosed objects that can be achieved by the present disclosure, as well as other technical effects that can be achieved by the present disclosure, will be set forth in the following detailed description and drawings, which are incorporated in the description of specific embodiments.

Drawings

In order to make the aforementioned and other objects, features and advantages of the present disclosure comprehensible, the present disclosure accompanied with figures is further described below.

Fig. 1 is a schematic structural view of a flushing device for a closed hydraulic system according to an embodiment of the present disclosure;

FIG. 2 is a cross-sectional view of the flushing device taken along G-G shown in FIG. 1 showing the internal configuration of the excess flow valve and the logic valve in accordance with an exemplary embodiment of the present disclosure;

FIG. 3 is a cross-sectional view of the flushing device taken along G-G shown in FIG. 1 showing the internal configuration of the excess flow valve and the logic valve in accordance with an alternative embodiment of the present disclosure;

FIG. 4 is a cross-sectional view of the flushing device taken along J-J shown in FIG. 1 showing the internal configuration of the shuttle valve according to an exemplary embodiment of the present disclosure;

FIG. 4a is an enlarged view of a portion of FIG. 4 at N, showing the configuration of the throttle portion;

FIG. 5 is a schematic view of the flushing device of the exemplary embodiment shown in FIG. 2; and

fig. 6 is a schematic view of the flushing device of the alternative embodiment shown in fig. 3.

Detailed Description

Reference will now be made in detail to the present embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements throughout. The specific embodiments described below with reference to the drawings are illustrative and intended to illustrate the disclosure and should not be construed as a limitation on the disclosure.

The disclosure relates to a closed hydraulic system, which mainly comprises a closed hydraulic pump, a pilot pressure source, a main oil cylinder, a flushing overflow valve and the like. The position of a swash plate of the closed hydraulic pump is controlled by controlling the pilot pressure signal, and then the output direction and the flow of the hydraulic oil in the hydraulic pump are controlled. Because of the closed system, the hydraulic oil heats quickly, and a flushing overflow valve is needed to separate out a part of hydraulic oil in the system for cooling.

The present disclosure provides a flushing device for a closed hydraulic system. The closed hydraulic system includes a hydraulic pump, a pilot pressure source, a master cylinder, etc., wherein a swash plate position in the hydraulic pump is controlled by controlling a pilot pressure signal so that a high-pressure oil passage and a low-pressure oil passage of hydraulic oil can be alternately switched between opposite first and second oil passages. The flushing device provided by the disclosure is used for being communicated with the low-pressure oil way and refluxing part of hydraulic oil in the low-pressure oil way to the radiator.

As shown in fig. 1 to 4, the flushing device provided by the present disclosure mainly includes: a valve body 100, and an overflow valve 200, a shuttle valve 400, and a logic valve 300 disposed within the valve body 100. The shuttle valve includes two inlets communicating with the hydraulic pump and one outlet, and the overflow valve is connected to the outlet of the shuttle valve. The shuttle valve is configured to selectively communicate a lower pressure one of the two inlets to the outlet to introduce low pressure oil into the spill valve. That is, the shuttle valve 400 mainly functions to communicate the low-pressure oil passage of the system with the relief valve 200 by comparing the high-pressure and low-pressure oil passages of the system for flushing and cooling of the hydraulic oil. The relief valve 200 has a main function of adjusting the output cooling hydraulic oil by setting different opening pressures, and also can keep the pressure of a low-pressure oil path in the system stable. Relief valve 200 opens during normal operation only when the pressure from shuttle valve 300 is above a predetermined pressure. The logic valve 300 is connected to the relief valve 200. The main function of the logic valve 300 is to selectively open or shield the function of the relief valve 200 by judging the input pilot pressure signal.

Specifically, as shown in fig. 4 and 4a, the shuttle valve 400 includes two shuttle valve inlet ports 400a, 400b and one shuttle valve outlet port 400c, and a shuttle valve spool 410 disposed in a chamber of the shuttle valve, shuttle valve springs 402 and 403 respectively disposed at both ends of the shuttle valve spool 410, and shuttle valve plugs 404 and 405 respectively disposed at outer ends of the shuttle valve springs 402 and 403. The pressure from the two shuttle valve inlets 400a, 400b is directed to the spring chamber where the corresponding side spring is located, respectively. The shuttle valve spool 410 further includes a recessed shuttle valve communicating portion 411 at the center, shuttle valve blocking portions 412 at both sides of the shuttle valve communicating portion 411, and a choke portion 413 (shown in fig. 4 a) between the shuttle valve communicating portion 411 and the shuttle valve blocking portion 412, the cross-sectional dimension of the choke portion 413 being slightly smaller than the cross-sectional dimension of the shuttle valve blocking portion 412 but larger than the cross-sectional dimension of the shuttle valve communicating portion 411. Corresponding to the exemplary embodiment of the present disclosure as shown in fig. 2, the shuttle valve 400 has a neutral position, and when the shuttle valve 400 is in the neutral position, the pressure from both inlets 400a, 400b is communicated to the outlet 400c through the restriction of the restriction 413. When the pressure from one shuttle valve inlet (e.g., the right inlet 400b) is greater than the pressure from the other shuttle valve inlet (e.g., the left inlet 400a), the pressure of the right inlet 400b is directed to the right spring chamber, the shuttle valve spool 410 moves to the left by the hydraulic oil pressure, and the communication portion 411 communicates the left inlet 400a (low pressure side) with the outlet 400c, thereby allowing the low pressure to enter the relief valve. When the pressure from the left inlet port 400a is greater than the pressure from the right inlet port 400b, the shuttle valve spool 410 moves to the right, and the communication portion 411 makes the right inlet port 400b (low pressure side) communicate with the outlet port 400c, similarly. Thus, the shuttle valve 400 always communicates the low-pressure oil passage of the system with the relief valve 200 for flushing and cooling of the hydraulic oil.

As shown in fig. 2, a relief valve 200, according to an exemplary embodiment of the present disclosure, includes a relief valve spool 206, a relief valve spring 207, a relief valve bonnet 210, a seal nut 211, a set screw 212, a damper 208 communicating the spring cavity with a discharge port 209, and the like. The relief valve element 206 has a pressure receiving end 206a (left end in the drawing) facing the valve seat 215 and a back pressure end 206b (right end in the drawing) facing away from the valve seat 100. The hydraulic oil from the shuttle valve 400 enters the spill valve from the pressure receiving end 206a of the spill valve spool 206 through the oil passage H, and when the pressure of the hydraulic oil is greater than the pressure set by the spill valve spring 207, the spill valve opens so that the hydraulic oil from the shuttle valve 400 enters the discharge port 209. It is understood that the above structure is merely an example of a relief valve, and those skilled in the art can adopt other structures of relief valves.

According to the present disclosure, the flushing device further includes a back pressure oil passage that connects the outlet of the shuttle valve 400 to the back pressure end 206b of the relief valve 200, the logic valve 300 is disposed in the back pressure oil passage, and the logic valve spool 303 is switchable between a first position at which the logic valve 300 blocks the back pressure oil passage so as not to affect the normal operation of the relief valve 200; in the second position, the logic valve 300 makes the back pressure oil passage communicate, and hydraulic oil is supplied to both the pressure receiving end 206a and the back pressure end 206b of the relief valve 200, keeping the relief valve 200 closed. In fact, the hydraulic pump can be alternately switched between the opposite first and second delivery directions, while the logic valve 300 is in the second position only at the initial moment of the switching process of the hydraulic pump from one of the first and second delivery directions to the other of the first and second delivery directions, so that the spill valve 200 is temporarily kept closed at this initial moment, thereby directly reducing the pressure fluctuations generated by the closed hydraulic system during the switching of the oil delivery direction.

Specifically, in the exemplary embodiment of the present disclosure as shown in fig. 2, the back pressure oil passage is provided inside the valve body 100, and includes, in order, an oil passage H, an oil passage X, an oil passage Y connected to the shuttle valve outlet, and an oil passage connected to the spring chamber of the relief valve back pressure end 206 b. The logic valve chamber of the logic valve 300 is disposed between oil passage X and oil passage Y. Those skilled in the art will appreciate that only a portion of the back pressure oil passage is shown, and the back pressure oil passage can be disposed at any suitable place in the valve body 100 as long as it introduces oil from the shuttle valve outlet to the back pressure end 206b of the relief valve.

In the logic valve chamber, a logic valve spool 303, a logic valve plug 305, logic valve springs 302 and 304, and the like are provided, and the logic valve springs 302 and 304 are provided at both ends of the logic valve spool 303, respectively. The logic valve spool 303 is formed with a communicating portion 310 and a blocking portion 320, wherein the blocking portion 320 blocks back pressure oil passages on both sides of the logic valve spool 303 when the logic valve spool 303 is in the first position, and the communicating portion 310 communicates back pressure oil passages on both sides of the logic valve spool 303 when the logic valve spool 303 is in the second position. More specifically, as shown in fig. 2, the logic valve spool 303 includes a cylindrical portion, the communication portion 310 includes an annular cutout groove formed on the cylindrical portion, and the blocking portion 320 includes a cylindrical surface of the cylindrical portion. Further, in the present exemplary embodiment as shown in fig. 2, the logic valve spool 303 is formed with a middle stopper portion 320a, two communicating portions 310a, 310b formed on both sides of the middle stopper portion 320a in the axial direction, and two end stopper portions 320b, 320c located on the opposite side of the two communicating portions 310 from the middle stopper portion 320 a. That is, in the exemplary embodiment of the present disclosure as shown in fig. 2, the intermediate blocking portion 320a is located between the two communicating portions 310a, 310b, at the neutral position.

Fig. 5 is a schematic view of the flushing device of the exemplary embodiment shown in fig. 2. In accordance with the present disclosure, the switching action of the logic valve 300 is actuated by a pilot pressure signal applied to both sides of the logic valve spool. The pilot pressure signal is derived from a control pressure that causes the hydraulic pump to switch the delivery direction between the first delivery direction and the second delivery direction. That is, the function of the relief valve 200 may be temporarily shielded according to the input pilot pressure signal at the initial time of the switching process.

Specifically, when no pilot pressure signal is input or the input pilot pressure signal is lower than the pressure set value of the logic valve, the shuttle valve 400 is in the neutral position, and the pressures from both inlets 400a, 400b are communicated to the outlet 400c through the throttle of the throttle portion 413. When the logic valve 300 is in the first position, the intermediate blocking portion 320a blocks the back pressure oil path, no pressure is supplied to the back pressure side of the relief valve 200, and only the pressure receiving end 206a of the relief valve 200 receives the pressure from the shuttle valve 400, the logic valve 300 does not affect the function of the relief valve 200.

When a pilot pressure signal is input from one side of the logic valve 300 and the input pilot pressure signal is higher than a predetermined pressure (at this time, the hydraulic pump is in the first input direction or the second input direction under the action of the pilot pressure, and the shuttle valve 400 becomes the first position or the second position under the action of the pressure from the hydraulic pump), the logic valve 300 moves rightward to a second position (for example, a right communication position in fig. 5) under the action of the pilot pressure signal, for example, the upper communication portion 310a makes the oil passage X communicate with the oil passage Y and further makes the back pressure oil passage communicate with each other in correspondence to the downward movement of the spool in fig. 2, and at this time, the pressure from the shuttle oil passage valve 400 acts on both the pressure receiving end 206a of the relief valve spool along the H and the back pressure end 206b of the relief valve spool via the back pressure oil passage, but since the force receiving area of the back pressure end 206b of the relief valve spool is larger than the force receiving area of the pressure receiving end 206a, the back pressure end 206b is also biased by the spring, and therefore the relief valve element is pressed against the valve seat and cannot be opened. At this time, the relief valve will be maintained in a closed state by the pressure difference between both sides and the action of the spring regardless of the pressure from the shuttle valve, that is, the relief function of the relief valve 200 is temporarily shielded.

When the logic valve 300 continues to move rightward to the first position, that is, the spool continues to move downward in fig. 2, the upper blocking portion 320b of the logic valve spool disconnects the oil passage X and the oil passage Y, the back pressure oil passage is blocked again, no hydraulic oil is supplied to the back pressure end 206b of the relief valve spool, the relief valve 200 only has the pressure receiving end 206a under the pressure from the shuttle valve 400, and the relief valve 200 returns to normal operation.

Subsequently, when the pilot pressure signal is input from the other side of the logic valve 300 and the input pilot pressure signal is higher than the predetermined pressure, the logic valve 300 moves leftward to a second position (for example, a right communication position in fig. 5), corresponding to fig. 2, in which the logic valve spool moves from bottom to top to the upper communication portion 310a to again communicate the back pressure oil path, and the hydraulic oil pressure from the shuttle valve is simultaneously supplied to both ends of the relief valve spool to keep the relief valve 200 closed, at which time the function of the relief valve 200 is temporarily blocked. Thereafter, the logic valve 300 continues to move leftward, that is, the valve element continues to move upward in fig. 2, and after passing through the intermediate blocking portion 320a and the lower communication portion 310b quickly, the lower blocking portion 320c blocks the back pressure oil path again, and at this time, the logic valve 300 does not affect the function of the relief valve 200, so that the relief valve 200 returns to normal operation.

In addition, when no pilot pressure signal is input from both sides, the logic valve 300 is in the first position of the middle position under the action of the spring to cut off the back pressure oil path, at this time, the function of the relief valve 200 is not affected by the logic valve 300, and the shuttle valve 400 is also in the middle position to lead the hydraulic oil to the pressure receiving end 206a of the relief valve 200 through the throttling part 413.

In an alternative embodiment of the present disclosure as shown in fig. 3, no restriction 413 is provided on the shuttle valve 400, i.e., both inlets 400a, 400b are disconnected from the outlet 400c when the shuttle valve 400 is in the neutral position. In this case, the logic valve spool 303 also includes a cylindrical portion, the communication portion 310 includes an annular cutout groove formed on the cylindrical portion, and the blocking portion 320 includes a cylindrical surface of the cylindrical portion. However, the logic valve spool 303 is formed with only one communication portion 310 and two blocking portions 320 located on both sides in the axial direction of the communication portion 310. That is, in an alternative embodiment of the present disclosure as shown in fig. 3, one communication portion 310 is located between two blocking portions 320.

Fig. 6 is a schematic view of the flushing device of the alternative embodiment shown in fig. 3. Unlike fig. 5, during the movement of the logic valve 300, the middle position is a second position communicating with the back pressure oil path, and both sides are first positions blocking the back pressure oil path. When the pilot pressure control hydraulic pump is not present, for example, when the system is in a standby state, the shuttle valve 400 is in the neutral position, both inlets are disconnected from the outlets, the logic valve spool is also in the neutral position at this time, and the communication portion 310 communicates the back pressure oil path, so that the relief valve remains closed. During operation of the hydraulic pump, whenever the pilot pressure controls the hydraulic pump to switch the delivery direction, the pilot pressure simultaneously controls the logic valve to change the direction, and during the up-and-down movement (shown in fig. 2) of the logic valve spool, the communication portion 310 briefly communicates with the back pressure oil passage, thereby briefly keeping the relief valve closed. The working principle is similar to that in the exemplary embodiment shown in fig. 5 and will not be described again here.

In addition, the present disclosure also provides a hydraulic pump for a closed hydraulic system. The hydraulic pump is alternately switchable between a first and a second opposite conveying direction, wherein the hydraulic pump comprises a flushing device as described in any of the embodiments above.

In addition, this disclosure still provides a closed hydraulic system. The closed hydraulic system comprises at least: a hydraulic pump as described above, and a hydraulic load.

In addition, the disclosure also provides a concrete pump truck. The concrete pump truck at least comprises: closed hydraulic system as described above.

The flushing device for the closed hydraulic system, the hydraulic pump, the closed hydraulic system and the concrete pump truck directly reduce pressure fluctuation generated by the closed hydraulic system in the process of converting the oil path conveying direction, and fundamentally reduce damage caused by the pressure fluctuation so as to prolong the service life of the whole system.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood in the art. The definitions set forth herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure.

The foregoing detailed description of the present disclosure has been presented for purposes of illustration only and not limitation, and it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the disclosure. The protection scope of the claims of the present disclosure should be determined as defined by the claims of the present application.

Claims (16)

1. Flushing device for a closed hydraulic system comprising a hydraulic pump and a hydraulic consumer, the hydraulic pump being alternately switchable between a first and a second opposite conveying direction, the flushing device comprising:

a shuttle valve including two inlets and one outlet and selectively communicating a lower pressure one of the two inlets to the outlet;

a relief valve connected to an outlet of the shuttle valve, wherein the relief valve opens only when pressure from the shuttle valve is above a predetermined pressure during normal operation;

characterized in that the flushing device further comprises a logic valve comprising a logic valve spool, the logic valve being connected to the overflow valve and the logic valve spool being switchable between a first position in which the logic valve does not affect the normal operation of the overflow valve and a second position; in the second position, the logic valve keeps the spill valve closed.

2. The flushing device of claim 1,

the overflow valve comprises an overflow valve core and a valve seat, the overflow valve core is provided with a pressure end facing the valve seat and a back pressure end far away from the valve seat, the flushing device comprises a back pressure oil path which communicates an outlet of the shuttle valve to the back pressure end of the overflow valve, the logic valve is arranged in the back pressure oil path, when the logic valve is at the first position, the back pressure oil path is blocked, and when the logic valve is at the second position, the back pressure oil path is communicated.

3. The flushing device of claim 1,

the logic valve is in the second position only at an initial moment of a switching process of the hydraulic pump from one of the first and second conveying directions to the other of the first and second conveying directions.

4. The flushing device of claim 2,

the logic valve spool is provided with a communicating part and a blocking part, wherein when the logic valve spool is at the first position, the blocking part blocks back pressure oil paths on two sides of the logic valve spool, and when the logic valve spool is at the second position, the communicating part enables the back pressure oil paths to be communicated.

5. The flushing device of claim 4,

the logic valve spool includes a cylindrical portion, the communication portion includes an annular slot formed on the cylindrical portion, and the blocking portion includes a cylindrical surface of the cylindrical portion.

6. The flushing device of claim 4,

the logic valve spool is provided with a communicating part and two blocking parts positioned at two axial sides of the communicating part.

7. The flushing device of claim 4,

the logic valve spool is formed with a middle block portion, two communicating portions formed on both sides in the axial direction of the middle block portion, and two end block portions located on the opposite side of the two communicating portions from the side where the middle block portion is located.

8. The flushing device of claim 7,

the shuttle valve has a neutral position in which pressure from both inlets is throttled and communicated to the outlet.

9. The flushing device of claim 8,

when the shuttle valve is in the intermediate position, the intermediate blocking portion of the logic valve spool blocks a back pressure oil path.

10. The flushing device of claim 1,

the shuttle valve comprises a shuttle valve spool, the shuttle valve spool comprises a sunken shuttle valve communicating part positioned in the center, shuttle valve blocking parts positioned on two sides of the shuttle valve communicating part, and a throttling part positioned between the shuttle valve communicating part and the shuttle valve blocking parts, and the cross-sectional dimension of the throttling part is slightly smaller than that of the shuttle valve blocking parts but larger than that of the shuttle valve communicating part.

11. The flushing device of claim 1,

the logic valve also comprises springs which are respectively arranged at two ends of the valve core of the logic valve.

12. The flushing device of claim 1,

the switching action of the logic valve is actuated by a pressure signal applied to both sides of the logic valve spool.

13. The flushing device of claim 12,

the pressure signal is derived from a control pressure that causes the hydraulic pump to switch the conveying direction between the first conveying direction and the second conveying direction.

14. Hydraulic pump which can be alternately switched between a first and a second opposite conveying direction, characterized in that it comprises a flushing device according to any one of claims 1 to 13.

15. A closed hydraulic system characterized by comprising:

the hydraulic pump of claim 14; and

and (4) hydraulic loading.

16. A concrete pump truck is characterized by comprising: the closed hydraulic system of claim 15.

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