KR20140001745A - Hydraulic circuit for lifting and lowering reaping part of combine harvester - Google Patents

Abstract

The purpose of the present invention is to reduce a time lag generated when lowering a reaper at high speed. To this end, a hydraulic circuit comprise: a pilot-operated check valve (11); a first switching valve (7); a first throttle (9) which is connected to the first switching valve (7) in parallel and restricts the flow of hydraulic fluid supplied from a hydraulic pump (4) to a hydraulic cylinder (2); a resistance valve (10) which is connected to the first throttle (9) in series and opens a valve when a primary fluid pressure reaches a predetermined pressure; a second throttle (12b) for restricting the flow of hydraulic fluid which flows into the pilot-operated check valve (11) backward to be drained; a third throttle (18) which has a flow path sectional area smaller than the second throttle (12b) and restricts the flow of the drained hydraulic fluid; and a second switching valve (19) for selectively switching a flow path of the drained hydraulic fluid into a flow path of the hydraulic fluid drained through the third throttle (18).

Description

HYDRAULIC CIRCUIT FOR LIFTING AND LOWERING REAPING PART OF COMBINE HARVESTER}

This invention relates to the hydraulic circuit for elevating the harvesting | reaping part of a combine.

Conventionally, a combine is generally equipped with a harvesting | removing part which can raise and lower freely in the front part of a body. For example, there is a desire to raise and lower the cutting unit at low speed when setting the cutting height, and to raise and lower at high speed after the end of the work or before the start of the work. Therefore, the hydraulic circuit which makes a hydraulic cylinder which raises and lowers a harvesting | reaping part possible to shift is proposed (for example, Unexamined-Japanese-Patent No. 06-113603).

When lowering the harvesting section, the hydraulic circuit of JP 06-113603 A selects and operates an electronic on-off valve having different flow rates connected in parallel to control the flow rate of the hydraulic oil discharged from the hydraulic cylinder while raising the harvesting section. At the high speed, the hydraulic fluid is supplied to the hydraulic cylinder at the high speed, and at the low speed, the hydraulic oil is switched to the bleed-off circuit which reliefs a part of the hydraulic oil from at least one of the electronic on / off valves and supplies the hydraulic cylinder. The flow rate of is controlled.

However, since the hydraulic circuit of Japanese Unexamined Patent Application Publication No. 06-113603 controls the hydraulic cylinder by a so-called bleed-off circuit in order to raise the cutting portion at a low speed, when the load applied to the cutting portion becomes large, the pressure of the hydraulic oil increases accordingly. As a result of the increase of the flow rate which rises and reliefs, the ascending flow rate greatly decreases, and the ascent rate decreases significantly.

Moreover, in the said hydraulic circuit, the hydraulic fluid drained from a hydraulic cylinder at the time of a low speed rise raises temperature by the friction at the time of passing through the electronic switching valve which limits a flow volume. Since the viscosity of the hydraulic fluid decreases as the temperature increases, the viscosity resistance of the hydraulic oil decreases as the temperature rises, and the hydraulic fluid easily passes through the solenoid valve. On the other hand, when the load is applied to the harvesting section, the pressure of the hydraulic oil also increases. Therefore, when the load is applied to the harvesting section in a state where the temperature rises, the load increases, and thus the passage of the electronic on / off valve becomes easier to pass. Since the relief flow rate of the hydraulic fluid increases as the flow rate increases, the flow rate supplied to the hydraulic cylinder decreases, so that the rising speed of the harvesting section is slowed down and the variation in the rising speed according to the load applied to the harvesting section is large.

In addition, even when the engine rotates at a low speed during idling or the like, even if it tries to raise the harvesting section at low speed, the discharge flow rate from the hydraulic pump is small in the bleed-off circuit, so that the flow rate exceeding the relief flow rate cannot be secured and the low speed cannot be increased. .

And the structure which changes the lifting speed of a harvesting | reaping part by selecting two electromagnetic switching valves from which a flow volume differs, and since a throttle for a low speed rising and a low speed falling is used in common, matching with a combine main body may be difficult.

Therefore, in order to solve the said problem, the hydraulic fluid supplied to a hydraulic cylinder by connecting a supply flow restriction throttle in parallel with the switchable opening and closing valve formed in a supply flow path, and switching the switching valve formed in a supply flow path to closing at the time of low speed rise. A hydraulic circuit has been proposed which makes it possible to switch the circuit into a meter-in-circuit which is controlled by a throttle for supply flow restriction (Japanese Patent No. 4994296).

Japanese Laid-Open Patent Publication No. 06-113603 Japanese Patent Publication No. 4994296

According to the hydraulic circuit disclosed in Japanese Patent No. 4994296, it is possible to suppress the fluctuation of the rising speed of the harvesting section according to the relief flow rate of the hydraulic oil and to exhibit an excellent effect that the low speed rise is possible even at the low speed rotation of the engine. In some cases, there is a slight time lag from the start of the high speed lowering operation to the actual start of the lowering of the harvesting section when the harvesting section is lowered at high speed, particularly when the hydraulic oil flow rate is low and the oil temperature is high, such as during idling.

Accordingly, the present invention is to further improve the hydraulic circuit disclosed in Japanese Patent No. 4994296, and to provide a hydraulic lift circuit for raising and lowering the combine which can shorten the time lag generated when lowering the cutting section at high speed. do.

As a result of earnest research by the present inventors, the time lag generated when the harvesting unit is lowered at a high speed has a throttle for supply flow rate restriction, in which the hydraulic oil from the hydraulic pump is formed for low speed rising when the harvesting unit is lowered at a high speed. It has been found that the cause is a path configured to drain through the first throttle).

Therefore, in order to achieve the above object, the hydraulic section for lifting the harvester of the combine according to the present invention is a hydraulic circuit for driving the hydraulic cylinder for lifting the harvester of the combine by the hydraulic oil sent from the oil tank through the hydraulic pump. And a pilot operated check valve for allowing back flow of hydraulic oil from the hydraulic cylinder using a pilot pressure, a first position for opening the hydraulic pressure primary port and a secondary port for the hydraulic cylinder hydraulic flow path, and the hydraulic pressure primary port and the pilot port. A third position for opening the secondary port for the pressure hydraulic flow passage and at the same time for closing the secondary port for the hydraulic cylinder operating flow passage and the tank port and closing the pressure primary port and the secondary port for the hydraulic cylinder hydraulic flow passage; The hydraulic pump connected in parallel with the first switching valve switchable to a position and the first switching valve A first throttle for restricting the flow rate of the hydraulic oil supplied from the hydraulic cylinder to the hydraulic cylinder, and connected in series with the first throttle and passing through the first throttle when the first switching valve is in the second position. A resistance valve for regulating hydraulic fluid to secure a pilot pressure of the pilot operated check valve, a second throttle for restricting a flow rate of hydraulic oil drained by flowing the pilot operated check valve back, and smaller than the second throttle And a third throttle for restricting the flow rate of the hydraulic oil to be drained, and a second switching valve for selectively switching the oil passage of the hydraulic oil to be drained into the oil passage of the hydraulic oil drained through the third throttle. It is characterized by.

The pilot operated check valve includes a check valve body, a seat on which the check valve body can be moved, a spring for elastically supporting the check valve body with the seat, the check valve body and the seat. It is desirable to have a pilot piston arranged so as to be able to slide freely in opposition therebetween.

According to the present invention, by connecting a resistance valve in series with a first throttle for restricting the hydraulic oil flow rate and raising the cutting section at low speed, pilot operation of the pilot operated check valve before the hydraulic oil from the hydraulic pump is drained through the first throttle. Since the valve is opened by the valve, the pilot pressure is quickly supplied to the pilot operated check valve to open the pilot operated check valve even when the flow rate of the hydraulic oil is small during idling or the like. The time lag can be reduced.

1 is a side view showing the main portion of a general combine.
It is a hydraulic circuit diagram which shows one Embodiment of the harvesting-lowering hydraulic circuit of the combine which concerns on this invention.
3 is a sectional view showing the principal parts of a hydraulic circuit block unit to which the hydraulic circuit of FIG. 2 is mounted.
It is a hydraulic circuit diagram which shows the modified form of the hydraulic circuit for harvesting | lowering part lifting of the combine which concerns on this invention.
5 is a hydraulic circuit diagram showing another modified form of the hydraulic circuit for harvesting and lowering of the combine according to the present invention.

EMBODIMENT OF THE INVENTION Embodiment of the hydraulic circuit for harvesting | lowering part raising and lowering of the combine which concerns on this invention is described below with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same component throughout the whole figure and all the Example.

First, when the schematic structure of a combine is demonstrated, a general combine is equipped with the harvesting | reaping part 1 in the front part, as shown in FIG. 1, and the harvesting | reaping part 1 is driven up and down by the drive of the hydraulic cylinder 2. As shown in FIG. Go up and down. As the hydraulic cylinder 2, a single-acting hydraulic cylinder can be adopted.

FIG. 2 is a hydraulic circuit diagram showing an embodiment of the hydraulic circuit for harvesting and lowering of the combine according to the present invention. FIG.

The hydraulic circuit basically supplies hydraulic oil from the oil tank 3 to the piston chamber 2a of the hydraulic cylinder 2 by the hydraulic pump 4 to move the piston 2b to connect to the piston rod 2c. While raising the harvesting portion 1 (see FIG. 1, the same below), the hydraulic oil of the piston chamber 2a is drained to the oil tank 3 to return the piston 2b to its original position, and the harvesting portion ( 1) is lowered.

Between the hydraulic pump 4 and the hydraulic cylinder 2, in order from the hydraulic pump 4, the flow path 5a, the electromagnetic switching valve 6, the flow path 5b, the 1st switching valve 7, the flow path ( 5c, the pilot operated check valve 11, the flow path 5d, the slow return valve 12, the flow path 5e are connected, and the bypass flow path 8 is connected to the flow path 5b and the flow path 5c. A first throttle 9 connected in parallel with the first switching valve 7 and interposed in the bypass flow path 8, and connected in series with the first throttle 9 to the bypass flow path 8. The resistance valve 10 is connected.

The resistance valve 10 is a kind of sequence valve, and opens the bypass flow path 8 when the bypass flow path 8 on the primary side exceeds the set pressure. The pilot operated check valve 11 has an external pilot port, and when the hydraulic fluid of a predetermined pilot pressure is supplied to the pilot pressure operating flow passage 11a through the external pilot port, the check valve body of the pilot operated check valve 11 is provided. Open (11b) (see FIG. 3) to allow backflow of hydraulic fluid. The set pressure of the resistance valve 10 is set larger than the pilot pressure of the pilot operated check valve 11. The slow return valve 12 has a check valve 12a and a second throttle 12b connected in parallel to the check valve 12a.

The word "throttle" refers to a mechanism that reduces the cross-sectional area of flow and causes resistance in the flow path or the fluid passage, and includes a fixed throttle, a variable throttle, a throttle valve, a throttle switching valve, and the like.

The electromagnetic switching valve 6 is an open center 4-port three-position switching valve having a pair of solenoids 6a and 6b and springs 6c and 6d in the illustrated example. The electromagnetic switching valve 6 is in the neutral position shown in FIG. 2 by the balance of the springs 6c and 6d in the non-excited state. In the neutral position, the hydraulic oil pumped from the hydraulic pump 4 to the oil passage 5a is drained to the oil tank 3 via the oil passages 13a, 13b, 14. When one solenoid 6a is excited, flow paths 5a and 5b are opened. When the other solenoid 6b is excited, the oil passage 5a and the oil passage 15 are opened, and the hydraulic oil pumped from the hydraulic pump 4 to the oil passage 5a is mounted on the combine via the oil passage 15. It is supplied to a hydraulic actuator (not shown) that drives other work equipment such as a tank lifter or an auger lifter.

The 1st switching valve 7 is a solenoid valve provided with a pair of solenoids 7a and 7b and a pair of springs 7c and 7d in the example of illustration, and is provided with a hydraulic pressure primary side port P and a tank port T ), A four-port three-position switching valve of a pump closed center having a secondary port A for a pilot pressure operating flow path and a secondary port B for a hydraulic cylinder operating flow path. The 1st switching valve 7 is a neutral position which closes between the ports PB between the flow paths 5b and 5c by the springs 7c and 7d when the solenoids 7a and 7b are non-excited (FIG. 2). Elastically supported). By exciting one solenoid 7a, the 1st switching valve 7 is switched to the position which opens the flow path from the port P to the port B between the flow paths 5b and 5c from the said neutral position. . Exciting the other solenoid 7b opens the flow path from the port P to the port A, and switches to the position which opens the flow path from the port B to the port T.

The relief valve 16 as a pressure control valve is connected to the flow path 5a between the hydraulic pump 4 and the electromagnetic switching valve 6. The relief valve 16 drains a part of the hydraulic oil to the oil tank 3 via the oil passages 17 and 14 when the hydraulic oil pumped from the hydraulic pump 4 to the oil passage 5a exceeds the set pressure, The pressure of the hydraulic oil to be supplied to the cylinder 2 is kept constant.

The oil passage 14 connected to the oil tank 3 is connected to the oil passage 5d connected to the secondary port (the hydraulic cylinder 2 side) of the pilot operated check valve 11. The flow path 14 is interposed with a third throttle 18 and a second switching valve 19 for opening and closing the flow of hydraulic oil drained from the third throttle 18 to the oil tank 3. The third throttle 18 has a flow passage cross-sectional area smaller than that of the second throttle 12b incorporated in the slow return valve 12. The second switching valve 19 is an electronic two-position switching valve that is elastically supported at the position of the check valve that closes the flow passage 14 by the spring 19a when not energized, thereby exciting the solenoid 19b. It switches to the position which opens the flow path 14.

The pilot operated check valve 11 is energized from the solenoid 6a of the electromagnetic switching valve 6 and the solenoid 7b of the first switching valve 7 so that the hydraulic oil from the oil passage 5b is supplied to the pilot pressure operating flow path ( When supplied as pilot pressure through 11a), the built-in check valve is pushed open to allow backflow of the working oil. The hydraulic oil which flowed back to the pilot operated check valve 11 is the oil tank 3 via the oil passage 5c, the 1st switching valve 7 (ports B and T), the oil passage 20, and the oil passage 14. FIG. ).

The hydraulic circuit is built in the hydraulic circuit block unit 21. 3 is a cross-sectional view showing a main portion of the hydraulic circuit block unit 21 in which the hydraulic circuit is incorporated.

As shown in FIG. 3, in the resistance valve 10, a rod-shaped valve body 10a is pressed by a spring 10b to a seat 8a formed at an end portion in a bypass flow path 8. . When the hydraulic oil is supplied to the primary side of the bypass flow path 8 and the primary pressure exceeds the set pressure, the valve body 10a is separated from the seat 8a, and the hydraulic oil flows through the bypass flow path 8 through the flow path 5c. ) Flows. When the valve body 10a is separated from the seat 8a, the separation distance from the seat 8a is regulated by the spring force of the spring 10b.

Referring to FIG. 3, the pilot operated check valve 11 includes a check valve body 11b, a seat 11c, a spring 11d for pressing the check valve body 11b with the seat 11c, The pilot piston 11e is provided. The pilot piston 11e is disposed to face the check valve body 11b with the seat 11c interposed therebetween, and is provided so as to be able to slide freely from side to side in FIG. 3. When the hydraulic oil is supplied to the pilot pressure operating flow passage 11a, the pilot piston 11e is pressed on the right side in Fig. 3, the rod portion 11g passes through the flow path hole of the seat 11c, and is applied to the pressing force of the spring 11d. In response, the check valve body 11b is pushed to the right in FIG. 3 to open the valve.

When the hydraulic oil is supplied to the oil passage 5b from the hydraulic pump outside the drawing, it is supplied to the bypass oil passage 8 and the pilot pressure operating oil passage 11a. The resistance valve 10 imparts resistance to the hydraulic oil passing through the bypass flow path 8, thereby securing the pilot pressure necessary for opening the valve of the pilot operated check valve 11 even when the supply flow rate of the hydraulic oil is small, After the pilot piston 11e moves the check valve body 11b away from the seat 11c, it is designed so that the valve body 10a of the resistance valve 10 may fall from the seat 8a.

In the hydraulic circuit of the first embodiment having the above-described configuration, in the case of raising the harvesting section 1 at high speed, the solenoid 6a of the electromagnetic switching valve 6 is excited to open between the flow paths 5a and 5b. At the same time, the solenoid 7a of the first switching valve 7 is excited to open between the ports PB between the flow paths 5b and 5c. As a result, from the hydraulic pump 4, the flow path 5a, the electromagnetic switching valve 6, the flow path 5b, the 1st switching valve 7 (ports P and B), the flow path 5c, pilot operation Hydraulic oil is supplied to the hydraulic cylinder 2 via the type check valve 11, the oil passage 5d, the slow return valve 12, and the oil passage 5e. At this time, the hydraulic oil opens the resistance valve 10 by passing the bypass flow path 8 by reaching the predetermined pressure, but since the flow rate is limited by the first throttle 9, the bypass flow path 8 is opened. The flow rate of the working oil passing through is less than the flow rate of the working oil passing through the first switching valve 7. At this time, the pilot pressure operating flow path 11a and the port AT connecting the flow path 20 are also opened. Referring to FIG. 3, the hydraulic fluid through which the pilot piston 11e passes through the flow path 5c. 3 is pressed to the left side, and the hydraulic oil of the pilot pressure operating oil chamber 11f of the pilot piston 11e is drained through the pilot pressure operating oil passage 11a and the oil passage 20.

Next, when raising the harvesting | reaping part 1 low speed, the solenoid 6a of the electromagnetic switching valve 6 is excited, the port between the flow paths 5a and 5b is opened, and the 1st switching valve 7 is carried out. Is set to the neutral position as the non-excited state, and closes between the ports PB between the flow paths 5b and 5c. As a result, from the hydraulic pump 4, the flow path 5a, the electromagnetic switching valve 6, the flow path 5b, the first throttle 9 of the bypass flow path 8 and the resistance valve 10, the flow path 5c ), Hydraulic oil is supplied to the hydraulic cylinder 2 via the pilot operated check valve 11, the oil passage 5d, the slow return valve 12, and the oil passage 5e. In this case, except for the amount drained from the relief valve 16, since the total flow rate of the hydraulic oil from the hydraulic pump 4 passes through the first throttle 9 through the bypass flow path 8, the hydraulic cylinder ( The flow rate of the hydraulic oil supplied to 2) is limited by the first throttle 9, and the ascending speed of the harvesting section 1 is lowered than in the case of the high speed rising.

When lowering the harvesting section 1 at high speed, the solenoid 6a of the electromagnetic switching valve 6 is excited to switch to a position for opening the flow paths 5a and 5b to open the first switching valve 7. The solenoid 7b is excited to open between the ports PA to communicate the flow path 5b and the pilot pressure operation flow path 11a, and further open the ports BT to flow between the flow path 5c and the flow path 20. Is switched to the position to be drained to the oil tank (3). As a result, the hydraulic oil supplied to the pilot pressure operation flow path 11a acts as a pilot pressure, and the check valve main body 11b in the pilot operated check valve 11 is opened to allow the back flow of the hydraulic oil. In this way, the hydraulic oil in the piston chamber 2a of the hydraulic cylinder 2 flows into the flow path 5e, the second throttle 12b of the slow return valve 12, the flow path 5d, and the pilot operated check valve 11. , The flow path 5c is flowed back, and is drained from the first switching valve 7 (ports B and T) to the oil tank 3 via the flow paths 20 and 14. The working flow rate drained to the oil tank 3 is limited by the drain flow rate by the second throttle 12b.

When the harvesting section 1 is lowered at a low speed, the solenoid 19b of the second switching valve 19 is excited to open the flow passage 14. As a result, the hydraulic fluid accumulated in the piston chamber 2a of the hydraulic cylinder 2 is transferred to the flow path 5e, the second throttle 12b of the slow return valve 12, and the third throttle interposed in the flow path 14 ( 18), it is drained to the oil tank (3). Since the third throttle 18 has a smaller flow passage cross-sectional area than the second throttle 12b, the flow rate flowing through the flow passage 14 is determined by the third throttle 18. Moreover, the electromagnetic switching valve 6 is in a neutral position, and at this time, the hydraulic oil from the hydraulic pump 4 is drained to the oil tank 3 via the flow paths 13a, 13b, 14.

As mentioned above, when raising the harvesting | reaping part 1 low speed, the piston movement speed of the hydraulic cylinder 2 is reduced by restrict | limiting the flow volume of hydraulic fluid by the 1st throttle 9. Therefore, at the time of low rise of the harvesting | reaping part 1, unlike the conventional bleed-off circuit, since it can switch to a circuit which is a meter and can drive the hydraulic cylinder 2, the fluctuation by a relief flow volume can be suppressed. Moreover, even if the flow volume of hydraulic fluid is restrict | limited by the 1st throttle 9, since the primary side pressure of the 1st throttle 9 is pressure-regulated by the relief valve 16, it passes through the 1st throttle 9 Fluctuations in the flow rate of the hydraulic oil are prevented.

Since the hydraulic pump 4 is driven by an engine (not shown), the discharge flow rate of the hydraulic pump decreases when the engine is rotated at low speed, for example, during idling or when traveling in a humid place. Even when the engine is in low speed rotation, even if it tries to raise a harvesting part at low speed, since the discharge flow volume from a hydraulic pump is small in a bleed-off circuit, the flow volume exceeding a relief flow rate cannot be ensured and it cannot raise a low speed, but in this invention, an engine In this low-speed rotation, even if a part of the hydraulic oil is drained from the relief valve 16, since the relief pressure of the hydraulic oil is secured, the low-speed rise is possible.

Moreover, since the 1st throttle 9 for supply flow rate restriction | limiting was separated from the 2nd and 3rd throttles 12b and 18 for drain flow rate restriction, matching with a combine main body becomes easy.

Furthermore, when lowering the harvesting | reaping part 1 as mentioned above, in the conventional hydraulic circuit structure which does not have the resistance valve 10 which is a characteristic part of this invention, it supplies from the hydraulic pump 4 to the flow path 5b. The hydraulic fluid passed through the bypass flow path 8, the first throttle 9, the flow path 5c, the port BT of the first switching valve 7, the flow path 20, the flow path 14, and then the oil tank ( 3) Since a path to drain is formed, a time lag occurs in opening the pilot operated check valve 11 especially when the operating oil input flow rate, such as during engine idling, is small, but in the present invention, a resistance valve ( By forming 10), since the pilot pressure necessary for opening the pilot operated check valve 11 can be immediately generated, the time lag can be reduced.

In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the technical idea of this invention.

For example, as shown in FIG. 4, the 2nd throttle 12b can also be formed in the flow path 20 instead of the slow return valve 12 of the said 1st Embodiment, and as shown in FIG. 2nd switching valve 19A is formed in the oil tank 3 side of the 2nd throttle 12b of the flow path 20, and it connects the 3rd throttle 18 in parallel with the 2nd switching valve 19A. It can also be set as a circuit structure.

1 mowing
2 hydraulic cylinder
3 oil tank
4 hydraulic pump
7 1st switch valve
9th throttle
10 resistance valve
11 Pilot Operated Check Valve
12b 2nd Throttle
18 3rd Throttle
19, 19A second switch valve

Claims (2)

As a hydraulic circuit for driving the hydraulic cylinder which raises and lowers the harvesting part of a combine by the working oil sent from an oil tank through a hydraulic pump,
A pilot operated check valve for allowing back flow of hydraulic oil from the hydraulic cylinder using a pilot pressure;
A first position for opening the hydraulic pressure primary side port and the secondary side port for the hydraulic cylinder operating flow path; and opening the hydraulic pressure primary side port and the secondary side port for the pilot pressure hydraulic flow passage; A first switching valve switchable to a second position for opening the tank port, and to a third position for closing the pressure supply primary port and the secondary port for the hydraulic cylinder operating flow path;
A first throttle connected in parallel with said first switching valve and for restricting a flow rate of hydraulic oil supplied from said hydraulic pump to said hydraulic cylinder,
A resistance valve connected in series with the first throttle and for restricting the hydraulic oil passing through the first throttle when the first switching valve is in the second position to secure the pilot pressure of the pilot operated check valve. Wow,
A second throttle for restricting a flow rate of the hydraulic oil drained by flowing the pilot operated check valve back;
A third throttle having a flow path cross-sectional area smaller than the second throttle, for limiting the flow rate of the hydraulic oil being drained;
A second switching valve selectively converting the flow path of the hydraulic oil to be drained into the flow path of the hydraulic oil drained through the third throttle,
The hydraulic circuit comprising a. The method of claim 1,
The pilot operated check valve includes a check valve body, a seat on which the check valve body can be seated, a spring for pressurizing and elastically supporting the check valve body with the seat, and the check valve body and the seat. And a pilot piston disposed so as to slide freely toward the hydraulic circuit.

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