JPH0338431B2 - - Google Patents

Description

Detailed Description of the Invention <Industrial Application Field> The present invention provides a concrete system that can reduce vibrations and noise generated when sucking and pumping ready-mixed concrete by driving a concrete pump and valve cylinder according to the condition of the ready-mixed concrete. This invention relates to a sequence drive device in a pump truck.

<Prior art> As shown in FIG. 6, a conventional sequence drive device for a concrete pump vehicle accumulates pressure oil from a hydraulic pump 1 in an accumulator 2, and the pressure in the accumulator 2 matches the set pressure of a sequence valve 4. Otherwise, the sequence valve 4 operates and pressure oil from the hydraulic pump 1 is supplied to one main cylinder 6 via the sequence valve 4 and the main cylinder control switching valve 5, and this main cylinder 6 operates to supply one main cylinder to the other. At the same time, the ready-mixed concrete is pumped from one concrete pump 8, and at the same time, the ready-mixed concrete is sucked into the other concrete pump 8 through the concrete valve 9, and then,
When the valve control switching valve 11 is switched, the pressure oil in the accumulator 2 is suddenly switched to the valve control switching valve 1.
1 to the valve cylinder 12, the concrete valve 9 is instantaneously switched, and when the pressure in the accumulator 2 reaches the set pressure of the sequence valve 4 again, the main cylinder 6 operates to open the concrete valve 9. There is a system that sucks ready-mixed concrete into one concrete pump 8 through a concrete pump 8 and simultaneously pumps the ready-mixed concrete from the other concrete pump 8.

<Problems to be Solved by the Invention> However, in the sequence drive device for the concrete pump vehicle, the concrete valve 9 is switched at high speed and under high pressure using the accumulator 2 each time the concrete valve 9 is switched. Sometimes there are problems with vibration and noise. Furthermore, the concrete valve 9 is switched by using the pressure oil from the hydraulic pump 1 and the pressure oil from the accumulator 2 to the valve cylinder 12.
Since the piston 14 is reciprocated at high speed and high pressure each time, there is a problem in that the sliding portion of the piston 14 and the contact surface of the concrete valve 9 are subject to severe wear.

Therefore, the purpose of this invention is to avoid using the accumulator 2 during ordinary fresh concrete pumping at low pressure.
The aim is to reduce the number of times the accumulator is used, reduce the number of times vibrations and noise occur, and reduce the amount of wear that occurs on concrete valves and valve housings by using the accumulator only when pumping fresh concrete with a poor mix using high pressure. .

<Structure of the Invention> In order to achieve the above object, a sequence drive device in a concrete pump vehicle of the present invention is connected via an oil path of a hydraulic pump and controls a main cylinder that drives the concrete pump and the main cylinder. A 3-position switching valve for main cylinder control,
A concrete valve for switching between sucking and pressurizing fresh concrete in the concrete pump; a valve cylinder connected to a hydraulic pump via an oil line to drive the concrete valve to control the concrete valve; and a valve control valve for the valve cylinder. An accumulator selection switch for selecting whether or not to use the accumulator in a sequence drive device for a concrete pump vehicle that includes a switching valve and an accumulator disposed in an oil path between the hydraulic pump and the valve cylinder. and a pressure switch operated by fluid pressure in an oil passage leading to the accumulator, and a pressure switch operated by turning on and off a contact of the pressure switch connected in series with a contact on the accumulator operating side of the accumulator selection switch. , the valve control switching valve is switched by the on/off operation of the timer switch section, and the pressure oil from the hydraulic pump is accumulated in the accumulator,
The present invention is characterized by comprising a timer for forcing the pressure oil of the accumulator to be fed to the valve cylinder.

<Examples> The present invention will be described in detail below with reference to illustrated examples.

As shown in FIG. 1, logic valves 25a, 25b, 25c, and 25d are connected to a valve cylinder 26a between a high pressure line 22a connected to the outlet of the hydraulic pump 21 and a low pressure line 22b connected to the tank 24. , 26b are connected. The valve cylinders 26a, 26b and the hydraulic pump 21
The high pressure line 22a between the accumulator 2
There are 8. A check valve 29 is provided between the accumulator 28 and the hydraulic pump 21, and the check valve 29 prevents the pressure oil accumulated in the accumulator 28 from flowing back. Main cylinder logic valves 31a, 31b, 31c, 31 are connected between the high pressure line 22a and the low pressure line 22b between the check valve 29 and the hydraulic pump 21.
The main cylinders 32 and 42 are connected via d. As shown in FIG. 2, a cylindrical concrete pump 34 having a larger diameter than the main cylinder 32 is connected to the main cylinder 32, and the main cylinder 32 causes a piston 34a of the concrete pump 34 to reciprocate. . Another main cylinder 42 and concrete pump 4 having the same structure as the above main cylinder 32 and concrete pump 34
4, the other ends of the main cylinders 32, 42 are connected to each other by a connecting passage 35, and one ends of the concrete pumps 34, 44 are connected to the outlet of a concrete hopper (not shown). A concrete valve 36 is provided at the outlet. By opening and closing the concrete valve 36, fresh concrete in the concrete hopper is sucked into the concrete pumps 34 and 44, and the suction is stopped. In addition, as shown in FIG. 1, the main cylinder control pilot switching valve 38
is a three-position switching valve, and the pilot chambers 38a, 38b at both ends are connected to the valve cylinders 26a, 26.
b via pilot lines 39 and 41, respectively, and the valve cylinders 26a and 26b operate to the end of their stroke and increase pressure to switch from the neutral position to a predetermined symbol position, and the main cylinder 32 , 42 are controlled. Furthermore, the three-position switching valve 45 for main cylinder control is connected to the high pressure line 22a and the low pressure line 22a.
b and the above-mentioned main cylinder control pilot switching valve 38
and controls the operation of the main cylinders 32 and 42. Further, the valve control pilot switching valve 46 is a two-position switching valve, and the pilot chambers 46a and 46b at both ends are connected to the logic valve 4.
The main cylinders 42 and 32 are connected to the main cylinders 42 and 32 via cylinders 8 and 49, respectively. A valve control switching valve 54 is connected to pilot lines 51 and 52 between the valve control pilot switching valve 46 and the high pressure and low pressure lines 22a and 22b. The valve control switching valve 54 is a three-position switching valve, and controls the opening and closing of the concrete valve 36. The switching valve 54 for valve control and the high pressure and low pressure lines 22a and 22b
A pressure switch PS is connected between the pilot line 51 and the pilot line 52. In addition, 70, 70, 70 are check valves,
71 is a relief valve.

Contact PS ₁ of the pressure switch PS is provided in a relay circuit shown in FIG. 3 in a concrete panel (not shown). That is, in the relay circuit, the power line 61a and the common contact C1 of the accumulator selection switch 62 are connected, and the relay coil R1 is connected between the accumulator non-operating side contact B of the accumulator selection switch 62 and the power line 61b, The connection point 64 between the relay coil R1 and the accumulator non-operating side contact B, and the connection point 7 between the common contact C1 of the accumulator selection switch 62 and the power supply line 61a
Between 1 and 1, there is a normally open switch that is a timer switch part.
We have a TA. A contact _PS1 of a pressure switch PS and a relay coil T of a timer are connected in series between the accumulator operating side contact A of the accumulator selection switch 62 and the power supply line 61b. The normally open switch TA is turned on and off in response to the energization and de-energization of the timer's relay coil T.

In addition, while connecting the power line 61a and the common contact C2 of the concrete pump drive switch 65, a relay coil R3 is connected between the normal rotation side connection E of the concrete pump drive switch 65 and the power line 61b, and the concrete pump Normal rotation side contact F of drive switch 65 and power supply line 61b
Relay coil R2 is connected between.

Further, a relay contact r2, a relay contact r1, and one coil S3 of the valve control switching valve 54 are connected in series between the power supply lines 61a and 61b. One coil S2 of the three-position switching valve 45 for controlling the main cylinder is connected between the connection point 66 between the relay contact r2 and the relay contact r1 and the power line 61b, while the relay contact r2
The relay contact r3 and the other coil S of the three-position switching valve 45 for controlling the main cylinder are connected between the connection point 68 between the power supply line 61a and the power supply line 61b.
1 are connected in series. Furthermore, the relay connection point r3 and the 3-position switching valve 4 for controlling the main cylinder are connected to the relay connection point r3.
The relay contact r1 and the other coil S4 of the valve control switching valve 54 are connected between the connection point 69 between the other coil S1 of the valve control switching valve 54 and the power line 61b.

In the sequence driving device for the concrete pump vehicle having the above configuration, first, when ordinary ready-mixed concrete is sucked and pumped by the concrete pumps 34 and 44, it is necessary to use the accumulator 28 because ordinary ready-mixed concrete has a high moisture content and is easy to pump. Therefore, the common contact C1 of the accumulator selection switch 62 of the relay circuit shown in FIG. 3 is connected to the accumulator non-operating side contact B. Relay coil R1 is excited and relay contact r1 is turned on. On the other hand, in order to rotate the concrete pumps 34, 44 in normal rotation, the common contact C2 of the concrete pump drive switch 65 and the normal rotation side contact E are connected. Relay coil R3 is energized and relay contact r3
is turned on. As a result, 3
One coil S1 of the position switching valve 45 is excited, and the other coil S1 of the valve control switching valve 54 is excited.
4 is excited. As shown in FIG.
1, while the valve control switching valve 54 is switched from the normal position Vo to the symbol position V4.
The high pressure from the high pressure line 22a is transferred to the pilot line 81, the 3-position switching valve 45 for main cylinder control located at the symbol position V1, and the pilot switching valve 3 for main cylinder control located at the symbol position V8.
8 to the spring chambers S of the first and third main cylinder logic valves 31a, 31c from the upstream side in the figure.
This will be communicated to S. Then, the main cylinder logic valves 31a, 31c are closed. On the other hand, the spring chambers S and S of the second and fourth main cylinder logic valves 31b and 31d from the upstream side in the figure are the pilot switching valve 38 for controlling the main cylinder located at the symbol position V8, and the main cylinder logic valve 38 located at the symbol position V1. The main cylinder logic valves 31b and 31d are open because they communicate with the low pressure line 22b via the control three-position switching valve 45 and the pilot line 82. As a result, high pressure oil from the high pressure line 22a is supplied to the main cylinder 42 via the main cylinder logic valve 31d, and the piston 34 shown in FIG.
a, 44a is activated to suck in fresh concrete from the concrete pump 44 via the concrete valve 36, while pumping the fresh concrete from the concrete pump 34. Furthermore, since the valve control switching valve 54 has been switched from the normal position Vo to the symbol position V4, the pressure oil discharged from the hydraulic pump 21 is fed to the high pressure line 22a, and this high pressure is passed through the pilot line 51. The signal is transmitted to the valve control switching valve 54 located at the symbol position V4. On the other hand, since the valve control pilot switching valve 46 has been switched to the symbol position V5, the high pressure is applied to the pilot line 51, the valve control switching valve 54 at the symbol position V4, and the valve control pilot switching valve at the symbol position V5. It is transmitted via the valve 46 to the spring chambers S, S of the logic valves 25a, 25c for the first and third valves from the upstream side in the figure. And the logic valve 25a, 2 for the valve
5c is closed. On the other hand, the spring chambers S and S of the logic valves 25b and 25d for the second and fourth valves from the upstream side in the figure are the pilot switching valve 46 for valve control located at the symbol position V5, and the switching valve for valve control located at the symbol position V4. 54, Pilot line 5
2 to the low pressure line 22b,
The logic valves 25b and 25d are opened. As a result, the high pressure oil in the high pressure line 22a is supplied to the valve cylinder 26b via the valve logic valve 25d.
a and 26b are activated and the concrete valve 36 is switched. Then, when the valve cylinder 26b operates to the stroke end, the valve cylinder 26b
Since the pressure b is approximately as high as the discharge pressure of the hydraulic pump 21, this high pressure is transmitted to the pilot chamber 38b of the main cylinder control pilot switching valve 38 via the pilot line 88, and the main cylinder The control pilot switching valve 38 is switched from the symbol position V8 to the symbol position V6.

Next, when concrete pumps 34 and 44 are sucking in and pumping fresh concrete with a poor mix that is difficult to pump due to its high aggregate content and low water content, the set pressure of the pressure switch PS is set to 100 kg/cm ² . shall be. Then, the discharge pressure of the hydraulic pump 21 is 100
Kg/cm ² or less, the common contact C1 of the accumulator selection switch 62 of the relay circuit shown in FIG.
Even if the contact A on the accumulator operating side is connected,
Since the set pressure of the pressure switch PS is set to 100Kg/ ^cm2 , the timer relay coil T is de-energized and the normally open switch TA is off, so the relay coil R1 is not energized and the relay contact r1 is not energized. Since the concrete pump drive switch 65 is turned off and the common contact C2 of the concrete pump drive switch 65 is connected to the normal rotation side contact E, the relay contact r3 is turned on and one pilot of the three-position switching valve 45 for controlling the main cylinder is turned on. While the coil S1 of the chamber 38b remains excited, one coil S of the valve control switching valve 54 remains energized.
4 is de-energized because the relay contact r1 is off. As a result, the three-position switching valve 45 for main cylinder control is held at the symbol position V1, while the valve control switching valve 54 is switched from the symbol position V4 to the normal position Vo. Further, since the main cylinder control pilot switching valve 38 is held at the symbol position V6 as described above, the high pressure from the high pressure line 22a is transferred to the pilot line 81,
The main cylinder logic valves 31b, which are second and fourth from the upstream side in the figure, are 31d, the main cylinder logic valves 31b and 31d are closed. On the other hand, the main cylinder logic valves 31a, 3
1c is open. Then, the pressure oil discharged from the hydraulic pump 21 is supplied to the main cylinder 32 via the high pressure line 22a and the main cylinder logic valve 31a, and the main cylinders 32 and 42 operate to pump out the poorly mixed fresh concrete. At this time, the high pressure line 22a
The high pressure from
Spring chambers S, S, a, 25b, 25c, 25d,
S, S is transmitted to the valve logic valve 25
a. Pressure oil from the hydraulic pump 21 is not supplied to the valve cylinders 26a and 26b.

Then, the discharge pressure of the hydraulic pump 21 is 100Kg/
cm ² or more, contact PS ₁ of the pressure switch PS shown in Figure 3 is turned on, but the normally open switch is turned on.
Since TA does not operate for 1 second, the normally open switch TA
is not turned on, relay coil R1 is energized and relay contact r1 remains on, while common contact C2 of concrete pump drive switch 65 is energized.
is connected to normal rotation side contact E, relay coil R3 is energized, relay contact r3 is turned on, and one coil S1 of 3-position switching valve 45 for main cylinder control is energized, while valve control The other coil S4 of the switching valve 54 remains de-energized. As a result, the three-position switching valve 45 for controlling the main cylinder is maintained at the symbol position V1, while the switching valve 54 for valve control is maintained at the normal position Vo.

The high pressure from the high pressure line 22a is transferred to the main cylinder via the 3-position switching valve 45 for main cylinder control located at the symbol position V1, the pilot switching valve 38 for main cylinder control located at the cylinder position V6, and the main cylinder logic valve 31a. The piston 3 of the concrete pump 34 is supplied to the cylinder 32.
4a has reached the stroke end, no more pressure oil is supplied to the main cylinder 32, and from this point on, the pressure oil discharged from the hydraulic pump 21 begins to be accumulated in the accumulator 28. At this time, the pressure of the pressure oil is at point H in FIG. Then, after 1 second, the pressure changes from 100Kg/cm ² to 120
Kg/cm ² , the normally open switch TA of the timer in FIG. Since the reversing side contact E is connected, the relay coil R
3 is energized, relay contact r3 is turned on, and the other coil S4 of the valve control switching valve 54 is energized. As a result, the valve control switching valve 54 is switched from the normal position Vo to the symbol position V4.
Also, the high pressure supplied to the main cylinder 32 passes through the pilot line 100 to close the logic valve 49, while the low pressure passes through the pilot line 100 to close the logic valve 49.
1 to open the logic valve 48, the pilot switching valve 46 for valve control is at the symbol position V.
5 to symbol position V7. the result,
The high pressure of the high pressure line 22a passes through the pilot line 51 to the valve control switching valve 54 located at the symbol position V4 and the valve control pilot switching valve 46 located at the symbol position V7 to the second and fourth valves from the upstream side in the figure. logic valve 25b for the valve,
25d is transmitted to the spring chambers S, S, and the valve logic valves 25b, 25d are closed. on the other hand,
The spring chambers S and S of the logic valves 25a and 25c for the first and third valves from the upstream side in the figure are the pilot switching valves 4 for valve control located at the symbol position V7.
6. The valve control switching valve 54 located at the symbol position V4 is connected to the low pressure line 22b via the pilot line 52, so the above-mentioned logic valve 2
5a and 25c are open. Therefore, 120 kg/cm ² of pressure oil accumulated in the accumulator 28 is supplied to the valve cylinder 26a via the valve logic valve 25a, and the concrete valve 36 is switched at high speed, resulting in 115 kg/cm 2 of pressure oil accumulated in the accumulator 28. At point I of ² , the valve cylinders 26a and 26b reach their stroke ends. Eventually, the pressure drops to point J of 100 kg/cm ² and the pressure switch PS is turned off. As a result, the timer's relay coil T is de-energized and the normally open switch TA is turned off, and the relay coil R1 is de-energized and the relay contact r1 is not turned off. While the coil S1 remains energized, the coil S4 becomes de-energized, and the three-position switching valve 45 for main cylinder control remains at the symbol position V1, while the valve control switching valve 54 remains at the symbol position V4. to the normal position Vo. In this way, pressure oil is accumulated in the accumulator 28 in a short time, and the pressure oil is immediately transferred to the valve cylinders 26a and 26.
6b, there is extremely little possibility that the pressure oil accumulated in the accumulator 28 will leak. Furthermore, since the accumulator 28 is used only in the case of poorly mixed concrete that is difficult to pump, the number of vibrations and noises generated from the concrete valve 36 and valve cylinders 26a and 26b can be reduced when pressure oil is pumped by the accumulator 28. Not only this, but also the amount of wear on the sliding parts of the valve cylinders 26a, 26b can be reduced. Furthermore, by making the set pressure of the pressure switch PS variable, the charge pressure of the accumulator 28 can be controlled, and it is possible to deal with fresh concrete of various poor mixes.

Further, when the ready-mixed concrete is to be pumped to a high place or a far place, the above-mentioned ready-mixed concrete can be pumped using the accumulator 28 in the same way as in the case of the above-mentioned poor mix of ready-mixed concrete.

FIG. 5 shows another embodiment, and the same components as those in FIG. 3 are given the same reference numerals, and the explanation thereof will be omitted. In this embodiment, instead of using the normally open switch TA as the timer relay contact, a normally closed switch TB is used as the timer switch part, and one contact C1 of the concrete pump drive switch 72 and the power line 61 are used.
A pressure switch PS is connected between the other contact A of the concrete pump drive switch 72 and one end of the timer relay coil T.
Connect contact PS1 of the timer relay coil T.
The other end is grounded, and one contact point C1 between the power line 61a and the concrete pump drive switch 72 is connected.
A normally closed switch TB of the timer and a relay coil R1 are connected in series between the connection point 74 between the two and the power line 61a. And the pressure is 120Kg/cm ²
At this point, the pressure oil accumulated in the accumulator 28 is supplied to the valve cylinders 26a and 26b all at once, but even if the pressure drops below 120Kg/cm ² during supply, the pressure oil switch PS will not exceed 120Kg/cm ^{2 .} Since it is set to turn on in the following, the timer's relay coil T is energized, the normally closed switch TB remains on for 2 seconds, and the relay coil R1 is energized. As a result, the coil S4 is energized, the valve control switching valve 54 is maintained at the symbol position V4, and even if the pressure drops below 120 kg/cm ² , pressure oil is supplied to the valve cylinders 26a and 26b for only 2 seconds, and the valve control switching valve 54 is maintained at the symbol position V4. Let the cylinders 26a, 26b reach their stroke ends. Also, in this case, as in the above-described embodiment, the accumulator 28 is used only in the case of poorly mixed concrete that is difficult to pump, so not only can the number of occurrences of vibration and noise be reduced, but also , 26b can of course reduce the amount of wear on the sliding parts.

<Effects of the Invention> As is clear from the above description, according to the sequence drive device for a concrete pump vehicle of the present invention, a hydraulic pump, a main cylinder, a 3-position switching valve for controlling the main cylinder, a concrete valve, and a valve cylinder are combined. an accumulator, an accumulator selection switch that selects whether or not to use the accumulator, a pressure switch that is operated by fluid pressure in the oil passage, and a timer switch that is operated by the pressure switch and turns on and off the timer switch. It is equipped with a timer that switches the valve control switching valve when activated, so only in the case of poorly mixed concrete that needs to be pumped at high pressure, the timer switch part of the timer can be turned on and off to switch the valve control switching valve. By switching between the two, the pressure oil from the hydraulic pump can be accumulated in the accumulator, or the pressure oil from the accumulator can be forced to be sent to the valve cylinder. Therefore, according to the present invention, it is possible to switch the concrete valve by operating the valve cylinder even with poorly mixed concrete that is difficult to pump,
Ready-mixed concrete with a poor mix can be pumped. Furthermore, according to this invention, since the accumulator is used only when pumping fresh concrete with a poor mix, which is difficult to pump, from a concrete pump, vibrations generated from the valve cylinder, oil passage, etc., are caused by the pumping of pressurized oil by the accumulator. It is possible to reduce the number of occurrences of noise and noise, and also to reduce the amount of wear on the sliding parts of the valve cylinder and the contact surface of the concrete valve.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the sequence drive device in the concrete pump vehicle of the present invention, Fig. 2 is a schematic diagram showing the main cylinder, concrete pump, and valve, Fig. 3 is a relay circuit diagram, and Fig. 4 is the pressure of pressure oil. FIG. 5 is a relay circuit diagram of a different embodiment, and FIG. 6 is a circuit diagram of a sequence drive device in a conventional concrete pump vehicle. 21... Main hydraulic pump, 26a, 26b... Valve cylinder, 28... Accumulator, 32,
42... Main cylinder, 34, 44... Concrete pump, 36... Concrete valve, 45...
...3-position switching valve for main cylinder control, 54...Switching valve for valve control, 62...Accumulator selection switch, PS...Pressure switch, T...
Timer, TA, TB...Timer switch section.

Claims (1)

[Scope of Claims] 1. A main cylinder that is connected via an oil path of a hydraulic pump and drives a concrete pump, a 3-position switching valve for controlling the main cylinder that controls the main cylinder, and a 3-position switching valve for controlling the ready-mixed concrete in the concrete pump. a concrete valve that switches between suction and pressure feeding; a valve cylinder that is connected to a hydraulic pump via an oil line to drive the concrete valve to control the concrete valve; a valve control switching valve for the valve cylinder; In a sequence drive device for a concrete pump vehicle, comprising an accumulator disposed in an oil path between a pump and the valve cylinder, an accumulator selection switch for selecting whether or not to use the accumulator; The pressure switch is operated by the fluid pressure in the oil passage, and the pressure switch is operated by turning on and off the contact of the pressure switch connected in series with the contact on the accumulator operating side of the accumulator selection switch, and the timer switch is turned on. - A timer that switches the valve control switching valve by turning off, so that the pressure oil from the hydraulic pump is accumulated in the accumulator or the hydraulic pressure of the accumulator is forced to be sent to the valve cylinder. Sequence drive device for concrete pump trucks. 2. In the sequence drive device for a concrete pump vehicle as set forth in claim 1, the timer switch section is normally closed, and the pressure switch is turned off when the pressure exceeds the set pressure of the accumulator. The switching valve for valve control is switched to the operating position, and the pressure oil is force-fed from the accumulator to the valve cylinder.
The pressure switch is turned on to operate the timer, and due to the operation of the timer, the timer switch closes within the time set by the timer, thereby maintaining the operating position of the valve control switching valve. On the other hand, the sequence drive device for a concrete pump truck is characterized in that the timer is opened after the set time to maintain the valve control switching valve in a neutral position. 3. In the sequence drive device for a concrete pump vehicle as set forth in claim 1, the timer switch is normally open, and the pressure switch controls the valve when the pressure is below the set pressure of the accumulator. The pressure oil from the hydraulic pump is started to accumulate in the accumulator by holding the switching valve in the neutral position, while when the pressure is below the set pressure of the accumulator, the pressure switch is turned on and the timer is activated. Due to the operation of the above-mentioned timer, the above-mentioned timer switch section is opened within the set time of the above-mentioned timer, and the above-mentioned valve control switching valve is held in the neutral position, and the above-mentioned pressure oil is accumulated up to the maximum pressure of the above-mentioned accumulator, and the above-mentioned timer switch is opened within the set time of the above-mentioned timer. A sequence drive device for a concrete pump vehicle, characterized in that the switching valve for valve control is switched to an operating position by closing after a set time.