JP2005224441A - Extremely low temperature cooling device for magnetic resonance imaging device, and magnetic resonance imaging device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extremely low temperature cooling device capable of continuing cooling at the time of the abnormal stoppage of a compressor without the need of a wide installation space, and a magnetic resonance imaging device. <P>SOLUTION: The extremely low temperature cooling device for the magnetic resonance imaging device is constituted of a refrigerator 3 for expanding helium and cooling a part to be cooled, the compressor 4 for compressing the helium, a first supply line 6a for supplying the helium compressed by the compressor 4 to the refrigerator 3, a recovery line 7a for returning the helium supplied from the compressor 4 to the refrigerator 3 and expanded in the refrigerator 3 to the compressor 4, a storage part 5 for storing the helium, a second supply line 6b for supplying the helium from the storage part 5 to the refrigerator 3, a discharge line 7b for discharging the helium supplied from the storage part 5 to the refrigerator 3 and expanded in the refrigerator 3 to the outside air, a switching means 16 for switching the supply of the helium to the refrigerator 3 to the one from the compressor 4 or the storage part 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a cryogenic cooling apparatus for a magnetic resonance imaging apparatus and a magnetic resonance imaging apparatus using the same, and more particularly to a cryogenic cooling apparatus for a magnetic resonance imaging apparatus for cooling a superconducting coil for generating a magnetic field and the same. The present invention relates to a magnetic resonance imaging apparatus using the above.

A magnetic resonance imaging apparatus obtains a tomographic image of a subject by a nuclear magnetic resonance spectrum generated when a subject placed in a spatially changing magnetic field receives a pulse of a high-frequency magnetic field. The magnetic resonance imaging apparatus is equipped with a static magnetic field magnet, a gradient magnetic field coil, and a high frequency coil. Among these, the static magnetic field magnet often uses a superconducting coil and is equipped with a cryogenic cooling device for realizing a superconducting state. This is for cooling the superconducting coil to a critical temperature (transition temperature) Tc (critical temperature) or lower to maintain the superconducting state.

A cryogenic cooling device equipped in a conventional magnetic resonance imaging apparatus creates a low-temperature state by adiabatic expansion of a compressed helium gas and a compressor for compressing helium gas as a refrigerant. The superconducting coil can be cooled to a cryogenic temperature of about several K to several tens K.

By the way, after a superconducting coil is made into a superconducting state, a compressor may be stopped abnormally by various causes. In that case, the connected refrigerator is not driven and the cooling function is lost.
In particular, when a direct-cooling type refrigerator for directly freezing the superconducting coil is used, the temperature of the superconducting coil rises rapidly due to the influence of intrusion heat and becomes higher than the critical temperature Tc. May cause the superconducting state to collapse (quench). In this case, the magnetic field disappears, and a nuclear magnetic resonance spectrum from the subject cannot be obtained, so that imaging cannot be performed, and the superconducting coil may generate a large amount of heat and be damaged.

Further, in order to re-drive the superconducting coil from which the magnetic field has disappeared, it is necessary not only to recool the superconducting coil but also to perform complicated adjustments such as excitation. this is,
It is not something that can be adjusted independently by the user's hospital or the like, but is generally performed by a manufacturer's service person. Re-driving takes about 1 to 3 days and is not easily performed.

In order to avoid such quenching at the time of an abnormal stop of the compressor, there is an apparatus disclosed in Patent Document 1. This apparatus is provided with a standby compressor that is driven when the normally driven compressor is abnormally stopped. According to such an apparatus, even when the normally driven compressor is abnormally stopped, the cooling function of the refrigerator can be maintained by driving the standby compressor.

Conventionally, as a device for avoiding an abnormal stop due to a power failure, a device including a generator for ensuring power supply and a control circuit that automatically starts at power failure and switches the power supply to the generator is also used. ing. According to this device, the cooling function of the refrigerator can be maintained even during a power failure.
JP 2000-292024 A

However, the apparatus disclosed in Patent Document 1 has a drawback that when the cause of an abnormal stop is a power failure, the standby compressor cannot be driven and cooling cannot be continued. In addition, even when the cold water circulation device for water cooling of the compressor is abnormally stopped, the standby compressor cannot be driven and cooling cannot be continued. This is because the cold water circulation device used for water cooling of the compressor is generally the same system as other cold water circulation mechanisms in the room where the cryogenic cooling device is installed, and the cold water circulation for water cooling of the compressor This is because it is considered that the water cooling mechanism of the standby compressor is often impossible when the apparatus is abnormally stopped.

In addition, in the case of using a generator for driving a cooling device at the time of a power failure, a large-capacity generator is necessary to secure driving power for the refrigerator, compressor and chilled water circulation device at the time of a power failure. Requires a power generation capacity of about a dozen kV. Further, such a large-capacity generator is large and has a drawback that a large installation place is required.

Accordingly, it is an object of the present invention to provide a cryogenic cooling device for a magnetic resonance imaging apparatus that can maintain cooling when the compressor stops abnormally and does not require a large installation space, and a magnetic resonance imaging apparatus using the same. .

In order to achieve the above object, a cryogenic cooling device for a magnetic resonance imaging apparatus according to the present invention includes a refrigerator that expands helium to cool a portion to be cooled, a compressor that compresses helium,
A first supply line for supplying helium compressed by the compressor to the refrigerator; a recovery line for returning helium supplied from the compressor to the refrigerator and expanded by the refrigerator; A storage unit that stores helium, a second supply line that supplies helium from the storage unit to the refrigerator, and helium that is supplied from the storage unit to the refrigerator and expanded in the refrigerator is released to the outside air. And a switching means for switching the supply of helium to the refrigerator from either the compressor or the storage unit. The magnetic resonance imaging apparatus according to the present invention Generates a magnetic field by a superconducting coil cooled by a cryogenic cooling device, collects magnetic resonance signals from a subject placed in the magnetic field, and generates a magnetic field of the subject. In the magnetic resonance imaging apparatus for obtaining a gas resonance image, the cryogenic cooling apparatus includes a refrigerator that expands helium to cool a portion to be cooled, a compressor that compresses helium, and helium compressed by the compressor. A first supply line for supplying to the refrigerator; a recovery line for returning helium supplied from the compressor to the refrigerator and expanded by the refrigerator; and a storage unit for storing helium; A second supply line for supplying helium from the storage unit to the refrigerator; a discharge line for discharging helium supplied from the storage unit to the refrigerator and expanded by the refrigerator; and the refrigerator Switching means for switching the supply of helium to either the compressor or the storage unit.

According to the present invention, it is possible to provide a cryogenic cooling device for a magnetic resonance imaging apparatus that can maintain cooling even when the compressor is abnormally stopped and does not require a large installation space, and a magnetic resonance imaging apparatus using the same. .

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a cryogenic cooling apparatus for a magnetic resonance imaging apparatus and a magnetic resonance imaging apparatus using the same according to the present invention. The magnetic resonance imaging apparatus of the present embodiment includes a bed 1 on which the subject OBJ is placed, a static magnetic field magnet 2 that is a superconducting coil disposed so as to surround a space in which the subject OBJ is placed, and is compressed. By expanding the helium gas, the refrigerator 3 for cooling the static magnetic field magnet 2 to a superconducting state, the compressor 4 for compressing high purity helium, and the high purity helium are compressed in advance. It is comprised by the helium cylinder 5 stored.

Here, although not shown in the figure, a gradient magnetic field coil, a high frequency coil, and a detection coil for detecting a nuclear magnetic resonance signal generated from the subject OBJ are provided inside the static magnetic field magnet 2. Furthermore, a sequencer for controlling the operation timing of each coil and a computer for controlling the apparatus and processing nuclear magnetic resonance signals to obtain images and spectra are provided.

An example of the refrigerator 3 is a Gifford-McMahon cycle refrigerator disclosed in Japanese Patent Publication No. 46-30433. Other Stirling refrigerators, Birmeier refrigerators, and Solvay refrigerators may be used as long as they generate cooling by expanding compressed refrigerant gas.

In the refrigerator 3, the high-pressure gas supply pipe 6 a for introducing the high-pressure helium gas supplied from the compressor 4 b of the compressor 4 and the helium gas expanded in the refrigerator 3 are discharged from the refrigerator 3. A low-pressure gas recovery pipe 7a for supplying to the compressor 4b of the compressor 4 is connected.

The high pressure gas supply pipe 6a is connected to a high pressure gas supply pipe 6b for introducing the high pressure helium gas stored from the helium cylinder 5 into the high pressure gas supply pipe 6a. The low-pressure gas recovery pipe 7a is connected to a low-pressure gas discharge pipe 7b for discharging the helium gas expanded in the refrigerator 3 to the outside air.

Here, the low pressure gas discharge pipe 7b has a surge tank 13 for avoiding a sudden increase in pressure due to a change in the flow of the flow path through which helium gas circulates, and outside air while discharging the helium gas to the outside. A backflow check valve 12 is connected so as not to be mixed into the low pressure gas discharge pipe 7b. The high-pressure gas supply pipe 6a, the high-pressure gas supply pipe 6b, the low-pressure gas recovery pipe 7a, and the low-pressure gas discharge pipe 7b are provided with gate valves 14a to 14d, respectively, and the flow of helium gas in the respective pipes. Can be blocked / opened.

The compressor 4 is electric and is connected to a commercial external power source 15a during operation. The compressor 4 includes a compression unit 4b and a refrigerator driver 4a. Electric power required by the refrigerator 3 is supplied from the refrigerator driver 4a. Although not shown, the compressor 4 has a mechanism for escaping driving heat to the outside by cold water supplied from outside. Here, when the chilled water circulation mechanism (not shown) for supplying chilled water stops abnormally, if the compressor 4 continues to be driven, there is a high possibility of causing a failure due to driving heat. Therefore, the compressor 4 includes a safety device (not shown) for stopping the driving of the compressor 4 when the cold water circulation mechanism is stopped.

The uninterruptible power supply 15 is connected to the electric wire 15b that supplies electric power to the compressor 4. The uninterruptible power supply 15 may be a commercially available device, and is intended to obtain AC power by converting DC power from a storage battery by an inverter. The uninterruptible power supply 15 can supply power to the control unit 16.

The control unit 16 includes a refrigerator driver 16a and an energization monitor 19b.
Reference numeral 9 b is connected to the valve opening / closing switches 17 a to 17 d and the pressure switch 18. The refrigerator driver 16 a supplies power to the refrigerator 3, and the refrigerator driver 4 a built in the compressor 4.
Even when is not driven, power supply to the refrigerator continues.

The valve opening / closing switches 17a-17d control the opening / closing of the gate valves 14a-14d. The valve opening / closing switches 17a to 17d are composed of solenoid coils and switching valves. When electric power is supplied to the solenoid coil, the switching valve is electromagnetically operated to switch the opening and closing of the gate valves 14a to 14d. Accordingly, when the control unit 16 is activated and the valve opening / closing switches 17a to 17b are driven, the opening and closing of the gate valves 14a to 14d is switched.

During normal times when power is supplied from the external power supply 15a, the gate valves 14a and 14b connected to the high pressure gas supply pipe 6a and the low pressure gas recovery pipe 7a are opened, and the high pressure gas supply pipe 6b and the gate valves 14c of the low pressure gas discharge pipe 7b are opened. 14d is closed. When the control unit 16 is activated at the time of a power failure of the external power supply 15a, the reverse occurs. The gate valves 14a and 14b connected to the high pressure gas supply pipe 6a and the low pressure gas recovery pipe 7a are closed, and the high pressure gas supply pipe 6b and the low pressure gas discharge pipe 7b are closed.
The gate valves 14c and 14d connected to are opened.

Here, the compressor 4 and the control unit 16 each include an energization monitor 19a, 19b.
The energization monitors 19a and 19b have solenoid coils c1 and c2 connected to the monitored circuits 19c and 19d, and switches s1 and s2. The solenoid coil c1 is connected to the monitored circuit 19c of the energization monitor 19a built in the compressor 4, and electromagnetically operates the switch by supplying electric power to the solenoid coil c1. A monitored circuit 19c of the energization monitor 19a on the compressor 4 side is a power supply circuit in the compressor 4, and the switch s1 is closed when a current flows through the monitored circuit 19c.

The monitored circuit 19d of the solenoid coil c2 built in the energization monitor 19b built in the control unit 16 is connected to a power supply circuit from the uninterruptible power supply 15 to the control unit 16, and is opened and closed by a switch s1. The switch s2 cuts off the power supply from the uninterruptible power supply 15 to the controller 16 when no current flows through the monitored circuit 19d.

With such a configuration, a function of supplying power to the control unit 16 when the compressor 4 is driven and not supplying power to the control unit 16 when driving of the compressor 4 is stopped is realized. The automatic switches s1 and s2 or the valve opening / closing switches 17a to 17d as described above may be switched manually in addition to the circuit switching means.

The high-pressure gas supply pipe 6b is connected to the pressure switch 18 described above. Pressure switch 18
Has a built-in atmospheric pressure switch, and cuts off the circuit from the energization monitor 19b of the control unit 16 when the gas pressure in the high-pressure gas supply pipe 6b decreases below a certain value. If the helium gas cylinder 5 runs out of helium, which is the refrigerant gas, and the valve opening / closing switches 17a-17d are operated to open / close the gate valves 14a-14d, the helium gas circulation system is returned to the normal state. It will be.

The operation status of the cryogenic cooling apparatus and magnetic resonance imaging apparatus according to the above-described embodiment is as follows.
It is shown in FIGS.

FIG. 2 shows a normal operation. Since power is supplied to the compressor 4 during normal operation, the power supply circuit to the control unit 16 is shut off by the energization monitors 19a and 19b. Accordingly, since the control unit 16 does not operate, the gate valves 14a and 14b connected to the high pressure gas supply pipe 6b and the low pressure gas discharge pipe 7b are closed. Therefore, the high-pressure helium gas introduced into the refrigerator 3 through the high-pressure gas supply pipe 6a is supplied only from the compressor 4. The low pressure helium gas discharged from the refrigerator 3 to the low pressure gas recovery pipe 7 a is introduced into the compressor 4.

In the cryogenic cooling device and the magnetic resonance imaging apparatus of the present embodiment, the part that functions in normal times is the part represented by the solid line in FIG. The helium gas circulates through the refrigerator 3 and the compressor 4 as indicated by arrows, and the cooling by the refrigerator 3 is continuously maintained, so that the static magnetic field magnet 2 that is a portion to be cooled can be kept at a low temperature.

On the other hand, FIG. 3 is a flowchart showing the operation when the drive of the compressor 4 is stopped in an emergency such as a power failure. First, as step S1, the driving of the compressor 4 is stopped. Possible causes of power outages include power outages and breakdowns. Further, it is conceivable that the cold water circulation device is stopped by the operation of a safety device built in the compressor 4 along with the stop of the cold water circulation device.

In step S2, the energization monitors 19a and 19b in FIG.
2 is switched, and power supply from the uninterruptible power supply 15 to the control unit 16 is started.

Subsequently, as step S3, along with power supply to the inside of the control unit 16, power is supplied to the refrigerator 3 via the refrigerator driver 16a and power is supplied to the valve opening / closing switches 17a to 17d.

Next, as step S4, along with power supply to the refrigerator 3 and the valve opening / closing switch 17,
The opening and closing of the gate valves 14a to 14d is switched. The gate valves 14a and 14b connected to the high pressure gas supply pipe 6a and the low pressure gas recovery pipe 7a are closed, and the gate valves 14c and 14d connected to the high pressure gas supply pipe 6b and the low pressure gas discharge pipe 7b are opened.

In the cryogenic cooling device of this embodiment, the part that functions in an emergency is the part represented by the solid line in FIG. High-pressure helium is introduced into the refrigerator 3 by performing high-pressure helium in the helium cylinder 5 through the high-pressure gas supply pipe 6b and discharging low-pressure helium from the refrigerator 3 to the outside air using the low-pressure gas discharge pipe 7b. Done as by. Therefore, until the helium in the helium cylinder 5 is exhausted, the refrigerator 3 can be cooled without changing from the normal state.

Here, since the low pressure helium is discharged to the outside air, the high pressure helium in the helium cylinder 5 continues to decrease. The cooling can be continued for about 30 minutes when used in a magnetic resonance imaging apparatus, for example, when five helium cylinders storing 7 cubic meters of gaseous helium are used.

FIG. 5 is a flowchart showing the operation when the compressor 4 is driven again after a power failure is restored. First, as Step T1, the restoration of the power failure and the restoration of the chilled water circulation mechanism are shown in FIG.
The driving of the compressor 4 is resumed. Next, as step T2, the energization monitors 19a and 19b switch the switches s1 and s2, and the power supply to the control unit 16 is cut off. At this time, the power supply to the refrigerator 3 is also switched to the supply from the refrigerator driver 4a of the compressor 4. Next, at step T3, the power supply to the valve opening / closing switches 17a to 17d is cut off simultaneously with the interruption of the power supply to the control unit 16 of FIG.

Next, as step T4, the opening and closing of the gate valves 14a to 14d is switched. The gate valves 14a and 14b connected to the high pressure gas supply pipe 6a and the low pressure gas recovery pipe 7a are opened, and the gate valves 14c and 14d connected to the high pressure gas supply pipe 6b and the low pressure gas discharge pipe 7b are closed. As a result, it automatically returns to the state having the normal function shown in FIG.

In the above-described embodiment, the storage and supply system is connected to the circulation system, and in the event of an emergency, a part of the high-pressure gas supply pipe 6a and the low-pressure gas recovery pipe 7a are shared. Compared to, the length of the pipe can be shortened and the entire apparatus can be miniaturized.

As mentioned above, although the Example of the cryogenic cooling device which concerns on this invention was described, this invention is not limited to the said Example. For example, in the above-described embodiment, a helium gas circulation system that is normally driven and a helium gas storage and supply system that is driven in an emergency are connected to one refrigerator 3. However, the present invention is not limited to this, and two refrigerators for emergency and normal use may be used, and a circulation system and a storage supply system may be provided respectively.

According to such a configuration, even when the normal refrigerator is stopped due to a failure or the like, the cooling can be continued using the emergency refrigerator, and the pipe for supplying and recovering helium gas It is preferable in that it is not necessary to switch the type and the power supply circuit to the refrigerator.

Moreover, in the Example mentioned above, although the superconducting coil cooled by the refrigerator 3 was only the static magnetic field magnet 2, it is not restricted to this. Superconducting coils may also be used for the above-described gradient magnetic field coils and high-frequency coils. In this case, a mechanism cooled by the refrigerator 3 may be used.

Further, in the above-described embodiment, the gate valves 14a to 14d are provided in the high pressure gas supply pipes 6a and 6b, the low pressure gas recovery pipe 7a, and the low pressure gas discharge pipe 7b, respectively.
It is not limited to this. Three-way valves may be provided at the junction between the high-pressure gas supply pipe 6a and the high-pressure gas supply pipe 6b and at the junction between the low-pressure gas recovery pipe 7a and the low-pressure gas discharge pipe 7b. A three-way valve is a gate valve that can be opened and closed in each of three directions. Such a configuration is preferable in that the number of parts constituting the apparatus is reduced.

According to the embodiment described above, a cryogenic cooling device and a magnetic resonance imaging apparatus that can maintain cooling in an emergency and do not require a large installation space are realized.

In the present embodiment, the uninterruptible power supply 15 is only required to secure power for driving the refrigerator. Taking a direct cooling type cooling apparatus for cooling a superconducting coil used in a typical magnetic resonance imaging apparatus as an example, it is only necessary to have an output of about 200 VA or more.

In the present embodiment, the uninterruptible power supply 15 is one of the configurations of the present embodiment, but is not limited thereto. In a building where the magnetic resonance imaging apparatus according to the present embodiment is installed, a power supply device that secures the power supply of the building may be provided. In this embodiment, since power consumed in an emergency is small, there is a possibility that a sufficiently required power amount can be supplied even by such a power supply device. In that case, the uninterruptible power supply 15 does not have to be part of the configuration of the present embodiment. Such a configuration is preferable in that the apparatus can be further downsized and noise can be reduced.

In this embodiment, in addition to the uninterruptible power supply 15, helium cylinders, the control unit 16, gate valves 14 a to 14 d, pipes connected to the helium cylinder 5, and the like are required. However, even when a backup system in the event of a power failure is included, it is possible to achieve a significant reduction in size and simplification compared to the case where a generator is used as a conventional backup system.

In addition, according to the cryogenic refrigeration apparatus and the magnetic resonance imaging apparatus of the present embodiment described above, noise can be reduced because it is small in size and low in output as compared with a conventional apparatus configuration using a generator. The magnetic resonance imaging apparatus is often installed at a hospital, and noise reduction is an important issue. Therefore, in order to reduce the noise when driving the generator in the conventional cryogenic cooling device,
Soundproofing equipment was necessary. However, in this embodiment, it is only necessary to use a small uninterruptible power supply, so that noise during driving can be significantly reduced as compared with a conventional large generator. Therefore, soundproofing equipment is not necessary. Also in this respect, according to the present embodiment, the construction cost can be greatly reduced and the space can be saved.

The block diagram which shows the Example of the cryogenic cooling device and magnetic resonance imaging apparatus which concern on this invention. The figure which shows the part which functions in the normal time in the cryogenic cooling apparatus and magnetic resonance imaging apparatus of a present Example shown in FIG. The flowchart which shows operation | movement when the drive of a compressor stops. The figure which shows the part which functions in an emergency in the cryogenic cooling device and magnetic resonance imaging apparatus of a present Example shown in FIG. The flowchart which shows operation | movement when the drive of a compressor restarts.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bed 2 Static magnetic field magnet 3 Refrigerator 4 Compressor 5 Helium cylinder 6a, 6b High-pressure gas supply pipe 7a Low-pressure gas recovery pipe 7b Low-pressure gas discharge pipe 12 Backflow valve 13 Surge tanks 14a-14d Gate valve 15 Uninterruptible power supply 16 Control units 17a to 17d Valve open / close switch 18 Pressure switch 19a, 19b Energization monitor

Claims (7)

A refrigerator that expands helium to cool the cooled part;
A compressor that compresses helium;
A first supply line for supplying helium compressed by the compressor to the refrigerator;
A recovery line for returning helium that has been supplied from the compressor to the refrigerator and expanded by the refrigerator, to the compressor;
A storage section for storing helium;
A second supply line for supplying helium from the storage unit to the refrigerator;
A discharge line for discharging the helium supplied from the storage unit to the refrigerator and expanded by the refrigerator;
Switching means for switching the supply of helium to the refrigerator from either the compressor or the storage unit;
A cryogenic cooling device for a magnetic resonance imaging apparatus. In a magnetic resonance imaging apparatus that generates a magnetic field by a superconducting coil cooled by a cryogenic cooling device, collects magnetic resonance signals from a subject placed in the magnetic field, and obtains a magnetic resonance image of the subject.
The cryogenic cooling device is:
A refrigerator that expands helium to cool the cooled part;
A compressor that compresses helium;
A first supply line for supplying helium compressed by the compressor to the refrigerator;
A recovery line for returning helium that has been supplied from the compressor to the refrigerator and expanded by the refrigerator, to the compressor;
A storage section for storing helium;
A second supply line for supplying helium from the storage unit to the refrigerator;
A discharge line for discharging the helium supplied from the storage unit to the refrigerator and expanded by the refrigerator;
Switching means for switching the supply of helium to the refrigerator from either the compressor or the storage unit;
A magnetic resonance imaging apparatus comprising: The switching means is
Detection means for detecting whether the compressor is driven or not,
Based on the detection by the detection means, when the compressor is not driven, helium is added to the second.
And a line switching means for preventing helium from flowing in the second supply line and the discharge line when the compressor is in operation. The magnetic resonance imaging apparatus according to claim 2. The refrigerator is connected to the first supply line and the recovery line;
4. The magnetic resonance imaging apparatus according to claim 2, wherein the second supply line and the emission line are connected to the first supply line and the recovery line, respectively. The refrigerator is
A first refrigerator connected to the first supply line and the recovery line;
The magnetic resonance imaging apparatus according to claim 2, further comprising a second refrigerator connected to the second supply line and the discharge line. The first supply line, the recovery line, the second supply line, and the discharge line, each provided with a valve for opening and closing a helium flow path;
The switching means is
5. The magnetic resonance imaging apparatus according to claim 4, further comprising means for controlling the operation of the valve. A three-way valve for restricting the flow path of helium, provided at each of the connection part of the first supply line and the second supply line and the connection part of the recovery line and the discharge line;
The switching means is
5. The magnetic resonance imaging apparatus according to claim 4, further comprising means for controlling the operation of the three-way valve.

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