JPH08313085A - Method and apparatus for controlling pressure equalization of cryogenic refrigerating machine - Google Patents

Abstract

PURPOSE: To lower the equalizing pressure of a refrigerant circuit by holding a refrigerant circuit between a compressor and expansion means in an open state for a predetermined time at the time of stopping the compressor, and feeding the gas refrigerant of the compressor to the expansion means side to reduce the gas refrigerant quantity at the compressor side. CONSTITUTION: When compressors 4, 8 are stopped due to the stop of a refrigerating machine R, switching means 54 is controlled to be switched by control means 61. The means 54 is held in an open state until a predetermined time is elapsed from the stops of the compressors 4, 8. Thus, the compressors 4, 8 are held to communicate with expansion means 41, the gas refrigerant in the high-pressure tube 15 of a refrigerant circuit 53 due to the stops of the compressors 4, 8 flows to the means 41 side by the differential pressure between the compressors 4, 8 and the means 41, and hence the gas refrigerant amount of the side of the compressors 4, 8 in the circuit 53 is reduced. In this manner, the equalizing pressure of the circuit 53 can be lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic refrigerator in which a gas refrigerant such as helium gas compressed by a compressor is expanded by an expander to generate cryogenic cold. TECHNICAL FIELD The present invention relates to a pressure equalizing control device and a pressure equalizing control method for controlling the pressure of a refrigerant circuit at the time of stop of pressure equalization.

[0002]

2. Description of the Related Art Generally, in a superconductor utilizing a superconducting phenomenon, liquid helium stored in a tank is used to keep its temperature below a critical temperature. Since it evaporates in the tank, it is necessary to cool and condense the evaporated helium gas to liquefy it, and a cryogenic refrigerator is used for this purpose.

As an example of a refrigerator for cooling the helium gas to a condensing temperature, there is conventionally known, for example, US Pat. No. 4,223.
No. 540, etc., a pre-cooling refrigerator and a J-
There is a refrigerator combined with a T refrigerator. The above pre-cooling refrigerator is a GM cycle (Gifford McMahon cycle)
And a refrigerating machine such as an improved solve cycle. The helium gas (gas refrigerant) compressed by the compressor is adiabatically expanded by the expander, and the temperature drop of the gas causes the cryogenic cold level in the heat station. .

On the other hand, the J-T refrigerator has a precooler for precooling by exchanging heat between the helium gas supplied from the compressor and the heat station of the expander in the precooling refrigerator, and the helium gas in a joule. Thomson inflates J-
It is connected to a T valve, and helium gas from the compressor is precooled by a precooler, and the precooled helium gas is expanded by Joule-Thomson with the JT valve to generate 4K level cold. It is like this.

[0005]

By the way, in this type of cryogenic refrigerator, the pressure in the refrigerant circuit is equalized after the compressor is stopped, and the restart after the stop is facilitated. In that case, if the compressor is of a positive displacement type such as a scroll compressor, the starting torque of the compressor can be made smaller as the pressure equalizing pressure is lower, and its operation reliability is improved. be able to.

However, when the refrigerant circuit has a simple closed cycle, the total amount of refrigerant used for equalizing the pressure in the refrigerant circuit is constant, so that there is a difference in the time required to equalize the pressure, There was a limit to lowering the final pressure equalizing pressure itself.

The present invention has been made in view of the above problems, and an object thereof is an open-cycle refrigerant circuit which is partially opened in a liquefaction tank for accumulating liquid refrigerant liquefied by expansion and cooling of the gas refrigerant. On the other hand, by utilizing the structural characteristics, the pressure equalizing pressure itself of the refrigerant circuit when the compressor is stopped is lowered without increasing the cost, and the operational reliability of the compressor is improved.

[0008]

In order to achieve the above object, in the present invention, when the compressor is stopped, the refrigerant circuit between the compressor and the expansion means is kept open for a predetermined time, The pressure equalizing pressure itself is lowered by causing the gas refrigerant on the compressor side to flow toward the expansion means to reduce the amount of gas refrigerant in the refrigerant circuit on the compressor side.

Specifically, according to the invention of claim 1, FIG.
As shown in FIG. 3, compressors (4) and (8) for compressing a gas refrigerant such as helium gas and an expansion means (41) for expanding the high-pressure gas refrigerant to generate cold are provided with high-pressure piping (1).
5) and a low-pressure pipe (3) are connected to each other, and a refrigerant circuit (53) and a liquefaction tank (DL) for accumulating a liquid refrigerant in which a part of this refrigerant circuit (53) is opened are provided. Refrigerant circuit (53) for the gas refrigerant evaporated in the tank (DL)
Inhaled into and compressed with compressors (4) and (8),
It is premised on a cryogenic refrigerator in which the compressed gas refrigerant is expanded by the expansion means (41) and a temperature drop due to the expansion generates a liquid refrigerant to be returned into the liquefaction tank (DL).

The opening / closing means (5) for connecting or disconnecting the compressors (4), (8) and the expansion means (41).
4) and the control so that the opening / closing means (54) is opened until a predetermined time elapses after the compressors (4) and (8) are stopped and the opening / closing means (54) is closed after the predetermined time elapses. And a control means (61) for controlling.

According to a second aspect of the invention, the control means (6
After the compressors (4) and (8) are stopped, the opening and closing means (5)
4) Open the time until the pressure inside the liquefaction tank (DL) rises to the set pressure.

According to the third aspect of the invention, as shown in FIG. 1 or 3, the opening / closing means (54) is provided to the opening / closing valve (AV) for opening and closing the high pressure pipe (15) and the low pressure pipe (3). And the gas refrigerant of the expansion means (41) is installed in the compressor (4),
While permitting return to (8), compressors (4), (8)
And a check valve (CV) that prevents the gas refrigerant from moving to the expansion means (41).

In the fourth aspect of the invention, as shown in FIG. 3, the on-off valve (AV) is a solenoid valve. Further, in the invention of claim 5, as shown in FIG. 1, the on-off valve (AV) is a pneumatic valve which is opened and closed by air pressure.

According to a sixth aspect of the present invention, there is provided a method for controlling the pressure equalization of a cryogenic refrigerator. In the cryogenic refrigerator as a premise of the first aspect of the invention, the compressors (4) and (8) are stopped for a predetermined period of time. Until the time elapses, the compressors (4), (8) and the expansion means (41) are communicated with each other, and after the elapse of the predetermined time, the compressors (4), (8) and the expansion means (41) are connected. It is characterized by cutting off communication.

[0015]

With the above construction, in the invention of claim 1 or 6, when the refrigerator is in the operating state, the opening / closing means (5
4) is opened and the compressors (4), (8) and the expansion means (4)
1) is communicated with. In this state, the compressor (4),
With the operation of (8), the gas refrigerant evaporated in the liquefaction tank (DL) is sucked into the refrigerant circuit (53), and the compressor (4),
The compressed gas refrigerant is compressed in (8), and the expansion means (41) thereafter expands the temperature of the gas refrigerant to lower it to a liquid refrigerant, which is returned to the liquefaction tank (DL).

When the refrigerator is stopped from the operating state and the compressors (4) and (8) are stopped, the opening / closing means (54) is controlled to open / close by the control means (61). First, the opening / closing means (54) is kept open in the same manner as the operating state of the compressors (4) and (8) from the stop of the compressors (4) and (8) until a predetermined time elapses. Be done. Therefore, the compressors (4), (8) and the expansion means (41) are held in communication with each other,
By stopping the compressors (4) and (8), the gas refrigerant in the high-pressure pipe (15) of the refrigerant circuit (53) flows toward the expansion means (41) due to the pressure difference between the two, whereby the refrigerant circuit (53).
The amount of gas refrigerant on the side of the compressors (4) and (8) decreases.

Then, when a predetermined time has passed since the compressors (4), (8) were stopped, the opening / closing means (54) is closed, and the compressors (4), (8) and the expansion means (41) are connected. The communication of is closed by the opening / closing means (54). Due to this interruption, the pressure in the liquefaction tank (DL) is reduced to the compressor (4),
It is possible to prevent pressure equalization at the same pressure as the (8) side, and it is possible to set the withstand pressure of the liquefaction tank (DL) low.

In this way, when the compressors (4) and (8) are stopped, the closing operation of the opening / closing means (54) is delayed for a predetermined time, and the compressors (4) and (8) and the expansion means (41) are delayed. ), And the refrigerant circuit (5) on the compressor (4), (8) side.
Since the amount of the gas refrigerant in 3) is reduced, the pressure equalizing pressure itself when the gas refrigerant is equalized in the refrigerant circuits (53) on the side of the compressors (4) and (8) can be reduced thereafter. . Therefore, when the compressors (4) and (8) are restarted in the pressure equalized state, the starting torque can be reduced,
The operational reliability of the compressors (4) and (8) can be improved.

The opening / closing means (54) can also be used to prevent equalization of the pressure in the liquefaction tank (DL) at the same pressure as that on the compressor (4), (8) side. The above effect can be obtained without increasing the cost due to the dual use of the opening / closing means (54).

In the invention of claim 2, the compressor (4),
Since the time from the stop of (8) until the opening / closing means (54) is opened is the time until the pressure inside the liquefaction tank (DL) rises to the set pressure, the pressure inside the liquefaction tank (DL) is set. When the pressure rises, the opening / closing means (54) is closed, and it is possible to reliably prevent the pressure inside the liquefaction tank (DL) from rising above the set pressure.

In the invention of claim 3, the opening / closing means (54)
Is composed of an on-off valve (AV) that opens and closes the high-pressure pipe (15) and a check valve (CV) arranged on the low-pressure pipe (3). Compressors (4), (8) and expansion means (41) are simply opened and closed.
It is possible to switch between communication with and disconnection of communication, and the structure of the opening / closing means (54) can be simplified.

In the invention of claim 4, the opening / closing valve (AV) is an electromagnetic valve, and in the invention of claim 5, the opening / closing valve (AV) is a pneumatic valve. Therefore, the specific structure of the opening / closing valve (AV) is can get. In particular, when the pneumatic valve that opens and closes by the air pressure is used as in the fifth aspect of the present invention, the on-off valve (AV) can be stably opened and closed without malfunctioning even when affected by a magnetic field or the like.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 2 shows the entire structure of a refrigerator (R) according to Embodiment 1 of the present invention. This refrigerator (R) is arranged in a compressor unit (1) and a vacuum chamber (D). And a refrigerator unit (31).

In the compressor unit (1), low pressure helium gas from the low pressure gas inlet (2) is supplied to the low pressure pipe (3).
Low-stage compressor (4) that sucks in through the compressor and compresses it, a heat exchanger (5) that cools helium gas discharged from the low-stage compressor (4), and this heat exchanger (5) A high-stage compressor (8) for further compressing the helium gas discharged from the intermediate pressure gas suction port (6) to a higher pressure together with the intermediate pressure helium gas sucked through the intermediate pressure pipe (7);
A pre-stage oil separator (9) for separating oil for compressor lubrication from the high-pressure helium gas discharged from the high-stage compressor (8).
And a heat exchanger (10) for cooling the high-pressure helium gas discharged from the former oil separator (9), and further separating lubricating oil from the helium gas discharged from the heat exchanger (10). A post-stage oil separator (11) and an adsorber (12) for adsorbing and removing impurities from the helium gas discharged from the post-stage oil separator (11) are provided, and the adsorbing side of the adsorber (12) is provided. One end of the high pressure pipe (13) is connected. The other end of the high-pressure pipe (13) is branched into a pre-cooling high-pressure pipe (14) and a JT high-pressure pipe (15),
The high-pressure pipe for pre-cooling (14) is a high-pressure gas outlet for pre-cooling (1
6) and the JT high-pressure pipe (15) is connected to the JT high-pressure gas discharge port (17).

Further, one end of a helium gas supply pipe (18) is branched and connected to the low-pressure pipe (3) between the suction side of the low-stage compressor (4) and the low-pressure gas suction port (2). There is. Further, one end of a helium gas return pipe (20) in which a high pressure control valve (HPR) is arranged is branched and connected to the JT high pressure pipe (15) which is a part of the high pressure pipe (13).
The other end of the helium gas return pipe (20) is assembled with the other end of the helium gas supply pipe (18) and connected to one end of the helium gas supply / discharge pipe (21). The other end of is connected to a buffer tank (Tb) that stores helium gas at a predetermined pressure.

The high-pressure control valve (HPR) automatically uses the helium gas in the high-pressure pipe (13) (JT high-pressure pipe (15)) as a pilot pressure when it rises above a set pressure. This high pressure control valve (HP
By opening the valve (R), the helium gas in the JT high-pressure pipe (15) (refrigerant circuit (53) described later) is transferred to the buffer tank (T).
Recovered in b).

The helium gas supply pipe (18) is branched into two branch pipes (18a) and (18b) in parallel on the way, and one of the branch pipes (18a) is fixed by a throttle for closing the flow passage. The valve (V2) and the normally closed first low pressure control valve (LPR1) are arranged on the low pressure pipe (3) side of the shutoff valve (V2), while the other branch pipe (18b) is the same. Shut-off valve (V3) and normally closed second low-pressure control valve (LP
R2) are provided. Each low pressure control valve (LPR
1) and (LPR2) automatically open as a pilot pressure when the pressure of helium gas in the low pressure pipe (3) drops below a set pressure.
The buffer tank (T
The helium gas in b) is the low pressure pipe (3) (refrigerant circuit (5
3)).

On the other hand, the refrigerator unit (31)
Includes a precooling refrigerator (32) connected to the high-stage compressor (8) of the compressor unit (1) in a closed circuit, a low-stage compressor (4) and a high-stage compressor (8). ) Is connected in series with the JT refrigerator (41) (expansion means). The pre-cooling refrigerator (32) is composed of a G-M (Gifford McMahon) cycle refrigerator.
Helium gas (gas refrigerant) in the -T refrigerator (41)
The helium gas is compressed and expanded to precool it.
The pre-cooling refrigerator (32) has a closed cylindrical case (33) arranged outside the vacuum chamber (D), and the case (3).
3) and a cylinder (34) having a large and small two-stage structure that is continuously provided. In the case (33), a high pressure gas inlet (36) connected to the precooling high pressure gas discharge port (16) of the compressor unit (1) through a flexible pipe (35).
And the flexible pipe (3) at the intermediate pressure gas inlet (6).
The low pressure gas outlet (38) connected via 7) is open. On the other hand, the cylinder (34) penetrates the side wall of the vacuum chamber (D) and extends inside thereof, and has a large diameter portion (3
The tip of 4a) is cooled and maintained at a predetermined temperature level.
Heat station (39) and small diameter part (34b)
Of the first heat station (39) is formed in the second heat station (40) cooled and maintained at a temperature level lower than that of the first heat station (39).

That is, although not shown here, in the cylinder (34), each heat station (3
Free-type displacers (replacers) that partition and form the expansion spaces are reciprocally fitted at positions corresponding to 9) and (40). On the other hand, the above case (3
In 3), a rotary valve that opens and closes each time it rotates,
A valve motor that drives the rotary valve is housed. The rotary valve has the high pressure gas inlet (36).
The helium gas flowing in from is supplied to each expansion space in the cylinder (34), or the helium gas expanded in each expansion space is switched to be discharged from the low pressure gas outlet (38). Then, by opening and closing this rotary valve, the high-pressure helium gas is expanded by Simon in each expansion space in the cylinder (34), and a temperature drop due to the expansion causes a cryogenic level of cold to be generated, and the cold is cooled by the cylinder (34). First and second heat stations (39), (4
Hold at 0). That is, in the pre-cooling refrigerator (32),
The high-pressure helium gas discharged from the high-stage compressor (8) is adiabatically expanded to heat stations (39), (4
0) to lower the temperature to precool later-described precoolers (46) and (47) in the J-T refrigerator (41),
The expanded low pressure helium gas is returned to the compressor (8) and recompressed.

On the other hand, the JT refrigerator (41) has about 4
A refrigerator that expands helium gas by Joule-Thomson in order to generate K-level cold, and the refrigerator (41) is a first to third refrigerator arranged in the vacuum chamber (D).
JT heat exchangers (42) to (44). Each of the JT heat exchangers (42) to (44) has a primary side and a secondary side.
The helium gas passing through each of the secondary sides exchanges heat with each other. The primary side of the first JT heat exchanger (42) has a high pressure gas discharge port (1) for JT of the compressor unit (1).
7) via a flexible pipe (45). Also, the first and second JT heat exchangers (42),
The respective primary sides of (43) are connected to the first heat station (3) of the cylinder (34) in the precooling refrigerator (32).
9) It is connected via a first precooler (46) arranged on the outer circumference. Similarly, the second and third J-T heat exchangers (4
The respective primary sides of 3) and (44) are connected to each other via a second precooler (47) arranged on the outer periphery of the second heat station (40). Further, the primary side of the third J-T heat exchanger (44) uses high-pressure helium gas as a joule.
Adsorber (49) to JT valve (48) to expand Thomson
Connected through. The JT valve (48) is connected to the liquefaction tank (DL) via a liquid helium return pipe (50). The liquefaction tank (DL) stores a predetermined amount of liquid helium, and the liquid helium cools an object to be cooled (not shown) to a cryogenic level. Further, the inside of the liquefaction tank (DL) is connected to the secondary side of the third JT heat exchanger (44) through a helium gas suction pipe (51). And this 3rd J-T heat exchanger (44)
Is connected to the secondary side of the first J-T heat exchanger (42) through the secondary side of the second J-T heat exchanger (43), and the first J-T heat exchanger (42) is connected. The secondary side of is connected to the low-pressure gas suction port (2) of the compressor unit (1) via a flexible pipe (52).

That is, the JT refrigerator (41) is a flexible pipe (45), (52), low pressure pipe (3), both compressors (4), (8) and high pressure pipe (3) JT. Refrigerant circuit (53) connected in series to the high pressure pipe (15) for use
This refrigerant circuit (53) is partly a liquefaction tank (DL)
The helium gas evaporated in the liquefaction tank (DL) due to the heat load of the object to be cooled is sucked into the refrigerant circuit (53) from the helium gas suction pipe (51) and the third to 1st J-T heat exchanger (4
High-pressure helium gas compressed by the high-stage compressor (8) while being sucked and compressed into the low-stage and high-stage compressors (4) and (8) through the secondary sides of 4) to (42). The first
In the third JT heat exchangers (42) to (44), heat is exchanged with the low-temperature low-pressure helium gas toward the compressor (4) side, and the first and second precoolers (46), (47). ), Respectively, at the first and second heat stations (39) and (40) of the cylinder (34), and then the JT valve (4)
In 8), Joule-Thomson expansion is performed to form liquid helium of about 4K, and this liquid helium is returned to the liquefaction tank (DL) through the liquid helium return pipe (50). The opening of the JT valve (48) is adjusted by the operation rod (48a) from the outside of the vacuum chamber (D).

As shown in an enlarged detail in FIG. 1, a fixed throttle type throttle valve (V1) for adjusting the flow rate and an adsorption of this throttle valve (V1) are provided in the middle of the JT high-pressure pipe (15). Bowl (1
An on-off valve (AV) that opens and closes the high-pressure pipe (15) is provided on the 2) side, and this on-off valve (AV) is a pneumatic valve that opens and closes by air pressure.

A check valve (CV) is provided in the middle of the low-pressure pipe (3) on the low-pressure gas inlet (2) side (upstream side) of the connection with the helium gas supply pipe (18). While the check valve (CV) allows the helium gas on the JT refrigerator (41) side to return to the compressors (4) and (8),
It has a function of preventing helium gas from moving from the compressors (4) and (8) to the JT refrigerator (41). In this embodiment, the opening / closing mechanism (V) and the check valve (CV) for connecting or disconnecting the compressors (4), (8) and the JT refrigerator (41) are used. 54) is configured.

The on-off valve (AV) has an air pipe (55).
The air pressure source (56) is connected via the
In the middle of 5), an on-off valve (A) for receiving air pressure from the air pressure source (56) in response to an electric control signal from the control device (61).
Open / close valve (AV) by switching the action or stop of action on V)
A pneumatic solenoid valve (57) for opening and closing is provided. Although not shown in the figure, a signal line is not shown in the control device (61), and a detection signal of a high pressure switch (HPS) for detecting the pressure of the high pressure helium gas discharged from the high pressure compressor (8) and a low signal. The detection signal of the low pressure switch (LPS) for detecting the pressure of the low pressure helium gas in the low pressure pipe (3) communicating with the suction side of the stage compressor (4), and the pressure in the helium gas supply / discharge pipe (21) ( A detection signal of a medium pressure switch (MPS) for detecting the internal pressure of the buffer tank (Tb),
Three protection switches (S
The operation signals of S1) to (SS3) are input.

That is, the control device (61) constitutes a control means, and in this control device (61), the opening / closing valve (AV) is controlled to open / close via the pneumatic solenoid valve (57), and the compressor ( During operation of 4) and 8), the on-off valve (AV) is opened to connect the compressors (4) and (8) to the JT refrigerator (41), while the compressors (4) and (8) are communicated. 8) is stopped from the operating state, the compressor (4), (8)
From the stop of the compressor until the predetermined time elapses, in detail, the pressure inside the liquefaction tank (DL) rises to the set pressure due to the pressure equalization in the refrigerant circuit (53) accompanying the stop of the compressors (4) and (8). The opening / closing valve (AV) is held in the open state in the same manner as the operating states of the compressors (4) and (8) until the time is reached, and the opening / closing valve (AV) is closed after the lapse of the predetermined time. There is.

In FIG. 2, reference numeral (24) denotes a part of the oil separated from the helium gas in the former oil separator (9) and the oil separated in the latter oil separator (11) for the lower stage. An oil return pipe for injecting into helium gas discharged from the compressor (4) and sucked into the high-stage compressor (8),
(25) is an oil return pipe for returning the remaining part of the oil separated by the former-stage oil separator (9) to the high-stage compressor (8), and (26) is an oil lower part inside the high-stage compressor (8). An oil injection pipe for supplying the oil to the oil return pipe (25) to inject the oil into the upper part of the compressor (8), and (27) shows oil in the lower part of the low stage compressor (4). ) An oil injection pipe for injecting into the upper part of the inside, and (28) is an oil equalizing pipe for communicating between the lower parts of both compressors (4) and (8) to keep the oil level of both compressors constant.

Next, the operation of the above embodiment will be described. When the refrigerator (R) is in an operating state, a part of the high-pressure helium gas supplied from the high-stage compressor (8) of the compressor unit (1) is supplied to the pre-cooling refrigerator (32). The helium gas expands in each expansion space in the cylinder (34) of the precooling refrigerator (32), and the temperature drop caused by the expansion of the gas causes the first heat station (39) to reach a predetermined temperature level and the second heat station (39). Heat station (4
0) are each cooled to a lower temperature level than the first heat station (39). The helium gas expanded in the expansion space returns to the compressor unit (1), is sucked into the high-stage compressor (8) through the intermediate pressure pipe (7), and is compressed.

On the other hand, J- in the compressor unit (1)
The on-off valve (AV) of the T high-pressure pipe (15) is connected to the control device (6
1) the high-stage compressor (8) is opened to communicate with the JT refrigerator (41), and the remaining high-pressure helium gas discharged from the high-stage compressor (8) is JT. Via the throttle valve (V1) of the high pressure piping (15) for the JT refrigerator (4
1) Enter the primary side of the first J-T heat exchanger (42), where it is heat-exchanged with the low-pressure helium gas on the secondary side toward the compressor (4) side and cooled from room temperature 300K to, for example, about 50K. After that, the first precooler (46) around the outer periphery of the first heat station (39) of the precooling refrigerator (32) is further cooled. This cooled gas is the second JT
After entering the primary side of the heat exchanger (43) and being cooled to, for example, about 15K by heat exchange with the low-pressure helium gas on the secondary side as well, the second heat station (40) of the precooling refrigerator (32). ) It enters the second precooler (47) on the outer periphery and is further cooled. After this, the gas is transferred to the third JT heat exchanger (4
4) enters the primary side and is further cooled by heat exchange with the low pressure helium gas on the secondary side, and then the JT valve (4
8). In this JT valve (48), the high-pressure helium gas is squeezed and expanded by Joule-Thomson into liquid helium of about 4K, and this liquid helium is liquefied (DL) via the liquid helium return pipe (50). Is supplied to. On the other hand, part of the liquid helium in the liquefaction tank (DL) evaporates due to the heat load of the object to be cooled, and this liquefaction tank (DL)
The evaporated helium gas in the helium gas suction pipe (51)
Is sucked into the secondary side of the third J-T heat exchanger (44) through the secondary side of each of the second and first J-T heat exchangers (43) and (42). It is sucked into the compressor (4) and compressed.

During operation of the refrigerator (R), when the compressors (4), (8) are stopped and the operation of the refrigerator (R) is stopped, the compressors (4), (8) During the period from the stop until a predetermined time elapses, the compressor (4) until then,
The open / close valve (AV) is opened in the same manner as in the operating state of (8), and J
The -T high-pressure pipe (15) is kept open, and the high-stage compressor (8) and the JT refrigerator (41) are held in communication with each other.
Immediately after the compressors (4) and (8) are stopped, the pressure in the JT high-pressure pipe (15) of the refrigerant circuit (53) is JT.
Since the pressure is higher than the pressure on the refrigerator (41) side, the helium gas in the JT high-pressure pipe (15) is J due to the pressure difference between the two.
It flows to the −T refrigerator (41) side, which reduces the amount of helium gas on the compressor (4), (8) side. Since the check valve (CV) is arranged in the low pressure pipe (3), even if the suction side of the compressor (4) becomes higher in pressure than the JT refrigerator (41) side, the compression is performed. Helium gas on the machine (4) side never returns to the JT refrigerator (41) side.

When a predetermined time has passed since the compressors (4) and (8) were stopped, the on-off valve (AV) is closed,
The on-off valve (AV) blocks communication between the compressors (4) and (8) and the JT refrigerator (41). Due to this interruption, the pressure in the liquefaction tank (DL) is reduced to the compressors (4), (8).
It is possible to prevent pressure equalization with the same pressure as the side.

At this time, the time during which the open / close valve (AV) is held open after the compressors (4) and (8) are stopped is the liquefaction tank (DL).
Since it is the time until the internal pressure rises to the set pressure, when the internal pressure of the liquefaction tank (DL) rises to the set pressure, the on-off valve (AV) will be closed. Therefore,
It is possible to reliably prevent the pressure inside the liquefaction tank (DL) from rising above the set pressure.

In this embodiment, when the compressors (4) and (8) are stopped, the on-off valve (AV) is opened for a predetermined time to open the compressors (4) and (8) and the JT refrigerator (41). ) And the helium gas on the side of the compressors (4) and (8) is reduced, the helium gas on the side of the compressors (4) and (8) is then closed with the on-off valve (AV) closed. The pressure equalized when the helium gas in the refrigerant circuit (53) is equalized can be reduced. Therefore, when the compressors (4) and (8) are restarted in the pressure equalized state, the starting torque can be reduced, and the operational reliability of the compressors (4) and (8) is improved. be able to.

The on-off valve (AV) is a liquefaction tank (D).
It is also used to prevent the pressure in L) from being equalized at the same pressure as the compressor (4), (8) side, so the dual use of the function of this on-off valve (AV) causes an increase in cost. Without the above, the above-mentioned effect can be obtained.

Further, the low-pressure pipe (3) has a check valve (C
V) is installed, the JT high-pressure pipe (15) (high-pressure pipe (1) when the compressors (4) and (8) are stopped.
The open / close valve (AV) on the side 3)) may be opened for a predetermined time and then closed, as compared with the case where both the high pressure pipe (15) and the low pressure pipe (3) are controlled to open / close by the open / close valve (54). The configuration of can be simplified.

The on-off valve (AV) is an air-pressure valve which is opened and closed by the air pressure from the air-pressure source (56). Since the on-off valve is controlled by the switching operation of the solenoid valve for air pressure (57), the on-off valve (AV) is opened. Even if is placed in a magnetic field, the on-off valve (AV) can be stably opened and closed without being affected by the magnetic field.

(Embodiment 2) FIG. 3 shows Embodiment 2 of the present invention (note that the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals and detailed description thereof will be omitted), In 1, the open / close valve (AV) is composed of a pneumatic valve, whereas
The solenoid valve is configured to open and close the JT high-pressure pipe (15) by receiving an electric control signal from the control device (61). Therefore, also in this embodiment, the same operational effect as that of the above-described first embodiment can be obtained.

[0047]

As described above, according to the invention of claim 1 or 6, a part of the refrigerant circuit in which the compressor and the expansion means are connected by the high pressure pipe and the low pressure pipe is opened in the liquefaction tank. , A cryogenic temperature in which the gas refrigerant evaporated in the liquefaction tank is sucked into the compressor and compressed, and the gas refrigerant compressed by this compressor is expanded and liquefied by the expansion means and returned to the liquefaction tank In the refrigerator, when the compressor is stopped, the refrigerant circuit between the compressor and the expansion means is kept open for a predetermined time to allow the gas refrigerant on the compressor side to flow to the expansion means side and the refrigerant on the compressor side. By reducing the amount of gas refrigerant in the circuit, it is possible to reduce the pressure equalizing pressure itself in the refrigerant circuit on the compressor side, while suppressing the cost increase and starting torque when the compressor is restarted. Smaller to improve its operational reliability It is possible to achieve.

According to the second aspect of the invention, the time from the stop of the compressor to the opening of the opening / closing means is the time until the pressure inside the liquefaction tank rises to the set pressure, so that the inside of the liquefaction tank is excessive. It is possible to reliably prevent pressure increase.

According to the third aspect of the invention, the opening / closing means includes an opening / closing valve for opening / closing the high pressure pipe, and a check valve arranged in the low pressure pipe for preventing the gas refrigerant from moving from the compressor to the expansion means. With this configuration, the structure of the opening / closing means can be simplified.

In the invention of claim 4, the on-off valve is an electromagnetic valve, and in the invention of claim 5, the on-off valve is a pneumatic valve. According to these inventions, a specific configuration of the on-off valve can be obtained. In particular, according to the fifth aspect of the invention, since the pneumatic valve as the on-off valve is opened and closed by the air pressure, the refrigerant circuit can be stably opened and closed without being affected by the magnetic field or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part in a first embodiment of the present invention.

FIG. 2 is a refrigerant circuit diagram showing the overall configuration of the refrigerator in the first embodiment of the present invention.

FIG. 3 is a view corresponding to FIG. 1 and showing a second embodiment of the present invention.

[Explanation of symbols]

 (R) Refrigerator (1) Compressor unit (3) Low pressure piping (4), (8) Compressor (13) High pressure piping (15) JT high pressure piping (31) Refrigerator unit (32) Pre-cooled refrigeration Machine (41) JT refrigerator (expansion means) (48) JT valve (53) Refrigerant circuit (AV) Open / close valve (CV) Check valve (54) Open / close mechanism (open / close means) (57) For pneumatic pressure Solenoid valve (61) Control device (control means) (DL) Liquefaction tank

Claims (6)

[Claims] 1. High-pressure pipe (15) comprising compressors (4), (8) for compressing a refrigerant gas such as helium gas and an expansion means (41) for expanding a high-pressure gas refrigerant to generate cold.
And a refrigerant circuit (5 connected by low pressure piping (3)
3) and a liquefaction tank (DL) in which a part of the refrigerant circuit (53) is opened to store the liquid refrigerant. The gas refrigerant evaporated in the liquefaction tank (DL) is supplied to the refrigerant circuit (5).
3) is sucked into and compressed by the compressors (4) and (8), and the compressed gas refrigerant is expanded by the expansion means (41), and the liquid refrigerant is generated by the temperature drop due to the expansion and the liquefaction tank. In a cryogenic refrigerator which is returned to (DL), an opening / closing means (54) for connecting or disconnecting the compressors (4), (8) and the expansion means (41), and a compressor (4) , (8) from the stop of the opening and closing of the opening and closing means (54) until a predetermined time has elapsed, and a control means (61) for controlling the opening and closing means (54) to close after the elapse of a predetermined time. A pressure equalizing controller for a cryogenic refrigerator. 2. The pressure equalizing control device for a cryogenic refrigerator according to claim 1, wherein the control means (61) opens the opening / closing means (54) after stopping the compressors (4), (8), and is liquefied. A pressure equalization control device for a cryogenic refrigerator, which is the time until the pressure inside the tank (DL) rises to a set pressure. 3. The pressure equalizing control device for a cryogenic refrigerator according to claim 1, wherein the opening / closing means (54) opens and closes the high pressure pipe (15), and the low pressure pipe (3). And permits the gas refrigerant of the expansion means (41) to return to the compressors (4) and (8), while the gas refrigerant from the compressors (4) and (8) flows to the expansion means (41). A pressure equalizing control device for a cryogenic refrigerator, which is configured with a check valve (CV) that blocks movement. 4. The pressure equalizing control device for a cryogenic refrigerator according to claim 3, wherein the on-off valve (AV) is a solenoid valve. 5. The pressure equalizing control device for a cryogenic refrigerator according to claim 3, wherein the on-off valve (AV) is a pneumatic valve that opens and closes by air pressure. apparatus. 6. High-pressure pipe (15) comprising compressors (4), (8) for compressing a gas refrigerant such as helium gas, and expansion means (41) for expanding the high-pressure gas refrigerant to generate cold.
And a refrigerant circuit (5 connected by low pressure piping (3)
3) and a liquefaction tank (DL) in which a part of the refrigerant circuit (53) is opened to store the liquid refrigerant. The gas refrigerant evaporated in the liquefaction tank (DL) is supplied to the refrigerant circuit (5).
3) is sucked into and compressed by the compressors (4) and (8), and the compressed gas refrigerant is expanded by the expansion means (41), and the liquid refrigerant is generated by the temperature drop due to the expansion and the liquefaction tank. In the cryogenic refrigerator which is returned to the inside of (DL), the compressors (4) and (8) and the expansion means (from the stop of the compressors (4) and (8) until a predetermined time elapses. 41)
And the communication between the compressors (4), (8) and the expansion means (41) is cut off after the lapse of the predetermined time, and a pressure equalization control method for a cryogenic refrigerator.