JP5618326B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a refrigeration apparatus, and more particularly to a refrigeration apparatus that freezes products in various stores.

  In various stores such as supermarkets and convenience stores, refrigeration apparatuses such as showcases and refrigerators are used for displaying refrigerated foods, frozen foods, fresh foods, and the like. This refrigeration apparatus usually includes a compressor, a condenser, an evaporator, and the like, and freezes various products by heat exchange using a refrigerant (see, for example, Patent Document 1).

  In such a refrigeration system, when the outside air temperature is high, such as in summer, the condensation pressure in the condenser rises, and it is necessary to increase the refrigerant to the condensation pressure, so the energy consumption by the compressor increases. Resulting in. Therefore, in order to prevent an increase in energy consumption, the size of the condenser is increased, that is, the addition of a condenser (refrigerant circuit) is performed. Thereby, the refrigerant volume of the whole condenser is increased and the increase in the condensation pressure is suppressed, so that energy saving can be realized.

JP-A-11-206014

  However, when a condenser (refrigerant circuit) is added as described above, if the outside air temperature becomes low, such as in winter, the condensation pressure in the condenser is too low. Liquefies and accumulates, and this phenomenon causes a shortage of refrigerant.

  The present invention has been made in view of the above, and an object of the present invention is to provide a refrigeration apparatus capable of suppressing a refrigerant shortage caused by a decrease in outside air temperature while realizing energy saving by adding a condenser. It is.

  According to a first aspect of the present invention, in the refrigeration apparatus, a compressor that compresses the refrigerant, a plurality of condensers in parallel that condense the compressed refrigerant, an expansion valve that decompresses the condensed refrigerant, and a decompressed refrigerant An evaporator for evaporating the refrigerant, and a refrigerant circulation passage for circulating the refrigerant; and a refrigerant inflow side of each of the plurality of condensers in the refrigerant circulation passage. A plurality of on-off valves for controlling the at least one refrigerant inlet side of the plurality of condensers on the downstream side of the on-off valve in the refrigerant circulation passage, and the refrigerant inlet side of the compressor A first refrigerant channel to be connected; a first on-off valve provided in the first refrigerant channel; for opening and closing the first refrigerant channel; and provided in the first refrigerant channel; A decompression section for decompressing the refrigerant flowing through the first refrigerant flow path; When it is detected that the outside air temperature has become lower than a predetermined value, and when it has been detected that the outside air temperature has become lower than the predetermined value, the outside air temperature on the refrigerant inlet side of the condenser communicating with the first refrigerant flow path And a controller that closes the provided on-off valve and opens the first on-off valve.

  According to a second aspect of the present invention, in the refrigeration apparatus according to the first aspect described above, as the plurality of condensers, a first condenser and a second condenser communicating with the first refrigerant flow path. And the third condenser, the refrigerant outlet side of the receiver, and the downstream side of the on-off valve in the refrigerant circulation channel, and the third condenser of the plurality of condensers. A second refrigerant channel connecting to the refrigerant inlet side, a second on-off valve provided in the second refrigerant channel and opening and closing the second refrigerant channel, and the third condenser A third refrigerant flow path connecting the refrigerant flow outlet side and the refrigerant flow inlet side of the expansion valve, and a third refrigerant flow path provided in the third refrigerant flow path for opening and closing the third refrigerant flow path An on-off valve, and when the control unit detects that the outside air temperature has become lower than a predetermined value, the refrigerant inlet side of the third condenser Close provided with the on-off valve is to open the second on-off valve and the third opening and closing valve.

  A third feature according to the present invention is the refrigeration apparatus according to the second feature described above, further comprising a temperature measuring unit that measures the outside air temperature, wherein the control unit is the outside air temperature measured by the temperature measuring unit. Is determined to be lower than a predetermined value, it is detected that the outside air temperature is lower than the predetermined value, and when it is determined that the outside air temperature is lower than the predetermined value, the refrigerant flow of the second condenser is Closing the on-off valve provided on the inlet side, opening the first on-off valve, closing the on-off valve provided on the refrigerant inlet side of the third condenser, the second on-off valve and the Opening the third on-off valve.

  According to the first feature of the present invention, even when the number of condensers is increased, when the outside air temperature becomes lower than a predetermined value, the refrigerant is decompressed and returned to the compressor from at least one condenser. As a result, it is possible to suppress the stagnation of the refrigerant due to the decrease in the outside air temperature, that is, the phenomenon that the refrigerant liquefies and accumulates in the condenser. Accordingly, it is possible to suppress the refrigerant shortage due to the decrease in the outside air temperature while realizing energy saving by adding the condenser.

  According to the second feature of the present invention, when the outside air temperature becomes lower than a predetermined value, the refrigerant in the liquid receiver is supplied to at least one condenser, so that the condenser functions as a supercooling heat exchanger. Will do. As a result, when the outside air temperature becomes lower than the predetermined value, the degree of supercooling of the refrigerant cannot be obtained, and a flash state occurs, that is, a state where the liquid refrigerant evaporates before reaching the evaporator and the refrigerant becomes insufficient. It becomes possible to deter. Therefore, it is possible to more reliably suppress a refrigerant shortage due to a decrease in the outside air temperature.

  According to the third feature of the present invention, since it is automatically detected that the outside air temperature has become lower than a predetermined value, an operator such as a store clerk confirms the outside air temperature with a thermometer, and the outside air with a switch or the like. Compared with the case where the fact that the temperature has become lower than the predetermined value is input, workability and convenience can be improved.

It is a figure which shows schematic structure of the freezing apparatus which concerns on one Embodiment of this invention. It is a flowchart which shows the flow of the refrigerant | coolant circulation process which the refrigeration apparatus shown in FIG. 1 performs. It is explanatory drawing for demonstrating refrigerant | coolant circulation operation | movement in case the outside temperature is more than predetermined value in the refrigerant | coolant circulation process shown in FIG. FIG. 3 is an explanatory diagram for explaining a refrigerant return operation and a refrigerant subcooling operation by a single condenser when the outside air temperature is lower than a predetermined value in the refrigerant circulation process shown in FIG. 2. It is explanatory drawing for demonstrating the refrigerant | coolant return operation | movement by two condensers when outside temperature is lower than predetermined value in the refrigerant | coolant circulation process shown in FIG.

  An embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a refrigeration apparatus 1 according to an embodiment of the present invention includes a compressor 2 that compresses a refrigerant, a plurality of condensers 3a, 3b, and 3c that condense the compressed refrigerant, and a condensed refrigerant. , An expansion valve 5 that decompresses the refrigerant, an evaporator 6 that evaporates the decompressed refrigerant, a refrigerant circulation passage 7 that circulates the refrigerant by connecting these parts, and various controls The control part 8 which performs is provided.

  The refrigerant circulation passage 7 is a passage through which the refrigerant is circulated by connecting the compressor 2, the condensers 3 a, 3 b, 3 c, the liquid receiver 4, the expansion valve 5, and the evaporator 6. It consists of connecting pipes (piping). The condensers 3a, 3b, and 3c are connected in parallel to the refrigerant circulation passage 7. The condenser 3a is a first condenser, the condenser 3b is a second condenser, and the condenser 3c is a third condenser.

  The refrigerant circulation channel 7 is connected to a first refrigerant channel 7a, a second refrigerant channel 7b, and a third refrigerant channel 7c, and further includes a plurality of on-off valves 9a to 9i and a plurality of reverse valves. Stop valves 10a to 10f are provided. As each on-off valve 9a-9i, an electromagnetic valve is used, for example. Each of the condensers 3a, 3b, and 3c is provided with a common blowing fan 11 and a temperature measuring unit 12 that measures the outside air temperature. Further, the evaporator 6 includes a blowing fan 13. Is provided.

  Here, the refrigerant circulates in the refrigerant circulation passage 7 while repeating the four steps of compression, condensation, expansion and evaporation. More specifically, the high-temperature and high-pressure gas refrigerant compressed by the compressor 2 flows into each of the condensers 3a, 3b, and 3c, is cooled by these condensers 3a, 3b, and 3c, and liquefies by releasing heat of condensation. And stored in the liquid receiver 4. The liquid receiver 4 absorbs fluctuations in the refrigerant amount in the evaporator 6 due to load fluctuations.

  Thereafter, the normal temperature and high pressure liquid refrigerant stored in the liquid receiver 4 flows into the expansion valve 5 and is decompressed by the expansion valve 5 so that the boiling point is lowered. The low-temperature and low-pressure liquid refrigerant in this state is boiled and evaporated by the evaporator 6 and refrigerates after taking away the surrounding heat. The evaporated low-pressure gas refrigerant flows into the compressor 2, is compressed by the compressor 2, becomes a high-temperature high-pressure gas refrigerant that can be liquefied by room temperature air, and flows into the condensers 3a, 3b, and 3c again.

  Each on-off valve 9a, 9b, 9c in the refrigerant circulation channel 7 is provided on the refrigerant inlet side of each of the condensers 3a, 3b, 3c in the refrigerant circulation channel 7. These on-off valves 9a, 9b, and 9c control the inflow of refrigerant to the condensers 3a, 3b, and 3c in accordance with control by the control unit 8. When each on-off valve 9a, 9b, 9c is opened, the high-temperature and high-pressure gas refrigerant compressed by the compressor 2 flows into each condenser 3a, 3b, 3c.

  The first refrigerant flow path 7a is downstream of the on-off valve 9b in the refrigerant circulation flow path 7 and on the refrigerant inlet side of the condenser 3b and downstream of the on-off valve 9c and on the refrigerant inlet side of the condenser 3c. And the refrigerant inlet side of the compressor 2 are connected. The first refrigerant flow path 7a includes two on-off valves 9d and 9e that open and close the first refrigerant flow path 7a, and a decompression unit 14 that depressurizes the refrigerant flowing through the first refrigerant flow path 7a. Is provided. For example, a capillary tube is used as the decompression unit 14.

  Each of the on-off valves 9 d and 9 e functions as a first on-off valve that opens and closes the first refrigerant flow path 7 a according to control by the control unit 8 and controls the inflow of refrigerant to the upstream side of the compressor 2. When these on-off valves 9d and 9e are opened, the refrigerant in the condensers 3b and 3c is returned to the upstream side of the compressor 2 via the first refrigerant flow path 7a and the decompression unit 14. At this time, the on-off valves 9b and 9c are closed.

  The second refrigerant channel 7b connects the refrigerant outlet side of the liquid receiver 4 to the refrigerant inlet side of the condenser 3c on the downstream side of the on-off valve 9c in the refrigerant circulation channel 7. The second refrigerant channel 7b is provided with an opening / closing valve 9f that opens and closes the second refrigerant channel 7b. The on-off valve 9f functions as a second on-off valve that opens and closes the second refrigerant flow path 7b in accordance with control by the control unit 8 and controls the inflow of refrigerant to the upstream side of the condenser 3c.

  An on-off valve 9g is provided between the refrigerant outlet side of the liquid receiver 4 and the refrigerant inlet side of the expansion valve 5. The on-off valve 9g is controlled so that the refrigerant in the liquid receiver 4 does not directly flow into the expansion valve 5, that is, flows into the second refrigerant flow path 7b. Specifically, when the opening / closing valve 9g is closed, the opening / closing valve 9f is opened, and the refrigerant in the liquid receiver 4 flows into the condenser 3c via the second refrigerant flow path 7b. At this time, the on-off valves 9c and 9e are closed.

  The third refrigerant flow path 7c connects the refrigerant outlet side of the condenser 3c and the refrigerant inlet side of the expansion valve 5. The third refrigerant channel 7c is provided with an open / close valve 9h for opening and closing the third refrigerant channel 7c. The on-off valve 9 h functions as a third on-off valve that opens and closes the third refrigerant flow path 7 c in accordance with control by the control unit 8 and controls the inflow of refrigerant to the expansion valve 5.

  An opening / closing valve 9i is provided between the refrigerant outlet side of the condenser 3c and the refrigerant inlet side of the liquid receiver 4 so as to approach the condenser 3c side. The on-off valve 9i is controlled so that the refrigerant that has passed through the condenser 3c does not flow to the liquid receiver 4 side, that is, flows into the third refrigerant flow path 7c. Specifically, when the on-off valve 9i is closed, the on-off valve 9h is opened, and the refrigerant in the condenser 3c flows into the expansion valve 5 through the third refrigerant flow path 7c.

  The control unit 8 includes a microcomputer that centrally controls each unit, a storage unit that stores various types of information and various programs, and an operation unit that receives operations from an operator. Note that a memory, a hard disk drive (HDD), or the like is used as the storage unit. The controller 8 controls the on-off valves 9a to 9i in addition to the compressor 2 and the fans 11 and 13. A temperature measuring unit 12 is electrically connected to the control unit 8. The temperature measuring unit 12 measures the outside air temperature and outputs the measured outside temperature (temperature signal) to the control unit 8. Various types of temperature measuring devices are used as the temperature measuring unit 12.

  Next, the refrigerant circulation process (refrigerant circulation operation including the refrigerant return operation and the refrigerant subcooling operation) performed by the refrigeration apparatus 1 described above will be described. In addition, the control part 8 of the freezing apparatus 1 performs a refrigerant | coolant circulation process based on various programs.

  As shown in FIG. 2, the control unit 8 first determines whether or not the outside air temperature measured by the temperature measuring unit 12 is lower than a first predetermined value (step S1). This makes it possible to detect that the outside air temperature has become lower than the first predetermined value. The first predetermined value is set in advance and is stored in the storage unit of the control unit 8.

  When it is determined that the outside air temperature is not lower than the first predetermined value, that is, not less than the first predetermined value (NO in Step S1), the outside air temperature is high, and therefore, the three condensers 3a, 3b, and 3c are used. Control for performing refrigerant condensation is executed (step S2).

  That is, as shown in FIG. 3, the control unit 8 opens the on-off valves 9a, 9b, 9c, 9g, 9i and closes the on-off valves 9d, 9e, 9f, 9h. As a result, the on-off valves 9a, 9b, 9c, 9g, 9i are opened, and the on-off valves 9d, 9e, 9f, 9h are closed, so that the refrigerant is supplied from the compressor 2 to the three condensers 3a, 3b. 3c, and reaches the liquid receiver 4, and then passes from the liquid receiver 4 through the expansion valve 5 and the evaporator 6 to return to the compressor 2 again.

  In FIG. 3, the open / close valve in the open state is white, the open / close valve in the closed state is shown in black, and the flow of the refrigerant is shown by a bold line (the arrow indicates the flow direction of the refrigerant). Similarly, in FIG. 4 and FIG. 5, the open / close valve in the open state is white, the open / close valve in the closed state is shown in black, and the refrigerant flow is indicated by a bold line (the arrow indicates the refrigerant flow direction). Has been.

  In step S1 of FIG. 2, when it is determined that the outside air temperature is lower than the first predetermined value (YES in step S1), the outside air temperature is again lower than the second predetermined value smaller than the first predetermined value. It is determined whether it is low (step S3). This makes it possible to detect that the outside air temperature has become lower than the second predetermined value. The second predetermined value is also set in advance and stored in the storage unit of the control unit 8.

  When it is determined that the outside air temperature is lower than the second predetermined value (YES in step S3), control is performed to return the refrigerant in one condenser 3b to the upstream side of the compressor 2 (step S4). Control which supercools a refrigerant | coolant is performed (step S5), and a process is returned to step S1 after that.

  That is, as shown in FIG. 4, the control unit 8 first closes the on-off valve 9b and then opens the on-off valve 9d. As a result, the on-off valve 9b is closed and the on-off valve 9d is opened, so that the refrigerant in the condenser 3b is returned to the upstream side of the compressor 2 via the first refrigerant flow path 7a and the decompression unit 14. It is. By this refrigerant return operation, it is possible to suppress the stagnation of the refrigerant in the condenser 3b, that is, the phenomenon that the refrigerant liquefies and accumulates in the condenser 3b.

  Further, as shown in FIG. 4, the control unit 8 closes the on-off valves 9c, 9g, 9i and opens the on-off valves 9f, 9h. As a result, the on-off valves 9c, 9g, 9i are opened, and the on-off valves 9f, 9h are closed, so that the refrigerant passes through the condenser 3a from the compressor 2 and reaches the liquid receiver 4. Thereafter, the refrigerant flows into the upstream side of the condenser 3c via the second refrigerant flow path 7b and is supplied to the condenser 3c. The refrigerant passes through the refrigerant circuit in the condenser 3c, is supplied to the expansion valve 5 through the third refrigerant flow path 7c, passes through the expansion valve 5 and the evaporator 6, and returns to the compressor 2 again. Therefore, since the refrigerant that has passed through the condenser 3a passes through the condenser 3c again, the condenser 3c functions as a supercooling heat exchanger. As a result, it is possible to suppress the occurrence of a flash state in which the degree of supercooling of the refrigerant cannot be obtained, that is, a state in which the liquid refrigerant evaporates before reaching the evaporator 6 and the refrigerant becomes insufficient.

  When it is determined in step S3 of FIG. 2 that the outside air temperature is not lower than the second predetermined value, that is, not less than the second predetermined value (NO in step S3), the two condensers 3b, 3c Control is performed to return the internal refrigerant to the upstream side of the compressor 2 (step S2), and then the process returns to step S1.

  That is, as shown in FIG. 5, the control unit 8 first closes the on-off valves 9b and 9c, and then opens the on-off valves 9d and 9e. As a result, the on-off valves 9b and 9c are closed and the on-off valves 9d and 9e are opened, so that the refrigerant in the two condensers 3b and 3c passes through the first refrigerant flow path 7a and the decompression unit 14. It is returned to the upstream side of the compressor 2. By this refrigerant return operation, it is possible to suppress the stagnation of the refrigerant in each of the condensers 3b and 3c, that is, the phenomenon that the refrigerant liquefies and accumulates in each of the condensers 3b and 3c.

  Here, after the process of step S5 or step S6 described above, if it is determined in step S1 that the outside air temperature is not lower than the first predetermined value, that is, not less than the first predetermined value (NO in step S1). ) Assuming that the outside air temperature has increased, the process of step S2 is performed, and control is performed to condense the refrigerant by the three condensers 3a, 3b, and 3c. In the above-described refrigerant circulation process (see FIG. 2), the processes in step S4 and step S5, which are processes after step S3, and the process in step S6 may be reversed.

  As described above, according to the embodiment of the present invention, the condenser 3b in parallel and the refrigerant inlet side of the condenser 3c and the refrigerant inlet side of the compressor 2 are connected by the first refrigerant flow path 7a. The controller 8 controls the on-off valves 9d and 9e that are connected and open and close the first refrigerant flow path 7a. Therefore, when the outside air temperature becomes lower than the predetermined value, the refrigerant is decompressed and returned to the compressor 2 from one or both of the condenser 3b and the condenser 3c. As a result, it is possible to suppress the stagnation of the refrigerant due to a decrease in the outside air temperature, that is, the phenomenon that the refrigerant is liquefied and accumulated in the condensers 3b and 3c. Therefore, it is possible to suppress a shortage of refrigerant due to a decrease in the outside air temperature while realizing energy saving by adding a condenser (refrigerant circuit).

  Further, when the outside air temperature becomes lower than a predetermined value, the refrigerant in the liquid receiver 4 is supplied to at least one condenser 3c, so that the condenser 3c functions as a supercooling heat exchanger. As a result, when the outside air temperature becomes lower than a predetermined value, the degree of supercooling of the refrigerant cannot be obtained, and a flash state occurs, that is, a state where the liquid refrigerant evaporates before reaching the evaporator 6 and the refrigerant becomes insufficient. Therefore, it is possible to more reliably prevent a refrigerant shortage caused by a decrease in the outside air temperature.

  Further, since it is automatically detected that the outside air temperature has become lower than the predetermined value, an operator such as a store clerk confirms the outside air temperature with a thermometer, and confirms that the outside air temperature has become lower than the predetermined value with a switch or the like. Compared with input, workability and convenience can be improved.

  Here, each condenser 3a, 3b, 3c does not necessarily need the same volume (size). For example, if the condenser 3c is a minimum size (a condenser having a size that is normally high in summer in each of the condensers 3a and 3b), the amount of refrigerant filled in the refrigerant cycle does not become extremely large, and the condenser 3c A high pressure drop can be achieved. In addition, as a size, condenser 3a> condenser 3b> condenser 3c is desirable.

  Even if the two condensers 3a and 3b are existing condensers, the condenser 3c, the first refrigerant flow path 7a, the second refrigerant flow path 7b, and the third refrigerant flow path 7c should be added. Thereby, the effect which concerns on the above-mentioned embodiment can be acquired. Existing condensers often fail to exhibit their original condensing capacity due to deterioration of dirt, aluminum fins, etc. over time. In particular, due to the temperature rise in summer in recent years, systems that use aged condensers are increasing the number of cases that cause high-pressure cuts. It is effective to add condenser 3c and auxiliary piping as a countermeasure for aged equipment. is there.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, some components may be deleted from all the components shown in the above-described embodiment. Furthermore, you may combine the component covering different embodiment suitably.

  For example, the number of condensers is not limited to the above-described three, and it is sufficient if there are a plurality of condensers. Specifically, if there are a plurality of refrigerant circuits (condensers) arranged in parallel with the refrigerant circulation passage 7. good.

  Further, in the above-described embodiment, the control unit 8 detects that the outside air temperature has become lower than the predetermined value by determining whether or not the outside air temperature measured by the temperature measuring unit 12 is lower than the predetermined value. However, the present invention is not limited to this. For example, it may be detected that the outside air temperature has become lower than a predetermined value by determining whether or not a button included in the operation unit has been pressed. In this case, an operator such as a store clerk checks the temperature in the store with a thermometer, and when the temperature is lower than a predetermined value, presses a button on the operation unit.

DESCRIPTION OF SYMBOLS 1 Refrigeration apparatus 2 Compressor 3a-3c Condenser 4 Liquid receiver 5 Expansion valve 6 Evaporator 7 Refrigerant circulation flow path 7a 1st refrigerant flow path 7b 2nd refrigerant flow path 7c 3rd refrigerant flow path 8 Control part 9a-9i On-off valve 10a-10f Check valve 11 Fan 12 Temperature measuring unit 13 Fan 14 Depressurizing unit

Claims (2)

A refrigerant that circulates a refrigerant by connecting a compressor that compresses the refrigerant, a plurality of condensers in parallel to condense the compressed refrigerant, an expansion valve that decompresses the condensed refrigerant, and an evaporator that evaporates the decompressed refrigerant A circulation channel;
A plurality of on-off valves that are provided on the refrigerant inlet side of each of the plurality of condensers in the refrigerant circulation flow path and control the inflow of refrigerant to the plurality of condensers;
A first refrigerant flow path downstream of the on-off valve in the refrigerant circulation flow path and connecting at least one refrigerant flow inlet side of the plurality of condensers and a refrigerant flow inlet side of the compressor;
A first on-off valve provided in the first refrigerant flow path for opening and closing the first refrigerant flow path;
A pressure reducing unit provided in the first refrigerant flow path and depressurizing a refrigerant flowing through the first refrigerant flow path;
When it is detected that the outside air temperature has become lower than a predetermined value and it has been detected that the outside air temperature has become lower than a predetermined value, a refrigerant inlet side of the condenser communicating with the first refrigerant flow path is provided. A controller that closes the provided on-off valve and opens the first on-off valve;
As the plurality of condensers, a first condenser, a second condenser communicating with the first refrigerant flow path, and a third condenser,
A second connecting the refrigerant outlet side of the liquid receiver and a refrigerant inlet side of the third condenser among the plurality of condensers on the downstream side of the on-off valve in the refrigerant circulation passage. Refrigerant flow path,
A second on-off valve provided in the second refrigerant flow path for opening and closing the second refrigerant flow path;
A third refrigerant flow path connecting the refrigerant outlet side of the third condenser and the refrigerant inlet side of the expansion valve;
A third on-off valve provided in the third refrigerant flow path for opening and closing the third refrigerant flow path;
Equipped with a,
When the control unit detects that the outside air temperature is lower than a predetermined value, the control unit closes the on-off valve provided on the refrigerant inlet side of the third condenser, and the second on-off valve and the second on-off valve A refrigeration apparatus characterized by opening a third on-off valve . A temperature measuring unit for measuring the outside air temperature;
The control unit detects whether the outside air temperature is lower than a predetermined value by determining whether the outside air temperature measured by the temperature measuring unit is lower than a predetermined value, and the outside air temperature is a predetermined value. If it is determined that the value is lower, the on-off valve provided on the refrigerant inlet side of the second condenser is closed, the first on-off valve is opened, and provided on the refrigerant inlet side of the third condenser. The refrigeration apparatus according to claim 1 , wherein the opened on-off valve is closed and the second on-off valve and the third on-off valve are opened .

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