JP5458717B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a method for recovering refrigerating machine oil in a refrigerating apparatus such as an air conditioner.

In a refrigerating apparatus using a compressor, refrigerating machine oil is often dissolved in the refrigerant discharged from the compressor. For this reason, an oil separator is provided in the discharge side piping of the compressor so that the refrigeration oil dissolved in the refrigerant is separated and returned to the compressor, and only the refrigerant is guided to the condenser. However, since the refrigeration oil cannot be completely separated even by the oil separator, it cannot be denied that the refrigerant in a state in which the refrigeration oil that could not be separated is introduced is led to the condenser.
JP 2004-286240 A

  As described above, the refrigeration oil that could not be separated by the oil separator is led to the condenser.For example, in an air conditioner, when passing through the indoor heat exchanger and the outdoor heat exchange, these heat exchangers and The amount of oil that reaches the inner surface of the refrigerant pipe and returns to the compressor decreases. In particular, in a separation type air conditioner in which an indoor unit having an indoor heat exchanger and an outdoor unit having an outdoor heat exchanger are connected by an inter-unit pipe, the inter-unit pipe is a long pipe (" In many cases, “commercial air conditioners”), the amount of refrigerating machine oil returning to the gas-liquid separator is smaller than in the case of short piping. As a result, it is considered that the compressor runs out of oil, wear of the sliding portion of the compressor becomes faster than usual, and the life of the compressor is shortened.

  An object of the present invention is to prolong the life of a compressor by appropriately maintaining the amount of refrigerating machine oil returning to the compressor and suppressing wear of sliding portions of the compressor.

The invention according to claim 1 forms a refrigeration cycle by sequentially connecting a compressor, a condenser, a decompressor, an evaporator, and a gas-liquid separator driven by a gas engine. The liquid refrigerant in which the gas is dissolved is stored, and the refrigeration oil accumulated in the lower part of the gas-liquid separator is located in the gas-liquid separator and returned to the compressor through the oil hole of the suction pipe connected to the compressor. In the refrigeration apparatus, a heating heat exchanger for heating the liquid refrigerant in which the refrigerating machine oil in the gas-liquid separator is dissolved to separate the liquid refrigerant from the refrigerating machine oil is provided, and the heat exchanger includes the gas A high-temperature cooling water that directly leads the cooling water from the engine, or a valve that switches this high-temperature cooling water with a radiator and switching to flow either an intermediate-temperature cooling water that is lower than this high-temperature cooling water,
When the temperature of the condenser is equal to or higher than a predetermined temperature or the discharge temperature of the compressor is equal to or higher than a predetermined temperature, the liquid refrigerant in the gas-liquid separator is heated with the intermediate temperature cooling water, and even with this heating, the condenser temperature Is switched to heating of the liquid refrigerant in the gas-liquid separator with the high-temperature cooling water, and the liquid refrigerant in the gas-liquid separator is The refrigeration oil separated by heating is returned to the compressor through the oil return hole.

According to this structure, the exhaust heat of the gas engine that drives the compressor is effectively used to heat the inside of the gas-liquid separator to separate the refrigerating machine oil dissolved in the refrigerant, and this refrigerating machine oil is supplied to the compressor. Can be returned.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram of a refrigerant circuit in an outdoor unit 100 used in a gas heat pump (GHP) type air conditioner according to an embodiment of the present invention. In this circuit diagram, the refrigerant circuit is indicated by a solid line, the cooling water circuit is indicated by a thick solid line, and the exhaust gas circuit is indicated by a one-dot chain line.

  The refrigerant circuit 110 in the outdoor unit 100 shown in FIG. 1 is connected in order clockwise from the gas engine 1, the compressor 3 connected to the gas engine 1 by the V-belt 2, and the compressor 3 via the refrigerant pipe. The oil separator 4, the four-way valve 5, the outdoor heat exchanger 6 cooled by the air sucked by the fans 17, 17, the electric valve 7 arranged in parallel, the plate heat exchanger 36, and the gas-liquid separator 11 are provided. The gas-liquid separator 11 is connected to the compressor 3 so that the refrigerant circulates. In addition, indoor units 140 and 150 are provided, and refrigerant pipes are connected to the indoor units 140 and 150 via on-off valves 9 and 10. The outdoor unit 100 and the indoor units 140 and 150 are connected by inter-unit piping.

  In FIG. 1, the solid arrows indicate the refrigerant flow in the cooling cycle, and the dotted arrows indicate the refrigerant flow in the heating cycle. By switching the four-way valve 5, these operations are performed. The cycle can be switched. The refrigerant circuit 110 includes a bypass valve 12, which is an electric valve, a liquid valve 13, which is an electric valve, a pressure switch 14, a high pressure sensor 15, a low pressure sensor 16, a check valve 18, and A subcooler 19 is provided.

  On the other hand, the cooling water circuit 120 in the outdoor unit 100 includes a hot water three-way valve 37 (also referred to as an electric cooler three-way valve), a cooling water three-way valve 20, a radiator 39, an air connected in order from the gas engine 1 through a cooling water pipe. A drain valve 40, a reservoir tank 22, and a cooling water pump 21 are provided, and the cooling water pump 21 is connected to the exhaust gas heat exchanger 23 of the gas engine 1 so that the cooling water circulates. An exhaust muffler 24 is connected to the exhaust gas heat exchanger 23, and an exhaust top 25 and a drain filter 26 are connected to the exhaust muffler 24.

  Further, as shown in FIG. 1, the gas engine 1 includes combustion gas cutoff valves 27, 27, a zero governor 28, a fuel adjustment valve 29 that is an electric valve, an air cleaner 30, a stepping motor 31, and an oil level switch 33. An oil pan 32, an oil pump 34, and an oil catcher 35 are connected to each other. By opening / closing the combustion gas cutoff valve 27 and the movement of the stepping motor 31, gas as fuel is supplied to the gas engine 1.

  In the cooling water circuit 120, a first path for returning the cooling water that has passed through the gas engine 1 to the gas engine 1 is formed by a piping path that connects the hot water three-way valve 37 and the cooling water pump 21. The cooling water that has passed through the gas engine 1 passes through the hot water three-way valve 37, the cooling water three-way valve 20, and the plate heat exchanging section 36 and returns to the first path, the hot water three-way valve 37, and the cooling water. A water three-way valve 20 and a third path that passes through the radiator 39 and returns to the first path can be formed.

  When the open / close state of the solenoid valve 54 is controlled by the control unit 70 and the solenoid valve 54 is opened, the cooling water discharged from the cooling water pump 21 through the cooling water pipe 53 is passed through the cooling water pipe 55. To the cooling water heat exchanger 81 (described later) provided in the gas-liquid separator 11. Similarly, when the solenoid valve 52 is controlled to be opened and closed by the control unit 70 and is opened, the cooling water discharged from the hot water three-way valve 37 through the cooling water pipe 51 is supplied to the cooling water pipe. It is led to a cooling water heat exchanger 81 provided in the gas-liquid separator 11 through 55. The cooling water led from the electromagnetic valve 52 to the cooling water heat exchanger 81 in the gas-liquid separator 11 exchanges heat between the cylinder and the exhaust gas in the gas engine 1, and the electromagnetic valve 54. The cooling water led to the cooling water heat exchanger 81 is cooled by the radiator 39 or the plate heat exchange unit 36. Therefore, the cooling water discharged from the electromagnetic valve 52 has a higher temperature than the cooling water discharged from the electromagnetic valve 54, and hence the cooling water discharged from the electromagnetic valve 52 is called high temperature cooling water. The cooling water discharged from is called medium temperature cooling water. A circuit through which high-temperature cooling water flows is referred to as a high-temperature brine circuit, and a circuit through which intermediate-temperature cooling water flows is referred to as an intermediate-temperature brine circuit.

  FIG. 2 is a diagram showing an example of the internal structure of the gas-liquid separator 11 shown in FIG. Medium-temperature cooling water supplied from the electromagnetic valve 54 (see FIG. 1) or high-temperature cooling water supplied from the electromagnetic valve 52 (see FIG. 1) is led into the gas-liquid separator 11, and the intermediate-temperature cooling water or high-temperature cooling water is supplied. A cooling water heat exchanger 81 is disposed to exchange heat between the cooling water and the liquid refrigerant in which the refrigerating machine oil stored in the gas-liquid separator 11 is dissolved. In addition, in order to perform heat exchange reliably, it is desirable to install the cooling water heat exchanger 81 so as to be positioned below the gas-liquid separator 11 in which the liquid refrigerant is stored.

  1 is connected to the cooling water inlet pipe C of the cooling water heat exchanger 81, and the cooling water outlet pipe D is connected to the piping of the gas-liquid separator 11 of FIG. B is connected.

  The air conditioner has a control unit 70 for controlling each unit of the outdoor unit 100 and the indoor units 140 and 150 in FIG. The control unit 70 includes various temperature sensors and is communicably connected to indoor control devices (not shown) of the indoor units 140 and 150. When the control unit 70 obtains a user instruction input to an indoor remote controller (not shown) via the indoor control device and performs a cooling operation, the four-way valve 5 is used as shown in FIG. Is switched to the position of the solid line (cooling operation position), and the refrigerant discharged from the compressor 3 by driving the gas engine 1 is caused to flow in the direction indicated by the solid line arrow in the figure so that the outdoor heat exchanger 6 functions as a condenser. While the indoor heat exchangers 141 and 151 (see FIG. 1) function as evaporators, when heating operation is performed, the four-way valve 5 is switched to the broken line position (heating operation position) and discharged from the compressor 3. The refrigerant thus flowed is caused to flow in the direction indicated by the broken-line arrows in the figure, causing the indoor heat exchangers 141 and 151 to function as condensers and the outdoor heat exchanger 6 to function as evaporators. In addition, the control unit 70 controls the opening degree of the motor-operated valves 7, 142, and 152, and adjusts the amount of refrigerant passing through the motor valves 7, 142, and 152 so that each conditioned room has a set temperature.

  Further, the control unit 70 controls the opening degree of the hot water three-way valve 37 and the cooling water three-way valve 20, and controls the flow rate of the cooling water flowing through the first, second, and third paths, whereby the gas engine 1 is controlled. The exhaust heat is recovered and the operating efficiency of the air conditioner is improved. More specifically, for example, when the temperature of the cooling water is low, such as immediately after the gas engine 1 is started, the cooling water is circulated through the first path. Further, when the temperature of the cooling water becomes high and the heating load is large during the heating operation, the cooling water is circulated through the second path, and the heat of the cooling water is collected by the refrigerant by the plate heat exchange unit 36. Thus, it can cope with the heating load and improve the operation efficiency. Further, when the temperature of the cooling water is high and the heating load is small during the heating operation, or during the cooling operation, the cooling water is circulated through the third path, and the heat of the cooling water is transferred from the radiator 39 to the outside air. Dissipate heat.

  Next, with reference to the flowchart of FIG. 3, the operation | movement at the time of the air_conditionaing | cooling operation of the above embodiment is demonstrated. When the processing of the flowchart shown in FIG. 3 is started, the following steps are executed. That is, in step S10, the control unit 70 (see FIG. 1) starts the cooling operation of the air conditioner. More specifically, the control unit 70 starts the gas engine 1 and starts driving the compressor 3, and switches the four-way valve 5 to a solid line position (cooling operation position), and compresses by driving the gas engine 1. The refrigerant discharged from the machine 3 is caused to flow in the direction indicated by the solid line arrow in the figure so that the outdoor heat exchanger 6 functions as a condenser and the indoor heat exchangers 141 and 151 function as evaporators. At this time, since the solenoid valves 52 and 54 are controlled to be closed, no cooling water is supplied to the gas-liquid separator 11.

  In step S11, the control unit 70 determines whether or not 10 minutes have elapsed from the start of operation. If 10 minutes have elapsed (step S11; Yes), the control unit 70 proceeds to normal operation step S12, and otherwise ( In step S11; No), the same process is repeated until 10 minutes have elapsed. The reason for waiting for 10 minutes to pass is that the motor-operated valve is used for the purpose of preventing liquid back to the compressor 3 (liquid phase refrigerant flowing into the compressor 3) in a transient state after the start of operation. This is to exclude such a case because the superheat degree may increase in some cases.

  In step S12, the control unit 70 performs a normal cooling operation. At this time, since both the solenoid valves 52 and 54 are closed, the cooling water is not supplied to the gas-liquid separator 11.

In step S13, it is determined whether or not the condensation temperature control or the discharge temperature control is necessary. If control is necessary, the process proceeds to step S14, and otherwise, the process proceeds to step S15. Condensation temperature control refers to the rotational speed of the fan 17 of the outdoor unit 100 so that the temperature T ₁ (see FIG. 1) of the outdoor heat exchanger is not more than a predetermined temperature and the pressure is not too high. Controlling the rotational speed of the engine 1 is discharge temperature control, in which the rotational speed of the compressor 3 is increased or decreased so that the temperature T ₂ (see FIG. 1) of the discharge-side piping of the compressor becomes a predetermined temperature or less. That is. When there is a need for such control, normal operation becomes difficult, and it is necessary to lower the driving ability such as lowering the rotational speed of the engine 1. Since the heating of the gas-liquid separator 11 leads to an increase in the high-pressure pressure of the refrigerant, the heating of the gas-liquid separator 11 in an operating state that does not enter such control is a prerequisite.

  In step S14, condensation temperature control and discharge temperature control are performed.

  In step S15, the control unit 70 opens the electromagnetic valve 54 of the medium temperature brine circuit. At this time, the electromagnetic valve 52 is closed. As a result, the cooling water discharged from the cooling water pump 21 flows through the cooling water heat exchanger 81 disposed in the gas-liquid separator 11 via the electromagnetic valve 54, and then passes through the cooling water pipe 56. And returned to the cooling water pump 21. As described above, since the cooling water discharged from the cooling water pump 21 is cooled by the radiator 39, the cooling water discharged from the gas engine 1 is medium temperature cooling water having a lower temperature than the cooling water discharged from the gas engine 1, for example, It is about 60 ° C.

  In step S16, it is determined again whether or not the condensation temperature control or the discharge temperature control is necessary. If the control is necessary, the process proceeds to step S17. Otherwise, the process proceeds to step S18.

  In step S17, the control unit 70 closes the electromagnetic valve 54 of the medium temperature brine circuit. At this time, since the solenoid valves 52 and 54 are controlled to be closed, the gas-liquid separator 11 is not supplied with cooling water.

  In step S18, the control unit 70 closes the electromagnetic valve 54 of the medium temperature brine circuit and opens the electromagnetic valve 52 of the high temperature brine circuit. As a result, the cooling water discharged from the gas engine 1 flows through the cooling water heat exchanger 81 disposed in the gas-liquid separator 11 via the electromagnetic valve 52, and then passes through the cooling water pipe 56. It is returned to the cooling water pump 21. As described above, the cooling water discharged from the gas engine 1 is high-temperature cooling water having a temperature higher than that of the medium-temperature cooling water cooled by the radiator 39, and is about 80 ° C., for example.

  In step S19, it is determined whether or not the condensation temperature control or the discharge temperature control is necessary. If the control is necessary, the process proceeds to step S20, and otherwise the same process is repeated.

  In step S20, the control unit 70 closes the solenoid valve 52 of the high-temperature brine circuit and opens the solenoid valve 54 of the medium-temperature brine circuit. As a result, the cooling water discharged from the gas engine 1 flows through the cooling water heat exchanger 81 arranged in the gas-liquid separator 11 via the electromagnetic valve 54, and then passes through the cooling water pipe 56. It is returned to the cooling water pump 21.

  Here, since the refrigerating machine oil has a property of being easily dissolved in the refrigerant as the pressure is higher and the temperature is lower, if the gas-liquid separator 11 can be maintained at a low pressure and a high temperature, the liquid refrigerant in the gas-liquid separator 11 and the refrigeration can be obtained. Machine oil is easily separated. For this reason, the gas-liquid separator 11 is heated by the heat exchanger 81, and the liquid refrigerant in which the refrigerating machine oil is dissolved is kept at a high temperature, so that the refrigerant stored in the gas-liquid separator 11 and the refrigerating machine oil dissolved in the refrigerant are stored. Separation from is promoted. The refrigerating machine oil separated in this way accumulates in the lower part in the gas-liquid separator 11 and is quickly returned to the compressor 3 through the oil return hole 80. In particular, when the condensation temperature control or the discharge temperature control is not required in step S13, the intermediate temperature cooling water is guided to the cooling water heat exchanger 81 in step S15. Further, in this state, when the condensation temperature control or the discharge temperature control is not required in step S16, the high-temperature cooling water having a temperature higher than the medium-temperature cooling water is led to the cooling water heat exchanger 81 in step S18. In this way, when the discharge temperature control is not required even when the medium temperature cooling water is used, the high temperature cooling water higher than the medium temperature cooling water is guided to the cooling water heat exchanger 81. For this reason, by utilizing the heat from the two types of heat sources having different temperatures, the separation of the refrigerant stored in the gas-liquid separator 11 and the refrigerating machine oil dissolved in the refrigerant can be surely promoted. Moreover, it can prevent that the temperature of a refrigerant | coolant rises too much by heating using a high heat source from a heat source with low temperature in steps.

  As described above, according to the embodiment of the present invention, the oil separator 4 is provided in the discharge side pipe 60 of the compressor 3 and separates the refrigeration oil contained in the refrigerant discharged from the compressor 3. Then, it is guided to the gas-liquid separator 11 through the return pipe 61. Although it is ideal that the refrigeration oil separated by the oil separator 4 returns to the compressor 3 quickly in order to maintain an appropriate amount of oil, the liquid back that liquid refrigerant flows into the compressor 3 together with the refrigeration oil is prevented. In order to do so, it is necessary to pass through the gas-liquid separator 11. Further, if the oil return hole 80 is simply enlarged in order to quickly return the refrigeration oil from the gas-liquid separator 11 to the compressor 3, not only the refrigeration oil but also the liquid is returned via the oil return hole 80 in this case. Since the refrigerant also returns to the compressor, there is a possibility of causing a liquid back. Therefore, by keeping the gas-liquid separator 11 at a high temperature, the separation of the liquid refrigerant and the refrigerating machine oil is promoted, and the oil return holes 801 are increased to a plurality at the lower portion of the suction pipe of the gas-liquid separator 11 as shown in FIG. Alternatively, as shown in FIG. 7, the refrigeration oil stored in the lower portion of the gas-liquid separator 11 can be smoothly returned to the compressor 3 by increasing the oil return hole 802 downward. In this case, the refrigerating machine oil 91 is stored below the liquid refrigerant 92.

A reference example using the heat of the exhaust gas of the gas engine will be described below with reference to FIG.

  FIG. 4 shows an embodiment using the heat of the exhaust gas. Specifically, the exhaust gas is used for heating the gas-liquid separator 11. When the solenoid valve 44 is opened and closed by the control unit 70 and is opened, a part of the exhaust gas at the outlet of the exhaust gas heat exchanger 23 is separated from the gas-liquid separator via the exhaust gas pipe 43. 11 is led to an exhaust gas heat exchanger 81 provided in the inside. Similarly, when the open / close state of the solenoid valve 42 is controlled by the control unit 70 and is opened, a part of the exhaust gas at the inlet of the exhaust gas heat exchanger 23 is passed through the exhaust gas pipe 41. It guides to the exhaust gas heat exchanger 81 provided in the gas-liquid separator 11. Since the exhaust gas discharged from the electromagnetic valve 42 has a higher temperature than the exhaust gas discharged from the electromagnetic valve 44, the exhaust gas discharged from the electromagnetic valve 42 is referred to as a high temperature exhaust gas. The exhaust gas discharged from is called medium temperature exhaust gas. A circuit through which high-temperature exhaust gas flows is referred to as a high-temperature exhaust gas circuit, and a circuit through which intermediate-temperature exhaust gas flows is referred to as a medium-temperature exhaust gas circuit. In short, the difference from FIG. 1 is that not the cooling water pipes 55 and 56 but the exhaust gas pipes 45 and 46 of the engine are connected to the gas-liquid separator 11 to heat the gas-liquid separator 11. In addition, what performs the same effect | action as FIG. 1 attaches | subjects the same code | symbol as the code | symbol of FIG. 1, and abbreviate | omits the description.

FIG. 5 is a diagram showing a reference example of the gas-liquid separator 11. As a method of attaching the cooling water heat exchanger to the gas-liquid separator 11, a cooling water heat exchanger 82 is wound around the gas-liquid separator 11. May be. In this case as well, like the cooling water heat exchanger 81 (see FIG. 2), it is desirable that the cooling water heat exchanger 82 be installed so as to be positioned below the gas-liquid separator 11 in which the liquid refrigerant is stored. .

In the above embodiment, the intermediate temperature cooling water and the high temperature cooling water are taken out from the outlet of the cooling water pump 21 and the outlet of the hot water three-way valve 37 in FIG. 1, but may be taken out from other places. In short, it is only necessary to obtain two different types of cooling water capable of heating the liquid refrigerant stored in the gas-liquid separator 11.

  Moreover, in the above embodiment, the cooling water heat exchanger 81 inside the gas-liquid separator 11 has a spirally wound structure, but may be, for example, a linear shape or a corrugated shape.

  Moreover, in the above embodiment, the refrigerating machine oil in the compressor 3 can be smoothly returned by heating the gas-liquid separator 11 within the predetermined range determined in advance.

  Moreover, in the above embodiment, the refrigerating machine oil separated by the gas-liquid separator 11 can be returned to the compressor 3 quickly and efficiently by the oil return hole. For this reason, the adhesion of the refrigeration oil inside the outdoor heat exchanger 6 pipe and the indoor heat exchangers 141 and 151 pipes is reduced, and improvement in the thermal conductivity of the outdoor heat exchanger 6 and the indoor heat exchangers 141 and 151 can be expected.

  In the above embodiment, the air conditioner has one outdoor unit 100 and two indoor units 140 and 150. However, the air conditioner has a plurality of outdoor units, One or three or more 150 may be provided.

  In the above embodiment, the case where the present invention is applied during cooling operation of a gas engine heat pump type air conditioner has been described as an example, but the present invention can also be applied during heating operation. During the heating operation, the heat energy of the cooling water and the exhaust gas enhances the heating capacity, so that the operating capacity increases in addition to the improvement of the returnability of the refrigeration oil to the compressor 3. Further, the present invention can be applied not only to a gas engine heat pump type air conditioner but also to other refrigeration apparatuses such as a showcase.

1 is a configuration diagram of a gas engine heat pump refrigeration apparatus according to an embodiment of the present invention. It is a figure which shows the detailed structure of the gas-liquid separator shown in FIG. It is an example of the process performed in the gas engine heat pump type air conditioner of FIG. It is a block diagram which shows other embodiment of this invention. It is other 1st Embodiment of the gas-liquid separator shown in FIG. It is other 2nd Embodiment of the gas-liquid separator shown in FIG. It is other 3rd Embodiment of the gas-liquid separator shown in FIG.

DESCRIPTION OF SYMBOLS 1 ... Gas engine 3 ... Compressor 4 ... Oil separator 6 ... Outdoor heat exchanger 11 ... Gas-liquid separator 60 ... Compressor discharge side piping 80 ... Oil return hole (oil return means)
81 ... Cooling water heat exchanger 100 ... Outdoor unit 140, 150 ... Indoor unit 141, 151 ... Indoor heat exchanger

Claims (1)

A compressor, condenser, decompressor, evaporator, and gas-liquid separator driven by a gas engine are connected in sequence to form a refrigeration cycle. The gas-liquid separator stores liquid refrigerant in which refrigeration oil is dissolved. In the refrigerating apparatus, the refrigerating machine oil accumulated in the lower part of the gas-liquid separator is located in the gas-liquid separator and is returned to the compressor through an oil hole of a suction pipe connected to the compressor. A heating heat exchanger is provided for heating the liquid refrigerant in which the refrigerator oil in the chamber is dissolved to separate the liquid refrigerant and the refrigerator oil, and the cooling water from the gas engine is directly guided to the heat exchanger. A high-temperature cooling water or a valve that switches the high-temperature cooling water so that either the high-temperature cooling water or a medium-temperature cooling water that is lower than the high-temperature cooling water flows through the radiator is provided, and the condenser temperature is equal to or higher than a predetermined temperature or Compressor When the discharge temperature is equal to or higher than a predetermined temperature, the liquid refrigerant in the gas-liquid separator is heated with the intermediate temperature cooling water, and even in this heating, the condenser temperature is lower than the predetermined temperature or the compressor discharge temperature is lower than the predetermined temperature. If not, the heating is switched to the heating of the liquid refrigerant in the gas-liquid separator by the high-temperature cooling water, the liquid refrigerant in the gas-liquid separator is heated, and the refrigerating machine oil separated by this heating is oiled A refrigeration apparatus characterized in that it is returned from the return hole to the compressor .

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