JP7230604B2 - Heat pump steam generator - Google Patents

Description

The present invention relates to a heat pump steam generator that generates steam by circulating water through a condenser of a refrigerant cycle.

2. Description of the Related Art Conventionally, a heat-pump type steam generator that generates steam by recovering exhaust heat from thermal waste water such as factory waste water and sewage waste water has been used.

For example, Patent Literature 1 discloses a heat pump device. In this heat pump device, the refrigerant compressed by the compressor is supplied to the condenser, and the water to be heated is supplied by the pump. The water to be heated that has been heated by exchanging heat with the refrigerant in the condenser becomes a two-phase flow of steam (vapor phase) and hot water (liquid phase) and enters the heated steam separator. The two-phase flow is separated into a vapor phase and a liquid phase in a vapor separator, and only vapor is taken out and supplied to an external vapor utilization facility.

When a heat pump type steam generator requires a larger amount of steam, it is conceivable to provide two condensers in parallel according to the required amount of steam as in Patent Document 2. In the circuit of Patent Document 2, the refrigerants discharged from the two condensers are expanded by one expansion valve after joining one system.

Japanese Patent Application Laid-Open No. 2013-2708 JP 2007-170683 A

By the way, in a circuit where multiple condensers are installed in parallel, uneven refrigerant flow rates and water supply amounts may occur due to the effects of pipe resistance, etc. In such cases, the heat in the condenser There is a concern that the replacement amount will deviate from the optimum design point, and the operating efficiency of the apparatus will decrease. In particular, in a circuit where the refrigerant from multiple condensers joins one system and then expands with one expansion valve, the amount of refrigerant for each condenser cannot be adjusted, making it difficult to correct unevenness. There is a concern that the operating efficiency will decrease.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat pump steam generating apparatus with high operational efficiency when a plurality of condensers are provided.

In order to solve the above-described problems and achieve the object, a heat pump steam generator according to the present invention includes a control unit, an evaporator that evaporates a refrigerant using an external heat source, and a compressor that compresses the refrigerant evaporated in the evaporator. A compressor, a branch path that branches the refrigerant compressed by the compressor, a plurality of condensers that exchange the heat of the refrigerant branched in the branch path with the water to be heated, and the plurality of condensers. a heat pump comprising: a plurality of expansion valves with variable opening degrees for expanding the refrigerant discharged from the corresponding condensers; a section, the condenser, a two-phase flow path through which the two-phase flow derived from the condenser flows, and water vapor for separating the two-phase flow supplied from the two-phase flow path into a gas phase and a liquid phase. a separator, a return path for introducing the liquid phase separated by the steam separator into the condenser, a water supply path for supplying heated water from the outside to the return path, and a steam generation unit including a steam delivery path for delivering a gas phase to the outside; and detection means for detecting a state quantity related to heat exchange amounts of the plurality of condensers, wherein the control unit includes the detection means The opening degrees of the plurality of expansion valves are individually controlled based on the state quantity obtained from the above.

The control unit identifies the condenser with the relatively large amount of heat exchange obtained from the state quantity detected by the detection means, and adjusts the opening degree of the expansion valve corresponding to the identified condenser. It may be relatively decreased.

The state quantity is the refrigerant temperature derived from the condenser, the detection means is temperature detection means for detecting the refrigerant temperature, and the control unit corresponds to the condenser having a relatively high refrigerant temperature. at least one of opening degree reduction control for reducing the opening degree of the expansion valve that has been opened, and opening degree increase control for increasing the opening degree of the expansion valve corresponding to the condenser having a relatively low refrigerant temperature. good too.

The state quantity is the flow rate of the heated water introduced into the condenser, the detection means is flow rate detection means for detecting the flow rate of the heated water on the inlet side of the condenser, and the control unit opening degree increase control for increasing the opening degree of the expansion valve corresponding to the condenser having a relatively large flow rate of the heated water, or opening the expansion valve corresponding to the condenser having a relatively small flow rate of the heated water; At least one of opening degree reduction control for reducing the degree of opening may be performed.

The state quantity is the heat flow rate of the water to be heated introduced into the condenser, the detection means is heat flow rate detection means for detecting the heat flow rate on the inlet side of the condenser, and the control unit comprises the Opening degree increase control for increasing the opening degree of the expansion valve corresponding to the condenser having a relatively large heat flow rate, or decreasing the opening degree of the expansion valve corresponding to the condenser having a relatively small heat flow rate. At least one of the opening degree reduction control that causes the

In the heat pump steam generator according to the present invention, the plurality of expansion valves are adjusted in such a direction that the heat exchange amounts of the corresponding condensers are balanced, thereby increasing the operating efficiency.

FIG. 1 is a circuit diagram of a heat pump steam generator according to a first embodiment of the present invention. FIG. 2 is a flow chart of a control procedure in the heat pump steam generator according to the first embodiment of the present invention. FIG. 3 is a circuit diagram of a heat pump steam generator according to a second embodiment of the present invention. FIG. 4 is a flow chart of the control procedure in the heat pump steam generator according to the second embodiment of the present invention.

EMBODIMENT OF THE INVENTION Below, embodiment of the heat pump type steam generator concerning this invention is described in detail based on drawing. In addition, this invention is not limited by this embodiment.

(First embodiment)
FIG. 1 is a circuit diagram of a heat pump steam generator 10A according to the first embodiment of the present invention. The heat pump vapor generation device 10A includes an evaporator 12 that evaporates the refrigerant by an external heat source, a compressor 14 that compresses the evaporated refrigerant, and a branch point (branch path) P1 for the compressed high-temperature and high-pressure refrigerant. and two steam generating system units 16a and 16b for exchanging heat with the water to be heated, respectively, and a control unit 18 for overall overall control. The refrigerant that has undergone heat exchange in the vapor generation system portions 16a and 16b joins at a junction (junction path) P2 and is returned to the evaporator 12, forming a refrigerant circulation circuit. A thermometer 20 for detecting the temperature of the refrigerant and a pressure gauge 22 for detecting the pressure are provided in the outlet path of the compressor 14 , and the respective detection signals are supplied to the control section 18 . The rotation speed of the compressor 14 is controlled by the controller 18 .

The heat pump steam generator 10A utilizes the waste hot water supplied through the water discharge path 24 as an external heat source in the evaporator 12 to evaporate the refrigerant, and the heated water supplied through the water supply path 26 is supplied to the steam generation system section 16a, At 16b, the high-temperature refrigerant is used to evaporate, and the generated steam is delivered from the steam delivery path 28 to the external steam utilization equipment side.

The vapor generation system unit 16a includes a condenser 30a to which the refrigerant branched from the branch point P1 is supplied, an expansion valve 32a with a variable opening degree that expands the refrigerant whose temperature has decreased by exchanging heat with the condenser 30a, A water supply pump 34a that feeds and supplies the heated water branched at the branch point P3 of the water supply path 26 to the condenser 30a, and separates the two-phase flow heat-exchanged with the refrigerant in the condenser 30a into a gas phase and a liquid phase. It has a steam separator 36a and a pressure regulating valve 38a for adjusting the pressure of the steam emitted from the gas outlet 36aa of the steam separator 36a.

The two-phase flow derived from the condenser 30a flows through the two-phase flow path 31a and is supplied to the water vapor separator 36a. The liquid phase separated by the water vapor separator 36a flows from the liquid phase outlet 36ab through the return path 33a and is returned to the condenser 30a. Water to be heated from the outside is discharged from the water supply pump P34a, passes through the water supply path 35a, joins and is supplied to the return path 33a at the confluence point P5. The steam whose pressure has been adjusted by the pressure regulating valve 38a is supplied to the confluence point P4. A thermometer (temperature detection means) 40a for detecting the refrigerant temperature is provided between the condenser 30a and the expansion valve 32a. A temperature signal from the thermometer 40 a is supplied to the controller 18 . The discharge amount of the water supply pump 34 a can be adjusted by the controller 18 . The degree of opening of the expansion valve 32a can be adjusted by the controller 18 . In FIG. 1, among the signal lines connected to the control unit 18, only the connection lines to the expansion valves 32a and 32b are represented by dashed lines. Fig. 3 is also the same.

The steam generation system section 16b is the same circuit as the steam generation system section 16a, and is configured in parallel with the steam generation system section 16a. A condenser 30a, a two-phase flow path 31a, an expansion valve 32a, a return path 33a, a water supply pump 34a, a water supply path 35a, a water vapor separator 36a, a pressure control valve 38a, a gas outlet 36aa, a liquid outlet 36ab, and a The thermometer 40a is connected to the condenser 30b, the two-phase flow path 31b, the expansion valve 32b, the return path 33b, the water supply pump 34b, the water supply path 35b, the water vapor separator 36b, the pressure control valve 38b, and the gas outlet 36ba in the steam generation system section 16b. , a liquid outlet 36bb and a thermometer (temperature detecting means) 40b, and have similar functions. The steam generation system section 16b evaporates the water branched at the branch point P3 in the condenser 30b, and supplies it to the junction P4 via the steam separator 36b and the pressure control valve 38b. The steam generated in the steam generation system section 16a and the steam generation system section 16b joins at the confluence point P4 and is delivered from the steam delivery path .

The water vapor separators 36a and 36b are provided with water level gauges (not shown), which detect the water level inside and supply it to the controller 18. FIG. The discharge amount of the water supply pump 34a is adjusted by the controller 18 so that the water level of the water vapor separator 36a is kept constant. The discharge amount of the water supply pump 34b is adjusted by the controller 18 so that the water level of the water vapor separator 36b is constant.

The heat pump steam generator 10A includes an evaporator 12, a compressor 14, a branch point P1 that is a branch path, condensers 30a and 30b, expansion valves 32a and 32b, and a confluence point P2 that is a confluence path. A heat pump section is formed including: Further, in the heat pump steam generator 10A, the condensers 30a and 30b, the two-phase flow paths 31a and 31b, the steam separators 36a and 36b, the return paths 33a and 33b, the water supply paths 35a and 35b, and the steam delivery A steam generator is formed including a path 28 . Note that this steam generation unit is different from the steam generation system units 16a and 16b. The steam generating system units 16a and 16b are vertically divided into a part of the heat pump part and a part of the steam generating part so that the invention can be easily understood.

FIG. 2 is a flow chart of a control procedure by the control unit 18 in the heat pump steam generator 10A. The procedure shown in FIG. 2 is repeatedly executed every minute time.

In step S1 of FIG. 2, the refrigerant temperature (state quantity) Ta between the condenser 30a and the expansion valve 32a is obtained from the thermometer 40a, and the refrigerant temperature between the condenser 30b and the expansion valve 32b is obtained from the thermometer 40b. Obtain the temperature (state quantity) Tb.

In step S2, an average temperature TA of the obtained two refrigerant temperatures Ta and Tb is obtained. That is, TA=(Ta+Tb)/2. When N systems (N>2) of steam generators are provided, the average temperature TA of the steam can be obtained by dividing the total refrigerant temperature of each system by N.

In step S3, the opening degree Vao of the expansion valve 32a and the opening degree Vbo of the expansion valve 32b are obtained by the following equations. It is assumed that the larger the openings Vao and Vbo are, the larger the openings are.
Vao = Vo + (TA - Ta) K
Vbo=Vo+(TA-Tb)K

Here, the constant Vo is the calculated opening degree of the expansion valve 32a and the expansion valve 32b for achieving the design degree of superheat suitable for the refrigerant circuit in the heat pump steam generator 10A. Since the expansion valves 32a and 32b are the same, and the condensers 30a and 30b are also the same, the constant Vo has a common value. In the case of specifications, or in the case of different specifications for the condenser 30a and the condenser 30b, the constant Vo may also be a separate value.

A constant K is a conversion constant of a change in opening degree of the expansion valves 32a and 32b per unit temperature with respect to the temperature difference ΔT1 between the refrigerant temperature Ta and the refrigerant temperature Tb. Constant K is, for example, an experimental value. The constant Vo and the constant K are pre-stored in the storage section of the control section 18 . The constant Vo and the constant K may be variables that change depending on the state of the heat pump steam generator 10A (for example, the state immediately after startup and the state during steady operation).

In step S4, the opening degree of the expansion valve 32a is adjusted to the opening degree Vao, and the opening degree of the expansion valve 32b is adjusted to the opening degree Vbo.

That is, the control unit 18 performs opening reduction control to reduce the opening of the expansion valve 32a or 32b of the system with the relatively higher one of the refrigerant temperature Ta and the refrigerant temperature Tb, and the expansion control of the system with the relatively lower one. and an opening degree increase control for increasing the opening degree of the valve 32a or 32b. Depending on conditions, either one of the opening degree increase control and the opening degree decrease control may be performed.

Further, a suitable temperature Td between the condensers 30a, 30b and the expansion valves 32a, 32b for achieving a suitable degree of superheat in the refrigerant circuit in the heat pump steam generator 10A is stored, and the suitable temperature Td is stored. and the average temperature TA, the above two equations, that is, Vao=Vo+(TA-Ta)K and Vbo=Vo+(TA-Tb)K, may be corrected based on the temperature difference ΔT2.

In the heat pump type steam generator 10A configured as described above, the steam generating system section 16a and the steam generating system section 16b are provided in parallel, and the flow rate of the refrigerant flowing through the condenser 30a and the condenser 30b is reduced by the line resistance. However, the expansion valves 32a and 32b provided in the steam generation system section 16a and the steam generation system section 16b, respectively, allow individual adjustment.

Further, based on the refrigerant temperatures Ta and Tb, the control unit 18 adjusts the expansion valves 32a and 32b in the direction in which the amount of heat exchange between the condenser 30a of the steam generation system 16a and the condenser 30b of the steam generation system 16b is balanced. are individually controlled. This brings the degree of superheat close to a suitable degree on the refrigerant circuit and increases the operating efficiency.

Since the heat pump steam generating device 10A is provided with two steam generating system units 16a and 16b, it is possible to generate more steam than when there is only one steam generating system unit. Furthermore, even if the required amount of steam is large, by providing multiple steam generation system units, the size of each steam separator, which is a pressure vessel, is excessively large because it is installed separately for each steam generation system unit. never become.

Although the above heat pump steam generator 10A is provided with two steam generation system units 16a and 16b, three or more such steam generation system units may be provided.

(Second embodiment)
Next, a heat pump steam generator 10B according to a second embodiment of the present invention will be described. In the heat pump steam generator 10B, the same components as those of the heat pump steam generator 10A are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 3 is a circuit diagram of a heat pump steam generator 10B according to a second embodiment of the invention. The heat pump steam generating device 10B is obtained by replacing the steam generating system portions 16a and 16b in the heat pump steam generating device 10A with steam generating system portions 42a and 42b.

In addition to the constituent elements of the steam generation system section 16a, the steam generation system section 42a includes a flow meter (flow rate detection means) 44a for detecting the discharge amount La of the water supply pump 34a and a flow rate for detecting the discharge steam amount of the pressure regulating valve 38a. meter (flow rate detection means) 46a. In addition to the constituent elements of the steam generation system section 16b, the steam generation system section 42b includes a flow meter (flow rate detection means) 44b for detecting the discharge amount Lb of the water supply pump 34b and a flow rate for detecting the discharge steam amount of the pressure regulating valve 38b. meter (flow rate detection means) 46b. In FIG. 3, the flowmeters 44a, 44b, 46a, and 46b are provided at the T-shaped branch of the pipeline to be measured, but they may be provided in series with the target pipeline.

The flowmeters 44a and 44b are provided upstream of the confluence P5. The flowmeters 46a and 46b are provided upstream of the confluence P4. The heat pump steam generator 10B further includes a thermometer 48 that detects the water temperature of the water supply path 26. As shown in FIG. The thermometer 48 is provided upstream of the branch point P3. Detection signals from the flowmeters 44a, 44b, the flowmeters 46a, 46b, and the thermometer 48 are supplied to the controller 18. FIG. The steam generation system units 42a and 42b of the heat pump steam generator 10B do not necessarily require the thermometers 40a and 40b of the heat pump steam generator 10A, but may be provided depending on the specifications.

FIG. 4 is a flow chart of a control procedure by the control unit 18 in the heat pump steam generator 10B. The procedure shown in FIG. 4 is repeatedly executed every minute time.

In step S11 of FIG. 4, the discharge amount (state quantity) La of the water supply pump 34a is obtained from the flow meter 44a, and the discharge quantity (state quantity) Lb of the water supply pump 34b is obtained from the flow meter 44b.

In step S12, from the obtained two discharge amounts La and Lb, the water supply amounts (heated water flow amounts) Vsa and Vsb per fixed time in each system are obtained by the following equations.
Vsa = ∫La
Vsb = ∫Lb

The integral symbol ∫ here indicates a definite integral per fixed time. That is, the water supply amounts Vsa and Vsb are constant multiples of the moving averages of the discharge amounts La and Lb, and are substantially average values.

In step S13, the larger one of the water supply amount Vsa and the water supply amount Vsb is set as the reference water supply amount VB. That is, VB=Max(Vsa, Vsb).

In step S14, the opening degree Vao of the expansion valve 32a and the opening degree Vbo of the expansion valve 32b are obtained by the following equations. Further, as described above, the constant Vo is the calculated opening degree, and the constant K is the conversion constant.
Vao=Vo-(VB-Vsa)K
Vbo=Vo-(VB-Vsb)K

In step S15, the opening degree of the expansion valve 32a is adjusted to the opening degree Vao, and the opening degree of the expansion valve 32b is adjusted to the opening degree Vbo. In addition, since the parenthesis of either one of the two expressions in step S14 is 0, the obtained value is equal to Vo. Therefore, here, one of the two condensers 30a and 30b with a relatively large amount of heat exchange is specified, the opening degree of the expansion valve 32a or the expansion valve 32b corresponding to the specified one is decreased, and the other For , the opening is fixed. That is, the degree of opening of one of the expansion valves 32a and 32b is relatively decreased with respect to the other.

In such a heat pump steam generator 10B, the control unit 18 performs opening degree increase control to increase the degree of opening of the expansion valve 32a or 32b of the system having a relatively large water supply amount Vsa or water supply amount Vsb. The expansion valve 32a or 32b of the smaller system has a constant Vo. In the heat pump steam generating device 10B, the control unit 18 performs opening degree increase control to increase the opening degree of the expansion valve 32a or 32b of the system with the relatively large water supply amount Vsa or the water supply amount Vsb or the opening degree of the system with the relatively small water supply amount Vsa or Vsb. At least one of opening reduction control for reducing the opening of the expansion valve 32a or 32b may be performed.

That is, the control unit 18 controls the expansion valves 32a and 32b in the direction in which the amount of heat exchange between the condenser 30a of the steam generation system section 42a and the condenser 30b of the steam generation system section 42b is balanced based on the water supply amounts Vsa and Vsb. are individually controlled. This brings the degree of superheat close to a suitable degree on the refrigerant circuit and increases the operating efficiency.

In addition, a suitable discharge amount Ld of the water supply pumps 34a and 34b when realizing a design degree of superheat suitable for the refrigerant circuit in the heat pump steam generator 10B is stored, and the suitable discharge amount Ld and the average discharge amount are stored. Based on the temperature difference ΔL from ((Vsa+Vsb)/2), even if the above two equations, that is, Vao=Vo-(VB-Vsa)K and Vbo=Vo-(VB-Vsb)K are corrected, good.

In the process shown in FIG. 4, in step S11, the discharge amounts La and Lb of the water supply pumps 34a and 34b are obtained from the flowmeters 44a and 44b, and the opening degrees Vao and Vbo are obtained based on these signal values. The processing may be performed based on the discharge amount (heated water flow rate) of the pressure regulating valves 38a and 38b by 46a and 46b. In a certain time span, the discharge amount of the input side water supply pump 34a and the discharge amount of the output side pressure regulating valve 38a are the same. This is because the volume is the same as the volume of water flowing through the steam generation system portions 42a and 42b.

Further, the means for detecting the discharge amounts La and Lb is not limited to the flowmeters 44a and 44b. good. Furthermore, since the discharge amounts of the water supply pumps 34a and 34b are controlled so that the water levels of the water vapor separators 36a and 36b are constant, respectively, the discharge of the water supply pumps 34a and 34b is controlled according to the water levels of the water vapor separators 36a and 36b. When the amount is determined, the value of the water gauge provided in the steam separators 36a and 36b may be used as the means for detecting the flow rate of the water to be heated.

Further, instead of the amount of water flowing through the steam generation system sections 42a and 42b, the opening degrees Vao and Vbo may be obtained based on the heat flow rates Qa and Qb of the water flowing through the steam generation system sections 42a and 42b. In this case, the discharge amounts La and Lb are replaced by the heat flow amounts Qa and Qb in the process shown in FIG. 4, and the constant K is adjusted appropriately. The heat flows Qa and Qb can be obtained from the discharge amounts La and Lb and the water temperature of the water supply path 26 (that is, the detected value of the thermometer 48).

The heat pump steam generator 10B includes two steam generation system units 42a and 42b, but the number of steam generation system units may be three or more. In this case, in step S13, the maximum flow rate may be selected from 3 or more and set as VB.

As described above, the heat pump steam generators 10A and 10B according to the present embodiment are provided with the two steam generation system sections 16a and 16b or 42a and 42b, and the heat exchange amounts of the condensers 30a and 30b are respectively is detected. Here, the state quantity related to the amount of heat exchange is a physical quantity that varies depending on the amount of heat exchange between the refrigerant and the water to be heated in the condensers 30a and 30b. is a physical quantity that can be estimated.

It goes without saying that the present invention is not limited to the above-described embodiments, and can be freely modified without departing from the gist of the present invention.

10A, 10B heat pump steam generator 12 evaporator 14 compressors 16a, 16b, 42a, 42b steam generation system unit 18 control unit 24 drainage path 26 water supply path 28 steam delivery paths 30a, 30b condensers 32a, 32b expansion valve 34a, 34b Water supply pumps 36a, 36b Steam separators 38a, 38b Pressure regulating valves 40a, 40b Thermometers 44a, 44b, 46a, 46b Flowmeters La, Lb Discharge amounts Qa, Qb Heat flows Ta, Tb Refrigerant temperatures Vao, Vbo Opening degree

Claims (4)

a control unit;
An evaporator that evaporates the refrigerant by an external heat source, a compressor that compresses the refrigerant evaporated by the evaporator, a branch path that branches the refrigerant compressed by the compressor, and a refrigerant branched by the branch path, respectively. a plurality of condensers for exchanging heat with water to be heated; a plurality of expansion valves with variable opening degrees for expanding refrigerant drawn from the condensers corresponding to the plurality of condensers; and the plurality of expansion valves. a heat pump unit including a confluence path for merging the refrigerant expanded by the valve and leading it to the evaporator;
the condenser, a two-phase flow path through which the two-phase flow derived from the condenser flows, and a steam separator that separates the two-phase flow supplied from the two-phase flow path into a gas phase and a liquid phase. a return path for introducing the liquid phase separated by the steam separator into the condenser; a water supply path for supplying heated water from the outside to the return path; and a gas phase separated by the steam separator. a steam generation unit including a steam delivery path for delivering to the outside;
detection means for detecting a state quantity related to heat exchange amounts of the plurality of condensers;
with
The control unit identifies the condenser with the relatively large amount of heat exchange obtained from the state quantity based on the state quantity obtained from the detection means, and the expansion corresponding to the identified condenser 1. A heat pump steam generator , wherein the opening degrees of the plurality of expansion valves are individually controlled so as to relatively decrease the opening degrees of the valves . The state quantity is the refrigerant temperature derived from the condenser,
The detection means is temperature detection means for detecting the refrigerant temperature,
The control unit performs opening degree reduction control for reducing the opening degree of the expansion valve corresponding to the condenser having a relatively high refrigerant temperature, or the expansion valve corresponding to the condenser having a relatively low refrigerant temperature. 2. The heat pump steam generator according to claim 1 , wherein at least one of opening degree increasing control for increasing the opening degree of the valve is performed. The state quantity is the heated water flow rate introduced into the condenser,
The detection means is flow rate detection means for detecting the flow rate of the heated water on the inlet side of the condenser,
The control unit performs opening degree increase control to increase the opening degree of the expansion valve corresponding to the condenser having a relatively large flow rate of the heated water, or to the condenser having a relatively small flow rate of the heated water. 2. The heat pump steam generator according to claim 1, wherein at least one of opening degree reduction control for reducing the opening degree of the corresponding expansion valve is performed. The state quantity is the heat flow rate of the heated water introduced into the condenser,
The detection means is heat flow detection means for detecting the heat flow on the inlet side of the condenser,
The control unit performs opening degree increase control for increasing the opening degree of the expansion valve corresponding to the condenser having a relatively large heat flow rate, or the expansion valve corresponding to the condenser having a relatively small heat flow rate. 2. The heat pump steam generator according to claim 1, wherein at least one of opening reduction control for reducing the opening of the valve is performed.

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