TWI657199B - Pumping system and controlling method for the same - Google Patents

Abstract

A pumping system includes a centrifugal pump, a suction pressure gauge, an outlet valve, and a controller. The centrifugal pump is used to extract the liquid of a liquid storage tank. The suction pressure gauge is connected to one of the suction ports of the centrifugal pump for measuring the suction pressure value of the suction port. The outlet valve is connected to one of the outlets of the centrifugal pump for controlling the amount of water discharged from the centrifugal pump. The controller is electrically connected to the suction port pressure gauge and is configured to control the outlet valve. The controller is configured to adjust the opening degree of the outlet valve according to the relationship between the suction port pressure value and a preset pressure value, and further change the centrifugal pump. Load curve.

Description

Pumping system and its control method

The invention relates to a pumping system and a control method, in particular to a pumping system with a centrifugal pump and a control method thereof.

Ballast water is a seawater that is used by modern ships (ships, passenger ships) to increase the weight of the hull to maintain the stability of the ship's weight when it is empty. Therefore, the ship will be equipped with a pump to draw seawater when the hull needs to gain weight, and to discharge seawater when the hull needs space for loading. Traditionally, the common pump on the ship has a Centrifugal pump, a steam drive reciprocating pump, a gear pump, a spiral pump, and the like. Due to the low cost and large flow rate of centrifugal pumps, centrifugal pumps are often used in large ships to reduce the time for extraction operations.

However, in the process of pumping the centrifugal pump, the ballast water is continuously drawn, which will gradually lower the liquid level, which will increase the saturated vapor pressure of the liquid and increase the probability of cavitation. Therefore, the speed and pressure of the liquid change with time, usually at the lowest pressure of the suction port of the centrifugal pump. The lower the pressure, the easier it is to absorb the liquid, but when the pressure is less than or equal to the saturated vapor pressure of the liquid at the delivery temperature. At the time, the liquid will partially vaporize, forming a large amount of vapor bubbles. These bubbles will enter the centrifugal pump along with the pipeline. As the air bubbles enter the centrifugal pump, they will rupture due to the increase of pressure and will condense rapidly. The partial vacuum generated by the disappearance of the air bubbles will cause the surrounding liquid to surge to the original at a very high speed. At the bubble, a considerable impact force is generated, causing the metal surface in the centrifugal pump to be corroded and fatigued and damaged.

When cavitation occurs, the centrifugal pump will generate noise and vibration, and the material damage will accelerate and shorten the service life, and the flow rate and head of the centrifugal pump will decrease. In severe cases, the flow failure will not work properly.

In order to avoid cavitation, the crew needs to monitor the centrifugal pump at any time during the pumping process. However, manpower monitoring is inevitably causing omissions, which makes the centrifugal pump often unable to continue pumping due to cavitation, which not only causes damage to the centrifugal pump, but also delays the drainage operation. Moreover, when the centrifugal pump stops running due to cavitation, the ballast water still has a certain amount of water at a liquid level. At this time, the crew is required to close the centrifugal pump and then change to another type of pump, such as a gear pump or a screw pump. Continue to pump the remaining ballast water. However, the equipment cost of the gear pump and the screw pump is relatively high, and the flow rate is far less than that of the centrifugal pump, resulting in a drastic decline in the progress of pumping.

It can be seen from the foregoing that the current operation of discharging ballast water on a ship is an operation that is very labor intensive, equipment and time cost.

The reason is that the creators, in view of this, adhere to the practical experience of relevant industries for many years, research and improve the existing defects, and propose a pumping system and its control method, in order to save manpower, equipment and time costs, and achieve better and practical. The purpose of value.

The main object of the present invention is to provide a pumping system and a control method thereof, and more particularly to a pumping system of a centrifugal pump and a control method thereof.

The invention provides a pumping system which mainly comprises a centrifugal pump, a suction pressure gauge, an outlet valve and a controller. The centrifugal pump is used to extract the liquid of a liquid storage tank. The suction pressure gauge is connected to one of the suction ports of the centrifugal pump for measuring the suction pressure value of the suction port. The outlet valve is connected to one of the outlets of the centrifugal pump for controlling the amount of water discharged from the centrifugal pump. The controller is electrically connected to the suction pressure gauge and used to control the outlet valve. The controller is configured to adjust the opening degree of the outlet valve according to the relationship between the suction port pressure value and a preset pressure value, and further change the load curve of the centrifugal pump.

The present invention also provides a control method for a pumping system, comprising the steps of: measuring, by a controller, a suction port pressure to measure a suction port pressure value of a suction port of a centrifugal pump of the pumping system; and transmitting the controller through the controller And determining whether to adjust an opening degree of an outlet valve connected to one of the water outlets of the centrifugal pump according to the relationship between the suction port pressure value and a preset pressure value, so as to adjust the load curve of the centrifugal pump.

According to the pumping system and the control method thereof provided by the foregoing invention, the controller can adjust the opening degree of the outlet valve according to the relationship between the suction port pressure value of the centrifugal pump and the preset pressure value, thereby being capable of performing the extraction operation. The suction port pressure value is dynamically adjusted to change the load curve of the pumping system to allow the centrifugal pump to continue to operate without cavitation. Therefore, it is possible to avoid the conventional centrifugal pump which is prone to cavitation damage and the problem that needs to be changed by other pumps which are higher in cost and have a smaller flow rate to continue pumping. That is to say, the pumping system of the present invention and the control method thereof can simultaneously save labor, equipment and working time and the like.

The above description of the disclosure and the following embodiments are intended to illustrate and explain the spirit and principles of the invention, and to provide further explanation of the scope of the invention.

The detailed features and advantages of the present invention are described in detail in the embodiments of the present invention. The related objects and advantages of the present invention will be readily understood by those skilled in the art. The following examples are intended to describe the present invention in further detail, but are not intended to limit the scope of the invention.

For a more complete and clear disclosure of the technical content, the purpose of the invention and the effect thereof, the present invention will be described in detail below, and the drawings and drawings are also referred to. 1 is a schematic view of a pumping system 1 of the present invention, which mainly includes a centrifugal pump 10, an inlet valve 20, an outlet valve 30, an opening detector 40, and a suction pressure gauge. 50. An outlet pressure gauge 60 and a controller 70.

Centrifugal pump 10 has a water suction port 11 and a water outlet 12, and the water suction port 11 can be connected to a liquid (such as oil, ballast water, etc.) stored in a liquid storage tank 2 through a pipeline, but It is to be noted that the present invention is not limited to the number of the liquid storage tanks to which the pumping system 1 can be connected, and may actually be connected to a plurality of liquid storage tanks via pipelines according to requirements, so as to simultaneously pump a plurality of liquid storage tanks. operation.

The centrifugal pump 10 is internally provided with an impeller (not shown) for high-speed rotation to generate centrifugal force, and the liquid of the liquid storage tank 2 is sucked into the central portion of the impeller via the pipeline and the suction port 11, and the rotation of the impeller causes the liquid to flow. During the process, kinetic energy is obtained and the pressure rises and the speed increases. Finally, the high-speed liquid is thrown out from the outer edge of the impeller into the volute casing which gradually expands outward, and finally discharged through the water outlet 12 to achieve the purpose of conveying the liquid.

The inlet valve 20 is disposed at the suction port 11 of the centrifugal pump 10, and can be adjusted, for example, by a valve regulator that communicates with the suction port 11 via the inlet valve 20, and the inlet valve 20 can be used to control the flow of liquid through the suction port 11. It is to be noted, however, that the present invention is not limited to the type of the inlet valve 20, and any valve that can be adjusted to control the flow rate through the suction port 11 of the centrifugal pump 10 is within the scope of the present invention.

The outlet valve 30 is disposed at the water outlet 12 of the centrifugal pump 10, and can be adjusted, for example, by a valve regulator (not shown) to control the flow of liquid through the water outlet 12. It is to be noted, however, that the present invention is not limited to the type of the outlet valve 30, and any valve that can be adjusted to control the flow rate through the water outlet 12 of the centrifugal pump 10 is within the scope of the present invention.

The opening detector 40 is disposed at the outlet valve 30 and can be used to detect the opening of the outlet valve 30. It should be noted, however, that the present invention is not limited to the design of the opening detector 40, and any detector that can measure the opening of the outlet valve 30 is within the scope of the present invention.

The suction port pressure gauge 50 is connected to the suction port 11 of the centrifugal pump 10 for measuring the suction port pressure value at the suction port 11. It is to be noted, however, that the present invention is not limited to the design of the mouthpiece pressure gauge 50, and any pressure gauge that can measure the water suction port 11 of the centrifugal pump 10 is within the scope of the present invention.

An outlet pressure gauge 60 is coupled to the water outlet 12 of the centrifugal pump 10 for measuring the outlet pressure value at the water outlet 12. It is to be noted, however, that the present invention is not limited to the design of the outlet pressure gauge 60, and any pressure gauge that can measure the water outlet 12 of the centrifugal pump 10 is within the scope of the present invention.

The controller 70 is electrically connected to the opening detector 40, the suction pressure gauge 50 and the outlet pressure gauge 60, and is electrically connected to the valve regulator on the outlet valve 30. The controller 70 includes a microprocessor, a software program, etc., which can perform the deduction, control the valve regulator, and complete and the opening detector 40, the suction pressure gauge 50 and the outlet pressure gauge 60, and the pumping system 1 Related calculations, and can be used to control, confirm, and communicate these parameters.

The controller 70 can be used to adjust the opening degree of the outlet valve 30 according to the relationship between the suction port pressure value of the suction port 11 and the preset pressure value of the centrifugal pump 10 according to the suction port pressure gauge 50, thereby changing the centrifugal pump 10 The load curve prevents cavitation from occurring in the centrifugal pump 10.

In detail, as shown in FIG. 2, it is a performance graph of the pumping system 1. When the centrifugal pump 10 is installed in the pumping system 1, the intersection of the load curve of the pumping system 1 and the head curve of the centrifugal pump is the operating point of the centrifugal pump, as shown by point A in FIG. However, as the liquid in the reservoir 2 is gradually drawn to gradually decrease its water level, the suction height L of the centrifugal pump 10 is gradually increased, which causes the Net Positive Suction Head Available of the pumping system 1 (Net Positive Suction Head Available, NPSHa) gradually decreases if the NPSHa falls below the Net Positive Suction Head Required (HPSHr) of the centrifugal pump 10 (ie, the centrifugal pump 10 itself is designed to specify the minimum saturated steam head at the current delivery temperature) Cavitation is caused by the allowable value). That is, when the suction port pressure value of the suction port 11 of the centrifugal pump 10 drops to the NPSHr (defined as a predetermined threshold value) of the centrifugal pump 10, cavitation occurs.

Therefore, when the suction port pressure value of the suction port 11 measured by the mouthpiece pressure gauge 50 decreases, the controller 70 causes the valve adjuster to adjust the opening degree of the outlet valve 30, for example, to reduce the opening degree of the outlet valve 30, The outlet flow rate of the centrifugal pump 10 is decreased. As can be seen from Fig. 2, when the outlet flow rate decreases, the discharge pressure rises, so that the suction port pressure value rises again, and the operating point changes from the aforementioned point A to point B, so that the centrifugal pump 10 remains It can be maintained in stable operation without cavitation. However, it is reminded that in order to prevent the controller 70 from adjusting the opening degree of the outlet valve 30 when the suction port pressure value decreases, a preset pressure value is defined, and the preset pressure value is greater than the preset threshold value (ie, NPSHr). And about 1.25 times the preset threshold. For example, when the preset threshold value is about -0.5 kg/cm ² , the preset pressure value is set to about -0.6 kg/cm ² . Therefore, when the suction pressure value of the suction port 11 measured by the mouthpiece pressure gauge 50 reaches the preset pressure value, the controller 70 starts to cause the valve regulator to adjust the opening degree of the outlet valve 30.

Please refer to the table below for the actual measurement data made by the inventor for a centrifugal pump with a displacement of about 250 m ³ and with the outlet valve being a butterfly valve. As shown in Table 1, if the opening degree of the outlet valve 30 is not adjusted during the pumping process, the centrifugal pump 10 will pump the liquid in the liquid storage tank 2 to a liquid level of about 0.29 meters (about 29 cm) to generate gas. Stopping or idling due to eclipse. Compared with Table 2, the controller 70 of the present case adjusts the opening degree of the outlet valve 30 through the valve adjuster according to the decrease of the suction port pressure value, or the controller 70 adjusts the outlet valve 30 according to the change of the liquid level height L. The opening degree can increase the suction port pressure value to allow the centrifugal pump 10 to continue to be maintained at the operating point for continuous operation, whereby the liquid can be further pumped to a liquid level of only about 9 cm.

 Table 1 Outlet valve opening (%) Suction pressure (kg/cm2) Outlet pressure (kg/cm2) Discharge (m3) Level height (m) 100 -0.4 0.5 286 5.7 100 -0.6 0.5 268 1.2 100 -0.6 0.02 0 0.29

 Table 2 Opening degree of outlet valve (%) Suction pressure (kg/cm2) Outlet pressure (kg/cm2) Discharge (m3) Level height (m) 100 -0.3 0.5 288 5.26 100 -0.4 0.5 281 4.00 100 -0.5 0.48 274 2.49 50 -0.5 0.64 270 1.81 50 -0.6 0.64 261 1.01 30 -0.6 1.57 260 0.91 30 -0.6 1.55 259 0.39 15 -0.4 6.0 45 0.30 15 -0.6 0.02 0 0.09

It can be seen that, by the pumping system described above, the problem that the centrifugal pump often stops due to cavitation and causes equipment damage and prolonged drainage time can be avoided, and the manpower can be continuously monitored to see if the centrifugal pump generates cavitation. The unnecessary cost of the phenomenon and the problem of avoiding the extension of working hours caused by manual operations.

In addition, referring back to FIG. 1, the pumping system 1 of the present invention further includes a user interface 80 that can be used to connect to the controller 70 for the user to monitor the pumping system 1 at any time.

In addition, since the opening degree of the outlet valve 30 cannot be adjusted to be completely closed, this causes a problem of clogging of the drain. Therefore, in the present invention, the pumping system 1 further includes an alarm 90 electrically connected to the controller 70. When the opening degree detector 40 detects the opening degree of the outlet valve 30 to a lower limit of the opening degree, for example, when the outlet valve 30 is fully open, 10% to 15%, the controller 70 no longer causes the valve regulator to adjust the outlet. Valve 30. At this time, the controller 70 causes the alarm 90 to issue an alert signal, which may be sound or light, and may notify the user via the user interface 80. In another case, when the outlet pressure gauge 60 detects that the outlet pressure value of the water outlet 12 reaches an outlet pressure bottom limit (for example, approaches zero), the liquid in the liquid storage tank 2 is almost evacuated. At this time, the controller 70 causes the alarm 90 to issue an extraction completion signal, which may be sound or light, or may be notified to the user via the user interface 80. At this time, the user can stop the operation of the centrifugal pump 10 through the user interface 80 to cause the controller 70.

The above is an introduction to the pumping system 1. Next, please refer to FIG. 3, which is a schematic diagram of the control method of the pumping system of FIG. 1, whereby the above-described pumping system 1 can be more understood.

First, the pumping system 1 as described above is first supplied, and the centrifugal pump 10 is turned on to start drawing the liquid of the liquid storage tank 2. Under normal circumstances, when the extraction operation is started, the opening degree of the inlet valve and the outlet valve of the pumping system are adjusted to be fully open, that is, the opening degree of the inlet valve 20 and the outlet valve 30 of the pumping system 1 will start when the extraction operation is started. Tune into full open.

Next, in step S100, the suction port pressure gauge 50 measures the suction pressure value of the suction port 11 of the centrifugal pump 10 in the pumping system 1 through the controller 70.

Next, the transmission controller 70 determines whether to adjust the opening degree of the outlet valve 30 connected to the water outlet 12 of the centrifugal pump 10 according to the relationship between the suction port pressure value and the preset pressure value, so as to adjust the load curve of the centrifugal pump 10 in conjunction. In detail, after the step (S100) of measuring the suction port pressure value, the step S200 is performed, and the controller 70 determines whether the suction port pressure value is less than or equal to the preset pressure value. As described above, the preset pressure value is set. It is about 1.25 times the preset threshold value (ie, NPSHr of the centrifugal pump 10). Therefore, if the controller 70 determines that the suction port pressure value does not reach the preset pressure value, the representative suction port pressure value is still greater than the preset pressure value, that is, the suction port pressure value is not close to the NPSHr of the centrifugal pump 10 and is still acceptable. In this case, the suction port pressure value does not need to be adjusted, and the centrifugal pump 10 can still maintain normal operation, so the above-described step S100 is continued through the controller 70 to continuously measure the suction port pressure value.

However, as the pumping progresses, the drop of the liquid level height L gradually decreases the suction port pressure value. Therefore, if the controller 70 determines that the suction port pressure value is less than or equal to the preset pressure value, the representative suction port pressure value approaches the centrifugation. The degree of NPSHr of pump 10 needs to be increased.

In this case, step S300 is performed immediately, and the controller 70 determines whether the opening degree of the outlet valve 30 detected by the opening detector 40 connected to the outlet valve 30 is less than or equal to the opening limit (eg, The foregoing is 10%~15% when the outlet valve 30 is fully opened. This step is to ensure whether the outlet valve 30 still has a small space before the opening of the outlet valve 30 is adjusted to avoid the opening of the outlet valve 30. An accident that is too small and causes excessive resistance to drainage, causing damage or even bursting of the valve.

Therefore, if the controller 70 determines that the opening degree of the outlet valve 30 detected by the opening degree detector 40 has not reached the opening degree limit value, the opening degree of the outlet valve 30 has a space that can be reduced, and at this time, Further, in step S400, the valve adjuster is used to adjust the opening degree of the outlet valve 30 through the controller 70. The degree of the outlet valve 30 is adjusted each time according to actual needs, and the invention is not limited thereto.

On the other hand, if the controller 70 determines that the opening degree of the outlet valve 30 detected by the opening degree detector 40 has reached the opening limit, the controller 70 will not cause the valve regulator to reduce the outlet. The valve 30 will cause the alarm 90 to send a warning signal to notify the user. In this case, step S500 is next performed, and the controller 70 determines whether the outlet pressure value of the outlet valve 30 detected by the outlet pressure gauge 60 connected to the outlet valve 30 is less than or equal to the outlet pressure lower limit value. If yes, the liquid representing the liquid storage tank 2 is almost evacuated, then step S600 is executed, the centrifugal pump 10 is stopped by the controller 70, or the alarm 90 is sent to notify the user that the extraction operation has been completed, and the control is executed. In this step, the device 70 stops the centrifugal pump 10 or causes the alarm 90 to issue an extraction completion signal, which can be adjusted according to user requirements, and can be performed simultaneously or only one of them can be performed. If not, it means that the centrifugal pump 10 is still draining and the liquid of the liquid storage tank 2 has not been pumped out. In this case, the centrifugal pump 10 can continue to operate to pump water, and the step S100 is again executed by the controller 70 to continue the amount. The suction port pressure value is measured until subsequently when the controller 70 determines that the outlet pressure value is less than or equal to the outlet pressure bottom limit.

It can be understood that, after the step S400 of reducing the outlet valve 30 is performed, the step S500 is further performed to determine whether the liquid of the liquid storage tank 2 is exhausted.

In short, after the start of the extraction operation, the pumping system 1 adjusts the opening degree of the outlet valve 30 by the relationship between the suction port pressure value of the centrifugal pump 10 and its preset pressure value, but the opening degree of the outlet valve 30. It will not be adjusted when the opening limit is reached. And by this adjustment, the load curve of the pumping system 1 is changed to maintain the operation of the centrifugal pump 10 until the outlet pressure value reaches the outlet pressure limit value, and the centrifugal pump 10 is not caused to be generated on the way. The eccentricity stops the extraction operation.

In summary, the pumping system and the control method thereof can adjust the opening degree of the outlet valve according to the relationship between the suction port pressure value of the centrifugal pump and the preset pressure value, thereby being dynamic when the extraction operation is performed. Adjusting the suction port pressure and then changing the load curve of the pumping system allows the centrifugal pump to continue to operate without cavitation. Therefore, it is possible to avoid the conventional centrifugal pump which is prone to cavitation damage and the problem that needs to be changed by other pumps with small flow and time-consuming pumping. That is to say, the pumping system of the present invention and the control method thereof can simultaneously save labor, equipment and working time and the like.

Although the present invention has been disclosed above in the foregoing embodiments, it is not intended to limit the invention. It is within the scope of the invention to be modified and modified without departing from the spirit and scope of the invention. Please refer to the attached patent application for the scope of protection defined by the present invention.

1‧‧‧ pumping system

2‧‧‧ liquid storage tank

10‧‧‧ centrifugal pump

11‧‧‧Water suction port

12‧‧‧Water outlet

20‧‧‧Imported valves

30‧‧‧Export valve

40‧‧‧Openness detector

50‧‧‧ suction pressure gauge

60‧‧‧Export pressure gauge

70‧‧‧ Controller

80‧‧‧User interface

90‧‧‧Alarm

L‧‧‧Stop height

S100~S600‧‧‧Steps

Figure 1 is a schematic illustration of the pumping system of the present invention. Figure 2 is a graph showing the performance of the pumping system of Figure 1. 3 is a schematic diagram of a control method of the pumping system of FIG. 1.

Claims (12)

A pumping system comprises: a centrifugal pump for extracting a liquid of a liquid storage tank; a suction pressure gauge connected to one of the suction ports of the centrifugal pump for measuring a suction port pressure value of the water suction port; An outlet valve connected to one of the outlets of the centrifugal pump for controlling the amount of water discharged from the centrifugal pump; and a controller electrically connected to the suction port pressure gauge and controlling the outlet valve, the controller for determining the pressure value according to the suction port The relationship of the outlet valve is adjusted in relation to a predetermined pressure value, which in turn changes the load curve of the centrifugal pump. The pumping system of claim 1, wherein the predetermined pressure value is 1.25 times the desired net positive suction head of the centrifugal pump. The pumping system of claim 1, wherein when the suction port pressure value is less than or equal to the preset pressure value, the controller causes a valve adjuster to reduce the opening degree of the outlet valve to change the centrifugal pump The suction curve increases the suction pressure value. The pumping system of claim 1, further comprising an outlet pressure gauge connected to the water outlet of the centrifugal pump for measuring an outlet pressure value of the water outlet. The pumping system of claim 1, further comprising a user interface electrically connected to the controller for the user to control the controller. The pumping system of claim 4, further comprising an alarm electrically connected to the controller; when the outlet pressure gauge detects that one of the outlet outlet pressure values is less than or equal to an outlet pressure lower limit value, The controller causes the alarm to issue an extraction completion signal or to stop the centrifugal pump. The pumping system of claim 1, further comprising an alarm and an opening detector, the alarm being electrically connected to the controller, wherein the opening detector is configured to detect the opening of the outlet valve; When the opening detector detects that the opening degree of the outlet valve is less than or equal to a lower limit, the controller causes the alarm to send a warning signal; wherein the opening limit is 10%~15% . A control method for a pumping system includes: measuring, by a controller, a suction port pressure to measure a suction port pressure value of a suction port of a centrifugal pump of the pumping system; and transmitting, according to the suction port pressure value, the controller A relationship between the preset pressure values determines whether the opening of an outlet valve connected to one of the outlets of the centrifugal pump is adjusted to adjust the load curve of the centrifugal pump. The control method of claim 8, wherein the preset pressure value is 1.25 times the required net positive suction head of the centrifugal pump. The control method of claim 8, wherein the controller determines whether to adjust the opening degree of the outlet valve connected to the water outlet of the centrifugal pump according to the relationship between the suction port pressure value and the preset pressure value. The step of adjusting the load curve of the centrifugal pump includes: determining, by the controller, whether the suction port pressure value is less than or equal to the preset pressure value; if yes, adjusting the opening degree of the outlet valve through the controller; if not, transmitting the control The step of measuring the suction pressure value is performed. The control method of claim 10, wherein the step of adjusting the opening degree of the outlet valve through the controller comprises: determining, by the controller, the one detected by the opening detector of the outlet valve Whether the opening degree of the outlet valve is less than or equal to a lower limit of the opening degree; if yes, determining, by the controller, whether an outlet pressure value of the outlet valve measured by an outlet pressure gauge connected to one of the outlet valves is less than or equal to an outlet pressure a bottom limit; if so, stopping the centrifugal pump through the controller or causing an alarm to send a warning signal; if not, performing a step of measuring the pressure of the suction port through the controller; if not, performing a adjustment through the controller The step of opening the outlet valve. The control method of claim 10, wherein the step of reducing the opening degree of the outlet valve by the controller comprises: determining, by the controller, the outlet connected to an outlet pressure gauge of the outlet valve Whether the outlet pressure value of the valve is less than or equal to an outlet pressure bottom limit; if so, stopping the centrifugal pump through the controller or causing an alarm to send an extraction completion signal; if not, performing the measurement of the suction pressure through the controller The step of the value.