JPS6151158B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> This invention enables two
The present invention relates to an improvement in a submerged pump capable of automatic alternating operation, which is constructed so that two pumps are operated alternately in liquid.

<Prior art> As shown in Fig. 1, the conventional pump of this type is
A mooring member 6.6' is provided at the lower end of the support member 5, which is fastened to the case 2 of the pump body 1 with the holder 3 so as to be substantially perpendicular to the liquid level 4.
and a buoy-type stop liquid level detector 7 moored thereto,
7' A mooring member 8 provided on the upper part of the support member;
Buoy type starting liquid level detectors 9, 9' moored to 8' and a mooring member 10 provided at the upper end of the support member
It consists of a master unit A and a slave unit B, each equipped with a buoy-type upper limit liquid level detector 11 moored to the base unit. In the figure, 12 is a discharge casing, 13 is an outlet pipe connected to it, 14 is a water inlet, 15 is a power cord, 1
6 is a liquid tank, and 17 is a floor surface of the liquid tank. Then, a starting liquid level 4b for the parent unit A is selected above the stopping liquid level 4a for the parent unit A, and a stopping liquid level 4d for the child unit is selected below the stopping liquid level 4a. is selected, a starting liquid level 4e for the child device is selected above the stop liquid level 4a, and an upper limit liquid level 4c is selected above both starting liquid levels 4b and 4e.

Now, when parent unit A and slave unit B are installed in the same liquid tank and liquid is introduced into the liquid tank, the liquid level rises. When the liquid level reaches level 4b, the buoy-type starting liquid level detector 9 floats up and detects the liquid level, thereby starting the electric motor of the parent unit A and starting draining the liquid. As a result of draining by parent unit A, when the liquid level drops and reaches the level 4a, the buoy-shaped stop liquid level detector 7 sinks and detects the liquid level, thereby stopping the electric motor of parent unit A. At the same time, a latching relay for process storage built in the master unit is driven to store the state of completion of the first liquid draining as the operation process of the slave unit.
As the liquid continues to be introduced, the liquid level rises again and reaches the level 4b. However, this time, because the process memory latching relay stores the child machine operation process, the main unit A is configured not to start even if the startup liquid level detector detects the liquid level. There is. The liquid level continues to rise, and when it reaches the level 4e, the buoy-type starting liquid level detector 9 of the slave unit B floats up and detects the liquid level, which in turn causes the slave unit to starts draining. As a result of the liquid draining by the slave unit B, when the liquid level decreases and reaches the level 4d, the buoy-shaped stop liquid level detector 7' sinks and detects the liquid level, thereby preventing the liquid from being drained by the slave unit. stops.
At this time, since the level of the liquid level 4d is set to be lower than the level of the liquid level 4a, the buoy-shaped stop liquid level detector 7 of the main unit A has already settled down and detected a drop in the liquid level. By doing so, the process memory latching relay built into the base unit is driven.
The state of completion of draining the liquid for the first time is stored as the main unit operation step. After the draining by slave unit B is completed, the liquid level rises again due to the continuous introduction of liquid and reaches the level 4b, and this time, the latching relay for process memory built in master unit A is activated. Since the operation steps are memorized, the buoy-type starting liquid level detector 9 detects the liquid level and starts draining the liquid by the parent device. Furthermore, if slave unit B malfunctions or if more liquid than the drainage capacity of slave unit B is introduced, the liquid level will rise beyond level 4e and reach level 4c, so the buoy type upper limit liquid level When the detector 11 floats up and detects the liquid level, the parent unit A is activated. Therefore,
If slave unit B is out of order, base unit A will
Further, when slave unit B operates normally, liquid is drained by both units. Such a conventional submersible pump capable of automatic alternating operation is configured such that a process memory latching relay built into the main unit A is driven by an output signal from the buoy-shaped stop liquid level detector 7 of the main unit. Therefore, even if the liquid level drops due to drainage of slave unit B, as long as the liquid level does not drop below the level 4a, the latching relay will not operate during the slave unit operation process. It was not possible to properly store the machine operation process, which alternates each time the base unit stops. Therefore, it was necessary to install the buoy-shaped stop liquid level detector 7 of the master unit A so as to be located above the stop liquid level detector 7' of the slave unit B. Such restrictions on installation increase the maximum level 4a of the residual liquid level, which has the disadvantage of making installation work difficult, especially when the floor surface 17 of the liquid tank 16 is not flat.

<Purpose> In order to eliminate the above-mentioned drawbacks, the present invention allows the buoy-type stop liquid level detector 7 of the master unit A to be installed either above or below the buoy-type stop liquid level detector 7' of the slave unit B. The purpose is to provide a submersible pump that can be operated automatically and alternately.

<Structure> The structure of the present invention in accordance with the above object is that a submerged pump consisting of a master unit to which a master unit control circuit is attached and a slave unit to which a slave unit control circuit is attached is placed in a liquid tank having a common liquid level. When the liquid level rises to the first starting liquid level, the master unit control circuit detects this with the first starting liquid level detection means and outputs the first starting signal. Specifically, a contact signal that closes in conjunction with the surfacing of the buoy serving as the first starting liquid level detection means is supplied to the parent unit starting means, and in response, the parent unit starting means supplies power to the electric motor of the parent unit. Then, the master unit is started and drained by the master unit, and when the liquid level drops to the first stop liquid level, which is selected below the first starting liquid level, the master unit control starts. The circuit detects this with the first stop liquid level detection means and generates a first stop signal, typically a contact signal that opens in conjunction with the settling of the buoy as the first stop liquid level detection means. and in response to this, the parent device stopping means cuts off the power supply to the electric motor of the parent device, stops the parent device, and prevents the parent device from draining liquid;
During this time, the process storage means alternately stores the master unit operation process and the slave unit operation process every time it receives the first activation signal, and when it stores the slave unit operation process, the Regardless of the start signal of
Preventing the activation of the parent device using a parent device startup prevention means,
Then, when the liquid draining by the parent device stops and the liquid level rises again and reaches the first starting liquid level, the process storage means receives the first starting signal output at this time and starts the process storage means. The activation process is memorized, and when the parent unit start prevention means prevents the activation of the parent unit and the liquid level rises to a second starting liquid level selected above the first starting liquid level, the next time In this case, the handset control circuit detects this using the second starting liquid level detection means, and typically closes the second starting signal in conjunction with the floating of the buoy as the second starting liquid level detection means. In response to this, the slave unit starting means supplies power to the electric motor of the slave unit, starts the slave unit, and drains the liquid by the slave unit, so that the liquid level is lowered. When the liquid level drops to a second stop liquid level that is selected below the first start liquid level, the slave control circuit detects this with the second stop liquid level detection means and issues a second stop signal. Typically, a contact signal that opens in conjunction with the settling of a buoy serving as a second stop liquid level detection means is supplied to the slave unit stop means, and in response, the slave unit stop means sends a signal to the electric motor of the slave unit. The device is characterized in that automatic alternating operation is made possible by cutting off the supply of liquid, stopping the slave unit, and preventing the slave unit from draining liquid.

<Example> FIG. 2 shows a situation in which a submerged pump capable of automatic alternate operation, which is an example of the present invention, is installed in a liquid tank. In this figure, each component is the same as each component shown in FIG. However, the stop liquid level 4a for the parent unit A is selected below the starting liquid level 4b for the parent unit A, and the starting liquid level 4e for the child unit B is selected above the starting liquid level 4b. is selected, and the stop liquid level 4 for the slave unit is below the starting liquid level 4b.
d is selected.

FIG. 3 shows an example of a master unit control circuit built in the master unit shown in A in FIG. In the figure, 20 and 21 are power supply lines, 22 is a step-down transformer, the primary side of which is connected to the power supply line, and one end of the secondary side is a buoy-type starting liquid level detector shown at 9 in Figure 2. output make contact Fb and auxiliary relay 23
is connected to the other end of the secondary side through the excitation coil. Fa is an output make contact of the buoy-type stop liquid level detector shown at 7 in FIG. The make contact 2 of the auxiliary relay 23 is connected to the other end of the secondary side.
3' and the excitation coil of the auxiliary relay 26 to the other end of the secondary side. 26' is a self-holding make contact of the auxiliary relay 26, which is connected in parallel to the contact 23'. Fc is an output make contact of the buoy type upper limit liquid level detector shown in 11 in FIG. 2, and one end is connected to one end of the secondary side, and
The other end is connected to the other end of the secondary side through the excitation coil of the auxiliary relay 25. 23″ is auxiliary relay 2
3, one end is the power supply line 20
In addition, the other end is a latching relay 2 for process memory.
It is connected to the power supply line 21 through the excitation coil 7. 28 is a power relay, one end of which is connected to the power supply line 20 through the contact 27' of the latching relay 27 and the delay action make contact 26'' of the auxiliary relay 26, and the other end is connected to the power supply line 21. 25' is a make contact of the auxiliary relay 25 and is connected in parallel to contacts 27' and 26''. 28' and 28'' are make contacts of the power relay 28, which are inserted into the power supply lines 20 and 21. 29 is the electric motor of the base unit A, and 30 is the ground. FIG. 3 is a sequence diagram of the main device control circuit shown in FIG.

Now, in FIG. 2, by introducing the liquid into the liquid tank 16, the liquid level rises, and as shown in FIG.
When the level shown in Figure A, 4a is reached, in the control circuit shown in Figure 3, contact Fa closes and resistor 2
Since a weak current flows through the excitation coil of the auxiliary relay 25 through the auxiliary relay 25, the relay enters a semi-excited state as shown in FIG. 4A, a. At this time, the contact 25' of the relay is not activated. When the liquid level rises further and reaches the level shown in FIGS. 2 and 4A and 4b, the contact Fb is closed in FIG. 3 and the auxiliary relay 23 is energized as shown in FIGS. 4A and 4b. Therefore, the contact 23' closes and current flows through the series circuit of the contacts Fa and 23', so that the auxiliary relay 26 is also energized as shown in Fig. 4A and c, and then as shown in Fig. 4d. As shown, after the delay time to has elapsed, the delay action contact 26'' closes.Meanwhile, in order to also close the contact 23'' at this time, the
As shown, the process memory latching relay 27
is energized to memorize the master unit operating process and its contact 27' closes. Therefore, contact 27' and contact 2
6'', the power relay 28 is energized, contacts 28' and 28'' are closed, and the motor 29 is started, as shown in FIGS. 4A and 4F. In this way, when the liquid level drops as a result of draining by the master unit A, the buoy-type starting liquid level detector 9 no longer detects the liquid level, so that the contact point Fb is closed as shown in FIGS. 4A, g, and h. Open again, auxiliary relay 23
becomes de-energized. However, the auxiliary relay 26 remains energized because it is also self-retained by the contacts 26'. Further, with continued drainage,
When the liquid level decreases and reaches the level shown in FIGS. 2 and 4A, 4a, contact Fa opens in FIG. At the same time as it becomes energized, the auxiliary relay 26 becomes de-energized as shown in FIG. Although it continues to memorize the operation process of the main unit,
Since the contact 26'' opens, the power relay 28 becomes de-energized and the motor 29 stops, as shown in FIG. Figure 2 and Figure 4 A, 4
When the level shown in b is reached, the contact point in Fig. 3 is reached.
When Fb closes, the auxiliary relay 23 becomes energized and the contact 23' closes, as shown in Fig. 4A, m, so that current flows through the series circuit of the contact Fa and the contact 23', and as shown in Fig. 4A, n. As shown, auxiliary relay 2
6 is excited. On the other hand, at this time, auxiliary relay 2
3 is energized, contact 23'' closes and the fourth
As shown in FIGS. A and O, the process memorization latching relay 27 is energized, and the child unit operation process is memorized this time, and the contact 27' is opened. After that, the fourth
As shown in Figures A and P, the delay action contact 26'' closes.Therefore, even in the transient contact state, no current flows in the series circuit between the contacts 27' and 26'', so the power relay 28 closes. The electric motor 29 does not start without being excited. Therefore, furthermore,
When the liquid level rises and reaches the level shown in Figures 2 and 4A and 4e, the electric motor of slave unit B starts, and as a result of liquid drainage by the slave unit, the liquid level decreases. , when the level shown in FIG. 4d is reached, the electric motor stops and the liquid draining by the child unit also stops. At this time, as shown in Fig. 2, if the buoy-type stop liquid level detector 7' of the slave unit is arranged above the buoy-type stop liquid level detector 7 of the master unit, the slave unit The drop in liquid level due to drainage is shown in Figures 2 and 4A and 4a.
Since the voltage does not reach the level of , no change occurs in the circuit shown in FIG.

If the buoy-shaped detector 7' of the slave unit is located below that of the master unit, the contact Fa opens before the slave unit stops draining, and the auxiliary relay 26 self-holds. It will be canceled. however,
When the liquid level rises and the contact point Fb closes after the main unit stops draining, that is, during the period when the process memory latching relay 27 memorizes the main unit operation process, as shown in FIG. , O, when the process memory latching relay 27 updates its memory to memorize the child unit operation process, as shown in FIGS. 4A and P, the closing of the contact 26'' is delayed and the power is In order to prevent unnecessary power supply to the relay 28, the auxiliary relay 26 must be in a state where the self-holding state is released, but as in the above operation example,
At the time when the drainage by the slave unit has stopped, the process memory latching relay 27 has memorized the slave unit operation process and the contact 27' is open, so it is impossible for the power relay 28 to be energized. Therefore, there is no problem in operation whether the auxiliary relay 26 is in the self-holding state or self-holding release state.On the other hand, if slave unit B malfunctions, or if the drainage capacity exceeds that of the slave unit, If liquid is introduced,
The liquid level rises above the level shown in FIGS. 2 and 4A, 4e and reaches the level shown in FIGS. 4B, 4c. Therefore, since the contact Fc in FIG. 3 closes, the auxiliary relay 25, which was in the semi-energized state as shown in FIG. 4B, becomes energized, and the contact 25' closes as shown in FIG. 4R. Then,
In order for current to flow through the contacts to the power relay 28, the contacts 27' and 2 are connected as shown in FIG. 4B and s.
6'', the electric motor 29 of the master unit starts. When the liquid level drops as a result of draining by the master unit A or the master unit A and slave unit B, the buoy-type upper limit liquid level detector 11 detects the corresponding level. Since the liquid level is no longer detected, the contact Fc opens again and the auxiliary relay 25 becomes semi-energized, as shown in Figure 4B and t.However, the excitation current required to maintain the contact once activated is supplied to the excitation coil of the auxiliary relay 25 through the contact Fa and the resistor 24.
The contact 25' is held closed as shown in u, and the motor 29 continues to operate as shown in v in the figure.

FIG. 5 shows an example of a handset control circuit built in the handset shown in B in FIG. In the figure, 50 and 511 are power supply lines, 52 is a step-down transformer, the primary side of which is connected to the power supply line, and one end of the secondary side is connected to the buoy-shaped stop liquid level shown at 7' in Figure 2. Detector output make contact Fd, resistor 5
3 and the other end of the secondary side through the excitation coil of the auxiliary relay 54. Fe is an output make contact of the buoy-type starting liquid level detector shown at 9' in FIG. 2, and is connected in parallel to contact Fd and resistor 53. 54' is a make contact of the auxiliary relay 54, one end of which is connected to the power supply line 50;
The other end is connected to the power supply line 5 through a power relay 55. 55' and 55'' are make contacts of the power relay 55, which are inserted into the power supply lines 50 and 51. 56 is the electric motor of slave unit B, and 57 is the ground.

FIG. 6 is a sequence diagram of the handset control circuit shown in FIG. 5.

Now, when the liquid level reaches the level shown in FIG. 2 and FIG. 6, 4d, contact Fd closes in FIG. As shown in Figure 6a, the relay is in a semi-energized state. At this time, since the contact 54' of the relay is not activated, no change occurs in the control circuit. When the liquid level rises due to the introduction of the liquid and reaches the level shown in FIGS. 2 and 6, 4e, the contact Fe closes in FIG. 5, and the auxiliary relay 54 is energized.
Contact 54' is closed as shown in FIGS. 6b and c,
Current flows through the power relay 55. Therefore, as shown in FIG. 6d, the contacts 55' and 55'' are closed, the electric motor 56 is started, and the slave unit B starts draining the liquid. As a result of the liquid draining by the slave unit, the liquid level decreases. Then, since the buoy-type starting liquid level detector 9' no longer detects the liquid level, the contact point is closed as shown in Fig. 6e.
Fe is opened again and the auxiliary relay 54 becomes semi-energized. However, since the excitation current necessary to maintain the once activated contact is supplied to the excitation coil of the auxiliary relay 54 through the contact Fd and the resistor 53, the contact 54' is closed as shown in Fig. 6f. The motor 56 is maintained in this state, and the motor 56 continues to operate as shown in g in the same figure. As a result of the liquid draining by the slave unit, the liquid level decreases as shown in Figs. 2 and 6.
When the level shown in d is reached, the contact point in Figure 5 is reached.
Since Fd is opened and the auxiliary relay 54 is de-energized, the contact 54' is opened as shown in FIG. 6h, and the electric motor 56 is stopped as shown in FIG. 6i.

In this way, the master unit A having a built-in master unit control circuit shown in FIG. 3 and the slave unit B having a built-in slave unit control circuit shown in FIG. 5 are operated alternately within the same liquid tank.

FIG. 7 shows another embodiment of the control circuit built into the master device shown in A in FIG. 2, and shows a circuit in which an electrode is used as a liquid level detector. In the figure, 70 to 79 are 20 to 2 in Figure 3.
The same components as 9 are shown. D is a rectifying diode, and C1 to C3 are smoothing capacitors. In addition, Pa, Pb and Pc are the buoy-type stop liquid level detectors shown at 7, 9 and 11 in FIG. 2, respectively;
These are a stop electrode, a starting electrode, and an upper limit electrode corresponding to a buoy-type starting liquid level detector and a buoy-type upper limit liquid level detector, and Po is a ground electrode.

Now, when the liquid level is at the level shown in the same figure and Fig. 2 4a, the diode D, auxiliary relay 76, and resistor R
A circuit is formed on the secondary side of the transformer 72 through the stop electrode Pa and the ground electrode Po. Therefore, a weak DC voltage appears across the smoothing capacitor C1, and the auxiliary relay 76 becomes semi-energized. When the liquid level rises to the level shown in the figure and FIG. 2 4b, the circuit from the excitation coil of the auxiliary relay 76 to the ground electrode Po via the starting electrode Pb2, the diode D, the auxiliary relay 73, and the starting electrode Pb1 Auxiliary relays 73 and 76 are energized in order to form a circuit to the ground electrode through
In the control circuit shown in FIG. 3, the same circuit state as when contacts Fa and Fd are closed is obtained. Base unit A
When the liquid level drops due to drainage, the starting electrode Pb
1. Since Pb2 leaves the liquid surface, the auxiliary relay 73 becomes de-energized. However, auxiliary relay 7
6 is supplied with a holding current through the resistor R, so the contact 76' remains closed and the third
In the control circuit shown in the figure, the same circuit state as when contact Fa is closed and contact Fb is closed and then opened is obtained. Furthermore, when the liquid level decreases and reaches the level shown in FIG. 7 and FIG. 2 4a, the auxiliary relay 76
becomes de-energized, and the same circuit state as when contacts Fa and Fb are opened in the control circuit shown in FIG. 3 is obtained. Similarly, when the liquid level rises to the level shown in Fig. 7 and Fig. 2 4c, the upper limit electrode Pc
Since the contact point Fc contacts the liquid surface, the auxiliary relay 75 shifts from the semi-energized state to the excited state, and the same circuit state as when contact Fc is closed in the control circuit shown in FIG. 3 is obtained.

In the above embodiment, as a means for detecting the liquid level,
Although buoy-type liquid level detectors or electrodes are used, for example, light beams, ultrasound, etc. can also be used. Furthermore, although the control circuit is constructed using relays, it can also be replaced with semiconductor elements. In particular, it is easy to replace the process memory latching relay with a semiconductor memory element.

<Effects> As described above, the present invention selects the first stop liquid level for the parent unit below the first starting liquid level for the parent unit, and A second starting liquid level for the child unit is selected above the first starting liquid level, a second stopping liquid level for the child unit is selected below the first starting liquid level, and The control circuit is configured to alternate and store the master unit operating process and slave unit operating process each time it is detected that the liquid level has reached the first starting liquid level. According to the invention, unlike the prior art, there is no need to detect that the liquid level has reached the stop liquid level for the parent machine and alternately memorize the operation process. Since it is sufficient to obtain a signal for stopping the base unit, there are no restrictions on the vertical relationship between the first stop liquid level and the second stop liquid level.

Therefore, the buoy-type stop liquid level detector of the master unit can be installed either above or below the buoy-type stop liquid level detector of the slave unit, and the operator can check the relative position of the stop liquid level detectors. Since there is no need to adjust the liquid level, installation work becomes easier and the residual liquid level can be kept low, which is an excellent effect. The above effect is particularly remarkable when the floor surface of the liquid tank is not flat.

Moreover, when the master unit start/stop control means stores the slave unit operating process in the process storage means and prevents the master unit from starting even if the liquid level reaches the first starting liquid level, A memory element that stores the slave device operation process as a process storage means, typically a switch element that changes from a conductive state to a non-conductive state in conjunction with the latching relay 27, typically the latching After the make contact 27' of the relay 27 is completely opened (becomes non-conducting),
After the elapsed time, a switch element, typically an auxiliary relay 2, which is inserted in series with the switch element and which should become conductive in response to the liquid level reaching the first starting liquid level.
Since the delay operation make contact 26'' of No. 6 is closed (conducted), both contacts 27' and 26'' are inoperable during the transition period from the parent unit operation process to the child unit operation process. Due to alignment, etc., the contact 26'' closes before the contact 27'' opens, and the motorized period 29 instantaneously receives undesired power supply.
This also has the excellent effect of reliably preventing the electric motor from operating unstably or wasting power.

[Brief explanation of the drawing]

Figure 1 shows the installation status of a conventional submersible pump capable of automatic alternating operation. In the same figure, A...Base unit, B...Slave unit, 5...Support member, 7, 7'
...buoy type stop liquid level detector, 9,9'...buoy type starting liquid level detector, 11...buoy type upper limit liquid level detector, Fig. 2 shows an embodiment of this invention, which is a liquid capable of automatic alternate operation. The installation status of the medium pump is shown. FIG. 3 shows an example of a master unit control circuit built in the master unit shown in A in FIG. In the same figure, Fa...output contact of the buoy-type stop liquid level detector shown at 7 in Fig. 2, Fb...output contact of the buoy-type starting liquid level detector shown at 9 in Fig. 2, Fc...11 in Fig. 2 Output contact of buoy type upper limit liquid level detector shown in 26...Auxiliary relay, 26''...Delay operation contact of auxiliary relay 26, 27...Latching relay for process memory, 27'
...Contacts of the process memory latching relay 27. FIG. 4 is a sequence diagram of the master unit control circuit shown in FIG. 3. In the figure, the horizontal axis indicates time.
FIG. 5 shows an example of a handset control circuit built in the handset shown in B in FIG. In the same figure, Fd...The output contact of the buoy type stop liquid level detector shown at 7' in Fig. 2, Fe...The output contact of the buoy type starting liquid level detector shown at 9' in Fig. 2, Fig. 6 shows the output contact of the buoy type starting liquid level detector shown at 9' in Fig. FIG. 6 is a sequence diagram of the handset control circuit shown in FIG. 5; In the figure, the horizontal axis indicates time.
FIG. 7 shows another embodiment of the base unit control circuit built in the base unit shown in A in FIG. In the same figure, Pa...stop electrode, Pb...start electrode, Pc...upper limit electrode, _P0 ...ground electrode.

Claims (1)

[Claims] 1. In a submersible pump consisting of a master unit and a slave unit buried in a liquid tank having a common liquid level, the master unit includes:
a first starting liquid level detection means that detects that the liquid level is at the first starting liquid level and outputs a first starting signal; and a liquid level selected below the first starting liquid level. a first stop liquid level detecting means that detects that the liquid level is at a first stop liquid level and outputs a first stop signal; a process storage means for alternating and storing the operation steps; and controlling the starting and stopping of the base machine based on the first start signal, the first stop signal, and the operation steps stored in the process storage means. a master unit start/stop control means, the master unit start/stop control means is interlocked with the process storage means, and is in a conductive state when the storage means stores the master unit operating process; The switch element 27' is in a non-conducting state when the operating process is memorized, and the switch element 27' stores "1" (excited state) in response to the first start signal, and in response to the first stop signal. It is linked to the auxiliary memory element 26 that stores "0" (de-energized state), and when the auxiliary memory element stores "1", it is in a conductive state, and when the element stores "0", it is in a conductive state. is in a non-conducting state, and furthermore, when the element memorizes "1", a series circuit with an auxiliary switch element 26'' which changes to a conducting state with a delay of a specific delay time to; A master unit control circuit consisting of an electric motor 29 that is directly or indirectly supplied with power is attached to the slave unit, and a second starting liquid whose liquid level is selected to be above the level of the first starting liquid is attached to the slave unit. a second start-up liquid level detection means for detecting that the liquid level is at the level and outputting a second start signal; a slave unit start means for starting the slave unit in response to the second start signal; a second stop liquid level detection means for detecting that the liquid level is at a second stop liquid level selected below the first start liquid level and outputting a second stop signal; A submersible pump capable of automatic alternate operation, which is equipped with a slave unit control circuit including slave unit stopping means for stopping the slave unit in response to a signal.