JPS5840676B2 - Axial thrust balance device for canned motor pump - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an axial thrust balancing device for a canned motor pump, and the present invention relates to an axial thrust balancing device for a canned motor pump, in which the axial movement of the rotor is detected by a detection coil provided in the stator of the motor, and the lubricant flowing through the bearing tongue is detected. It controls the flow rate and balances the axial thrust.

Technical background of the invention and its problems Since canned motor pumps mainly handle chemical liquids, they are often required to be corrosion resistant. Therefore, steel ball bearings cannot be used, and slides made of carbon, Teflon, etc. cannot be used. Bearings are commonly used.

However, due to the unbalance of the axial thrust due to the axial thrust generated by the rotation of the impeller, the axial wear of the slide bearing is significant, and if the bearing wear progresses and the rotating part and fixed part come into contact, the pump may become inoperable. This may lead to accidents, so early replacement of the bearings is required, and inspection and maintenance is extremely troublesome.

Conventionally, various technical improvements have been made to balance this axial thrust, examples of which will be explained with reference to FIG.

A pump casing 1 is integrally connected to a front flange 4 of a stator frame 3 that constitutes the main body of the canned motor via a front bearing housing 2, and has an impeller 5 built therein.

Further, a rear bearing housing 7 is coupled to the rear flange 6 of the stator frame 3, and a shaft to which a rotor 10 is fixed via a front bearing 8 and a rear bearing 9 between the rear bearing housing 7 and the front bearing housing 2. 11 is rotatably supported.

Note that the impeller 5 is fixed to one end of this shaft 11 via a bolt 12.

Further, a projecting edge 14 is provided on the inner periphery of the front wall 13 of the impeller 5, and a fixed orifice 16 is formed by providing a slight gap 15 between the outer periphery of the projecting edge 14 and the continuous cylindrical surface of the casing 1G. Further, on the outer periphery of the rear wall 17 of the impeller 5, a projecting edge 18 having a diameter larger than the projecting edge 14 of the front wall 13 is provided, and this projecting edge 18 and the projecting edge provided on the front surface of the front bearing housing 2 A fixed orifice 21 is configured with a slight gap 19 provided between the fixed orifice 20 and the fixed orifice 21 .

Then, the projecting edge 2 of the front bearing housing 2
A projecting edge 22 is provided on the inner diameter portion of the impeller 5, and a variable orifice 26 is formed by making the end surface 23 of the projecting edge 22 and the back surface 24 of the rear wall 17 of the impeller 5 face each other with a slight gap 25 therebetween.
is configured.

Reference numeral 27 indicates a balance hole bored inward from the outer circumference of the variable orifice 26 portion of the impeller 5, and 28 indicates a projecting edge 20 of the fixed orifice 21 and a projecting edge 22 of the variable orifice 26.
A balance chamber 29a constructed between the two is a circulation pipe, one end of which is connected to the discharge port 30ζ of the casing 1, and the other end connected to the rear bearing housing 1.

31 is a stator, 32 is a stator can, 33 is a rotor can, and 34 is a stator can 32 and a rotor can 33.
It is a gap between

35 is a gap formed between the inner surface of the casing 1 and the front wall 13 of the impeller 5; 36 is a gap formed between the vortex chamber peripheral surface of the casing 1, the rear wall 17 of the impeller 5, the fixed onofice 21, and the front bearing housing 2; The gaps 37 are formed between the front bearing housing 2 and the rotor 10, and the gap 38 is a gap formed between the rear bearing housing 7 and the rotor 10.

Reference numerals 39 and 40 are thrust collars that are pressed into and fixed to the shaft 11, 41 is a stator main winding, and 42 is a suction port of the casing 1.

Now, when the canned motor pump having such a configuration is operated, the suction port 42 is opened by the pumping action of the impeller 5.
The liquid sucked in is discharged from the outlet of the impeller 5, and part of it flows into the gaps 35 and 36 on both sides of the impeller 5.

Since the gap 15.19 of the fixed orifice 16.21 is small and the flow path resistance is small, the gap 35.36
The pressure of impeller 5 increases in one cavity 35.
A force that pushes the impeller 5 to the left in the figure (hereinafter referred to as the rear) acts in the other gap 36c, and a force that pushes the impeller 5 to the right in the figure (hereinafter referred to as the front) acts in the other gap 36c.

The liquid that has flowed into the balance chamber 28 through the gap 19 in the fixed orifice 21 flows out from the balance hole 27 through the gap 25 in the variable orifice 26 to the outlet of the impeller 5 again. Due to this resistance, the pressure in the balance chamber 28 increases, and a force that pushes the impeller 5 forward acts.

On the other hand, the liquid branched from the discharge port 30 passes through the circulation pipe 29 and lubricates the rear bearing 9.
The stator 31 passes through the gap 34 between the rotor can 33 and the rotor can 33.
and after cooling the rotor 10, the front bearing 8
The oil is lubricated and circulated through the balance hole 27 of the impeller 5 from the outlet of the impeller 5 to the discharge port 30 again.

When this circulating flow passes through the gap 34 between the stake can 32 and the rotor can 33, the pressure in the gap 38 increases due to the flow path resistance of the gap 34, and a force that pushes the rotor 10 forward is exerted.

Therefore, if these forces acting on the shirt HH are balanced, the axial thrust will be balanced.

Now, when the impeller 5 moves rearward, the gap 25 between the variable onofices 26 narrows, flow resistance increases, the pressure in the balance chamber 28 further increases, and the force pushing the impeller 5 forward becomes stronger.

On the other hand, the flow path resistance of the fixed orifice 16.21 is almost unaffected by the amount of overlap due to the back and forth movement of the impeller 5, and takes a nearly constant value, and the flow path resistance of the air gap 34 is also substantially unaffected by the amount of overlap caused by the back and forth movement of the rotor 10. The pressure in the air gap 35.3638 is almost constant because it is almost unaffected and takes an almost constant value.
Therefore, the impeller 5 is pushed back forward and the axial thrust is balanced when the forces acting on the shaft 11 are equal from front to rear.

Conversely, when the impeller 5 moves forward, the variable orifice 2
The gap 25 between the shafts 11 and 6 widens, the flow path resistance decreases, and the pressure in the balance chamber 28 decreases, the force that was pushing the impeller 5 forward weakens, the impeller 5 is pushed back, and the force acting on the shaft 11ζ moves back and forth. The axial thrust is balanced when it becomes equal.

However, in the canned motor pump having the above configuration, in addition to the force that pushes the impeller 5 back and forth due to the pressure of the air gaps 35 and 36 and the balance chamber 28 acting on the pump section, the force that pushes the impeller 5 back and forth also acts on the motor section (also here, the front bearing housing 2 Gap 3 formed between the rotor 10
A force pushing the rotor 10 backward is exerted by the pressure of 7, and a force pushing the rotor 10 forward is exerted by the pressure of the gap 38 formed between the rear bearing housing γ and the rotor 10. The force that pushes the rotor 10 depends on the flow rate of the circulating fluid that circulates from the discharge port 30 through the circulation pipe 29 to the rear ring 9, gap 38, gap 34, gap 37, front bearing 8, and balance hole 27. , a complex element is added in that the flow rate of the circulating fluid changes due to a change in the pump discharge pressure accompanying a change in the pump discharge volume, and the axial thrust generated in the motor section changes. For example, at the rated discharge volume of the pump Even if the axial thrust of the canned motor pump as a whole is balanced by adjusting the hole diameter, number of holes, and hole position of the balance hole 27, if the pump discharge rate changes, it becomes difficult to maintain the balanced state, and the bearing Wear progresses.

Furthermore, in other conventional axial thrust balancing mechanisms, it is difficult to balance the axial thrust over a wide range of pump discharge amounts.

Purpose of the Invention The present invention has been made in order to improve the above-mentioned drawbacks, balance the axial thrust over a wide range of pump discharge volume, and significantly reduce the load on the bearing. It attempts to balance the axial thrust by detecting movement in the axial direction and controlling the flow rate of lubricant flowing through the bearing.

Summary of the Invention The present invention provides a canned motor pump in which the axial thrust changes with changes in the flow rate of bearing lubricating fluid.
(a pair of detection coils 44 provided respectively)
a, 44b and these rain detection coils 44a, 44b are connected to rectifier circuits 45a, 45b, respectively, and both rectifier circuits 45
a and 45b are connected in series with each other to form the rain detection coil 4.
4a.

Detection circuit 4 that detects the difference in voltage after rectification of 44b
8, a control circuit 49 that compares the differential voltage detected by the detection circuit 48 with a set voltage corresponding to the axial movement amount of the rotor 10 of the motor and generates a signal, and a pipe through which bearing lubricating fluid passes. 29a, 29b, 55.56 (
The rain detection coil 44 . .

control valve 53 depending on the voltage induced in 44b.
．． 53b, 53. ．． 53d is opened and closed to control the flow rate of the bearing lubricating fluid.

Examples of the invention Next, embodiments of the present invention will be described based on the drawings.

In the figure, parts that are the same as those in the device in Figure 1 are designated by the same symbols.
The explanation will be omitted.

2 is a longitudinal sectional view showing a first embodiment of the present invention, FIG. 3 is a sectional view taken along line I-1 in FIG. 2, and FIG. 4 is a block diagram of the electric circuit of the present invention.

In the first embodiment, both ends of the magnetic gap facing surface of the stator 31 of the canned motor pump of the apparatus shown in FIG. Detection coil 44. .

44b is provided, and this detection coil 44a.

44b are respectively connected to rectifier circuits 458 and 45b made up of diodes and capacitors, for example, and the AC signals from the detection coils 443 and 44b are converted and smoothed into DC voltages proportional to the amplitudes thereof, and output terminals 46a and 46, respectively.
A detection circuit 48 is configured to be extracted between the common point 47 and the point 47.

The control circuit 49 is composed of two comparison circuits 50a and 50b, two set voltage generation circuits 51a and 51b1, and one drive amplifier circuit 52, and the comparison circuit 50c is connected to both output terminals 46.46ba of the detection section 48.
A and a set voltage generating circuit 51a are connected, and both output ends 46a of the detection section 48 are connected to the comparison circuit 50b.

46b is connected to a set voltage generation circuit 51b, and the output terminals of these comparison circuits 50a and 50b are connected to a drive amplifier circuit 52, respectively.

The output end of the drive amplification circuit 52 is connected to a control valve provided in the middle of the circulation pipe 29a, for example, an electrically operated valve 53a, and the electrically operated valve 53a is opened or closed in response to signals from the comparison circuits 50a and 50b. is configured to do so.

Note that 58 is a slot of the rotor 10.

Next, the operation of the first embodiment will be explained.

First, when the power is turned on and the rotor 10 is rotated, an excitation current flows through the stator main winding 41 (in accordance with the power supply voltage).
A magnetic flux is generated that interlinks with the stator main winding 41, and this magnetic flux is connected to the rain detection coil 44a.

44- This interlinks and induces a voltage.

The voltage induced in the rain detection coils 448, 44b is
The amplitude of the induced voltage in each of the rectifier circuits 453 and 45bl is converted and smoothed into a proportional DC voltage V3, V5, which appears between the output terminals 46a and 46b of each of the rectifier circuits 45a and 45b and a common point 47.

The voltage between these output terminals 46a and 46b is a DC voltage V which is the difference between DC voltages 3 and 2b.

It is. FIG. 8 shows the amount of change in the DC voltages Va, ■b, and ■o with respect to the axial movement amount X of the rotor 10 when the slot 58 of the rotor 10 is not skewed. When moved, the magnetic flux distribution state at both ends of the air gap 34 changes, and the detection coils 44a, 44b
The voltage induced in v3. changes accordingly, and the DC voltage v3. ■b, ■.

changes.

In FIG. 8, the curve Fu represents the detection coil 44a on the front bearing 8 side with respect to the axial movement amount X of the rotor 10.
The curve Ru represents the change in the DC voltage va caused by the detection coil 44b on the rear bearing 9 side with respect to the axial movement amount X of the rotor 10. DC voltage V.

The change in the amount of axial movement X of the rotor 10 is expressed by the curve F
It is expressed as a curve Fu-Ru obtained by subtracting the curve Ru value from the value of u.

Therefore, the axial movement amount X of the rotor 10 and the DC voltage ■
.

There is an almost proportional relationship between the two as shown in the figure.

If the slot 58 of the rotor 10 is skewed,
It was also confirmed by the experiments of this patent applicant, that the rotor 1
Detection coils 44a, 44b depending on the rotation direction of
The DC voltage V3. (2) The value of b is also different, so the DC voltage V is the difference between the two.

The value of also depends on the direction of rotation.

FIG. 9 is a graph showing the relationship between the DC voltages va, ■b, ■o and the axial movement amount X of the rotor 10 when the slot 58 of the rotor 10 is skewed, when the rotor 10 is viewed from the front. When the slots 58 are skewed clockwise from the front to the rear, the solid line shows the change when the rotor 10 rotates to the right, and the dotted line shows the change when the rotor 10 rotates to the left.

Canned motor pumps do not require forward or reverse rotation and operate in a constant rotational direction, so the DC voltages va, vb,
The relationship between VC and the axial movement amount X of the rotor 10 ultimately appears as either a solid line or a dotted line.

Note that if the direction of skew is counterclockwise, the ninth
In the graph shown in the figure, the solid line indicates when the rotation is to the left, and the dotted line indicates when the rotation is to the right.

The following explanation is for the case where the skew is in the clockwise direction and the rotor 10 is rotating clockwise, or when there is no skew.

V is the voltage of the curve Fu-Ru when the rotor 10 and stator 31 are operated with the same position in the axial direction.

(V if there is no skew.

-0) In the first embodiment, the voltage vf when the rotor 10 moves and the thrust collar 39 and the front bearing 8 begin to contact each other, and the voltage vr when the thrust collar 40 and the rear bearing 9 begin to contact each other. For,
The setting voltage v1 of one setting voltage generation circuit 51a and the setting voltage ■2 of the other setting voltage generation circuit 51b are respectively,
Set Vf>Vl>Vo>V2>Vf, and set the voltage V between the output terminals 46a and 46b.

When the following relationship exists, the operation of the drive amplifier circuit 52 is set as follows.

vo〉■When 1, the drive amplification circuit 52 operates the electrically operated valve 5
Generates a signal to close 3a.

When vl>vo>v2, the 1-drive tank width circuit 52 does not generate a signal, and when v2>vo, the drive amplification circuit 52 generates a signal from the electrically operated valve 5.
Generates a signal to open 3a.

Now, under these setting conditions, when the rotor 10 moves forward and the voltage o between the output ends 46a and 46b exceeds the set voltage v1, the electrically operated valve 53a begins to close.
The flow rate of the circulating fluid flowing through the circulation pipe 29a decreases, and the pressure in the gap 38 begins to decrease, so that the force that was pushing the rotor 10 forward begins to weaken.

And the voltage V between the output ends 46a and 46b.

The electrically operated valve 53a is further closed until σ becomes equal to or less than the set voltage V, and at the same time, the flow rate of the circulating fluid gradually decreases, and the pressure in the gap 38 further decreases, so that the rotor 10 is returned to the rear. , resulting in output ends 46a, 46
Voltage between b■.

is less than the set voltage ■1 (when this happens, the electrically operated valve 53a
stops closing and is held in that state, keeping the axial thrust balanced.

This time, the rotor 10 moves rearward and the terminal 46a.

46b voltage V.

falls below the set voltage v2, the electrically operated valve 53. begins to open, the flow rate of the circulating fluid flowing through the circulation pipe 29a increases, and the pressure in the gap 38 begins to rise, so that the rotor 10
The force that was pushing him forward began to grow stronger.

And the voltage ■ between the output terminals 46a and 46b.

The electrically operated valve 53a continues to open until the voltage becomes higher than the set voltage ■2, and at the same time, the flow rate of the circulating fluid increases and the pressure in the gap 38 further increases, causing the rotor 10 to move back forward. Output end 46a.

46b voltage V.

When becomes equal to or higher than the set voltage v2, the electrically operated valve 53a stops opening and is maintained in the current state, thereby maintaining the balance of the axial thrust.

Next, FIG. 5 shows a second embodiment of the present invention,
In the first embodiment, the circulation pipe 29a connected to the discharge port 30 of the casing 1 is removed, and a new circulation pipe 29b is connected to the rear bearing housing 7 and the suction side of the pump such as a suction pipe or suction kunk, for example, to the suction port 42 of the casing 1. A control valve, for example, an electrically operated valve 53b is provided in the middle of the circulation pipe 29b,
A gap 36 and a gap 37 are provided in the front bearing housing 2.
A passage 54 is bored through which the two communicate with each other.

Therefore, in this second embodiment, since the pump suction side, that is, the suction port 42 of the casing 1 is at low pressure,
The flow direction of the circulating fluid flowing through the front bearing 8, the rear bearing tongue 9, and the gap 34 between the stator can 32 and the rotor can 33 is opposite to that in the first embodiment.

In other words, the liquid that entered the gap 36 from the outlet of the impeller 5 is
A portion of the flow flows into the gap 37 from the passage 54, lubricates the front bearing 8, passes through the balance hole 27, and circulates to the outlet of the impeller 5, and the rest lubricates the front bearing 8.
It passes through the gap 34 between the rotor can 33 and lubricates the Noah bearing 9, flows into the suction port 42 of the casing 1 through the circulation pipe 29b, and circulates again to the outlet of the impeller 5.

The action of the circulating fluid on the rotor 10 is opposite to that in the first embodiment, and the pressure in the gap 37 increases due to the flow path resistance in the gap 34, exerting a force that pushes the rotor 10 backward.

If this force, the force due to the pressure in the air gaps 35, 36, and the force due to the pressure in the balance chamber 28 are balanced, the axial thrust is balanced.

Now, when the control circuit 49 is configured in the opposite manner to the first embodiment, that is, when Vo>vl, the drive amplifier circuit 52 operates as the operating valve 53b.
When ■1'''2■o>V2, the 1 drive tank width circuit 52 does not generate a signal, and when ■2>Vo, the drive amplification circuit 52 generates a signal to open the electrically operated valve 5.
If the setting is made to generate a signal to close 3b, the rotor 10 will move forward and the output end 46a.

46b voltage V.

When exceeds the set voltage v1, the electrically operated valve 53b begins to open, and the flow rate of the circulating fluid flowing through the circulation pipe 295 increases.As a result, the pressure in the gap 31 begins to rise, and the force pushing the rotor 10 backward becomes stronger. is returned to the rear, resulting in a voltage V between output terminals 46a and 45b.

When becomes less than the set voltage (■1), the electrically operated valve 53b stops opening and is maintained in that state, thereby maintaining the balance of the axial thrust.

This time, the rotor 10 moves backward, and the output ends 46a, 4
Voltage V between 6b.

When becomes lower than the set voltage ■2, the electrically operated valve 53b begins to close, and the flow rate of the circulating fluid flowing through the circulation pipe 29b decreases.As a result, the pressure in the gap 37 begins to decrease, and the force that was pushing the rotor 10 backward weakens, causing the rotor to 10 is returned forward, resulting in a voltage V between outputs 46a, 46b.

When becomes equal to or higher than the set voltage V2, the electrically operated valve 53b stops closing and is maintained in that state, thereby maintaining the balance of the axial thrust.

Next, FIG. 6 shows a third embodiment of the present invention,
In the first embodiment, a bypass pipe 55 is branched from the middle of the circulation pipe 29a between the rear bearing housing I and the electrically operated valve 53a.
The distal end of the bypass vibe 55 is connected and communicated with the pump suction side, for example, the casing suction port 42, and an electrically operated valve 53o as a control valve is provided in the middle of the bypass vibe 55.

Therefore, this third embodiment is different from the first embodiment in that the circulation pipe 29 is connected to the discharge port 30 of the casing 1. In contrast to the OM, which changes the pressure in the gap 38 by controlling the flow rate of the circulating fluid flowing into the circulation pipe 29. The circulating flow is diverted from the bypass pipe 55 to the suction port 42 of the casing 1, and the flow rate passing through the bypass pipe 55 is controlled to flow into the circulating pipe 29. This is to control the flow rate of the circulating fluid flowing into the gap 38 from there.

In other words, when the rotor 10 moves forward, the electrically operated valve 53o is opened to increase the flow rate of the circulating fluid flowing into the bypass pipe 55, thereby reducing the flow rate flowing into the gap 38, thereby lowering the pressure in the gap 38. When the rotor 10 is returned to the rear and the rotor 10 is moved backward, the electrically operated valve 53o is closed to reduce the flow rate of the circulating fluid flowing into the bypass pipe 55 and increase the flow rate flowing into the gap 38. 38 to push the rotor 10 back forward and balance the axial thrust.

In addition, in the description of the third embodiment above, the circulation pipe 29
Electrically operated valve 53. Although the valve 53a is merely used as a communication port and does not operate as such, the electrically operated valve 53a may also be operated.

In that case, the electrically operated valve 53o is closed and the air gap 38
When the pressure of the circulation pipe 29. increases, the electrically operated valve 53a is opened and the circulation pipe 29. The electrically operated valve 5
3o is opened and the pressure in the gap 38 decreases, it is better if the electrically operated valve 53a is closed and the flow rate of the circulating fluid flowing through the circulation pipe 29a is reduced to facilitate the pressure drop in the gap 38. Effective.

Next, FIG. 7 shows a fourth embodiment of the present invention,
In the first embodiment, the circulation pipe 29a is removed, the rear liquid injection pipe 56 is connected to the rear bearing housing 7, and the lubricant is injected into the rear bearing housing 7 through the rear liquid injection pipe 56. A pump 57 or other liquid feeding device is connected, and an electrically operated valve 53d is installed between them.

Therefore, in the fourth embodiment, unlike the first, second and third embodiments, the bearings 8 and 9 were lubricated and the stator 31 and rotor 10 were cooled by pumping liquid. On the other hand, since the clear mother liquid of the pumped liquid is injected into the rear bearing housing 7 from the rear liquid injection pipe 56 using the lubricating liquid injection pump 57 or other liquid feeding device, slurry etc. are added to the pumped liquid. If foreign matter is included, using this method can prevent abnormal wear of the bearing due to foreign matter entering the bearing 8.9.

In the fourth embodiment, when the rotor 10 moves backward, the electrically operated valve 53d is opened to increase the rear liquid injection flow rate, increase the pressure in the gap 38, push the rotor 10 back forward, and reverse the flow. When the rotor 10 moves forward, the electrically operated valve 53d is closed to reduce the rear liquid injection flow rate,
By reducing the pressure in the air gap 38, weakening the force that was pushing the rotor 10 forward, and returning the rotor 10 rearward, the axial thrust is balanced.

In addition, if the lubricant injection pump 57 is a pump that can control the discharge amount, such as a metering pump, the electrically operated valve 53
Instead of d, the discharge amount of the lubricant injection pump 57 may be controlled.

In the four embodiments described above, the flow rate of the circulation pipe and the I-bypass pipe is controlled by an electrically operated valve, but instead of an electrically operated valve that opens and closes the valve continuously, the valve has two operations of opening and closing. The same effect can be obtained by using an electromagnetic valve that performs only this operation, and controlling the periodic interval of the opening and closing operations of the electromagnetic valve by a control circuit to adjust the flow rates of the circulation pipe and the bypass pipe.

Effects of the Invention The present invention electrically detects the forward and backward movement of the rotor of a canned motor, controls the bearing lubrication and cooling fluid flow rate, and automatically balances the axial thrust, thereby reducing the pump discharge amount. It is possible to provide an axial thrust balancing device for a canned motor pump that can achieve balance of the axial thrust over a wide range, significantly improve bearing wear, and has extremely high utility value in industry.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a conventional axial thrust balance device, Fig. 2 is a sectional view showing a first embodiment of the present invention, Fig. 3 is a sectional view taken along the line l-111 in Fig. 2, and Fig. 4 is a block diagram of the electric circuit, FIG. 5 is a sectional view showing the second embodiment of the present invention, and FIG.
The figure is a sectional view showing the third embodiment of the present invention, FIG. 1 is a sectional view showing the fourth embodiment of the invention, and FIG. 8 is the axial direction of the rotor when the slots of the rotor are not skewed. FIG. 9 is a graph showing the voltage change of the detection unit with respect to the movement amount X. FIG. 9 is a graph showing the voltage change of the detection unit with respect to the axial movement amount X of the rotor when the slot of the rotor is skewed. 31...Stator, 41...Stator main winding, 44a, 44b...Detection coil, 48
...Detection circuit, 49...Control circuit, 2
9a, 29b, 55. 56...Pipe, 53a, 53b, 53o,
53d... Control valve.

Claims (1)

[Claims] 1 In a canned motor pump in which the axial thrust changes due to changes in the flow rate of bearing lubricating fluid, the inner diameter of the stator main winding at both ends of the magnetic gap facing surface of the motor's stator (a pair of detection coils installed on each side, a detection circuit that connects each coil to a rectifier circuit and connects both rectifier circuits in series to detect a difference in voltage between the two detection coils after rectification; a control circuit that generates a signal by comparing the voltage with a set voltage corresponding to the axial movement amount of the rotor of the motor; and a control pulp that is installed in a pipe through which bearing lubricating fluid passes and opens and closes based on the control signal from the control circuit. An axial thrust balance device for a canned motor pump, characterized in that the control pulp is opened and closed in accordance with voltages induced by both detection coils of the detection circuit to control the flow rate of the bearing lubricating fluid.