JPS6356437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to reducing axial thrust of a submersible pump driven by a dry motor.

In a pump, energy is imparted to the fluid by the rotation of the impeller, so a pressure difference occurs before and after the impeller. Therefore, a hydraulic axial thrust acts on the impeller due to this pressure difference. For example, in the case of a submersible pump as shown in FIG. 1, an impeller 1 is fixed to a rotating shaft 3 by an impeller nut 2, and the rotating shaft 3 is rotated by a dry motor 4. A shaft seal 5 is provided in a portion of the rotating shaft 3 between the impeller 1 and the motor 4 to prevent leakage flow from the outlet of the impeller 1 from entering the motor 4. When the pressure in the shaft seal portion 5 becomes high, the shaft seals are doubled and an oil chamber 6 is provided between the shaft seals 5 to prevent water from leaking with oil. The motor 4 is isolated from the atmosphere by the shaft seal 5, but the pressure inside the motor is usually about atmospheric pressure. On the other hand, the casing 7 is formed to cover the impeller 1, and has a front side wall 1 of the impeller 1.
A, a wear ring 8 is attached to the opposite surface of the rear side wall 1b, forming a slit 9 to seal leakage flow from the impeller outlet to the suction port 10.

With the above configuration, a significant pressure difference occurs between the gap 11 surrounded by the impeller 1 and the casing 7 and the suction port 10, and since the diameter of the suction port 10 is larger than the rotating shaft 3, the impeller When rotated, an axial thrust T is generated from the rear side wall 1b toward the front side wall 1a. This axial thrust T corresponds to the pressure in the shaded area in FIG. do. here,
T _F is the thrust acting on the front side of the impeller, T _B is the thrust acting on the back side of the impeller, T _P is the thrust due to the suction pressure of the flowing water, and T _M is the thrust due to the change in momentum of the flowing water.

If excessive shaft thrust is applied to the pump, it is necessary to consider the strength of the bearing or shaft so that it can withstand this thrust, and the bearing and shaft become considerably larger. a
As shown in the figure, a balance wheel 12 is provided near the impeller back boss to reduce the pressure near the impeller back boss to about the suction pressure, thereby reducing the suction port thrust (T _P +T _M ) and the back wear ring 13. The thrust T _B2 acting on the side wall of the balance chamber 14 on the smaller diameter side is balanced.

However, when the suction pressure changes depending on the usage conditions like a submersible pump, the amount of change in the thrust T _P due to the change in suction pressure becomes extremely large as shown in Fig. 2b, and the front side wall 1a of the impeller A reverse thrust from the side toward the rear side wall 1b may occur. For example, in a submersible pump type reverse circulation drilling device used for civil engineering foundation work, a submersible pump 22 is disposed above a drill bit 21 for excavating the ground, as shown in FIG. 4, to discharge excavated earth and sand to the ground. In this case, the submersible pump changes its position depending on the excavation depth, but since the excavation depth can exceed 100 m, the change in pump suction pressure exceeds 10 Kg/cm ² . On the other hand, since the pressure inside the motor remains at atmospheric pressure regardless of the excavation depth, the balance of pressure acting on the rotor at the shaft seal is lost, resulting in the thrust shown in equation (1).

T _P = P _S ×π/4D ² _SF (1) Here, P _S is the suction gauge pressure, and D _SF is the shaft diameter of the shaft seal.

In the submersible pump used in the aforementioned reverse circulation drilling equipment, the maximum value of the axial thrust is 400 kg, and the change due to the discharge amount is about 200 kg, whereas the axial thrust changes due to changes in suction pressure. The weight is approximately 800Kg.

Changes in shaft thrust due to suction pressure are caused by imbalance of pressure in the shaft seal, so it is recommended to change the motor from a dry type motor to an oil-filled motor and apply pressure from the ground according to the suction pressure, or use a hydraulic motor. However, in the case of oil-filled motors, auxiliary equipment for oil filling is required, and in the case of hydraulic motors, if the excavation depth is deep, the flow of hydraulic oil in the oil supply and drain pipes may be reduced. This had the disadvantage that motor efficiency significantly decreased due to increased loss.

Also, in 1921, an idea was developed to balance the thrust force acting on the impeller using the pressure on the pump discharge side.
It is described in Utility Model Application Publication No. 17324. However, in this device, the shaft, impeller, and annular plate are moved in the axial direction to change the axial clearance between the annular die and the casing, and between the impeller and the casing, thereby reducing the pressure acting on the balance chamber 9. Since the thrust force is controlled and balanced, the rotating shaft and impeller move in the axial direction every time the suction pressure changes, which not only makes the pump unstable, but also allows the thrust bearing to move in the axial direction. Bearings are required, making the device complex. In addition, water flows from the pump discharge side to the water passage 13, the chamber 9, and the water drain hole 17.
(For the reference number, refer to the drawing in the above publication) and flows to the suction side of the impeller, so the differential pressure between the pump discharge side and the impeller suction side becomes extremely large. There is a problem in that the pump efficiency also decreases because a large amount of water flows.

The present invention provides a submersible pump that reduces changes in shaft thrust due to changes in pump suction pressure, has a simple device, does not require a structure in which the rotating shaft is moved in the axial direction, and also hardly reduces pump efficiency. The purpose is to

A feature of the present invention is that in a submersible pump that is driven by a dry motor and has an impeller having a rear side wall and is rotatably supported by a casing, a cylindrical member extending in the axial direction is formed on the rear side wall of the impeller. A wear ring is provided in the casing so as to form a slit in the radial direction with respect to the member, the wear ring portion, the impeller, the casing,
A balance chamber is formed by a shaft seal that seals the gap between the casing and the rotating shaft, and a pressure balance tube is provided to connect this balance chamber and the pump discharge tube, and the cross-sectional area of this balance tube is Another advantage lies in that the wear ring portion is configured to have a larger radial slit area.

Embodiments of the present invention will be described below with reference to FIGS. 5 to 8.

Figure 5a shows an embodiment of a submersible pump used in a reverse circulation drilling device. A back blade 15 is provided, and a cylindrical member extending in the axial direction is formed on the rear side wall 1b of the impeller, and a wear ring 13 is formed to form a slit in the radial direction with respect to the cylindrical member. is provided in the casing 7 to seal against leakage. 14 indicates the wear ring 13, the impeller 1, the casing 7, and the casing 7 and the rotating shaft 3.
This balance chamber 14 and the pump discharge pipe are communicated through a pressure balance pipe 16. Since this invention has the above-mentioned configuration, the static pressure acting on the side wall of the impeller is as shown in FIG. 13
By making the slit area A _W larger than the cross-sectional area A _B of the balance pipe, the differential pressure before and after the wear ring (that is, the leakage flow) can be set small, and therefore the axial thrust can be adjusted to an arbitrary value under a certain suction pressure state. Can be set to a small value.

A _W = π×D _W ×ε＞ π/4×D _B ² = A _B ……(2) Here, D _W is the wear ring diameter, ε is the wear ring radius clearance, and D _B is the balance pipe diameter. It is.

If the specified axial thrust cannot be obtained with the above configuration alone, the height ratio t/s of the back blade can be changed, or the diameter of the back wear ring can be set to a different value from the diameter of the front wear ring. However, these are all within the scope of this invention.

Next, we will discuss the characteristics due to changes in pump operating conditions.
FIG. 6 shows the change in the static pressure ratio at the impeller outlet of this pump depending on the discharge amount. Normally, the flow at the impeller outlet becomes smaller on the small discharge side, and the absolute flow velocity increases, so the reaction rate, that is, the ratio of the static pressure at the impeller outlet to the total pressure, becomes smaller, and the flow loss inside the casing decreases due to the flow loss inside the casing. The ratio of the static pressure at the impeller outlet to the total head increases on the large discharge volume side.
It is close to 1.0 and decreases to about 0.7 on the small discharge amount side. Although the values shown in FIG. 6 are specific to this pump, this tendency of change in the impeller outlet static pressure ratio depending on the discharge amount can be applied to almost all pumps.

Therefore, the difference between the discharge pipe static pressure and the impeller outlet static pressure is small on the large discharge amount side, as shown in Figure 7.
It is large on the small discharge amount side. Between the static pressure at the impeller outlet and the static pressure at the wear ring, there is a relationship expressed by equation (3), which is related to the swirling speed of the fluid between them. The static pressure of the wear ring portion decreases by a substantially constant value from the static pressure at the impeller outlet, and as a result, the differential pressure before and after the balance tube increases on the small discharge amount side.

P _W = P ₀ −ρ/2 (ω×β) ² [r ₀ ² −r _W ² ] ...(3) Here, P _W is the static pressure at the wear ring, P ₀ is the static pressure at the impeller outlet, ω is the swirling angular velocity of the impeller, β is the swirling angular velocity ratio of the fluid to the impeller, ρ is the density of water, r ₀ is the outer diameter of the impeller, and r _W is the radius of the wear ring.

On the other hand, in reverse circulation drills, as the excavation depth increases, the length of the pump discharge pipe also increases, which increases the flow resistance associated with discharging muddy water, and shifts the pump operating point toward the small discharge volume side. Therefore, both the pump suction pressure and the differential pressure acting on the balance pipe increase with excavation depth, but generally the area of the balance chamber is sufficiently wider than the shaft cross-sectional area of the shaft seal, so
Thrust T _P due to suction pressure and thrust T _B2 acting on the balance chamber due to a slight change in the balance pipe differential pressure
is balanced.

FIG. 8a shows an embodiment of a fresh water submersible pump according to the present invention, in which a wear ring 8 is provided on the front side wall 1a and the back side wall 1b of the impeller 1 to seal leakage flow, and a boss on the back side of the impeller 1 is provided. A pressure balance pipe 16 is provided on the opposite casing wall 7 in the vicinity of the pump discharge pipe, which is connected to the pump discharge pipe.
Normal submersible pumps are not used by continuously changing the water depth, but when comparing deep piping conditions and shallow piping conditions, the discharge resistance is approximately proportional to the length of the piping. Therefore, the same effect as described in FIG. 5a can be obtained. Note that when there is no back blade on the impeller side wall, the influence of leakage flow on the swirling speed of the fluid appears strongly, and when the direction of the leakage flow is different between the front side wall side and the front side wall side, the swirling angular velocity of the fluid increases. Since the ratio β is significantly different on both sides, the axial thrust from the back side to the front side of the impeller increases as shown in FIG. 8b. Therefore, even in the case of a submersible pump for fresh water, it is desirable to provide a back blade on the back side of the impeller depending on the usage conditions.

As explained above, according to the present invention, a pressure balance pipe is provided near the rear boss portion of the impeller that connects the opposing casing wall and the pump discharge pipe. The pressure also changes, and changes in axial thrust due to suction pressure can be easily reduced. It is particularly effective for submersible pumps for reverse circulation drilling equipment, where the suction pressure constantly changes significantly and the pump operating point moves toward a lower discharge amount side in response.

In addition, in the present invention, the balance chamber and the pump discharge pipe are directly connected by a pressure balance pipe, and the area of the radial slit in the wear ring on the back of the impeller is larger than the cross-sectional area of the balance pipe. The water flowing into the balance chamber from the pump discharge pipe through the balance pipe flows into the impeller outlet through the back of the impeller, so the following functions and effects can be obtained. . In other words, by setting appropriate values for the cross-sectional area of the balance tube and the area of the wear ring slit at the time of design, it is possible to balance the thrust force acting on the impeller. Since there is no need for a structure that moves the shaft or impeller in the axial direction, the device can not only be simplified, but also
A stable submersible pump without axial vibration can be obtained. In addition, since the water in the balance chamber is configured to flow to the impeller outlet, the differential pressure between the pump discharge side and the impeller outlet is small, so only a small amount of water flows to balance the thrust force, resulting in pump efficiency. is also improved compared to the conventional one. Furthermore, since the slit area of the wear ring is larger than the cross-sectional area of the balance tube, the flow rate of water for thrust balance is determined by the cross-sectional area of the balance tube, and therefore the flow rate of balance water does not need to be increased. Since the area of the wear ring slit can be increased, the pressure acting on the balance chamber can be reduced, and the axial thrust can be set to an arbitrarily small value.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional submersible pump, Figure 2a
is an enlarged sectional view of the pump part in Figure 1, Figure 2b is a pressure distribution diagram of the pump in Figure 2a, Figure 3 is a diagram showing thrust changes due to changes in suction pressure of the submersible pump,
Fig. 4 is a diagram of a reverse circulation drill device, Fig. 5a is a sectional view of a pump according to the present invention;
Figure 5b is a pressure distribution diagram of the pump in Figure 5a,
7 is a diagram illustrating the change in static pressure at the impeller outlet with the discharge amount, FIG. 7 is a diagram illustrating the operating points of a submersible pump for a reverse circulation drill, and FIG. FIG. 8b is a sectional view of the pump, and FIG. 8b is a pressure distribution diagram of the pump shown in FIG. 8a. 1... Impeller, 4... Dry motor, 7... Casing, 8, 13... Wear ring, 15... Back blade, 16... Balance tube.

Claims (1)

[Claims] 1. In a submersible pump driven by a dry motor and having an impeller having a rear side wall rotatably supported by a casing, a cylindrical member extending in the axial direction is formed on the rear side wall of the impeller, and a cylindrical member extending in the axial direction is formed on the rear side wall of the impeller, and A wear ring is provided in the casing so as to form a narrow gap in the casing, and the wear ring, the impeller, the casing, and a shaft sealing part seals the gap between the casing and the rotating shaft. A balance chamber is formed, and a pressure balance pipe is provided to connect the balance chamber and the pump discharge pipe, and the radial slit area of the wear ring portion is larger than the cross-sectional area of the balance pipe. A submersible pump characterized by comprising: