JPS6017293A - Submersible pump - Google Patents

Abstract

PURPOSE:To reduce the variation of the axial thrust due to the suction pressure by varying the differential pressure in a pressure balance pipe for connecting a pump discharge pipe with a casing wall opposed in the vicinity of the back-surface boss part of a vane wheel, in correspondence with the variation of the suction pressure of a pump. CONSTITUTION:A pressure balance pipe 16 connected to a pump discharge pipe is installed onto a casing wall 7 opposed in the vicinity of the back-surface boss part of a vane wheel 1. Therefore, the static pressure acting onto the side wall of the vane wheel 1 is represented by the figure, and though the leak flow passing through the balance pipe 16 flows to the outlet side of the vane wheel 1 from the pump discharge pipe, the differential pressure between before and behind a weiring ring 13 (namely the leak flow) can be set small by setting the area of the narrow slit part of the weiring ring 13 larger than the sectional area of the balance pipe 16. Therefore, the axial thrust which is generated towards the front-surface side wall 1a from the back-surface side wall 1b side by the revolution of the vane wheel 1 can be set to an arbitrary small value.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to axial thrust reduction in submersible pumps driven in dry mode.

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 model 4. A shaft sealing portion 5 is provided in a portion of the rotating shaft 3 between the impeller 1 and the model 4, and the impeller 1
This prevents leakage flow from the outlet from entering the mode model 4. When the pressure in the shaft seal 5 increases,
The shaft seals are doubled and an oil chamber 6 is provided between the shaft seals 5 to prevent water leakage with oil.

The moldle 4 is isolated from the atmosphere by the shaft seal 5, but the pressure inside the moldle is usually about atmospheric pressure. On the other hand, the casing 7 is formed to cover the impeller 1, and the front side wall 1a of the impeller 1.

A wear ring 8 is attached to the opposite surface of the rear side wall 1b, forming an IPIII1 section 9 to seal leakage flow from the impeller outlet to the suction port 10.

Due to 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,
When the impeller 1 is rotated, it moves from the back side wall 1b side to the front side 1i.
An axial thrust T occurs toward 1i 1 a. This axial thrust T corresponds to the pressure in the shaded area in Figure 2'(b), and depends on the pressure distribution on the front and back sides of the five impeller I, the momentum of the flowing water passing through the impeller 1, the suction pressure at the suction port, etc. Change. here.

T is the thrust acting on the front side of the impeller, Tg is the thrust 1 acting on the back side of the impeller, Tp is the thrust due to the suction pressure of the flowing water, and 1゛□ 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 absorbs this thrust, which requires the bearing and shaft to be larger. As shown in Figure 2 (,), a balance hole 12 is provided near the boss on the r side of the impeller 1 to reduce the pressure near the boss on the back side of the impeller to about the suction pressure, and to TM) and the thrust TB2 acting on the side wall of the balance chamber 14 on the smaller diameter side than the rear wear ring 13.

However, when the suction pressure changes depending on the usage conditions, such as in a submersible pump, the amount of change in thrust 1゛2 due to the change in suction pressure becomes extremely large as shown in Figure 2 (b), and the impeller A reverse thrust may occur from the front side wall 1a side toward the rear side wall 1b. For example, in a submersible pump type reverse circulation drilling device used for civil engineering foundation work, as shown in FIG. 4, an ice pump 22 is disposed above a drill bit 21 that excavates the ground, and discharges excavated earth and sand to the ground. In this case, the submersible pump changes its position depending on the excavation depth, but the excavation depth is 10
Since the distance exceeds 0 m, the change in pump suction pressure exceeds 10 kg/cJ. On the other hand, since the pressure inside the motor is atmospheric regardless of the excavation depth, the balance of pressure acting on the rotor at the shaft seal is lost, resulting in the equation (
]) A thrust is generated.

'rP=plIX-D"llF... (1)
Here, P9 is the suction gauge pressure, and DIIF is the shaft diameter of the shaft seal portion.

The submersible pump used in the reverse circulation drilling equipment mentioned above has a maximum axial thrust of 400 k
g, the change due to the discharge amount is about 200 kg, while the change in the axial thrust due to the change in suction pressure is about 8
00 kg.

Changes in shaft thrust due to suction pressure are caused by unbalanced pressure in the shaft seal, so change the mode from a dry mode to an oil-filled mode and pressurize from the ground according to the suction pressure, or use a hydraulic mode. However, in the case of an oil-filled model, auxiliary equipment for oil filling is required, and in the case of a hydraulic model, if the excavation depth becomes deep, the flow of hydraulic oil in the oil supply and drain pipes may occur. This has the drawback of significantly reducing model efficiency due to increased loss.

This invention reduces the change in the axial thrust caused by the change in the pump suction pressure, and is achieved by providing a pressure balance pipe that connects the pump discharge pipe and the opposing casing wall near the rear boss of the impeller. .

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

FIG. 5(a) shows an embodiment of a submersible pump used in a reverse circulation drilling device, in which the front side wall 1a and the back side wall 1b of the impeller 1 have static pressure iq on the impeller side wall.
A and a back blade 15 are provided to prevent the intrusion of earth and sand, and the back side of the impeller 1! lb is provided with a wear ring 13 to seal leakage flow, and a pressure balance pipe 16 connected to the pump discharge pipe is provided on the casing wall 7 facing the vicinity of the rear boss portion of the impeller. Since this invention has the above-mentioned configuration, the static pressure acting on the side wall of the impeller is as shown in FIG. The slit area AV of the ring ring 13 is the cross-sectional area A of the balance tube. By making it wider, the differential pressure (that is, the leakage flow) before and after the wear ring can be set small, and therefore the axial thrust can be set to an arbitrarily small value in a certain suction pressure state.

Aw ” x X Dw X E) X DB'
=Ag (2) where Dw is the diameter of the wear ring, ε is the radial clearance of the wear ring, and Dn is the diameter of the balance tube.

In addition, if the specified axial thrust cannot be obtained with the above configuration alone, it is possible to change the height ratio t/s of the back blade or by setting the back wear ring diameter to a different value from the front wear ring diameter. , the objectives can be achieved, but all of these are 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 a wooden pump depending on the discharge amount. Normally, on the negative side of the impeller outlet, the outflow angle becomes smaller 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 impeller mountain mouth static pressure to the total head is close to 1.0 on the large discharge side, and decreases to about 0.7 on the small discharge negative side. Although the 6th value is a unique value for this pump, this tendency of change in the single-blade table outlet static pressure ratio depending on the discharge shell can be applied to almost all pumps.

Therefore, the difference between the discharge pipe static pressure and the blade protrusion static pressure is small on the large discharge claw side, as shown in FIG.

It is large on the side with a small discharge amount. 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 at the wear ring section decreases by approximately 2 constant values from the static pressure at the vane level, and as a result, the differential pressure before and after the balance tube becomes larger on the side of the small discharge member.

P w = P g ((+1 Xβ)” [ro' r
w2)... (3) Here, PW is the static pressure of the wear ring, P.

is the impeller outlet static pressure, 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, ro is the impeller outer diameter, and rw is the wear ring radius.

On the other hand, in a reverse circulation drill, the length of the pump discharge pipe increases as the excavation depth increases, so the flow resistance associated with discharging muddy water increases and the pump operating point shifts to the side with fewer dischargers. Therefore, both the pump suction pressure and the differential pressure acting on the balance pipe increase with excavation depth, but the area of the balance chamber is generally much larger than the shaft cross-sectional area of the shaft seal.

With a slight change in the balance tube differential pressure, the thrust TP caused by the suction pressure and the thrust T, 2 acting on the balance chamber are balanced.

FIG. 8(a) shows an embodiment of a fresh water submersible pump according to the present invention, in which wear rings 8 are provided on the front side wall 1a and the back side wall 1b of the impeller 1 to seal the flow. A pressure balance pipe 1 connected to the pump discharge pipe is installed on the casing wall 7 facing the vicinity of the rear boss of the impeller.
6 is provided. 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, exactly the same effect as described in FIG. 5(a) of MS5 can be obtained.

In addition, when there is no back blade on the side wall of a single impeller, 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 back side wall side, the swirling of the fluid becomes Since the angular velocity 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. 8(b).

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. In particular, it is very effective for submersible pumps for reverse circulation drilling equipment, where the suction pressure always changes significantly and the pump operating point shifts toward the side with a smaller discharge capacity.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional submersible pump, Figure 2 (a) is an enlarged cross-sectional view of the pump part in Figure 1, and Figure 2 (b) is a pressure distribution diagram of the pump in Figure 2 (a). Fig. 3 is a diagram showing thrust changes due to changes in suction pressure of a submersible pump, Fig. 4 is a diagram of a reverse circulation drill device, Fig. 5(a) is a cross-sectional view of the pump according to the present invention, and Fig. 5(b) is shown in Figure 5 (
Fig. 6 is a diagram illustrating the change in the static pressure at the impeller outlet with the discharge amount; Fig. 7 is a diagram illustrating the operating points of the submersible pump for reverse circulation drill; FIG. 8(a) is a sectional view of another pump according to the present invention, and FIG. 8(b) is f! A pressure distribution diagram of the pump shown in Figure S8 (,). 1... Impeller, 4... Dry model, 7... Casing. 8.13...wearing ring, 15...back blade, 16...balance tube. X 1 Zuatsu 3 (2)

Claims (1)

[Claims] In an ice pump that is driven by a dry mode and has an impeller with a rear side wall rotatably supported by a casing,
A submersible pump characterized in that a wear ring is provided on a rear side wall of an impeller, and a pressure balance pipe is provided that connects a casing wall on the inner diameter side of the wear ring and a pump discharge pipe.