JP2003184781A - Centrifugal pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal pump having improved pump efficiency and suction properties whereof the impeller has both a main plate and a side plate or only the main plate by restricting leak quantity from impeller liner parts. <P>SOLUTION: In this centrifugal pump whereof the impeller 2 has both the main plate 2b and the side plate 2d or only the main plate 2b, a fixed side inner circumferential surface and a rotational side outer circumferential surface of the liner parts 2c, 2e as leak restriction parts of the impeller 2 are constituted of throttle mechanisms 4a, 4b that can contact with each other. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugal pump in which an impeller has a main plate and side plates, or has only a main plate, and limits the amount of leakage from the impeller liner portion to improve pump efficiency and suction performance. The present invention relates to a centrifugal pump having improved performance.

[0002]

2. Description of the Related Art FIG. 7 is a view showing a general structure of a centrifugal pump, and FIG. 8 is an enlarged view of an impeller liner portion of FIG. As shown in FIG. 7, an impeller 2 is arranged inside the pump casing 1, and a casing cover 3 is fixed to an opening portion of the pump casing 1 on the high pressure side. One end of the rotor 5 is inserted into the casing cover 3, and the impeller 2 and the shaft sleeve 8 a are fixed to the one end of the rotor 5 via bolts 21.
Near the center of the rotor 5, bearings 9a and 9b that support loads including axial thrust, radial thrust, and self-weight acting on the rotor 5 are arranged. These bearings 9a and 9b
Are arranged in the bearing casing 15. The bearing casing 15 rotatably supports the rotor 5 via bearings 9a and 9b.

In order to limit the amount of high-pressure pumped liquid that has passed through the impeller 2 from the balance hole 2a of the impeller 2 to the impeller inlet, as shown in FIG.
The outer peripheral surface of the liner portion 2c of the main plate 2b and the inner peripheral surface 3a of the casing cover 3 form a throttle mechanism 4a in which a radial gap b1 is secured. Similarly, in order to limit the amount of return to the inlet of the impeller 2, a diaphragm mechanism that secures a radial gap b2 between the outer peripheral surface of the liner portion 2e of the side plate 2d of the impeller 2 and the inner peripheral surface 1a of the casing 1. 4b is formed. A mechanical seal 17 is attached to the inner circumference of the casing cover 3 in order to minimize the amount of the pump handling liquid leaking from the high pressure side of the pump casing 1 to the atmosphere side.

In such a centrifugal pump, a part of the pumped liquid whose pressure has passed after passing through the impeller flows back to the suction part which is a low pressure part. That is, a part of the pumped liquid that has been pressurized is discharged from the outlet of the impeller 2 between the main plate 2b of the impeller 2 and the casing cover 3, the throttle mechanism 4a, the balance hole chamber A.
Inside, it passes through the balance hole 2a and returns to the entrance of the impeller 2. The amount of leakage that flows back is Q1. Also,
Similarly, a part of the pressurized pump handling liquid after passing through the impeller passes from the outlet of the impeller 2 between the side plate 2 d of the impeller 2 and the casing 1 and the throttling mechanism 4 b to the inlet of the impeller 2. Reflux to. The amount of leaked back current is designated as Q2.

The leakage amounts Q1 and Q2 do not flow out from the pump discharge port but only recirculate inside the pump, and do not perform effective work. Therefore, there is a power loss enough to recirculate these leak amounts, and the pump efficiency is reduced. In a specific centrifugal pump, the greater the leakage amount Q1 or Q2, the more remarkable the decrease in pump efficiency.

Further, the leakage amount Q1 that has passed through the balance hole 2a becomes a reverse flow component with respect to the normal inflow at the inlet of the impeller 2. In addition, the leakage amount Q that has passed through the throttle mechanism 4b
2 is an orthogonal component with respect to the normal inflow at the inlet of the impeller 2. Both the leakage amounts Q1 and Q2 disturb the normal inflow at the inlet of the impeller 2, so that the suction performance decreases. In a specific centrifugal pump, the suction performance is more significantly reduced as the leakage amounts Q1 and Q2 increase.

Therefore, the radial gaps b1 and b2 may be made small in order to suppress the deterioration of the pump efficiency and the suction performance to a minimum, but these radial gaps are made to prevent mutual contact and galling. There is a minimum value. The minimum value of the radial gaps b1 and b2 is generally about 0.2% of d1 and d2 when the liner diameters d1 and d2 are 100 mm or less, and about 0.15% when the liner diameters d1 and d2 are 100 to 150 mm.
It is about 0.12% at 0 to 200 mm, and about 0.1% when it exceeds 200 mm.

Further, in order to reduce the radial gaps b1 and b2, the inner peripheral surface 3a of the casing cover 3 and the inner peripheral surface 1a of the pump casing 1 have good slidability such as fluororesin (Teflon (registered trademark)). There is a system in which an annular ring is arranged to limit the amount of leakage. With this method, when the ring is new,
Although it has the effect of limiting the amount of leakage, the fluororesin (Teflon (registered trademark)) is worn or deformed with the elapsed time of operation, and eventually the radial gaps b1 and b2 become large, so the amount of leakage increases. .

[0009]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and in a centrifugal pump in which the impeller has a main plate and side plates, or has only the main plate, the impeller liner section is used. An object of the present invention is to provide a centrifugal pump that limits the amount of leakage and improves pump efficiency and suction performance.

[0010]

In order to achieve the above-mentioned object, the present invention is an impeller leakage amount limiting part in a centrifugal pump in which an impeller has a main plate and side plates, or has only a main plate. The fixed-side inner peripheral surface and the rotating-side outer peripheral surface of the liner portion are constituted by a diaphragm mechanism that can contact each other. Further, the present invention, the impeller has a main plate and a side plate, or, in a canned motor pump having only the main plate, the fixed-side inner peripheral surface and the rotation-side outer peripheral surface of the liner portion which is the leakage limiting portion of the impeller, It is characterized in that it is composed of a diaphragm mechanism that can contact each other.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing the structure of a centrifugal pump according to the first embodiment of the present invention, and FIG. 2 is an enlarged view of the impeller liner portion of FIG. Except for the impeller liner portion, it has the same structure as the conventional example shown in FIG. The same or corresponding parts as those of the conventional example are designated by the same reference numerals, and the duplicated description thereof will be omitted.

As shown in FIG. 1, an impeller 2 is arranged inside the pump casing 1, and a casing cover 3 is provided at the high pressure side opening of the pump casing 1.
Is stuck. One end of the rotor 5 is inserted into the casing cover 3, and the impeller 2 and the shaft sleeve 8 a are fixed to the one end of the rotor 5 via bolts 21. Near the center of the rotor 5, bearings 9a and 9b that support a load including axial thrust, radial thrust, and self-weight acting on the rotor 5 are arranged.
9 b is arranged in the bearing casing 15. The bearing casing 15 is connected to the rotor 5 via the bearings 9a and 9b.
Is rotatably supported.

A mechanical seal 17 is provided on the inner circumference of the casing cover 3 in order to minimize the amount of the pump handling liquid leaking from the high pressure side of the pump casing 1 to the atmosphere side.
I am wearing.

As shown in FIG. 2, the rotary ring 18a is housed in the case 19a and fixed to the outer circumferential surface of the liner portion 2c of the main plate 2b of the impeller 2, and the inner circumference of the casing cover 3 facing the rotary ring 18a is fixed. A fixed ring 20a is fixed to the surface to form a diaphragm mechanism 4a that can contact each other. Further, the rotary ring 18b is housed and fixed to the outer peripheral surface of the liner portion 2e of the side plate 2d of the impeller 2 in the case 19b, and the fixed ring 20b is provided on the inner peripheral surface of the pump casing 1 facing the rotary ring 18b. The diaphragm mechanism 4b is fixedly formed so as to be in contact with each other. The material of the fixed rings 20a and 20b is a hard material such as ceramics,
The materials of the rotating rings 18a and 18b are, for example, hard and porous ceramics. That is, when the inner peripheral surfaces of the fixed rings 20a and 20b contact the outer peripheral surfaces of the rotary rings 18a and 18b, the outer peripheral surfaces of the rotary rings 18a and 18b are worn and scraped.

Here, a method of determining the radial clearances b1 and b2 will be described. During the operation of the centrifugal pump, a radial thrust acts on the impeller 2, so that the rotor 5 bends about the bearings 9a and 9b as fulcrums as shown in FIG. It becomes the maximum deflection point. For a particular centrifugal pump, the maximum deflection is proportional to the magnitude of this radial thrust. This maximum deflection amount is obtained by calculation, and is the same as the deflection amount of the rotor 5, the radial clearance b
1 and b2. That is, the radial gaps b1 and b2
Is determined to be the same value as the maximum deflection amount of the rotor 5.

The smaller the radial gaps b1 and b2 are, the smaller the leak amounts Q1 and Q2 can be, so that the pump efficiency and the suction performance can be improved. For that purpose, it is necessary to reduce the radial thrust and the maximum deflection amount. As a means for reducing the radial thrust, there is a method of vertically installing a centrifugal pump. By doing this, the weight of the rotating parts is equal to
Since it acts in the axial direction, the thrust in the radial direction can be reduced. Further, by changing the deceleration shape of the pump casing 1 from the single volute type to the double volute type or the diffuser type, the radial thrust in the single volute type is reduced to about 25.
It can be reduced to%. As a means for reducing the maximum amount of deflection, the rotor 5 may be made of a material having a large longitudinal elastic modulus E,
It is effective to increase the shaft diameter of the rotor 5. This is because the amount of deflection of the rotor 5 is inversely proportional to the product EI of its longitudinal elastic coefficient E and the second moment of area I.

With this structure, pump efficiency and suction performance can be improved as compared with the conventional centrifugal pump. The reason will be described in detail below. The flow rate Q flowing through a cylindrical gap having no groove such as the throttle mechanisms 4a and 4b shown in FIG. 2 can be calculated using the formula described in the Mechanical Engineering Handbook edited by the Japan Society of Mechanical Engineers. According to it, Q = C × A × (2 × g × ΔH) ^1/2 ... Equation 1 where C: flow coefficient A: area of gap g: gravitational acceleration ΔH: differential pressure.

From the same handbook, the flow rate coefficient C is C = 1 / {λ × L / (2 × b) +1.5} ^1/2 ## EQU2 ## where λ: friction coefficient L: clearance Length b: Radial gap.

The friction coefficient λ is a function of the Reynolds number Re of the liquid flowing in the gap and can be calculated by the following equation. Re = u × d / ν Formula 3 where u is the flow velocity in the gap, d is the diameter of the gap, v is the kinematic viscosity.

Among the variables of equations 1 to 3, gravitational acceleration g
Is a constant, the length L of the gap, the radius gap b and the diameter d of the gap portion are constants if the pump is specified, and the area A of the gap can be calculated from the diameter d of the gap portion and the radius gap b, The kinematic viscosity ν is a constant if the liquid handled by the pump is specified. However, the remaining variables, flow velocity in the gap u, friction coefficient λ, differential pressure Δ
H cannot be specified. If the flow velocity u in the gap is known, the Reynolds number Re can be calculated, the friction coefficient λ can be obtained from the Moody diagram, and the flow coefficient C can be calculated. Then, if the differential pressure ΔH is known, the flow rate Q can be calculated.

Therefore, in order to calculate the flow rate Q, the centrifugal pump shown in FIG.
The pressure of each part was measured while operating at a pole of 50 Hz. FIG. 8 is a diagram showing variable names for measuring the flow rate of the throttle mechanism in the centrifugal pump shown in FIG. As shown in FIG. 8, the specifications of this pump are the outer diameter of the impeller D2 = 198 mm.
(See FIG. 7), the diameter d1 of the diaphragm mechanism 4a is 92 mm, the length L1 of the gap is 12 mm, and the radial gap b1 is 0.25 m.
m, diameter of diaphragm mechanism 4b d2 = 92 mm, length of gap L
2 = 12 mm and the radial gap b2 = 0.25 mm. The maximum deflection of the impeller 2 is about 0.15mm.
Is. From the result of the pressure measurement, the differential pressure of each part at the highest efficiency point is ΔH1 = 22.5 m in the throttle mechanism 4a part,
In the diaphragm mechanism 4b portion, ΔH2 = 27 m.

Here, assuming the flow rate Q0, the flow velocity u in the gap is calculated, and the Reynolds number Re is obtained. From the obtained Reynolds number Re, the friction coefficient λ is read on the Moody diagram, the flow coefficient C is calculated, and the flow rate Q is calculated by using the differential pressure obtained from the result of the pressure measurement. Then, this flow rate Q is compared with the assumed flow rate Q0, and if different, the flow rate Q0 is replaced with the flow rate Q, recalculation is performed, and repeated calculation is performed until both agree. The exact flow coefficient C is determined when both match.

When only the liner portion of the conventional example is changed to the structure of the present invention and calculated by the above-mentioned calculation formula, the leakage amount Q1 to the impeller back surface at the highest efficiency point is about 65 L in the conventional example.
(Liter) / min (minute), which is about 3 in the present invention.
It is 6 L (liter) / min (minute). Further, the leakage amount Q2 to the impeller inlet at the highest efficiency point is about 71 L (liter) / min (minute) in the conventional example, but is about 40 L (liter) / min (minute) in the present invention. Therefore, according to the present invention, it is possible to reduce the leakage amount Q1 to the impeller back surface and the leakage amount Q2 to the impeller inlet.

FIG. 4 is a view showing the structure of the centrifugal pump according to the second embodiment of the present invention. In FIG. 4, the impeller 2 includes
There is a main plate 2b, but there is no side plate 2d. Other configurations are the same as those shown in FIG. In this embodiment, only the leakage amount Q1 to the impeller back surface can be reduced.

FIG. 5 is a view showing the structure of a canned motor pump according to the third embodiment of the present invention, and FIG. 6 is an enlarged view of the impeller liner portion of FIG. The liner portion of the impeller 2 is shown in FIG.
It has the same configuration as the liner section shown in FIG. However, in this pump, as shown in FIG. 5, the motor rotor 10 is
Since the rotor 5 is fixed to the rotor 5 by welding or the like, even if the shaft diameter of the rotor 5 is substantially the same as that of the rotor 5 of the centrifugal pump as compared with the centrifugal pump, the rotor rotor 10 has a motor rotor 10 as much as that of the centrifugal pump. The second moment of area I increases. That is, as compared with the centrifugal pump, the maximum deflection amount can be reduced and the radial gaps b1 and b2 can be reduced, so that the leakage amounts Q1 and Q2 can be further reduced as compared with the first embodiment.

Next, the overall structure of the canned motor pump shown in FIG. 5 will be briefly described. An impeller 2 is arranged inside the pump casing 1 of the pump section, and
A casing cover 3 is fixed to the high-pressure side opening of the pump casing 1. One end of the rotor 5 is inserted into the inside of the casing cover 3, and the distance piece 6, the thrust plate 7 a, the shaft sleeve 8 a and the impeller 2 fitted to the rotor 5 are attached to the bolt 2 at one end of the rotor 5.
It is fixed through 1. On the other hand, on the other end of the rotor 5, the thrust plate 7b and the shaft sleeve 8b are attached to the bolt 22.
Is fixed through.

Inside the casing cover 3, a part of the pump handling liquid whose pressure is increased by the impeller 2 is stored in the bearing 9a.
The through hole 3b leading to the portion is provided. The rotor 5 is rotatably supported on both sides of the rotor 5 via a pair of bearings 9a and 9b. The rotor 10 of the motor unit is fixed to the substantially central portion of the rotor 5. A flow path is formed between the can 12 a of the rotor 10 and the can 12 b of the stator 13. A through hole 14 penetrating in the axial direction is formed inside the rotor 5, and the through hole 14 is open at both sides including the bolts 21 and 22 at both ends. The space between the end cover 11 and the bearing 9b on the opposite side of the impeller and the suction side of the pump communicate with each other through the through hole 14.

[0028]

As described above, according to the present invention,
By providing the throttle mechanism that can contact each other, the amount of leakage to the back face of the impeller and the amount of leakage to the inlet of the impeller can be reduced, so that the power for circulating them can be reduced and the pump efficiency can be improved. Also, since the amount of leakage to the back of the impeller can be reduced, the flow velocity that returns to the impeller inlet through the balance hole is reduced, and the amount of leakage to the impeller inlet can be reduced. The flow velocity returning to the impeller decreases, and the backflow component and the orthogonal component decrease with respect to the flow velocity flowing from the suction port to the impeller inlet, so that the suction performance can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a centrifugal pump according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of the impeller liner portion of FIG.

FIG. 3 is a simplified diagram illustrating deflection of a rotor.

FIG. 4 is a sectional view showing a centrifugal pump according to a second embodiment of the present invention.

FIG. 5 is a sectional view showing a canned motor pump according to a third embodiment of the present invention.

FIG. 6 is an enlarged view of the impeller liner portion of FIG.

FIG. 7 is a cross-sectional view showing a conventional centrifugal pump.

8 is an enlarged view of the impeller liner portion of FIG. 7.

[Explanation of symbols]

1 pump casing 2 impeller 3 casing cover 5 rotor 6 distance pieces 7a, 7b Thrust plate 8a, 8b shaft sleeve 9a, 9b bearing 10 rotor 11 End cover 12a, 12b can 13 Stator 14 through holes 15 Bearing casing 17 Mechanical seal 18a, 18b rotating ring 19a, 19b case 20a, 20b fixed ring 21,22 volts

Claims (2)

[Claims] 1. In a centrifugal pump in which an impeller has a main plate and side plates, or has only a main plate, the fixed side inner peripheral surface and the rotating side outer peripheral surface of a liner portion, which is a leakage limiting portion of the impeller, are mutually A centrifugal pump characterized by comprising a throttle mechanism capable of contacting with. 2. A canned motor pump in which an impeller has a main plate and side plates, or has only a main plate, wherein a fixed inner peripheral surface and a rotating outer peripheral surface of a liner portion that is a leakage limiting portion of the impeller are provided. A canned motor pump comprising a throttle mechanism that can contact each other.