JPH0518468A - Mechanical seal for recirculation pump - Google Patents

Abstract

(57) [Abstract] [Purpose] The water pressure acting on the rotary ring and static link of the mechanical seal is reduced, heat generation due to sliding of the pump shaft is reduced, deformation due to heat generation and water pressure is mitigated, and leakage from the seal surface occurs. Prevent. [Constitution] The pump shaft 4 is covered with a shaft sleeve 9, a rotary ring 24 is attached to the lower part of the shaft sleeve 9, and the rotary ring 24 is sandwiched between the upper stationary ring 25 and the lower stationary ring 26 as an outer cylinder. It is provided at the bottom of 20a. A first stage seal chamber 22 and a second stage seal chamber 21 are formed in the outer cylinder 20a. Each of the seal chambers 21 and 22 is provided with springs 14 and 19 and first and second stage pressure reducing mechanisms 12 and 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical seal for a recirculation pump for circulating primary cooling water of a light water reactor.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional recirculation pump used in a light water nuclear reactor. In the drawing, reference numeral 1 is a casing, and an impeller 2 arranged in the casing 1.
Is rotated by a pump shaft 4 supported by an underwater bearing 3.

A labyrinth seal 6 and a mechanical seal 7 are provided in the casing shaft 5 penetrating portion of the pump shaft 4.
And a heat exchanger 8 are provided respectively, and these constitute a pump shaft shaft seal portion. Then, in the shaft seal portion of the pump shaft 4 when the recirculation pump is used, the cooling water flows along the outer periphery of the mechanical seal 7 in order to cool the mechanical seal 7, and circulates to the mechanical seal 7 via the heat exchanger 8 and the cooling water. Part of the labyrinth seal 6
It flows downward through the part to prevent leakage of recirculated water.

The mechanical seal has a cartridge structure as shown in FIG. That is, the mechanical seal includes a shaft sleeve 9 covering the outer peripheral surface of the pump shaft 4, a first-stage mechanical seal rotating ring 10, a first-stage mechanical seal stationary ring 11, a first-stage depressurizing mechanism 12, a shaft sleeve 9 and The first-stage U-cup 13 for sealing between the first-stage mechanical seal rotating ring 10, the first-stage spring 14 for contacting the rotating ring and the stationary ring of the first-stage mechanical seal, and the second-stage Mechanical seal rotary ring 15, second stage mechanical seal stationary ring 16, second stage decompression mechanism 17, second stage U-cup 18 for sealing between shaft sleeve 9 and second stage mechanical seal rotary ring 15. , Supports the second stage spring 19 for contacting the rotary ring of the second stage mechanical seal and the stationary ring and the rotary ring or stationary ring of the mechanical seal And a ring or the like. The mechanical seal rotating ring is fixed to the shaft sleeve 9, the mechanical seal stationary ring is fixed to the outer cylinder 20 serving as the cartridge body, and the shaft sleeve 9 is fixed to the pump shaft 4, so that rotation of the pump shaft 4 is prevented. Along with this, the contact surfaces of the rotating ring and the stationary ring slide, and sealing against rotation is performed on this sliding surface. The outer cylinder 20 is attached to the outer cylinder cover 27, and a cooling water flow path 28 is formed in the outer cylinder cover 27.

[0005]

In the conventional recirculation pump described above, the mechanical seal 7 seals the pump shaft 4 to prevent the reactor water from leaking. However, in the boiling water reactor, In this case, as shown in FIG. 4, the mechanical seal has a cartridge structure covered with an outer cylinder 20. That is, two stages of seal parts, which are a pair of a rotating ring and a fixed ring, are incorporated in the cartridge,
Cooling water with a water pressure of 70 kg / cm ² is 35 kg / cm ² by the decompression mechanism 12.
Is depressurized to enter the second-stage seal chamber 21, further depressurized to atmospheric pressure by the depressurization mechanism 17, and circulates to remove heat generated by sliding on the seal surfaces of the mechanical seal rotating ring and the stationary ring. ..

By the way, in the mechanical seal, the first-stage and second-stage mechanical seal rotating rings 10 and 15 are fixed to the pump shaft 4 through the shaft sleeve 9, and the first-stage and second-stage mechanical seal stationary rings 11 are provided. , 16 are fixed to the outer cylinder 20 of the cartridge, and the outer cylinder 20 is fixed to the pump casing 1. When the recirculation pump is used, the first-stage and second-stage mechanical seal rotating rings 10 and 15 rotate together with the pump shaft 4. The first and second stage mechanical seal rotating rings 10 and 15 and the stationary rings 11 and 16 slide on the sealing surfaces. If an excessive load is applied, the seal surface will be abnormally worn, or excessive heat will be generated, resulting in deformation due to heat generation or a large water pressure of 35 kg / cm ² , so deformation due to water pressure will cause leakage of the mechanical seal. ing.

Further, when the reactor is started up, the pump shaft 4 rises by about 2 to 3 mm as the output rises. Therefore, the seal surfaces of the shaft seal 9 and the mechanical seal rotary rings 10 and 15 of the first and second stages are excessively large. There is a problem that cracking occurs due to sliding heat generation due to the application of various loads.

The present invention has been made to solve the above problems, and reduces the water pressure acting on the rotary ring and the stationary ring of the mechanical seal, reduces the heat generation due to the sliding of the pump shaft, and deforms due to the heat generation or water pressure. It is an object of the present invention to provide a mechanical seal for a recirculation pump that can alleviate the above and prevent leakage from the sealing surface.

[0009]

According to the present invention, an impeller disposed in a pump casing is rotated by a pump shaft, and a labyrinth seal provided in a casing cover penetrating portion of the pump shaft and a labyrinth seal above the labyrinth seal. In a mechanical seal for a recirculation pump provided with first-stage and second-stage depressurization mechanisms, the pump shaft is covered with a shaft sleeve, and a lower end portion of an outer cylinder holding the first-stage and second-stage depressurization mechanisms. Is provided with a pair of stationary rings, and the rotating ring attached to the lower portion of the shaft sleeve is sandwiched between the pair of stationary rings to form a third-stage depressurizing mechanism.

[0010]

In the mechanical seal according to the present invention, the mechanical seal cooling water circulates around the outer periphery of the mechanical seal to remove the heat generated by the sliding of the seal surface by the drive of the recirculation pump. By providing two stages of sealing chambers provided with a pressure reducing mechanism and providing a third stage sealing mechanism, the pressure acting on the mechanical seal can be reduced.

The forces acting on the seal surfaces of the first and second stage rotating rings and the fixed ring are the pressure of the cooling water and the spring force. In the recirculation pump, the pressure of the cooling water is much higher than the spring force.Therefore, the pressure of the cooling water acting on the sealing surface is reduced to reduce the wear of the sealing surface and the sliding heat generation. The deformation can be mitigated, the mechanical deformation due to the pressure of the cooling water can be mitigated, and the leakage from the seal surface can be prevented. Further, since the force acting on the first-stage and second-stage U-cups is reduced, it is possible to reduce the frictional force generated by the friction between the first-stage and second-stage U-cups and the shaft sleeve, and the excessive force acting on the sealing surface is achieved. Load can be prevented, and leakage from the sealing surface due to abnormal wear can be prevented.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the mechanical seal for a recirculation pump according to the present invention will be described with reference to FIGS. In the figure, the same parts as those in FIG. 4 are designated by the same reference numerals.
Further, the mechanical seal according to the present embodiment is applied to the recirculation pump shown in FIG. 4, but is not limited to FIG.

In this embodiment, the mechanical seal basically has a cartridge structure as shown in FIG. 2 similarly to the conventional example shown in FIG. No. 1 in this cartridge
Stage and second stage rotating rings 10 and 15 and stationary rings 11 and 16
There are two one-to-one sealing parts, the first and second stage pressure reducing mechanisms 12 and 17, the third stage pressure reducing mechanism 23, the first and second stage rotating rings 10 and 15, and the fixed ring. First and second stage springs 14, 19 for contacting 11, 16 and first and second stages for sealing the shaft sleeve 9 and the first and second stage rotating rings 10, 15 U cups 13 and 18
Rings for supporting the first and second stage rotating rings 10 and 15 and the fixed rings 11 and 17 are provided. The first-stage and second-stage rotating rings 10 and 15 are attached to the pump shaft 4 via a shaft sleeve 9, and the fixed rings 11 and 16 are attached to a long outer cylinder 20a which serves as a cartridge body. When the recirculation pump is used, the first and second stage rotating rings 10 and 15 rotate together with the pump shaft 3, and the first and second stage fixed rings 11 and 16 have the cartridge main body on the pump casing cover 5. It is stationary because it is fixed. The reactor water seal is sealed at the sliding surfaces where the first and second stage rotating rings 10, 15 and the fixed rings 11, 16 are in contact. The third decompression mechanism 23 comprises a decompression rotary ring 24, an upper decompression stationary ring 25 and a lower decompression stationary ring 26. The outer cylinder 20a is attached to the outer cylinder cover 27, and a cooling water flow path is formed in the outer cylinder cover 28.

Next, the operation of this embodiment will be described.
At the pump shaft shaft seal part when using the recirculation pump,
As shown in FIG. 3, the cooling water flows on the outer periphery of the mechanical seal 7 to cool the mechanical seal 7, and circulates to the mechanical seal 7 via the heat exchanger 8.

The cooling water is branched from the control rod driving water system, and its water pressure is 70 kg / cm ² . Therefore, the outer cylinder 20
A water pressure of 70 kg / cm ² acts on the outer circumference of a.
The pressure is reduced to about 1/3 by three pressure reducing mechanisms 12, 17, and 23 attached to the. That is, the cooling water flows into the third pressure reducing mechanism 23 by the water pressure is depressurized from 70 kg / cm ² to about 40 kg / cm ² 1-stage seal chamber 22 which is provided in the lower portion of the outer cylinder 20a, then the first stage 20kg by decompression mechanism 12
The pressure is reduced to about / cm ² and flows into the second-stage seal chamber 21, and is further reduced to atmospheric pressure by the second-stage pressure reducing mechanism 17 and circulates around the mechanical seal.

Next, the operating state of the decompression device with respect to the rise of the pump shaft 4 due to the increase in the output at the time of starting the reactor will be described with reference to FIGS. FIG. 2 shows the state of the rotating ring 24 and the stationary rings 25, 26 before the pump shaft 4 is lifted. Before the pump shaft 4 is raised, the decompression rotary ring 24 is arranged in close contact with the lower decompression stationary ring 26, and maintains a gap of about 20 to 30 microns, and cooling water flows through this gap to reduce the pressure. Pump shaft 26
, The gap between the two is maintained at about 20 to 30 μm as before the pump shaft 4 was raised, and the pressure is reduced in the gap during this period.

In this way, the outer cylinder 20a of the cartridge is extended and lengthened below the first stage rotating ring 10 and the stationary ring 11 to provide the third pressure reducing mechanism 23 between the shaft sleeve 9 and the outer cylinder 20a. The first and second stage rotating rings 10,
The water pressure acting on 15 and the stationary ring 11, 16 can be reduced to about 20 kg / cm ^2, and it is possible to mitigate wear due to sliding of the seal surface, heat deformation due to sliding heat generation and mechanical deformation due to water pressure. Becomes Furthermore, since the force acting on each U-cup 13, 18 is reduced, the frictional force between the shaft sleeve 9 and the first-stage and second-stage U-cups 13, 18 accompanying the rise of the pump shaft 4 at reactor startup is Decreased, first stage and throw 2
The U-cups 13 and 18 of the step can slide easily, and
Stage and second stage rotating rings 10 and 15 and stationary rings 11 and 16
It is possible to prevent leakage from the sliding surface in contact with. In the above embodiment, the pressure reducing ability of each pressure reducing mechanism is 1
Although it is set to about / 3, the value is not limited to this value. Further, although the surface of the rotating ring 24 is flat, it may be formed in an uneven shape, and the surface may be hardened by coating or the like.

[0018]

According to the present invention, the hydraulic pressure acting on the mechanical seal is reduced to reduce abnormal wear of the pump shaft, thermal deformation due to sliding heat generation, mechanical deformation due to water pressure, and friction resistance of the packing. It is possible to prevent leakage from the sliding seal surface.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a mechanical seal for a recirculation pump according to the present invention.

FIG. 2 is a vertical sectional view for explaining the operation in FIG.

FIG. 3 is a vertical sectional view showing a recirculation pump for explaining a conventional example.

FIG. 4 is a vertical cross-sectional view showing a conventional mechanical seal for a recirculation pump.

[Explanation of symbols]

1 ... Casing, 2 ... Impeller, 3 ... Submersible bearing, 4 ... Pump shaft, 5 ... Casing cover, 6 ... Labyrinth seal, 7 ... Mechanical seal, 8 ... Heat exchanger, 9 ... Shaft sleeve, 10 ... First stage Rotating ring, 11 ... 1st stage fixed ring, 12 ... 1st stage decompression mechanism, 13 ... 1st stage U-cup,
14 ... 1st stage spring, 15 ... 2nd stage rotating ring, 16
... 2nd stage fixing ring, 17 ... 2nd stage decompression mechanism, 18 ... 2nd stage U-cup, 19 ... 2nd stage spring, 20, 20a ...
Outer cylinder, 21 ... Second-stage sealing chamber, 22 ... First-stage sealing chamber,
23 ... Third stage decompression mechanism, 24 ... Rotating ring, 25 ... Upper stationary ring, 26 ... Lower stationary ring, 27 ... Outer cylinder cover, 28 ... Cooling water flow path.

Claims (1)

Claim: What is claimed is: 1. An impeller arranged in a pump casing is rotated by a pump shaft, and a labyrinth seal provided in a casing cover penetrating portion of the pump shaft and a first part above the labyrinth seal. In a mechanical seal for a recirculation pump provided with a first-stage and a second-stage depressurization mechanism, a shaft sleeve is covered on the pump shaft, and a lower end portion of an outer cylinder holding the first-stage and second-stage depressurization mechanisms is provided. A recirculation pump, wherein a pair of stationary rings is provided, and a rotary ring attached to the lower portion of the shaft sleeve is sandwiched between the pair of stationary rings to form a third stage pressure reducing mechanism. Mechanical seal for.