A method for accurate positioning and adjustment of mechanical seals

Abstract

This invention relates to the field of nuclear power plant maintenance technology, and particularly to a method for accurately positioning and adjusting a mechanical seal. The method involves: conducting a preliminary analysis of the cause of leakage in the pump's mechanical seal; determining that the leakage is caused by a mismatch between the pump rotor's axial centering and the mechanical seal's positioning position; proceeding to the next steps; completely disassembling the pump or replacing the mechanical seal, and axially centering the pump rotor; measuring the total and partial rotor misalignment before installing the mechanical seal, adjusting the thickness of the rotor centering adjustment ring, and placing the pump rotor at the zero point; performing accurate positioning adjustment of the mechanical seal, checking the deviation between the mechanical seal positioning plate and the positioning groove, determining the rotor's deviation, and measuring the deviation using a dial indicator; adjusting the thickness of the mechanical seal's half-ring according to the measured deviation, and adjusting the mechanical seal's moving ring to the correct designed working position. This invention can identify the cause of mechanical seal leakage and improve the operational reliability of the pump's mechanical seal.

Description

Technical Field

[0001] This invention relates to the field of nuclear power plant maintenance technology, and in particular to a method for accurately positioning and adjusting a mechanical seal. Background Technology

[0002] The mechanical seal of the main feedwater pump in nuclear power plants frequently experiences excessive leakage. The mechanical seal used in the main feedwater pump is model SAFV1 / 147-E1-A1. This type of mechanical seal features a spiral pumping ring structure on the rotating sealing ring. During seal rotation, the coolant circulates internally, transferring heat from the seal cavity to the closed-loop cooling water via a heat exchanger, thus cooling the seal face. Two filters are installed to remove impurities from the medium, protecting the seal.

[0003] The accurate positioning of a mechanical seal is achieved by aligning the mechanical seal positioning plate with the mechanical seal positioning groove. When the mechanical seal is in the correct operating position, the positioning plate should be able to be inserted into the positioning groove, and the dynamic and stationary rings should be in their standard design operating positions. To ensure accurate mechanical seal installation and positioning, the positioning plate is typically removed from the positioning groove last, after pump assembly, to ensure the dynamic and stationary rings are in their correct design positions and achieve optimal sealing performance.

[0004] However, in the actual operation of nuclear power plants, faults such as excessive leakage and failure often occur due to the mismatch between the rotor centering and the mechanical seal positioning dimensions, resulting in mechanical seal positioning deviation. Currently, the operating nuclear power units have experienced multiple failures of excessive leakage in the main feedwater pump mechanical seal, which seriously affects the safe and reliable operation of the equipment. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for accurately positioning and adjusting a mechanical seal, analyze and confirm the cause of mechanical seal leakage, and improve the operational reliability of the pump mechanical seal by adjusting the relative positions of the dynamic and static rings of the mechanical seal.

[0006] This invention provides a method for accurately positioning and adjusting a mechanical seal, comprising the following steps:

[0007] Step 1: Conduct a preliminary analysis of the cause of leakage in the pump's mechanical seal;

[0008] After analysis, the cause of the leakage is determined. If the cause of the leakage is determined to be the positioning deviation between the pump rotor and the mechanical seal, then proceed with the next steps.

[0009] Step 2: After completely disassembling the pump or replacing the mechanical seal, perform axial centering of the pump rotor;

[0010] Step 3: Determine the zero point position of the pump rotor;

[0011] If the bearing housing cover is not installed, install the main thrust bearing block centering adjustment ring and thrust disc and lock them.

[0012] Set up a dial indicator on the thrust plate end face, push the pump rotor toward the drive end, so that the pump rotor is at the zero point position, and record the initial reading A1 of the dial indicator;

[0013] Step 4: Accurately position and adjust the mechanical seal;

[0014] When the pump rotor is at the zero position, check whether the mechanical seal positioning plate is aligned with the positioning groove on the mechanical seal bushing.

[0015] If there is a deviation, determine the direction of the rotor deviation and use a dial indicator to measure the amount of deviation.

[0016] Adjust the thickness of the mechanical seal's half retaining ring according to the measured deviation, and adjust the mechanical seal's moving ring to the correct design working position.

[0017] Preferably, in step one, the cause of leakage is determined by the water film thickness, the sealing water temperature at the driving end and the non-driving end, and the friction power of the mechanical seal.

[0018] If the water film on the non-drive end mechanical seal becomes thinner, the frictional power increases, which is reflected in the rising temperature of the sealing water. In this case, the cause of the leak is determined to be that the pump rotor is biased towards the non-drive end. If the water film on the non-drive end mechanical seal becomes thicker, the frictional power decreases, which is reflected in the falling temperature of the sealing water. In this case, the cause of the leak is determined to be that the pump rotor is biased towards the drive end.

[0019] Preferably, in step two, the method for axially centering the pump rotor is as follows:

[0020] Before installing the mechanical seal, measure the total and partial rotor movement, and adjust the thickness of the centering ring to ensure the pump rotor is in the middle position.

[0021] Preferably, in step four, the method for measuring the deviation is as follows:

[0022] If the rotor is biased towards the drive end, push the pump rotor towards the non-drive end until the mechanical seal positioning plate is aligned with the positioning groove, read the dial gauge reading A2, and calculate the deviation value (A2-A1).

[0023] If the rotor is biased towards the non-drive end, push the pump rotor towards the drive end until the mechanical seal positioning plate is aligned with the positioning groove, read the dial gauge reading A2, and calculate the deviation value (A1-A2).

[0024] Preferably, in step four, the method for increasing or decreasing the thickness of the mechanical seal half-ring is as follows:

[0025] For non-drive end mechanical seals, if the rotor is biased towards the drive end, the thickness of the half retaining ring of the non-drive end mechanical seal is reduced accordingly, with a reduction value of A2-A1; if the rotor is biased towards the non-drive end, the thickness of the half retaining ring of the mechanical seal is increased accordingly, with an increase value of A1-A2.

[0026] For the drive-end mechanical seal, if the rotor is biased towards the drive end, the thickness of the half retaining ring of the drive mechanical seal is increased accordingly, with an increase value of A2-A1; if the rotor is biased towards the non-drive end, the thickness of the half retaining ring of the mechanical seal is decreased accordingly, with a decrease value of A1-A2.

[0027] Compared with the prior art, the mechanical seal accurate positioning and adjustment method of the present invention first analyzes the relationship between mechanical seal leakage, water film thickness, water film stiffness, sealing water temperature and friction power to find the root cause of excessive leakage at both ends of the mechanical seal. Adjusting the relative position of the pump rotor and the mechanical seal can ensure that the mechanical seal is positioned in the correct design working position when the pump unit is running, and can ensure that the mechanical seal is in the best condition during operation, avoiding the mechanical seal leakage failure. Attached Figure Description

[0028] Figure 1 This graph shows the temperature variation trend of the sealing water at both the drive and non-drive ends. Detailed Implementation

[0029] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0030] An embodiment of the present invention discloses a method for accurately positioning and adjusting a mechanical seal, comprising the following steps:

[0031] Step 1: Conduct a preliminary analysis of the cause of leakage in the pump's mechanical seal. After analysis, determine the cause of the leakage. If the cause of the leakage is determined to be a positioning misalignment between the pump rotor and the mechanical seal, proceed with the subsequent steps.

[0032] Step 2: After completely disassembling the pump or replacing the mechanical seal, perform axial centering of the pump rotor;

[0033] Step 3: Determine the zero point position of the pump rotor;

[0034] If the bearing housing cover is not installed, install the main thrust bearing block centering adjustment ring and thrust disc and lock them.

[0035] Set up a dial indicator on the thrust plate end face, push the pump rotor toward the drive end, so that the pump rotor is at the zero point position, and record the initial reading A1 of the dial indicator;

[0036] Step 4: Accurately position and adjust the mechanical seal;

[0037] When the pump rotor is at the zero position, check whether the mechanical seal positioning plate is aligned with the positioning groove on the mechanical seal bushing.

[0038] If there is a deviation, determine the direction of the rotor deviation and use a dial indicator to measure the amount of deviation.

[0039] Adjust the thickness of the mechanical seal's half retaining ring according to the measured deviation, and adjust the mechanical seal's moving ring to the correct design working position.

[0040] According to the present invention, when the mechanical seal of the pump leaks, a preliminary analysis is conducted from aspects such as the correct positioning of the mechanical seal, the relationship between the leakage amount of the mechanical seal and the thickness of the water film, as well as the sealing water temperature at the drive end and the non-drive end and the friction power of the mechanical seal.

[0041] Research and analysis have revealed that when the pump axial centering is not appropriate, the thickness of the centering adjustment ring in front of the thrust plate needs to be increased or decreased to achieve the purpose of axial centering of the pump rotor. If the accurate positioning of the mechanical seal on the non-drive end is not taken into account when adjusting the axial centering of the pump rotor, the moving ring may deviate from the design position and become biased towards the drive end. In this case, the mechanical seal positioning plate will no longer be able to be inserted into the positioning groove, which may easily lead to the mechanical seal deviating from the design position after maintenance. This will result in insufficient rigidity of the sealing water film of the non-drive end mechanical seal, causing an increase in the water film thickness and thus a larger leakage.

[0042] Besides leakage along the gap between the sealing surfaces, mechanical seal leakage can also be caused by other factors such as damage or deformation of the auxiliary sealing ring, or gaps formed by excessively rough surfaces of the parts in contact with it. However, these factors can be relatively easily eliminated. The leakage of mechanical seals mainly occurs through the gap between the dynamic ring and the stationary ring.

[0043] Assuming the mechanical seal end face is perfectly flat, the formula for leakage rate of fluid flowing laminarly along the radial annular gap is derived from the simplified Navier-Stokes equations:

[0044]

[0045]

[0046] Where: Q - mechanical seal leakage; d m - Average diameter of the sealing end face; ho - Liquid film thickness; p1 - Medium pressure; p2 - External pressure; b - Width of the sealing surface; η - Dynamic viscosity of the liquid film; A - Area of ​​the sealing end face; W - Friction power; v - Average linear velocity of the sealing surface.

[0047] As can be seen from the calculation formulas (1) and (2), when the thickness of the sealing water film increases, the leakage will gradually increase; when the thickness of the water film decreases, the friction power of the mechanical seal will increase, which can cause the temperature of the sealing water in the mechanical seal chamber to rise.

[0048] If the accurate positioning of the non-drive end mechanical seal is not taken into account when adjusting the axial centering of the pump rotor, the dynamic ring may deviate from the design position. This can cause the dynamic ring of the non-drive end mechanical seal to be biased towards the drive end relative to the mechanical seal positioning plate, resulting in a thicker water film on the non-drive end mechanical seal and thus causing excessive leakage.

[0049] If the mechanical seal deviates from its design position due to axial splitting, the sealing water film thickness at one end of the mechanical seal will increase, while the sealing water film at the other end will become thinner. A thicker water film will result in greater leakage, while a thinner film will increase friction power. This increase in friction power will be reflected in the temperature change of the sealing water in the sealing chamber. By analyzing the temperature change trend of the sealing water in the sealing chamber, it can be found that the temperature of the mechanical seal water at the driving end is always higher than that at the non-driving end. The temperature trend graph is shown below. Figure 1 As shown.

[0050] The mechanical seal water flow rate, shaft seal cooler cooling water flow rate, sealing water filter flow area, and jacket cooling water flow rate are designed to be exactly the same for both the drive end and the non-drive end. Under the same mechanical seal water flow rate, shaft seal cooler cooling water flow rate, sealing water filter flow area, and jacket cooling water flow rate, the sealing water temperature reflects the mechanical seal friction power.

[0051] Depend on Figure 1 It is known that the sealing water temperature at the drive end is consistently higher than that at the non-drive end, indicating that under the same external conditions, the frictional power of the mechanical seal at the drive end is higher than that at the non-drive end. The water film thickness at the drive end mechanical seal is relatively thinner than that at the non-drive end, objectively proving that the pump rotor's position relative to the mechanical seal positioning plate is biased towards the drive end. It is precisely because the pump rotor is biased towards the drive end that the water film thickness at the non-drive end mechanical seal is thicker, thus causing excessive leakage at the non-drive end mechanical seal.

[0052] Therefore, based on the above analysis, if the water film on the non-drive end mechanical seal becomes thinner, increasing frictional power and resulting in a higher sealing water temperature, the leak is determined to be caused by the pump rotor being biased towards the non-drive end. Conversely, if the water film on the non-drive end mechanical seal becomes thicker, decreasing frictional power and resulting in a lower sealing water temperature, the leak is determined to be caused by the pump rotor being biased towards the drive end. Based on the identified leak causes, the pump should be completely disassembled or the mechanical seal replaced, and the pump rotor should be axially centered. When axially centered, it is crucial to ensure the accurate positioning of the mechanical seal to guarantee that it is in its standard design position during pump operation, thus preventing the recurrence of excessive mechanical seal leakage.

[0053] The specific adjustment steps are as follows:

[0054] Before installing the mechanical seal, measure the total and partial rotor movement, adjust the thickness of the centering ring, and ensure that the pump rotor is in the axial center position to ensure accurate centering of the pump rotor.

[0055] With the bearing housing cover not installed, install and lock the main thrust bearing centering adjustment ring and thrust disc. Do not install the auxiliary bearing in this step. Place a dial indicator on the thrust disc end face and push the pump rotor towards the drive end, bringing the pump rotor to the zero position.

[0056] The zero point position is: push the pump rotor towards the drive end so that the thrust disc is in close contact with the main thrust bearing;

[0057] Check whether the mechanical seal positioning plate is aligned with the positioning groove on the mechanical seal bushing; specifically including:

[0058] Insert an endoscope from the bearing cover to the mechanical seal positioning plate, and use the endoscope to check whether the mechanical seal positioning plate is aligned with the positioning groove on the mechanical seal bushing.

[0059] If there is a deviation, determine the direction of the rotor deviation and use a dial indicator to measure the amount of deviation.

[0060] The method for determining the deviation is as follows:

[0061] If the rotor is biased towards the drive end, push the pump rotor towards the non-drive end until the mechanical seal positioning plate is aligned with the positioning groove, read the dial gauge reading A2, and calculate the deviation value (A2-A1).

[0062] If the rotor is biased towards the non-drive end, first remove the main thrust bearing, then push the pump rotor towards the drive end until the mechanical seal positioning plate is aligned with the positioning groove, read the dial gauge reading A2, and calculate the deviation value (A1-A2).

[0063] Adjust the thickness of the mechanical seal's half retaining ring according to the measured deviation to adjust the mechanical seal to the correct design working position.

[0064] The method for increasing or decreasing the thickness of the mechanical seal's split retaining ring is as follows:

[0065] For the adjustment of the non-drive end mechanical seal, if the rotor is biased towards the drive end, the thickness of the half retaining ring of the non-drive end mechanical seal should be reduced accordingly, with a reduction value of A2-A1; if the rotor is biased towards the non-drive end, the thickness of the half retaining ring of the mechanical seal should be increased accordingly, with an increase value of A1-A2.

[0066] For adjusting the mechanical seal on the drive end, if the rotor is biased towards the drive end, the thickness of the half retaining ring of the mechanical seal on the drive end should be increased accordingly, with an increase value of A2-A1; if the rotor is biased towards the non-drive end, the thickness of the half retaining ring of the mechanical seal should be decreased accordingly, with a decrease value of A1-A2.

[0067] Using this method, which involves axially centering the pump rotor while ensuring the accurate positioning of the mechanical seal, can guarantee that the mechanical seal is positioned in the correct design working position during pump operation. This ensures that the mechanical seal is in optimal condition during operation and avoids leakage failures.

[0068] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0069] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of accurately positioning adjustment of a mechanical seal, characterized by, It comprises the following steps: Step 1: preliminary analysis of the leakage cause of the mechanical seal of the pump; The leakage cause is determined by judging the water film thickness, the sealing water temperature of the driving end and the non-driving end and the friction power of the mechanical seal; If the water film of the non-driving end mechanical seal becomes thinner, the friction power increases, and the sealing water temperature rises, it is determined that the leakage cause is that the pump rotor is inclined to the non-driving end; if the water film of the non-driving end mechanical seal becomes thicker, the friction power decreases, and the sealing water temperature decreases, it is determined that the leakage cause is that the pump rotor is inclined to the driving end; After analysis, if it is determined that the leakage cause is that the pump rotor is deviated from the mechanical seal positioning, the subsequent steps are executed; Step 2: after the pump is disassembled or the mechanical seal is replaced, the pump rotor is axially centered; Step 3: the zero position of the pump rotor is determined; In the case that the bearing chamber cover is not installed, the main thrust pad centering adjusting ring and the thrust disc are installed and locked; The pump rotor is pushed to the driving end, so that the pump rotor is in the zero position, and the initial reading A1 of the dial gauge is recorded; Step 4: accurate positioning adjustment of the mechanical seal; When the pump rotor is in the zero position, it is checked whether the mechanical seal positioning plate is aligned with the positioning groove on the mechanical seal shaft sleeve; If there is deviation, the rotor inclination is determined, and the deviation amount is measured by using the dial gauge; According to the measured deviation amount, the thickness of the mechanical seal half clamp ring is increased or decreased, and the mechanical seal moving ring is adjusted to the correct design working position; The method for increasing or decreasing the thickness of the mechanical seal half clamp ring is as follows: For the non-driving end mechanical seal, if the rotor is inclined to the driving end, the thickness of the non-driving end mechanical seal half clamp ring is correspondingly reduced, and the reduction value is A2-A1; if the rotor is inclined to the non-driving end, the thickness of the mechanical seal half clamp ring is correspondingly increased, and the increase value is A1-A2. For the driving end mechanical seal, if the rotor is inclined to the driving end, the thickness of the driving mechanical seal half clamp ring is correspondingly increased, and the increase value is A2-A1; if the rotor is inclined to the non-driving end, the thickness of the mechanical seal half clamp ring is correspondingly reduced, and the reduction value is A1-A2.

2. The mechanical seal accurate positioning adjustment method according to claim 1, characterized by, In step 2, the method for axially centering the pump rotor is as follows: Before installing the mechanical seal, the total runout and half runout of the rotor are measured, and the thickness of the centering adjusting ring is adjusted, so that the pump rotor is in the middle position.

3. The mechanical seal accurate positioning adjustment method of claim 1, wherein, In step 4, the method for measuring the deviation amount is as follows: If the rotor is inclined to the driving end, the pump rotor is pushed to the non-driving end until the mechanical seal positioning plate is directly opposite the positioning groove, the reading A2 of the dial gauge is read, and the deviation amount A2-A1 is calculated; If the rotor is inclined to the non-driving end, the pump rotor is pushed to the driving end until the mechanical seal positioning plate is directly opposite the positioning groove, the reading A2 of the dial gauge is read, and the deviation amount A1-A2 is calculated.

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