As the core equipment of the condenser vacuum system of the power plant, the 2S-185A two-stage water ring vacuum pump has a direct impact on the unit efficiency and energy consumption performance due to its operational stability. However, pump shaft wear is one of the most common failures of this type of equipment, often leading to unplanned downtime, a surge in maintenance costs, and a shortened equipment life. This article analyzes the structural characteristics, wear mechanism, and management strategy to provide a systematic solution for power plant engineers.

I. Structural characteristics of the pump shaft 2S-185A and challenges of the working environment

1.1 Unique structure of the two-stage water ring pump

The 2S-185A vacuum pump adopts a two-stage series impeller design to achieve a higher vacuum degree through two-stage compression (the ultimate vacuum can reach 2.7kPa). Its pump shaft needs to drive two-stage impellers at the same time and bear composite loads:

• Radial alternating load: The eccentric installation of the impeller (eccentricity is about 4-6mm) causes the water ring to have periodic resistance to the blades, and the measured single-stage radial force can reach 200-300N;
• Axial thrust: The gas pressure gradient generated by the two-stage compression forms an axial thrust, and the single-stage axial force range is about 500-800N;
• Vibration load: When the impeller is scaled or the dynamic balance fails, the imbalance exceeds the ISO1940 G2.5 standard (≤0.5g·mm/kg), and the vibration speed can exceed the 4.5mm/s threshold.

1.2 Key stress areas of the pump shaft 2S-185A

Measurement data of a power plant dismantling case show (Figure 1) that pump shaft wear is concentrated in the following areas: Bearing mating surface, Impeller keyway, Shaft shoulder transition section.

II. Analysis of the deep mechanism of pump shaft wear

2.1 Coupling effect of metal fatigue and micro-motion wear

Fatigue wear: Under the action of alternating stress, the maximum shear stress on the 2S-185A shaft surface can reach the yield strength of the material; Crack initiation cycle: When the stress amplitude Δσ>200MPa, the crack initiation life is less than 10⁶ cycles (corresponding to a running time of about 3 months).

Micro-motion wear: The slight sliding of the inner ring of the bearing and the shaft causes oxidative wear. The analysis of the wear debris composition shows that Fe₃O₄ accounts for more than 60%; in one case, when the contact pressure of the mating surface dropped from the design value of 80MPa to 45MPa, the wear rate increased by 3 times.

2.2 Chain reaction of lubrication failure

Statistics of multiple faulty pumps show that 60% of wear is directly related to lubrication abnormalities:

a) Grease film rupture: When the bearing temperature is >90℃, the consistency of lithium-based grease drops from NLGI level 2 to level 1, and the grease film thickness decreases from 25μm to 10μm;

b) Pollutant intrusion: Water vapor penetration causes the grease acid value to increase (>1.5mgKOH/g), accelerating oxidation and gelation;

c) Improper relubrication interval: After exceeding the manufacturer’s recommended cycle (usually 2000-3000h), the wear volume increases exponentially.

III. Key influencing factors and quantitative evaluation

3.1 Amplification of material and process defects

a) Case comparison:

A plant pump shaft (40Cr quenching and tempering treatment, surface roughness Ra0.4μm): average life 48000h;

B plant pump shaft (45 steel normalizing treatment, Ra1.6μm): life only 22000h, wear rate increased by 1.8 times.

b) Metallographic analysis:

For shafts that do not meet the HRC28-32 hardness requirements, the surface martensite content is <70%, and the wear resistance decreases by 40%; when the thickness of the nitride layer is insufficient (<0.2mm), the contact fatigue life is shortened to 1/3 of the standard value.

3.2 Hidden hazards of installation errors

a) Impact of centering deviation: When the coupling offset is >0.05mm, the additional bending moment increases the shaft deflection by 15%; the axial force generated by the angle deviation of 1° can reach 20% of the design load.

b) Bearing clearance control: The axial clearance of double-row tapered roller bearings should be controlled at 0.08-0.15mm. Too tight (<0.05mm) will cause excessive temperature rise, and too loose (>0.2mm) will cause impact load.

The wear of the 2S-185A pump shaft is essentially the result of the combined effects of the mechanical environment, material properties and operation and maintenance management. By quantitatively analyzing the wear mechanism and establishing a preventive maintenance system, the life of the pump shaft can be significantly extended. It is recommended that power plants establish a closed-loop management process that includes design review, condition monitoring, and standardized operations to reduce the unplanned downtime rate to below 0.5% and achieve a leap in equipment reliability.

When looking for high-quality, reliable vacuum pumps, YOYIK is undoubtedly a choice worth considering. The company specializes in providing a variety of power equipment including steam turbine accessories, and has won wide acclaim for its high-quality products and services. For more information or inquiries, please contact the customer service below:

E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229

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