The steam turbine fire-resistant oil system is the core link to ensure the adjustment accuracy and safety of the unit. As a key power equipment, the outlet pressure stability of the circulating pump F3-V10-1S6S-1C20L directly affects the control performance of the EH oil system. When the outlet pressure fluctuates, it may cause problems such as delayed action of the turbine valve and load fluctuation.

I. Mechanical structure factors

1. Internal wear and clearance change of the pump body

The circulating pump F3-V10-1S6S-1C20L adopts a plunger structure. After long-term operation, the matching clearance between the plunger and the cylinder body may expand due to wear. When the clearance exceeds the design value (usually ≤10μm), the high-pressure oil will leak through the clearance, resulting in a decrease in volumetric efficiency. Experimental data show that for every 1μm increase in the clearance, the outlet pressure fluctuation amplitude may increase by 3%-5%. In addition, the wear of the distribution plate will lead to uneven oil distribution, further exacerbating the pressure pulsation.

2. Coupling alignment deviation

The installation alignment of the motor and the circulating pump shaft directly affects the transmission stability. If the radial deviation of the coupling exceeds 0.05mm/m or the angular deviation exceeds 0.1°, the pump shaft will oscillate periodically. The actual measurement case of a power plant shows that when the deviation is 0.08mm/m, the pressure fluctuation frequency is synchronized with the base frequency of the speed (such as 1500rpm corresponds to 25Hz), and the fluctuation amplitude can reach ±0.5MPa.

II. Influence of oil characteristics

1. Anti-fuel oil contamination and bubble problem

When the density of EH oil is 4%, its viscosity is about 32cSt (40℃). If particulate matter or water (water content>0.1%) is mixed in the oil, the flow characteristics will be significantly changed. For example, when particles larger than 5μm are stuck in the valve core gap, it may cause an instantaneous flow mutation; and water will reduce the compressibility of the oil and cause pressure oscillation.

2. Bubble precipitation and cavitation effect

When the local pressure of the system is lower than the saturated vapor pressure of the oil, the air dissolved in the oil will precipitate to form bubbles. When these bubbles collapse in the high-pressure area, they produce microjets that impact the inner surface of the circulating pump body, which is called cavitation. Cavitation not only causes noise and vibration, but also causes the pump’s flow output to fluctuate periodically. Studies have shown that when the oil temperature exceeds 60°C, the risk of cavitation increases by more than 30%.

III. System design and operation issues

1. Insufficient pipeline resonance and damping

If the natural frequency of the outlet pipeline of the circulating pump F3-V10-1S6S-1C20L coincides with the pressure pulsation frequency, resonance will occur. For example, after the transformation of a unit, the pipeline length increased from 3m to 5m, and its natural frequency dropped from 120Hz to 75Hz, which is close to the 25Hz fundamental frequency harmonic (3 times the frequency) of the pump, resulting in a 2-fold increase in the pressure fluctuation amplitude. Installing an accumulator or adjusting the pipeline support can effectively suppress such problems.

2. Filter blockage and bypass opening

When the return oil filter of the EH oil system is blocked, the pressure difference exceeds 0.35MPa, which triggers the bypass valve to open, and the unfiltered oil directly enters the pump inlet. Pollutants (such as metal debris and aging particles of seals) will accelerate the internal wear of the circulation pump, forming a vicious cycle of “blockage-bypass-increased pollution”. Statistics show that about 40% of pressure fluctuation failures are related to untimely filter maintenance.

IV. Operation and maintenance factors

1. Frequent start and stop and sudden load changes

The circulation pump F3-V10-1S6S-1C20L needs to overcome the inertia of the oil at the moment of starting. If the motor acceleration curve is too steep (such as 0-rated speed time <2s), it will cause the outlet pressure to overshoot. Tests on a 600MW unit show that after the start time is adjusted from 1.5s to 3s, the pressure overshoot drops from 1.8MPa to 0.6MPa.

2. Aging and leakage of seals

After the shaft seal or flange seal ring ages, external air may be sucked into the pump inlet. A gas mixture of 1% volume fraction can reduce the effective flow rate by 5%-8%. Regularly replace fluororubber seals (recommended cycle 2 years) and use helium mass spectrometry to detect leaks, which can control the leakage rate within 1×10⁻⁶ mL/s.

V. Solutions and optimization suggestions

1. Real-time monitoring and early warning: Install vibration sensors and pressure transmitters, and identify cavitation or mechanical failure characteristic frequencies through FFT analysis.

2. Fine management of oil quality: Keep NAS 1638 grade ≤5, water content <0.05%, and test acid value every month.

3. Structural improvement: Use tungsten carbide coating for severely worn plunger-cylinder pairs, increase hardness to HRC70, and extend life by more than 3 times.

4. System damping optimization: Install a pulsation damper at the pump outlet to reduce the pressure fluctuation amplitude by 60%-80%.

The outlet pressure fluctuation of the circulating pump F3-V10-1S6S-1C20L is the result of the coupling of multiple factors such as mechanical wear, oil degradation, system resonance, etc. Through refined maintenance, real-time monitoring and targeted transformation, the pressure fluctuation can be controlled within ±0.2MPa, significantly improving the reliability of the turbine regulation system.

When looking for high-quality, reliable oil 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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bladder with seal kit NXQ-A-10/10-L-Y
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