The steam turbine electro-hydraulic servo valve G761-3005B is the core actuator of the steam turbine control system in a thermal power plant. Its performance is directly related to the load regulation accuracy, stability and safety of the unit. However, the servo valve is susceptible to anti-fuel oil contamination and jamming problems during long-term operation, resulting in control signal distortion, response hysteresis and even valve core jamming, which ultimately leads to serious consequences such as unit vibration, overspeed or shutdown. This paper systematically analyzes its failure mechanism from the two dimensions of anti-fuel oil contamination control and servo valve jam prevention, and proposes targeted strategies to improve the reliability of the servo valve under extreme working conditions.

1. Fire-Resistant oil contamination control: the basis for ensuring the long-term stable operation of the servo valve

1. Pollution sources and hazards

Although anti-fuel oil (such as phosphate-based hydraulic oil) has the characteristics of high flash point and low volatility, it may still be polluted due to the following reasons under high temperature, high pressure and frequent start-stop conditions:

Particle pollution: impurities in the system pipeline, bearing wear debris or aging particles of valve seals enter the servo valve G761-3005B with the oil, resulting in obstruction of the valve core movement.

Water pollution: Water vapor or condensed water in the air penetrates into the oil circuit, causing oil emulsification, reducing lubricity and accelerating the rust of metal parts.

Air pollution: Pipeline leakage or pump suction causes air to mix into the oil, forming bubbles, destroying the stability of the oil film, and aggravating the vibration and wear inside the valve body.

Chemical pollution: Long-term contact between fire-resistant oil and metal parts may produce chemical reactions, generate corrosive byproducts, or generate deposits such as colloid and paint film due to oil oxidation.

The accumulation of pollution will significantly shorten the life of the servo valve G761-3005B: particulate matter causes valve core scratches or jams; moisture and air cause seals to swell or harden; chemical pollution accelerates corrosion and clogging of the precision matching surfaces inside the valve body.

2. Pollution control strategy

(1) Source prevention

System cleanliness management: During the equipment installation stage, strictly clean the pipeline and oil tank to ensure that the oil passes through a high-precision filter device (such as an online oil filter) before entering the servo valve.

Sealing system optimization: Use oil-resistant and high-temperature resistant sealing materials (such as fluororubber or polytetrafluoroethylene), regularly check the sealing of connecting flanges and valve interfaces to prevent the intrusion of external impurities.

Oil quality monitoring: Regularly test the particle size, moisture content and acid value of the oil to ensure that it meets the ISO 4406 standard (such as particle size ≤16/13 level, moisture content ≤0.1%).

(2) Operation and maintenance measures

Graded filtration system: Set up a multi-stage oil filter at the outlet of the main oil pump and the inlet of the servo valve G761-3005B, using a “coarse filter + fine filter” combination to intercept impurities of different particle sizes. For example, the coarse filter intercepts particles larger than 5μm, and the fine filter filters to 1-3μm.

Oil regeneration technology: Remove moisture, gas and oxidation products from the oil through processes such as centrifugal separation, adsorbent purification or vacuum dehydration to restore its physical and chemical properties.

Regular replacement and oil replenishment: According to the operating time or pollution index, the oil replacement cycle is formulated, and the same batch and brand of fire-resistant oil are used when replenishing oil to avoid chemical reactions caused by differences in additive components.

(3) Online monitoring and early warning

Oil status monitoring: Install an oil spectrometer or iron spectrometer to monitor the composition and concentration of metal wear particles in real time, and predict abnormal wear inside the bearing or valve body.

Pressure and flow monitoring: Track the pressure fluctuations at the inlet of the servo valve through a pressure sensor. Abnormal pressure drop may indicate filter blockage or oil line contamination.

2. Prevention of servo valve jamming: Full-cycle management from design to operation and maintenance

1. Jamming mechanism and typical manifestations

The jamming of the servo valve G761-3005B is mostly caused by mechanical wear, oil performance degradation or thermal deformation, which is manifested as follows:

Valve core movement hysteresis: tiny particles are embedded in the gap between the valve core and the valve sleeve, resulting in a prolonged step signal response time.

Static friction increases: Oil contamination or temperature changes cause the lubricating film to fail, the friction coefficient between the valve core and the valve sleeve increases, and even “stuck” occurs.

Dynamic stability decreases: Stuck causes the valve core oscillation frequency to deviate from the design value, causing system pressure fluctuations or control signal distortion.

The direct consequences of stuck include unit load regulation lag and main steam valve failure. In severe cases, it may trigger the protection system to malfunction, resulting in unplanned shutdown.

2. Preventive measures and optimization solutions

(1) Design optimization

Material and structure improvement: The valve core and valve sleeve of the servo valve G761-3005B are made of high-hardness, low-friction coefficient materials (such as cemented carbide or nitrided steel) to improve wear resistance. Optimize the valve body flow channel design to reduce local pressure pulsation caused by sudden changes in oil flow rate and reduce vibration-induced micro-motion wear.

Redundant design: Key components (such as valve core springs) use a double spring structure to avoid single-point failure; set up a backup oil circuit or bypass channel to deal with flow interruptions caused by sudden stuck.

(2) Operation and maintenance management

Precision assembly and alignment: Use a laser alignment instrument to calibrate the coaxiality of the servo valve and the actuator during installation, and control the deviation within 0.01mm to avoid aggravated wear due to eccentric operation. Use a chipless assembly process to prevent metal debris from contaminating internal components.

Temperature and pressure control: Maintain the oil temperature in the range of 55-65℃ through the cooling system to avoid the decrease in oil viscosity and aging of seals caused by high temperature. Monitor system pressure fluctuations to avoid frequent impact of the valve core on the valve seat under overpressure or underpressure conditions.

(3) Status diagnosis and preventive maintenance

Vibration and noise analysis: Capture the vibration spectrum of the valve body through the acceleration sensor to identify abnormal high-frequency vibration (such as high-frequency noise caused by valve core jamming). Compare historical data, analyze the correlation between vibration amplitude and unit load, and locate potential fault points.

Regular disassembly and maintenance: Disassemble the servo valve G761-3005B every year for internal cleaning, replace wearing parts (such as O-rings, filters), and check the clearance between the valve core and the valve sleeve (it is recommended that the clearance be controlled within the range of 5-10μm). Use a microscope to observe the wear marks on the surface of the valve core and evaluate its remaining life.

The reliability of the turbine electro-hydraulic servo valve is the core element to ensure the safe operation of the unit. By strengthening the control of anti-fuel oil pollution and the prevention of jamming, the whole chain optimization from material selection, system design to operation and maintenance management can significantly extend the life of the servo valve and reduce the risk of unplanned downtime.

When looking for high-quality, reliable servo valves, 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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