Servo valve SM4-20(15)57-80/40-10-H607H is the core control element of the steam turbine digital electro-hydraulic control system (DEH). Its precise valve core-valve sleeve matching clearance is usually only micrometer level (about 3-5μm). As the working medium, the cleanliness of fire-resistant oil directly affects the dynamic response, control accuracy and life of the servo valve. If there are solid particle contaminants (such as metal chips, oxides, fibers, etc.) in the oil, it may cause the following problems:

1. 1. Valve core erosion and wear: Hard particles impact the valve core surface under the drive of high-pressure oil flow, resulting in blunting of throttling edges and scratches on the sealing surface, causing increased leakage and decreased pressure gain.
2. 2. Dynamic response failure: Tiny particles block the nozzle baffle or valve core movement clearance, causing jamming, lag or even complete jamming.
3. 3. Electrochemical corrosion: If the resistivity of the oil decreases (such as water or acidic degradation products in the fire-resistant oil), it may accelerate the electrochemical corrosion of the metal parts of the servo valve.

I. Case Analysis: Analysis of the Cause of Short-term Failure of a Servo Valve in a Power Plant

Failure phenomenon: A newly purchased SM4-20(15)57-80/40-10-H607H servo valve in a power plant failed after only two days of operation after installation. Disassembly revealed obvious scratches and wear marks on the valve core surface.

Root cause analysis:

1. New oil contamination was not treated

New fire-resistant oil may carry NAS7-8 level contaminants when leaving the factory, while the servo valve SM4-20(15)57-80/40-10-H607H requires the oil cleanliness to reach NAS5 level or below. The power plant did not perform 24-72 hour circulation flushing of the new oil according to the specifications, nor did it use a high-precision oil filter (such as a 3-5μm filter element) to filter it, resulting in hard particles such as metal oxides directly entering the servo valve.

2. Residual pollution from system installation

The welding slag left over from pipeline welding and the metal debris mixed in during the installation process were not completely removed. These pollutants form a “micro-cutting” effect under high-pressure oil flow (usually 14-21MPa), quickly wearing out the valve core surface.

3. Filtration system failure

The clogged filter element may not be replaced in time on site (such as failure to monitor the filter pressure difference alarm), or the magnetic filter is not configured to absorb ferromagnetic particles, resulting in continuous entry of particles into the servo valve.

II. Key maintenance recommendations

For the SM4-20(15)57-80/40-10-H607H servo valve, the following measures must be taken to ensure oil cleanliness:

1. New oil handling specifications

Before injecting new oil, it must be flushed through a 5μm filter element until the oil particle size meets the standard (NAS level 5 or below).

When the oil tank filling volume exceeds 10%, a special flushing plate must be used to isolate the servo valve to prevent pollutants from directly impacting the valve body.

2. Online filtration and regeneration

Configure a two-stage filtration system: a 10μm metal filter in the front to intercept large particles, and a 1-3μm precision filter in the rear to protect the servo valve.

A silicon-aluminum regeneration device is used to adsorb acidic degradation products, maintain resistivity>5×10^9Ω·cm, and prevent electrochemical corrosion.

3. Operation monitoring measures

Monthly test the particle size, acid value, moisture and resistivity of fire-resistant oil, and focus on monitoring the number of particles with a particle size of 5-15μm.

Regularly check the magnetic filter and clean the adsorbed iron filings (recommended once a quarter).

Through the study of actual cases, we can find that the early wear failure of the servo valve SM4-20(15)57-80/40-10-H607H is directly related to the lack of oil cleanliness management. By standardizing the new oil processing process (such as the missing flushing step in the case), strengthening online filtration and regular monitoring, the life of the servo valve can be effectively extended to more than 5 years. For high-precision hydraulic systems, fire-resistant oil cleanliness management should be regarded as a core maintenance project that is equally important as equipment maintenance.

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

Yoyik offers various types of spare parts for steam turbines, generators, boilers in power plants:
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Coil R901175657 AS 30703
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