The wear of the sealing surface of the pneumatic stop valve is a common problem that affects the sealing performance and service life of the valve. The underlying causes are usually related to mechanical friction, medium erosion, operating conditions, and improper maintenance. The following is an analysis of the specific reasons and additional explanations: 

1. Medium factors 

Particulate matter erosion: 

If the medium contains solid particles (such as sand grains, dust, crystalline substances, etc.), during the valve opening and closing process, these particles will repeatedly rub against the sealing surface like sandpaper, causing surface scratches, grooves or deformation. For example, in scenarios such as mine drainage and chemical raw material transportation, this type of wear is particularly noticeable. 

Corrosive medium: 

Strong acids, strong bases or chlorine-containing media can corrode the sealing surface materials, reducing their hardness and accelerating wear. For instance, stainless steel sealing surfaces may suffer from pitting corrosion in a hydrochloric acid environment, while rubber sealing rings may expand and deform in high-temperature oils. 

Corrosion phenomenon: 

When the flow velocity of the medium is too high or the pressure drops suddenly, cavitation (air erosion) may occur, forming tiny bubbles that burst instantly, generating shock waves, which can cause surface pitting or peeling on the sealing surface. 

2. Mechanical Friction and Stress 

Frequent opening and closing: 

The pneumatic stop valve operates by the movement of the valve disc driven by the cylinder. If the opening and closing frequency is too high (as in an automated control system), the sealing surfaces will suffer fatigue wear due to repeated contact. For instance, a valve that is opened and closed dozens of times per hour may have a sealing surface wear rate that is several times faster than that of a valve with a lower frequency of operation. 

Insufficient preload: 

When the preload force (sealing pressure) between the valve disc and the valve seat is insufficient, the medium pressure may cause the valve disc to undergo a slight displacement, resulting in poor contact between the sealing surfaces in some areas, creating a leakage channel and accelerating wear. 

Installation deviation: 

If the valve stem and the center line of the valve seat are not aligned during valve installation, it will cause the valve disc to tilt, resulting in uneven force on the sealing surface on one side and causing uneven wear. For instance, stress in the pipeline or an uneven connection of the flange may lead to such problems. 

3. Material and Structural Defects 

The hardness of the sealing surface material is low: 

If the sealing surface material (such as soft sealing rubber or hard sealing alloy) has insufficient hardness or does not match the medium, it is prone to being scratched by particles. For instance, rubber sealing rings may harden and crack at high temperatures, while carbon steel sealing surfaces may undergo sulfidation corrosion in sulfur-containing media. 

Unreasonable structural design: 

Improper contact angle between the valve disc and the valve seat, surface roughness or flow channel design may cause turbulence of the medium or local high pressure, which can aggravate wear. For instance, right-angle valve discs are more prone to stress concentration compared to rounded-corner valve discs. 

4. Improper operation and maintenance 

Illegal operation: 

If the valve is opened or closed forcefully before the medium is completely drained or the pressure is released, it may cause impact damage to the sealing surface. For instance, when a high-temperature steam valve is opened under pressure, the valve disc may get stuck due to thermal expansion, and forced operation may scratch the sealing surface. 

Maintenance deficiency: 

Failure to replace worn-out seals for a long time, failure to remove impurities from the medium, or failure to lubricate the valve stem regularly will all accelerate the aging of the sealing surfaces. For instance, an air actuator lacking oil may cause the valve stem to become stuck during movement, thereby indirectly damaging the sealing surfaces. 

Environmental factors: 

High temperatures, low temperatures or strong radiation environments may cause the performance of sealing materials to deteriorate. For instance, rubber sealing rings may become brittle at low temperatures, while metal sealing surfaces may undergo creep relaxation at high temperatures. 

5. Other factors 

Pneumatic actuator failure: 

Leakage in the cylinder, malfunction of the solenoid valve, or incorrect control signals may cause the valve to fail to open or close properly, keeping the sealing surfaces in a semi-contact state for a long time, which can lead to micro-wear. 

Excessive flow rate of the medium: 

High-speed media (such as steam and gas) have a stronger erosive force on the sealing surface. Especially when the valve is throttled, the local flow velocity may exceed the design value, leading to increased wear. 

Solution suggestions 

1. Material optimization: Select wear-resistant and corrosion-resistant sealing materials (such as hard alloys, ceramic coatings) based on the characteristics of the medium. 

2. Structural Improvement: Adopt a streamlined valve disc design to reduce fluid turbulence; increase the hardness of the sealing surfaces (such as through surface hardening treatment). 

3. Operating Specifications: Avoid frequent opening and closing. Ensure that the medium pressure is released before proceeding with the operation; Regularly inspect the performance of the pneumatic actuator. 

4. Maintenance: Regularly remove impurities from the medium, replace worn-out sealing components; lubricate the valve stem to reduce friction. 

5. Environmental Control: In extreme temperature or corrosive environments, special protective measures (such as heat insulation covers, anti-corrosion coatings) should be adopted. 

By conducting targeted analysis of the causes of wear and taking preventive measures, the service life of pneumatic stop valves can be significantly extended, ensuring the safe operation of the system.